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

From: Don Slusarczyk <don_at_slusarczyk.com>
Date: Sat, 23 Oct 2010 00:32:15 -0400

> 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.
>
> I am no "indoorist" but this sounds like too little static stability
> margin. Why not just move the CG forward for SSM equal to "large stab"
> layout?
>

If you move the CG forward then the benefit of what was being tested,
actually what the spreadsheet was showing goes away as there is a lot
of incidence and consequential trim drag. Scale models fly with small
tails, high incidence and forward CG but they also are not duration
models and typically are speed sensitive.


> Small horizontal tail area and small tail moment arm does not
> /necessarily/ equal a model that's unstable in pitch. Adequate pitch
> stability is simply a matter of locating C.G. far enough forward for a
> safe SSM.
>

The model is pitch stable it just had poor recovery. What good is an
indoor model that bumps the ceiling then can not recover, or encounters
rough air and takes excessive time to recover. For max duration you want
as little SSM as you can practically get away with. Forward CG and
higher incidence is fine but reduced duration is the price paid.


> What am I missing?
>
> Bottom line is every wing/stab/TMA combination /can/ be optimized for
> best duration.
>
> --Don D.
>
>
But all that matters is which has the MAX overall duration. You can
optimize an EZB with a 10% tail and a 40% tail. But the 40% tail will win.

Don S
Received on Fri Oct 22 2010 - 21:32:24 CEST