Tail flutter!

[I Can Computer Services]

I presume you are all familiar with the Quicksilver GT500. Those who have
flown one will no doubt be aware of the in flight trim and how it works. I
am designing a small single seater. I too would love this in flight trim
assembly on mine. This would involve having a single strut connection on
each tailplane to allow the leading edge to be raised and lowered as
required. My issue is with flutter in such a configuration. What are your
thoughts regarding elevator static balancing as insurance against the onset
of flutter. I expect no more than 60knots from this bird.

DIYUL

[Kevin Horton]

On Sun, 23 Nov 2003 23:44:26 +1100, I Can Computer Services wrote:

> I presume you are all familiar with the Quicksilver GT500. Those who have
> flown one will no doubt be aware of the in flight trim and how it works. I
> am designing a small single seater. I too would love this in flight trim
> assembly on mine. This would involve having a single strut connection on
> each tailplane to allow the leading edge to be raised and lowered as
> required. My issue is with flutter in such a configuration. What are your
> thoughts regarding elevator static balancing as insurance against the
> onset of flutter. I expect no more than 60knots from this bird.
>
> DIYUL

Elevator static balancing is not necessarily the whole answer. You can
get flutter if the horizontal stablizer can twist, if the CG of the
HS/elevator combination is behind the axis that the HS twists around, in
simple terms.

Flutter prevention is a black art. The best bet is probably to find a
successful design, such as the GT500, and slavishly copy every detail.
Stiffness is very important.

Don't assume that you can't get flutter below 60 kt. I saw an amazing
video years ago where a poorly designed and/or constructed ultralight
experienced catastrophic flutter during the take-off roll. Fortunately
the plane came apart before it got airborne, so I don't think the pilot
suffered serious injury.

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

[DJFawcett26]

>I saw an amazing
>video years ago where a poorly designed and/or constructed ultralight
>experienced catastrophic flutter during the take-off roll. Fortunately
>the plane came apart before it got airborne, so I don't think the pilot
>suffered serious injury.

I have a sneaking suspicion in that case the structure was entirely
insufficient. In general, I agree with Kevin. But a good rule of thumb is
overbalance much like the Russian, assuming your structure is reasonably
designed and sufficiently stiff.

If you are so concerned, I would recommend getting an analytical flutter
analysis on your design. That too will give you another level of confidence.
There are several companies (2 or 3) that can do a pretty good job at a very
reasonable price.

Good Luck on your design

[Harry O]

I have a set of plans for the Ritz ultralight. An interesting concept.
Unfortunately, the prototype experienced aileron flutter at less than
60knots and came apart killing the designer. The design mods made afterward
increased the stiffness of several components including the wing, ailerons,
tail, and controls. I doubt that it was an ultralight afterward. Anyway, I
have never seen one completed after that.

> > My issue is with flutter in such a configuration. What are your
> > thoughts regarding elevator static balancing as insurance against the
> > onset of flutter. I expect no more than 60knots from this bird.
>
> Don't assume that you can't get flutter below 60 kt. I saw an amazing
> video years ago where a poorly designed and/or constructed ultralight
> experienced catastrophic flutter during the take-off roll.