Motor spin direction and propeller rotation

[newBB]

Hi guys, so I'm building a fixed wing UAV with a tractor configuration. As part of my OSC, I have to write a pre-flight checklist. This is my first time building a UAV so I'm quite clueless. I'm reading that the propeller has to 'face' the right direction in order to generate proper thrust w/ less noise etc - this I understand.

However, I'm also reading that the motor and propeller must spin in the correct direction and I don't understand how to know which direction the motor/propeller should spin in? I'm reading this a lot for quadcopter cases but i'm not sure what the deal is for a fixed wing UAV...do the motor and propeller always spin in the same direction as each other? i thought they do but now im not so sure. Also, as part of a pre-flight checklist, should I include checking if the motor and propeller spin in the correct direction and also checking if the propeller is 'facing' the correct way? is it possible to check the motor spin direction on a fixed wing uav immediately before flight or is that dangerous or something?

Any help would be appreciated, thank you so much !

 

[Matthewdupreez]

Hi guys, so I'm building a fixed wing UAV with a tractor configuration. As part of my OSC, I have to write a pre-flight checklist. This is my first time building a UAV so I'm quite clueless. I'm reading that the propeller has to 'face' the right direction in order to generate proper thrust w/ less noise etc - this I understand.

However, I'm also reading that the motor and propeller must spin in the correct direction and I don't understand how to know which direction the motor/propeller should spin in? I'm reading this a lot for quadcopter cases but i'm not sure what the deal is for a fixed wing UAV...do the motor and propeller always spin in the same direction as each other? i thought they do but now im not so sure. Also, as part of a pre-flight checklist, should I include checking if the motor and propeller spin in the correct direction and also checking if the propeller is 'facing' the correct way? is it possible to check the motor spin direction on a fixed wing uav immediately before flight or is that dangerous or something?

Any help would be appreciated, thank you so much !

ok.. so you get ccw props and cw props.. (counterclockwise and clockwise)
they work properly when they are facing the correct way... normally with the text showing the size of the props facing forward.
then yes testing the direction of the motors when spinning can be dangerous... those props have a nasty habit of relieving you of some flesh..
but it can be done push the throttle to the lowest possible setting... that will allow the motor to turn then... keep your fingers out of the way.. test the direction with you finger...
or just power the plane up to whatever throttle is necessary for it to start moving... if it moves backwards... motors is spinning in wrong direction.... if it moves forward you're good to go

 

[Ratcheeroo]

The propellor is connected directly to your motor drive shaft so it can only spin in the direction the motor is spinning. My understanding is that for a front mounted engine(engine at front of plane) the prop should spin in a counter clockwise direction, my other understanding is that the prop should also be facing the right direction, so if you look at your prop you will see that one side is marked with numbers(indicating prop size and pitch) and that when you install the prop you should be able to read the numbers when looking from the front. Once you have done this as part of the build there should be not be a need to check this preflight as it will always be this way unless for some reason you disconnect your ESC from the motor, which is something that you just normally wouldn't do. Flitetest has a video I believe covering this - Power Pods. Hope this helps you out

 

[Matthewdupreez]

The propellor is connected directly to your motor drive shaft so it can only spin in the direction the motor is spinning. My understanding is that for a front mounted engine(engine at front of plane) the prop should spin in a counter clockwise direction, my other understanding is that the prop should also be facing the right direction, so if you look at your prop you will see that one side is marked with numbers(indicating prop size and pitch) and that when you install the prop you should be able to read the numbers when looking from the front. Once you have done this as part of the build there should be not be a need to check this preflight as it will always be this way unless for some reason you disconnect your ESC from the motor, which is something that you just normally wouldn't do. Flitetest has a video I believe covering this - Power Pods. Hope this helps you out

flitetest normally uses ccw props (ithink).... but some people may accidentally use cw props in which case the will have toi change the thrust angle of the motor and also make sure that the motor spins clockwise

 

[quorneng]

Just remember for a propeller the rotation direction (clockwise or counter clockwise) is when viewed facing the front of the propeller.

In this case it is a counter clockwise (CCW) 10" diameter 8.25" pitch prop.

 

[Ratcheeroo]

flitetest normally uses ccw props (ithink).... but some people may accidentally use cw props in which case the will have toi change the thrust angle of the motor and also make sure that the motor spins clockwise

I'm still not clear on the whole CW/CCW thing but I will say that the only FT plane that I have built that has a CCW prop is my MS P-38, one engine has a CW, the other a CCW

 

[CappyAmeric]

I'm still not clear on the whole CW/CCW thing but I will say that the only FT plane that I have built that has a CCW prop is my MS P-38, one engine has a CW, the other a CCW

You have a counter-rotating configuration. My P-38 is the same. That makes it so either engine can be critical engine In the event of engine failure - which is a by-product of P-factor. Twins that don’t use counter-rotating props have more critical engine-out issues associated with P-factor. Counter-rotating with props sweeping inward at the top of the cycle helps cancel out P-factor in a climb too.

 

[Ratcheeroo]

You have a counter-rotating configuration. My P-38 is the same. That makes it so either engine can be critical engine In the event of engine failure - which is a by-product of P-factor. Twins that don’t use counter-rotating props have more critical engine-out issues associated with P-factor. Counter-rotating with props sweeping inward at the top of the cycle helps cancel out P-factor in a climb too.

good to know, thanks

 

[quorneng]

Counter rotating props on a twin is not just an 'engine out' issue but they also remove any torque effect that would be present in a single.
In other words you can apply full power on take off without the plane tending to 'swing' and by the same token it is safe to immediately apply full power in a low and slow situation like a last minute 'go round'.

 

[CappyAmeric]

Counter rotating props on a twin is not just an 'engine out' issue but they also remove any torque effect that would be present in a single.
In other words you can apply full power on take off without the plane tending to 'swing' and by the same token it is safe to immediately apply full power in a low and slow situation like a last minute 'go round'.

Not too slow or low - because even if both engines are running, an engine might fail. All twins have a minimum controllable air speed (VMCA). Slower than that with power on one engine, and the remaining engine failed, the aircraft rolls over and cannot be controlled without removing power from the remaining engine. VMCA has such a rapid effect, it almost always results in a crash when low to the ground. Almost all twins have VR speeds higher than VMCA for that reason, don’t try and fly, even with 2 engines, slower than VMCA because if an engine fails, the aircraft is at risk of upset.

 

[newBB]

ok.. so you get ccw props and cw props.. (counterclockwise and clockwise)
they work properly when they are facing the correct way... normally with the text showing the size of the props facing forward.
then yes testing the direction of the motors when spinning can be dangerous... those props have a nasty habit of relieving you of some flesh..
but it can be done push the throttle to the lowest possible setting... that will allow the motor to turn then... keep your fingers out of the way.. test the direction with you finger...
or just power the plane up to whatever throttle is necessary for it to start moving... if it moves backwards... motors is spinning in wrong direction.... if it moves forward you're good to go

thank you so much for your reply. my prop is this: https://www.rcworld.co.uk/acatalog/APC-8X5--Propeller-E_LP08050.html . How do you know which direction your motor (and so propeller) should spin in?

 

[newBB]

The propellor is connected directly to your motor drive shaft so it can only spin in the direction the motor is spinning. My understanding is that for a front mounted engine(engine at front of plane) the prop should spin in a counter clockwise direction, my other understanding is that the prop should also be facing the right direction, so if you look at your prop you will see that one side is marked with numbers(indicating prop size and pitch) and that when you install the prop you should be able to read the numbers when looking from the front. Once you have done this as part of the build there should be not be a need to check this preflight as it will always be this way unless for some reason you disconnect your ESC from the motor, which is something that you just normally wouldn't do. Flitetest has a video I believe covering this - Power Pods. Hope this helps you out

thank you!!

 

[newBB]

flitetest normally uses ccw props (ithink).... but some people may accidentally use cw props in which case the will have toi change the thrust angle of the motor and also make sure that the motor spins clockwise

thank you !!

 

[newBB]

Just remember for a propeller the rotation direction (clockwise or counter clockwise) is when viewed facing the front of the propeller.
View attachment 194741
In this case it is a counter clockwise (CCW) 10" diameter 8.25" pitch prop.

this helped a lot, thank you!

 

[Quinlan Sauter]

thank you so much for your reply. my prop is this: https://www.rcworld.co.uk/acatalog/APC-8X5--Propeller-E_LP08050.html . How do you know which direction your motor (and so propeller) should spin in?

Depending on if you have a ccw or cw prop your motor should spin either ccw or cw if you have a cw(or ccw) prop and your motor spins ccw then just switch any two of the tree bullet connectors on the esc and motor (that is if you are running a brushless system) this will reverse your motor and get you up and running.

 

[leaded50]

You have a counter-rotating configuration. My P-38 is the same. That makes it so either engine can be critical engine In the event of engine failure - which is a by-product of P-factor. Twins that don’t use counter-rotating props have more critical engine-out issues associated with P-factor. Counter-rotating with props sweeping inward at the top of the cycle helps cancel out P-factor in a climb too.

Didnt the P-38 had opposit direction rotating props than many others orginally? Or was it another ....

 

[CappyAmeric]

Didnt the P-38 had opposit direction rotating props than many others orginally? Or was it another ....

Good point! I think FT decided to make them outer-sweep because the original P-38 did that. Normally, inner sweep is what is done in modern twins with recip engines.

 

[quorneng]

Inward sweep is preferred as in the case of an engine failure the torque of the good engine likely now at full power tends to raise the wing of the dead engine so improving control.
The prototype P38 originally had inward sweep props but it produced some unwanted turbulence problems so it was changed to outward sweep. The consequence of this was an engine failure just after take off usually resulted in loss of control and the death of all but the most experienced pilots. It reached such a proportion in service that it required a specific engine failure routine to be established by Lockheed. This required reducing the power on the good engine (not exactly a natural act) stopping the climb and then letting the speed slowly increase to the minimum single engine full power manoeuvring speed.
Outward rotation remained on all versions of the P38.