View Single Post
  #7  
Old December 15th 09, 08:13 PM posted to rec.aviation.soaring
Bruce
external usenet poster
 
Posts: 113
Default Optimum CG Range

Eric Greenwell wrote:
Bruce wrote:
Eric Greenwell wrote:

Why is the ability to stall in a steep turn a useful criteria? It sounds
like a safety problem to me.

I expect it has to do with efficiency.

If your CG is such that your control inputs are minimised - you reduce
drag. In the case of steep thermalling, it reduces safety - because
you can now stall and theoretically spin.

There can be few things as frustrating as my experience with my (new
to me) Kestrel 19. First flight I wanted to be cautious so set the CG
at 35%. Then the day was booming - but with tight strong thermals, and
I was continually running out of elevator. Stick against the back stop
and the thermal is still tighter.

My Cirrus with it's all flying tail never had that problem. Of course
you could depart controlled flight if you got too enthusiastic...


At 35%, you are a long way from stalling in a steep turn. With a more
rearward CG, you would turn tightly enough, but still without enough
elevator to stall in a "tight" turn.

Hi Eric

That is the point I was trying to make.

With the CG so far forward the behaviour is really benign, but I can't
get enough elevator to stall her. Even straight and level the nose just
wallows around at the back stop with ~38kt indicated.

I will be moving the CG back until I can stall it, or the handling
deteriorates, then move it a little forward. There is no virtue in being
able to stall in a tight turn, just efficiency in not holding undue
control deflection.

Bruce