Coffin Corner?

[Chunks]

Can somebody please explain to me what this is?

[fritzi]

The coffin corner is refered to a speed at which your stall speed is very close to your Max mach speed.

A good example of a aircraft which constatly flies "within" the coffins corner is the U2. If I recall correctly, at max altitude the difference between max mach and stall speed is only around 5 KIAS.

[rotornut]

At max Mach speed what happens? Is it a compression stall?

[Go Smoke]

In aerobatic parlance we some times refer to 'Coffin Corner' as that place in the flight envelope that when plotted usually occurs in the top right hand corner but can also be bottom right hand dependant on situation.

Theoretically it is when you are pulling max +ve g whilst at or near Vne or have bust it and are approaching Vd in an energy gaining attitude.

So, whatever you do you're a dead man pull more G and suffer a structural failure or bust Vd and equally suffer a structural failure.

In reality the thing to do is pull more G as exceeding permissible loading will, in likelihood, bend the aircraft rather than cause catastrophic failure and the chance of getting it back on the ground is greater than if you exceed Vd and get flutter.

I had a distinctly unpleasant experience in coffin corner whilst inverted in a 45 degree down line 5 kts off Vne
pushing -ve 4 G. The elevator started to flutter (due to a worn bush in the linkage) and then the whole rear end of the aircraft started a sympathetic warping, oscillation.

I was at 4000' and the banging was heard clearly on the ground!
A change of underwear and a couple of stiff ones later and I could talk about it but that is as close to 'Coffin Corner' as I want to go for a while.

[capt.sparrow]

You have a slow speed stall buffet which i presume you are aware of. You also have a high speed stall buffet when in simple terms you are going fast enough that laminar flow over the aerofoil becomes too turbulent. As you increase altitude your slow speed stall increases - ie you stall at a higher speed. If you carry on up eventually your slow speed stall and your high speed stall become coincidental. At or near this point if you fly slower you stall, if you fly faster you stall - so you go home in a coffin.

[Tarnished]

I always thought the Coffin Corner applied to twin engine aircraft where you were below a safe single engine recovery speed in the good old days where aircraft "had" to operate in that region. IE that area where you had insufficient rudder authority to control the swing if you lost a donk on or about take off.

t

[buzzc152]

I've always understood coffin corner as that speed/altitude combo where slow and high speed stall speeds are very close together.

The way out of it is to descend......... carefully.

[BOAC]

buzzc152
That too is my understanding.The way out of it is to descend......... carefully. The reason it got its 'name' was because you.........cannot!

[Onan the Clumsy]

I thought it was something to do with helicopter flying and there was a graph with altitude verses speed or something and a big block shaded in at the bottom left hand corner. Something about it being dangerous to operate in that area.

Anyone know what that's about? Is that getting stuck in your own downwash?

[BOAC]

Is that getting stuck in your own downwash? - sounds about as unpleasant as 'vortex ring':D :D

[Jaime S]

Coffin corner is the altitude where Vx and Vy are the same.
It is also where the vario reads zero at best climb speed and full power.

Note that best climb speed will be both Vx and Vy, you will have an aggressively nose high attitude and full power. If you increase speed, you go down because you are not manteining a climb speed and attitude (just as when you pitch down while flying at a sensible altitude). If you increase your angle of attack, you simply stall.

[south coast]

onan...

i am no helicopter pilot, but what i think you are refering to is 'dead mans curve'.

this is a curve on a graph where you are too low to auto-rotate back down to earth slowly, but high enough to fall down with quite a thump!

hence, dead mans curve, but helichopter people, please correct me if i am wrong, just what i have picked up from the discovery channel...

[rotornut]

Anyone know what that's about? Is that getting stuck in your own downwash?

south coast is correct. It's called the "dead man's curve". If you want, I'll send you a copy of a height/velocity diagram. PM me, if you are interested, you too, south coast.

[John Farley]

Coffin corner is certainly the common name given to the top left hand corner of the flight envelope (top being high and left being slow)

All aircraft become unflyable at some point due to low speed whether we call it a stall or whatever we think the airflow is doing does not really matter and those details will vary from type to type. Many subsonic aeroplanes (but not all) go out of control at some high mach number or other (again it does not matter why) Coffin corner is where the low speed limit and the high mach limit are coincident.

For some modern and high speed aircraft they may not actually go out of control at high mach but may have a design mach limit imposed. A few have neither and so do not have a coffin corner.

When Walter Gibb set the world altitude record at 65,889ft in a B2 Canberra with Olympus engines on 29 August 1955 you had better believe he got right into the corner….

At max Mach speed what happens? Is it a compression stall

rotornut

There are about as many varied reasons for an aircraft to go out of contol due to mach number effects as there are for loss of control at low speed.

In both cases you will no longer be able to properly control one or more of the following: pitch attitude, roll attitude, yaw attitude or height. In a few cases this may be because one of your controls has hit the stops in many others the handling just becomes too erratic (like a wing drops or there is an uncontollable pitch trim change)

About the only generalisation that applies to the high mach end is that shock waves are spoiling the way the aircraft is flying. (They could stop a control from working, they could cause asymmetric lift or drag, they might spoil wing lift they could cause pitch up and so on).

JF

[Willard W. Willard]

I seem to remember a phenomenon from the fifties when the early jet fighters still had weak engines.
If you got too slow turning base or final you would be stuck in a high aoa situation descending too fast.If you pulled you stalled and if you put the nose down you crashed.
there was not enough power to climb out of the situation.(The Sabre-Dance)

WWW

[ThinkRate]

I found a very useful description of Q coffin corner -and other high altitude aerodynamic effects and phenomena- in an article by David Ison in Proffessional Pilot Magazine that can be found here:

An introduction to the peculiarities of high-altitude aerodynamics (http://www.propilotmag.com/March/article1_mar.html)

TR
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[mono]

Isn't this the corner of that smelly hut where all the smokers sit?? Cough, cough.

:O :O :O

Sorry I just couldn't resist.

[south coast]

na, not tonight love, i'm washing me 'air...

remember the old anti-smoking adverts?