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Can I temporarily use a 11 x 7 prom on my Magnum GP 40?

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Old 07-25-2013, 08:32 AM
  #1
carl24bpool
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Default Can I temporarily use a 11 x 7 prom on my Magnum GP 40?

Can I temporarily use a 11 x 7 prom on my Magnum GP 40?

I've only got one propellor left until my new 10 x 6 ones arrive.

How will I fair if I use a Graupner 11 x 7 instead for a while?

will it screw my engine or anything?
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Old 07-25-2013, 08:59 AM
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Default RE: Can I temporarily use a 11 x 7 prom on my Magnum GP 40?

Cut tips 3/8 to 1/2" each and balance. You can also sand a very small amount off the back trailing edge for 1-2 inches from tips. This will provide
a washout for the tips which is always good for picking those lost RPMs that your uncut portions drag down.
A .40 will turn a 11-7. Way back in time, 10-6 was standard for .29-35 and 11-5 to 11-7 was standard for .40.
If your magnum .40 is rather new, I suggest cutting the tips for a couple hours running time. Then back to your standard.

Example of prop stuff. We used to have races with a standard sport model, .40 sized Super Tigre, 9-7 prop. That model was a bear to land with the 9-7.
For fun place a standard 10-6 on it and it was better. For real flying and fun place a 11-4 on it and it was MUCH better to land, a bit slower, but aerobatics were

(IMO) 10 times better.
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Old 07-25-2013, 10:54 AM
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Default RE: Can I temporarily use a 11 x 7 prom on my Magnum GP 40?


Carl an 11/7 is to much load for those GP magnum forties. You will run the risk of constant overheating and the resulting deadsticks.

All is not lost as Hoss suggested you certainly can cut it down and I would not get fancy about it and just use a straght cut. Here in the first photos is the best procedure for cutting down a prop to assure both blades have the same length. For that small venturi engine I woud cut it down to a 9.5 /7 and do not try to change the blade planform or pitch. Of course do balance agine after cutting or reshaping.

The last photo is a typical modelers supply of props. Nope ya never can have enough.


John
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Old 07-25-2013, 03:31 PM
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Default RE: Can I temporarily use a 11 x 7 prom on my Magnum GP 40?

I want the messed up one in the lower left center . lol ENJOY !!! RED
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Old 07-25-2013, 04:30 PM
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Default RE: Can I temporarily use a 11 x 7 prom on my Magnum GP 40?

Jeez, John.. got enough props there?

I have about 50 or so and I thought that was a lot.

CGr
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Old 07-25-2013, 05:52 PM
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Default RE: Can I temporarily use a 11 x 7 prom on my Magnum GP 40?

Well Heck CG a mans got to have his props 'eh. Oh OK you can have the messed up one in the lower left center RED besides I ain,t messed with single bladers in a long time
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Old 07-25-2013, 06:23 PM
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Default RE: Can I temporarily use a 11 x 7 prom on my Magnum GP 40?

How long are you actually going to have to wait for the 10x6's to get there? The plane will fly differently with the 11x7, and not in a good way. The engine will lug and not get into the RPM where it makes decent horsepower. I'll say stick with the combination that's been working for you and be patient until your props come in.
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Old 07-26-2013, 02:01 AM
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Default RE: Can I temporarily use a 11 x 7 prom on my Magnum GP 40?


Quote:
ORIGINAL: jester_s1

How long are you actually going to have to wait for the 10x6's to get there? The plane will fly differently with the 11x7, and not in a good way. The engine will lug and not get into the RPM where it makes decent horsepower. I'll say stick with the combination that's been working for you and be patient until your props come in.

I think this may be my best bet.

As it happens thought the 11 x 7 was fitted to an irvine 40 or 42 (can't remember number) when I bought a Ripmax trainer ready built. Perhaps someone was uneducated about the correct choice of prop I guess.
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Old 07-26-2013, 04:05 AM
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Default RE: Can I temporarily use a 11 x 7 prom on my Magnum GP 40?

Post came and no prop.

Called the model shop to be told it only got posted yesterday after me ordering it Monday. What a joke. I'll just order online next time.

The other prop WILL be getting cut down if the others don't arrive tomorrow. I can;t go all weekend without flying.
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Old 07-26-2013, 04:39 AM
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Default RE: Can I temporarily use a 11 x 7 prom on my Magnum GP 40?

An 11x7 is also too much for either an Irvine 40 or 42 as well as the Magnum GP 40 and yes was an inappropriate prop to start with..

Agine if cutting down 9.5 x 7 would be appropriate for the GP 40 and only reducing diameter with no attempt to change blade planform or pitch. These involve additional skills and techniques and beyond the scope of what you want to do.

John
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Old 07-26-2013, 06:46 AM
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Default RE: Can I temporarily use a 11 x 7 prom on my Magnum GP 40?

Thanks john. I'll havea go at cutting it down since I'm itching to get out tonight. Never mind tomorrow.

Perhaps I can whittle one out of some wood? I have a big pile of willow waiting to be mulched in the garden. [:-]
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Old 07-26-2013, 08:53 AM
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Default RE: Can I temporarily use a 11 x 7 prom on my Magnum GP 40?


Quote:
ORIGINAL: carl24bpool

Perhaps I can whittle one out of some wood?

And this is the way its done. A rather lengthy and time consuming process that has its rewards but I would not recomend this for you. You are in to big a hurry. Cutting down a prop though is a time honored technique that is relitively simple.

Reread Jesters last post in your other thread as he has intimated many gems there that you need to carefully consider.

John
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Old 07-29-2013, 02:18 PM
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Default RE: Can I temporarily use a 11 x 7 prom on my Magnum GP 40?

Thats some very nice handywork there.

What sort of wood do you use? are they maple?
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Old 07-29-2013, 03:16 PM
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Default RE: Can I temporarily use a 11 x 7 prom on my Magnum GP 40?

That I believe is just a straight grain fir.

John
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