Why didn't the Concorde have flaps or slats? It's well known that the Concorde had no flaps or slats.  The lack of high-lift devices considerably reduced lift at low speeds, requiring the Concorde to take off and land at higher speeds and angles of attack than if it had been equipped with flaps and slats.  As well as greatly increasing drag (and thus fuel consumption) during takeoff and landing, this greatly increased the force carried by the main landing gear and the speed at which its tyres had to spin; as a result, if and when a tyre blew out (due to, for instance, a piece of debris left by the previous airplane to use the runway), the results would be much worse than with a tyre blowout on a subsonic airliner.

Interestingly, a "Concorde B" was planned for Concorde 217 and onwards, which would have been equipped with slats (although still no flaps); this, along with slightly larger wings and more powerful engines, would have allowed the Concorde B to dispense with afterburners, considerably increasing its fuel efficiency and range.  Unfortunately, production ended with Concorde 216, the aircraft immediately preceding the first Concorde B, so no Concorde Bs were ever built.

Why didn't the Concorde, as built, have flaps or slats?

Why no flaps?

Flaps change the pitching moment of a wing. After all, they add lift over the full chord, so the sum of the increased lift attacks at about mid-chord, which is a quarter chord aft of the regular lift. If there is no separate tail surface to compensate for the pitching moment caused by that extra lift, the aircraft will quickly pitch nose-down and crash.

Next, flaps change camber and, therefore, are destabilizing the wing. Without a stabilizing tail, a cambered delta configuration will become unstable. The only camber which is helpful for delta wings is at the leading edge and must be compensated by a little trailing-edge up deflection of the control surfaces. Positive camber near the trailing edge is destabilizing and can only be tolerated on a flying wing with artificial stability augmentation.

Why no slats?

Slats are helpful for delaying flow separation to higher angles of attack and allow a wing to create more lift. To understand their effect, it is not enough to consider what they do to the flow around the wing, but also the effect of the wing on the slat needs to be understood. A slat is like a small wing flying just ahead, and therefore in the upwash, of the main wing. The wing will induce a very high lift on the slat and in turn see its suction peak around the leading edge greatly reduced, which helps in keeping the flow downstream attached. The comparison plot below should illustrate this effect nicely:

Figure 36 from A. M. O. Smith's paper "High Lift Aerodynamics"

But a delta wing at high angle of attack does not have attached flow on its upper side. It makes use of flow separation at the leading edge which creates a powerful vortex over the upper wing. This is called vortex lift. So for take-off and landing, deploying leading edge devices would help Concorde only a little - they are most helpful in the region just before vortex lift kicks in. This would be for subsonic cruise, for which the original Concorde wing was completely unsuitable. Adding camber at the leading edge would had increased subsonic L/D a lot, so the subsonic cruise segments (like all flight above land) and flight in holding patterns would had been much more efficient. That was not considered initially, and the lower complexity of an un-slatted wing was preferred.

With Concorde B, a span increase and the addition of variable leading edge droop (no slats!) were proposed. The picture below is taken from the original web site which has been the source for the site you linked to in your question.

Concorde B aerodynamic improvements (picture source)

If you now look how the L/D would had been improved by this, it becomes obvious were the leading edge devices helped most. The L/D improvement at take-off and landing, by the way, can be mostly attributed to the span increase.

Concorde A and B aerodynamic efficiency comparison (picture source)

This information is missing from the site you linked to, but is essential for understanding why Concorde B had variable droop added: It should help to extend range beyond the Paris-New York connection and allow more efficient subsonic flight (especially the hold at 250 kts).


Does F-35 flight stick have a trackball? There is a trackball-looking thing on the side of F-35's side stick.
What is this? Is this actually a trackball?

There is also another round looking "button", although a bit different from the first one, on the lower back of the stick:

(The images are from here)

That appears to be a button, not a trackball.
From pg. 17 in a presentation, Active Stick & Throttle for F-35 - Joseph Krumenacker - NAVAIR Flight Controls / JSF Vehicle Systems - 16 October 2008, found here:
It is used to engage/disengage stick sensitivity in hover. Inadvertent movement of the stick would disengage the altitude hold.
Engaging that S-5 button increases the force to needed to 'disengage'.

solution was a pilot-engageable “gripper” mode, in
which an altitude-hold augmentation could be
quickly engaged and disengaged
– with gripper engaged, longitudinal stick breakout
force is significantly increased to prevent
inadvertent disengagement
Pros

Hover stick force is “significantly higher” and provides pilot direct tactile feedback and
confirmation that the flight control system is in control of height axes
Push through or paddle off to begin vertical landing

Cons

Remembering to select height hold
More buttons required


What is the validity of doing 2D airfoil simulation for axisymmetric bodies? I am currently working on axisymmetric bodies like fuselages/droplets etc. For this, I am interested in the point of flow separation (if there is) and velocity components at a certain point in space.

I know that XFoil is capable of doing this in a short fraction of time/effort compared to CFD for 2D sections.

What is the validity of taking this approach towards axisymmetric bodies?
With this I mean: using the cross section of the axisymmetric body and simulating this 2D cross section in XFoil, or any other 2D airfoil simulation programme.

Or: can I change the software in some way such that it can represent the physics better?

Xfoil analyzes airfoils, not wings, and as such does not account for wingtip effects so its results are invalid for bodies of revolution or even low aspect ratio wings.

More generally, you can reference this answer about the derivation of wing lift from airfoil data. It boils down to the fact that aspect ratio has a massive impact on the 3D flow around the wing. For high AR wings the flow at most sections is close to what can be predicted with a 2D method, but this condition does not hold for slender bodies or near wingtips.

To phrase it differently, we can only apply the results from 2D simulations to wings by avoiding 3D effects. In the case of slender bodies, the entire flowfield is impacted by 3D effects.

Since flow separation is dependent on the pressure field around the body, you need to have an accurate idea of the 3D flow to reliably predict separation points.


Does the flap settings for the best lift/drag ratio change with speed on the Diamond DA20-A? As I've recently started time building in DA20, I've noticed the AFM suggests flaps at T/O for a glide. Being very intrigued by this I run across this post. Although I appreciate Peter's reply that does throw some light I'm not quite clear with it and I'd like to elaborate on it further. As the topic is closed, and the forum advises against asking for more clarification, I open a new topic here.

Diamond DA20-A1 FM says:

Climb

Wing Flaps: T/O or UP
Airspeed:   65 kts

further elaborating with a table:

altitude:      0-4000 ft, flaps T/O:  65 kts, flaps UP:  69 kts
altitude:   4000-7000 ft, flaps T/O:  63 kts, flaps UP:  65 kts
altitude:  7000-10000 ft, flaps T/O:  62 kts, flaps UP:  -- kts
altitude: above 10000 ft, flaps T/O:  59 kts, flaps UP:  -- kts

Cruise

Throttle:  as required
Prop. Speed Lever:  1900 - 2400 RPM
Wing Flaps: UP

Gliding

Wing Flaps:  T/O
Airspeed at 1609 lbs (730 kg) (vIAS): 72 kts

I deduce there is a speed below which flaps at T/O create more lift than drag and it is therefore beneficial to have them down, however in the whole ATPL syllabus  I've never run across such a thing - a specific speed at which lift/drag ratio for flaps down changes.

I can understand it's either up or down for the best L/D ratio but I don't get why does it change at a specific speed? Unless the reason is the limitation by Vfe (81 kts) when pilot eventually must retract the flaps even at the cost of lower L/D ratio. If that is the reason, then I don't understand why would someone design a wing that's less efficient to fly in Cruise then in Climb?

So, my final question: does the flap settings for the best lift/drag ratio change with speed, or the wing is not flying at its best efficiency in cruise?

Besides, if we compare climb with gliding speed, we can see that in a climb flaps are to be retracted at 69kts (and even lover as altitude increases), while in glide they are to be at T/O position at 72kts. Where does this difference come from?

You did the right thing when asking a new question. Comments are poorly suited for the explanation of non-trivial issues.

Now follow several links to older answers. They should help to explain a couple of things, such as:

what flaps do to L/D.
how thrust changes over speed for propeller aircraft.
and how efficient propeller airplanes are in cruise.

  does the flap settings for the best lift/drag ratio change with speed?

Below you see the polar plot from the first linked answer. It shows the airfoil drag in 2D flow. Clearly, the best L/D is achieved with the +10° flap setting, but at this setting the airfoil becomes rather poor below a lift coefficient of 0.3. In order to reduce drag, the flap should be raised when flying fast enough so that the lift coefficient drops below that value.

So the answer is yes, the optimum flap setting does change with speed. Only the flap setting for the overall best L/D will be found at the same flap setting, but then this best L/D can only be reached at one specific lift coefficient (which is equivalent with one specific speed if mass does not change).

  I can understand it's either up or down for the best L/D ratio but I don't get why does it change at a specific speed?

It does not change at a specific speed. It changes continuously with lift coefficient (and, implicitly, speed). If you compare specific flap angles, you will find crossover points when the L/D of one flap setting drops below that of another flap setting as the lift coefficient changes. Normally, airplanes only allow a few specified flap angles, so it might seem that L/D changes abruptly when changing flap angles. However, flaps could also move continuously, adapting the wing to its optimal setting for each operating point.

  why would someone design a wing that's less efficient to fly in Cruise then in Climb?

Cost. GA aircraft don't have the complex flap systems of airliners and, consequently, have a much larger wing than what is required for cruise. Wing area is sized for the mandated minimum airspeed of 61 kts or less and installed power means that the airplane at low level cruises at a speed where friction drag dominates and induced drag is almost negligible. While technically possible, the complex high-lift systems of airliner wings would make any GA airplane a lot more expensive, a death trap for untrained pilots and a maintenance nightmare.


What is a typical range of air temperature used for engine inlet cowl anti icing? So i was searching the internet for engine inlet cowl anti icing and found that usually compressor bleed air is used to prevent the ice formation in several parts of the aircraft.
I am mainly interested in the inlet cowl anti icing section.
So the compressor bleed air is usually around 450 F ( correct me if i am wrong ).
I assume that this is not the temperature used for anti icing and before it is used for this purpose it is cooled down either because of the pressure difference or it passes through a heat exchanger or something else.
What is a typical range of air temperature used for the cowl anti icing and most importantly what is the lowest limit that is capable to prevent ice formation?
Thank you in advance.

Anti icing systems that use bleed are either "run-wet" or "evaporative".
Run-wet systems heat the surfaces to below the water boiling point, say 140-160F.  Supercooled drops hitting the surface are kept from freezing on the leading edge, but can run back and refreeze on the unprotected areas. In that case the "lowest" temperature is whatever keeps the water liquid until it's off the protected surface.
Evaporative systems heat the surfaces to above the boiling point of water, say 220-230F, so the supercooled drops that strike immediately turn to vapour, like spitting on a steam iron, and no ice can form farther back.  In that case the lowest temperature is the boiling point plus a margin.
You use an evaporative system if you can't tolerate runback ice (otherwise you'll use a cheaper and less demanding run-wet system).  On a wing, this will be related to the airfoil's stall behaviour with runback ice, and a non-slatted wing with a supercritical airfoil (which tends to have poor stall behaviour) will typically have an evaporative system.  If you can live with run-back ice because the wing is tolerant ice forming aft, or if the wing has a slat system that makes it tolerant of ice forming aft with slats out, you may use a run-wet system because of the lower heat demands and costs.
On cowls, same sort of thing; you'll use a run-wet system if the engine is not too sensitive to runback ice forming and distorting the flow on the inside surfaces of the cowl or breaking off and hitting the fan blades, or if it is, an evaporative system, that will keep the cowl leading edges in the mid 200sF.
On the General Electric CF-34, the bleed that supplies the cowl is blended with ambient air to cool it down using an air ejector at the entrance to the cowl piccolo system, where the hot air is dumped into a larger duct from an ejector nozzle, which pulls ambient air in with it and mixes them together. By the time the air is entering the piccolo duct, it exits from little holes cooled off quite a lot, and then it has to fill a space and transfer heat through the skin to the leading edge outer surface, so the it might still be 300-400F (after leaving the bleed port at 500F) or more even when being dumped into the leading edge of the cowl, in order to keep the leading edge skins heated to more than 220F.
If a cowl has a run-wet system, these temps will be much lower obviously.
The upper temperature limit is mostly related to the temperature tolerance of the leading edge and adjacent structure (such as heat treat state and the effects of heating/cooling cycles on the structure etc).


What is the slowest fixed-wing airplane? It's easy to find information about the fastest airplanes, in different categories (e.g. X-15, SR-71, the Concorde etc), but what is the slowest one? Which powered, manned airplane is capable of sustained level flight at lowest velocity?

The Gossamer Albatross is a human-powered plane with a top speed of 29 km/h (18mph).

It was used to cross the English Channel and seems to meet the criteria of the question.


How does an elevator offload function works in fly by wire flight control systems? In some fly by wire systems I found that there is no trim in the traditional sense. I believe it is because the forces that pilot feels on the stick are artificial. I was told that those fly by wire systems has elevator offload functionality that moves H-stab.

Can anyone explain how elevator offload functionality is implemented?
Does the artificial feel system generate force in response to airspeed and vertical acceleration? (like making pilot push harder for every knot/every G away from the trimmed state?)
Is trimming necessary for FBW systems and if so How does the fly by wire system implements the trim?

Regarding the first point, from Lufthansa Technical Training Manual for 777, page 30:

  Elevator Offload Function
  Operates only in the AirCommands to Determine when the Elevator is not at the Neutral Position for more than two seconds minimum.Commands the Horizontal Stabilizer to move as a Function of Airspeed. The Movement of the Horizontal Stabilizer then causes the Elevator to move to the Neutral Position


How can I politely remind ATC that I'm waiting for instructions or clearance? (background: low-hour, low-experience, private pilot.)

I've got an issue regarding talking to air traffic controllers, especially when I think they may have messed up, yet still giving them the respect they deserve as hard working professionals.

One common scenario is when I'm ready to go, along with multiple other planes, all coming from various taxiways.   I know the tower tries hard to clear us each more-or-less in the order we've called up.   But when one plane feels they've been badly skipped, or possibly forgotten, it can get awkward.

I've heard a pilot say (very politely, and with good cause):

  "Tower; Arrow-23: Did you forget about me?"

only to have the tower come back with a snappy and frustrated:

  "I'm doing the best I can.  I'll get you all out of here as fast as I can.  Just wait your turn!"

Obviously, that didn't go very well.

On the other hand, I've tried to be patient for awhile, only to learn that the Tower really did overlook me, and sequenced several planes out in front of me.

On the ground, its wasted fuel, HOBBS, and time.
But in the air, it can be more significant.

Sometimes I've had tower miss actually clearing me to land.If they're trying to sequence me in, I stay on an extended the downwind leg for a long time, waiting to be cleared before turning base.  But if they really did get busy and overlook me, I can end up well out of position.

If I call and ask, sometimes they'll get a little testy with me if they are just busy.
If I stay silent, I might've been skipped/forgotten, and end up flying downwind for a long time.

Whats the most appropriate, friendly, and polite way to check in and make sure nothing got missed, without sounding accusatory?

There's lots of advice I can give you here, but the answer is really that the degree of communication tower wants/needs depends on your local tower (and to some degree the individual controllers).

Perhaps the most universal piece of advice I can give you is to think like a controller.  Listen to the frequency and get a picture of what's going on in the airspace before you call them, and when you get good at it you'll also get good at knowing what kind of a situation you're flying in to (Is the airspace empty, or are there 4 planes in the pattern for landings, 3 in the opposite downwind shooting touch-and-gos, and a jet arrival on an instrument approach that just got dumped on the tower inside 7 miles barreling in & messing everything up?)

Also remember that from a controller's perspective of priorities ("Safe, Orderly, Expedient") speed doesn't count for much when compared to the other two requirements of the job (and aircraft on the ground are inherently Safe and Orderly unless they do something stupid like go charging across the hold-short line). Unfortunately for us pilots delaying the plane on the ground (that isn't moving, and is thus unlikely to hit anything) is generally preferable to trying to maneuver and delay the ones in the air (that can't stop moving unless they hit something, which is generally considered to be a Bad Thing).

For a masters class in "thinking like a controller" call your local tower and ask to arrange a tour / shadow a controller for an afternoon. Spending the day in the cab is a great way to get an appreciation for how crazy things can get up there.
You can usually Google up the phone number, or call Flight Service or your local FSDO and ask. For most towers it's relatively easy to set up a tour (they'll ask for a driver's license and possibly FAA certificate number to do a background check and make sure you're not completely insane).

The rest of this post is just my personal view on getting along with controllers based on doing most of my training & flying at a pretty busy towered field (According to the FAA's ATADS "Tower Operations" ranking KFRG was #42 in 2013).

On The Ground

When you're ready to go call tower and tell them - Something like Tower, Cessna 12345 number one runway 32, ready to go. is usually plenty (if your airport is configured such that there may be some question as to where you are specify which taxiway/intersection you're at).

After you call the tower and tell them you're ready my experience is you're not likely to be forgotten about. You may be sitting there for a while (my personal record is about a half hour at the hold-short line), but the tower can usually see you sitting there at the runway end waiting. They want to get rid of you, they just need a hole big enough that they can get you onto the runway and airborne without creating any conflicts.

If you are forgotten (it does happen sometimes - you'll see other aircraft being cleared for takeoff who called the tower to report ready after you, or the controller changes, or you've been listening and are pretty sure the airspace is clear but you're still waiting) a polite call to remind the tower you're ready to go isn't out of order. Just don't be That Guy calling every couple of minutes, and if the controller gets a little snippy just be the better person and shrug it off.

In The Air

In the air is a slightly different story.  Sometimes it can take me 3 or 4 calls to get tower to even acknowledge my existence on busy days (again, you don't want to be That Guy calling the tower every 10 seconds - you should have a picture of what's going on in the airspace, and if the controller is busy you may have to circle outside their airspace for a while).

Once you've made contact a good controller will communicate with you and tell you what they need you to do and where they want you to report, where to turn base, or who they want you to follow.

If you feel like you've been forgotten a well-timed position report is usually the best way to remind the tower you exist (and as a bonus it helps everyone else with their mental picture of the airspace too).
For example on an extended downwind for runway 01 at Republic you'll pass Sunrise Highway (a pretty easily identified road, and if you miss it you'll spot the train tracks right after it), the inner shore of Long Island, and the outer shore of the barrier beaches. Reporting each of those points while waiting for tower to call your base generally works (if they genuinely forgot about you they'll usually have an "Oh S%$^!" moment when you call them over the outer shoreline and turn you in for a 7-mile final).

One exception to my position reports technique is landing clearance -- I generally do something to remind myself if I've been cleared to land (fold a chart, turn my kneeboard, etc.) and if I don't recall being cleared I'll call somewhere between 500 feet and the threshold with something line Tower, confirm N12345 landing clearance? (Where depends on the conditions of the day - sometimes they crank out departures pretty tight & if someone's rolling waiting until they're airborne is usually a good idea).
Sometimes they cleared me and I missed it.
Sometimes they didn't clear me and they do.
Sometimes they have an "Oh S%$^!" moment (they forgot about me, have a conflict, and I go around).

All of those situations are generally preferable to landing on a runway someone else may have been told they can use.


Are tracked landing gear systems still in use and development? In the 1940's and 1950's, there were several tracked landing gear systems developed for the purpose of allowing landing on soft ground and/or using particularly heavy aircraft such as the B-36.

Are any such systems still in use and/or development?

(I have been searching and found quite a few examples but none in recent decades except for a proposal that suggests that it would be feasible to deploy modern improved tracked landing gear on C-130's, C-17's and 747s.)

For the first half century of manned flight, landing gears overwhelmingly had only a single, large wheel per leg. This was the cheapest and simplest way to ensure ground mobility, but ran into trouble when aircraft grew in size. When the XB-36 prototype started testing in 1946, only three airfields in the US were able to tolerate the 156 psi pressure of its single main wheels.

For operating from unprepared surfaces, tracked gears were the straightforward transfer from tank experience to landing gear design.

Tracked main gear on the XB-36 prototype (picture source)

However, another route which was tried at about the same time was to increase the number of wheels the aircraft rests upon. With hindsight, the multi-wheel way was the better solution and has prevailed. When used with large, low-pressure tires it does not exert significantly more ground pressure than a tracked gear.

Some early and rather extreme examples for the multi-wheel route include the Arado 232 four-engine tactical transport aircraft. Only 20 were produced, however.

Arado 232 from up close. No prize for guessing why it had the nickname "Tausendfüssler" (millipede) (picture source).

When it comes to designing large aircraft for soft field operations, the Ukrainian design bureau Antonov has unsurpassed experience. This comes to bear in the landing gear of the Antonov 124, shown below (source). When you have 24 wheels to spread the load out, even 400 tons might not be too heavy, especially when the tire pressure can be adjusted from the cockpit.

An-124 in a botched landing. No worry, the gear will tolerate this kind of abuse, too.

Therefore, the research on tracked gears has come to an end shortly after it begun, and even the B-36 ended its days on a four-wheel bogie. Today, every large airplane has at least two wheels per leg for redundancy and sometimes a lot more.


Why do airliners pitch up during cruise? In my experience as a passenger, when the plane stands at the airport and you enter it, the aisle is pretty much horizontal. (Obviously, I've never flown on a DC-3). After takeoff we pitch sharply upwards (duh!), but even after the captain comes on the PA with "we have now reached our cruise altitude", the aisle continues to point a few degrees upward. Usually it's only at "we're starting our descent into XYZ" that the body returns to a more or less horizontal pitch.

Why is this? I have some hypotheses, but don't know which, if any, of them hold truth.

It's just how the aerodynamics happen to work out. (Unlikely -- it would seem to be a simple engineering matter to attach the wings to the body at an angle such that the right angle of attack for cruise flight corresponded to the body being horizontal).
Pitching the body upwards slightly allows it to generate some lift, free of a proportional increase in drag relative to pushing the cylindrical body straight through the air.
Passenger jets are deliberately designed such that they never need to pitch lower than horizontal in a routine descent, lest passengers might panic and think they're nosediving to their death. (Also unlikely, unless there is really no hidden costs in terms of drag, etc.)
Landings might be more difficult if the plane had to point its nose downwards in order to get closer to the ground -- the nosewheel would hit the runway first. (On the other hand, simply leveling out would count as a flare, so it's not clear to me that's actually a disadvantage).

Mainly the options 2 and 1 from your list.

What nobody mentioned so far, but is rather important here is that the angle of attack depends on speed1 and weight. While the "speed" does not vary much for most airliners, the difference between empty and fully loaded airliner is rather large.

Now if the fuselage was tilted down, it would generate lift directed down and associated drag with the net result of simply a lot of extra drag. So the aircraft is designed so that it does not fly (in level cruise) pitched down even when light. But that means that when it is fully loaded, it flies slightly pitched up, because it needs more lift and higher angle of attack to get it.

1 It depends on the "indicated speed", which is not speed at all but rather dynamic pressure expressed as speed at which it would occur when moving through air of standard sea level pressure (1013.25 hPa). The pressure at high altitudes where airliners normally fly is significantly lower, so the indicated speed is usually does not exceed 250 knots when true speed is well over 400 knots.


Why does it feel like a plane stops in mid-air during approach? At some stage while on approach to an airport in a commercial jet, it feels like the plane is almost coming to a complete stop in mid-air. Is this maybe as a result of the flaps engaging or the landing gear creating drag?

Lowering flaps and gear will add significant drag, which causes the plane to decelerate. Your body feels that, but without visual reference to the ground, your brain has no way to know what speed it was traveling before or after that deceleration.
This is an example of “spatial disorientation”, where the brain gets confusing inputs and comes to the wrong conclusion about what is actually happening. Pilots have instruments to tell us what is actually happening, which we are trained to trust over the suspect data our bodies are giving us, but passengers don’t have that advantage.


Why do the B747 of NASA Shuttle Carrier Aircrafts (SCAs) need additional vertical stabilizer? Here is picture of B747 SCA of NASA and the AN-225 SCA. There are additional vertical stabilizer in the tip of the elevator to the Boeing's, while the AN-225 is designed with the vertical stabilizer located at the tip of the elevator. As we know, AN-225 was also designed and intended to carry Soviet's Aircraft. Then my question, why do the B747 of NASA Shuttle Carrier Aircrafts (SCAs) need additional vertical stabilizer?

The AN-225 was designed primarily for carrying the Buran, so they didn't have to make structural changes to an existing design to accomodate the carrying of the shuttle. The aircraft was purpose built for that mission (although it never really saw much of that in practice).

The NASA 747 on the other hand, is a stock 747 that they added the ability to carry the Space Shuttle on its back. They couldn't remove the vertical stabilizer on the 747. Due to the shielding effect of the airflow when the shuttle is attached, they needed additional yaw control that required them to add the outer stabilizers.

The 747's used by NASA were converted passenger aircraft. The first one, N905NA was acquired from American Airlines made in 1974, the second one N911NA was bought from Japan Airlines, built in 1973 and acquired by NASA in 1990 or 1991.


What is this abandoned airplane parked in Tegel airport? This airplane is parked in Tegel airport. Probably something extremely common, but can you please help to identify it?

In the far corner of Tegel Airport, to the southwest (here a satellite image), lonely a plane with a special story rots: The Boeing 707 was a gift from the manufacturer to the Lufthansa and landed in 1986 by tricky preparations as the first Lufthansa aircraft in West -Berlin. Otherwise only Allied aircraft could fly through the east corridor. Lufthansa donated the plane to the Berlin Technikmuseum, which, however, can not do anything with it. Every now and then, the airport fire brigade on the Boeing exercises in case of emergency.

https://www.tagesspiegel.de/mediacenter/fotostrecken/berlin/flughafen-tegel-das-vergessene-flugzeug/13531996.html


What are the eyesight requirements for a medical certificate in India? Does it matter what your eye power is, if your vision can be corrected to 6/6 (20/20) vision?

The DGCA's relevant requirements adheres and refers to ICAO Annex 1 (see pages 3 and 4). Here's the relevant text from Annex 1:
Class 1

6.3.3.2 Distant visual acuity with or without correction shall be 6/9 or better in each eye separately, and binocular visual acuity shall be 6/6 or better. No limits apply to uncorrected visual acuity.

Class 2

6.4.3.2 Distant visual acuity with or without correction shall be 6/12 or better in each eye separately, and binocular visual acuity shall be 6/9 or better. No limits apply to uncorrected visual acuity.

(Emphasis mine.)
The above is for the requested uncorrected visual acuity, but it is not the full text, e.g., if the correction is surgical, there is more fine print to read.


What is the absolute velocity change through compressor+burner? I thought that the velocity going through a turbojet increased as it went through the compressor and the burner. Intuitively, if the pressure/enthalpy increases, so would the velocity, right? I came across with this image, though:

As you can see, this image says that overall velocity actually decreases at the exit of both compressor and burner.

What is the logical explanation behind this? Shouldn't the compressing/burning effect actually accelerate the flow?

The flow enters the compressor at approximately Mach 0.4 to 0.6 in order to ensure a high mass flow with still subsonic compressor blade speeds. Compressing the air allows to reduce flow speed, and between compressor exit and combustion chamber is a diffusor to reduce flow speed even more. Why? To ensure a high degree of combustion! The longer the reactants remain in the combustor, the better. And large combustors are heavy, so they are kept as short as possible.

As soon as the air heats up, it picks up speed. In that respect your graph is not quite correct (or it assumes a rapidly widening cross section through the combustor). But the general relation between pressure and speed is right: While no energy is added or removed, the sum of pressure energy and kinetic energy of the flow is constant. While both the compressor and the combustor add energy and the turbine removes it again, the nozzle is such a region of constant energy. Here the remaining pressure of the flow is converted into speed.


Are Crew Resource Management (CRM) and other Human Factors methods effective? I help in giving human factor training in both the start up phase and in the biennial continuous training. I am a bit tired of my students...especially those in aviation long term, being disillusioned in this subject. I have tried to find statistics or information where I can show that sitting the human factor training has in fact helped in the prevention of accidents and incidents in the maintenance environment. But have been unsuccessful in finding this information. Wondering if anyone knows where I could find this? Thanking you in advance. :)

A student of mine, who has a background in industrial engineering and is an emergency medicine physician, has morphed his career to include the application of CRM into emergency medicine and operating room procedures.  The health industry has in general been moving that way because it is saving lives and lawsuits.

Several people have published retrospective analysis of aviation accidents, which tend to contrast the kinds of errors which occurred prior to CRM, and the changes in flight deck politics.

Military team operations, firefighting and other industry segments have started incorporating CRM into their training, and with measurable result.

Much of CRM today was developed  in response to significant aircraft disasters in the 1970's coupled with research at NASA and some universities which provided more insight as to how crews work together.  As an example, the unquestioned authority of the senior captain, was a factor in an alarming number of major accidents.  That protocol has been substantially replaced with a more collaborative protocol, and there are fewer accidents involving the same aspects of flight crew dynamics.

The medical application paper referenced below probably has statistics and material you might find particularly useful in your training.

Journal Articles:
https://www.tandfonline.com/doi/abs/10.1207/s15327108ijap0104_3

A medical application reference which talks about lessons learned in aviation:
https://www.emsreference.com/printpdf/47

A scholarly critical data driven analysis:
https://apps.dtic.mil/dtic/tr/fulltext/u2/a502230.pdf

  Technological advances continue to attempt to improve reliability and safety in
  aviation. Design considerations throughout the acquisition process must also continue to
  expound on integrating humans, including our cognitive and physiological capabilities, as
  fundamental aspects of aviation systems. Nevertheless, CRM training continues to be the
  primary method in mitigating the number of mishaps due to human crew coordination
  error in aviation. The program must go beyond simple training requirements and become
  more in grained into the culture. Perhaps the evidence found in this study suggests a
  transformation of cultural acceptance is gradually occurring.


Why doesn't extending the flaps on a B-2 send it into an uncontrollable dive? The Northrop-Grumman B-2, a tailless-flying-delta-wing aircraft, has a set of flaps along its trailing edge, as seen (for instance) in this cutaway diagram:

(Image from Funker530.)

But tailless delta-winged aircraft (except for those few equipped with canards) can't generally use flaps, because a tailless canardless delta-winged aircraft has no way of countering the nosedown pitching moment produced by extended flaps.

How does the B-2 avoid pitching down uncontrollably when its flaps are extended?

I don't think the flaps are used as high lift devices. Watch this video of a B-2 landing. Perfect view:


Why must some 'dangerous items' be in check-in baggage? What is the rationale behind forcing passengers to check in dangerous items?

What makes liquids and gels more dangerous in the cabin? Why would a lithium ion battery be less dangerous as check-in luggage? Wouldn't that even be more dangerous when you put lots of batteries in the cabin, since one could catch fire and spread to all other batteries where passengers are?

Generally, "dangerous" things that might be used as weapons are required to be kept out of the cabin. For instance, you can have firearms in checked baggage, but not carried in the cabin.

Given what's been learned about terrorist planning, there were plots to bring liquids on board an aircraft that could be combined to form an explosive. To counter that threat, the amounts & types of liquids that can be brought on board have been limited. Since the liquids in isolation are safe, they're allowed in normal quantities in checked luggage.

In the case of Lithium Ion batteries, the concern is less their use as a weapon, and more about a defective battery catching fire. If this were to happen in a cargo hold, the fire would cause other things to start burning as well before the cargo smoke detectors alert the crew to what's going on. So the priority is to keep lithium ion batteries out of the cargo hold. They're allowed in the cabin (with some restrictions) since you're pretty likely to notice your cell phone getting hot & smoking if it's in your pocket, and with that sort of early notice, the fire can be dealt with before it's caught large volumes of material on fire as well.

At least that's the theory. I don't know how many times it's been put to the test. In at least two cases (the Samsung Note 7 phone, and hover boards), devices which are considered to be at high risk of catching fire are simply kept off the aircraft altogether.


Why are Stratolaunch's engines so far forward? Stratolaunch's engines hang from pylons, not under the wing, but entirely forward of the wing's leading edge.  (Even farther forward than, say, the 747's.)  What benefit does this have, to compensate for the heavier pylons?

The forward location has two benefits:

Wing upwash is smaller, so the flow direction at the intake varies less with speed and altitude. This makes the intake more efficient and requires less robustness in its layout.
The forward location shifts the wing's center of gravity forward and gives it better flutter damping. How that works is explained here.

Wing torsion in combination with the two fuselages will produce a flutter mode where both fuselages pitch in opposite direction, torquing the center wing in the process. The slender wing in combination with the high pitch inertia of the fuselages will result in a very low flutter frequency. I suspect that damping this mode is of paramount importance for the Stratolaunch.
I also suspect that the high wing on a high fuselage allows more vertical distance between engine and wing, so the exhaust stream will pass below the lowered flaps. The high turbulence in the exhaust stream would put additional loads on the flaps; to avoid this, Boeing uses exhaust gates or a gap in its trailing edge flaps. Such a gap would not be needed with the lower engine position of the Stratolaunch. However, to place them lower does not require to shift them forward, too.


What is this pod at the wing-tip of a U2? In this image of a U2S, what it the very unaerodynamic looking pod at the wing-tip? It looks like it holds some sort of sensor package. However, it doesn't seem to appear on all U2s (at least not based on photos on Wiki).

Source: Wikipedia

The pod contains the Radar Warning Reciever (RWR). The variant in the picture is the TR-1B, which had wingtip mounted RWR units. According to globalsecurity.org:

  The Air Force has fielded new electronic countermeasures on the aircraft, giving it a jamming capability and upgraded radar warning equipment with wing-tip mounted digital receivers.

As an another exmaple, SAAB seems to have put RWR on the wingtips of Gripen, though the equipment are certainly different (U-2 uses AN/ALQ variants).

Note that the bottom of the 'pod' has (wingtip) landing skid at the bottom and navigation light on the side. The RWRs face outside at an angle of ~45$^{\circ}$. This (containing RWR, skid and nav lights in a single package) is a later design and was added to the exiting U-2Rs as retrofit. It was not avialble in the earlier models.


Why was the Sikorsky Firefly built but never flown? Sikorsky Firefly is the electric helicopter that has been built but never flown. How do such histories happen?
If the design looked so unsafe that there was not enough courage of trying, why this was not discovered much earlier? If they changed they mind, lost the investor, why not to try at least once anyway if there is already a machine standing ready to power up? Is there any certification for even the first ever flight a prototype may fail to pass?
Stories like "a single prototype was tested but not more ordered" look much more logical (they did not like it after the tests).
What are the most usual reasons behind the "built, never flown" histories?

The director of Sikorsky Innovations Chris Van Buiten called it a

technology demonstrator and research platform that will let us explore the technology, partnerships and technical collaboration...

On 2010 July 29 Verticalmag.com reported

First flight is anticipated later this year, upon completion of ground tests and safety of flight reviews in accordance with Sikorsky standard practice for all aircraft programs.

It vanished from the news a few months later.
Ten years later, it may be hard to get someone from Sikorsky Innovations to speak on the record about Firefly's abandonment, something that the company might consider embarrassing.  But it seems likely that some ground tests failed (cooling? software?), and either the partnerships with the companies providing the batteries, motor, software, etc., weren't important enough to the company (or its owner, Lockheed Martin?) to address those defects, or its other projects became more important.


Why is carburetor heat unnecessary at full throttle? Questions like How does aircraft design affect carburetor ice? show how carburetor mount point affects the relative passive heating of the carburetor by the engine, but I've never learned why full power eliminates the need for carb heat.

Looking at how Wikipedia depicts carb ice:

Regardless of the carb's mount point on the engine, high throttle wouldn't get rid of the ice on the throttle valve, heat generated by high throttle doesn't affect the temperature of the air flowing in.

Further, when the throttle is full open, there is a greater airflow speed across the neck of the carb and hence a greater temperature drop.

So, what explains why high throttle eliminates the need for carb heat in Lycoming/Continental engines?

Thanks!

The icing you are talking about is called "throttle ice" and actually just forms around the edges and back side of the throttle butterfly.  It's not really related to the venturi that is upstream; it's from the pressure drop caused by the restriction of the throttle plate (the high vacuum on the back side you might say) along with the presence of vaporizing fuel, which massively boosts the temperature reduction caused by the pressure drop because the evaporating fuel is absorbing a lot of heat from the air stream.

It's the temperature drop from this pressure drop at the butterfly, plus the effect of evaporating fuel, that turns ambient humidity into carb ice.  On a fuel injected airplane you only have the butterfly valve without fuel present, and the temperature drop from that alone isn't sufficient, and therefore you don't need carb heat on injected engines (just an alternate air source in case of impact ice on the air intake).

Anyway, when the throttle is wide open, the pressure drop downstream of the butterfly caused by the throttle restriction is minimal. As a result, the chilling effect of the pressure drop and of evaporating fuel is also minimal. Because of this you won't get ice formation as readily (not impossible, just relatively unlikely) when the passage has say only a 5 or 10% restriction at WOT, vs say, an 80% restriction at a low power setting.  For a given ambient temperature/humidity, carb ice always forms more easily the more the throttle is closed.

One of the worst airplanes for carb ice was the 65 hp J-3 cubs where the carb receives very little conductive or radiant heat from the engine due to the carb mounting and the cowl with the exposed cylinders.  Descending with the engine at or near idle on a 65 deg F high humidity evening was begging for a carb ice related stoppage, and liberal use of carb heat was advised even if there were no signs of icing.  Carb ice at WOT wasn't too much of a problem, but you can never be sure.  Always err a little on the overuse side with carb heat, especially on Continental powered airplanes which are a bit more sensitive to all this due to the way the carb is insulated from the crankcase, at least until you get to know the engine's quirks.


Can a class 1 medical certificate be obtained when glasses are needed to achieve 20/20? Will I be able to obtain an FAA/DGCA class 1 medical certificate if I have a power of -5.75 and -6.25 in both my eyes?

It says "you should be able to maintain 20/20 vision with/without glasses" and yes, I can achieve vision with glasses.

Yes, you can (provided you don't have any other disqualifying conditions).

14 CFR 67.103 Eye

  (a) Distant visual acuity of 20/20 or better in each eye separately, with or without corrective lenses. If corrective lenses (spectacles or contact lenses) are necessary for 20/20 vision, the person may be eligible only on the condition that corrective lenses are worn while exercising the privileges of an airman certificate.

  (b) Near vision of 20/40 or better, Snellen equivalent, at 16 inches in each eye separately, with or without corrective lenses. If age 50 or older, near vision of 20/40 or better, Snellen equivalent, at both 16 inches and 32 inches in each eye separately, with or without corrective lenses.

In your case, you will have a limitation placed on your certificate that says that you must wear corrective lenses while performing the duties under your Class-1 medical certificate.


Why are passenger cabins white? Almost every passenger cabin in a commercial aircraft is white with a little bit of grey. Why are they in these colors?

Source

The picture in your question shows the answer: Most lighting in the cabin is done indirectly, so you don't see the light source directly. Instead, light is reflected off the cabin interior. If you would paint that interior in gaudy colors, you would have undesirable effects. Colored surfaces absorb some wavelengths, so the brightness in the cabin is reduced. Plus, the selective reflection will shift the color of the light.

Newspaper and magazine paper would not be white anymore, but have the color of the cabin interior. As @mins correctly points out, the brain can compensate for this. It will, however, make it difficult to read text printed in the color of the cabin interior because it would no longer stand out from the background.
The color pictures in the magazines would look funny. If you now think people could switch on the reading lights: Note how few passengers actually know how to operate them.
The food you get served would look funny. It is already not a pleasure to look at in most cases, but in colored light it gets even worse.

While it might be fun momentarily to be in a room with mood lighting, being exposed to this one color for the full length of the flight without a possibility to escape (except for closing your eyes) will offend most passengers.


Flying a twin engine aircraft with 2-axis control I believe a twin engine aircraft, with 2-axis control (i.e. Rudder and Elevator), under normal circumstances is flyable.
But is it safe at all?
If one of the engine dies, will the rudder alone be sufficient to counter the consequent  roll/yaw?

For an ultralight with rudder only roll control, which achieves lateral control with a lot of dihedral to create a really strong roll/yaw couple, the issue would be how much reserve rudder authority is there once enough has been applied to counteract asymmetric thrust.  That would determine how much roll rate you could still achieve trying to yaw toward the dead engine. If the engines are reasonably close together, it would probably be flyable but you would have a lot less turning authority into the dead engine than away from it.  In the end, you would have to go try it to see what happens, or get someone to do it with an RC model version.

I think your problem is more to do with simply single engine performance.  If one quits you are now at 50% power.  Using two engines doubles the chance of engine failure, and if you can't climb decently on a single engine, you're still in a glider after a failure, just one with a flatter glide.  IIRC, the Lazair twin was just able to maintain level flight on one engine at lower altitudes, and it was pretty clean as ultralights go.  The Bloop being a lot draggier, you would probably need more total HP that it uses as a single, to have decent reserve power when one fails.


Is the ILS only used for landing when weather conditions are poor? Either I'm missing something, or this article clearly suggests, that pilots are using ILS for landing only in bad weather conditions. Which could lead to an assumption, that in perfectly clear weather they're landing always or nearly always in visual.

Even though I'm completely new to aviation, I was always sure that ILS is used on every landing procedure, no matter if weather conditions are good enough to do it visually. ILS landing seems to be faster, more precise, more safe, and thus -- in my naive opinion -- should be used whenever it is available (i.e. whenever ILS is commissioned and operational).

What am I missing?

The relevant question is not whether or not the ILS system is used at all, but when the pilot switches from ILS to visual.

At the beginning of an ILS approach, the ILS signals function as a navigation aid, helping to make sure that the aircraft is lined up correctly with the runway from a longer distance out than the runway itself would be visible clearly enough to the naked eye even in good weather.

At some point during the approach, the runway will be clearly enough in sight that the pilot can actually land the plane visually. The latest point at which this is allowed to happen is the "decision height" -- if the runway is not reliably in sight by then, a go-around must be executed.

The lower the decision height, the larger demands are placed on the accuracy and reliability of the ILS equpiment -- losing the ILS signal due to interference for a few seconds while still six miles out is much less critical than losing the signal for a few seconds right before touchdown.

It is possible (if all the involved equipment is maintained and certified to high enough standards) to have a decision height of 0 feet so the ILS/autopilot flies the aircraft all the way to touchdown, but doing this requires all other aircraft moving around on the airport surface to observe extended safety distances to the runway to minimize the risk of radio signals bouncing off their fuselages and sending a blind-landing aircraft astray. This can have bad effects for capacity, so in normal operation landings are done with a nonzero decision height.

In fact, most airports don't spend the additional maintenance cost needed to certify their ILS systems for zero decision height ("category III" ILS operation), or do it only for some of their runways. In case of bad weather at busy times, some flights will just have to divert to other airports.


What are the "parts" of a SID procedure? In the ARINC 424 (downloadable from this link), the following information about SIDs procedures is given in the section 5.7 Route Type (RT TYPE):

As you can see, it appears to me that a procedure is formed by three parts. My questions are the following:

Is a SID made from 3 parts: Runway Transition, Common Route, Enroute Transition?
If yes, how are they related between one another? What is their order starting from the airport?
Could you provide an example from chart that shows these 3 parts?
Is there anything else i should consider in order to put together all the parts of a SID?

I hope my questions even make sense.

FAA Order 8260.46F - Departure Procedure (DP) Program describes "... the policy, guidance, and standardization for initiating, developing,
processing, and managing the Departure Procedure (DP) Program."

Your questions are broad-based, but Order 8260.46F should provide the answers you are looking for.

Here are two figures from Order 8260.46F.  These figures are accompanied by descriptive text and illustrate the type of information in the Order which should be responsive to your questions:


For an aircraft, what are the differences between nonlinear and linear equations of motion? So, as far as I understand, linearized equations of motion are just nonlinear equations of motion converted to linear EoM's using approximations and assumptions to simplify/remove elements from the equations.

In an aircraft, what are these nonlinear EoM's? If, for example, I stuck my airplane in a wind tunnel to determine the entire set of aerodynamic coefficients, would that cover all of the nonlinear portions of the equations of motion?

Thanks!

Equations of motion (EQM) define how a rigid-body accelerate and rotate given any arbitrary external forces and moments. They are no more and no less than Newton's Second Law. When expressed in body-frame, the EQMs are:

$$\bf{F}_B = m (\dot{\bf{V}}_b+\bf{\omega }_b \times \bf{V}_b)$$
$$\bf{M}_B=\bf{I}\dot{\bf{\omega }}_b$$

where $\bf{F}$ is body forces, $\bf{M}$ is body moments, $m$ is mass, $\bf{V}$ is inertial velocity, $\bf{\omega}$ is angular velocity, $\bf{I}$ is moments of inertia, and $\times$ is the cross-product operator.

The above are vector equations, which correspond to 6 scalar equations. At this point, there is no concept of aerodynamics. Notice how the equations are inherently nonlinear, so long as there are body forces/moments that depend on the state variables (e.g. velocity, orientation, etc). This is true for most forces, with the notable exception being gravity.

Aerodynamics is nonlinear in that aerodynamic forces and moments do not change linearly with flow incidence, rate of rotation and velocity, except if the changes are small. In general, quasi-steady aerodynamic force is a nonlinear function of flow incidence, rate of rotation, Mach number, Reynolds number, etc. To capture these, N-D lookup tables constructed from estimated/measured data are generally employed in simulation models.

Quasi-steady assumption itself may not be adequate in some flight conditions, such as during rapid maneuvering or stalled flight. In these circumstances, the description of aerodynamics may need to be time-variant.


What happens to the control systems of a BAe 146 when the aircraft runs out of fuel? On a BAe 146, is there any way to control the aircraft when it's out of fuel? Does the APU run on a separate tank? Can the engines be windmilled for power generation?

is there any way to control the aircraft when it's out of fuel?

Yes

  Does the APU run on a separate tank?

No.

  Can the engines be windmilled for power generation?

Yes.

Control

Pitch and roll can be controlled mechanically.

The rudder needs hydraulic power - which can be provided from the emergency DC battery via a pump if the systems are configured appropriately for this by the pilots.

There is a magnetic compass and a minimal set of other instruments powered by the emergency DC bus.

Fuel / Generators

The four engines, including the two with generators, each have a separate feed tank that is fed from the main tanks.

When fuel stops reaching the feed tanks, warnings are shown/sounded in the cockpit. I vaguely recollect the feed tanks may have something like 20 mins fuel (could be less).

The APU is fed from the same main fuel tanks as the main engines.

Electrics

The electrical system has three modes

normal
essential
emergency

I believe that there is 30 minutes electrical power available from the emergency battery that powers the EMERG DC bus. There is an inverter that takes power from EMERG DC and provides power to the EMERG AC bus.

RAT

An overview schematic (allegedly for 146) does not show an emergency ram-air-turbine (RAT) generator.

Hydraulics

There are two Hydraulic systems, yellow and green. Each powered by a separate engine.

There is a DC pump that provides hydraulic power to the yellow system from EMERG DC power. There is a switch in the cockpit to control this.

Windmilling

A limited amount of hydraulic power can be generated by windmilling the engines but the pilots have to reduce the load on the engines by deselecting the standby generator.

One of the windmilling engines will be driving the emergency fuel pumps (obviously uselessly if you actually run out of fuel mid-air, rather than having problems with main pumps)

References

QualityWings flight simulation manual :-(
satcom.com


Are there any cameras inside a plane? Are there any cameras inside a plane to watch out the activities of passengers?

Yes

AIRCRAFT CABIN SURVEILLANCE SYSTEM
Surveillance system for aircraft interior (2002)
Surveillance Cameras In Aircraft Cabins (2002)

  JetBlue Airways is the first U.S. carrier to get approval from the Federal Aviation Administration to install video cameras on all its airplanes.
  JetBlue is a successful start-up carrier based at New York's John F. International Kennedy airport. Soon after the Sept. 11 hijackings, the airline installed bullet-proof cockpit doors on all its planes. And it was the first carrier to match all luggage to passengers.

  The airline has outfitted one plane with the video surveillance system, and plans to have its 23 other jets equipped with the miniature cameras within the next few months.

  The cameras are positioned to cover the entire cabin. Some are visible, others are hidden so they cannot be tampered with

In-flight surveillance could foil terrorists in the sky (2008)

  The European Union's Security of Aircraft in the Future European Environment (SAFEE) project uses a camera in every passenger's seat, with six wide-angle cameras to survey the aisles. Software then analyses the footage to detect developing terrorist activity or "air-rage" incidents, by tracking passengers' facial expressions.

A350 cabin surveillance contract (2012/2013?)

  KID-Systeme has been selected to supply cabin surveillance equipment for the Airbus A350 XWB family of aircraft. The integrated solution will include both a cockpit door surveillance system (CDSS) and a cabin video monitoring system (CVMS).
  The CDSS provides pilots with a clear view of anyone in the area of the cockpit door, enabling them to take the appropriate action when entry to the cockpit is requested. The CVMS allows both the pilots and the cabin crew to view passengers.


Do different planes (category) aim differently in the 'final stages before flaring'? (youtube.com)

Do different planes (categories A through D) aim differently in the final stages before flaring? I'm asking about precision runways.

The reasons I ask:

An ILS' glide slope is not coincident with the PAPI for example (when does the shift from G/S to PAPI occur?)
There may be differences in the touchdown zone markings
Airplanes come in different cockpit heights and approach speeds.

By 'final stages before flaring', I mean when the landing is manually flown in VMC, when the shift from looking down to up occurs.

Example: you may be on the G/S but off the PAPI when you look up, which one do you follow based on the category?

There is plenty of anecdotal information all over the internet, so I'm looking for as factual an answer(s) as possible based on experience. This post for example (pprune.org) offers contradicting advice, one quotes a document saying, "PAPI provides guidance down to flare initiation," and mostly others saying to ignore the PAPI.

Because of the downrange offset between the PAPI and the GS antenna, only a P3 (jumbo jet size) PAPI (14 meters eye to wheels) gives a more or less parallel path between the ILS glide slope and the pilot's eye so that they are both aligned on short final.  The other PAPI categories all have a deviation between the ILS slope angle and the PAPI slope angle, so that if you stay on the ILS glideslope all the way down, at some point the eye height becomes too high for the PAPI and you will see three whites even though you are right on the ILS.

You take this into account in training to learn to resist the urge to dive to correct because the last thing you want is to increase sink rate close to the ground. So really, once you are really close in, inside the airport boundary, you don't rely on the PAPI lights.  If you were on-slope in a stabilized approach configuration at Vref at decision altitude, you just have to hold the pitch attitude and speed with maybe a few small pitch tweaks based on the runway sight picture and you will cross more or less at a wheel height of 50 ft. The goal is to hear "50" from the GPWS just as the threshold is passing below, and the speed tape pointer is right at Vref.  From there the touchdown point takes care of itself using the normal flare/thrust reduction procedure you use for that airplane.

This Transport Canada Staff Instruction regarding the design of PAPI installations and issues with harmonizing them with ILS approaches gives some useful background: https://www.tc.gc.ca/media/documents/ca-opssvs/AC_302-009.pdf


Is there a recommended time to pause before transmitting, after changing to a new frequency? Does any aviation authority have a recommendation of how long to listen after changing to a new frequency before making a transmission?

source

I was always taught:

Change frequency
Give it a good 3 count
If no one is talking, transmit

The FAA just advises a pause as per the AIM [4-2-1] but gives no time specifically

  a. Listen before you transmit. Many times you can get the information
  you want through ATIS or by monitoring the frequency. Except for a few
  situations where some frequency overlap occurs, if you hear someone
  else talking, the keying of your transmitter will be futile and you
  will probably jam their receivers causing them to repeat their call.
  If you have just changed frequencies, pause, listen, and make sure the
  frequency is clear.

You will also learn to anticipate the flow. For example if you hear a controller issue something you should expect to hear the aircraft read it back. Once you get a feel for the cadence of chatter you will have even less issues.


Was flying a helicopter below building height against FAA regulations? I'm referring to this incident: https://twitter.com/Dacheslow/status/1267638389421072384

Some people were saying it was illegal under FAA rules to fly that low and close to a crowd, and also to use a medical-designated helicopter to carry out police activity. Can anyone weigh in?

I don’t know exactly where in DC that happened, though I would say it’s highly probable that it was a public or law enforcement helicopter, or a lifeflite helo as virtually nothing else is allowed to fly VFR in the FRZ over DC without a lot of planning and waivers.

Helicopters, under general operation, are going to have to conform with §91.119(a), (d)(1), which state you must operate the helicopter at an altitude that, if a power unit were to fail, a landing can be made without creating an undue hazard to persons or property on the surface.  In the case of the helo in question, it’s a Eurocopter EC 135, which is a multi engine aircraft.  I don’t have the performance charts for that helo handy, but I believe it either can hover OGE or perform and aurtorotation landing at near standstill should an engine fail.

There’s also the fact that, as many cities right now are under a state of emergency, public vehicles may be forgoing a lot of regulations on flight ops for that reason.  The helo may also be looking for a place to land and hoping the people below can make a space for it.  I’m not sure here.


Is medical certification required for flight attendents? In the history of stewardesses: "In the earliest days of commercial flight, there were teenage cabin boys, and the first female stewardesses had to be registered nurses."

The 2009 book Flying Across America: The Airline Passenger Experience by Daniel L. Rust says, "*Dressed in hospital whites or military-style uniforms, a 'sky girl' of the 1930s not only served meals and soothed nerves...*

Is any type of medical certification required for flight attendants in the US or other parts of the world?

One of the first flight attendants anywhere, Ellen Church was also a registered nurse and certified pilot. She was unable to find work as a commercial pilot but she did have another influence on the nascent flight attendant industry: she convinced a major airline to hire only nurses.

She approached BAT (the forerunner of United Airlines) looking for a pilot's job, a futile hope for women in those days. But the BAT exec did like Church's other suggestion: that commercial airliners carry nurses on board.
Smelling a publicity coup, and figuring that on-board nurses would help quell the public's fear – very real at the time – of flying, he sold her proposal to the boys at the top. BAT hired eight nurses, including Church, for what it thought would be a three-month experiment.

These early flights attendants bore little resemblance to their modern counterparts, however

They were expected to haul luggage, screw down loose seats, help with fueling the plane and finally, at day's end, help the pilots push the plane into the hangar.

In modern aviation, trying to hire a registered nurse as a flight attendant doesn't seem to be a requirement. Here's Delta's page on hiring and it says

While specific positions will have unique requirements (example: Flight Attendant minimum age requirement is 21 years of age; see individual job descriptions), you must possess at least a H.S. diploma/GED equivalent, be at least 18 years of age, and possess current authorization to work in the U.S. to work at Delta.

The individual job descriptions are for language knowledge. None list a nursing degree as a requirement.
What changed? Well, mainly the medical profession. Nurses today have a LOT more educational requirements. Additionally, a lot more places use nurses. So nurses are in high demand now. Adding that requirement onto a flight attendant job would make the position more expensive and harder to fill.
Additionally, there might be legal liability. While simple medical devices (like AED devices to restart a heart) supplement and can prove of some limited use, imagine a flight attendant having a nursing degree and someone has a medical emergency or dies on their aircraft. Suing the airline would be a tempting. Legal liability is a very real problem here

A colleague of mine, however, was not as fortunate and encountered a much more serious condition -- urosepsis -- on a flight to London. [snip] My colleague missed her connecting flight, as did many passengers, and the other physician had to accompany the patient to the local ER because the emergency medical service worker did not want to be held liable for the IV line the ICU physician had inserted before the plane landed.

And

Unfortunately, liability is a very real concern, particularly in scenarios when you're not practicing in your regular clinical setting. Generally, physicians are covered by the Aviation Medical Assistance Act of 1998, which protects physicians who provide in-flight emergency medical assistance in the same way that state Good Samaritan laws do. It goes without saying that you do not have to volunteer if you do not feel comfortable with the situation or are concerned for your own safety. If you have had a few drinks or have taken sedating medications, you need to use your judgment about whether to respond.
Since you are volunteering and not technically on duty, under the 1998 law, you are covered as long as you don't engage in any willful misconduct or commit gross negligence. You should make yourself aware of the law's limitations. Many physicians feel a moral obligation to help in a medical emergency, and, thus, we can find ourselves in these situations.

If passengers leap into action to help a distressed patent, the airline avoids liability.


What is the history of "Joker" and "Bingo" fuel terms? Why do we use, in military aircraft, the words "Joker" and "Bingo" to indicate the fuel status of the aircraft? What is the history of these two terms?

"Bingo" originated with aircraft carrier operations.  "Bingo" actually means to divert.

The official US Navy definition of "BINGO" is: "An order to proceed and land at the field specified, utilizing a bingo profile. Aircraft is considered
to be in an emergency/fuel critical situation. Bearing, distance, and destination shall be provided."

CV
NATOPS MANUAL

If the aircraft carrier was operating in an area that had a land based alternate airport, it would be called "Bingo Ops". "Bingo Fuel" was the amount of fuel remaining to safely reach the "Bingo Field". The "Bingo Field" was the closest land based airfield which could be used as a backup in case the aircraft was unable to land on the aircraft carrier for any reason. Examples could be a fouled deck due to a disabled aircraft, or unusable arresting gear system.

Other military, and even civilian operators, have since adopted "Bingo Fuel" to mean minimum fuel to safely reach an airport.

My own research shows that there is no definite answer to the origin of Bingo.

"Joker Fuel" is a predetermined amount of fuel in excess of Bingo Fuel.


Are there any LSA aircraft that can be flown IFR in IMC? Are there any LSA aircraft that are IFR certified? A LSA would be the perfect private commuter plane for an instrument rated private pilot.

If not, what are the most cost effective airplanes that are IFR certified? Is there anything cheaper than a C172?

Just to be clear: I am asking about aircraft that are IFR certified, meaning that they can be flown IFR in IMC conditions. I am also aware that there is a huge difference between different countries with regard to aircraft certification so my question is mainly about the U.S.

Sorry to reanimate this rather old question, but I'm surprised none of the previous answers mentioned the Evector SportStar MAX, which has a model that is IFR equipped and which was available several years before this question was asked. From its POH (section 1.2):

  Certification basis

  SportStar MAX complies with the ASTM F2245-07a Standard Specification for Design and Performance of a Light Sport Airplane, issued by ASTM International Committee F37.

  IFR version complies with FAR 91.205 requirements, ...

Here's a Plane & Pilot review of the IFR version, and here's a Press Release from Evector about this model.

Evektor followed the MAX model with the Harmony, and at least one place on their website suggests it too is available in an IFR equipped version.


Why do Airbus sidesticks add their inputs? There have been a couple of Airbus disasters where, in the confusion leading up to the crash, both pilots have attempted to control the aircraft with their sidesticks at the same time. In the absence of either pilot using the priority button, the effect of this is that both inputs are added, and the result clamped to the maximum single input.

On the face of it, this is a very curious design decision. Obvious alternatives include prioritising the left-seat stick (unless the priority button is used), or even averaging (instead of summing) the inputs.

Are the original reasons for this design decision documented? Is there an advantage to summing the inputs?

I believe that there is some logic in the design, actually, even if I don't really fancy it. If you think of the traditional yoke as a control element where a certain force (or moment, rather...) results in a certain change of flight path, then if both pilots apply the same force (rather than targeting the same deflection), the resulting aircraft reaction is more pronounced than if only one pilot applies that force, although probably not with linear relation. The sidestick controlled flight control system does the same.

What is missing much more, to my mind, is feedback to one pilot about what the other one is doing with the stick. I believe that having them interconnected or back driven would probably not have been such a bad idea.


Do different types of missiles indicate different lock tones to the pilot? Are there different lock tones for different types of missiles, e.g. air-to-ground (AGM) or anti-ship (AShM)? If so, what information do the tones give the pilot? Are they a way for the pilot to know which type of missile is selected?

Lock tones are normally used for (surface/air)-to-air infrared homing missiles. Air-to-surface missiles don't "growl".

The tone is used to indicate missile readiness and quality of lock, not the type. Phantom pilots in Vietnam used to cycle between all available Sidewinders to check which seeker had the best tone then put the worst one to be last in the firing order (source: "Sierra Hotel : flying Air Force fighters in the decade after Vietnam" book, page 12)

At first there was a volt-meter in the cockpit to do that, but during development testing they figured out looking inside the cockpit in a dogfight to check if the missile is ready to fire wasn't a good idea, hence the tone frequency was introduced (source: Fox Two).


What open databases with aircraft, airlines and country exist? As the above question states, I'm looking for an open database that I can access. I'm building a plane spotter app, and need a lot of data.

The data needs to be downloaded.

Geographic (routes, land-based infrastructure) data:

http://ourairports.com/data/
http://openflights.org/data.html

Coordination (scheduling, flight numbers) data:

http://www.virtualradarserver.co.uk/FlightRoutes.aspx

Aircraft (registration) data:

List of national government registers - http://www.gatwickaviationsociety.org.uk/registers_official.asp
ICAO address country prefixes - http://www.kloth.net/radio/icao24alloc.php
(old) id and routing data - http://www.libhomeradar.org/download/index.php


Are there any best practices for transitioning from paper logbooks to electronic logbooks? I've started flying again, and some of the things/places I fly are more interested in time in type than my old paper log shows. I'm considering going to some form of electronic logging (currently for Android and/or Linux but likely moving to iPad next year for EFB compatibility).

Question: When I start up with a new program, do I merely summarize my flight experience and ignore the tail number and a/c type? I've flown a few different birds in my time, and trying to go back through 3 logs and setting everything correctly would be a royal pain.

Logbooks are an interesting blend of personal and professional recordkeeping.  The FAA doesn't really make a big deal about what method you use to log your flight time, just as long as you log all flight time which you're going to later use to justify currency or a new certificate.

This means that you can do whatever works best for you, as long as you (and your future employers) are happy with it.

When I transitioned to Safelog, I decided to spend a few weeks worth of evenings and just enter everything, line by line.  I did this because I had a lot of spare time, and because from now on I've got a pristine digital copy of everything, which is a nice feeling.

However, this is certainly not necessary, and there is no reason why you couldn't summarize your totals with one or a few line items.  In fact, Safelog provides a function to do exactly that: you create a pseudo-aircraft type which is defined as "summarizes several aircraft".

You can get as coarse (1,302 hours in airplanes) or as fine (389 hours in blue C-172M's with the funny starter that sounds like you just dropped a shot glass in a garbage disposal) as you want.

I would say that whatever you choose to do, just be sure that you enter it using a format which will be compatible when you switch from Android to iPad.  It's bad enough to do it once, why put yourself through the hassle of doing it twice?


What clues would have indicated KAL 902 was off course? Korean Airlines Flight 902 was shot down by a Soviet fighter in April 1978 after the pilot turned through 150 degrees and entered Russian airspace. The New York Times reported it happened around 8.30 pm Paris time, so this happened during sunset. But if he had kept to the correct course, he should have been flying over the North pole and into the middle of the day.

Given that magnetic compasses are not helpful at this latitude, the aircraft did not have an inertial navigation system, and the Earth's surface (if visible) is presumably similar in both directions, what other clues could the pilot have to his heading?

In other words, for flying at high latitudes in the late 70's, what checks were available to the accuracy of navigation?

According to the German Wikipedia the 707 has been equipped with LORAN-C and VOR. It most likely also had (at least one)
Gyroscopic Heading Indicator.

Wikipedia does not tell something about this concrete plane but these devices where available since the 1950s and there is no reason why this particular plane should not have them.

So from a technical point of view the crew should have been able to detect the deviation from the planned path, given that they had some training in using all of that equipment, and that not all of them broke altogether during the flight (before the rocket hit).


Is a turbocharged piston aircraft the same thing as turboprop? Simple question, and I've always assumed that they are the same thing, but I'd like feedback from someone who knows more than me :)

They are both internal combustion engines that have a turbine in their exhaust that is used to power a compressor to pressurize the air before it is used for combustion.

In the turboprop, the turbine also powers the prop.  In between the compressor and turbine, the fuel/air mixture is burnt without significant moving parts.  Without the turbine and compressor, a turbine engine is essentially a tube with heating element in it.

In a turbocharged piston engine, you have an otherwise normal piston engine which turns the prop.  The turbine is in the exhaust from the piston engine and powers the compressor pushing air into the piston engine.  The turbine and compressor are not connected to the prop though.

Here they are as diagrams along with some other types of engine.


Any FAA or other regulations prohibiting taxiing between parked aircraft? So the other day I was getting checked out at a local FBO, after returning to the ramp, instructor told me to taxi between two parked (tied-down aircraft). It was a tight squeeze but I taxied at about 1 MPH and I looked at left wing while instructor kept an eye on right wing. I really didn't think anything of it. Note, access to the other side of the line was blocked off by some vehicles so we couldn't taxi in from the back, hence cutting between two parked aircraft. However, we could have shut down on the front and pushed the aircraft back into its parking spot.

However, about 5 minutes later, a car drove up to us as we were securing the aircraft. It was the owner of one of the aircraft that we taxied next to. He spoke to the instructor, I didn't hear exactly what he said, but it was something about not taxing so close to his aircraft. Personally, I have no problem, pushing the airplane back into its spot, but it got me thinking about what regulation if any is implicated here.

I looked, and didn't find anything. So my question is whether there are any FAA, airport or other regulations or rules that prevent a small aircraft from taxiing between two parked aircraft on the ramp? I don't think there is any legal authority prohibiting taxiing between aircraft, or how many feet you must keep from a parked aircraft.

This reminds me of the aviation joke:

Aircraft Squawk - Left main almost needs to be replaced.

A&P Response - Almost replaced left main.

In this case:

Aircraft owner - You almost hit my airplane.

Me - You're welcome.

There isn't any such regulation.  That part of the airport is a "non movement area" (if you want a reference).  Of course, you want to be a good neighbor, and not toss rocks, etc.  I usually push my airplane into parking, and pull it out before engine start.  But that is just me.


How often are passenger oxygen masks deployed? In commercial passenger aviation, how frequent (or infrequent) is the case that oxygen masks deploy?

Please include links to statistics.

Very, very rare, probably in the range of sinlge digits per 100,000 flights (for major first-world airlines, perhaps higher elsewhere).

I'll try to get you a more numeric answer tomorrow.

Posting an answer now so that I can edit it, evem if the question gets closed between now and then.

"Opinion based", horsefeathers!


What are the opimum values of Cl during descent? Statistical Analysis of A320 aircraft shows the Cl values to be as under: cl_value. L is assumed to be 0.5*MaximumLandingWeight of A320 as the Aircraft is about to land.

The Units used are: Flight Level(feet), rho(lb/feet^3, V(feet/s), for the sixth column, 1/2(rho.V^2.S.)

The cruise Cl values are as under:

When compared to cruise the CL during descent is very small. Is this an acceptable result?

I am going to work in SI units for all engineering work, anything else would cause instant insanity on my side. I'll leave the altitude in feet (isn't used) and convert speed from knots to m/s so you can follow the flow easily. Since $C_L$ is unitless it should not matter what units you use in the calculation as long as you are consistent.

Altitude: 34000 [ft] (not used)
$V$ (true air speed): 442 [knots] = 227 [m/s]
S = 112.6 [m2]
$\rho_0$ = 1.225 [kg/m3]
$\frac{\rho}{\rho_0}$=0.322 [-] (from your table)
$\rho$ = $1.225 \cdot 0.322 = 0.394$ [kg/m3]
$\frac{1}{2}\rho V^2 S$ = $\frac{1}{2} 0.394\cdot 227^2 \cdot112.6 = 125\cdot10^4 $[N]
$m$ = MLM = 64500 [kg]
W = $m\cdot g$ = $64500\cdot 9.81$ = $63\cdot10^4$ [N]
$C_L$ = $\frac{W}{\frac{1}{2}\rho V^2 S}$=$\frac{63\cdot 10^4}{125\cdot 10^4}$ = 0.5

I did take full maximum landing mass for this calculation. If you want to apply corrections then note that the $C_L$ value scales linearly with the mass.

One further note:

I assume your data is derived from ADS-B. ADS-B transmits groundspeed, whilst you should work with true airspeed in these formula's. The difference between them is the tailwind (or headwind) component.


Could D.B. Cooper know where he was landing, when he parachuted? The background story is a hijacking that happened 1971.

The hijacker, referred to as D.B. Cooper, jumped from a Boeing 727 using the aft airstair. He knew in what air corridor he was (Victor 23, heading south to Mexico from Seattle) and the time.  The mount St. Helens (8,365'), was about 10 miles north to him. Portland was 20 miles south. He had however zero visibility of the ground. It was nighttime and raining heavily. I suppose he would not see any lights from Ariel (WA), 10 miles north to his position, and which has a population of about 700 nowadays.

With what precision could D.B. Cooper know where he would fall?

There is another related question, but not a duplicate here: Would a 90 kg object jettisoned from an aircraft create a detectable movement?

We have no idea how much he did know, but it's possible he had a basic idea. The fact he came up with the plan at all suggests some kind of aviation background (the air stair, for example, wouldn't occur to many people): so we can probably assume at least some basic navigation ability, especially with how thought out the plan appears to be.

He knew where the aircraft was starting from. He knew the airspeed it would travel at (100 knots, just above stall speed), which would give him a rough idea of how far it had travelled – particularly if he had information about the wind at that level.

Distance = Time x Speed... so all we're missing is the Time. If he knows how long they've been travelling, that's sufficient to allow him to have a reasonable idea of where they are along a known track, particularly if he carried a compass.

It's hard to be sure without the precise weather conditions available, but even in rain then as long as you're below the cloud layer, I wouldn't be surprised if Cooper could see the lights of either Portland or, more likely (considering the angle) Ariel: towns are pretty visible from the air. For example this photo is London from 10,000ft. Admittedly London is quite a lot bigger than Ariel, and the weather is clear, but considering the "closer" areas of the picture are a couple of miles, and the "distant" areas are more like 20 miles away, it's fairly easy to see how even a small town can be quite visible.

(source: https://www.flickr.com/photos/andygocher/12836895204)

Note that at 100 knots ground speed the aircraft is travelling at ~2 miles per minute across the ground. I can't find any wind data, but considering the 8:13 jump time was only approximate, it's more than possible that he saw the town below and a mile or two below and behind the aircraft, took a minute or so to prepare, and then jumped when 4-5 miles from the town.

He probably didn't know precisely where he was, but there's a reasonable chance that he saw a town below and that was sufficient for him to attempt the jump. He had the equivalent of over a million dollars in his pocket, he only had to find a town and get on a train in order to escape.

We also have no idea whether he had a chart or similar in his bag, nor whether there was any potential visibility of Mount St Helens (possible, considering the 1/4 moon that night). It's unlikely at 10 miles, but they'd passed it earlier and he may have used it as a point of reference.

In short: he probably had a rough idea of the region (to within 50 miles or so) and quite possibly had just seen a small town.

Did he know what town it was? Probably not, but he likely didn't care either: he had enough money that as long as he survived the jump and walk into the town, it probably didn't matter what the town was.


Can an aircraft at 10,000 feet have sea level pressure in the cabin? Right now at my university we are busy with a project for designing a conceptual aircraft. Our aircraft is in the CS-23 range, this airplane is a small cargo aircraft with the option for carrying injured passengers (so like an ambulance aircraft).

Our aircraft will have a cruise height at 10,000 ft. We want to make this aircraft pressurised but our question is therefore, is it possible to pressurise the aircraft from inside below the normal 8,000ft. So for example, we are flying at 10,000 ft but we want to have the inside pressure having the same as on sea level if that is possible, or is it only possible to pressurise the inside at 8000ft.

Thank you in advance.

If you design the aircraft, shouldn't you be answering that question? If it is part of your aircraft's mission to fly at 10.000ft whilst maintaining sea level cabin pressure, then you should design it that way.

Why would it only be possible to pressurize the inside to 8000ft? Not to 9000ft, 7000 ft or any other arbitrary altitude?

Of course the construction of the aircraft needs to be able to withstand the forces caused by pressure difference between the inside of the cabin and the outside. And the pressurization system needs to be able to maintain the pressure at sea level, so compensating for any air leaks in the pressure vessel.

For an initial feasibility study you could look at the pressure difference on the hull when an aircraft is flying at FL430 whilst maintaining cabin pressure at 8.000ft. Note thate the Boeing 787 maintains the cabin altitude at 6.000ft, while operating at 43.000 ft.

Compare that to the pressure difference between 10.000ft and sea level.
Looking at those pressure differences should give you a feeling whether or not it is easy to achieve your objective.


Can airline pilots communicate with dispatchers? Is it possible for airline pilots to communicate with dispatchers? If so, what methods do they use? A special radio channel?

Yes, and it is a regulatory requirement that it is so.

§121.99   Communications facilities—domestic and flag operations.
(a) Each certificate holder conducting domestic or flag operations must show that a two-way communication system, or other means of communication approved by the FAA certificate holding district office, is available over the entire route. The communications may be direct links or via an approved communication link that will provide reliable and rapid communications under normal operating conditions between each airplane and the appropriate dispatch office, and between each airplane and the appropriate air traffic control unit.

The typical way to contact dispatch is through SELCAL which allows two way communications between two specific parties over HF or VHF radio.  To contact a dispatcher we would tune the COM associated with SELCAL to the proper frequency (these were charted on company airport pages and you would use one from an airport nearby that you are overflying) and then use our handheld microphone (with keypad) to dial a code for our dispatcher, which is noted on our release paperwork.
As long as you are monitoring a SELCAL frequency and dispatch (or someone else with your aircraft code) calls you, the airplane will announce "SELCAL" and typically a light or some other visual notification will come on.
Once connected, you talk to your dispatcher over that com radio the same as you would talk to ATC.  From there your dispatcher can connect you to maintenance, med link, or anyone else you might need to talk to.
For larger airplanes typically used on overwater routes you will probably also find a satellite phone in the cockpit that can be used as an alternative way to call dispatch.
Textual communications to and from dispatch are also possible using ACARS.


Why do the Lycoming HIO-360 A1A and IO-360 engines produce different power? I have just acquired an aerobatic aircraft fitted with a Lycoming HIO-360 A1A. Reading the specs on the engine I see it has the higher (8.7:1) compression of the 200hp IO-360 engines, which seem mainly to make that power at 2 700 rpm, but this one actually makes the same power (180 hp) of the 8.5:1 carburetter engines, but at higher rpm (2 900) than they turn. This was a helicopter engine originally which I think accounts for the higher rpm rating, but it seems to me wholly counter-intuitive that an engine with the same swept volume, fuel injection for greater efficiency AND more revs would make - relatively - so little power. Can anyone explain this?

Helicopter engines have different operating parameters than aircraft engines. They operate in a narrower power band and the difference in horsepower would be due to  camshaft lift and duration optimized for that power band.