Microlighters

any takers how much thrust one will get with the plane tied down? I intend useing a daw scale as a test between two props. now the next question; if you set the pitch up for max thrust on the ground what will happen when you start rolling?!?! just some food for thought.

Hi,
Demon wrote:

so be careful not to make the pitch too fine

That is what probably will happen with the "draw scale method"

Unfortunately a fixed pitch prop will only give you optimal power at a certain speed/rpm. Say you had a Rotax 582 Motor, with a max of 6800 rpm, and you fitted a prop with such a fine pitch, that it would rev 6800 rpm at full throttle, with the aerie standing still. You would now get the maximum "pull" on the drawscale. However this engine/prop combination would be quite useless, because the moment you start to move, your engine will rev higher than 6800 rpm, and you would have to throttle back during take-off, probably not so clever. The prop you eventually select will be a compromise between a cruise prop with a relatively coarse pitch, or a finer climb pitch. If you need the power for takeoff, possibly consider a prop that gives you close to max engine rpm at takeoff speed. If you need a prop for good cruise performance, I would look at the torque curve of the motor, and then try find a prop that sits pretty much in the top of the curve for cruise. However at the end, it will be a compromise. To find this compromise, you probably would have to do some experimenting with both props.

Regards,
Arnulf

I find with 582 that the difference between static and flying max is about 300rpm. I normally set my prop for static rpm of 300 below the point of max torque.

Jeees guys - this is way too scientific for me - I will stick with letting Piet De Necker make all those kind of decisions. I will go as far as torquing the bolts properly and getting the tracking right!

Thanx Guys
Im aware that the draw scale method is flawed so it is purely a means of measure and the test will be done extensively and there will be run`s etc. We were just interested to see what we will get. Also to see where on the rpm scale, useing Piet`s prop as a measure, we will get the same pull (newtons for duck ) as I said purely for academic reasons.

san

Would you please be so kind and let us have the results.

And please be careful when fiddling around an aerrie thats got the motor running at high power

yp Im sure if Im not carefull Ill get it chop chop!! No problem as soon as we do it I will make al public. It just depends on Duck an when he has time.

San