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Old 22nd Mar 2006, 16:32
  #68 (permalink)  
LEM
 
Join Date: May 2003
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Elevator full down (i.e. stick full forward) will only effectively weight transfer onto the nosewheel, leading to "wheel-barrowing" (a condition of directional instability). It won't, by any useful measure, decrease the wing's AoA. Why? Think of a depressed oleo as only being able to soak up shock i.e. weight-bearing oleos are effectively incompressible to flight-control inputs - therefore fully-down elevator will just load up the nosewheel. It won't depress the nose oleo appreciably more, nor take any angle-of-attack off the wings.
OVERTALK, that's where we disagree. I believe a full forward stick can change your AoA by say a couple of degrees, depending on type, of course.

Remember, we're having a very hard time braking on this slippery surface, so the nose oleo isn't compressed by a braking momentum.

And another point where we disagree is that reverse thrust does produce a pitch down effect.

Actually, the pivot being the main wheels, reverse thrust produces a pitch up effect, even on low mounted engines like a B737, unlike in flight where it would produce a pitchdown effect.

I can't believe it's so hard to understand...


Btw, maybe pushing the scenario to the limit will help get a clearer picture.
Imagine the worst case, an airplane with no spoilers.
Or simply the pilot forgetting to arm them.
Or simply a model without any spoiler!
Upon touch down, the wing is "still flying", and as speed decreses, lift gradually decreases.
Of course after touchdown one can get the impression the wing is fully stalled.
Not so, especially after you've lowered the nose.
The Aoa will not be beyond the stall limit at all, and the wing is still producing lift.
What would you do? Push or pull?

I suggets you push, my friend, to reduce the attitude (yes, the nose oleo IS compressible!), and decrease the residual lift as much as possible.

It's as natural as that. I know the tail will produce some lift, but that's almost nothing if compared to the lift loss on the wings.

Now, if this scenario is right without spoilers, probably it's still right with spoilers extended.

My assumption is that spoilers kill only a fraction of the lift.

If this is NOT true, then you're right.

MFS should have the numbers about the exact percentage, at least on his type.

LEM

Last edited by LEM; 22nd Mar 2006 at 16:50.
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