From: Harley Michaelis <[EMAIL PROTECTED]>
To: Mark Drela <[EMAIL PROTECTED]>
Subject: Re: [RCSE] Why RDS did not work for me... long
Date: Wednesday, May 30, 2001 8:30 PM
I'm glad to see fellows the stature of Mark, Oleg, John, Blaine and Dennis
(who pilots the Aerosonde), etc., making contributions to this discussion.
I just this afternoon did the little balsa mockup for which I offered
plans
for the asking. My original one is larger, made of light ply and was
getting shopworn, anyway.
After hinging the flap and aileron with 1/2" wide adhesive tape, I found
the optimum locations for the bends in the shafts. Incidentally, for the
flaps there is one and only one acceptable location for the bend. It is
found by rotating the shaft to the 90 degree down flap location with the
bent end in the pocket. That sets it. To simulate a shaft that can't move
along its axis, I glued little blocks to butt the upright "handle" ends of
the shafts with the elbows located in the optimum spots. That simulates a
rigidly fixed servo and the shaft in the coupler, rigidly secured with
setscrews on a flat.
I have 2 pair of small, flat-headed nails positioned along each shaft so
it
can neither move side to side or up and down. The shafts and the pockets
are in a common geometrical plane at neutral. Everything is open to
visually observe and it is easy to feel what goes on.
Rotation of the shafts provides a smooth and unrestricted action of the
flap and aileron. The pockets freely move fore-aft along the bent end of
the shaft during deflection. I have a continuous hinge about 6" long along
the bottom for the flap. This not a well-bonded hinge and it is too short
to be practical, but after may deflections it is intact and I don't see
that anything is tearing it away. There is something *not happening* that
is expected to be a source of a problem.
The mockup rather closesly simulates a real installation in many ways. As
to the vertical bearing plate that would be used, my suggestion is that
the
slot in it be sized to allow no side to side play and whatever is needed
to
freely move in the other plane. However, at least in this mockup, no such
motion is possible and does not seem to be needed. No binding is evident.
It appears the vertical motion in a real installation would be miniscule.
Oleg. . .if you will provide your address, I will send you this mockup.
Anyone wanting the latest mockup drawing and text, just ask.
From: Mark Drela <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Subject: Re: [RCSE] Why RDS did not work for me... long
Date: Wednesday, May 30, 2001 1:44 PM
A sloppy support bearing will NOT increase the slop in the
position of the control surface. The supprt bearing does have
to be hard and strong though because lateral and vertical forces
are exerted from the pocket friction and geometry of the RADS.
This makes the torque shaft lever against the support bearing.
I dunno about this. I don't see why the support bearing has to be
"hard and strong", when it also has to have slop. A bearing with
slop is mechanically equivalent to no bearing at all, at least for
deflections within the slop limits. Might as well leave it off.
As Blaine pointed out, all the moment is taken up entirely by the
two-point contact between the shaft arm and the pocket walls
(one point is at the shaft tip, the other is at the pocket edge).
It seems you want the bent-over shaft arm to float freely up and down
via flexing of the drive shaft between the servo and the bend. The
vertical load on the flap is then taken up only by the hinge,
avoiding the hinge failure that Oleg saw from a kinematically
overconstrained linkage.
- Mark
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