A friend of mine and I were discussing prop tip speed.  He says he has heard from several sources that the optimum prop tip speed for models is around 600 feet per second.  He sent me a file from an RC website, which includes the following:
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"Tip Speed is measured in feet per second and a formula is provided below to find this measurement. For model airplane purposes, the best tip speed for efficiency and noise requirements is 600 feet per second. This is due to
compressibility losses and the fact that subsonic airfoils do not work well in transonic/sonic speeds with required sound levels.
 Feet Per Second (ft/s) = RPM x diameter in inches x .00436
 For example, to find the tip speed of a 10x6 on a .40 size engine running at 13,500
 RPM, the equation would be 13,500 x 10 x .00436 = 588.6 ft/s.
 To find the correct diameter at 600 ft/s, use this formula:
 Diameter in inches = 138,000 / RPM
 Using a .40 engine running at 13,500 RPM, the equation would read as follows:
 138,000/13,500 = 10.22
 Rounding down, the correct diameter is 10"
For both of the above formulas, use RPM for the optimum power band of your engine. Consult your owner's manual if you do not know this number."
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13.5K on a 10" prop is higher than we typically run in stunt (although we are in this range with an OS.25FX that gets happier the smaller the prop and the faster we run it, and we are testing props as small as 9x3. 

I recall when I was interested in speed that tip speed becomes a factor when it approaches sonic velocity, but that doesn't seem to be a problem in stunt.

I know many prop reworkers pay special attention to the tips. 

Is there any information related to prop tip speed that is useful to stunt gruntz?

Thanks!
Kim Mortimore

Paul,
Sounds like the clues that you have entered the realm of the transonic are not too hard to recognize!   

Kim

Hi Kim

You will almost never  see any props running over super sonic speeds, The compressability factor cause huge drag and requires  tremedous horse power to push thru the SOS.The speed of sound is approximately 760mph , and not many motors out there will push a prop thru that speed and drag

As a general rule a propeller should NEVER be used over 550mph , even then unless your paying attention to tip shape, your going to have howling noise and lotsa drag , not to memtion the wasted power

An optimum maximum tip speed for achieving a low noise is 400mph. Over that and there is a big increase in noise. A Good example ,R/C Aerobatics ,where low noise is an advantage. Many F3A models avoid going above 375mph tip speed.
At any rate you will not make many friends at the  field with over 450MPH tip speeds much less  700 plus  tip speeds

Regards
Randy

Dean has several times recommended a bit lower speed to the RC pattern folks for lower noise.  He had a neat graph a couple years ago with measured noise levels vs. rpm, which was used to come up with the 130 factor.  130 / rpm(in thousands)= prop diameter in., or 130/prop dia(inches)=rpm
A little F2D engine usually runs in the 30K range, so the prop diameter should be around 4.7 in. to keep it quiet(fat chance of that happening).  I've found many times that pushing that 130 factor makes the engine/prop a lot noisier.  Fortunately most stunts planes aren't in that zone.