What purpose do wing root seals serve? What is the use of wing root seals? What kind of leaks are possible without having wing root seals, and if the seal is broken what kind of issues can airplanes face?

One thing the wing root seal does is keep water out of the join between the fuselage and the main spar. Water in there could corrode the spar or, if it is wooden, cause it to rot.


Where can I find the correct POH for my Cessna 152? I'm training in a C152 and the POH in the backseat has seen its days and I can barely use it, much less keep it from being getting worse than it is. This is a 1983 C152 Trainer aircraft. A lot of questions that I am doing in my flight planning and solo quizzes can be answered through the POH but because the plane is shared I don't want to take it out of the cockpit because it would anger other pilots who also need it. Is there a resource online I can find the POH? Also, I'm not sure but I figure I can't use any C152 POH, it has to be the one for my year and model, is that true too?

Strictly speaking the POH/AFM is specific to your airframe as it generally contains the weight and balance information which will be unique to your airframe as it is equipped. Thus you should always reference the POH that is in the plane for the most accurate source of information.

For example here is a nice scanned PDF of a POH for a C152. You should confirm that the numbers match those in the POH for the airframe. As long as they do you can use it for reference. The POH does not need to match for the specific year but it does need to match for the given aircraft configuration and setup in regards to the engine and performance data as well as any data related to things like extended range tanks etc.


Why do all airliners have life jackets? According to this question, life jackets are not mandatory in planes that do not fly over large bodies of water. However, I have never been on an airline flight without life jackets (and the corresponding safety demonstration).

Why do airlines not remove the life jackets from planes that fly over land? The plane would be lighter and the safety demonstration shorter. Moreover, it can not be hard to dedicate different planes to different routes and avoid returning the life jackets each time the plane has to fly over water.

The plane would be lighter.

Not by much.

  It cannot be hard to dedicate different planes to different routes.

This adds to the logistics difficulties in scheduling the airframes. It's MUCH easier if all the airframes can be used on all the routes.

  Returning the life jackets each time the plane has to fly over water.

This involves extra down-time/logistics before the airframe can fly the next trip.

You've used the phrase, "large bodies of water"; think about if the airplane needed to ditch in a "small body of water". It would be preferrable that all people had life jackets and thus a chance to live.


Has anybody done gliding experiments with exact replicas of the birds or other real world flying creatures? The most obvious way to verify if birds are stable or not in at least gliding flight would be to make the exact rigid model of the bird (including weight distribution) and launch it into flight. The simplest approach that even early aircraft inventors may have tried is to use a frozen real bird.

Are there any references about anybody trying such experiments? Pure logical or mathematical analysis is outside the topic of this question.

The closest I know of are several attempts to build models of pterosaurs.

Since the head with its long beak is ahead of their center of gravity, the configuration is statically unstable in yaw and needs continuous control corrections. On the other hand, this instability provides very quick responses. This YouTube movie contains footage of a Pterodactyl model made by Paul MacCready in flight. Note that Paul had attached a conventional tail for the first flights to statically stabilize the model in pitch and yaw. Later in the flights this tail was removed. The small skin area between the legs was most likely not sufficient for pitch stabilization, and small changes in wing sweep were used to stabilize the animals in pitch, just like modern birds still do.

Another branch, the Rhamphorhynchoidea, had a tail which provided additional lateral and longitudinal control. Palaeobiologists are still arguing, however, whether the tip of the tail was oriented horizontally or vertically in flight.


Is it practical to become an airline pilot in order to travel internationally? I am a person with very diverse interests and a lot of life goals I want to achieve. One of them is becoming an airline pilot (just working as one for a year or two) and the other is traveling the world.

I would like to combine two goals in one, that is becoming an airline pilot after I finish college and travelling the world at the same time, i.e. flying intercontinental flights.

So, my question is basically this: Is it possible to learn to fly and become an airline pilot within about 3 years (let's say age 20-23), then immediately get employed as an airline pilot and fly intercontinental routes (even as a co-pilot)?

No, this is not a good idea, and No, it is not possible finish your education at 23, and then get employed as an intercontinental airline pilot.

It seems you have a distorted idea of what an airline pilot actually does. An intercontinental airline pilot usually spends just 24 hours at the layover destination. Much of that time is spent sleeping to recover from the fatigue of the long haul flight and sleeping to prepare for the next long haul flight. Not much time for sight-seeing.

The first requirement for becoming an airline pilot is a love of aviation and aircraft.  Most airline pilots today have been passionate about aviation since an early age.

You will never be successful unless you are passionate about aviation due to all the roadblocks and hardships you will have to overcome in order to reach your goal.

To say that you only want to do it for 1-2 years is proof enough that you don't have what it takes.


What are outer marker horizontal dimensions at 3 degrees ILS path? What is the outer marker "distance" along the flight path of a 3 degree ILS?

I provide my two approaches below, but as they contradict each other, I am asking this question to learn the proper answer.

Approach #1: Wikipedia says OM horizontal dimensions is an ellpsoid of 2400 x 4200 ft (I assume the former is the dimension parallel to aircraft's path ) at 1000 ft. I assume vertically OM signal is of conical shape, therefore its horizontal size expands and should be (proportionally) larger at higher altitudes. At 3 degree glideslope, altitude range for OM crossing is between 1200 and 2100 ft (4 NM and 7 NM respectively). This gives an answer to my question equal to a range between 2400 * 1.2 = 2880 and 2400 * 2.1 = 5040 ft.

Approach #2: Flying at 100 kts, I can hear OM for ca. 12 seconds at 4.4 DME. This translates to 2000 ft of OM length at height of 1500 ft. Empiria does not give a range, but still contradicts wikipedia and is much more reasonable number, as I cannot remember hearing OM for almost half a minute while flying over...

As Ron Beyer commented, it's more of a flat ellipsoid (egg), not a cone.

Full Image

Another site shows that image:

From the United States Standard Flight Inspection Manual, the tolerances are:

Minor axis being parallel to approach:


Are there any safety mechanisms to prevent emergency slides deploying inside an aircraft? Does this kind of situation happen, or is this a test situation? Are there mechanisms to prevent inward deployment of emergency slides?

Yes, they can inflate into the cabin. The FAA has been criticized for not taking better action regarding this and several other escape issues. Consider what happened on July 6, 2013 when Flight 214 struck the sea wall while landing...

Here is a direct quote:

  During the crash two of the inflatable chutes deployed into the cabin. The first chute, which blocked the forward right exit, nearly suffocated a flight attendant and was deflated by a pilot with a fire axe from the cockpit. The second chute expanded toward the center of the aircraft near the fire. It trapped a second flight attendant until a co-pilot deflated it with a dinner knife.

When I worked for Continental Airlines, a slide would deploy unexpectedly either while the aircraft was stationary at the gate or while the attendants were opening the door (no fault of theirs). I have never heard of a slide deploying while in flight.


Are all student pilots required to have a TSA background check or just non-US Citizens? I know that non-US Citizens have to go through approval with the TSA before beginning flight training, however could one avoid that fee by waiting until after getting Citizenship to start flight training?

I am a Resident Alien and currently considering starting flight school, I'm just wondering if waiting until I apply for Citizenship in 2021 is worth doing or if I could start now.

My fear is that I am already 30 and would like to eventually get a position as a Part 135 pilot. I am worried that I am already too old to be making such a change and thus adding time would just be making the situation more hopeless than it may already be.

This page on the FAA website has details on getting your student pilot certificate.

• Resident and US citizen student pilots follow Student Pilot’s
Certificate Requirements.
• Foreign student pilots (non-resident) follow the Alien Flight Student Program

It appears from your question that you should follow the same procedure as US citizens.
Refer to AC 61-141. Everyone must get a TSA screening before being issued a Student Pilot Certificate.

6.3 The Flight Instructor Verifies the Applicant’s Government-Issued Photo ID.
The flight instructor verifies the applicant’s identity and
enters information from the applicant’s ID. If the applicant cannot
present acceptable ID, discontinue the application process. Verify
that the applicant has entered a correct date of birth. IACRA will not
process an application unless the applicant is within 90 calendar-days
of his or her 14th birthday or older. If the applicant is not of
sufficient age, discontinue the application.
7.8 TSA Security Vetting and Temporary Certificate Availability of the Paper Method.
Provided the applicant is not deemed a security
risk and is at least 14 years of age, the Airmen Certification Branch
issues a permanent Student Pilot Certificate and mails it to the
applicant. Applicants must also wait to receive a permanent plastic
certificate in the mail.


Why do uncontained engine failures still occur? One of the absolute requirements of an aircraft turbine engine (usually some sort of turbofan or turboprop) installation is that, in the event of a destructive failure of the engine, the engine cowling must be able to contain any and all fragments released in the process.  In layman’s terms: engine blow up, engine parts stay in cowling.  The cowling’s ability to contain an engine disintegration must be demonstrated in testing.  All of this has been the case, without exception, for decades.

And, yet, uncontained engine failures continue to occur.  As recently as October 2016, a 767’s engine exploded during takeoff.  (Yes, I know about the one with the 737 earlier this year, but that one’s still under investigation, and, as such, off-topic until the NTSB releases their final report.)

Why is this?  It can’t be for lack of testing capability, as the engine manufacturers can and do – indeed, are required by law to – blow up engines in their test stands to verify their inability to escape their cowlings, and causing an engine failure for such a purpose is ridiculously easy: wrap some detcord around a fan or turbine blade (to test against the engine throwing a blade), tie it to a fan or turbine disk (to test against one of the rotors seeing fit to come apart in flight), or wrap it around the engine shaft (to test against a shaft separation and consequent turbine overspeed and disintegration, LOT 007-style), run the engine up to full blast, and push the button.  So why do engine cowlings still sometimes fail to contain rapid unplanned engine disassemblies?

One of the absolute requirements of an aircraft turbine engine (usually some sort of turbofan or turboprop) installation is that, in the event of a destructive failure of the engine, the engine cowling must be able to contain any and all fragments released in the process.

No, there is not. The requirement is that the engine cowling must be able to contain fragments released in case of a single blade failure.

If just a blade fails, it will often break more downstream, but as long as it is just blades breaking loose, the casing should be able to stop them and generally does.

However if the disk that holds the blades itself breaks, the energy is much higher and the cowling can't stop that. It is not really possible to make it strong enough to contain this as it would be too heavy for flight, so it is not a requirement.

All¹ the recent cases of uncontained engine failures were that the whole disk broke and left the engine in several large pieces.

¹ The Southwest flight 1380, B737 near Philadelphia on Apr 17th 2018 is a kind of exception. It was only a blade failure, but it was also initially contained. The blade that failed was actually stopped by the cowling. However then a secondary failure of the inlet cowling itself, well ahead of the fan, occurred and that was what caused the further damage and injury.


How does a Secondary Surveilliance Radar send data? When aircraft are detected by radar and their transponders 'ping' back to the radar site, this data is passed over data network cables to the air traffic controllers.

Is there typically any specialist equipment (high safety certification?) to send the data from the radar site on to the data network? Or is it something as simple as a server/PC with a network card?

I'll describe the typical Mode-S radar system based on my mostly European experience. Details will vary but the general concept applies world wide.

The radio signal received from the aircraft is digitized, CRC checked,  compared to and combined with data from earlier transmissions from the aircraft. This data is usually encoded in ASTERIX format (typically category 048PDF) and transmitted over a datalink to a surveillance data processing system (SDPS) in the ATC centre. From the SDPS the data is further distributed to various client systems, among which the air traffic controller display system is one.

The radar processing itself is partly dedicated hardware and partly COTS (commercial-off-the-shelf) infrastructure. This is housed in a standard server cabinet. Network components are typically COTS high quality systems and duplicated for redundancy.

The datalink from the radar site to the ATC facilities can take many forms. Every country has its own regulator and local telecom market peculiarities, leading to a variety of implementations. Often a dedicated line will be used, usually with a backup line as well. Sometimes two telecom providers are used that have to provide fully independent data paths to the ATC centre. In a few cases radio links are used to connect surveillance systems, I know of surveillance systems (not radars) that use satellite links.

Within the ATC centre usually duplicated or triplicated networks are used for redundancy. These can be UTP or glassfibre networks. These are again based on COTS high availability/integrity components.


Why are wings not tapered all the way to reduce vortex drag? Wingtip vortices are created by, well, wingtips. These vortices create drag. One of the approaches to reducing this drag is taper the wing,

source

source
Will eliminating the wingtip, as on the lower left, eliminate these vortices, and thus eliminate induced drag? Why or why not?

One of the approaches to reducing this drag is taper the wing

No, not at all. The vortex strength depends on the lift at the center wing. This strength invariably tapers to zero towards the wingtip, regardless of the wing's geometric taper ratio. The taper ratio will only change the local gradient, not the absolute decline in vortex strength. In the end, what happens at the tip is insignificant for the shape and strength of the wake.


Why are airspeed gauges labeled above Vne? Examples:

Cessna 150L Vne = 141 knots (162 MPH), gauge labeled to 170 knots. It looks like there's room to extend the scale to 180.
Cessna 152 Vne = 149 KIAS, gauge labeled to 170.
Cessna 172R Vne = 163 KIAS, gauge to 200

Is the extra range deliberate? Is there a use for it?

Is this specific to Cessna models? I browsed instrument panel photos and didn't find a non-Cessna example. For most aircraft, it seems the range extends past Vne only to the next convenient round number.

I can think of several reasons, why you would want to have some extra room:

The fact that you should not exceed $ V_\mathrm{ne} $, does not mean you never actually do. It would be good to know by how much you are currently exceeding it, so you can decide how to react to this situation.
Not every aircraft model gets their own specific gauge. Cessna probably has a few gauges available and put the one with the smallest extra room above $ V_\mathrm{ne} $ on the aircraft. This is quite similar to cars, where you get the same speedometer on most models of a car, despite having different engines and thus different maximum speeds. It is simply cheaper to produce (and certify) only a few different airspeed indicators.
The aircraft's $ V_\mathrm{ne} $ might change with modifications installed at a later time (like an aerodynamic upgrade package). It would be nice, if the avionics would not need to be exchanged for this.

As to whether or not it is specific to Cessna: A quick Google search for "PA28 airspeed indicator" shows several Pipers with a lot of extra room (although some only have around 10 knots). I assume this is not much different for other aircraft manufacturers and just depends on which gauges where available.


What happens to Ryanair aircraft after they leave the airline? According to the fleet renovation and the short age of all their aircraft (6.5 years), what happens to Ryanair's aircraft after their time in the company? Are there other companies willing to accept Ryanair's aircraft configurations?

Most of Ryanair's fleets is sold upon delivery and leased back from lessors. The lessors will then lease the aircraft out to another airline for as long as its safe for the aircraft to be flying.

An example for MSN 29921 would be:

EI-CSF    24. May 2000    Ryanair
C-FTCX    28. Mar 2008    CanJet
OK-TSJ    05. May 2015    Travel Service
C-FTCX    05. Nov 2015    CanJet
C-FTCX    04. Dec 2015    Air Transat
SP-ENO    30. May 2016    Enter Air

(planespotters.net)


When approaching a stall, is the first priority to apply power or lower nose? I’ve always wondered. And I’d assume it’s the same regardless of aircraft? But when approaching a stall would the main priority be adding more power?

I ask because what if a crew was on final for landing and approached a stall, the rear end is dropping and the nose is rising. I feel like the flaps at their current position during landing, would only make matters worse? And applying power could make more lift with a poor angle of attack?

Would a crew lower the flaps in that situation, after applying more power and pushing the control columns forward?

The instinct drilled into a pilot's head from the beginning as the primary response is "lower the nose" to lower AOA.  If you learn in a glider, that's the only option, so it's easy to drill the instinct into peoples' heads (one reason that glider training before power is so good for pilot skills later).  In a power plane, it's lower the nose and add as much power as you need, but lower the nose must be the first instinctive action.  How much to lower the nose depends...

In a non FBW jet (FBW is another story, the computers taking care of things on your behalf whether you want them to or not), the stall training you get for low altitude stalls (you don't get to an actual stall - you start from stick shaker onset) is lower the nose but not too much, add thrust to maximum, and regulate the pitch attitude to stay just above stick shaker onset (just above the speed tape's "barber pole", the red broken band that indicates the stall region) and if flaps are at landing setting, call for retraction to go-around flap once you have stopped descending and are accelerating with decent speed margin above shaker.

The objective is to minimize the altitude loss as you recover airspeed.  At shaker onset you still have some margin above the actual stall and if you're close to the ground you don't want to dive, so you just tease the pitch to hold it on the edge of shaker.  You will generally use this procedure for any stick shaker event in denser air, below, say, 10000 or 15000 ft.  As a general rule, you do not make configuration changes with gear and flaps until you have got yourself in a good situation energy wise (not sinking, accelerating - although there may be variations from a/c type to type) because retracting flaps can increase your sink rate and the standard procedure with gear is not to retract until there is a positive climb rate.

At high altitudes, especially above 30000 ft, the stick shaker recovery method is much more aggressive and you are trained to actually push over enough to lose several thousand feet and not be concerned with altitude loss. In the thin air the practice of teasing the pitch to stay just above shaker doesn't work so well, because the air is thin but the inertial mass of the machine is unchanged and that can get you into trouble if you fly it the way you do down low.  You can find yourself back into the shaker/pusher/stall break region if you work the pitch to manage AOA on the edge of shaker the way you would close to the ground.

One of the events that lead to special high altitude stall recovery training during recurrent training was this famous (within the business) Pinnacle Airlines incident with a CRJ200 (quite a harrowing read; I don't think it was mentioned in the report, but the post crash fire was caused when they slid into a back yard garage with a meth lab in it).


Vector to final on RNAV approach with the Intermediate and final segments are not aligned Consider the RNAV 30 approach to C83 (Byron, CA),

On a recent training flight requesting vectors for the approach, ATC pointed us to the MOVDD IF before cutting us loose (informing us that we would be getting a vector to that fix). The segment between here and the FAF is 11 degrees off from the final segment. On a GTN650 at least (and I assume other similar Garmin devices), selecting “Vectors” as the approach method gives you the FAF line with your deviation from it & sequences from the FAF. This seems not correct for flying this particular approach. The best my CFI & I could come up with was to enter the approach as being flown from the IAF (SMONE) then select “Direct to MOVDD” sometime before reaching it (such as when ATC gives the last turn), after which the GPS will sequence to the intermediate-to-final segment. But this seems non-standard. What do others do in this situation?

Since most fatal accidents are during approach, it is important to maintain 100% compliance with the procedure and have a clear understanding of what your FMS will do with different modes.
There is an important Garmin / FMS distinction between:

Selecting "Activate Approach" mode when navigating to a fix leading to an approach sequence, and;

Navigating directly to the FAF via ATC vectors by selecting  "Vectors to Final" ("VTF") mode.

If you select Vectors to Final in G1000 or G3000 (likely similar to your G650), the following things happen (from memory, I may have missed a few):

The waypoints in the flight plan are bypassed (but remain inactive in the plan and available to re-navigate direct to) and the FAF is made active;

Approach mode is engaged (which increases needle sensitivity);

If you have a non-GPS approach loaded, the frequency for that approach is made active and the needles switch to the relevant indication (green needles for ILS for example);

If you are navigating to a GPS waypoint, the FMS turns off lateral guidance and engages roll-mode (if you are in Heading mode, that mode is maintained);

The HSI Bearing Needle is set to the final approach course (or outbound course for a back course approach);

A graphical magenta line representing an extension of the line between the touchdown zone and the FAF is drawn on the map.

It would be unusual to use VTF (in IFR conditions) without being under some form of ATC guidance on vectors and terrain clearance - Hence 'Vectors' to Final. The use for VTF mode is usually when the pilot receives a clearance as follows:

ATC: N188L, six miles from BABPI, turn right heading 280, maintain two thousand six hundred until established on final approach course, cleared RNAV runway 30 approach Byron Airport.
Pilot: Right turn 280, two thousand six hundred until established, cleared RNAV 30 approach, 88L.

(The italicized sections are meaningful; look them up in the Pilot Controller Glossary)
At that point (assuming already at 2600), the pilot

Affirms the correct approach is loaded in the FMS flight plan;
Dials in 280º on the heading bug;
Engages heading mode, and;
selects Vectors to Final and the Garmin will then auto engage the approach from the FAF inbound. (Since this is a LPV approach, the Garmin will also intercept the vertical flight path.)

A contrary but common clearance might also be:

ATC: N188L, cleared direct MOVDD, cross MOVDD at or above three thousand, cleared RNAV runway 30 approach Byron Airport.
Pilot: Direct MOVDD, MOVDD at or above three thousand, cleared RNAV 30 approach, 88L.

In this case, there is a distinctly different FMS sequence:

Affirm the correct approach is loaded in the FMS flight plan;
Select MOVDD in the flight plan (this will be either an IAF or an IF);
Select Direct To - Enter - Enter to make active;
Select FMS mode (if not already selected and skipping the part to make sure the ship does not jump uncomfortably towards MOVDD);
Engage Approach Mode;
The Garmin will now auto sequence the approach including auto selecting green needles to fly an ILS or VOR if required. The Garmin will also intercept the vertical flight path if available.

You state in your question ATC pointed us to the MOVDD IF before cutting us loose (informing us that we would be getting a vector to that fix)
So what you do is:

Enter Direct To MOVDD and fly that course;
Select Activate Approach when you are cleared to fly that approach;
If ATC gives you a vector (perhaps because ATC does not want you to go straight there) then you enter heading mode and use the bug for that vector. Reset Direct To when ATC stops vectoring you.
Even if you receive a vector, you continue to have MOVDD as the active waypoint and you do not engage VTF unless you receive a clearance and a vector related to that clearance with the intent of you ending up on the final approach course near the FAF or a linear extension of the final approach course.

For illustration, consider the approach to KEGE (below, with the Vectors To Final magenta line drawn.
If you were to select VTF well outside of the IAF for this approach (and you were not under ATC POSITIVE CONTROL) there is a high risk that you would hit the 11,200 foot mountain just 7 miles from the FAF on the magenta line.
If VTF is engaged at a time when the pilot does not understand the sequence or limitations, BAD THINGS CAN HAPPEN! The FMS itself does not maintain terrain clearance for you.


What does an owner/operator need to do to legally rent out their aircraft? I am interested in knowing all regulations apply to about what an owner operator needs to do to legally rent their aircraft out for private/business usage or flight instruction.

What inspections?
Insurance requirements?
Anything else?

I assume renting your aircraft out is under part 91.

As Farhan noted, the rules are essentially the same as if you buy a plane to provide instruction in it.

Inspections and Maintenance

In addition to your required annual inspection you will also be required to complete a 100-hour inspection every 100-hours of operation.

Insurance

You will need a commercial insurance policy which allows you to rent the aircraft.
This policy covers the aircraft, so you will also need (or at least want) general liability insurance and all the other trimmings that come with operating a business.

Everything Else

This is a broad category. There's no way we can cover it all. You will however need to consider:

Maintaining an adequate stock of "service spares" to maintain the aircraft.
Tires, light bulbs, oil, oil filters, 5606 hydraulic fluid, etc. - As an individual owner you may be OK with being down for a week waiting for parts, but as a rental operation that will lose you customers.
Having a relationship with a mechanic to do the maintenance
Owner-Performed Preventive Maintenance goes out the window when the aircraft becomes a rental - you may still be able to assist your mechanic, but you can no longer do & sign-off on things like oil changes.
Vetting your renters
Rental aircraft at an FBO/Flight School live a hard life. If you like your plane and want it to stay in good condition you'll need to vet your renters a bit more thoroughly than "You have a pilot's license and you went around the pattern without hitting anything" - Find the kind of pilots who will police their trash from the cabin, lean the mixture appropriately, etc.


Can you identify this scrap cockpit section I found in a scrapyard? I recently found a scrap cockpit in a scrap yard, and I'm hoping there's enough remaining to identify the aircraft type from pictures.
Unfortunately, all are taken through fencing as I don't have access to the compound.
Imgur Link

Going by the cockpit glazing, I'd say that's a Hawker Siddeley HS.748:


Could an airplane dock with a set of wing extensions while airborne? I figure there are limitations to wingspan while on the ground but could we engineer wings that stay aloft or get towed to allow a plane to 'dock' with them in order to fly higher/longer/more efficiently?

Actually, a similar concept was tested by the USAF in the 50s (like most things in aviation, it seems).  Under the name of Project Tom Tom, the military was looking into the possibility of coupling a parasite fighter (an F-84 in this instance) to a B-36 as a long-distance escort as it flew into the Soviet Union by joining the two aircraft together at the wingtips.  Flying as such, the F-84 would actually power down its engines during coupled flight and could receive fuel from the B-36.  However, the aspect with greater relevance to the question is that the B-36 would actually derive an aerodynamic benefit from this arrangment as well.  In theory, the combined aircraft would also benefit from having an artificially elongated wing as well, and, while I remember reading last year that this actually did result in superior fuel efficiency for the combined aircraft during cruise, I am at a loss to find that source right now.  At any rate, with respect to this question, the B-36 effectively docked with a pair of "wing extensions" (in this case, a pair of F-84s) while in flight and derived a benefit in cruise.  A video of the concept can be found here:

            .  Also, more reading can be found in this text Flying Aircraft Carriers of the USAF: Wing Tip Coupling by Brian Lockett.

Naturally, there were significant downsides to this idea.  While the F-84 actually did manage to engage the coupling mechanism on the B-36 on test flights, logging at least a couple hours of continuous, coupled flight, significant stability and safety issues were uncovered during testing that led to the scrapping of the project.  As noted in a quote from the project summary report:

  The wing-tip coupling mechanism as developed and flight tested in the Tom-Tom program is not considered satisfactory for tactical use and was barely acceptable for test flying. It appeared that a new difficulty and a now shortcoming were uncovered on virtually every test flight. The extent of rework necessary before the coupling mechanisms as designed were acceptable as flight test articles is covered under the DESIGN section of this report.

Similarly, issues with aeroelasticity turned out to be a much larger issue than originally expected (in part because of the change pitching/heaving forces as well as wing mass distribution and stiffness at the joint).  I think that Aurora Flight Sciences ran into similar issues when they were designing an entry for DARPA's Vulture project...the idea was to join multiple vehicles (that were essentially flying wings) to create a super-efficient, high-altitude, solar-powered, surveillance aircraft.  Due to conflicting requirements on wing structure and aircraft weight, I think that ultimately didn't fly...but I don't have any of the details for that.  Just what I remember from a presentation I saw many years ago.

At any rate, I guess that my answer is: yes, it could.  But it is VERY difficult and dangerous to do (at present).


What is the difference between a spin and an uncontrolled roll in an high speed dive? A comment I had on another (now deleted) question states that Air china 006 didn't spin. For me it was a spin (unwanted roll due to asymmetrical stall). The comment states it was "it was a slow roll during a very-high-speed dive".
How can I make the difference between both? What makes this occurrence of uncontrolled roll not a spin?

In the beginning of the article on Wikipedia it is stated that the plane experienced "high G forces and high speed". Not knowing the story of the flight but with this statement we can suppose that it wasn't a spin but rather a spiral dive. But when reading the full story it is stated that the lose of engine 4 leads to a decrease of the speed, that the pilot didn't had any rudder control, applied full left yoke and yet the airplane was still rolling right. Those are clear sign of a spin and not a spiral dive!!
A spin begin in situation where asymmetric stall occurs. In this situation the airplane start spinning on the yaw axis, the external wing creates more lift wherase the inner wing is stalled and drops, thus driving the nose down. But the main characteristic in a spin is that your airspeed is very small (which doesn't mean that the sink rate is not high) but prevent extreme aerodynamic loads on the aircraft and the g loading remain somewhat close to one during the spin. In one word the airplane is falling vertically from the sky spinning on itself, wing inclination can be close to 0 up to 90° depending on the aircraft.
On the other hand a spiral dive can occurs without any stall. When starting a turn if you let the nose drop, the inclination will increase and your speed will increase. At one point pulling on the yoke will only  tighten the turn and increase g forces but will not move the nose up. This situation can happen when you're focused on something on the ground and start turning to see it better. If you don't pay attention the nose will drop and it's a one way trip as you are focused on the ground and not your instruments. You reach VNE and loose control of the aircraft. In this situation the aircraft is flying a tight spiral to the ground with high wing inclination always increasing which can be seen as a slow roll.
In a spin you mostly use your rudder pedal to stop the rotation and then pull on the yoke wherase in a spiral dive you need to use the yoke to reduce inclination first and then pull. Adding some yoke to stop rotation in a spin will not help and worse may even flatten it and increase rotation speed. Using rudder pedals in a spiral dive won't have much effect, you need to bring down the inclination, level the wings and this is mostly done using the yoke while keeping your flight coordinated with rudder input if needed. Therefore it is important to differentiate both situations if you want to come out of one of them alive.


Numerous questions regarding ARINC429 protocol I recently made significant progress in my understanding on the ARINC429 thanks to a user on this site, but I after reading more into it, I may have confused myself a little bit. Any help on any of the following questions is greatly appreciated.

I found a specification pdf online, but it contradicts (i think) some of the other information I have gotten. The link to the pdf is here. Is it safe to assume that information is accurate enough to rely on? Assuming this book is a proper document on the ARINC429 specification
If the above is correct, is it correct that BNR data fields are represented in positive two's complement with bit 29 indicating its sign (positive/negative)? Wouldn't that just be regular binary with bit 29 indicating the values sign?
The scale factor applies starting from the MSB (bit 28) and continues halving with each bit between 27 and 11. The actual value translation would be applying the scale factor to each sig bit and adding the values of all the sig bits together to get the final value and using bit 29 to identify if its +/-. Is any of that correct at all?
How does the resolution work? I got confused a lot by that. What is it? How does it affect the data field?
Can somebody explain BNR format of the data field and how to translate it? I feel like I may have read too many different sources and got confused by the variance in explanations....haha

Resolutions in the A429 spec are approximate, so calculate them yourself.

Resolution = Range / (2^significant bits)

Here is one way to do it:
Load your 32 bits into a signed 32-bit integer.
Shift left 3 so the sign bit is now in bit 32.
Shift right (32-significant bits)-1 to form a 2's complement "fixed-point" number.
Convert to float and multiply by the resolution.
Done.

Note that when a signed integer is used the high bit is sign extended on the shift right.

"Fixed-point" is also known as "scaled" in some circles. It's a method of storing and performing math on a real number using an integer rather than using a float. The resolution is the weight of one lsb bit. The resolution is documented somewhere and multiplied by the integer to get the float when debugging and such, but machine code does not "know" that you think of it as a float.

The range is key to fixed -point numbers because it bounds the value. The number of significant bits affects the accuracy. You could use the wrong number of significant bits and still get a "usable"  number but with a possible loss of accuracy if you choose one that is too small. Beware that unused low bits are sometimes repurposed for status flags, etc., so don't expect these to alway be zero. Also, the specs describes an ideal standard but in the real world liberties are taken with labels repurposed as needed.

Because of the way 2's complement integers work, the max positive value possible will be the range minus the resolution. For instance, you can get exactly -180 degrees but not quite +180 degrees.


How to avoid talking over others when using different send/receive frequencies? Related to this question about flight services: when I talk to FSS over the generic or the local receive-only frequency while listening to the VOR voice channel, how do I avoid talking over others on the same frequency?

Intuitively, I'd listen to the frequency I'm going to be transmitting on for a bit, then send my request, and then wait for a reply on the other frequency, but that seems like it would be distracting to configure in the radio.

So how would I configure my radio for contacting FSS in this way?

Edit: this is specifically about the case where other aircraft do not necessarily hear the controller speaking to you, so they may start transmitting at any time while I'm receiving the response.

In the specific case of a flight service receive-only frequency you will be able to hear other aircraft transmitting in that frequency (you still listen to your com radio, so treat the transmitting part just like any other transmission and wait for a break before you key the mic).

In the more general case when you have one controller (or Flight Service Specialist) working multiple frequencies you call in when the one you're transmitting on is quiet (and in the case where you're receiving Flight Service over a VOR wait for that to be quiet too).

The controller or FSS will answer you if they're free. If they're busy on another frequency or a landline they'll respond with "Aircraft calling, stand by" (or if they're really busy and don't hear you you won't get a response and you'll try again in a minute).
It's not a perfect system, but it works pretty well most of the time.


Why wasn't Saint-Exupéry able to cover more distance before his 1935 desert crash? Is there any source that provides more details on Saint-Exupéry's desert crash in 1935 than Wikipedia does:

  On 30 December 1935, at 2:45 a.m., after 19 hours and 44 minutes in the air, Saint-Exupéry, along with his mechanic-navigator André Prévot, crashed in the Libyan desert, during an attempt to break the speed record in a Paris-to-Saigon air race and win a prize of 150,000 francs. The crash site is thought to have been near the Wadi Natrun valley, close to the Nile Delta.

I find hard to understand how flying for nearly 20 hours between Paris and Saigon can lead any plane to as short distance as middle Libya?

Google Maps shows a distance of approx. 1950 miles straight line between Paris and Wadi Natrun, which gives us nearly exactly 100 mph of speed, which is only half of Caudron Simoun's speed.

What am I missing? Is it / was it a regular practice to fly "that slow" on such large distances?

There are 6000 more miles to fly between Wadi Natrun and Saigon, according again to Google Maps. With 100 mph we have 60 hours of flight plus additional 20 hours already flown. Which gives us a total distance of 8000 miles or 80 hours with this speed. Was there any aircraft and pilot, in 1935, able to manage such trip, even assuming breaks in flight for fuel refilling and resting?

This site has more details on why it took so long to get to Libya
https://www.thisdayinaviation.com/30-december-1935-wind-sand-stars/

After taking off at Paris, Saint Exupéry followed the Seine to the valley of the Loire and continued south, crossing the southern coast of France near Marseilles. The fliers had been over the Mediterranean Sea for a short while when they saw fuel leaking from the left wing. Prévot calculated that they had lost 20 gallons (76 liters) of fuel. They turned back and landed at Marignane to repair the leak and refuel before continuing.  Saint Exupéry wrote, “I drank a cup of coffee while the time lost hurt like an open wound.”
Once again heading across the Mediterranean toward Tunis, they encountered low clouds and heavy rain which forced them down to just 60 feet (18 meters) over the water. They flew along the coast of Sardinia as the weather improved.
F-ANRY crossed the coast of Africa at Bizerte, Tunisia, and about fifteen minutes later landed to refuel. With two hours of daylight remaining, Saint Exupéry and Prévot took off again, now heading toward Benghazi, Libya. They landed there at 11:00 p.m., local time, and in just twenty minutes the airplane had been refueled and once more, they were airborne.
Flying east after moonset, Saint Exupéry and Prévot were in total darkness. After three hours a faint glow of his navigation lights on the airplane’s wingtips told Saint Exupéry that he had flown into clouds, with visibility measured in just feet.
At a time when there were no navigation aids, pilots had to navigate by their compass, airspeed indicator and clock. Though Saint Exupéry had met with meteorologists to plan his flight, there was no way to update the weather information after takeoff. He had no way of knowing whether an expected tailwind had held, or if it had changed; was his speed across the ground faster or slower than planned? Had the wind blown him right or left of course? Had the atmospheric pressure changed, causing his altimeter to read higher or lower than the airplane actually was? Flying across the emptiness of the  Sahara Desert with no landmarks, in total darkness and now just a few feet of visibility, he and Prévot could only guess at their position.
4 hours, 15 minutes after taking off from Benghazi, the C.630 crashed into gently rising terrain at 170 miles per hour (274 kilometers per hour).

More on the plane:

The Société des Avions Caudron C.630 Simoun was a four-place, single-engine, low-wing monoplane with fixed landing gear. It was built of wood, with the surface of the wings and fuselage covered in plywood sheet then covered with doped fabric. Carefully curved aluminum sheet metal covered the top and bottom of the fuselage. The C.630 was 8,70 meters (28 feet, 6½ inches) long with a wingspan of 10,40 meters (34 feet, 1½ inches) and height of 2,25 meters (7 feet, 4½ inches). The airplane’s gross weight was 1,230 kilograms (2,712 pounds).
The engine was an air-cooled, normally-aspirated 9.500 liter (579.736 cubic-inch-displacement) Renault Bengali 6Pri inverted inline six-cylinder overhead-valve (OHV) engine rated at 180 cheval vapeur (177.5 horsepower). The left-hand-tractor, direct-drive engine turned a two-bladed, metal Ratier variable-pitch propeller. The propeller could be set to coarse pitch by a mechanic prior to takeoff, then an air bladder mechanism could change it to fine pitch for cruise flight.
The C.630 had a maximum speed of 310 kilometers per hour (193 miles per hour). The service ceiling was 7,500 meters (24,606 feet) and normal range was 1,260 kilometers (783 miles). Twenty C.630s were built before production changed to the slightly improved C.631.

Not a lot different than my Cessna Cardinal, which is a little wider (35'6"), 4 seats, fixed gear, and 180 HP Lycoming engine with constant speed (variable pitch) prop totally controlled from within the cockpit. Service ceiling only 14,600 feet (altitude where climb rate drops to under 100 ft/min). Gross weight 2,500 lbs. Max speed (never exceed speed) is 192 mph, with max cruising speed of 158mph (speed not to exceed except in smooth air). Cardinal carries less fuel most likely, just 50 gallons, my best range at 10,000 ft is 615 miles.  I think our longest flight has been about 4 hours, can only listen to ATC for so long!


Will the 737 Max 10 have MCAS? With the fuselage plugs forward of the wing, would this mean the engines are closer to CG, therefore no need for MCAS?

The fuselage length is immaterial. The problem of the Max series relates to the positions of the engines versus the wing, and their aerodynamic interference near the at high alpha. The amount of fuselage ahead of the wing or behind the wing is not a major factor here.


Could the vertical stabilizer be removed on the NASA X-57? I was reading this article about how NASA will develop this new X-57 X-plane which has many tiny electric motors mounted on the wing.

Now, I wonder: How come this aircraft still has a vertical stabilizer? I thought that one of the points of having many tiny electric motors was that you needn’t worry about an engine failure (one engine fails, you shut down the one on the opposite side; you still have 12 working, no big deal). You probably don’t have to worry about lateral stability either, because those motors can probably easily stabilize sideslip oscillations (a bit like on a quadrotor, where you can maintain a stable hovering position thanks to accelerometers and fast control feedback).

Am I missing something?? If so, isn't there a way to downsize the stabilizer a little bit? How would you go about calculating that?

EDIT: I realize the problem of power failure, but couldn't it be just avoided by carrying lots of independant battery packs (instead of a central big one), so you can be sure that you statistically never lose control of all your engines?

Differential thrust is not a good way to control the yaw of an airplane. For one thing thrust control has to be extremely quick, if it takes even a second between a control input and the thrust response then you won't have adequate control over the airplane. For another you are entirely dependent on having engine power available for stability, if you lose your electrical system or your battery goes dead then so are you!

Another reason differential thrust is not a good idea is that at full power the only way to create differential thrust is to reduce power on one side. If I'm on climbout and I need to yaw I will lose climbing power, this means I would have to reduce my flight path angle to maintain airspeed. If I'm close to stall speed a sudden reduction in power could make me enough airspeed to stall. Not good. The only way to really mitigate against this is to increase motor power and restrict the maximum power a pilot can get. This is extra weight and cost.

Lastly, the X-57 has the engines all down the wings, this means that when the engines are going they will be producing airflow over the wing. Differential thrust means that the engines are forcing more air over one wing than the other, the wing getting more airflow will create more lift, this has the following undesirable characteristics:

A yaw input will have to be coordinated with reverse aileron to maintain level flight, a strong yaw input would need a stronger aileron change. This means badly coordinated controls and would not be very intuitive
At high angles of attack, for instance close to stall speed, sudden reduction of thrust over one wing could stall it while the other wing keeps flying, this would lead to a snap-roll and possible loss of control. In short it's dangerous.

Comparing quadcopter technologies to the technology going onto the X-57 is a bit of a misnomer:

Quadcopter motors are small and the blades are small compared to what will be used on the X-57, the ones on an airplane will be much bigger and will have a much larger response time as a result due to the longer moment arm
A quad has a higher thrust to weight ratio than the X-57 will, so less power available for differential thrust


I am 14 and want to be a pilot but don’t know how Currently I am 14, turning 15 and live in Victoria. I have this aspiration to become a commercial pilot, but I don’t know how.

Should I start flying now? Should I get a private pilot license by 16? What should I study for VCE? Do I need to go into aviation for university, or is there a special flying university? How bad is the competition? What are all the stages of becoming a pilot starting from 15 years of age? Should i enrol in a flying school now?

I know it is a lot to answer, but I really am passionate. Thanks.

Erica

PPL is a very good choice to begin with your pilot career.
- You got quite a good knowledge which will be really usefull when you go for the CPL.
- You begin to collect flying hours (which is the most important thing to get a job).
- And you may realize if you are fit to fly (sometimes wishes don't match reality).

University is fine, but afaik nowadays airline companies don't ask for such degree when you apply for a job. However, it'd be a bonus.
Competition was hell years ago ('07-17), in particular for those with very low flying hours, never the less, currently companies are hiring a lot.
Sorry but I know nothing about VCE (I'm not aussie), but, if I can change your question to ' What should I begin to study to get ready for PPL/CPL?', then I'd say that you must get ready for the two subjects which trouble the most students. Principles of flight, and General Navigation.
I don't know if they are out of reach from your current knowledge, but, you may give it a try. I'd suggest you to use the Oxford books, or Jeppesen ones. Both are really good ones.
And about the stages, in my opinion:

PPL (fly as much you can)
CPL
Try to get a job (probably Flight Instructor (get FI license)
Apply for a company

Good luck


Definition of a Deep Stall I've been doing some research for a uni assignment and I noticed that the RQ-11B uses a "deep stall landing" to get back onto the ground. What I don't understand though is how this aircraft gets into a deep stall, so far every definition of a deep stall that I've seen says that for an aircraft to be in a deep stall, the horizontal stabilisers are in the wake of turbulent air from the stalled main wings. The aircraft in question has high mounted wings and a conventional tailplane, so even in straight and level flight the horizontal stabilisers are below the dirty air from the wings and so when the angle of attack is increased, the tailplane only gets further away from this airflow.

So the main question is, is there another definition of a deep stall that doesn't need the horizontal stabilisers to be in the dirty air from the stalled wing.

This is the aircraft or rather SUAV in question

I believe you are correct and the terminology they used was incorrect. What possibly is being described is sometimes called "mushing". Some aircraft are capable of having the airspeed bleed off until the elevator is all the way up - it then mushes with a high descent rate to the ground.

I owned a Navion that would do this. If you slowly bleed the airspeed off and add full elevator it will end up with a 500-600fpm wallowing descent and severe buffeting (full aileron may be needed as the wings rock side to side).

Several Piper aircraft are also similar such as the PA-28-140 Cherokee. The Cherokee is known to run out of stabulator during flares and can pancake onto the runway - no damage but an embarrassing hard thump.

I have flown just about all the single engine and small twin engine Cessna's and none of them will do this. They have lots of elevator and are always capable of a nose dropping full stall.

Captain "Sully" Chesley Sullenberger reported he was aware the flight computer of the Airbus A320-214 did this (US Airways Flight 1549, "Miracle on the Hudson") and deliberately held the yoke all the way back and let the aircraft mush onto the Hudson River.


Are there any plans to make the QF-16 into a drone for actual combat missions, or a fully autonomous fighter? It appears to a naive layman like myself that the QF-16 is an excellent platform to use for remote controlled missions akin to that of other drones. Except that the F-16 appears to have a broader mission envelope than a Predator or Global Hawk. For one, the F-16 is in general quite capable against the majority of the world's active combat aircraft. As I'm sure anyone qualified to answer knows better than myself, it has a proven record in a variety of air to air missions, dogfighting, and ground attack missions.

Are there any other drones, besides the QF-16 that are even remotely as capable, in comparison, and that already exist, in large numbers, like the QF-16?

The benefits of this should be obvious. The QF-16 is after all a disposable aircraft, yet one that is at least somewhat capable. With a drone, no pilot life is at risk. With an autonomous drone, no pilot is required at all for the actual fight, only planning of the mission. This should be an obvious advantage, and from what little I can tell, various---albeit less capable---drones exploit this advantage already.

Just to provide some more context: Many interesting things can be easily imagined, the F-22/F-35 often talks of using fourth generation aircraft as a "force multiplier" by feeding them data from its sensors, such as target information. Such a force multiplier with autonomous, disposable aircraft seems rather interesting to say the least.

I'd like the know if there are any plans to use the QF-16 as a drone for combat missions, and if not, why not?

I'd also like to know if there are any plans to use the QF-16 as an autonomous fighter, as in, program the target into the aircraft, and send it on its way, and have it return, all without any pilot input.

The last question is the most interesting to me. Is there any publicly known research in this direction? Towards making autonomous combat aircraft? Perhaps the QF-16 platform is greatly underpowered both in terms of hardware and avionics (sensors) to realistically (even if the software could be developed) to act in such a manner.

Are there any plans for such things? If not, why not? Are other aircraft in consideration, or is it in general a bad idea? Why?

There seems to be some ongoing research into just that:

  There is an effort underway to develop a UAV version of the F-16. This would be based on the QF-16, the remotely controlled target version of the F-16. The air force is already in the process of converting 210 retired F-16s to QF-16s and it was noted that with a little extra work the QF-16 could be turned into a combat UAV for dangerous missions like SEAD (suppression of enemy defenses) or attacking ground targets guarded by heavy air defenses.

Other research is often related to sixth generation fighters, which are often described as being "optionally manned" meaning that they can fly with or without a crew onboard.

F-16s currently being converted into QF-16s are older models which are likely to require more maintenance per flight hour, and as always it is a matter of capability vs cost vs other platforms. The biggest question for such a conversion is whether or not an imagined MQ-16 would bring capabilities not already covered by existing UAVs to the table, and how expensive it would be to support this.


How do conventional missiles fly? With the exception of cruise missiles, most missiles don't have any obvious lifting device.

If you watch a missile being fired, prior to its rocket firing it does exactly what you'd expect: momentarily plummet toward the earth. And yet the moment it ignites, it stops falling completely, but without any pitch that you'd expect to counteract gravity; even big missiles like the Phoenix or HARM seem to have gravity-defying characteristics.

Missiles that fire on the rail seems to experience no drop at all.

AIM-9M launch from an FA-18F source

There's a good slow-motion video of the firing of an AMRAAM here.

Now this isn't magic, so I presume either a) the little fins make adjustments so that the rocket is, despite appearances, pointing a little downwards or b) the fins are smart enough to configure themselves to provide the lift needed to keep the missile in the air. But it might be neither.

The question is - generally, how do conventional missiles fly?

Air-to-Air guided missiles are little airplanes. If there are only fins at the tail, it's a ballistic rocket, basically a fin stabilized artillery shell accelerated by a rocket motor instead of an explosion in a pipe.

On missile like AMRAAM, Sidewinder, or Sparrow, the vanes are wings and the missile is a rocket powered aircraft that can climb, descend and turn as required.  The vanes/wings don't have to be very big because the thing is going superdupersonic.  The X plan form means the wings can support and control the missile equally well in any axial position.

The front vanes are movable and do the controlling.  It's effectively a rocket powered robot canard aircraft on a suicide mission, really.

Since the missile accelerates to >Mach pretty quickly and operates supersonically, the wings/vanes use a supersonic airfoil profile, either biconvex (like the F-104's airfoil) or a diamond profile.  The vanes on the AIM-9M look like biconvex airfoils.

The missile descends when it is first launched because it's going too slowly for its teeny tiny supersonic wings to do enough lifting, and has to accelerate first.

Now, for a change of pace, slow something like an AMRAAM or Sidewinder down to subsonic speed, make the fins bigger and provide control surfaces on the rear ones, power it with a turbojet instead of a rocket except for boosting it into the air, and you have the CL-89 surveillance drone, basically a reconnaissance cruise missile that flies hither and yon at low level taking pictures.


Why can't some airports handle heavy aircraft while others do it easily (same runway length)? As I've seen in this video, they operate flights from Bournemouth airport all the way to Barbados on a Boeing 787-8. As Bournemouth runway length is 2,271 m (7,451 ft), it can handle aircraft such as Boeing 787 fully loaded.

In Kiev Airport (Zhuliany) in Ukraine, runway length is 2,310 m (7,579 ft). But the maximum it could handle is an Airbus A320.

Airport authorities keep telling us that they need more money to extend the runway length. And after that they will be able to handle larger airplanes such as the Airbus A321, but still not as big as the Boeing 787.

Another city is Kherson (Ukraine), the runway is 2,500 m long and can only handle the Airbus A321.

Are the local authorities misleading the passengers? They keep telling us that they need more investment/money. It looks like they are lying to us.

There are a few possible reasons Bournemouth (EGHH) can support a Boeing 787 but Kherson (UKOH) can't. Runway length is definitely not the issue. The runway at EGHH is 2271 metres long, the one at UKOH is 2500 metres long.

The runway at UKOH is slightly narrower, though: 42 metres compared to 46 metres at EGHH. Whether this has operational significance, I do not know.

Another thing to compare is the strength of the pavement, which is expressed as a Pavement Classification Number, or PCN.

The PCN of the runway at EGHH is 46/F/B/X/U, at UKOH it is 28/R/C/X/T. Those values can be decoded like this:

EGHH: Load carrying capacity: 46, flexible pavement (typically asphalt), high strength, high tire pressure supported.
UKOH: Load carrying capacity 28, rigid pavement (typically concrete), low strength, high tire pressure supported.

This is a bit technical, but what it means, in essence, is that the pavement at UKOH is not nearly as strong as that at EGHH. The 787 has a max takeoff mass of around 230 tons, so it needs some pretty strong pavement to support it.

Finally, the rescue and fire fighting services provided at the two airports is different. EGHH provides up to CAT 9 (capable of handling aircraft up to 76 metres long and 7 metres wide (fuselage width)). UKOH provides only CAT 7 (capable of handling aircraft up to 49 metres long and 5 metres wide.

The 787-8 (the smallest of the 787 variants) is 56,7 metres long and 5,77 metres wide. So most likely, what's keeping Kherson Airport from handling 787's is a big investment in new pavement, and maybe the need to buy a few extra fire trucks.

Then of course, there's also the whole question about capacity of the terminal building, size of gates and various equipment (push back trucks, stairs, jet bridges etc.). Those things are a bit harder to compare directly, though.


Why do similar Airbus and Boeing aircraft use different flap and slat mechanisms? Why do most Boeing aircraft and their corresponding Airbus counterparts have different flaps and slats mechanisms (747 and A380, 737 and A320)? I'm assuming a lot of these mechanisms are patented. For example, the 747 is equipped with Krueger flaps while the A380 has the leading edge droop as slats.

While the aircraft you mention would appear to be similar, this is not really entirely true. Specification wise yes, but the period it was designed in has a huge impact. For instance:

The first flight of the Boeing 737 was in 1967, with the Airbus A320 following considerably later in 1987. (20 years later)
Boeing 747 first flew in 1969, the Airbus A380 followed in 2005. (36 years later)

Each redesign is expensive and time-consuming so if there is no conceivable benefit it is not done. There is no clear cut equation on when a certain type of slat and flap mechanism is chosen:

The operating environment changes over time. One important consideration is the landing speed (and corresponding runway length). This for instance limited the Boeing 707 greatly, and it was likely that Boeing might not wish to run into the same problem with the B747 to enable it to serve as many markets as possible at a time when airports were not so advanced. For this reason they put in the very complicated triple-slotted flaps. (For comparison, look at the A380 which has caused headaches as airport operators have to modify and/or rebuild facilities to accommodate it)
Aircraft have become lighter over the years with the introduction of new materials, production techniques and better optimized engineering.
Technology has become better at modelling, so we can be less conservative in design choices as there is a better idea of the end result. This applies not only to the structure but also aerodynamics.

The bottom line is that you take the values and look at a few different designs. You choose the one that best fulfills your criteria (not only in performance but also what you can build) and go with it, and this choice would change over time. If the Boeing 737 would be built today, the details most probably be fairly different.

What does this mean?

The A380 for instance only has single slotted slats. When the B747-8i recently received a new wing design, it shifted from triple to double and single slotted flaps.
Both the A350 and B787, designed roughly around the same period, both have the rear single slotted flaps and (to large extent) the same slat design.


What protection does Vno provide? VNO, the airspeed where the green and yellow arcs meet on the airspeed indicator, is the "maximum structural cruising speed" (FAR 1.2). An airplane should only be flown above VNO in calm air. Comparing this to VA, the speed below which the airplane will stall before reaching its load limit, what protection does VNO provide? Turbulence that mimics a full deflection of a control surface would likely qualify as extreme, but what's the middle ground?

VA varies by airplane weight. Does VNO vary by weight, and is the calculation the same?

In short, VNO doesn't provide you any protection, it just tells you that flying that fast puts you in a regime where structural damage will occur before increased load factor will cause a stall -- regardless of weight.

For part 23 airplanes that are not turbine powered and VD has not been established, 23.1505(b) establishes VNO must be established such that it is between VC,min and 0.89*VNE.  Section 23.335 defines VC as a multiplying factor of the square root of wing loading at design maximum takeoff weight.  For normal and utility category airplanes, VC is design cruising speed and is be between 33 √(W/S) and 0.9 VH where W/S is wing loading at the design maximum takeoff weight.  The factor 33 may be scaled as low as 28.6 based on W/S values greater than 20 (the regs do not provide units on any of these numbers...).   VH is the maximum forward airpseed in level flight at maximum continuous power at sea level.

Section 23.335 also defines VA and the only relation to VC is that VA need not exceed VC.

We can see from this information that establishing VNO is a design choice based ultimately upon maximum possible wing loading as a guideline and unlike VA stall speeds are not involved in the calculation.

What you can take from this is that VA will vary by weight (because this affects the stall speed) but VNO is based upon wing loading at max gross takeoff weight and is constant with actual weight.

Flying slower than VA you will stall before causing structural damage.  Flying faster than VA you will cause structural damage before stalling the airplane.  VNO will be at least the VA or higher.  Flying below this speed doesn't really tell us anything (VA is better for that), but flying above this speed lets us know the design margins for load factor induced structural damage are such that we don't want bumps or abrupt control deflections because we can damage the airplane.

Regulation excerpts.

  §23.1505   Airspeed limitations.

  (b) The maximum structural cruising speed VNO must be established so that it is—

  (1) Not less than the minimum value of VC allowed under §23.335; and

  (2) Not more than the lesser of—

  (i) VC established under §23.335; or

  (ii) 0.89 VNE established under paragraph (a) of this section.

  (c)(1) Paragraphs (a) and (b) of this section do not apply to turbine airplanes or to airplanes for which a design diving speed VD/MD is established under §23.335(b)(4). For those airplanes, a maximum operating limit speed (VMO/MMO airspeed or Mach number, whichever is critical at a particular altitude) must be established as a speed that may not be deliberately exceeded in any regime of flight (climb, cruise, or descent) unless a higher speed is authorized for flight test or pilot training operations.

  §23.335   Design airspeeds.
  Except as provided in paragraph (a)(4) of this section, the selected design airspeeds are equivalent airspeeds (EAS).

  (a) Design cruising speed, VC. For VC the following apply:

  (1) Where W/S′=wing loading at the design maximum takeoff weight, Vc (in knots) may not be less than—

  (i) 33 √(W/S) (for normal, utility, and commuter category airplanes);

  (ii) 36 √(W/S) (for acrobatic category airplanes).

  (2) For values of W/S more than 20, the multiplying factors may be decreased linearly with W/S to a value of 28.6 where W/S=100.

  (3) VC need not be more than 0.9 VH at sea level.

  (c) Design maneuvering speed VA. For VA, the following applies:

  (1) VA may not be less than VS√n where—

  (i) VS is a computed stalling speed with flaps retracted at the design weight, normally based on the maximum airplane normal force coefficients, CNA; and

  (ii) n is the limit maneuvering load factor used in design

  (2) The value of VA need not exceed the value of VC used in design.


What is ground effect? We've all heard the "acts like a cushion of air" explanation tossed casually around by CFIs.

There's also plenty of books and reference materials that give a detailed, accurate, and complete explanation of ground effect, and which are incomprehensible to most student pilots.

What's the simplest way to accurately explain ground effect?

It's impossible to give a correct AND simple explanation I think. I would explain it like this if I was asked:

The downwash from the wings and the downward component of the wingtip vortices create a higher than normal pressure area below the wings because the air hits the ground and can't "escape", increasing lift.

Induced drag is reduced because wingtip vortices (causing drag) can't fully develop close to the ground.


Is there any regulation to ensure that life jackets and safety cards are on-board? On many flights, I was told that a life jacket is under my seat and safety card is in the pocket in front. Is there any regulation that ensures that life jackets and safety cards are on-board on all flights?

The FAA has a similar requirement (commercially under part 121)

  (a) Except as provided in paragraph (b) of this section, no person may
  operate an airplane in any overwater operation unless it is equipped
  with life preservers in accordance with §121.339(a)(1) or with an
  approved flotation means for each occupant. This means must be within
  easy reach of each seated occupant and must be readily removable from
  the airplane.

  (b) Upon application by the air carrier or commercial operator, the
  Administrator may approve the operation of an airplane over water
  without the life preservers or flotation means required by paragraph
  (a) of this section, if the air carrier or commercial operator shows
  that the water over which the airplane is to be operated is not of
  such size and depth that life preservers or flotation means would be
  required for the survival of its occupants in the event the flight
  terminates in that water.

In other words they are only actually required (per FAA regulations) when operating over water so not every plane (route provided) technically needs them. However many airplane seat bottoms may double as a personal flotation device so many planes are equipped with them by the nature of their construction.


Is it better to reduce drag or increase lift? Essentially my question is, in general is it better to have a lower drag or a larger lift. I know lift to drag ratios are used as an indicator but I think these don't give the best picture. For example, I'm running a 2D airfoil analysis and for 2 cases the CL/CD changes varies between 80 and 160 (obviously doesn't account for 3D drag). So you'd expect the best option as CL/CD as 160.
However the CL/CD only looks at the % change. So if the % increase in drag is say 70% and for lift it's 10% CL/CD will be larger for the increased drag but the amount of increase in lift force greatly outweights that of the drag (an increase of 175N of lift vs reduction of 14N of drag).
I guess it would depend on the application as well.
Any help would be greatly appreciated, thanks in advance!

Your lift will be prescribed and cannot be freely chosen. So what you need to do is to minimize the drag that goes with this given lift.
In straight flight lift needs to equal weight. In turns, the centripetal force is added to this. At high speed a small angle of attack will produce that lift while at low speed the angle of attack needs to be high. In most cases, takeoff and landing requirements will determine minimum wing size and the maximum lift coefficient of the airplane. In order to not drag around massively oversized wings, most airplanes use flaps to have a decent maximum lift coefficient for takeoff and landing while minimizing their wetted surface at high speed in order to keep drag down.


A modern replacement for DH.82's Gipsy Major engine While I deeply appreciate any vintage aircraft that is powered by their original engines, I was wondering if there are any modern replacement engines available for the de Havilland Tiger Moth aircraft with Gipsy Major engines installed that require no or minor modifications of either the aircraft and/or the engine itself?

The Avia (now LOM) M132 4 cylinder inverted inline might fit. Some adaptation work is probably required.


What is a IATA aircraft sub-type? I am currently reading docs regarding slots, where the following is mentioned:

All SCR messages in linked (turn-around format) using aircraft
subtypes only (e.g. 73G or 738 instead of 737).

Not sure what is meant by the above sentence. My understanding is that whenever you submit slot requests with SCR messages you need to use the IATA aircraft code as defined here.
The Worldwide slot guidelines also mentions:

Operating a flight in a significantly different way to the allocated
slot – including a different service type, aircraft subtype, aircraft
capacity, or origin/destination – without the prior confirmation of
the coordinator as set out in 8.10;

So what is exactly the difference between an aircraft type and an aircraft subtype? Does the link provided above refer to aircraft subtypes?

When the 737 is a type, the 737-700 (IATA: 73G) and 737-800 (IATA: 738) are sub-types. They have different capacities and differing weights. Other documents will use the word "variants" where your document uses "subtypes".
Related info here.


Why is the seat belt mechanism on airplanes so different from the the one on cars? You pull a flap on airplane seatbelts, you push a button on car seatbelts. Why?

As Roe pointed out you don't necessarily pull a flap on airplane seatbelts -- Sometimes (particularly in newer light GA planes from the 1990s and on) you push a button just like you do in a car, other times it's the "utility buckle" (flap buckle) - sometimes with a shoulder harness attach peg or other attach mechanism, and sometimes you'll find rotary buckles, where you turn a knob to release the belt (particularly common in aerobatic aircraft, with 4-point or 5-point restraints).  I've attached a little gallery of belt types below (and this isn't even complete - military aircraft hafe some downright funky buckles!).

This variety is why the FAA requires flight crew to instruct passengers in the operation of the seat belts.

So, why are the belts in airplanes different?  And why are there so many types?
Each belt is good at something different, and each belt has its own set of drawbacks.

The automotive style push-button belt is very familiar to infrequent flyers.
Most people who are going to get on a plane have been in a car (they probably rode in one to the airport), so familiarity with automotive-style seatbelts can generally be assumed. This is great when you take someone for a flight who isn't a frequent airline passenger.
The drawback to the automotive belt is it's not as easy for rescuers to operate, and the push-button mechanism can jam - particularly in fires where the plastic shell can melt/fuse (in cars the belts are often cut by rescuers because it's easier/faster than dealing with the button). If your passengers are injured in an emergency and can't operate the belt it may be difficult for you to locate and press the button to assist in evacuation.
The "utility buckle" flap belt is easy for rescuers & cabin crew to operate.
The exact opposite of the push-button belt's chief drawback: It's really easy for cabin crew or rescurers to find a utility buckle on a belt by feel and yank the flap to release it (try it some time: Buckle someone into an airplane seat, close your eyes, and find/release the buckle. The hardest part is finding the belt if they're wearing bulky clothes). It's also relatively hard to jam a utility buckle, and relatively easy to inspect them to determine if they're damaged.
The drawback to the utility buckle is that not everyone has been on an airplane (or in a really old car that uses them), so they might not be familiar with "Lift the flap to release the belt", and in a panic situation it may take them a few seconds to remember what to do.
The rotary buckle is unique and kind of awesome for what it's built for.
Rotary buckles make it easy to attach 4 or 5 point restraints, and to release all or part of them quickly.  (The buckle shown in the photos is single-function - turn to release - but dual-function buckles exist where you can press the button in the center of the buckle to release the shoulder straps, or turn the knob to release everything.)
The big drawbacks to rotary buckles are their novelty: On the ground you usually only find them on 5-point racing harnesses, and in the air they're pretty uncommon too (mainly aerobatic aircraft as I mentioned earlier). They're probably the last type of buckle a passenger or rescuer would expect to have to deal with, and particularly with the dual-action buttons they can present a challenge in a panic egress (passengers will hit the button and release the shoulder harnesses, but they're still restrained by the lower portion of the belt - this can cost precious time for them to realize they have to turn the knob).


Why would a fighter use the afterburner and air brakes at the same time? I was looking for air brake pictures on different fighters, and then I saw a Tornado using afterburner and air brake at the same time! Air brake duty is to reduce speed, isn't it? So why would a fighter burn so much fuel to increase thrust and then use speed brakes simultaneously?

The first photo is from the Tornado Role Demonstration Team's display at RAF Leuchars in September 2012 (source).

That Sep '12 show or its preparation is on YouTube. Most of the instances of the air brakes as seen from the cockpit (looking behind) are followed by the swing-wing extending and the afterburner turning off (you can tell from the sound of the variable nozzle actuators).

While the photos are cool, I'd say it's just perfect timing before the pilot turned off the afterburner while slowing down.

Such example (above) can be seen after 7:40 in this video. Notice the wing position, and from the video notice the aforementioned sound once the wing is extended.

Another possible reason is slowing down for the spectators to see and hear the afterburner. That can also coincide with the fake bomb drop – a pyrotechnic wall of fire, the smoke of which can be seen in the first photo in the question (example below).

An RAF Tornado GR4 carries out a mock bombing run (BBC)


How does the ICAO VOR separation apply to reciprocal radials? If two aircraft are on VOR radials that are apart by 15 degrees or more and one aircraft is at least 15 DME out, they are considered laterally separate. I read this rule in ICAO documents but my question is what if radials are 180 degrees apart and one aircraft is 15 DME out? Would they still be considered separate? I don't think so because they would be reciprocal to each other in this case. Then what are the limitations of above mentioned VOR separation rule?

The mentioned VOR separation does not apply that way.

You commented:

If one aircraft is moving towards the VOR on radial 90 and other is also moving towards the VOR on radial 270, both are maintaining FL360 and first aircraft is 15 NM away from the VOR, are they separated?

Both aircraft in this scenario will be on a head-on collision course.
ICAO Doc 4444 references Annex 2 Appendix 3 for the table of cruising levels. In your scenario both aircraft should not be on the same FL, and should be separated vertically (the east/west or north/south rule depending on the country). (Does ATC direct flights to fly eastbound at odd levels and westbound at even ones?)

The reason for that criteria shown above is because of the 95% containment of the VOR when less than 50 NM away is 4 NM, that is the plane can be left/right of the radial by upwards of 4 NM. To understand that, move both planes closer, still on the same 15° separation, and take into account that they may not be exactly on the radials (loss of lateral separation).
The VOR separation you quoted takes that into account, but not to the full extent, for that reason some states say it should be increased to 30° (from 15°), or make it 35 NM at 15° (not 15 NM). (Twenty-Eighth Eastern Caribbean Working Group Meeting)


How can I stop being too high or low when on base and final? I'm a student pilot having trouble with landings, and problems are occurring in the pattern on base and on final;  I am either too high or too low. As a result, I feel I have lost confidence.

I feel like I am relying on my instructor to tell me what to do next instead of me flying the plane. How do I improve this situation?

Also, it has been suggested that I stop using the simulator as this is teaching me bad habits.

I think one thing that does not get emphasized enough:
Pilots do not land airplanes!In fact, we try to keep the airplane flying as long as possible!  We systematically rob the airplane of energy (energy from engine power, energy from airspeed, energy from altitude) until the plane can no longer fly, and settles gently on the runway.

But even as the plane is landing, the pilot is still trying to coax it back into the air to remove as much energy as possible.  A big student mistake is to point the airplane at the runway, and try to force it to land there.  That leads to landings too fast, too high, big bounces, porpoising, and sometimes nose-in crashes.

So don't think about "how am I going to land this thing?"  Instead think about "How am I going to remove more energy from the equation to lose altitude and airspeed?"

A landing is a series of precise targets you are aiming to hit, each with less energy than the last one (but each one still with enough energy to keep flying and be safe)

Each target consists of Position (horizontal and altitude), airspeed, and descent rate.  You hit each of these targets at 3 different points on a square (abeam the numbers, downwind-to-base, and base-to-final) Hitting a target that consists of a position + airspeed + descent rate is not easy! But the more precisely you can hit each target, the easier the next part is.

Although I hope I'm repeating the same instructions you've already heard, for the sake of the Site, let me re-iterate the standard instructions for a C-172.

Be level at TPA (airport + 1000 feet), and at a cruise speed of approximately 100 kts.  The runway should be approx 3/4 of the way up your strut.
When you are abeam the numbers, Carb Heat (if applicable), throttle back to approx 1,600 RPM, and pull-back as necessary to maintain altitude (the consequence will be that you slow down).
Watch your speed, altitude and position.  Drop flaps 10° when speed allows, and aim to hit a speed of 85 kts, an altitude loss of 250 feet, and have the numbers at 45° behind you, all at the same time.
Turn the corner to base, using approximately 30° of bank angle.  Continue to reduce speed (by pulling back) to hit 75 kts, and drop altitude another 250 ft. (you're now 500 ft above the runway).  Add Flaps 20 when appropriate.
Turn the corner to final.  You can "oval" your turn if you are undershooting the centerline, but do NOT over-bank if you have overshot the centerline.
Aim for the centerline, acquire a PAPI/VASI, keep an eye on your airspeed relative to approach speed (68 kts).
Watch 3 and ONLY 3 things:

Airspeed (Slowing towards 68 kts)
Centerline (left? right? on target?)
Slope (PAPI/VASI? Light configuration).

Keep repeating "Airspeed, Centerline, Slope" out loud, describe if you're too far/too close on each one, and describe how you're going to correct.  For example:

"Airspeed: 75 kts; too fast; pulling back to slow down"
"Centerline: Left of center; coming slightly right"
"Slope: 3 red+1 white is too low; adding power to slow descent"
(repeat!)

When the runway is made, drop final flaps, engine to idle, and prepare to flare when you're about 10-15 feet, and hopefully right at the numbers.

Remember that your altitudes are 1000, 750, 500, touchdown.
And your airspeeds are 85, 75, 65.


How could I find the air velocity and lift force? As shown below I have this information as shown below in the picture. I got the density according to the ISA standard  = 1.225[kg/m^3]  and  =  (−0) is calculated as below :

α=−4: CL=0

α=16: CL=0.025∗(16+4)=0.5 according to the diagram below:

I just want to know how to find the velocity and lift force?.

The lift force law is like this =(1/2)  ^2

The indicated airspeed is the result of computation using basically the static pressure from the static pitot and the dynamic pressure from the dynamic pitot.
Further to apply your formula in addition to CL and the density, you need to know the active area S of the wings which at high speeds may depend on the speed itself, so you need the wings specific data.


How does PF or "pilot flying" and PNF or "pilot not flying" affect logging? How does PF or "pilot flying" and PNF or "pilot not flying" affect logging for pilots operating in a two-pilot environment?

Here are some granular examples...

How should actual instrument be logged? Should a PNF be able to log actual time if they are monitoring during instrument conditions?
How should landings be logged? Should a PNF be able to log landings they were not at the controls for?
How should approaches be logged?

Any insights are appreciated. This question is in reference to FAA regulations only.

While the question is fairly broad, looking at 61.51 is a good place to start, as well as 61.57 for some of the currency stuff.
But let's try and work out some of your examples:
How should actual instrument be logged? Should a PNF be able to log actual time if they are monitoring during instrument conditions?
61.51(g) is what dictates the logging of instrument time:

(1) A person may log instrument time only for that flight time when the person operates the aircraft solely by reference to instruments under actual or simulated instrument flight conditions.
(2) An authorized instructor may log instrument time when conducting instrument flight instruction in actual instrument flight conditions.

So barring any legal interpretations out there or regulations I'm missing (note, I'm not an instrument rated pilot nor attorney), a strict reading of the reg would indicate that only an authorized instructor, conducting instrument flight instruction, can log instrument time when not operating the aircraft.
How should landings be logged? Should a PNF be able to log landings they were not at the controls for?
The short answer is no. Assuming the landings are being logged for currency reasons, 61.57(a)(1)(i) states that the person had to be the sole manipulator of the flight controls. 61.57(b)(1)(i) says the same thing, but for night currency.
How should approaches be logged?
Again, I'm guessing this would be for instrument currency, at which point 61.57(c)(1) would be in play.

Within the 6 calendar months preceding the month of the flight, that person performed and logged at least the following tasks and iterations in an airplane, powered-lift, helicopter, or airship, as appropriate, for the instrument rating privileges to be maintained in actual weather conditions, or under simulated conditions using a view-limiting device that involves having performed the following -
(i) Six instrument approaches.
(ii) Holding procedures and tasks.
(iii) Intercepting and tracking courses through the use of navigational electronic systems.

Again, I'm not an instrument pilot, but despite "sole manipulator of the controls" verbiage being absent in this particular paragraph, I'm guessing the FAA would construe it to be the same.
Of course, I'm more than happy to be corrected should I be wrong.


How can a military combat pilot indicate surrender? If a military pilot is captured by an enemy, how can he indicate that he has run out of ammunition to engage in combat or is not in a position to retaliate? Does he use lights, radio, and/or flares?

There is no universally accepted means of surrendering an aircraft. According to Humanitarian Policy and Conflict Research at Harvard University,

  Aircrews of a military aircraft wishing to surrender ought to do everything feasible to express clearly their intention to do so. In particular, they ought to communicate their intention on a common radio channel such as a distress frequency.

They can do other things like rocking the wings, jettisoning the weapons, flashing navigational lights etc. However, none of these are universally accepted or even have a clear meaning in the heat of combat. So the best course of action will be to bail out.

If a pilot is captured by an enemy, there would be no need to surrender.


Can flight data recorders be hacked? In the event of a plane crash such as MH17, and the flight data recorders (FDR, a.k.a. "black boxes") are potentially in the "wrong hands", is it theoretically possible to:

open the FDR and close it again without leaving traces?
alter or selectively erase data of the FDR?

In other words, can an FDR professionally be tampered with as opposed to purely destroyed for the purpose of hindering an investigation?

Yes.  Black boxes aren't designed to be tamper-resistant.

The hard part is not the physical act of tampering with a black box, it's constructing a coherent false narrative of what happened during the time period.  The FDR records 80+ channels of data, which an investigator can correlate against each other, against data in the quick access recorder, against ACARS reports, and against the physical condition of the airplane itself.

For example, say you want to "prove" that an airplane's engines were shut down mid-flight, leading to a crash.  You could modify the FDR's record to show a throttle setting of "closed" and an engine RPM of 0, but the exhaust temperature would still be high, the fuel tank levels would still be dropping, and analysis of damage to the turbine blades would show a mix of axial and circumferential bending around the entire circumference of the blade disk, rather than the pure axial bending on a single side that would be expected if the engines had stopped spinning.


Can one purchase a Cessna 182JT-A although it has not yet been certified? To the best of my knowledge, Cessna's 182JT-A has not yet been certified. At least I couldn't find on Google any indication that it has. Lots of items that certification is "imminent" but no real facts.

Yet, I see them for sale and YouTube has videos of them flying. Am I correct in believing that it is possible to buy one and then operate it as an experimental aircraft?

They did have an engine out failure about a year ago which set everything back a bit.  They've had it at Osh a couple of years now.  Two years ago they were saying around the end of '14 beginning of '15.  Last summer, they were saying months.  If you're really curious, I would talk to the manufacturer in Kansas.  Dealers really aren't part of the FAA approval process...

I wouldn't read too much into the range calculator.  I would imagine that they would be adjusting numbers numerous times before release as they get more data.


How can flying high minimize drag and increase fuel efficiency? As a plane goes higher, the engines have to work harder to compensate for the air density, therefore it will require more fuel in order to provide the same power at lower altitudes.

But I always hear that flying high means less fuel burnt.

How can that be the case?

Flying higher means less drag because the air is thinner; therefore, you can fly faster at altitude and hence travel farther on less fuel.

However, flying higher also means less oxygen available to burn your fuel, so available horsepower decreases with altitude.

There is a special altitude at which these two effects (drag reduction and available power reduction) achieve a crossover point. This is called the critical altitude and it is there where you achieve optimum cruise and best economy.

If you want to fly higher than critical altitude, you will fly slower because the power loss is greater than the drag reduction and you will spend more time in the air.


How strong is the A380 fuselage-wing joint? The Airbus A380 has a maximum take-off weight of almost 600 tons. How strong does the joint between the wings and the fuselage have to be so it doesn't break? And how could it be trusted unless real-time fractures don't occur? How was it tested? I mean, you cannot accomodate such a big joint in a wind tunnel except in computer simulations.

how could it be trusted?

Like all aircraft, type certification requires that these be tested. I think the wings are tested to 1.5 x their load limit.
A380: STRUCTURAL STATIC TESTS

The A380’s structural static tests on began in November 2004, in preparation for the first flight clearance.
The tests included: Flight Test Installation (FTI) calibration test, maximum wing bending at limit load, ailerons and spoilers functioning test during max wing bend, fuselage pressure test, and fatigue tests and flight cycles simulation.

They place an airframe into a test rig and increase the load on the wings until the wings break. The empirical evidence is compared with the predictions made by mathematical models.

Airbus A380 wing test

Airbus A350 wing test ... (A350 torture video)

Boeing 787 wing test