What can I do to correct Dutch Roll on my scratch built?
I recently converted the conventional tail on my scratch-built HLG to a
V-tail, and on test flight it was just all dutch roll, which had not
previously been a problem. Am I correct in thinking I need more effective
vertical area, either through more V-tail span or more V-tail dihedral? Or
is it something else?
From : Don Stackhouse
Yes, that's what it sounds like. Dutch roll means too much dihedral and/or
not enough vertical fin effect, while spiral instability (when turning, the
model wants to tighten up into a "graveyard spiral") is the result of not
enough dihedral or too much fin.
If you used the old (but very, very wrong!) "rule of thumb" of making the
V-tail the same projected area as your original tail, then your tail is too
small. It should have the same total area as the original tail.
If the tail is the right size, but you're still getting dutch roll, then
you need more dihedral in the tail.
The other thing that will aggravate this condition is too much weight in
the wingtips, but if you didn't have dutch roll with your previous
conventional tail, this probably isn't the problem.
Good luck, and please let me know how it works out!
Don Stackhouse @ DJ Aerotech
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