static thrust

Aircraft props generally work best in turbulence-free air...

/daytripper

That is to be expected. Draw out some vector diagrams of the air movement and you should find that the draft from the fan reduces the angle of attack of the prop blades, which will indeed reduce the thrust.

But the POWER the prop delivers to the airplane is equal to the thrust times the airspeed. As an airplane gains airspeed, the thrust goes down but the delivered power goes up.

rj

Great test! The scale is measuring thrust plus the drag of the plane. So the results might be indicating the drag effect. Did the prop unload? That is, did the RPM increase?

snipped-for-privacy@uvm.edu wrote in news:1186358825.442531.308910 @r34g2000hsd.googlegroups.com:

you'd expect the thrust to drop when the prop unloaded. If it was a high- pitched prop and much of it was stalled, then the thrust could go up with airspeed, but otherwise it will drop.

Current should drop, too.

Further complicating the picture, as the other posters have suggested - the fan puts out a very 'dirty' airflow - very turbulent; that will cut the prop's efficiency. And the fan puts drag on the airframe, so you'd need to take measurements with the motor off & prop removed, then take them with the prop on & motor running, and see what the difference is if you want to remove the drag effect. Won't compensate for the lost thrust due to prop blast on the airframe, of course, but . . .

Well I have done some more measurements and it seems it is only useful for comparing props, batteries and motors. I suppose I should collect more data ie; watts, rpm. I had thought about the air current beyond the diameter of the prop blowing on the airframe. I guess the prop wont see the airframe as a load until the plane gets moving. If I find anything of interests I will comment. Thanks for the comments.

jjb