DIYbanter - View Single Post - Fwd: Reno Air Race

Beryl[_6_]

wrote:
...
The elevator - and the trim tab - do a LOT of work on a race plane at
500mph. And a lot at 200 too.

Explain! I haven't seen any explanations here, just claims. Richard
claims the nose must forcibly be held down at 500 mph.

The airplane is nose-heavy already, it must be held up. If it takes 200
lbs of downforce at the tail to hold the nose up at 200 mph, it also
takes 200 lbs of downforce to hold the nose up at 500 mph.

We want that 200 lbs of force to come with as little drag as possible at
500 mph. Can anyone explain how full nose-down trim tab deflection +
pushing the stick forward will produce the necessaty 200 lbs of
downforce at the tail?

It will do it because the stabilizer incidence is all wrong for 500 mph.
The stock stabilizer rigging is a compromise, to work acceptably through
the whole speed range. At 500 mph it's pushing the tail down too hard,
so Richard has to trim, and push the stick, to help hold the tail back
up. The tail surfaces are working against each other. Pitched up/down
crap hanging out in the wind.