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Old Jan 19, 2015, 11:32 PM
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Joined Jul 2014
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Question
Prop Direction

Hi ,
Just before xmas I bought the flight test mini scout as my first ever scratch build.
I got my electrics from HK and I think I got it all basically right I bought a 250 size multi rotor motor called THE BEAST I also got the suggested props from hobby king.
So here is where this beginner is struggling, the props I got where in pairs (I got some 5inch and some 6 inch) now it seems that these multi rotor prop pairs are opposite to each other.
The scout power pod is set up for the "left hand tendency"
So my question looking at the front of the plane with the numbers on the prop facing forward should my motor spin clockwise or anticlockwise.
Mt first flight was a success but I broke a prop on landing when I used the next prop I noticed it was pushing air the wrong way so I switched the bullet connectors the second flight was very very very quick indeed with a spinning crash on take off.
So any answers to my scout build question would be great.
Thanks.
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Old Jan 20, 2015, 02:28 AM
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slebetman's Avatar
Malaysia, Selangor, Kajang
Joined Jun 2009
1,483 Posts
Looking from behind the prop should spin clockwise. Which means that looking head-on the prop should spin anti-clockwise. It's more typical to see the prop spinning from behind though as that's what you see when you launch/take-off. Nobody really wants to be in front of the prop when it's spinning.

The prop that's spinning the other direction are typically designated "R" for reverse. Often this is printed on the number side. For example 6x4(R).

The clockwise direction comes from the fact that most real propeller driven aircraft have their prop spin clockwise. Some early WW1 and earlier planes have counter-clockwise props. The big exception is Russian planes. Russian designers, from the time of the Tsars through Soviet rule all the way to today standardized on counter-clockwise props. A few Russian planes use clockwise props, probably to make it more compatible for export market, but the majority use counter-clockwise props.

You can of course use either direction (as demonstrated by Russian aircraft designers). The only difference is that a counter-clockwise prop should have a bit of left thrust added instead of right thrust.
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Old Jan 20, 2015, 10:03 AM
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bz1mcr's Avatar
United States, MI, Houghton Lake
Joined Dec 2002
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Quote:
Originally Posted by Hoboelephant View Post
Hi ,
Just before xmas I bought the flight test mini scout as my first ever scratch build.
I got my electrics from HK and I think I got it all basically right I bought a 250 size multi rotor motor called THE BEAST I also got the suggested props from hobby king.
So here is where this beginner is struggling, the props I got where in pairs (I got some 5inch and some 6 inch) now it seems that these multi rotor prop pairs are opposite to each other.
The scout power pod is set up for the "left hand tendency"
So my question looking at the front of the plane with the numbers on the prop facing forward should my motor spin clockwise or anticlockwise.
Mt first flight was a success but I broke a prop on landing when I used the next prop I noticed it was pushing air the wrong way so I switched the bullet connectors the second flight was very very very quick indeed with a spinning crash on take off.
So any answers to my scout build question would be great.
Thanks.
Most planes will have a "left hand tendency" when using a normal prop. (Normal is CCW when viewed from the front. That is CW when viewed from behind.) That is because that set up causes the torque applied to the motor to raise the right wing and lower the left wing. So, with neutral controls most planes will lower the left wing and turn to the left. Often this tendency is reduced by adding some right thrust to the motor.

What you did is the correct procedure for using a reverse rotation prop. If everything else is perfect using the reverse prop will just make it fly with a right hand tendency. It should not change the speed or cause a spinning crash. That is most likely pilot error or wind.
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Old Jan 20, 2015, 08:35 PM
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Malaysia, Selangor, Kajang
Joined Jun 2009
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Quote:
Originally Posted by bz1mcr View Post
What you did is the correct procedure for using a reverse rotation prop. If everything else is perfect using the reverse prop will just make it fly with a right hand tendency. It should not change the speed or cause a spinning crash. That is most likely pilot error or wind.
That is IF the plane has zero thrustline adjustment. But if the plane has right thrust built-in and then uses a reversed prop that would result in double roll torque.

I know what double roll torque feels like because I've flown a push-pull plane configured with both props spinning the same way. If I didn't have any experience flying aerobatics and doing harriers I can tell you that I would have definitely crashed that plane. The tendency to snap roll on take off could easily be described as a "spinning crash".
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Old Jan 20, 2015, 08:41 PM
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Joined Jul 2014
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Ok,
Thanks for the response (and the Russian history lesson) guys.
Now that I have that clear I have looked into my building process and it seams that I have installed my power pod into the scout upside down (did I mention this was my first scratch build) thus the thrust angle is to the left not to the right. (A massive overthrow to the wrong side )
Solution to this problem is already done as per my successful maiden flight all I need to do is use the reverse props change motor direction back to clockwise my plane wont be perfect but it will work and the up side is I also bought the Flight Test Mini Speedster as well this I can install the power pod correctly and use my standard direction props on this so I use all the Multirotor prop pairs.
Thanks again for the input
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