Why is most aircraft livery painted, rather than vinyled? I just watched a recent AVWeb YouTube video about vinyl decals. In it the owner of Plane Decal says compared to paint, vinyl offers:

a more flexible choice of designs
a cheaper solution - a GA aircraft costing \$5,500 vs \$20-25k.
a quicker install - 6.5 hours vs 6 weeks

Are these assertions correct? It leaves me wondering why aircraft are painted at all if this is the case? What are the cons?

I'm interested in both GA and commercial perspectives, since Bud mentions they've outfitted both.

Here's the video for those who are interested:

Changing the status quo always takes time. Aircraft have been painted almost since the dawn of flight (and the very earliest aircraft were still doped to stretch the fabric over the skeleton). That is reason in itself for antique and historical aircraft and their replicas to be painted instead of vinyled.

In addition, most liveries come factory-installed right alongside the host of other options available. Most high-end private jets as well as the big commercial ones are built-to-order inside and out, including the customer's brand livery. That livery, much like the factory color of a car, often stays with the plane its entire life, with only routine touch-ups performed as a normal part of maintenance. Refitting a fleet with new livery and/or interiors, until very recently, wasn't done often; Southwest's "Canyon Blue" livery change was noteworthy, as was AA's fleet rebadging, and neither airline bothered repainting planes that are on the way out anyway; the aging Super 80s as well as the 757s and some 767s are still in classic AA silver livery and will be that way until they're retired from the fleet.

So, aftermarket vinyl livery's market share is already somewhat limited; people buying a new jet will get their livery applied at the factory, and people buying a used jet and wanting the livery changed significantly are in for quite an expense even if they choose vinyl; the old painted livery will usually have to be removed and the plane refinished in a new base coat before the new vinyl decals are applied.

I would also venture, having seen aftermarket vinyl applied to other vehicles, that even if the utmost care is taken in applying it, the decal is always going to look like a decal, and it may not age well even with a meticulously-maintained airframe. If you're paying \$65 million (base price) for a G650, \$25,000 (or even \$100,000) for custom livery is a drop in the bucket.

Now, your 172 or Piper Cherokee sport pilot might be very interested in personalizing his plane on this kind of budget, as would an aircraft club of part-owners, or your self-employed commercial pilot like a crop duster or charter bush pilot. Vinyl on small planes thus makes more sense; however, it's still a significant expense, and a purely cosmetic one, so it's still rare to see a plane's factory paint scheme change significantly aftermarket, except for niche uses like aerobatics and stunt flying.


Would it be beneficial to have rotors AND propellers instead of a tiltrotor? Would it be beneficial for tiltrotor aircraft if they had BOTH rotors and propellers, instead of the hybrid proprotors that are neither good propellers nor good rotors?
Like imagine the V-22 Osprey with additional propellers for example mounted on the wings, which are turned off in helicopter flight and when the airplane transitions into airplane mode, the turbines switch from powering the rotors to powering the propellers via transmissions and the rotor blades pitch to an angle where the drag is reduced. Then the plane would be only powered by propellers, which are better for airplane flight and could achieve higher speeds. Would that be possible and if so, why has nobody tried to do this?

There are 2 major problems. First is the weight you'd incur from:

Extra rotors/propellers
Transmission components (the V22 already has a transmission in case of an engine failure, it's already more complex than you'd ideally want but it's necessary for safety)
Structural components to support the forces from the propellers and extra transmission

It's lighter to turn the engine and rotor together, and probably more reliable.
More importantly the rotors have aerodyamic issues at higher speeds. Remember the rotors are still up there, and they must be dealt with. You could:

Fold them away or back: you'd need a mechanism capable of stowing and unfolding the rotors in an airstream, which means weight
Have them produce no lift: this means they will be dead weight so they will take away from payload
Use them for lift: this would be similar to a gyrocopter, where a rotor is unpowered but produces lift from forward flight. There's aerodynamic limitations due to the differences in lift from advancing and retreating blades which would limit your top speed


Why the lack of faster piston-powered planes? There aren't very many fast piston airplanes in production. By "fast" I mean, if you look back in the early to mid 20th century, before turbines won out, there were lots of piston airplanes in production that pushed the practical velocity limit of propeller-driven aircraft, cruising 360+ knots in military planes, sometimes as fast as 330 knots in commercial airliners. And this was with a terrible understanding of aerodynamics and piston engines compared to today.

Today, for both singles and twins, the fastest speeds around aren't much higher than 200 knots. ~240 knots in the case of the very fastest couple available airplanes like the Cessna 400 and fastest Mooney.

There are indications that with modern materials and engineering, much faster speeds can be achieved using piston engines already available. The Cobalt CO50 Valkyrie design claims to push a spacious 4 person cabin up to 260 knots with a single 350hp engine. The recently-certified Diamond DA-62 can move a spacious 7 passenger cabin at ~200 knots using only a pair of 180hp engines.

Why aren't there more faster piston airplanes available? Would the market not be interested in piston powered planes that could do 300 knots? Shouldn't you be able to make almost those speeds for a very small plane powered by a single commonplace 350hp engine? Shouldn't you be able to make those speeds in a more spacious plane with a pair of commonplace 350hp engines?

My understanding of the marketplace is that the #1 reason people choose piston is cost. And isn't the cost of operating piston engines, even two piston engines versus a single turboprop, much much lower? How much does a 350hp turbocharged piston engine cost brand new, 50k-60k dollars? So even buying a pair of them is 100k-120k dollars. And then how much does a single comparable turbine engine cost? ~800k dollars with proportionately higher rebuild costs per flight hour? Plus 20%+ higher SFC than a piston?

Basically, I see the Piper M600 listed at 2.8M USD, or the TBM930 listed at 3.9M USD, and I don't understand why it would be hard to achieve nearly the same performance for a fraction of the price using a pair of cheap piston engines. For example the Piper M350 has the same 6 passenger cabin as the M600 and also includes pressurization, and with a single 350hp engine makes over 210 knots on a very old airframe with a list price of under 1.2M USD. If you basically built the same airplane but reoptimized for twin engines and using modern materials and aerodynamics, shouldn't you be able to achieve near 300 knots by adding another piston engine? And shouldn't you be able to sell the resulting airplane for well under 2M USD and with a significantly advantaged SFC and therefore range and payload than the M600?

The power requirement of an airplane grows with the cube of speed. When you fly fast with an airplane which needs to comply with a set minimum speed imposed by regulations, your drag coefficient is nearly constant, so flying faster does two things to a propeller aircraft:

Drag goes up with dynamic pressure, which is proportional to speed squared
Thrust goes down with the inverse of speed.

Power is thrust times speed, so if the the 350 hp get you to 210 knots, doubling the installed power can only bring you to 264 knots. A turbine can still make limited use of the increased dynamic pressure by ram recovery, so here the thrust decrease over speed is not quite as bad as for piston engines.

Expressed in an equation, the power $P$ demand for a given speed $v$ is:
$$P = \frac{D\cdot v}{\eta_{Prop}} = \frac{\rho\cdot v^2\cdot S_{ref}\cdot c_D\cdot v}{2\cdot \eta_{Prop}} \rightarrow v = \sqrt[\Large{3}{}]{\frac{2\cdot P\cdot\eta_{Prop}}{\rho\cdot S_{ref}\cdot c_D}}$$

If you want to fly fast with better efficiency, you need to increase the minimum speed - note that the landing speed of many fast piston aircraft was around 100 mph. Now you need a long runway, and for operation in bad weather or at night infrastructure for instrumented approaches, and you will end up at airports where turbine fuel is easy to get and cheap, but piston fuel will be hard to find and expensive.

As with all expensive machinery, you need to use it often to justify the expense. Now your fuel cost will factor in, and will make a piston engine rather unattractive.

Fast piston aircraft were only built while turbines were not yet available. As soon as turbines emerged, all fast piston designs were obsolete. And aerodynamics in the early 1940s were already very advanced; engineers back then built airplanes which would be impossible to design with the engineers of today. Back then, they got fully manually controlled airplanes into the air when today everyone would refuse to do it without hydraulic boosters at only half the flight speed. They could design cooling ducts which actually increased thrust, an art which is (almost) lost today.


How can I easily keep track of my landing count during pattern work? PPL Student pilot, ~20 hrs
Hi,
whilst doing some pattern work I frequently find myself unable to keep accurate track of the number of landings. There's an AFIS at my home airport who keeps track (because they charge fees) but there are a few "flatrate" (you pay for 5 landings, but it's flat-rate after 5) air fields or some free gras strips where nobody keeps count.
The flat-rate one is particularly hard, the pattern altitude is just 650 ft and it's very tight, so there's barely any chance even on the downwind to scribble a note on paper or so.
I've tried using a "lap timer" function on my watch, scribbling lines on a tally sheet etc, but am prone to forget to add a line when things get busy. My multi-tasking capability hasn't improved to the point where I can do too many things at once.
An extrapolation of flight time and time per pattern isn't always giving me the correct answer either.
Would the Pros have any tips on what might be a useful way to keep an accurate count of the landings? How are you doing that?
Update 14/07/2020
Based on the @Bianfable's tip, I've installed "Altimeter Plus" on Android, and had that active. I thought I'd share the results with you:

My problem is solved. I've flown 11 patterns, which are clearly visible (marked yellow). I've done two engine failure after takeoff trainings, marked blue. The red marker must have been a sensor error; I don't remember crashing between the first and second landing. The green markers are forced landings w/o power, aborted at about 350 feet each.
The bad thing about it: Although it was gusty and there were strong winds, I can now see that my altitude control could be improved in the pattern. I don't ever remember being more than 50 feet off, but the data suggests otherwise.
Once again, fabulous tips all, but this was the winner. Phone in my pocket keeps count, and provides reprimands to beat oneself up about after landing. Great! Even provides pretty accurate flight time, next time I'll try and activate it on top of the hour for easier calculation of what time second "x" actually is.
Next time I'll also have phyphox running and will measure the acceleration on landing. The next thing to improve...

The trick my CFI taught me is to use your Course Deviation Indicator or ADF to keep track of landings. After your first landing, bug a course of 010. After your second landing, bug 020. You can reach over and adjust the knob after every landing without having to juggle a pen and a notebook. It's still a manual step, though.
You could also use a product like Foreflight or CloudAhoy or even a service like ADSBExchange to count the number of approaches you made after the fact.


What did this ATC call mean? Audio Clip

There is a rwy 24 in this airport. I'm not sure but the aircraft callsign likes 'TBN3BV'. I tried to find what the aircraft type is but I couldn't. Does somebody know what type of aircraft this is?

The aircraft was approaching to land and had number 3. I think there was traffic close to the aircraft. So the controller said make S-turn for safety...is it correct?

I sometimes make L/R360 or 270 to avoid other traffic but, I've never made S-turn while approaching to land.

I want to know what the controller said because I missed some word and I wonder if I can make S-turn while approaching to land. If I could, should I make two half circle?

They said "TBM" "Three-Bravo-Victor" (3BV). TBM is the aircraft make, a TBM and 3BV is the last 3 letters of the callsign.

The maneuver really isn't traffic avoidance so much as exactly what the controller said, spacing. They need to keep a minimum distance between traffic so having the TBM (a fast aircraft) perform an S-turn allows the aircraft in front of it more time to get further away.

Usually if you are in the pattern they will ask for a 360 turn, but if you are in a long straight-in and they just need a little bit of spacing, they will ask for the S-turn. For the S-turn approach you would simply turn 90 degrees to the course, then roll 180 degrees to face the opposite direction, then 180 degrees back around and 90 degrees back on course.


How frequent are TCAS resolution events? The question is a little open, but I'm wondering how many TCAS resolutions (i.e. the serious type) occur every week or month over sizeable region like the United States or Europe.

I found a very interesting paper from 2007 that analyzed TCAS performance. They analyzed recorded data to come up with 1 RA per 116 flight hours.

  Over this time period, monitoring took place for approximately 190
  days, and roughly 200,000 Mode S flight hours were observed within the
  sensor’s 60 nmi coverage area. We observed a total of 1725 RA events,
  corresponding to an average of 9 RAs per day, or approximately one RA
  every 116 flight hours.

They explain that the data was taken in the Boston area, so the high amount of traffic contributes to the high number of RAs.

This thread on Airliners.net suggest differently, at least in the sense that for those pilots it is a matter of a few over years, depending on where they typically fly.


Why does the Boeing 777X have a flight deck similar to the 787 and not to the previous 777? Almost 3 years ago I posted this question, Why didn't the A330neo and A320neo share the cockpit of the A350?, and short answers were:

  "it's what the market wanted"

  "there is a huge disadvantage to drastically changing the cockpit when going from an A320 to the A320 NEO or from a B737-300 to the B737-700, or 737 NG to 737 Max, and that has to do with the existing fleets."

Ok, I surely understood those ones, even if I specifically cited examples like complete transformations of B737 flight desk in 40 years history (explained as well in the second answer, thanks to sort of "compatibility mode" for old pilots).

I recently discover that new B777x has a flight deck almost equal to B787 (here a video) and not to previous generation B777 so argumentations explained so well in past answers are not suitable for this model.

Generally it seems that Boeing is "more courageous" in their updates than Airbus that seems more traditional (I am an Airbus fan but in this case, this seems the truth).

Anybody knows why B777X is so different from the original model, considering that efficiency seems increased of about 15%, something like difference between A330 and A330neo, or A320 and A320neo that share more things with original models?

The reality is that the 777X is not all that different from the 777 when considering cockpit procedures or 'user interface'. What is different is the hardware platform(s) that are used.

I worked for a supplier to Boeing for the 787. The stated goals for the 787 from Boeing were fairly straightforward. The design shall require a maximum of 5 days transition training for 777 pilot with a goal of 1 day. On the support side, there was a push to greatly reduce maintenance and upgrade costs. These are driven by the hardware and system architecture.

So the big change with the 787 was moving from the Honeywell AIMS and A629 based network to the Collins/GE A651 and A653 based Common Core System and A664 based network. The result of that platform change is why the flight decks look so different and that's what you see in the videos.

I can say with authority that in the 787 design our overriding directive was to make it look and behave like the 777. While a keyboard and a window on a widescreen display looks different from a control and display unit (CDU), the key functions and display behave the same.

So now with the 777X, the hardware is an evolution of what's in the 787. It uses the same basic open architecture and also follows the tenet of minimal changes that will require crew training.

So ultimately, the 777X is operationally similar to both the 777 and 787 while the hardware and software infrastructure follows the 787.

The impact of training is significant.  As explained to me by a United rep, when one senior captain retires it generates 10 to 15 training requirements as crews move up in the system. Every day of training costs them a lot of money.


What are the black boots on this Extra 300's prop? I normally think of black boots on a prop as being for de-icing. However, the Extra 300 is not suitable for known-icing conditions, or even IMC flight. (It's AFM says "Only VFR flights at day are allowed").
Considering the Extra 300's aerobatic mission, the gyroscopic loads on the engine are fierce. The upshot is that the manufacturer would not include a single extra gram more than necessary here.
So why are they there/what do they do? It has the owner and I stumped.

The inner portion of the blade is protected by a self-adhesive PU-strip, unless the blade is equipped with a de-ice boot.

The outboard edge as you can see in the very lower-right corner is protected with a stainless steel erosion sheath. Since the inboard section is slower (radial speed), its protection is a lighter polyurethane-strip/tape.

The Extra 300's service manual lists the 3-blade prop as one of two MTV-9 series (you can see the MT logo already in your photo). The above quote and illustration are from the MTV-9 series operation manual from mt-propeller.com. An example tape is the 3M 8663HS, which comes in black or transparent.


What component of an aircraft is most likely to fail? Given how rare airplane component failures have become today, I'm curious, are there still any components which are commonplace on aircraft, but still see a high failure rate? If so, why are these components used?

If not, are there any specific regulations to prevent this kind of thing?

Aside from the obligatory "The Pilot" answer, there are some components on an aircraft that will certainly fail at a higher rate than other components.
From the Piston GA side of the equation I can name a few (some of which are also applicable to turbine aircraft).

Incandescent Light Bulbs
A lightbulb is a supremely unreliable device: A delicate bit of wire is suspended in a thin glass envelope and heated until it glows - then subjected to vibration (from the engines, turbulence, etc.) in flight. We use them all over the airplane -- Position lights, landing lights, cockpit instrument lighting, etc. If you think about how often incandescent light bulbs burn out in your house it's probably not surprising that they fail quite often on aircraft. One such failure lead to a famous crash.

  We still use incandescent lightbulbs because they're cheap: A $0.25 light bulb can be replaced multiple times before its cost even approaches the capital investment in a better solution.
  Modern aircraft are incorporating an increasing number of LEDs to replace incandescent lightbulbs - these solid-state devices have a lower failure rate (and other benefits).

Batteries
Much like your car aircraft rely on batteries for some functions (like starting the engines or the APU). Batteries have a finite service life and will eventually fail to hold a charge and need to be replaced.
Sometimes battery failures can be rather dramatic.

  We still use batteries because hand-propping aircraft can be dangerous, and getting the APU turbine up to speed without a battery would be nearly impossible. Also if the engine-driven generators fail the battery is a useful source of electricity to help you get to a safe landing site.

Spark Plugs
Piston engines are spark-ignition, and spark plugs have a variety of failure modes (they can become fouled with lead or carbon deposits, the internal resistor can fail, or the electrodes can simply wear out).
These failures are not uncommon: Statistically if you fly piston aircraft long enough you'll probably encounter at least one of them.

  We use spark plugs for obvious reasons: Unless the fuel is ignited it doesn't generate any power. Without power the propeller doesn't turn (at least not very fast), so there's no thrust. No thrust means no flying.

Tires
Tires are another aircraft component with multiple failure modes. Interesting ones include leaks (air leaving the tire at a rate fast enough to be a problem), "catastrophic" failures where the tire explodes or disintegrates while rolling, and "self-protective" failures (where the tire reaches a temperature that melts the fusible plug and causes it to deflate to prevent it from exploding).

  Tires are also used for an obvious reason: Aircraft that constantly belly-land require expensive maintenance (to say nothing of the damage they do to the airport), and the alternatives - skis, pontoons, or flying boats - are limited in the areas from which they can operate.

Air Filters
On piston engines there is normally an intake air filter which is designed to keep dust and grit out of the engine. These filters can fail by becoming clogged (which I suppose isn't really a failure: The filter is doing its job), and certain paper filters can fail by disintegrating and being ingested into the engine (the FAA has issued airworthiness directives on this subject).

  We still use air filters - even the paper kinds that can disintegrate - because ingesting dirt into a piston engine greatly accelerates wear. The required maintenance on the air filter costs less than increased overhaul frequency.


To do the holding pattern or not? Full size: http://155.178.201.160/d-tpp/1710/06656ILD5.PDF

So for the plate, if we were approaching from the southwest on the ILS or the LOC/DME, would we have to conduct that holding pattern if we were cleared for the approach before reaching the IAF (not a straight in, not vectored, not timed, etc.)? Also, the MAP would be TFD 7.5 DME correct? How do I confirm that is the MAP?

Yes, you have to fly the hold.
If you're cleared for the approach, but you're not getting vectors to the final (or one of the other things you mentioned), the approach begins at the Initial Approach Fix (in this case, TFD) and you need to fly the full procedure, which will include the hold.

No, the missed approach point is 1,743 MSL (It's 7.5 DME for a localizer approach)
This is an ILS approach, so you go missed when you arrive at decision altitude and don't have one of the three required elements to descend further:

Visibility
Safe descent to landing
At least one of the required runway environment elements in sight

If you're shooting it as a localizer approach, you go missed when you cross the localizer and the needle flips. at 7.5 DME, a maneuver which is badly illustrated on this chart.  Thanks TomMcW!


If engine rotation was in reverse would it result in some kind of thrust reverser? I mean if you rotated the propeller the other way would it result in reverse thrust.I wonder this because the propeller has to rotate in a certain direction to produce thrust, but would putting it in reverse cause a force to help stop the airplane?

And does this system exist with planes that have propellers?

The propellers are like airfoils. Just as the airfoils do not produce useful lift if flown backwards, the propellers don't produce thrust if spun in opposite direction.

Source: www.quora.com

That being said, it is possible to obtain reverse thrust from propellers by setting a negative pitch, similar to the airfoil being flown upside down.

Source: 12charlie.com


What is the purpose of wing stiffeners? There are very few articles as to what wing stiffeners are on the internet, so my question is what are wing stiffeners?

When you have a thin sheet that is put under a shearing load like a spar web as shown, the sheet, being flexible, has very little resistance to bending under compression out of its surface plane (or buckling) at which point its ability to resist the shear force is lost.  The stiffener just gives the flat web some resistance to compression buckling by making it less flexible; "stiffening" it in other words.


Why require a minimum of 1500 hours to become an airline pilot? In the United States, under parts 61 standards for pilot certifications, for a person to apply for an airline transport pilot certificate one of the aeronautical experience minimums is a minimum of 1500 hours total flight time. Most ICAO compliant countries require similar numbers.  My first question on this would be why so many? It’s true that you want airline pilots to be experienced and no doubt I would not expect an airline to make someone a captain of a large, turbine airplane without a minimum of say 2000 hours with a lot of that being hard instrument and weather time but why require a first officer to need a minimum of 1500 hours for an ATP?
I’m aware prior to 2014 that the FAA allowed part 121 first officers to fly with only a commercial pilot’s license for the right seat and the 1500 hour rule only came about after the Colgan air crash in 2009.  People argue that this is what is resulted in only one commercial airline fatality over the past 10 years.  Still I wonder why an arbitrary number 1500 was chosen for an airline transport pilot certificate. Now I am also aware that this is not always the case. For instance graduates of approved part 141 schools can get a ATP with only 1200 hours TT with a aviation related associates degree, 1000 hours TT with an aviation related bachelor’s degree and military pilots with 750 hours TT can apply for an ATP directly.  My only thoughts would be, if part 61 training is so terrible that it requires a person to put in 1500 hours in a Cessna prior to applying for an ATP, what makes an aviation bachelors program superior or military flight training as compared to it, and why not simply train pilots under parts 61 to the same standards as the military does?
EDIT
Some other thoughts on this topic:  Well the military does allow people to operate large turbine powered aircraft with FAR less that 1500 TT, they’re in a position where they simply have no other alternative.  You can’t give a fresh 2nd Lieutenant 1500 in T-6 or T-38 prior to dispatching him/her to an F-16 squadron somewhere as its simply not affordable with trainer aircraft costing several thousand an hour to operate and training budgets already tight.  So they’re sent off to a active unit with 200 to 300 hours total time.  The downside is that, even in peacetime, military aviation units suffer horrendously hi accident rates as opposed to their Part 121 counterparts.  As I understand it, the USAF alone had 39 class 1 mishaps in 2018.  It’s an unfortunate fact that, as much as primary flight training could teach you, it’s only a license to practice your craft; flying is an artform and takes a lifetime to master and there are a lot of dangers out there.  That being said, mass hours alone are really not good experience.  It requires APPLICABLE experience to matter.  An aviator train did a small part 61 flight school in central Iowa and logs 1500 hours flying Cessnas locally as a CFI is nowhere near ready for the rigors and stress of an airline pilot, but a pilot with 500-600 hours TT with complex, instrument, and multi-engine turbine time in high density airspace around major cities is far more likely to success here.
It bothers me that these kinds of regulations are written this way, without any thought to the practicality of it. It’s also strange that way, since, most of the FARs are very practical and based on well researched information as well as accidents in the past.  It also bothers me that it causes new pilots to bear an extreme burden to build those kinds of flight hours for a career, which may or may not be beneficial to them. I’m just curious what the FAA’s thought process was in recommending the scheme

The 1500 hours is requirement for ATPL (airline transport pilot license), which is needed to command a multi-member crew. But in most of the world the CPL (commercial pilot license) with a 250 hour requirement is sufficient to fly as a co-pilot (F/O), and that used to be the case in the USA as well. And those hours include any spent getting the private license and instrument, multi-engine and type ratings.
My understanding of why the USA started requiring ATPL for F/Os as well is that it was only indirectly related to safety and had most to do with job market. At the time it was introduced the large supply of aspiring pilots led to very low wages in the regional airlines, and with that tendency to also overload the pilots and save money across the board, ultimately affecting safety. Raising the requirement aimed to limit this by making pilots more scarce.


How is supercruise achieved? Wikipedia article tells that supercruise is a condition when an aircraft can achieve velocities above Mach one without using the highly inefficient afterburners. But still, there are not a lot of engines which can achieve this.

What is the specific requirement for an engine to achieve supercruise? Why can't most of the engines reach supercruise without reheats enabled?

It's less about the engine and more about the combination of engine and plane. Theoretically, all that is needed is for the engine(s)' thrust without afterburners to be able to overcome the plane's inherent drag at a speed greater than Mach 1. Simple, right?

Well, to do that, you're up against some pretty heavy physics. First and simplest, given a drag coefficient for the aircraft in a "clean" configuration, the drag force increases on the square of velocity. So, to go twice as fast, you need four times the thrust with all other things being equal. Jet engines simply don't scale that way; you need a bigger engine to provide more max thrust, and then all things aren't equal anymore.

Second, planes aren't built like cars, where in many cases there's enough room under the hood to drop in a bigger engine block and a turbocharger to double power for negligible additional weight. Fighter designs have to essentially wrap an aerodynamic skin as tightly as possible around the pilot, engine, avionics and fuel storage. For the longest time, engine efficiency was pretty static, therefore more thrust meant more engine. A bigger engine means a bigger plane, which means more drag, which offsets the thrust gains and thus the speed increase of the larger engine.

Thirdly, there are some complex aerodynamic changes involved as a plane transitions the sound barrier. Airflow into the engines increases at higher speeds, which reduces the compression ratio of the engine; the intake turbines become less and less efficient as speed increases, and thus you get less and less benefit from the "bypass" airflow of the turbofan. Afterburners are more or less a simple way to continue to get more thrust after the intake turbines are no longer significantly compressing air, by taking that air, dumping a bunch of extra fuel in it and riding the prolonged explosion. This, however, uses ten to fifty times the aircraft's cruising fuel flow rate.

The F-22 achieves supercruise in part by extending the efficient operating range of the engines with "variable bypass". At lower airspeeds, engine bypass is increased to allow the turbofans to increase thrust with minimum fuel. At higher airspeeds when the turbofan effect decreases, compressor bypass is reduced to put more air into the combustion chamber (along with more fuel), which increases thrust beyond the normal compression limit more efficiently than simply burning the bypass airflow with an afterburner.

Finally, there is the simple requirement of supercruise in an aircraft's mission profile. Not many things in air combat occur at supersonic speed; you can't dogfight effectively at Mach 1 because your sustainable turn rate is measured in miles, you often can't drop gravity ordinance (bombs) because they won't fall away from the aircraft in a stable or predictable way, and in the case of the Raptor you have to open payload doors to deploy your weapons and that will increase your drag right there.

Supercruise has a singular purpose; to increase the speed of the aircraft's transit to and from the target zone without sacrificing range by dumping fuel into the afterburners at ten to fifty times "military power". For an air superiority fighter (combination interceptor/dogfighter), that's very important, but the F-22 was the first U.S. fighter developed from the ground up to take advantage of the latest technological progress in aircraft design such that it could be achieved. The last time U.S. fighter designers got an opportunity to design a "cost-is-no-object" superfighter was almost 40 years ago with the F-15, and the two major fighter designs to enter U.S. service in the interim, the F-16 and F/A-18, were the result of a design competition specifically intended to create a lower-cost multirole fighter to serve as the bulk of the air fleet.

Other supercruise-capable fighters designed by NATO allies reached production first; the English Electric Lightning interceptor is considered the first supercruise-capable production fighter (predating the coining of that term), and the Dassault Rafale is reported to be supercruise-capable in certain mission-ready configurations up to Mach 1.3, and beat the Raptor to market by about 2 years, though the Raptor has a substantally higher top speed under full military power (100% non-afterburning throttle).


Aviation terminology for 'in the field' I'm writing a sci-fi story involving aircraft and space craft. I'm struggling to get the terminology right for referring to a pilot being 'in the field' either on a mission or a training exercise. I have a feeling there is a phrase for this but I'm struggling to think of it.

An American armed forces general expression for this is "operational"


What are "Alternate Minimums"? As I asked question about weather minimums yesterday, I've read some material including TERPs. And In the FAA 8260.3b, 'Taking and Landing Minimims' 3.1 there is one sentence "alternate minimims, when specified, must be stated as ceiling and visibility."

But I don't know What alternate minimums exactly means because I am not native English speaker. I have used English dictionary to find exact meaning but failed.

What is the difference between approach minimums and alternate minimums?

FAR 91.169 states that IFR flight plans must include an alternate airport unless the weather is at least 2000 ft ceiling and 3 miles visibility, from one hour before to one hour afterwards (1-2-3 rule).

The same regulation also states that the alternate airport must meet the following critera:

  (c) IFR alternate airport weather minima. Unless otherwise authorized
  by the Administrator, no person may include an alternate airport in an
  IFR flight plan unless appropriate weather reports or weather
  forecasts, or a combination of them, indicate that, at the estimated
  time of arrival at the alternate airport, the ceiling and visibility
  at that airport will be at or above the following weather minima:

    (1) If an instrument approach procedure has been published in part 97
    of this chapter, or a special instrument approach procedure has been
    issued by the Administrator to the operator, for that airport, the
    following minima:

      (i) For aircraft other than helicopters: The
      alternate airport minima specified in that procedure, or if none are
      specified the following standard approach minima:

      (A) For a precision approach procedure. Ceiling 600 feet and visibility 2 statute miles.

      (B) For a non-precision approach procedure. Ceiling 800 feet and visibility 2 statute miles.


Why do we complete wing bending tests? My question is simple.. Why do we need wing bending tests, what can we learn from them and how can this help us evolve the product?

Transport category airplanes, which includes most aircraft in commercial passenger service, must meet the FAA regulations in 14 CFR Part 25. Some relevant excerpts are as follows:

§25.305
The structure must be able to support ultimate loads without failure
§25.307
Structural analysis may be used only if the structure conforms to that for which experience has shown this method to be reliable. In other cases, substantiating tests must be made to load levels that are sufficient to verify structural behavior

Ultimate loads are the absolute maximum loads that a structure must carry without failure. These are loads will be extremely rare and result in permanent damage to the structure, but with the structure still intact the aircraft should still be able to land safely.
The FAA will not certify the design if the manufacturer cannot prove that the structure is capable of meeting these requirements. One option is using computational simulations. Modern analysis techniques are very powerful. However, analysis is useless if you can't show that it is also reliable. Structures like wings are extremely complicated. Once the materials become permanently deformed, the behavior changes and the analysis becomes even more complicated.
So if you can't prove that computational methods will work, you have to do a test of the structure. Fatigue is similarly difficult to predict, so aircraft are generally subjected to multiple lifetimes worth of load cycles with special test rigs to understand how the parts will hold up.
When the Boeing 777 wing was tested, it failed at 4% over the required load. This shows that even the limited analysis capabilities (compared to today) were very accurate, but the only way to find out for sure is to test it. Analysis will always have some amount of error. If the analysis had been a few percent off the wing would have failed the test.
So the analysis for the 777 was shown to be reliable, but only in the case they tested. If a new design differs significantly, this adds some uncertainty into the analysis. Will it still be reliable in the new case? The only way to know for sure is to test it.


What is a G-Check and what are the differences relative to other checks? Tried looking for a definition on wikipedia for a G-Check. The wikipage only mentions A,B,C,D checks.

Any ideas what a G-check exactly is? I think I found an article stating it is a 7500 hr major inspection. What is considered a major inspection relative to a minor?

It's tough to tell based on your question, but I think you are talking about an inspection due to an over-G reported on a flight either by the pilot or the flight control system post-flight report.

Maintainers will do inspections of known stress points on the aircraft to look for breaks, cracking or loosened parts and then declare it safe for flight or fix anything out of tolerance.  For a low level over-G, this could be pulling a few panels.  For higher level over-Gs it could be 8 hours worth of work


What does the * (asterisk) next to radio and nav aid frequencies on Jeppesen charts refer to? For Bournemouth, all radio frequencies and LOC IBMH are marked with an asterisk - *

Many other airports also have these markings, such as: Southampton, Alderney, Jersey, Guernsey, Exeter...
However, Cardiff doesn’t have an asterisk preceding to its radio frequencies:

But it does have one before LOC ICWA
What does an asterisk, preceding a frequency, refer to?

It means that this frequency is not always available (not always staffed). From the Introduction to Jeppesen Navigation Charts:

8 - Indicates the service is part time.

And further below:

Navaid boxes include the navaid name, identifier, Morse code, and frequency. A letter "D" indicates
DME capability with an asterisk indicating part time.


Does night takeoff and landing currency also count for daytime currency? My initial thought is that night currency satisfies daytime currency, but what gives me pause is FAR 61.57(a)(2) notes that a non-current pilot is allowed to conduct day VFR or day IFR flights without passengers to obtain currency.  There is no mention of night flight being allowed.  This seems to imply that day flights are required for daytime currency.

Yes, night landings satisfy the requirements of §61.57(a)(1) for both nighttime and daytime currency.

The wording of the regulation is not crystal clear, and some (including me) have thought that the wording of (a)(2) required daytime landings for daytime currency. This is not the case, per the following interpretation from the FAA (Springfield, IL FSDO, dated 16 April 2014):

  Please note, in this section, there is no mention of a day or night differences in the regulation.

  In 14 CFR 61.57(b) the regulation specifically mentions the requirement for Night Takeoffs and Landings and the time period they can be completed in.   If the passenger carrying will be done at night, the additional requirements of 14 CFR 61.57(b) must be met.

  The night takeoffs and landings, as required by 14 CFR 61.57(b), will qualify for both the day and night requirement, provided all other requirements are met.   The day takeoffs and landings will NOT qualify for the night (section (b)) requirement though.

  Stanley E. Swank II
  Aviation Safety Inspector
  Springfield, IL FSDO, AGL-19

Other sources on the Internet agree with this interpretation:

Eric Gideon at askacfi.com:

  ... your three takeoffs and landings to a full stop at night will also fulfill the recent flight experience requirements for day currency.

A thread at pilotsofamerica.com.


For a private GA pilot, when is an endorsement needed for a particular type of aircraft? If I've done my training say 85% in a C152 and 15% in a C172, then upon my earning my PPL, what am I allowed to fly legally?  I assume the 152, but not sure about the 172. Is this indicated somehow in my logbook? When is a separate check out required for a new airplane and assuming the same type (i.e., SEL, fixed gear, fixed pitch prop, non pressurized, etc.), what would this typically entail?  Is this an FAA requirement or a liability requirement for clubs, etc.?

There are two aspects here, one what is required legally and then what may be required locally.

From a legal standpoint (in your case) the basic PPL will allow you to fly single engine, fixed pitch prop, under 200HP, fixed gear aircraft. If you want to go over 200 HP you will need a High Performance check out and log book endorsement. For a constant speed prop/folding gear/movable flap (all 3 are required to require this endorsement) plane you will need a complex endorsement in your log book. You may want to fly something like a Piper Cub which will require a tail wheel endorsement. If you are lucky enough (and have the funding to do so) you may find your self in a small pressurized single (or twin) like the Piper Meridian or TBM 900 these planes will require a high altitude checkout as well. AOPA has a nice summary of the endorsements here. If you want the full FAA FAR regs you can find them here.

Now as for a club or school that depends on a variety of factors including their insurance and their personal limits. I'll offer some personal experience which seems to be pretty par for the course. The flight school I fly from requires a checkout in type from every new renter before you can fly it even if you have a PPL and the proper endorsements. They don't have an official amount of time but it usually takes about an hour with an instructor. The former flight school I was at had the same deal with the exception of their Saratoga which they also required an instrument rating (along with their checkout).

My buddy's flight club is somewhat similar. They require a check out in their Archer and Dakota to fly solo. They also have a Lance which they require 25 hours time in type and a 5 hour check out in the plane.

As for your log book you should be logging the full type of aircraft for every flight. For example when I fly the Warrior I make sure to note PA-28-161 and the Archer I fly is noted as PA-28-181 when I record hours this way I can note time in type at a detailed level.

For what its worth with the PA-28 airframe it seems that some places to allow you to fly the lower rated planes if you are checked out in the higher power ones. The same basic frame was built in a 140, 160, 180 and 235HP variant over the years and has little differences aside from useful load and V speeds. For example at the place I go if you are checked out in the Archer first you are allowed to fly the Warrior with out a checkout.

This will also extend to ownership should that be the path you go down. In that case you insurance company may require a certain amount of hours of time in type before you are allowed to solo your plane. Keeping that in mind you are not actually prevented from buying the plane and will be insured under the stipulation that the first hours in the plane are with an instructor. When a buddy of mine (instrument rated and close to 600 hours at the time) upgraded from his 72 Archer to a 95 Saratoga HP his insurance company mandated he do 25 hours in type with an instructor before taking the plane solo. The first 25 hours he flew his plane were with an instructor (this included transporting the plane from the factory in Vero Beach to his home field).

You can legally fly both planes once you have your PPL. What someone will let you fly should be pretty well addressed above. Neither the 172 or 152 requires a specific type rating like larger planes do.


May a commercial pilot transport an owner in the latter’s experimental aircraft for compensation? Say Olive Oyl owns an RV and wants to hire Popeye, a commercial pilot, to fly her to the beach in her aircraft, which has an experimental certificate. May Popeye legally accept compensation for this flight?
One might hastily conclude that the prohibition in FAR 91.319(a)(2) applies

§ 91.319 Aircraft having experimental certificates: Operating limitations.
(a) No person may operate an aircraft that has an experimental certificate —
     (1) For other than the purpose for which the certificate was issued; or
     (2) Carrying persons or property for compensation or hire.

but at least paragraphs (e), (f), (g), and (h) of the same section make exceptions that allow for-hire use. Well known for-hire uses in experimentals include ferry flights, instruction, test flights, aerial survey, and acceptance flights.
“Operate” and related terms have technical definitions in this context, provided in FAR 1.1.

Commercial operator means a person who, for compensation or hire, engages in the carriage by aircraft in air commerce of persons or property, other than as an air carrier or foreign air carrier or under the authority of Part 375 of this title. Where it is doubtful that an operation is for “compensation or hire,” the test applied is whether the carriage by air is merely incidental to the person's other business or is, in itself, a major enterprise for profit.
Operate, with respect to aircraft, means use, cause to use or
authorize to use aircraft, for the purpose (except as provided in
§ 91.13 of this chapter) of air navigation including the piloting of aircraft, with or without the right of legal control (as owner,
lessee, or otherwise).
Operational control, with respect to a flight, means the exercise of
authority over initiating, conducting or terminating a flight.

In the scenario above, are both Olive Oyl and Popeye operating the aircraft simultaneously? Who has operational control?
Interpretation of FAA regulations seems heavily weighted in favor of protecting the ignorant public from the general risks of flying and especially from unseemly outfits who may find irresistible the temptation to cut corners. Owners and those who otherwise provide the aircraft that will carry them or their property have different incentives and receive different treatment, cf. FAR 91.319(e)(2) and FAR 91.319(g).
If Olive Oyl asserts that she is not running a commercial operation and is paying Popeye for his services, do they have a legal leg to stand on?

This one seems pretty straightforward to me. 91.319(a)(2) applies (because in the scenario you have described the pilot would be carrying persons - Olive - for compensation or hire).

Popeye could accept compensation to reposition the aircraft (with no passengers or cargo onboard) as a ferry pilot, but not to operate the aircraft for the purposes of transporting persons or property (besides the aircraft itself and the incidental things it might carry like extra oil) - even if the person happens to be the owner of the aircraft.


How can the radar range for ATC be estimated based on stated maximum radar range? Is there a way to estimate the maximum effective range of a naval radar for air traffic control functionality, based on the radar's stated overall max range?

For instance, if a naval radar that has targeting functionality states that it can detect artillery fire at a maximum range of 75NM, is there a way to estimate its range for air traffic control purposes (e.g., a max range of 75NM translates to about a max functional range of 25NM for air traffic control?

A radar system designed to track artillery shells is likely to be entirely useless as an air traffic control system.

To improve their utility radar systems reject signals outside their design parameters. This means that stationary elements (buildings, landscape features, etc.) are ignored, as are objects with velocities well outside the target range. There may be other optimisations.

The muzzle velocity of an artillery piece is typically well in excess of the speed of sound (Reference) A radar system designed to handle artillery shells may reject many subsonic traces, and thus ignore most aircraft that you might want to have some control over.

Of course, you could reprogram or repurpose the electronics, but then you wouldn't really have a naval radar anymore.


Has any accident been caused by poor time management, despite a perfectly done checklist? This is a question I've heard from an aviation psychologist. I've searched on that but couldn't find a satisfying example. The full question is:

Has there been any accident which was caused by poor time management by the crew, despite a perfectly done checklist?

Thanks in advance.

Time management generally means selecting the most important things to do given limited time. And in context of aviation that means following the common maxim “aviate, navigate, communicate”. Which is occasionally called a checklist, but usually not.

Aviate means keeping the plane under control and inside the flight envelope, navigate means knowing where you are and where you are flying, and communicate if there is someone who should know, meaning mainly the air traffic control. And most checklists, except some memory items, only come after these three.

So an accident due to poor time management means the crew got preoccupied with something and basically forgot to monitor the flight path—there is plenty of those—and despite correctly executed checklists means the distraction involved a checklist, probably a non-normal one (dealing with some failure)—I am not sure how close the accidents I can remember of the top of my head come.

Eastern Air Lines flight 401 on 29th December 1972 is probably the best known accident that comes to mind. The crew executed their before landing checklist, but that revealed one issue. And the crew became so preoccupied in troubleshooting it that they failed to notice they inadvertently turned off the altitude hold.
In some sense the Dana Air flight 992 on 3rd June 2012. The crew correctly configured the aircraft for best glide in response to a dual engine failure, but then the pilots kept trying to restart the engines and neglected to prepare for the possibility of forced landing. The checklist for engine failure does mention this though, so ultimately they didn't execute it correctly.
The Distraction in cockpit category on the Aviation Safety Network seems most relevant, but not sure which of the accidents qualify. Maybe this Avianca 727 on 17th March 1988 or this Sky Executive L410 on 21st May 2002?

There is probably more, but it is relatively hard to search.


What should pilots state initially when telephoning a weather briefing facility for preflight weather information? I've gotten this question wrong multiple times on practice tests. Sporty's study buddy claims the information is sourced from AIM 7-1, but it's nowhere to be found.

Correct answers included:

The intended route of flight and destination
Tail number
Identify themselves as pilots

What is the actual authoritative language that covers this test question?

It's in the AIM 5-1-1(f):

When requesting a preflight briefing, identify yourself as a pilot and
provide the following:

Type of flight planned; e.g., VFR or IFR.
Aircraft’s number or pilot’s name.
Aircraft type.
Departure Airport.
Route of flight.
Destination.
Flight altitude(s).
ETD and ETE

Personally, I've never given or been asked for the aircraft type (although I have it on my LMFS profile so they should have it), but the other items come up. My typical request is something like this:

This is N12345, I'd like a standard briefing for a VFR flight from
KMDQ to KLOU at 5500', ETD at 1600Z, ETE 2h15


What is the effect of aft centre of pressure movement on static longitudonal stability? During studying for my Air Transport Pilot License (ATPL) I encountered a question answer which said that aft center of pressure movement increases longitudinal stability. If this is true, I cannot seem to wrap my head around the concept of why this is so.

Moving the CP aft will have the same effect as moving the CG forward: increased longitudinal stability.

The arm of the Lift force is now increased and the ratio of momentum generated by the wing vs horizontal stabilizer is decreased, leading to positive longitudinal stability.


Why is ram air not used for air conditioning in airplanes? If the ram air is used for air conditioning, the airplane doesn't need a heat exchanger, cooling fan and cool the bleed air from compressor. So why do modern planes use bleed air cooled by ram air?
My guess would be mass of the air. The compressed air has more mass in small volume.

The problem is pressure. In order to use outside air for the cabin, it needs to be pressurized. Otherwise you could not reach higher pressures inside the cabin than outside.
The advantage of using bleed air is that this air is already pressurized, so you don't need to do any additional work. It is however too hot to be used as cabin air directly, so a PACK (Pneumatic Air Cycle Kit) is used to reach lower temperatures using ram air for cooling.
Ram air cannot be directly used without increasing its pressure. On the Boeing 787, which is equipped with bleed-less engines, the outside air therefore needs to be pressurized with electrically driven compressors:

In the no-bleed architecture, electrically driven
compressors provide the cabin pressurization
function, with fresh air brought onboard via
dedicated cabin air inlets. This approach is
significantly more efficient than the traditional
bleed system because it avoids excessive energy
extraction from engines with the associated
energy waste by pre-coolers and modulating
valves. There is no need to regulate down the
supplied compressed air. Instead, the compressed
air is produced by adjustable speed motor compressors at the required pressure without significant
energy waste. That results in significant improvements in engine fuel consumption.

(Boeing Aero Quarterly - 787 No-Bleed Systems, emphasis mine)
Note however that this compression also adds heat to the air, so the air still needs to go through a PACK before it can be used as cabin air:

In the 787 electrical architecture, the output of the
cabin pressurization compressors flows through
low-pressure air-conditioning packs for improved
efficiency. The adjustable speed feature of electrical motors will allow further optimization of
airplane energy usage by not requiring excessive
energy from the supplied compressed air and
later regulating it down through modulating valves
resulting in energy loss.
Avoiding the energy waste associated with
down regulation results in improvements in engine
fuel consumption, and the environmental-control
system air inflow can be adjusted in accordance
with the number of airplane occupants to achieve
the lowest energy waste while meeting the air-flow
requirements.

(Boeing Aero Quarterly - 787 No-Bleed Systems, emphasis mine)
You can see the inlet for the compressors and the ram air inlet in the following picture:

(image source)


Are Belarusian ATC recordings available for Ryanair Flight 4978? I am interested in locating the ATC recordings of Ryanair Flight FR4978, LGAV to EYVI, 23/5/2021, that had a forced diversion to UMMS in order to arrest a passenger.
I have looked online but couldn't find any recordings available, the closest I found was https://www.liveatc.net/, but wasn't able to find the relevant files, because I don't know the ARTCCs of the controllers they were talking to.

Not every country allows recording and publishing of ATC communication. The UK for example does not: Is it illegal for Joe Public to listen to ATC in the UK?
While I don't know for sure, I'm guessing Belarus does not allow it. LiveATC has a coverage map, which shows the destination airport EYVI (Vilnius) is covered, but nothing in Belarus is:

I therefore doubt you will be able to get the recording. Since the incident is currently being investigated by multiple countries and organizations, a recording or a transcript might be available in the future as part of the investigation report.


Do flares affect IR tracking devices? If an IR device, such as a tracking FLIR system (not a heat-seeking missile), tracks an aircraft and that said aircraft would launch flares. Is the IR tracking device likely to be confused by the flares?

Obviously, the point of defensive flares is to decoy missiles. I want to know if other IR devices tend to be as fooled as a missile.

I want to know if other IR devices tend to be as fooled as a missile.

No.

Modern imaging systems are not susceptible to flares in the same fashion as older missile seekers, which is precisely why modern missiles like the ASRAAM and AIM-9X use imaging seekers.

The reason flares worked at all was due to the physical layout of early missile seekers. These used a photocell detector that was sensitive across a wide field of view, on the order of 90 degrees. The trick is how do you use a device that basically provides a "yes, there is something in front of me" to track a target down to the sub-degree precision needed to actually hit it from long range?

The common solution, the "chopper", was to point the photocell forward and place it immediately behind a spinning metal disk with rectangular slices cut out of it following the pattern of slices on a pizza. As the disk rotated, the slices would periodically line up between the target and photocell, causing the photocell to give off a brief flash of power. For instance, if the target was above the missile, the photocell would see it whenever one of the slices was oriented vertically.

The frequency of the pulses was the same as the speed of the disk's rotation. These were sent into a smoother that produced a sine-wave output that peaked, in time, where the target was located. That means that the phase of this output encodes the relative angle between the missile and the target. By comparing this signal to the signal driving the disk motor, the resulting "error signal" directly encodes the direction the missile has to turn.

Early missiles were this simple, feeding the amplified output of the sensor directly into the control surfaces. The resulting flicking motions of the controls became known as "bang-bang". This was extremely inefficient, so a number of additional tricks were used.

The main one was to adjust the motion of the controls by the "angle-off", the angle measured from the missile centerline to the target (as opposed to the angle around the missile body, like a clock). Recall that the slits are rectangular. This means that the amount of time that the signal is present, it's pulse width, is dependant on how far the target is from the center of the disk.

For a target near the center, there is an almost constant signal because the linear motion of the slit is much slower (think of a record turning) and the slits are very close together. In contrast, a target near the outside instead creates very brief flashes at a single time. By subtracting the averaged signal from the raw signal you can determine the angle-off.

So here's why flares were so effective...

For simple bang-bang systems, the flight controls would suddenly start receiving more than one signal. As the aircraft flew away from the flare, the controls would begin flicking back and forth, causing it to track to the center of the two. This not only made it miss the target, but could lead it to run out of energy due to all the drag from the constantly moving controls.

In the case of the more sophisticated sensors, which includes many early missiles like the Sidewinder, flares can be even more effective. That's because when the signal from a target at the center is evened out it goes to zero, so if the missile is tracking properly it has little signal to work with. As the flare moves away, the aircraft's signal remains low but the flare's becomes huge, drawing the missile away from the aircraft. As the missile centers on the flare its signal disappears too, but hopefully after the aircraft has exited the seeker's field of view.

Both concepts only work if the flares move away from the aircraft with some speed - they are generally useless on helicopters for instance. For these types of roles, a new system was created. This normally consisted of an electrically heated block of metal or ceramic, with a series of metal shutters in front of the block. The shutters flicked open and close, producing random flashes of IR on the seeker. This caused the guidance signals to have random peaks, causing the missiles to fly around tracking the phantom signal. Another concept uses a low-power IR laser and a scanner like the ones in a supermarket to cause the beam to periodically pass by the missile, presenting a similar random pattern.

None of these systems work against imaging systems or seekers. For one, they no longer use timing to create the control signal, but instead use a variation of contrast tracking. Hot block decoys image at the same location as the target, so they simply increase the tracking signal, precisely the opposite of what you want. Flares, in theory, can still work, but even trivially simple image recognition systems can measure the size of the IR signals and immediately reject small objects like flares. And with modern processors, one can easily calculate the speed of all of the objects and look for ones that are rapidly slowing down.

Flares still have considerable utility against man-portable and older ground-launched missiles for the simple reason that most of the ones you are likely to meet in the field, including both fSoviet and US models, use some variation of a chopper. You can also release massive numbers of flares and attempt to obscure the target when the missile is far away and it cannot resolve the flares, but that can be accounted for by tracking the release points.

Against a modern missile, flares are generally useless. This has led to the concept of a towed decoy that is essentially a small plane on a wire. These can, theoretically, fool imaging seekers, but I suspect they are not as effective as one would wish. Thus the move to longer and longer-ranged missiles, where the fight really comes down to who has the best radar - which is likely always going to be "the west".

Another approach that is seeing some interest is the use of IR lasers to dazzle the seekers. These generally use UV seekers to look for rocket motors and then scan a laser around that area. If the laser hits the missile it can blind the sensor long enough to escape. I'm not sure if any such system has been deployed.


What is the meaning of AFT in airworthiness directives? What is the meaning of AFT in airworthiness directives?

The average flight time (AFT) is defined as flight hours (FH) divided by flight cycles (FC) accumulated by an individual airplane since the airplane's first flight, specified in hours and hundredths of an hour.


How does having multiple ATC towers affect airport operations? I know there are airports with more than one ATC Tower, though I only know it from my own country (SCHIPHOL - EHAM). This airport has two towers called Tower-Center and Tower-West. Tower-West is built because of a sixth runway (18R - 36L), that wasn't clearly visible from Tower-Center. (They found this out after completion of the sixth runway.)

How common is it an airport decides to built a second tower, and are there a certain rules or limitations before the decision can be made?

Next to that; what are the practical consequences for pilots and ATC's? Do they not only switch between startup- and ground-controllers but also between several ground controllers?

At larger airports it is fairly common to have more than one tower, but it all comes down to how well the tower controllers can see airplanes.  Sometimes they have different towers for ground control frequencies and tower control frequencies, and the position of the tower is optimized for the appropriate task.  For very large airports, they may need towers in different areas of the airport to properly see airplanes at each runway.

As far as practical consequences it doesn't matter much whether they have one or more towers.  At very busy airports they split up the tower/ground controllers/frequencies because one person can only control so many airplanes at a time.  For instance, there may be one controller for the North runway and one for the South runway.  In this case, there could be only one ground controller, or there may be two or even more, depending on the complexity of the ground operations.  With multiple ground frequencies, if you need to taxi from one controlled area to another, the controller that you are talking to will tell you to hold short of a particular point and contact ground on the other frequency.  Once you contact the second controller, they will clear you to continue taxiing.

In short, it is very specific to the local conditions, and they do what they have to in order to properly control the traffic.


What did Paris' de Gaulle airport look like before the t2 expansion? Charles de Gaulle airport (CDG/LFPG) in Paris had great expansion in the new century, including new runways and terminal 2 buildings.

What was the airport layout before the great expansion?

You will hardly find anything complete on the web as :

at the time of the expansion a bunch of years ago, you didn't have that much computer assisted medias to produce representative documents.
most accurate documents are inside old books you can only access at specialized libraries, rare copies owned privately or museums.
Because Charles de Gaulle is a french airport, you'll likely to find what you're looking for in french !

I do have an Air France magazine with Charles de Gaulle history til 2002, and another dedicated to the Terminal 2F extension, but because those are copyrighted materials, I can't post them here. Sorry.

Though, you can head to the following sites :

http://www.entrevoisins.org/paris-charles-de-gaulle-de-1945-1975.aspx
(video - if you don't mind quality of the era)

http://www.aeroportsdeparis.fr/groupe/presse/40-ans-paris-cdg/photographies
(a couple pictures)
http://airinfo.org/2014/03/07/paris-charles-de-gaulle-fete-ses-40-ans-video-photos/ (dedicated copy of the above)

http://www.goussainlivres.com/librairie/librairie/aeroport-roissy-charles-de-gaulle=198.html
(one small cropped overview from a book - bear in mind that most relevant structures of the airport is inside that picture and everything around are empty areas)

Basically, you only had the Terminal 1, and one runway. Airport name was "Paris Nord" before becoming "Roissy-en-France", then finally called "Charles de Gaulle" just before inauguration (8 of March, 1974). And initial planned extensions were identical copies of the Terminal 1 all other the place including where T2 and T3 are today. Sorry, I can't post a plan from the Air France book, but it's rather similar to the one you can spot in the video above.

There are also rare documents you could retrieve from old magazines issued at the time (Air & Cosmos to name the one I know of) or magazines like EntreVoisins (used to collect them at Maison de l'Environnement, Athis-Mons, near Delta Museum) which sometimes raises issues about noise pollution from Paris Airport platforms (comparative maps of the airport through the years)


Is there a formula for calculating the pivot point of an aircraft while turning on the ground? I'm working on a program that requires a taxiing passenger aircraft (of any model) to perform a semi-accurate turn given a steering angle of the front landing gear. For this I need to calculate the pivot/center point for the aircraft to rotate around. There seem to be a few factors that influence this (including some basic specifications of the aircraft) but I can't seem to find even a general equation that breaks it down.

I'm aware that there are also a number of more complex factors that would influence this, but for my purposes I'm assuming an ideal situation with minimal interference.

Thanks in advance!

The pivot point will be where an imaginary line through the rear wheels and an imaginary line perpendicular to the front wheel intersects.

So if θ is the steering angle and d is the distance between the front wheel and a point halfway between the rear wheels then

X = d • tan(θ)

will give you the distance from the point between the rear wheels to the pivot point.


How to calculate the induced drag coefficient? In an exercice of Flight mechanic, I have to compute the drag coefficient at zero lift: $C_{D0}$.We saw in class two ways to find it :

$$
C_{D0} = \frac{\pi AR e}{4E_{max}^2}
$$

With $AR$ the aspect ratio, $e$ the Oswald number and $E_{max}$ the maximal Lift-to-drag ratio. I don't have the value for the two last ones in my exercice so I can't use this formula.

We saw another way, by using the polar definiton: $C_D = C_{D0} + kC_L^2$ with $C_D$ the drag coefficient, $C_L$ the lift coefficient and $k$ the induced drag coefficient. In order to use it I just need to find the value of $k$ but the only formula that I have is:

$$
k = \frac{1}{\pi e AR}
$$

And I still need the value of $e$ the Oswald number. Is there a way to compute $e$ ? I didn't found any on Internet. If not, is there another way to compute $k$ without $e$ ?

Thanks for your help and sorry if I don't have the proper english vocabulary.

There's no way to calculate $e$ without using computational fluid dynamics (CFD) since it involves the calculation of complex three-dimensional flow interactions with the wing geometry (lift loss due to wingtip vortices).

For most aircraft, 0.8 is a pretty good estimate, so this is probably the value you're expected to use. If you need a more accurate number for your particular problem, you'll either have to know the specific aircraft model (in which case you would likely have to calculate $e$ given $AR$ and ${C_D}_0$, $C_D$, and $C_L$ for a certain state) or be given a number to use for the problem.


Can an appropriately-fitted UAS (of any size category) be flown in Class B airspace? If I fitted an Unmanned Aircraft System (UAS) with an operating Mode C transponder and maintained two-way radio contact with ATC, could my UAS be cleared into class B airspace in the USA?

(Inspired by:

What legal actions would be taken against a drone pilot if they flew a drone into class B airspace?
)

In general, no, you can't.

Public (Governmental) Use

The FAA maintains a page on Public Operations of UASs. There are a couple of ways governmental organizations (excluding the armed forces) can fly a UAS:

It can fly in accordance with the limitations set out in Public Law 112-95 Title I, Subtitle B, Section 334 (c)(2)(C), which are that the FAA will:

  (C) allow a government public safety agency to operate unmanned aircraft weighing 4.4 pounds or less, if operated—

    (i) within the line of sight of the operator;
    (ii) less than 400 feet above the ground;
    (iii) during daylight conditions;
    (iv) within Class G airspace; and
    (v) outside of 5 statute miles from any airport,
    heliport, seaplane base, spaceport, or other location
    with aviation activities.

So, obviously, that's a no-go for Bravo.

It can apply for a Certificate of Waiver or Authorization from the FAA, which "permits public agencies and organizations to operate a particular aircraft, for a particular purpose, in a particular area." According to the FAA,

  The FAA works with these organizations to develop conditions and limitations for UAS operations to ensure they do not jeopardize the safety of other aviation operations. The objective is to issue a COA with parameters that ensure a level of safety equivalent to manned aircraft. Usually, this entails making sure that the UAS does not operate in a populated area and that the aircraft is observed, either by someone in a manned aircraft or someone on the ground to ensure separation from other aircraft in accordance with right-of-way rules. Common public uses today include law enforcement, firefighting, border patrol, disaster relief, search and rescue, military training, and other government operational missions.

So, unless you have a really convincing argument, it sounds like the FAA is very unlikely to include in your COA authorization for your UAS to enter Class B (or get anywhere near it, for that matter.)

Civil, Non-Hobbyist Operation

The FAA also maintains a page on Civil Operations of UASs. That page summarizes how civil UAS operations can be approved as follows:

  There are presently two methods of gaining FAA authorization to fly civil (non-governmental) UAS:

  Section 333 Exemption – a grant of exemption in accordance with Section 333 AND a civil Certificate of Waiver or Authorization (COA); this process may be used to perform commercial operations in low-risk, controlled environments. Instructions for filing a petition for exemption are available here.

Surely, operating in Class B isn't "low risk" (though I suppose you could argue it's "controlled,") so this certainly seems like a no-go.

  Special Airworthiness Certificate (SAC) – applicants must be able to describe how their system is designed, constructed, and manufactured, including engineering processes, software development and control, configuration management, and quality assurance procedures used, along with how and where they intend to fly.

    a. SAC in the experimental category – may be used for civil aircraft to perform research and development, crew training, and market surveys; however, carrying persons or property for compensation or hire is prohibited. FAA Order 8130.34 is used by FAA inspectors to issue experimental airworthiness certificates and special flight permits to UAS. For more information, please contact the Airworthiness Certification Service, AIR-113, at 202-267-1575.

    If the FAA determines the project does not present an unreasonable safety risk, the local FAA Manufacturing Inspection District Office will issue a Special Airworthiness Certificate in the Experimental Category with operating limitations applicable to the particular UAS.

    b. A UAS type and airworthiness certificate in the Restricted Category (14 CFR § 21.25(a)(2) and § 21.185) for a special purpose or a type certificate for production of the UAS under 14 CFR § 21.25(a)(1) or § 21.17. For more information, please contact the Los Angeles Aircraft Certification Office at 562-627-5200.

(Bold emphasis is mine, italics emphasis is from the FAA.)

For UASs with a Special Airworthiness Certificate, FAA Order 8130.34C specifies in Chapter 3, Section 1.3 (Flight Test and Operating Area) that:

  All proposed flight test and operating areas outside of restricted airspace must be approved by the FAA. Flight test and operating areas will be coordinated with the air traffic component of AFS-80.

and that:

  The flight test area and operating area must be over open water, or sparsely populated areas, having light air traffic. The FAA is required to evaluate each application to determine that the proposed flight area does not exceed that which is reasonably required to accomplish the program.

Certainly, Class B doesn't qualify as "sparsely populated areas, having light air traffic," so this, too, seems to be a no-go.


The F16's maneuver envelope is better under 15000 feets but usually they will go much higher altitudes. Why? The F-16's maneuver envelope is better under 15K feet, but they  go much higher. Why do they put in that compromise position?

For most aircraft, the advantage of flying high is that the air is thinner, so you go faster for the same fuel burn.

For fighters, height gives you the ability to dive to gain speed, giving them the option for intercept a lower plane, or run away faster than a lower plane can follow. If they're relying on their own radar, it also allows them to see further around the curve of the earth. As Ron mentions, it also puts you out of range of some SAMs, and gives you more time to react to others.

Lastly, while the F-16's manoeuvre envelope may be better at lower altitude, what matters is the manoeuvre envelope of the aircraft they might have to fight, and the altitude they choose to fight at. The relative difference between the two types is more important than any absolute value.


What is the term for an aileron that’s also used as a ground spoiler? Ailerons and spoilers1 have a considerable amount in common; both are wing-mounted panels, hinged at their leading edges, that move up and/or down to alter the aircraft’s aerodynamic characteristics.

Ailerons are mounted on the wing’s trailing edge, are useful only during flight, and move up on one side and down on the other to increase the lift of one wing, decrease it on the other, and roll the aircraft to one side.
Spoilerons (also known as “roll spoilers”) are mounted on the wing’s upper surface, are useful only during flight, and move up on one side to decrease the lift and increase the drag of that wing, rolling and yawing the aircraft towards that side.  They are more useful than ailerons at low speed, as (unlike ailerons) they do not increase the angle of attack of any part of either wing, create proverse rather than adverse yaw, and, thus, are immune to the crossover-airspeed phenomenon inherent to ailerons.2
Lift/drag spoilers move up symmetrically to decrease the lift and increase the drag of both wings simultaneously, either in flight (when they are called “flight spoilers”; this enables the aircraft to descend more quickly, or to use a higher power setting on approach,3 without excessively increasing its speed) or on the ground (in which case they are known as “ground spoilers”; this enables the aircraft to slow down more quickly during a landing or rejected takeoff, both by increasing the aircraft’s drag and by dropping its weight onto the wheelbrake-equipped main landing gear); they can be (and almost always are) combined with spoilerons, to provide a single spoiler system with both spoileron and flight/ground spoiler functions.

As ailerons are useful only during flight (since an aircraft generally can’t  roll left or right on the ground,4 due to said ground being in the way), the aileron panels on most aircraft don’t do much of anything useful on the ground.  It isn’t too hard to visualise a system in which the ailerons, when on the ground, deflect upwards to decrease lift and increase drag, acting as additional ground spoilers, but I’ve no idea what these combined ailerons/ground spoilers would be called; “spoileron”, as noted above, is already taken by a different type of system (one using asymmetrical spoiler deflection in flight to roll and yaw the aircraft).

What would be the term used for a control surface that functions as an aileron in flight, and as a ground spoiler on the ground?

1: (and flaps)

2: Additional advantages of spoilerons over ailerons are that, being located on the wing’s upper surface rather than at the trailing edge, they do not interfere with flap placement, and are much less prone to causing the wings to twist when deflected; as a result, some aircraft use only spoilerons (and no ailerons), either to allow flaps to be placed along the full span of the wings (thus reducing takeoff and landing distances and speeds) or to allow the use of thin, flexible wings at high speeds without encountering wing-twist-induced control reversal.  Disadvantages of spoilerons are their lower maximum control authority at intermediate speeds and their greater total drag penalty.

3: A higher approach power setting makes go-arounds safer by reducing the time needed for the engines to spool up to full power; this is especially important for jets, as jet engines are slow to accelerate, and accelerate ever more slowly from lower and lower initial power settings.

4: Barring a collapse of one or more of the main landing gear, which is not generally a planned, or desired, occurrence.

The action of a ground spoiler is essentially that of a lift dumper, which also acts as an airbrake.

As far as I am aware there is no special term for an aileron which also performs this function. Several Airbus types use the technique but their literature just calls them ailerons. On the A380 at least the spoiler action is initiated by the Speed Brake lever.

Of course, "spoilerons" are not quite the same, as these are spoilers used differentially for roll control during flight.

It is not too uncommon for a device named for one function to do double duty in another. For example "landing flaps" are often also (partially) deployed for takeoff - as of course is "landing gear" - and on some older types the servo tabs also double as trim tabs.


What is this turn called and how is it performed? I've found pictures and videos of jets rotating 90 degrees so that one wing points straight down to the ground and the other is straight up, then they suddenly turn away from their course while remaining in that position.

Here's a video of that maneuver (link goes to 2:10).

What are the aerodynamics that can make this kind of turn possible? In a lot of YouTube videos this type of turn happens after aerial refueling. Is this type of turn possible on a large airliner, and if it is, when do pilots of this airliner ever use this method in flight?

The maneuver is called a "breakaway maneuver" or simply a "break", it's also sometimes colloquially referred to as "peeling off" in the context of aircraft leaving formation. You can see it more clearly in this video:

This is a standard maneuver used when disengaging from a intercepted target, or as a way to safely exit formation flight ensuring that the departing aircraft is clear of the rest of the formation group.
It also has tactical advantages as seen in the photo you posted (when being tracked by an infra-red/heat-seaking missile, dropping flares and a hard breakaway is one technique used to convince the missile that the flare is actually your engine, by getting your real heat source out of its "line of sight" quickly).

Aerodynamically the breakaway maneuver is nothing more than a steep turn: Roll the aircraft into the desired bank, setting power and pitch up to maintain your altitude and airspeed in the turn as desired.
A Cessna 152 flying in formation could break away using the same maneuver, though the bank angle and airframe loading (G forces) would need to be maintained within the aircraft's limitations.

The primary difference with fighters and attack aircraft is that the bank angle is dramatically steeper (in the extreme, a 90-degree "knife-edge" bank) and the turn much tighter because these aircraft have the excess power (thrust) required to sustain flight in that configuration and are sturdy enough to withstand the G loading induced by a "hard pull" in the breakaway maneuver. The abrupt wings-up turn along with the nice roar you get advancing the throttles makes the maneuver an impressive one for airshow crowds to watch.


How much does go-around cost? What is the extra cost of aborted landing and go-around for typical "big" airliner?

We can look at financial data from airlines to estimate these figures.

In addition to fuel, there will also the extra duty time for the crew, some delay in schedule, and extra flight time on the aircraft. The delay in schedule can be difficult to estimate, but other costs of operation can be estimated. A short flight would take 1.5 hours, and the go around might take 0.2 hours.

Based on the financial data, an MD-83 might cost about 6000 dollars/hour to operate. This includes all direct operating expenses. This means that the regular flight would cost about 9000 dollars to operate, and a go around would cost about 1200 dollars. Since a go around uses a lot of fuel, the figure may be a bit higher.

The figures for a Boeing 747-400 show about 15000 dollars/hour to operate, and a Boeing 777-200 about 12000 dollars/hour to operate. That would make an 8 hour flight 120,000 dollars and 96,000 dollars respectively, with go arounds costing 3000 and 2400 dollars respectively. Obviously, for longer flights, the go around will cost less proportionally than for a shorter flight.

As DeltaLima mentioned, the cost of not doing a go around (which includes making this decision early enough) can be substantially higher. Loss of or even just damage to an aircraft will cost much more time and money.

To see if these numbers make sense, this report mentions that an empty MD-83 would need 1000 kg of fuel for a go around and new approach. It also mentions that a ferry flight from Paris Orly to Olbia, Italy, would normally require 6800 kg including reserves. If reserves are about 1600 kg, this would mean that the flight would use 5200 kg of fuel.

If jet fuel costs 3 dollars per gallon, this comes out to 985.72 dollars of fuel for a go around, and 5125.73 dollars of fuel for a regular flight. This figure seems reasonable along with the figures above.


Why does indicated stall speed change? Aviation confusing me... I’ve read that stall speed doesn’t change (IAS) no matter what altitude you’re flying - of course under specific conditions ISA, 1G level flight, no wind, gross weight etc. then why I keep witnessing for example in the Boeing 737-800 PFD (primary flight display, intend to the barber pole) that at low altitude let’s say your stalling speed is around 140CAS when at cruise level stalling speed is way above - approximately 220CAS (random number) Why is that ? Doesn’t stalling speed must to be the same at all altitudes?

Thank you all for your answers!

It happens because of a compressibility error in the airspeed indicator (yes, even in the digital ones, since the error is not mechanical, but a physical property of the air).

As you might be aware, the speed indicated on your instruments is not really a speed at all, it is actually a pressure. Your pitot measures a deltaP between static and pitot and displays that pressure difference on a scale noted in knots.. we call that Indicated Airspeed.

This indication, because of changes of density, can be quite a bit different from your actual True Airspeed, but people didn’t care all that much about this difference, since the way the wing flies is reliant on that deltaP pressure difference anyway, so that you will actually stall at the same Indicated Airspeed, but not at same True Airspeed. (there is less density higher up but you are now traveling a bit faster, so the effect cancels out and the wing will behave the same)

The instrument was kept as it is in the cockpit (even though today we call it Calibrated Airspeed after a few changes) as a very usefull indication to the pilots.

Ok, now back to the question: turns out when planes begun flying faster and faster, a second error, caused by compressibility appears, that makes the airspeed indicator over-read. The pitot pressure is reported higher than it should be because at high speeds the air compresses in the pitot and makes the pressure there artificially higher, the deltaP is higher, thus our Indicated Airspeed is higher. Of course, this pitot tube phenomenon is not happening on the wing, so now we have a problem: we have a high speed indicated at the instrument, but most of it is actually just compressed air. Our Equivalent Airspeed is in fact much lower. And the wing will in fact always stall at the same Equivalent Airspeed. That means your Indicated Stall Speed in the cockpit will be ever higher as you climb because of compressibility.

Now, instruments were still kept to display IAS instead of the EAS, and a provision has been made where the stall barber pole advances up as you climb to make up for compressibility error

Then why haven’t the instruments been changed to show EAS directly? That is a harder question to answer definitively. I suppose by now people were already too used to having IAS in the cockpit, and the error is only really a factor for jet planes flying above (say) + 20 000 feet at speeds above Mach 0.5.


What kind of liquid can be seen 'leaking' from the bottom of a Boeing 737-800 engine? I was on holiday over the Christmas holidays, and was sat in the airport awaiting our plane back to England, looking out of the large window which over looked aircraft that have just landed and the passengers get of, when a Boeing 737-800 turned up, looking at its left engine (I could not see the right engine from my viewpoint), I saw a clear liquid leaking from the bottom of it, what was this liquid, and were might it of come from?

source: wikipedia

I have circled were I think the liquid came from on the left engine in the picture above.

There is really no telling without being there & getting a sample of the fluid.  A mechanic can tell the differnce between hydraulic fluid vs engine oil vs fuel vs etc, but the place where any of them would come out is essentially the same spot under the engine.

In general, any of the above is uncommon but far from unheard of, and in small amounts is no big deal.  The fittings aren't supposed to be leaking, so a mechanic will probably end up fixing whatever it was, but the hazard from a few drops just isn't all that great.  Sure, the idea of "oh, just a fuel leak, no big deal" intuitively sounds pretty bad, but the fact of the CFM engine is that the motor is incredibly tolorant of this sort of thing with nothing bad actually happening.  It needs to be checked out because something isn't exactly right, but there would have to be several other things go wrong as well (each of which is pretty rare) before anything bad actually happens.

Some lines are allowed no leakage at all, while others actually do have a "drops per minute" limit for what is allowed without needing maintenance action.  Not being a 737 mechanic, I couldn't tell you offhand which fluids are in which category.  If I see it leaking, I call the mechanic & he can sort it out.

Of course, in the days of the big radial engines, the saying was that when it's leaking, that means there's still fluid in it, and when it stops dripping, THAT is what's bad, because that means you don't have any more oil!

We're a long, long ways from those old days!


What does "FG BNK" mean in a metar? Here's the KLAX METAR 2153Z observation:

  KLAX 102153Z 27010KT 10SM FEW002 BKN200 24/16 A2997 RMK AO2 SLP147 FG
  BNK S-NW T02390156 $

It means fog bank from S to NW of the station, although it's not codified.
The remarks section (after RMK) does not always use official codes. In this case, BNK neither appears in the FAA's 7900.5, nor WMO publications.
To quote the 7900.5:

14.18. Remarks (RMK)
(...)
Where plain language is called for, authorized contractions, abbreviations, and symbols should be used to conserve time and space. However, in no case should an essential remark, of which the observer is aware, be omitted for the lack of readily available contractions. In such cases, the only requirement is that the remark be clear. For a detailed list of authorized contractions, see FAA Order 7340.1, Contractions.

By checking 7340.1, BNK doesn't appear on its own or with FG, only in GRBNKS and SNBNK. Since no contraction in 7340.1 was available, the manual entry was made in as clear manner as possible.
For completeness, if the fog bank had affected the station, the proper code that would have been used before RMK would have been BCFG (fog patches). BC is likely derived from the French banc de brouillard (fog bank).


Is it reasonable for flight economy to correct banking tendencies with stick and rudder? An aircraft with side-by-side seating but only one person aboard should fly banked.  Banking decreases lift and more elevator is needed than in leveled flight which increases drag. Correcting the banking with ailerons and rudder also increase drag. Which is better for economy?

You might be better off correcting weight imbalance with more fuel in the opposite wing if possible.  Then fly with fuel selector on both as long as you can.  This should give you better economy than trimming aerodynamicly.

Notice this also true for weight too far forward or aft.  Good balance helps in the air.


What classes of aircraft require hydraulic flight controls? All commercial airliners such as the Boeing 737 or Airbus A320 or heavier aircraft require an hydraulic system that can power actuators, which generate the required forces to move the control surfaces in all phases of flight. Smaller General Aviation aircraft do not need this.
But what about aircraft in between? Is there a minimum MTOW above which aircraft are required to or generally have an hydraulic system? Can you make examples of lighter aircraft which have it?
For example I was wondering about the an aircraft like the 19-passenger commuter Beechcraft 1900:

Hydraulic flight controls are not mandatory for a specific class, but above some size and speed it will be hard to fulfil all certification requirements without at least adding some hydraulic boost.
Historically, aircraft used manual controls. With increasing size and speed, the forces went up and increasingly clever force reduction systems were invented to keep stick forces within limits.

On the first flight of the Messerschmitt Me-321 glider it was found that control forces especially in roll were way too high, so a second pilot with a second stick was installed.
The Dornier Do-335 or the Republic P-47 used a telescopic stick: At low speed the stick was short and could move through the full range of aileron deflections while at high speed it could be telescopically extended. This limited the motion range but improved the leverage of the pilot.
The English Electric Canberra used internal balances for the ailerons and a spring in the aileron controls to limit the stick forces. At top speed the control horn could still move through its full range but the achievable aileron deflections were only a few degrees - still enough for sufficient roll agility, however.

Ailerons have mass. There is a spring. Something that moves. Every engineer should think next: What about flutter? With more complex force reductions, the chance grew that something unexpected happens and failure modes multiplied. In the end, introducing hydraulics solved so many problems that de facto above a certain speed and size combination no other option makes sense.
I have worked together with Rockwell (formerly North American) on a two seat jet trainer; a size and speed combination that would have had manual controls 60 years ago. I proposed to use the same force reduction mechanisms that were used on the F-86, but in the end a hydraulic boost was selected. Why?

Nobody had any experience with manual controls anymore. After so many years, all F-86-era engineers were long retired or had passed away.
The North American archives had been thrown away years before, so no documentation was left on how to properly design a manual control system for that speed range.
The hydraulic boost system was easy to install, used standard components and was cheaper to design because everybody was familiar with the technology.

As I said before: Don't get me started on how exactly you can tailor roll stick forces - this will be a post that will be much longer than anything I have written here before.