What operational differences were there in WWII for constant speed vs. fixed pitch propeller warbirds? I have read about the operational differences between constant speed and fixed pitch propellers.

Being a World War II buff, I was reminded of reading once about both principles being used in period fighter planes, with the Germans preferring one and the British preferring the other, but that's about all that I can recall. (That might have been a solid 20 years since...)

So, my question is:

How would the above-mentioned "operational differences" apply to WWII-period warbirds specifically, and does anyone have links or pointers to relevant reading material?

I think a period warbird has a quite different set of requirements on its performance and handling characteristics, which is why I think this separate question is warranted.

I'm not so much interested in the fine technical details (I don't want to build / maintain / model one of those planes based on this information), but rather striving for a better understanding of the relative performance characteristics of those (IMHO) most beautiful planes of all time.

When war broke out, almost all high-performance military planes on all sides had variable-pitch propellers. Not necessarily constant-speed types, but adjustable nontheless. There was no difference between German and British planes.

If there was a difference it was the use of manually-adjustable propeller pitch, which was widely used in German airplanes, versus constant-speed propellers, which found more use in British airplanes. However, both sides had both types of propellers in their fleet, so it is hard to make a generalization.

Operationally, the manual adjustment gives the pilot more control, but increases workload because the pitch has to be adjusted when flight speed changes. This was less burdensome in bombers, but in fighter aircraft a manual adjustment would keep the pilot busy during dogfights.

Early types of the aircraft involved did indeed use fixed-pitch propellers, like early versions of the Me-109 A and B or the Hawker Hurricane Mk.I. By 1939, both types had long since converted to variable-pitch propellers.

Older airplanes with fixed-pitch propellers were still used for training or liaison, but not near the front lines. Exceptions are aircraft like the Polikarpov Po-2 which was used for night attacks until the Korean war. It had such a limited speed range that a variable-pitch propeller would not had made sense.


Are there cases of aircraft moved off runway by pushing them with vehicles? And now something completely different for Summer holidays. Arthur Hailey was a RAF pilot who wrote Airport, a novel which later was adapted as a movie by George Seaton. The action is said taking place at Chicago Lincoln International, a fictitious place comparable to O'Hare, while Illinois is under a severe snow storm.

The suspense revolves around a Boeing 707 stuck at an exit, blocking a long runway. Another 707 needs the runway for an emergency landing.

Source: YT

Bakersfeld, the airport manager, wants to push the stuck plane off the runway with snowplows. Joe Patroni, chief mechanics for TWA wants to save the airplane by moving it by its own power.

Clocks are ticking... airports are closing... fuel is starving... Patroni's cigar has gone out.
Bakersfeld releases the snowplows!

What is today's way to:

Prevent a commercial aircraft to be stuck near the runway.
To quickly remove an airplane from the runway should that be necessary.

Is there actual cases of aircraft removed à la Bakersfeld?

Pushback trucks are called that for a reason, they push aircraft :)

They could be used to push or pull a stuck airliner like you mention, IF the muck isn't so bad they themselves get stuck trying that is. Most AFAIK aren't exactly designed for off road operations.


Which aerobatic manuvers should I restrict myself to if I wear glasses? Are there aerobatic maneuvers which I should never attempt if I wear glasses? Or, is there a specific G-loading which is not recommended for pilots who wear glasses?

I'm not into competitive aerobatics. I will not pull 6~7Gs or perform violent maneuvers like snap turns. However I do like to flip the world around just for the fun of it.

If you're talking about what they call Gentleman's aerobatics - that is only controlled positive G maneuvers like aileron rolls, barrel rolls, Immelmanns, inside loops, split-S, Cuban Eights, etc. there shouldn't be a problem here as the loading will hold your glasses on your face.  For additional support you might consider a blackstrap for your eyewear, similar to what basketball players wear.

More extreme aerobatics involving negative G flight, tumbling, gyroscopic maneuvers, etc would not be recommended using free fitting corrective eyewear as they will probably come lose and can become a FOD hazard in the cockpit, in addition to losing your myopia correction.  Goggles with corrective lenses would be recommended here as well as contact lenses.


Why does a jet's combustion energy propel the engine forwards rather than acting equally in all directions to create zero thrust? I'm a novice.  I have high school physics and I've seen many explanations of how a jet engine works.   To paraphrase: Fans compress air into a chamber where combustion energy is created, which spews out the back of the engine, propels the plane forwards in a typical Newtonian action/reaction way, and also spins more fans that in turn spin the previously mentioned compressor fans.    I know that's not a precise explanation but it just serves to introduce my question.
Why does the combustion chamber not act more like, say, a hand grenade?  That is, why doesn't the energy act equally in all directions?  What makes it directional?   I have never understood this from the dozens of school-level explanations I've seen on the topic.   Why does the energy from combustion cause the "low pressure turbines" at the rear of the engine to drive the compressor blades and not the other way around?  Or the most likely scenario in my flawed understanding, why doesn't the energy act equally on all the fans in the front and back of the engine to create no net propulsion?

The layperson answer is:
You are making air expand in a contained space but giving it an escape path in a particular direction that is easier to take than making the container blow up.  When I was a kid and it was possible for kids to buy firecrackers from the corner store, I used to like to make rockets out of them to propel balsa gliders.  You rolled the end of the firecracker between your fingers to make the packing fall out so it was open at one end, and taped it to your glider.  When the fuse burned down and the gun powder lit off (just after you threw the glider), the expanding gases went out the open end, making a nice rocket that ran about a second.  Close off the open end, like a normal firecracker, so the gases have nowhere to go, and it blew up (which would occasionally destroy my gliders when I didn't roll out enough of the packing - good thing they only cost a dime in 1967).
So air is being made to expand and you give it somewhere to go.  Since the front end is open as well, why it doesn't go back out the front is simply because the engine is packing in air from that direction faster and harder than the burning air can push back, relative to its fairly easy path out the tail pipe, so it takes the "easy way out" (jet engines can back flow if things go off kilter - you will sometimes see flames coming out the front during "stall/surge" events).
In taking the easy way out, it's still has to accelerate to high velocity to make it through an opening that is constricted, and there's your Newtonian thrust reaction.
The last part is, you put a windmill, a turbine, in the high velocity flow and use the windmill to drive a compressor to keep the air being packed in at the front.  You are extracting some of the energy in the flow going out the turbine section to power air-packing equipment at the other end, to keep the cycle going by itself without any external help.  Basically you are redirecting a part of the energy of the burning fuel air mixture to keep the cycle going instead of making thrust.
In a piston engine, you have a similar energy transfer effect, in a radically different format, to self-sustain the cycle. Air burns in a cylinder's combustion chamber and forces the piston down to drive a propeller, but some of that rotation energy is being used to drive the adjacent piston on its compression stroke, redirecting a part of the energy of the burning fuel air mixture to keep the cycle going instead of making torque at the prop.
The jet engine does the same thing in a linear fashion using aerodynamic forces instead of closed spaces inside cylinders, depending on the inertia and velocity of the flow (like a hallway packed with people running in one direction - forget about trying to run the other way) to channel all of the forces where they need to go to keep the cycle going.


How should I handle a change of address for a Student Pilot License in the USA? I have moved to another place from current address with in same city, Do I have to change my address to the new one on my FAA Student Pilot License? If yes, how do I do it?

You can change your address with the FAA online.  You do not need to get a new plastic certificate.

http://www.faa.gov/licenses_certificates/airmen_certification/airmen_services/


What is the purpose of aluminium foil on the wheels? I saw this plane on a remote ramp at BKK today.  What is the purpose of aluminium foil on the wheels?  Does it mean the plane is in mothball?  I don't see other planes, even in maintenance, with aluminium foil on the tires.

In respect of the photo's license, I am the owner of the picture and authorize anyone to use my photo for any purpose except illegal activity.

They are reflective covers to protect the tires from the elements, especially UV. Similar to the shades visible in the windscreen. Goodyear says:

  Aircraft tires, like other rubber products, are affected to some degree by sunlight and extremes of weather.
  While weather-checking does not impair performance, it can be reduced by protective covers. These covers
  (ideally with light color or aluminized surface to reflect sunlight) should be placed over tires when an
  aircraft is tied down outside.

It also protects the tires from other substances like oil and hydraulic fluid.

The plane is not necessarily mothballed. I would expect it to be parked much more out of the way in that case. But the wheel and window covers do suggest that they expect it to be parked there for some time.

Information is a bit sparse, but it appears that Happy Air only has that one Saab 340 now, but since September all flights are operated by Nok Air, who operates Dash 8 Q400, ATR 72-500, and 737-800 aircraft.


Is airframe heating a concern at subsonic speeds? It is a well-established fact that airframe and skin heating due to air friction is a significant concern with supersonic aircraft.

However, below Mach 1 (i.e. typical commercial aircraft flights at normal cruising altitudes), is there any sort of measurable heating to the airframe/skin that can be observed or needs to be dealt with in some manner?

Yes, aerodynamic heating is observed even at speeds that are well below Mach 1.

The practical application of this heating is the difference between Total Air Temperature, TAT, and Static Air Temperature, or SAT.  In essence, SAT is the actual temperature of the air, while TAT is the temperature that the moving aircraft "feels" due to aerodynamic heating.  When climbing and descending at low and medium altitudes, ice can accumulate on an aircraft when the TAT gets close to or below freezing. A common rule is to turn engine anti-ice protection on when in visible moisture (rain, snow, cloud, etc) once the TAT is below +10 degrees Celsius, since some cooling may occur in the inlet and you want to have a margin of error.

It is common to be descending at, say, 300 knots, in IMC (i.e. in clouds) and observe a TAT above +10, then when slowing down to be below 250 KIAS below 10,000', the temperature drops several degrees so that anti-ice is now required -- the difference being the additional heating that is lost as the aircraft slows down from 300 knots to 250 knots.

At high altitudes, roughly 30,000' or slightly above, where the TAT is always well below zero (although still above the SAT), a different limit is noted: below -40 degrees Celsius, the air itself is too cold to have enough moisture to cause icing, so in climb & cruise below -40, the anti-ice can be turned off.  (In descent in IMC, the anti-ice is turned on regardless of the SAT, because descending into air that CAN support icing without your ice protection turned on could make your day far too exciting -- in a bad way!)

Also, at very high altitudes on a cold day, it's possible to have temperatures that are low enough that the freezing point of your jet fuel can be a concern.  Again, this is a matter of TAT, because that's what the structure of the aircraft feels.  One solution if the fuel tank temperature begins to approach the freezing point it to increase speed, which will raise the TAT somewhat.  If that's not enough, then descending to warmer air is about all that's left.

Bottom line, at sub-sonic conventional jet aircraft speeds, aerodynamic heating is very much a factor.


How can I get the velocity-power curve for a particular aircraft? The answer for How does wind affect the airspeed that I should fly for maximum range in an airplane? refers to a velocity/power-required curve.

As far as I can tell, this curve can't be deduced from information in the flight manual.

I suppose one could experiment and determine what power setting is required in order to maintain level flight at a bunch of airspeeds (or for a glider, record the sink rate, which is proportional to the negative of the power-required, at a bunch of airspeeds). Would that be accurate enough? Are these curves available from the manufacturer?

You are right, this curve has to be tested. Of course, during development a lot of simulation and wind tunnel testing is done to get the power required, but it still needs to be confirmed in flight test. The interaction of power plant and airframe can be quite complex, and only testing will ensure that the data is correct.

If it is not part of the manual, the plane's manufacturer will certainly have the power curves. Did you ask them for the data? And I would expect that you will find some data points in any handbook which will allow you to approximate the power curve. Start from the trim condition (basically, thrust equals drag) and calculate the curve with the help of a parabolic polar. Like that:

$$T = c_D\cdot q\cdot S$$

$$P = T\cdot v = (c_{D0} + \frac{c_L^2}{\pi\cdot AR\cdot\epsilon})\cdot v^3\cdot\frac{\rho}{2}\cdot S$$

Of course, now you need to get the zero-lift drag coefficient $c_{D0}$ somehow from one datapoint in the manual. Same goes for values like propeller efficiency or intake losses, because the listed power of the engine will not be what is effectively employed to generate thrust.

Nomenclature:
    $T$  thrust
    $v$  airspeed
    $q$  dynamic pressure
    $\rho$  air density
    $S$  wing area
    $c_L$  lift coefficient
    $AR$  aspect ratio of the wing
    $\epsilon$  the wing's Oswald factor


What is the effect of non-LASER light sources on pilots? After all the media coverage about people pointing lasers at commercial aircraft, I started to wonder what was so special about lasers.

It seems to me that the amount of distraction that could be done with a 5mW laser is significantly less than what could be done with something else.

For example, if I bought/borrowed the light beam from the Luxor hotel, put it in my backyard, turned it on, and pointed it at the planes flying out of a major airport, I would expect that pilots might have some more issues with a 4.3 Billion candela beam than with a 5mW laser (right?)

However, I can't find any laws against it, so would this technically be legal?

Alternatively, what if I just wanted to swing that beam around in the sky, and it accidentally crossed the path of a plane?  Are there different laws regarding unintentionally hitting a plane with something like this?

The short answer is "If you intentionally pointed the Luxor beam at an aircraft (flying low enough for it to constitute a hazard) you would probably be arrested".  The real question is What would they charge you with?, and the FAA regulations aren't where you want to look for that: You need to look in the "United States Code".

18 U.S.C. 39A makes it an offense to aim a laser pointer at an aircraft. It goes on to define "laser pointer" as:

  any device designed or used to amplify electromagnetic radiation by stimulated emission that emits a beam designed to be used by the operator as a pointer or highlighter to indicate, mark, or identify a specific position, place, item, or object.

The Luxor beam certainly isn't that, so you're safe there.

Instead you will probably be charged under a creative application of 18 U.S.C. 32(a)(5), which says

  Whoever willfully … interferes with or disables, with intent to endanger the safety of any person or with a reckless disregard for the safety of human life, anyone engaged in the authorized operation of such aircraft or any air navigation facility aiding in the navigation of any such aircraft … shall be fined under this title or imprisoned not more than twenty years or both.

While this law was originally conceived to deal with in-person threats (kicking down the cockpit door and clobbering the captain with a frying pan) it would not take a very creative US Attorney to make the argument that shining a 40 billion candela light at an aircraft's cockpit would "interfere with or disable" the flight crew, and shows a "reckless disregard for the safety of human life".
Similarly it would not take much creativity to argue that swinging such a beam around in the sky in an area where it may interfere with aircraft operations would also show a "reckless disregard for the safety of human life", unless you took the time to file an appropriate hazard NOTAM.

Note that in my initial statement I said that you would be charged if the aircraft were flying "low enough for it to constitute a hazard" -- as has been pointed out non-coherent light source intensity falls off according to the inverse square law, and with sufficient altitude the Luxor beam is just a bright spot on the ground and doesn't have anywhere near the effects of laser illumination.

The Luxor's beam was in fact part of a study on the effect of lasers and high intensity lights in relation to air traffic safety. That section of this report (and indeed the entire thing) makes for interesting reading.


When can I descent below the MDA if the approach light system does not have red terminating bars? Specifically, I'm a little confused about Sec 91.175(c)(3)(i) which states:

  The approach light system, except that the pilot may not descend below
  100 feet above the touchdown zone elevation using the approach lights
  as a reference unless the red terminating bars or the red side row
  bars are also distinctly visible and identifiable.

From what I understand, I'm allowed to descend up to 100ft above the touch down zone elevation (TDZE) if I'm able to see and identify the red terminating bars on the approach light systems (ALS).

However, what happens when the ALS does not have the red terminating bars (for e.g. MALSR and MALSF)? Do I maintain my MDA even if I have part of the ALS in sight?

You can descend down to 100ft above TDZE if you have any ALS in sight. You need an ALS with red lights (ALSF I & II) to go below that.

Red terminating bars/red side row bars help you find the threshold. Think of an ALS with red lights as being in the same category as Runway/lights/markings, Threashold/lights/markings, Touchdown Zone/lights/markings, VASI/PAPI, and REIL. Any other type of ALS (MALSR, MALSF, etc.) has the 100ft above TDZE restriction put on it when it is the only thing you can see.

@mins linked to a couple of helpful articles in the comments.


Are airliners searched after each flight? When a commercial airplane lands at an airport, is it always searched for suspicious objects?

At the end of the Airplane's day (It's last flight for the day) It's the mechanics and the cleaners' turn to be on the plane.

The mechanics start out by performing the daily check or overnight check, it's like a routine checklist to make sure that your airplane is well maintained and ready for another day of flying. They also look at the Cabin Log books of the aircraft for any maintenance issue the flight crew has encountered during the day.

These issues could be anything:
ex:

"Seat at Row 28 won't recline properly"

or

"Sink is clogged"

and while the mechanics are resolving those cabin issues along with their daily checks, the cleaners also start their work. Cleaning all the seats, galleys and lavatories. They are not particularly looking for bombs, but they make sure to report any lost items they've found during cleaning.

Almost the whole cabin is cleaned up and inspected. So if anything is left, it will be found. Even the life jackets underneath your seats are accounted for, so if anyone decided to leave something under there, the mechanics would spot it.


What's the thrust coefficient for a convergent nozzle? As you know, the Ideal Thrust Coefficient of convergent-divergent nozzle is calculated using this equation:

But what about a convegent nozzle? Is there any equation to calculate the Ideal Thrust Coefficient for a convergent nozzle?

Image from: this link

It’s exactly the same equation, but now the throat is at the exit. So, Ae = A*, and so the areas disappear from the last term.


Which MEL categories would ground a commercial airliner if they're inoperative? Which Minimum Equipment List (MEL) categories would require a commercial airliner to be grounded (Aircraft On Ground or AOG) if they're inoperative? For example, any category A MEL item is considered an AOG item; is it the same for category B items?

If a piece of inop equipment CAN be deferred using the MEL, then the aircraft isn't grounded. When there is no MEL relief & the part has to be changed out is when you have an AOG scenario.


What is the ideal volume distribution for minimization of transonic drag? I am aware what the area rule states - my question is what is defined as "as smooth as possible area distribution" - Is there a formula for the curve?

Since Drag is proportional to S'', the key is to derive a shape that has a minimum S''.

The result is the Sears-Haack body.

  The Sears–Haack body is the shape with the lowest theoretical wave drag in supersonic flow, for a given body length and given volume.

The area is given by:

$$ S(x) = \frac {16V}{3L\pi}[4x(1-x)]^{3/2} = \pi R_\text{max}^2[4x(1-x)]^{3/2}$$

And the radius is given by:

$$ r(x) =  R_\text{max}[4x(1-x)]^{3/4} $$

Image source


What are those arrow markings on the wing? I recently flew on a Boeing 737-800 and found these arrow markings on the wing. What are they for?

They are the overwing exit markings. You can see them in full in the following photo.

Boeing 737 Max overwing exits. By Oleg V. Belyakov - http://spotters.net.ua/file/?id=110706&size=large, CC BY-SA 3.0, Linkec

This is because as already noted in another answer, B737 does not have self inflating slides for its overwing exits and as such, the passengers need some guidance for exiting, to prevent them from going the wrong way.

Pessini

The above image shows the procedure for using the overwing exit.


Why can't an Airbus A330 dump fuel in an emergency? It was reported recently that the Swiss flight LX18 from Zurich to New York had detected an engine issue shortly after take-off and decided to land back in Zurich.

Apparently, the Airbus A330-343 cannot just dump the fuel and, fully tanked, was too heavy to land safely, so it had to fly for 5 hours in a loop just to burn the excess kerosene.

Would it have been too complicated to implement a fuel draining mechanism?
What would have happened if they couldn't fly for 5 hours and had to emergency land right away? Wouldn't this inability to drop fuel be a safety hazard?

To supplement Jimmy's answer, if they had to land right away, they could have; it just would've resulted in an overweight landing being recorded, and which on most airliners triggers a special inspection of the landing gear and its attaching structure, and if nothing is permanently bent or cracked or broken, you are good to go.

An overweight landing in itself shouldn't result in damage unless the landing was hard, the overweight condition using up some of the structural safety margin, and if you know you are landing overweight you will take extra care to land smoothly.

Depending on the airplane, an overweight landing may apply a "penalty" so to speak, accelerating some inspection interval, or advancing a life limit on a structural component in the gear, or some other negative impact maintenance cost wise.  So there may be a significant incentive to avoid it from a long term cost perspective even if it means wasting 5 hours of fuel going round and round in a hold.

In the case mentioned, the crew would have consulted with the airline's Maintenance Control organization on the private company radio frequency to discuss whether to land overweight or not, and if there wasn't an urgent need to land, the Capt would have agreed with Maint Control and burn off the fuel to avoid the overweight landing and its ramifications.


Were leading edge ailerons tested? So far I have never come across any testing being done on having the ailerons and/or elevators on the leading edge of a wing, rather than on the trailing edge.
Does anyone know of such tests existing?
It somehow makes sense to me to have the controlling surface in the strongest part of the wing, which is not the trailing edge. Having all the 'heavy stuff' in front of the main carrying component, allows for a fairly light trailing part. Moreover the force applied on controlling the leading edge is less, because it changes the airflow without causing extra drag.

They were tested in 1935. Since ailerons are thin (thickness-to-chord ratio), they were placed in a leading edge slot, and it was dubbed slot-lip aileron. The study's conclusion is:

The slot-lip ailerons appear to be usable as a form of lateral control device that shows promise of giving improved lateral control and stability at the high angles of attack through the stall, with negligible lag, light control forces, and relatively simple construction. It is desirable that additional tests be made to find the yawing moments given by these ailerons and the effect of the slot on the drag.

The aforementioned additional tests were carried out in 1937; of note:

The more forward the slot-lip is, the higher the lag (control delay after input). It works best when the slot-lip is in the rearmost 20% of the wing.

My understanding of the lag is that it's due to the delay in relieving the low-pressure behind the aileron as it deploys, especially nearer where the lowest pressures exist on the upper surface.

Much higher drag in the order of +10% at high speed and +35% in climb attitudes.

Weick, Fred E., and Joseph A. Shortal. "Development of the NACA Slot-lip Aileron." (1935). https://ntrs.nasa.gov/citations/19930081340
Shortal, Joseph A. "Wind-Tunnel and Flight Tests of Slot-Lip Ailerons." (1937). https://ntrs.nasa.gov/citations/19930091678


What angle are front rotors of tandem helicopters tilted and why this value? I've read that the front rotor of tandem helicopters are tilted forward so that you can get a forward velocity with no nose-down pitching of the fuselage, but what angle is used for this tilt and why this value?

Is this angular value chosen such that you can have no nose-down pitching at the design-point operation of the helicopter? ie, if the helicopter is designed to cruise at 150ktas, is the forward rotor's angle set such that your forward force cancels the total drag at this velocity and maintain no fuselage pitching? And if you wanted to go faster than 150ktas, you would just have to pitch the whole helicopter to get the rear rotor's upward thrust to join in to accelerate forward?

The forward tilt of the main rotors with respect to the fuselage is not related to the tandem rotor design, but to a combination of fuselage lift and the need to also provide thrust with the main rotor.

First off, a review of other tandem designs shows that those not related to the CH-47 do not always share the forward tilt:

Bell XHSL-1 prototype

Filper Research Beta 200A

McCulloch YH-30

Piasecki H-21B

Yak-24

And looking at non-tandem helicopters, we also find a similar tilt:

Sikorsky CH-53

NHIndustries NH90

Mil V-12

Mil Mi-26

The reason is twofold:

A helicopter obtains its thrust from the same place as most of its lift: from the main rotor. This means that in forward flight the main rotor will always have its tip plane slightly tilted forward to counter the drag acting on the airframe.

Furthermore, large helicopters like the tandem designs you ask about experience significant aerodynamic forces on the fuselage at high speeds. To mitigate these, the main rotors are installed at an angle so that in cruising attitude the lift component from the fuselage will be positive. You can see it more clearly in flight:

NHIndustries NH90 in flight

Sikorsky CH-53 in flight

Boeing CH-47D in flight

I could find some corroboration of the fuselage lift effect in this Boeing report which includes a lift curve for the fuselage attained via wind tunnel tests. As you can see $\alpha_{zero-lift} \approx 4.5^o$

As to what is the exact angle, that depends on the design and is ultimately optimized after extensive testing, if deemed worthwhile.


What is this odd large sign near Aalborg airport/millitary airport? I have recently moved to Aalborg in denmark and while riding my bike each morning I cycle past these large signs pointing out into the water. I assume they are for aircraft at the nearby millitary/civillian airport because of how large they are and how they point directly out into the water in a relatively calm stretch of water on the edge of the city so nobody could see them.

The signs are quite large, about 1-1.5m in diameter and the poles are about 6 or 7 meters tall

The one interesting thing that made me think maybe its not to do with the airport is how it's actually quite far away (and also not lined up even slightly with the runway). In fact, they are almost perpendicular to the runway, about 4km away across the water.

I'd love to hear your thoughts on the matter, and apologies in advance if they turn out to be some other kind of markings. I am very curious to know!

It's a maritime navigation aid. I'm fairly rusty, but I'm pretty sure it's a form of lead mark. When seen from the water, as you travel towards the mark, if you keep the diamond centred between the circled dots, it will have you travelling in a straight line down the centre/safest path of a channel.

It will normally be associated with a channel through shallow water, or a hazardous bend, or promontory, or breakwater, or a safe entrance or exit course for a harbour, or similar. Sometimes there may be a progression of such marks to enable zigzagging along an irregular waterway with a minimum of course changes.


What is a good place to start learning about pulse jets? I'm a student who is curious about designing his own pulse jet engine, I am wondering if there are any schematics designs, notes, and other related materials I could/should study to learn about these engines. Where can I find such things and what is a good place to start?

You could try this website on home made pulse jets looks like it has some good info. These guys are selling some plans and have info as well. Here is an interesting instructables... And here is another DIY one. You may also be able to dig up some of the work that was done with them during WWII with a bit of directed searching on some public archives (as it may be more or less public record now). Of course physics and engineering text books will always be of help but there may not be any pulse jet specific ones.

PSA: You should take extreme caution when building and testing something like this. You will presumably be burning jet fuel (or another comburent) in a home made combustion chamber which can lead to very bad things. Care should always be taken when firing up an engine (of any kinda) for the first time. Welds should be double checked, metal choice is important and please wear safety goggles!


Why has Boeing used mini winglets on the 737-200? I found mini winglets just in B 737-200. What's the differences between mini winglets and the blended ones which Boeing uses in more recent versions?
(picture source)

When originally Richard Whitcomb of NASA developed the winglets, he developed the split winglets with one above and one below as shows in image below:

The one above starts at 0.4x chord from the leading edge. For a test program on KC-135 tanker, which I suppose was first application of the winglets, they used the type of winglets shown in the question:

Conceptually there is no difference in the "mini-winglets" and the "Blended winglets" While I think almost all the wingtip shapes are more or less of same efficacy, I can think of couple of reasons for variations seen among various aircrafts - One is patents taken for some shapes would force other OEMs to come up with different shapes. Second is weight of the wingtip vis-à-vis the reduction in fuel burn. Typically winglets reduce fuel burn by ~3-8% but in some cases, the increased weight can off-set majority of the fuel burn or even prove to be more than compensating for it, especially on shorter hauls. One may be able to make a lighter blended winglet using co-bonded, co-cured composite structure as compared to the short winglet mentioned in the picture which with say bolted joints might end up heavier. I think it would be difficult to say make any generalised comment on this.


What infrastructures are required for airlines to send PNL messages? There are lots of information about Type-B messages sent by airlines on IATA website but they have not stated under what communication systems (cable, teletype, intranet, internet, etc.) these messages are exchanged. What are these systems?

It's not just one. Private networks are used such as the IP-based ARINC AviNet, AFTN Teletype, etc.

For the specifics and standards, that information is not freely available (>\$3000). From IATA manuals, go to the Passenger tab, then the Security & Facilitation section. Or click here.

  IATA's Passenger Data Exchange Support Plus package provides governments with all necessary standards, helpfully grouped in a single purchase.

The following example is for France (may not be current):

There is also a presentation on the IATA website you may want to download and check.


What are typical values of the lift-to-drag ratio for normal small aircraft? Hi I am trying to do a rough estimation of forces acting on an aircraft wing and would like to know what kind of lift to drag ratio is normal. The exact profile hasn't been chosen yet, but the aircraft weighs less than 1800 kg and has a wingspan of around 13 m. The cruise speed is roughly 70 m/s.

As I understand, the maximum load factor to consider is 3.8, so the maximum lift is about 67,000 N; but how would I go about getting an estimate for the drag?

The maximum L/D values for existing aircraft span a wide range, from 7.5 for the Zodiac Ch701 with floats to 21.5 for the Berkut 360. Source: Light Sport and General Aviation Airplane Comparison and Harloff Performance Factor. This comparison comprises 93 types, and that is normally where a drag calculation starts: You find a similar type and use that as a baseline.

For the wing drag you calculate the lift distribution for several angles of attack (try XFLR5 for this) and get the induced drag for the weights and speeds that belong to those angles. Now you need to know your airfoils and add their drag. Next, add increments for the interference with the fuselage, for fairings, gaps and probes using data from this book. Yes, it is more than half a century old but physics hasn't changed since then.

Drag is normally not the biggest in-plane load on a wing but lift at high angle of attack. If you need to calculate loads for a structural design, make sure you don't omit that particular load case. Don't be surprised: That lift has a strong forward-facing component.

If you are new to this, try to calculate several of the aircraft for which data exists. Only by doing this you can be sure that what you do gives good results. Drag calculation needs some experience and is, when done well, a lot of work.


What are the requirements to obtain the ATP license in Canada? How much exams does a person need to do in Canada do become a ATP pilot and how many hours will be needed to become a pilot, for example ground school time, flight hour time etc....

The requirements for ATP Aeroplane are in CAR 421.34. You can read the details yourself, but in summary:

Be at least 21 years old
Hold a Category 1 medical
Pass 3 written exams
Hold a Commercial Pilot Licence - Aeroplane (valid for both day and night flight)
Have 1500hrs total time, of which at least 900 must be in aeroplanes (see the regulation for more details on night, XC and instrument time)
Within the last 12 months, demonstrate instrument flight and emergency procedures in a multi-engined aeroplane


Why are RVR values reported in good visibility? I just pulled the METAR for KLAX. Why are they reporting an RVR value for runway 25L if visibility is 9 statute miles?

KLAX 281553Z 00000KT 9SM R25L/2400VP6000FT FEW012 FEW045 18/08 A3000 RMK AO2 SLP157 FU FEW012 FU FEW045 T01780083 $

It looks like that METAR was corrected to

  KLAX 281553Z COR 00000KT 9SM FEW012 FEW045 18/08 A3000 RMK AO2 SLP157
  FU FEW012 FU FEW045 T01780083 $

Note the COR for corrected. The corrected METAR does not include RVR.

Including a screen grab of aviationweather.gov in case they dont keep the info up for a long time.


What licenses/endorsements or type ratings do you need to fly a fighter jet? As the title says, what endorsements and licenses do I need to obtain before I can legally fly a decommissioned single seater fighter jet or trainer jet (like a L-39 Albatros or even a F22 when the time comes)

Simply assume I could afford everything the jet needs and the jet itself, I am aware that a lot of jets (mostly newer) will never see civilian pilots.

I am mostly asking for the Netherlands / EU, but I am interested in American laws as well, if there are big differences.

In the US, the FAA's requirements for obtaining authorization to fly former ,military aircraft is included in 8900.1 Volume 5, Chapter 9, Section 2.

It is quite lengthy and covers more than just former military aircraft. As others have pointed out, most of these aircraft do not have a Type Certificate. They normally have a Special Airworthiness Certificate in the category Experimental Aircraft  Exhibition. Requirements to fly the aircraft are spelled out in the aircraft's operating limitations which are issued with the Special Airworthiness Certificate.

From 8900.1:

  A.    Background. The FAA requires pilot authorizations to operate
  some aircraft in the experimental category, including some former
  military, all turbojet‑powered (for this section, all turbojet‑powered
  includes all turbofan‑powered), all rocket‑powered, and all large
  (over 12,500 pounds maximum gross takeoff weight (MGTOW)) aircraft,
  and any other aircraft requiring specific pilot skills. Examples of
  such models are the Northrop F‑5, Bell P‑63, MiG‑15, Ju‑52, Mi‑24, and
  the BD‑5J. The FAA also requires authorizations to act as PIC of large
  or turbojet‑powered aircraft undergoing type certification.

  1)    The requirement for an FAA authorization to act as PIC of
  certain experimental aircraft is contained in the FAA‑issued aircraft
  operating limitations. Pilots are required to comply with the
  FAA‑issued operating limitations by 14 CFR part 91, § 91.9(a).

  2)    Because these aircraft are not type certificated (TC), a type
  rating is not available. In the absence of type ratings for these
  aircraft, it is the FAA’s objective to ensure, for the pilots flying
  these aircraft, a level of safety and proficiency similar to what is
  available for an aircraft with a type rating.

The specific pilot requirements are also spelled out in the document:

  A.    Former Military Turbojet/Turboshaft‑Powered Aircraft. To be
  eligible for an authorization to act as PIC of a former military
  turbojet/turboshaft‑powered aircraft, an applicant must:

  1)    Possess at least a U.S. private pilot certificate with an
  appropriate category and class rating for the configuration of the
  aircraft;

  2)    Hold an instrument rating;

  3)    Possess at least a valid U.S. third‑class medical certificate or
  equivalent (U.S. Military Flight Medical or U.S. driver’s license in
  accordance with the FAA BasicMed process (pilots using BasicMed may
  not exceed 250 knots indicated airspeed (KIAS)));

  4)    Have logged a minimum of 500 hours of pilot flight time in the
  aircraft category and have completed the U.S. armed services
  qualification checkout described in this section; or have logged a
  minimum of 1,000 hours pilot flight time, including 500 hours as PIC
  in the aircraft category, and have completed the training requirements
  of this section; and

  5)    If the aircraft is capable of supersonic flight, have a minimum
  of 250 hours of pilot flight time as PIC of a fixed‑wing
  turbojet‑powered aircraft, in a Group V, VI, or VII aircraft (see
  Figure 5‑173), or present proof of completion of a U.S. military
  qualification in a supersonic turbojet‑powered aircraft.

  B.    Former Military Propeller‑Driven Airplane. To be eligible to
  serve as PIC of a former military propeller‑driven airplane that has a
  MGTOW exceeding 12,500 pounds, or which has a horsepower rating of
  more than 800 horsepower and a VNE that exceeds 250 knots, an
  applicant must:

  1)    Possess at least a U.S. private pilot certificate with an
  appropriate category and class rating;

  2)    Possess at least a valid U.S. third‑class medical certificate or
  equivalent (U.S. Military Flight Medical or U.S. driver’s license in
  accordance with the FAA BasicMed process (pilots using BasicMed may
  not operate an aircraft with a MGTOW above 6,000 pounds));

  3)    Have logged a minimum of 500 hours of pilot flight time; and

  4)    Have completed the training requirements of this section.

That last item can be a challenge as it requires finding someone with the proper authorization to provide the training.

More information is available at the FAA Vintage & Experimental Aircraft Program web page.


How does the A320 FMGC (autothrust, autopilot) decide which radio altimeter readings to use? How does the A320 (or other Airbus FBW aircraft, for that matter) decide which radio altimeter reading to use (say, for FMGC functions like autothrust), or whether to reject the radio altimeter data altogether and throw an ECAM to the pilots?  It's certainly not a full voting system, considering that the A320 only has two radio altimeters, not three...

(For the curious: I ask because the flight profile from the ACA 624 mishap bears some resemblance to what would happen if the power rolled back on very short final without the crew noticing.)

First of all, RA1 is showed on the captain PFD and RA2 is showed on the F/O PFD. If one is detected as failed, the functional one is showed in both PFDs. This behavior is fixed, there is no way for the pilots to change it (instead, you can change the IR and ADR data with the relative knobs on the pedestal).
Now, two questions bring up:

How the system detects a failure in one RA if you have only 2 RAs and it cannot perform voting?

In this case, the only way to detect the failure is the self-detection, i.e. the control hardware and software specific to each RA performs the sanity checks. Since you cannot vote, there is no way to externally detect which one failed if they disagree (unless you cross-check with other data like database terrain or similar, but I doubt it does that). The disagreement triggers the ECAM message "NAV RA DEGRADED".

What the systems (GPWS, GLS, windshear, FWC, etc.) use if the two RAs disagree?

According to this Airbus document:

GPWS uses RA1
AP1/FD1 uses RA1
AP2/FD2 uses RA2

It doesn't state about other systems using RAs, probably they use only one side like GPWS and AP. At least these systems use RA information: reactive windshear, GLS autoland, TCAS, ROW, because in case of RA1+2 failure they are on the INOP SYS list. The FWC (Flight Warning Computer) is also using the RA signals to compute the flight phase (for example, to inhibit certain ECAM messages on takeoff and final). I can't find any information on FWC, it probably just disables message inhibition.
Differently it is in the A380, where you have 3 RAs, so they can vote, and all the systems use to the same value.


What is this item on the nosewheel of the Sukhoi PAK-FA? I noticed a small item on the rear side of the nose wheel in multiple images of the Sukhoi PAK-FA, shown below.  The item in question appears to be a grille wrapping around the back of the tires and I cannot think of any reason to put something like this on an aircraft's landing gear.  Does anyone know what function it serves?

Image credit Dmitry Zherdin.  Obtained via Wikimedia Commons.

Image credit Alex Beltyukov.  Obtained via Wikimedia Commons.

It is a mud guard/FOD deflector, which is found in almost all Russian combat aircraft operating from land bases.

This is basically a reflection of the Russian philosophy of aircraft operations:

  The fact is that most Russian fighters and attack aircraft were built to operate in pretty horrific conditions, ones that would chew up and destroy their western counterparts. Features that allowed them to do this usually included twin tire nose gear and a mud and debris catcher located behind the nose wheels.

The nose debris deflector prevents debris being ingested by the air intakes (which are to the rear of nose wheel) and damage to the airframe. According to ausairpower.net, it also has:

  Alternate intakes for the propulsion system, as seen on earlier Flankers.

for rough field operations, similar to Mi-29. The image below shows the add-ons.

Detail of inlet and lower fuselage area (Sukhoi); image from ausairpower.net

The FOD deflector is similar to that of the Su-27's, as shown below:

Su-27 nose landing gear, from another answer; originally from maybach300c.blogspot.com


Why aren't there any widebody propliners for the high-density short-haul markets? Jetliners come in both narrowbody (one aisle) and widebody (two or more aisles) versions, but all propliners, to the best of my knowledge, are narrowbody aircraft.

Now, granted, one of the big reasons for having widebody airliners is to have an aircraft big enough to cross continents and/or oceans with a profitable passenger load, and trans[continental/oceanic] routes are (at least in civil aviation) exclusively the province of jets, because speed.

However, in places with lots and lots of huge, densely-populated cities packed fairly closely together, such as much of East Asia, passenger numbers are so high as to require the use of large widebodies even on very short-haul routes - and, on short-haul flights, propliners hold a considerable advantage over jets (jets are horribly inefficient in the dense air at low altitudes, and short-haul flights aren't long enough for an airplane to have time to climb to long-haul cruising altitudes, whereas propeller aircraft, with their lower speeds, and, thus, lower drag, do just fine going low, and short-haul flights are short enough that slower aircraft aren't a major disadvantage; this is why, even though propliners are essentially extinct in long-haul airliner service, they continue to take a large chunk of the short-haul market).  A widebody propliner would be perfectly-suited for these sorts of jam-packed short-haul markets.

So why aren't there any?

Not enough thrust (i.e., too many engines)

Taking the lightest wide-body, the Airbus A310-200, its MTOW (max takeoff weight) of 144-164 tonnes is >2 times that of a Boeing 737NG at 65-85 tonnes. A 737 equivalent in MTOW in the prop world is the C-130 at 70 tonnes, and it needs 4 propellers.

So we are looking at 8 propellers for an A310-sized wide-body, or 4 contra-rotating propellers, already 6 too many either way for the airlines.

A comment claims that a turboprop engine can be designed as big as needed, what's missing is that the bigger the torque, the more blades are needed, which will essentially turn a prop into a fan. A relevant post is, 'How does a fan differ from a propeller?', where Peter Kämpf compares the disc loading of propellers and fans.

Propellers on a C-130 Hercules: 259.25 kW/m²
Turbofans on a small BAe 146: 4254.35 kW/m²

Propellers driven by piston engines are the most efficient, followed by turboprops, but they don't have the thrust of jet engines. Try and picture how many propellers would be needed to lift a Boeing 747. In the commuter/regional range of 100 passengers, turboprops have great efficiency, but go bigger, and fewer engines win.

On paper all is possible, the issue is making a civilian product that makes sense, in this case, number of engines. (Airlines care about the bottom line, the military not so.)

More parts is higher maintenance cost. For turboprops some figures are in this AOPA table from Oct 2016 (variable cost that incl. maintenance):

4-pax single-turboprop is \$535.84 per hour (Piper M600)
9-pax single-turboprop is \$508.73 per hour (Cessna 208 Caravan)
8-pax twin-turboprop is \$1,194.69 per hour (Beechcraft King Air 350i)

So capacity has little impact on the variable cost, unlike the number of engines.

Fuel economy (bomber vs. airliner)

Let's call the number of engines/propellers/parts, "A", and fuel economy, "B". For the airlines, "A" tips the balance when the number of engines exceed 2, i.e., that is why civilian turboprops are of the regional size.

Comparing 4x extreme-end turboprop engines with contra-rotating propellers (8 propellers in total like on the An-22 that's been suggested in a comment), with say 2x GE CF6 jet engines (like on the lightest wide-body airliner), when it comes to only "B", is a different question that requires context:

The reason why the Bear is turboprop powered (same engine as the aforementioned An-22), is because it's a long-range bomber with loitering in mind, not a short-range wide-body airliner as asked. Turboprops were also considered for the B-52.

Addressing other comments:

The A400M was suggested as a plane that makes it possible, it doesn't. Its MTOW minus OEW minus Fuel is 15 tonnes, or 115 pax + luggage and no cargo. Also note it's only 4 m wide internally, narrower than the narrowest wide-body, the 767 at 4.72 m. This is confirmed by its max troop capacity of 116, design-wise because most of its length is to accommodate a ramp.

Ignoring all that, it's still got 2 engines that the airlines can do without.

  cargo compartment: width 4.00 m x height 3.85 m x length 17.71 m

(wikimedia.org)

A comment saying the C-130 is already wide, it is not. It's only 3.02 m wide on the inside. A 737 by comparison is 3.54 m. And wide-bodies start at 4.72 m, which allows a twin-aisle (2+3+2) configuration, one more seat than the 6 abreast single-aisle 737.

Build it lighter (composites): In the history of airliners, whenever progress was made toward lighter materials, wings are built bigger for more efficiency, and so is the cabin, because the airlines want more passengers for the same MTOW, otherwise they can't stay afloat. A prime example is the 787, it uses lighter materials, and ended up heavier than the plane it replaced, because its efficiency comes in part from the bigger wings.

Regarding the noise, military turboprops (and jets) are very noisy, but when it comes to passenger transports, turboprops match the jets. This research for example compared the noise level in the cockpits (one of the loudest parts of a plane) of similar-sized planes (A319 and Dash 8), and the turboprop was the quietest.


In the US, in the last 50 years, have there been any accidents known to involve a student pilot intentionally practicing stalls in solo flight? In the US, in the last 50 years, have there been any accidents known to involve a student pilot intentionally practicing stalls in solo flight?

This question is asked in the context of civilian flight training in single-engine land airplanes.

I've heard of at least one flight school prohibiting student pilots from practicing stalls solo.

Yes.

I did a search of the NTSB database, limiting my search to final reports with a search term of "practicing stalls." This lead to about 50 reports. I scanned the reports where the aircraft was a typical trainer, such as a Cessna 172 or Piper Cherokee. I found three reports this way that involved a solo student pilot practicing stalls. Interestingly, only one of these seems to be due to a failure to recover from the stall.

12/2/1990 A student pilot experiences engine roughness and eventual failure during stall practice. Cause: failure to apply carb heat during low power settings, leading to carb ice.

3/22/1989 A student pilot fails to recover from a stall, while practicing too low to the ground. A factor involved was the featureless, snow covered terrain that made it difficult to gauge altitude above the surface.

11/5/1982 A student pilot experiences engine failure due to a stuck valve during stall practice.


KC-130: What are the four tanks/tube on the wings in between the engines used for? On the KC-130, what are the 4 tanks/tube on the wings in between the engines used for?

I've seen them in photos but without explanation. I cannot find any mention of them whatsoever. If not storage tanks then what else would they be used for?

The tanks between the engines on each wing are external fuel tanks. The pods outboard of the #1 and #4 engines are aerial refueling pods which house the hoses and drogues that are reeled out when refueling other aircraft.

This page has several examples of the outboard pods trailing drogues for refueling.  These pods are unique to KC- and MC-130 variants. One example:

The inboard external tanks (between engines 1 & 2 and 3 & 4) are found on most variants of the C-130.


Can someone identify this plane? This aircraft was circling very low during the day, wondering if anyone could identify this plane.

this was spotted flying over the san francisco bay area.

Going by probability it's likely a KC-130 as there are quite a few of those in the world. The recognition feature would be that it has four teardrop pieces of underwing gear with the external fuel tanks inboard and the drogue refuelling systems on the outboard.  There are no other obvious lumps or bumps in the picture to indicate other mission equipment such as cameras or weapons systems to narrow down which particular variant it could be.


Do autopilots in non-glass cockpits feed off of the gyro instruments? Do autopilots in non-glass cockpits feed off of the gyro instruments to determine aircraft attitude, heading and rate of turn? Or do they have their own internal gyros? Since I can set the heading using the heading bug, I suppose it needs to be able to read the heading-bug offset at the very least, so there's some connection.

Yes, they do. Also for glass cockpit, the autopilot uses the sensors that are used for the displays (ADC, AHRS, etc).
Here are some extracts from the FLM of the SA 365N Dolphin, describing the autopilot and coupler (I selected only parts relevant to the question):


Open source drone technologies What is the best place to understand the details of drones?  Preferably something open source.  Books would also be helpful.

I can think of a couple of open source UAV projects:

Paparazzi is a complete system of open source hardware and software for Unmanned Aircraft Systems, including autopilots and a ground control and planning station. All of the hardware plans and software source code you need to make a drone from scratch are available on github. But not everyone has the equipment to make a printed circuit board at home.
Open pilot is an autopilot for UAVs. They also sell hardware if I remember properly, which might make it a bit easier if you're just starting.

If you just want a simple introduction to flying drones, DIY drones has a quick guide to the basics.


What is differential braking? How is differential braking different from regular braking? How do you accomplish differential braking and why would you need to use it?

Aircraft with toe brakes have the brake pedals at the top of the rudder pedals.  You press the left one with top of your foot and it applies the left brake(s).  Press the right one to apply the right brake(s).  Normally you press them at the same time and with the same force to keep the airplane from veering to one side (imagine just locking up the brakes on one side of the airplane).

Differential braking is when you press one brake pedal harder than the other.  It is used as an additional form of directional control when:

You have no other forms of steering (either because the steering has failed or there is no nose-wheel steering)
The rudder/nose-wheel steering is not effective enough (because you are going too slow or the wind is too strong).

You want to be careful when doing this, though because you can over do it and create more directional control problems than you originally had.  If you use differential braking during the takeoff roll, it will increase the amount of runway that you use since you are applying the brakes (even though it is only on one side, it will keep you from accelerating as fast).


Is it at all possible (or safe) to pursue a pilot's license with a history of mental illness? I am in my late twenties. To put it bluntly I have a history of mental illness going back to my teens. My quick summary:

Diagnosed with depression and prescribed Wellbutrin in my teens. I discontinued without doctor approval and stopped going to psychiatry.
Diagnosed with ADHD in college and prescribed a litany of drugs to "try" including Adderall, Ritalin and Vyvanse. All were stopped with approval by my doctor because of horrible side effects and lack of any therapeutic effect.
Mid 20s (~1 year ago) had an anxious breakdown due to an online harassment campaign and voluntarily committed to a mental hospital, spent 48 hours there. Left the hospital with an SSRI and Klonopin (benzo) prescription.
Recently I discontinued SSRI use and switched back to Wellbutrin, have not taken Klonopin in 6 months or so but my doctor has had me keep it around in case of panic attacks.

I would say I have my depression under control but I have had 1 panic attack in the past six months.
I have been interested in aviation since I was a child and recently considered the idea of potentially pursuing a PPL, but I'm not hopeful. I'm 100% certain this would not be possible in the near future due to my current medication (Wellbutrin.) My doctor is confident that I can taper off this medication in the next 3 months however, and he views me as more or less stable. I don't feel anxious or depressed anymore and I haven't in some time. I like to think this is all behind me.
Is there any chance of attaining a medical in the far future (maybe 3 years of total stability from now), or is it pretty much not going to happen in this lifetime? Is it even a good idea to attempt to learn to fly, or should I stay far away from an airplane forever given my history?
Thanks for reading.

I have no medical degree, but I can give you some things to consider:
Even as a hobby, flying is at times a high stress environment. You must stay alert at all times, and the ability to maintain functionality even when all hell breaks loose is highly desirable. It's not all clear blue skies and three degrees of freedom. You got checkrides, new things to learn, old things to remember, and pretty much everything you do might end up badly.
You correctly point out that medication that effects cognitive capabilities is a strict no-go. As such, a history of using them might not exclude the possibility of ppl level medical certificate, but would require jumping through some hoops, with no guarantee of succes.
Any history of suicidal tendencies is pretty much a 100% no-go. Just a not, you do not mention this, but I'll let the cat out of the bag anyway.
Your anamnesis has quite a listing of various mental issues. You do realize this is a major obstacle, which is a good start. Loading high expectations on PPL licence would not serve your recovery well, but my non-expert opinion backed up by some real life examples is, that a person can shed even quite severe mental issues, and regain & maintain "full functionality" without any medication.
In your case the minimum requirement would be a long period of stability. Be honest to yourself and do not push it. If you get on top of things naturally, you might be good to go for PPL in some point in future. But do not risk you mental health on it, not but pushing towards it, and not by hanging on to it if you get there. As I wrote in the beginning, flying is a high stress environment at times, and it can trigger all kinds of unexpexted reactions. There is absolutely no loss or shame in putting the safety of yourself and the others above your dreams.
Flying is so much fun it's hard to describe it, but there are many other things just as fun, even more so.
Dream big, but don't let your dreams run you, or they will ruin you.


What is the meaning of flap detent names (e.g., 10 degrees)? When I extend my flaps to 10 degrees, what exactly is the 10 degrees measuring?  Is this referring to the angle of the flap blades themselves, the new angle of the wing chord, the change in the new critical angle of attack or something else?

The "Degrees" of flap deployment generally refers to the deflection from the neutral (0° - flush with the rest of the wing) position of the flaps.

For most GA aircraft this is an actual angular measurement - 10° of flaps corresponds to the flaps lowering 10° from their neutral position, but the degree of travel can also be given as a percentage (0-100%). The aircraft's maintenance manual will specify the actual travel (and specify how it is to be measured), and if specific position detents are provided there will usually be "rigging limits" specified for where each position stop must be & how accurate the control position must be at each stop.


How does the CFM LEAP-1B engine achieve the same efficiency as the LEAP-1A despite its lower bypass ratio? The CFM LEAP engine comes in 3 variants (1A, 1B, 1C). The larger LEAP-1A and LEAP-1C variants have bypass ratios of 11:1, while the smaller LEAP-1B only has a bypass ratio of 9:1.  For turbofan engines, we know that the higher the bypass ratio, the higher the propulsive efficiency of the engine, which results in a lower fuel consumption.

So how does the CFM LEAP-1B engine achieve similar efficiencies to its larger siblings when its bypass ratio is considerably lower?

Bypass ratio (BPR) alone never tells the whole story.

Take a low BPR engine and add to it a bigger fan, now you have higher BPR. Does that mean better efficiency? No. The reason is simple, by keeping everything the same, the same combustor/turbine do not have the right power/design to turn the now bigger fan at the optimum speed (slow fan).

But if you use a smaller fan on an already high BPR engine, which is the -1B case (approx. 8 inches smaller), then the thrust will be lower, which is indeed the case (approx. 130 vs. 143 kN). Since the combustor and OPR (overall pressure ratio) haven't changed, they can easily drive the now smaller fan at the right speed.

The other benefits the -1B have that may offset the lower BPR are the lighter weight (2 fewer turbine stages), lower duct loses, and the Max's cruise Mach, which is 0.01 faster than the neo – the slightly faster speed means slightly less time burning fuel for the same distance, and also slightly better inlet compression.

The LEAP SFC values aren't public yet. The official statement is:

  The advanced LEAP engine provides a 15 percent improvement in specific fuel consumption (SFC) compared to today's CFM56 engines.

That can also mean compared to the CFM56 of the respective plane, which is different for the A320ceo and 737NG:

  CFM56-5A1
  A320-211/-311
  0.330 lb/lbf hr

  CFM56-7B24
  737-700/-800/-900, 737-700BBJ/-800BBJ2 (option)
  0.370 lb/lbf hr

Source: jet-engine.net

The main reason there has been an increase in BPR in recent times, is because of the higher OPR they've been able to design (powerful small cores). Without OPR, you can't drive big fans at the right speed using small cores.

The slide below by Safran also shows why BPR alone is not the full picture:

(Safran via forum-ae.eu)

Related: Why does the CF6 have a lower bypass ratio than the TF39?


What is the exact meaning of CAVOK and CAVU? How are they used by pilots and ATC? Do CAVOK (ceiling and visibility okay) and CAVU (ceiling and visibility unlimited) have formal definitions worldwide?

CAVOK, source: formercaptain.ca

Are they used in ATC communications?

CAVOK is formally defined in ICAO Annex 3 ( APP3-2 2.2 Use of CAVOK ) . You can hear it at the airports where there is no ATIS , when ATC communicates the weather info.
CAVU is not formally defined in Annex 3 .

When the following conditions occur simultaneously at the time of observation:
 a) visibility, 10 km or more, and the lowest visibility is not reported;
 b) no cloud of operational significance;
 c) no weather of significance to aviation as given in 4.4.2.3 and 4.4.2.6;

information on visibility, runway visual range, present weather and cloud amount, cloud type and height of cloud base shall be replaced in all meteorological reports by the term “CAVOK”.


What does the phrase “flight attendants: stand by for all call” mean? At the end of an announcement on a recent flight, a crew member said: “flight attendants stand by for all call”.  What did the crew member mean and what exactly were the flight attendants waiting for?

"Flight attendants stand by for all call" commands the cabin crew to be ready at their station to report to the  chief purser via intercom.

See the explanation on this and other airline phraseology on
askthepilot.com


Does the PA-44's squat switch disable the stall warning? I've read the AFM and looked online about the gear system for the PA-44 Seminole and there is apparently a squat switch on the right main gear that disables the stall warning whilst on the ground. However during my pre-flight I have tested the stall warning with the battery master and avionics master on and it worked.

Is the stall warning squat switch not a feature on the newer PA-44s any more? The one I train in is about a year old now.

Are you sure you're talking about the stall warning? I believe you're talking about the horn that activates when in the landing configuration with no gear down(e.g throttle retarded, flaps down).

The 44 has 2 electric stall warning tabs that won't be actuated on the ground.


Why are RC rotor blades different from helicopter blades? Why do toy (RC) helicopters have curved flat surfaces and larger rotors on true helicopters have a solid aerofoil shape?

If the rotor was mechanically strong enough to lift the desired weight, is there any (aerodynamic) advantage to the solid aerofoil over the simpler curved surface?

Surely toy manufacturers could "close the bottom" of the rotor (equating to the aerofoil shape) even if it was hollow with negligible increase in weight.

I understand the Bernoulli effect does not necessarily apply to the RC rotors and it may be simply a Coanda effect but they do seem to lift well with just electric motors.

I have seen discussion that there is a "scale up" effect but why and if so at what size does the simple rotor start to fail... one foot, three feet, ten feet? Is there any data to indicate when the transition from this simpler design to a fully extruded solid rotor is required?

If the rotor was mechanically strong enough to lift the desired weight

It wouldn't be. Because of the square-cube law, lift and mechanical strength grow with second power of linear size, but weight grows with third power. The result is that at RC-scale, everything has plenty of power and strength even if made sloppily (and thus cheaply) from common materials while human-carrying-scale is really stretching capabilities of the materials and engines we have.

A highly cambered airfoil would not be strong enough for full-scale helicopter blade.

  is there any (aerodynamic) advantage to the solid aerofoil over the simpler curved surface?

I believe there is. No modern aircraft uses highly cambered airfoil.

  Surely toy manufacturers could "close the bottom" of the rotor (equating to the aerofoil shape) even if it was hollow with neglible increase in weight.

No. Efficiency is not that important at RC scale and hollow plastic is much more difficult to make (remember, plastic is made by injecting it into a mold).

  I understand the Bernoulli effect does not necessarily apply to the RC rotors

Airfoils is an airfoil whether it is flying straight or rotates. And since Bernoulli's principle is just conservation of energy for fluid flow, it always applies to it. It does not, however, mean concave lower surface would mean higher flow speed and lower lift, because the length of the path has nothing to do with lift. The air above the wing is faster—and reaches the trailing edge long before the air below—for completely different reasons. Highly cambered wings do have higher lift. They just have even higher drag.

  it may be simply a Coanda effect

Coandă effect is about a fluid jet surrounded with still fluid around it, but there are no jets of air involved here, so it can't be Coandă effect.

  but they do seem to lift well with just electric motors

That's the square-cube law again making the aerodynamic performance so much better relative to weight at RC scale.

  I have seen discussion that there is a "scale up" effect but why and if so at what size does the simple rotor start to fail

It is not just scale up (square-cube law):

Quad-copters with fixed pitch rotors (typical of the toy ones) are not controllable with failed engine. Human-carrying craft have to be.
Fixed pitch rotors deal poorly with horizontal speed, because the lift asymmetry creates big loads. Large rotors need to lead-lag and flap to compensate for this.

Both making quadcopters impractical at large scales.

Usually, quad-copters are made up to low tens of kilograms maximum weight. But where exactly is the limit might be hard to tell since larger ones may not be made simply because there is not much use for them.


Why was a Lockheed L-1011 chosen by Orbital ATK for its Pegasus launches? Not sure whether this fits better here in Aviation, or would be better suited for Space, but since the question is about a terrestrial aircraft, I'll start it out here.

The topic of my question is why was the Lockheed L-1011 chosen by Orbital ATK as its aircraft launch platform for its Pegasus spacecraft launches?  On the surface, choosing an L-1011 seems odd because it's no longer being manufactured (not a big deal, probably), but also with so few airworthy L-1011 aircraft still in existence, it seems like an odd choice, being such an unusual aircraft from a maintenance and spare-parts standpoint.

Is there some performance reason that they chose to use an L-1011 that makes it a better aircraft for their launch purposes than other aircraft of similar size that have higher numbers of still-flying airframes?

One reason the L-1011 was chosen was that the keel beams on the L-1011 are spaced such that they could create an opening inside the aircraft for the verticle tailfin of the Pegasus when mated to the bottom of the aircraft and do so without jeopardizing the structural integrity of the airframe. This allowed them more clearance than other aircraft although the L-1011 still have to be jacked up to mate the Pegasus.

Second, while the L-1011 is no longer manufactured, there are enough of them still sitting around that getting parts was still an option, and in fact, sometimes entire aircraft were available for purchase.

Third, they were able to acquire their own L-1011 simulator from Delta and they operate it on a regular basis to maintain their flight currency. Since they own it they can make modifications to it to allow them to not only simulate their training environment but also their launch environment.

And lastly (although may not have been a consideration) some of the pilots of the Stargazer were Lockheed test pilots.

For more information, you should watch this short video:

NASA Edge Program - OrbitalATK ICON Program


Has an earthquake ever complicated or prevented a safe landing/takeoff? This question on being able to see ground effects of earthquakes from the air got me wondering:

No doubt a severe earthquake at the wrong time could hinder even experienced pilots, but I expect a minor one may be unnoticeable or simply cause a mildly unsteady landing:

  "An earthquake--really?  I thought that felt a little weird"

Are there any known instances of an earthquake during approach/landing/takeoff? What were the results?

Naturally if there exists any video that'd be helpful.

Yes, there have been aircraft landing at the moment an earthquake hit. Here is an article about one in 2011: Air NZ plane landed as Christchurch earthquake hit

"It was creepy as... as the plane came down, you could see all the windows in the terminal just rolling, and all the shuttles that go out to the plane were in the tarmac just rolling.
"Somebody shouted out 'oh my god, it's an earthquake!'"
"We came down and couldn't get out, and there was a big shake while we were still in the plane. Then we sat there for an hour.

This is of course from the point of view of a passenger, not the pilots.


Why does the F-117 Nighthawk look different than other stealth planes? The F-117 Nighthawk has flat angled lines where most later designs (B2, F22, F35) have very smooth lines. Why the difference? Are the newer designs 'more stealth'? Do they use a different design to handle better? Is there another reason the distinct angled look is avoided in later designs?

The question, 'Why do many stealth aircraft have a similar shape and design?', is close, but doesn't really address why the F-117 stands out from the rest.

Left: F-117, right: F-22.

Initial work on Radar Cross Section (RCS) reduction concentrated on absorbers and had started in Germany late in WW II. The Americans were not interested at the time, but British scientists documented the results and gained early insights in US RCS research when they pooled their results in the 1970s.

Lockheed started work on the systematical reduction of RCS when they discovered the academic papers of Petr Ufimtsev, a Russian mathematician who explained how to calculate the reflection of radio waves from the 1960s on. Their initial success with RCS reduction on the SR-71 was more luck than systematic work. At the same time, similar insights were gained in Germany where a manned prototype of an aircraft (MBB Lampyridae) similar to the Have Blue prototype proceeded up to wind tunnel tests. Then the program came to the attention of US authorities which quickly put an end to it.

In all those cases, the major idea was to restrict the surface to large, flat panels because the edges, not the total area, determine how much energy is radiated back. In that respect, the German design was much cleaner than both the Have Blue and the F-117, but I digress. Those designs can be called first-generation stealth aircraft.

When Northrop joined the RCS work, they found that even curved panels work well - after all, it is edge reduction and alignment which reduces RCS most. Their initial prototype was for a battlefield observation aircraft (in contrast to the Lockheed attack aircraft) which was called Tacit Blue.

When work on stealth prototypes was opened at the end of the Cold War, all engineers could pool their knowledge and combine the work on absorbers, edge reduction and edge alignment. This gave rise to the second generation of stealth designs which look indeed quite different to those of the first generation. What also influenced the designs was more understanding of the tactical value of stealth, so the second generation designs do not optimize RCS above all else but arrive at a compromise which combines low frontal RCS with good agility and multi-role capabilities.

Koyovis is right, but it was not only computer power but also the limitations of early RCS codes which were based - at least in case of Lockheed - on the ideas of Petr Ufimtsev, and he in turn used analytical methods which did not allow to investigate the RCS of curved surfaces. However, the computers at the time were already powerful enough to allow the F-117 to fly at all - in contrast to the MBB design, it is unstable and uncontrollable without artificial stabilization.


How to get registration from ICAO 24 bit code? The description of PlanePlotter claims that it can determine the registration letters from the ICAO 24 bit address algorithmically for some countries.

The only thing i got so far is how to get the country. Any clues?

Edit:

After some more research I found some information in the book "Principles of Avionics" by Albert Helfrick:

  Generally, there is no algorithm giving a one-to-one correspondence
  between ICAO 24 bit addresses and the registration number of the
  aircraft. Some ICAO member states did have an algorithm that would
  translate ICAO 24 bit aircraft addresses to registration numbers but
  ICAO strongly suggested the practice to stop.

Algorithm for swedish registrations: http://www.transportstyrelsen.se/publicdocuments/PDF165.pdf

Apparently (according to these folks) some countries use an algorithm to generate their ICAO (Mode S) 24-bit IDs. For those countries, you can simply reverse the algorithm and get a registration given the Mode S ID.

Others countries allow you to download their registration database, complete with the Mode S identifier (you can get the US registration database here) - it's a simple matter to load this into your own software and map the ICAO/Mode S ID code to a registration number.

As the folks at Gatwick Aviation Society have noted, some countries are tight-lipped about how their codes are assigned (and who they're assigned to), so these lookups are probably not complete.


Can the parking brake be set on an 737-800 if the aircraft has no power? If a 737-800 has no power ('dead' airplane), is it still possible to set the parking brake on? If so, how?

This function is provided by the parking brake valve which is an electrically-operated hydraulic valve that, when the parking brake is commanded to be set, closes and traps hydraulic pressure in the brake lines. You set the parking brake by pushing both brake pedals all the way down, and then pulling up on a separate lever that locks the pedals in the applied position and at the same time commands the parking brake valve to close and trap the hydraulic fluid. You can then take your feet off the brake pedals.

If there's no electrical power, that valve can't close. If there's electrical power, but no hydraulic power from the pumps, that valve can close, and the hydraulic pressure to hold the brakes is then supplied by the accumulator. But that's not as reliable as having the hydraulic pumps operating, and you're not assured that the pressure supplied by the accumulator is sufficient to prevent airplane movement.

Moreover, closing the parking brake valve doesn't ensure a perfectly sealed system. Over time, internal leakage will mean that, if hydraulic power isn't constantly supplied, the trapped brake pressure will gradually leak to the point that the brakes can't hold the airplane, even though the parking brake lever and the brake pedals in the flight deck are still locked.


How does VFR work in countries other than USA? What does hi and lo mean? I saw that at https://skyvector.com/ the VFR sectional charts were available for the USA only. Do other countries use the same format for sectional charts?

Additionally What does Lo and Hi mean at this website?

The "hi" and "lo" represent en-route high altitude and en-route low altitude.  The difference between the two is the transition altitude when switching from flying with reference to height to referencing altitude

The transition altitude varies from country to country (e.g. typically 18000 for the US and 3000 in the UK unless varied - 6000 in the London area for example) and can be found in various publications and on the en-route charts themselves.

The structure of airspace is consistent world-wide with some variations which are always marked on the relevant charts. There are far too many small variations to go into any detail here.

Finally, the charts themselves. Because the structure is consistent, the charts are also consistent although there are cosmetic differences such as the symbols used, colours used and certain pieces of useful information which may or may not be printed upon them.  The differences are easy enough to  learn quickly.  I've flown VFR in the  UK and the US and the charts look different, but are fundamentally the same. Within an individual country, charts may even differ cosmetically if the airspace is particularly busy when the chart makers may choose to omit less important information.


How long can the stop in a stop-and-go be? When a pilot is cleared for a stop and go, how long does this allow them to be stopped on the runway?

I'd like to know if there is a limit in regulations or at least guidance for this.

The AIM covers this briefly (bolded the important part) but effectively you cant sit there very long:

  4−3−22. Option Approach

  The “Cleared for the Option” procedure will permit an instructor,
  flight examiner or pilot the option to make a touch−and−go, low
  approach, missed approach, stop−and−go, or full stop landing. This
  procedure can be very beneficial in a training situation in that
  neither the student pilot nor examinee would know what maneuver would
  be accomplished. The pilot should make a request for this procedure
  passing the final approach fix inbound on an instrument approach or
  entering downwind for a VFR traffic pattern. After ATC approval of
  the option, the pilot should inform ATC as soon as possible of any
  delay on the runway during their stop-and-go or full stop landing.
  The advantages of this procedure as a training aid are that it enables
  an instructor or examiner to obtain the reaction of a trainee or
  examinee under changing conditions, the pilot would not have to
  discontinue an approach in the middle of the procedure due to student
  error or pilot proficiency requirements, and finally it allows more
  flexibility and economy in training programs. This procedure will only
  be used at those locations with an operational control tower and will
  be subject to ATC approval.

The way I read that is effectively you come to a stop and get going as soon as possible. If you intend on doing anything else you should inform ATC. I take this to be a time limit of, as soon as you stop, get going again.


What are these hooks and tassels on the nose? What are the hooks and tassels hanging down from the nose of this aircraft?

The things hanging on the left and right side of the nose are pitot covers. They cover the pitot tubes located here:

(Boeing 737 Airplane Characteristics for Airport Planning)

The covers are there to protect the narrow inlets from contamination or blockage:

  Pitot tubes are normally covered when the aircraft is parked for more than a short period of time to reduce the chance of blockage or contamination.

(Pitot Static System on SYKbrary)

They are usually painted red and have REMOVE BEFORE FLIGHT written on them:

(aircraftcovers.com)

Related:

What is the use of this remove before flight cover on the nose of a Bombardier Global 6000?
What steps have been taken to rule out instrument failure due to blocked static ports or pitot tubes?

The cable connected to the right side of the aircraft (left on your image) is the ground power cable. You can see it larger in this image:

(pinterest.com)

Related:

What is the cable connected to a plane for?
What powers an aircraft prior to the APU being switched on?
What's the plug used on airliners for ground power?


Why is the drogue parachute jettisoned on the runway? Why is the drogue parachute of a military plane jettisoned on the runway? Why not drag it to the parking area for safe removal, inspection, and repacking?

For several reasons.

First to protect the drogue from damage by scraping on the pavement
second to prevent it from becoming snagged on nearby objects
third to prevent metal components on the drogue from hitting and damaging the tail of the aircraft,
and fourth to make it easier to taxi back to the ramp without the need for higher power setting to overcome the drag and prevent damage to the drogue from this jet blast.

One downside to jettisoning the drogue at a lower speed (< 40 kts) is that it now creates a FOD hazard on the runway and requires a waiting cleanup crew to retrieve it before another recovery is possible.


What would be a suitable aircraft for a short haul freight forwarding business? I just graduated with an Aeronautical Science degree and I am planning on starting a freight forwarding company.  It would need to be high payload capable and relatively fuel efficient, the route that would be flown everyday is only 300 miles one way.

You would have to provide more answers to the comment I made above.

But for a relatively small payload (<4000lbs), I'd say you can't go wrong with a Cessna C208 Caravan.  You can buy a good used C208B Super CargoMaster for just shy of $1 million.

Another recommendation for that route would be the DeHavilland DHC-6 Twin Otter.  Payload is increased by 1000 lbs or so over the Caravan and you have the additional safety of two engines for over water operations.  The downside is that these aircraft are fairly prized and will set you back about $ 3-4 million.

Another heavy lifter with an excellent reputation behind it, even after 80 years of service, is the venerable Douglas DC-3/C-47.  You call, we haul 6,000lbs to just about anywhere within fuel range.

All of these aircraft are extremely rugged and have a good reputation after decades of hard use in bush flying.  They are capable of operating on short, rough airstrips - a good benefit in case you decide to expand to more remote destinations within Cuba and can carry tremendous loads.  They're also turbine powered using PT6 engines (except for the DC-3) so fuel is readily available anywhere in the world as is maintenance and spare parts.


Is is possible to land a midsize commercial plane on an Ford Class aircraft carrier? I'm story-boarding a novel. I'm toying with the idea of contriving a situation in which a midsize commercial aircraft is forced to make an emergency landing on an aircraft carrier. I read here that the largest plane to land on an aircraft carrier is a C130 Hercules, which it did as a series of tests. Its maximum weight when performing these tests was 121,000 lbs. At this weight, it required only 460 feet to land. And it did so without use of a tailhook, or any other arresting mechanism. The brand new Gerald R. Ford class carrier is 1,106 feet long. The landing strip on the carrier is somewhat shorter. I couldn't find numbers on this, but from photos, I would estimate that the landing strip is a little more than 800 feet long. Which leads me to my first question:

In an emergency situation, could an aircraft use the full length of the aircraft carrier's deck to land?

Assuming the answer to the above is yes, this means that our commercial aircraft has somewhat more than twice the distance to make its landing than the C130 did. Let us assume that the commercial aircraft is a B737 Classic, weighing aobut 140,000 pounds, just a little more than the C130 did during the tests. This leads me to my main question:

Could a 737 Classic safely make an unarrested emergency landing on a Gerald R. Ford Class aircraft carrier?

By safely, I mean without any passenger death. I expect that any such landing attempt would result in significant damage to the aircraft and the carrier. On one hand, the numbers seem to suggest that if a C130 can do it, so could a B737. On the other hand, I would expect that the C130, as a military aircraft, is more robust than a commercial aircraft, and perhaps able to better meet the conditions required to land on a carrier.

Also, I realize that in an emergency situation it may be safer for the aircraft to make a water landing near the carrier, and then for the passengers to evacuate onto inflatable rafts, finally to be brought aboard shortly thereafter. I will have to invent a situation which requires the plane to land on the carrier.

A Classic 737's maximum landing weight is about 114,000# for a -300, less for a -500, more for a -400.  But that is max. Down to "almost empty" gas tanks, knock another 8 or 10,000# off of that. Less than full pax/cargo load, several more thousand pounds off.
With a stiff breeze, say 20 knots, plus the carrier at max speed, you have maybe 50 knots of headwind. With that sort of headwind, can you stop a mid- to light-weight 737 in 1000' using full flaps, max reverse, and max brakes?
I don't have the charts with me, but I suspect you totally could, and in fact it wouldn't even be all that close. No margin for error if equipment fails, but if everything works right, those jets can stop quite well. And 50 knots on the beak is a LOT of headwind... "groundspeed" over the deck would be like 60 or 70 knots, and you can lose that in a lot less than 1000'.
I've flown C-130's and 737's, and the rate of descent on an assault landing in the Herk is nothing the 737 couldn't handle.
So... carrier landing... good to go?
Not so sure.  Compared to carrier aircraft, the 737 wingspan in WIDE -- even for the "little" -500.  That limits where you can plan your rollout so that you don't have an unacceptably high risk of clipping the island. Without playing with scale drawings of a 737 and the Ford's deck, I couldn't even guess if or how the geometry would or wouldn't work out.
Alternate plan that is probably no more risky for the passengers and might be a LOT safer for the carrier: ditch your (nearly out of fuel) jet close to the carrier, and have the carrier's helos and the small boats of the battle group pull the survivors off the wings or out of the water. With calm water, you get a "Sully" scenario (except with wings filled mostly with air, rather than jet fuel... Better buoyancy). In rough water, the risks go up. Way up.
But in that sort of weather, the deck landing gets lots more risky as well.
I suspect the deck landing would neither be allowed nor requested, but not for reasons of stopping performance.


What is the difference between a Boeing Line number and a Block number? We know that every Boeing aircraft has a Line number, Block number, and MSN number. I want to know what what does it mean by this Line Number or Block number. and what are the difference among these terms.

Here is Boeing's Examples

Block numbers

ZA001 Onwards - B787-8
ZB001 Onwards - B787-9
ZC001 Onwards - B787-10
ZD001 Onwards - rebuild of prototypes
ZE001 Onwards - B787-9 with customizations

Line numbers are the serial number of the aircraft of that aircraft type

Serial Number is the manufacturers serial (basically the number of aircraft they have built up to that aircraft)

Airbus doesn't use the Boeing Line/Serial numbers, they use a different system where the aircraft serial number is in fact the aircraft line number and the total # of the aircraft being built.


With wind, what will a perfectly circular flight path relative to the surrounding air look like from the ground? Let's suppose that an airplane flying at a uniform airspeed follows a perfect, level, closed circular trajectory with respect to the mass of air. Now, seen from the ground, and in the presence of a constant wind, will no longer be a circumference. What would it be...?

It will be this :

http://www.aeroexperiments.org/images/grndtrck.gif

Pilot's of slow-flying aircraft like hang gliders and paragliders see tracks like these all the time on their GPS displays, as they circle in a thermal updraft in the presence of strong wind.

Depending on the strength of the wind, the "curliques" may become so stretched out that they don't form enclosed loops at all, just "points", i.e. a "scalloped" line.  This happens when the windspeed is greater than the airspeed. That means that the aircraft never makes any progress in the upwind direction at any point in the circle.

Related:
http://www.aeroexperiments.org/nocss.shtml
http://www.aeroexperiments.org/introcircles.shtml
http://www.aeroexperiments.org/circles.shtml


Is it possible to build 'Contra-rotating' EDF? Is it possible to design an EDF (Electric Ducted Fan), with two counterrotating blades, that will have more thrust than two separate EDFs with the same blades?

The primary reasons you'd want contra-rotating pairs with conventional (unducted) propellers are cancellation of torque/P-factor, and delivering more power with a limitation on diameter (tip speed, usually, or landing gear height).

Neither of these really applies to ducted fans; it's easy to null out the slipstream rotation with fixed vanes in the duct, and flow is always perfectly axial so there's no P-factor to worry about.  Further, pitch can be built high enough to absorb the needed power without supersonic blade tips, and generally is.

Bottom line, there's nothing to be gained from the extra weight and complexity of contrarotating fans in a duct compared to just using a slightly larger fan and motor to deliver the increased thrust you're chasing.


What costs less energy? Roll or Yaw? Let's say you want to perform a turn anywhere from 1 to 90 degrees. Which will cost less energy? A bank or a yaw?

Using the rudder does produce extra drag, because the control surface is deflected for a time.

Using ailerons to bank also produce extra drag, but more than that, at a roll angle the lift direction will not be perfectly vertical. You will either lose altitude (that needs to be regained), or increase speed.

That's why I didn't want to phrase the question as "less drag". Lost energy could be in the form of drag, worse lift angle, lost altitude, maybe other things I haven't thought of.

I'm interested in large commercial aircraft as well as "ideal" aircraft with no adverse-torques (all control surfaces are aligned with the center of mass).

When you turn by yawing you are skidding the airplane to point the nose to the side, to offset the trust vector to move the plane sideways as it's going forward.  The rate of turn you can achieve this way is very low and there is a massive drag of being in a skid as you slither around like a car on ice with the fuselage side presented to the airstream.  To the extent that the airplane has a roll/yaw couple (roll caused by yaw) you will have opposite aileron to keep the plane from banking into the skid; more wasted energy serving no purpose.

When you turn by banking you offset the lift vector to move the plane sideways as it moves forward.  There is no sideslip so the drag is only increased by the small amount caused by the increased elevator and AOA, and the minor drag of the moderately displaced ailerons and rudder (to the extent they are displaced at all once the rolling action is complete).

Because you are moving through a fluid, a skidding turn is like turning a car by drifting it on a dirt track, a banked turn is like going around on a banked corner, where you don't even have to turn the steering wheel to keep aligned with the road as the car changes direction.  Which way is more efficient?

To find out I tried it on my own plane, a homebuilt PL-2. I flew it at 2000 ft, holding 70kt, close to max L/D for this plane, and applied full rudder with a bit of opposite aileron to maintain wings level (not much aileron is required on this plane), adjusting power to hold altitude at 70kt in the skid.

My plane has a manifold pressure gauge even though the prop is fixed pitch, useful for knowing precise power settings. It took 19" MP @ 1900 RPM to hold a skidding turn with full rudder at 70 kt and the turn rate was about 90 deg in 30 sec, or about Rate 1.  This is about 55 HP on the Lycoming O-290 D2.

I then took out the rudder and banked into the turn (about 15 degrees bank was required to maintain Rate 1) to maintain the same rate of turn as the skidding turn but in a coordinated bank.  To keep from climbing I had to reduce power.  I ended at at about 16" MP @ 1700 RPM, in a banked level Rate 1 turn at 70 kt, which is somewhere around 45 HP.

So it took somewhere around 20% less power to maintain a banked turn at Rate 1 than a skidding turn at Rate 1 when flying near max L/D.  The extra drag of the skid was also quite obvious in the deceleration when applying the skid with rudder vs rolling into the coordinated turn.

With airliners, turning by skidding is out of the question because with swept wings you get a powerful roll rate as soon as you yaw a couple degrees and you will quickly run out of opposite aileron trying to keep the wings level.