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Propellors: which is the leading edge?

#1
How do you tell which is the leading edge of a prop? What are the visual clues? Please refer to the photo when answering.

While I’m sure getting it right matters, a friend with pusher plane says he just flips a regular prop over with no problems.

A or B.jpg
 

Ketchup

4s mini mustang
#2
In the picture a is the leading edge. You can tell because if the prop is placed down with the letters pointing up, the leading edge should be the part of the prop that sticks up higher. Also, when the prop is spinning, the leading edge is the “front” of the blade (that’s why it’s called the leading edge... it leads).
 

ElectriSean

Eternal Student
Mentor
#3
While I’m sure getting it right matters, a friend with pusher plane says he just flips a regular prop over with no problems.
This works, but the motor has to be reversed which is also no big deal. The only difference between normal props and pusher props is the direction they are intended to travel. The only difference between CW and CCW brushless motors is the thread on the shaft.
 

sprzout

Knower of useless information
Mentor
#4
This works, but the motor has to be reversed which is also no big deal. The only difference between normal props and pusher props is the direction they are intended to travel. The only difference between CW and CCW brushless motors is the thread on the shaft.
And even then, that's not that big of a deal - a lot of people will just use a nylon lock nut (it's got a piece of nylon in the end that helps to deform and hold the nut on the post so it won't vibrate loose) or a little bit of Loctite Threadlocker Blue (Read the labels - this is the medium strength and is non-permanent; the Loctite Threadlocker Red is permanent bond and NOT what you want to use unless you want to ruin your motor!.
 

DamoRC

Well-known member
Mentor
#6
The numbers are not always on the blade. Sometimes they are on the hub.

Simple rule - the numbers always face the direction in which the plane is intended to fly. Then when the motor is running the plane should pull forward. If it doesn't, the motor direction needs to be changed, not the prop.
 
#7
My problem with all this, and why I asked the initial question, is finding a real pusher prop.

When used with my prop-saver, all the props I’ve found only sit securely on the shaft (and up against the prop saver) with their reducer/adapter-side towards the motor. Mounted like this, to work as a pusher means that the designed following-edge becomes its leading-edge. So, the motor spins one way and the prop is an inefficient pusher. Reverse the motor and the prop efficiently makes the plane go backwards.

Where can I find a prop that will work with my motor? Or make all the other ones function properly?
 

sprzout

Knower of useless information
Mentor
#8
My problem with all this, and why I asked the initial question, is finding a real pusher prop.

When used with my prop-saver, all the props I’ve found only sit securely on the shaft (and up against the prop saver) with their reducer/adapter-side towards the motor. Mounted like this, to work as a pusher means that the designed following-edge becomes its leading-edge. So, the motor spins one way and the prop is an inefficient pusher. Reverse the motor and the prop efficiently makes the plane go backwards.

Where can I find a prop that will work with my motor? Or make all the other ones function properly?
There ARE real pusher props out there; APC makes some. I've bought several from my local hobby shop.

For example:

https://www.apcprop.com/product/7x4ep/

This is a 7x4 prop for an Electric motor, in pusher manufacture. Look for ones with the P designation, to indicate "pusher"...
 

Wildthing

Well-known member
#9
If the plane goes backwards you have the motor and possibly the prop going the wrong rotation. Props no matter whether it is a cw or ccw (tractor or pusher) the letters always face forward
 

quorneng

Well-known member
#11
I would agree that most conventional rotation props will only sit neatly on a prop saver as a tractor unless you can find & fit a suitable bush.
If however you change to using a prop adaptor rather than a prop saver the prop will be secure either way round so it can be used as a pusher.
LockNut.JPG
As the motor is in effect running reversed, which tends to undo a conventional nut rather than tighten it, in this case a second lock nut has been added.
 
#12
I've bought APC props, and they have the same issue as others. With my prop-saver, the reducer/adapter-side of the propeller must sit facing towards the motor. So it works as inefficient pusher, having the designed following edge being used as the leading edge.
Looks like I'll have to glue up my own adapters.
Thanks for all the feedback.