ughturtle

I have heard that one can use a tractor prop put on bachwards in place of a pusher prop. If this is so how efficient will the tractor prop be?

ho2zoo

My Feedback: (5)

Nope, a tractor prop put on backwards is still a tractor prop. It just doesn't work as well.

jetmech05

True ho2zoo has it correct. You can't replace a tractor prop for a pusher backwards

JohnBuckner

My Feedback: (1)

Yup, add another positive reinforcement to what the fellows have said. At one time where throttles were not avalible and still in venues such as controlline deliberately installing a prop backwards is done to slow an airplane down that flys too fast. and it works great.

Now you Can use a conventional 'tractor' prop mounted backwards in a pusher configuration if you reverse the direction of the motor/engine. Reversing the direction of an electric motor can be relatively easy. However reversing the direction of a glow/gasoline engine can be a major challenge. Although some glow engines of the past made reversing pretty easy most all modern engines reversing is not practical for the most part.

John

daveopam

My Feedback: (9)

Ran into this before. Visualize it like this. While holding the prop in front of you look down the length from the tip of the blade to the hub. The pitch will run like this I/I . The I I being the hub the / being the pitch of the prop. Now turn the prop so the back of it is now facing the other way and look down it again. You will stil get this I/I .

David

ughturtle

Hi DAVE I performed your prop suggestion, and what I saw is there wasn't any differance in the pitch direction. From this one could assume that using a tractor prop backword would work . I wonder how efficient it would be? Any ideas?

JohnBuckner

My Feedback: (1)

[QUOTE=ughturtle; From this one could assume that using a tractor prop backword would work . I wonder how efficient it would be? Any ideas? [/QUOTE]


Yes as all the responders above have indicated: It will work in the right direction, although at much reduced thrust.

That means the airplane will fly much slower, have less climb and be more sluggish on the controls because of the lower speed.



John

Top_Gunn

My Feedback: (6)

I think the OP has somehow gotten the idea from Dave's post that putting a tractor prop on a pusher will work if you put it on backward, despite numerous posts (including Dave's) pointing out that it won't. unless you can reverse the rotation of the shaft. The fact that the pitch direction is the same when the prop is reversed doesn't mean that reversing it will make it work on a pusher, it means just the opposite.

daveopam

My Feedback: (9)

Ughturtle, A pusher prop is going to be a pusher prop no matter what direction the prop is installed on the motor. The direction of the pitch is what make's a pusher different from a tractor. Turning it around as I indicated still makes the pitch go the same direction. If you look down the blade of a pusher and a tractor side by side you will see the pitch is opposite no matter which way the prop is facing. As John stated above the prop will work as a pusher both ways, but the prop was designed to turn one direction so turning it around will still blow the air the same direction, but not as efficiently.

David

JohnBuckner

My Feedback: (1)

John

da Rock

It will produce very little thrust UNLESS...........

Unless you've put that pusher prop on an electric motor. We use pusher props all the time on twin engine electric models. Set that motor up to run clockwise. Put the pusher on with the curved side of the airfoil facing forward. And fly.

But what you're talking about... doesn't work good enough to do.

Top_Gunn

My Feedback: (6)

And (apart from the electric motor situation) what little thrust a tractor prop on backward will produce will be in the wrong direction, if it's on an engine pointing toward the plane's tail. The problem isn't that it won't work well enough, it's that it won't work at all..

ughturtle

Thanks all for the input.

da Rock

Put a prop on backwards on a fuel engine (that won't run backwards), and the prop will work about the same way a cambered airfoil works when it's airplane flies inverted. Not well at all. There are quite a few aerobatic planes with cambered airfoils. They fly inverted. Their AOA when inverted, like any prop on backwards, doesn't really "produce lift in the wrong direction". They produce lift very poorly but in the right direction.

Top_Gunn

My Feedback: (6)

Yes. But if you have a non-reversible engine pointed toward the plane's tail (i.e. an engine in the pusher position), putting on a tractor prop, either forward or backward, will produce lift in the wrong direction. It will pull the plane backward, not push it forward.

The original post here proposed doing exactly that: using a tractor prop on a pusher, and putting the prop on backward. And one of his later posts seemed to say that he still thought that would work. My post was about what would happen if he tried that, not about what would happen if he took an ordinary plane and put the prop on backward. You and I both understand what will happen in both these cases, but I'm not clear on whether the OP gets it. My concern about your post wasn't based on a belief that you had said anything wrong, it was that the OP could have understood it as referring to his situation (engine in the pusher position). The part that concerned me was your telling him that what he was talking about wouldn't work well enough. Don't we both agree that it wouldn't work at all?

da Rock

Do we agree that it wouldn't work at all?

We haven't been talking about the same it, that I can tell. But I absolutely agree that your "it" wouldn't work at all.

Up until the popularity of electric motors that can run both ways, clockwise and counter clockwise, the first answer to the Original Post covered "it" pretty well. In order to bring the issue up to date, I've been fuddling and muddling along in hopes modelers who haven't noticed will pick up how today the prop situation isn't as restrictive as it used to be.

Hope we both got across what "it" was we wanted to get across.

Top_Gunn

My Feedback: (6)

I agree that the second post gave the right answer. But in the sixth post, the OP still seemed convinced that what he proposed to do would work, which was why i joined in. For all I can tell, he still thinks so. The "it" I was talking about was the OP's proposal. I thought you were talking about that, too, since your answer quoted him and referred to "your proposal." Sorry if I misunderstood you.

da Rock

It's not clear which way he's going. But if he has an electric motor, either prop will work. If fuel, his tractor backwards or forwards won't work, he needs a pusher.

Top_Gunn

My Feedback: (6)

I know that. The question is whether the OP knows it. It's also unclear sometimes what people mean when they say to put a prop on backward. A guy in my club many years ago had a pusher with a glow engine and a pusher prop. He put the prop on with the curved side of the blade facing back (i.e. toward the tail) and argued with me when I told him to put it on the other way.