Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

prop conversion 2 blade to 3

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Old 10-03-2007, 04:01 PM
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frenchie79
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Default prop conversion 2 blade to 3

OK speed boys, I have a small Kobra with a 46 stuffed in it. Anything larger than a 9" prop hits the ground. What would be a good conversion for a 10x7 or 11x5 2 blade to a 3 blade?????? To many RPMs with a 9".
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Old 10-03-2007, 06:13 PM
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Default RE: prop conversion 2 blade to 3

Frenchie:

Have you ever seen a 3 bladed prop on a national Q-500 or 40? No. On WW11 war birds, yes, 3 and 4 bladed. That was a no choice option. The large engines required big props, much biger than the airframe design would allow, hence the multiple blades. The 2 blade design is simply more efficient. Same general principals in boat props. At one time, the U control speed guys were running 1 bladed props. In boat drag racing, we used 2 blade hydroplane props if you wanted to go fast top end and live on the edge, used 3 blades to get out of the hole faster, but lost out on the high end side. The more efficient hydroplane 2 blade props had a interesting effect of pushing the bottom rear of the boat out of the water, ok for a true hydroplane boat with the front sponsons in the water. With a flat bottom boat, sort of got squirley over 100 mph. Fun to watch, not so fun to drive. Suspect the multi bladed sub props are for noise reduction design, but don't know. Hope this helps. ENJOY
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Old 10-03-2007, 06:19 PM
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Default RE: prop conversion 2 blade to 3

Run a 9x9 or 9x8 two blade. If you must run a three blade try a Master Airscrew 9x7, not a bad sport prop.
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Old 10-04-2007, 08:39 AM
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Default RE: prop conversion 2 blade to 3

I'll buy both and give them a try-Should have the plane ready to test in a week. Thanks for the replys.
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Old 10-04-2007, 10:31 AM
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Default RE: prop conversion 2 blade to 3

What engine are you running....??

For most .46 size engines on the market, they are well within usable rpm range with a 9x7 or 9x8 2 blade prop bolted on.

For something like the TT46 or OS46FX or AX on the stock muffler, you will want to prop it to run around 15,000-16,500 ground peak rpm for best power.

3 blade will slow you down and reduce performance. But sometimes they look cool [8D]
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Old 10-04-2007, 09:14 PM
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Default RE: prop conversion 2 blade to 3

I put a Magnum 46 in the plane. Had it in a box and wanted to use it-so buy a kit! you no the story. On the test stand i was running 16050 on a 9x7 APC, 15870 with a 9x8 MAS. You don't think thats to high. What do you think it will unload at.
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Old 10-05-2007, 12:57 AM
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Default RE: prop conversion 2 blade to 3

the MAS doesn't track well use Graupner

Clement
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Old 10-05-2007, 07:59 AM
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Default RE: prop conversion 2 blade to 3

Here is the problem, picture shows a 9x7 prop and the tail is not completely level. Only a 1/2 to 3/4".
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Old 10-05-2007, 09:07 AM
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Default RE: prop conversion 2 blade to 3


ORIGINAL: frenchie79

On the test stand i was running 16050 on a 9x7 APC, 15870 with a 9x8 MAS. You don't think thats to high.
No
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Old 10-05-2007, 11:44 AM
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Default RE: prop conversion 2 blade to 3

ORIGINAL: frenchie79

I put a Magnum 46 in the plane. Had it in a box and wanted to use it-so buy a kit! you no the story. On the test stand i was running 16050 on a 9x7 APC, 15870 with a 9x8 MAS. You don't think thats to high. What do you think it will unload at.
Those RPMs are ideal...... and indicate a good running engine.

For flight, richen up the engine about 600 rpm down from those peaks before launch.
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Old 10-05-2007, 01:05 PM
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Default RE: prop conversion 2 blade to 3

So set the engine for about 15,400 to 15,500-Will do. Thank-you
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Old 02-07-2008, 09:50 PM
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Default RE: prop conversion 2 blade to 3

does the kobra need any mods for a 46 ax?
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Old 02-07-2008, 11:11 PM
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Default RE: prop conversion 2 blade to 3

I usually convert two blade props to one.[]
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