Re: 40% Stab size or 20%?

From: ykleetx <ykleetx_at_gmail.com>
Date: Sat, 23 Oct 2010 04:19:42 -0000

Don S,

You're on the money. Here are the tail volume and CL for 37,30,20,10% stabs:

tail volume coeff: tail moment * tail area / wing chord / wing area
1.6, 1.25, 0.80, 0.39

CL: .354, .324, .226, -.018

Can you explain the significance of tail volume?

Thank you!

-Kang




--- In Indoor_Construction_at_yahoogroups.com, Don Slusarczyk <don@...> wrote:
>
> 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 - 21:19:50 CEST