Groen Bros. DARPA Award

Steve R wrote:
"boB" wrote in message
...

Shiver wrote:


He is a big big champion of the vertical (centerline) stabilizer on
gyros and I do believe has had his share of arguements with the
developers of the RAF gyros on this subject. He has talked about the
dangers of buntover with resulting death in this group at various
times.

Buntover??? In my reading I haven't run across that term. I know how to
keep from causing the normal spike knock, tail boom strikes, 0 G pitch
down and mast bumping problems. From the word, is it a forward pitchover
caused by the horizontal stabilizer being too low?

--

boB,
SAG 70


Buntover is just another term for a power push over (PPO). From what I've
gathered in my reading through the years, it's not as much an issue with the
horizontal stabilizer as it is with the placement of the engines thrust line
relative to the vertical CG of the aircraft. Gyros like the stock RAF2000
have the thrust line at a significant distance above the vertical CG of the
aircraft. That imparts a nose down moment when under power. The main
rotor, because it's tilted aft in flight, offers a counter force to the
forward pitching moment. If you unload the main rotor enough, there's not
counter force to that forward pitching moment caused by the engine thrust
line being above the CG and over she goes.

A properly placed and sized horizontal stab can go a long way toward
reducing the possibility of this problem but it doesn't address the root
cause. That being a thrust line that's not properly in line with the
vertical CG of the aircraft. At least that's my understanding. If I'm too
far off on this, I'm sure someone will correct me! :-)

Fly Safe,
Steve R.



Thanks Steve. That sounds like two forces working against each other.
That doesn't seem to be efficient as far as strain on the systems.
Something similar on my Sprint II with the engine and prop above the
vertical CG. If the engine quits or even when throttling down the nose
pops up which screwed up my landings early on. I had been fixed on the
RAF2000 but hadn't really looked at the competition before. I
appreciate all the advice.


--

boB,
SAG 70

U.S. Army Aviation (retired)
Central Texas - 5NM West of Gray Army Airfield (KGRK)