3 or 4 blade props

[Chris Bradbury]

Hi folks, just finishing a 100" C130 Hercules and am looking for people's opinions and advice on props. It's an electric model btw.

Maximum size I can run is 12", but I want to run 11", as this will give me 1.5" between props. Pitch wise a 7-8 is about right for the speed I want.

At the moment I've tested some master airscrew 3-blade props as this is the right sort of look (4-blade would be better), however they are very inefficient. I'm only getting 505 watts at 39 amps from an 11x7, after getting 500 from a 10x7. I have tried a softer 11x7 prop of a different design and got 630 watts, but it's too soft to actually use in flight. I'm looking for around 650 watts per motor, so am sure 11x7 or 11x8 3-blade will do it, but need a better, more efficient brand.

Can anyone recommend a better brand?

Has anyone tried the Graupner 3-blade? Are they efficient?

Ps, I know 3-blade isn't as efficient as 2-blade, but as I say, I can't go bigger, so need the 3-blade for the extra pull.

[Alan Cantwell 1131]

the 3 blade can also give you extra drag, on the full size, they have massive gearboxes, with lekky, it may be prudent to try a gearbox, i have used graupner 3 bladers, and they are better, but noisier than the master series, i use the graupners on WW11 models, soley because the blades look more like blades from that era, but, i have no lekky experince, only I.C.

[Ron Pearman]

I have used these - http://www.giantcod.co.uk/blade-sport-p ... 7_222.html when he has got them in stock. They are very good.

[Chris Bradbury]

Thanks Ron, I have tested one of those too, but sadly the closest pitch in 11" is 8.5 and this gives me 725 watts at 55 amps, which is plenty of power, but a little too much for the motors to cope with in the long run. They were very efficient though from what I tested, so these are currently my reserve prop if I can't find something closer, I'll just have to limit throttle travel if necessary.

With only 11" props I won't need a gearbox on a brushless out runner like I'm using, though you're right I would on something like brushed 600's.

I may just order a Graupner to try if they are better Alan. I'm not too worried about noise from props this small. Though with four of them it may be quite nice.

Thanks for the advice so far.