2 to 4 Blade Propeller Conversion
09-23-2005, 01:43 PM
#1
2 to 4 Blade Propeller Conversion
Have a TF Giant P-51D Mustang and a U.S. Engines 41 going into it. U.S Engines reccomends a 18x8 for break in then running a 18x10 or a 18x12. I found some nice wood 4 blade propellers from Zinger but am looking for how to calculate the difference in diameter from a 2 blade to a 4 blade prop. Any thoughts, ideas or suggestions? Thanks!
09-23-2005, 02:07 PM
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09-23-2005, 02:08 PM
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RE: 2 to 4 Blade Propeller Conversion
Hi,
The P51 uses a 5" spinner, so only 6 and 1/2" of 18" prop will protrude. A four blade will be smaller diameter with even less prop sticking out. This is why most of the four blade installations use a reduction drive. With no reduction it may take a 15 or 16" four blade prop. Performance will suffer. The scale prop is about 24" in diameter. Why don't you make up a dummy spinner and four bladed prop for display?
Dave
The P51 uses a 5" spinner, so only 6 and 1/2" of 18" prop will protrude. A four blade will be smaller diameter with even less prop sticking out. This is why most of the four blade installations use a reduction drive. With no reduction it may take a 15 or 16" four blade prop. Performance will suffer. The scale prop is about 24" in diameter. Why don't you make up a dummy spinner and four bladed prop for display?
Dave
09-23-2005, 03:46 PM
#4
RE: 2 to 4 Blade Propeller Conversion
Wouldn't keeping the same diameter effect the RPM's? as in drop them a fair amount? If I can get a 4 blade on it without losing too much performance, I would rather that than taking the prop off and swaping it with a static display every time I show it... keeping a functional prop on it would be ideal.
09-23-2005, 04:13 PM
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RE: 2 to 4 Blade Propeller Conversion
Load changes faster with changes in diameter than with changes in pitch..... blade load approx =
dia*dia*dia*pitch.
dia*dia*dia*pitch.
09-23-2005, 04:15 PM
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RE: 2 to 4 Blade Propeller Conversion
I am curious as to why you would want to have a four blade prop. With each blade added, efficiency goes down, caused mainly by turbulence initiated by the preceding blade. Full scale planes have to use multi blade props to absorb the power. This is rarely a problem with models unless noise or ground clearance becomes an issue. If appearance is what you are concerned about, I think you should be a whole lot more interested in the lousy flight performance you would get with a four bladed prop.
09-23-2005, 04:19 PM
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RE: 2 to 4 Blade Propeller Conversion
Its not only the drop in RPMs that you need to be concerned about..
Yes, larger prop will slow down motor.. TOO large a prop will cause
motor to have to 'over work'.. As in, not run well..
Where the US41 will fly the plane,, you are already at minimum power
by using that motor... Now,, to slow down the motor by using a larger
prop,, is basically a disaster looking for a place to happen..
As Dave Wallace puts in the above, by using the proper size four
blade you will loose too much diameter which will loose wayyy
too much performance...
This basically equates to an extremely narrow USABLE RPM
range and rather marginal flying chareteristics..
Simply put.. A no fun plane..
Yes, larger prop will slow down motor.. TOO large a prop will cause
motor to have to 'over work'.. As in, not run well..
Where the US41 will fly the plane,, you are already at minimum power
by using that motor... Now,, to slow down the motor by using a larger
prop,, is basically a disaster looking for a place to happen..
As Dave Wallace puts in the above, by using the proper size four
blade you will loose too much diameter which will loose wayyy
too much performance...
This basically equates to an extremely narrow USABLE RPM
range and rather marginal flying chareteristics..
Simply put.. A no fun plane..
09-23-2005, 04:42 PM
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RE: 2 to 4 Blade Propeller Conversion
A tiny fourblade will not look any better, or more scale than the correct 2 blade. I doubt you will find a 4 blade that will fly the plane with a US 41.
