How does the DA 40 NG automatically control the mixture, pitch and power by just providing one throttle? I'm a student pilot and here at my school we have the older gen DA40s which have individual lever for mixture, pitch and power.

I was looking at this video of the DA40 NG, and got quite curious as to how everything from prop to mixture is automatically controlled, and on top of that you don't need to do any run up checks!

Tried using google but nothing really came, so I thought this would be the right platform to ask and satisfy my curiosity.

According to Diamonds website the NG engine is a:

  Austro Engine AE 300 turbocharged common-rail injected 2.0 liter diesel engine with 168 hp and EECU single lever control system

The prop is a:

  3 blade MT hydraulic constant speed propeller features advanced blade geometry for efficient performance, low vibration and noise. It is automatically controlled by the engine’s digital engine control through a conventional hydraulic governor.

From the sounds of it, it is as close to a full FADEC (Full Authority Digital Engine Control) unit as you can get

It is controlled by a computer module just like your modern fuel injected car.


NOTAM - What means "no shoulders along taxiways" in German? can anyone explain to me what "no shoulders along taxiways" means?
I know what shoulder markings are, but I don't know how to translate them.

Are there German people? :)
Thank you!

The NOTAM you copy doesn't mention taxiway shoulders anywhere. It says there is work going on on the shoulders of the runway and apron, and that a taxiway is closed.

As to taxiways not having shoulders, quite possible. The hard shoulder is the area outside the marked road surface, this can sometimes be extremely narrow.


Where can I find detailed steps on how to perform all ACS maneuvers? All the maneuvers outlined in the Airman Certification Standards (slow flight, power on stalls, short field, etc.) have been taught by my instructor to me but on no occasion have I received reference material for each of these maneuvers. I find after long periods of not practicing these, it can sometimes become easy to interchange the order of operations of 2 steps in a given maneuver. I have my checkride scheduled and need to be able to reference these.

Where can I find the individual steps in each required maneuver?

Aircraft: PA-28-140 / Piper Cherokee

To be clear: I know that the ACS itself has bulleted items identifying required things the candidate must be able to demonstrate, but this still doesn't detail how to perform the maneuver.

Interesting question.  In the past, the preamble to the PTS showed reference material that can be used to throughout the PTS.

With the new Airman Certification Standard (ACS), those references are incorporated into each task.  For slow flight below it lists the references as FAA-H-8083-2, FAA-H-8083-3 and POH/AFM.

 Private Pilot Airplane ACS

Undoubtedly, it will list the Airplane Flying Handbook as a reference.  All the maneuvers and techniques are in that book.  It is generic and the POH takes preference if there are disagreements.

Airplane Flying Handbook (FAA-H-8083-3)

Risk Management Handbook (FAA-H-8082-2)


How do large airliners de-ice in flight? How do large airliners de-ice their surfaces in midair? In smaller planes like the ATR or the caravan there are deicing boots as per picture:

How is this achieved on bigger aircraft, as there seems to be no such mechanism?

Putting this as an answer rather than a comment because of its length.

In response to @romkyns comment, perhaps the 787 pilot knew of the heating elements within the wing but was simply telling how ice was normally handled. I really can't imagine him getting through his type rating oral without knowing that.

Had you asked me the same question back when I was flying 747-100 and -200 aircraft, I would have replied thus:

Icing isn't typically a problem because you're usually not in it long enough at a slow enough speed that the ram air temperature rise doesn't get the temperature above freezing.

If you are getting ice on climb out at your normal climb speed, it was usual to ignore it knowing that the icing would soon stop as you gained altitude, and then what icing you had would soon sublimate. If the icing was severe enough to warrant your attention, the usual remedy was to just speed up to get more ram air temperature rise, but you would, of course, be sacrificing some of your climb rate. The U.S. has a 250kt speed limit below 10,000 feet, but you don't have to (or at least didn't have to back then) observe that if there was an operational need to go faster, and generating enough heat to take care of icing was considered a good reason. You normally wouldn't have to think about that though because a 747 climbing out with flaps up has a minimum safe airspeed in excess of 250 anyway.

One indication that the icing was serious was that ice buildup on the windshield wipers would set them to vibrating and giving off a loud buzzing sound. If you let them do that too long, they could depart the aircraft. As I understood it, the time for that to happen was cumulative over the past occurrences as well as the current occurrence, as it was a matter of fatigue.

If you were icing on the approach and didn't want to or couldn't speed up, you could heat the wing leading edge with pneumatic air as described in previous answers. However, it was the leading edge slats that were heated, and when you selected the first notch of flaps, that deployed the leading edge slats, and the heated pneumatic air escaped with little or no effect.

Only once in 10 years of 747 flying did I use the leading edge heating. We were in a holding pattern at low altitude waiting for our turn for an approach into Brussels.


What is this 'runway number' automatic readout system on a flight deck? I was watching this flight-deck video (starts at 11:13) of a Turkish Airlines Boeing take off from Istanbul and just as they accelerate on the take off roll there seems to be an automatic voice in the background reading out the runway name, "Runway 35 Right".

Is this a standard safety feature? Never heard it before. I've only heard the ATC give the clearance manually.

Is it an aircraft feature or an airport system or a combination? Is it meant to prevent incidents where pilots line up on a parallel taxiway / runway?

That's indeed the plane. It's equipped with a RAAS (Runway Awareness and Advisory System).

It also provides other call-outs, such as remaining runway length, approaching a runway, being on a runway, staying for too long on a runway, among others.

It is indeed a safety system, to make sure runways are not mixed up, and awareness of being on a runway in low visibility, for example. It is not standard on all planes, for example from the linked article:

  In 2015 the largest European low cost carrier Ryanair announced it would equip their entire fleet by the end of 2016 with RAAS as an investment in its commitment to safety.

The system does not require airport equipment, it requires a software update to the plane's EGPWS and the on board GPS. If an airport is not in the EGPWS database, such as some of the infrequently used GA airports, the system won't be able to call-out the runways.

The system was certified in 2007, but I haven't been able to confirm the entry into service date, but it's been around for a while. According to the Wikipedia link, Alaska Airlines introduced it in 2008.


Is there a method for calculating change in V-speeds with a change in weight for a Cessna 172? For example, what would the rotation speed (Vr) and stall speed (Vs) be at maximum takeoff weight versus flying with a single occupant? (2297 lb vs 1807 lb)

Instead of doing detailed calculations like you were in a jet, there is a useful rule of thumb advocated by author/instructor William Kurshner for working that out, which while not exact down to a fraction of a knot, is conservative and easy to do and is therefore perfect for regular GA flying.

Reduce Vs/Vr by half of the percentage of the weight reduction.  So if stall speed is 50kt at gross, and the weight reduction from 2297 to 1807lb is about 21%, and half of that we can round up to about 11%, your stall speed is going to be about 45 kt at that weight.

So if I was using say, 55kt as a rotation speed at gross (I seem to remember that's what it was on the 172), I'd use about 49 kt at 1807 lb.  Close enough for 99.9999999999% of normal operation in a Chevy Biscayne Of The Air like the 172.


Can an airport fine an aircraft for being too noisy? I stumbled upon this article (sorry, in French!) stating that in order to avoid fines, Ryanair pilots start take-off procedures at the beginning of the runway (rather than at the "intersection"), with extra engine power (24klb instead of 22klb in Brussels airport) -> this allows pilots to take tighter turns and avoid the noise-sensitive Brussels region.

I know that most (if not all?) major airports have noise monitoring terminals (NMT) in their vicinity which constantly measure the noise as it is perceived on the ground.

From the article, it seems like a single aircraft can be fined for being too "noisy" (i.e. noise generated at monitor above a certain limit). If such is the case:

What is the noise fining policy around an airport / Are there internationally agreed rules on noise limits around airports?
Is it common practice (is it even possible) to "single out" an aircraft and fine the pilot/company for generating too much noise on ground?

Ill answer this for the FAA (here in the US) but keep in mind this differs around the globe.

The FAA outlines some of their noise abatement information here. They created a special website that has a lot of the data here if you are interested.

There are 2 basic scenarios here in the US, towered and un-towered operations. There can be a noise abatement or related procedure in place in both cases and it is both the pilots and towers (when applicable) responsibility for knowing them and abiding by them. Some of them may be set in place by local governments (if its say a municipal airport) and you may face local legal action for violating them.

At a towered airport that has a noise abatement the tower will generally not vector you to that area or have you use a given runway provide conditions allow. For example when I fly out of KPNE there is an abatement in place, in this case they only list Rwy 15 arrival (stay above the glide slope) however there is another abatement in place on the weekends to keep you from flying over the heavily residential areas early in the morning. The tower vectors you appropriately for that one.

(source)

At un-towered airports there may be a published noise abatement that you are requested to follow. For example I fly out of KDYL which has a noise abatement in place (to keep you from flying over downtown). In this case we can see it noted in the AFD. Although its not fully explained the procedures are for RW 23 turn to 250 as soon as practically possible, for RW05 no turns under 1200 ft. and there are no touch and go's at any time.

(source)

In both cases the procedures have a similar outcome to what you have described, keep the airplanes away form the populated areas. The procedures vary heavily per airport and scenario but all generally strive for the same outcome.

The FAA advises you to first report a violation to the airport but also provides contact info for directly reporting to the FAA. You can single out a given aircraft by accurately reporting the time of the incident (and if its visible) describing the aircraft. Granted it can be difficult at an un-towered field to know who exactly was departing if no one was around to see it or on the radio to hear it. Once reported the local authorities may have the right to fine you for the violation (if that is the punishment on the books). For example in the NY/NJ area the Port Authority handles the violations and does hold the ability to issue fines.

Long beach airport lists their fines on their site

  If a plane violates the Noise Ordinance, how much are they fined?

  The initial phases of our violation process are educational: the first
  time an owner/operator violates, they will receive a complete packet
  including a copy of our Noise Ordinance, an outline of what the
  infraction was, a letter from GANC offering assistance with
  procedures, and a warning letter asking them to contact noise
  abatement staff.
  The second violation involves a notification letter
  of infraction and a request for a written noise abatement program,
  where we ask the owner/operator to communicate how they plan to
  operate without violating our ordinance in the future.
  The third violation is a fine of $100 dollars. The fourth and every subsequent fine of 300 dollars. Please note that Military aircraft
  are exempt from this policy.

And it looks like, according to the regulations, the airport manager issues the fine and the payments go to the airport. This may vary by jurisdiction on how they chose to govern things like this. Over all the answer to your question is, yes airports can fine pilots (well really owner/operators) for noise violations.

There are also noise limits on aircraft that deal with engine noise but are generally handled during the certification phase of the air frame. This helps to reduce airport noise overall.

As for global regulations the IATA has outlined some stuff here with the full text here. ICAO has a set of policies you can find some references to here.


How are aeronautical charts made? How are aviation charts made? What kind of techniques are used?

From what I understand a GA aircraft equipped with:

A camera: takes images of the ground
Radar: calculates altitude and detects obstacles

Mapping starts with basemaps, with topos (DEMs or digital elevation models) and geographic features.  Then cultural overlays are added.

The charts in US utilize a national spatial reference system. Today this is done with GIS/Mapping software. Then overlays for aviation data, such as man made obstructions, and air navigation data is added.

The (old) process has been the topic of many articles in pilot journals. The newer process is rapidly evolving, as the government transitions to AWS / cloud based applications.

To address your questions, the DEMs may have been created with RADAR and integrated with topo data, but today LIDAR is the norm.  LIDAR data helps with man made structures as well, while not as good as SAR RADAR, it can still show catenary and power line structures.  Those metallic structures show up very well in SAR due to their conductivity.


Does the rudder need to be held throughout a coordinated turn? It's widely known that to perform a coordinated turn, rudder must be turned as well as ailerons. My question is what to do after the desired bank angle is achieved?

In the Airplane Flying Handbook we read:

  After the bank has been established in a medium
  banked turn, all pressure applied to the aileron may be
  relaxed. The airplane will remain at the selected bank
  with no further tendency to yaw since there is no
  longer a deflection of the ailerons. As a result, pres-
  sure may also be relaxed on the rudder pedals, and the
  rudder allowed to streamline itself with the direction
  of the slipstream.

So does that mean that the pedals will remain in "shifted" position as a result of the rudder remaining slightly turned?

I also wonder how this is imitated in simulators (I'm using FlightGear) as all (even expensive) simulator pedals return to "zero" position themselves?

When you deflect the ailerons, you increase lift on one side of the wing and decrease it on the other. This causes a parallel increase of the local induced drag where lift is increased and vice versa. The consequence of that is a yawing moment which needs to be corrected with rudder deflection.

Once your ailerons are neutral, this yawing moment goes away, but now your airplane is in a constant yawing motion which increases airspeed on the outer wing and swings the tail around, so your vertical tail sees some sideslip even if your ball is centered. The airspeed differential between inner and outer wing causes some friction drag differential which tries to pull the aircraft out of the yawing motion. Depending on the tendency of the rudder to follow a sideslip, you will need some pressure to keep the yawing motion going.

It is hard to be more specific, because details depend on the particular airplane.

In most of the airplanes I have flown, you also need to keep some aileron deflection to keep your bank angle constant. Here are two effects which go against each other, so again the details depend on the particular aircraft. One effect is caused by the airspeed difference which causes a lift difference between inner and outer wing. To correct this, you need to deflect the aileron against the bank. The other effect is caused by the different centrifugal forces of the masses of the inner and outer wing. The whole wing is moving at the same angular velocity, but centrifugal acceleration is the product of the square of the angular velocity and the radius of your motion. Since the outer wing flies at a larger radius than the inner wing, the masses of the wing will try to pull the aircraft level. This needs aileron deflection into the bank. If you are lucky, both effects cancel each other out, but normally they don't.


What are the factors behind increasing aircraft window sizes? Modern airliners like the Airbus A380 and Boeing 787 have bigger windows than older designs, like the Boeing 737 and Airbus A320.

What factors have led to this change of window size, opposite to the trend of almost every other thing in the interior of the plane becoming smaller in size (like the seats).

In the early years of the jet age, which followed closely on the introduction of pressurized hulls, there was much fear of stresses specifically in the area of the window openings due to the loss of two DeHavilland Comets. Subsequent Comet hulls had different shaped, rounded, smaller windows and that trend continued in other pressurized, typically jet-powered, aircraft.

Only with modern CAD systems and new materials knowledge could windows be made larger again. The newest aircraft designs reflect that progress.


Are there any aerospace examples of applying a boat tail? A way to reduce the pressure drag of bluff bodies is to apply a tapering of the tail (so called boat tailing)

I know some (extreme) examples of this method of drag reduction applied to cars:

Source

And I know that this a feature of the Very low drag bullet

Source

I was wondering if there are any aerospace applications?

This depends on the mission the plane is built to fit. Some planes need the cargo space so the tail is less tapered but most planes have at least some taper. Diamond Aircraft have very tapered tail sections

(source)

Even the older GA designs like the Piper Seminole have a good deal of tail taper

(source)

Larger planes have some tail taper as well however sometimes there is less as there are often systems in the tail like the APU or there is storage space.

(source)


Do planes return to service after non-fiery crashes? A Turkish Airlines flight recently ran off the runway and ended up on its belly in a field. The landing gear were damaged, but the plane didn't burn and the fuselage remained intact.

Are planes involved in this sort of accident repaired and returned to service, or are the planes usually scrapped?

If the aircraft can be economically repaired (there is no major structural damage, and we're not talking about an aircraft already scheduled to be retired) then it's likely the aircraft will be repaired and returned to service. When you spend several million on an aircraft you aren't going to throw it away for a few tens or hundred thousand dollars worth of damage, particularly as it's probably insured.

If the aircraft is structurally compromised to the point where repairs would not be economical (or if we're talking about an older aircraft which has given many years of service and is due for retirement) it would probably be written off and scrapped for any salvageable parts (either repairing it to a condition where it could be ferried to a "boneyard" or dismantled and cut up at the accident site - whichever option is less expensive for the airline).

As one particularly famous datapoint, the Gimli Glider had an off-airport landing with a nose gear collapse in 1983. The aircraft was repaired, returned to service, and flew until 2008 (a little under 25 years of additional service after its incident).


Why does the US Marines continue to fly the AH-1 Cobra, retired by the US Army in the late 90s? My father flew Bell AH-1 Cobra for the United States Army in the late 1970s and a young man in my daughter's USN winging class (July 2017) was being assigned to Camp Pendleton to fly Cobra's for the United States Marines.  From talking to my father and reviewing the Cobra wiki page, it appears that the Army retired the Cobra in the early 1990s.  However, it seems the Marines have continued to fly the Cobra, though AFAICT, they seem to have moved to the twin Super Cobra:

I am aware that other attack helicopters followed the Cobra and that the Army adopted the AH-64 in the mid 1980s.

What's not clear is why the Army retired the Cobra but the Marines continued to fly it.  Or, perhaps another way to ask this question would be, why does the USMC favor the Cobra over the newer AH-64?

Well this ain't your father's Cobra.  Literally.

The current incarnation of the Huey cobra for the Marine Corps, which is called the AH-1Z Viper,  sometimes referred to as the King Cobra continues to be the backbone of the Marines attack helicopter force for several reasons.

Like all Huey cobra models, the AH-1Z and the USMC current utility helicopter, the UH-1Y Venom, make use of a common power plant, transmission and rotor set, tailboom and avionics architecture, saving quite a bit on spare parts.  The USMC quotes an 86% commonality between the UH-1Y and AH-1Z airframes.  And, as both the UH-1Y and the AH-1Z constitute a single acquisitions program, it saves a lot of time and costs trying to begin another weapons procurement program for the Corps.  This is also the reason the Huey Cobra even came into existence in the first place.

As helicopters have hit the upper limit in terms of performance, the procurement of a brand new airframe over an existing design doesn't offer many advantages and costs considerably more.  Simply upgrade the engines, add in a modular avionics bay with modern infrastructure facilitating upgrades to modern mission systems and modern weapons, and modern defensive countermeasures systems, and you have help that's as good or better than any existing attack platform out there.

The AH-1Z is comparable to the AH-64 Apache weapons system but remains slightly faster, carries a greater payload and has a 33% greater range than the Apache, all preferred attributes for shipboard operations.


Does being out of trim affect drag? If the aircraft is not trimmed correctly and either the pilot or autopilot is having to use constant pressure on the elevator does this increase drag?

Normally not; details depend on the control system and by how much the aircraft is out of trim. The force produced by the empennage will be the same in the trimmed state and when out of trim, only the control forces are different.

Let's examine the different possibilities:

Adjustable spring (as used on some light aircraft and gliders): The elevator deflection will be identical to the trim position, so there is no difference at all.
Trim or servo tab on the elevator: The tab deflection will be different, but the elevator position will be practically identical. For tab angles of less than 10° relative to the elevator there should not be any difference in drag.
Adjustable stabilizer: Now the elevator deflection will be different, and depending on the trimmed state the deflection angle might cause higher airfoil drag. If the elevator deflection relative to the stabilizer is more than 10°, a slight drag increase can be expected.

If the power consumption of the autopilot is higher in the out of trim case, this might cause higher generator loads and more engine power is needed to keep it powered. But this effect should be very small.


How is an aircraft aligned at a jet bridge? I see these jet bridges (or aerobridges) at nearly every new airport I go to. How are aircraft aligned with these bridges, particularly the A380 which has doors on both decks?

How are aircraft aligned with these bridges

They are not (but read on)

Aircraft are aligned to a point on the concrete, not to the jetbridge(s).

It is the jetbridge itself that carries out the final alignment to the aircraft door.

Jetbridges are actually motor vehicles with wheels, tyres, motors and (often) steering. It just happens that their rear end is tethered and their bodies articulate and/or telescope to accomodate the motion at the "front" end..

You drive one using a set of controls at the end furthest from the terminal building

-jet bridge controls

- driving a jet bridge

I believe some also have what is effectively variable height suspension like old Citroens (except I imagine it is hydraulic or jack-screw).

The aircraft is driven to the terminal so the nose wheel follows a  guide line and stops at a marking appropriate for the aircraft type. Then the jet bridge is driven up to the aircraft door.

As the aircraft is gradually burdened with self-loading freight and sinks on it's suspension, the jetbridge metaphorically bends its knees so that the SLF don't trip up or fall into the aircraft. That is, the jetbridge maintains alignment, the aircraft is pretty passive in the job of alignment.

I have to admit I didn't notice these jetbridge controls for many years as I was usually either busy rushing to my seat or busy rushing to the baggage reclaim. One time there was a delay at the aircraft door that was long enough for my bored gaze to alight on the controls and for the thought to briefly wander across my mind - "I wonder what would happen if I pressed that ..."


Attempting to determine whether a flight took place We had some houseguests recently who were scheduled to take American Airlines flight 2953 from SAV to ORD (May 16, 2019). They called and said that there had been a mechanical problem with the plane and that the flight had been cancelled. Since I had the flight information, however, I had already been tracking the flight status, and I saw that the plane was still scheduled to depart, and then I saw that it had taken off and landed, albeit with a delay. (The guests came on another flight the next day.)

I didn't confront the guests, of course, but I am curious to know whether there is any possible explanation for the discrepancy (i.e., other than that there was some other reason for the delay that they didn't wish to share with us). Could the flight have been cancelled and then rescheduled without their knowing it? Could the plane have been returned to ORD without passengers, and it showed up on the flight tracker as the regularly scheduled flight? Or is there some other possibility?

That flight did indeed happen:

https://flightaware.com/live/flight/AAL2953/history/20190516/1632Z/KSAV/KORD

It was scheduled for 12:22PM, but actually left the gate at 1:43PM (about 1 hour and 20 minutes late).

It was scheduled to land at 1:28PM, but actually landed at 3:25PM (about 2 hour late).

It looks like it took an extended detour to Missouri to avoid a weather system, resulting in the extra delay.

While the flight was not canceled, it is possible that passengers were offered free re-booking opportunities due to the weather system.  Your house guests may have taken that on the belief the flight might be canceled.


What is "alternate takeoff" in this PT6A performance table? I am flight mechanic, and I would like to know about this performance limitation:

What is the definition of alternate take off?
Why is the alternate take off temperature limit (ITT) lower than max. cont. ITT?

Alternate Take-off is a reduced power option feature, similar to flex thrust on turbofans.  The aircraft manufacturer will provide performance data applicable to the reduced power setting that can be used when circumstances permit.  It's all about reducing wear and tear by not running the engine as hard if it's not essential.
The Max Continuous power setting is intended for emergencies (mostly single engine climb, or both engine climb in some marginal situations, or maintaining altitude single engine where you are one engine and high terrain makes it imperative to not descend) and as such is rarely used, so there is a higher limit to allow even a tired engine to make Max Continuous HP in a critical situation.
The reduced AT ITT limit reflects the objective of limiting wear and tear with a power setting used regularly, whereas the MC limit reflect the balls-to-the-wall limit the engine can take for extended periods when the power is desperately needed.


What is the gross weight limit for a Light Sport Aircraft? In the US, I see a lot of LSAs stating their take-off or gross weight limit as 1320lbs.  Can some of these planes have a higher physical limit and that 1320lbs is just more a category limit?

Yes, 1320 pounds is the regulatory Gross Takeoff Weight for Light Sport aircraft.
From the AOPA website:

Light sport aircraft are defined as simple, low-performance, low-energy aircraft that are limited to-
1,320 pounds maximum takeoff weight for aircraft not intended for operation on water; or
1,430 pounds maximum takeoff weight for aircraft intended for operation on water.


Does this chart show a heliport in class D airspace without a control tower? I was looking at the Los Angeles area on sky vector, and I noticed a tiny little triangular class D area right next to LAX. It shows that the height of the class D goes up to 2,500, but I couldn't see an airport in there, not even on the TAC.
Only if you click on "LA West Heli" on the top right on sky vector can you see that there is a heliport in that little area called "Chevron Refinery". On airnav, it says the identifier is 4CA6, and it says it does not have a control tower.
I have so many questions. Why is it class D if it has no control tower? Can a heliport even be class D? Why the actual heliport not appear on the sectional or even TAC? Can someone help me? :)

The triangular area you’re referring to is actually the LAX class D airspace.
The heliport itself is uncontrolled. It is not that uncommon for an uncontrolled heliport or airport to be within the surface area of a controlled airport. Departing aircraft are required to contact tower as soon as practical after takeoff, and arriving aircraft are told that landing is at their own risk.


How do Hoerner Wingtips work? I was just reading up about different methods of reducing drag through the different wingtip designs when I come across Hoerner Wingtips.

So after some research, I have two questions.

According to this article on pg 1, it states that "The convex underside accelerates the speed of the air passing under the tip to a velocity more equal to that of the air flowing over the top of the tip, thereby creating streamline flow." How exactly does acceleration of air occur just by having a convex underside?
As we can see, the effective wingspan using Hoerner Wingtips can be increased without increasing geometric wingspan.

How does a Hoerner Wingtip enable vortices to be generated further away, therefore increasing effective wingspan?

Thank you! :)

How exactly does acceleration of air occur just by having a convex
  underside

Just like the curved forward surface of a wing does it. Imagine for a moment that the air flows along a straight path: Now it would "see" that the surface below it curves away from its path of travel, and if that path would remain unchanged, a vacuum between the wing and the air would form. Reluctantly (because it has mass and, therefore, inertia), the air will change course and follow the wing's contour. This requires lower pressure, to make the molecules overcome their inertia and change direction.

Near the tip the flow has a sideways component, flowing away from the center on the lower side. This sideways flow, coupled with the sideways curvature on the lower wingtip, creates suction. This area of lowered pressure will suck in more air from inside. In essence, the curved lower side of the Hoerner wingtip extends the suction which is found on the upper surface of the wing to the side of the wingtip.

  As we can see, the effective wingspan using Hoerner Wingtips can be
  increased without increasing geometric wingspan.

Well, that is at least what Hoerner claims. Maybe it does move the peak suction of the wingtip vortex a little outside, but this has no effect on the flow field behind the wing and the eventual location of the trailing vortex. Below is a graphical overview of different wingtip shapes and their sideways location of the core of the tip vortex.

Wing-tip shape and tip-vortex location for a family of wings (picture source)

However, this is not relevant for induced drag. In the end, the strength and width of the rolled-up vortex sheet behind the wing indicates the amount of induced drag. Induced drag itself is the horizontal component of the resulting pressure forces on the wing (see here or here for more on that). The tip vortex is sucked into that vortex system regardless of its initial location. See below for an illustration:

B-747 with contrails (picture source)

You can see that the outer contrails of this Boeing 747's engines wrap around the contrails of the inner engines. This shows how the air is pushed down in the wake of the wing and that the centers of the vortices are slightly inboard of the contrails of the outer engines.


Is there a age limit to become a CFI? I’m a new PPL and I would love to become a CFI in the next 2 years (or so). My objective would be to transfer what I know (and will have learned) to aspiring pilots. I’m older, though (just about to turn 60). Put it bluntly: am I too old? I know that we can’t talk about people being too old for almost anything these days, but I really would like to know if anyone (e.g. a flight school) would hire an instructor who not only brings rather thin experience (300-400 hrs by then) but combines it with rather ‘advanced age’. The benefit for a school would be that this would be my ‘forever-job’ (first, part-time and then full-time after I retire from my ‘day-job’ in a few years), not a stepping stone to an airline career. Please, feel free to tell me what you really think…

A flight school won't care too much about your age if you have the required medical.  And mentally, your age is an overall plus since a flight school would generally prefer a mature individual in it because they want to teach to a 25 year old who's just building time.  The turnover with flight schools is quite high so the prospect of getting say at least 5 years out of you is another plus because they may be only getting 2-3 years out of younger instructors in the current environment (often they are basically only hanging on to get to 1500 hours under the "Colgan Rule" craziness).

I would say that that if your health is fine and shows no signs of problems over the next 5 years at least, you should definitely go for it.  You might even get a school to commit to hiring you, or at least giving you a shot (it's going to come down to how good a teacher you are), if you train with them.

With the general shortage of bodies all through the system, I don't see any downside if you really keen on doing it.  If you gain a reputation as a good teacher students will gravitate to you over the youngsters.


Why is the DC10/MD11/TriStar vertical stabilizer noticeably smaller than other contemporary aircraft? Why is it that these planes had vertical stabilisers that were noticeably smaller in proportion the aircraft itself to other aircraft? I understand that they had the engines mounted on the tail but couldn't the surfaces have been made larger? Doesn't this make it more difficult to control during flight as the surface is way smaller? Maybe is had some other mechanism in the engine that could compensate for the smaller area of the vertical fin?
I've added some images of the DC10, the TriStar, Boeing 767 and A310 which are aircraft that are sort of comparable in era and age and the most interesting one is the TriStar which so small:

Two characteristics drive vertical tail size in airliners:

Critical engine out: Here the tail needs to compensate the yawing moment of the live engine on one wing.
Yaw damping: This is aided by a yaw damper, but enough damping must remain for the case of a failed damper. Especially the dutch roll eigenmode is driving tail size.

On the other hand the tail should not be bigger than absolutely necessary to keep drag and weight down. On the Tristar, the big intake added so much tail area that a relatively small tail was sufficient. Note that the engine intake on the Tristar is much longer than on the DC-10 because of the S-duct. The flow must be brought down to the engine without internal flow separation, which is made easier when the intake is longer.

Since in the engine-out case only one third of total thrust creates the yawing moment which the tail needs to overcome compared to one half of the thrust in case of the A310, the vertical tails of both the Tristar and DC-10 are smaller relative to that of the A310. The A310 is a shortened version of the A300, so the reduction in fuselage length made an especially large vertical tail necessary. If you look at the vertical tails of the MD-80, the Il-62 or the VC10, they are even smaller since very little yawing moment needs to be compensated in the engine-out case. Adding to this, the T-tail configuration makes the existing tail more effective due to the endplate effect (PDF!) of the horizontal tail on those three types.

Vickers VC10 (left) and Tristar (right) tankers in flight (picture source).


Does the altitude or attitude of an aircraft affect GPS accuracy? Of course we are assuming an effective signal is being received.

I live near Idaho Falls, Idaho with a field elev of 5300ft. If I shoot an approach will GPS be more or less accurate then landing at Seattle or LA?

Does the accuracy of GPS change with aircraft altitude or attitude?

Altitude has little effect, as long as you don't descent into a valley. Mountains shield the GPS signal, resulting generally in lower accuracy and lower integrity levels.

Attitude does matter, steep turns can result in the airframe shielding GPS signals from the antenna. Again, the effect is a lower accuracy and integrity.


Could a plane with an electric turbine engine generate enough lift to provide a electric areodynamic lift and runway to space? This question is similar to my previous ones but configuration is different and so is the question.

Could a modified electric turbine engine (E-Fan) plane create enough of its own lift not to burden an electric rail that is evenly supported by electric powered blimps and rail (similar to a 3rd rail of a train) while carrying a payload (like the space shuttle) to the edge of space? The problem with a high power electric engine is the is the supply of electricity and weight of the engine and battery . The blimps and rail are necessary to provide the amount needed without a huge battery. Rockets still can be used at the end of it.

Assuming maximum altitude for the highest blimp is 74,000 feet, and the rail to be angled at 15 degrees, it gives us a rail length of 285,000 feet. The HiSentinel stratospheric airship flew that high, and was able to carry only 36 kg.

The steel rail/rope would weigh roughly 5.5 million kg. Based on steel density and a good sized rope, to withstand the elements. So we'll need 154,000 blimps to carry the rail. That's 1 blimp every 2 meters. Blimps are huge.

While the idea is highly imaginative (good thing), engineering tends to solve problems, not create ones. Would the blimps (if they fit in the sky) power down between launches? Or stay aloft?

You might want to check out the Stargazer:

  [A] Lockheed L-1011 TriStar that was modified to be used as a mother ship launch pad for Pegasus rockets. As of June 2012, 35 rockets have been launched from it.

RE: How much lift could an electric engine powered plane provide if the power source was provided externally?

What you are asking is like having a plane not carry fuel and instead have a long fuel hose attached to a fuel pump on the ground. Ignoring all the problems associated with that, one will help you understand the problem: pumping the fuel.

Pumping electricity over such a long wire / rail will require high voltage / low current (just like power lines). Which means the E-Fan-like plane and all the blimps will need to carry their own super heavy transformers (as I wrote above, one high-altitude blimp lifts 36 kg, which we've already used for lifting the rail).


What is the groundspeed history of an aviation of such as a Boeing plane? I would like to see groundspeed data of civil aircraft for distances such as 300 miles. What could it look like for a popular model such as Boeing 737?

If what you're asking is to see groundspeed history of a certain type of aircraft, you can choose a type here:  aircraft type airborne now

Then follow the links to see its flight track history as shown here: Flight Aware Track History


Does the HAL LCH have fly-by-wire? Is Automatic Flight Control System (AFCS) the same as Fly-by-wire?

If not what's the difference?

  India’s Hindustan Aeronautics Limited (HAL) has carried out the first
  flight of a Light Combat Helicopter (LCH) using an indigenously
  developed Automatic Flight Control System (AFCS), the state-owned
  aerospace and defence company announced in a statement on 31 January.

Source:

https://www.janes.com/article/77568/hal-tests-indigenous-flight-control-system-for-light-combat-helicopter

AFCS is just a fancy word for autopilot.  Autopilots for helicopters are a bigger deal than on fixed wing airplanes, due to the difficulty in flying them, so it's no small thing to develop one.  In the end however it's still just a computer than can operate servos attached to the controls to move the mechanical controls in place of the pilot when it's turned on.

Fly By Wire is a whole different universe, where there is a computer(s) between the pilot and the flight controls, with no mechanical interface at all, and the pilot makes inputs that tell the computer what the pilot wants to do, and the computer decides how to move the surfaces.


How is an aircraft painted? How is an aircraft painted?

I've always wondered how an air plane was painted and what steps it required to accomplish this task.

Prestige Aircraft Inc describes the process here: http://www.paintaircraft.com/the-process.html

  Upon delivery of the aircraft a thorough inspection will be made with the owner. At this time any details and or problem areas will be defined prior to starting. Items such as windows, plastic parts, dents and corrosion will be discussed.

  All control surfaces, inspection plates, cowlings and fairings will be removed prior to stripping.

  Engine and remaining plastic/fiberglass parts will be covered with protective aluminum tape or plastic as appropriate.

  Airframe will be chemically stripped, removing all old paint and primers using aircraft grade paint strippers.

  Airframe will be pressure washed with hot water to remove any stripper residue.

  Airframe will be acid etched and “Alodyned” to further clean and enhance paint adhesion.

  Airframe will be further cleaned with mineral spirits prior to priming with epoxy chromate primer.

  Aircraft epoxy primer will be lightly sanded. At this time any dents and scratches will be repaired and reprimed.

  All fiberglass and plastic parts will be sanded and repaired as necessary, primed and prepared for top coating.

  Airframe and parts will be top coated with 3 coats Aircraft Grade Jet-Glo or Dupont Polyurethane paint. Trim colors, Reg. #’s and appropriate logos and placards will be applied.

  After painting, control surfaces are checked for balance as per mfg. Instructions. Hinges and control linkages are lubed prior to re-installation with new hardware.

  Freshly painted inspection plates and fairings are installed using new stainless steel screws and nylon washers.

  New stainless steel cowling fasteners are installed at an extra cost where appropriate.
  Wing walk is applied and new rubber wing root moldings are installed,(low wing aircraft).

  Windows are polished, interior is cleaned and vacuumed.

  A final inspection is made with emphasis on detail and overall quality.

  All appropriate log book entries are made and signed.


What is the difference between dry operating weight and dry operating mass? What is the difference between dry operating mass and dry operating weight in the context of rotorcraft?

What is the formula for converting mass to weight?

Weight is a force.

Mass is a property of matter. Acceleration makes mass produce a force. Specifically, a mass in the gravitational field of Earth effects a weight force on its support. The relation between both is the gravitational acceleration g, which is standardized to 9.80665 m/s² (approximately 32.174 ft/s²), as in Weight = Mass · g.


Does a nuclear weapon (B-61) equipped F-35 have the same nuclear confirmation failsafes as other nuclear device delivery aircraft? Several sources cite that the F-35 will be able to be modified or simply equipped to carry some variant of the B-61 nuclear bomb. However, I know that most strike aircraft such as the F-15 Strike Eagle seat two crew as so for nuclear weapons there must be confirmation of arming the weapon by both crew members. No variant of the F-35 seats two, so I assume that there must be some way of having two-factor authorization of this protocol anyways. Is there a publicly known practice of arming nuclear devices on the F-35 or any other single seat aircraft or were the sources stating it could deliver the B-61 incorrect?

Traditionally many single seater aircraft have had nuclear weapons capabilities.

To name a few:

A-4
F-104
F-105
F-84
F-16
A-7 (I think)
F-102
F-106
F-88
F-101

This list isn't exhaustive. The release of the weapon will typically be authorised before takeoff, the pilot then having the electronics on board to enter the final arming codes that will bring the weapon life. I'm not in the know about the exact procedures here, but my guess is someone on the ground acts as the first of the two keys before the flight starts, and the pilot entering his codes into the arming console during the flight acts as the second. This is far more reliable and less error prone than having the code transmitted to the weapon during flight over a radio link which may be jammed, detected, or simply not work in a nuclear war scenario.


Is a high alpha sideslip possible and safe? Is a high alpha sideslip possible and safe?

We use a sideslip to increase drag when trying to reduce altitude before landing on a short runway, etc., which is crossing your rudder and ailerons, to produce an angle to the intended direction, usually in level flight.

Is it possible to do a sideslip at an AOA of say 15 deg for even more drag, assuming stall angle is at 30 deg?

You would be risking your life.  Cross controlled approaches should only be done well above stall speed and only after testing at a higher altitude.  Increasing AOA will slow your plane down.  If you recognize being high early in the pattern, you might be better off going ABOVE Vbg and slip, which makes the plane glide much less efficiently.  Spoilers act in a similar manner.

Do a proper approach and use your flaps/spoilers.  If it is allowed, forward slip to increase rate of descent at your preferred approach speed.  If you can't make the runway GO AROUND.  Changing speeds on short final will make judging the landing much more difficult.

In an emergency landing it is far better to over shoot the field and roll into fence, trees, etc at 10-20 mph than to risk losing control of the plane.

As a side note, only deltas come close to 30 degrees AOA before stalling, and these tend to drop like a rock when slipped if their vortex lift is sufficiently disturbed.  Slats and flaps will significantly increase stall AOA, but at the expense of much more drag.

Generally a bad idea.


What aircraft is this? Yesterday, I saw a strangely-shaped aircraft in the sky.

Searching for "aircraft silhouette" on the web, I found this picture within seconds on a vector graphics site. It describes perfectly what I saw, so there is nothing else I can say about the aircraft.

But I did not find any information what aircraft it is.

The wings are not swept and those stubs at their front look like propeller engines. But it seems as if there are fans at the rear of the fuselage...

So, does anybody know what aircraft this is?

EDIT:

@DeltaLima: Not bad. I'm pretty sure that this picture really shows an A-10. The picture is part of a larger one, and the other aircrafts were military ones, too.

I saw the aircraft it in Geneva, near GVA airport. Now, I doubt that I saw an A-10 there, as the last A-10 left Germany a while ago, and afaik there are none in Switzerland or France. If I neglect the stubs (which I may have noticed on the picture only), it could also have been  one of those at the GVA airfield, which have a comparable shape.

EDIT 2:

Meanwhile, I'm quite sure that it was one of those labelled A, B, C on this picture from google maps (though, B and C are pretty much the same):

The airfoils as well as the elevator were definitively not (significantly) swept and there was no gap between the airfoils and the fans in the silhouette.

Maybe, it was one of those, maybe, it was a similar aircraft. May be, it really was an A-10.

So, this are three 'maybes'. Lets add another:

Maybe, we put this question on hold as there will be no definitive answer.

But thanks a lot for your contributions!

It seems to me that it is an  Fairchild Republic A-10 Thunderbolt II, commonly know as "Warthog".

(Source: wikipedia)

The "stubs at the front of the wings" are pods in which the main landing gear is stowed after retraction.

If you are in doubt that it was military, it might have been a business jet like the Cessna Citation II / Bravo / Mustang, which has a similar planform albeit without the stubs in front of the wing.

Using the replay function of Flightradar 24 you may be able to find out which exact aircraft it was. The coverage at low levels is not so good for all aircraft though.


How can I avoid flight simulator software reinforcing bad habits? While looking into getting into flying I've seen in several sources that using flight simulator software typically creates and reinforces bad habits. Most articles say that it reinforces "instrument" flying which is not practical.

Is there some other action I should incorporate into learning to fly that would maybe help me avoid focusing too much on the instruments? Or would the simple introduction of things like pedals, flight sticks, etc be enough help to avoid this issue?

I posted this answer on FB a while back:
I’m a commercial pilot as well as a flight sim fan with somewhere in the neighborhood of 7000 hours logged on Flight Simulator and Falcon 4.0 games.  I disagree with the assertion that the sims are so different from the real thing.  While it is true that the kinesthetics of being in a real airplane are different from the sim, the handling and behavior of the sim is so close to the real thing that the same mistakes I make in the sim I make in the real thing.  They are also very effective platforms for practicing instrument flying and approaches.  It’s not surprising that Redbird makes use of a proprietary version of FSX for its flight simulators.
That being said there are several notable areas where the entertainment sims can be off from the real thing:

Avionics may be simulated poorly or unrealistically.  Alabeo payware is a major offender here.

Games do not adequately simulate weather hazards.  Flying into a thunderstorm in FSX is a benign experience.  This can kill you in real life.

ATC interaction is appallingly unrealistic, akin to having an adult conversation with a talking Barbie doll.  Probably the worst offender is XPlane’s default “ATC” which is absolutely nothing like the real thing.

Airport and navigation databases are terribly out of date and cannot be updated.  This appears to be changing with the advent of Flight Simulator 2020 which periodically updates its airport and nav databases, but FSX and XPlane are horrible.  This dramatically affects realism when flight planning IFR flight and shooting practice approaches, as, at least in the case of FSX, the default approaches are now 14 years out of date!

Terminal departure and arrival procedures are often not modeled properly or absent altogether, making operations from major airports unrealistic, especially for jet flying.

Considerable errors exist in the default terrain as well as airports. Some of the worst instances I’ve found were in FSX and include an airport in the middle of a 1000ft deep pit.  Ft Worth Meecham Intl. has the peculiar obstacle hazard of floating houses along the glidepath to runway 35.  Gustaf III / St Bart’s and Courchevel are wretched as well.

Some sims (FSX) suffer from control lag ie a delay time between control input and movement of the control surfaces, creating an unrealistic control response which makes it difficult to fly demanding maneuvers eg aerobatics accurately.

Some sims are developed around certain types of aircraft and do not replicate other aircraft or systems well.  FSX turbine and jet engine simulation is a great example of this.

Edge of the envelop flight characteristics such as spins and aerobatics are often modeled poorly or completely absent in these games.

Ground handling and and takeoff and landing characteristics are unrealistic compared to the real thing.  This is really apparent when flying tailwheel airplanes, particularly in XPlane.

There are fixes to some of these problems.  Some payware aircraft are extremely realistic - VRS’s F-18E and RealAir’s BE60 Duke and Lancair Legacy quickly come to mind as does PDMG’s 737NG and 777 aircraft.  Additional addons for weather as well as cockpit avionics like Flight1’s GNS430/530 and GTN650/750 GNSS heads are great examples as they use the Garmin trainers as their core. ATC add-ons and Live ATC in multiplayer games alleviate the controller flaws in the default software.
If  you do intend to use a desktop flight simulator software to train on, I suggest that it be used as a means to augment actual training in an aircraft following the instructions of a CFI.   This allows you to accomplish a lot of training on basic airmanship and a fraction of the total cost compared to actually going out flying in the real airplane. While it diminishes the principle of effect during learning, It can accomplish a great deal of goals in terms of rote procedures and psychomotor practice.   Again a good flight training syllabus should be followed under the direct supervision of a certified flight instructor combined with actual flight training in an airplane.  When that’s done desktop flight simulators can be extremely useful to a budding airman. I learned how to do crosswind landings using FSX  and have always been very good at them ever since.   If training is done solely by means of a desktop simulator and self-didiaction,  this can lead to negative outcomes, such as incorrect use of the flight controls.  I remember one point early on in my flight training, there was another student working with a flight instructor who had logged in a lot of hours in desktop flight simulators by himself prior  to beginning flight training.   He had developed the undesirable habit of using elevator trim in order to maintain altitude during cruise flight wile playing sims and it took a great deal of work from his flight instructors to break him of this habit and install the correct use of trim in order to neutralize control pressures when in cruise.


What is the purpose of including sea level pressure and temperature in a METAR? In a METAR such as this one:

  KGOK 161553Z AUTO 18011KT 4SM BR OVC007 07/05 A3011 RMK AO2 SLP201
  T00670050

Translated to:

  Jan 16, 1553Z, Automated. Mist, Wind from 180° at 11 knots, 4 statute
  miles visibility, Ceiling is Overcast at 700 feet, Temperature 7°C,
  Dewpoint 5°C, Altimeter is 30.11. Remarks: automated station with
  precipitation discriminator sea level pressure 1020.1 hectopascals
  hourly temp 6.7°C dewpoint 5.0°C

Why would I want/need to know, or what would I do with, this information in the remarks section:

  sea level pressure 1020.1 hectopascals hourly temp 6.7°C dewpoint
  5.0°C

The sea level pressure allows pilots to calibrate their altimeters to make sure they are accurate. KGOK is 1069 feet elevation, if a pilot were to set their altimeter to 1020hpa (or 30.11 inches of mercury as used in the US, that's the A3011 in the METAR) then their altimeter would read 1069ft at ground level.


What is meant by "Outbound leg timing begins over/abeam the fix, whichever occurs later" in FAR/AIM 5-3-8? In FAR/AIM, 5-3-8. Holding part, There is a sentence that says

  (b) Outbound leg timing begins over/abeam
  the fix, whichever occurs later.

I got to know that the word 'over' is for parallel or teardrop entry. But I still can't understand the intention of 'whichever occurs later'.

Could anybody explain this more specifically?

The text is written that way to take into account the various type of holding entries. In case of a parallel or teardrop entry, the outbound leg starts after passing over the fix. In all other cases the outbound leg start after passing abeam the fix, following a turn that starts over the fix.

Case 1: Established in a holding pattern

So when established in a holding pattern, the outbound leg starts abeam the fix.

The sequence is:

inbound leg
pass over the fix
turn outbound
pass abeam the fix
outbound leg
turn inbound
repeat from 1.

In this case it is clear that the time of the outbound leg should start when you pass abeam the fix, which occurs later in the sequence.

Case 2: Entry into holding pattern

Case 2.1: Parallel Entry into holding pattern

When entering the holding using a parallel entry ((a) in the diagram) the sequence  is:

fly to the fix
pass over the fix
turn outbound course
outbound leg (on non-holding side)
turn to inbound leg
intercept inbound leg
follow sequence for established in a holding pattern

In this case the timing of the outbound leg should start when you pass over the fix. From this, it follows that the outbound time will include the time spent in the outbound turn (3.).

Case 2.2: Teardrop Entry into holding pattern

When entering the holding using a teardrop entry ((b) in the diagram) the sequence  is:

fly to the fix
pass over the fix
turn outbound course
outbound leg (30 degree into holding side)
turn to inbound leg
intercept inbound leg
follow sequence for established in a holding pattern

In this case the timing of the outbound leg should start when you pass over the fix. From this, it follows that the outbound time will include the time spent in the outbound turn (3.).

Case 2.3: Direct Entry into holding pattern from holding side

When entering the holding using a direct entry from the holding side ((c) in the diagram, sector on the holding side) the sequence  is:

fly to the fix
pass over the fix
turn outbound
pass abeam the fix
outbound leg
turn inbound
follow sequence for established in a holding pattern

In this case it is clear that the time of the outbound leg should start when you pass abeam the fix, which is later in the sequence.

Case 2.4: Direct Entry into holding pattern from non-holding side

When entering the holding using a direct entry from the non-holding side ((c) in the diagram, sector on the non-holding side), you may not complete the turn before being abeam the fix. In that case the sequence is:

fly to the fix
pass over the fix
turn outbound course
outbound leg
turn inbound
follow sequence for established in a holding pattern

In this case it is clear that the time of the outbound leg should start when you pass over the fix. From this, it follows that the outbound time will include the time spent in the outbound turn (3.).


Why are airplanes described as the safest method of transportation? I will have my first flight tomorrow. It is my first time that I get into an airplane, and by the time am  writing this post, I am feeling anxious and stressed a lot. I even don't talk to anyone as it is the last day of my life and need to live it alone. I read that this is called "fear of flight" or "phobia of airplanes".

I read online on all related sites, that the airplanes are the safest transportation mode. I could die with a car accident while I am getting to airport 20 times more than be killed in an airplane crash.

All sites said that I should understand more about airplanes, and that would release the tension and make me better.

I am thinking to cancel the flight and the 330$ will go through the wind as we say in my country, and not be refunded. I read a lot of things but all are technical, and I didn't understand any single word, especially that I am a person that don't have any mechanical or technical background to understand it.

My doctor told me to start taking "Xanax" and that would help me be fine on my less than 2 hours flight (most of it is over the sea that's why I am more anxious).

Why are airplanes the safest method of transportation? Why aren't ships the safest? Because in 3 years I didn't hear of an airplane that sank.

Good news

The good news is: you really are safe in an airliner, so safe that you could spend every minute of every day of the the rest of your life flying in one, and still not face any greater meaningful risk of a disaster.

It's difficult to answer your question why it's so safe (i.e. what makes it safe), but the record is there, plainly, that it is so safe.

Bad news

The bad news is: if one has an irrational fear of flying, then no objective facts or understanding will help lessen it.

If the fear is based on misunderstanding or lack of knowledge, then of course learning more will help overcome it. However, that's not the basis of a phobia, or the kind of fear you seem to be describing.

Advice to understand flight and aircraft is well-meaning, but not actually that useful. Someone can have an excellent understanding of aviation
engineering and aerodynamics and all manner of subjects, and know that it is exceptionally safe, and still suffer from crippling fear of actually flying.

Everyone is different, but such fear is often brought on by an event or change in life that has nothing whatsoever to do with flying, but somehow gets expressed in a fear of flying.

The comfort and support of another person on board could be the most valuable thing you seek before your flight. I'd suggest expressing your fear, without embarrassment or shame, to the staff at the gate. They and the crew on board will have helped people in such cases many times before, and they are good at it.

Simply getting used to an object of fear is one of the best ways of dealing with it.

I hope you make your flight, and I hope to hear that having done it once, the fear diminished by being stared down, and that subsequent flights render it lesser still. Please tell us about it here.


What are these openings on the TBD/TBM Avenger? I've been looking at some pictures and models of the TBF1 and TBM3 Avengers, a torpedo and dive bomber from WW2. I've noticed in some cases there are these openings/slots towards the leading edge of the wing on the top, and it seems as if they pass through to an opening to either the very leading edge of the wing, or just below it. The strange thing is that I've seen many pictures and have noticed that in most models these openings/slots are absent. I'm pretty sure they're more common on the TBM3 than the TBD1, if at all. I was wondering what function these have. I have seen one 3D computer model that shows it's just essentially a rectangularly shaped hole going through the entire wing, though I'm not sure if the modeler just guessed at this. Any ideas of what this might be? You might need to zoom in to see them better.

It's a leading edge slot used to improve low speed handling.

Excerpt from Wikipedia:

  Partial-span slots are usually found only on the outboard portion of
  the wing where they ensure airflow over that portion of the wing will
  remain unstalled at higher angles of attack than the inboard portions
  of the wing. This ensures the wing root stalls first and contributes
  to docile stall behaviour and maintaining aileron control throughout
  the stall.

You'll notice that the slot is directly in front of the ailerons. Since the TBMs landed on aircraft carriers very close to a stall, the slot ensured adequate roll control during approach and landing.


How does the efficiency of a turbofan compare between take off speeds and optimal conditions? I know turbofans are less efficient than propellers due to accelerating a smaller mass of air faster. So my question here is not comparing turbofans vs other engines, but compare how inefficient is a turbofan operating at take off and low speeds compared to that same turbofan in its optimal conditions?

In other words, how much is the efficiency loss? Are we talking about 5% or about 50%?

Also, why exactly that loss of efficiency happen (again, compared to the same engine at optimal cruise conditions)? Is it just the speed differential between the exhaust and aircraft airspeed, or is it something to do with the compressor/turbine efficiency?

To compare the efficiency we need to use the thrust specific fuel consumption (TSFC). It's the fuel per unit time per unit thrust.

(Georgia Institute of Technology)

The lower the y-axis value (TSFC/TSFC0), the more efficient the engine is. TSFC0 being TSFC at sea-level and standstill. Speed increases TSFC, whereas altitude (more precisely: decreasing ambient temperature) lowers it a bit.

Taking the extremes from the example above:

M0.4 at sea-level is a ratio of 1.45
M0.8 at 11 km (FL360) is a ratio of 1.675

On ground a turbofan engine is more efficient than in cruise when it comes to fuel consumption per thrust given.

But if you're comparing different airplanes, then the distance covered is also taken into account.

  Fuel consumption per [distance] can be a more appropriate comparison for aircraft that travel at very different speeds.

(Source)

For supersonic jet engines it's different as shown above.


Do controllers take wind into account when giving headings? When ATC gives you headings to fly, do they consider wind correction? In theory they should because they call it a heading and not a track, but do they? After all, the heading they want you to fly depends on wind direction and airspeed.

Or do they actually mean track instead of heading?

When the controller says heading, he means heading.
So if he wants you to go into a specific direction, he will take wind into account. The reason for issuing heading are:

Every aircraft can fly it, because a compass is fitted on every aircraft. Track keeping requires more sophisticated avionics.
If two aircraft fly adjacent to each other, the wind will offset them by the same amount and therefore separation is assured.

Quite often a controller will ask you to report your present heading prior to instructing a one so he can make more accurate adjustments to your course, especially if you were under own navigation before being vectored.

With Mode S radars and the right equipment in the aircraft, the current heading can be downloaded from the avionics without the pilot being aware of it.


What is the purpose of extending one degree of flaps (perhaps with spoilers)? What would be the use of one degree of flaps? And is there any reason to use both flaps and spoilers combined?

Normally, one degree of flaps in fact only translates to an extension of the leading edge devices (e.g. slats), trailing edge flaps remain fully retracted.

On some aircraft this configuration can be used for take-off.

Combination of flaps and spoiler is for example used in slow flight on steep descends. The flaps ensure that the wing doesn't stall, the spoilers dump part of the lift and act as airbrakes to keep the speed under control.


How do Throttle control and Propeller control work together? I haven't been able to understand.

If propeller control controls the pitch of the blades in a constant speed engine, what do the throttle control do?

I've seen (in some normal operation manuals for some planes) that you have a Torque limit and control the Torque with the throttle control, and the RPM with the Propeller Control, but, if the propeller is spinning always at the same speed and the blades are positioned at the same pitch how can the throttle reduce or increase thrust?

In a constant speed prop, the prop control lever basically changes the speed of the prop (it is not always running at the same speed as you indicate in your question, but rather once the speed is changed by the prop control lever, the governor keeps it at that speed). If power (or airspeed) is changed, the blade angle will automatically change in order to keep the prop turning at the same speed (within the limits that it is designed for).

Since adding power would normally increase the speed of the prop, the governor automatically changes the blade angle in order to keep it at the same speed.  The same is true when power is reduced or airspeed is changed.

Thrust is changed by engine power because, even though the prop is turning at the same speed, the angle of attack of the prop has been changed, which changes the amount of thrust.

For more general information about how a constant speed prop works, see this question and answers:
How does a Constant Speed Propeller Work?


What is the correct phraseology for "runway 03 R”? What phraseology is normally used for "runway 03 R" by air-traffic control and pilots?

A couple of possible options I came up with:

runway zero three R
runway three R
runway zero three right
runway three right

Is there any standard or preference of one form or the other to reduce confusion during communication?

Runway 03 R would be pronounced as

  Runway Zero Three Right

As ever, although British, I thoroughly recommend CAP 413 the UK's Radio Telephony manual:

https://publicapps.caa.co.uk/modalapplication.aspx?catid=1&pagetype=65&appid=11&mode=detail&id=6973

It's mostly ICAO compliant and barring small differences, should contain plenty of information for most operations. You'll see all runways are stated using two digits. Unfortunately I can't find an example of parallel runways in there.

One important note

  Runway Zero Three Right

Designates runway 03R, as opposed to runway 03L.

However,

  Runway Zero Three Righthand

Designates runway 03 and a right hand circuit. Very different things! In real life the chance of confusion is fairly slim, but it's worth noting.

  Is there any standard or preference of one form or the other to reduce confusion during communication?

Absolutely. Considerable effort has gone into the standardisation of air traffic communications in order to decrease the risk of misunderstanding. Page 6 onwards of CAP413 above goes into excruciating detail about how to utilise numbers, for example.


Runway Number Landing and Departure Left Traffic Question If I am "departing runway 36", what does that mean? I understand that runway 36 is at the north end of the runway (360 magnetic); So my question is does the aircraft start at the north end 36 and take off on the south end 18? Or am I starting at the 180 position and taking off at the 360 position/runway 36?

And when landing is it the same or opposite? "Final for runway 36", does that mean the plane is touching down on the 360 north end of the runway heading to stop on the 180/runway 18 side?

There is a misunderstanding here. It is incorrect to say

  runway 36 is north end of the runway

Runway 36 is the entire runway, with traffic moving to the north (i.e. facing about 360 degrees, magnetic).  Runway 18 is the same north/south strip of pavement, with traffic moving to the south (i.e. facing about 180 degrees).

If you're lined up ON runway 36, you're at the south end of it, facing north.  If you're on final for 36, you're south of the runway, pointing at it -- again, facing north.

If you are taxiing on the airport surface and need to cross that runway somewhere in the middle, it is correct to be cleared to "cross runway 36..." or to "cross runway 18..." or even to "cross runway 18/36...", typically followed by the taxiway you're to use: "... on taxiway Alpha."  If there is no direction associated with the use, people typically refer to "Runway 18/36" in order to be clear, although sometimes you'll hear only one designation used.  Either way works in that case.

The "Approach End of runway 36" is the end of the runway that you first cross on approach, so the south end.  The "Departure End of runway 36" is the end that you cross after having departed on that runway -- so the north end.  And, the "departure end of runway 36" is the same end of the same strip of pavement as the "approach end of runway 18".  Which description is used depends on context -- i.e. if runway 18 is active (i.e. aircraft are arriving from the north & departing to the south), then controllers are more likely to talk about the approach or departure end of runway 18, than to refer to things in terms of runway 36.


What's the difference between an airplane that stalls nose down or just mushes in a stall? What's the difference between an airplane that stalls nose down or just mushes in a stall?

I understand most GA planes go nose down after a stall, but some GA planes
don't drop their nose at all, they mush (they just drop in altitude).  How are these planes different?  Is their CM curve near horizontal, instead of negative, so that they fly almost neutral with little static margin? Or do they have a high horizontal tail volume and so with stick back, they just stay almost horizontal, or other?

You are absolutely right that it has to do with the pitching moment (Cm) characteristics of the aircraft. Take a look at the sketch below illustrating three different pitching moment characteristics:

In all the cases, you can assume that the CLmax occurs around 12deg AOA (not presented here). Cm1 is the aircraft that would present a distinct nose-down upon reaching CLmax. This is also known as a pitch bucket, because of its shape, and is good for stall identification and recovery as the aircraft tends to un-stall itself.

Cm2 is the mushy case. With increasing aft column pressure, the AOA will continue to increase, while the airspeed may stagnate. No stall identification is naturally provided to the pilot.

Cm3 is anything from stick lightening to outright pitch up, depending on the aggressiveness of the instability. This is a common characteristic for high speed aircraft that have large LE sweep and the stall does not originate from the root of the wing.

As mentioned by Carlo, the degree of nose-down or nose-up would also be CG dependent. Aft CG would always have smaller pitch bucket and worse pitch up (if exist).


What noises can you hear as a passenger? I'm just curious as to what the noises are that you can hear as a passenger in the cabin of an airliner?

For example (ignore the crew talking), the noise at 7:09 - 7:30 on this video; is that the flaps?

What other sounds might a passenger be able to spot?

There are loads of noises you might hear; there are fuel pumps, hydraulic pumps, air circulation, adjustment screws, servos, and on Airbus aircraft a strange clanking noise when you go over bumps in the tarmac.

On the ground you may hear (and feel) cargo pallets rolling on the hold, and the hold doors being opened and shut. In-flight you have engine noises and air flow noises.


Difference between general visual inspection and pre-flight check inspection I know the definition of general visual inspection (GVI) but I cannot understand the differences (if there are) with a pre-flight check inspection.

I am new in the field and I am not a pilot (don't worry...) but I would be glad if anyone could clarify this for me.
Thanks.

A GVI is a maintenance procedure that has to be performed by a mechanic qualified to do so, to satisfy a Maintenance Program requirement, and which will require a maintenance release to be signed off.

A pre-flight inspection is an inspection performed by a pilot in command (or someone delegated by the PIC - like a First Officer, or a mechanic) to satisfy the PIC that the aircraft is safe for flight.

The pre-flight, being a look-over to make sure nothing has fallen off, is dribbling fluid, or is flat, is going to be more superficial than a GVI and usually doesn't involve getting your hands dirty (at airlines it's usually done by the First Officer while in uniform) and normally doesn't involve opening access panels or doors (but could).  Also the pre-flight is a whole-aircraft once-over while a GVI is usually system or zone specific in keeping with its Maintenance Program objectives.


Is there any equation to bind velocity, thrust and power? I am designing a remote controlled airship. I will tune it so that the lift given by Archimedes' Principle will exactly balance the weight of all the structure. It will be propelled by brushless motors with propellers on them.

As far as I have understood, for some given velocity $v$ the drag force $D$ will be given by the air pressure, some shape dependent drag coefficient $C_D$, the surface $S$ that the airship offers to the wind, and finally the squared velocity $v^2$.

Now, to keep some speed, obviously the thrust $T$ must equal the drag $D$. Now, I need to get to some equation for the power that I need to offer such thrust at such speed, given that I am using non-ideal engines, with non-ideal propellers etc. From a barely theoretical point of view, I know that if I want to apply some force to an object that moves at some speed, I will be using some power $P \sim Fv$. Now, since the thrust is generated in some way that actually looks very dispersive, I would like to know if there exists some relationship between the power $P$, the velocity $v$ and the thrust $T$, given some specific motor and some specific propeller. In particular, what are the parameters that one needs to know to get to this relation?

On example, I can imagine that some efficiency parameter for the engine, its RPM rate, its voltage, the diameter of the propeller, the pitch of the propeller, these are all going to be relevant to the equation I am looking for, but I wouldn't know how to explicitly figure out that.

It such a relation doesn't exist in an obvious or general way, could you just give me an idea of the efficiency of the propulsion? I mean, I know that $P \geq Tv$, but how much bigger is it in general? Do these quantities share the same order of magnitude, or the dispersion is very big compared to the actual propulsion?

As you can understand, I am not an expert at all on the subject, so I would appreciate anything that could get me started.

Thank you again!

A propeller accelerates the air of density $\rho$ which is flowing through the propeller disc of diameter $d_P$. This can be idealized as a stream tube going through the propeller disc:

The air speed ahead is $v_0 = v_{\infty}$ and the air speed aft of the propeller is $v_1 = v_0 + \Delta v$. The propeller effects a pressure change which sucks in the air ahead of it and pushes it out. Since the mass flow must be equal ahead and behind the propeller, the stream tube diameter is bigger ahead of the propeller and smaller downstream. In reality, there is no neat boundary between the air flowing through the propeller and that surrounding it, but for computing thrust this simplification works well if the airspeed is identical across the cross section of the propeller disc.
The mass flow (mass $m$ per unit of time $t$, written as a derivation) is: $$\frac{dm}{dt} = \pi \cdot\frac{d_P^2}{4}\cdot \rho \cdot \left( v_{\infty} + \frac{\Delta v}{2} \right)$$
The mass flow is written as the volume of air with density $\rho$ per time, moving through the propeller disk with the diameter $d_P$ at a speed that is the median between entry and exit speed. The thrust is mass flow times speed change: $$T = \pi \cdot\frac{d_P^2}{4}\cdot \rho \cdot \left( v_{\infty} + \frac{\Delta v}{2} \right) \cdot \Delta v$$
If the engine has the power P, the thrust is net power divided by airspeed in the propeller disk. To arrive at the net power, you multiply the rated engine power by the propeller efficiency $\eta_{Prop}$ and the electric efficiency $\eta_{el}$: $$T = \frac{P\cdot\eta_{Prop}\cdot\eta_{el}}{\left( v_{\infty} + \frac{\Delta v}{2} \right)}$$
A good engine will have an electric efficiency above 90%, and a good propeller will give you an efficiency between 80% and 85%. Efficiency goes up with lower $\Delta v$, so a big, slowly spinning prop is better than a small, fast one.
An airship will not move fast, so the $v_{\infty}$ is low. In the static thrust case it is zero, and the thrust equation can be simplified:
$$T_0 = \frac{P\cdot\eta_{Prop}\cdot\eta_{el}}{\sqrt{\frac{2\cdot T_0}{\pi\cdot d_P^2\cdot\rho}}} = \sqrt[\LARGE{3\:}]{P^2\cdot\eta_{Prop}^2\cdot\eta_{el}^2\cdot\pi\cdot \frac{d_P^2}{2}\cdot\rho}$$
To actually know your $v_{\infty}$, you need to know the drag $D$ of your airship. The general equation is $$D = A\cdot c_D\cdot\frac{\rho}{2}\cdot v^2$$ with $A$ the frontal area of the ship and $c_D$ its drag coefficient. S. Hörner (page 14-1) gives the drag coefficient of LZ126 (later Los Angeles) as $c_D = 0.023$ for the hull alone and $c_D = 0.071$ for the complete ship, including nacelles, fins and all.
A similar result is given in NACA Report 394 which documents the tests done on models of Goodyear Zeppelins in the NACA variable density wind tunnel in 1932. There is another source, NACA Report 117 by Max Munk, written in 1921 and supposedly collecting the results of German measurements on Zeppelins which can be found here.
Your model will not achieve such low values, however, because it will fly at a lower Reynolds number, which means that friction will be higher in relation to other forces. Depending on the size and speed of your model, pick a value between 0.15 and 0.3 for first calculations.


Why are there no RNAV (ILS) approaches? While studying the PBN (FAA Order 8260.58A) and TERPS (FAA order 8260.3D) documents, I still have some trouble figuring part of the logic behind the naming and definitions of the published IAP Charts. Specifically, I still have not figured out which Lateral Navigation System is combined with which Landing System (if this is how it's done in practice). Take the following examples:

Technically, ILS is a landing system, to the best of my understanding, at least. I expect that it can be combined with any Lateral Navigation System used in-flight, as long as the necessary equipment is available. Therefore, I would expect to find charts using RNAV with ILS. This would mean, to me, that, "RNAV-equipped" flights can still use an ILS Landing System. Is this combination possible?
According to Chapter 3 of the PBN manual, the RNAV(GPS) procedures can also be combined with a GLS Landing System. However, I have not found any published IAP chart mentioning the GLS minima. To my understanding the RNAV(GPS) procedures with GLS Landing System are published separately under the name "GLS". Is this correct?

My confusion can be described, in short, as follows: because I have seen RNAV (GPS) procedures being combined with LPV or LNAV/VNAV, which are Landing Systems, and ILS is also a landing system, I thought that the general idea is that Lateral Navigation Systems are combined with Landing Systems when designing IAP procedures. Is this correct? If yes, where can I find the possible combinations. If no, then what is the logic behind this, what am I missing?

You are confusing some terminology.
RNAV (GPS) approaches can have several different sets of minima.

See the example RNAV (GPS) Y 28L at O'Hare:

It has:
LPV
LNAV/VNAV
LNAV
sets of minima.

LPV is an instrument approach procedure (IAP) with localizer-type precision and with vertical guidance, (hence the name LPV), provides a pilot with a "ILS-style" approach complete with a decision altitude (DA) but using GNSS equipment instead of VHF equipment like that used for an ILS.  Usually the lowest weather minimum of the 3.

LNAV/VNAV is another line of minima with baro-aided (altimeter-based) vertical guidance including a DA but the weather minimum is usually a bit higher than LPV.

LNAV-only is the least precise of the 3 and is a non-precision approach, no vertical guidance, includes a minimum descent altitude (MDA) instead of a DA.  This is a "dive & drive" approach similar to Localizer or VOR approaches.  Normally has the highest weather minimum due to the nature of non-precision approaches.

There are RNAV (GPS) approaches and there are ILS approaches, but there are no RNAV ILS approaches.

Note: There might be a rare exception to this as described in appendix C of FAA Order 8260.58A CHG 2: If the aircraft/aircrew/airline are performance-based-nav (PBN) capable & authorized there could be an IAP constructed with a radius-to-fix intermediate segment leading to an ILS final segment, whereby, the crew would navigate with GNSS equipment on the RF segment and then transition to ILS equipment for the final segment.  I would say in my experience this type of approach construction from the US TERPS is very rare.

I will add that WAAS is to LPV as GBAS is to GLS.  GLS is only available at 2 airports in the US, while RNAV approaches with LPV minimums are available at a great many US airports, adding a "ILS-like" utility to those airports without incurring the infrastructure cost of adding the ground equipment necessary for ILS approaches.

WAAS capable GPS receivers are prevalent; while very few aircraft (the Airbus A350 is one example) have GBAS capable GPS equipment.


Can passenger plane do an aileron roll and fly upside down? I've researched this topic and as far as I can tell any plane can fly upside down if it's already in this position. It just needs to be angled enough so that its wings are angled upwards. I believe Boeing 777 can do this although I can't find any video proof.

But my real question is whether Boeing 777 can do aileron roll. From my understanding plane needs to pitch upwards a bit to gain altitude and then start to roll sideways. While doing this it will loose all lift and starts falling downwards until it is upside down and gains lift again. What are the requirements for this? What is the minimum speed it needs to achieve before attempting the roll? Is Boeing 777 structurally sound to survive the attempt? I imagine it was not designed for this but is it possible?

And a bonus question: can you link me a video of any bigger sized plane doing that?

In fact this has been done before.  A well documented case is of "Tex" Johnston rolling a 707.  In general airliners cannot do sustained inverted flight as they lack a fuel system (and lubrication system) for sustained inverted flight.

A barrel roll is readily executable. Youtube has a video of Tex Johnston doing a barrel roll.

Edit: I gave a quick answer and felt guilty about it. There is more to the story. The OP talks about aileron rolls. An aileron roll is a maneuver where the plane does not substantially change altitude. The G forces will be negative at some point, and it is more "violent" than a barrel roll.  A barrel roll is a maneuver where the plane is rolled about the longitudinal and lateral axis, if you will, a loop and a roll in one.  Properly executed the barrel roll is a positive G maneuver.

Years ago, when I was young and some old geezer was teaching me aerobatics, he would climb into the plane with a full cup of coffee.  My job was to get to the practice area, and execute some maneuvers, including barrel rolls in each direction, without spilling his coffee.


Is Iqaluit Airport closed? After seeing this question (and its answers):

Why did the Swiss International Air LX40 (a 777-300ER) emergency land at Iqaluit airport?

my interest in Iqaluit (and its airport) was piqued.  But, the satellite/aerial view in Google Maps shows the single runway at YFB (ICAO: CYFB) closed (big "X"s painted on the runway).  Refer to below screenshot (Google maps satellite view):

Best I can tell, this satellite imagery was taken recently ("Copyright © 2017...")

Is Iqaluit Airport closed?

At the time of the imagery, it appears the airport was undergoing major renovation, now completed at least insofar as the runway is concerned. See iqaluit-airport-s-runway-gets-a-facelift-as-construction-completed. During the reconstruction they kept a minimal portion of the runway open for operations, enough to bring 757s in but not enough to get 767s in.

If you look at the image, note all the construction activity and also the parked aircraft. Note that the Xs are on the right side of rwy 34, and leaving the left half of the runway open. Farther down the rwy the Xs are in the middle, so I believe the image was taken while they were reconstructing the rwy while leaving enough of it usable for operations.


Is the word “bomb” muted in inflight movies? I was recently on a transatlantic flight and watched the movie Steve Jobs on the plane’s entertainment system. Every movie I tried, including that one, had a message right at the start saying the movie had been edited for content.

In one scene, the caracter of Steve Wozniak is fiddling with a watch and the character of Steve Jobs makes a joke it looks like he’s messing with a bomb. Those words were muted. The word “bomb” (and one or two words around it) were gone from the movie. I even rewinded to make sure, and the words were indeed gone.

Is there some weird law that forbids the use of the word in inflight entertainment systems? It there is, it’d be particularly weird since you need to plug headphones to listen to the movie in the first place, so it’s unlikely you’d cause hysteria. In addition, the word was pronounced again later on in the movie but wasn’t muted then. It was less clear audibly, though, so it’s feasible it wouldn’t have been caught by the automated system (if any is used).

The airline was TAP, and the entertainment systems are individual per seat.

This might be dependent on the airline?

I usually fly Emirates and the movies are not muted for the word "bomb". Maybe because each seat has its own entertainment console?

In the old days when there was one giant projector that displayed movies (which was later replaced by TVs that articulated from the ceiling) - I suppose in these scenarios it might be prudent to mute words or scenes.


Is there a list of part 121 and/or 135 operators? While looking into this question, I found a list of certificated air carriers on the US Department of Transportation website (there's a list of commuter air carriers too). But, the list doesn't say if each one operates under part 121 or part 135, which the DoT seems to consider an FAA question anyway:

  As noted above, the economic authority issued to air carriers by the
  Department is separate from the safety authority (commonly referred to
  as Part 135 or Part 121 Operations Specifications) granted to them by
  the Federal Aviation Administration (FAA).  For safety authority
  application procedures and related questions, air carriers should
  contact the appropriate FAA flight standard district office based upon
  the geographical location of the air carrier

The FAA site has a lot of information about part 121 operations, but at least as far as I could see there's no list of 121 or 135 carriers anywhere on their site.

Is there a list somewhere of current part 121 and/or 135 operators?

I have not found a list, but you can search for an airline here.

There is a link on the page to definitions of the terms. Basically, "domestic" and "flag" are FAR 121 operations, and "commuter" is FAR 135 operations.

There is also an unofficial database here that will tell you which FAR an airline operates under.


What are the benefits of a non-orthogonal (scissor) tail-rotor? Why is the tail-rotor of some helicopters (e.g., Boeing AH-64 Apache) made of non-orthogonal (scissor) blades?

What are the aerodynamic benefits (or any other benefits) compared to the orthogonal cruciform option?

(Source)

(Source)
The comments and answers already say it's for noise reduction. What's more intriguing is the how:
The blades are not coplanar (image).
The tail-rotor of the Apache rotates clockwise (video) when viewed from the port side. The nearest blades (nearest plane) to the viewer are the leading blades of each group. A group is two close blades regardless of plane, e.g., 1 and 2 as labelled above are a group, 1 is leading.
The thrust of the tail-rotor is being directed away from the viewer (port to starboard), which means the viewer is looking at the pressure side of the rotor.
Below on the left is what it looks like from behind the Apache. This arrangement allows the trailing blades (2 and 4) to miss the wake from the ones ahead of- (and closest to-) them.
(Own work) Left: Apache; Right: coplanar normal spacing. View is from behind and thrust is left to right.
This L scissor configuration, as it is known, where the lower blade is leading yields more thrust due to the better interaction.

Based on extrapolation of the test results and calculations, the increase in thrust over a conventional four-bladed rotor of the same dimensions is about 10%. Rozhdestvensky attributes Bell's failure to come to similar conclusions to their use of a very small model.

And quieter, too
Noise measurements during flyovers were made with a Havoc having the four-bladed scissors tail rotor and the three-bladed tail rotor from the Hind. The two rotors made about the same noise at low speed but at high speed the scissors rotor was quieter. The primary reduction was in the "broad-band" frequency range from 600 Hz to 2000 Hz. Much of the noise at these frequencies is due to the effects of the tail rotor working in the confused wake of the main rotor. The scissors rotor apparently acts more like a two-bladed rotor in this situation.
(Helicopter Aerodynamics Volume II, p. 72.)


Has there ever been an commercial airplane with rear-facing seats? Has there ever been a commercial airliner that the seats have been facing rearwards? It sounds like rear-facing seats would be significantly safer. In addition, the procedure for rear-facing bracing (https://en.wikipedia.org/wiki/Brace_position), seems significantly simpler and more obvious than traditional methods.

Some airlines do offer rear facing seats in business/first class. However, this is more to save space than for increasing safety. For example, British Airways offers a mix of forward and backward facing seats in its business class.

Source: Forbes.com

BAC Hawker Siddeley Trident offered rear-facing seats while it was in service. (Note the visible cockpit).

Source: airliners.net

Armed forces of a number of countries use rear facing seats, like the RAF and USN in their C-2 Greyhounds.

"C-2A interior DN-SD-03-16988" by Camera Operator: PH1(AW) Shawn P. Eklund, USN - US Defense Visual Information Center photo DN-SD-03-16988. Licensed under Public Domain via Commons.


How much can 3 fans 7 inches in diameter and each a generating 160 cubic feet per minute airflow rate lift? I'm working on a hoverboard project and am having trouble finding out the maximum weight these fans could lift.

You have volumetric flow rate and diameter, so you have the $\Delta v$ ($v = A \dot V$) and you have the mass flow rate ($\dot m = \varrho \dot V$) and that gives you the momentum per unit of time a.k.a. force ($\dot p = \Delta v\cdot\dot m = F$).

Run the numbers yourself, but don't get high hopes—the result is tiny (of course; you need a couple of metres diameter to lift a human with useful efficiency).


What does this statement about steep descent mean? Source: Wolfgang Langewiesche - Stick and Rudder; An Explanation of the Art of Flying

In the first chapter the author mentions, in a glide, if you want to descend more steeply, you want to want to point your nose less steeply.
And if you want descend less steeply you point your nose more steeply.

What is the reason for this?

The statement is only true if you fly at a speed below the best glide speed. For simplicity, let's look at a glider: Below you see the plot of the L/D ratio over speed of the DG-1000 two-seater glider:

Glide ratio over speed diagram for three different wing loadings (source). If we just look at the lowest wing loading (leftmost curve), the best L/D can be achieved when flying at 95 km/h. Minimum speed is around 62 km/h, so it is entirely possible to fly along at 80 km/h. When the pilot reduces the angle of attack, the aircraft will pitch down and speed up. If it now flies at 90 km/h, he has just improved his L/D from 43 to 46, so he will descend less steeply when dropping the nose.

Note that our flight path angle is now less steep, and the change in attitude is less than the commanded change in angle of attack. Nevertheless, the pitch attitude is reduced and the pilot has the impression that he dropped the nose.

The same is true in reverse when slowing down. When approaching the stall speed, large angle of attack changes will result in relatively small speed changes, so the effect of a steeper descent when pitching up becomes more pronounced as the airplane slows down.

The underlying reason is the fact that drag will increase when the pilot moves away from the best L/D speed. Slowing down will increase drag, and more drag will result in a steeper descent. As soon as he shifts his starting point to higher speeds, things reverse and the aircraft will descend more steeply when the nose is lowered.

Adding an engine will not fundamentally change this behavior. It is only easier to explain when using gliders.