From: billphil@ix.netcom.com (Badwater Bill)
Newsgroups: rec.aviation.homebuilt
Subject: Flutter Testing Question-Test Flight of the RV-6
Date: Wed, 24 Jun 1998 00:02:07 GMT

Here's a good question.  You "On Topic" boys will like this one.


>Bill,
>
>A quick question from an aging student pilot with only one PhD.  Doesn't
>flutter (wing or control surface) occur very suddenly and then continue
>even though you then slow down to a lower speed where it stops.  I can
>imagine that, unless there is plenty of damping in the structure, that
>there will be some hysteresis, so that the fluttering structure suffers
>damage before you can get it stopped again.  Therefore, sounds like a
>dangerous region to explore.
>
>Just curious.
>
>Bob

Good question.  Flutter dampens out very rapidly once you get below
the resonance speed.  It doesn't continue because it isn't
harmonically driven at the lower speed.  However, it's quite divergent
once it starts and you keep the same airspeed. Your control surfaces
can separate in a second or even less.

How you test for it is that you start in a known region.  You start
with a straight and level power setting where you've already tested
for flutter, put the airplane in a shallow dive to increase speed by
20 knots and trim for a nose-up attitude.  Pull up about 10 degrees
and as you pass through the airspeed you want to test (10 knots less
than the dive speed), you wrap the stick on the side punch the rudder
or smack it in pitch.  If she flutters you are about 10 knots slower
in a heartbeat and the flutter will dampen out (theoretically).  If
everything is okay you simply up the speed by 10 knots and try it
again.  Wear a parachute and plan your escape, i.e. get your canopy
ready to eject etc.  The last test I did was to take the airplane to
240 mph, pull up and smack the stick from the side at 230 mph in the
climb.  No flutter so that ended the test.

 We have some other problems now however that must be solved before we
can fly again.  I expect these to be solved by Thursday.  If they are,
I'm going up and test it in the stall series.  I'll determine Vs
first, then Vso, accelerated stall characteristics etc.  My main
concern here is that she has no goofy characteristics that will kill
these guys if they stall her inadvertently.

After that. I'll do a few rolls, spilt-S her and loop her a couple
times to get the entry IAS speeds for them to play with initially.  No
snap maneuvers or spins, however.  This airplane is not a nice machine
in a spin so you just keep her out of them.  The big thing I want to
determine is how easy or hard it is to keep the airplane out of an
inadvertent spin.

After all of that's done we'll move on to timed climbs and speed runs
to see how she performs.  I'll have to take her over the hill and buzz
the whorehouse a couple times too.  That's essential for any new test
bed.  No pun intended.


BWB