Gary,
I have had similar experience with the program. I think that Lew Getlow
said something in his book to the affect of maximum duration is usually
achieved in a trim configuration that is just short of stalling. I think we
could debate this observation endlessly, but Bernie Hunt's program is
effectively telling us that lowering the static stability margin as a
percentage of wing cord increases duration.
I if you increase the aspect ratio on the horizontal stabilizer, the
program almost always predicts an increase in duration. However, whether
its boom length, C.G. shifts or horizontal stabilizer plan form changes, it
never says whether or not the model will be stable enough to fly well in a
real flying site. I have found that a negative static stability margin in
the program almost guarantees my models will not fly.
Also, changing the boom length should not change the decalage because the
wing angle of attack does not change nor does the stabilizers angle of
incidence. At shorter boom might realistically be stiffer than a longer
boom of the same weight.The reduction in boom flex may make it appear as
though the decalage changed but, geometrically speaking nothing should have
changed.
Just some thoughts,
Nick
On Fri, Feb 24, 2012 at 8:44 AM, <Warthodson_at_aol.com> wrote:
> **
>
>
> I have been using Bernie hunt's program to see what the affect of
> varying the boom length might be. The version of the program I have has
> Steve Brown's F1D entered into it.
> The only parameter I changed was boom length. For the purposes of this
> experiment I did not change the boom weight. The result was as follows:
> Shortening the boom 1" (from 19.5" to 18.5") increased the time & reduced
> the static stability margin.
> Lengthening the boom 1" (from 19.5" to 20.5") decreased the time &
> increased the static stability margin.
> I was expecting a longer boom to increase time because I thought that the
> decalage (angle of attach difference between wing & stab) would be less
> with the stab farther back. Also, with the weight of the stab farther back
> I thought the CG would be closer to the neutral point & the static
> stability margin would be less. I would like to hear your opinions on the
> affect of boom length. And, yes I know that a longer boom length might
> require a heaver boom, but not necessarily.
> Thanks,
> Gary Hodson
>
>
>
Received on Fri Feb 24 2012 - 06:36:43 CET
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