| What is the distance between the tip of a fan blade and the inside of the nacelle for a turbofan like the Rolls Royce Trent 900? Does this distance change significantly during cruise due to thermal expansion?

up vote3down votefavorite | When an aircraft stalls, do all or most lift forces abruptly disappear or is this transition continuous? Will the aircraft drop from the sky like a brick or can this (losing lift and altitude) happen so gradually that it will be entirely unnoticed from the crew and passengers?I'm troubled by this sentence on Wikipedia referring to the AF447 disaster: "The aircraft remained stalled during its entire 3 minute 30 second descent from 38,000 feet (12,000 m)" (source: https://en.wikipedia.org/wiki/Air_France_Flight_447#Accident) It seems the crew were unaware of the stall condition. (But let's not discuss the reasons here)If lift abruptly disappears when entering a stall, wouldn't people notice a considerable loss in perceived body weight at least as long the aircraft accelerates downward and builds up vertical speed downward. I expect that the airframe experiences enormous drag in the vertical direction once downward speed is being built up and it probably reaches an equilibrium condition limiting its fall rate.But if lift disappears abruptly during the stall, then you should have a sensation of free fall (no weight) at least during a short time. Is this the case or does lift diminish continiously during a stall?PS: While writing the question i have searched and found those Lift-AoA diagrams (like this: https://www.grc.nasa.gov/www/k-12/airplane/incline.html) that should be able to answer the question. Basically my question is: How quickly does Lift drop off to the right of the diagram. All diagrams i found did not in fact go much beyond the stall condition.lift stallshareimprove this question | asked 21 hours ago

Scrontch23126
|    |   | This article might help give you a better understanding of stalls. Long story short: you won't fall out of the sky.– JimyPP 21 hours ago
2 |   | "wouldn't people notice" you'll be surprised to know what people do not notice. To the point, there is quite some literature (and accidents) about senses deceiving pilots. – Federico 21 hours ago
1 |   | @Federico indeed and there is quite a recent video in Skybrary (can be found here ) explaining that problem, called sensory illusions – Stelios Adamantidis 21 hours ago
   |   | Lift does not disappear at the onset of a stall. Find a pilot to take you up and demonstrate a stall, in a lot of aircraft it is a gentle break and simple recovery. This is one of the things I don't agree with in the new airman certification standards, they teach recovery before the stall (fine) but never fully stall the airplane. – Ron Beyer21 hours ago
   |   | It's worth noting that a Cessna stalls in a very different manner to a large swept-wing aircraft – Ben 3 hours agoadd a comment

1 Answeractiveoldestvotesup vote2down vote | You make some valid observations: not all lift disappears after the stall, and at the event of stall there is a downward acceleration that may or may not be perceived.Let's start with what happens after the stall. Measurements on airfoils have been taken over 180°, and they show that after the stall, lift drops back until flat plate lift is achieved at the same angle of attack. Increase AoA further, and lift increases again. An example for a relatively thin airfoil from this document:

Pull the aircraft back far enough to 45°, and the CLCL is even higher than when it stalled! Of course, the drag will be huge compared to normal operating circumstances, and any fixed wing other than a military jet fighter or a VTOL won't have enough power installed to fly at such angles of attack.Isn't there a perceived loss of body weight during the acceleration to stall. Yes there is, but it does not last long, is not necessarily very powerful, and could be referenced to other factors than stall, such as turbulence. Once the CLCL - αα curve hits the trough at 15°, the acceleration stops and weight perception returns to normal. And it's sensory perception, the body only really understands what is happening if all sensory organs are aligned (vision, motion, sound), and can only react in a composed manner if it anticipated the cues and is trained in how to respond. Otherwise we just fight or flee.You mention the case of AF447. It was in a fully developed stall and descending with on average 10,000 ft/min, but the onset to stall was different. It was very gradual, and it was a high speed high altitude stall: there simply is not enough air up there to provide enough lift for the weight of an airliner. It can stall at AoA of zero, then start to fall, as a result of which the AoA changes but the pitch attitude of the aircraft does not, and your body is still aligned with gravity in a dark cockpit where the horizon cannot be seen. No physical cues on what is happening whatsoever!

up vote4down votefavorite | Aviation headsets have Noise Reduction and a larger jack (1/4") than most PC headset counterparts (1/8"). But there are many excellent quality PC headsets with sound-proofing materials which eliminate external noise. So can I just plug in my PC headset using an adaptor? (Let's assume that I have a PC headset of equally good build quality, and comfort)EDIT: What exactly are the functions of an aviation headset?I've already looked at this topic, and this doesn't answer my question - I understand what Aviation Headsets do, but I'm asking (out of academic interest) whether they can be replaced with a superb quality headset for a PC, like for example, the Kingston HyperX Cloud II. If not, what exactly is different other than quality and noise cancellation? Again, this is for academic interest...general-aviation radio-communications radio headsetshareimprove this question | edited 20 hours ago

ymb134.6k493180 | asked yesterday

Anand S12518
|    |   | There is a company that will add a microphone to Bose noise-cancelling headphones so you can use them in place of more expensive headsets. I haven’t used them, but people on different blogs seem to like them. uflymike.com – JScarry 16 hours agoadd a comment

3 Answersactiveoldestvotesup vote5down vote | Can you physically make it work? Yes. But you have to have an adaptor that fixes several compatibility issues.Headphone impedanceImpedance is usually referred to in high and low range. Military headphones are low impedance, 19ΩΩ. Civil aviation uses 300ΩΩ, high impedance headphones. Impedance matching is not vital, but can cause some problems with sound quality. Using a low-Z headset with a high-Z output can cause distortion. A low-Z headset will also be more sensitive, so you would have to turn the volume down. You could run the risk of damaging the headset or your hearing if you have the volume up too far. The headphones you listed in the question are 60ΩΩ, which is somewhat of an in-between. There's no real standard, but low-Z are usually less than 32ΩΩ And high-Z is usually above 100ΩΩ.In the recording studio we considered high-Z headsets to be "universal" meaning that you could plug them in anywhere and they would work, but might be limited in volume. I used a set of low-z phones, since I could plug them into a line output and actually hear it. I was always careful to make sure volumes were turned down before I plugged them into the com boxes. They were pretty sensitive.Microphone impedanceThis will make a bigger difference than the headphones. Military systems use 5ΩΩ, low impedance mics. Civilian systems use high-Z, 80-300ΩΩ amplified electret Mics. The headset you listed in the question lists 2.2kΩΩ which would be work, depending on how much amplification it has. Aircraft coms use a vox circuit to cut out noise that opens when you speak. Depending on whether there is a way to adjust the mic input the level may be too much or too little for the vox system. Too little and it won't open when you speak, too low and it will stay open and you will hear all the aircraft noise.Phantom powerElectret mics require a power source to operate. They can either contain a battery or run off phantom power, which is a voltage supplied by the device it's plugged into. Some aircraft intercoms provide phantom power. I'm unable to find any standard voltage, but it appears the David Clark aviation headsets run on 8-16v. The standard voltage from a PC audio card is 5v. The headset you listed in the question shows that it requires 2v. I presume that, since it's made for PC use it's intended for 5v, but will operate as low as 2v. There's no way to know if 8-16v would overload it, so you would have to either adapt the phantom power or run it on a battery.ConnectorsAviation mics have different physical plugs.Most commonly the headset itself uses a 1/4" phono plug, wired the same way as older audio headsets with 1/4" plugs.

The microphones in aviation headsets are seperate and use a somewhat aviation-specific .206" TRS plug.

Helicopters and military aircraft use a completely different .281" TRRS plug for both headset and mic.

Airbus uses a 5-pin XLR connector for both mic and headset.

Judging from the fact that people have schematics posted on the web on how to adapt aviation headphones for non-aviation use, but not the other way around I would speculate that even the best non-av sets don't meet the challenges of aviation. Some of the physical design characteristics, such as the pressure exerted on the head pads, etc. are probably quite different from the non-av sets.If you look at prices, aviation headsets run well more than twice the price of equivalent quality non-av sets. I'm sure some of that extra price is in design characteristics of the av sets. But, I also suspect that manufacturers will take the exact same sets, change a couple of resistors, put different connectors on them, add the word "aviation" to the box then add $500 to the price.Images sourceAviation data found at Acousticon websiteshareimprove this answer | answered 11 hours ago

TomMcW12k336111
| add a commentup vote2down vote | Yes you can use PC headsets if the right conversion plug is in place, and some work on the electronics is done. The frequency response of the average aviation headset is lower than that of an average headset that is used for listening to music, simce the aviation headset only has to reproduce the voice signals transmitted over the radio. A frequency range of between 400 and 4000 Hz suffices for voice transmission, most standard PC headsets can reproduce a much higher range.Keeping the aircraft noise out is something that PC headsets are usually not designed for though. Aviation headsets clamp the rubber seals around the ears, not a standard PC feature. Active noise reduction works well for constant noise like air hiss, the ANR cannot suppress the noise effectively during frequency changes. A PC headset has no shielding for the cable, so electronic interference is not kept out of the signal path, and the engine sparks may show up in the sound.shareimprove this answer | edited 8 hours ago | answered 19 hours ago

Koyovis9,58042868
| 1 |   | I'd wonder if the squelch capabilities of the mics on those headsets can handle the cockpit noise. – Carlo Felicione 19 hours ago
   |   | Thanks! BTW, what's up with the fuss being made about "impedance values"? Is it dangerous? – Anand S16 hours ago
   |   | @CarloFelicione What you're talking about is "vox" not squelch, although people tend to use them interchangeably. The vox is a function of the radio, not the mic. Some mics have an adjustment for output level which will affect when the vox system opens and closes. – TomMcW 13 hours agoadd a commentup vote2down vote | Sure you can. Just make sure when you make some quirky write up about the audio system not working, you let the A&P know you were using said headsets. I once worked on a "chronic" audio system problem for days not realizing the same crew member had been writing it up. Out of dumb luck, one of the guys I was working with ran into him at a bar and he was discussing how much he loved his Bose headsets. That sort of ignorance wasted whole days of our time.Not all pilots have the luxury of altering their audio systems. The correct answer to this should be somewhere on the spectrum of "No" to "Situational."

 When returning from each flight, during which it is subjected to adverse conditions, say arctic weather, desert heat or just moderate conditions, how is an aircraft evaluated to accurately keep track of its lifespan?If the method is a standard: "this aircraft has had "this many" hours of flight, & therefore, there are "this many" hours left for the aircraft before it is rendered not worthy for service" then this method doesn't consider the various conditions the aircraft is subject to during each flight, which impacts the aircraft's lifespan at varying degrees. I trust there is a more accurate method of evaluation