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"Push me - pull you props on one motor?

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Old 02-11-2007, 11:44 AM
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Geoffinpdx
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Default "Push me - pull you props on one motor?

Hi, Sal,

I recently got lured into buying an AXI 2208-26 from you thanks to one of your ads right here on RCU. (The bit about "the wife's gonna kill me if I don't move 'em out" worked!) After receiving it I got to wondering if anyone's successfully driven props at both ends of such motors, for such applications as a Cessna Skymaster or one of the WWI planes that had fore and aft engines in one nacelle. I asked this question on Wattflier, and was told that I'd have vibration problems from the long shaft to the rear prop on a Cessna-type installation. The boat builders use long shafts, so why not us?
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Old 02-11-2007, 06:14 PM
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Default RE: "Push me - pull you props on one motor?

Hey Geoff

Not speaking from experience....... but got me thinking
Sounds like a novel approach.... gotta remember boat props lot smaller, but that aside, might work fine....
just need a stiff enough shaft and well balanced props it seems......
Could add a vib dampener or some mid shaft bearings..... figure those turbo fan jets run multi compressor blades at very high RPM, on what seems common shafts???

And I remember in Thailand big long canoes,..... powered with gimbaled, stern mounted auto engines, driving about 10-15' long prop shaft, just housed in a tube, off the back the engine block..... no additional support......
No rudders, just pivoted the whole engine and prop shaft as one, for steering direction..... and those props way out there......

Maybe house the propshaft in tubing, for stiffening and damping..... worth a mockup try anyway....... now some guys on "AB thread" might could do the same with the Blitz,...... you could "prop" it to them..... stop on over, a very diverse crowd, lots of designs flying about......
PDX huh......couple more us crazy ORs there already.... just track me there, where I usually hang out..... just don't tell 'em I sent you, no point starting off on the wrong foot!!!!
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Old 02-11-2007, 06:41 PM
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Default RE: "Push me - pull you props on one motor?

Uhhh, Jim, I've been sniffing CA fumes all day, so don't have a clue what the "AB thread is!" I asked this question in the "Ask Sal" thread earlier today - will see what Sailplane Sal sez... I think I wil make a mockup though, with a veeeery slightly off-center support bearing in the middle to prevent harmonics. GM did it with the solid driveshaft cars they built in the 1960s and it worked. Carbon's really rigid, though, so dead straight might be better.

Limmie know when you get up this way!

Geoff
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Old 02-12-2007, 01:56 AM
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Default RE: "Push me - pull you props on one motor?


ORIGINAL: Geoffinpdx

Uhhh, Jim, I've been sniffing CA fumes all day, so don't have a clue what the "AB thread is!" I asked this question in the "Ask Sal" thread earlier today - will see what Sailplane Sal sez... I think I wil make a mockup though, with a veeeery slightly off-center support bearing in the middle to prevent harmonics. GM did it with the solid driveshaft cars they built in the 1960s and it worked. Carbon's really rigid, though, so dead straight might be better.

Limmie know when you get up this way!

Geoff
I think its possible to do. The problem with having one motor drive two props is that you do not gain any power as the tolal allowable lkoad on the motor would still have to be the same. You would lose some total thrust as you would have to use smaller props and hence lose efficiency. Siunce it is very easy to run tow electric motors in the same plane and not worry about differing RPM, why not simply use two motors?
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Old 02-14-2007, 10:57 PM
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Default RE: "Push me - pull you props on one motor?

Hey Geoff
Just click on "rcverse" to get to my profile,..... and then click on any previous post, besides these two,....... and you'll likely be there in "Does Anybody Fly....AB" thread, as I don't post much of anywhere else......
Sal is probably right about not much to gain in effieciency...... usually smaller props for higher speed, less amps, and sacrifice thrust.... and motor will still only take so much load, but if trying to keep weight to minimum, maybe a gain???? ......does shaft and prop, weigh less than a second motor??? two small props, less efficient than one bigger ????

but then, if just need something to occupy your creative mind, why not..... I've never tried it!!!!

I get up that way, on the clock, once twice a week, but no time to play...Work!!!! But maybe we can put something together one of these days..... Ever do the McMinnville Airshow, become a regular for me,..... good show if you never made it, and the Evergreen Air Museum certainly worth the trip from PDX.......

I have a bias for EP gliders, done some biz with Sal too, that brought me here,...... and curiosity about "two props one motor??",...... one of our crew mounted two props to make a four bladed prop, on single outrunner..... worked, but not sure any gain......
Same guy now building Blitz with just a pusher, but original design is for push pull set up with two motors..... thought you might have an interesting option......
So like I said track me to AB Thread, and pick up on the assortment, always something goin on......usually too much to keep up with...... we even get into gliders Sal, stop on by....
its wide open there....

you get my EPP corsair in the mail Sal??? looks like maybe got them in, but I missed you guys on Saturday, Usually I'm on the road, when you guys on the phones, it seems.....
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Old 02-15-2007, 09:58 AM
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Default RE: "Push me - pull you props on one motor?

Do have the Corsairs in stock, so my guess is that it was sent.
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Old 02-15-2007, 08:49 PM
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Default RE: "Push me - pull you props on one motor?

Jim, see the PM

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