I'm looking for some sort of formula to determine static thrust.  I'm trying an O&R 29 FRV, which gives 7800 RPM with a 10-5 B-Y&O on 15% nitro with 28% castor oil.  I'd like to know how much static thrust I'm getting from that combo.  That will determine what size stunter (and how heavy) I should consider.

The motor appears near-new, and probably not yet broken-in.

Floyd in OR

Floyd,

What is tricky is that the static thrust is a function of your prop--it doesn't really depend on the motor at all, just how fast it is being spun around. I know that sounds "obvious", but the issue is that with another prop, lets say an old Top Flite 10-5 or even an APC 10-5 will have different static thrust values, even at the same rpm.

So there would be two ways to get what you want.

1) Put the prop airfoils and info into a propeller calculator and then run several rpms. This isn't trivial unless you can approximate the airfoil with some actual known NACA airfoil. I've played with a couple of propeller calculators and this is always the "rub". Here is a link to one that I have used.
http://www.drivecalc.de/PropCalc/index.html

Here is a link to Martin Hepperle's site.He also has a propeller calculator. http://www.mh-aerotools.de/airfoils/index.htm


2) Build yourself a thrust stand. It isn't too hard to do. The reason I have never bothered is quite frankly I don't believe it is worth the effort to measure static thrust. To me it is only relevant for my Bi-Slob since it is the only CL plane I have that "flies" at zero airspeed on the prop!

Now if I could get access to a wind tunnel,I would make up an electric motor test stand and you could make a lot of nice measurements of how the propellers behave in the real world.