ba97
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"pushing" Vs "pulling" Props

Mon Jul 26, 2004 4:29 am

Please excuse my naivete on this:
Is there any engineering design reason why props are on the front of the plane or engine on commercial aircraft, thus "pulling" compared to backwards facing and "pushing". I have seen pictures of some military planes (German I think) and small private planes with a prop on the rear of the plane. With the overwhelming majority on the front, I expect there is a definite reason but then why the oddities?
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Starlionblue
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RE: "pushing" Vs "pulling" Props

Mon Jul 26, 2004 5:14 am

While I am not 100% sure, I would say the main problem is weight distribution. Before long propshafts were feasible, putting the prop in the ass of the plane was not possible because the weight distribution would be off with an engine mounting behind the wing. With wing mounted props (as with wing mounted jets), you want the weight to be on the front of the wing to decrease the tendency of the wing to twist up.

As far as I have been able to discern from previous discussions of pushers on this forum, they are theoretically as efficient as pullers.

Problem #2: Air AFTER the plane is more turbulent. Pullers get less turbulent air and so can be more efficient. I'm not entirely sure about this one.

Problem #3: At least in smaller fighters, the pilots don't enjoy bailing out only to be chopped to pieces by their own prop.

The German plane you are referring to is probably the Do-335 Pfeil. Yes, it had a pusher prop and rear engine, but it ALSO had a nose prop and front engine. Very cool plane http://www.aeroflight.co.uk/profile/d335top.htm. The Pfeil resolved the bailout problem by having a jettisonable prop and fin.

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L-188
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RE: "pushing" Vs "pulling" Props

Mon Jul 26, 2004 1:30 pm

All other things being equal a pusher prop won't be as efficent because of the turbulent air comming off the wing, Nacelle, or cabin ahead of it.

There is also issues of prop clearence on take-off, prop damage from rocks kicked up by the mainwheels.
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MD-90
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RE: "pushing" Vs "pulling" Props

Mon Jul 26, 2004 2:37 pm

Also prop damage from things flying off the engine, and the fact that they can be hard to cool.

But for some designs it makes good sense.



Practicality (Progressive Aerodyne Searey)



Weight distribution (Piaggio P.180 Avanti)
 
canoecarrier
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RE: "pushing" Vs "pulling" Props

Wed Jul 28, 2004 7:07 pm

I've always been a fan of the Cessna 337, with both a pusher and a puller. IIRC, you do a seperate multi checkride since it has counter rotating props.
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Alessandro
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RE: "pushing" Vs "pulling" Props

Wed Jul 28, 2004 10:19 pm

Also the Beechcraft "starship" got the pulling props..
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Starlionblue
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RE: "pushing" Vs "pulling" Props

Thu Jul 29, 2004 12:19 pm

Shouldn't that be pushing?
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

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