Patrick Quarterman asks:
>I built a V-tail Chrysalis and am having trouble with flutter in the tail
on launch. I pretty much followed the plans so no variations to worry about.
I just had another person ask the same question through our website. This
problem occurs occasionally, and this is virtually ALWAYS the result of
looseness and/or springiness in the ruddervator control linkages. Make sure
that the pushrods are as straight, light and stiff as possible, and also
check for holes in the servo arms and the control horns that are a loose
fit for the pushrod wire. For the servo arms, you may need to replace the
arm or drill a new hole in between the existing holes to get a tighter fit.
On the control horns back at the ruddervators, you can plug the old hole
with cyanoacrylate, then re-drill the hole. Also check for slop in the
control surface hinges (too much space in the hinge between the aft edge of
the stabilizer and the leading edge of the ruddervator can cause this), and
for too soft a mounting for the servos. If the pushrod is flexing, try to
minimize or eliminate any bends in the rod. If it's flexing in the middle,
try adding a support, slightly forward or aft of the middle of the rod
(having the unsupported segments of the pushrod slightly different in
length is better than supporting it exactly in the middle), loose fitting
around the rod so it keeps it from bowing to one side, but leaves it free
to slide back and forth. Generally the hole the pushrod runs through in F3
is enough of a support (assuming you didn't make that hole so big that it
doesn't restrain the pushrod flex), but in stubborn cases a second support
mid-way down the tail boom can help as well.
Whatever you do, make sure that the linkages for both ruddervators match
each other. If they don't, then the two ruddervators won't move the same
distance when given the same command. Every time you give it an elevator
command it will also inadvertently get an unwanted rudder command mixed
with it, and vice versa.
Contrary to one of the other comments on this thread, the pushrods have an
excellent stiffness to weight ratio compared to music wire or Kevlar
pull-pull cables. There's an article in "Ask Joe and Don" on our website
that analyses this in depth. It turns out that although the Kevlar
pull-pull system is the lightest, it also has the worst stiffness to weight
ratio; the conventional wood+wire pushrod (assuming you have the holes in
the servo arm and control horn fit properly, and the pushrod is straight
and well-supported enough that it doesn't flex) is actually the best of the
three.
David Enete's comments about launch technique are very appropriate, and
apply equally well to just about any other HLG as well. Pulling down on the
model at the end of the throw does not add any useful energy to the throw,
and puts enormous stresses on the wings, in addition to exciting any
flutter tendencies that may be present.
As far as Kris Harig's comments about wing flutter, that is generally the
result of using the wrong covering material and/or not having it shrunk
properly, along with exciting it with bad throwing technique as described
by David Enete. We went to a lot of extra trouble in the design of the
Chrysalis to eliminate the need for any D-tube sheeting on the leading
edge, since this is a very common problem area for a great many beginners.
However, as a result, the wing does rely on the covering for quite a bit of
its torsional stiffness. If you use a lightweight covering such as
lightweight Ultracoat, lightweight Oracover, or Micafilm on the wing,
especially on the inboard panels, or if the covering is applied loosely,
the torsional stiffness will not be high enough and the wing is likely to
flutter on launch. Regular weight Ultracoat or Oracover, or regular or
transparent Monokote work fine. Of these, the stiffest and lightest in our
experience seems to be transparent Monokote, although Ultracoat and
Oracover are somewhat tougher. We've had good results with all of those three.
Don Stackhouse @ DJ Aerotech
[EMAIL PROTECTED]
http://www.bright.net/~djwerks/
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