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In the pilot's introductory book "Stick and Rudder" it claims that a nose-up glide is possible. It doesn't state how, why or when. It implies it's possible to do and maintain a constant forward velocity.

Is this possible? I really don't see how, unless the aircraft has what I assume would be an extremely unusual design, where the wings would have to have a reverse angle of incidence of the common designs.

Glancing through clancy's Aerodynamics, it seems that the force of lift acts upward, and slighly behind the normal of the chord. Given a glide has no thrust, I can't see how the net forces could balance with the drag to maintain forward velocity if the nose is up.

Thanks

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up vote 4 down vote accepted

The essence of a glide is that the aircraft is descending. Just like a car rolling down a moderate grade, it is trading potential energy to replenish the kinetic energy lost to drag.

Whether the nose points up or down only relates to the angle of attack, which only relates to speed. An aircraft traveling at slow speed has a higher angle of attack, so its nose will point up, compared to when it is traveling at high speed.

One of the things you learn in flight training is how to handle a loss of power. There's a mnemonic for that: ABC

  • A: Trim for the Airspeed (65 kts in a C172) that gives you the best glide range. This is fairly slow and nose-high. (There is even a somewhat slower speed that gives you less range but more time aloft.)
  • B: Look for the Best landing site, be it a field, road, or if you're lucky, an airport.
  • C: Look in the Cockpit for what you can do, like trying to restart the engine, and Calling on the radio.

So, under A, you can see that a slow glide is relatively nose-up, even while the aircraft is descending.

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Thank you - so just to confirm, when in A you say nose high, that refers to the absolute angle the ground would make with the fuselage? –  Jodes Feb 27 '13 at 16:41
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@Jodes: No. That would depend on how the wings are mounted, what the glide ratio is, and what the speed is. For the C172, the glide ratio is about 9:1, so the descent angle would be about 6 degrees down. The angle of attack would be about 10-15 degrees up, totalling about 4-9 degrees above horizontal. I'm not sure what angle the wings are mounted at. It also depends on the pilot's height and how high the seat is adjusted w.r.t. the cowling. There's no natural line indicating "true horizontal" on an airplane. It's all relative. At high speed it feels like falling out the front. –  Mike Dunlavey Feb 27 '13 at 17:01
    
Thank you so much! –  Jodes Feb 27 '13 at 20:52
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