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

From: Don Slusarczyk <don_at_slusarczyk.com>
Date: Sat, 23 Oct 2010 22:52:29 -0400

The spreadsheet only deals with static stability. My way around that was
to make sure the tail volume was large enough. In regards to stab Cl,
if the stab Cl is greater than the wing that implies it is at a higher
angle of attack (since we are using similar airfoils). You can not fly
an indoor model with the stab at a higher angle of attack than the wing.
Even at zero-zero setup the stab is at a "lower angle" because of the
downwash angle from the wing (at least predicted by the spreadsheet). So
the stab is automatically at a lower angle of attack and therefore must
be at a lower Cl than the wing so if you have the wing at 0.8 Cl, and
you have 3 degrees of downwash then the stab is running at 3 degrees
less angle of attack so the Cl must be lower, and assuming a lift slope
curve of about .1/degree, that means 3 degrees = .1*3 = .3 so 0.8 -.3=
.5 so the stab is at 0.5 Cl when the wing is at 0.8. So I always made
sure all designs on that spreasheet were no greater than 0.5 Cl for the
tail.

Don

> Does approaching .5 stab Cl indicate slower pitch recovery? If so, what's a good number at the other end - for increased pitch recovery?
>
> I'm looking at setting up a new model with better recovery to take advantage of thermal conditions in case I get to attend a certain central European heatbox contest again. It would be interesting to see that kind of performance hit to expect.
>
> --- In Indoor_Construction_at_yahoogroups.com, Don Slusarczyk<don@...> wrote:
>> The wing Cl is fixed in the sheet I posted the link to, it is 0.8 You
>> have to monitor the stab CL if it gets above ~0.5 then you will most
>> likely not have a flyable model configuration. I did find another
>> version where I made wing Cl a variable.
>>
>> Don
>>
>>
>>> Which row is Cl in? I see Coeff of lift for the stab in row 36, but I assume you are talking about the Cl for the wing, or maybe even the total Cl?
>>>
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Received on Sat Oct 23 2010 - 19:52:39 CEST