Hi all,
I'm building a plane for which i'll be using a .40 engine as a pusher. Due to the space i'm limited to a 6 inch propeller. I've found 3 bladed 6x4 pusher props, and I was thinking if it would not be too much load to have 2 such propellers on the engine.
Thanks.

A 6 bladed prop would be very inefficient

What about a ducted fan?

If you can only fit a 6 in prop, why not use a smaller engine. A 40 will have the power but you can't use it. Like having a bigblock in a lawn mower. It has the power but won't do anymore than the smaller one, Find an engine that can load right on the size prop you have to use and it will be lighter too.

Dauntae

Hej!
Sounds strange!
What kind of strange animal (airplane) is it you have?? Any pictures?

If the plane is heavy enough to require a .40 it will never get off the ground with a 6 - 4 prop. I don't care if you have 10 props on it.

Thanks for the responses.
I'm building a shuttle in the pusher configuration. The thing is that I want the propeller inside the fuselage (keeping it scale) and the only available engine I have for it is a HP .40
Florin

By the way, i'm keeping it as light as possible, even a smaller engine would do fine, it's just that the .40 is the one I have.
What about a sinle 3 bladed 6x4 pusher prop for the .40?

This really sounds like it should use a ducted fan...

i think i've seen ducted fans for glow engines in pusher configuration, any idea where to get such thing?
as for the ducted fan, i'm really not looking for speed just something that would work... perhaps use a larger ducted fan than a .40 takes?
thanks.

Jim,


It ain't necessarily so (© George & Ira Gershwin - Porgy and Bess 1935)...

Watch this [link=http://www.youtube.com/watch?v=yyHySgD6l08]Antonov An-70 video[/link].


The front prop has 8 blades and the counter-rotating rear prop has 6.

It seems effective, at over 82% efficiency.

Also see the [link=http://www.airbusmilitary.com/press.html]Airbus A400M[/link]. A single prop with 8 blades absorbing 11,000 HP. Scroll down to the photos.

Those props are counter rotating though. Also, the prop design wasn't purchased at the hobby shop.

Florin, if you are building a scale shuttle, how are you going to get air into the prop, be it ducted fan or a standard prop??

Don

There is a scale Space Shuttle that belongs to Henry Kin, one of the members of my local RC club, Greater Cincinnati Radio Controlled Club. Here is a link to video of one of the flights. [link=http://www.gcrcc.net/Videos/Shuttle_Maiden.wmv]Maiden Shuttle Flight [/link]

It is rocket-powered though, and Henry is working to improve controlability. One of the latest improvements is to launch it from a large airplane that carries it to altitude.

Here are a few pictures of the Shuttle mounted to it's carrier plane. [link=http://www.gcrcc.net/img/club_mtg_pics.html]March 2007 Meeting Pictures[/link]

It is hard to imagine how you could make a Shuttle look scale, with any intake opening large enough to fly the plane. Perhaps you should consider powering it with a rocket motor too?

either i'm using propeller or fan, puller or pusher, as long as it's inside the fuselage i'll need some cheater holes i guess and modify the design for air intake correct?

It was either Chip Hyde or Jason Shulman who put 2 APC props on the same shaft for a 4 bladed prop setup. He was flying at shows and in competetion with it.

I can personally attest to the success of putting two props on one shaft. I saw this done on a "ducted fan" home-built built by an older club member. Nobody doubts his methods because that distinguished gentleman somehow makes the seemingly impossible work just great!
Two, three blade props stacked on the shaft would definately improve the rotational inertia but the thrust?... try and see....

The funny thing about trying something new is the amount of people denouncing it before the testing and the amount of people praising it after it works!

I'll do some loading tests...

Of course, Jazzy.


Success is known to have thousands of fathers, while failure is obviously an orphan...

I did give my examples for success.

When you say the 40HB is the only engine you have ,tells me your not wanting to buy a jet or turbo fan setup because of expense. Most guys don't read between the lines and money is no object. Provided you have a long enough prop shaft you can put 2 of these togeather with 2 small alignment pins drilled in the hub half way between shaft hole and where blade starts for the best strengh. Don't glue (waste) the prop back hub and washer or nut will keep pins in place. This set up should yeild a 12x4 pusher prop load perfect for a 40 HB.
http://www.masterairscrew.com/index....WPROD&ProdID=3
That prop inefficentcy at the RPM you will turn is HOGWASH. You'll now have a 6 blade pusher .