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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

Well-known 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...
 

L Edge

Active member
#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..
 
#12
Hello, I know that a LONG time ago there was some sort of document that showed which prop to use with which motor. Is that still available somewhere on this site? If not, I'm looking for the maximum size of a 3-bladed propeller that the Flite Test "Radial" 2218B 1080kV Brushless Motor would be safely able to use?
 

sprzout

Knower of useless information
Mentor
#14
Hello, I know that a LONG time ago there was some sort of document that showed which prop to use with which motor. Is that still available somewhere on this site? If not, I'm looking for the maximum size of a 3-bladed propeller that the Flite Test "Radial" 2218B 1080kV Brushless Motor would be safely able to use?
There's a website, ECalc, that a lot of us use.

https://ecalc.ch

You have to pay for its use, but it's $6.50/year, and WELL worth it.
 
#16
The motor data sheet usually states the maximum prop size. A two bladed prop will also be more efficient than a 3 bladed one.
Was thinking about the Corsair, which my wife just bought me for my birthday. Obviously I would use the two bladed prop for general flying, but would like to put a scale-looking three bladed prop on it eventually. Given the wingspan, a scale prop would be 14.6 inches, which seems very large, but there are other options that are closer to the size of the prop that comes with power pack c. There is a nice looking 11 inch three bladed prop available from Motion RC for their Corsair, with a very scale looking hub and blades. Was thinking that would be a nice addition, but didn't want to over-stress the motor or ESC.
 

quorneng

Well-known member
#17
Without using a Watt meter you are asking for trouble using significantly different and particularly multi blade props.
What ever the maximum amps the current 2 blade uses must be considered the maximum without risking the ESC.
A 3 blade is likely to be smaller and less efficient so will degrade performance a bit.
 

Paracodespoder

Well-known member
#18
Hello, I know that a LONG time ago there was some sort of document that showed which prop to use with which motor. Is that still available somewhere on this site? If not, I'm looking for the maximum size of a 3-bladed propeller that the Flite Test "Radial" 2218B 1080kV Brushless Motor would be safely able to use?
Check out @DamoRC ’s testing on the ft 2218 over on post #83 of this thread. That should get you the information you need, good luck on your build if you haven’t finished it already ;).
 
#19
Check out @DamoRC ’s testing on the ft 2218 over on post #83 of this thread. That should get you the information you need, good luck on your build if you haven’t finished it already ;).
I haven't even started it yet! :) I have a project on the table, a large Hall's Bulldog Racer, that was only half finished, and I have another half finished project in the closet, so I promised myself that I would NOT start the FT Corsair until the Bulldog was finished. It has been a great motivator, having the Corsair waiting in the wings! :)