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Engine basics => Engine set up tips => Topic started by: rustler on December 04, 2007, 03:05:13 PM
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I hear the rule of thumb for 3 bladers is 1" less dia. than a 2-blader. Any ideas for a 4-blader?
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1" additional less diameter and/or pitch, depending on the plane/engine combination make a good starting point. Experimentation WILL be required!
Ralph
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And of course any increase in the number of blades increases proportionally the chance for the extra blade to
snap you very smartly on the top of your knuckle or 2....I can remember using a tri-bladed prop on an Enya many moons ago...I think I still have traces of that scar...But when you are young and foolish..one is also bulletproof..Now thats funny!
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The definition of middle aged is when you realize you are no longer IMMORTAL! LL~
As far as finger strikes, that's why electric starters were invented. HB~>
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Thanks guys. I think this may be the way to go for these larger engines now coming on stream. Otherwise it's going to be either ground clearance probs or v. tall u/c's.
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Four bladed props. One more reason to learn the "Back Slap" starting method. y1 H^^
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I hear the rule of thumb for 3 bladers is 1" less dia. than a 2-blader. Any ideas for a 4-blader?
That is a good rule for props of the same blade size area, however it will depend on who makes the 3 blade, there are many 3 bladers that you can run the same size as the 2 blades, some are higher aspect ratio blades and turn pretty easy.
Best to try them first before cutting...you can always make the blades smaller, but it's a little hard to make them longer ;D
Randy
Randy
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How about *4 bladers*, Randy? ;D
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I suspect that Randy's outlined rule for 3 bladers still applies. If you have a 4 blade that is long and narrow with a flat back, probably out to try it first before cutting it down. It will depend largely on the engine and the design of the prop. I've only used a 4 blade once and had some GP problems. I didn't fool with it long enough to sort it out, but I did like the traction it provided. Very cool.
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How about *4 bladers*, Randy? ;D
HI Bill
Randy's post is correct, many 4 blade props are high aspect ratio and thin. People making 4 blades by just screwing or milling slots and putting 2 wood props together are most likley going to need to go at least 1 inch down size, and maybe even up to 1.5 to 2 inches. This will depend on how easy the prop turns.
Interesting , I have found 4 blades to drive very good and give a "turbine" like feel to the motor-plane..however they are very noisy. Some will really howl.
Stick with an odd number of blades if you want quiet! even numbers are much more noise
Randy
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I was just musing over the Parrott P-47 with a certain ST 46 that you know about. It would be interesting to me to try a 4 blader on that one.
I didn't hear back from you about the message i sent..... ?? ?? ??