How can I calculate the thrust of a fan given the diameter of the blade? How do I calculate the thrust of a multicopter fan blade from its diameter?

I am searching for a multicopter blade that can provide a thrust of 15 - 20N.

Being someone who doesn't have any experience in avionics, I searched online for such blade believing that I could find the thrust the blade can provide, but every website for a multicopter wing, only the diameter is provided.

Is there a formula that provides thrust of a blade from its diameter?

I checked out your original post, and the Quora post referenced in it. The thing is that what is mentioned there is simple impulse dynamics: there is a magic disk with no drag that accelerates air going through it. It's a theory that works if you realise the limitations, allows for quick ROM estimations, and can provide even more useful info when some drag effects are included in the form of propeller/rotor efficiency. The Quora post is not incorrect, but it is a simplification and it is valid for a different scale.

For a magic disk, all you need to know is the disk area, it does not even need to have a mounting axis. For a real propeller/fan that is not optimised yet, the following parameters need to be considered:

Blade radius, resulting in the disk area.
Rotor RPM, together with the blade radius resulting in tip velocity.
Blade pitch
Blade chord
Blade profile
Number of blades

Between your application and the Quora helicopter disk, there are the following differences that need to be catered for:

Your rotor is small. Reynolds effects start playing a big role here, with a much thicker boundary layer. Departs further from the impulse theory than an average helicopter rotor: increases power demand.
Your rotor is ducted: reduces power demand by about 35% for small rotors, see figure below.
Your rotor is a fan: increases power demand. Every added blade requires proportionally more power for a an increase in thrust that gets smaller with every blade.
Your rotor has difficulty bringing the air in. A curved duct restricts incoming air flow, increasing power demand and putting a cap on maximum thrust.

So we need to use data from small scale rotor research. Here is a masters thesis researching just that, unfortunately with an underpowered motor so the results are only valid for low Mach numbers. If we look at the highest Mach number in the graph and compare data points for Thrust = Lift, we can see an increase in $C_T$ (is a measure for thrust) of 0.047/0.035 = 35%.

$C_T$ is defined here with reference to the ducted fan wetted area, and it is not very clear which units are used. There is a graph of thrust force vs. rotor rpm:

6000 rpm with a 9.5" rotor equates to a tip Mach of 0.22. Propellers can run with a tip speed of up to 0.75 Mach before compressibility effects occur, that would be 20,000 rpm for this configuration. Extrapolating the curve to 20,000 rpm would result in about the 15 - 20 N mentioned in the OP.

It's a 3-blade rotor. Thrust can be further increased by increasing blade pitch and increasing number of blades, each increase requires an increase in power as well. Unfortunately the research does not mention power required for each thrust config found, but:

Appendix A has some provisional power curves for other rotors used in the project. It also mentions the use of a gearbox to increase rotor rpm, something OP may wish to consider as well.
A table with a motor trade study used in earlier research is included, outlined below.


Has there ever been a report of a helicopter flying into a downburst? I was recently flying my quadcopter and it started to go out of control. It was because I was flying it below a ceiling fan which acted as a mini downburst shoving the little quad to the ground.

So have there ever been reports of a helicopter accidently flying into a downburst?

Yes, it would be really amazing if it had never happened. Since "reports" are only required in the case of accidents, here are extracts from three NTSB summaries:

WPR13CA155

  During descent for an off-airport pinnacle landing, the helicopter
  encountered a downdraft about 75 to 100 feet above ground level (agl),
  and the pilot receiving instruction increased collective input. The
  flight instructor advised the pilot receiving instruction to be less
  aggressive using the collective as the flight continued to the landing
  area. As the helicopter descended through about 10 to 25 feet agl, it
  encountered a second downdraft, and the pilot receiving instruction
  increased collective again, which was followed by a decrease in rotor
  rpm.

ANC09LA098

  During the approach to the 5,657 foot level site, the pilot said he
  encountered a downdraft as the helicopter approached the site, and the
  helicopter descended below his anticipated approach path. He initiated
  a go-around, but the helicopter continued to descend, and landed hard,
  about 150 feet short and down slope of his intended touchdown point.

WPR09CA470

  As he flew the helicopter out of the leeward side of the peak, he
  encountered a downdraft. He maneuvered the helicopter toward a wide
  open valley that descended about 5,000 feet below. The downdraft
  pushed the helicopter into the face of the mountain, despite the
  pilot's application of full collective and descending flight into the
  valley.


Helicopter tail horizontal stabilizer angle In helicopters what factors decide the horizontal tail stabilizer angle?
By angle I mean that in some helicopter they are -6 deg relative to tail boom while in some -3 deg.
These angle were remain fixed although provision is there to change the angle.

The stab angle influences the pitch attitude in cruise, allowing the body of the machine to be flatter (more nose up) than it would be without it, by pushing down on the tail with speed.  It also dampens pitch oscillations of the body under the rotor disc.  A designer will come up with a stab area and incidence that is estimated to provide the necessary down force for a desirable cruise attitude for a particular machine, then adjust as required during flight testing.

The Blackhawk takes it much farther; the stab is a moveable control surface that allows attitude control over a very wide speed range.


Why is the maximum endurance for a piston aircraft at sea level? The Canadian Flight Training Manual stated this when talking about maximum endurance:

For reciprocating engines, maximum endurance is achieved at sea level.

The book does not explain further as to why. Air density is my first guess, when the engine gets a better mixture of air to burn with its fuel, and so we get the most power for the same amount of fuel.
But if that is true then it sort of contradicts why maximum range is at higher altitude.

Try working it from the other end. A propeller needs to generate a certain amount of thrust to maintain a given indicated airspeed to fly.
In thinner air, it must turn faster to do so.
Turning faster is higher RPMs.  Higher RPMs mean more engine friction.
More fuel must be burned per unit time to overcome engine friction at higher RPMs.
RPMs to generate a given amount of thrust are lowest at sea level
(maybe lower in Death Valley (on a colder day)).
Because the horsepower requirement for maximum endurance speed is much lower than the maximum rated output, the horsepower loss due to thinner air is not an issue until one is higher up.  This is why "leaning" is required at higher altitudes.
But "air density" is the correct answer.


Do 121.5 MHz ELTs have to be replaced with 406 MHz models? There has been a lot discussion about replacing 121.5 MHz emergency locator transmitters (ELTs) with 406 MHz ELTs, since 121.5 MHz ELTs are no longer monitored by satellite.

Are private planes required to have 406 MHz ELTs for operation? Is there a deadline for conversion? Since this is a country-by-country regulation, I am interested in

Canada
U.S.
Mexico
Bahamas
Europe
Australia
(other countries, if information is available.)

I can't speak for the other countries, but at the moment (December 2013), at least in the United States, the answer is no.

The FAA and the FCC have been engaged in a bit of a regulatory battle of wills on this subject, (most recently in March of 2013, and covered by AOPA, EAA, and AvWeb pretty extensively) - Basically the FCC wants us to take our 121.5MHz woop-woop boxes and make them go away, because they're pretty lousy for search-and-rescue, and the FAA is, for the moment, telling the FCC to get stuffed because regulating aircraft is the FAA's job.

Now just because you don't have to replace your ELT doesn't mean you shouldn't -- to be honest a 121.5MHz ELT is not much better than having no ELT at all (COSPAS-SARSAT doesn't monitor 121.5 anymore), so you should consider the type of flying you do, and the likelihood of an incident where the ELT might be useful.

The new 406MHz ELTs are vastly superior to 121.5MHz units for search-and-rescue performance, and if I were running a commercial operation, or flying regularly in an area were search-and-rescue help may be hard to come by if I had an emergency (like say Alaska) I'd fork over the cash for a GPS-enabled 406MHz ELT to replace the ancient 121.5MHz unit in my plane in a cold second.


What is the incidence angle of a propeller in the terminology of the Wright Brothers and how did they obtain it? What is the angle of incidence of a propeller in the terminology of the Wright Brothers and how did they obtain it?

In Feb. 1903 (see Screw Test 1903, page 8), using a 0.58 hp engine, the Wright brothers tested a propeller characterized by:

Diameter, D = 8.5 ft

Pitch = 15 deg

Surface, $S = 2\ ft^2$

RPM = 245

They measured what appears to be the static thrust and got:

Thrust = 18.75 lbf

Based on the assumption that the propeller can be modeled by a wing (Pitch = 15 deg, Surface = $2\ ft^2$, Lift = 18.75 lbf) having its entire area concentrated in a single point (called  the Center of Pressure, C.P.) traveling at RPM = 245 on a circle with the diameter 0.824 x D, $V_{wing} = RPM \times \pi \times 0.824 \times D$, the Wright brothers evaluated its Drag and from Lift, Drag and Pitch using trigonometric relations they obtained the Normal (perpendicular to the chord) and Axial or Tangential (along the chord) components of Lift + Drag (the resultant force) and some angles related to them.

Now comes something I do not quite understand.

The two brothers calculated a reference force defined as:

Total Normal = $k \times S \times V_{wing}^2$ = 24.8 lbf,

where

$V_{wing} = RPM \times \pi \times 0.824 \times D = 61\ \mathrm{mph}$

$k =$ Smeaton’s coefficient $= 0.0033\ \mathrm{lbf} \cdot \mathrm{ft}^{-2} \cdot \mathrm{mph}^{-2}$

Further, the Wrights divided the Lift by the Total Normal

$\frac{\mathrm{Lift}}{\mathrm{Total\ Normal}} = 0.756$

and from this 0.756 they drew the conclusion that the angle of incidence is 7¼ deg. The question is why? What is this angle of incidence and how can it be calculated?

Update

The correspondence between the percentage 0.756 and the angle of incidence, 7¼, comes likely from a table like this (which is for a slightly different wing curvature):

Percentage of air pressure at various angles of incidence

However, as the propeller did not move, the incidence angle of its equivalent wing appears to be identical with the pitch of the same wing and they are not. Why?

According to various scholars, the Wright brothers were referring to "angle of attack" when they used the term "incidence." They actually published an article by the same title, so the fact is well-established.
References include the following:

In Wilbur's time, the "angle of incidence" was what we now call the "angle of attack" -- the angle at which the wing of an airplane meets the wind (wright-brothers.org).

and

In the Wright's own words: "The lift is thus balanced against the normal pressure on the resistance surfaces ... Therefore, the lift ... at the given angle of incidence (angle of attack) is to the pressure on a square plane of equal area at 90° as the sine of the (...)
(wright.edu)

The angle of attack of a propeller is defined in various ways, a summary of which is here.

The angle at which this air (relative wind) strikes the propeller blade is its angle of attack.


In what way(s) will making an airplane electric help to make it "quiet"? In this blog I read about the Quiet Flight Initiative, which - if I understand correctly - will be quieter than a comparable carbon fueled plane at least in part because it is electric. It's an engineering challenge associated with Embry-Riddle Aeronautical University.

What aspects of the plane design - when switching from combustion engine to electric motor - will help reduce noise? I had thought that most external aircraft noise heard on the ground (in this case, National Parks) is associated with the propellor, and so noise is closely linked to performance, not the particular method of torque generation.

You are right, propeller noise is dominant in case of GA aircraft, but not all propellers make the same noise. Much depends on blade loading and tip speed - making the propeller larger and letting it turn more slowly will improve efficiency and reduce noise. This has worked very convincingly for model aircraft over the last 30 years. GA engines are normally ungeared, so their propeller speed and diameter are the same. Switching to a geared IC engine like a Rotax 914 not only makes the engine lighter but also the propeller less noisy. Switching to an electric motor, which can produce high torque at low speed, will allow to exploit this effect to the fullest.

Other sources of noise will profit from electrification, too. The exhaust noise will be completely avoided, and airframe vibrations will be greatly reduced. Radiator noise will fall away, too. It is a small source of noise, but every bit counts.

What will be left is the noise of the slower propeller(s) and aerodynamic noise. Now landing gear retraction would be the next big step in noise reduction.


What is the maximum side slip angle that can be achieved by a F-16? During which flight regime is maximum side slip needed (apart from take-off and landings in cross winds)? I have learned that during a knife edge maneuver, the side slip angle plays a crucial role in maintaining the flight path angle.

What is the maximum side slip angle that can be achieved by an F-16?
And if possible, how does the F-16 compare to other planes of different roles?

Knife-edge flight is an aerobatic maneuver where an airplane is flying on its side for an extended period of time without ascending or descending.

Notice it says aerobatic, i.e. for show. There is no point doing it on a mission (or otherwise) in an F-16.

Spoiler: it can't be flown in an F-16.

  The flight control computer (FLCC) of the F-16 further incorporates limiters governing movement in the three main axes based on attitude, airspeed and angle of attack (AOA); these prevent control surfaces from inducing instability such as slips or skids, or a high AOA inducing a stall. The limiters also prevent maneuvers that would exert more than a 9 g load.

  — Wikipedia

One source mentions 10° of beta (sideslip angle) as an extreme and unusual for an F-16.

  Departure from controlled flight / Rudder input

  The Aileron Rudder Interconnect (ARI) automatically provides rudder input according to pilot roll input
  to reduce sideslip during turns. Pilot induced rudder does not improve turn performance but increases
  departure possibility.

  Yaw FLCS

  Since the rudder is mostly controlled in flight by the FLCS through the ARI (Aileron Rudder
  Interconnect) the pilot should in theory have no need to use the rudder in flight. To prevent pilot
  induced rudder movement which can create adverse effects the FLCS automatically limits its use.
  Rudder authority is reduced as a function of AOA, roll rate and CAT config to prevent departure from
  controlled flight.

  — BMS manual

Note: Crosswind crabbed flight is not a sideslip. The flight is coordinated (ball centered). Since the wind pushes the plane off track, the pilot corrects by pointing into the wind, that's all.

Just as tailwind or headwind has no effect on the flight dynamics, so is the crosswind. A plane flies inside a mass of air, if the mass of air happens to be moving, it only affects the navigation (where the plane is actually going, and how fast/slow).


What fraction of air intake becomes bleed air in airliner engines? Gas turbines typically bleed air from the late compressor stages. Some of this air bypasses the combustion chamber and is expanded through the turbine to prevent the blades from becoming too hot. I believe bleed air is also used to provide hydraulic control of the control systems and also for utilities such as air conditioning and electricity generation.

I am interested to know just how much of the air intake to the gas turbine compressor becomes bleed air. I'm also interested in knowing how much of this bleed air goes to each application e.g. Utilities vs. turbine cooling vs. hydraulic control.

I suspect it varies a fair bit so I am mostly interested in how this occurs on larger airliners that would typically fly long international flights.

Indeed about 1-2% of compressed air is bled off for cooling turbine disks and blade roots. When turbine inlet temperatures are higher than 1350K, the turbine blades must be internally cooled as well, and up to 15% of compressor air may be required as bleed air for cooling. Source

Bleed air is also used for aircraft systems. If we take a typical airliner such as the B737NG, compressed air can be supplied by either the engines, the APU or an external air chart, and is used for the following purposes:

Air conditioning & cabin pressurisation, which are both subject to regulation quality standards.
Wing & engine thermal anti-icing
Engine starting
Hydraulic reservoir pressurisation. The reservoirs are pressurised to ensure that hydraulic fuel reaches the hydraulic pumps.
Water tank pressurisation

Compressed air is tapped from the engine 5th and/or 9th compressor stage. Air supply is regulated according to demand and varies according to flight stage - during flight stages with relatively high engine power (take-off, climb, most cruise), 5th stage compressed air only is used. During low engine power conditions such as approach and landing, 9th stage compressed air is used for the pneumatic systems as well. This air is under higher pressure, and hotter, than the 5th stage air.

Exactly how much bleed air is used for the systems is hard to get a reference for, but here is an estimate for the CFM56-7B18:

Bypass ratio = 5.5:1, Air mass flow = 307 kg/s => hot flow = 307 / 5.5 = 55.8 kg/s
Cabin air systems refresh the whole cabin volume every 2-3 mins. Let's take 2 minutes, without recirculation.
Internal volume of a 737NG is about 400 $m^3$ (from fuselage width and length of an -800).
Air density = 0.94 kg/$m^3$ (we'll take cruise conditions, cabin air density @ 2,000 m)
Aircon flow = 400 * 0.94 / 120 = 3.1 kg/s

There are two engines, so the percentage of flow used for the aircon and pressurisation would be 3.1 / (2 * 55.8) = 2.8% maximum. Please again note that this is a ROM value which I will gladly give up for an official reference.

As a magnitude check: the APU brochure mentions 154 pounds of air per minute = 1.16 kg/s for environmental control and engine start. The APU can deliver air conditioning on the ground without the engines running so that would be the right order of magnitude.

Final estimate: bleed air for air conditioning is between 1 - 3 kg/s is about 1 - 3% per engine.

Bleed air is not used for:

Hydraulic power generation. The hydraulic pumps are engine driven pumps (via a gearbox) and electrical pumps, powered by the AC system
Electrical power generation. This is provided by Integrated Drive Generators, from a generator in the APU, and from the batteries through an inverter.

Source: own work from open source on-line pilot training courses.


Is there a software to calculate parameters from certain inputs on a flying wing? I want to build something similar to this

https://www.parrot.com/de/drohnen/parrot-disco-fpv#parrot-disco-fpv-details

but with two holes in the wing, where I want to put two propellers. But I need to make the proper calculations (shape and size of the wings, I'll work on the propellers separately). It should be a simple design, just a prove of concept.

Is there a software that can help me do this? I can have an idea of the weight I need to lift, the velocity, and need the design (with the two holes).

Yeah you could start with X-plane, which claims that it can figure out the flight characteristics from geometry parameters. It is based on laminar flow theory and on classic aeroplane shapes and configurations, but it is a start. They have something called Plane Maker which could serve your application.

FlightGear is a similar program, open source so you can study the code to see how it works, then try to find relevant lift and drag data on the interwebs, NASA servers for instance.

Good luck with the modelling effort.


Why do NY ARTCC Standard Operation Procedures have different altitude limits than the NY Class B airspace? The NY Class B airspace is defined, officially, as seen in this document, which can be found in the VFR Class B Graphics in the FAA website. In this graphic (and in the corresponding shapefile, Class Airspace), the flight altitude limits can clearly be seen, for example 70/30 in the "outer ring", meaning, below 7000 FT and above 3000 FT.

However, in the specific SOP definitions for the NYARTCC, here, different altitude limits can clearly be seen, for example in the DEP 4L LAND 4L/R.

Why are these two limits incompatible? Which ones are technically "officially" valid?

The commenters have a good point that the SOP documents you liked are for hobbyist simulation and are not necessarily faithful reproductions of real-world procedures. But even in the real world who owns which specific volume of the air at which specific altitudes is not necessarily correlated with the regulatory airspace class for a given volume of air at a given altitude.
The two altitude limits are different (not "incompatible"!):

One is regulatory, and binding on pilots. No pilot may operate in the Class B airspace, unless they have received a clearance from ATC allowing them to do so. For IFR aircraft, they will receive their clearance on the ground; they will be cleared to fly a certain route at a certain altitude, and it does not matter what airspace class the route crosses or enters, because they have already received a clearance to fly that route. For VFR pilots, they may operate as they wish in Class E airspace, but before entering Class B airspace must receive a clearance from ATC telling them which heading to fly at what altitude. (There are similar but less restrictive requirements that VFR aircraft must abide by to enter Class C or Class D airspace.)
The other is not regulatory, and has to do with ATC. Regardless of the airspace classification of any volume of air, one and only one specific control position is responsible for all aircraft operating within that volume. The document you found lays out the boundaries (in 3D space) for those volumes of air, which are not directly relevant or known to pilots. The volumes will be designed so that certain activities (arrivals joining the localizer and coming in to land, or departures climbing away from the airport) can be monitored and controlled by only one controller without unnecessary handoffs.


would a dimpled heat shield reduce heat transfer during reentry? Would a large ceramic golfball absorb less heat on reentry than a standard sphere?

"The difference in the flowfields around a smooth sphere and a rough, or dimpled, sphere can be seen above. Since the laminar boundary layer around the smooth sphere separates so rapidly, it creates a very large wake over the entire rear face. This large wake maximizes the region of low pressure and, therefore, results in the maximum difference in pressure between the front and rear faces. As we have seen, this difference creates a large drag like that seen below the transition Reynolds number"(http://www.aerospaceweb.org/question/aerodynamics/q0215.shtml).

Would the reduction in heat absorbed be significant enough to warrant a larger payload via lessening the weight of the heat shield?

Near as I know, the key to designing good re-entry vehicles or shielding is large flat plates, primarily because the design ensures the energy transfer from kinetic and potential energy of the craft to thermal energy  occurs mostly in heating the air flowing around the shape rather than the craft itself.  It sounds kind of counter intuitive, but doing this ensures the spacecraft remains as cool as possible and the least risk to structural damage from heating exists.  Therefore reducing drag is these applications is not a top priority.


Can I become a Commercial Pilot if I had OCD? In a few weeks, I am going to get off my medication for OCD treatment. The FAA says if episodes are severe enough to cause disruption of vocational or educational activity then I should be disqualified. In the very beginning that was the case, but now school helps me not to think about it.

The FAA says if I am on medication or have suicidal ideation then I should be disqualified. Well, considering I am getting off my medication in a few weeks that means it's not a required medication, right? And I have never had any suicidal thoughts.

Maybe. It depends on how severe the OCD was, the root causes of the disorder, the length of time since the last episode and the likelihood of future recurrence. The aviation medical system is set up to be conservative for good reasons, the cockpit is a bad place to become fixated.

If your condition is/was stress related then I would expect it to be a no, flying can be very stressful at times, you have to be able to handle fluid, difficult scenarios.

Your best answer will be from an Aviation Medical Examiner, I suggest you speak to one, it's what they're for.


Are runway safety areas for both emergency landings and aborted take-offs? Is a runway safety area at the end of a runway provided specifically for safe emergency landing of aircraft using it and are required to abort takeoff just before or after reaching the critical V1 speed? Does it mean that at big international airports with a number of runways, each and every runway is to be provided with its own runway safety area?

Yes, the runway safety area is to provide a buffer zone for aircraft that leave the runway for whatever reason, including rejecting a take-off late or by overshooting on landing. It's not specifically for an "emergency landing": sometimes the emergency might only arise during the course of the landing, for example tyres bursting or pilot error.

If it were only for emergency landings, then parallel runways probably wouldn't need to all have a RSA, because the distress aircraft could be offered the one runway that has one. But in fact every runway needs an RSA, because any landing might suffer a runway excursion.


Are gate ramps sloped? If you’ve ever seen an airliner park at its gate, you’ll likely note that sometimes it will move beyond slightly beyond its designated parking line. However, you may see that after the brakes are applied the aircraft moves back in “reverse” onto the correct parking line. It appears to me that this is as a result of gate ramps being at an angle. Is this correct? If not what are other possibilities for this phenomenon?

(Source) Drain system.

ICAO SARPs Annex 14 does not mention a direction of slope, it only says:

  Recommendation.— On an aircraft stand the maximum slope should not exceed 1 per cent.

So that's fairly level. But tiny slopes are needed, but not necessarily facing away from the terminal. They are needed to guide the rain (and any fuel) toward the trench drain system.

Not always are the drains parallel to the terminal and behind the parked aircraft. They can be parallel to the plane's longitudinal axis or even at the terminal.

I have never seen a parking that intentionally overshoots the mark. What you may have seen is a small backward jerk, like when trains stop. That's due to the offloading of the nose landing gear.

Pilots are guided in via stand guidance systems or ground marshallers. And they stop when the stop sign is shown. Guidance systems are never calibrated to overshoot the spot (the pilot might end up having to blame the birds).


Can I continue school for the PPL in another country in another flight school, if it is still inside EU? I am attending flight school for PPL at the moment at a flight school in Italy.

Next year I will study in Germany. It is possible that I will not have finished the PPL until then. Now theoretically the university is still very near at my home place (3 hours with the car), so I could somehow manage to finish my license.

However, would it theoretically be possible to continue my license in Germany at another flight school? I can speak Italian, German and English fluently, so language wouldn't be a problem.

Laws within the EU can vary, however I would assume it would be possible to carry on training in another country, however I am not sure.

The best way to know, would be to ask your flight school! :)
They may know, and could contact the school you want to move to and work out a deal.

Best of luck

EDIT: In my country (Australia) it is possible to continue training overseas, even though we are not part of an EU style union.

EDIT 2: As I stated, if you currently undertake flight training, your instructor would know better than any online message board.


How do SIDs work in New York City? I've started working to make airport files for an online ATC game, and my first airport is Newark Liberty (DP: https://flightaware.com/resources/airport/KEWR/DP/all/pdf).  What I already understand is that there are various climbs valid for different runways, and that the SID directs each aircraft to its first fix.  What I don't understand is how the climb is determined for each aircraft.  I also want to know how often airplanes use the SIDs, as I sometimes see planes on Flightradar not following the climb paths.

Thanks, this has confused me for a week or two.

The LIB4 and EWR4 SIDs, and others like them with just a bunch of VORs, are designed to give ATC maximum flexibility and assume radar vectors. Basically, you take off, make a turn or two to get clear of the airport (and any low obstacles), and then ATC will vector and climb you based on conflicts with other planes at that moment, so you'll probably never get the same instructions twice. There is no real plan; it's literally made up on the spot by each controller for each plane.

The PORTT4 (RNAV) SID is completely different: you have various specific routes to follow and detailed climb plans for each. Many such arrivals and departures in an area will be carefully designed to never conflict with each other (the top and bottom altitudes listed usually indicate there's another SID/STAR crossing 1000ft above/below at that point), so ATC just watches to make sure everyone follows the plan—and gives out shortcuts when possible. Unfortunately, that SID is only valid for two of the six runways, though presumably they're the ones used most often.

Note the latter's lost comms procedure is just to follow the charted plan you're expecting to follow anyway, though without any shortcuts, whereas the former has an entirely different (and uncharted) plan that you'd probably never follow otherwise.


Where is the fuel stored on an aircraft’s wing? Maybe guys could provide me with a picture I originally thought the anti-shock pads were fuel tanks, but somebody recently told me that they are stored in the wing, so where are they stored at. The aircraft I refer to are like the (b737), (b747-8)(b787)(a-350)

This depends on the aircraft. In many cases there is a tank inside the wing. In some cases it can be stored in a soft bladder in the wing and in other cases the wing its self is the tank.

Here is an in wing tank

Here are some in wing fuel bladders.

Mooney was known for having integrated fuel tanks in their wing designs. Here are some pictures of the tanks being resealed. They are notorious for needing a reseal every now and again but they do save in weight. Modern composite structures often don't lend to this design as jet fuel or avgas and composites don't really mix.

Here is a nice cutaway of the A330 to show where the tanks are.

It should be noted that you can generally pump fuel between the tanks however care must be taken when this is done because it can greatly effect the CG. This podcast has some really interesting information on how complex it was to manage the fuel weight on the Concorde and how it needed to be pumped around the tanks during various phases of the flight just to keep the plane stable.


Is quadcopter design scalable? I've been recently introduced to the world of mini aircraft, specifically, quadcopters - building them, flying them, calibrating them (apparently, it's such an important point that it deserves its own place on the list :) .

I'm about to finish building my own quadcopter (as soon as I can get a power distribution board - hard to find, it seems), and my hands are itching to try and fly it as soon as possible. I've learned a lot about how planes / helicopters / quads fly while in the process of building one. But maybe I haven't not learned enough about it, and was hoping you can help me with one question I have.

I think I've learned enough about the types of propellers used in these vehicles, power requirements, controllers, calibration, and whatnot. While searching about these things on the net, and asking a few friends about their experiences, a thought came into my mind:

Wouldn't be nice if I could, basically, scale all the components of this small, 330mm vehicle I'm building, to make something bigger?

I mean, bigger as in big enough to carry one, maybe 2 people around ?

Can I really say "hey, let's build a frame X times larger, with stronger materials, lets get 4 motors X times bigger, let's use 4 X-sized variable pitch propellers" and so on and so on, and actually be able to build a quadcopter able to carry people in it?

(Yes, yes, I know I'm basically saying "let's build an actual size helicopter, but with 4 propellers instead of one".)

Do you think this is a feasible approach to build such a thing? Is it even remotely possible? Have you had any experience doing such a thing? Any comments will be highly appreciated.

Ducted fan designs like quadcopters are actually somewhat simpler in some ways to design and build than single-rotor helicopters, because the nature of the design means that the rotors don't need the complex mechanical linkages of a helicopter's main rotor; the four rotors can control pitch and bank simply by varying RPM, and so each one can be a fixed-pitch propeller. The design becomes more stable with a variable-pitch rotor design as the possibility of varying thrust with a constant rotor speed reduces unwanted roll moments from gyroscopic forces, but that throws the simplicity argument out the window (and helicopters have potential roll problems during throttle-up as well, some of which had to be solved before the thing could even take off).

Yaw is a little trickier, and one potential limiting factor to scaling up the design. The problem is that with all four rotors in a fixed vertical orientation, which is the simplest mechanically, there's nothing to produce lateral thrust to turn the aircraft around the Z-axis (straight up from the ground through the 'copter in level flight). Options include:

One laterally mounted fan. Simple to design, but you're adding one more fan to a design with a lot of high-speed spinning parts already, and the fan would either have to stop and start in opposite directions very often (easy with a little DC motor and plastic fan on a model, much more difficult when scaled up), or the blade pitch would have to be variable, to allow variable thrust to either side while the rotor turns in one direction) which increases complexity again.
Two lateral fans, one facing each direction; by varying their power (they'll probably both be spinning at a low idle while in flight) you provide yaw. Advantage is mechanical simplicity of each fan, disadvantage is having not four, not five but at least six fans, reducing "mean time between failures" of at least one of them increasing required maintenance that much more to ensure it doesn't happen in flight.
Arranging the main four rotors such that each rotor rotates the same way as the rotor in the diagonally opposite corner, and opposite the other two. By reducing the power of fans rotating in one direction and increasing the power of the other, you can induce yaw as the craft will yaw opposite the direction of the faster rotors due to the torque imbalance, without causing the aircraft to also pitch or roll as the total forces in those planes stays constant. The advantage is reducing the need for additional rotors; the four main rotors can provide motion in all three planes. The disadvantage will be slower yaw rates and increased maximum thrust requirements of each rotor basically allowing any two rotors to maintain required lift (a good requirement to have, not a great one to rely on everyday).
Putting the main rotors in tilt mounts and tilting them in rotationally-symmetric ways to induce yaw. It's an intuitive way to induce yaw, and the same tilt-rotor system would also reduce the amount of pitch required of the full aircraft to produce forward motion; just tilt the rotors and keep the fuselage level. Disadvantages include increased mechanical complexity, and the gyroscopic precession induced by trying to tilt a rotating mass which can cause the craft to tumble off its lift vector.

Other potential problems with the quad-rotor design include ensuring reliable power distribution (including maintaining some control if a rotor or an engine gives up completely), the lower inertia of the smaller rotors reducing the effectiveness of autorotation in an emergency, the need by many potential customers to fold the design up more compactly than its flight configuration, and the inherent fragility of the design with ducted fans on pivots in the corners of the aircraft, making it more vulnerable to fatal damage in "combat environments" (translated; everyone not on your side shooting whatever they have at you). Because the U.S. military has been a major customer of rotary-wing aircraft and a primary source of R&D funding, the survivability of the design against things like small-arms fire that a helicopter can typically take a few hits from is a definite point of consideration.

The last problem plaguing the quadrotor is more fundamental, and it is the lack of an answer to this simple question: what can a "full-size" quadrotor aircraft do that cannot already be done as effectively and cheaper with a traditional helicopter? The primary reason quadrotors make good UAVs is that it's easier for a computerized fly-by-wire system to keep them stable, but that is their only advantage to date compared to a single-rotor helicopter, so until the aircar becomes a serious legal and engineering possibility and people want a rotorcraft that is as easy to fly as a car is to drive (or at least easier than a helicopter where you pretty much cannot let go of the cyclic, ever), the quadrotor will likely remain small-scale.


Does one have to practice engine failures in flight training? Are engine failures practiced normally? What exactly are the reasons? Is there a particular type of failure that is required training for all pilots worldwide?

From a general aviation standpoint here in the US, yes. Engine out landings and general procedures are practiced during your PPL training. No particular failure is trained for because there are really only 2 situations, the engine is running or the engine is not running. The procedures for different planes vary but generally you set for best glide, pick a touchdown point (airstrip if you can) and head for it. Once in route you can attempt a restart if you can identify the problem and solve it. on some planes you can feather the propellor and such.

That being said that generally applies to single engine planes, in a twin engine plane there are a few more situations depending on the design of the plane. In a twin you may have a "critical engine" as such engine outs are practiced with that in mind and the procedures are adjusted appropriately.

As for the why...

There are lots of things that can take out an engine like a bird strike, a mechanical failure, a fire etc. The fact of the matter is that it does happen  all be it not that often, you would be a fool not to prepare.

Anecdote:

When I started my training I got curious about piston engines cutting out so I began to ask around. Youtube videos aside, I was only able to actually find one guy who knew a guy that once lost an engine. Engine manufacturing has come a long way since the advent of airplanes and engines are simply more reliable than they once were. Here is a great article that touches on some of the twin engine points about reliability. While it does happen and you should never assume "this wont happen to me" engines are much better than they were 50 years ago when some of the requirements were made for the tests and training standards.


Why is Transition Altitude fixed but Transition Level is not? In Jeppesen approach plates we see that the Transition Altitude of the aerodrome is fixed but the Transition Level is not fixed and is given by ATC. What is the reason for this?

The point of flying on QNH is to keep you from flying into terrain, which is at a constant altitude above sea level, so TA is fixed.
Once you are high enough that terrain can’t be a problem and you only have to worry about hitting other planes, everyone can transition to QNE. However, because TL must be physically above TA, the difference between QNH and QNE will dictate what the lowest usable flight level is.


How to identify shock waves and expansion waves on a representation of the mach number? This image is a representation of the Mach number for $M_{\infty}=2.0$
I am very new to CFD and high speed aerodynamics. I'm trying to analyse this image, specifically to understand why the velocity decreases behind the trailing edge.
On the following image, I've tried to identify shock waves (1 and 3) and expansion waves (2) when the direction of the flow changes. However, after an expansion wave, the velocity should increase and it is not the case here so my interpretation must be false. How?

Thank you

Your airfoil is traveling supersonic at around Mach 2.

First the flow encounters a bow shock. Away from the leading edge, the bow shock morphs into an oblique shock. You can clearly see Mach number rapidly decreasing after the shock.
After passing through the thickest point of the airfoil, the expansion wave begins due to gradually increasing expansion angle. You can see Mach increasing, all the way up to around Mach 2.2.
At the trailing edge, the flow encounters a compression angle if you consider the wake as a boundary. Here, an oblique shock is encountered. Since oblique shock is less powerful than a normal shock, you can clearly see that Mach isn't decreasing as much as after the bow.


What is the geoid undulation used for in aviation? In addition of the altitude found on aerodrome information, the French AIP also mentions the value of the geoid undulation::

AIP for Lyon - Saint Exupéry (LFLL)

Geoid undulation is also found in Belgium, Switzerland, Poland, Morocco, Qatar, Sweden... AIP to name the ones that appear on the first pages of Google results.

US FAA on its side mentions the ellipsoidal height directly.

On the figure below:

Ellipsoidal height is $h$,
Geoid undulation is $N$
Orthometric height is $H$

Source

A GNSS receiver determines the ellipsoidal height $h$, and can display the orthometric height $H$ by adding/subtracting $N$ from grid values embedded in the device.

Is there any use of $N$ in aviation? In the cockpit?
Are the values of altitudes found on aviation charts equal to $h$ or to $H$ or something else? Does 821 ft expresses $H$ or $h$ for this aerodrome?

Note: As visible on the figure, the vertical direction determined by using $H$ is different than the one determined by using $h$, and if an aircraft is 35,000 ft above the ARP of Saint Exupéry, this gives two possible horizontal positions, which for aircraft can be very distant.

Earth gravity is not uniform due to the non-uniform distribution of mass/matter. Above is the standard model used to describe the undulation (up/down differences) of the geoid: Earth's sea surface's shape based on gravity and rotation (winds and waves are unaccounted for).

GNSS satellites orbit around Earth's center of gravity (a single point). So there will be differences between what a GNSS measures based on its model of the Earth (based on this single point: ellipsoid), and the actual.

Not all countries adhere to the standard above, hence the difficulty is agreeing to a model. GNSS devices use look-up tables to correct for the difference (the two spheres in your post are the difference between what the satellite sees and what it should see).

Cockpits show neither to the pilots. They use indicated or pressure altitudes/levels that work on the barometric pressure.

For cockpit indications: GNSS systems can't substitute for pitot-static measurements because everyone needs to have the same system and have a reliable refresh rate that is independent of external sources. As the image below shows, a pressure based altitude/level is also undulating due to the non-uniform surface pressure and lapse-rates. Planes fly up and down in level flight but it's hard to notice.

(Source)

For charting the terrain: Whichever system a country uses to mark the terrain on its charts, they will state the source in the AIP, as you've demonstrated. For the geoid, countries may even use different models as I wrote earlier.

The good news is each local station will correct the QNH based on the sea level pressure based on the country they are in.

RE edit:

821 ft is the 'H', which is the above MSL elevation after taking into account the geoid. 'h' is what an uncorrected GNSS receiver measures (982' in that picture), and needs to correct by 'N' (161'). Positive undulation is removed since it's above the 'ellipsoid datum'.

What is it used for?

Not used in the cockpit. It is used for local charting (standards differ from place to place; AIP's mention the source).

RE note:

  If an aircraft is 35,000 ft above Saint Exupéry airport, then this gives two possible horizontal positions, which for aircraft can be very distant.

No. But I have to explain why. There is no diagram online to explain it since it's a no, so I made my own erroneous diagram.

blue is geoid
dashed in ellipsoid
red is uncorrected receiver height (minus the bit travelling through the Earth)
green circle shows the different surface locations based on the normals from the different ellipsoid heights down to the geoid (what is proposed; it is not correct)
(ξ, η) is the deflection of the vertical, the angle stems from the ground, since the topography (different from geoid) is not illustrated above, it stems from where the geoid and ellipsoid meet (a correct sea level for both models)

Deflection of the vertical:

Imagine a table with non-uniform legs, such that two opposite corners are at on the same level, and the other two are not. If I place a ball on that table, it will move toward the lower corner.

If I want to measure this table's level against the ceiling/ground, I will need two vertical angles, one north-south and one east-west. If we had one angle, we wouldn't know the level's direction. That's why two angles are used.

Measuring this deflection is a key element in knowing the undulation (it changes from location to location). That's the angle that is causing this confusion.

x and y:

Now imagine yourself on top of a monument, this monument has x and y ellipsoid coordinates. You then attach yourself to a weather balloon and climb straight up (with reference to gravity). Your handheld GNSS receiver will not show different x and y values for two reasons:

x and y are not derived from z (whether corrected or not)
your ellipsoid (x, y) location has nothing to do with the undulation

The undulation is a correction for the z, it does not shift your [physical and measured] present location regardless of altitude. If the height (red line) is straight up from the monument, then left and right of the red line are different undulations for different locations.

Note that I couldn't draw the erroneous normals on the other side of the red line if I wanted to.

Check this article: How do GNSS-derived heights differ from other height systems? It explains where high accuracy is needed, and the issues that may arise when two countries with different geoid systems decide to build a bridge between them.

As @JanHudec mentioned, EGPWS needs the correction because its model is ellipsoid. So country x needs to have a system by which they measure the geoid, its undulation, and report to the aviation industry the correction. That's why when an airport is not in the database, the pilot gets, "caution, terrain," when they are on a good approach.

Another application is minimizing the drift of the inertial navigation systems, since they inherently indicate the astronomic vertical. It's cheaper to just correct the drift via the GNSS such as on the Boeing 787 (align-in-motion).


What is the meaning of "pass well clear" in the ICAO right of way rules? ICAO Annex 2 states under 3.2.2.1:

  An aircraft that is obliged by the following rules to keep out of the
  way of another shall avoid passing over, under or in front of the
  other, unless it passes well clear and takes into account the effect
  of aircraft wake turbulence.

How should the term "well clear" be correctly interpreted?

Does this sentence also imply, that the right of way rules only have to be applied, if the expected minimum distance to the other aircraft is below "well clear"?

This is probably one of those rules which is deliberately a bit open to interpretation. For example, a glider pilot will be happy to pass under another glider when hill soaring at 40 knots much, much closer than they would be if cruising at 100 knots! Other pilots will probably use standard separation minima, for example 500 feet might be acceptable in the powered circuit but 1000 feet is allowed in certain airways.

SKYbrary suggests that "well clear" means 500 feet, but again points out that it might not be sufficient when using TCAS.

The implication is of course intended. If one is "well clear" by 20,000 feet there is no need to take avoiding action!


What is that instrument with two knobs and what looks like range rings? I just flew a Piper Warrior today and I got confused with the instrument shown below, it's the one above the CDI and to the right of the altimeter.

WX-10 Stormscope

The WX-10 System consists of a display, remote processor, and an antenna. This Stormscope offers thunderstorm information on a bright green CRT display. The more the dots on the display are clustered together, the stronger the storm activity. Up to 256 dots may be displayed. The WX-10 also has a Forward mode to concentrate the display and processing power on the airspace ahead of you.
— bennettavionics.com

See also: Wikipedia: Lightning detection § Aviation use


What were those two military helicopters that I recorded? I have recently recorded two military helicopters. Here is a screenshot of it:

It is hard to tell from such a low resolution picture. Due to the shape of the narrow body, they look like USMC Bell AH-1 SuperCobra. It is probably the AH-1Z Viper version based on the four blade rotor.


Can PPL, CPL, and ATPL be completed within a year? It took me about 8 months to complete my PPL, because I struggled to go solo and I haven't started my CPL training yet due to financial set back.

I've heard about students who completed their PPL training in 2 months.

Is it possible to complete PPL, CPL and Frozen ATPL in 12 months and how do you go about it? And also, are there any cases? The one I've seen is 18 months.

Considering the fact that you have to write CPL exams, ATPL exams, IR, Night Rating, 100 PIC hours and other related tasks.

Given the hours required for the ATP, the chance of doing that rating alone in under a year seems pretty remote.

Getting the private and commercial certificates done inside of a year is entirely possible, although not cheap. The writtens for the ATP are no big deal, but the hours simply will take a lot of time, as well as the right employment opportunity, to get.

The number of FO's at smaller (regional) airlines who have been flying for several years but who don't yet have their ATP attests to the time required. You can (and generally have to) pay for the flight time to get your Commercial, but paying for all the flight time required for an ATP is simply beyond those of whose last name isn't Gates, Bezos, Trump, or etc.


How criminal is it to take off without authorization? In the US, how would someone like the Seattle guy be punished (that is, plane heist without passengers, unauthorized take-off and midair stunts ) if he hypothetically had not died, but landed the plane intact?

Background story: Richard Russell, Who Stole Plane Near Seattle

The FAA has limited ability to enforce criminal actions for non-compliance with FAR's. Essentially the pilot (certificated or not) would be subject to either Informal Procedures/Settlements, Certificate Actions, or Civil Penalty.

The FAA's policies, procedures, and guidelines are located in the FAA Compliance and Enforcement Program, Order 2150.3B.

In the case of stealing an aircraft by a non-certificated individual, the only recourse the FAA would have is civil penalties. The authority for the FAA is located in 14 CFR 13.14 or 13.18. The FAA has the authority to issue civil penalties up to \$400,000 against "persons other than individuals and small business concerns" (aka large businesses) or for individuals and small businesses up to $50,000.

In the case of the stolen aircraft, the charges would probably be theft and whatever other federal/local charges could be levied, but the FAA would probably not intervene here.

Teen aircraft thief sentenced to 13 months in prison (60 days served)
Felony theft charges for stealing airplane
Barefoot Bandit

It isn't strictly "illegal" to disobey an ATC "order". A PIC (supposing they are a licensed pilot) can disregard ATC if they feel that the safety of the flight would be in jeopardy if the order was followed. Specifically this is allowed by JO 7110.65W, page 3-3-1 and 14 CFR 91.123.


Does EASA allow IFR, NVFR or SVFR in gliders? Is it legally possible in Europe to get clearances for IFR, night VFR or special VFR while flying gliders? Specifically, I'm interested in sailplanes, powered sailplanes and ultralight sailplanes (MTOW below 472.5kg).

It's not possible to get IR for any of those. I think EASA now has flying in clouds rating for gliders. For night flying you will need a glider that is certified to do that. I don't know any manufacturers of night gliders. Blaniks had an option to fly at night but most of them cannot fly now at all.

SVFR may be possible in theory but it will be crazy. Maybe you can be towed in special VFR but this will be dangerous. It also depends on whether the country in which you are flying allows SVFR.


What is the metal bit in the front of this propeller spinner? What is that grey spirally bit in front of the propeller mounted on this Shvetsov ASh-62 radial engine?

It is a fitting for a Hucks Starter.

Photos from Vintage Wings Canada


What does pneumatic operated and electrically controlled means? I was going through A 320 FCOM and didn't understand this term

Pneumatic operated: actuation by using air pressure. By opening a valve, high pressure air enters a cylinder, causing a piston to be pushed out. Typically, actuators of this type have two valves connected to two separate chambers, allowing for movement both ways.
The valves need opening and closing, though. This is what the "electrically controlled" part means: a small electric (typically electromagnetic) actuator will open or close based on an electric control signal.


When should pilots observe a "Sterile Cockpit"? A "Sterile Cockpit" means avoiding all conversations and actions not related to flight during important flight times.  (eg. No extraneous conversations, no non-important electronics, no eating, etc)

Commercial pilots are told to observe Sterile Cockpit below 10,000 feet.

But what about Private Pilots who may rarely ever go above 10,000?  When do you begin observing sterile cockpit?  When do you consider it safe to talk with passengers, take a snack, or fiddle with the new GPS?

The "sterile cockpit rule" is an informal name for 14 CFR 121.542 and 14 CFR 135.100.  It says that no non-essential duties may be done during a critical phase of flight which is defined as "all ground operations involving taxi, takeoff and landing, and all other flight operations conducted below 10,000 feet, except cruise flight".  In your example, once they level off at cruise, even if it is below 10,000 feet, it no longer applies.

While this doesn't apply to Part 91 operations like you describe, it is a very good idea to follow the rule anyway to prevent distractions and increase the level of safety.

As far as the GPS, I would recommend fiddling with it on the ground before you takeoff and be familiar with its operation before you need to use it.  Being heads down for an extended period of time is never a good idea (unless you have a safety pilot along to keep an eye on things and look for traffic)!

The full text of the regulation is:

  §121.542   Flight crewmember duties.

  (a) No certificate holder shall require, nor may any flight crewmember
  perform, any duties during a critical phase of flight except those
  duties required for the safe operation of the aircraft. Duties such as
  company required calls made for such nonsafety related purposes as
  ordering galley supplies and confirming passenger connections,
  announcements made to passengers promoting the air carrier or pointing
  out sights of interest, and filling out company payroll and related
  records are not required for the safe operation of the aircraft.

  (b) No flight crewmember may engage in, nor may any pilot in command
  permit, any activity during a critical phase of flight which could
  distract any flight crewmember from the performance of his or her
  duties or which could interfere in any way with the proper conduct of
  those duties. Activities such as eating meals, engaging in
  nonessential conversations within the cockpit and nonessential
  communications between the cabin and cockpit crews, and reading
  publications not related to the proper conduct of the flight are not
  required for the safe operation of the aircraft.

  (c) For the purposes of this section, critical phases of flight
  includes all ground operations involving taxi, takeoff and landing,
  and all other flight operations conducted below 10,000 feet, except
  cruise flight.

  Note: Taxi is defined as “movement of an airplane under its own power
  on the surface of an airport.”

NASA has a great article called The Sterile Cockpit which goes into a lot more information, and includes some interesting statistics from the ASRS database about accidents/incidents that were in some way caused by not following this regulation:

  48% were altitude deviations

  14% were course deviations

  14% were runway transgressions

  14% were general distractions with no specific adverse consequences

  8% involved takeoffs or landings without clearance

  2% involved near mid-air collisions due to inattention and
  distractions.

Abiding by the sterile cockpit rule can help you to avoid situations like that! The article also gives some examples from the database and talks about a couple of crashes that were attributed to lack of compliance.


What is the main difference between an ETOPS certified and non-ETOPS certified plane? ETOPS stands for Extended-range Twin-engine Operational Performance Standards, a rule which permits twin engine aircraft to fly routes which, at some point, are more than 60 minutes flying time away from the nearest airport suitable for emergency landing.

However, it does not mean that a non-ETOPS plane physically cannot fly an ETOPS route, as American Airlines proved when they accidentally used a non-ETOPS certified plane to operate ETOPS-required LAX-HNL route. Everything went well except the cancelled return flight.

So, what is the difference between an ETOPS certified plane and a non-ETOPS certified plane when they are the same model?

The FAA ETOPS certification requires certain standards from both the airline (the operator) and the aircraft (the manufacturer).

As far as the manufacturers are concerned, the ETOPS certification is given for a particular aircraft-engine combination satisfying certain requirements. The FAA ETOPS Rules Section A deals with the Airplane-Engine Type Design Approval. According to the document, the type approval involves a two step process:

  First, the FAA determines that airplane systems meet certain design standards for safe operations during an airplane diversion.

Some of these requirements are:

The aircraft should have at least three independent electrical generators.
The auxiliary power unit (APU) (when required) can start after the airplane has been cold-soaked for several hours and can run reliably for the remainder of the flight.
System safety analyses have to show that expected system failures will not prevent safe landing at a diversion airport.
Systems with time-limited capabilities (typically cargo fire suppression) need to have the capacity to support a maximum-length diversion,
including a 15-minute allowance for a hold or go-around at the diversion
airport

  The second part of the approval process is an evaluation of engine in-
  flight shutdowns and other significant airplane system failures that have
  occurred while the airplane-engine combination has been in service.

The aircraft-engine combination should have at least 250,000 engine-hours for evaluation, though this can be reduced with compensating factors. The airplane-engine combination should maintain a target IFSD (In Flight Shut Down, defined as "When an engine ceases to function (when the airplane is airborne) and is shut down, however briefly, whether self induced, flightcrew initiated or caused by an external influence.") rate at or below 0.02 per 1,000 engine-hours for 180min ETOPS approval.

The manufacturer should also demonstrate that flying with OEI doesn't cause undue stresses to the aircrew and is safe for the airframe.

The ETOPS design approval has to be applied for with the FAA and obtained after the relevant processes. Thus, the same aircraft will not have ETOPS approval if the engine is different or even the same aircraft-engine combination won't have ETOPS approval if used by another airline or if no certification was sought.

There is another method of getting ETOPS approval called the 'early' ETOPS approval which

  ...takes a systems approach to the development of an airplane and engine. ... an applicant must demonstrate that the design flaws on previously designed airplanes are not present in the new airplane. The applicant must also consider how the maximum length flight and diversion affect the design and function of airplane systems to ensure that they have the capability and reliability for safe ETOPS flight.

After being ETOPS certified, the airplane-engine combination and the operator are under continuous monitoring with the certificate being withdrawn in case of lapses or if the IFSD rate goes above the target rate and the manufacturer's corrective action does not eliminate the unsafe condition.

As far as the LAX-Hawaii incident is concerned, according to American Airlines Spokesman, both aircraft (the 'correct' ETOPS airplane, A321H and the wrong one sent, A321S) had the same configuration, but

  There are two small differences in terms of equipment to allow ETOPS certification. Since you can’t divert for medical [on a Hawaii bound flight], you’re required to carry extra medical oxygen on board and an extra fire suppression canister

There are also reports that the (ETOPS certified) A321H has extra fuel tanks, which the (non ETOPS certified) A321S didn't have, though the AA spokesperson had said that the fuel tanks and range were the same.


Does the EASA/FAA require additional life vests, and life vests for infants/children? Is there some requirements (EASA or FAA) for additional life vests, and life vests for infants/children on-board estimation?

From the FAA's Flotation Equipment for In-Lap Children InFO (Information for Operators):

The FAA recommends:

  Consider installing flotation equipment designed specifically for in-lap children.

(Emphasis mine.)

We also find:

  If an air carrier provides flotation equipment for in-lap children that is located or operates
  differently from the typical flotation equipment for other occupants, then additional information
  regarding that special equipment would be required in the briefing given to passengers.

Which means it will briefed to the passengers if it is present. (Too many if's.)

For the FAA, there is no requirement to have multi-sized flotation devices. Remember, seat cushions work well, and infants aren't good swimmers, but they also don't panic in water (maybe not all of them).

  A reflex called the bradycardic response makes babies [up to 6 months] hold their breath and open their eyes when submerged in water, says Jeffrey Wagener, a pediatric pulmonologist in Colorado. (Source)

Cute video: Baby's first swim - underwater!


Why are the Constellation's nosewheels canted inwards? Why are the nosewheels on the Constellation canted in a few degrees? Is it to ensure both tyres have ground contact during tight ground turns?
I've observed that on the A320 during tight turns that one wheel comes completely off the ground. The A320 nose leg also sits at an angle; would it benefit (if needed) from angled nosewheels?

http://www.ipmseaglesquadron.org/ES-Forums/index.php/topic,1639.0.html

@JohnK gives an excellent explanation for castor - the horizontal offset between the steering axis and the tire contact point.
But maybe the question is about camber. That is the angle between the vertical axis of the tire and the vertical direction relative to the ground. The camber angle on the Connie's nose wheels is called positive camber, and an extreme case can be found on the tractors of that time. Curiously, it is a distinct characteristic only of US tractors like the John Deere (left) and Farmall (right) tractors below (picture source).

The reason is easier steering in rough terrain. As a tractor discussion board explains:

I have read that positive camber is intended to align the kingpin axis with the center of the tire contact patch. Supposedly this reduces the force required to steer the axle. If that theory is true, then changing the height of the tires would change the intersection point of the camber angle and the kingpin angle; it's improbable that swapping between, say, the correct R4 tires and the correct R1 tires for your tractor would make significant differences.
However, I am not convinced by the theory that the positive camber is there for steering ease. Here is why: I think it would be easier to roll a tire around in a circle than it would be to simply twist it, especially if one considers the tire will be pushing dirt out of the way as it twists.
I think the reason for the positive camber is to attenuate the camber thrust that can occur when the tires encounter uneven terrain. This would tend to help the tractor track straighter, and require less steering input to maintain a straight course. That characteristic, along with the caster geometry, should make the tractor track straight naturally, rather than tending to turn more when either a steering input is made or some uneven terrain is encountered.

The author of this post has his own theory; however, the point made in his first sentence actually has merit: Since steering in automobiles and European tractors is made easier when the steering axis runs through the contact point of the tire with the ground, positive camber is an attempt to reduce the steering roll radius of the twin tires which indeed should make steering easier.

Steering axis inclination reduces the roll radius in cars (picture source); since the sideways axis inclination could not be used in nose gears or tractors, both resorted to tire camber.


Does Russia still use a Snowtam to report normative brake friction? Does Russia still use the normative (Russian) brake friction when reporting Snowtams for their airports? What about former Soviet (CIS) countries?

Long story short, as best I can tell everywhere except Kazakhstan uses the ICAO SNOWTAM format. Kazakhstan uses two different Russian formats depending on what airport you're at, which is an interesting approach to say the least.

First, the Russian format is described here, it's a decimal value where less than 0.31 is "unreliable" and more than 0.41 is "good". In fact, there are two Russian values: the "raw" value as measured directly by a friction device, and the "normative" value that is derived from the raw one (although I couldn't find any explanation of how). I guess that the raw value is supposed to be the actual coefficient of friction.

The ICAO format, on the other hand, is an integer value from 1 to 5.

(Incidentally, I'm aware that I'm blurring the distinction between format and values here, but since there is so little definite information on this topic available - at least in English - I don't think it matters much.)

The Russia and CIS AIP includes a Snow Plan 2013-2014 that states:

  [...] friction coefficient will be distributed by means of SNOWTAM in
  ICAO format (Annex 15)

That immediately suggests that Russia and the CIS now use the ICAO format, and considering the lack of any information about Russian format SNOWTAMs in the AIP or on the web in general, it seems very likely that the ICAO format is now the main or only one in use.

However, Kazakhstan appears to be an exception. There is a permanent NOTAM for Almaty airport (ICAO: UAAA) in Kazakhstan that includes this remark:

  K0706/13 NOTAMN Q) UAAA/QFBCS/IV/M/A/   /   /4321N07702E A) UAAA B)
  1312010001 C) PERM E) AT ALMATY AERODROME THE INFORMATION ON RUNWAY
  BRAKING ACTION IS TRANSMITTED BY ATIS AS FOLLOWS: IN ENGLISH-IN VALUES
  OF ESTIMATED SURFACE FRICTION RELATIVE TO MEASURED ''SFT'' FRICTION
  COEFFICIENTS. IN RUSSIAN-IN NUMERICAL VALUES OF NORMATIVE ''RUSSIAN''
  FRICTION COEFFICIENTS.

There is a very similar NOTAM for Shymkent (ICAO: UAXX) that includes this almost-but-not-quite-the-same remark:

  K0707/13 NOTAMN Q) UAXX/QFBCS/IV/M/A/   / A) UACC UATT UAII B)
  1312010001 C) PERM E) AT ALL AERODROMES EXCEPT ALMATY THE INFORMATION
  ON RUNWAY BRAKING ACTION IS TRANSMITTED BY ATIS OR ATC AS FOLLOWS: IN
  ENGLISH-IN VALUES OF ESTIMATED SURFACE FRICTION RELATIVE TO NORMATIVE
  ''RUSSIAN'' FRICTION COEFFICIENTS. IN RUSSIAN-IN NUMERICAL VALUES OF
  NORMATIVE ''RUSSIAN'' FRICTION COEFFICIENTS.

There is no similar NOTAM for any major Russian airport.

If I put all this information together, it appears that:

Russia and the CIS now use the ICAO format for SNOWTAMs
Almaty in Kazakhstan reports braking action in the 'raw' Russian format
All other Kazakhstan airports report braking action in the 'normative' Russian format


Do any manufacturers have plans to use turbojets in future aircraft? What is the state-of-the-art in turbojet design? Turbojets have largely been superseded by turbofans (or turboprops for low-speed flight). Are there any aircraft being planned that would use turbojets?  I'm also interested whether there has been any improvement in turbojet design over the last few decades.

The first jets were turbojets simply because the turbine could only support its own compressor. They kept an edge for supersonic flight and will be the engine of choice if we ever design another Mach 3+ aircraft. Also, micro jets for cruise missiles and model aircraft turbines are turbojets to keep them simple. However, the analysis of modern jet warfare showed that the overwhelming majority of flight time is spent at high subsonic speeds, and there a turbofan makes more sense.

Now all modern combat jet aircraft use turbofans, even though their bypass ratio is rather low (around 0.5).

Commercial jet transport engines are solidly turbofans since half a century and have slowly increased their bypass ratio to about 9, less for smaller engines. Now three-spool engines or geared turbofans are state of the art, because they allow more freedom in optimizing the rotation speed of the different sections inside the engine.

Turbojets have benefited from better, more heat-resistant materials and airfoils for turbo machinery just as much as turbofans, but modern designs are overwhelmingly turbofans, so turbojets generally represent a much earlier technological level. To give you an example: The first turbojet used in operation, the Jumo 004, had a mass of more than 700 kg and produced 8.8 kN of thrust. The engine of the Eurofighter, the EJ200, is only slightly bigger in mass and has similar dimensions, weighing 990 kg, but produces seven times the thrust of the Jumo 004. With reheat, thrust is more than 10 times that of the Jumo 004, which had no afterburner. The pressure ratio could be increased from 3.2 to 26 (that is the progress in compressor aerodynamics), and the turbine entry temperature from 840°K to 1800°K (that is the progress in materials).


Will depression from 20 years ago prevent me from being an airline pilot? I was diagnosed with clinical depression at age 16 and was on prozac for a year.  During that time I coped and after six months I tried taking myself off the medication because I did not like the feeling of being medicated.  I have been free of this for nearly 20 years.  I have had no relapses, I have never been medicated since then.  I also attribute my falling into it in the first place due to lack of coping skills since I was so young, given my life experiences since then I don't know how I let myself "slip".  However, will this prevent me from ever becoming an airline pilot?  I have saved up the money to go....  Even if I get evaluated and given a clean bill of health does this doom me to be forever be thrown on the "reject" pile???

It does not sound like a dealbreaker, however I'm not an aviation medical examiner. I do not think that depression diagnosed when you were a minor would prevent you from becoming a commercial pilot now, I do not even know if you would be required to declare it to an airline on an application. The biggest hurdle you would have is the medical I would expect. You might need to have a psychiatric evaluation, or it might be far back enough that isn't necessary. It likely depends on the severity of the depression you were diagnosed with on the DSM (diagnostic and statistical model of mental disorders, a tool used by professionals to assess and diagnose mental conditions) scale.

My recommendation would be to talk to an aviation medical examiner. Many pilots deal with, or have dealt with depression, sometimes severe, so it should not be hard to answer. You lose nothing by trying.


Is the cargo door on this airplane really malfunctioning? Recently, I saw that video:

EDIT: I removed the Facebook video link which would require sign up for anyone without an account. I've re-uploaded the video here:
https://vid.me/8WYI

In general, this guy's videos seem to me more like a "conspiracy theories" thing, but I hadn't the time to study them and find the underlying faulty logic. So, in that particular video, he claims that the cargo door of an aircraft wasn't working properly and the ground staff simply decided to use a heavy load on the lever in order to open it (or something like that).

Because of that incident the plane shouldn't be allowed to fly (that's what he claims) and also there is immediate safety concern for the people on the ground because of the weight they used.

My questions are:

Is the cargo door in that airplane really malfunctioning?
Do the ground staff follow a standard procedure for the "workaround"?
Although I understand that the way the weight is "hanged" on the that
lever is not a safe solution, my logic says that it could never fall
from that position. Am I right?

It appears as though the locking handle for the door has some sort of switch in it to allow for full extension of the door only if the locking handle is pulled full forward and, for whatever reason, the door handle won't move into this fully extended detent on its own.  While the workaround is jury rigged at best, it doesn't seem to pose a flight safety issue unless the door can't be locked when fully closed.  It's just another video from an ignoramus in the terminal with a cellphone camera.


How can a CFI renew their certificate with the FAA during the government shutdown? My CFI certificate expires at the end of the month. I have completed the required Flight Instructor Renewal Course ("FIRC"), but when I called my local FSDO to make an appointment to submit my renewal application for a new CFI certificate I discovered that the FAA is shut down. If the shutdown continues through my CFI expiration date, can I renew my certificate with the FAA after the expiration date?

Short answer is no, but there is a way to renew your CFI while Federal Government is shutdown. However, it's not through the FAA because so long as the FAA is shut down it cannot process applications.

(After a few hours of freaking out at the thought of having to redo my CFII check ride, I discovered there is a solution to this.

While the FAA is not processing applications during the government shutdown, the FAA has authorized certain non-federal employees to accept and process airmen applications for CFI renewal AND to issue temporary flight instructor certificates. These are called Airman Certification Representatives (ACR), and are defined as:

  Airman Certification Representative (ACR). An ACR is an individual representing a specific FIRC provider who is authorized under Title 49
  of the United States Code (49 U.S.C.) § 44702(d) to accept airmen
  applications for renewal of a valid flight instructor certificate from
  successful graduates of that provider’s FIRC and to issue temporary
  flight instructor certificates

Source: Advisory Circular 61-83J.


How could a turbocharger experience over-boosting due to cold oil? How can cold oil cause a turbocharged engine's automatic waste gate to stick, leading to over-boosting?

Diagrams I've found online for waste gates don't appear to indicate a connection between it and cylinder oil.

The wastegate system uses engine oil pressure to drive the wastegate actuator, and this oil pressure is metered to the actuator by a controller that senses manifold pressure and throttle position and admits more or less oil to the actuator to drive the wastegate butterfly valve, to achieve the manifold pressure commanded by the throttle opening.

The responsiveness of the control system is sensitive to oil viscosity.  When the oil is cold, the controller and actuator is sluggish and laggy because of the thick oil, which can lead to overboosting when the throttle is opened quickly and the wastegate is unable to keep up, resulting in excess flow through the turbine and excess boost.


In the event of a crash over thick snow or a forest, would it be safer inside the aircraft or free-falling? I just saw this question about humans surviving terminal velocity free-falls, sometimes even with little injury depending on the surface conditions, particularly over forests, hills, or thick snow cover.

That made me wonder, if a passenger of:

a large commercial aircraft, perhaps a Boeing 737
crashing from 5000 meters or higher
above a large forest or thick snow

had the choice between free falling and buckling up to crash with the aircraft, which option would offer him the greatest chance of surviving?

I'm thinking the plane might offer lower falling speed, and physical protection, but also pose the dangers of giant engines, explosions, and crushed metal / shrapnel. Perhaps the answer is that over a forest, the free fall could be safer, and over snow the plane could be safer, but that's pure speculation on my part.

Statistically, there has got to be graphs you can combine to show the number of airplane crashes to fatalities and a graph with skydives (without a chute/malfunctions) to fatalities. I'd venture to say that the odds are far greater to surviving an airplane crash than a freefall.

Let's look at the factors...

A freefall:

your velocity in not slowed by anything
your body is not protected by anything
you have no control on where to 'crash'

A crash landing:

passengers are slowed greatly by the aircraft
passengers are greatly protected physically (airframes are designed to minimize risks from explosions, shrapnel, and crash G's)
there is a greater chance the aircraft can be controlled somewhat to crash in the best place.

The only time it would be better to jump without a parachute is if you are this guy or the aircraft is about to be torn apart.


Will prior hospitalization for alcohol intoxication prevent the issuance of a first class medical cert.? I recently went to the hospital for alcohol intoxication, will that cause any issues getting my first class medical exam this week? I live in the US, I am a college student and I have rarely drank before; this was mostly a case of not eating and not drinking often. And trust me I don't even want to touch a bottle of alcohol for a very long time.

Possibly, but not necessarily.
First, nobody here is an AME, and a message board is the wrong format, if any of us were, to ascertain all the relevant facts.
Second, you'll need to put that hospitalization on the form you fill out for the exam. To omit it would be a criminal offense, so don't do that.
There are at least two things the AME will consider about what happened. First, is there any lasting damage from that incident? Second, does this indicate enough of an issue with alcohol that it has to go to OKC for their consideration? Both of those questions turn on the specific facts of your case. If both are "no" then your chance of losing the medical may be pretty low. Otherwise... it's all about how your case stacks up with the FAA rules and procedures.
Your best answer may be to consult with one AME to whom you are NOT applying for the medical, and get his expert opinion. Then, with that knowledge, apply (or don't) to your AME for the Class 1.
But please don't substitute internet forum opinions for professional medical advice from an actual doctor.


How can I find which engines are used on the different A320 weight variants? When looking in the type certificate for the different configurations of the A320, I found a lot (really, more than 50) weight variants listed. But none seemed to mention the actual engine paired with that specific weight variant. Is there something I am missing, or is there another way of finding out?

Each section will list the specific models that it applies to. For example, in the Maximum Certified Masses section for the A320 (1.III.13), you'll see the first section applies to the A320-211/A320-212/A320-231, and it lists the 19 variants of these models.

Next you consult the engines section (1.III.5), which will tell you, for example:
A320-211 - Two CFMI CFM 56-5A1 jet engines (MOD 20141), or CFM 56-5A1/F jet engines (MOD 23755).


How can a tug be referred to as company? I was listening to some [REAL ATC] MD-80 DELTA CRASH at LaGuardia Airport and noticed something just after 8:41. My question isn't about the accident, but actually about a request to the LaGuardia Tower from Tug1 (or Truck1, it's not clear, although the CC calls it Tug1 it sounds like Truck1) where the tug asks "Tug1 at company, we can cross Papa?"

I understand that the term company is used during ATC communications to tell one plane of a company (such as American Airlines) that they are talking about another airplane from the same company.

But how can a Tug/Truck be referring to a place as company?

I just saw BowlOfRed's comment, and listened to it again and I could make it out this time as "Tug 1 and Company". So, basically, when used with vehicles, using "and company" will often indicate that there's more than one vehicle in the group(or possibly aircraft in tow), and whoever's being addressed is in charge of talking for them. Just like when a flight of aircraft is flying or taxing, whoever's talking for the flight, that callsign is used for the whole group.

For other examples of "and company": During snowplow operations, usually you'll just have 1 driver in a group talking to Ground/Tower for that group, and they're also in charge of reporting when all their group is clear of runways or other movement areas. Other times, it's when airport operations is escorting(via vehicle) other vehicles on the airport, from survey crews to construction crews.


Can the ECS work in an unpressurized cabin? Can you control the cabin temperature if the cabin is unpressurized? What if the "cabin" isn't really that big, like a fighter aircraft?

For example, could I cruise in comfort at 20,000 ft in an unpressurized cockpit with an oxygen mask and heater?

If the cabin is unpressurised, the temperature could be controlled to a limited extent- this is usually done in a number of helicopters.

You can certainly cruise at 20k feet without a pressurized cabin - WWII pilots regularly did this with supplemental oxygen and heated clothing- though I'd hardly call it comfortable.


Is it possible to fly with counterbalanced single blade engines? Refer the image for counterbalanced single blade (Source http://www.aviastar.org/helicopters_eng/bo-103.php).

In ground school, they took us for aircraft inspection at end of our ground school classes. The instructor told us that "counterbalanced single blade engines" are efficient.

I have 2 questions here

Why development under these fields are stopped (Bo-102/103)?
How Single blade will be efficient than 2 blades rotor-craft engines?

Both Bo-102 and 103 were experimental aircraft, with Bo-102 more of a jig than an actual aircraft. They were used a testbed for various technologies and the single blade rotor is only one of them , with the main thrust being in the development of (hinge-less) rigid rotor and (glass fiber reinforced) composite blades.

The single blade rotor offers some advantages over the (normal) multi-blade configurations like,

The blade passes through 'clean' air and is thus more efficient compared to the multi-blade configurations, where the (following) blade passes through the turbulent (wake) air from the previous blade, at-least in hover.
The single blade propeller is compact and for this reason, is used in some self launching gliders which fold their propellers inside their fuselage,like the Alisport Silent 2 Targa.

However, there are significant problems associated with this design,which makes it (mostly) unsuitable for widespread use.

For reducing vibrations, the blade has to be counterbalanced by a mass, which is practically dead weight. While this may be acceptable for small and lightweight propellers used in gliders, this is a major problem in helicopter blades, which are significantly heavier. For example, the Mi-17 Main Rotor Blade weighs ~140 kg.
If the mass is  kept low, the lever arm is huge and this increases drag.
Though the blade may be  balanced at the pitch axis (to reduce vibrations), torque induced in the rotor blade (due to lift) will cause significant vibrations. As the torque is increased, if the weight is fixed, the rotor will tend to rotate the engine and rip it off. The only way to prevent this is to balance the blade, both aerodynamically and centrifugally, which is easier said than done.
The same problem arises as the drag of the blade is different from that of the mass arm, with a torque being created parallel to the axis of rotation.
The rotor blades usually 'cone' in flight; this means that the lift vector is slightly tilted towards the center, not concentric with the rotor plane.
The blade has aerodynamic forces acting on it while the balance weight does not. Due to this, the precess differently, which causes unbalance and vibration.


How much lift comes from the fuselage on modern jets? I understand this question is broad, but specifically referencing modern jets where composites are used a lot to get complex surfaces (such as in the Beechcraft Premier 1), how much of the total lift is generated by the fuselage versus the wings, perhaps as a percentage of total lift? The fuselage is obviously a lifting body and I’ve noticed the same in other current designs.

Not as much as potentially possible. This thread lists the numbers for some common aircraft and should give you a general idea, it seems to be ~10%

  747:

  Wings: 89.5%
  Fuselage: 13.1%
  Horizontal Tail: -3.7%
  Vertical Tail: .1%
  Nacelles and Pylons: 1%

  P-51D:

  Wings: 92.9%
  Fuselage: 7.7%
  Horizontal Tail: -.7%
  Vertical Tail: .1%

I belive the center bulge on the bottom is also there to allow for a floor recess in the cabin making it easier to get around.


Is there an equivalent of cash transportation in air cargo? Some cargo (cash for banks, precious art pieces, gold, jewellery,...) are transported in bullet proof trucks with armed guards while travelling by road. Sometimes it may also be escorted by police.

Is there an equivalent for air transport? How is protecting handle for such cargo when transported by air (both at the airport (load breaking and ground operations) and in flight)?

Decades ago, when we moved checks at night for Federal Reserve clearing, we would sometimes have sealed bags which were cash.  On my flights, I never had an armed guard on board, but on taking off and landing, we were met on the ramp by an armored truck with armed guards on a routine basis.

The impression I had is that checks and other paper were the main cargo, and that cash and bullion were minor incidentals.

Related, items of national security are routinely carried by scheduled airliners, and are placed into the hold by cleared individuals, and then the hold is opened upon arrival, in the presence of cleared individuals who retrieve the packages.  Contents are logged, in the event of compromise.  Similar parcels are also handled by the major parcel and courier enterprises, with slightly different processes.


Can an automatic vane-based stabilizer really work? Can the pitch stabilizer in the picture really work for a plane or glider?

The image shows an automatic pitch stabilizer (the mechanism in the black rectangle) that is based on the vane 50 whose movements up and down would drive, with the help of a force amplifier system, the horizontal front elevator of a Wright glider or plane in such a way as to maintain the aeroplane in horizontal flight.

More precisely if, for a reason or another, the plane have the tendency to dive there will appear a vertical component of the relative wind that will push the vane 50 upward and, through the mechanism already mentioned, the vane will drive the front rudder in such a way as to make the apparatus climb again. If the plane tend to rise, the vane will go down and command the front rudder to make the plane descend.

The question is, can this mechanism really work, at least theoretically? (A stabilizer based on a pendulum is a fallacy, it will not work. In an accelerated system (the plane) the pendulum does not align to the vertical).

Source: US patent No. 1075533 (filed by WRIGHT Co in 1908)

(I am not interested in answers regarding the automatic stabilizer in roll, also described in the patent. It is based on a pendulum and it can not work. My question is only about the pitch stabilizer.)

UPDATE:
My question has nothing to do with a pendulum stabilizer. The vane-based stabilizer (the subject of my question) works on a completely different principle. In consequence, the answers given to this question, that refer strictly to a pendulum stabilizer, do not help.

Yes, this vane-based stabilizer really did work. In fact the pendulum system for direction control also worked as it was used to sense yaw in a slip, just like the ball in a turn and bank indicator.
The entire system worked so well that Orville Wright received the 1913 Collier Trophy "For development of the automatic stabilizer" after demonstrating it for the judges.
The Wright Bros work in automatically controlled flight was overshadowed the following year when Elmer A. Sperry won the 1913 Collier Trophy "For gyroscopic control".
WRIGHTS DEVELOP AUTOMATIC STABILIZER

In the fall of 1913, Orville installed the stabilizer on a special Wright Model E airplane that utilized a single pusher propeller. He kept the details of the stabilizer secret even from the Wright Company. He purposely waited until the last day of the year to fly for the prize.
He invited the Aero Club’s judges to Huffman Prairie to see a demonstration of his new device on a cold snowy day, December 31st.
He turned up his coat collar, put on a pair of goggles and took off. He made a total of 17 flights.
His most spectacular flight consisted of 7 full circles of the field with both hands held in the air. The automatic stabilizer kept the same angle of bank and almost the same altitude. He wowed the judges and was awarded the prize on February 5, 1914.
The stabilizer was then offered as an option for use with the sale of Wright 1910-1911 Model B flyers.
However, it saw little use, because on June 18, 1914, a young Lawrence Sperry, as part of a great safety competition, unveiled a totally new type of stabilizer to the world. The safety competition was jointly sponsored by the Aero-Club de France and the French War Department.
In his demonstration flight, Sperry took off from the Seine in a Curtiss C-2, climbed to altitude and flew back down the river. At the appropriate moment, his mechanic, Emile Cachin, crawled 7 feet out on the wing as Sperry lifted his hands from the controls and stood up in the cockpit. The plane sped by the judges as the crowd went wild.
What Sperry had done was adapt a balancing mechanism invented by his father, Elmer, for counteracting the rolling of ships, to an airplane. The device employed two gyroscopes that performed the function of the pendulum and vanes in the Wrights’ device.


What's this black rectangle painted on the side of a V-1 flying bomb? A friend sent me a photo of the V-1 flying bomb on display at the Air Zoo in Kalamazoo. What's the black painted rectangle on the side of the fuselage?

The writing isn't much help... Nicht auftreten is the German equivalent of "No step," but I don't know what Abstellpallung means, except that abstellen is "to cut off / shut down." I can't find Pallung in any German dictionary. The label appears to be pointing to the black rectangle, which appears to just be painted on.
I also can't find this rectangle in online V-1 photos.

A "Pallung" is a piece of wood (or something similar) that prevents ships (or something similar) from falling over when they are on land. "abstellen" means to put something down (such as luggage) or into storage. There are some recent articles that contain the word "Pallung" on google news, such as this one.
Assuming that the book depicted in this pdf is authentic, you can see what an Abstellpallung for a V1 looks like on page 29, indicated by the letters b and c:

Note that the text twice says "Markierung am Rumpf beachten!" (mind the markings on the fuselage), which probably corresponds to the black rectangles mentioned by the OP.

(Some native German users have indicated that they have never heard the word. Neither have I, until today. I am not sure about other languages, but in German, some domains have very specific vocabulary that a layman will almost never get in contact with. One example of this is anything connected with ships, another one is hunting, and there are probably some more. The manual contains another example just in the preceding sections (what does "heißen" mean here?). So "I have never heard the word" may just mean that someone is not familiar with some particular domain.)


How does an airborne DME unit differentiate itself? The FAA's IFR handbook glosses over a keypoint:

  The aircraft DME transmits interrogating radio frequency (RF) pulses, which are received by the DME antenna at the ground facility. The signal triggers ground receiver equipment to respond to the interrogating aircraft. The airborne DME equipment measures the elapsed time between the interrogation signal sent by the aircraft and reception of the reply pulses from the ground station. This time measurement is converted into distance in nautical miles (NM) from the station.

Which is: how does one airborne DME ignore the replies meant to other planes?

Wikipedia says:

  The aircraft interrogates the ground transponder with a series of pulse-pairs (interrogations) and, after a precise time delay (typically 50 microseconds), the ground station replies with an identical sequence of pulse-pairs. [emphasis added]

So is the pulse-pair unique to each unit? Or does the DME unit listen for replies and then picks a different pulse-pair for itself?

ICAO Annex 10 mentions 4 modes:

  Mode W, X, Y, Z. A method of coding the DME transmissions by time spacing pulses of a pulse pair, so that each frequency can be used more than once.

But it is unclear to me how each airborne DME achieves a unique interrogating signal.

Just the basic concept would be great if the radio theory is too complicated.

As the Wikipedia article states, there are two modes - SEARCH and TRACK. In SEARCH mode, the DME interrogates with up to 150 pulse pairs per second. Similarly, in TRACK mode it interrogates at up to 30 PP/S.

What it doesn't say is that the interrogations are not evenly spaced at a fixed rate. The DME uses a pseudorandom number generator to vary the transmission interval over a set range. Since the DME knows the timing sequence it sent, it can look for replies that match that sequence.

The airborne DME can use the knowledge of when it made an interrogation and the maximum round-trip time for the maximum 200 nm range (just over 2.5 msec) to avoid non-correlated replies (to other a/c). The higher rate in SEARCH gives it more opportunity to detect the replies as it has no knowledge of range in search and thus has to scan for the entire range. Once it has detected the ground station replies by finding a correlated sequence of pulse pairs, it can switch to TRACK mode. The lower rate is acceptable once the range is established and the reply window can be narrowed.

As a note; mode X and Y are in use and differ only in the pulse pair timing, 12 usec  for X and 30 usec for Y.  Modes W and Z were set for DME/P and to my knowledge are not in current use.