Propeller question

Cox International Mon May 10, 2021 12:03 pm

For buyers looking for a "pusher" prop, we offer this one, together with instructions on how to mount / run, so that leading and trailing edges perform in the proper direction:

https://coxengines.ca/propellers/cox--049-propeller-left-hand-pusher-5-x-3-5.html

Conversely, can any right-hand prop be mounted "hub-reversed" and run left-hand (pusher mode) without degrading performance?

davidll1984 Mon May 10, 2021 12:26 pm

I don't know about the different type of propeller that could offer better performance but I can give you something with the motors to use is the small modification I made to improve the performance with two trust washers the friction is greatly reduced resulting in less wear less friction possible to mix two types differing from one metal to one fenolic wit the tee dee engine two washer wil Not fit direct modification To crankcase and prop drive plate one washer One with a larger inside diameter to fit over the larger portion of the crankshaft

Marleysky Mon May 10, 2021 6:50 pm

Do ya like to read? If not, here’s some homework for ya!

https://journals.sagepub.com/doi/full/10.1177/1756829316638206

There are a couple of pictures just to keep you interested!!

Levent Suberk Tue May 11, 2021 5:55 pm

It works.

1/2A Nut Tue May 11, 2021 10:29 pm

You can fly the prop as a puller with a reed engine.
The TD is limited to pusher only unless you have a left hand crank.

Small Cox Logo

dirk gently Wed May 12, 2021 3:29 am

Cox International wrote:can any right-hand prop be mounted "hub-reversed" and run left-hand (pusher mode) without degrading performance?

I see no performance-related reason why it wouldn't work.
However, I don't like the idea of running the engine in the "wrong" direction, because that will have a tendency to loosen the prop screw while running, rather than tightening it when running in the "normal" direction. Not sure how much of a problem that would be in practice.
Obviously, running the engine "backwards" is only an option for reedies.

Cox International Wed May 12, 2021 11:37 am

Not sure if the question has actually been answered to a degree of certainty.

The way we see it is that every propeller has a leading as well as a trailing edge. If the prop is mounted "hub-reversed" and run in the opposite direction, then the aerodynamics remain the same but one ends up with a "pusher" prop.

Of course TD engines would need a LH crank and there will be the "screw-coming-loose" issue.

Was just looking for a confirmation because we constantly get requests for pusher props.

Surfer_kris Wed May 12, 2021 12:16 pm

Most people may well prefer pusher props, as the running direction of the engine then stays the same.

Appart from the prop screw issue, there is also the need for a reverse spring starter and relearning how to flip the prop etc.

Cox International Wed May 12, 2021 12:54 pm

Surfer_kris wrote:Most people may well prefer pusher props, as the running direction of the engine then stays the same.

Appart from the prop screw issue, there is also the need for a reverse spring starter and relearning how to flip the prop etc.

Yes, except that pusher props are almost non existing.

Also, we do sell the LH starter springs.

ajcoholic Fri May 14, 2021 8:07 pm

Cox International wrote:Not sure if the question has actually been answered to a degree of certainty.

The way we see it is that every propeller has a leading as well as a trailing edge. If the prop is mounted "hub-reversed" and run in the opposite direction, then the aerodynamics remain the same but one ends up with a "pusher" prop.

Of course TD engines would need a LH crank and there will be the "screw-coming-loose" issue.

Was just looking for a confirmation because we constantly get requests for pusher props.

Yes, 100% if you mount a tractor prop backwards, and run the engine in the opposite direction, you have a pusher configuration. Also, I have run many reedies as pushers, and have never had the prop screw loosen. Ever.

andrew Fri May 14, 2021 11:54 pm

ajcoholic wrote:Yes, 100% if you mount a tractor prop backwards, and run the engine in the opposite direction, you have a pusher configuration. Also, I have run many reedies as pushers, and have never had the prop screw loosen. Ever.

Andrew --
Nice to see a name from the old RCU group showing up here. Don't be a stranger.

The "other" Andrew

Marleysky Sun May 16, 2021 3:26 pm

Ok! It’s movie time!

https://m.youtube.com/watch?v=0bP2MH3LqvI

batjac Sun May 16, 2021 9:54 pm

Cox International wrote:Conversely, can any right-hand prop be mounted "hub-reversed" and run left-hand (pusher mode) without degrading performance?

For all practical purposes, a prop doesn't care whether it's pushing or pulling. The only real considerations of using a tractor prop in a reed engine as a pusher are 1) the air flow around the fuselage before getting to the prop, and 2) the drag on the drive plate against the crankcase. As a tractor, it's in clean air and is most efficient. As a pusher, it's in dirty air and not as efficient. As for the case drag, I don't know if the drag of the back of the prop hub in a pusher configuration is more or less than the drag of the crank hub against the face of the thrust bearing in the case. But as for the prop itself, as long as the curve is forward, it's good to go.

The Dr. Doolittle Mark

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