[rebel-builders] Moose Structural Failure ! Possible rudder

[Ben Ransom]

Hi Ted,
Way too exciting ...glad to hear it wasn't crazier in the air and a
relatively good outcome.

I'm a little surprised NTSB didn't followup to ask about your speed.

I experienced aileron flutter in my Kolb ultralight long ago. I was at
Vne, 500ft above runway, showing off at an ultralight fly-in. Definitely
too exciting for those 2-3 seconds, and somehow immediately recognizable
as flutter (aka the devil). Later, after very very thorough review
(mostly my own, but in consult with the Kolb designer/engineer), I
concluded mine was aileron hinge placement and to a lesser degree,
friction or slop between the control stick and aileron. I throw in the
latter (friction), because that is always a variable among even
standardized builds. My Kolb (KXP) is a bit of a derivative design, still
per plans from the factory, but not out there in big numbers and I think I
ended up being a flight-test data point that simply had not yet been
encountered. (I fixed it with increased aileron hinge area and changed
hinge placement.)

Best of luck getting to the bottom of it. I suppose flutter is the easy
guess, but in any event hard to argue against mass balancing that thing.
-Ben

On 10/4/11 2:49 PM, "Ted Waltman" <ted@vafm.org> wrote:

[quote]I posted two pictures (Area 107 S/M-Fuselage) of my buckled fuselage due
to
what I suspectËœbut have not yet confirmedËœis rudder flutter. Below is a
synopsis of the eventËœfrom which I and my passengers are blessed to have
survived. I will post more information on this event as I further analyze
the structure while I make repairs--and after I receive input from NTSB
investigators who are looking at the plane in person.

Note: No rudder counter-weight / balancing is required by the build
manual.
The standard rudder is therefore aft (aft of rudder hinge point that is)
heavy. I added electric rudder trim (servo motor & related hardware) as
well as a curved rudder top--both of which add yet more weight aft of the
rudder hinge point.

I believe this video illustrates what happens with a rudder whose weight
is
aft of the hinge point is very telling (47 seconds longËœwell worth
watching!!): http://tinyurl.com/44p6o35 (when he waves his hand in front
of
the rudder he is simulating a wind gust).

Rest assured, when I make repairs, I will dynamically balance both my
rudder
and my elevator (which already has some counter-weight but perhaps not
enough?).

Ted Waltman

Moose N384JP Denver, Colorado

-----------

Event synopsis

----------

Departed 18V at approximately 7:40 a.m. after filling fuel tanks
completely
full (80.0 total gallons) and checking oil full at 16 quarts. Climbed to
5,500‚ cruise altitude on heading of approximately 97 degrees magnetic on
a
direct course to KHYS.

After approximately âˆ