REFLECTOR: exceeding Vne and Airventure cup race

[Scott Derrick]

I'll put in my $0.02 since I have experienced the exact same thing, 
though at a lower speed.

I was in the process of re-rigging the plane to get it to fly straight 
and level hands off. This had been going on for a couple of months as I 
would try something and fly for a week or so and then modify again. I 
had just adjusted both rudders , one I moved outboard, one I moved 
inboard, the purpose was to get the ball in the middle. I had flown the 
plane for about 8 hours with the adjustment with no noticeable problems, 
ball dead in the middle, fuel flow perfect from both tanks(your really 
big slip indicator).

While getting out of Vegas's airspace they changed their mind and had me 
stop a climb, descend and turn, immediately! Without pulling power I, 
made it so, and while the airspeed was going up through about 190 kias 
the airframe started to shudder. I chopped power and pulled up and the 
shudder stopped. Scared the crap out of me and my wife.. After a short 
and tense discussion we continued the flight home at a normal 140/150 
kias, at 11,500 ft.

Testing the airframe with a friend and A&P/IA on board we determined it 
was the right rudder/winglet/wing doing the flutter. The whole wing 
would shake up and down as the winglet was vibrating in and out at a 
speed above 190 kias. This was the rudder I had shimmed inboard. I had 
talked to Brendon earlier and he suggested this may be the problem. I 
had shimmed, or unshimmed depending on how you look at it this rudder so 
it's trailing edge was slightly inboard of the winglet's trailing edge. 
This "could" and did allow the rudder to unload at 190 kias. The rudder 
is designed to always be loaded inboard in flight at all times. The 
spring is really just for very low speeds when their isn't enough wind 
to load it up.

I shimmed it back out so the rudder's trailing edge is just slightly 
outboard of the winglet's trailing edge and no flutter up to 215 kias, I 
did some shallow turns and pull ups at that speed also.

Tim, I would suggest you look into this to see if your flutter has the 
same root cause that mine did. I agree its a scary experience.

Scott

gpoole wrote:
>
> *What an interesting read Tim – thanks! Would you care to fill us in 
> on the advice you received from Duane on the rudder flutter fix?*
>
> * *
>
> *Greg in **Sydney*
>
> STd RG E
>
> *gregpoole at saaachapter11.com* <mailto:gregpoole at saaachapter11.com>
>
> -----Original Message-----
> *From:* reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] 
> *On Behalf Of *TimRhod at aol.com
> *Sent:* Thursday, 3 August 2006 4:46 PM
> *To:* Reflector at tvbf.org
> *Cc:* TimRhod at aol.com
> *Subject:* REFLECTOR: exceeding Vne and Airventure cup race
>
> I have read quite a few comments on the speeds of the velocities in 
> the airventure cup race an also discussion on exceeding the factory 
> Vne. For what it is worth I would like to share my experience with 
> both . I have a XLRG with a continental IO-550 with 10 to 1 
> compression pistons and duel plasma 3 electronic ignitions. Rated 
> horsepower is 370HP During my initial test flying phase I tested 
> flutter characteristics to 210 knots Indicated with no adverse 
> effects. After 70 flight hours now I entered the airventure cup race 
> and so in preparation for that I did some more high speed testing. 
> Knowing that this race would be flown at minimal altitude I first did 
> a full power level run at 1000ft AGL. I indicated 217Kts straight and 
> level. No sign of flutter. Then knowing I would be diving to the pylon 
> turns in the race I decided to push the indicated speed higher a few 
> knots at a time shaking the controls to try to induce flutter. I 
> tested to 230Kts indicated in a straight shallow full power dive. No 
> Adverse effects. Having decided I would not fly the plane any faster I 
> was satisfied with the testing. Next I started to practice diving to 
> the pylon and banking to turn around a pylon. In my first diving turn 
> at about 600 ftAGL right over the airport all hell started shaking the 
> airplane like a buzzing bee at about 220 kts I immediately pulled 
> power and nosed up and the vibration stopped. I was pretty shook up by 
> the vibration and wanted to get on the ground immediately in case 
> something decided to come off. So I made a quick high sink nose too 
> high landing which after getting out of the plane I noticed about 1/2 
> inch of my MT prop missing on each blade. UGGGG.... Then I discovered 
> that the vibration had come from flutter of the left rudder. It was 
> beat up enough that I had to fill and sand where the rudder meets the 
> fuselage but there was no apparent sign that it was going to come off 
> at the hinges. If the flutter had continued it probably would just of 
> destroyed itself leaving the hinges attached. Time to push the plane 
> back into the hanger and drag my sorry butt home. Next day Email MT, 
> Velocity, and Reflectoites what to do about the prop. All told me to 
> cut it off equally on each blade, epoxy and or glass the ends, sand 
> and countor, run it and if no vibration it should be ok. That's what I 
> did. Now its the day before the race. I tightened the return spring on 
> both rudders and decided not to fly faster than 215 kts level and 200 
> kts diving and turning. Race day brought great weather. On take off as 
> I passed through 210 kts the left rudder started to flutter again. 
> Pulled power an it stopped. It was not near so violent this time 
> probably because of tightening the rudder return spring. Put foot on 
> left rudder pedal and held pressure then gradually increased speed up 
> to 215kts indicated flying straight and level. As long as held rudder 
> pressure there was no flutter. So I held left rudder pressure for the 
> entire two hour race and pulled power and slowed to 200 kts for diving 
> an turning around pylon turns. The race ended and I finished with a 
> speed of 230 MPH for the 500 mile race. WE had about a 15mph head 
> wind. The prop worked fine with no adverse effect of being an inch 
> shorter. At Oshkosh I talked to Duane Swing at length about the rudder 
> flutter and he recommended some diagnostic work and a fix which I am 
> presently doing. So Next year I should be faster in the race. Watch 
> out Pat I'm on your tail and closing. Congrats this year on 247MPH . 
> We had a great time at the race an I would encourage lots of us 
> Velocities to take part next year. It was really fun, exciting and 
> memorable.
>
> Tim Rhodenbaugh
>
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