My quad project has been running for over a year now and since the beginning i've been using APC 10x4.5 and EPP 10x5 props without big problems. Nevertheless I prefer the APC's.
I've been surfing a lot of multirotor threads and have seen a lot of quads, hexas using the graupner Eprops. I offcourse had to try this and ordered the 10x5 version.
These props are very good and concerning balancing, they are spot on.
The only thing I noticed during a flight test was that I had to use about 65% of THR to hover where as the APC only need 50 %.
So what are the maim advantages of using the Eporp over other brands?
Or should I get a bigger eprop?
I use the KDA 20-22L motors.
Replies
Vincent, a larger diameter is generally better, but rather than answer your question specifically, I'd like to expand the scope of this discussion.
Most in the electric multicopter hobbyist community rely on empirical experimentation and experience as their guide. Some have provided hovering endurance data versus different prop selections to help support their choices.
Commercially-available model airplane propellers are meant for just that - model airplanes. Consequently, they are designed to work flying forward, hence the X-number for the advance ratio, which is a function of the pitch of the blades. Generally speaking, higher advance ratios are meant for lighter, faster planes. However, static thrust - the force produced by the propeller when the craft is not moving forward - offers a whole different set of aerodynamic priorities. It is this operating condition that airplane propeller makers care the least about, yet it is precisely what we in the rotorcraft discipline value the most. For my eCopter(tm) prototype, I gave up trying to find something suitable and had to make my own propellers. Model helicopter rotors have their own unique compromises which do not benefit us in the fixed-pitch hovering world either.
I have found that props marketed as "electric" are meant for airplanes without much torque and are not particularly fast. They are generally larger in diameter, but tend to use thinner airfoils which have a high lift-to-drag ratio for efficiency and lower advance ratios to prevent section stalling at low speed. This does not make them ideal for us, despite the fact that they're marketed as "electric". On the contrary - we need high lift coefficient airfoils set at a high pitch just below the stall angle for maximum static thrust.
If you're really adventurous and want to play around with different designs, I suggest going here and downloading the JavaProp application:
http://www.mh-aerotools.de/airfoils/javaprop.htm
Martin Hepperle's site is a fantastic resource for researching model plane aerodynamics.