Why are there no longer any biplanes? Is there an aerodynamic reason why the concept of biplane or triplane has been completely abandoned? Practically all planes were biplanes in WW1, and in WW2 practically none were developed.

Firstly, there are:
For example this company currently makes a biplane
But the main reason is that they're inefficient, and don't really do much that a monoplane can't.
They produce a lot of drag compared to the amount of lift they produce, meaning they use a lot of fuel to travel the same distance. They have fairly poor visibility, which is usually considered a bad thing!
They do have a few advantages - they have a good roll rate, making them quite maneuverable, and they have a very low stall speed and can fly on little power, meaning they can fly slowly very well (where their increased drag doesn't make much difference: drag increases with the square of airspeed)
Overall, though, the above makes them suited only to aerobatics, which can also be performed by monoplanes. Advances in wing design and composite materials take away most of the advantages of a biplane for any other use: ie actually travelling (the main purpose of an aeroplane) and carrying a load.
Overall, then, they're more complex than a monoplane, less efficient, and aren't much more manoeuverable. They have more disadvantages than advantages.
Biplanes were popular in WWI not because of any inherent advantage, but simply because technology hadn't advanced far enough to allow any other options. Once the monoplane was properly developed, it allowed much higher speeds (450mph for a late WWII fighter, 300mph for an Early WWII fighter, compared to around 120 mph for a late WWI fighter). High speed fighters beat low speed fighters (at least before stealth technology and guided missiles)
There were a few leftover biplanes in WWII - The Fairey Swordfish torpedo bomber was one of the most widely used, as the low speed and good lift from the biplane design allowed it to carry a heavy torpedo, while the drag issues didn't matter at the slow speeds they needed to fly to be able to release the torpedo properly and on target. Others were the Gloster Gladiator (UK), Fiat CR.42 (Italy) and Polikarpov I-15 (Soviet Union) which achieved varying levels of success in the early stages, but were well and truly outclassed when facing even early-war monoplanes.
This answer on a similar question gives some useful context about the direct advantages and disadvantages. It doesn't directly explain why biplanes fell out of favour, but it may help understand my own answer here.


What is the typical aircrew for a cargo flight? What is the typical aircrew for a civilian (not military) cargo flight? From my limited web searches, it seems that there would be three crew members:

Pilot
Co-pilot (I assume there must always be minimum of two people in the flight deck, in case anything happens to the primary pilot)
Loadmaster, a crew member responsible for loading and unloading cargo, and for assuring load balance during the flight.

Are these indeed three minimal, required crew members for a cargo flight? Are there any others that are required or optional? What is typical for a long haul cargo flight, and what is typical for short haul. (Rather than precisely defining how many hours is long haul or short haul--I'm not even sure--I'll leave that open for the answerers, since I'm really not sure what to expect.)

The context of this answer is 747-100 and -200 freighters at two airlines during the 1990s flying both civilian and military freight.

In the case of the 747-100 and -200 you had a 3-man cockpit crew: Captain, First Officer, and Flight Engineer. With the 3-man crew, there was no regulatory need to carry an additional pilot for a long flight. The 747-400 has, of course, a 2-man cockpit, but I don't know what the long-haul regulatory requirement was/is for an additional pilot.

There was no regulatory requirement to carry a loadmaster. If you were going between two stations that you regularly operated between, a loadmaster might not be carried if each station had trained loadmasters. However, if you were on a multi-leg, multi-day trip including stops where there wouldn't be loadmasters, one would be on-board (and maybe two if one of them was being trained). The loadmasters sometimes stayed with the airplane (or at least they used to) for periods of a few days to as much as two weeks even though the cockpit crews were changed out every day. Every few days the loadmasters would check into a close hotel for a quick shower or use a shower at an airport maintenance facility or some such. What always dismayed me was that they seemed to exist solely on catered food on the airplane for the entire time. While the airplane was in the air they slept when they weren't eating. Hopefully by now loadmasters are unionized and have better working conditions.

A mechanic was often carried if the airplane was having troubles or if it was being dispatched into Africa or other places where competent maintenance would not be available.

If you were carrying horses, there would be handlers with them. The one time I carried horses, they had a handler for each horse. Also, if you were carrying sensitive or very expensive cargo, there would often be someone to watch over it.

If it was a military cargo flight, there would sometimes be a 'military courier' or two aboard.

Jumpseaters were common, sometimes a lot of them depending on where you going, where you were coming from. The old 747s had 2 jumpseats in the cockpit and, typically, at least 8 first class seats on the upper deck, and often a bunk or two. I noticed in the accident report for the 747 freighter loss at Bagram that there were 7 persons aboard.


Is NOAA GFS winds aloft data available for applications? Where can I find the NOAA's winds aloft data in a form that I can use in an application? I plan to develop a software able to calculate the flight path of a lighter than air aircraft or drone using windspeed data from the NOAA Global Forecast System.

See the following web page:

http://www.nws.noaa.gov/tg/general.php

This page describes getting started with the HTTP or FTP access to NOAA weather service APIs.


Why do commercial helo pilots wear helmets? I've been on my fair share of commercial helo rides, primarily in Canada.  Over the course of more than ten rides in three different kind of helos (Bell 407, 412, and I think one other) there was only one time when the pilot wasn't wearing a helmet.

It's worth noting that these flights were taking off and landing in very remote areas of the Selkirk mountains, usually on glaciers.

At the same time, I have been around (US) flight schools since I was 15 years old, and I've never seen an instructor or student helo pilot (flying R22s and similar) wear a helmet.  Also, fixed wing pilots don't wear helmets.

Why do commercial helicopter pilots wear helmets, when instructors and students don't?

It's a little hard to see, but here's a photo of one of the choppers, and you can see that the pilot is wearing a helmet.

The same reason as anyone would wear a helmet - to protect their cranium in circumstances when there is the possibility of damage to that area of the body.

Helicopter operations are often low level, sometimes over dangerous terrain and, unlike fixed wing aircraft, they do not have the option to glide away from an engine failure. Low-level operations may not afford the pilot the altitude required for a successful autorotation landing so there is the possibility that they will be going down hard and fast.

Taking an example of low-level flight over forestry resulting in a forced landing, this may be survivable, but the pilot will be thrown around quite a bit as the aircraft is buffeted by the trees as it goes down. Some head protection would be important to the survivability of this crash.

There are a few other reasons I could think of apart from the main one above

Some helicopters operate with doors open, up where the birds fly around. A seagul to the head would not make for a happy flight
Noise - helo's can be louder than Fixed wing and the helmets could provide better noise cancelling
Specialist helo operations such as S&R use equipment such as night vision, which could be mounted on a helmet
Habit - ex-military helicopter pilots could just be in the habit of wearing a helmet, and carry this over to civilian operations.


What is the ferry range of an A380? The Wikipedia entry for the A380 gives the maximum range at design load as 15,700 km. The equivalent entry for a Boeing 747-400 gives around 14,000 km but distances of 18,000 km have been performed in demonstrations. So I infer the ferry range for the A380 would be even higher.

Is it specified anywhere? Has a flight by an A380 in excess of 15,700 km been performed to date? Could it fly between any two suitable airports on Earth, i.e., farther than 20,038 km?

You have asked several questions. I'll try to answer them in order to clarify.
Is the ferry range specified anywhere?
From the Airbus website, we find for the Engine Alliance GP7000 engine option the ferry range is ~9,600 NM. Let's just say it's 9,500 NM.
A: 9,500 NM. Also, waiting for the right trade winds can increase you range.

Can an A380 fly between any two airports on Earth?
If you place the originating marker over Dubai, UAE, then the A380-800 can fly to any airport on Earth except a region in South Pacific Ocean. This area (a circle of around 6500 km diameter) has many small island states (French Polynesia, Cook Island, American Samoa etc.).
(gcmap.com)
A: Yes, probably over 99% of airports.

Has a flight by an A380 in excess of 15,700 km been performed to date?
None that I could find. The longest flight of A380 (currently) is QF 8 (with duration 16:50 hours).
We know that A380 (October 25, 20071) is much newer than 777 (June 7, 19952) and 747 (January 22, 19703). In future, there can be attempts to fly it in excess of 15,700 km.
A: No record so far.

What is the ferry range of an A380?
This was your original question. Most of the flights mentioned on the Wikipedia article you referred to were either delivery flights or for demonstration purposes. For such flights, you can have:

lesser people on board
lesser equipment (seats etc.) so more space to add extra fuel tanks

With the above two changes, the result would be:

Less people = Less weight. The aircraft will weigh less and its range can increase.
Less seats = Less weight. The aircraft will weigh less and its range can increase.
More space to add fuel tanks. The aircraft's range will increase.

In addition, A380-800 has cargo volume of 6500 cubic feet. If we have a hypothetical rubber tank which fills all this space, we can add 184,000+ L of additional fuel than the original capacity of 323,546 L. This can increase the range over 50%.
This website contains pictures of additional fuel tanks. As you can see, those are inflatable and can adjust to the space available.
A: It depends.

1: Introduction with Singapore Airlines
2: Introduction with United Airlines
3: Introduction with Pan American World Airways


Can you fly a helicopter without a driver's license? Assuming one  does not have a driver's license, is it possible for one to obtain a pilot's license to fly a helicopter? Cost is not the question here. I want to know if one can never obtain a driver's license (for ground, motor vehicles) and still be able to obtain a pilot's license to fly helicopters, planes, etc.

This is applicable for the U.S. only.

Here's a a video where a CFI discusses this very question. There's no rule that says you need a driver's license to obtain a certificate to fly in the US. The real question is why you can't obtain a driver's license. If you have a medical problem that disqualifies you from driving, that will likely pose a far larger issue getting a medical to fly. Similarly, any drug or alcohol problem or conviction must be reported to the FAA. If your driver's license was suspended or revoked due to drug or alcohol, that must be reported as well. These issues are reviewed on a case-by-case basis, as the FAA wants to be satisfied that you will not try to fly while impaired. Beyond those types of problems, if you simply don't own a car and never wanted to learn to drive, nothing is stopping you from getting a license to fly.

Note that you will need some sort of government-issued photo ID. A passport or state-issued non-driver ID should be fine. You might also run into the practical problem that it may be difficult to get to/from airports in many regions without driving, so you'd have to find alternate transportation.

Finally, there is one sort of connection between driver's licenses and flying in the US. Pilots with a valid driver's license can fly Light Sport Aircraft without obtaining the otherwise-required third class medical certificate. A few rotorcraft (like this one) qualify as LSA. There are, however, significant restrictions on these operations, such as the requirement that they can't fly at night or carry more than one passenger. This rule does not override the medical requirements to fly, but requires the pilot to certify him/herself able to fly safely instead of receiving that certification from a Aviation Medical Examiner. In other words, if there's a reason you wouldn't be able to obtain a third class medical, then you are not allowed to fly a LSA using only a driver's license.


How comes lift is less than weight on take-off? If $$lift=weight * cos(angle)$$ this means that lift is less than weight during takeoff.

Could someone please explain me why it is so

Indeed, what puzzles a lot of people is that excess lift (excess as in more than we need for weight) it not what makes an aircraft climb.

Of course, a take-off is a dynamic situation which doesn't really call for a balance of forces and momentum, so the situation is a bit more complicated to explain, but let's try a thought:

Imagine it this way: If lift > weight you will accelerate 'up-'wards (ie. balloon style). Air will come not only from the front moving backwards, but also from above moving below. The relative air moving past your wing is now coming from front and slightly above. This decreases your angle of attack and thus decreases lift, usually up to the point where lift = weight again.

If lift< weight, the opposite happens (ie. accelerate downwards) and air will move from below the wing towards up. This increases the angle of attack, increases the lift, and again lift will match the weight.

It's basically a statically stable system, where the only really stable position ,if you think about, is when lift equals weight (in straight-level flight, mind you. For climbing and descending you have the formula stated in your question).

If you want to climb, increasing lift is not the way to go !


How often do GA pilots use the Autopilot approach feature while landing? While flying in simulations, I found that using the Approach feature is very beneficial for riding the glide slope (clear weather or not), however, while watching videos of GA pilots, I do not see it performed too often. Which brings me to my question as to whether that is a common practice, or if it is frowned upon unless it is necessary for a safe landing?

It's a perfectly acceptable practice, provided you disengage the autopilot upon reaching minimums and hand fly it the rest of the way.  Some manufacturers, like Cirrus, recommend flying a coupled autopilot approach.

I won't sit on the fence about this.  Learning how to fly coupled autopilot approaches are fine, but I insist all my students learn how to hand fly approaches, both as part of their initial instrument training and for all instrument proficiency checks I administer.  If I were an examiner I would insist on seeing instrument applicants demonstrate hand flown approaches on their checkrides as well.

Autopilots are great but their use can begin to atrophy their flying skills and it can come back to bite them, particularly in an emergency.

As to the exact numbers of GA pilots who fly coupled autopilot approaches, that's probably going to depend on the pilot and the equipment in his/her aircraft.  Pilots with autopilots installed are probably going to be much more likely to use them and be more comfortable flying approaches this way.


What are the effects of communicating on VHF/UHF on a RMI's ADF needle? Say you've properly tuned an ADF station in COMP mode so that the BRG needle on your RMI is pointing towards your station. Then you tune the same ADF frequency on your V/UHF radio. Does anything happen to your needle at this point? How about when you transmit on that frequency?

Edit: Meant RMI

NDBs in the U.S. transmit between  90 kHz and 535 kHz, and VHF is between 108 and 137 MHz. Of the VHF frequencies, the nav/com is only capable of transmitting between 118 MHz and 137.

So aside from electromagnet interference, no VHF radio should transmit on a frequency that he ADF receives.


If I ferry an aircraft to the United States (from say the UK) is it a commercial or private flight? If I am paid to ferry an aircraft from the UK to the US and then leave the aircraft in the US, is it a private or commercial flight?

I am not carrying passengers or cargo, but perhaps the aircraft itself becomes cargo if it is left in the US.

I guess my question follows on somewhat from this below:

What is the difference between a private and a commercial flight according to the US Customs and Border Protection?

This question was answered in an earlier (2013) message.

Generally, if you are ferrying an airplane and are compensated as a commercial pilot, are not carrying passengers or cargo for hire, you are operating under Part 91 of the US federal aviation regulations.  That you are a paid ferry pilot is not relevant.

See 19 CFR 122.1(d) A "commercial aircraft" is any aircraft transporting passengers or cargo for money or other consideration.

As you are not transporting passengers or cargo (both of which would be covered under the commercial operator rules) or you have a passenger as a friend or the aircraft owner who does not pay for passage, you are ferrying an aircraft which is covered as a private flight.

Make absolutely certain you understand how the US eAPIS system applies to you as a foreign national bringing the aircraft into the US, and you have appropriate documentation and the owner is prepared to jump through whatever hoops Customs needs to get the aircraft ashore.  The US Customs Guide for Private Flyers is a useful reference.

Simon, I disagree with your understanding.  There are many operations which are not commercial, with paid pilots.  An example of this is a corporation owns an airplane which requires a pilot.  The corporation can hire a pilot to fly its airplane and carry its parts/executives/employees/friends.  While the pilot must carry a commercial certificate and carry at least a Class II medical certificate, the flight is not considered a commercial flight, nor is the the company considered a commercial operator since it does not hold out its aircraft for hire, unless its in the air carriage business.  If on the other hand that same aircraft owner decided to carry the company next door's freight and executives and charge them for it, that changes the story.


Which commercial aircraft are capable of computer-only landings, without human assistance? Currently what models of commercial aircraft are capable of landing and safely stopping the aircraft, without any human assistance, other than inputting instructions to the onboard computers.

None. While a number of aircraft are certified for autoland with automatic rollout until safe taxi speed, and some can have the autopilot control rollout until the aircraft completely stops, no commercial aircraft has autopilot control of various critical parts for landing such as the flaps and the landing gear.


What is the explanation for the different lines in the payload/range diagram for the Airbus A320? In the A320-200's 'AIRCRAFT CHARACTERISTICS AIRPORT AND MAINTENANCE PLANNING' document. It presents the A320's PL/R capabilities as:

Firstly, I would like to know: What are the 3 different MTOW's listed? Is it for different seating layouts? eg 'high density' vs 'business + economy' or what? Note that 73.5(78) tonnes is the MTOW listed on Airbus's website, seen here, but they don't clearly indicate what the figure in brackets indicates.

Secondly, does the payload axis include passengers as well as cargo? If so, if the maximum amount of passengers is listed as 180, how much additional cargo can the aircraft carry, both in the cargo hold and overhead luggage trays? i.e. what model does the airlines/airframers use to estimate the weight of 180 passengers?

There are two different Maximum Take Off Masses (MTOM) listed in the graph: 73.5 T and 78 T. This is only a small selection. The Airbus A320 has many variations due to modifications to fuel tanks, fuselage, engines, wings and landing gear. The following MTOMs have been certified (EASA PDF): 66 T, 67 T, 68 T, 70 T, 71.5 T, 73.5 T, 75.5 T, 77 T and 78 T.

In addition to the variation in MTOM, there are variations in the number of fuel tanks installed. The A320-100 series have either 2 or 3 tanks, while the A320-200 series can have up to 5 tanks. More fuel tanks allow an increase in range at the cost of payload. Even on short flights additional tanks will decrease the maximum payloads due to their structural weight. The brown line in the chart represents an A320 with one Additional Centre Tank (ACT) installed.

Payload includes passengers as well as cargo. Assuming an average adult weight of 88 kg (EASA PDF) including carry-on luggage, 180 passengers weigh 15840 kg. Depending on the variant of A320 you take, that leaves a couple of tonne margin for other payload such as check-in luggage or fuel to increase the range.

For more on estimating aircraft loading, see this question.


Do turbofan engine cowlings dilate during spool-up? I was watching this Youtube video, portraying a Fokker 70 taking off. I wouldn't have noticed if it weren't for a comment, but during spool up (~ 3:24 in the video), it appears as if the engine cowling is dilating. (See image below, if you don't want to watch the video). According to the person who left the comment, this is due to the pressure changing.

I'm having real trouble accepting this — though I do see it with my own eyes, I'm finding it more intuitive to believe something else is going on (I would think something related to the camera, though it seems to be well secured and I can't see any other perspective change).

In the end, since intuition is a poor tool for discovering the truth, I decided to ask:

Do turbofan engine cowlings really dilate due to spooling up, and is it really because of pressure difference? And is it the whole cowling or only the inlet that dilates?

Now that's an interesting phenomenon! I do not believe that this is a case of an illusion of any sort, or the engine dilating. What the video probably shows, is the engine slightly turning towards the window as takeoff thrust is being applied.

Engine mounts are not 100% rigid, this can easily be observed on pretty much any passenger flight if you can see the engine. Any movement of the fuselage and/or wings, and the engines are clearly "bouncing around". The reason for this is to act as a damper between the engine and the rest of the airframe.

In the case of the plane in question, applying T/O thrust imposes a significant force on the engine mounts and the part of the fuselage that the mounts are attached to, resulting in a small inwards turning of the engine nacelles, thus making it appear as if the cowling is expanding.

This video shows the exact same phenomenon from a slightly different perspective. At approximately 2:15 mark, as T/O thrust is applied, a red mark on the outer flap mechanism fairing dissapears from view as the engine is shifted a bit.

And to further prove my point (having some extra time by chance), here are two images I've created to make this phenomenon more visible:

This is a combination of two crops from the video. Exact same location, but different time. The other is just before T/O thurst is applied, the other just before brakes are released. Image is divided into four segments, two of former, two of latter point in time. A vertical and horizontal lines are added for clarity to separate segments "Dilation" is clearly visible:

The second image is a combination of the same original images as before, but full frame. They are layered on top of each other, and the one on the top is defined as "difference" layer in Pixlr. This creates an effect that shows areas of the images that differ from each other as bright, while similar areas are dark:

As you can see, bright area is visible around engine nacelle. Also horizon line and the runway edge are bright, these brighter lines widen towards the right edge of this composite image. This is because the aircraft tilts from the thrust being applied against the brakes.


Can I legally own and fly fighter jets in the UK? I’ve seen a similar post, but it applied to America. Could I own and fly a BAE Systems Hawk T1 in the UK? What kind of regulations are there? Obviously it would have to be unweaponised but I was just wondering about the specifics.

I don't know of any privately owned Hawks, but there are many ex-RAF jets in private ownership, like the Jet Provost, Lightning, Gnat, Meteor, Vampire, and others I can't remember. The Ministry of Defence sells fixed-wing airplanes and helicopters occasionally at auction; when they retire the Hawk T1 you could be able to pick one up.
This CAA document goes over many of the particulars, a quick summary is that in almost all cases they would be under a permit to fly. This would require an inspection to clear it for the permit, and an (un)healthy dose of paperwork. I know of no way to get these aircraft certified, but you can get them cleared for night and IFR flight with extra paperwork and continued inspections, provided the aircraft is equipped for it. You can also get a permit to fly faster than 250kt below 10,000ft, which in a jet like the Hawk would be an advantage. Flying abroad on a UK permit aircraft is just more paperwork: you have to get permission from all the countries you'd fly over and land at, which is generally a formality, and restricted to day VFR.
One of the challenges you would find is keeping the plane airworthy. There are a few organizations that restore and maintain ex-military jets; you'd want to find out if they'd be able and willing to take it on for you before you buy it.
Of course you'd also need an awful lot of money. Jet Provosts (50s era trainers) are at the low end of jets as costs go and they still cost £600 per hour to operate!


What regulations apply to a VFR flight from South Africa to Namibia? I just would like to know what kind of flight plan, permissions, en route airway paths and other factors that need to be considered?

Other than the passport, PPL license and aircraft documentation and so forth.

For SA to Namibia:
Factors to consider

Buying all the appropriate charts.
Clouds: if you can't maintain the required separation, you need to switch to IFR, which means the plane needs to be IFR-equipped, and for you to be IFR rated.

Sources: Namibia AIP GEN 3.2 and ENR 1.2

En route airway paths
All airways from SA to Namibia are Class A, so VFR is not allowed along ATS routes.
Source: Namibia AIP ENR 3

Permission
You need overflight permission from Namibia, else there's an up to N\$50,000 fine or 5 years imprisonment. It is submitted 24 hours before.
Source: SA AIC D 012/2014

Flight plan – yes
Across international borders flights do require flight plans (the ICAO type) in accordance with ICAO SARPs Annex 2 (Rules of the Air), which both SA and Namibia require.
Sources: SA and Namibia AIPs GEN 1.2

See also:

SA AIP
Namibia AIP

For any other countries that share a border, refer to the respective AIPs.


How do aircraft refueling in-air deal with wake turbulence? Many fighter planes have the capability to refuel in air. When a plane moves in air, turbulence is generated at its back. To refuel, the fighter plane must come near to the parent plane (which has fuel in it).

When fighter plane reaches the back of parent plane, it is actually in the turbulent zone of the parent plane. How does fighter plane manage to fly and precisely adjust its position even in the zone of turbulence?

Ex US Navy pilot here.  I flew the S-3 Viking, which refueled via the probe/drogue method, as opposed to the USAF flying boom method.  I can confirm that the receiving plane is below the wake turbulence of the tanker, maybe by 8–10 feet.  Although, even if you should ride up into the wake, the sensation is perhaps not as violent as you might think.

The technique they teach is that you just fly formation.  You do NOT fixate on the basket (this is the 'drogue' part of the apparatus, which resembles a big badminton birdie).

Instead, you must position the tip of your probe about 4 feet aft of the basket, stabilize, then smoothly add throttle until contact is made.  You may need to hit the basket at a couple of feet per second relative velocity in order for it to latch.

Then you have to maintain position.  It's just formation flying, really.    The hose apparatus on the tanker measures your position fore and aft – when you are within limits for fuel transfer, a light goes on.  So, as the receiving pilot, you fly formation and maintain your position fore and aft so that the light stays lit.  When you've taken on your gas, you need to exit straight back.  Too much vertical offset can cause the basket to 'whip' as it disconnects.  You can smash a canopy this way – I've seen it happen, and it's pretty colorful.  You won't soon  live it down.


What is a "high-bypass geared turbofan," and why is it so much more efficient? According to the article Bombardier’s CSeries Gamble Is Facing Longer Odds, this new plane from Bombardier uses a new engine technology that will improve efficiency over its rival 737 series and A320 series airplanes, to the point where it will be able to complete on a seat-mile efficiency basis with larger airplanes, enabling it to bypass hubs:

  The linchpin for the CSeries was a new concept for engines developed
  by Pratt & Whitney, known as a high bypass geared turbofan. The new
  engine design promised exceptional fuel savings of up to 20 percent
  and unusually low noise levels.

What's the theory behind this new engine, and what are the underlying numbers that make it competitive with larger airplanes?

The fan section of a turbofan engine is driven by the low pressure (LP) spool. This means that it is connected to two parts of the engine:

The LP compressor, which must compress the air before it enters the high pressure (HP) compressor
The LP turbine, which must receive the air after it exits the HP turbine

The problem is that the HP section is efficient at high RPM. But the fan will reach aerodynamic limits as the fan tips pass supersonic speed. Fan blades are also harder to contain in the event of a failure as they spin faster. So to accommodate the fan, the LP section has to spin at a slower speed, which makes it harder to match with the high RPM HP section.

There is also a limitation on air flow. The fan must be able to move a maximum amount of air, which is takeoff power at sea level. But it must also be able to function efficiently at cruise level, where the flow is faster but much less dense.

Engine companies use different strategies to deal with these limitations.

GE mainly makes the LP sections larger in diameter. This allows the blades to have a high velocity at lower RPM. This this requires the air flow to change direction more rapidly.

Rolls Royce has created a 3 spool design, which allows each section to spin at a more optimal RPM. This adds complexity to the design.

Pratt and Whitney is going with the geared fan approach. Similar to turboprops, there is a gearbox to allow the fan to spin at a lower speed than the engine spool that is driving it.

This allows the turbine spool to operate at a more optimal RPM while still allowing the fan to spin more slowly. A slower fan can be larger, allowing for a higher bypass ratio.

A high bypass ratio allows a turbofan engine to drive more air (produce more thrust) for less air going through the core (burn less fuel). Modern large aircraft have engines like the GE90 on the 777 (9:1 bypass), with the latest engines on the 787 going even higher with the GEnx (9.6:1 bypass), and Trent 1000 (10.8:1). Smaller aircraft like the 737 and A320 currently use engines like the CFM56 (5.5:1), with the new LEAP going higher (9:1 or 11:1). The PW1000G goes even higher (up to 12:1).


What made the 2707 so superior? A book I have (Boeing, Planemaker to the World) includes how many orders and planes received of all of Boeing's major models as of the date it was printed. It said the 2707 (Boeing's failed SST) got 125 orders. That seems a lot, compared to the very small amount of concordes and TU-144s that were ever made. What made the 2707 so superior that 125 of them were ordered?

The plane was designed for a US funded competition which it won, after it would get 1 million dollars in funding for further development which automatically means that the 2707 would be the cheaper plane to buy and that it had the US Government Stamp of Approval. This also meant that there were political reasons to commit to buy one of them.

The reason it won that competition is because it was slightly less loud, slightly more efficient and more technologically advanced than its competition.


Is a biennial flight review valid for any airplane category? If I do a biennial flight review (BFR) in a glider, does it also satisfy my BFR requirement for powered flight (ASEL)?

Yes.  61.56(c)(1) calls for "an aircraft for which that pilot is rated."  The reg does not require a review for each category/class.

And as further confirmation, AOPA's Pilot's Guide to the Flight Review specifically states:

  The satisfactory completion of a flight review allows you to exercise
  the privilege of pilot in command in all categories and classes of
  aircraft on your pilot certificate.


Why is there a hole in one of the layer of an airplane's windows? On a commercial airliner, there is a hole in one of the layer of the passenger windows.

See here:

and here:

Or in more detail:

Can you explain the physical reasons for this design choice?

Aircraft windows are multiple layers thick. The side facing the passengers is just a plastic sheet, since they wouldn't want the passengers scratching up the actual expensive glass window. Beyond the inner pane there are two actual structural window panes. The outer one is normally the one bearing the load, while the inner one serves as a backup.
However, since pressure changes in the cabin during the flight, it's also necessary to equalize the pressure between the window panes, and hence the little hole. A hole of that size would not jeopardize pressurization even if the outer pane blew out. Note the label "Breather Hole" in the diagram below.

There is a rubber seal around the outside of the two panes so it would be a bit of a pain to open a hole to cavity from the side. Apart from that, the windows are pretty tight together and by keeping it where it is there is nothing in the vicinity such as dust that could gradually be pulled in.
Since the air in between the panes is colder, it's not unusual to see ice crystals forming around the hole as the more humid cabin air enters the cavity.

(source: gentex.com)
787 Window
This diagram includes the electric shade system of the 787 which is fairly similar. Since the two outermost panes carry no structural purpose you can just have them equalize air as you please.


Is it legal to land aircraft in national parks and state forests in Australia? I was reading about the (very) short takeoff and landing capabilities of the SuperSTOL light aircraft and it occurred to me that it would be pretty easy to set down in a national park or other remote area so long as there was a reasonably flat clearing and visibility.

But what are the regulations regarding legally landing in such places?

The answer to your question, is yes and no.

CAR 92 (1) states that:

  An aircraft shall not land at, or take-off from, any place unless: ... (d) the place... is suitable for use as an aerodrome for the purposes of the landing and taking-off of an aircraft; and, having regard to all the circumstances of the proposed landing or take-off (including the prevailing weather conditions), the aircraft can land at, or take-off from, the place in safety.

As you can see, you are able to takeoff and land away from a proper aerodrome provided it is safe to do so. As you can see here, misjuding this level of safety can be fatal.

The Civil Aviation Advisory Publication (CAAP) 92-1(1) provides guidelines on what constitutes a safe landing/takeoff field other than an aerodrome. These safe areas are known as Aeroplane Landing Areas. Although the CAAP is only a guide, it is highly recommended that any area you choose to operate from meets these minimum standards.

So you are allowed to takeoff and land outside of an actual aerodrome. But your question includes national parks. The rules surrounding these are outside of my knowledge (and they vary from state to state) , but I do know that many parks carry restrictions on vehicle entry, and the types of activities permitted. I would therefore find it very surprising if you received permission to land a plane in their park (if you found a safe landing site in the first instance).

EDIT: Some commercial flying is permitted within national parks. For instance, they use helicopters and a person on a sling rope to collect crocodile eggs in Kakadu. Obviously then some activities can be approved in a national park. I'd say it all depends on the specific park and the activity being performed. Private flying away from an aerodrome? You would have to check. In any case, my answer to your question is you can land out bush somewhere but possibly not in a national park.


What can cause a watchdog failure in an INDRA MSSR? I am responsible for Mono-pulse Secondary Surveillance Radar (MSSR) system that resets itself after a watchdog failure.
So far I have found the following:

An unwanted number of replies are received by it.
A noise test was also done but the test didn't find any interference,
The system is running smoothly, but suddenly from west direction an excess number of replies are received which cause my MSSR to reset.
this interference time is only occasionally, it come out whenever they wanted,
The Frequency Allocation Board team has been contacted to find out the source of this interference,  but since it happens only occasionally they are also unable to find it.

If someone has experience on it or face the same issue kindly reply as soon as possible.

1) What I expect is that there is a transmitter (or multiple) on 1090 MHz to the west of the RADAR that does not conform to the ICAO standard. I would start by looking at the decoded replies that the MSSR is receiving (not in ASTERIX format, but raw datagrams format. I believe the INDRA MSSRs can provide this). This may give a hint as to what the cause is(e.g. a certain 24 bit address range, certain downlink formats only, received power level, etc.).

2) Are there any military bases to the west of your RADAR? Or RADAR manufacturers? A transponder manufacturer? It may help to contact them. (Likely they will deny any experiments are going on, but the problem may suddenly disappear. It happened before).

3) Atmospheric tunneling may cause a specific transmission path only to exist under certain weather conditions (e.g. inversion layers) . Can you find any correlation between the interference and weather conditions?

4) Do you have multilateration systems covering the same area. The multilateration system may be able to locate the source.

If nothing else helps, you may have to install an array of 1090 MHz receivers and multilaterate the source.


Is there a more specific term than 'flight line' for straight lines flown during flight? I work for a small software startup, where its just my boss and I. Prior to this job, I had no experience with aircraft. We have a client that uses our software to fly a pattern over an area, where they fly straight for a while, turn around, and fly back over an adjacent area. They do this so that they can canvas an entire area. I sketched out what this looks like below.

      (start) ---------------------> (turn around)
                                    )
(turn around) <---------------------
             (
              ---------------------> (turn around)
                                    )
(turn around) <---------------------
             (
              ------------>    (and so on)

My boss refers to one of these straight flights as a "flight line". When I looked up the term "flight line" though, I found that it has a few different meanings all related to where the aircraft is parked or serviced on the ground.

So my question: Is there a more correct term than "flight line" that describes the patterns our client flies, which are these sets of straight lines?

Although my aviation knowledge is not all encompassing, I would argue that you, your boss, and your software company may want to know your audience as well as possible. The same terminology can mean different things to different segments of society. For instance, uncontrolled airspace/airfield would mean something totally different to a pilot than it would mean to the media or general public.

A quick search of the Federal Aviation Regulations/Airmen’s Information Manual, the Pilots Handbook of Aeronautical Knowledge , and the Airplane Flying Handbook only garners results describing specific areas of an airfield and the personnel working there. My experience in civilian aviation and in the military is consistent with this usage. When pilots, ATC, and others in the aviation field describe an aircrafts path, they use terms such as the following:

Route
Return route
Round-robin route
Great circle route
Flight path
Leg
Direct leg
Course
Direct course
Track

The term you are probably looking for is Transect pattern consisting of transect lines.

Someone more knowledgeable might have a better term.


Are the Boeing 747-8 engines more efficient than the 747-400 engines? So I was doing some research on the Boeing 747-8/4 engines. I discovered that the PW4056/62 (747-400) has a much lower bypass ratio and weighs a lot less, and it is much smaller than the GEnx-2B67 (747-8). So it really seems the PW4084 is the more efficient engine. If it is not true than what improvements have been made on the  GEnx-2B67 to make it the more efficient engine? GEnx-2B67 engines

PW4056/62 engines

Yes. According to GE, the GEnx-2B consumes 15% less fuel than the CF6, which was contemporary to the PW4084 on the 747-400.

The bypass ratio of a jet engine makes it more efficient, not less. A higher bypass ratio provides more thrust from the fan air, which means the core section can use less air and therefore less fuel to provide less thrust. This increase in efficiency is the reason turbojets evolved into turbofans and have been increasing in bypass ratio as technology improves.

One consequence of a higher bypass ratio means the engine does get larger and heavier. However, the increase in efficiency is more than enough to offset these costs.

Besides increasing the bypass ratio, there have been many internal improvements in the GEnx line of engines, discussed in the GE link above. These changes include composite fan blades and fan case, which can be lighter than the metal alternatives. Throughout the engine there are also aerodynamic improvements to increase the efficiency of air flow through the engine, as well as more new materials and manufacturing technology.


What helicopter is this in The Walking Dead? The reason I am asking this is because I want to do a 3D model of it. You can see it in this screenshot from The Walking Dead. At first I thought it was a UH-1H, but the main rotor doesn't look anything like a UH-1H main rotor.

(Source)

It is a UH-1 Huey.

  ... in the first episode of this sci-fi horror TV series about zombies in Atlanta, we see a pair of US army UH-1 Huey transports, painted with 'air cavalry' insignia, have been abandoned in a hospital car park.— rotaryaction.com

Looks like the main rotor has sunk down, should be higher up. Maybe a salvaged gearbox caused it to drop. Otherwise it's the same aircraft.


How can a Cessna cut the wing of a Boeing? I read days before about the collision of the flight PSA Flight 182 on September 25, 1978. I was wondering how is it possible that a Cessna 172 can CUT Boeing's 727-214 wing. There is a video with the moment: video.

Is there an explanation of how this can happen scientifically?

An airliner wing is built to be as light as possible. Its strength is calculated to withstand the stresses of flying, i.e. lift equally distributed over the wing, bird strikes on the leading edge.

The wing consists of one or more spars from the fuselage to the wingtip, ribs perpendicular to the spars and skin panels. All of these are made from thin aluminium: the spars (the main loadbearing structure) are a few mm thick outside the landing gear and engines.

Fire a one-ton object into the wing at a few hundred km/h and you can do a lot of damage. Even if that object is another aircraft with similar construction.

The damage gets worse if the wing hits the Cessna's engine block, but the accident descriptions I've seen don't say if that was the case.

Don't assume the animation is accurate. The Cessna won't slice cleanly through the wing, there would have been a collision in which both structures are crumpled and roughly torn apart.


How often does fuel dumping from planes in flight actually occur? There are a couple of questions about the emergency procedure of fuel dumping, used to reduce the weight of airplanes to be able to land.

This is certainly interesting, regarding environmental affects, safety aspects, and maybe some archaic fascination for huge fuel-air clouds.

How relevant these questions really are depends on how often fuel dumping is done.

But I don't know how often it is actually done, in incidents per year globally.

I understand that the procedure is used only in emergency cases, but not only in very few very extreme situations. It's about getting the weight down to be able to land safely, and the overweight is from fuel not yet used up on the flight.

So the procedure is needed whenever there is a need to urgently land, and there is not enough time to burn the fuel in flight.

That seems to mean that severe medical emergencies of individual passengers may be a reason? That happens much more often than drastic technical problems I assume, so it would be a strong factor.

Now, I'm interested in some rough total estimate about how often fuel dumping happens, and the main factors, like minimal emergency cases that can lead to a fuel dump.

I'd simplify the scope by considering only commercial aviation, ignoring military and general aviation - but I do not see that as important, use the data you have at hand.

These two reports cite that the US Air Force at one time jettisoned fuel nearly 1000 times per year. The second report also mentions that commercial airlines reported 485 instances of fuel jettison over a 5 year period. The commercial reports are only for maintenance related cases though, not including scheduling or weather reasons.

Both of these figures date from the 1970s. Military standards have been changed since then to reduce the frequency of it. The first paper assumed that in 1995, military fuel jettisoning was "infrequent".


How many warning signals are voiced in modern airliners? Some warning signal in modern airliners are voiced, like TCAS warning and GPWS warning (PULL UP!).

And how many warning signal are voiced in the modern airliners?

Moreover, where is the sound produced?

Modern airliners have voice warnings in a number of systems like,

Ground Proximity Warning System
Terrain Collision Avoidance System
Windshear Alerts
Radio Altitude callouts
Trim
Fire Detection
Autopilot configuration
Pressurization systems
Landing gear system
Stall/overspeed warning.

The amount of voice warnings vary from aircraft to aircraft. For example, airliners.net has the following list of voice warnings in Bombardier CRJ-200 (other than GPWS and TCAS):

  "APU" APU overspeed or overtemp

  "Door" open or unsafe passenger door indication

  "Jetpipe Overheat" overheat indication in jetpipe/pylon

  "Smoke" smoke detected in cargo area of lavatory

  "Config Autopilot/Flaps/Spoilers/Trim/Brakes" Aircraft not properly
  configured for takeoff

  "Wing Overheat" Overheat in fuselage wing anti-ice ducts

  "Anti-ice Duct" Bleed air leak in fuselage or wing anti-ice ducts

  "Bleed Air Duct" leak in different part of bleed air duct system

  "Brakes" brake overheat

  "Config Brakes" here again because it's for having the parking brake set
  while airborne

  "Gear Disagree" disagreement between gear indications and handle position

  "Gear Bay Overheat" overheat in main gear bay

  "Nose Door" Nose gear door open after gear fully extended and locked or >250
  knots

  "Engine Oil" oil pressure <25 psi

Initially, most of the voice warnings were recorded voices. However, more and more modern systems (like in newer 737s) are using computer generated voices.


Is there a published airspeed and TPA for Class B approach at San Diego International? I live in San Diego almost directly underneath the downwind leg of the normal approach (from the north) to Lindbergh Field (KSAN).  The Class B airspace for the entire downwind and base leg areas is between 10,000 and 4,800 feet.  Every night I stand out on my back deck and watch the approaches being flown overhead.  It appears to me that the airspeeds and altitudes of these approaches are very similar and I'm curious about what they are.  Are these published anywhere or is there some accepted norm for a typical airliner approach to a sea level airport?  Although I could be mistaken, as I watch the turns from downwind to base and base to final, it appears that the altitude is held fairly constant and that final descent doesn't start until final approach. If anyone has any insights, I'd be interested to hear what they are.

Almost every major airport (Class B) would have what's called a STAR, a Standard Terminal Arrival Route. Busy Class B traffic doesn't necessarily follow a TPA (Traffic Pattern Altitude).

For runway 09, the STAR doesn't show a speed limit. Some STARs have speed limits.

But that's not to say the speed is at the pilot's discretion, as the airplane approaches an airport it's standard for the crew to slow down and prepare the plane for landing. The air traffic control (ATC) can also issue speed restrictions to properly space the arriving traffic, they have the bigger picture.

For the downwind leg you can expect something like 200 knots indicated, which can translate to a bit over or under 200 knots of ground speed, depending on the wind. That's 230 mph or 370 km/h.

As the planes join the final approach segment, the altitude would indeed be level in most cases, and further descent would commence as you said, on final approach.

No published speed limit on downwind. The line with an arrow pointing to IFSOX.

For altitude it's 4000 feet, the *3000 is the minimum to clear any obstructions. 2400' for the base leg.

Above is a chart legend.

Final approach descent begins about 10 nautical miles to touch down, as illustrated from 2100 feet for this particular approach to runway 09.

Numbers in this answer are for one particular approach to one runway, figures vary.

Source: skyvector.com

Class B around KSAN is a bit complicated in shape, but the base/floor is mostly 2800' for the southern published downwind area (if you overlay the STAR on a VFR chart). Airline/IFR pilots don't need to worry about that chart as they'll be following the aforementioned STAR or guided/vectored by ATC.

I misread the question, from the north it's 6000 feet and 210 knots, the BAYVU (pronounced bay-view) FOUR ARRIVAL (STAR). That should be downwind for runway 27. The same principles apply, different figures.

See where you live (coordinates), download all the STAR charts, and you'll have a better picture of your night sky. Note: some STAR charts are not-to-scale.


What regulations govern the quality management system for producers of aircraft components? I am looking for FAA documents and regulations regarding the quality management system for producers of aircraft components.
Specifically I would like to know what is a production certificate .

Furthermore may I download those regulation somewhere ?

From FAA, Production Certificate:

  A production certificate is an approval (document) to manufacture
  duplicate products under an FAA-approved type design (e.g., type
  certificate or supplemental type certificate). The holder of a
  production certificate may obtain an airworthiness certificate for
  aircraft produced under the production certificate without further
  showing. To obtain one, the production application and approval
  process must be followed.

See also:
Production Approval - Regulations & Policies (link).


What is the strange object on 737-800 exterior, on the aft right side? I was unable to locate this on a "real life" picture of the aircraft, so have attached an image from my simulator. What is the function/purpose of this object on the exterior of the 738? It seems like it would decrease efficiency so it must surely serve an important role? Thanks.

It's the air inlet for the Auxiliary Power Unit (APU).

Slide 18 here has an image labelled "APU Air Inlet door with Vortex Generator". The inset image on the slide looks almost exactly like your posted image.

I found a much better image here, captioned "Boeing 737-800 with APU inlet".

There is some discussion about why the 737 has vortex generators for the APU on this thread on PPRuNe.


How to correctly interpret the taxi procedures in ICAO Doc 4444? I have a question to ICAO Doc4444, Chapter 12.3.4.7, Taxi procedures for departure, c).

My question is how to interpret the following, knowing that words in parentheses are mandatory, and words in square parentheses indicate optional additional words.

  TAXI TO HOLDING POINT [number] [RUNWAY (number)]
  [HOLD SHORT OF RUNWAY (number) (or CROSS
  RUNWAY (number))] [TIME (time)];

I assume that this can be exploded to 12 variants (not including TIME at the end of each variant which would give another 12 variants).

TAXI TO HOLDING POINT
TAXI TO HOLDING POINT A1
TAXI TO HOLDING POINT A1 RUNWAY 09
TAXI TO HOLDING POINT RUNWAY 09
TAXI TO HOLDING POINT HOLD SHORT OF RUNWAY 30
TAXI TO HOLDING POINT CROSS RUNWAY 30
TAXI TO HOLDING POINT A1 HOLD SHORT OF RUNWAY 30
TAXI TO HOLDING POINT A1 CROSS RUNWAY 30
TAXI TO HOLDING POINT RUNWAY 09 HOLD SHORT OF RUNWAY 30
TAXI TO HOLDING POINT RUNWAY 09 CROSS RUNWAY 30
TAXI TO HOLDING POINT A1 RUNWAY 09 HOLD SHORT OF RUNWAY 30
TAXI TO HOLDING POINT A1 RUNWAY 09 CROSS RUNWAY 30

My questions are:

Is my number of variants correct?
All variant are instructions to taxi to a holding point, in case 1, holding point is obvious to the pilot due to runway in use? Correct?
In all cases, the instruction gives clearance to taxi to a holding point without follow up by any other clearances, but for
case 5, 7, 9, 11 the pilot must wait at holding point short of runway 30 (for stopbar light etc. to be opened). Correct?

Below are my answers to your specific numbered questions.

I believe there are 4 variations of taxi clearance you might expect to receive in your scenario:

a.  Taxi to RW 09

b.  Taxi to RW 09, hold short RW 30

c.  Taxi to RW 30

d.  Taxi to RW 30, hold short RW 09
This is incorrect.  You will never receive taxi clearance to an undefined “holding point”.
Basically correct, but there are no traffic lights or stop bars on any taxiways I have ever seen.

Regarding #1, those are the four possible combinations of a basic clearance, i.e. you are either allowed to cross the off-duty runway or you are not, and there are but two runways.  However, that doesn't mean that you might not hear variations to this.  While pilots and controllers strive for standardization there is some variety.  For example, while not required to do so, it isn't unheard of for a controller to say "taxi to RW 09, cleared to cross RW 30."

To provide some additional context, clearance to taxi to an active runway clears the pilot to cross any off-duty runways that may intersect the taxiway.  If the pilot is cleared to taxi but told to hold short of an intersecting runway, further clearance to cross and continue taxiing will be made on the radio.

The actual words “holding point” (in my experience) are never used.  Clearance to taxi to a runway presumes the pilot will taxi right up to the painted hold-short line and stop there before switching frequencies and requesting takeoff clearance from the tower controller.  The tower controller will then clear the pilot to either take off, line up and wait, or continue holding short.

At most airfields serving general aviation aircraft there is widened section of the taxiway in the hold short area for performing engine run-ups and final takeoff checks.  However, the ground controller will never clear you to this “holding point”, but will instead clear you to the runway in use.  It is up to the pilot to use this area as needed, and then taxi up to the hold short and switch to tower frequency when ready for take off.


What is the purpose of these labels on an aircraft's wings? During a flight on an Airbus neo I was looking at the wing on my left, and noticed a set of labels on it. A few can be seen in the below image:

(The third one on the right is not readable, I was focusing on capturing something else.)

After a bit of working on it I think I found part of the pattern, with letters starting from A in the front of the engine and going B, C, D, etc. while moving farther from the front, and R, L and T standing for Right, Left and Top.

Now, while building a Lego plane set it could absolutely make sense, or maybe if you buy a plane from IKEA... But why on a real life aircraft? Just for something like visual inspection after build?

Closer than you may think: notice that these panels all have fasteners visible-- these panels are removed frequently for engine work.  The labels are there so that the maintenance crews can both more easily reattach the panels, and so when they're inspected (again as part of maintenance) you're can quickly confirm that everything is in the right place.

When you have a plane in parts, all the panels start to look very similar lying on a workbench... Having the labels makes things more efficient and safer.


Why are SBAS-equipped planes exempt from the preflight prediction check? My question stems from this other question: Why is training regarding the loss of RAIM given so much more emphasis than training regarding the loss of SBAS?
Two answers say losing RAIM puts a question mark on the integrity of the GPS position. And losing SBAS only affects LPV approaches.
Yet from this other question, Why weren't SA-On GPS units updated to become SA-Aware?
According to Advisory Circular (AC) 90.114A CHG1, now and past 2024, SBAS-equipped planes do not need to do a preflight prediction check.
Why skip the important RAIM prediction step?

RAIM = Receiver autonomous integrity monitoring
SBAS = Satellite-based Augmentation System
LPV = Localizer performance with vertical guidance

The slide refers to ADS-B integrity, which requires a different integrity level than RNP. The ADS-B preflight check they refer to is a different than the check for RNP.
The FAA requires an integrity bound of 0.2 NM or less for ADS-B. For RNP2 (en-route) and integrity bound of 4 NM is sufficient. RNP-approach requires and integrity bound of 0.6 NM.
The probability of not achieving the integrity level required for ADS-B is significant for TSO C129 (SA ON) installations, much lower for TSO C196 (SA Aware) installations and insignificant for TSO C145/146 (SBAS) installations.
The better performance of thw SBAS installations is because SBAS does a few things to improve integrity:

it is an extra GPS satellite at a fixed (geostationary) position.
it supplies parameters for an error correction model that improve the accuracy of GPS signals received by the GPS receiver
it does its own integrity monitoring of the whole GPS system and reports any issues with GPS within 6 seconds to the WAAS receivers.


Why do most commercial airplanes use hydraulics instead of electric/servo motors? I'm sure it's possible to use servo motors to get precise control of the ailerons, elevators or the rudder. But still, hydraulics are widely used instead.

Hydraulics do have a disadvantage that a damage to the hydraulic pipes can cause loss of control. Even with redundancy, there are cases where all three hydraulic lines get damaged at the same time and there's complete loss of control (can't remember the example). I think in some smaller aircrafts servo motors are used. But why not in the larger ones. Is it because of the torque required?

What are the issues with using electric motors?
If used what are the safety concerns?
In terms of safety, how different are they from hydraulics?

I'm sure it's possible to use servo motors to get precise control of the ailerons, elevators or the rudder.

No, it isn't. Primary flight control actuators require both rather high forces and quick response time. Electric motors can provide either, but both at the same time is a problem. Hydraulics is still better for that combination.

Note that other actuators that don't require the fast response time (like flaps, gear or horizontal stabilizer foreplane (elevator trim)) are electric in some aircraft.


When should I use "cross" and "pass" on radio telephony? Talking about "vertical" plan (altitudes, flight level) and "horizontal" plan (positions, way points), according to the standard phraseology FAA/ICAO, is there any difference, in the usage of, between TO CROSS and TO PASS?

When related to a significant point, there is no difference between pass and cross. For altitude/FL only pass is used.

The phraselogies used by ATC is described in ICAO Doc 4444 (Air Traffic Management / PANS-ATM), chapter 12, phraseologies. The document explains the meaning for ATC, therefore to be understood and used by pilots.

  12.3.1.2 LEVEL CHANGES, REPORTS AND RATES

  EXPEDITE CLIMB (or DESCENT) [UNTIL PASSING (level)]
  AFTER PASSING (significant point)

  12.3.1.4 TRANSFER OF CONTROL AND / OR FREQUENCY CHANGE

  AT (or OVER) (time or place) [or WHEN] [PASSING/LEAVING/REACHING (level)] CONTACT (unit call sign)
  (frequency)

  12.3.1.10 ADDITIONAL REPORTS

  REPORT PASSING (significant point)
  REPORT PASSING (three digits) RADIAL (name of VOR) VOR

  12.3.2.3 MAINTENANCE OF SPECIFIED LEVELS

  MAINTAIN (level) UNTIL PASSING (significant point)
  MAINTAIN (level) UNTIL (minutes) AFTER PASSING (significant point)

  12.3.2.4 SPECIFICATION OF CRUISING LEVELS

  CROSS (significant point) AT ( or ABOVE, or BELOW)
  CROSS (distance) MILES, (GNSS or DME) [(direction)] OF (name of DME station) OR (distance) [(direction)] OF (significant point) AT (or ABOVE or
  BELOW) (level)

  12.3.2.8 SEPARATION INSTRUCTIONS

  CROSS (significant point) AT (time) [OR LATER (or OR BEFORE)]
  ADVISE IF ABLE TO CROSS (significant point) AT (time or level)

  12.3.3.1 DEPARTURE INSTRUCTIONS

  AFTER REACHING (or PASSING) (level or significant point) ( instructions)

  12.3.4.12 TURN OR CLIMB INSTRUCTIONS AFTER TAKE-OFF

  AFTER PASSING (level) (instructions)

  12.4.2.3 PARALLEL APPROACHES

  YOU HAVE CROSSED THE LOCALIZER (or GBAS/SBAS/MLS FINAL APPROACH COURSE)

If another wording is used in some country, the differences must be explained in the country AIP, at section GEN 1.7. For USA (FAA AIP), Doc 4444 differences are found at GEN 1.7-23. There are none related.


Can a handgun shot take down a commercial airliner? Most airplanes, when taking off or landing, are in range of small arms fire, i.e. your every day handgun.

Is it possible to take down a commercial airliner by shooting at it with a handgun? Would one shot be enough, or would several be needed?

shooting at it with a handgun

That's really going to depend on the handgun.

James Bond carries a Walther PPK - this is a .32 calibre popgun with rather limited use outside of a small office. Direct hits on people are usually survivable unless you take a round in the heart or brain. Chances of even hitting an airliner during takeoff or approach are zero - it simply doesn't have the range, and that tiny subsonic projectile will get deflected by the aircraft's wake.

Skipping the middle range and going straight for the hand-cannons, we might get somewhere with a Desert Eagle or a Smith & Wesson 500. Remember the posters for the first Terminator movie? The one where The Ah-nuld is wearing sunglasses and holding up some light artillery? These are bigger. At close range, both guns can crack an aluminum engine block1 and are one-shot kills on most things smaller than a rhino. Hitting an approaching widebody isn't all that difficult - it's coming toward you, the angle isn't changing, and it's a rather big target.

But aircraft are large, complex systems with a lot of redundancy, so in order to actually take it down we have to hit something critical. Hitting a 767 right in the nose will destroy the weather radar and (maybe, if it has enough energy left) poke a 1/2 inch hole in the forward bulkhead. No one will notice. The flight-deck windows are rather strong, apparently a police sniper tried to take out a hijacker on the flight deck way back in the 1970s and the rifle round (far more powerful) just pock-marked the window. Several hostages were promptly shot as a result.

The best shot (ha!) is the engines. They don't like ingesting bits of metal but just hitting the fan won't do much. You would have to get very lucky to get the round into the engine itself, where it will promptly do a lot of very expensive damage.

But even if one engine literally goes boom it still won't crash the plane. Pilots practice for an engine failure on takeoff all the time, and an engine failure on landing is almost a non-event.

Hydraulic lines for control surfaces are certainly sensitive, but they are well buried in the structure and there are several independent systems. You won't get them all.

So, in conclusion, handguns are sufficiently ineffective at bringing down large aircraft that we really don't need to be concerned about them. There's a reason air forces around the world prefer missiles or 20mm cannon2 for this sort of thing. Geese, however, are quite effective if released in sufficient numbers along the takeoff path. Rather noisy though - you won't hide 500 of them anywhere near an airport without someone noticing.

Internet legends of a .50 cal being able to kill a truck refer to the MUCH larger .50 BMG round, available in explosive and armour-piercing and rightfully categorized as a first-class military weapon.
The projectile's the size of your thumb, and the gun fires 6,000 rounds per minute. It'll do your plane like a chainsaw.


Why would some flights use props instead of jets? Two years ago I flew from Tel Aviv, Israel to Tromso, Norway via Riga and Oslo. The Tel Aviv-Riga leg was flown in an A320, and the Riga-Oslo and Oslo-Tromso legs were flown in prop planes, Fokker airplanes I think.

What considerations are used to determine what type of plane will fly for a particular journey?

Obviously the choice would be limited to whatever aircraft the carrier has available, but given reasonable choice of any aircraft that seats the required amount of passengers, what considerations are used to decide on props or jets? Runway size? Fuel efficiency for short / long trips? Weather or temperature (both current and typical)?

I believe this question is answered here and a nice comparison can be found here but the short answer is efficiency. If memory serves jets gain their efficiency at high altitude moving fast and generally over a long distance. If you are going on a short hop turbo props will be more efficient overall. This chart provides a nice outline of the difference in efficiency.

As for large piston pounders I am not sure of the efficiency but I would think the cost of keeping one running is high simply based on their age (no one is really making big piston planes anymore as far as i know). History channel has a nice show "Ice Pilots NWT" about a freight/passenger airline that still runs DC-3's and the general issues they have with them many of which is related to finding parts.

That being said not all airlines had the money to jump right into jets when they came out. Lots of turbo-props are still flown simply because there is no reason to replace them.


What is this flat plate sticking out of the tail of Learjet 24D? What is this protrusion on the tail of Learjet 24D (shown just above the avro museum logo) and what is its function?

Learjet 24D Tail closeup

Zoomed out image of the Learjet tail

Source: images were taken by yours truly

It's a VOR antenna. You can find more information about it in similar questions like this one or this one.


Approx 1948 Brasil Brazil Airliner...what is it? Taildragger? What plane is this? It's a taildragger, 4 blade prop, twin engine plane. The photo was taken approximately in 1948, maybe in Brazil?

The airliner in the picture is a Vickers VC.1 Viking, registration LV-AFI, of the former Argentinian operator Flota Aérea Mercante Argentina.

According to this source, the plane served the
Secretaría de Aeronáutica under registration LV-XFJ for less than a month, from 10.9.1947 till 4.10.1947 before transferring to FAMA.

After FAMA, the plane in question served Fuerza Aérea Argentina from 4.5.1949 till 11.11.1951 under registrations T-80 and T-50.

Wikipedia: Vickers VC.1 Viking

Wikipedia: Flota Aérea Mercante Argentina (in Spanish)


Can I get a photo with the pilots? Could I, as a passenger, get a picture with the pilots in the cockpit before takeoff/after landing? I'm asking specifically about any rules that would deny a passenger into the cockpit. I know this is too broad and subject to change from airline to airline, but generally would I be allowed? What about domestic vs international flights?

I don't know about the situation specifically in the US, but in my - mostly European - experience crew are happy to welcome you to their office after flight.

When I feel the need to see the cockpit or discuss things with the pilots I try to ask the flightcrew before take-off if I can meet them after the flight. Sometimes I explain my interests to the cabin crew and often they will arrange the visit. In a few cases I just asked while deboarding.

Depending on the aircraft type and airport situation you have to think about the logistics a bit. In single aisle aircraft, if you start a discussion with crew while deboarding, you are blocking the queue. This gives the feeling that it is an inconvenient moment and reduces your chances. So if you ask at the last possible moment, make sure most people already exited before you.

However, if passengers are transported to the terminal by bus, you will be holding the bus since you are the last to get off. This reduces the time you can spend in cockpit drastically. If you expect to be bussed to the terminal, ask cabin crew before the descent and don't wait until everybody has exited.


Can someone identify these two Bell helicopters seen in the Czech Republic? I would like to ask you for help with identification of two particular airframes.

On Sunday 13 May 2018 around 11.45 local time, I took a picture of two Bell UH-1s south of Brno, Czech Republic. I had only wide lens, so it is not very detailed shot. From what I can see, the heli on the left is very likely Bell 212 (or UH-1N), wearing some colorful paint, maybe in SAR version (it probably has also some sensor ball under nose, or reflector), the heli on the right appears to be Bell 214 wearing military camo or dark paint (green or brown), also with sensor ball. They were flying from east to west, approximately in direction from Slovakia to Germany.

Is anybody here able to help me with as precise identification of these two helicopters as possible: version, operator, tail number...?

The mystery has been solved.
Those two helicopters are Agusta-Bell AB 212 operated by Italian Air Force (Aeronautica Militare) coming for Tiger Meet in Poznan, Poland. Their flight route was a little bit confusing because they were VFR flight avoiding CTR.
The more colorful one wears new special tiger paint: https://www.planespotters.net/photo/836257/mm81151-aeronautica-militare-italian-air-force-agusta-bell-ab-212
The second one seems to wear standard camo: https://1.bp.blogspot.com/-czFFf-7KQyA/Wvu5eNjjgXI/AAAAAAAAMQs/qN9qakgSI9QTmqfosho3Dr6DVmHl-nTNwCLcBGAs/s1600/NTM05.jpg
Thank you, Walker, for your input!


Why do some aircraft have 4 nosewheel doors? The A380 has 4 nose-wheel doors. Look:

Source: Airliners.net

Why does it have 4 nose-wheel doors?

Having multiple door sections for the nose gear is a common design. Looking closely at the photo below may make the reason more clear:

When the nose gear retracts, it swings forward. You can see that the wheels will need a larger opening than the narrower strut. So instead of having one door with a strange shape or that is larger than it needs to be, it is split into two sections. This also allows the forward doors to be closed once the gear is extended, which reduces drag.

Splitting the doors down the middle allows for symmetry, and it reduces the amount of surface area each hinge or actuator must support. This results in 4 separate door sections.

Looking at the main landing gear, you can see it uses a similar design. For example, the outboard gears swing inwards on retraction. The doors that cover the main gear bays are larger, and are only open during extension or retraction, and are otherwise closed. The smaller doors at the locations of the struts remain open.


Are there limitations on taking off or landing if airport lighting such as the VGSI (PAPI) is out of service? There are many types of airport lighting that aid pilot to land safely such as ALS, VGSI or runway lights. And some instrument approach procedures state that their weather minimums must be raised in case the ALS is out of service.

However, I think those aeronautical lights are not essential for pilots, they're just aids. In case the airport lighting such as VGSI (PAPI) is out of service, are there limitations for landing or take-off?

There wouldn't be any limitation on taking off with the VASI/PAPI out of service, unless it involved a requirement to return to the airport where the VGSI would be required (see below).  That would be a very extreme case, because it would mean that

the rules + the existing weather require the ability to return to the departure airport (i.e. a "takeoff alternate" is either not authorized or none is available), and
no other runway (including the same strip of concrete, landing in the opposite direction) is available at the same airport (tailwind component could cause this), and
this is a case (discussed below) where a VGSI inop prevents an approach to 'this' runway.

That's going to be a very rare combination.

So, when can an inop VGSI prevent an approach?  There are cases where US TERPS rules do require an operative VGSI in order to conduct certain operations -- mostly at night.  I've seen plates where a VGSI is required for circling operations to a given runway at night, and in one case where you couldn't fly any instrument approach, even an ILS, to the particular runway without the VGSI.

The latter fell in the category of TERPS rules that don't make intuitive sense... if I'm flying the ILS glideslope, by the time I'm going visual I'm so close to the runway that you'd think obstacle clearances have all been met & nothing remaining (in front of the aircraft) could possibly be a factor.  It was a memorable discussion because it seemed to make so little sense.  But, the restriction was published, and without the VGSI that runway wasn't usable.

The general case, however, is that the VGSI can be inop with no effect on the ability to fly an approach.  In 99.9% of the cases, it won't matter.  But for an obstacle in the right spot, you can get the note on the approach plate stating the requirement, and in that case, it matters.

But it's very uncommon.


Caravan 208B EX Glide ratio What is the glide ratio for the new EX Cessna 208B with 8750 amphibian floats?

You would have to ask someone in the engineering dept at Wipline for an actual number info@wipaire.com.

I have enough float time to be willing to stick my neck out and make a somewhat educated guess. I recall from somewhere that the Caravan on wheels with a feathered prop has a really good L/D by single engine airplane standards, somewhere around 12.

Based on personal experience the glide of most seaplanes is pretty brick-like; I would say a good ballpark would be about a 1/3 to 1/2 reduction in L/D from the land plane.  So for a 208 on amphibs I'm guessing it's going to be between 6 and 8.  If you find out hard data from Wipline, let us know the actual number so I can find out how far off I am.

Fortunately, the PT-6 is so reliable the risk of a power off glide from the engine letting you down is pretty tiny.


Is a weather briefing required? Are pilots legally required to obtain a weather briefing prior to some or all flights?

Yes, at least for flights that are not in the "vicinity" of the airport.
FAA CFR 91.103

Each pilot in command shall, before beginning a flight, become familiar with all available information concerning that flight. This information must include--
(a) For a flight under IFR or a flight not in the vicinity of an airport, weather reports and forecasts, fuel requirements, alternatives available if the planned flight cannot be completed, and any known traffic delays of which the pilot in command has been advised by ATC;

You are not required to call Flight Services for a weather brief, but you are required to get the weather reports (which can be called a personal brief). If you do all flight services and happen to have an accident, then your accident will contain the details about your call.


Would a ducted fan with a nozzle like a jet engine have more thrust than a normal ducted fan? I'm trying to design a miniature ducted fan engine for a small project, but I'm not too sure how much contraction should happen between the fan and the end of the engine, if at all.

Engines like this  or this look like they have very little contraction at all, but why not use the pressure created by the fan and contract the space making the output velocity higher?

This is the same sort of principle behind the bypass air of a turbo fan engine and I don't see why not to use it.

but why not use the pressure created by the fan and contract the space making the output velocity higher?

That is exactly how the pressure energy added by the fan is converted into thrust. Thrust, after all, is the product of the speed increase between free stream and exit flow, mass flow and nozzle area.

That real jet engines don't show so much contraction is due to the expansion of the core gas flow from heating. If you don't add heat, your exit area should be quite a bit smaller than the entry area.

If by "normal ducted fan" you mean one where the duct is simply a cylinder of constant diameter, then yes, a properly designed nozzle will create more thrust.


Why did this departure from Buenos Aires seem to delay heading northeast? It was going from Argentina to Germany and after takeoff it went over a town and then it went direct to Germany. Why did it go over the town instead of going directly to Germany?

Source

It's following a departure procedure.

(chart source)

The path flown matches the route described for departing Runway 11 with the La Plata 6B departure.

See the map here to visually match up the described departure procedure with the flown path.


How does the Boeing 777's yoke of both the captain and the first officer have synchronized movement? On Airbus planes, the side stick of both the captain and co-pilot are not synchronized in movement, meaning if you the captain moves the side stick, the co-pilot's side stick will not move together. If the co-pilot moves the side stick while the captain does, it will be a dual input.

However, on the Boeing 777 is also a fly-by-wire(FBW) design. But if you watch a 777 cockpit during flight, both of the captain and the co-pilot's yoke moves.

How is that done? Are both of the yokes connected by one mechanical system, and that mechanical system feeds the pilot input to the conputer? Or is it done electronically, with motors or other stuff?

From the FCOM v2 (9.20.1):

  The primary flight control system uses conventional control wheel, column, and
  pedal inputs from the pilot to electronically command the flight control surfaces.
  The system provides conventional control feel and pitch responses to speed and
  trim changes. The system electronic components provide enhanced handling
  qualities and reduce pilot workload.

  [...]

  The columns and wheels are connected through jam override mechanisms. If a
  jam occurs in a column or wheel, the pilots can maintain control by applying force
  to the other column or wheel to overcome the jam.

  The rudder pedals are rigidly connected between the two sides.

So yes, there is a direct mechanical link between the control columns, but it can be overridden.

Edit:

As John K pointed out in the comments, the technical term for the mechanical link is a torque tube with a breakout mechanism. The details are described in patent US5782436A:

  When a sufficient amount of force is exerted on the un-jammed control, the connection of the swivel arm to one side of the torque tube will disconnect due to the force applied overcoming the force of the spring holding connection in place.


Can anyone identify this tri wing twin engine WW1 plane Can anybody identify this WW1 or earlier plane? This tri-wing plane has two engines, most others I have googled have only one.

Gianni Caprioni's 1918 Ca 4 triplane bomber, shown here with Caprioni and three companion aircraft. It has a twin boom tail and a pusher prop in the center pod, so it is a triengine triplane.

source


Would a tumbleweed sucked into a jet engine on takeoff cause a serious problem? I saw tumbleweeds going across flight path in El Paso, TX and it made me wonder, especially after seeing what birds can do.

Would a tumbleweed ingested by a jet engine on takeoff cause serious problems?

Luckily tumbleweed rolls and doesn't fly [like some geese].

I tried to check how much an average one weighs, I couldn't find out. But it will cause some degree of damage. The engine can fail, but if it's just one tumbleweed then it's just one engine, it'll be serious but not dangerous. Airliners can fly with one engine inoperative, they are designed for it.

If it happens before the airplane reaches what's called a V1 speed, the flight crew can just abort the takeoff.

I didn't find any occurrence/report of it happening before. And it hasn't been tested before (they test using chicken guns).

Airport tower controllers and ground staff are vigilant in spotting such things, as this story shows:

  Escorted back for questioning!


Is it legal to board a plane dressed like a flight crew member if you are not a crew member? Just out of curiosity: Are flight crew suits reserved to certain persons or can just be worn freely, provided one doesn't use company logos or other protected brand markings. If the country does matter, then in UK.

(Picture source)

Are the insignia like golden stripes or cap regulated by a public authority? Now questions of security may also be invoked by the Captain, or dictated by airline's rules, but that's not my main point, though explanations are welcome.

Without a precedent, there is no answer about legality. The French law about military uniforms (and by extension postal workers if they are government employees) is based on the Geneva Convention based on precedents and war crimes.

Disguised as a postal worker, René Veuve acquired and transmitted information about crucial enemy infrastructure, such as Le Bourget airport, an oil refinery and an underground rocket factory.

In this case René was a hero, now imagine the opposite happening from the Axis powers.

For this question, no one on the internet can/should say whether it's legal or not for a civilian to wear a generic* pilot's uniform and board a flight.
The precedents we have show that those who did it, did it for illegal reasons, not for fashion.
* For the non-generic uniforms as in this case, a man was charged in the U.S. with falsely impersonating persons privately employed. But I'd say from a distance you can't tell the difference, and so a prosecutor may ask for the same charge (only one way to know).
Security
The airport security may stop the good-looking person for questioning and they will be searched. Because that's one way to try to get contraband in/out of a country.

Man Carrying Cocaine Pretends to Be Delta Pilot at JFK Airport

If flying internationally, the border control officer may have a question or two to the non-pilot in uniform.
For the U.S., pilots in uniform are required to show two IDs:

(...) one from their company and one from the government, to be checked against a secure flight crew database.

It may be seen as a way to skip the security lines.
Airline / flight crew
The airline personnel may object and deny boarding because it may be taken as an impersonator with a malicious intent to gain access to the cockpit.

Frenchman impersonating pilot caught in cockpit of US Airways plane

Passengers don't know better, and the airline may not like it for their passengers to think their pilot is sleeping (see story below), or worse, drunk (or will they deny drinks?).

Pilot caught napping in business class while trainee flew the plane

Airline passenger accused of impersonating a pilot is rumbled

Man was wearing a Cathay Pacific uniform and claimed he was off-duty. Flight attendants grew suspicious and soon learned he was not a pilot.

Note: Not all airlines allow their staff to wear uniform when off-duty.
In other news, a drunk pilot in uniform may cause panic and stress to passengers, what if that civilian is also intoxicated?

Common sense says to avoid that.
I don't think we will find an aviation regulation for that, it will be a local matter fit for Law.SE, i.e., if you were denied boarding, do you have the legal grounds to sue the airport/airline?
Once someone tries it, sues the airline/airport, and the court passes a sentence, then we'll know (for one jurisdiction at least).


How do flight procedure designers decide when to assign an altitude constraint to a waypoint? I am studying procedure design manuals (TERPS, PBN 8260.58A manual, ICAO PANS-OPS 8168 manual etc.) and I haven't found any guidelines concerning altitude constraints that can be imposed on a waypoint.

Take, for example, JFK's DEEZ FIVE departure. CESID has an "AT or ABOVE 2500" altitude constraint. Is there a reason that an altitude constraint was imposed on CESID, rather than on e.g. SKORR or YNKEE?

Another example, as far as STARs are concerned, is SEA's HAWKZ SEVEN. There is a Minimum Enroute Altitude for each leg, which is more than enough both for obstacle clearance and for communication. Why did the designers decide to an "At or ABOVE FL220" at PTERA? And why at PTERA and not e.g. at KRIEG, KNGDM or WRUSL?

Can someone point me in the right direction?

Altitude limits on these procedures have to take many different things into account, including obstacle clearance and communication, but also radar coverage, separation from other procedures and airspace, the overall profile of the procedure, noise abatement, and more.

The at or above 2500 restriction on the DEEZZ is similarly included in the other SIDs at KJFK. The main reason could be that the NYPD operates helicopters out of Floyd Bennett Field below that area, and the Jamaica Bay seaplane base is also nearby. Another reason could be to keep aircraft above the approach for runways 4L and 4R, though I'm not sure they would use those at the same time. It could also help noise abatement for the homes and parks in the area.

In the case of the HAWKZ, my guess on the altitude restriction is to keep all the aircraft on those segments at approximately the same altitudes. It seems like an aircraft could be lower than FL220 at PTERA without other issues, but the lower an aircraft descends, the slower it flies, and it would become difficult to work a slower aircraft in with the faster stream of traffic at the higher altitude. This sort of restriction is not uncommon on STARs that begin relatively far out.


Is it feasible to replace a C152's engine with multiple small turbine engines? If I wanted to remove the piston engine from a cheap plane like a Cessna 152 and add small turbine engines with an equivalent thrust but weighing less, where would be the best place structurally to mount them? I'm thinking one small turbine on each side of the tail and two on the wings.

What problems may I expect?

Have a look at the Cri-Cri propeller and jet versions.  Yes, jets can be mounted near the nose, but the plane must still balance at within its specified CG range.  This is why removing the engine in front and placing jets in back is out (unless you want to really go crazy and mount a Gatling in the front). Remember, it must balance.
However, at Cessna (152) speeds, props are vastly more efficient, so a $turboprop$ is not out of the question and, indeed, these are found on crop dusters.
"Pocket jets" are also found on motor gliders, and I have often thought of putting 4 of these on a sailplane.
However, another key consideration is how much stress an airframe can take.  With jets come higher speeds.  These planes are built to flying within a certain speed "envelope" regardless of propulsion source.
The "Screamin' Sasquatch" may interest you.  Here a jet is mounted on a sturdy bi-plane, and yes, it works.


How could an airliner as big as B777 make a U Turn on ground? I just heard about this 4 month old incident, where a United Airlines B777 made a U-turn, while it was on way to runway. What is the turning radius required to make such a U-Turn? Also, is so much space available near the taxi area at the IGI Airport? At last, is this a common practice for airliners to do?

Turning Radius, as found in a planning document:

28.7m for a Boeing 777-200
34.7m for a Boeing 777-300

Rotating around one a point a bit off the wing to allow both wheels to roll throughout.

Minimum Pavement Width

47.5m for a Boeing 777-200
56.0m for a Boeing 777-300

Source

Be aware that this is not exactly ideal- visibility from the flightdeck is not great and you do not want the gear running into the grass or edge lights. An Emirates A380 screwed up in Warsaw not too long ago when trying to pull this stunt.

Since this width is not normally provided by the runway (even Heathrow only has 45m and 50m runway width), you will add turning pads at the end unless there are taxiways you can use instead.

Source


How is a sideslip maintained (aerodynamically)? (Public domain image that I've modified.)

The initial rudder deflection to the left creates a side force that points right and yaws the plane to the left.

NASA puts it this way:

  For the vertical stabilizer and rudder, the orientation of the airfoil causes a side force to be generated. With greater deflection of the rudder to the left, the side force increases to the right.

But in a forced slip, isn't the fin's airfoil now in a negative angle-of-attack (from the perspective of the earlier force). How is the force maintained?

I'm looking for an answer regarding only the yaw, ignoring the roll/pitch side effects.

(Source)

Here's a representative image of the variation in lift coefficient with respect to angle of attack.  The same airfoil is considered in a "clean" configuration, with a deflected flap, and then with both flap and slat (you can ignore the last, which is the uppermost example).  You can see that, with deflected flap (or, shall we say, rudder) the lift slope shifts upwards, changing the lifting generated at a given angle of attack since the rudder deflection has, effectively, changed the airfoil's camber.

Hence, while the airfoil's angle of attack has changed, the lift generated at that angle of attack has also changed.  Cambered airfoils can generate lift at negative angles of attack and so, for a given rudder input, the aircraft will assume a steady sideslip angle where the induced yawing moment is in equilibrium with any restoring moments generated by the rest of the airframe.  From my time flying gliders, this could be illustrated by the fact that, no matter how much rudder I put in, I could only make the aircraft yaw so far--there just simply wasn't enough aerodynamic control authority to overcome the force you mention as well as unbalanced yawing moments generated by the fuselage and wings.  But, at the same time, I could intuitively change my sideslip angle by proportionally varying the amount of rudder I put in or, to be consistent, I could modify the aircraft's equilibrium position in yaw by incrementally "changing the camber" of the vertical tail.


What are the approximate glide angles for modern passenger jets? What is a typical glide angle for a modern passenger jet with engines idling, with full flaps and with the gear down?

It must be in the region between 1/5 (11.3°) and 1/10 (5.7°), and closer to the shallower angle. I guess you want the value at 1.3 times stall speed - without a speed an answer would be impossible.

Once the glide ratio drops below 1/5, the energy dissipation is too quick to allow rotation for a soft touchdown with idle thrust. On the other hand, a glide ratio much in excess of 1/10 will make the aircraft float along the runway in ground effect, which makes the precise selection of the touchdown point (at the correct touchdown speed) hard. Spoilers help to adjust the glide path angle to steeper values, so the aircraft with flaps and gear fully deployed but the spoilers in should have a glide angle around 5° to 7°.


Does a history of social anxiety significantly damage commercial pilot career prospects? Yeah, I've had a history with social anxiety although it's all sorted now because I got therapy. I was wondering if it's important that I disclose this to employers or just lie if asked? Would they be able to find out? And yeah, if I did disclose this would it harm the chances of me achieving my dream of being a commercial pilot?

I ask this as I know people with a history of depression aren't meant to be commercial pilots.

I don't know about the question in your title, but I can answer the question in the body:

  I was wondering if it's important that I disclose this to employers or just lie if asked?

No, you should not lie about your medical history. If you knowingly lie about your medical history, and it subsequently comes out, it could cost you your career - including the tens of thousands of pounds (or euros or dollars) you spent on getting your CPL or ATPL. Even if you have insurance against losing your medical certificate, they almost certainly won't pay out in this case, leaving you with a debt bigger than a student loan and no job to pay it off. It'll also make it much harder to get a medical certificate in future and return to flying status.

Worse yet, if the reason this comes out is because of an accident, you may face a criminal investigation because you flew knowing that your medical certificate was not valid, regardless of whether you think your condition could have contributed. You can't expect your employer (ex-employer) to stand up for you in this case.

Although I have a class 2 medical in the UK, I'm no expert in the medical requirements. It would surprise me if a past mental health condition which doesn't really affect your ability to fly, and which was successfully treated without medication, would stop you getting even a class 1 medical. It would probably just mean more uncomfortable questions in the medical exam, and probably having to get a written opinion from the psychiatrist who treated you. That might cost you some time and cash in the short term, but it's worth it to know it won't come back to haunt you later.


Why was the U-2 so different from the SR-71? Both were designed for the same goals: taking photographs at high altitude, avoiding radar. Both were designed by the same company with a few years apart. Yet one is a "jet glider", with large wingspan, small chord, subsonic, and the other is a ultra high speed, delta wing airplane.

Why did these two planes took such different approaches to perform similar tasks? What would be the pros/cons of each? The SR-71 was developed later, so it could be seen as a better approach, yet it was retired, while the U-2 is still in use.

Because the requirements were different. When U-2 was developed, the requirement was for an aircraft which would fly high at 70,000' due to the (mistaken) belief that the Soviets would be able to detect and engage aircraft only below that altitudes.

Once the U-2 entered service however, it became obvious that they could detect U-2 (they complained about the overflights, though misidentifying the aircraft), and once an aircraft was shot down, it became obvious that U2 isn't going to be of much help.

SR-71, which came later, was the result of a requirement which expected it to not only fly higher, but more importantly, faster. Interestingly, the Soviets went the same way with the Mig-25R.

The main reason for the retirement of spy aircraft was the advent of reconnaissance satellites, which are immune to being shot down (not that it is impossible, but no one has done it except in tests). Spy aircraft are still operated only over areas where the threat from anti-aircraft systems are extremely limited or non-existent. At the time of its retirement, the USAF accepted that even the SR-71 is not invulnerable:

  In congressional testimony, Air Force Chief of Staff Gen. Larry D. Welch identified the increased survivability of reconnaissance satellites, SR-71 vulnerability to the Soviet SAM-5 surface-to-air missile and the cost of maintaining the SR-71 fleet.

As for why U2 has outlived the SR-71, the main reason is the operating costs- the operating costs of SR-71 is quoted to be anywhere from \$85,000 to \$200,000 per hour, while the U-2 costs much less than that (incidentally, U-2s operating cost is less than that of its proposed replacement, the RQ-4 Global Hawk).

From the same source as above:

  The Air Force decision to retire the Blackbirds in 1990 is based on several factors. ... The cost factor is the most significant to the Air Force because it limits expenditures in other areas. Reagan Administration Air Force Secretary Edward C. Aldridge Jr. estimated that the money used to operate the SR-71 fleet could operate and maintain two tactical fighter wings.