stunthanger.com
Design => Engineering board => Topic started by: Lauri Malila on June 05, 2013, 09:54:18 AM
-
Hello.
A friend of mine has a prop like this in his model (electric pylon racing). He is a world champion, so there must be a reason for it. He said that acceleration after corner is better and as a side-effect, the prop is also less noisy. I did not measure the noise but unlike with a more normal prop, I could hear the motor gearbox noise. That made me think...
The prop in the picture cannot be used in stunt as it is, as it's something like 10x22".
Luckily, I have a brand new square file.
Lauri
-
Interesting. I assume you're talking about the sawtooth trailing edge, not the fact that it's a folder.
-
Yes, Tim. Folder or not, it makes no difference. Maybe in starting :)
-
A quick web search on "sawtooth edge prop" coughs up some patents for quiet fans:
http://www.docstoc.com/docs/49147175/Propeller-Fan---PDF (http://www.docstoc.com/docs/49147175/Propeller-Fan---PDF)
https://www.google.com/patents/EP0711925B1?cl=en (https://www.google.com/patents/EP0711925B1?cl=en)
It appears from the patent claims that the sawtooth trailing edge reduces turbulence with thin, high-lift blades. The patents are about reducing noise, but mention efficiency gains as a nice side effect -- your guy likes the increased efficiency.
I'm not sure if you'd get the same effect with a flat-pitch stunt prop, as the advantages seem to be related to the front-back pressure differential, which is going to be less with a flatter pitch.
I did notice at the Northwest Regionals that there seems to be a wide variation in the amount of propeller noise among the electric guys -- some planes are whisper quiet, while others make so much prop noise they're almost as bad as a well-muffled IC setup. I have no clue what the effect is, though.
Got any junk CF props? A cutoff wheel? Some sand paper? Maybe it's time to experiment!
-
Isn't that a saw tooth leading edge?
Or am I seeing the a pusher model there. ???
-
Isn't that a saw tooth leading edge?
Or am I seeing the a pusher model there. ???
D'oh. I bet it's the same principle. Somehow. Maybe.
-
D'oh. I bet it's the same principle. Somehow. Maybe.
Nah, I am betting its all about inducing vortices, reducing stalling, keeping flow attached blah, blah, blah.....
-
It's humpback whale technology. They have the ripples on the leading edge of their flippers.
I'm sure someone posted something about it a few months ago. A wind turbine manufacturer is promoting the technology, but others say it's hocus pocus.
-
Isn't that a saw tooth leading edge?
Or am I seeing the a pusher model there. ???
TE Chris,
Clockwise engine rotation.
Leckies run the same both ways.
-
??
It's normal, anti clockwise rotation. Zigzag is in blade leading edge.
I'm not a specialist but to me the thing seems to be several small vortexes instead of one big vortex in tip. Plus, maybe similar flow effect than with vortex generators. Interesting but propably not worth the trouble with our reynolds numbers. My main interest is in noise reduction.
I have tried all kinds of fancy blade shapes (like in APC's) but for some reasons the engine adjustment became much more critical. L
-
Depends what is clockwise and what is normal VD~
in any case yes, it should be on leading edge, but its function is not "several small vortexes instead of one big vortex in tip", the function is to make 1/ higher speed at LE and thus reaching higher RE number and 2/ make little bit spanwise crossleading flow just like VG or zigzag turbulators does and so make some attached turbulence and so keep flow attached
Unfortunately it is not copletaly clear HWERE flow separates on our props, electric motors give chance to hear sound of prop and thus optimize it, but I am sure that some props separates on upper side at large spippage while others make bubble at LE wit low or negative slippage (while braking), depending on airfoil shape ... it is very easy to hear, if it makes stronger noise after corner while climbing, it separates on top, if it makes that sound while diving, it separates at LE on lower side.
IC engines are noisy, but anyway, I remember that effect with piped low pitch props while diving or on bottoms of figures. I also think that buble helps to brake the prop and not to allow overrewing (I wrote it somewhere some X0 years ago :-P .. may be even on compuserve), so it could be even countereffective, I think it is better to think also what it does aerodynamically then to solve only sound :- ))
-
If it aids acceleration out of corners then it sounds like a good thing for constant speed precision maneuvering.
Igor, perhaps this 'saw tooth' is like under cambered props in that it drag properties are more similar anywhere along the plotted curve.
-
Turbulators?
-
Check out www.whalepower.com