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Model Forum / Radio Controlled / Air Models / June 2004Pusher prop, does it differ from tractor prop?
Hi, I want to scratch build an electric plane with a pusher prop. I was told that I need a special pusher prop, but I can't find any locally. Why is it not good to use a regular prop turned backwards and have the motor reversed in rotation? Wan | I want to scratch build an electric plane with a pusher prop. I was | told that I need a special pusher prop, but I can't find any locally. | | Why is it not good to use a regular prop turned backwards and have the | motor reversed in rotation? That'll work fine. Reversing a motor with a glow plane isn't as easy as it is with an electric, but with an electric you can often do exactly what you're suggesting. Do be aware that electric motors often need to be re-timed to run efficiently backwards.  SignatureDoug McLaren, dougmc@frenzy.com Join the collective. Meet distinctive individuals. Travel to distant eco-spheres. And assimilate them. > | I want to scratch build an electric plane with a pusher prop. I was > | told that I need a special pusher prop, but I can't find any locally. [quoted text clipped - 8 lines] > Do be aware that electric motors often need to be re-timed to run > efficiently backwards. Thanks, Doug. The motor I plan to use is a geared brushless and I don't think it needs to be re-timed? Perhaps I should have concerns about cooling the motor since the air will not be blown through? Wan > > | I want to scratch build an electric plane with a pusher prop. I was > > | told that I need a special pusher prop, but I can't find any locally. [quoted text clipped - 16 lines] > > Wan If it is a sensorless brushless motor, it will not have to be re-timed. >>| I want to scratch build an electric plane with a pusher prop. I was >>| told that I need a special pusher prop, but I can't find any locally. [quoted text clipped - 11 lines] > Thanks, Doug. The motor I plan to use is a geared brushless and I > don't think it needs to be re-timed? No, just swap any two leads in it to reverse it. > Perhaps I should have concerns about cooling the motor since the air > will not be blown through? > > Wan The efficency of the propeler will be very low . You can have pusher prop at tower hobbies. > Hi, > [quoted text clipped - 5 lines] > > Wan > > Hi, > > [quoted text clipped - 5 lines] > > > > Wan You could try carving your own - it's not difficult although can take quite a bit of time, but there is a great deal of satisfaction to be had when your model flies with the prop you made. Malcolm > You could try carving your own - it's not difficult although can take quite > a bit of time, but there is a great deal of satisfaction to be had when your > model flies with the prop you made. > > Malcolm And how many times have _you_ done that? > > You could try carving your own - it's not difficult although can take > quite [quoted text clipped - 5 lines] > > And how many times have _you_ done that? Many many times. I started as a teenager in the late 1950s when I didn't have much money to spare on my hobby. A piece of wood and my time cost very little. The cost of a new prop was nearly as much as a half pint of fuel which, at the time, I couldn't make but later learned how and still do from time to time. I'm talking diesel here, not glow, but have mixed my own glow fuel as well. Latest carving was for a 10 X 5 to run in an OS Wankel given as a present last Christmas. I most likely won't need the prop for anything else apart from, possiby, my Black Magic which is powered by a PAW 19D. I'll send you instructions if you really want. Malcolm > > You could try carving your own - it's not difficult although can take > quite [quoted text clipped - 5 lines] > > And how many times have _you_ done that? Forgot to mention that I have carved both pusher and tractor props. When I first wanted a pusher, there were none available from my local shops so the only way was to make my own.. Malcolm >> Why is it not good to use a regular prop turned backwards and have the >> motor reversed in rotation? > ... > The efficency of the propeler will be very low . You can have pusher prop at > tower hobbies. The efficiency of the propeller won't change at all. The efficiency of the motor might decrease. Or not. That depends on the concrete motor. SignatureBest regards, Andrey Tarasevich The efficiency would be exactly the same. If the motor is reversed and the prop turned around, it will be blowing the same as it would have been sucking in normal mode. -- Paul McIntosh http://www.rc-bearings.com > The efficency of the propeler will be very low . You can have pusher prop at > tower hobbies. [quoted text clipped - 8 lines] > > > > Wan > The efficency of the propeler will be very low . You can have pusher prop at > tower hobbies. Rubbish. >>Hi, >> [quoted text clipped - 5 lines] >> >>Wan I have emailed several prop manufacturers and all have assured me that a pusher prop is a mirror image of their tractor props. Mount a tractor prop on the engine to where you can read the face side of the prop from standing in front of the plane looking back at the motor. The face side of a tractor prop points forward regardless of whether its mount on the front, or the back of the plane. Reverse the motor's rotation and everything should work just fine, and be just as efficient as a pusher prop. Assuming the electric motor is as efficient reversed. >Hi, > [quoted text clipped - 5 lines] > >Wan > Hi, > [quoted text clipped - 3 lines] > Why is it not good to use a regular prop turned backwards and have the > motor reversed in rotation? That's what everyone else does Wan. Only slimers that can't run backwards properly need a specaial prop. > Wan > > Hi, > > [quoted text clipped - 7 lines] > > Only slimers that can't run backwards properly need a specaial prop. TNP, Very interesting. I was checking my new AXi 2212/34 and it was rotating clockwise looking at it from the front, wrong for a tractor prop. The leads to the motor were correctly connected to color code. Then I switched the power leads, red to black, black to red, and it ran correctly. Would switching ANY two leads do the same as suggested by another poster here? Wan In a brushless motor, yes. Switch all three leads and it won't change the direction. PCPhill "> TNP, Very interesting. I was checking my new AXi 2212/34 and it was > rotating clockwise looking at it from the front, wrong for a tractor > prop. The leads to the motor were correctly connected to color code. [quoted text clipped - 6 lines] > > Wan >>>Hi, >>> [quoted text clipped - 17 lines] > Would switching ANY two leads do the same as suggested by another > poster here? Yes. > Wan Wan opined >> > Hi, >> > [quoted text clipped - 11 lines] >rotating clockwise looking at it from the front, wrong for a tractor >prop. The leads to the motor were correctly connected to color code. >Then I switched the power leads, red to black, black to red, and it >ran correctly. >Would switching ANY two leads do the same as suggested by another >poster here? That is what an article I read claimed. -ash Cthulhu for President! Why vote for a lesser evil? > Wan opined > [quoted text clipped - 25 lines] > Cthulhu for President! > Why vote for a lesser evil? Thanks everyone. Everything I've read here have been reassuring that I can use a tractor prop as a pusher. The major reason why a pusher plane is to keep my gear box from being broken on bad landing by having the prop in the rear. (I'd rather build a tractor plane) A direct drive would eliminate the gear box, but why don't they make gear boxes with less brittle plastic? And there is no glue I know of that will adhere to that plastic for repairs. No more geared motors for me in the future. Wan >>Wan opined >> [quoted text clipped - 37 lines] > > Wan Crash less. Besides you can get spares. > >>Wan opined > >> [quoted text clipped - 38 lines] > > Wan > Crash less. Besides you can get spares. Is this you speaking, TNP? Absolutely crash less! But where can I get spares now? I expressed the same sentiments in my other post about direct drive and prop sizes. Wan >>Crash less. Besides you can get spares. > > Is this you speaking, TNP? > Absolutely crash less! But where can I get spares now? I expressed the > same sentiments in my other post about direct drive and prop sizes. Not sure what box you have. But see other post for lots of places to get box spares. > Wan > >>Crash less. Besides you can get spares. > > [quoted text clipped - 3 lines] > > Not sure what box you have. But see other post for lots of places to get TNP, Thanks for the suggestion. I book marked several sites and found the gearbox I needed. I will be studying as to what else is available. I also found one the motors I purchased, an AXI 2212/34 bruhless for a little less than what I paid at the hobby shop. But I have it sooner. For what it's worth, I'd rather have a brushless direct drive than a geared one. Perhaps because they're more efficient without the gears? Wan |
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