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General question about Propellers

#1
Im looking at trying to build a B-17 with 4 engines each with a 3 bladed propeller. I know that with multi engined aircraft you generally want half the engines turning CW and the other half turning CCW. My question is, are there any 3 bladed propellers with a CCW rotation out there?
 

DamoRC

Well-known member
Mentor
#4
6 to 8 inch range will probably not be that hard to find. Check the usual online sellers (HK, BG). Also have a look at MotionRC, they have a small selection of 3-blades that might suit your needs.

Do you have motors already? The extra blade will create more load for the motor so good to confirm that it can turn the three blade props beforehand.
 

DamoRC

Well-known member
Mentor
#6
Cool - 4 of these will have a lot of oomph!.
I did some thrust testing on this motor recently and you can see the results here. Depending on how big you want to build (scale prop is approx 1/9th wingspan), you should have no probs driving and 8 inch three blade with this motor on 3S for a nice round 6 foot span.
 

quorneng

Active member
#9
With electric there is no such thing as a "pusher" prop.
Brushless motors can be made to rotate either way round so any prop can be used a pusher.
The reason for using a pair of CW and CCW props on a twin is simply to eliminate the effects of motor torque.
The only down side of using a CW prop, or CCW as a pusher, is the prop nut will tend to undo rather than be self tightening.
Many quad motors have left handed prop threads for their CW props.
 

sprzout

Knower of useless information
Mentor
#10
With electric there is no such thing as a "pusher" prop.
Brushless motors can be made to rotate either way round so any prop can be used a pusher.
The reason for using a pair of CW and CCW props on a twin is simply to eliminate the effects of motor torque.
The only down side of using a CW prop, or CCW as a pusher, is the prop nut will tend to undo rather than be self tightening.
Many quad motors have left handed prop threads for their CW props.
There are ways to counteract that - Nylon bushing lock nuts, a bit of low strength Loctite on the threads, or even just doing what you're supposed to do and check it after every flight, and before you take off, to make sure everything's tightened down. It's never going to guarantee 100% that the prop won't fly off, but it will help...
 
#11
Another source of props is APC.com. In fact, this company has load of data on each of the props. Maybe you can correlate that with finding right motor. Company does all kinds of composite props ranging from slow speed to FAI props for 200 mph pylon racing..