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  1. #1
    150+ Forum Groupie choffmann's Avatar
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    coffin corner question

    Hi folks,

    hereīs a question for the pro pilots amongst us (posted this similarly on pprune.org, but no sufficient response, yet):
    Is there an impact of weather, especially winds, on coffin corner parameters, and if so, what impact?
    Let me go into details:
    Coffin corner is where the stall speed line and the max mach velocity cross, right? It is encountered on a definite altitude, right? It depends on aircraft type, of course.
    Now: if you experience a strong tail wind, I understand, the engine stall probability and thus the stall speed increases (*). Is that correct? If so, does this lower your coffin corner altitude(#)? If you are at a relatively high flight level, letīs say FL370, and you suddenly experience a strong tail wind, can this lead to engine stall?
    I have read many AF447 threads in various forums. Of course, the actual cause of this specific accident is not clear by far. And I donīt want to participate in the debate. My question is "generally speaking" of flight physics. I just wondered, if the setting with high FL, heavy aircraft (due to full tanks) and sudden severe weather conditions, could have been a contributing factor.
    I have enclosed a picture to clarify what I mean:
    Attached Files Attached Files

  2. #2
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    Re: coffin corner question

    Winds will have no effect on engines.

    A strong tailwind following a strong headwind on the approach to land may make airspeed control very difficult,, leading to a wing stall.

    At a high altitude and a fast airspeed ( in the coffin corner) clear air turbulance has been know to increase airspeed enough ,in some cases to push the aircraft out of the envelope.
    The wing ,of say a learjet , is shaped in such a way that the speed of the air going over the top of the wing is going much faster than the airspeed of the plane.
    At mach.83 for example, the speed of the air over the wing may be very close to the speed of sound ,mach .87 for example.
    If the aircraft speeds up suddenly, the air over the wing will reach Mach 1. The wing of most GA aircraft are not designed to go the speed of sound and what happens is the center of pressure/lift will suddenly move back over the wing and effectively stall the wing. this is aircraft upset followed by uncontrollable spin.

    Some lears had a stick puller which pulled the nose up to slow airspeed when the jet travelled too fast at a high altitude.

    At a very high altitude the coffin corner refers to the very narrow part of the aircraft manouvering envelope , the small difference between stall speed and overspeed conditions.

    Hope this explains some of it to you.

    Most jet engines have a continuous ignition switch that was used during take-off,icing conditions,landing, and turbulance.(TILT)
    This prevented the engines from flaming out if they gulped or were starved of air momentarily. Basically spark plugs that relit the flame if they went out very similar to the start switches.

  3. #3
    150+ Forum Groupie choffmann's Avatar
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    Re: coffin corner question

    Thanks spitfire9!

    At a very high altitude the coffin corner refers to the very narrow part of the aircraft manouvering envelope , the small difference between stall speed and overspeed conditions.
    Ok, if I got you right, then any aircraft travelling in high altitude may possibly reach the lower or upper limits by getting into extreme weather conditions. So this COULD have been a contributing factor for AF447(?). (as I said, donīt really want to speculate).

    Chris