Apr 07, 2015, 09:49 AM
Registered User
France, IdF, Lagny-sur-Marne
Joined Feb 2007
749 Posts
Quote:
 Originally Posted by Montag DP Paul, I haven't done that. But, I don't really see the need either. Since you can already specify the Reynolds number, Cl, and Mach number for every operating point, you can just set up your operating points so that Re*sqrt(Cl) is constant, with the value determined based on the model weight, altitude, etc. Dan
Yes but you can only choose one of the following for all Re : "min-drag" or "min-sink" and "max-glide".

e.g. if I want min-sink at low Reynolds (thermalling) and max-glide at high Reynolds (to get through sinking air between two thermals).

Have you read Martin Simons series of articles on RC soaring here:
http://www.rcsoaringdigest.com/pdfs/Simons_UTSS.pdf

I suppose you have.

Paul
Apr 07, 2015, 11:25 AM
Sink stinks
United States, GA, Atlanta
Joined Apr 2005
4,626 Posts
Quote:
 Originally Posted by Paul_BB Yes but you can only choose one of the following for all Re : "min-drag" or "min-sink" and "max-glide". e.g. if I want min-sink at low Reynolds (thermalling) and max-glide at high Reynolds (to get through sinking air between two thermals). Have you read Martin Simons series of articles on RC soaring here: http://www.rcsoaringdigest.com/pdfs/Simons_UTSS.pdf I suppose you have. Paul
Paul,

Here's how I would handle that problem. You can let me know if I'm being dense. In either of those cases (thermalling or flying between thermals), the lift is going to be known, so you can compute the Cl based on the flight speed and wing planform. Then compute the Reynolds number and Mach number as well for that flight condition. Finally, optimize the airfoil for 'min-drag' at each of these operating points. The reason being that if Cl is specified, all three types of optimization amount to minimizing the drag, even though the objective function may be computed differently.

Dan
Apr 07, 2015, 12:06 PM
Registered User
France, IdF, Lagny-sur-Marne
Joined Feb 2007
749 Posts
Quote:
 Originally Posted by Montag DP Paul, Here's how I would handle that problem. You can let me know if I'm being dense. In either of those cases (thermalling or flying between thermals), the lift is going to be known, so you can compute the Cl based on the flight speed and wing planform. Then compute the Reynolds number and Mach number as well for that flight condition. Finally, optimize the airfoil for 'min-drag' at each of these operating points. The reason being that if Cl is specified, all three types of optimization amount to minimizing the drag, even though the objective function may be computed differently. Dan
Thanks Dan,

I'll think about it and give it a try tomorrow.

Regards,
Paul
Apr 09, 2015, 11:57 PM
Registered User
Joined Mar 2015
3 Posts
Quote:
 Originally Posted by Montag DP Everyone, I've uploaded a new version which includes a constraint to generate symmetrical airfoils....
Thanks for that, I'll give it a spin tonight.
 Apr 10, 2015, 01:30 AM Registered User France, IdF, Lagny-sur-Marne Joined Feb 2007 749 Posts Well, it didn't work. But don't bother Dan.
 Apr 10, 2015, 01:57 AM Registered User Brisbane, Australia Joined Feb 2002 1,242 Posts Dan, I'll admit I was a bit confused by the choice of "min-drag" or "min-sink" and "max-glide". Since the analysis is being performed on a 2D aerofoil, and not a complete wing, I couldn't see how you could calculate min sink or max glide conditions ? And isn't the min-drag optimisation being performed for each operating point independently, with the penalty functions and weights being used to determine the overall optimal aerofoil ?