Re: Re: 40% Stab size or 20%?

From: Don Slusarczyk <don_at_slusarczyk.com>
Date: Fri, 22 Oct 2010 23:50:01 -0400

On the simulations you are running what are the CL value on the stab you
are getting? Are they close to zero or negative in value by chance? Also
what is your tail volume value? below 1.0?

What was happening in the real world is the model would fly trimmed but
when disturbed that is when the trouble started they simply did not want
to recover. Bernie did some full size EZB tests as he saw the same thing
with tiny tails running low CL values on the spreadsheet. It just did
not work. My recollection on the flight tests is from emails we
exchanged back and forth about 8-10 years ago but the end result was it
did not work. I think it was really due to low tail volume as the stab
was so small and as you say the wing has to go back to move the CG
forward so small tail and small moment arm = low tail volume = model
that does not like to recover when disturbed.

Don

> Hi, Don,
>
> Thanks for your post. I'm surprised that stability is an issue. I assume that when using a much smaller stab, like 10 or 20%, while maintaining the same boom length, you will have to move the wing back an appropriate amount to gain pitch equilibrium and stability. In the design program, this is exactly what I had to do. I decreased stab size and moved the wing back to get SSM back to about 10% (10% is roughly what I target for in my EZBs).
>
> Some clarification would be appreciated. Thank you.
>
Received on Fri Oct 22 2010 - 20:50:05 CEST