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What happens if a sailplane has no horiz stabilizer or elevator?
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January 19th 04, 04:40 PM
Andreas Maurer
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On 18 Jan 2004 11:53:31 -0700,
(Mark James Boyd)
wrote:
Just imagine what forces your movable weight will exert under a g load
different than 1? For example, when you are flying through a vertical
gust?
I'd imagine it will behave the same as an attached one pound ballast
weight on the upper part of the rudder of the glider used to
balance the rudder. Perhaps I'm missing your point here...
You are correct - but you have the horizontal stab that dampens the
motion (remember that the whole fuselage and tail acts as a weight!).
This is the cause why you need something aerodynamical to control your
pitch, and why weight shifting does not work.
It does not matter whether the damping is done by a horizontal
stabilizier or the airfoil/wing design of a flying wing.
Now this a very interesting point. Whether the weight is above
or below the C.G. seems to also have an effect.
Yes - and don't forget that the control authority of hang gliders is
extremely limited. If the gravity vector is not pointing "downwards"
(seen from the pilot's coordinate system) they have absolutely no
control at all. Inverted flight is out of question, and they are able
to fly their loopings only with some tricks.
It seems this weight shift idea is just a very fine refinement.
It's intention is to reduce that tiny bit of additional
drag caused by moving surfaces or trim. I agree this is
not anywhere near "the most important invention," but just a
fun winter mind-teaser.
This is what is already being done - by water ballast in the tail that
fixes the CG at a position that is close to perfect for all flight
situations.
There have already trials been made (with ASH-25) to determine the
influence of performance of different CG positions in different
situations (cruise, climb, thermalling), and the inluence was nearly
immeasurably if the CG was moved to a supposedly "more optimum"
forward position during cruise.
The performance gain in a glider with rearward CG is (as you point out
for Cessan and airliners) often dramatic, especially in climb rate.
Bye
Andreas
Andreas Maurer