Do pilots ever increase the cabin altitude intentionally? Is it true that some pilots increase the cabin altitude slightly to calm down potentially disruptive passengers for safety reasons? For example, footballers who have just won a championship.

I've never heard of this "trick" being used or recommended, although the limits of what I've heard are pretty much limited to US commercial aviation.

If you climb the cabin from the usual 8000' to 10,000', the incremental gain in "sleepy" factor is a little bit but not all that much.  If you climb it above 10,000', then you might "encourage" a few of the more tired/drunk/elderly folks to go to sleep, but now you're into the realm of operating outside of normal practices, and you need to start considering things like, the pilots both need to be on oxygen, the flight attendants may get "tired" quicker than the passengers do, anybody who is elderly or in poor health may start suffering consequences, and then there are company policies and national regulations to consider.

If you raise the cabin above about 14,000 - 15,000' depending on your specific aircraft, then you'll end up activating the automatic passenger oxygen masks, and now you've got some serious 'splainin to do!  (#1, it's a bunch of work for maintenance to repack them, and the aircraft is grounded until they do, and #2 you open yourself up to all sorts of issues if you still have a long way to fly at high altitude to get to your destination!)

I'm going to guess that in the history of aviation, this sort of trick probably has been used at some point, but the opportunity for the uncomfortable questions along the lines of, "okay, tell me again, you did what exactly???" to which the best available answer is along the lines of, "um, well, it, ah, seemed like a good idea at the time, sir..." is awfully high.

I certainly wouldn't recommend it.

Yes, it is true that some pilots do this for that exact reason. If you're literally asking if it ever happens, you will have difficulty finding documentation, so I can only tell you what I have heard from a an aviation college professor who has claimed to have done this for the very reason the asker is describing.

When I was in college, one of the professors who would fly on behalf of the university, told us about a time that he did this to get the basketball team to calm down.

Whether or not it works, I do not know, and I have never done it nor would I because it is unethical.


What ISA temperature to use in the density altitude calculation? In the density altitude formula: DA = PA + [120 x (OAT - ISA Temp.)], should one use the ISA temperature at the field elevation or the ISA temperature at the pressure altitude?

Calculating Density Altitude

Density altitude in feet = pressure altitude in feet + (120 x (OAT - ISA temperature))

Altimeter Pressure altitude is determined by setting the altimeter to 29.92 and reading the altitude indicated on the altimeter.
OAT stands for outside air temperature (in degrees Celsius).

ISA stands for standard temperature (in degrees Celsius).

Keep in mind the standard temperature is 15 degrees C but only at sea level. It decreases about 2 degrees C (or 3.5 degrees F) per 1,000 feet of altitude above sea level. The standard temperature at 7,000 feet msl, therefore, is only 1 degree C (or 34 degrees F).
For example, the density altitude at an airport 7000 feet above sea level, with a temperature of 18 degrees Celsius and a pressure altitude of 7000 (assuming standard pressure) would be calculated as follows.

18 – 1 = 17
17 x 120 = 2040
2040 + 7000 = 9040 feet Density Altitude

This means the aircraft will perform as if it were at 9,040 feet

ISA is 15 degrees C at sea level. For the calculation, decrease temperature by 2 degrees C for every 1,000 ft of altitude above sea level.


Is PVC tubing a good material for helicopter airframes? Been thinking of getting into the hobby of building ultralight helicopters, and would PVC tubing be a good choice to build the overall airframe?

No. The strength to weight ratio of PVC is poor compared to aluminum and you would end up with a very heavy, albeit cheap, machine, and will be even worse when compared to carbon fibre tubing, which would be the optimal choice performance-wise.  Extruded aluminum tubing would likely be the best choice cost wise.  Forget about building a plumb-O-copter.

PVC pipes are strong and flexible. 1 1/2" diameter pipe type SDR-26 is thinner-walled and weighs only .3 pounds per foot! That's three pounds per ten-foot length which only costs eight dollars each at Home Depot. PVC cement can form a solid integrated bond when applied thickly and left on for ten seconds to melt the surface before mating.
However, PVC is breakable when bent, so the airframe must have a lot of reinforcement braces to reduce the amount of bending of longer sections.
Strength-TEST.!!  Test test, the strength of every section using sandbags. Get an EAA member to advise you on this.
Regarding self-bendability: I just tested a 10' length of 1 1/2" PVC type SDR-26 plastic pipe and when suspended it at center and each end drooped down 1/2" is all. I doubt that any ultralight designer would incorporate any unbraced pipe lengths longer than 2'.


Relationship between wing aspect ratio and speed For some reason, I cannot find a relatively straightforward source online which discusses the relationship of wing aspect ratio and how it affects speeds of an aircraft.

Specifically, is there a decrease in efficiency to fly at a faster cruise speed as the aspect ratio of the aircraft's wing increases? Could an aircraft with a high aspect ratio - similar to those of gliders - travel at the same cruise speed as a jet?

Thanks in advance!

It's really the other way around, speed of the aircraft affects aspect ratio.

Hawks fold their wings to dive at high speeds, and have them straight out for lower speeds.
At high speeds the main concern is drag.  The less drag, the faster you can go.  At lower speeds, the main concern is lift.  Here a higher aspect wing is more efficient.

  Why not use a smaller high aspect wing at higher speeds, and just vary the sweep?

This is done, but along with higher speed comes greater aerodynamic forces.  This is one reason why modern fighters feature low aspect wings and deltas.  These are simply much more able to withstand higher G forces.

The variable sweep wing concept was developed in the 1950s and 1960s, but generally carries a weight penalty.  Variable camber is widely seen in airliners today.
Some military aircraft, such as the B-1 bomber, use variable sweep to expand their useful
flight envelope, giving them the ability to "get low and fast".

Cruise missiles, optimized for one speed only with little abrupt maneuvering, can be found with very simple high aspect swept wings, which offer an improvement in drag over a lower aspect wing, thereby increasing fuel efficiency and extending range

There is no direct relationship with speed and aspect ratio, indeed, high subsonic aircraft such as airliners, that strive for maximum efficiency, are seen with increasingly higher aspect ratios in recent years.

Structural strength is the main limitation which continues to challenge engineers today.


Why do many aircraft have both all-moving tailplanes and elevators? Many aircraft - particularly large commercial airliners - have both an all-moving tailplane (horizontal stabiliser) and elevators. (They also have a small third moving element on the trailing edge of the elevators too.)
As far as I can tell, all these surfaces do exactly the same thing, ie cause a change a pitch. Indeed this answer confirms that both stabiliser and elevators have the same effect, although hints there may be differences at transsonic speeds, something that doesn't apply to most airliners.
I understand trim is concern, but ultimately you're just trying to point the nose up or down. Especially with computers calculating optimum angles, having two control surfaces, which may counteract each other, seems to add a lot of complexity.
Of course there must be some advantage to having both, I'd like to know what that is?
 737 empennage (source)

Moving each part has different effect on drag:

Moving just the elevator increases camber, producing large force which is useful for manoeuvring, but it also produces more drag.

Moving the whole stabilizer, keeping the camber low, produces less drag for the same force, which is good for cruise efficiency.

That's why the elevator is used for control and the forward part of the stabilizer for trim.

The arrangement adds complexity, but it also adds redundancy. If one of the actuator breaks and jams, the aircraft is still controllable using the other part enough to make a safe landing.

Related - stabilators are aerodynamically required for super sonic fighters to maintain elevator authority. Interesting history to read about its discovery and Chuck Yeager. If I recall correctly, it boils down to trim tabs do not work and can kill you once you exceed the speed of sound due to the shock wave propagation.
For general aviation, which do not use fly by wire, a stabilator provides greater elevator control because less physical force it required for movement. It is typically augmented with an anti servo.
Google Mach tuck, stabilator and antiservo for interesting materials both basic and technical.


Has this Google Maps imagery of 4 planes on a runway been tampered with? The image below is of Google Maps (30 May 2018) of Amsterdam Schiphol's Aalsmeerbaan (36R).

It shows 4 planes on the runway and a fifth that's about to land. When you zoom in, all planes seem identical.

Has this image been tampered with or could there be an explanation for this?

Google Maps and Google Earth are made by stitching together many different images to create the illusion of a single massive picture of the globe.

The image you are seeing was almost certainly made by an aerial photography plane passing overhead of another plane landing.  In multiple snapshots, it captured the same plane on final, touching down, rolling out and stopping.

The images were assembled together to line up the ground and all static elements.  But items that are moving appear multiple times in different images.

What looks like tampering is actually multiple exposures, plus cross-channel rolling shutter (the color fringes).  If you measure the spacing of the aircraft images and the size of the fringes, you can infer that it's one aircraft slowing down after touchdown.  You can even see the puffs of smoke that show the main gear touching down before the nose wheel.  Here's a careful analysis.


Has an airplane ever been launched from a train? Presumably helicopters have landed and lifted off railroad flat cars.

Has an airplane ever been launched from a train?

(my artwork)

F-84 during project ZELL testing (info provided by jwenting)

It's not a train, but Brendan O'Brien (with the O'Brien Flying Circus) has an act where he lands a Piper Cub on a moving trailer, towed by a car. There are some YouTube-clips showing this, including a take-off (around 1:50). Regarding your earlier comment on 'as close at it gets': I think this is it.

After many Google searches and investigating on this topic, I find no evidence that an airplane has ever been launched from a train.

First of all, it would be unlikely for a person to risk an entire airplane along with themselves doing something so dangerous. By considering this fact, I doubt that an airplane has ever been launched from a train.

Second of all, by attempting such a thing would risk a catastrophe. This would probably cause an explosion that would no be so pretty.

So I have come to the conclusion that an airplane has never been launched from a train.


Why do we need to starve the engine before turning it off? This question is for Piper Tomahawk, but I guess applies to any small aircraft.

Why do we need to use the fuel mixture to starve the engine before turning it off with the key? Why can't we just turn it off with the key like in a car?

The reason is the large spinning thing on the front. Residual fuel in the engine has been known to auto-ignite (i.e. combust without a spark), causing the prop to spin, causing serious injuries and deaths. A lean cutoff reduces the risk that someone handling the prop will get maimed or killed.

In a car when you turn the engine off usually it is in park or neutral, so if the engine turns a few revs the car goes nowhere, even if it is in gear the car may lurch but that's generally it. Modern car engines have electronic fuel injection and electric fuel pumps, some modern push-button gasoline engines are stopped by performing a lean cut-off, turning off the injectors before the plugs, most work by just stopping ignition. Diesels don't have spark plugs, they rely on compression alone, so cutting off fuel is the only way to stop them.

This is a basic question that should be covered by your ground school, flight instructor and your primary training.
The vast majority of certified piston-engine airplanes have two (redundant) magnetos for ignition.
The mag switch in OFF position grounds the magnetos so they don't produce a spark even when they are turning (like if you pull the prop through a 180 degrees.)
The ground wires are called P-Leads. If the ignition switch or one or both P-lead should fail (open the ground circuit) the magneto(s) may be "hot", that is, they can produce a spark in the spark plug and ignite any fuel in the cylinders. This will kick the prop over with great force and possibly hit anyone/anything in the prop arc.
By pulling the mixture to cutoff position, starving fuel from the engine to shut it down, you greatly reduce the risk of a surprise/unwanted engine start when the prop is next moved.
You might just move the prop level to allow attaching your tow bar after flying, or someone may handle the prop for no reason at all (curious children or just idiots at the airport/airshow/fly-in) and if the engine makes a spark and fuel is available (shut-off carb "rich") there could be an injury, death, and resulting lawsuit.
Teach your flying guests, especially children, to never touch the prop unless they are certain it is safe. The key may be left on, or the mixture rich, and accidental starting can occur.
Your handy pilot's checklist should have "Mixture - idle cutoff" in the "Before Starting"  and "Shutdown"  sections.
Lastly, never leave a nosewheel towbar connected when you are not moving the airplane. It is very easy to forget it before starting the engine, and ANY PROP STRIKE REQUIRES A PROP INSPECTION AND ENGINE TEARDOWN/INSPECTION. Add "Towbar Stowed" to your preflight checklist.


If the map (reading) light bulb is burned out in my own Cessna 210, what are my options if I want to fly FAR Part 91 under night-time VFR? If the map (reading) light bulb is burned out in my own Cessna 210,  what are my options if I want to fly FAR Part 91 under night-time VFR staying in the traffic pattern doing touch and goes?

Can I change the light bulb myself (non- A&P mechanic) and go?
Do I have to have an A&P supervise my work if I change the light bulb myself.
What action, if any, do I have to take in order to be in compliance with the FARs.

As the owner, you (likely) may replace the bulb yourself
It comes down to the complexity of the work.
Owners can now do far more preventive maintenance than the 32 listed items
For many years, the FAA treated the 32-item list in 14 CFR Appendix A to Part 43 as exhaustive. The interpretation was that if an item or procedure did not appear in section (c), then it was not preventive maintenance. Case closed
However, in 2009 the Coleal Legal Interpretation, produced by the FAA's Office of Chief Counsel, superseded the prior rules. It specifically calls out and contradicts the understanding that the 32-item list is exhaustive.

Even though the introductory text of subparagraph (c) states that “[p]reventive maintenance is limited to the following work ....” (emphasis added), in view of the broader definition of preventive maintenance in section 1.1, we believe that such limitation is not controlling. Similarly, for the same reason, we also believe that the following sentence in Advisory Circular 43-12A … is overly restrictive. That sentence, found in Paragraph 3(b)(1), states: “If a task or maintenance function does not appear in the list, it is not preventive maintenance.” As with the other paragraphs of Appendix A (i.e., on major repairs and major alterations), the lists are better viewed as examples of the tasks in each category – they cannot be considered all-inclusive. There are, no doubt, many “simple or minor preservation operations [tasks]” and many “replacement[s] of small standard parts not involving complex assembly operations” performed daily, especially on small general aviation aircraft that the agency would consider to be preventive maintenance, though they are not included in the 32 listed items. It is our understanding that Flight Standards' Aircraft Maintenance Division is planning to clarify this issue in a future revision to the AC.

In short, the list of 32 items is not exhaustive.
Is the map light preventive maintenance?
So we know that there is preventive maintenance which can be done which does not fall on the list. However, this does not imply that all maintenance is preventive. The specific question has to do with the map light.
Looking through 14 CFR Appendix A to Part 43, we find:

(c)(17) Replacing bulbs, reflectors, and lenses of position and landing lights.

So it is clearly within the domain to replace exterior bulbs. The question becomes whether accessing the interior map light bulb in a Cessna 210 is low complexity or high complexity.
Your A&P might be able to give you some guidance, although IMHO a good yardstick is that any part designed to be IRAN'ed with nothing more than a Swiss-army knife is pretty clearly "low complexity" and should fall under owner preventive maintenance.

A map or reading light is not part of the Required Equipment List for night VFR or night IFR.

You are free to go with just a flashlight if you want.
(Technically, you don't even need that)


How does the angle of attack vary in turns? I read somewhere that when the aircraft banks to turn, its angle of attack increases.Since angle of attack is the angle between the relative wind and chord line, how does turning increase it? Is it because the relative wind is now from different direction or is it because the wing that goes higher meets the air at a higher angle?

Just to avoid some confusion that I feel in your question:

It doesn't!

That is, it doesn't happen by itself. The pilot or autopilot must actively pitch up (and possibly do other adjustments, e.g. increase thrust). Without active control, the angle of attack will stay about the same (initially), and the airplane will start descending if it enters a turn, because the lift becomes insufficient for level flight (see pictures in other answers).

Really 2 questions here:

  Since angle of attack is between the relative wind and the chord line, how does turning increase it?

For the average GA wings pictured, in cruising flight, the wing is generating more than 4x more lift force than the engine thrust force.  When rolled to the side, the wing will start to pull the plane side ways.  Acceleration in that direction will reduce the angle of attack on the wing but increase the angle of attack on the "downward lifting tail", resulting in a condition closer to the original angle of attack.

Whether or not the tail will force the wing to a higher AOA by itself will be a function of tail area and design (and pilot elevator input).  A well designed plane should not show any bad habits here.

  Is it that the wing that goes higher meets the air at a higher angle?

No, both when when rolling and when banked, the higher wing has a lower AOA than the inside wing, but the "high" wing has aileron down and the "low" wing has aileron up.  This changes the AOA picture considerably and again will depend on design.

The bottom line is, because of increased drag and less vertical lift while turning, it is foolish not to add a little power or to dive a little to increase airspeed a little when "low and slow", like in a landing pattern.  This is much safer than increasing AOA in a turn by any means.


Do biplanes need bigger tail volume coefficients than monoplanes? Do biplane ultralights need bigger tail volume coefficients than monoplane ultralights?

Horizontal Tail Volume Coefficient

I understand that biplanes don't need a larger horizontal tail coefficients vs a monoplane of the same total wing area and same wing span. This is because the chord is would be half of the monoplane, but there are two wings, so the "total chord" is the same, so the horizontal tail volume coefficient does not need to increase. I'm told a typical tail volume coefficient for light airplanes is 35%.

I understand that the horizontal tail volume may actually be lower than that of a monoplane if the wings are staggered, the wings acting like a reflex wing and reducing the wing moment, so a smaller horizontal tail volume may be used in this specific case.

Vertical Tail Volume Coefficient

I understand that the vertical tail volume coefficient on a biplane is twice as large  as that of a monoplane with the same span, as there are two sections of span that the vertical tail needs to control. I'm told a typical vertical tail volume coefficient is 3.5% for light aircraft.

Is this correct?

Tail volume is a measure for the ability of the tail to compensate for the destabilizing pitch moment created by the wing in case of the horizontal tail and for adverse yaw in case of the vertical tail. This pitch moment is proportional to the square of the wing chord (one factor comes from the area, the second from the lever arm), so if you compare two otherwise equal designs, one of which is a biplane and the other a monoplane of twice the chord, the dimensionful horizontal tail volume (expressed as tail surface times tail lever arm) of that monoplane needs to be twice that of the biplane. To counter adverse yaw, however, the dimensionful vertical tail volume is the same.

Tail volume is normally made dimensionless by referencing it to the wing area and the mean aerodynamic chord (for the horizontal) or wing span (for the vertical tail). Since the area of both designs is the same and the MAC of the monoplane twice as large as that of the biplane, both dimensionless horizontal and vertical tail volumes become equal even though the dimensionful horizontal tail volume of the monoplane is twice as large.

However, if you compare wings of the same aspect ratio (which might be a better basis), both the chord and the wing span of the monoplane are larger by a factor of √2 but there is only one wing to consider versus two in case of the biplane. Now the dimensionful horizontal and vertical tail volumes for the monoplane are larger by a factor of √2.

Only when you make the chord of both wings equal (doubling the span of the monoplane in the process) will the dimensionful horizontal tail volume of both designs be equal but now the vertical tail volume needs to be twice as large.

Wing stagger with the same incidence on both wings would move the biplane closer to the monoplane with twice the chord whereas a lower incidence on the rear wing would indeed create that reflex effect and reduce the instability of the wing. Still, you need control power to change angle of attack quickly enough for maneuvering, so I would be careful with any further reduction of tail volume even if the staggered biplane wing by itself is stable already.

Do biplanes need bigger tail coeefficients than monoplanes (of equal wing area)?

Here's where building free flight models and testing them in cross wind conditions is very helpful.  As a designer, it is important to consider wing and tail functionality.  Many "tailless" designs, such as deltas, have adequate stability without a separate and distinctive "tail". Reducing chord and increasing aspect increases the need for a separate, stabilizing "tail".  Some designs put the "tail"(canard) in front to decrease stability and increase maneuverability.

You may find biplanes need a smaller vertical volume than a mono plane of similar wing area.  This is consistent with designs of 100 years ago, where "slab sides" also aided in lateral stability.

The testing for for vertical tail volume can be done by releasing the plane in a cross wind, and seeing if it "points" into the wind or turns away.  Many mono plane designs, particularly with excessive dihedral "effect", will roll and turn away from the wind.  Biplanes seem to be less prone to this, possibly due to a shielding effect of the lower wing to the upper wing from the cross wind.

Tests for adequate horizontal stabilizer size will include adequate directional and static stabilility, but also there is one very important aspect of inertial rotation effect for larger aircraft.  The horizontal stabilizer needs to be larger to arrest pitching momentum before it exceeds stall AOA and effectively reduce AOA faster than it increases from relative wind shift from downward acceleration as the plane "sinks" from loss of lift.  This issue is much less common in GA sized aircraft unless aft CG limit is abused.

One may also find a wider wing, or 2 "staggered" wings, reduces the need for a horizontal stabilizer.  But keep in mind using the wing as a stabilizer may reduce its efficiency of lifting, it's primary task.  Notice "flying wings" have yet to replace the classic "wing and tail" design of modern sailplanes, though they can be very stylish looking.

There are many factors which go into the sizing of the vertical and horizontal stabilizer. For a (low Mach number) recreational aircraft, adequate "anhedralling" (side area below the CG) helps eliminate the need for excessive V stab area, as well as a longer torque arm (longer fuselage).

Evaluation of 120 years of existing and proven aircraft design, and choosing the parameters of desired performance, may be more useful than "rule of thumb".  Essentially, it is a trade-off of stability, maneuverability, and drag before software is needed to keep one from crashing.


If a pilot ejects, what is the autopilot programmed to do? If a pilot uses their ejector seat during flight, what is the autopilot programmed to do?
As a developer myself, I'd want to build in a way for the plane to try and save itself if possible (to save money) by auto-landing, or at the very least, calculate the nearest least-populated area for a crash-landing. So I'm wondering if anything like this is even written into the software.

I would want to build in a way for the plane to try and save itself if possible (to save money) by auto-landing

Had the situation allowed saving the airplane the human pilot would definitely have tried that first. The fact that a trained fighter jet pilot decided to eject from an aircraft knowing that the ejection was a last resort and could be deadly, signifies that the plane was not able to be flown safely anymore.

On top of numerous irrecoverable problems at that point, one of the most significant issues is the fact that ejection destabilizes the flight path and the increased drag (because there is no longer a canopy on top) makes it even harder to safely glide that jet, let alone land it somewhere.

There is nothing much autopilot can do at that point.

There have been two famous incidents that are related to your question but afaik neither of them involve Auto Pilot.

1989 Belgian MiG-23 crash
Cornfield Bomber

It's just like saying I know the airplane can be saved but my computer will take care of it, I'm outta here. See you at the Court Martial.

Some commentators have noted that I did not answer one basic question:

  Don't forget to answer the question "If a pilot ejects, what is the autopilot programmed to do?", even if the question seems moot

This question is too broad: there are numerous models of fighter jets all around the world, built by a number of manufactures and internal details of which are closely guarded secrets. You are not going to generally find out a manual on the web listing all the actions that the autopilot software will perform after a bail out. If the OP can narrow down the question to a certain model one can research and try to find something but I don't believe its going to be an easy find. Hence I'm sorry I don't have an answer to that question. I hope someone more knowledgeable goes ahead and posts an answer to that.

I imagine there's probably a switch such that over enemy or unknown territory the plane self-destructs. But you don't want this over your own training areas such that some kind of controlled landing may be programmed in when in training mode.


Why Didn't the USSR Build An X-15? In the history of aerospace engineering in the United States, the X-15 is lauded as a critical and necessary step on the path to manned spaceflight. Throttle-able chemical rocket propulsion systems, reaction controls, and pressurized flight suits were all major design features of the X-15 that eventually found their way into future successful spacecraft.

Given the obvious resources the USSR put into the space race and their numerous successful missions, why did they never build a hypersonic space-plane akin to the X-15?

I like the X-15, it was certainly an amazing airplane, but the truth is there were few benefits to the space program from the X-15.  It was far from a critical or necessary step:

The Mercury space suit was a direct derivative of the BF Goodrich Navy Mark IV, which had been in use for years. It wasn't developed for the X-15
The rockets used in the space program were completely different from the X-15. They were orders of magnitude stronger for one thing, used different fuels and completely different designs. Throttle-able rocket propulsion systems weren't new
The X-15 thermal protection system was of no use to the space program, which had to deal with far higher temperatures

There were some benefits:

It was a good source of astronauts: several pilot from the program went on to the NASA programs, including Neil Armstrong
Data from the X-15 missions were used in the X-20 Dyna Soar spaceplane which never flew, but it eventually morphed into the space shuttle

As to why didn't the Soviets make one, they didn't need it. Their manned space program built off of their ICBM development efforts which were successful. If the US hadn't built the X-15 the manned space program would most likely never gone the space shuttle route, but that wouldn't have been any sort of deal breaker.

Most of the X-15 data, like most NASA research studies are made available to the public.  Why spend millions of Rubles on a space plane testbed when you can examine the research data for free after the other guy spent the cash and built one?

And, apparently, as both the US and USSR space shuttles bear a VERY similar appearance to each other, it appears that both sides came to similar conclusions as to the best configuration for a space plane based on hypersonic research data from the X-15 program.


Where to get flight dynamics for a flight sim model? Once, a while ago, I tried to create a Flight Simulator X model for an aircraft that I wanted a model of, but was soon overwhelmed by having to guess so much of the flight dynamics. Is there somewhere where I could get detailed information about the flight dynamics of aircraft without contacting the manufacturer, a pilot, or having the plane itself to run tests on? I mean for things like drag at different mach, drag coefficient created by the landing gear, lift coefficient created by the flaps, detailed stuff about the engines, etc.

Unfortunately I have no experience with how FSX models aircraft, but at a guess, it's model requires extensive experimental data from a real aircraft to truly get the right parameters.

And that's something no hobbyist is likely to be able to do. For that matter, it's pretty difficult for a pilot to do, since actually recording the relevant data is difficult, and some of what you need to know requires doing things with the aircraft you probably shouldn't do in most circumstances.

X-Plane's flight model and aircraft creation tool is far more forgiving. You still end up having to guess a lot of parameters, but they are generally less critical to basic handling.

All you really need to get a decent flight model out of X-Plane is a good set of reverence pictures, an eye for detail (so your model matches the geometry properly), and ideally the correct airfoil profiles and engine specifications.
(Primarily the thrust and power)
For the most part, good reference models and diagrams, and the information you'd find in the Pilot's operating handbook is enough to create a decent flight model in X-Plane.
It certainly won't be perfect, and you'll probably have to tune it, but it's a much easier task than getting that data needed for an FSX model.

I have the good fortune of being a student pilot, and as such I decided to attempt a model in X-Plane, and found that while it was far from perfect, (and needs a lot of improvement to be a 'good') model, it's behaviour was much closer to the real aircraft that I fly regularly than I was ever expecting given how much I had to guess.

I had to guess everything from the aileron deflection angles to the propeller geometry, wing airfoil choices and more, and still the resulting model was only slightly off from the real thing insofar as I know how the real aircraft flies.

I guess that's not an overly helpful answer in a direct sense for an FSX flight model, but I fear it just isn't going to be at all easy to find the information you need to make a flight model that isn't fundamentally broken in FSX, let alone accurate.

X-Plane is just far simpler to work with when you don't have a lot of information...

Whether that's worth the downsides of X-Plane (especially the consequences of switching if you already have a heavy investment in FSX), I don't know.
But it's worth keeping in mind if you are particularly fond of amateur aircraft design.

(It's even plausible to create fictional designs in x-plane for which no real-world data could ever exist in theory, and still get a good idea of how such a design likely would fly if it did exist.)

As for FSX potentially having better flight models in some cases? Maybe. But this is likely going to be the flight models of expensive add-on aircraft models that were made with the help of the manufacturer and pilots qualified to fly the real aircraft.

That's not going to help you any if you don't have access to those kinds of resources.

A hand-tuned model matched to exact real-world data may well work better than a physics based model if you have good source data.
But if your source data is lousy (as it is for most of us unfortunately), then the physics based model will be much more reliable most of the time...

I havn't worked with it yet, but maybe this utility can help you.


Efficiency of Flyboard engine From what I understand (not much), you need good specific impulse to travel long distances with, say, flyboard.

I know that RP1 has good specific impulse. I wonder if he used it, and what type of oxidizer/propellant would be most efficient for this task, and feasible (very small engine, not that high temp) .

To be specific: The question is if the efficiency (in terms of travel distance per unit mass of fuel) could be improved by choosing another type of engine/fuel?

I'm not directly familiar with the engines Zapata uses on the Flyboard Air, but I'd hope they're using a kerosene derivative like JP-1 or commercial Jet-A.  Alternatives (gasoline, diesel, various alcohols) have no better energy content per volume, and some (alcohols) considerably less.

There is no case (for low altitude atmospheric flight) in which a rocket can beat an air-breathing jet for specific impulse/specific fuel consumption -- because of the need to carry oxidizer, instead of just using the air for that purpose, the amount of fuel/oxidizer available is limited by tankage.  This is why airliners, warplanes, and private business aircraft use jets or turbine driven propeller engines instead of rockets (not to mention the far higher durability of a turbine compared to a rocket engine).

Feasible, but then you have to carry rocket fuel and oxidizer (such as liquid Hydrogen and liquid Oxygen, both refridgerated and under pressure), vs just readily available fuel (Jet-A), and getting oxidizer (O2) from the air all around us.


Was there more than one incident or accident where an Airbus FBW aircraft reverted to mechanical backup? There was an accident Smartlynx A320 training flights MYX-9001 at Tallinn on Feb 28th 2018, where ELAC pitch control failed due to fault in the stabilizer actuator, and then both SECs failed due to the command and monitor boards responding differently to a short bounce, so only mechanical backup was left for pitch control (fortunately the crew managed to land the aircraft and had just some broken panels).
It is the only instance I heard of where the mechanical backup had to be used. Was there any other incident or accident of an Airbus FBW aircraft (A320 or later model) where only mechanical backup control was available?

Sadly yes, there was at least one other flight, XL Airways Flight 888 from 2008 on which the use of the mechanical backup trim wheel might have saved the plane.


When do I have to contact Centre when departing/arriving at an airport with an ATF? I'm looking at St-Frédéric airport in Quebec, Canada (CSZ4) and specifically at the "COMM" section. It says that there is an Aerodrome Traffic Frequency (ATF) on 122.8 but it also seems to say that you need to contact Montreal Centre (135.025) on arrival and departure:

Does this mean that Montreal Centre is to be contacted only when the ATF (UNICOM) is not operating, or do I have to contact it at all times?

The Aerodrome Traffic Frequency is a frequency for aircraft to use to aid self-sequencing at airports where a control tower is not operational. Another name for it is the Common Traffic Advisory Frequency. 122.8 MHz was the original frequency designated for UNICOM use and remains one of the more common ones.
The APP/DEP frequencies listed tell pilots that, if they desire to talk with ATC (as IFR flights probably would!), they need to contact Montreal Centre on 135.025 once airborne. Montreal Centre is also the arrival frequency that would help IFR arrivals get established on an instrument approach procedure, if one existed. Centre most probably does not have radio coverage to the ground on this frequency, and even if they did they would not provide towered-airport control services.

Its a mandatory frequency airport which means that aircraft are supposed to notify center when they arrive or depart.


How to replace two propellers on the same aircraft reaching the time limit? When both propellers of the aircraft reach the time limit (60 month) and need to be replaced, can both propellers be replaced at the same time and perform only one flight test to reduce time on ground or should they be replaced one at a time just for safety or to investigate any discrepancy that may arise?

Since replacing a propeller with the same propeller that is in the Type Certificate is not a major repair, the FAR(s) (CFR Title 14) that most apply are 43.7 and (assuming the airplane is under Part 91) 91.407.

43.7 states:

  (a) Each person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance shall use the methods, techniques, and practices prescribed in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques, and practices acceptable to the Administrator, except as noted in §43.16. He shall use the tools, equipment, and test apparatus necessary to assure completion of the work in accordance with accepted industry practices. If special equipment or test apparatus is recommended by the manufacturer involved, he must use that equipment or apparatus or its equivalent acceptable to the Administrator.

  (b) Each person maintaining or altering, or performing preventive maintenance, shall do that work in such a manner and use materials of such a quality, that the condition of the aircraft, airframe, aircraft engine, propeller, or appliance worked on will be at least equal to its original or properly altered condition (with regard to aerodynamic function, structural strength, resistance to vibration and deterioration, and other qualities affecting airworthiness).

So you must follow the maintenance manual and put the airplane back in a state at least as good as original. If you think that putting them both on does not qualify to satisfy this requirement, then you should do them one at a time. If it does satisfy this, then in that case, 91.407 comes into play, which states:

  (a) No person may operate any aircraft that has undergone maintenance, preventive maintenance, rebuilding, or alteration unless—

    (1) It has been approved for return to service by a person authorized under §43.7 of this chapter; and

    (2) The maintenance record entry required by §43.9 or §43.11, as applicable, of this chapter has been made.

  (b) No person may carry any person (other than crewmembers) in an aircraft that has been maintained, rebuilt, or altered in a manner that may have appreciably changed its flight characteristics or substantially affected its operation in flight until an appropriately rated pilot with at least a private pilot certificate flies the aircraft, makes an operational check of the maintenance performed or alteration made, and logs the flight in the aircraft records.

  (c) The aircraft does not have to be flown as required by paragraph (b) of this section if, prior to flight, ground tests, inspection, or both show conclusively that the maintenance, preventive maintenance, rebuilding, or alteration has not appreciably changed the flight characteristics or substantially affected the flight operation of the aircraft.

I would argue that a propeller change cannot be satisfied by (c) above and does require a flight test. However, there is nothing that requires separate flight tests UNLESS the maintenance manual requires it, in which case part 43.7(a) from above comes into play. But as a "fail safe" a good run-up on the ground at high throttle with the brakes applied, followed by an inspection of the work can give good confidence in the work prior to the flight test.

It would probably be safer to replace one at a time in case the propellers were defective. Better safe on one good prop than sorry on two bad ones.


What's the function of the plate behind the wheels of the Pilatus Porter? Anyone knows what's the plate behind the wheel of the Pilatus Porter for?

Looks like a sort of gravel kit.
Real gravel kits are used by jet powered aircraft to land on rough airfields.
In this case though, the engine is in front, so it is likely that it is only there to reduce the amount of dirt raised when landing/taking-off so to reduce the chances of damaging the aircraft.
From the official PC-6 Porter brochure via pc-6.com (PDF), they call this option a mudguard:

MUDGUARD

And according to a service bulletin (pilatus-aircraft.com; PDF) there were prone to fatigue:

Operators have reported failures of the mudguard supports and stone guard mounting yokes. The failures are caused by fatigue damage.

Federico hit the nail on the head.  It’s a gravel kit and works similar to the mud flaps on trucks.  On rough airstrips, it prevents rocks, gravel and other FOD from striking the airframe and damaging it during the ground roll.


What is the difference between Assumed Temperature and Derate takeoff thrust? Airlines like to avoid a full thrust takeoff as it increases the wear on the engine. There are two methods to achieve this: Assumed Temperature and Derate.

In the Assumed Temperature method, the takeoff performance is calculated by commanding the engine to mimic the thrust produced if the outside temperature is higher. Derated takeoff thrust basically tells the engine to pretend it is a weaker engine.

Both methods result in a takeoff thrust setting that is lower than 100% power. What are the differences between these methods, and how do the flight crew choose between the two?

The difference is in the minimum control speeds ($V_{mcg}$ and $V_{mca}$).

In Assumed Temperature takeoff thrust, the pilots are allowed to advance the thrust levers to full rated takeoff thrust. However, in Derated takeoff thrust, the levers should not be increased beyond the fixed decate limit, otherwise a engine failure may result in loss of directional control.

From Boeing 737 FCTM (my emphasis):

  The fixed derate is considered a limitation for takeoff. Takeoff speeds consider ground and in-air minimum control speeds (VMCG and VMCA) at the fixed derate level of thrust. Thrust levers should not be advanced beyond the fixed derate limit unless conditions are encountered during the takeoff where additional thrust is needed on both engines, such as windshear. A thrust increase, following an engine failure could result in loss of directional control.

The minimum control speeds are calculated based on the full rated takeoff thrust. The rated thrust is lowered in Derated takeoff but not in Assumed Temperature takeoff. Therefore, by calculating the minimum speeds based on a lower engine rating, the pilots can be ensured that sufficient directional control can be maintained on a slippery runway, whereas there is no such guarantee for Assumed Temperature takeoff.

On a dry and long runway, there is no operational difference between Assumed Temperature and Derated takeoff.

From the Boeing 777 FCTM (my emphasis):

  Reduced takeoff thrust (ATM) may be used for takeoff on a wet runway if
  approved takeoff performance data for a wet runway is used. However,
  reduced takeoff thrust (ATM) is not permitted for takeoff on a runway
  contaminated with standing water, slush, snow, or ice.

And:

  Derated takeoff thrust (fixed derate) may be used for takeoff on a wet
  runway and on a runway contaminated with standing water, slush, snow, or
  ice.

The Boeing 737 FCTM has a nearly identical description.

The A330/A340 FCTM explains that the slower $V_{mcg}$ / $V_1$ can also allow increased MTOW on short runways:

  When taking off from short or contaminated runways where ASDA [Accelerate-Stop Distance Available] is the limiting factor, a reduction in the minimum control speeds may generate a take-off performance benefit and a higher MTOW.

Both methods will give you an N1 setting that's less than what you'd have if you used actual temperature & no derate (i.e. max takeoff thrust).  The computations to get to that N1 setting are different, but at the end of the day, the pilots (or the autothrottle) sets a particular N1, and you go fly.  Which method, derate or assumed temperature, or both, that you used to get to that N1, isn't really all that important.

For the pilots, the company will probably tell them which method to use.  Or the performance computations will consider whatever permutations are out there, and spit out an answer -- derate to XXk, assume temp of YY degrees, or maybe both.  And the pilots put that into the FMC, and you go fly, knowing that the N1 that you get at the end gives you enough performance to do all the things you need to do: 35' at the end of the runway if you lose one at V1, meet obstacle clearance criteria, etc.

The derate method is typically less granular than assumed temperature -- you have two or maybe three derate setting you can select, and that's that.  But those steps may be pretty big steps.  The software can step an assumed temperature up one degree at a time to find exactly the minimum power that's needed to meet all the criteria.  But there is some limit to what temperature you can assume, and if you have the really light airplane on a really long runway, even assuming that max temperature may give you lots of performance to spare, and so in order to bring the thrust down to being only what you really need and no more, you need the bigger "bite" of a derate.

There is a human factor to consider, in that if the crew is selecting a derate and entering an assumed temperature, you want to be sure that they did that process right, and (particularly if conditions or runway change) you don't end up with the wrong combination of derate + assumed temperature.  If Plan A was to derate two steps down & use the actual temperature, then Plan B was to derate one step down & assume 45 degrees C, the hybrid of not changing the derate (leaving it at two steps down) AND assuming 45 degrees C will give you less thrust than either Plan A or Plan B, and you want to make sure that an error like that can be reliably trapped.

But again, that sort of decision of what method(s) are used is made more by the company and the performance software than by the individual crew.  As a pilot, put what you're given into the box, verify that it's right, and go fly.  I'm not overly concerned which computational path the software used along the way to telling me to set 88.3% N1.


What is MCAS trying to fix on B737 MAX? New sources such as Seattle Times and Aviation Week provide a pretty good overlay of the MCAS function on B737 MAX. However, I'm unclear as to the issue that MCAS is attempting to fix. From what I can gather, the larger nacelle led to a shortening of the pylon height, leading to altered aerodynamics at the wing/pylon/nacelle junction. At high AOA, this leads to a higher pitch-up moment than on the NG (dispelling other popular theories, it has nothing to do with the thrust line or nacelle CG).

In Seattle Times, it talks about shock formation at the junction, indicating that this is not a low Mach problem. However, transonic regime is usually not limited by stall but by deterrent buffet. Can someone with the knowledge clarify? If it is a stall issue, is it a lack of stall identification (lack of distinct pitch down) or is the aircraft experiencing a pitch-up without MCAS?

From The inside story of MCAS: How Boeing’s 737 MAX system gained power and lost safeguards by Dominic Gates and Mike Baker:

During flight tests to certify an airplane, pilots must safely fly an
extreme maneuver, a banked spiral called a wind-up turn that brings
the plane through a stall. While passengers would likely never
experience the maneuver on a normal commercial flight, it could occur
if pilots for some reason needed to execute a steep banking turn.
Engineers determined that on the MAX, the force the pilots feel in the
control column as they execute this maneuver would not smoothly and
continuously increase. Pilots who pull back forcefully on the column —
sometimes called the stick — might suddenly feel a slackening of
resistance. An FAA rule requires that the plane handle with smoothly
changing stick forces.
The lack of smooth feel was caused by the jet’s tendency to pitch up,
influenced by shock waves that form over the wing at high speeds and
the extra lift surface provided by the pods around the MAX's engines,
which are bigger and farther forward on the wing than on previous
737s.
(...)
Under the proposal, MCAS would trigger in narrow circumstances. It was
designed "to address potentially unacceptable nose-up pitching moment
at high angles of attack at high airspeeds," Boeing told the FAA in a
proprietary System Safety Assessment reviewed by The Times.

Another article from The Seattle Times published in March makes mention of a high speed stall:

Designed to activate automatically only in the extreme flight situation of a high-speed stall, this extra kick downward of the nose would make the plane feel the same to a pilot as the older-model 737s.

This indeed points to a stick-force-per-g test, as @Jimmy mentions in a comment. Since the B737 has a fully irreversible hydraulically actuated flight control system, with an artificial feel that is proportional to dynamic pressure but not to load factor, the obvious mechanism for "lack of smooth force feel" would be having to release the column to some extent due to extra nose-up moment that the aircraft generates.
It is very plausible that the added lifting surfaces from the engine pods create a larger pitch-up moment than the 737NG has in the same circumstances. I'm not really sure how the supercritical airflow over the MAX wing differs from that of the NG to create extra pitch-up.
All of that is the original limited cure for the stick-force-per-g tests. If this was the only thing that needed to be fixed, all would probably have remained well. But the first linked article also mentions:

The flight-test pilots had found another problem: The same lack of smooth stick forces was also occurring in certain low-speed flight conditions. To cover that issue too, engineers decided to expand the scope and power of MCAS.

As you can see, The Seattle Times is my source of information as well...there is no additional information on what were the "certain low-speed flight conditions".

One last attempt to point out the elephant in the room and please don't delete this just because it is my answer. By all means, feel free to criticize it.
What everybody seems to not want to see, is that trim issues are supposed to be non critical by definition. Regardless of what controls the trim surfaces. That goes for all aircraft,... except the 737.
What that means is that these crashes expose a biased certification culture between Boeing and the FAA that dates back 60 years. This played a crucial role in the success of all 737 models. It gave the 737 an advantage over its competitors. MCAS puts that advantage at the expense of aviation safety. It is cutting an already cut corner. Mad Max on top of Mad Max. That is what makes it so dangerous. That is the reason for the crashes and all the dead people. Sweet talking that is not very productive.
The 737 is by concept not overly stable. MCAS attempts to overcome an unacceptable part of that. It does so by controlling the pitch using the trim surfaces. The 737 configuration does not allow for automated trim surface control. It effectively puts two pilots behind the yoke. Should MCAS fail, one of those pilots trims down, while the other pitches up. That, no 737 can not deal with. (due to what happened in the 60's)
EDIT: To answer the question: "What is MCAS trying to fix on B737 MAX?" you can look in two directions. Either you conclude that it must be something unique to the 737 Max, so you look at those things. That is to an enormous extend jumping to conclusions, because that is by no means certain. The other thing to look at is what MCAS does. For some strange reason, I'm the only one looking in that direction. Worse than that, I get people aggravated by writing about it. Not because its a wrong answer. If you change the question to: "What does MCAS do on B737 MAX?" which is not all that much of a change, it clearly points the way I'm looking. Meanwhile a question asking for a reason gets nothing but excuses. Its as if I'm insulting someones religion. Totally weird. MCAS was designed to work on dedicated trim surfaces only, which the 737 simply doesn't have. But hey, who cares?
The craziest thing about MCAS is, that if Boeing would have simply not installed MCAS, that most likely would never have resulted in any crash. Ask any capable and experienced Max pilot. Sure the pitch would surprise him, but no way would it make him crash. At the angles at which this happens, he is concentrated on flying the airplane. Its not a whole lot different from weird heavy turbulence and he can easily handle that. MCAS serves absolutely zero aerodynamic purpose. No aircraft does, ever did or ever will need MCAS. MCAS is faking it for the money. The reason it failed is for the money. Yes, it sells lives. The thing it is trying to fix on the 737Max is the financial insolvability of the project. Nothing more, nothing less.
If you don't want to know that answer, then what's the purpose of asking the question?


Why did Air France flight 447 fail to recover from the stall? I have read the wikipedia entry about the accident but I don't understand why did the stall happen and why the plane couldn't recover from the stall.

Correct me if I am wrong but I would think a plane would naturally recover from a stall situation by pitching down the noise by itself with no control inputs needed and gaining speed (due to the fall).  The AoA would be back to safe values to generate lift again and the plan would be stabilized.

I don't get how a plane like that would fall from 35,000 feet with its engines set at 100% thrust.

I‘ll attempt a very brief answer based on the report against your questions:

1) Why did the aircraft stall?
The aircraft stalled because crew pitched the aircraft up beyond the performance limit at that altitude (they pitched into a climb which the available engine thrust could not sustain, bleeding off speed until the aircraft stalled).

2) Why was power not reduced?
I don’t know, but in my view that didn’t play a crucial role, either.

3) Why did the aircraft not pitch down by itself?
Because crew didn’t realise they were stalled and continued to apply „nose-up“ control input. Seemingly inconsistent behaviour of the stall warning system and unexpected parameters on their instruments (i.e. a combination of speed and vertical speed not ever seen in normal flight) contributed to the situation.

This ties in with another current question about why we do not have larger elevators on airliners, and highlights the potential of accelerated stalls.

Aircraft need proper air flow over the wing to produce adequate lift.  This is a function not only of speed, but also of angle of attack.  The lift to angle of attack chart illustrates this.

One of the key functions of a properly designed horizontal stabilizer is to push the nose down when the plane sinks.  The design parameter is to have this have adequate area on the H stab to lower the nose as it sinks before it stalls.  The pilot adds power to resume level flight.

The other critical factor is center of gravity.  A forward set CG again pulls the nose down as the plane slows.  Forward set CG acts as a counter balance to elevator trim to stabilize air speed to a desired range: slower - nose down, faster - nose up.

It is the position of the elevator that creates the AOA to stall the aircraft.  If the elevator is stronger than the torques created by Hstab while sinking and forward CG, the plane cannot sufficiently reduce AOA.

Sadly, even with power applied, the stall can not be broken until the elevator is released.  In the report of this incident, although pitch did not exceed 15 degrees relative to the horizon, AOA exceeded 35 degrees even with throttle at TO/GA, and the aircraft was falling at over 10,000 feet per minute.  Weight and balance were within limits.


Why does elevator input move the turn coordinator ball in steep turns? When practicing steep turns, I'm running into an unusual phenomenon.  If the airplane is losing altitude in coordinated flight and I apply aft stick pressure to pitch up and correct, I notice that the ball swings to the outside of the turn indicating a skidding condition.  Conversely if the airplane is gaining altitude and I release back pressure to the stick to descent, the ball always swings to the inside of the turn, indicating a slip.  This seems counter intuitive as one would think that an increase in AoA to gain altitude would result in increased adverse yaw, requiring more rudder pressure in the direction of the turn and less rudder pressure when the nose is lowered resulting in a lower AoA and adverse yaw.

I suspect the reason here has to do with the direction the nose is being forced in by the elevator input during the turn.  At a steep bank angle the nose is inadvertently being pulled inside the turning flightpath which results in a skidding condition, which should, therefore, be countered by less rudder pressure in the direction of the turn.  Conversely when elevator pressure is reduced, the nose would tend to stray outside of the tangential flightpath, resulting in a slipping condition.  The end byproduct of this would be reduced or even cross control inputs needed to maintain coordinated flight.  Can anyone else confirm this?

In a steep turn you are making power changes, pitch changes and also making constant corrections with aileron to hold the bank angle, without even realizing it.  Once established in the turn some airplanes require a bit of in-turn aileron to hold the bank angle, some hold the bank with neutral aileron, and some require top aileron to keep from overbanking.  The top and down aileron inputs are inducing constantly changing adverse yaw forces which come and go, changing torque effects from the engine with power adjustments are producing changing yaw forces, and gyro precession from the prop from pitch motions are inducing yaw forces which come and go, and there are bumps, and you start running into your own wake.

In other words, you are in a machine pulled along by a big torque producing gyro that is slithering and sliding around in a gas with half a dozen forces and moments interacting on it simultaneously.  With all the subtle forces and inputs happening during a turn, I don't think you can identify and act on a single phenomenon like that.   What you have to do is, well, just do whatever it takes to hold the bank angle, altitude and center the ball and don't overthink it.

If you fly gliders, which use a yaw string that is more sensitive than a ball, even without the torque and gyro effects of an engine, the yaw string drifts this way and that while in a turn, seemingly independent of the aileron position some of the time. You generally make stabs of rudder in concert with aileron, but sometimes the yaw string seems to have a mind of its own and you just do what you have to do with your feet.

Imagine a banked plane in four scenarios. In each scenario the plane maintains the same vertical speed (it does not accelerate up or down).

The plane is banked but not turning. The aircraft creates 1G of lift by angling through the sky in an uncoordinated manner and does not turn at all. The direction of lift is pointed straight up, and the ball moves to a position opposite it, pointed strait to the ground.
The plane is banked, but in a slip. The aircraft does turn but not as much as it should given the angel of bank. The aircraft is generating 1G of lift in the vertical direction, but not enough lift in the horizontal to put the combined vector perpendicular to the wings. The ball falls partway towards the ground.
The plane is in a coordinated turn. The aircraft is generating 1G of lift in the vertical direction and just enough lift in the horizontal direction to put the combined vector perpendicular to the wings. The ball is centred in the gauge.
The plane is in a skidding turn, it is turning faster than it should given the angle of bank. The aircraft is still generating 1G of lift in the vertical direction, but now it is generating more than the required amount in the horizontal direction, and the combined vector is past perpendicular. The ball moves to the outside of the turn.

The essential part here is that unless the aircraft is entering a climb or coming out of a dive, it is producing 1G of lift in the vertical direction. If the plane increases or decreases the amount of total lift produced, the direction of the vector will change accordingly. If the direction of the vector does not match the angle of bank you will be uncoordinated. Too much bank, or not enough lift gives a slip, too little bank or too much lift gives a skid.


Why is water-contaminated fuel bad, but water-injection is not? A "wet" takeoff of a KC-135 with J57 engines—By USAF Photographer (USAF photo) [Public domain], via Wikimedia Commons

Why is water-contaminated fuel bad, but water-injection is not?

The way I understand it, water-injection lowers the combustion temperature, which is good and bad, good for cool yet increased power-output / mass flow, bad for wasting [unburnt] fuel.

Why is then water dangerous when a trace amount of it is found in fuel? What's the worst that can happen apart from black exhaust and higher power?

Water-injection in jet engines and piston engines is mixed with fuel before it enters the combustion chamber, so I'm thinking fuel already mixed with water should not be any different. Of course I'm wrong. But why?

Because of the quantity of water in the fuel, as opposed to a careful introduction of water into the combustion process.  Typical water contamination is bad in fuel tanks as water is denser than aviation fuels and settles at the bottom of the tanks.  Aviation fuels are also hydrophobic (non-polar) and so do not readily mix with water.  Therefore water will settle unmixed at the bottom of the tanks, in the fuel sumps or feeder hoppers and when ingested into the engine will fuel starve it and cause it to shut down.  Water in fuel lines can also freeze there during cold weather, causing fuel starvation as well.

Fuel samples should always be taken of the gas when it is both in storage as well as prior to flying the aircraft, especially after rainstorms or the aircraft has sat on the ground for long periods with low fuel in the tanks in a humid environment.  Fuel samples should also be taken approximately 30 minutes after refueling and the gas allowed to settle in the tanks.  A preflight sample of water contamination taken from the fuel tank sumps of a GA aircraft can be seen here.

Water injection, however carefully controls the amount of water going into the engine along with fuel at the point of combustion, allowing for continued engine operation.

Water injection is introduced into the combustion chamber to cool the temperature which allows for a higher rpm of the engine which gives you more thrust. This occurs after the fuel has ignited.  Water contamination means poor ignition where water and fuel are trying to combust resulting in possible flameout.


Can I fly a glider in Europe on a Canadian Glider License? I currently live in Canada as a Permanent Resident and I recently received my Canadian Glider Pilot License. I will be going to Europe soon so I was wondering what I have to do to be able to fly a glider there. I will be going to the Netherlands if this makes any difference and I still have my Dutch Citizenship. Do I have to convert my license or just do some extra training?

Also would it help if I got a FAA glider certificate/endorsement on top of my TCCA license?

In general, it is difficult to convert to EASA. You can find more information here however I suspect the easiest method will simply be for you to phone them up.

I think the bureaucracy will probably be more hassle than it's worth. It's not like Transport Canada where you can just get a FLVC (Foreign Licence Validation Certificate) or whatever (that was a pleasent suprise after our CAA in the UK!).

If the glider has Canadian registration, you can fly it anywhere in the world. If it doesn't, it depends on which registration it has and in what country you have to fly. Each country is different, and the further west you go in Europe, the more anal[-retentive] the bureaucrats. UK is the worst, as you go east in Europe it gets easier and more laid back. I have an N-registered glider in Germany so I can fly it any time I want, but I can't fly a D- glider. Unfortunately, to get the correct answer for any country you have to navigate their regulatory bureaucracy, which can be pretty thick in many places.


Do most commercial jets have a negative lifting body? I took a look at some example airfoils and noticed they all seem to have a downward hook at the end. I believe this draws the air downwards, creating a reaction force upwards: lift.

Now here is a typical wide-body jet profile:

Notice how the fuselage points upwards at the tail. I'm not talking about the vertical stabilizer, not the horizontal stabilizers either. I'm talking about the fuselage getting narrower and narrow at the tail. It tapers to a point, but the taper flows upwards.

I'm sure this shape has to do with avoiding tail strikes. But is seems to me like it also incurs negative lift. Does the tail draw air upwards, creating a reaction force in the downwards direction and thus negative lift?

You are right, the upsweep at the tailcone allows the pilot to rotate the aircraft during take-off and landing without touching the ground with the rear fuselage. When such a tail strike  happens, the aircraft needs to be inspected and repaired, and incorrect repairs after a tail strike have already caused loss of life.

While most Boeing fuselages show some downslope of the upper tailcone contour, this effect is even more pronounced with all Airbus aircraft except the A380. There the upper contour of the tailcone is straight. Military transports with a rear ramp show even more upsweep to keep the heavy ramp short, and most need additional strakes to limit the area of separated flow there at low speed.

This upsweep adds a small downforce and, since it happens away from the c.g., a pitch-up moment. First, at the transition from the cylindrical section to the tailcone you find a strong suction peak at the high curvature region on the lower fuselage. Also, the lower side of the tailcone has a lower pressure than the upper side. Both create the downforce and the pitch-up moment. However, a three-dimensional body of a very low aspect ratio like the fuselage has a very low lift curve slope, so even the strong upsweep creates a small moment when compared to the contribution of the horizontal tail surface.

The local flow at the tail is dominated by the wing wake. To create lift, the wing has to deflect the flow downwards, and this produces a local flow direction at the tailcone which aggravates the situation created by the upsweep. The best indication for the local direction of flow is the rain diverter above the rear fuselage door. See below the rear door of the A320: To create the lowest possible drag, the rain strip is aligned with the local direction of flow during cruise. When flying at lower speed, the downwash is even stronger.

A320 rear fuselage (own work, based on this source)

When a body generates aerodynamic force, most of that force will be generated very close to the leading edge, as that is where the center of pressure is located. Relatively little is happening at the trailing edge, with respect to the generation of pressure differentials - you do still need to pay attention to the trailing edge in order to ensure that airflow is smooth and doesn't 'separate', but it's not the first place you should be looking to determine if the body, as a whole, will generate lift.

FWIW, a lot of modern aircraft fuselages are designed as lifting bodies, in order to help improve efficiency and performance, so, on the whole, they will be generating some amount of lift throughout most, if not all stages of flight.


When would a pilot request a "VMC descent" or "VMC climb"? Can anybody explain what's the point of this and in what kind of situations a pilot needs it?
ICAO Doc 9432 "Manual of Radiotelephony"

8.3.3 An aircraft may request a clearance to climb or descend maintaining own separation while in VMC, in daylight, below 10 000 feet in airspace classes D and E. The clearance shall include information on essential traffic.
Example:
P: FASTAIR 345, REQUEST VMC DESCENT TO FL 60
C: FASTAIR 345, DESCEND TO FL 60, MAINTAIN OWN SEPARATION AND VMC FROM FL 90 TO FL 70, TRAFFIC WESTBOUND FRIENDSHIP FL 80, ESTIMATING WICKEN VOR AT 07.

It would be needed when otherwise the flight path would not be cleared because ATC cannot ensure separation with the conflicting traffic. The pilot agreeing to maintain their own separation in VMC allows the level change to be cleared despite the conflicting traffic.

In the case of a VMC descent, this frequent request by pilots prevents them from having to be vectored for a formal ILS approach which may otherwise take them many miles (typically 10-30mi but in congested airspace can be closer to 100mi) from the air field. This saves them time, money, and distance.

After a pilot requests this, the controller will often request they report if or when they can navigate to the airport under VFR conditions and switch them to a much quicker and more direct VFR approach.


Do you have to update weight and balance charts after installing new avionics? The POH always has weight and balance charts. Let's say you install some new avionics, hence changing the weight of the aircraft. Do you need to update the POH binder with new weight & balance charts? What about take-off/landing distance information?

For the US under the FAA, Yes you do!

From the FAA WB handbook

  Changes of fixed equipment may have a major effect upon the weight of
  the aircraft. Many aircraft are overloaded by the installation of
  extra radios or instruments. Fortunately, the replacement of older,
  heavy electronic equipment with newer, lighter types results in a
  weight reduction. This weight change, however helpful, can cause the
  CG to shift, which must be computed and annotated in the weight and
  balance record.

For larger repairs.

  Repairs and alterations are the major sources of weight changes. It is
  the responsibility of the FAA-certificate mechanic or repairman making
  any repair or alteration to know the weight and location of a change,
  to compute the CG, record the new empty weight and EWCG in the
  aircraft weight and balance record, and update the equipment lists.

Generally this is done by the shop that installs them. If you as the owner/operator installs them (which you are permitted to do to some extent) you may need to have a new WB drafted up.

This is also checked at anual every year,

  The FAA-certificated mechanic or repairman conducting an annual or
  condition inspection must ensure the weight and balance data in the
  aircraft records is current and accurate. It is the responsibility of
  the PIC to use the most current weight and balance data when operating
  the aircraft.

Yes, the empty weight and center of gravity data does need to be updated.

Anytime weight or center of gravity is changed, the mechanic must update the aircraft weight and balance. This information must be available to the pilot prior to flight, and is often included in the POH as an additional sheet or otherwise copied into the flight manual. In this way, the answer to your larger question is, yes.

However, if you are referring to the generic charts for the purpose of calculating weight and balance, the answer is no, these generic charts do not require updating. Conversely, an approved Airplane Flight Manual (AFM), will generally include weight and balance information that is specific to that aircraft. This information should be updated, or a note should be made invalidating the outdated data and referring the flight crew to the current data.

Typically when a change such as avionics installation takes place, the mechanic will compute a weight and balance change based on the item weight and installation position. However, the aircraft can be re-weighed to satisfy the same requirement.

The FAA states that mechanics should update the weight and balance record whenever an alteration such as an equipment change takes place. See the following paragraphs from page 1-3 of FAA-H-8083-1B, the "Weight and Balance Handbook".

  Changes of fixed equipment may have a major effect upon
  the weight of the aircraft. Many aircraft are overloaded by
  the installation of extra radios or instruments. Fortunately,
  the replacement of older, heavy electronic equipment with
  newer, lighter types results in a weight reduction. This
  weight change, however helpful, can cause the CG to shift,
  which must be computed and annotated in the weight and
  balance record.

  Repairs and alterations are the major sources of weight
  changes. It is the responsibility of the FAA-certificate
  mechanic or repairman making any repair or alteration to
  know the weight and location of a change, to compute the
  CG, record the new empty weight and EWCG in the aircraft
  weight and balance record, and update the equipment lists.

Note that the aircraft weight and balance record is generally a part of the aircraft maintenance logbooks, which are typically not carried on board the aircraft. The change in weight and balance is typically noted in the POH by inserting a photocopy or otherwise transferring the applicable information. In regards to these choices of where to store the required maintenance information, including the current weight and balance data, the operator is often free to choose according to convenience. There is no general requirement in 14 CFR to carry current empty weight and center of gravity data on board the aircraft for flights operating under §91.

Flights operating under 14 CFR, Subchapter G will, or may, have different operating requirements. For example, an air carrier authorized to operate under §135 is generally required to carry, on board the aircraft on flights operated under §135, a completed load manifest documenting weight and balance computations. However, for flights operated under §91, such documentation is not generally required.

Note: This answer addresses operations under FAA jurisdiction.


Is excess lift or excess power needed for a climb? As answered in this question, aircraft need excess power - not excess lift - to climb. This is plausible when the aircraft's thrust vector has a vertical component (its nose and engine points upwards), but I challenge the requirement of excess power for every case.

Please take a look at the following cart. The thrust gets delivered by a propeller at the rear and the thrust vector is always horizontal. A wing attached to a vertical beam is free to move up and down.

When the cart gets accelerated and reaches a certain speed, the lift acting onto the wing gets greater than the wing's weight, leading to a climb of the wing. Please notice that - because thrust is horizontal - the chemical energy burned goes into kinetic energy of the cart and/or heat energy (due to overcoming drag). No power invested by the propeller goes into potential energy of the wing; the climb of the wing is done purely by lift.

Did I miss something?

As the answers to your original question already explained, you do need extra lift to accelerate upwards. Once the wing is set into a vertical motion, however, lift again exactly equals weight to keep the wing at a constant vertical speed (if we neglect thrust and drag for a moment). No extra lift is needed to maintain that vertical speed. Only when you want to accelerate further up, extra lift is needed.

The increase in potential energy comes indeed from the propeller, because the lift vector of the climbing wing is tilted backwards, adding a horizontal component that needs to be compensated by extra propeller thrust.

Now let's look at your experiment in detail: I assume the wing has some mass, is rotationally locked and slides up and down that pole without friction. If you accelerate the car, at some point its speed will just be right for the wing to create exactly the lift to cancel out its own weight. At this speed the wing will be stable at any position along the pole. If it slides down a little, its angle of attack $\alpha$ will increase and create more lift, stopping the downward motion. The reverse is true for any upward motion. See below for an illustration of the principle. The cyan vector is the vector sum of the flow due to forward motion (blue) and vertical motion (red), and this is what the wing will "notice".

When the car accelerates further, the lift will increase and now become greater than the weight. The wing will accelerate upwards until its vertical speed will reduce its angle of attack by enough to reduce the vertical aerodynamic forces to exactly equal its weight. Now you have the same situation as before, but not at zero vertical speed, but at a positive vertical speed which will make sure that the wing pops out at the top of the pole unless there is some stop. When the wing hits the stop, the vertical motion ceases, the angle of attack increases and the wing will lift up not only itself, but also part of the car's weight.

Note that I now spoke of the vertical components of the aerodynamic forces, not lift. When drag is added, it will add a vertical component when the wing is in motion. Lift is defined as the sum of aerodynamic forces perpendicular to the flow direction at infinity and drag parallel to it. This cumbersome definition makes sure that local distortions in the flow field do not impact the direction of lift and drag. The direction of lift for the climbing wing will point slightly backwards and the direction of drag slightly downwards. This will add some drag component to the sum of the vertical aerodynamic forces, and lift needs to increase to compensate for this. The horizontal component of lift will now add to the drag and the forces on the pole, so more force from the propeller is needed to push the climbing wing through the air. This extra force is needed to increase the potential energy of the wing on its way up. For a descending wing, the reverse is true: Now drag will add some vertical component and lift will be slightly slower. The forward component of lift will now push against the pole, reducing the force the propeller needs to provide. The reduction in potential energy now reduces the horizontal aerodynamic forces.

An airplane is slightly different, because it is free to pitch up or down and the angle of thrust will pitch with it. This will enable the pilot to select the flight path and the amount of lift the wing creates, but again the vertical motion will make sure that any excess lift will translate into increased vertical speed and a lower angle of attack, so the excess lift vanishes. In a climb, thrust needs to be bigger than drag in order to increase the potential energy of the airplane, and now the vertical component of the tilted thrust vector will support some weight, reducing the amount of lift needed to support the weight.

The other answer (and the basic premise) are misleading. Aviation is a careful balance of just about everything, and you rarely get more of one without losing some of the other.

Consider a rocket. No wings, and thus no lift. Sea level, 0m/s to orbit on 8 minutes. Everything done with a rather ridiculous amount of power.

Now consider an airship. Also no wings, but excess lift. Goes up all by itself. The engines are purely for maneuvering, if you remove them we usually call the thing a balloon.

One of the most ridiculous things I ever heard was a flight instructor who claimed that the throttle controls altitude and the elevator controls speed. I called complete BS on the statement and asked if he found himself flying toward some cumulo-granitus would he prefer to add power or yank back rather sharply on the controls?

What he was trying to get across was that in the extremely narrow regime of straight and level flight*, adjusting power will affect speed which affects lift, and the plane will eventually stabilize at a different altitude after a power adjustment. Adjusting pitch will change your speed almost immediately, but your altitude will change as well. You could arrange a demonstration of adjusting power and pitch simultaneously and having nothing else change, but that basically proves my point. If you want to slow down (for example, landing) do you leave the throttle at full and pull the stick all the way back? Of course not. It's a very delicate balance, and it's something pilots spend a lot of time learning. Or if you work for certain asian airlines you just have some very expensive computers handle it for you.

Yes, we spend a lot of time there, but consider how precise you need to be. A fraction of a degree, uncorrected, in any axis will result in you crashing before you run out of fuel.


Does runway 32/33R at Madrid actually have a kink in it? In this satellite image of Madrid airport (MAD/LEMD)...

Source:Google maps satellite view
Alternate link from maps.google.nl still renders incorrectly for me, but appears fine for others...

...it appears that there is a very noticeable left kink in the landing area of runway 32/33R.

According to what I can interpret from Jeppesen's airport data, there doesn't appear to be any indication of this kink:

Page 50 of Jeppesen hosted by uvairlines.com.

Is that kink actually there, or is it an artifact of Google's processing of  different images? There is obviously something going on, as you can see both RWY32 & RWY33 markings in the image, while Jeppesen clearly identifies it as 33.

If that kink is actually there, what impact does that have on a pilot landing? I believe the touchdown target is the two long, solid bars at the top left of the image, which excludes the kink, however, there is enough rubber to indicate that touchdowns have occurred much closer to the threshold than that.

An interesting feature of your question is the apparent double-exposure of runway number in your image. And I suspect it will also account for/explain why you see a kink in an image.

Occasionally, runways change number. The reason for this is basically that runways only have 36 possible designations (1-36) however a runway designated 18 may be orientated anywhere from 175-184 degrees. Usually the actual orientation of the runway is rounded to the nearest 10. hence, a runway pointing at 184 degrees would be designated "Runway 18".

Magnetic variation drifts over the years (eg, 10 years ago Southern UK was +3 degrees, now it is +1). This may make a runway which was once 184 degrees magnetic now 186 degrees and that would require its designation to change from "Runway 18" to "Runway 19".

Now, as for your image, I would guess that Google have taken a grab when it was Runway 32, and (at least partially) again once it had been re-designated (and repainted!) Runway 33. This is backed up with the airport's wikipedia article:

  On 20 September 2012, both runways 15/33 were renamed as 14R/32L (the longest) and 14L/32R (the shortest).

The act of stitching images together, and the image processing algorithms in use, mean you get kind of a partial of one image and partial of the other. It is almost certainly not there in real life, and thus has no effect on the pilot's handling around that runway.

No, this is just an image registration artifact.


Landing currency day and night on same ride? Assume you know when sunset was on a particular day you decided to fly (e.g. 8:30 local time). If you took off at 8pm, repeated 3+ landings in the pattern, then left the pattern for about half an hour, returned into the pattern at home airfield, did 3+ more landings to full stop at night...did you achieve the objective of landing currency for both day and night, and if so how do you normally log the landings?

As pilots we often talk about night flying and daytime flying meaning when it is dark or light, but for logging time and for currency in the US there are specific definitions that we must pay attention to.

  FAR 1.1 General Definitions

  Night means the time between the end of evening civil twilight and the
  beginning of morning civil twilight, as published by the American Air
  Almanac, converted to local time.

Day is not defined in the FARs but the definition of night implies that it is the time between the beginning of morning civil twilight and the end of evening civil twilight.

The Air Almanac is published annually on CD-ROM but you can find sunset, sunrise, and civil twilight times for specific locations at the US Naval Observatory website or in ForeFlight.

The time between sunrise/sunset and twilight is 26-30 minutes depending on the time of year. Since you can easily find sunrise/sunset information in newspapers, the weather channel, etc. you can estimate twilight fairly easily.

Currency

  §61.57 (b) (1) … no person may act as pilot in command of an aircraft
  carrying passengers during the period beginning 1 hour after sunset
  and ending 1 hour before sunrise, unless within the preceding 90 days
  that person has made at least three takeoffs and three landings to a
  full stop during the period beginning 1 hour after sunset and ending 1
  hour before sunrise, and…

VFR Weather Minimums
Only Class G airspace has different minimums depending on night and day and they use the standard night definition—end of evening twilight to the beginning of morning twilight.

Aircraft Lights
Aircraft lighting is required between sunset and sunrise.

  §91.209 During the period between sunset and sunrise no person may 1.
  operate an aircraft unless it has lighted position lights, 2. park or
  move an aircraft in an area of an airport where night operations are
  being conducted unless it is clearly illuminated, has position lights,
  or is in an area marked by obstruction lights.

Aeronautical Experience Requirement
In order to obtain a private pilot certificate night training is required. The commercial pilot certificate required solo night flights. In these cases the standard night definition—end of evening twilight to the beginning of morning twilight—applies.

Special VFR
AIM 4-4-6 g. Special VFR operations are prohibited between sunset and sunrise unless the pilot is instrument rated and the aircraft equipped for IFR flight.

Logging Night Flying Time
Logging of night flight should be made in accordance with Part 1 definitions, which is from the end of evening civil twilight to the start of morning civil twilight. This differs from the definition used for night currency.

Summary

• Position lights – sunset to sunrise

• Special VFR – except sunset to sunrise unless instrument rated

• Carry Passengers – 1 hour after sunset to 1 hour before sunrise

• Everything else – evening twilight to morning twilight

The answer to your question.

Now that we have that out of the way, we can look at the requirements for carrying passengers.

  §61.57   Recent flight experience: Pilot in command. (a) General
  experience. (1) Except as provided in paragraph (e) of this section,
  no person may act as a pilot in command of an aircraft carrying
  passengers or of an aircraft certificated for more than one pilot
  flight crewmember unless that person has made at least three takeoffs
  and three landings within the preceding 90 days, and—

  (i) The person acted as the sole manipulator of the flight controls;
  and

  (ii) The required takeoffs and landings were performed in an aircraft
  of the same category, class, and type (if a type rating is required),
  and, if the aircraft to be flown is an airplane with a tailwheel, the
  takeoffs and landings must have been made to a full stop in an
  airplane with a tailwheel.

  (2) For the purpose of meeting the requirements of paragraph (a)(1) of
  this section, a person may act as a pilot in command of an aircraft
  under day VFR or day IFR, provided no persons or property are carried
  on board the aircraft, other than those necessary for the conduct of
  the flight.

You can remain current for carrying passengers in the daytime by making three takeofffs and landins either with or without passengers. If you are not current, you may regain currency as long as you don’t have passengers.

A separate regulation governs night currency—where night is 1 hour after sunset until 1 hour before sunrise.

  §61.57   Recent flight experience: Pilot in command.** b) Night
  takeoff and landing experience. (1) Except as provided in paragraph
  (e) of this section, no person may act as pilot in command of an
  aircraft carrying passengers during the period beginning 1 hour after
  sunset and ending 1 hour before sunrise, unless within the preceding
  90 days that person has made at least three takeoffs and three
  landings to a full stop during the period beginning 1 hour after
  sunset and ending 1 hour before sunrise, and—

If you are night current then you have satisfied §61.57 (1) and so you are also day current.

Notwithstanding the fact that legal night starts 1 hour after the 8:30 sunset per FAR 61.57(b),

  (b) Night takeoff and landing experience. (1) Except as provided in paragraph (e) of this section, no person may act as pilot in command of an aircraft carrying passengers during the period beginning 1 hour after sunset and ending 1 hour before sunrise, unless within the preceding 90 days that person has made at least three takeoffs and three landings to a full stop during the period beginning 1 hour after sunset and ending 1 hour before sunrise, and—

say you split your flying between some landings before 9:30 pm and some after, sufficient to meet the requirement.

It's simple.  The time you were airborne prior to 9:30 goes in the "Day" column, and the time you were airborne after 9:30 goes in the "Night" column.  In "Remarks" you write in something like "3 day landings and 4 night landings completed".

That's all you need to do.


Do jet contrails impact weather? Do jet contrails impact weather at the ground?

Short answer

Based on past observations and a study led by Patrick Minnis from NASA, contrails could result in increasing the temperature over the ground by 1°C every 30 years over the US.

From a study by German researchers Ulrike Burkhardt and Bernd Kärcher, the effect of contrails is comparable in other areas with a similar level of air traffic.

Because the air traffic is said to be about to increase very quickly, the effects of contrails on the temperature may increase too.

Contrails and natural cirrus: So similar that studies are difficult

Contrails are like cirrus, and actually some just become persistent cirrus. Sometime it's difficult to tell which one is a condensation trail, which one is a natural cloud. This makes more difficult the study of contrails effects, and introduces many uncertainties that need to be reduced:

(source)

The current studies take into account only the young contrail-cirrus, because they are still relatively easy to differentiate from natural cirrus, due to their linear shape. Most aged contrail-cirrus are not differentiable and are not counted as aircraft generated. This means the current results potentially under-estimate the effects of contrails.

Pertaining to the discussion, contrail-cirrus as clouds:

Induce a cloud-feedback, i.e. the coupling between cloudiness and surface air temperature.
Induce a radiative forcing, they increase the portion of the energy not re-emitted to space. The quantity is expressed in mW/m².

Increasing the air temperature has a link with increasing ground or oceans temperature, but the two notions mustn't be mixed. However cirrus are suspected to play a role in the global warming, because they could introduce a positive feedback into this warming.

Study: Coverage and effects of contrail-cirrus

Global radiative forcing from contrail cirrus published in Nature in 2011 was a study to evaluate the contrail-cirrus coverage, and its impact. Conclusion:

  Aviation makes a significant contribution to anthropogenic climate
  forcing. The impacts arise from [...] and from changes in cloudiness in the
  upper troposphere. An important but poorly understood component of
  this forcing is caused by ‘contrail cirrus’—a type of cloud that
  consist of young line-shaped contrails and the older irregularly
  shaped contrails that arise from them.

The estimated effect is depicted on this map (mW/m²) from the study:

Net effect of contrails (CIC) warming compared to other aviation factors of warming:

(source)

Study: Effect of contrail-cirrus on US climate

NASA conducted a study in 2004: Patrick Minnis, J. Kirk Ayers, Rabindra Palikonda, and Dung Phan -- Contrails, Cirrus Trends, and Climate.

This study was analyzed in Science Daily: Clouds caused by aircraft exhaust may warm the US climate:

  Using published results from NASA's Goddard Institute for Space
  Studies (New York) general circulation model, Minnis and his
  colleagues estimated contrails and their resulting cirrus clouds would
  increase surface and lower atmospheric temperatures by 0.36 to 0.54 degrees Fahrenheit per decade.

Aviation radiative forcing in 2000: An update on IPCC (1999)

This study was included in a new one by R. Sausen et al. in 2005. It shown the radiative forcing by aircraft could have been slightly underestimated:

Source: Aviation radiative forcing in 2000: An update on IPCC (1999) - R. Sausen

The US surface temperature is increasing by 1°C every 30 years: I would say this is very significant for plants, life, water cycle, oceanic currents, etc.

Also look at @Simon good answer about the increase of the difference between night and day temperatures, by more than 1°C, during the 3 days civil air traffic was forbidden on September 2001. This increase seems to confirm contrail-cirrus limit cooling on night time.

Not in a real sense. yes they do put water vapor in the air. so does drying your clothes in the dryer. or taking a shower. or driving your car. while it makes a visible cloud the amount of water is much less than cars traveling the same distance due to the fuel efficiency of flight vs. driving.


What is this partially disassembled aircraft in the desert? I found this plane on Google Earth. I'm guessing it is being deconstructed, as there are no factories nearby. What countries could it have originated from?

The coordinates are 35°54'10.9"N, 117°43'51.6"W. Here's the location on Google Maps.

The plane is about 41 feet long, and seems to have had a wingspan of about 30 feet.

Also, if it is possible, what kinds of planes could this be?

Sorry if this question is not really possible to answer. I'm a complete beginner at aircraft.

So, you found what looks like an F-8 missing a wing in the middle of the USN's Air Warfare Center at China Lake.

It resembles the F-8 a lot:

Image Source

As @Andrew said in a comment, the plane might be an F-11 which has a little closer resemblance to your picture.

Image Source