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Engine basics => Engine set up tips => Topic started by: jim gilmore on December 21, 2010, 02:11:40 PM
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I'm am curious that it is often stated that multiple propellers are less efficient than multiblade props.
What I am curious about is why multi blade props and contra rotating props are used on real aircraft ?
Is that the only way to use enough power with the high hp that the airgraft has ?
Kind of like putting a lawnmower engine in a 1/2A model?
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Hi Jim,
I am curious to see the answers! I am not personally heard that multiple props are less efficient than multi blade props, so I cannot comment on that.
I do seem to remember from somewhere that torque plays a major decision on using contra rotating props of full size aircraft. And I have read some stuff Randy Smith did on his fluid driven contra rotating props in CLPA.
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Jim,
In general you start adding blades when you have extra hp and not enough ground clearance to use a two blade prop or the power plant needs to turn at a higher speed that would push the blade tips faster than Mach 1. Another thing that is done is to go to wider blades but that is not the best way, in some designs they (the designer) was willing to give up some top end performance. Some of the turbo prop designs have so much power multi props were used to absorb it while maintaining tips speeds and ground clearance (on some of the bombers you can't lift the ship to high because of having ground crews loading it).
For stunt multi blades are used for ground clearance to avoid having a ship look like its on stilts.
Best, DennisT
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Some of the team race,speed and free flight flyers have used single blade props and some that I talked to said that the single blade prop works better because of less turbulance for the blade to pass through, more blades-more turbulance! If you are interested, contact Bill Lee or some of the other experts for information.
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I was talking all multi blade simge engine as in the bouton paul defiant with conter or contra rotating props.
I knew that for speed they say 1 blade but I have never seen a real 1 blade aircraft at all. NOT MODEL that is.
So I kinda wondered why they never tried a 1 blade prop in any kind of real aircraft racer.
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I was talking all multi blade simge engine as in the bouton paul defiant with conter or contra rotating props.
I knew that for speed they say 1 blade but I have never seen a real 1 blade aircraft at all. NOT MODEL that is.
So I kinda wondered why they never tried a 1 blade prop in any kind of real aircraft racer.
Hi Jim,
I thought you were talking about that. Torque cancellation is still a reason, I think. And there must be another good reason since Randy has done counter rotating props in Stunt and Bob Hunt talked about it with me years ago.
I have seen those six blade props (5 or 6 or 7 ??) on a British WWII fighter. Probably a Mk "something" Spitfire. I know the reasons I have heard for that is the engine sere so strong but they were limited in LG length and so on for prop clearance.
If nothing major is posted by this afternoon (it's 1:25AM! LOL!!) I will move this to the "Engines" section were more might willing to comment who actually know. ;D
Merry Christmas!
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Guys,
I've flown stunt with props having from one to four blades.
I flew my canard with a one blade prop, just to see if I could. It was no problem. The model didn't accelerate real quick on release for take off, but once up to speed, the was no problem flying the pattern. I've always thought that you simply have to trim what you have, to do what you what you want it to do.
I personally like 3 blades, the way they look and being able to make a shorter landing gear.
Of course now that we're using electric power and left hand props, I have to now make my own left handed 3 blade.
Arch
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Like this one on plane-a-day. Something about being able to get to altitude fast.
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Thanks Bill for explaining the move. I really did not know what to put the question under.
May a topic area for random thoughts ?
Merry Xmas!
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Thanks Bill for explaining the move. I really did not know what to put the question under.
May a topic area for random thoughts ?
Merry Xmas!
Merry Christmas, Jim! I just thought it would get more looks here, and it sorta goes with "Engine set ups"! ;D