What is the main difference between Class C and B Radar Service? What is the main difference between Class C and B Radar Service?

  Class C service provides approved separation between IFR and VFR
  aircraft, and sequencing of VFR aircraft to the primary airport.

  Class B service provides approved separation of aircraft based on IFR, VFR,
  and/or weight, and sequencing of VFR arrivals to the primary
  airport(s).

What does approved mean?

The term is not "approved", it is the complete phrase Approved Separation. This is the standard FAA term for what was previously called either standard separation or radar separation, and means "separation in accordance with the applicable minima in [FAA Order 7110]".

The separation minima are further defined in the JO 7110 family of FAA Air Traffic Control orders, which you can find linked from the page above.


Does it ever happen that increasing the prop RPM without moving the throttle actually decreases the thrust and power delivered to the airframe? A) In an airplane with a piston engine and a constant-speed prop, flying at some given airspeed with the manifold pressure and RPMs in a typical cruise configuration, would it ever happen that increasing the prop RPM higher and higher without moving the throttle would at some point actually start to decrease the thrust and power delivered to the airframe?

Assume no electronic engine controls such as FADEC.

I'm imagining a case where flattening the pitch of the prop blades would decrease the thrust and power delivered to the airframe, because the prop blades would be meeting the local airflow at a lower angle-of-attack, despite the increase in RPM.  I guess an extreme case would put the prop blade at a small negative angle-of-attack to the local airflow, so that the prop was acting to drive an increase rather than a decrease in the engine RPM-- obviously this would increase the RPM but would decrease the thrust and power delivered to the aircraft, at least in the forward direction.

B) It occurs to me now that such a thing might happen at lower throttle positions but not at higher throttle positions.  So a second part of this question is, on final approach with the throttle at idle, is it true that the prop exerts more of braking effect on the airframe when the prop lever is set for high rpm than when the prop is set for low rpm?

C) And the third part of this question is, for some given airplane cruising at some given airspeed with RPM and manifold pressure initially "square", what is an example of the highest initial manifold pressure at which we might find that advancing the RPMs higher and higher without changing the throttle setting might eventually cause a drop in the power delivered by the prop to the airframe?  Or is this something that would only happen at very low power settings, such as would be used in a descent, and would never happen at any power setting capable of sustaining level flight at any airspeed?  (This is basically a more refined version of part A.)

The intent of the question is that the advance in the RPMs is intentional and goes no further than the max allowable RPM of the engine and prop.  Clearly a "runway" prop would be an extreme example of these dynamics but the question is intended to be constrained to the normal allowable operating envelope of the prop and engine.

Some related questions and answers on ASE--

Manifold pressure vs rpm vs power obtained and more about constant speed prop

On a constant speed propeller, how is blade pitch related to airspeed and efficiency?

You may get a speed increase but it's likely to be almost too small to detect (although this depends a lot on the plane and propeller combination).

When you increase prop RPM leaving MP constant, you are increasing the engine brake horsepower although there is a small drop in MP when you do that (and the opposite happens when you reduce RPM) that limits the total horsepower increase.

Say you have a Lyc O-360. Running it at "23 square", 2300 RPM and 23" MP, the engine is making roughly 108 HP at the prop.  If you raise the prop to 2700 rpm from 2300, and the MP stayed at 23", you are now making about 128 HP.  But actually it's not quite, because increased velocity demand of the intake flow drops the MP a bit with the throttle butterfly unchanged.  If you went from 2300 to 2700 the MP would drop somewhere around 1" of MP and this would reduce the engine's brake HP to 120.  Still more than 108.

At the high RPM, you will also likely have the prop operating at a less efficient blade angle from low blade AOA - the governor doesn't know or care what the blade angle is, it just rotates them to load to blades to keep the RPM where it's set by the prop control (a spring pushing on a set of flyweights) so there will be another minor loss from the blades being at a sub-optimal AOA.  Say, optimistically, 3%. So you end up with the equivalent of maybe 112-115 HP in net thrust compared to what you had before (this can vary a lot with different propellers).

So the result is, in a best case condition, you actually only increased the net thrust by a few percent and taking into account of the power-required-increases-at-the-square-of-the-speed aspect, there is a net airspeed increase of maybe a couple mph at best. If the prop efficiency really dropped off badly, you might find yourself going slower by a knot or two.

It also matters how you do it. If you were cruising along and raised the RPM suddenly by shoving the control forward, you will get a temporary deceleration as the governor unloads the blades to raise the RPM (it will also overshoot the redline giving that WEEEEEEEEOOWWWWWWWW sound you sometimes hear when pilots do that) and then the plane will slowly catch up.

If you just raise the RPM gradually, the proper way to do it, there should be little obvious acceleration or deceleration, but the speed may creep up or down a little bit and after things settle down you'll be a few knots faster, the same, or maybe a couple knots slower because the prop was operating at a very inefficient blade angle and the losses exceeded the minor Brake HP increase of the rise in RPM.

If you're at a very low manifold pressure setting, just off idle say, and the prop control is at Max RPM, the prop governor has a "command" (fly weight spring pressure) to let the engine run to redline and regulate RPM there, but the engine isn't making enough torque to spin the blades at redline.  The governor will unload the blades trying to do that, until the blades reach the fine pitch limit.

Or, if you're at full throttle/Max RPM and pull the throttle way back, at some point the blades hit the fine pitch limits and the RPM starts to drop from redline.  The prop has "come off the governor".  Now the prop is effectively an overly fine fixed pitch prop.  If you are at a certain fairly low MP, say 16", with the RPM at, say, 2200, and you move the prop lever up to Max RPM, the RPM may rise just a little as the blades were already near the fine pitch stops to keep 2200 RPM at 16". Add throttle, and the RPM rises like a fixed pitch until the RPM matches whatever RPM the prop lever is set to, and it "comes back on the governor" as the blades are moved off the fine pitch stops to keep the RPM at the selected setting.

As a general operating technique, you always lead with RPM on power increases, and lead with throttle on power decreases.  And you get to know that each RPM change affects MP and learn to allow for it with each RPM change. For example, if you are climbing at 24 square and want to cruise at 22 square, you'll reduce the MP to about 21.5-ish, then reduce RPM to 2200, knowing that this will pick the MP up to 22"-ish, requiring a minimal subsequent throttle tweak to get it right on.


Is engine shp directly correlated with its payload capacity? For a turboshaft engine, does increasing its shp also increase its payload capacity?
What are the other factors determining the payload capacity of a helicopter?

This is a complicated question, here is a simplified answer.
Generating lift requires setting in motion a large quantity of air, as downwash. More lift requires more downwash, and that requires setting in motion a larger quantity of air- which requires more horsepower applied to the main rotor shaft.
Note however that the rotor blades are designed to generate their optimum lift at a certain design speed and angle of attack, which means that if you add horsepower you would also have to increase the rotor blade span and/or add more blades to absorb and make best use of the additional power- all while maintaining the blade tips subsonic, and not overstressing the blade attach points or the main transmission gears and shafting.
In addition, more power to the main rotor disc means more torque reaction, and you'd need to redesign the tail rotor to counteract that.
All this means that you cannot increase payload by simply increasing the shp of the engine.


How can I tag along on an Atlantic crossing? I'm a private pilot based in the US and interested in tagging along on a North Atlantic crossing. I have too little experience to dare to attempt it myself, but I'd love to experience it. Does anyone know if there is a way of making that happen? E.g. are there pilots who take guests along? Or are there legal or insurance impediments?
Many thanks for any information!

Contact companies that do ferry/delivery services.  You'd probably have to pay for your own immersion suit, IF someone was willing to let you come along.  Yes insurance will also probably be an issue.


Is there an ideal lift distribution for human-powered aircraft? Is there an obvious, ideal lift distribution for human-powered aircraft?
Elliptic or Bell (unloaded tips) distribution?
For this who will tell the Bell distribution, I have a counter-question ready, why don't put wires to wingtips to reduce bending moment at root and use elliptic distribution?
So what is the purpose of any Bell distribution, if the wing is designed correctly?

The essential feature of a human-powered aircraft is to maximise aerodynamic efficiency, which is to say to minimise drag for a given amount of lift. This is what the bell curve achieves. The elliptical distribution minimises drag for a given span, which says nothing about the lift available. The bell curve also gives you a lighter structure for a given amount of lift. Yes you can brace an elliptical wing for reduced weight, but you can brace a bell wing for an even greater reduction.
Also, the ideal distribution will depend on things like how tightly you want to turn. The inner wing will tend to stall, the outer wing to drag backwards (adverse yaw). Jonathan Bowers at NASA has shown that achieving the bell distribution through significant washout can create negative tip drag and proverse yaw. UK pioneer JW Dunne published as much in 1913. Washout also greatly reduces the problems of tip stalling and Dunne's biplanes proved wholly unstallable.
No doubt computer simulations could help refine the exact optimisation of washout, airfoil variation and span loading for the flight regime envisaged, as they did for Bowers' PRANDTL-D research drones, but it is not going to be far from the classic bell distribution.


How do slats reduce stall speed? I've read in PHAK that slats reduce stall speed, but in what way? Is it because of the increase in surface area?

It's because leading edge devices allow a higher Angle of Attack.

The four types of leading edge devices work by pointing the nose of the wing downwards so that at higher AoA there is no flow separation at the upper surface near the nose. Deflecting the slats does not increase $C_L$, the aeroplane must increase AoA to do that. Lower stall speed comes with the higher $C_{Lmax}$

From this answer, which also contains a graph showing that flaps increase $C_L$ at constant AoA.


What happened during this foggy landing? Several years ago, I was flying from the USA to Buenos Aires. That's a very long flight, and it was overnight for us.  When I woke up it was early in the morning and we were over Argentina.  I don't remember exactly what the plane was, but it was a very large jet. 767 or something like that.

As we got close, the pilot came on the intercom and announced that it was too foggy down below to land, but we still had plenty of fuel reserves left and so he was going to fly in circles for a while and see if the rising sun didn't burn off some of the fog.  After about 15 minutes, he came on again and said that the fog was burning off, and we were about to begin our descent into Buenos Aires.

I was in a window seat, and I looked outside.  We went into a cloud... and never came out.  Literally the first clue I had that we were anywhere near the ground is when I felt the wheels hit the runway.  And to this day I've always wondered what in the world was going on in the cockpit.

I don't care how good the pilot's eyes were; there was zero visibility outside that airplane.  That fog we were in was the metaphorical "pea soup", and he could not possibly have landed visually.  But we came down safe, exactly where we were supposed to be, which means he must have made some sort of instrument-guided landing.  But if he was capable of making a perfect instrument landing at that runway all along, why was the fog reducing visibility ever a concern in the first place?

Does anyone here have enough experience to explain what happened that morning?

I don't care how good the pilot's eyes were; there was zero visibility outside that airplane. That fog we were in was the metaphorical "pea soup", and he could not possibly have landed visually.

What you see from a passenger window has little relationship to what the pilot is looking for and can see out his windshield. The pilot is looking for lead-in lights (there's a lot of them) and a sequence flasher that creates the effect of a ball of light starting at the beginning of the lead-in lights and traveling to the runway. In low visibility the tower will typically turn them up to maximum intensity. These lights are very bright, so much so that after catching sight of them I usually asked for them to be turned down. None of this light system is visible from the passenger cabin of a large aircraft save for the fact that you might notice a glow outside as the airplane passes over them when it's dark.

  the pilot came on the intercom and announced that it was too foggy down below to land, but we still had plenty of fuel reserves left and so he was going to fly in circles for a while and see if the rising sun didn't burn off some of the fog.

Another thing that the pilot can do if he has the fuel and if the sun is about to set, is to loiter until it gets darker. The runway visual range (RVR) will generally increase considerably in the dark.

There are other things at play as well. In patchy and/or blowing fog, what the RVR reads may not accurately reflect what the visibility is anyplace in the runway environment save where the RVR instrumentation is.

Occasionally, local politics can also be a factor. In the 1980s I used to fly into an airport that had as its only air service the commuter airline I was flying for. The local government and chamber of commerce very much wanted to keep that air service. The problem was fog. An unwritten accommodation was reached that took advantage of the rule that once inside the outer marker, you can continue the approach even though the RVR dropped below the minimum required. We knew that if the reported RVR was right at the minimun required when we were cleared for the approach, we might well be told after reporting passing the outer marker that it was a lesser value.

In two years of flying for that commuter, I never failed to land on the first approach at that airport and neither did most of the captains.

I suspect that in today's hypersensitive regulatory environment, this accommodation might not be possible, and I also don't know if the rule is still in force that permits you to continue an approach once inside the outer marker.


F-111 emergency landing with no wheel; what is done to reduce risks when loosing a wheel? There's an interesting incident described here about an F-111 that lost a wheel during take off.

Couple of questions:

What are the relative risks of an ejection vs a no-wheels belly landing. I mean obviously the costly loss of airframe. But is the risk to life pretty even odds?
In a conventional aircraft (e.g. civillian) ejecting is just not an option so belly landings are the norm. But in an F-111  is a belly landing still safer than a controlled, planned ejection?

The film interviews the pilots & they say something to the effect of

"It's good that someone on the ground noticed. Otherwise we'd have tried landing without even knowing that we didn't have a wheel."

Are there no sensors etc. that'd detect they had lost a wheel? Any other indirect indications based on asymmetric drag, hydraulics etc. that one may expect? In other words, how likely is it that one loses a whole wheel but  does not know.

Are there standard procedures where ATC uses binoculars etc. to check visually whether all seems OK with a landing aircraft (wheels etc.) I know they will check on request, but is there any standard protocol?

Don't military airfields lay down foam for emergency landings? Or is there a downside to foam on the runway?

What are the relative risks of an ejection vs a no-wheels belly landing. I mean obviously the costly loss of airframe. But is the risk to life pretty even odds?

  In a conventional aircraft (e.g. civillian) ejecting is just not an option so belly landings are the norm. But in an F-111 is a belly landing still safer than a controlled, planned ejection?

Ejecting is an extremely violent event, often resulting in the pilot being removed from service for an extended time period, or permanently. 1 in 3 suffer back fractures or other major complications. Ejecting is possibly an end-of-career move for pilots (at best, an end-of-life one at worst). Belly landing on the other hand isn't usually a bad event, typically the aircraft is repaired and returned to service. In an ejection, the aircraft is a total loss, not to mention a rather large unguided bomb.

  Are there no sensors etc. that'd detect they had lost a wheel? Any other indirect indications based on asymmetric drag, hydraulics etc. that one may expect? In other words, how likely is it that one loses a whole wheel but does not know.

No, there are no "wheel fell off" sensors. There are possible sensors to tell the pilot of low tire pressure, and certainly have sensors for hydraulic pressure. That isn't to say though that getting a low tire pressure means a wheels-up landing, landing on a flat tire is entirely possible. Drag probably isn't going to be significant, at least not enough to notice outside of gusts or other factors. That being said, having a wheel "fall off" is an extremely rare event, probably so few that you could count them by hand.

  Are there standard procedures where ATC uses binoculars etc. to check visually whether all seems OK with a landing aircraft (wheels etc.) I know they will check on request, but is there any standard protocol?

Not typically, but ATC often watches departing aircraft with binoculars, not necessarily looking for missing parts though. In clear visual conditions, it would probably be pretty apparent that a wheel fell off to people on the ground, at the very least the next departing aircraft who had to avoid it on the runway. Usually when something falls off the aircraft, the runway needs to be closed while they do a FOD (foreign object debris) removal run.

  Don't military airfields lay down foam for emergency landings? Or is there a downside to foam on the runway?

Yes, military airports can lay down AFFF (aqueous film-forming foam) on the runway, but you don't always need to. The down side is that it causes the aircraft to slide quite a bit further than it may be planned, and it's incredibly hard to clean out. If there isn't much of a risk of fire, its better to just belly it down in the grass. Or just let it slide on the runway. Most military aircraft can dump fuel and land without much fire risk.

By the way, if you think it is impressive to belly-land an F-111 after a wheel falls off, you should watch this video about an Israeli pilot who landed an F-15 with one wing!!!.


What is the difference between azimuth and heading? What is the difference between azimuth and heading?

I understand heading, track, radial, course and bearing but I don't know what azimuth is. I rarely hear it used. The Wikipedia definition is a horizontal angle measured clockwise from a north base line or meridian. How does that differ from heading?

Bonus question: when atc tells you there's a plane at your 2 o'clock, is there a word for that?

A heading (in the general case of moving "forward") is the direction your nose is pointed in. This may not be your course (as discussed here).
Headings are measured from onboard a traveling vehicle or object (e.g. from the cockpit of an aircraft or the bridge of a ship at sea).

An azimuth is a bearing, more precisely a compass bearing from a specific point of observation like a radar station. (The "North" used as a reference may be either magnetic or true depending on the system you're working with, but for purposes of this discussion it doesn't matter.)
Often the point of observation is fixed (ground radar, a control tower, an artillery spotter, etc.), though it need not be as long as the observation can be mapped to a compass bearing somehow.

Bonus Answer: The "O'Clock" positions are an informal type of relative bearing as mins noted: The 360-degree circle is broken up into 12 chunks (30 degrees each) for easier scanning, with "12 O'Clock" being directly in front of you and "6 O'Clock" directly behind.

An important caveat to be aware of is that when ATC provides a "clock bearing" for traffic it's relative to the aircraft's course (12 O'Clock is aligned with the aircraft's track over the ground as shown on the radar). Depending on wind there may be considerable variation between your course (direction of travel) and your heading (direction the nose is pointing), so the called traffic may appear in a different location when you look out your window.


What should a pilot do if they feel sleepy? What should a pilot of any large commercial passenger airplane do if they feel sleepy?

What is the maximum time per day during which  the pilot may control the airplane ?

If a pilot is not rested enough to safely operate the aircraft, they should not fly. If a pilot is flying and falling asleep, they should switch out with another pilot or land.

Current FAA regulations for domestic flights generally limit pilots to eight hours of flight time during a 24-hour period.

For the Air Force, actual flight duty periods vary depending on the aircraft type and mission but we are required to get 12 hours of crew rest with the opportunity for 8 hours of uninterrupted rest prior to flying.

You can read the FAA's Fact Sheet on Pilot Flight Time, Rest, and Fatigue here.


If pilots in a A320 or 737 had a dual engine failure, would they add flaps for the landing? Would this not be smart to do because you may come in a little fast, therefore the flaps would send you back up? Or would you absolutely want flaps in this situation

Flaps steepen the descent angle - in other words, you run the risk of falling short of the runway. So in a glide you keep the flaps up until you can be certain of making the landing point. Once the landing is guaranteed, you can then deploy gear as well as flap to slow down as much as possible - being aware that these actions will further reduce the gliding range, so constant reevaluation is required.


What is the impact of camber on CLmax? I was reading Aerodynamics for Engineering Students by Houghton and saw the following graph:

A lot of other sources say that increasing camber increases CLmax, like the graph below.

I am a little confused by what camber actually does to CLmax? An explanation which focuses on the physics would be very helpful!

Camber directly affects the amount of circulation an airfoil can generate, adding camber will always generate a higher zero alpha lift coefficient (intersection of the lift coefficient curve with the x=0 axis) up until a point that there is too much camber to sustain attachment.
This leads directly to the question asked - does camber increase CL_max? For any given AOA, there is an ideal suction side geometry that generates a pressure distribution that is always on the edge of separating. Liebeck defined this ideal shape but only for laminar flow, for which the boundary layer equations are closed form, this was all based on the work of Stratford who came up with the ideal pressure recovery. Having a surface that is about to seperate everywhere can even be true for a symmetrical section at some inclination, although it's not going to look like a NACA 0012/15 or anything familiar. The effect of the pressure surface on the amount of circulation generated, is much more insignificant than the suction surface, but it is not zero. Therefore, a cambered airfoil will make slightly more load at max CL than a symmetric section.
In reality, there is no magic button to increase, decrease camber. Airfoils are complex geometries that cannot be driven by one parameter without affecting everything else. Adding camber by 'bending' the airfoil somewhere near the front of the chord will give some more circulation, but also probably increase the departure angle, and create a risk of separation towards the trailing edge where the pressure recovery is too steep for the boundary layer to cope with.
Unfortunately there is no easy +camber = +max lift coefficient relationship, but for a cambered and non-cambered airfoil designed to operate on that separation limit, the cambered airfoil will generate slightly higher max lift.


Why does the US use two types of aerial refueling? There are two main types of aerial refueling, the boom and the drogue. The US uses both, while most other countries use just the drogue.

How are they different and why does the US use both?

The flying boom method uses a rigid boom which is "flown" by an operator in coordination with the pilot in order to make a connection with a receptacle on the second aircraft. The boom is retracted when not in use. Though it can do damage if it comes in contact with an aircraft, the operator can quickly move the boom if needed.

The probe and drogue method uses a trailing hose with a basket on the end. Pilots will guide a probe on their aircraft into the basket to connect with the hose. The hoses are retracted when not in use. Though the crew has less control of the drogue, which can still cause damage, there is less danger to the aircraft than from a boom, and it could allow the aircraft to stay further away from the tanker.

The boom method was developed early on in the Cold War, when Strategic Air Command had many large bombers that needed to be refueled. They needed a method that would transfer fuel as fast as possible in order to reduce the time it took to transfer the large amounts of fuel needed. Because the boom is rigid, it is capable of a higher transfer rate. The importance of bombers meant that SAC got their way, and the KC-135 fleet was equipped with booms. Today, almost all US Air Force planes capable of aerial refueling use the boom system.

The US Navy on the other hand, along with most aircraft in other countries, uses the drogue system. Though this method is not capable of the high transfer rates of a boom, it is much more flexible. A refueling aircraft may only be fitted with one boom, and this requires extra design work and integration with the fuselage. The drogue system, on the other hand, is more simple, and does not need a dedicated operator. This means that it can be more easily fitted to the refueling aircraft, even other fighter planes, and larger aircraft can have multiple drogues.

Another point is that smaller aircraft such as fighters are not capable of receiving fuel at the full rate the boom provides, so they have less benefit from the system. Although a boom can have a drogue adapter attached, this still commits the tanker to one aircraft at a time and one type of system per flight. Also, aircraft such as helicopters cannot use a boom system.

When the Air Force was looking at a replacement for its tanker fleet in the early 2000s, a study was done to determine what standard the new tanker should support.

The report suggests some options for the best combination of methods. In the end, the Air Force selected the KC-46 for the contract, which will include both the boom and the drogue options for refueling. This will provide better support to aircraft from other branches or countries, while maintaining support of the existing aircraft that use a boom.


How to calculate bending moments and shear forces on a wing? I am trying to create a MATLAB script to plot the Bending Moment Diagram (BMD) and Shear Force Diagram (SFD) as a function of spanwise distance, x, along a wing from the wing root (x=0) to the wingtip (x=b/2).

I will be considering the case where the lift generated by the wing is 2.5 times the weight of the wing (so n=2.5).

The three main forces I plan to consider in this analysis are:
1) The weight of the engine (Point load)
2) The weight of the wing (uniformly distributed load)
3) The lift generated by the wing (bell loading distribution)

My question is this: how can I set up an equation for the bending moment and shear force as a function of spanwise distance, x, despite a non-uniformly distributed load being considered in combination with a point load and a uniformly distributed load?

The classes I have taken at college have only covered BMD and SFD for uniformly distributed loads, so I am a bit confused as to how to go about setting up a numerical model for a non-uniform load.

Thanks a lot.

I would highly recommend to discretize your problem, for two reasons:

You are using Matlab which is most suitable for a discrete approach anyways
More complex load cases will make analytical continuous modelling difficult. This is why these kind of problems are typically solved numerically

So now the question how can we discretly regard this problem? For the wing bending moment, this is pretty straightforward. First of all, lets make a small sketch.

The process of discretization is now to look at equally spaced points of the wing seperated by the distance Δd. I call them discretization points. I have labeled them in the following sketch as a vertical line numbered as 1, 2, 3 ... until point i.

What you need to do now, is to calculate the force acting on each discrete point. This part in turn is divided into two parts:

Calculating the exact shape of the different forces: Therefore force of motor weight, force of the wing structure and as a function of these two, the bell function of the lift
Integrate the wing lift force and structural weight force from discretization point k-1 to point k.

Now you have the exact weight acting on each point k (simply the integration of the wing lift force and the structural weight force from point k-1 to point k). Calculating the bending moment is now straightforward. For example, the bending moment at point i-1 is just the force acting on point i times the distance from point i-1 to i:
$$ M_{i-1} = i \cdot \Delta d \cdot F_i $$
the bending moment at point i-2 is now therefore:
$$M_{i-2} = 2*\Delta d \cdot F_i + \Delta d \cdot F_{i-1}$$
and so forth and so on.
The shear force at these points is even simpler. It is just the sum of all forces at the different outboard. So for example at point i-2:
$$ F_{i-2} = F_i + F_{i-1} $$
You can see that this type of equations can be easily programmed in Matlab. If you program this a bit cleverly, you can even play around with different values of Δd, which enables you to see the effects of discretization.
Hope this helps. If you need more help with the code, feel free to ask.


Where do most fighter jets and combat aircraft mostly get shot? ex: body, wings, engine area etc I'm wondering where fighter jets mostly get shot. I'm trying to design a plane that might help this issue if most planes get shot in the wings. If they get shot elsewhere I guess I'm going to have to come up with new ideas.

It all depends on the types of weapons employed, the aspect of the attacking and defending aircraft and the off-boresight angle between the aircraft in question.

Air to air and surface to air missiles employ proximity fused HE Blast / rod or pellet fragmentation warheads in them.  They are guided to close proximity with the target aircraft and explode like hand grenades, spraying the targets with shrapnel, damaging structure, engines, fuel and hydraulic lines, even the pilot.  Sites of damage depend on the angle of missile impact as well as the proximity of the target within the lethal blast radius of the warhead and thus how concentrated the spread of the shrapnel pattern is.

Air to air gunnery is much more akin to bird hunting with a shotgun and less like modern guided weapons.  The most effective air to air gun systems against fighters tend to be smaller caliber weapons with high rates of fire and high muzzle velocities resulting in flat ballistic trajectories with good range.  The ideal gun kill is maneuvering up on the target's six o'clock and pumping rounds into the aft fuselage and engines.  High angle off kills can also be accomplished by leading on your target, then firing a burst which the target then flies through and gets peppered with rounds, again similar to hunting flying water fowl.  In an off angle shot the burst will be widespread over the dorsal surfaces of the fuselage and wings.


Is there an ideal air temperature for best performance in a light aircraft? I know cold air is better for engine performance in general, colder air is also denser making lift components stronger(from what I understand).

I was just wondering if there is a temperature or a range of temperatures that offer the best performance overall?

Is there a temp that covers all areas such as takeoff/climb performance, cruise etc. or is it something where each performance area has its own "sweet" spot?

Let's use common flight trainers like the C172 as the example.

Good Evening Alex,
just for the record I'm a Private Pilot with about 150 hours of flight time, I would recommend speaking to a Flight instructor if you have any more questions about Aircraft POF. (principles of flight and performance)

Best Performance can be narrow down to a simple formula
Best Performance = High Pressure + Low Temperatures

1 hectopascal is equal to 30ft change
1º celsius is equal to a 120ft change  br>

If you are looking for the landing and T/O I would suggest looking a Performance charts-which


Do some helicopters require classes, type ratings, or special endorsements, the way some airplanes do? I've been looking online for the different ratings and classes of helicopters but I can't find much.

For example in fixed wing aircraft you have retractable gear, constant speed propeller, IFR, multi-engine, tricycle gear, etc.

I am curious to know what the helicopter equivalents are. What does a basic helicopter rating allow you to fly? What comes after that?

I can't see a connection between "classes" of helicopters and ratings.

You also don't specify which jurisdiction so I will answer for the UK CAA which I know.

To fly any helicopter under VFR needs nothing more than your license, gained on any type, and a type rating for the specific aircraft.

For example, I gained my license on the R22.  I am therefore also type rated on it.  The second aircraft I learned to fly was the B206 which is jet powered.  I didn't need anything extra than the appropriate type rating.

I can fly any helicopter for which I am rated under VFR.  If I had an IFR certification, I could fly any helicopter I am rated for under VFR, and any IFR certified helicopter for which I am rated under IFR.

"Difference training" is simply part of the the type rating.  For example, if I ever learned to fly a craft with a retractable undercarriage, I would be rated to fly that type, but not another type with retractable gear.

What does differ is the type of license, e.g. CPL or ATP.  I would need that license in order to carry passengers for hire and to conduct other commercial operations, but I still need a type rating on whatever helicopter I use to carry those passengers.

Put it this way, the day after I gained my license, I could climb into any helicopter and act as pilot under training.

Hope that's all clear!


What are the consequences of attaching an unused extra engine under Boeing 747 wing? It turns out Boeing 747 can carry an extra engine under its left wing in case there's need to transport an engine somewhere far away. The engine is attached between the body and the left inner engine and isn't operational during such flight.

What implications does that have on the airplane operation? I guess drag is increased notably and also drag increases only for left wing and so the plane should tend to well, turn left in case engine thrust is equal on both sides of the plane so now engines under right wing have to produce more thrust or something like that. Also the engine weighs quite a lot so less cargo may be put into the plane. Also fuel consumption increases and flight range decreases accordingly.

Is that all? What are the consequences of attaching an extra engine under Boeing 747 wing?

Operationally you would be more restricted in terms of trimming. Back when we had manual loadsheets there would be a demarcated area '5th pod operations limit'. Only the gods of the loadsheet deptartment would be allowed to do the loadsheet for these flights. I think Qantas would put a loadsheet man on board for these flights but I could be mistaken.

The flight would be re-timed as the usual 90 minute turnaround time would not be sufficient. I believe 2 hours on top of the regular turn was the norm.

An additional fuel stop was usually required as the fuel-burn was atrocious with that big thing hanging off. The weight penalty was compensated by reducing cargo.

I was working in Singapore in the 80s and we usually had Qantas doing this a few times a year. The engines were ex-SIN .. I don't know if they were overhauled in SIN or if they came into SIN on another freighter. At the time there were not many B747 freighters operating into Australia. I believe Flying Tigers had one but that was from US to Australia to SIN.. It did not do SIN-Australia.


What does "maximum update interval" mean for Mode S GICB registers? Transponders have registers for Mode S data and configuration. These registers are updated periodically to provide Mode S services such as ADS-B Airborne Position squitter.

DO-260B and similar documents have Register Allocation Tables that states maximum update intervals for each register(if applicable).

But there is also a register timeout mechanism that states "if a register can not be updated within twice the maximum update interval, it shall be zeroized".

So, what happens if certain register is updated at every (1.5 * maxUpdateInterval) ? Are these maximum update times mere suggestions or is there another rule that forces us to update registers at most maximum update interval?

If you update the register, the values will be set to the values provided.
From that moment, a timer starts running. When the timer reaches 2 * maxUpdateInterval, the register will be set to all zero.

If a radar extracts the register before the 2 * maxUpdateInterval is reached, it will get the values provided at the update. If it will extract the register after 2 * maxUpdateInterval is reached, it will get all zeros in the reply.

For ADS-B, transmission of the register is inhibited (IIRC) when the register is set to all zeros.


Is the nose cone of the MiG-21 adjustable in-flight? In some of the photos I saw of the MiG-21, the nose cone was extended and in others it was shortened. So, is the nose cone of the MiG-21 adjustable in-flight to allow for increased/decreased air flow?

I noticed on a video yesterday from another question regarding the nose cone of the MiG that the SR-71's engine cones are adjustable, so that led me to believe the MiG's might be as well, though nobody mentioned it specifically in that particular question.

Yes, it moves forward as the speed increases. Its purpose is "to slow the flow of air from supersonic flight speed to a subsonic speed before it enters the engine."
From Wikipedia:

The air flow to the engine is regulated by an inlet cone in the air intake. On early model MiG-21s, the cone has three positions. For speeds up to Mach 1.5 the cone is fully retracted to the maximum aft position. For speeds between Mach 1.5 and Mach 1.9 the cone moves to the middle position. For speeds higher than Mach 1.9 the cone moves to the maximum forward position.
On the later model MiG-21PF, the intake cone moves to a position based on the actual speed. The cone position for a given speed is calculated by the UVD-2M system using air pressures from in front and behind the compressor of the engine. On both sides of the nose there are gills to supply the engine with more air while on the ground and during takeoff.

You can watch it move on YouTube.
(Source) The aforementioned gills.

Related: What are the merits of an inlet cone/spike/centerbody vs. a 2D inlet?


What is this airstrip in Mali? While randomly browsing on Google Earth and Bing Maps I found an airstrip in Mali.
Normally you assume a small village/mining site in the vicinity of the airport but other than the ruins of a supposed old settlement nearby I could not find anything.
Does anyone know the name of the airfield or any info why it is there? On Google Maps there is an image attached with an airplane (Beech King Air maybe) but not convinced it was taken there.

This seems to be the "Assedreme airport and seismic camp", according to Openstreetmap. Aviation Africa has a picture.

This is most likely a now disused airstrip for a base camp for seismic oil and gas exploration. Seismic exploration is a technique for searching for oil and gas deposits by measuring the reflection of artificial seismic waves (simple introduction at oilandgaslawyerblog.com).

The airstrip seems to have been built in 1985, expanded in 2008, and then abandoned. This fits pretty well with an article describing exploration in Mali, which states that lots of seismic exploration was carried out in Mali in the 70's and 80's, with renewed interest in the 2000's.

As J Walters pointed out in a comment Algerian exploration company ENAGEO mentions using this airstrip for its operations in a presentation from 2009.


When were civilian aircraft first directed between aerodromes by air traffic control? I feel fairly certain that when the Wright brothers flew, they did not need to contact air traffic control for clearances.

These days, it isn't uncommon for the entirety of a flight to be under ATC control, from before leaving the departure gate to after landing. Even flights in uncontrolled airspace can make use of services provided by ATC.

Ignoring early departure and late approach and landing, and instead focusing on the en-route or cruise part of flight, when was the first time civilian aircraft were directed or guided from one aerodrome to another by air traffic control (or perhaps rather, what would later evolve into modern ATC; I doubt it was called "air traffic control" at the time) in a manner similar to today's? Where in the world did this take place?

In 1920, Croydon Airport, London was the first airport in the world to introduce air traffic control.

In the United States, air traffic control developed three divisions. The first of air mail radio station was created in 1922 after World War I when the U.S. Post Office began using techniques developed by the Army to direct and track the movements of reconnaissance aircraft.

In 1930, the first radio-equipped control tower in the United States began operating at the Cleveland Municipal Airport.

(Source)


Why runway 13L/31R of JFK Airport does not mention any Threshold Crossing Glide Path Height for its reciprocal end? I am studying FAA's airports legacy file and its corresponding layout data. I noticed that runway 13L/31R of JFK Airport lacks a Threshold Crossing Glide Path Height, as one can also confirm from this site. Is there any "standard" value that one can apply here? Neither the official aforementioned legacy file nor any relevant website mention a Visual Glide Path Angle either.
In comparison, runway's base end mentions both a Threshold Crossing Glide Path Height (74' AGL) and a Visual Glide Path Angle (3.00 degrees).

I would be grateful if someone could point me in the right direction.

That information is shown on the approach plates

It appears that 31R is not equipped with a VGSI. At least not that I can find. That would be why the data is missing.

On 13L the GS and VGSI are both 3°, but since the VGSI is located about 300ft further down the runway than the GS antenna the TCH is higher.


How do you perform a gear-up landing in a large airliner? How do you perform a gear-up landing in a large airliner (say, a Boeing 747)?  Would you fly it like a normal landing, or are there special considerations (angle of touchdown, use/non-use of thrust reversers, etc.)?

Assuming that the pilots have tried everything possible and the gear just does not like to come down:

The general rule is to find a long runway, touch down as slow as possible. Here are sections extracted from Boeing 777's Flight Crew Training Manual:

Dumping fuel

  If time and conditions permit, reduce weight as much as possible by burning off or jettisoning fuel to attain the slowest possible touchdown speed.

Elevator

  After touchdown lower the nose gently before losing elevator effectiveness.

Rudder

  At touchdown speed, the rudder has sufficient authority to provide directional control in most configurations.

Speedbrakes

  (...) speedbrakes should be extended only when stopping distance is critical. Extending the speedbrakes (...) may compromise controllability of the airplane.

Reverse Thrust

  (...) an engine making ground contact could suffer sufficient damage such that the reverse mechanism may not operate. Selecting reverse thrust (...) may produce an additional asymmetric condition that makes directional control more difficult. Reverse thrust should be used only when stopping distance is critical.

Landing technique

The technique varies with the combination of failure. If one side of the main gears is missing, land the plane to the side of runway which corresponds to the extended main gear. I.e. if the left gear is down and right gear is up, land on the left side of the runway instead of centerline. Maintain wings level for as long as possible, and be prepared to brake on the left side to maintain directional control.

If all the gears decide to hide in the gears bay, land on centerline and use rudder to maintain directional control. Rudder is effective until airspeed drops too low.

After landing

Evacuate the aircraft as necessary!


Do real aircraft have something close to the GPS/NAV modes in FSX? I am a long-time flight simulator player and also very interested in aviation. In FSX, all aircraft have a GPS/NAV knob which allows the pilot to switch between direct GPS autopilot and VOR navigation Autopilot. However, when I look at the main panel of a real Boeing cockpit, I don't see a GPS knob but I do see NAV V and NAV L buttons.

I know what NAV V and NAV L are (V for vertical autopilot, and L is the same as the NAV mode in FSX that keeps the plane on course), but do real aircraft (specially Boeing) have any function to keep the aircraft automatically on course and direct it toward the destination without using a VOR? Something that works very much like the GPS mode in FSX?

And in FSX I have to manually set the VOR frequency based on the navigation chart, in real life do the pilots have to do the same, or do they have some more advanced features?

In the Boeing world, LNAV is Lateral Navigation, and VNAV is Vertical Navigation.

When LNAV is engaged, the autopilot will follow the Flight Management Computer (FMC) guidance laterally, i.e. left & right.  When VNAV is engaged, the autopilot will follow the FMC guidance vertically, i.e. climbs & descents.

LNAV is conceptually pretty simple: you have a magenta line on the map, your desired course, and the autopilot will follow it.  The points defining your course are database points in the FMC that may but certainly do not have to correspond with VOR's or other conventional NavAids.  You can use LNAV to fly VOR-to-VOR, or it can fly point-to-point-to-point equally easily.  (You don't have to tune any frequencies in either case.)

VNAV is a little more complicated, because you may only be cleared for some of what the FMC wants to do vertically.  Simple example: you're cruising at FL370, planning to start down at a given point so as to cross AAA at FL240, and then continue the descent to cross BBB and 10,000' and 250 knots.  ATC clears you to "descend at pilot discretion, maintain FL 290."  That means you can start down at whatever point you want, but until you get cleared lower later on, you can't descend all the way to FL240 or 10,000.  Yet.  Or maybe the controller needs to put you at FL350 right now to avoid a traffic conflict 100 miles ahead, and your clearance is "descend now and maintain FL350, pilot discretion FL290."

It's a lengthy section of Ground School how the pilot sets up the FMC and the mode control panel to accomplish all of this, but hopefully that illustrates some of the complexity of VNAV.

It's a good system; under typical conditions you can go into LNAV and VNAV shortly after takeoff and stay in them both until shortly before landing, and the FMC gives you smooth (mostly) and efficient guidance.


How do you repair a grounded aircraft at a remote location? If a large passenger airliner needs repair at a remote airport without services, are there "flying repairshops" that can swoop in and do the work on site?

If you can, you'll fly in maintance yourself to get it fixed, perhaps by chartering a cargo plane on the way. If you can land the aircraft, you can probably get any spare part in through the same runway, with varying degrees of difficulty.

If it's bad, Boeing has an Aircraft On Ground team who should be able to fix pretty serious damage. Often, it may just be patched up until it's good enough to fly to get it to a place with better facilities.


Is the KC-135 landing gear life limited? I'm looking for information about the KC-135 landing gear. Specifically I want to know if its life limited and if so where is it documented? If its NOT life limited where is that documented? I'm talking about gear that has regularly been maintained or gear that's been overhauled. I've been looking on the internet and a variety of 135 manuals.

All landing gears have a limited lifespan unless they undertake in really, really big maintenance, as we saw with the Antonov 225, which went under maintenance for 18 months! And the KC-135 is no exception. Most landing gears last about 20 years, and the one's of the KC-135's is designed for 30 years. But even though it was designed for only 30 years, the operators of the KC-135 still extend it's life by a lot, with as you said, regular maintenance. So, you might see some KC-135 landing gears that are 40 years old!

Aging landing gear life extension
The committee is concerned that the Air Force has been extending the use of aircraft landing gear far beyond their original design life. The KC-135 was designed for a 30-year lifetime, but will retire at 86 years and the B-52, designed for a 30-year life, will retire at 94 years.

Source: congress.gov


Is there's any risk using modern C++ compiler on DAL A Display Application Flight Software? I am C++ enthusiast and I like to design and architecture my software with latest C++ features specially with templates,  but I have been struggling hard to find a way.
The compiler we use for LynxOS-DO178 RTOS with PowerPC architecture is more than decade old, with poor optimization, lack of several features, and often times just ending up in "internal compiler error". Code bloating occurs with simple template instantiations, which could be easily remove with latest compilers.
All ideas and innovative improvements are simply stopped by the fact that our compiler cannot support this and that.
I believe I could get a tool chain for my cross-platform development supporting somewhat latest versions of GNU GCC/G++. But not sure if that can be ever certified for DAL A SW.
We have now C++14, approaching to C++17, still I have this question do we have anything modern yet from C++ that sees "light of sun" on a critical SW ?
What are the risks, cons, etc for a flight critical SW ?
Bjarne Stroustrup recently announced core C++ guidelines, that resolves around use of modern C++11/14 and templates, but can we ever use those on Flight DAL A SW ?
Not sure if this a right platform to discuss this, if someone knows a better platform please direct me to that.

The issue with many things in flight safety is that the status quo is well understood. Changing something introduces a whole body of unknowns, and considerable circumspection will be applied by the people charged with ensuring safety. This is why piston engines in many light planes are almost identical to those used half a century ago - they're known to work - and why there is considerable inertia when it comes to updating your software tools.

Ultimately, the only way things are likely to move is when somebody builds a case for updating the tools that shows sufficient commercial benefit to overcome the additional cost of certifying the final product.

It won't be enough to simply argue that a new compiler has this or that set of new features. You'll need to demonstrate that using the new compiler will allow you to provide a set of new features that you can't provide with the old one, and that this will lead to a tangible increase in sales.

Good luck!


Do airlines prefer younger pilots after a cpl? I am currently 26, female and making financial arrangements to pursue a cpl after 2 years. The location probably will be Canada or USA. I am wondering if 29 is too late for commercial airlines. Do the airlines prefer younger pilots? Is there a max age limit for commercial airlines?
Thanks for the help.
Cheers,
Litali

29 is not too late for them. It might be too late for you, depending on where you are in your life now.

First off, a CPL won't cut it to fly for most Part 121 or Part 135 outfits, including major airlines, cargo haulers etc. As of 2013, the requirements to get on the flight deck of a commercial airliner include an ATPL, which requires a minimum of 1500 hours (1000 if you attend a four-year flight school).

A CPL, with instrument rating and an endorsement to ferry passengers for hire, would allow you to fly for a company like NetJets, or for a corporate or government jet fleet, though you'll face stiff competition for those jobs; they're fairly cushy and well-paid for the required experience, and you'll find a lot of ex-military and ex-airline pilots beating down the door. You'd also be able to fly foreign-registered aircraft for a non-US airline, as long as the jurisdiction hasn't adopted a similar rule as the FAA's.

When you get your ATPL, with only the 1500 hours and no other airline experience, you'll likely land your first gig as First Officer on a regional route. This is your toehold into a career in flying, and to be perfectly honest if you don't absolutely love to fly I would tell you to do anything else, especially if you've already started a life (married, kids, mortgage). The average starting salary for a regional FO is about \$22,500 per year, which for a 40 hour work week is a meager \$10.75 an hour. You would literally make more working full-time as a barista in Sea-Tac Airport serving coffee to the pilots than flying the puddle-jump between there and Portland. And that's just the average; you can expect half the currently flying pilots with less than 1 year experience to make less than that. You are virtually guaranteed to make more money doing anything else that requires more than a high school diploma.

It gets better, but it takes a career to do it. Senior captains flying the big widebodies on major transcontinental and intercontinental routes make six figures, in excess of \$175k in some cases. Most of this is the airlines trying to retain their most experienced pilots for just a little longer by giving them the most profitable routes for which they can pay the pilots more. The other part is making up for the peanuts they pay you in your early years.

For the majority of your career, your entire life will fit in a carryon and/or a garment bag; flying regionals, you'll make the same flight five to ten times a day and have a good chance to get back to your home city, but on regional pay you'll be hard-pressed to afford more than a single-bedroom flat. As your experience grows, your promotions will naturally lead to longer flights on bigger jets, with the best-paying routes being intercontinental flights where you'll sleep on the plane two nights out of three. Many pilots have month-to-month arrangements with their landlords to rent a single room to crash in and store anything that doesn't fit in their flight bag. This will be your life for 20-30 years.

It is extremely common for newly retired pilots and their spouses to invest in a "pilot's house"; while most retirees are downsizing from the house they raised kids in, most pilots are finally able to settle down in one location for the first time in their lives, and are buying McMansions in cash at about that same age, with savings from the last few years of their flying career.

All in all, flying sounds like a glamorous, "see the world" job, but you have to be sure you can live with the downsides. Your spouse will essentially be a single parent (if you have kids), you'll be living in a small apartment for most of your life and will move several times, requiring your spouse to have a career that allows easy relocation, and you might only be home every other day if not less often, depending on the airline's scheduling model; it's fairly common especially among LCCs to run "end-to-end" routes instead of "hub and spoke", and that could mean you'll start in New York, run hops through Chicago, Atlanta and Dallas with your eight hours allowable flight time per day, then sleep in Dallas and fly the reverse route the next day back to New York.

Just to make a direct comparison, my wife has a cosmetology license (haircuts, nails, spa treatments) in Texas. To get that license required a 2-year course of study and 1500 hours total instruction and guided practice. Her first year with that license, she made about $33000, almost 50% more than a first-year airline pilot. The economics of the airline industry (and the regulations in the cosmetology industry) are bass-ackwards.


Can a Boeing 777 be hacked? All this confusion over flight 370 has me wondering if it would be possible to hack into an airplane and control the autopilot or other on-board systems in a way that the pilots couldn't regain control.

I know some basic searching reveals some articles such as this one. If the plane can't be hacked, could someone with the proper knowledge snip or disable the pilot's override?

Disclaimer: I know 0 about aviation, but I am a programmer. So my guess would be that anything that doesn't have a physical disconnect would be vulnerable to being hacked without being able to override it.

Additional Disclaimer: This is a question about curiousity / possibility, not a how-to.

As of currently, the answer to this question is in principle no for commercial aircraft, at least not remotely. There are two parts to this:

From a system perspective:

Aircraft systems could probably be 'hacked'- assuming you could for instance screw up the flight computer by changing the chips in the belly- but there is no way you could really pull this off without the pilots noticing the course being way off from the compass for instance, so they'd figure out and shut it off. Many systems are not connected in a way that allows them to be cause damage to others. Systems are also pretty dedicated- if it's supposed to fly the plane, that's what it does, if it's supposed to navigate, that's what it does.
Systems on aircraft generally a have limited, if any, connection to the outside world. There are a few systems that have the ability to connect to the ground, and this is generally limited to simple text messages. Most of the electronics on the 777 are from the type's introduction in 1994. A decent analogy I think is trying to hack an early cell phone remotely.

And from a practical standpoint:

Aircraft are generally very stiff when it comes to changes- they are often approved in a certain configuration, and that then sticks, so there's little need to change stuff, and hence it's not possible. This applies to the autopilot and flight controls- once it's there, it stays there.
As a few people have pointed out, these systems are proprietary and closed source, making it difficult to program them if you're an outsider, but in theory it might be possible.

The fact that no aircraft, even the computer-intensive Airbus, have really been hacked to any extent, the notion that the entire aircraft would be taken over and flown somewhere is impossible.

As for original question link:

  “The FAA has determined that the hacking technique described during a
  recent computer security conference does not pose a flight safety
  concern because it does not work on certified flight hardware,” he
  said.

  “The described technique cannot engage or control the aircraft’s
  autopilot system using the FMS or prevent a pilot from overriding the
  autopilot,” said Dorr.

  “Therefore, a hacker cannot obtain ‘full control of an aircraft,’ as
  the technology consultant has claimed,” said Dorr.

On a similar accord, I think I heard a story about a Bombardier Dash 8 that got a computer virus once, but I think it never got beyond the navigation system, the most processing intensive part. Unfortunately, I can't find a source for this.


Is there always a stall if you exceed a specific angle of attack? So lets consider that the stall angle (=Cl max) of a B747 is at 16° (in clean configuration). Does this mean, that, at whatever speed you are flying (i.e. 500 knots), you would stall if you go on a climb angle of more than 16°? So there is no need to always reduce the speed to the stall speed (which might lie at around 150 knots...).
I am just wondering, since, if you fly in the microsoft flight simulator with a big jet, you can have an angle of attack of 30° and more, and not stall until you get to the stall speed.

Is there always a stall if you exceed a specific angle of attack?

Yes, stall depends only on angle of attack. However

  Does this mean, that, at whatever speed you are flying (i.e. 500 knots), you would stall if you go on a climb angle of more than 16°?

No. Climb angle and angle of attack are completely different things.

This image from How It Flies shows the four different angles involved. Pitch is the angle between aircraft floor and horizontal, wing incidence is angle between aircraft floor and wing¹, angle of climb is angle between direction of flight (a.k.a “flight path” or “relative wind”) and horizontal and finally angle of attack is angle between direction of flight and wing.

The image shows that angle of attack + angle of climb = pitch + wing incidence.

Up to stall, lift depends approximately linearly on angle of attack and square of speed (and on air density). In straight flight the forces on the aircraft need to be balanced, so angle of attack will be such that they are. If you increase pitch, the angle of attack will increase, which will cause unbalanced force, which will cause upward acceleration and that will increase the climb angle at the expense of the angle of attack again.

So if you go on a climb more than 16°, the angle of attack will not significantly differ from what it is when you fly level at the same speed.

  I am just wondering, since, if you fly in the microsoft flight simulator with a big jet, you can have an angle of attack of 30° and more, and not stall until you get to the stall speed.

No, you can't. You, however, can climb at 30° or more, for a while before you run out of speed. Which at low altitude is actually quite long; the jet engines are designed to have enough power at high altitudes where air is much thinner and to allow taking off when one engine fails late in the take-off roll. Therefore low with all engines operating at full power you have quite a bit of extra thrust available.

Also note, that stall does not mean loss of all lift. You only loose part of it. A significant part, but not all. Stalled aircraft is still controllable (though ailerons effect is reversed) and some aircraft (though this would be fighters, not airliners like 747) may even have enough lift and thrust to maintain altitude when stalled.

¹ Specifically, the zero-lift line of the wing. This coincides with the chord of symmetric wings, but cambered wings have it tilted up.


Why do forward-swept winged fighters have the main wings in the back? These are the only 2 fighter jets I know of with forward-swept wings. (Su-47 and X-29, they're both still experimental). As you can see, they both have their wings in the back, not the middle.

Why is this? To me it seems like those wings in the far rear place the center of lift very aft, meaning a constant nose-down torque.

Is there something precluding a conventional-tailed aircraft with forward-swept wings?

These are just two canards with forward-swept wings. There is no general rule that the wing has to be in the back once it is swept forward. In both particular cases the configuration was selected to achieve the highest degree of agility possible. If you command a pitch-up in a conventional configuration, you first need to decrease lift in order to achieve your eventual goal to increase lift. In a canard, however, a pitch-up command achieves a lift increase immediately.

To prove my point that conventional configurations can also be forward-swept, here a few examples:

The first big forward swept aircraft, the Junkers 287 research airplane (picture source). The odd engine placement was the result of optimizing the cross section distribution for transsonic flight (what is today called area ruling). The white spots are pieces of sticky tape to attach wool tufts for flow visualization, and the canisters below the wing engines are rockets to shorten the take-off run. The aerodynamically shaped canister on the tripod right ahead of the vertical tail houses a film camera for tuft observation in flight.

Here is a real oddity: The Akaflieg Berlin B11 forward-swept tailless glider (picture source). It was never completed because the center of gravity turned out to be too far back. Also, the stall characteristics would have been - how should I say - interesting.

Most two-seater gliders use a slight amount of forward sweep to place the rear pilot at the center of gravity, so the plane can be flown by a single pilot without the need of adding ballast.

The HFB-320 Hansa Jet was more successful, and here the forward sweep was selected to keep the cabin free of the wing spar (picture: Eric Tammer / source: PlanePictures.Net). However this configuration was not trouble-free, either.


How does the idle speed adjustment in a Stromberg NA-R9B float-type carburetor work? What is the purpose of the idle speed adjustment in a Stromberg NA-R9B float-type carburetor? In what situation do we adjust the idle speed?

The idle speed adjustment in any engine is to control the minimum RPM that an engine reaches, in other words how quickly it will run with the throttle all the way off. You want the idle speed to be high enough that the engine will not stop running when the throttle is pulled back, but not so high that it wastes fuel. On a carbureted engine the idle speed is typically adjusted using a set screw which allows a mechanic to quickly adjust the idle speed. This would be done when the airplane is serviced as part of its regular maintenance, or out of the service cycle if there's a reported problem.

The idle speed adjustment is unrelated to the mixture control and is not adjustable in flight.


Why did flight NH175 divert back to Los Angeles? In the news recently is All Nippon Airways flight NH175, which returned to LAX after four hours towards NRT when it was discovered that a passenger aboard did not have the correct ticket, although his ticket was nevertheless to Tokyo. Two points immediately come to mind:

If a security issue was suspected, why did they not immediately begin diverting to the closest available airport that could accommodate a 777?
If there was no security issue, why did they not simply continue to Tokyo?

Perhaps another way to state the overall question is to ask why ANA protocol necessitates a return to the originating airport in this case.

You're already aware that the flight crew followed ANA's security protocol.
Yes the flight was closer to PANC, for example. Approximate location based on average ground speed and time it took to return to KLAX is shown below (to make sure there weren't any map projection antics).
(gcmap.com)
Security protocols are not public, but we can deduce from the timeline of the events what had happened.
The cabin crew became aware first (not the airline ops), which means the passenger was likely to be the one to bring the issue to them. Boarding a different painted airplane nowadays than the one on the ticket is no biggie with code-sharing and whatnot, honest mistake.
"While" on the way back, the airline ops discovered it was a mistake, when exactly, no reporter says. Maybe it was soon after.
Let's flip the question.
Why not KLAX?

Does this passenger have their [perhaps suspicious] checked-in luggage on board? Probably not.
Can we search them and their carry-ons? Yes.
Did they come forward? Possibly.
Do we have handcuffs on board? Yes.
Can we overpower this one person? Yes.
Are we willing to arrange (logistics) for their accommodation and ticket back to KLAX? No.
Do we have different flight and cabin crews to takeover the plane in PANC if needed (duty hours)? Hard to arrange.

How about arranging for the whole plane accommodation until said crew arrives? Harder to arrange.

Then proceed with protocol. Reacting and overreacting are different. In conclusion, there was no rush to quickly get rid of the passenger.

Addendum: Here by coincidence Alaska is also part of the US, a different route means you're going to burden another country with unneeded trouble, and as the police confirmed, there was no security risk (while the plane was headed back).


Why was the A340 developed with four engines? The predecessor to the A340 program begun in 1982, when Airbus released the first specification of the designated TA9 and TA11 programmes and in 1986 the TA9/TA11 programmes were officially launched as the A330 and A340 development programmes.
By 1986 Airbus, with their 310 aircrafts, as well as Boeing, with their 757/767 aircrafts, already had twin-jets flying under the ETOPS90 and ETOPS120 rule, introduced in 1985.
Meanwhile Boeing presented the predecessor to the 777 programme, the 767-X ("enlarged" 767) in 1986, but due to customer demand launched the clean sheet 777 twin-jet programme in 1988.

Reading up on that history, I wonder why Airbus did not opt to redesign the A340 with two engines, rather than four.
I judge, that by the mid-80ies, the feasability of two engines for a widebody long-range aircraft with more than 300 passenger was already clear. The loosened ETOPS rules meant, that even regulators were paving the way for such an aircraft.

What was to rationale of Airbus to develop the A340 into a four-engine airliner, while at the same time, Boeing was developing the 777 as a two-engine airliner?

EDIT:
I found another question and answer, which states that ETOPS was the reason. But ETOPS rules were introduced in 1985, while A340 development programme was launched in 1986. So Airbus made a decision despite being ETOPS already in place.

Hindsight is 20/20.

At that time, nobody could be sure the ETOPS rule would be extended the way it eventually was. The 1985 extension was a gift from the FAA to Boeing, so US carriers could use the Boeing 767 for transatlantic services. The 1989 extension to 180 minutes allowed them to cover all domestic routes with a single type when before they needed three-engined types (TriStar and DC-10) to fly to Hawaii.

Not everyone at that time was in favor of introducing ETOPS: McDonnel-Douglas said in 1984:

  ETOPS "represents a 'totally new risk' that the industry has a limited capability to offset."

and

  "… the possible adverse consequences of premature extension of the operating limits can never be balanced by economic gain."

Especially Lufthansa had been sceptical of using two engines for long range and was a driver for the A340 development. Also, Airbus had experienced FAA chicanery before (remember that the A300 was banned for a while because of its slightly higher ground pressure loads). Airbus simply assumed that this kind of chicanery would be repeated when they went with a two-engined long range version.

That only changed when Boeing introduced the 777. Now Boeing was pressing for an ETOPS extension ("early ETOPS") and the FAA duly obliged. But that was in 1995, a full decade later and after Boeing had done extensive ground and in-flight testing, including running engines for a quarter of a million hours. ironically, the positive experience with the A320 in its first two years of operation helped to convince the sceptics of the merits of early ETOPS.


Is 'cost sharing' different between jet and prop powered aircraft? I half remember, sometime in the past, there were different costs in turbine powered aircraft that were allowed to be put into the bucket for cost sharing.

Do I remember correctly or incorrectly?

If this a correct memory, what are the additional shareable costs in a turbine powered aircraft?

addendum:  My ancient brain has come up with some vague answers.

IE, the hourly payments for engine and airframe maintenance.  This was comparable to rental cost, but because  it is a defined amount in a turbine totally owned by the pilot, it was quantifiable.

I give up.  I have searched and can find no reference in the FARs concerning this question - just the current one about pr0-rate sharing that we all know and love.

Perhaps the 91F and 91K parts have replaced the vaguely remembered item from the 1980s.

Thank you for the opportunity to ask.


In what circumstances could a 787 stay powered on continuously for 248 days? The FAA has issued an airworthiness directive for the 787:

  SUMMARY: We are adopting a new airworthiness directive (AD) for all
  The Boeing Company Model 787 airplanes. This AD requires a repetitive
  maintenance task for electrical power deactivation on Model 787
  airplanes. This AD was prompted by the determination that a Model 787
  airplane that has been powered continuously for 248 days can lose all
  alternating current (AC) electrical power due to the generator control
  units (GCUs) simultaneously going into failsafe mode. This condition
  is caused by a software counter internal to the GCUs that will
  overflow after 248 days of continuous power. We are issuing this AD to
  prevent loss of all AC electrical power, which could result in loss of
  control of the airplane.

I'm curious: Are there any circumstances under which a 787 would remain powered continuously for 248 days?

[Edited to add a follow-on question:]

Boeing has said "If there is a definitive record of a powercycle within the last 120 days, no operator action is immediately required."  Does that happen? 120 days?

What is the longest period a passenger aircraft might conceivably be continuously powered on?

Aircrews seldom have to power off an aircraft completely (also known as a cold and dark cockpit). Airliners usually stay powered on at the gate. This is known as a "short turn-around": engines are stopped, the APU is stopped, but electrical power and air conditioning is still supplied by ground equipment.

This has the advantage of minimizing turn-around time (after all, airliners are meant to stay in the air to make money). The cabin also has to be cleaned and prepared for the next flight at this time, so something must power the lights.

It is theoretically possible to stay on this way for 248 days. However, airliners have scheduled maintenance, which completely powers off the aircraft. They are also powered off if the expected time at the gate is long. So, in reality, it's very unlikely to have an airliner powered continuously for 248 days.


What are those bumps on top of the Antonov-225? What are those bumps on top of the Antonov-225? What are they for? And what are they called?

According to the Airliners.net forum, they are fairings that cover hardpoints used for attaching outsize loads.

  Outsize loads that cannot fit into the capacious cabin (including Buran and Energiya components) are carried 'piggyback', the load supported on two main attachments above the center section. These supports and other smaller ones along the fuselage top are faired over when not in use.

The text is quoted from aeronautics.ru (web archive link).

Please note that the two large ones were not used for carrying the Buran space shuttle, as shown in the photo posted below. (More pictures here.)


How is a type rating administered for aircraft that do not comply with 91.109? Let's say you have a demilitarized A-10 (this isn't too farfetched an idea, as this SDSM&T proposal for a replacement thunderstorm research aircraft demonstrates).  With an empty weight twice the 12,500 pound limit, it clearly requires a type rating; however, there was only one two-seat A-10 (the YA-10B) ever built, and it likely isn't airworthy any longer.  (It is on static display at Edwards AFB.)

So, how would you train a civil pilot to get their A-10 type rating?  Would it be a simulator-only exercise, or a long ground school followed by a solo signoff?

The short of it is that most such ex-military aircraft, and replicas built new to spec on these designs, do not have a "type" as defined by the FAA at all. Because the absence of a type means the aircraft can't be certified as airworthy in the normal way, and pilots of these aircraft cannot receive a type rating to fly them, the certification of aircraft and pilot is a bit different.

The aircraft must first be issued an FAA "Special Airworthiness Certificate". This is essentially a slightly more rigorous form of airworthiness inspections for type-rated aircraft and virtually identical to that for experimental and/or home-built aircraft, resulting in the certification of the craft as airworthy in general even though it does not fall into a predefined aircraft type for which FAA instructors can issue type ratings.

The airman, because he can't be certified to fly a non-existent FAA aircraft type, must receive a special rating certification called a "Letter of Authorization", allowing the pilot to fly aircraft of a specific model, and/or a "set" of aircraft that have similar configuration, power, weight and other operational specifications and limits (but that aren't similar or common enough for a type rating). The training required for an LOA includes a combination of ground school and flight school containing information and in-flight training on the specific model to be authorized. But, when it is not possible or practical to do in-flight training in the exact model of aircraft to be authorized (usually because the aircraft in question is a single-seater with no two-seat configuration available), flight training in a "similar" aircraft can be a substitute. Pilots of vintage single-seat warplanes like P-51s typically get their flight training for the category in something similar to what military pilots of the day would have used, such as an AT-6. If the flight school just happens to have a Twin Mustang laying around, that would be even better, and also more directly applicable to multi-engine warbirds like the P-38.

Back to your example, say you get your hands on a "de-fanged" A-10 (which would require a ton of ballast weight to be added, literally; the GAU-8 weighs about as much as a Cadillac, but I digress). All flying examples are single-seaters; however, the avionics, especially of the original A-10A without the glass cockpit upgrade of the PEUP program, are comparable to any 70's-era jet trainer. So, you could receive flight training in a T-33, which is a trainer-compatible straight-wing turbojet with more similarities in its flight characteristics to the A-10 than differences. Coupled with ground instruction and/or simulator time on the specific systems of the A-10 (Which won't include any weapons integration, but honestly for the A-10A that was a single FLIR display and the arming/firing switches, and the C variant only upgraded that to a pair of MFDs; other than relative positioning, the flight instruments of the A-10 would be familiar to any PPL), you could be certified to fly your A-10 solo without any flight hours in an A-10 specifically.

The same might apply to aircraft that do have two-seater variants but where the flight school is unable to procure one. If you won the Powerball, and put a chunk of that money into your very own milsurp F-15C (\$38 million a pop back when they were being made and that's in late 1970s dollars), it's highly unlikely your local flight school would be willing to pony up for an F-15D two-seat configuration to train you on it (unless you bought the plane for them with another big chunk of your lottery winnings). They might, however, have a T-38 in their inventory or be able to loan one from the nearby naval air station, which would give you a primer into the capabilities of a multi-engine turbofan ex-military fighter. Honestly, though, if you wanted to fly an F-15, you'll probably want a two-seater, and your CPL, so you could give rides to paying customers and offset the cost of running this beast (typical fuel load without droptanks, 13,500 lbs which is about 1,985 gallons. With Jet A running about \$4.85/gallon, the cost of a fillup would be somewhere in the $10,000 neighborhood which would give you a cruising range of about 1,000 miles, so you could offer this as a special type of jet taxi).

Here's some more reading on the subject: FAA Flight Systems Information Management System - 8900.1 V5 Chapter 9 Sec 2 - Airman Qualification Requirements for Aircraft for Which the Operating Limitations Require an FAA‑issued Authorization to Act as Pilot in Command


Are instrument lights required for night VFR flight in an SLSA? Our flying club is operating an SLSA that has all the exterior lights as required by FAR 91.205(c).  But don't the instruments that are also required by 91.205(b) need lights as well?

Cockpit lighting is not required to be present as required Night VFR equipment under Part 91 general flight rules.  That being said, there is the following Part 23 Certification Requirement for external and cockpit lighting.

§23.2530 External and cockpit lighting.
(a) The applicant must design and install all lights to minimize any adverse effects on the performance of flightcrew duties.

Under the terms of this regulation one could make the argument that an OEM applying for a normal category type certificate will need some type of effective cockpit illumination to minimize adverse effects on aircrews.


On average, how many landings does a student pilot need before their first solo? On average, how many landings does a student pilot need before their first solo?
I know it depends on individual students, but roughly what is the number?
Or you can just tell me your experience.

My logbook shows 29 landings, with 11 hrs logged in an Aircraft Single Engine Land aircraft (ASEL) when my instructor stepped out and sent me off on my first solo flight.

I think those figures were typical for students at my flight school. It is probably also fairly typical for students at most §141 flight schools, such as mine.

Now, there can be a significant difference between the experience of training under §61 and training at a §141 flight school. The schedule at §141 schools tends to be more fast-paced than what many students might experience doing §61 flight training. Since students must systematically complete the curriculum at §141 schools, a certain minimum level of experience will be in place before a student solos. However, this curriculum also lends itself to a student being ready to solo after a fairly defined period of time. A student training under §61 might take longer to be ready to solo due to a number of factors, including a possibly more relaxed training pace. On the other hand, §61 training can also give an instructor the freedom to solo a student after less time than might be typical.

I don't have any hard data outside of my own experience and what I have observed, but I would guess that a typical §141 student will solo after about 20-40 landings and 10-15 hours. I would guess that a typical §61 student will solo after about 20-60 landings and 10-25 hours.


What's the maximum range an A350-900 can reach at TOW of 250,606 kg and full payload? When the TOW (takeoff weight) of an A350-900 is 250,606 kg (because of runway length limitation), with maximum payload, what is the maximum range it can reach using the chart above?

It is easy to figure out for a Boeing 787 since Boeing provides different brake release slopes, as shown below, unlike the A350 chart.

Since Airbus does not publish this in the charts, we have to calculate it ourselves. You are asking about an Airbus A350-900 with a TOW (TakeOff Weight) of 250,606 kg. This weight would then consist of:

$$ \text{TOW} = \text{OEW} + \text{Payload} + \text{Fuel} = 142 \, 400 \, \text{kg} + 53 \, 300 \, \text{kg} + 54 \, 906 \, \text{kg} $$

based on typical OEW (Operating Empty Weight) and max. payload from Wikipedia. This leaves us with about 54.9 tons of total fuel. Not all of this fuel will be usable however, since the aircraft still needs some fuel reserves: $ \text{Fuel} = \text{Trip Fuel} + \text{Reserves} $.

To calculate the range of the aircraft, we can use the Breguet range equation (see e.g. this answer):

$$ \frac{\text{TOW}}{\text{LW}} = \exp \left( \frac{R \cdot g \cdot b_f}{v \cdot L/D} \right) = \exp(f \cdot R) $$

We are only interested in the TOW, LW (Landing Weight) and the range $R$, so I combined all the other aircraft specific factors into one factor $f$. The landing weight can be calculated via the fuel use:

$$ \text{LW} = \text{TOW} - \text{Trip Fuel} = \text{TOW} - (\text{Fuel} - \text{Reserves}) $$

We now have to solve for the two unknowns $f$ and the reserve fuel. For this, I read off two values from the plot you provided:

We now have two given ranges for known masses:

At MTOW and max. payload (resulting in 84.3t of total fuel) the range is about 5800NM.
At MTOW and max. fuel (about 112.6t based on about 25t of payload) the range is 8600NM.

By plugging these values into the Breguet equation, one can numerically solve for the unknowns:

$$ f \approx 5.2711 \times 10^{-5} \; \text{NM}^{-1} \;\;\; \text{and} \;\;\; \text{Reserves} \approx 10\,545 \, \text{kg} $$

We can test, if these parameters make sense, by plugging in no payload at maximum fuel:

$$ R = \ln \left( \frac{\text{TOW}}{\text{LW}} \right) / f \approx 9698 \, \text{NM} $$

This range is consistent with the value where the magenta line crosses the range axis.

Now moving back to your numbers. We can now plug in a TOW of 250,606 kg at maximum payload. The trip fuel will then be:

$$ \text{Trip Fuel} = 54 \, 906 \, \text{kg} - 10 \, 545 \, \text{kg} = 44 \, 361 \, \text{kg} $$

This gives the final answer:

$$ R = \ln \left( \frac{\text{TOW}}{\text{TOW} - \text{Trip Fuel}} \right) / f \approx 3696 \, \text{NM} $$


Does having permission waive the 500 foot distance requirement in 91.119(c)? The FAA expressly forbids flying within 500' of people, structures, etc...:

§ 91.119 Minimum safe altitudes: General.
Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes:
.
.
.
(c) Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.

It's hard to find much wiggle room in the plain meaning of this statement. However I feel like there would be an exception when either the structures in question are your own (or otherwise authorized by the owner) or the people on the ground are somehow participating in the flight (such as judges for a flour drop).
Nonetheless, no exception exists in 91.119(c). Is there an exception anywhere else, perhaps in a LOI or AC?

See 91.905, List of rules subject to waivers:

91.119   Minimum safe altitudes: General.

In other words, 91.905 allows the FAA to issue a waiver to 91.119, e.g. for airshows. The form for requesting a waiver is here, and the FAA can set more or less whatever conditions they like for granting one.


What error is left uncorrected when "fast IRS align" is done? As far as I understand, there are two ways to align the IRSs in B737s: "Full align" and "fast align."

For a full alignment, you rotate the IRS selector from OFF to NAV, and for a fast alignment, you roate the selector placed at NAV from ALIGN back to NAV.

The 737 FCOM explains that a fast alignment "automatically updates alignment and zeros ground speed error." What error is left uncorrected when "fast IRS align" is done as opposed to when a full alignment is made?

Your question presumes that a "fast align" can be performed instead of a "full align", but is in some way deficient. But this is not the actual usage.

Starting from cold (unpowered), the IRS must always go through a full alignment to find true north, a process which takes about 7 minutes. The IRS is also manually given an initial position, usually via the FMC 'POS INIT' page. From then on, the IRS will maintain its sense of true north, but will gradually drift in position and ground speed due to the slight errors in the accelerometers. The amount of drift is small enough not to be a significant problem even for the longest flights of which the aircraft is capable, but the IRS should be re-aligned to a known state and position before each new flight. During a turn-around, the IRS could be given a full alignment, but since it is already aligned to true north, that is actually unnecessary - all that does need to be done is to reset the accelerometers to zero when the aircraft is actually stationary and give the IRS a new initial position. That is the purpose of the "fast align". The result should not be in any way 'deficient' from a full aligment, it is just saving the unnecessary and time-consuming step of determining true north when the IRS already has that alignment.


What is the purpose of the hold at JNC on the Grand Junction Seven SID? There is a hold on the Grand Junction Seven SID.

I would expect it is there so that ATC could hold you until you reach the enroute MEA but there is no written reference.

So, what is the reason for the hold?  It is certainly not obvious from the plate or departure procedure.

If you look at the chart, you'll see that after takeoff you will arrive at JNC from either the east or the northeast. Transitions then proceed back in an easterly direction (045 to 113 degrees).  With the possible exception of the Rwy 29 departure with the BRICK transition, the SID requires a course reversal at JNC. The charted hold provides a means and protected airspace for the course reversal.

And as you surmise, some aircraft may require climbing in the hold to reach the MEA.


How long is the horizontal stabilizer on a Boeing 737? I can never find information about the length of the horizontal stabilizer all I can find is the height of the vertical stabilizer.

According to this Boeing pdf (page 39), the total length of the horizontal stabilizer on a 737-800 is 47 ft 1 in.


What will be the performance penalties of increasing the wing area of a delta winged aircraft to obtain a lower approach speed? Delta winged aircraft such as the Dassault Mirage III have an approach speed of 170 knots as specified by the manufacturer.

The Mirage F1 was designed to have a lower take off and landing speed than the Mirage III, what would it have taken to reduce the Mirage III landing speed to 135 knots by increasing wing area and reducing wing loading, and installing the F1 engine, and adding leading edge extensions (without adding canards)?

Could this be done by reducing maximum speed to say Mach 1.4 instead of Mach 2 without sacrificing climb performance?

Some figures:
Mirage III
Thrust: 60.8 kN
Rate of climb: 83 m/s (16,300 ft/min)
Wing Loading:274 kg / sq m

Mirage F1
Thrust: 70.6 kN
Rate of climb: 243 m/s (47,835 ft/min) at high altitude

There is a formula relating change in stall speed to weight of aircraft, not sure if it is applicable here.

What you describe would probably work. In fact rate of climb and operational ceiling would improve. So too would maximum payload. But Mach 1.4 would have been a bad joke.

But your question reads a bit like "How can we improve on the Mirage III wing without doing all the things that were subsequently done to improve on it?"

One approach taken on the contemporary Convair deltas; F-102, F-106 and B-58, was to apply leading-edge camber with a conical profile, apex at the root and widening towards the tip. Developed by NASA, the technique significantly improved low-speed handling and, because it was designed to stay within the root shock cone, had surprisingly little effect at supersonic speeds. The second two designs were both capable of Mach 2. Even the F-102 just about reached your Mach 1.4, despite poor area ruling.


Do airports use automated ground operation systems? I'm interested to know if any airports use an automated ground operation system guide planes between gates and vise/versa from/to landing strips/tarmacs.

Advance Surface Movement Guidance & Control Systems (ASMGCS) in different levels are being used for this purpose.  Many airport in the world uses the concept of Follow Green, where the aircraft is supposed to follow the green taxiway centre line lights to reach the parking stand after vacating runway and vice versa.  Surface Movement Radars combined with MLATs aid for these purpose.

You can find more information on this from ICAO Doc 9830.


Is there a general approach for designing a Trimmable Horizontal Stabilizer? What is the general design flow when designing a Trimmable Horizontal Stabilizer (THS) and the attached elevator?

I assume you would dimension the max. positive/negative deflections of the THS to meet longitudinal trim requirements over all cg ranges, airspeeds, flap configs and then add the elevators on top of that to fulfill the manoeuverability requirements (pitch rate). But I guess there is more to it.

In other words:
How do you derive the maximum deflections of THS and elevator each?
(compared to a non-moving stabilizer design)

I'm not asking for specific formulas, but rather for the general approach. If you can recommend some detailed references about it, I would be really thankful.

You always look at both in combination.

The first step is to use tail volumes that have worked before. This is enough for preliminary design.

When the design advances further, you have load cases to cover which combine trim and manoeuvring demands and you use trim settings and elevator deflections in combination. The useable deflection range changes with trim settings, because when the tailplane needs to produce a sizeable downforce to trim deflected fowler flaps on the wing, it cannot tolerate the same positive elevator deflection as in straight flight with lightly loaded tailplane.

Also, speed, load factor and loading determine the downwash angle on the tail. The useable stabilizer range varies with the downwash angle, so each load case needs to be looked at by itself.

Next, you pick the tailplane size and deflection range which covers all load cases and verify the result in the wind tunnel and flight test.


How often does fan blade out happen? Jet engines are designed to contain a fan blade failure, and the engines and airplanes are designed with this type of failure in mind. This is more critical in the modern high-bypass designs with large fans. Pictures from bird strikes sometimes show pretty severe damage, but I don't remember any that actually lost a fan blade.

How often does a jet engine actually lose a fan blade?

This is different from a rotor burst, which is uncontained (like with Qantas Flight 32).

I found the following rather surprising statement in a (probably quite old) University of Southamption document

Rolls-Royce has never had a service failure of conventional fan blades in over 40 million hours of operation, and there have been no service failures of wide-chord blades in over 10 million hours of operation (Baldwin 1993).
In one incident, RB211-535E4 engines on a Boeing 757 were struck by a flock of Canada geese near Chicago – some seven birds, each around 3 kg, were ingested.  The wide-chord fan blades withstood the impact, which was some eight times greater than the requirements for certification, and the engine did not have to be shut down in flight.

So far as I know, bodies like the NTSB don't collect statistics on blade failure events.