Re: Flutter & Swept Wing Aircraft

From:         jharuni@london.micrognosis.com (Jonathan Haruni)
Organization: Micrognosis, a division of CSK(UK)
Date:         16 Apr 94 00:56:40 
References:   1
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Richard G. Estock (estock@gandalf.rutgers.edu) wrote:
> As I understand it, on a 7X7 wing there is in succession an:
> 	inboard flap
> 	inboard spoiler
> 	tabs (2)
> 	aileron
> 	outboard flap
> 	outboard spoiler

Sorry, I don't know about flutter.  But I do know the wing configuration
of a 747.  Near the body there is a set of flaps at the trailing edge,
one at the leading edge, and a set of spoilers on top of the wing.
Moving towards the tip, next there is the inboard engine with an aileron
at the trailing edge of the wing, behind the engine.  Moving
outwards, you have an outboard set of flaps and spoilers as before, then
the outboard engine, then finally another aileron at the trailing edge
of the wing near the tip.

> Not that I doubt anything, but I am curious as to why a 747 needs all 
> these flaps, spoilers, etc., and how they are used in actual practice.

The inboard aileron is very small, and is for high speeds.  During cruising
I see it deployed just a few degrees for minor adjustments, and about
10 or 15 degrees for turns.  The outboard aileron is relatively much bigger,
and is used at low speeds - I've only ever seen it kick in on final approach,
and then both ailerons are deflected 20 or 30 degrees just for small amounts
of roll.  At very low speeds, the outboard spoilers on one wing are used
to assist the ailerons - the are raised about 20 degrees to drop the
wing inside the turn (though they're not actually used in turns, only to
level the plane on final approach.)  After landing all the spoilers are
raised to about 75 degrees.   All these angles are from my observations
from inside the plane, they're not accurate.

That explains why there are multiple ailerons and why the outboard
spoilers can be actuated seperately.  As for the flaps being split, and for
why the outboard spoilers are physically separated from the inboard ones,
I think it is merely because the the inboard engine pod occupies all the space
in the wing - there isn't enough room for spoiler actuators or for a whole
set of flaps.  The trailing flaps are enormous - three panels which, when
retracted, nest into each other.


Jonathan Haruni