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Pusher configuration

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Old 06-02-2012, 10:02 PM
  #1
mylamo
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Default Pusher configuration

I am in the midst of drawing up a pusher design
using a PAW .19. Finding suitable props , ie 9 X 4
or something close is really hard so I was thinking
that I may be better off with a CCW crank.
Does anyone know if this animal exists and the
possible habitat ?
Ralph
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Old 06-03-2012, 12:51 AM
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Default RE: Pusher configuration

Try talking directly with PAW, they have good customers service.

Another option would be the Enya .15 or .25 diesels, they are really nice. There you simply rotate the front 90° and you can run the engine in the other direction and use regular props.
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Old 06-03-2012, 04:11 AM
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Default RE: Pusher configuration

Both APC and Master Airscrew have quite extensive pusher prop ranges-while Zinger has a huge range-do a search for 'pusher propellers' at www.towerhobbies.com Graupner do pusher props as well-but seem a bit hard to find............ Punctilio props in the UK do a big range-but mainly in the larger sizes (worth an inquiry though)

ChrisM
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Old 06-03-2012, 05:10 AM
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Default RE: Pusher configuration

There's no reverse crank on PAWs spares list, and I've never heard of such a thing - still, it wouldn't hurt to ask them.

You didn't mention whether this is a ballraced engine - would you really want to be running a plain bearing engine as a pusher?
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Old 06-03-2012, 05:43 AM
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Default RE: Pusher configuration

They don't have a 9x4 pusher prop but there are 8x6, 9x5 and 9x6 pusher props. Zinger makes a 9x5 wood prop that could be modified if you needed a 9x4. Since the engine can handle 10x6 props OK, wouldn't a 9x6 be better?

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Old 06-03-2012, 06:17 AM
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Default RE: Pusher configuration

Yes 9x4 sounds too small for a diesel, that's what I use on the PAW 09 and get 10500rpm. Something around 10x4-10x6 props would be better.

The PAW doesn't have any thrust washer in stock form, but a few brass shims would be enough I think in order to run it as a pusher.
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Old 06-03-2012, 07:59 AM
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Default RE: Pusher configuration

I used to think that one could not use a bushed crankshaft engine in pusher configurations. But they have done so many times over the years. I remember seeing airplane plans for pusher planes over the years, some from the early control line days and even free flight too. Some simple engines like the Cox .049's, Gilbert engines, and others used to have control line pusher planes that the engines were mounted on. So if they were doing it all this time in the past, it shouldn't be a problem, even today.

I would think the main risk is if the engine has enough fore and aft play that the crankpin on the crankshaft can touch the backplate. But one can use some thin metal shims to stop that from happening. Also the oil being forced out through the front end keeps the back of the drive washer and front of the crankcase well lubed too, so that shouldn't be a issue. More modern bushed crank engines have a thin steel shim or washer in between the drive washer and front of the engine, so users can use the electric starters on the engines better too.

There are a number of plans and many plans were built using them of the Curtis Wrioght Junior pusher plane, free flight, control line and RC. The British versions all show small diesel engines being used on them.

Here is a delta plane under construction, the plane and plans date back to circa 1952 http://www.rcgroups.com/forums/showt...1134557&page=2
There were not many ball bearing crankshaft engines back then either.


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Old 06-03-2012, 09:32 AM
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Default RE: Pusher configuration

Thanks for all the suggestions . I have a .19 TBR and
used to fly it with a 9X4 and 9X5 but I have run them
on larger props. Earl, I had not given aft play much
thought but fore play I have heard of but not often
witnessed.
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Old 06-03-2012, 09:38 AM
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Default RE: Pusher configuration

The PAW engines usually needs to be adjusted to have a suitable fore and aft play, this is mentioned in the manual too. For CL it doesn't matter much but for RC you don't want the crank pin to hit the backplate at low revs.
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Old 06-03-2012, 02:26 PM
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Default RE: Pusher configuration


Quote:
ORIGINAL: steve111

There's no reverse crank on PAWs spares list, and I've never heard of such a thing - still, it wouldn't hurt to ask them.

You didn't mention whether this is a ballraced engine - would you really want to be running a plain bearing engine as a pusher?

Hi Steve, I bought a PAW .19 TBR in left-hand crank version several years ago. Yes, they probably do have left-hand cranks

as spares. But I agree with the others, I wouldn't use a plain bearing engine in a pusher configuration either.

Tony
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