What was the yearly number of MiG-15's produced? Wikipedia's article on the MiG-15 only states a basic number of 12,000 produced natively, with up to 6,000 more produced in other countries. But it does not list any years for this.

When did mass-production start and end for the MiG-15 in the Soviet Union? This would at least let us divide 12,000 by the total years to get an average production rate. Ideally I'm looking for the number built each year, as this will surely vary year to year.

There is hardly anything that can't be found with the help of a few friends and the Library of Congress. "Истребитель МИГ-15 (MiG-15 Fighter)" ISBN 9785857290194 Pp.52-57.

Plant No.1 (Kuibyshev):

             MiG-15    MiG-15bis    MiG-15Pbis     UTI MiG-15bis
1949 Plan    550
     Actual  510
1950 Plan    300       350                          50
     Actual  301       401                          50
1951 Plan              792         5               365
     Actual            820         5               371
1952 Plan              425                         315
     Actual            460                         333
1953 Plan
     Actual    2                                   127

Non-flyable [what the heck is that??] MiG-15: 2 in 1949, 4 in 1950.
10 knock-down UTI MiG-15 kits were produced in 1951.

Plant No. 153 - Novosibirsk

             MiG-15    MiG-15bis    MiG-15Pbis     UTI MiG-15bis
1949 Plan    550
     Actual  144
1950 Plan    300        500
     Actual  308        360
1951 Plan              1173
     Actual    1       1196
1952 Plan               840
     Actual             863
1953 Plan                                          200
     Actual               1                        209
1954 Plan                                          700
     Actual                                        715

Plant No.381 (Leningrad): 1949 - 75 MiG-15

Plant No.21 (Gor'ky):

             MiG-15bis (type 53)    MiG-15Rbis (type 55)
1950 Plan    350
     Actual  367
1951 Plan    937                     60
     Actual  992                     64
1952 Plan    395                    300
     Actual  425                    300

Plant No.31 - Tbilisi

             MiG-15bis (art. 50)
1951 Plan     30
     Actual   35
1952 Plan    190
     Actual  190

Plant No.126 - Komsomo'ls'k-NA-Amure

             MiG-15                 MiG-15bis
1950 Plan                           250
     Actual    1                     42
1951 Plan                           337
     Actual                         362
1952 Plan                           400
     Actual                         428

Plant No.292 - Saratov

             MiG-15    MiG-15bis    MiG-15Sbis
1950 Plan              275
     Actual    8?      131
1951 Plan              457          100
     Actual            509           49
1952 Plan              350
     Actual            354

Plant No.135 - Kharkiv

                UTI MiG-15
1950 Plan              25
     Actual             6
1951 Plan              50
     Actual            50
1952 Plan             150
     Actual            85
1953 Plan             150
     Actual           158
1954 Plan             200
     Actual           212

Plant No.99 (Ulan-Ude)

                UTI MiG-15
1951 Plan              75
     Actual            29
1952 Plan             125
     Actual            53
1953 Plan             150
     Actual           127
1954 Plan             200
     Actual           206
1955 Plan             225
     Actual           245
1956 Plan
     Actual           173
1957 Plan
     Actual           113
1958 Plan
     Actual           106
1959 Plan
     Actual            65

Totals for the USSR (may contain errors, haven't double-checked):

|      | Combat MiG-15 and variants |  UTI MiG-15   |
| Year | Plan          | Actual     | Plan | Actual |
| 1949 | 1175          |  729       |    0 |    0   |
| 1950 | 2325          | 1911       |   75 |   56   |
| 1951 | 3891          | 4033       |  490 |  450   |
| 1952 | 2900          | 3020       |  590 |  471   |
| 1953 |    0          |    3       |  500 |  621   |
| 1954 |               |            | 1100 | 1133   |
| 1955 |               |            |  225 |  245   |
| 1956 |               |            |    0 |  173   |
| 1957 |               |            |    0 |  113   |
| 1958 |               |            |    0 |  106   |
| 1959 |               |            |    0 |   65   |


Should I use given resolution or calculate resolution based on the max range and number of sig bits? In ARINC429, Should I use given resolution or calculate resolution based on the max range and number of sig bits given?
ForeExample, to calculate Ambient Static Pressure (Label-203, Equipment ID - 10A),
Given Range (Min to Max): 1.5 to 20
Given No of SIG. bits: 11
Given Resolution: 0.016
Calculated Resolution:
MAX RANGE / 2 ^ (No of SIG. bits)
20 / (2^11)
20 / 2048
= 0.009765625.

Question 1: What will be the Ambient Static Pressure value if all the 11 bits are 0.
Question 2: Should I use given resolution or calculated resolution for my LSB value?

It's important to recognize the the resolution provided in the ARINC 429 spec is an approximation so you can't necessarily use that exactly as it is.
From the commentary in section 2.1.6 Data Standards

For convenience, all binary word ranges in
Attachment 2 are shown as whole binary numbers
rather than such numbers less one least significant
bit value. Also, the resolutions shown are
approximate only. Accurate resolutions can be
determined, if required, by reference to the range
values and numbers of significant bits for the words of
interest.

In order to provide a range of 1.5 to 20, the label will have an actual range of 0-32, which with 11 significant bits, will provide an actual resolution of $\frac{32}{2048} = 0.015625$ (approximated to 0.016 in the ARINC 429 spec)


Do crosswind takeoffs increase the chance of a compressor stall? I watched this video on YouTube:

The video shows some pretty impressive take-offs in serious crosswind. Honestly, they looked even scarier than crosswind landings.

It also made me wonder: In such conditions, when there is significant yaw due to the crosswind, and paired with the high engine setting, isn't there a significant risk for compressor stalls? Are there some formulas for calculating maximum crosswind particularly for takeoffs, or something like that, taking into consideration engine performance/response?

The general FAA regulation on turbine engines on airliners is § 25.939

§ 25.939 Turbine engine operating characteristics.
(a) Turbine engine operating characteristics must be investigated in flight to determine that no adverse characteristics (such as stall, surge, or flameout) are present, to a hazardous degree, during normal and emergency operation within the range of operating limitations of the airplane and of the engine.
(b) [Reserved]
(c) The turbine engine air inlet system may not, as a result of air flow distortion during normal operation, cause vibration harmful to the engine.

The FAA has published Advisory Circular 25.939-1 which provides more detail as to how this regulation should be met. The takeoff phase is critical for safety, so the FAA requires testing to show that:

No adverse engine operating characteristics (mild, moderate, or severe) should exist after the power setting phase (normally completed by 60 to 80 knots) of the takeoff procedure through attainment of the enroute configuration and climb to 1,500 ft. above the airport.

The "adverse operating characteristics" are defined in more detail earlier in the AC. So to answer the question, no, it is required by law that jet engines have no issue with takeoffs in crosswinds. The faster an aircraft is moving, the less the crosswind airspeed component is. Once the aircraft is flying, aside from control inputs or changes in the atmosphere, the air stream comes from straight ahead.
The highest amount of relative crosswind will actually occur while the aircraft is sitting on the ground. Note that unlike the takeoff phase:

Taxiing: No adverse engine operating characteristics (mild, moderate, or severe) should exist during taxiing except for operation in crosswinds and tailwinds where mild adverse operating characteristics are acceptable.


What do these instruments do? This is sort of the reverse of an aircraft-identifcation question.

I am attempting to build a virtual model of a Gee Bee R1 (for fun). Unfortunately I haven't had much luck finding plans or images of the inside of an R1 cockpit. The best I could find is this image of a miniature model of a R2 instrument panel:

And this still from a video about a modern-day flying replica (also an R2):

Having desperately reached as far as the second page of google images without success, I've given up trying to find anything better. But if anyone knows some better sources, please let me know!

With very limited actual knowledge about any sort of aircraft, I have no idea which doohickeys do what. So my actual question is, can anyone identify what each of these things likely indicates or does?

For the panel image that you provided, I should be able to identify all major instruments:

A: Magnetic Compass - Pretty self explanatory. Note that in the real aircraft, A and K may have been switched.

B: Vertical Speed Indicator (VSI) - Indicates vertical speed, either up or down, in feet per minute.

C: Engine Tachometer - Indicates engine revolutions per minute (RPM)

D: Sensitive Altimeter - Indicates feet above Mean Sea Level (MSL). Adjustable for atmospheric pressure via Kollsman knob.

E: Air Speed Indicator - Measures indicated air speed, most likely given in MPH for this vintage aircraft.

F: Artificial Horizon - Gyro instrument giving an indication of an artificial horizon; shows pitch and bank variations.

G: Amp and Volt Meter - Amps are indicated on the left, volts on the right.

H: Oil Pressure and Temperature Gauge - Oil pressure is indicated on the left, in PSI, and Temperature is indicated on the right, in °C.

I: Clock - Probably an "8-Day", spring driven, hand wound device.

J: Magneto Switch - Control for ignition systems. This control only shows three detents. There should probably be four detents: Off, L, R, and Both (L and R refer to Left and Right magnetos).

K: Directional Gyro with Inclinometer - The bottom part is the Inclinometer (ball), indicates coordination and skid or slip. The top part is the Directional Gyro. Note that in the real aircraft, K and A may have been switched.

The inscription reading "NR2100" is indeed the aircraft registration, typically used as part of the aircraft callsign.

The knob below A is likely used to set the gyro compass (K) that should be in that location.

The knob below F is likely to adjust the pitch indication on the artificial horizon (F).

The red knob between F and E is probably meant to be a knob to cage the artificial horizon (F) and should actually be placed in the location of the screw directly above and left of that red knob. See the Bee Gee Z panel I linked to below.

The knob between E and D is probably meant to be a larger knob that might be part of a pull control. I have no real idea of what it is, but my guesses would start with carb heat, primer, starter engagement pull knob. Could be many other possible functions.

Reference the photos in this album by Roger Ritter depicting a Bee Gee Model Z. I understand that it is not the same model that you are looking for, but the cockpit layout is very similar, and should be informative. His photos helped me confirm the identification of the gauges in the panel image you provided. Photo album linked only, due to image copyrights.


How does a jet engine handle suddenly entering a lot of rain? From my related question, it seems that an engine suddenly shut off would suffer from dangerous differential cooling from the airflow. This differential cooling would cause the engine to warp.

So now I'm wondering about a jet engine that suddenly enters rain. Wouldn't this initially cause severe differential cooling and thus warping, maybe even cracking? (P.S. would the same thing happen from entering a thick, dark cloud?)

How does the engine handle a huge amount of sudden rain ingestion? To me it seems like the sudden cooling on one side of the engine would cause thermal contraction, causing all sorts of problems.

EDIT: There seems to be a lot of comments about rain certification for engines and the fact that jets fly through rain all the time with no problem. I'm not questioning any of that. What I want to know is, how a jet engine handles the differential cooling caused by rain without warping or cracking?

In another question there is an excellent answer for how thermal expansion is handled in a jet engine.  It's an established fact that jet engines can handle fast temperature swings.  Have you watched how fast an ITT gauge goes up when starting an engine? My answer will focus on rain's effect on a jet engine.

The first thing to understand is that jet engines take a lot of air. That's why they can handle bizarrely heavy rainfall or even water on the runway splashing into the engine from the tires (this water jet has the fun name "rooster tails"). The Airbus 320, for example, goes through 27,000 liters of air every second during takeoff. 2 That means even during rigorous FAA certification testing the concentration of water ingested never gets higher than 20 g of water for every cubic meter of air.  See FAA Part 33.78 Appendix B

In order for you to understand why the water has little cooling effect I have to describe what happens when an engine takes in water, assuming you know the basic parts of a jet engine.  The air/water mixture enters the compressor, and the fan blades in this compressor are spinning rapidly enough to catch a lot of the water and like a centrifuge this water is spun towards the walls.  This helps prevent water from entering the combustion path on a bypass engine, but it does not prevent water from following the gas path, especially on an engine with no bypass around the gas path.

The engine must now adjust for the extra water in the air, and engines are very good at adjusting for these kinds of changes in conditions.  If there's more than one independent compressor rotor, for example, the rotor speeds will change to keep the air moving smoothly and ensure a correct pressure drop across the compressor, called "compressor rematching."  The engine will also increase the fuel to air ration to compensate for the water.  These two processes evaporate the extra water through thermodynamic heating, not through heat transfer.  In essence, the first stages of the engine are providing the extra energy to evaporate the water, so little differential cooling occurs, even if the amount of rain is rapid.

One thing to note here is that the engine actually runs hotter than normal instead of cooler than normal during these events, due to the reasons noted above as well as the extra thrust provided from the water injection.

All the parameter changes noted above reduce your margins for engine flame out and compressor stall.  In practice, an engine should flame-out or surge before water can cause a big enough thermal change to cause engine damage.  If you think about it, the amount of temperature change needed to cause a problematic warping of an engine should be a lot more than the amount required to cause the engine to quit running.

So we've established that jet engines are good at expanding and contracting due to thermal changes.  We've also established that relatively speaking we're actually not talking about a ton of water here, just a few grams per cubic meter of air, which would take a small percent of the engine power to evaporate (~1% by my calculations). Most of the extra water is evaporated not by cooling down engine parts, but by making the early stages of the engine work harder.  Finally, the reduced margins caused by water intake mean that you'll surge or flame-out before you get to warping engine parts.  These principles should apply regardless of whether the water ingestion begins in a matter of seconds or ramps up over several minutes.

In conclusion, in "Investigation of Engine Power Loss and Instability in Inclement Weather,"(pdf)  the FAA noted "Engines typically are not damaged during a heavy rain encounter. Usually the most severe situation is to experience multiple engine flameout or surge with a subsequent pilot initiated engine shutdown."  The report then went on to note that the two incidents where engine damage had occurred from rain were over-temperature events, not from differential cooling.  So your biggest worry when flying through even storm-of-the-century rainfall should not be whether your engine will warp from rain cooling things down.


Is it possible for more than one airplane intercept the ILS at the same time? I was watching a timelapse video yesterday of the approaches on a busy airport (I don't remember which one), and I saw that about 3 or 4 planes were lined up and descending at the same time (they were far from each other) and that got me thinking:

Is it possible (from a technical perspective) for more than one airplane to intercept the ILS signals (glideslope and localizer) at the same time?

Yes, since the ILS is just a set of radio signals emitted and received by aircraft, there can be more than one aircraft established on localizer and glidepath. The ILS does not lock or tune onto one single aircraft, it continuously broadcasts the localizer and glidepath signal.

Since the localizer and glidepath antennas are located at the end of runway for the localizer and at the side of the runway for the glidepath, you will only need to worry about interference by aircraft on the ground, where they are close to the antennas and can deflect the signal due to proximity. This is why there are protection areas and aircraft need to hold at certain holding points, e.g. CAT II holding points when CAT II approaches are in use.

Aircraft in the air can also interfere and deflect the signal, however the emitted signals spread in a cone, so other aircraft still can receive the correct signals.

To quote KeithS from one of the comments:

  [...] basically, the localizer is projected from the far end of the runway, and the glideslope is projected from the side of the runway at or near the touchdown target. Thus, aircraft in line to touch down on the ideal target will have good line-of-sight to both transmitter pairs (unless there's an aircraft in the ILS Critical Area)

(Image Source: www.aopa.org)

(Image Source: nustyR AirTeamImages (found via LondonReconnections))

(Image Source: When is an aircraft cleared to land?)


What is the purpose of having a robotic arm fly a Boeing 737? What is the aim of using a robotic arm instead of embedding the system on a plane? I read the 'Robotic Co-Pilot Autonomously Flies and Lands a Simulated Boeing 737' documentation but it didn't help me to understand.

The fundamental benefit is that the operator doesn't have to make a lot of adjustments on "legacy" airplanes, they can "simply" install the arm on the existing aircraft that they already have in service.

And this is the main selling point for such a device, they are not marketing it to operators that still have to buy or lease an airliner, but to those that already have one and might want to reduce the number of pilots they have to employ.

Gürkan Çetin notes in the comments that this device is not certified (yet). That's partially the point of such demonstrations, to convince authorities that it can be certified, and to incentivate operators to lobby for their approval.


Airfoil- concave top and bottom I remember building a radio controlled model in the early 90s with concave wing  ribs/surfaces top and bottom...both sides of the wing were undercambered...

It was a very great flying model...60" wingspan...and it flew as well as any other airfoil design...it was a testy build, covering the wing surfaces with monokote..other than that it was a fun craft...never understood how it flew so well by violating all the 'rules?'

It's because the "rules" people are traditionally taught about creation of lift, basically that a wing is a semi-venturi that is sucked up by venturi effect as it moves, is a gross oversimplification that overlooks most of what is going on, which is the wing motivating a large package of air to move down and creating a Newtonian action/reaction, of which the venturi effect is a part.

Anything that is more or less flat-ish, moved through the air at some angle, will make some amount of lift if it's able to induce some of the air to move from up here to down there as it passes.  The front door of your house, your hand stuck out the window of a car, or a wing with a weird reverse curve on top.  Enough to make an RC airplane fly at least.  Probably wouldn't work so well with a full size one.


Does the FAA restrict the color of pilot seat belts? In the US, is there a legal restriction to prevent the use of bright red pilot seat belts in GA aircraft?

No, there's no regulation on the color; the restraints just have to allow the crew to perform all their duties.

The old 23.785 regulation said:

  (e) The restraint system for each crewmember must allow the crewmember, when seated with the safety belt and shoulder harness fastened, to perform all functions necessary for flight operations.

The new 23.2535 regulation says even less:

  Safety and survival equipment, required by the operating rules of this chapter, must be reliable, readily accessible, easily identifiable, and clearly marked to identify its method of operation.

And empirically, there are many colors available. Googling will bring up plenty of images.


How does rudder size influence its ability to produce lateral lift? Does anyone know how the area, height and width of a rudder affect how well it provides lateral lift? I've heard that the most effective rudders are around 35% of the vertical stabiliser MAC but is there any maths to back this up?

The figure of 35% might be ideal for a rudder on GA aircraft with decent effectiveness and high enough control forces so a good control feel is achieved.

Generally, a rudder on a vertical tail is like a flap on a wing. It changes both camber and incidence of the vertical when deflected, thus helping the pilot to adjust the lateral lift force acting on the whole vertical. Therefore, the same formulas as those for flaps can be used for rudders.

A simple approximation for the amount of lift coefficient change per flap deflection angle $\eta$ is
$$c_{l\eta} = \sqrt{\lambda}\cdot\eta$$
where $\lambda$ is the relative chord of the flap and $\eta$ needs to be in radians.

Hermann Glauert derived a formula using potential flow theory that is sligthly more complex:
$$c_{l\eta} = c_{l\alpha}\cdot\frac{2}{\pi}\cdot\left(\sqrt{\lambda\cdot(1-\lambda)}+arcsin\sqrt{\lambda}\right)$$

I plotted both together with a correction of the Glauert formula using wind tunnel data above. It is remarkable how close the simple formula matches the experimental data already.

To be effective, the control forces on a rudder must not be too high, but also not too low in order to give good feedback to the pilot. For GA aircraft and gliders, a relative chord of 25 - 35% has been found to give the best combination. Control forces grow with the square of the relative chord of their control surface since both their area and the lever arm of the additional forces acting on them grow linearly with their relative chord.

In order to calculate the lateral lift change of the whole vertical, you need to know its lift curve slope $c_{l\alpha}$ which is affected by its aspect ratio and sweep angle, just like a wing is.


How is the emergency exit row handled when there are no passengers aboard eligible to sit in an exit row seat? Based on Roddy's question about nobody volunteering for the exit row, I can imagine a related but more extreme scenario: what if there are no passengers on the plane who are eligible for an exit row seat? (Say if you had a charter flight full of seniors.)  Do the exit rows simply remain empty in that case? How would the operator ensure that the overwing exits are usable in case they are needed?

In such an extreme case, the row would be unoccupied.

Nothing says that the row has to have people in it; I've had flights with under a dozen passengers, and if everybody had seats up front, the row would be empty, and that's okay.

You can't have unqualified people in the Emergency Exit row -- that's the limitation. Nothing requires the FA's the move qualified people into the row. That typically does happen (and as has been pointed out elsewhere, that row is often desirable due to legroom), but it's okay if the row remains empty.


Why is "Affirm / Negative" used instead of "Yes / No"? Does anyone know why we use Affirm and Negative in RT, rather than Yes and No? I assume it's to prevent confusion with accents and other languages - but Yes and No sound very different to me!

Why do we say "TANGO" on the radio for the letter "T"? Because "T" could get garbled or misunderstood to be "B", "E", "or "V". "NO" could become "oh?", "YES" could become "us", and so on...the possible interpretations and permutations of short, monosyllabic words are many. Use a big word and it will be hard to confuse with others...


Do I need a digital or analog scanner to listen to Air Traffic Control? I'd like to buy a scanner to listen to Air Traffic Control (e.g. Tower, Approach, etc.). It would be used mostly at either Washington National [DCA], Dulles [IAD], or Baltimore [BWI]. Would I need a digital or analog scanner to hear these transmissions? Thanks!

The voice communications for air traffic control is all analog (AM to be specific). A scanner that works in that frequency range on AM should be fine. Although a switch to digital has been considered, there is just too much coordination and investment required.

A good reference to find the right frequencies is AirNav. It will list all the frequencies for an airport.

Another good reference for many frequencies, not just airports, is RadioReference. The database there will tell you exactly how each channel is transmitted, so you know what type of radio you will need to listen to it.

Also keep in mind that ATC transmissions are line-of-sight, so you will have to be close to a ground station to hear it. The "rubber duck" antenna included with a lot of scanners is fine but a better antenna will help to improve reception. Also, military aircraft use a higher frequency range, and a lot of cheaper scanners will not receive this.


How can I get a license to fly an F14? Say I have $x million to buy an F-14 Tomcat and am physically fit (I think) to be able to fly it. Is there a short pilot training course I can attend to get licensed to fly it?

Anybody with the resources and connections to buy an F-14 could probably find a former Navy CFI to get them up to speed.  Otherwise no, there is no existing course you can simply attend.  There just isn't enough demand to run such a business.


Are there any reported cases of noise from helicopters causing damage to property? In the Netherlands, three cases have been reported of Chinook helicopters' rattle noise (low frequency sound) damaging solar panels. The Dutch defense ministry recognises this problem and the lawyer representing some of the victims says these may be the first cases (worldwide). Source (in Dutch)

I'm wondering if there are any more of such cases (possibly involving damage to property different than solar panels or involving different helicopters). I found the following literature study on rattle noise (in Dutch, sources mostly in English). The study states that damage to buildings is possible according to laboratory tests, however, as far as I can see it does not name any real world examples of such damage.

My question is if anyone knows of any such damage (different from this report in the Netherlands) to (civilian) property caused by rattle noise from helicopters.

The article states that it's not even clear the damage was caused by the helicopters, that there is no other known incidence of such damage being caused by helicopters, and that a scientific study has shown that while in theory there could be damage such has not actually been shown to be caused.

In other words, it looks suspiciously like a group of people who want the helicopters gone from a nearby airbase lawyering up with some spurious and dubious claim for which there is no evidence whatsoever, hoping to win public opinion and probably environmentalists rather than having an actual legal case at all.

This is not unheard of in the Netherlands (and elsewhere).

So in short: the article in BN de Stem answers your question already: there is no known instance of such damage happening, and even in this case it's mere speculation that it's happened at all.


Where to relocate a bomb on a plane to minimize damage? In a video blog I saw today on the net, an airline Captain said: "if a bomb is found on board in-flight, pilots are trained to relocate it someplace where it would do the least damage" without further details as to what place standard operating procedures suggest in this case.

Where should the pilot put the bomb to have the best chances of limiting the detonation damage and rescuing the plane ?

We covered that stuff during recurrent training and for the CRJ Regional Jets we were told to place it in the forward galley in front of the service door (opposite the main door) and cover with with as much weighty stuff as possible, wet blankets, heavy coats, and such.

You had the mass of the galley to protect the flight deck to some degree, and in theory the explosion would blow out the service door, hopefully leaving the structural frame surround intact, so that overall, it would have the least impact structurally for the fuselage as a load bearing tube with the peak stress just ahead and behind the wings.

In theory... nobody actually believed it would save the plane unless it was fairly small device, but as a calculated strategy to make the best of a hopeless situation, it made sense.

Don't know about other jets, but I would expect that the overall logic is similar.


Unmanned Drone vs Conventional Manned Fighter in Combat: How realistic? How far are we / Is it even viable to think of a scenario where a drone gets employed to counter a conventional manned fighter?

I can see several benefits:

Free of the G-restrictions of a human the drone is free to undergo far more severe manouveres
Cheaper testing costs since a drone crash isn't as expensive / as unpalatable as the death of a test pilot
More risk appetite during actual combat since a human life is not at stake
The removal of the cockpit and life support / protective systems (e.g. No O2 tanks / No pressurization / No ejector seats) leading to a weight reduction, performance improvement and design flexibility. Perhaps allowing greater munitions loads etc.
The possibility of undertaking some version of suicidal yet mutually destructive manouveres that are out of question in conventional dogfights.

On the other hand, several limitations I can think of:

Poorer field of vision & situational awareness of a remote drone operator operating via cameras and sensors
The lag between control and reaction inherent to today's drone remote operator systems. Though how much of this could be improved via better technology is a crucial question. The current generation seems to use Ku band satellite signals. Could some form of ground network (but beyond enemy reach) provide more responsive controls? How close have we approached the fundamental physics latency limits even with existing satellite transmission technology.

As a totally different alternative, is the possibility of an unmanned, autonomous drone realistic? How far are we on the AI / sensors side where a autonomous decision engine can realistically be a good match for a human adversary in a dogfight. The autonomous option would make the control lag issue redundant.  (Redacted to focus the question on manned drones)

We're nowhere near good enough with our AI for a computer simulant to best a human pilot in a dogfight unless the odds are further stacked against the human (computer flies a superior aircraft, computer has enhanced knowledge of "reality", computer has advantage in numbers, computer ignores physical limitations of plane or pilot without consequence). Most computer pilot AIs in combat sims are some combination of the very simplistic "locate your opponent, put your lift vector on him and pull up hard" and the more complex "human is doing this, so the best counter-move is this". There's also no small amount of "I am a game, the purpose of my existence is to be enjoyable for the human, so while I must present a challenge, I must not require my human to attend a year of combat flight school before he stands a chance".
These are the basics of ACM taught to every fighter pilot, however these strategies will get you shot down against a competent human pilot every time, for two reasons:

"Line up and pull up" tends to settle you into a horizontal "one-circle" turning fight to conserve energy. In that fight, the first pilot to realize it's happening and pull vertical can tighten the turning radius by trading speed for altitude, getting inside and cutting across his opponent's turning circle for a good if somewhat high-offset firing chance. If the opponent sticks with "line up and pull up" he will do just the opposite, trading altitude for speed, increasing his turning radius and putting his tailpipe in front of his opponent's nose.

Moves and countermoves in air combat are a fluid dance that computers are plain bad at. Computers can beat humans in chess because the number of valid moves is fairly low, so the computer can calculate the most advantageous chain of several dozen moves quickly. However, computers are relatively bad at Go, because both the total game tree complexity and the available moves on each player-turn are massive.
Air combat is similar; while there are a few basic strategies, there are infinite possibilities, and because air combat, though "turn-based", involves a different kind of "turn" from those in chess or Go, the computer doesn't get to sit there and think about its move for several seconds; it has to make the best move it can think of in a fraction of a second or else the human will get to make several "moves" before the computer reacts to the first one, and the way computers think, making it decide quickly usually boils down either to simplifying the decision-making or deciding in a random way.

Prioritization is still an area where computer AI is weak. Against one opponent, where your objective is to shoot that opponent down, a computer could do quite well. Facing the primary mission objective of completing a bombing run, with potentially hundreds of aircraft in the sky and thousands of military (and civilian) ground vehicles and people in a combat theater, making the decision of what object deserves your primary attention any given second is something even human pilots don't always do well. Most AIs in combat sims are fairly scripted; either the purpose of an enemy's existence is to shoot down the player, or it focuses on its mission until it cannot ignore the player. Real combat is somewhere in between, especially when your mission is something like CAS or BARCAP where your job isn't one fixed point on the ground or one plane in the air.

Now, computers have some advantages that are considered "cheating" in combat sims but would apply to an unmanned fighter against a manned one. First is the ability to sustain maneuvers in excess of a human's G-limit. As long as the airframe can handle it, the computer can pull 12g turns, or -12g, whatever. Second is that the weight of a human, plus the "man-machine interface" of the cockpit systems, is greater than the mass of a computer directly connected to the instrumentation. The computer is also much faster at working with the aircraft's systems than a human could ever be, so a computer pilot, within a couple seconds of seeing a "blip" on the radar, could have the target locked up, while a human, given the same blip at the same time, would still be slewing tracking gates in the B-scope.
A third big advantage is 720* visibility. Humans have about a 170* "cone" of visual response, and a fairly poor 5-10* window of actual focus and acuity. With an unmanned craft, we can install cameras covering virtually 360* around the aircraft in the horizontal and vertical, and have the computer monitor and track objects within the full field of vision, as well as in IR or other non-visible light spectrums, much more efficiently than a human could do the same with the same camera systems.
Therefore, the first fully unmanned combat aircraft is very unlikely to look or work like a manned one, because its designers will have done things that would be bad decisions in a manned craft, but will give the computer a maneuverability, speed or visibility advantage that could compensate for more simplistic decision-making of the AI.


Are 'human factor' specialists consulted during the UX design of cockpit controls and avionics? I have always been struck by the complexity of cockpit controls. Aviation specialists are always on the hunt for ways to reduce cognitive overload on pilots to reduce human error.

That being said, air crash investigations have proven in a number of incidents that labelling, controls interactivity, affordances and other interface design issues impact on how pilots operate.

So, I have few questions:

How do human factor specialists and user experience designers differ (or not) when it comes to designing for avionics?
If user experience design skills are so different from human factor skills, wouldn't they be required when designing avionics?
If they are not so different has anyone came across a situation where user experience skills were utilised within the aviation industry?

My thesis, which I wrote so long ago that I no longer recall the title, was a complete redesign of the Boeing 747 cockpit from a human factors and usability point of view.

My designs, which were submitted to Boeing at the time, likely helped create the foundation for the modern glass fly-by-wire cockpit.

At the time, glass cockpits did not exist (the term refers to the glass in the CRT monitors that were eventually used within the cockpit, later replaced by LCD displays).  Fly-by-wire, which is the concept of replacing conventional flight controls with an electronic interface, was in its infancy.

I remember working tirelessly to create a comprehensive new human interface for pilots that would minimize errors and improve safety.

My research was based in the cognitive sciences, which consisted of university coursework in human physiology, neuroanatomy (rudimentary at the time), psychology, statistics, engineering, computer science, mathematics, linguistics, neural networks (the very first ones), and artificial intelligence.  It was a rigorous and diverse education.

I spent hours and hours watching films of pilots performing a vast array of different procedures.  Sometimes they were successful, and sometimes they were not.  When they were not, it often resulted in serious consequences.  I spent long nights listening to hour after hour of dialog between air traffic controllers and pilots.  I studied detailed accident and near-accident reports.  I also interviewed pilots and spent a fair amount of time inside commercial cockpits, between flights, gathering essential data.

One of the challenges that I vividly recall was reducing complexity for pilots, while keeping the tasks difficult enough so they would stay engaged to their tasks and not fall asleep or become distracted.

The most rewarding part of developing my thesis was converting the cockpit from what I called a control-based center to a task-based center.  Up until that time, most controls available to pilots were designed to directly impact a flight control surface such as the rudder.  There were some rudimentary "intelligent" controls to perform basic horizontal and vertical navigation (but nothing that integrated the two!).

I designed a new system that was based on high level tasks that the pilot would need to perform.  No longer were ailerons, elevators, flaps, and thrust the focus.  Instead, I changed the focus of the cockpit to center on essential tasks such as taking off, landing, route planning, communications, and traffic and weather avoidance.

During this work, I learned that I had to seamlessly integrate my human factors engineering and user experience design skills.  In my opinion, and from my personal experience, they always need to be.

Whenever I fly, I ask to take a look at the cockpit after we land.  It's a joy to see the evolution of my designs.  Whether I was the originator of these designs or one of many human factors engineers who came up with them at the same time, I will never know.  But similarities of the current designs to what I proposed in my thesis many years ago gives me a little insight into a possible answer to that question.


What is missing from a non-afterburning engine to prohibit the use of afterburning? What components are missing in a non-afterburning engine that an afterburning engine does, so that it can't use afterburning?

The afterburner, of course.

In simplest sense, the afterburner is just an extension attached to the engine where the fuel is dumped into the exhaust, resulting in an inefficient but huge increase in thrust.

Turbojet with and without afterburner; image from aerospaceweb.org

In the above image, you can see the basic schematic of the afterburner- it basically consists of a long tube placed in between the turbine and the nozzle in which additional fuel is added and burned. The (afterburner) tube is quite simple, consisting of mechanisms to spray fuel into the exhaust and ignite it.

This image shows an actual afterburner, from the F/A -18 (F404 engine). As you can see, its quite simple.

... sailor Ryan Draper ... inspects an F/A-18 afterburner in the jet shop aboard the Nimitz-class aircraft carrier USS George Washington (CVN 73). Image from gizmodo.com


How are redundant twin engines coupled on a helicopter? I understand that a Eurocopter EC135 can fly on only 1 engine.

In this instance, is the dead engine power turbine still coupled to the rotor? Does it freewheel? Is there a clutch to disengage it? If not, does the power turbine draw air through the dead engine?

Multiple-engine configurations use multiple freewheeling units that couple the rotor with the engine and allow the first to revolve faster than the latter but not the other way around. If just one of the engines fails, the freewheeling unit for that particular engine will effectively disengage the engine from the rotor (as the rotor is now revolving faster than the failing engine), allowing the other engine(s) to drive it.

How a freewheeling unit functions on a mechanical level is described on page 6 of this document.


In which countries can I fly an FAA compliant Part 103 ultralight? İf I have a legal part 103 ultralight as defined by the FAA, in which countries may I fly this ultralight in the world in addition to the USA?

Although the formula for compliance is somewhat different, in general you can fly an ultralight that is compliant with FAR 103 in Canada as a Basic Ultralight.  The major difference is it has to be registered (not certified in any way, just registered with call letters), and you need an Ultralight Pilot Permit to fly it.


Is there a way to calculate thrust without running experiments? Is there any way to calculate the thrust generated without conducting experiments? In my case I need to figure out thrust generated by electric duct fans and/or turbojets.

For the case of an electric motor driving a propeller, you can get a rough approximation for the thrust t from the power p consumed by the motor when the plane is flying with a constant velocity v, since $p = t \times v$. Of course, you should use coherent units, as newtons, m/s and watts, and include a large correction factor, as the real efficiency will be very far from 100%...

For the stationary case, in Wikipedia (entry 'disk loading') you can find an expression for the stationary case, derived from momentum considerations.


Why does the Eurofighter Typhoon pitch up on brake release? In the video here of an airshow take-off, it's noticeable that when the brakes are released there's a brief but pronounced fluctuation in pitch as the aircraft accelerates.

This is something you see in very fast accelerating cars / dragsters, but I believe that is caused by the torque through the rear wheels, which is obviously not the cause here.

The same thing can be seen on an F-16 but much less pronounced.

Certainly for the Typhoon, the nose-wheel oleo doesn't seem to be particularly compressed as it's held under braking. I'd guess that you want to ensure that there's no chance even the slightest bit of any upward vector in the engine thrust while you sit on the tarmac, otherwise your brakes might not work, but that doesn't really explain the wobbling.

 source

When the brakes are on, they apply a backwards force that counters the engine thrust. This force is applied at ground level, and the engine thrust is higher. These two forces result in a moment that forces the nose down, compressing the nose gear slightly.

When the brakes are released, the moment disappears and the nose gear extends.

Another factor here is that the Eurofighter (and F-16) has its air-intake under the fuselage, which forces the designer to put the nose gear behind the intake, closer to the main wheels than other aircraft. That means the nose gear has a shorter lever-arm to resist pitching. It's set up with the same spring rates and damping because it's primary job is to react to bumps in the ground, so it's more sensitive to pitching.


In the compressor characteristic, what does this value represent? $$ ? = \frac{m_t* \sqrt{T_3}}{P_3}$$

All I know is that it is a material property of a turbine, it has something to do with the mach number, and is used for calculating $W_T$. It's kinda similar to the corrected mass flow rate but I guess I'm wrong.

I don't have any books on aerodynamics and I feel kinda lost...

In German it is called "Ähnlichkeitsparameter", a comparison parameter for the compressor state. This one in particular is a non-dimensional mass flow comparison parameter. To be more correct your equation is actually missing the gas constant "R" under the square root (together with temperature) to make it non-dimensional. This non-dimensional mass flow factor makes it possible to compare different scenarios like high altitude and high speed at low temperatures as well as low speed, sea level conditions. Just like we do with the lift coefficient on wings.

It's not a material property of any particular engine or compressor, just an operating point with a dimensional mass flow m (kg/s), T3 being the total pressure (K) at station 3, P3 being the total pressure at station 3 (Pa) at that time. Station 3 is entry into combustion chamber.

This factor usually comes up in compressor maps (in German "Verdichterkennfeld"), where you plot the compression ratio (pi) on the y-axis over this mass flow parameter on the x-axis. These maps can tell you how much the compressor can compress the air without stalling.

https://en.wikipedia.org/wiki/Compressor_map


Can a pilot use ILS when cleared for a visual approach? When cleared for a visual approach, do airline pilots still use the localiser/glideslope or GPS or even the autopilot, or is it strictly a "visual" approach?

Yes, the localiser, ILS glideslope, and/or GPS-generated glidepath are still used as a reference during the visual approach. Sometimes the visual glideslope indicators (like VASI or PAPI) are either inoperative or not available. (Interestingly, the visual indicators and instrument-generated glidepaths are sometimes not coincident.)

Pilots sometimes choose to leave the autopilot engaged during such an approach. Some Charted Visual Flight Procedures (like the FMS Bridge Visual 28R at SFO) lend themselves to leaving the autopilot engaged for almost the entire approach. In addition, some operators may stipulate that autopilot use is mandatory.


What's the shape and place of the tip vortex in a propeller, depending on propeller sense of turning? If the propeller vortex is placed and has changing features depending on the propeller sense of turning, both in traction and pusher configuration, knowing about this may have an interest for the design of multi-propeller airplanes.

I too am unsure exactly what your question is but propeller blades shed vortices at the tips just like wings and rotor blades. This vortices and their paths can be seen when the weather conditions are right as in this photograph. (I don't own this image)

You can find many more of these types of images with a quick google search. The vortices roughly follow the advance ratio of the propeller at the moment they form. There would be little difference to the formation of vortices for push or pull configuration.


Are there any preventive measures against bird strikes while in flight? Most of the preventive measures for bird strikes are at/around the airport but what are some of the ways that can be used to prevent bird strikes on the plane as it is climbing or in flight?

Airports engage in a number of strategies to reduce the number of birds nearby that might cause strikes. This has been addressed in a previous question: What are the ways to keep the birds away from airfields?

Avian Radar also exists:

  Avian radar[44] is an important tool for aiding in bird strike mitigation as part of overall safety management systems at civilian and military airfields. Properly designed and equipped avian radars can track thousands of birds simultaneously in real-time, night and day, through 360° of coverage, out to ranges of 10 km and beyond for flocks, updating every target's position (longitude, latitude, altitude), speed, heading, and size every 2–3 seconds. Data from these systems can be used to generate information products ranging from real-time threat alerts to historical analyses of bird activity patterns in both time and space.

https://en.wikipedia.org/wiki/Bird_strike#Flight_path

  Installations include civil applications at New York/John F Kennedy International Airport, Chicago/O'Hare International Airport and Seattle-Tacoma although the majority of both deployment and development activity is still focussed (sic) on military air movements.

https://www.skybrary.aero/index.php/Detection_of_Bird_Activity_Using_Radar

  MERLIN Avian Radar System technology...is used...to detect and monitor hazardous bird activity on and around airfields for bird-aircraft strike hazard management.

https://detect-inc.com/bird-control-radar-systems/


Do cockpit panels have an indication that oxygen masks in cabin have been deployed? Do cockpit panels have an indication that oxygen masks in cabin have been deployed for Pilot information?

Yes, there is an indicator for passenger oxygen status.

(Image Source: www.b737.org.uk)


What performance issues/symptoms can a pilot expect while taking off above MTOW? Lately I've been flying a Cessna 162 Skycatcher, primary as a cheap way to build time towards the Instrument Cross Country requirement and my glider club's hours requirement to tow gliders.

One issue with the 162 is it's relatively low Useful Load.  Here are some figures relevant to my question:

Maximum Takeoff Weight: 1324
Equipped Empty Weight: 857
Useful Load: 467
Weight of full fuel: 24*6 = 144
Weight of 3/4 fuel: 18*6 = 108
My Weight: 215
Max Weight of passenger full fuel: 108.24
Max Weight of passenger 3/4 fuel: 144.24

Note: All Weights above are in pounds(lbs).

Because weight is an issue with this plane and almost any passenger I would consider bringing along, there is a diagram in the FBO's flight book that can be shown to the person fueling that depicts points inside the tanks that denote full, 3/4, 1/2, etc:

Last week, I did a flight with a 130 pound passenger.  On the first refueling I was sure to show this diagram to the person filling to ensure he only filled to 3/4.  I generally make it a habit to inspect the tanks after fueling to ensure they have not gone over the asked for amount.  Takeoff was normal with no noticeable degradation in performance.  Note: the fuel gauges in the 162 tend to show the same value whether the tanks are full or 3/4 full, with no noticeable decrease until until values go below 3/4.

We then proceeded to fly roughly 1.5 hours to another airport.  At that airport, I went through the same routine but (in a hurry of course, isn't that how most mistakes are made!) I did not follow up to ensure he had not "overfilled" the tanks.  On takeoff, I noted a notable (though by no means catastrophic) degradation in performance:

I needed more runway to rotate.
I could not climb above 55kts (Vx/Vy in the 162 are 57/62).

As I was able to climb at a safe enough airspeed, things seemed to stabilize and I had no other issues, I chose to proceed with the return flight.  Performance for the rest of the flight was fine with no extra RPM needed to cruise or do later climbs.

It wasn't until I was thinking about it later that it occurred to me that the refueler might have filled my tanks to full.

So my question is, do these symptoms sound indicative of being overweight?  Or, more generally,
What performance issues can a pilot expect while taking off above MTOW?

Note: I have reviewed several questions related to this, including:

Can a commercial airliner be too heavy to take off?
Does weight and balance of an airplane matter more on takeoff?
Questions tagged with weight-and-balance

However, I didn't find a question dealing specifically with the performance degradation felt by a pilot taking off above MTOW.

Update

After thinking on this a bit more, reading some of the answers and talking it over with my daughter (the passenger mentioned and a pilot in her own right), I'm leaning towards a different conclusion.  Since I was first checked out in the 162 last winter, this was the first time I'd had a passenger.  My first takeoff was from KJYO (5500 feet runway length / 390 ft elevation), whereas my second was from Eagles Nest (W13) (2004 ft runway length / 1436 ft elevation).  My new theory is that what I felt on the second takeoff was the added weight I wasn't used to since I've flown the previous 20+ flights alone.  I believe I didn't notice this as much on my first takeoff because I had much more runway to work with.

Nonetheless, I think the question and answers are still relevant/useful.

Firstly, you did goof up by not checking what the refueler did. Your life depends on that fuel, and in light aircraft the gauges are notoriously unreliable. We've probably all done it but we shouldn't - always check!

However going off your figures you might have been what, 20 pounds overweight? That shouldn't cause such a massive decrease in performance. MTOW isn't an on/off switch. It's a point that has been selected as the maximum allowable limit - with a safety margin built in. You should never exceed MTOW even by a bit, but if you do you will (hopefully) live to see your kids birthday thanks to that margin.

I've flown a C172 right at MTOW (actually about 5kg under but close enough). Acceleration is slow, meaning you use more runway. Rotation actually feels normal thanks to ground effect, but once you leave that you notice a degraded climb performance. If you're over MTOW these effects are the same but amplified. If you are very overweight, you will climb in ground effect but will struggle to go much higher than 20-30ft.

As for your flight though, it could have been affected by a tailwind or high temperature/low atmospheric pressure. What was the temperature like on the second leg? Vy will theoretically get you the best climb rate even above MTOW so it doesn't make sense that you could climb below but not at that speed. Maybe there was something localised affecting the ASI, or, if I may be so bold, your technique on the day wasn't 100% :)


Is there a standard format to exchange airspace information in electronic form? I am looking for information about airspace definitions.

On maps they look great and a pilot has no problem reading maps and NOTAMs, but what about autopilots? Do they use some kind of standardized interface/database? If it exists, where is it defined?

I am not specifying a country because hopefully there only one standard (or an extremely limited set). Should this not be true, I would like to focus on Europe and North America.

The majority of GPS navigators and FMS have a dataloadable navigation database.  The actual database each uses is typically encrypted and compressed using proprietary algorithms.  The source data for all of these databases normally start out in ARINC 424 format.  Unfortunately, A424 is not available free of charge.

  ARINC 424 is an international standard file format for aircraft navigation data maintained by Airlines Electronic Engineering Committee and published by Aeronautical Radio, Inc.. The ARINC 424 specifications are not a database, but a "standard for the preparation and transmission of data for assembly of airborne navigation system data bases".

The databases are compiled by companies such as Jeppesen. Jeppesen collects the data from the controlling agencies around the world, checks it, and merges it into a world-wide database that they then sell (typically via subscription).

Some information for US airspace is available directly from the FAA.  It is not in a format that can be directly loaded onto aircraft, but may be of use offline.


How does bank angle differ from roll angle with respect to stability in fixed-wing aircraft? I would like a clarification on bank angle and how its different from roll angle with respect to to fixed wing aircraft. It is my understanding that the bank angle is a result of rotating the aircraft body to the stability frame, implying that if the angle of attack $\alpha$ and the side slip angle $\beta$ are zero then, and only then the bank and angle and roll angle are the same. Based on Stevens and Lewis Aircraft Control and Simulation (which doesn't define bank angle) the rotation from body to stability(wind) frame is given by
$$
C_{w-b} = \begin{bmatrix} &\cos\alpha \cos\beta & \sin\beta & \sin\alpha cos\beta \\ &-\cos\alpha\sin\beta & \cos\beta & -\sin\alpha\sin\beta\\ &-\sin\alpha & 0 & \cos\alpha  \end{bmatrix}
$$

Therefore, the bank angle $\mu$ I think is given by:
$$\mu \triangleq \begin{bmatrix} &\cos\alpha \cos\beta & \sin\beta & \sin\alpha \cos\beta \end{bmatrix} \begin{bmatrix} \phi \\ \theta \\ \psi\end{bmatrix} $$

where $\phi,\, \theta,\, \psi$ are standard aerospace Euler angles defined based on a 3-2-1 rotation.
My specific questions are:

1) is my understanding and calculation of bank angle correct? If not can someone point me to a good resource for this. I was surprised to be able to find a clear definition and formula quickly.

2) by multiplying the second and third row of $C_{w-b}$ with Euler angles we obtain a set of other two angles relative to stability frame. Do these angles have any names or specific role in aerospace dynamics/control?

In my experience, "bank angle" and "roll angle" mean exactly the same thing. I've only ever heard of one meaning of either term.

For completeness, here are some "plain English" definitions of all three Euler angles:

Pitch is the angle that the nose (the longitudinal axis) forms with the horizon. If the nose is pointed at the horizon, the pitch is 0°; if it's pointed straight up, the pitch is 90°; and if it's pointed straight down, the pitch is -90°.

Heading (sometimes called "yaw angle") is the horizontal direction that the nose is pointing, measured clockwise from true north.

Bank angle (sometimes called "roll angle") is the amount that the aircraft would have to roll (rotate around its longitudinal axis) in order to bring the wings level (which is to say, bring the lateral axis parallel with the horizon), with the top side of the aircraft facing above rather than below the horizon.

Pitch ranges from -90 to 90. The other two angles have a range consisting of a full circle; I think bank is usually expressed as a number from -180 to 180, and heading as a number from 0 to 360.


At what angle of deflections do rudders become inefficient? This article (picture) says rudders for ships can deflect 35° max,so at what aoa does an airplane rudder lose its efficiency,at what " angle of deflection " does it start to stall ?

The only time you should be using full rudder is when doing a side slip - such as turning the yoke for a left turn but pressing right rudder, so you are descending and looking to your left as the plane goes forward tracking down the runway direction.  Normal coordinated turns, you would not use anywhere near that much rudder while turning.

I just found a NASA Test Report on my plane, a Cessna Cardinal, that lists control deflection amounts as a reference for a light general aviation airplane:

Angle of attack,           -4° - +20° ± 0.5°

Sideslip,                 -15° - +15° ± 0.5°

Pitch angle,              -15° - +15° ± 0.5°

Roll angle,               -75° - +75° ± 0.5°

Rudder deflection,        -24° - +24° ± 0.5°

Stabilator deflection,    -20° - + 5° ± 0.5°

Right aileron deflection, -20° - +20° ± 0.5°

Left aileron deflection,  -20° - +20° ± 0.5°


What kind of airplane is this that has blue cheatlines and a protruding side cover? Consider:

Which airplane is this? I suspect it is Russian, but it's too poor quality for me to tell. I'm pretty sure it is military.

Below is the full photo, it's an Ilyushin Il-22PP Porubshchik electronic warfare plane.

  The Il-22PP Porubschik was designed in late 2000s on the basis of the Soviet Il-18 passenger aircraft made in mid 1970s. According to media reports, the aircraft is capable to disable most modern electronic warfare systems installed on foreign planes, air defense systems, as well as unmanned aerial vehicles.

Image and article: https://www.ruaviation.com/news/2017/3/31/8382/


How does the engine wash improve engine performance? According to maintenance manual, we usually carry out engine wash (CFM56) with pure water as scheduled task. Pure water is injected into the engine from the LP compressor inlet while the engine is cranked.

I wonder if the engine performance would improve significantly after having a wash.
What is cleaned from the engine gas path? is it carbon residue or something else.

As it is said that the water should be injected at 1 o'clock position on the LPC (aft view), why does it need to be at that specific position? does it clean certain components at that position?
Thanks for your explanation.

A performance increase after a compressor wash is expected to happen, but it does not return to the original performance as there are more degradation mechanisms at play. This answer explains that organic build-up causes a change in airfoil shape causing the recoverable performance degradation. Another source may be deposition of salts and dissolved constituents to deposit on the blades as a result of ingesting salt water from which the water evaporates in the hotter stages of the compressor. E.g. erosion is a non-recoverable degradation (for a compressor wash). This is clearly shown in the figure below.

From: Modern Gas Turbine Systems, High Efficiency, Low Emission, Fuel Flexible Power Generation, Woodhead Publishing Series in Energy

  I wonder if the engine performance would improve significantly after having a wash.

The performance increase is considered significant enough, else we would not go through all the trouble of performing the procedure. Fuel costs is one of the major direct operating costs, reducing fuel costs by washing the engine doesn't only save money, it also reduces the amount of used fuel (nice green image for the airline).

  As it is said that the water should be injected at 1 o'clock position on the LPC (aft view), why does it need to be at that specific position?

This could be done to prevent build-up of water in the lower section; now it has to travel half the engine down, by the time it reaches that location the water will be transported aft by the churning blades. The water is therefore better distributed, which is confirmed by this practical answer.


Is it possible to suffer barotrauma during decompression? Barotrauma is damage of lungs by air overpressure and may occur at overpressure as low as 30 kPa (4 psi). Overpressure in most aircraft is about double that value. So is it possible to suffer barotrauma when rapid1 decompression occurs? In an airliner or only in small airplane? And did it happen?

1If the decompression is explosive and the aircraft falls apart almost certainly, but it does not matter as all occupants will be dead either way. Only consider the case when the aircraft remains controllable.

Briefly: yes, it's possible (but very unlikely); small pressurized aircraft are the more likely scenario; maybe it has happened but if so it's very rare.
According to the FAA's AC on Aircraft Operations at Altitudes
Above 25,000 Feet Mean Sea Level or Mach
Numbers Greater Than .75 it's possible and more likely to happen in a smaller pressurized aircraft:

(a) Explosive Decompression. A change in cabin pressure faster than
the lungs can  decompress. Most authorities consider any decompression
that occurs in less than 0.5 seconds as  explosive and potentially
dangerous. This type of decompression is more likely to occur in small
volume pressurized aircraft than in large pressurized aircraft and
often results in lung damage. [...]
(b) Rapid
Decompression. A change in cabin pressure where the lungs can
decompress faster than the cabin. The risk of lung damage is significantly lower in this decompression compared to an explosive decompression.

Unfortunately they don't cite any statistics or source for the statement "often results in lung damage" so it isn't clear when it has actually happened. Other sources suggest that it's very rare, for example Beyond the Black Box: The Forensics of Airplane Crashes says this:

The Air Force reports no serious injuries resulting from rapid
decompression with open airways, even while wearing an oxygen mask.
However, disastrous, even fatal consequences can result if the breath
is forcibly held with the lungs full of air. [...]
Lung damage is considered nearly impossible in a commercial aircraft
because of the large volume of air inside the plane. [...] Even Aloha
Flight 243 [...] did not decompress fast enough to cause internal
injuries.

In other words, it's not going to happen unless you hold your breath, but another source says that you won't be able to do that anyway:

I've had pilots tell me they would be able to hold their breath [in order to extend the time of useful consciousness]. That won't happen. First of all, the surprise of
the event will override any defensive measure you may have thought you
could put into place. Secondly, the rapid change in pressure
differential will make it impossible to hold your breath. (Remember,
we can be talking about a pressure differential of 8.8 PSI. Let's put
these pressure differentials into perspective. A differential of 8.8
PSI is 1267 pounds per square foot.

I think the surprise is a key point here: the flight or fight response increases your breathing rate so even if it were physically possible to hold your breath it's extremely unlikely that you would do so.
Interestingly, Google finds numerous sources that claim lung injuries are commonly caused by aircraft decompression, but I couldn't find any source that mentioned a specific incident or even any statistics on it. I did find one book that studied 47 incidents of aircraft decompression but there was only one single barotrauma event among them and it affected the ears, not the lungs.


Could a commercial plane seat configuration look like a troop carrier? I wonder whether Michael O'Leary has already seen that. I am pretty sure he would be eager to implement the idea. However, is that feasible - both from a legal, and as a security policy - for commercial planes transporting civilians? Maybe military personnel can be trusted to evacuate the plane faster than average civilians in case of emergency.

Source: dailymail.co.uk

Legally, you would need to find a seat that passed the FAA's 16 G "side facing" requirements. The AC that covers the 16G rule has some text that may be of interest on this matter. The FAA admits that its an ongoing area of research and that currently special tests need to be undertaken to certify one. (bolded for emphasis)

  d. Side-facing Seats.

  (1) General. All seats occupiable for takeoff and landing are subject
  to the specified dynamic test conditions. Included are side-facing
  seats and both single occupancy and multiple place seats, such as
  divans. Compliance with the structural requirements should be
  demonstrated for side-facing seats, using the same conditions for the
  test and pass/fail criteria as for fore- and aft-facing seats. The
  seat should be loaded in the most critical case structurally. Means of
  restraining the ATDs may need to be adapted to ensure adequate
  retention during the test. The application of floor distortion will
  need to be assessed on an individual basis, depending on the design of
  the fixation of the seat. The injury criteria of § 25.562 are not
  adequate to demonstrate equivalent safety of side-facing seats when
  compared to fore- and aft-facing seats. To demonstrate equivalent
  safety fully in the absence of such specified criteria, the applicant
  must use other injury criteria which may be derived from the
  automotive industry, which uses side-impact ATDs.

  (2) Assessment
  criteria. Research into side-facing seats is ongoing. As research
  proceeds, the FAA will work toward establishing a more definitive
  policy with respect to the acceptance of side-facing seats. Until
  then, in the absence of specific compliance guidance, the FAA is
  prepared to assess side-facing seats on the following basis:

  (a) The
  seat must demonstrate compliance with the structural requirement.

  (b)
  If an acceptable side impact ATD has not been used with assessment of
  the corresponding injury criteria, it must be shown that the occupants
  are restrained in a manner that prevents substantial energy absorption
  by body to body contact (on a multiple occupancy seat) and which,
  using the best available engineering judgment, minimizes injury to the
  occupant(s).

The way this reads in short (at least to me) is that the FAA does not really test side facing seats all that often but they are willing to if an appropriate means of testing is devised, you can prove that people smashing into each other wont cause any serious problems and that your seats will be ok when a shock wave passes through the floor (same as the forward/aft facing seats).

The FAA also has an extra supplement for potential injury from side seat configurations thats worth taking a read through "Supplemental Injury Risk Considerations for Aircraft Side-Facing Seat Certification"

On the evacuation note the FAA does not really care what the seat orientation is in terms of evacuation. If you are talking about converting a modern airframe you likely could not place a seat in front of the over wing exits but other than that so long as you comply with the evacuation time limits you will be good to go (from a strictly certification stand point). Since this configuration still has rows similar to that of a normal airliner I dont see why you would not be able to properly demonstrate evacuation capacity in this configuration.

The biggest issue I see here is a lot of toes getting run over, and knees bashed by a galley carts...


Is it possible to have two different makes of engine on a single twin-engine aircraft? Is it possible to have to have two different makes of engines which are generating almost similar thrust for a twin-engine aircraft?

Yes it is possible.

For example :

  A Boeing 777-200ER using GE engines . The first engine = GE90-94B and the second engine = GE90-115B .

This is called engine intermixing.

  On 737 sometimes The more powerful engine is derated to the same level as the other engine, and we had to do full power takeoffs everytime. As long as the FMC is aware of the intermix, pilots are allowed to use autothrottle.

Here are the sources for your further reading :
Source 1
Source 2

Following is another example:

  Models with engine intermix already certified

Aircraft models / Engines        Engines allowed

A310-221 / PW JT9D-7R4D1         1 or 2 JT9D-7R4E1
(48000 lb *)                     50000 lb*
                                 (A310-222)

A310-222 / PW JT9D-7R4E1         1 or 2 JT9D-7R4D1
(50000 lb *)                     48000 lb *
                                 (A310-221)

A310-308 / GE CF6-80C2A8         1 or 2 CF6-80C2A2
(57860 lb*)                      52460 lb*
                                 (A310-304)

A300B4-605R / GE CF6-80C2A5      1 or 2 CF6-80C2A3
(60200 lb*)                      58950 lb*
                                 (A300B4-603)

Note (*): Static thrust limit at sea level for takeoff with OAT 30°C.

For these aircraft models, the new engine(s) is (are) installed with no hardware change nor rating change.


Why did the F-104 Starfighter have a T-tail? The F-104 Starfighter was launched in 1954, nine years after WWII. It had short stubby wings and a T-tail. According to wiki, the short stubby wings caused inertia coupling and the T-tail reduced this.

My question is: is that really the reason why the F-104 had a T-tail? How does that help reduce inertia coupling?

EDIT

@aeroalias answer has many of the reasons for the T-tail. Had edited the question with some additional info, it was suggested to put this in an answer instead.

The initial preliminary designs had the horizontal tail in multiple locations (including in-line with the wing and cruciform), before settling on the T-tail by December 1952. The reason for selecting the T-Tail is given by Glenn L. "Snake" Reaves, Lockheed Production Flight Test Pilot in the F-104 Test Pilot notebook as

The high tail position was selected ... after extensive wind tunnel tests (which) proved that the location was necessary to obtain optimum stability and control about the pitch axis throughout the wide Mach range. The position also results in minimum transonic trim changes while accelerating to supersonic.

Another advantage was that the high tail on the swept vertical fin reduced interference drag. While the problem was inertial coupling was quite well known during 1950's, the design of the F-104 was frozen during the same period, so it is difficult to tell conclusively if that is the reason for F-104 having a T-tail.
The test pilot notebook also has some explanation about how the T-tail reduces the problem of inertial coupling:

If we now consider two facts about these rolling maneuvers, it will become clear how inertial coupling builds up:

The sideslip build-up is controlled by the induced rolling moment.

As sideslip builds up, the centrifugal or rolling forces increase and this tends to displace the aircraft fuselage perpendicular to the flight path.

The T-tail controls the the sideslip build-up by inducing a rolling moment. From the same document:

... the high tail position of the horizontal stabilizer raised the center of pressure.

Image from F-104 Test Pilot notebook

... whenever we sideslip an aircraft, a rolling moment is induced that resists the sideslip. This induced rolling moment is generally termed dihedral effect.
... with any sideslip, the restoring force acting through the center of pressure does not act through the c.g of the aircraft. Therefore, a sideslip condition actuates the restoring force on the tail but at the same time, induces a roll. ... now that we have raised the tail and consequently the center of pressure and the positive dihedral effect has been increased considerably.

The T-tail reduced inertial coupling by preventing sideslip buildup.


Which FAA regulations cover the certification of aircraft engines? Aircraft certification is covered by 14 CFR 23 and 25, what parts cover aircraft engines?

The relevant section of the FARs for engine certification standards is 14CFR33 - AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES, with 33.31 through 33.57 dealing with reciprocating (piston) powerplants & their testing requirements, and 33.61 through 33.99 being the equivalent for turbine powerplants.

There are also the 33 series Advisory Circulars dealing with such fun topics as how to comply with the Bird Ingestion Certification Standards (33.76-1A).


Where in the FAR or AIM is a high speed taxi defined? While monitoring coms I recently heard a Cessna Centurion that had just cleared the runway request a "high speed taxi", which was approved by the tower. I'm assuming that means he wants to taxi at a faster than normal rate to his FBO of choice. Are high speed taxis defined somewhere as something you can request of ground control?

There's no definition in the AIM or regulations, as far as I know, but there is one in the P/CG, sort of (emphasis mine):

  HIGH SPEED TAXIWAY− A long radius taxiway designed and provided with
  lighting or marking to define the path of aircraft, traveling at high
  speed (up to 60 knots), from the runway center to a point on the
  center of a taxiway. Also referred to as long radius exit or turn-off
  taxiway. The high speed taxiway is designed to expedite aircraft
  turning off the runway after landing, thus reducing runway occupancy
  time

So at least as far as the FAA is concerned, a high-speed taxi may be up to 60kts.

As for requesting it, you can request more or less anything. There's an active EAA chapter at my local airport and pilots who are in the process of building and testing aircraft sometimes request a high-speed taxi on the runway. The controllers don't question it or set any speed restrictions, it's all on the pilot. I suppose if things were busy they might deny the request, but the pilots know to do these things at quiet times anyway.


Why do fighter aircraft manufacturers still focus on making their planes more dogfight-worthy? In today's age, when dogfights are simply a relic from the past, why do manufacturers keep on increasing their aircraft maneuverability, in order to make them better dogfighters. It is more understandable if they were to make stealthier or more efficient fighters, but when the dogfight is extinct, why make planes even more agile and maneuverable?

That same thinking, "dogfighting is dead", got the USAF and USN in serious trouble in Vietnam. The U.S. Armed Forces were convinced that the next major war would be against the Soviet Union directly, in theaters including Europe, Alaska and Canada, and as a result, fighter designs succeeding the very successful Sabre and Super Sabre day fighters used in Korea began emphasizing standoff capabilities, believing the aerial threat would come from various classes of nuclear bomber, calling for fast, long-range missile-armed interceptors as a counter.

That war, thankfully, never materialized. Instead, the U.S. was pulled into more or less another Korea, a proxy war fought between Soviet-supplied and trained Communist forces against a U.S.-backed fledgling democracy. The big, heavy U.S. F-4 Phantom interceptor and F-105 Thunderchief light bomber, neither of which had internal guns, found themselves facing the older like-minded successor to the MiG-15s they faced in Korea, the MiG-17, coupled with the MiG-21 close-range interceptor. Instead of the long-range standoff air war the USAF was built for, US pilots were ambushed at close range by guns and infrared missiles, resulting in a piss-poor 2:1 kill/death ratio in aerial engagements, compared to the 14:1 ratio they enjoyed in Korea.

The result was increased attention paid to "air combat maneuvering", and an emphasis on this style of combat in the next generation of fighters adopted by the U.S. military. The F-14 and F-15, though intended to bring back dogfighting (and they did), turned out to be big, fast interceptor-style fighters like their predecessors, that still only had a clear advantage in BVR engagements. So a group of USAF generals, seeing what its allies had been doing with the F-5 Tiger that the Joint Chiefs had more or less passed on (a few trainers, a few aggressor planes, but no combat adoption), commissioned the LWF competition, which would produce the F-16 and F-18 lightweight multirole fighters with an emphasis on the close-quarters maneuverability that the Communist powers never really forgot.

The F-22 splits the difference between the F-15 and F-16's air combat strategies, producing a heavier but highly maneuverable fighter that excels at air combat at any range (but is so expensive that so far the USAF have only deployed them in situations where they would never face any real threat). The F-35, however, is rapidly becoming a disappointment; compared even to the F-16 or F-15E it will replace, it "can't climb, can't turn, and can't run", and the A variant is the only one with an internal cannon (which carries only 182 rounds of ammunition compared to the F-22s 480, the F-15's 650 and the F-16's 510); the STOVL B variant and the Navy's C variant won't have guns at all.

In today's military theater, the U.S. enjoys "air supremacy"; we're fighting largely paramilitary forces with practically zero air to air capability. Tomorrow's theater, however, may be quite different. Diplomatic relationships with a number of Russian-supplied nations including Russia itself are souring day by day, and the U.S. could easily find itself drawn into conflicts over Taiwan, the Korean peninsula, India/Pakistan, the Ukraine, etc, where they'd face militaries fielding Russian jets purpose-built to mix it up at visual range.

In short, while the U.S. hasn't directly fought a conflict against a serious air threat since Vietnam, there are a lot of potential near-future conflicts in which they would get their chance, facing the Sukhoi PAK-FA or Chengdu J-20 with skilled Chinese or Russian pilots at the stick. Even if these fighters aren't fielded in mass numbers, the U.S. would still face the Russians' direct answers to U.S 4th and 4.5-generation fighters, including the MiG-29 and Su-27/30/33.  Many variants of these were specifically designed to out-maneuver the U.S. F-15, F-16 and F-18 (which would likely be the first jets in-theater), and which would still be a match for the F-22 in a visual-range "furball".


During an engine restart procedure, what are the purposes of a.) throttle back to idle and b.) primer "in and locked"? I was making some study flashcards today for Emergency Procedures in the Cessna 162 POH, and realized that I don't quite understand steps 2 and 6 of the ENGINE FAILURE DURING FLIGHT (Restart Procedures):

  1. Airspeed .................. 70 KIAS (best glide speed)
//2. THROTTLE Control .......... IDLE (pull full out)
  3. CARB HEAT Control Knob .... ON (pull full out)
  4. FUEL SHUTOFF Valve ........ ON (push full in)
  5. MIXTURE Control ........... RICH (if restart has not occurred)
//6. PRIMER (if installed) ..... IN and LOCKED
  7. MAGNETOS Switch ........... BOTH (or START if propeller is stopped)

I think understanding the why behind all of the checklist procedures will help me remember them better.

Source

Idling, or closing the throttle, might help break up any ice that may have formed and caused the engine to quit. That's why it's followed by Carb Heat On.

Also, a failed engine (of any type) is best restarted at idle power. Otherwise the extra fuel will either flood or overheat the restart. But nevertheless, always stick to whatever the checklist says.

  Throttle ice forms when your throttle is partially closed, typically between cruise power and idle. As air moves through the the Venturi in your carburetor, it decreases in temperature, condensing water vapor from the air. The water then starts freezing to the carburetor parts, restricting airflow. Eventually, you'll start losing RPM or manifold pressure, your engine may start running rough, and if the ice gets bad enough, your engine will quit.

If a primer is inadvertently left in the pulled / unlocked position, it may flood the engine with fuel.


Is excess lift or excess power needed for a climb? As answered in this question, aircraft need excess power - not excess lift - to climb. This is plausible when the aircraft's thrust vector has a vertical component (its nose and engine points upwards), but I challenge the requirement of excess power for every case.

Please take a look at the following cart. The thrust gets delivered by a propeller at the rear and the thrust vector is always horizontal. A wing attached to a vertical beam is free to move up and down.

When the cart gets accelerated and reaches a certain speed, the lift acting onto the wing gets greater than the wing's weight, leading to a climb of the wing. Please notice that - because thrust is horizontal - the chemical energy burned goes into kinetic energy of the cart and/or heat energy (due to overcoming drag). No power invested by the propeller goes into potential energy of the wing; the climb of the wing is done purely by lift.

Did I miss something?

As the answers to your original question already explained, you do need extra lift to accelerate upwards. Once the wing is set into a vertical motion, however, lift again exactly equals weight to keep the wing at a constant vertical speed (if we neglect thrust and drag for a moment). No extra lift is needed to maintain that vertical speed. Only when you want to accelerate further up, extra lift is needed.

The increase in potential energy comes indeed from the propeller, because the lift vector of the climbing wing is tilted backwards, adding a horizontal component that needs to be compensated by extra propeller thrust.

Now let's look at your experiment in detail: I assume the wing has some mass, is rotationally locked and slides up and down that pole without friction. If you accelerate the car, at some point its speed will just be right for the wing to create exactly the lift to cancel out its own weight. At this speed the wing will be stable at any position along the pole. If it slides down a little, its angle of attack $\alpha$ will increase and create more lift, stopping the downward motion. The reverse is true for any upward motion. See below for an illustration of the principle. The cyan vector is the vector sum of the flow due to forward motion (blue) and vertical motion (red), and this is what the wing will "notice".

When the car accelerates further, the lift will increase and now become greater than the weight. The wing will accelerate upwards until its vertical speed will reduce its angle of attack by enough to reduce the vertical aerodynamic forces to exactly equal its weight. Now you have the same situation as before, but not at zero vertical speed, but at a positive vertical speed which will make sure that the wing pops out at the top of the pole unless there is some stop. When the wing hits the stop, the vertical motion ceases, the angle of attack increases and the wing will lift up not only itself, but also part of the car's weight.

Note that I now spoke of the vertical components of the aerodynamic forces, not lift. When drag is added, it will add a vertical component when the wing is in motion. Lift is defined as the sum of aerodynamic forces perpendicular to the flow direction at infinity and drag parallel to it. This cumbersome definition makes sure that local distortions in the flow field do not impact the direction of lift and drag. The direction of lift for the climbing wing will point slightly backwards and the direction of drag slightly downwards. This will add some drag component to the sum of the vertical aerodynamic forces, and lift needs to increase to compensate for this. The horizontal component of lift will now add to the drag and the forces on the pole, so more force from the propeller is needed to push the climbing wing through the air. This extra force is needed to increase the potential energy of the wing on its way up. For a descending wing, the reverse is true: Now drag will add some vertical component and lift will be slightly slower. The forward component of lift will now push against the pole, reducing the force the propeller needs to provide. The reduction in potential energy now reduces the horizontal aerodynamic forces.

An airplane is slightly different, because it is free to pitch up or down and the angle of thrust will pitch with it. This will enable the pilot to select the flight path and the amount of lift the wing creates, but again the vertical motion will make sure that any excess lift will translate into increased vertical speed and a lower angle of attack, so the excess lift vanishes. In a climb, thrust needs to be bigger than drag in order to increase the potential energy of the airplane, and now the vertical component of the tilted thrust vector will support some weight, reducing the amount of lift needed to support the weight.


How come diverterless supersonic inlets haven't been discovered much earlier? DSI's seem like such an absolutely elegant solution to a problem that has, so far, been solved in a truly overly complicated way.

So, if I'm not missing out on some important small speck of knowledge that complicates DSI's way, way more than being a bump to subsonicize air (of course a slight bit more than that, but you get the idea), then I feel like it is justified for me to get the well-known "this stuff is way too easy to be true"-feeling.

To actually ask the question: Are DSI's really as easy of a solution as they seem right now?

Designing a DSI inlet is not so simple. It required CFD, a field which had existed for a while but was still viewed with some suspicion in the 1990s. CFD is computationally intensive, so the field has benefited from the massive advances in computing power since the invention of the transistor.

  The DSI traces its roots to work done by Lockheed Martin engineers in the early 1990s as part of an independent research and development project called the Advanced Propulsion Integration project. The concept was developed and refined with Lockheed Martin-proprietary computer modeling tools made possible by advances in Computational Fluid Dynamics, or CFD. CFD is the science of determining a numerical solution to the governing equations of fluid flow and advancing this solution through space or time to describe a complete flow field of interest—in this case, the flow field of a fighter forebody, inlet, and inlet duct.


Why can't armrests be raised on window and aisle seats? I noticed that armrests on all the flight's I've taken recently can't be lifted on aisle and window seats (the edges of a row).

Last time I flew, I got lucky: I was alone on my row and as such I was able to lay down to sleep. However, it was hard to make myself comfortable as that armrest was pressing on my spine when I tried laying down with my back to the window.

Also, it would be much easier to get out of my aisle seat if I could lift the armrest. I'm a pretty tall guy, so I always feel like a contortionist trying to get out of my seat.

What's the problem with letting people raise the armrest on window and aisle seats?

I'm guessing it's some sort of safety issue, because the mechanism seems to be the exact same one as the other seats, just with an extra locking mechanism added.

Apparently, it can be done, atleast in some aircraft; even in those cases, the armrests are locked, unless one knows the location of the release button.

As for why, it seems that there is a possibility that the upright armrests can be an obstacle (for people in the next seat row) and FAA expects the cabin crew to ensure that the armrests are in forward condition prior to takeoff/landing. According to FAA Volume 3, Chapter 33, Section 3 Instrument and Equipment Requirements,

  Inspection of the Hardman Model 9500 and other passenger seats installed on several aircraft, disclosed that the armrest in the upright or stowed position can protrude approximately 45 degrees aft the seat back. In the event of an emergency evacuation, protruding armrests could present an obstacle between seat passageways, obstructing emergency exit access. Air Carriers should emphasize to F/As that prior to takeoff and landing they verify that the armrests are in the normal forward/down position in order to ensure that they do not obstruct the passageway between the row of seats leading from the aisle to the emergency exit.

As this is a problem in aisle seats (armrests in middle seats cannot go back usually), they have to be fixed forward or atleast locked in position. This is the reason for them to be locked in case of aisle seats. As for window seats, the sets are usually made in a row and you don't really know if the seat will end up in window or aisle i.e. whether the row will get fixed on left or right (or middle, in widebodies). Net result is that both the ends of the row are fixed just to be sure. In other words, the windows armrest is a collateral damage.


Can delamination be detected early? When a composite structure is hit, the impact causes shockwaves which travel through the structure, and cause delamination. Delamination reduces the strength of the composite structure and may cause the structure to break at a fraction of the load it would have carried before the impact.

Delamination and its ill-effects can be reduced, for instance by adding metal at strategic points of the aircraft. But once delamination occurs, how can it be detected? What measure (if any) have been implemented to detect delamination on aircraft?

There are multiple non-destructive methods to detect delamination in composite materials.

In case the delamination occurs on the surface, it can be easily found by visual inspection. This is the easiest method to detect delaminations; however, this is useful only if the delaminations are visible from the outside (i.e. they are on the surface), which is rarely the case, at-least in aircraft.
Ultrasonic testing- In this method, ultrasonic waves are passed through the surface of the material and the response is monitored. Depending on the condition of the material (whether it has defect or not), the ultrasonic waves behave differently.

Source: cnde.iastate.edu

The ultrasonic method used can be through scan (with the transmitter and reciever on the opposite sides of the part) or pulse echo method, where the transmitter/reciever 'listens' to the ultrasonic sound reflected back from the defect or the other end of the part. There are three main methods of ultrasonic scanning in use:

The A-scan presentation displays the amount of received ultrasonic energy as a function of time.
The B-scan presentations is a profile (cross-sectional) view of the part. Here, the travel time of the sound energy is displayed along the vertical axis and the linear position of the transducer is displayed along the horizontal axis.
The C-scan presentation provides a plan-type view of the location and size of defects.
Tap test, using a coin or an instrumented hammer- This is the most widely used method in the field as it requires minimal instrumentation. However, it requires a trained operator, who can distinguish between the normal and delaminated composite from the sound. Instrumented hammers are also available, where the frequency response of the part can be analyzed for identifying defects.

Source: amumagazine.com

Thermography- Here, an energy source is used to produce thermographic contrast between tthe defect on the part. This is useful in detecting shallow subsurface defects, but is rarely used in field operations.

Infrared thermography Source: seattleinfrared.com

X-Ray radiography (or CT scan in some cases)- This is a very accurate method for detecting internal defects; however, the equipment requirements mean that it is usually used in the place of the OEM, though some field equipment is available for military uses.

Fatigue crack under X-Ray, Source: vidisco.com

There are some other methods like the acoustic emission and lasers, which also can be used for detecting delamination. The table below gives some of the methods used for detecting defects in a manufacturing environment

Source: amumagazine.com


Was the foil in older FDRs reused when it ran out, or replaced? Before magnetic tape became the standard recording medium for flight data recorders, most FDRs used a long strip of metal foil that had altitude, airspeed, etc. traces scratched into it by a set of styli inside the FDR (although a few very early FDRs used wire recording instead).  Judging from a number of NTSB accident reports that mention FDRs where the foil had run out and been taped down at the end for maintenance, this presumably wasn’t a continuous loop of foil (although I can’t imagine it would have been hard to implement a continuous-loop system; it seems to me that, to make such a system workable, all you would have had to do would have been to squeeze the foil through a set of metal lips to flatten out the old traces just prior to passing under the sticks), but, instead, one that had to be removed and dealt with by maintenance when it ran out.  When a foil FDR became full and was removed for maintenance, were the traces flattened out of the foil and the foil reused, or was the strip of foil replaced with a new, empty strip (with the full strip presumably being either discarded or possibly stored in an archive somewhere)?

Those older FDR's are known as "foil oscillographic recorders." This technology is similar to the old recording barometers, which were used for, among other things, providing evidence of altitude in glider record-attempt flights. Just as in these barometers, the recording surface was not reusable in those FDR's. When it would run out, it needed to be changed. The FDR's had an indicator which showed how much usable foil was left in terms of hours. The rolls of foil were 200 ft long and ran at 6 inches per hour when the aircraft was operating, about 400 hours' worth. This was an inspection item on the aircraft.

In addition, the foil was made of Inconel, which is known as a "superalloy" that is resistant to very high temperatures. It would be very difficult to remove the tracings of data without specialised equipment, and in reality the tracings removed material from the protective surface coating on the foil. If you recycled it the quality of the data could be impacted by corrosion.

This very cool video illustrates how these FDRs worked.