Re: [Flightgear-devel] YASim vstab question

[Maik J. <mj...@gm...>]

Hi,

Joacim Persson schrieb:
> On Sun, 2 Jul 2006, Maik Justus wrote:
>   
>> src/FDM/YASim/airplane.cpp in function void Airplane::solveHelicopter()
>> from
>>    applyDragFactor(Math::pow(15.7/1000, 1/SOLVE_TWEAK));
>>    applyLiftRatio(Math::pow(104, 1/SOLVE_TWEAK));
>> to
>>    applyDragFactor(Math::pow(1, 1/SOLVE_TWEAK));
>>    applyLiftRatio(Math::pow(1, 1/SOLVE_TWEAK));
>>     
>
> Actually, that won't work. :P
>
> The idea is that the solver shall determine Cd (and other parameters)
> for surfaces by /iteration/. We can't set the value directly like
> that because we simply don't know it, and neither does the fuselage or even
> the surface compiler. There is a start value, but it can be up to 10000
> iterations (or more! ;) from a sane value.
>
>   
Yes, it's only a workaround. It now uses the result of the J3.
> To do it "the yasim way" we would need a similar iterative solver
> for helicopters like for winged aircrafts, based on cruise&approach data or
> whatever can be available. (possibly incorporated in ::solver())
>   
Probably we have to go this way. But it would be rather complicate (e.g. 
the "elevator-control" of the ch47 is different from other helicopters).
> We could on the other hand let the model designer set and tweak the
> fuselage Cd manually in the config file.
>   
That would be the easier way. Maybe it make sense to look, which results 
the solver get for different airplanes.
> (and one raised to the power of any real number is still one ;)
>
>   
Yes, you are right. But if you use the "old"

	applyDragFactor(Math::pow(15.7/1000, 1/SOLVE_TWEAK));
	applyLiftRatio(Math::pow(104, 1/SOLVE_TWEAK));

Yasim tells you

Solution results:       Iterations: 0
  Drag Coefficient: 15.700000
  Lift Ratio: 104.000000
  .
  .
  .
That is why I did not delete the pow calculation.

Maik