Re: [Jsbsim-devel] Modelling a windmilling propeller

[David C. <dav...@co...>]

On Saturday 29 December 2007 01:54, Craig Meyer wrote:
> That is, I need to know if does the following things (and would like to
> enhance the model if not): 1) The way a propeller becomes a
> not-very-efficient windmill when spinning too slowly for the given
> airspeed. 2) How, when that happens, it actually imparts a torque on the
> engine, causing it to speed up. 3) Plus, I'd like to define a propeller
> based on a symmetric (NACA four-digit) airfoil.

I believe the model already does this, as long as you define a full set Cp/J 
and Ct/J curves in the prop configuration file, including extending the curve 
below the horizontal axis.

I would like to test the model to make sure.

I don't mean to highjack this thread, but this is a good time to argue that we 
could use a position freeze in JSBSim.  That is where the model goes through 
its normal iterations at each time step, but doesn't actually move anywhere, 
creating a wind-tunnel like environment.  In this case we could set a model 
up in a glide at a given speed/altitude with the engine off then experiment 
with various prop angles and take thrust and rpm data.  A single button press 
could engage/disengage the position freeze.  The implementation is pretty 
easy I think - you just ignore the final calculation of the model's new 
position.  I brought this up a few years ago, but I don't think we ever did 
it.  If not, then maybe we could now?  I'd be happy to get to it.

Dave