What were the typical dimensions of a WW2 US bomber formation? The idea behind daylight raids was that bombers were more accurate when they could actually see targets so the damage inflicted would be concentrated more so that a night time carpet bombing.*

All of the footage I see, including CGI in movies, depicts large formations of US bombers giving the impression that the "precision" raids were anything but precision.

What was the "footprint" of an average American daylight raid?  If you had to draw a 2D box on a map, what values would you assign to length and width?

*Not saying that it was done to protect civilians, clearly the objective was to destroy strategic targets.

The size of the bomber formations (bombers streams) varied significantly depending on the number of bombers , the time , location and other things. The most common figure quoted figure is around 70 miles long and  5-6 miles wide (for ~500-600 bombers). However, the formation's footprint depended on a number of factors ranging from the navigator's skill to the wind in that area.

The figures vary wildly. For example, from the book Mission to Berlin: The American Airmen Who Struck the Heart of Hitler's Reich:

  The stream of more than one thousand Eighth Air Force bombers, from one end to another was 360 miles long. ... on ... February 3, 1945, when the first flying fortresses reached Berlin, the last bomber was over the Zuiderzee in Holland.

This extreme length is a consequence of the situation late in the war, where allied air armada roamed European skies without bothering much about the Luftwaffe. The time spent over the target, on the other hand was quite small-

  ... each Fortress crew would spend only between thirty and sixty seconds over the center of Berlin itself...

Note that there was no such thing as precision bombing in WWII (except for some special cases), though the accuracy did improve over the war. Of course, some of this was due to the way the 'target' was designated- anywhere 1000' of the aiming point was good enough. From The United States Strategic Bombing Survey:

  Conventionally the air forces designated as "the target area" a circle having a radius of 1000 feet around the aiming point of attack. While accuracy improved during the war, Survey studies show that, in the over-all, only about 20% of the bombs aimed at precision targets fell within this target area. A peak accuracy of 70% was reached for the month of February 1945.

Accuracy of RAF night bombing improved from ~20% in 1942 to > 90% in 1945. Of course, the British target was comparatively larger- anything within a 3 miles radius of the aiming point was a 'hit'.


Does aircraft allways rotate about center of gravity like weather vane about pivot point? When gust of wind hit plane form side,does plane allways rotate about center of gravity like weather vane about pivot point or  CG as pivot point  is just "math areegment" for easier solve equation?
If one force(wind gust) act at body which is not at CG,body will translate and rotate,but center of rotation will not be at CG.
Because only rigid object in space far from other influences will rotate about its center of mass.
If does ,why plane allways rotate about CG?
(boats dont do that, but only differnce in air and water is  fluid density?)

It's purely a mathematical trick, but a very good one at that. In reality, pure rotations around the center of gravity are rare.
The key is that it's often convenient to split movement of a body into translations and rotations. So we need some definition to distinguish between a rotation and a translation. For example, consider lifting a pencil from a table on one end. Intuitively, there's definitely some rotation as the pencil is now at an angle, but is there also a translation? The end of the pencil resting on the table has not translated at all, while the end you picked up has translated a lot. So we can describe the same situation by pure rotation around the point resting on the table, or a combination of a translation of the point you're holding and a rotation around that point, or anything in between.
By defining rotations and translations with respect to the center of gravity, you simplify a lot of equations, and you can analyse the system with a free body diagram. If all forces in one direction sum to exactly zero, you will have no translational acceleration, and only rotational acceleration. In reality of course, forces rarely sum to exactly zero, so there's always some translational acceleration of the center of gravity.


What is the purpose of the Boeing SCAP module? The Boeing SCAP module will be used to calculate the takeoff and landing performance data. But what exactly does the Boeing SCAP module contain and how is it used to calculate takeoff and landing performance for the aircraft?

The Standardized Computerized Airplane Performance (SCAP) interface is a standardised model for calculating aircraft performance of air transport category aircraft. The SCAP standard is developed and maintained by IATA and leading aircraft manufacturers.

From the IATA website:

  One particularly complex requirement is the calculation of takeoff performance data. Most airlines use programs supplied by the airplane manufacturers for each airplane type, and interface these programs with their own computer operating environment, airfield database, and data output format requirements.

  In order to reduce the development effort for the airlines
  (interfacing with different airplane manufacturers' programs) and
  manufacturers (meeting individual airline requirements for
  customer-specific features) there are clear advantages in
  standardizing as much as possible the input/output features of these
  programs, and also data formats.

  Having recognised this potential benefit, IATA, ATA and several
  manufacturers set up a Standardized Computerized Airplane Performance
  Task Force (SCAP TF).

A  SCAP module is a FORTRAN program that implements the SCAP standard. It takes a set of well defined inputs to produce a well defined output.

The advantage of this approach is that it is possible for a third party to design a software program that requires aircraft performance data without having access to this proprietary data. The software can then be used for aircraft performance calculations of any aircraft as long as it has access its SCAP modules.

There are 6 SCAP specifications for Takeoff, Landing, Climbout, Inflight, Noise and APM (Aircraft Performance Monitoring).

I don't have access to the official SCAP specification, but from what I can find online I gather that for take-off performance the following is required:

TODA (Take-Off Distance Available)
TORA (Take-Off Run Available)
ASDA (Accelerate Stop Distance Available)
runway elevation
runway surface condition
runway heading
wind speed and direction
ambient Temperature
QNH
MEL/CDL items affecting performance
max take-off thrust and reduced (FLX) option
anti-icing options
flap settings
V1/VR (fixed or opt)
V2/VS (fixed or opt)
minimum acceleration altitude
actual take-off weight

I gather the landing SCAP module needs:

LDA (Landing Distance Available)
runway surface condition
runway elevation
runway heading
wind speed and direction
ambient temperature
MEL/CDL items affecting performance
approach type (CAT I/II/III)
anti-icing options
presence of residual ice
flap setting (fixed or opt)
expected landing weight


Could clouds on aircraft wings produce lightning? As air is accelerated over the wing, pressure drops and so does temperature, which is reduced to dew point and finally a cloud forms, which can be seen on humid days. My question is, can this cloud formed over the wing of an airplane produce lightning activity just like some other kinds of "normal clouds"?

Lightning occurs when an electrical charge is built up within a cloud, due to static electricity generated by supercooled water droplets colliding with ice crystals near the freezing level. When a large enough charge is built up, a large discharge will occur and can be seen as lightning (from Wikipedia).

So you need two things for lightning to occur- a charge buildup in a place and a charge gradient (difference in charge, like between two clouds or cloud to surface) for lightning to occur.

Based on this, there is little chance of any charge buildup and discharge in the condensation over wings- it is too short lived for any charge buildup within itself and the charges over the aircraft wings are  dissipated by the static wicks in the trailing edges- so no chance of 'cloud' to wing surface either.


How much weight does a blisk save? A Blisk is a bladed-disk, all one monocoque component.

So the blades do not have to be inserted and secured, and they are not removable. No nuts and bolts either.
The downside is that any serious damage to one blade, and the whole blisk must be replaced. The upside, I have heard, is that they save weight. Wikipedia says "efficiency improvements of up to 8% are possible." but I'm not interested in aerodynamic efficiency right now. I'm interested in weight savings.
So the question is, how much weight can you save? Is it really significant? Interested in compressor and turbine blisks and I would not be surprised if the answer varies between them.

Very significant.
A research on blisk cost estimation with funding and data provided by Rolls-Royce states:

Integrally bladed discs, commonly known as blisks, are currently found in axial-flow compressors of gas turbine engines. Fig. 1 shows that blisks require significantly less material because the dead weight from the blade roots, disc lugs, and the disc structure required to support these features, is no longer required. This leads to a weight saving of up to 30% (Rolls-Royce, 2005), permitting higher blade speeds and consequently higher pressure ratios per stage (Steffens, 2001). A blisk compressor therefore requires one third fewer rotor stages to achieve the same total pressure ratio as a conventional design (Steffens, 2001). [emphasis added]

Fig. 1. Blisk weight saving.

Langmaak, Stephan, et al. "An activity-based-parametric hybrid cost model to estimate the unit cost of a novel gas turbine component." International Journal of Production Economics 142.1 (2013): 74-88. (PDF)


Do/why don't spaceplanes suffer from flutter? Spaceplanes tend to have beefier, stiffer parts than normal aircraft, at least partly due to drag-reduction being less of a concern. But they also experience far higher airspeeds during reentry.
Yet I've never heard much, if anything, about flutter, or any other form of aeroelasticity being a problem on any of them. Maybe that's because I don't know much about existing or past spaceplane programs? But still, I'd be interested to know.
I can imagine some candidates for the reason why flutter might be less severe:

the frequencies are so high and modes so many and so uncoordinated that too much energy is dissipated as heat and sound, leading to simply vibration with no damage.
the sheer stiffness of the vehicle moves flutter frequency out of reach. (Which sounds rather far-fetched for me)

Hoping to find an answer, I Googled about aeroelasticity of the Shuttle, and got this document. It's rather long, so ATM I haven't drawn any conclusions from it.
It would be nice if someone has any background info on what the designers of the Shuttle (which I would guess is the best known spaceplane) faced during development in relation to flutter.

Not Shuttle specific, but there are generally two ways to prevent flutter of a control surface; for a manually operated surface, you balance it to put the surface's CG at or slightly forward of its hinge line, so that motions of the parent surface have a neutral (if CG on the hinge line) or counteracting (if CG is forward of the hinge line) influence on exciting sympathetic motion in the surface (that is, if the wing flexes up, with the CG aft the surface it "trails" the motion and displaces down relative to the wing attachment, putting it on the hinge line neutralizes this effect, and putting it forward of the hinge line has the opposite effect, creating an inertial moment in the same direction as the wing motion).
If the surface is hydraulically powered using irreversible hydraulic actuators, balancing of the surface generally isn't required and flutter protection is from the rigidity of the hydraulic connection (both in holding the surface from moving, and also acting as a passive damper when unpressurized). You can usually tell an airplane with irreversible hydraulics because there are no tabs or balance horns, or offset hinge lines, and the center of gravity of the surface will be some distance aft of the hinge axis.
So jets with irreversible hydraulic controls typically have unbalanced control surfaces that depend on the hydraulic actuators themselves for flutter prevention, and may also require additional passive damper units if the number of actuators used doesn't meet the minimum damping requirements following loss of an actuator. Service backlash limits for surface hinge attachments and actuator connections (resulting in surface free play) are largely a function of maintaining the rigidity of the system for flutter resistance.
The Shuttle having hydraulically driven control surfaces, you can be sure that flutter resistance is ultimately coming from the hydraulic actuators and the stiffness of the connections and structure (I don't know if the shuttle uses dedicated flutter dampers to back up the actuators).


What is a 'deep stall' and how can pilots recover from it? West Caribbean Airways Flight 708 which crashed in 2005, fell victim when their plane encountered a deep-stall. From my understanding, only certain planes can 'deep-stall'

How can pilots recover their plane to recover from a deep stall?

A deep stall or a super stall is a condition where the wake of the wing impinges on the tail surface and renders it almost ineffective. The wing is fully stalled, so the airflow on its upper surface separates right after the leading edge, which produces a wide wake of decelerated, turbulent air. Consequently, the dynamic pressure at the tail surface is much smaller than in unstalled flight, which is the main reason for the reduced effectiveness.

Consider this case: The aircraft flies in a nose-up attitude, but on a downward flight path. Consequently, the angle of attack of the wing $\alpha$ is much beyond its normal operating range, causing a fully separated upper surface flow. Due to the T-tail configuration, the wake is hitting the elevator such that all of it is shielded from the regular airflow.

The pitching moment of this configuration over angle of attack (blue line) looks something like this. First there is a stable region with a negative gradient at low values of $\alpha$, followed by a minimum when the wing stalls, and then a region with a positive gradient, where the separation unfolds and the tail moves into the wake from above. This region is unstable in pitch, so without control input the aircraft will not stay there, but either pitch down or up until it reaches a stable region again. At high angles of attack follows another stable region with a negative gradient:

Note that we have two trim points, one in the regular range of the angle of attack, and one way out to the right. In both cases the aircraft has a stable trim condition, so small disturbances are answered with force changes which will keep the aircraft at one of these points. Between the two, there is another equilibrium point, but here the airplane is unstable. If it pitches up slightly there, the pitch up will accelerate until it reaches the upper trim point.

Now consider the control power of the horizontal tail. When it flies in undisturbed air, it can trim a wide range of angles of attack. In the deep stall condition, however, its control power is much reduced, resulting in a much smaller range of trimmable angles of attack. If the lower end of this range is right of the point where the pitching moment crosses into positive values (here at $\alpha$ = 24°), the aircraft cannot escape with elevator deflections!

Please note that the control power is not sufficient to enter the deep stall with quasi-stationary trim changes. The pilot needs to pitch up quickly and has to overshoot the static trim range in order to cross into the stable region above 30° angle of attack. There, his range of trimmable $\alpha$s is too small to achieve the same overshoot backwards.

To get out of this trap needs other changes: Either shift the center of gravity forward, or try to drop one wing. Unfortunately, both the ailerons and the rudder will also be much less effective due to the massive separation and the wake. In a number of cases, even experienced test pilots could not escape this condition.


Why do airliners on autopilot climb during cruise? Several years ago I was a passenger on a near cross-country flight when the pilot came on the PA and announced that we were climbing towards our cruise altitude, on autopilot, and as our fuel load was burning off, and the plane's weight lessened, we would be climbing about another five thousand feet from our cruise altitude.

I wondered why the autopilot, instead, would not make micro-adjustments to the angle of attack to maintain the same altitude, rather than waste fuel making an unnecessary climb.

I realize that maintaining the same exact altitude is probably not realistic, but autopilot, I would think, ought to be able to maintain cruise altitude within about one thousand feet.

This was on a Southwest flight, so it had to be a Boeing 737.

Climbing further while cruising is saving fuel, not wasting it.

First, every airplane has an optimum angle of attack for most economical cruise. If it loses mass (due to fuel consumed), it needs to adjust either its altitude or its speed to keep that angle of attack. The goal is to keep dynamic pressure, the product of air density and the square of airspeed, constant. Since you want to reach your destination in the shortest time, climbing into less dense air is the better option.

Secondly, gas turbines need less fuel per unit of thrust when flying in colder air. As long as the plane stays in the troposphere, it will fly more economically when it flies in colder air.


Are there all terrain landing gears for planes? Is there a landing gear set up that will allow a single engine plane (also, allowing for tundra tires than what is not available for current water skids) to land on rough grass and water?
The wheels in the picture folds back to not case drag in the water; maybe the water-skid for a plane could work in this way for tundra tires?
Like this pictures landing skid but with tundra tires instead of those little ones.

The closest anyone has come to something that could be called a feasible all-terrain gear is the Air Cushion Landing System developed by Bell Aerospace and tested initially on a Lake Buccaneer, which lead to a test of a system Bell developed for the DeHavilland Canada DHC-5 Buffalo under a joint program between DH, the Canadian Govt, and the USAF.

The cushion was inflated by a pair of P&W PT-6 turboshaft powered inflation sytems (a kind of ducted fan setup), which are in the sponsons on each side of the fuselage.  The testing was completed in 1977.  I dimly remember that the biggest problem with the system was wearing out of the bottom surface of the cushion (it wasn't open like a hovercraft skirt, but more like an air mattress with an array of holes in the bottom, and the bottom surface would brush the ground and wear out really fast).  That and the obvious performance penalty issues (you're giving up a lot of payload to haul all that gear around) kind of killed it.
It could take off and land on any flat surface, and being a Buff, only needed a few hundred feet of space (the DHC-5 Buffalo could land and take off from a soccer field, and the normal version once did so in a civil defense demo in New York City, causing numerous calls by apartment dwellers to report the "crash" in a park).
I worked on this airplane as a mechanic when it returned from the test program to DH in 1979, removing the tip floats and the cushion system and patching the fuselage up before it was returned to its RCAF operating squadron.


Do some flying techniques wear aircraft out quicker than others? In the 2012 film Flight, the cause of the mechanical failure is a sort of worm-screw that controls the rear tailplane. And I believe that in real life failures in those devices have been implicated in one or more crashes, with people shocked that there were no fail-safe mechanisms.

Do airline pilots feel or have a responsibility not to subject a machine to extreme mechanical stresses? Or is the assumption that nothing they can really do has not been foreseen by the designers?

Do some individual flying techniques, used by pilots, wear aircraft out quicker than others?

Full context:

This 2012 film, with Denzel Washington, aired last night on UK TV.

I think I have seen bits of it before... this time around for various reasons I also missed a small part of it.

If you haven't seen the film this question might not be of interest.  If you have, and you're interested in flying, you probably remember it: it involves a "hero pilot" implausibly "inverting" a commercial airliner which is plummetting downwards, and eventually doing a crash landing where most people walk out alive.

One of the main "themes" of the film is that the pilot, played by Denzel Washington, is a "maverick": he is an alcoholic and cocaine-snorter, etc. He is drunk when he gets on the plane, and drinks more during the flight.

The thing that I'd like to ask about is this: the cause of the mechanical failure is a sort of worm-screw which controls the rear tail plane... and I believe that in real life failures in these devices have been implicated in one or more crashes, with people shocked that there was no failsafe mechanism, etc.

But another aspect of the film is the very "dramatic" take-off: the plane takes off in a very bad storm, and "Denzel" takes the plane through some very macho manoeuvres in order to get out of the "bad air" and find some "good air".  The passengers are terrified and the plane is rolling all over the place, while the co-pilot is saying that the plane is flying too fast.

The "investigation" sequence of the film, which is the bulk of it, never seems to pose the question about the advisability of "macho" flying techniques and the possibly culpability of a pilot when taking a plane to its mechanical "limits".  The clear position of the film is that the aircraft was simply "bad" (and recommended maintenance procedures hadn't been followed, etc. etc.).

Do pilots flying commercial airliners feel or have a responsibility not to subject a machine to extreme mechanical stresses, as far as is humanly possible, or is the assumption that nothing they can really do has not been foreseen by the designers?  Do some individual flying techniques, used by commercial pilots of passenger aircraft, wear aircraft out quicker than others?

Let’s start out by agreeing that “Flight” got lots and LOTS of details very very wrong in more ways than 1 thread can list.  Any pilot who did a tiny fraction of what the “hero” does in that movie would be reported, and drug/alcohol tested, and fired, in very very short order.  Whoever decided to write a script with that sort of thing going on as its premise, has his head planted very firmly in an alternate reality to the one that the rest of us live, and fly, in.

That out of the way, let’s talk about the specific questions asked, starting with the “dramatic takeoff.”  In the military, there can be missions where “you do have to go out, you don’t have to come back” — i.e. your chances of survival may not be very good, but this is war & you’re going to launch. In the airline world, the reverse is the case: takeoffs are optional, landings are mandatory.  If you don’t see the path for the whole flight being completed safely, you don’t take off. Period, dot, end of story.  There is no airline flight out there these days that is “the last flight out of Saigon” (where you’re going to attempt the takeoff because the alternative is just too awful).  If the weather around your departure airport is dangerous, then you wait until it isn’t.  If you think you’re going to need “macho maneuvers” to get out of town, you have no business taking off.

There will be times when what looked like a decent ride turns out not to be, or you knew that the ride would be somewhat bumpy & things turn out to be worse.  That’s the limitation of how much information you have about the atmosphere.  And yes, you will be working to find a better ride.  However…

There is nothing particularly exciting about finding a better ride — it’s simply the same sort of climb or descent that’s used getting to and from cruise altitude. And changing course to find a better ride will be the same 20-30 degree bank turn that everything else is maneuvering the airplane. Nothing dramatic, nothing macho, nothing wild.
Also, if the unexpectedly bad ride scares the passengers, well, that’s the way things can go, but if what the PILOT is doing is scaring the passengers, then HE IS SCREWING UP!  There is essentially no scenario you can come up with where doing something that scares the passengers is the right answer.  If you got to the point where something “scary” is required to avert disaster, then either you’ve had the one-in-a-million combination of bad things happening to you, or else you screwed up by letting yourself get to that point.  (Okay, rolling inverted in the movie to control the uncontrollable pitch is in that sort of category. Could that have actually worked for the Alaska flight? No idea. But that’s how creative you have to get to come up with any sort of scenario which such crazy behavior makes sense.)

If the copilot is telling the captain that he’s flying too fast, then one of two things is going on: either the copilot doesn’t understand what is & isn’t “too fast” (which can happen), or else the captain is, in fact, flying too fast.  And any captain that makes very many copilots uncomfortable like that is going to be having a talk with his Chief Pilot before very long.

  “Do pilots flying commercial airliners feel or have a responsibility
  not to subject a machine to extreme mechanical stresses…?”

Yes, absolutely. And the Flight Data Recorder will record what happens. If you do something that grounds an airplane for an inspection and/or repairs, you’ll probably be explaining yourself to somebody before too long.  More than that, you have a responsibility to your passengers to give them a safe flight, as comfortable as possible, with as little drama as possible.  And sometimes that means that things won’t happen on schedule, because we’re going to wait out whatever adverse weather condition is out there.

  “ … or is the assumption that nothing they can really do has not been
  foreseen by the designers?”

Airliners today are pretty tough, but a sufficiently negligent pilot can mishandle them to the point of catastrophic failure. (Fly-by-wire gives some protections in this regard, but also allows for failure modes that are easier to catch in non-FWB aircraft — Air France 447 as an example of the latter.)  The designers known that somewhere in the aircraft’s lifespan, the flaps will be oversped, and there is ample safety margin there.  But if you go pulling 9 G’s on a full airliner, the designers can’t help you, and you are absolutely beyond any margins they gave you.

In general, the range of techniques that 99.9% of airline pilots will use won’t greatly affect the service life of an aircraft. It will be limited (typically) by pressurization cycles more than by anything else.  And that’s because the culture IS to keep things safe, and calm, and as smooth and as low-drama as possible.

Did I mention that “Flight” really is about an alternate universe mostly unrelated to our own?


What is the purpose of the small fins on top of the wing surface of Boeing aircraft? I've noticed on most Boeing aircraft that there are small fins on the upper surface of many of their wings. They are about one inch high and maybe two inches long (it's difficult to judge size from inside the passenger cabin without any reference) and spaced about a foot apart.

On the 737 there are eight of them spaced about a third of the way from the wing's root to its tip. On the 757 and 777 they are spaced out to almost the wing's tip, and I can't see them on any pictures of the 747's wing.

Here's a picture of them on the 737's wing:

What purpose does these serve?

The only thing I can think of is that they somehow discourage span-wise airflow, but they seem too small and short to accomplish much. The stall fences I've found in pictures via Google are all much larger and extend around and under the leading edge.

OTOH, a diagram I found here suggests that they are placed at just about the place where the airflow turns span-wise.

They must serve some purpose.

They are called vortex generators, and their function is to create a small vortex which re-energizes the boundary layer. Here is a better picture which also shows that their leading edge is swept like that of a delta wing:

Vortex generators on a T-45 (picture source)

In essence, they are small wings which each create their own delta wing vortex. This vortex mixes fast-moving air from outside the boundary layer with the air close to the wing surface, which has been slowed down by friction. This helps

at low speed to delay flow separation at high angle of attack
at high speed to avoid an oscillation of the shock position when the supersonic pocket of flow over the wing is decelerated in a shock which can cause local flow separation.

The diagram in your question about "Leading edge vortexing" is very misleading. Air does not flow like shown by those arrows.

An airfoil initially accelerates the air which flows over its top surface and decelerates it again over its rear part. On swept wings, this acceleration-deceleration only affects the orthogonal speed component, so the speed component in span direction remains unaffected. This is the reason for the higher Mach capability of swept wings, but also causes the air to flow first inwards and then outwards while transversing the wing's upper surface. The diagram shows no such inward flow, which is wrong.

In addition, friction decelerates the air flowing around a body, such that a layer of decelerated air surrounds each surface of an airplane. The thickness of this boundary layer increases with flow length, and on a swept wing this friction will initially mostly affect the orthogonal flow component. At around mid chord you will find air which has been decelerated mostly in its orthogonal speed component (since this component was so high over the forward part) and now will be subject to more deceleration of the orthogonal component, so that only the spanwise component will be left over the rear part of the boundary layer. Now this boundary layer will only flow off in span direction, such that a massive increase of slow, low-energy air will be collecting towards the tips.

A thick boundary layer will cause early flow separation, so when the angle of attack is increased, the flow at the tips of a backward swept wing will separate first. This will cause lift loss, and since the tips are also the rearward part of the wing, will shift the aerodynamic center forward. This in turn will make the aircraft pitch up, which aggravates the stall condition. If the separation happens asymmetrically, the aircraft will roll in addition to pitching up.

Both vortex generators and wing fences help to reduce this cross flow and delay flow separation on the outer wing at high angle of attack. Vortex generators also help to prevent boundary layer separation past a shock at transsonic speeds when placed close to the leading edge, something a wing fence is incapable of. Therefore, they are more helpful and have displaced wing fences on many swept wings.


How does the efficiency of a fixed wing compare to a rotary wing? Is fixed wing more efficient than rotary wing?

If yes, why is that?

Helicopters use more fuel than airplanes (considering everything else being equal).

When helicopters are traveling slow, they need more energy to hold their weight. When traveling fast (according to their standards), the rotor drag is very high. This is the primary reason they need more power. More Power = More Fuel.

Conventional aircraft have much less drag at a given weight and speed than a helicopter.

Helicopters travel slow. When they burn more fuel per hour and travel slowly, fuel consumption per mile is much worse. They also stay low. Most have turbine engines, turbines burn lots of fuel at low altitudes.

Wikipedia has a good article about energy efficiency in different vehicles.

  Two-seater and four-seater flying at 250 km/h with old generation engines can burn 25 to 40 liters per flight hour, 3 to 5 liters per
  100 passenger km.
  The Sikorsky S-76C++ twin turbine helicopter gets about 1.65 mpg-US (143 L/100 km; 1.98 mpg-imp) at 140 knots (260 km/h; 160 mph) and
  carries 12 for about 19.8 passenger-miles per gallon (11.9 litres per
  100 passenger km).


Could Concorde have used swing wings? Would it have been possible to equip the Concorde with swing-wings to help with lift at lower speeds? The delta wings on the aircraft worked well at high speeds, but it took a long time for it to achieve takeoff speed. A swing-wing would give it the aspect ratio for low speeds and delta form for the high speeds.

Actually, the Boeing design for the SST (Super Sonic Transport), the Boeing 2707 had a swing wing (swing wing was the hot thing during that time). It is instructive to look at what happened to that design.

Image from up-ship.com

The 2707 concept was a larger aircraft, with a 174' wingspan for TO/landing and low speed regime (In comparison, Concorde had a 84' wingspan and carried half the passengers). While the wings were swept back, the wing area increased from 1828 $m^{2}$ to 2743 $m^{2}$.

The engines were carried on the stabilizers. During the development Boeing had significant problems associated with the swing wing mechanism. Concerns about stability and payload capability lead the design to be lengthened and added canard to the front to meet rotation requirements, though the new design 2707-200 kept the swing wings.

Image from up-ship.com

However, these changes did little to solve the problems. When kept near the centerline, the hinge mechanism interfered with the undercarriage. The hinge mechanism was so heavy that it negated the advantages of swing wing, leading to a very poor payload to weight ratio. Studies indicated that the aircraft would run out of fuel halfway across the Atlantic, essentially killing the project.

Due to this, Boeing decided to use a fixed wing platform in its next iteration, the 2707-300, which looked quite similar to Concorde.

"Boeing 2707-300 3-view" by Nubifer - Own work. Licensed under CC BY-SA 3.0 via Commons.


Is there AOG liability? From Wikipedia:

  Aircraft on Ground or AOG is a term in aviation maintenance indicating
  that a problem is serious enough to prevent an aircraft from flying.
  Generally there is a rush to acquire the parts to put the aircraft
  (A/C) back into service, and prevent further delays or cancellations
  of the planned itinerary.

I know AOG is a really serious issue for an airline. What I want to learn is the liability and how far it extends. For example; if AOG happens:

how long can this airplane stay in that airport?
what is the airports role in this situation? Do they help them out or just charge the amount they stay on the ground?

how long can this airplane stay in that airport?

The aircraft is "AOG" so it cannot leave. It needs to stay as long as it takes to complete the necessary repair.

  what is the airports role in this situation? Do they help them out or just charge the amount they stay on the ground?

The airport usually would charge the airline the parking fee. The parking fee is a small cost of not having an aircraft available in revenue service.


Is it possible to 'retrofit' electric flight control actuators to replace existing hydraulic actuators on aircraft? Read a bit about the potential cost savings of replacing existing hydraulic aileron actuators on large commercial aircraft such as the A350/380 with electrohydraulic/electromechanical actuators.

Airbus estimated that it achieved approximately 1,000 pounds of weight reduction on the A380 aircraft when a hydraulic aileron actuator is replaced by electrohydraulic or electromechanical actuator.
Source: http://mil-embedded.com/articles/motor-control-more-electric-aircraft/

Does anyone know if there are any ongoing efforts anywhere into replacing existing actuators with the 'more electric' EHAs/EMAs? Any insight is appreciated!

Technically it's entirely possible to replace these actuators but it's unlikely they will because the economics don't work out. The weight savings you get will be offset by the costs from design, recertification and installation. It's not as simple as bolting something on.

When you make a big change like this to an airplane you have to take into account the changes it will bring. The actuator may be a different shape, the loss of weight in one area will change the balance of the airplane and affect its structures in ways that have to be accounted for. The forces the new actuator design will put on structures must be accounted for.

Electric actuators need electricity, that means you need to generate it and supply it. You'll have to run wires for it, maybe change the engines generators so they supply more juice. You may have to change the Ram Air Turbine so control can be maintained if engine power is lost. The airplane's control systems may have to be modified. Emergency procedures, maintenance manuals must be changed, people have to be trained, etc. Finally, all this must be certified with the FAA, EASA, and other bodies before passengers can be taken, only then can the actuators actually be replaced.

All this costs a lot of money to do, which is why major retrofits like that are rarely done, the ton of weight they save isn't worth the costs of doing it, even over 10 years of flying.


Why can't helicopters or Zeppelins drop fire-fighting material on burning buildings? There have been a number of tragic cases where tall buildings have caught fire for various reasons, and fire-fighters on the ground appear to have been unable to reach the upper stories with fire hoses.

As a child watching 9/11 unfold, I remember wondering why, given that helicopters were being used to film the events, it would not be possible for helicopters, or perhaps airships, to be loaded with water or foam and fly over burning buildings, dousing them.

Of course, in retrospect, I understand that the World Trade Centre buildings were so vast and the fire (and structural damage) so enormous that this would have made little practical difference.  But what about cases of relatively smaller tower blocks, such as the recent tragedy in the Grenfell block in London?

I assume that there must be some practical reason why this cannot be done, on the grounds that this is something which presumably would be being done if it were possible.

Is it simply that the weight of a large amount of water would be too heavy for a helicopter to carry?  Would this apply to airships?

First, they have been used, like in case of the Federation tower fire in Moscow on 2012. The image below shows a Kamov Ka-32A11BC being used to fight fire in that case.

Helicopter fighting Federation Tower fire in Moscow; image from dailymail.co.uk

According to a news article

  The Ka-32A11BC proved its fire-fighting credentials in April 2012, when a blaze engulfed ... the 67th floor at the Federation Tower in Moscow, Russia, more than 270 meters above ground level. ... the fire was only contained after two Ka-32As belonging to the Russian Emergencies Ministry were called into action and ferried in water from the nearby Moscow River.

However, there are multiple issues in using helicopters for urban firefighting.

Helicopters are all but powerless is case of fires breaking out over the lower floors. Even in the above case, the helicopters were useful only as the fire broke out in the top floor of the (then under construction) skyscraper. For lower floors, the helicopter would have to carry the spraying equipment in the fuselage, which would make the useful payload impractical. Airships are all but useless in this case, while even helicopters would have difficulty getting through the buildings.
Firefighting using helicopters is not a precision business as it would be difficult to position the helicopters directly overhead due to the intense heat and the turbulence produced. For safety, the helicopters have to fly higher, which reduces efficiency due to winds.
Aerial firefighting is a costly business. As LA times puts it:

  It costs up to \$14,000 a day to keep an air tanker on call and as much as \$4,200 per hour to put it in the air. Heavy-duty helicopters, the workhorses of aerial firefighting, can cost \$32,000 a day on standby, plus \$6,300 per hour of flight time.

and this in the US where the need to put out forest fires is all but certain.  Major fires in skyscrapers are infrequent and too scattered around the world to justify the expense of keeping a helicopter on standby in any given city.
The crew have to trained for this- firefighting is a dangerous business:

  But unpredictable atmospheric conditions make flying over wildfires difficult and dangerous. Thirty-seven firefighters have died in aerial firefighting accidents in the last decade.

Urban environment with high rise buildings and power lines pose a separate set of challenges.
Water and firefighting slurry supplies have to made available- this is important in cases where for example, the rivers are seasonal. Not only is the normally used firefighting slurry costly, it is also not environment friendly.

  ... the slurry, which is rich in nitrogen, can harm fish, wildlife and watersheds, despite agency guidelines to prevent drops onto vulnerable areas.

  Aerial firefighting is expensive. Tankers cost upwards of \$6,000 per hour to operate. The slurry itself averages about \$2 per gallon, and the Forest Service used almost 9 million gallons of it last year.

Airships have the same issues, and some more (payload and speed/maneuverability come into mind).


Why do pilots announce the cruising altitude of a flight? At some early stage in the flight, why will commercial pilots announce the cruising altitude of the flight?

No real reason other than it keeps people from bugging the flight attendants by asking "how high are we??".

It also lets the flight attendants know that the aircraft is at cruise so won't be climbing and making the carts harder for them to push around.


What is the difference between Jet Wash and Jet Blast? I was reading about Wake Turbulence in Wikipedia and got to know about Jet Wash and Wing Vortex. According to Wikipedia, Jet Blast is the movement of air from the jet exhaust. Isn't this same as Jet Wash? What is the difference between the two?

Jet Blast is the force or wind generated behind a jet engine, particularly on or before takeoff when high/full power is set, but also when the aircraft is taxiing.

When an object moves through air (or some other medium, e.g. a spoon through nutella), air is disturbed. This disturbance or wake is known as wake turbulence. It can also be called jet wash.

The difference is that jet blast is only because of engines. Jet wash or prop wash or wake turbulence is because the airplane moves through air.

If Mr Kevin Fast runs at say 100 mph doing this (see picture below), you can notice significant wake turbulence, although the engines are off and there is no jet blast.


If all aircraft were TCAS-equipped, how would this change ATC routines? « The primary purpose of ATC worldwide is to prevent
  collisions, organize and expedite the flow of air traffic, and
  provide information and other support for pilots. » (source)

If all aircraft were equipped with TCAS, in what ways (if any) would this change ATC operation ?

Think of the ATC system as the road network, traffic lights, road signs, and police.  TCAS is a standalone device in your car that warns you the guy coming at right angles to the intersection in front of you is going to run the light and T-bone you.  Whether you have such a device or not, it doesn't change how the traffic control system work.

TCAS has been around for 40 years and it didn't change the way traffic is controlled because it's a stand alone system that only impacts the crew on board the airplane that gets a TCAS warning.

TCAS is mostly to protect big aircraft from incursions from small aircraft, that are hard to see and that ATC can't always prevent. What got it going in the first place was the famous crash in LA where the DC9 on an approach overran a C-172 back in the late 70s.


How to get the correct angle when doing a visual appoach before landing? Before landing, without ILS, how can you get the correct vertical angle and know when you're too high or too low?
I think there are some red and white directionnal lights next to the runway that can tell you if your angle is correct, but I'd like to know precisely how a nice approach is done.
Do pilots sometime just figure it out because it's a habit? Is it more difficult if the runway is surrounded by an ocean?
I'm talking about commercial airliners as it seems more simple with small aircrafts.

PAPI

An airport might have Precision Approach Path Indicator (PAPI) lights set up. I believe these might be what you are thinking of. They are discussed in Chapter 2 of the AIM.

Here are two pictures to show them at night.

The first, shows a plane that is on the correct glide path. Firstly, they are normally installed to the left of the runway, and according to the AIM, red should be on the right, so, I believe the picture has been flipped, however you could still use them as is.

If you are right on the correct glide scope for that runway, you would see two white and two red. .2 degrees high would show three white and one red, and .5 degrees high, or higher, four white.

Conversly, .2 degrees low will show three red and one white, and .5 degrees low or lower will show all four red.

Red and White is Just Right. All Red, You're Dead.

VASI

There might also be VASI, or Visual Approach Slope Indicator, lights. These are in many different configurations. They are also discussed in the AIM at the same link I posted above. An example of a two bar VASI light setup is shown below.

The VASI lights are the two sets of two lights next to the runway (just above the row of green lights. They are set up so that white over white is too high, red and white both showing, on glidepath, and red over red is too low.
The mnemonic for those is: red over white, alright; red over red, you're dead.

For more information, there is the AIM Page, the PAPI Wikipedia Page, the VASI Wiki Page, plus there are many other pages which are useful. If you search (using Google or BING, for example) for "runway lights papi" or "runway lights vasi" you'll get many hits.

One last comment here. The correct glide path for an airport is not always the same. If there is/are an obstacle, the glide path might be higher/steeper. If the runway is lighted, using PAPI and/or VASI lights, use them! They will keep you on the correct glidepath for whatever runway you're trying to use.

Good Luck and Safe Flying!


Does empennage height above the main wing matter Am still in my preliminary design, am already wondering as to how high above the wing should the empennage (tip of vertical stab) be?

The critical aspect for Vertical stab height is its rolling torque and how it affects the balance of total side slip forces on the aircraft, including wing, fuselage, landing gear, engine mounts.

As viewed from the side, for the same area, a higher aspect Vertical stab will create more rolling torque and be structurally weaker than a more square design.

More important is Vertical stab area, your weather vane, which affects directional stability and spiral stability.  Very important to get this right.  Adequate area is needed to avoid "Dutch Rolling".  Note that a high wing design needs less dihedral, there for can have a smaller Vertical stab.

Also, the tractor propulsion design, with the CG (and wing)  set as far forward as possible, also lowers the Vertical stab and Horizontal stab area requirement, resulting in significant reduction of drag.

But, unless extreme performance is needed, it is best to slightly overdesign the empennage and play it safe.  Study of existing designs past and present will be of great help.


Is there a legal maximum altitude? In the US, is there a highest legal altitude allowed for certain planes and does it depend on the plane? I heard from a sort-of-reliable source that the maximum is 45,000 feet but I haven't been able to confirm this. I ask since a plane I travelled in very recently was travelling at an altitude of over 55,000 feet and, when it did, turbulence was terrible (some told me I was lucky to be alive).

Note: I have tried Googling this and have found no answers.

There's no legal limit of how high you're allowed to fly by law: there's no law that says

  It is illegal to fly above X,000ft

In some juristictions there are more specific laws, eg

  It is illegal to operate an unpressurised aircraft above 25,000ft

However, each aircraft has a service ceiling when it is certified, and it would be generally illegal to operate the aircraft above this altitude (because it's unsafe).

I'm fairly confident that you weren't at 55,000ft. No currently-operating commercial airliner I know of has a service ceiling higher than 45,000ft (the newer -800 version of the 747) and they almost never operate above 41,000ft. A few private jets can go a little higher, up to around 50,000ft, but I know of no non-military/experimental aircraft which is currently capable of going much above 50,000ft, even if you were daft enough to try.


What process do I follow to land a civilian aircraft on a military base? Let's say I have business on a US military base (e.g. JBLM), and I'd like to fly a privately owned aircraft there. What is the process I follow before the flight to get approval to land, and once I'm enroute to ensure everything goes smoothly?

Landing at a US military base isn't all that hard (I've landed at Ft. Drum before), you just have to get prior permission (PPR) (submitted at least 30 days in advance and confirmed within 24 hours according to 32 CFR 855.8), and need to have a "good reason" (as determined by them).

32 CFR 855, Table 1 (which is quite long) includes the purposes that are normally allowed.

You will be required to submit the following forms to the base commander (See the A/FD):

DD Form 2400 - Civil Aircraft Certificate of Insurance
DD Form 2401 - Civil Aircraft Landing Permit
DD Form 2402 - Civil Aircraft Hold Harmless Agreement

32 CFR 855 contains the regulations pertaining to US Air Force airfields (and the rules are similar for each branch).

855.1 - Policy includes:

  (1) Normally, landing permits will be issued only for civil aircraft
  operating in support of official Government business. Other types of
  use may be authorized if justified by exceptional circumstances.
  Access will be granted on an equitable basis.

  ...

  (3) Any aircraft operator with an inflight emergency may land at any
  Air Force airfield without prior authorization. An inflight emergency
  is defined as a situation that makes continued flight hazardous.

855.5 - Responsibilities and authorities. includes:

  (6) Will not authorize use of Air Force airfields:

  (i) In competition with civil airports by providing services or
  facilities that are already available in the private sector.

  Note: Use to conduct business with or for the US Government is not
  considered as competition with civil airports.

  (ii) Solely for the convenience of passengers or aircraft operator.

  (iii) Solely for transient aircraft servicing.

  (iv) By civil aircraft that do not meet US Department of
  Transportation operating and airworthiness standards.

  (v) That selectively promotes, benefits, or favors a specific
  commercial venture unless equitable consideration is available to all
  potential users in like circumstances.

  (vi) For unsolicited proposals in procuring Government business or
  contracts.

  (vii) Solely for customs-handling purposes.

  (viii) When the air traffic control tower and base operations are
  closed or when a runway is restricted from use by all aircraft.


When to turn on deice boots? This video says (at 25:06) that you should do it as soon as possible.
but I just learned in class that you should wait for an ice build up then turn it on vs just turning it on. This would prevent an ice bridge to form:

But in the clip it says modern de-ice boots don't have the problem mentioned in the picture.

There was a belief that activating de-icing boots too early could result in an ice bridge forming over the boot and rendering it ineffective. This led to a recommendation that de-icing boots should not be activated until a significant build-up of ice had occurred.

(Source: FAA)

Recent testing has established that modern de-icing boots are not susceptible to this problem, and advice from the FAA has been changed.

In InFO9007 (dated 5th May 2009) the specific advice given is:

  Pilots should follow the boot activation and operating procedures
  specified in the AFM or FAA approved operator’s manual for the
  airplane they are flying

And further:

  If the AFM does not have specific boot operation procedures or if ice
  thickness is difficult to judge, pilots should not be reluctant to
  cycle modern boots at the first sign of ice accretion and then as
  needed.

A 'modern boot' is defined in the same publication as having

  less than 1.75 inch diameter tubes, operating pressures of 15 psig or
  greater, and fast inflation/deflation times

It also suggest that any aircraft built later than 1960 is likely to have modern boots.

Essentially, for most cases that you might encounter the video clip is correct, and your class instructor is wrong.

That said, the definitive guide should always be the Pilot's Operating Handbook for the aircraft you are flying.


What is the effect of altitude on true airspeed? I know that wind is taken into account when we compute the TAS(true airspeed) and GS(ground speed). However what is the relationship between the TAS and altitude?

For example: What is the true airspeed on the level flight if the headwind is 20 mph and ground speed is 100 mph at 30,000 feet altitude?

If you know GS and local wind speed, the TAS always the same, regardless of altitude. The true airspeed is called "true" because it is exactly how fast you are moving relative to the air. Picture it as a person in a weather balloon (which does not move relative to the surrounding air, i.e., TAS=0), pointing a radar gun at your aircraft to measure its speed. The results would be the same regardless of altitude, temperature, pressure, etc. This is what sets TAS apart from pretty much any other speed like IAS, CAS, EAS and Mach.

Only at truly ridiculous altitudes you would have some problems with calculating TAS, due to the increased orbital radius from the center of the Earth. However, at this point, you're well into the near vacuum of space which means that the whole concept of 'air' speed is quite silly.


Can a passenger force a Go Around? Sorry if this question is too stupid, but I wonder what would happen if a passenger on the first row just behind the cockpit (ie. on a 737) starts screaming "GO AROUND" when the plane is about to touch down. Can it confuse the pilots?

Not likely. Pilots wear headphones, so we cannot hear the idle prattle of the pax in the hold. In any case, we don't take orders from passengers. Think about that for a second: would you like it if aircraft pilots followed the instructions of a crazy screaming passenger? What if there were TWO crazy screaming passengers giving contradictory commands? Which one should we obey?

In any case, nowadays cockpit doors are closed during flight anyway.


Does ATC use True Course or Ground Track? Reading the practice questions for PAR, I came accross this

  ATC advises, "traffic 12 o`clock." This advisory is relative to your
  A) true course
  B) ground track
  C) magnetic heading

I was inclined to got for A) but isn't that the same as B)?
Neither are defined in PHAK glossary.

A heading is the direction the plane's nose is pointed. A course is the direction it is actually traveling. The difference between the two depends on wind.

A true heading or course is corrected for magnetic variation; a magnetic heading or course is not.

Track and course are often used interchangeably, but technically a "course" refers to what you intend to do while a "track" refers to what you actually do.

ATC can only see your ground track on their radar screens, so logically that would be their reference for traffic advisories--and you may look in the wrong direction if you don't realize that, which I suspect was the point of the question.


How to trim in level flight when speed increases? What is required to happen to control surfaces and trim tabs to remain trimmed in straight and level flight, as speed increases? (for a GA propelled aircraft)

My manual tells me that the elevator should be further deflected downwards, and its trim tab further upwards.

I understand the reason for the trim to deflect in the opposite direction of the elevator (to help maintain it in that position), but don't get it for the elevator.

The angle of attack is lower for the faster flying aircraft. More speed means more dynamic pressure, and in order to create the same lift (weight did not change, after all), less angle of attack is needed to create the needed amount of lift.

Now it is important to know that the angle of attack (more precisely, the difference between the actual and the zero-lift angle of attack) on the wing is higher than on the tail if the aircraft is statically stable. If the aircraft accelerates, the relative amount of lift loss on the wing is less than on the tail, because both experience the same reduction in angle of attack. To keep the balance between both the same, this extra lift loss on the tail needs to be compensated by some downward elevator deflection. The center of gravity did not change, and the center of lift must be shifted to the same longitudinal station in order to maintain level flight.

Fun fact: When transitioning from sub- to supersonic speed, the elevator must be trimmed trailing-edge-up, because now the center of pressure moves back on both wing and tail, so their lever arms around the center of gravity change.


What happened to the Boeing 737.X design? What happened to the B737.X design that depicted a downward nose much like the B787? It is not apparent in the B737 Max 8.

Boeing was considering designing an all-new airplane to replace the 737 around 2020. Having been in production for over 40 years and through 3 major versions, it seemed like it was finally time to leave the 737 type behind.

However, Airbus decided to upgrade the main competition to the 737 to create the A320neo. The A320neo is more efficient than the 737NG and will be entering service in 2016. Boeing watched orders accumulate for the A320neo and felt that they would lose too much market share in the single aisle market if they waited until 2020 to introduce a new plane to compete with the A320neo.

The high number of orders for the A320neo convinced Boeing to scrap the new plane concept, and focus on just new engines for the 737, in order to get a plane on the market to compete with the A320neo. This allowed the 737MAX to be scheduled to enter service in 2017, less than 2 years after the A320neo. While the MAX does not have as many improvements as a new design would have, it has helped narrow the gap in orders to the A320 series. A new plane still 5 or 6 years away while the A320neo enters service would not have nearly as many orders, meaning the Airbus would be quickly increasing their market share with the A320neo.

A similar situation has happened with the 777, although it is still a much more recent design. The 777X is a more significant redesign than the 737MAX, but the update is needed to compete with the new A350 that is already in service.


Aviation history. My dad PM of F-14 My father was Prog mgr of F14. Where can I sell or donate his memorabilia or where is site to help?

I would suggest that you contact the Naval Aviation Museum at NAS Pensacola FL to discuss donating or loaning them.  That way his legacy can live on with a plaque stating "Items in this display donated by ___, NAVAIR Program Manager F-14 Tomcat Systems, 1972 - 1986". (or something similar)


Was the B727's wing supercritical (even if not so designed)? The Boeing 727's wing upper surface appears unusually flat, especially at the root (Albeit at an angle).  Refer to the images linked below:

airlinereporter.com

Flickr

Also from Flickr

Was the B727's wing designed as supercritical? Did the B727's wing behave in a supercritical fashion, even if it wasn't explicitly designed as such?

I've got an aged book on pre-design of aircraft, which states that the B727 wing thickness was 13% at root and 9% at tip, average thickness 11% chord. $M_{M0}$ = 0.9, first flight of prototype is noted as 1963.

The 727 was a derivative of the 707: first flight 1957, average thickness 10% chord, $M_{M0}$ = 0.9. So the 707 wing was even thinner than B727, Mach number is the same. Profile of both airliners is not listed as a NACA profile.

The book references the first research paper on supercritical profiles as T.G. Ayers: Supercritical Aerodynamics Worthwhile Over A Range Of Speeds, published in 1972, nine years after the B727 prototype flew. The profiles depicted in the report seem to be thicker than those of the B727.

The photos in the question focus on the wing root, however the shape of the wing root is not indicative of that of the rest of the wing, but determined by a lot of structural and aerodynamic factors: placing of landing gear, fairings for aerodynamic interference etc. Furthermore, the overwing exit is there and evacuation of passengers should not be too difficult, caused for instance by a bulgy shaped cross section. It would make sense if this bit of the wing was designed mainly with evacuation in mind.

So it appears from the published date of the research work on Supercritical wing design, and from the similarity with the much older B707: no, the B727 did not have supercritical wing profiles.

Update

The main advantage of a supercritical wing is that it enables reducing the wing sweep. There was some progress between 707 and 727, because wing sweep was reduced from 35º to 32º on the 727. However, the A320 has a comparable $M_{M0}$ and has wing sweep of 25º. So again without knowing what exact wing profile was used and based on order-of-magnitude checks, it does not look like the 727 had supercritical wing profiles.

The profiles of supercritical wings I've seen are flat on top indeed, and horizontal and thickish and have a characteristic curve at the end. Flatness per se does not indicate that the profile is supercritical, for example NACA 23015 isn't.

 The horizontal flat bit on top allows the supersonic area to expand calmly again, but it needs to be horizontal, like indicated in this figure from E. Torenbeek, Synthesis Of Subsonic Airplane Design:

Update 2

A fascinating film explaining how high subsonic speed was achieved before supercritical rear loading profiles were implemented on aircraft. Discoveries like these are what I love about the Aviation SE site. From this question & answer


How do aisle lights show the direction to exits? Lights in the aisle will guide you towards an exit.

I've sat through a lot of safety briefings (for commercial scheduled passenger flights) and always found this sentence especially uninformative. Usually the cabin crew pantomime will include some vague gestures towards the floor of the aisles at this point, but even with airlines that use pre-produced videos for their briefings it seems that the video never actually shows those guiding lights in action.

Are they moving dots of light in the floor that chase towards the nearest exit row? Are they fixed lights that are shaped like arrows, pointing to the exits? Or just a strip of light that will tell me, "here is the aisle", but I'll need to figure out by myself which way along it to crawl?

The Floor Proximity Emergency Escape Path marking requirements (for transport category aircraft certified under FAR Part 25) have to meet the specific requirements as noted in the regulatory excerpt below.  There are different configurations that may be used to satisfy the regulations.
FAR §25.812   Emergency lighting. (excerpt):

(...) In the dark of the night, the floor proximity emergency escape path marking must enable each passenger to—
(1) After leaving the passenger seat, visually identify the emergency escape path along the cabin aisle floor to the first exits or pair of exits forward and aft of the seat; and
(2) Readily identify each exit from the emergency escape path by reference only to markings and visual features not more than 4 feet above the cabin floor.

Here is a sample from the Flight Safety Foundation showing an example of floor proximity escape path markings.

(Source)
Also, here is a link to a Flight Safety Foundation article regarding floor proximity lighting.


Do I need to descend towards the Minimum Descent Altitude if I have the airport in sight? I have some questions about circle-to-land approaches.

If we have the runway in sight above MDA, do we need to continue to descend to MDA on downwind? Can we just keep fly like a traffic pattern until abeam aiming point and then start the descent?

Similarly, If during circle to land approach we lose the runway on downwind but we are above MDA, do we need go missed still toward to the runway? Since we are above MDA we should still have obstacle clearance....

No, you do not need to descend all of the way to the MDA if you have the required visibility to continue. In fact, I would recommend against it since it puts you awfully close to the ground while you are maneuvering to align with the runway.  Why do that if you don't have to?

MDA stands for Minimum Descent Altitude, and is just that.  The minimum.

As far as going missed, you would fly the missed approach in the same way because while you may have obstacle clearance where you are now, the missed approach procedure assumes that you fly it the correct way, and in this case you just have some extra padding since you started out higher.


Can the VNAV Path angle be modified in a Boeing 737 NG? In the Boeing 737 NG series, can the usual 3 degrees Path angle used for VNAV Descent be modified through the FMC to another angle?

In the 737 NG, the descent angle is never entered by the pilot into the FMC. One enters a Cost Index, or alternatively a descent speed that's desired, and the FMC, considering forecast winds, computes the Top of Descent point and the angles that it expects to fly in order to achieve that speed.

But, it never tells the pilot what descent angle it's planning to use (although you can see the present vertical angle to a specified waypoint/altitude). Whatever the angle it's planning, you can steepen it or shallow it by increasing or decreasing (respectively) the planned descent speed or Cost Index.

But, unlike some other FMC's, the 737's never explicitly tells you the planned descent angle for enroute operations.

(On an approach, it's a different story; there your gradient path is coded with the waypoints, and it is displayed on the LEGS page. But the user can't change values in the database like that. Speeds, yes; GP angles, no. A pure visual approach, with only a runway-end waypoint is the ONLY time you can specify whatever angle you wish... but that's only to the runway itself, and not at all usable on any other leg.)


Which part of the boundary layer(chordwise) contributes most to friction drag? fore? aft? Why? along the chord of a wing/airfoil section, which portion of it creates the most friction drag through the boundary layer?
Is it in the fore section, close to the stagnation point? or the aft section

It depends on the airfoil and the free stream conditions, but some general trends can be observed.

First, skin friction drag is dominated by viscous effects, so the laminar or turbulent quality of the layer is important. Laminar layers are less draggy that turbulent ones, mostly by merit of being thinner. This means that the leading edge will often suffer less viscous drag until the boundary layer transitions from laminar to turbulent, which may happen next to the stagnation point or further downstream. The layer will then continue to grow, so, for attached flow without re-circulation bubbles, the friction maximum can be expected to be near the trailing edge (not necessarily on it).

Second, for this viscous friction to be drag in the usual sense, it has to provide a force opposed to the direction of flight, so one would integrate its product with such a vector along the surface of the airfoil. This would mean, again, that the leading edge contributes less than its fair share, as friction forces directed up or down relative to the free airstream are not drag.

So the general answer would be that the aft part of an airfoil provides a larger friction drag contribution than the fore.


How are multiple frequencies monitored at once? In a tiny single-engine aircraft like a Cessna, all the way up to a modern jetliner like a 747, it seems the cockpits of modern aircraft have at least 4 separate airband radios, for monitoring up to 4 different frequencies at once.

However, the cockpit has only one up to (rarely) three occupants wearing headsets.

When Ground calls you and says, "monitor Tower, on 121.65", Tower wants to tell you something from that frequency, but Ground also wants you to stay on their frequency.

By which mechanism are multiple frequencies monitored by one or more (fewer than the number of radios/frequencies) crew members?

all the running cockpit radios are heard at the same time, mixed into the same audio

how to know which transmissions came from which freqs?

switches that cause exactly one of the radios to be "active" in the headsets at once, and the other ones are not heard in the headsets

how to monitor multiple freqs this way, without missing transmissions or switching back and forth so quickly it would be unreadable?

I've looked around, but I can't understand how multiple frequencies are easily monitored at once, without running into the problems I mentioned in my guesses.

So how can a pilot alone, or a pilot with a first officer, listen for their callsign on multiple frequencies at once?

First let's get rid of some misunderstandings:

Many smaller aircraft have just one single radio.
Being told to monitor a frequency does not mean you have to listen to two frequencies at once. See: Being told to monitor a frequency, when are you allowed to transmit on that frequency? Any controlled flight will always be under the control of exactly one controller, never more at the same time.

Now, as for actually listening to multiple radios at once, that is certainly possible, and quite normal on large airliners. In the cockpit of an airliner there will often be up to somewhere around 10 different audio inputs, each with their own volume control. This can include 2-3 VHF radio, an HF radio, NAV radios, communication with ground crew (pushback/handling), as well as audio from the cabin (the PA) and probably a few others. All these audio streams are merged into one, based on the individual volume controls.

Recently having had the opportunity to join a crew on a flight on the jumpseat, I was quite amazed at how good the pilots were at distinguishing between the multiple audio inputs, even when different people spoke at once. But with practise, it's actually not hard to see how it's done. Each audio channel will have a different "topic", using different key phrases and words. An ATC ground unit will be talking about taxiing, whereas the tower will be talking about taking off and landing. And the cabin PA will be explaining how to fasten your seatbelt to a bunch of passengers not paying attention. And of course then there is the fact that people all have different voices. Sometimes it is easy (a female on one frequency and a male on another) and sometimes it is more tricky, but I have never heard two people with the exact same voice.


What is the immediate cause of liftoff? If I understand correctly, when a plane transitions from takeoff roll to being airborne, it is not something that happens "by itself" when the airspeed is high enough, but is caused by deliberate pilot input somehow.

Which control surfaces are involved in causing the plane to lift off?

Is it an ordinary nose-up movement of the elevators? That is, the elevators create negative lift that pushes the tailplane down, which makes the entire aircraft pivot around the main gear and increases the wings' AoA enough to create lift that takes the plane off the ground.
Or is it something that increases lift with unchanged attitude, such as a symmetric aileron movement, or an additional flaps extension? And then after the plane is airborne it is rotated to climbing attitude?

The descriptions I can easily Google up point towards 1. However, while that makes perfect sense for tricycle gear I don't see how that would work with taildraggers. Pushing down on the tail would just increase the downward force on the tail wheel rather than change the AoA.

As the elevators rotate to get a negative pitch angle to the horizontal (moving the tip of the elevator upwards), a pressure difference is created causing it to produce a downwards force, and as a result the aircraft pivots around the landing gear, rotating upwards.
As it does so, the wing starts to generate more lift, as can be
seen on the graph below. The higher the angle of attack- the more
lift, since the lift coefficient becomes higher, up to where stall starts.
When the lift exceeds the weight, the aircraft will lift off.

For taildraggers, the tail is normally rotated up at a low speed while the aircraft continues to accelerate, and once a sufficient speed is reached, the tail surface is again lowered, causing the wing to increase the AoA and to lift. Footnote: If I'm not mistaken, this is more of an act to improve control and reduce drag, since at some point the aircraft will lift off on it's own with it's tail-down angle of attack.


Adjustment for non-balanced passenger loads? It is well established (How Centre of Gravity (CG) is adjusted? and elsewhere) that adjustments can and need to be made to insure that airplane loading maintains a suitable center-of-gravity for the aircraft fore/aft.  However, these questions and answers appear to deal only with fore/aft adjustments.  Does a plane such as the MD-88 which has unequal seating (3 seats on the port (left) side of the aisle and 2 on the starboard (right)) have much of an issue with port/starboard balance, and if so, is there standard way of dealing with more passenger weight on the port side of center-line?

I would assume this could be handled with unequal fuel tank loading in each wing, or air surface adjustments, but am curious if in practice this is an issue or not.  Or is there anything built into the design of the aircraft to handle this expected unequal passenger loading?

Asymmetrical lateral loads within the fuselage are not far enough away from the longitudinal axis to generate any significant moment arm.  It is an issue, but not one that is planned around or proactively compensated for.  Any imbalance in flight can easily be overcome with a little bit of aileron trim.


How to choose a flight school? I am considering enrolling in a PPL course, and am getting information about the flight schools in my city (Rome, Italy).

What should I be looking for?
How can I choose among them?
Their fees differ by at least €3000. Are there differences between the schools that justify such different prices?

I'm not sure how it works in the EU as I am an American PPL student but let's ignore the small specifics and look at some general points.

Number of planes

Where I fly there are 2 flight schools; one has a fleet of about 20 planes from Grumman trainers all the way up through a Seminole. The other school has 2 planes... The obvious thing here is down time. The fact is that planes break, need routine checks and get rented by other students. A flight school with more planes (and an appropriate amount of instructors) will be able to handle these issues better. Many times I have booked a plane to find that it's in the shop and I get assigned another plane (same make and model).

Type of planes

While you cant be as picky here since sometimes geography limits you, some schools may be significantly more expensive than others. One of the nearby fields flight schools I looked at had just bought a new fleet of SR22's and were renting them at 250 USD an hour wet compared to the 100 USD an hour wet that I pay for a Piper Warrior. This can make a big difference in cost of training. Not that you are thinking this far in advance but if you do intend to one day buy a plane you may want to consider training in the type although its hard to say what kind of plane you would buy before you start flying :). If you intend on getting your instrument rating (I assume there is an EU equivalent) you will also want to make sure you are at a place that has instrument-capable planes and possibly even a precision approach system.

It also stands to reason that a place with older planes may see more down time as the planes may need more service but most old planes that I have flown are well kept. Here in the US trainer planes need to be inspected every 100 hours so they are out somewhat frequently for that already.

Number of instructors

Here in the US many instructors are doing so to get enough hours for their ATP. With that in mind instructors are subject to leave at any time if they make their hours and find a commercial job. Bigger schools will be able to reassign you to another instructor or may have better luck hiring a new instructor to fill the gap.

Type of airport

Again sometimes you can't be picky here because of geography but training at a towered airport as apposed to an uncontrolled field can help you hone in your radio work from day one. A bigger slightly more busy airport may also give you real experience with things like wake turbulence avoidance. Most larger airports also tend to have 2 runways which can help you on those windy days (depending on direction and such). They also tend to have better services like plowing, precision approaches, fuel (not all airports have gas!), pre-heats that don't take 20 minutes to show up etc. This can also be a but of a curse sometimes as larger airports are subject to traffic and you may find your self sitting on the runway waiting to take off on a nice day.

Cost

This can be a big factor for some people. Some are lucky enough to have the money to fly where its easiest for them (close to home or work) etc., while others don't have this luxury and must fly where its the cheapest. Here in the US a cheap school will still get you the same PPL that a super expensive place with a brand new SR22 will. So if your goal is simply to fly and cost is a serious factor there is nothing wrong with going with the cheaper option (which may involve driving a bit farther) as long as you factor in the potential down time of the planes or difficulty of booking them.


Is there a relationship between transonic buffet magnitude and altitude? Transonic buffet happens at mach 0.95.  The correlated true airspeed varies with altitude.  Does the transonic buffet magnitude also vary with altitude, and if so, how?

Transonic buffet, or Mach induced buffet, or high speed buffet, is a flow separation due to the combined presence of shockwave and "high" angle of attack. The boundary layer separation results in random high frequency vibrations. As the AOA increases, the separation and the associated vibrations worsen, up to the point where the crew can no longer read the instrumentation and perform normal flight duties; this point is called deterrent buffet.

For a single Mach number, the AOA (or $C_{L}$) associated with buffet onset is generally constant; there will be some differences due to CG position, the associated trim and Reynolds number effects. During aircraft design and flight testing, the buffet onset boundary similar to the one below is mapped out. As you can see, the general trend is a decrease in buffet onset boundary with Mach (though the trend can reverse depending on the airplane).

(Image modified from https://www.researchgate.net/figure/Typical-buffet-onset-curve-and-separation-mechanisms-defining-the-boundaries_fig2_270086469.)

Flying at the same Mach number at a higher altitude means that it will have smaller dynamic pressure than flying at a lower altitude. This translates to a higher AOA at the higher altitude, which means that the buffet intensity will be higher. In other words, for the same Mach and weight, the maneuver margin is decreased the higher it flies, independent of its climb capability.


What is this aircraft with pipes at the flight deck windows? This image comes from a site about aircraft tractors:

What could be the reasons for this old aircraft to have pipes at the flight deck windows and to be moved near a forest?

In most commercial aircraft, the cockpit windows are the most easily opened/removed.

(Image Source)

Why the windows typically open is a topic for another question, but mostly it is for the crew to be able to communicate with the ground personnel and for rapid evacuation.

Some older aircraft like the 707 in the original post are used primarily as training devices. The aircraft in the original post is a Boeing 707 in Germany used for evacuation training. The most likely explanation is that they put in portable air conditioning units to be able to cool the cabin while they filled it with people. The vents are angled down so that water does not enter the air conditioning system.

Specifically regarding the aircraft in the post, this is a Boeing 707 located at the Tegel Airport in Berlin, Germany. It has a lot of history being an aircraft that was hijacked and then later smuggled back into Germany in the night by an American crew as a gift from Boeing to celebrate the city's 750th birthday.

You can read more about the Tegel 707 on this website and some more information about the hijacking of El Al Flight 219.


How do the shockwaves (supersonic and hypersonic) interact with the structure? My main question is why spaceplanes are conceptualized as pointy and lengthy, dart-like machines. What would happen if they were more like flying wing?
I'm hypothesizing a bit and I am not sure what would happen if a flying wing type of aircraft (most notable example B-2) were to go supersonic or hypersonic. So let's push B-2 to Mach 20.
How would the shockwaves interact with the structure? Would they remain oblique within supersonic regime (a)? Would they transform into bow shockwaves in hypersonic or cross the structure (b)?

Aircraft with Flying wing configuration, such as the B2 bomber, fly at high subsonic speeds. During such a case, the airflow is at a high subsonic speed at the leading edge, and accerelates through to supersonic speeds as it moves over the front - upper portion of the wing surface. As the wing profile (chord wise) changes to converge towards the trailing edge, the airflow attempts to decelerate from supersonic to subsonic speeds. However, this transition is only possible through a chordwise oblique shock wave. Now, this oblique shocks profile will look like the blue line in your diagram above, but will be sitting at some near-mid chord position.
If the flying wing body is increases speed towards sonic velocity of the air, then this chord wise transition shock wave will become stronger and move just in front of the body leading edge. Finally, once the body is moving at supersonic speeds, the transition shock will become a bow shock in front of the leading edge. In addition to this, there will also be two termination shock waves sitting at the leading edge, one for the upper surface airflow and the other for the lower.
The angle of the shock wave profile will be greatest at low supersonic speeds, but beyond the bow stick sitting in front of the leading edge will narrow in angle and so will its spanwise angle. At hypersonic speeds, the distance between the front shock and leading edge will reduce, leading to immense heat energy being impinged onto the body.
Hope this helps


Why don't contra-rotating propeller configurations with more than two propellers exist? I wasn't able to find a single example of more than two propellers stacked axially in a contra-rotating configuration. There is a huge number of contra-rotating propeller setups, but it is always a combination of two propellers on the same shaft, not four or six.

Why isn't a piston engine used to run more than two standard propellers on a single shaft? Hasn't it been tried (or tested at least) in 100+ years of aviation history?

(This question isn't about turbofans/turbojets, but I also couldn't find anything for ducted fans: two props on a single axis is a maximum.)

Blade-solidity is explained here:
Contra-rotating props explained here:

An increase in a number of blades does seem to reduce the efficiency, whereas an increase in propellers on an axis seems to increase the efficiency.

No, stacking more propellers will reduce efficiency. The case with two is an exception because the second propeller benefits from operating in the slipstream of the first. In total, both propellers accelerate the air backwards without adding swirl losses.

However, propeller efficiency goes down with increasing flow speed ahead of the propeller. This means that every other propeller operating in the accelerated flow of a preceding propeller will have lower efficiency. Generally, it will be better to spread the propellers out sideways than to put them in line.

Note that contra-rotating props are the exclusive realm of very powerful engines with very high disk loading. The most recent designs prefer to use more blades and avoid the heavy gearbox, but the efficiency of such props is poorer than that of propellers with lower disk loading and fewer blades. In a way, the efficiency of the eight-bladed propellers below is similar to that of four two-bladed propellers in sequence, but it is much easier to build with all blades and their pitch mechanism in one hub.

T-56 engines with Hamilton-Sundstrand NP2000 propellers on an LC-130. Photograph by Robyn Waserman, National Science Foundation (Date Taken: November 21, 2008)


Why do landing gear bays in commercial aircraft not have a fire extinguishing system? Landing gear bays in modern commercial aircraft have fire detectors installed, but there is no fire extinguishing/suppression system in this area.
What is the logic behind having fire detection in this area when we don’t have extinguishing?
Why doesn't this area have fire a extinguishing system like other unpressurized areas like engines and APUs.

Cost/Weight/Complexity, the usual reasons why you avoid to add another systems. But let's analyse if you really need it.
Easy to prevent
From the data of this Boeing document:

at least 62% of the wheel well fires are caused by applying excessive grease
at least 11% of the wheel well fires are caused by hydraulic leaks
at least 3%  of the wheel well fires are caused by incorrect application of solvents

From the fire protection standpoint the landing gear is a quite simple device: maintenance staff should pay attention where and how much grease they put, pay attention where solvents are put, and the only flammable liquid is the hydraulic fluid. An engine is much more complex, you have many flammable fluids (fuel, hyd, oil), many pipes and extreme forces, which make the maintenance error and engine damage more probable. Then, causes can also be external (like bird strikes). This makes an engine fire event probability much more higher.
Moreover, most of all events of wheel well fires appear after landing (i.e., after braking), which is still a serious problem, but not as serious like in-air fire.
Rare
Wheel well fire are 10x less probable than engine fires and 1.5x less probable than APU (source):

There were only 2 fatal accidents related to wheel well fires: Propair Flight 420
 and the Nigeria Airways Flight 2120. In both cases pilots were unaware of the fire and they didn't take any countermeasure.
Easy to solve
Just put the landing gear down. The >= 200 kts air does the rest. If it doesn't work, at least the most flammable materials (rubber, hyd pipes) and the heat source are now outside the aircraft frame and it will take more time to reach the wheel well, so you have more time to land.
Since wheel well fires are caused by high brake temperatures, the procedure is even usually applied before the fire actually exists. For example, the HOT BRAKES procedure of Airbus requires to lower the landing gear (and turn on the brake fan, if available) as soon as the brakes become overheated, potentially preventing in this way the fire event.


Can I apply for a Gold Seal any time, or only when I renew my CFI certificate? Basically my CFI certificate expires almost a year from now, but I have met the requirements for Gold Seal. Can I obtain my Gold Seal now, or do I have to wait until its time to renew my CFI?

You can apply now. It will be reissued every time you renew your certificate.

http://www.pilotratings.com/goldseal.html


Is there any way for the baggage carrier to add some fake luggage? For the sake of a story that I am writing, is there any way that a conspiracy luggage carrier could add some luggage to given aircraft?

Specifically:

Is there still a man power used for the purpose of transporting luggage from the check-in to luggage trolley?
If yes, how do any of them know which luggage transportation belt they are supposed to deliver particular luggage to?
Are man present at all anywhere in the luggage sorting and transportation zones or is this today a fully automated process?

I am asking about a large international airport / Heathrow, if that matters.

The exact process varies quite a bit from airport to airport and even sometimes from terminal to terminal within an airport. But assuming a relatively modern terminal at a relatively busy airport, most of the process is heavily automated to reduce both labor and error.

Bags will be taken by conveyor to a security station, where a human watches them pass through various scanners. Then they get sorted by machines onto belts going to various parts of the terminal, and then belts going to each gate. This is why bags all get a big white tag with one or more barcodes on it, connected to a database that (hopefully) knows where each barcode should be sent.

Once the bag arrives at the gate, a human will transfer it (just a few feet) from the belt either onto a baggage cart (for smaller planes) or into a Unit Load Device (for larger planes), where it then waits to be loaded onto the plane. Notably, all bags on the same cart or in the same ULD will be waiting for the same plane.

At the other end, a human transfers the bag from the cart or ULD onto to the belt, and it goes back up into the system to be scanned and sent either to a different gate or off to baggage claim.

A single baggage handler can't really change much. They could intentionally misload a bag on the wrong aircraft (heck, they do it often enough by accident), but that is only easy if the "right" aircraft were at the same gate, or at least near enough to move the bag without another handler noticing the odd behavior, and there's no guarantee they'd be assigned to that gate at the right time since baggage crews move around a terminal pretty fluidly as planes come and go. And the "mistake" would be quickly detected when the plane was unloaded at its destination, unless of course a handler there was part of the same conspiracy. Many airline employees have been caught smuggling drugs this way, and presumably many more haven't been caught, so it's completely realistic.

More practical for a true conspiracy, though, would be planting, bribing or blackmailing someone who can simply change the database that says where a particular barcode should go. There are systems that check to ensure a passenger and their luggage aren't separated, so you'd need to attach the bag to someone who you'd be certain wouldn't miss the flight, and then detach it at the other end so you didn't get caught.

Overall, it is a lot simpler to trick "the system" into unwittingly doing your nefarious work for you rather than having a grand conspiracy of humans trying to outwit said system. But it may not make as good of a story.


Does the FAA verify or authorize VFR flight plans? It's possible (and, at least by AOPA, encouraged) to submit flight plans for VFR flights, but ATC still do not perform many of the services they provide for IFR.

Suppose I submit a flight plan for a Piper Cub under which I take off, climb to FL10,000, and dock with the International Space Station before landing on the White House front lawn? Or, slightly less egregiously, a plan under which I clip an ADIZ but I don't mark it as DVFR?

Will the flight plan be rejected when I try to submit it? Will Flight Services refuse to open it? Will they open it anyways and just let me do my thing?  Are they required to verify it in some way?

First, one small clarification: ATC doesn't offer any services to an aircraft on a VFR flight plan unless you call and request them.

This short Ask ATC video from AOPA has some useful comments:

Controllers don't know anything about your VFR flight plan
VFR flight plans are for search and rescue purposes only
Even if you call ATC and request flight following, they only enter the destination into their system, not your route (I assume that's because your route could be 'follow that river and then that interstate')

The key point is that VFR flight plans are recorded and managed by FSS, not ATC. So, does FSS accept whatever they're given? I couldn't find a direct answer to that question, but the FAA's procedures for receiving and handling VFR flight plans (see Chapter 6) don't include any steps to "validate" the plan (whatever that would mean anyway). Although there's a lot of detailed, tedious information there so I may have missed something :-)

In fact, this AOPA explanation implies that no one even looks at the route unless it's as part of the SAR process:

  ETA plus one hour

  Within a half-hour of becoming overdue or at ETA plus one hour, the
  search is widened by sending an INREQ (information request) to flight
  service facilities along the route (which is why the route of flight
  is specified on the flight plan). If [the pilot] had been on an IFR flight
  plan, the INREQ would have gone out at ETA plus 30 minutes.

The bottom line seems to be that no one really cares about your VFR flight plan unless it's actually needed to find you. So even if you can enter a nonsense plan, it wouldn't be a very good idea.


A pilot faces a medium-term loss of their medical. What can they expect? This closely related question asks about what options a pilot has when facing a permanent loss of medical.

However, not all disqualifying conditions are permanent. Maybe you got an interesting disease known for its 7-month contagious period. Maybe you broke an important, slow healing bone. At any rate, whatever silly thing you did to yourself, you will be flying again, but it will take several months.

As a pilot, what options do you have during this period of your career?  Are you likely to be furloughed?  Assigned alternate duties? I'm interested in answers relating primarily to the United States or Europe.

It will first and foremost depend on the carrier you are working for and if they have anything in place for such a case. There are personal insurance policies out there to cover this exact case, like this one and this one. Some carriers may offer policies like this in house for their employees as well.

If available to you it might be possible to spend some time in the sim without a medical or (if you are allowed to) instruct and work with other pilots at the company for ground based instruction.