ORIGINAL: HighPlains
High Plains explained something with regards to tip speed recently. It's not just the mathematical result of a prop spinning on a stationary engine, but with the prop in forward motion that had an effect on the relative tip speed to the air molecules it encounters.
I don't remember if that effect was additive or not.......
Tip speed of a flying airplane is the helical distance the prop travels divided by time.
If you know the rpm and the airspeed, you calculate the tip speed due to the rpm and diameter first. Then with that and the airspeed in the same units do the following
Square both terms, add together, and then take the square root.
Example time:
250 ft/sec forward speed
21,000 rpm with 8.75'' prop
21,000/60 = 350
(8.75x pi)/ 12 =2.291 ft
350x2.291=801.8 ft/sec tip speed static
801.8 x 801.8=642,820
250x250=62,500
sum = 705,320
Square root of 705,320 = 839.8 ft/s actual tip speed
Could you check these #'s and see if I have it right?
297.87 ft/sec forward speed
29584 RPM with a 5 inch prop
29584/60 = 493
(5xpi)/12 = 1.308ft
493x1.308 = 644.84 ft/sec tip speed static
644.84 x 644.84 = 415,818.62
297.87x297.87 = 88726.53
sum = 504545.15
square root of
532,186.49 = 710.31ft/sec tip speed or 484.3 mph??? (what Mach.# is that?)
At least I'm back at the first figure I got for prop tip speed I still can't believe it was possible.
The only problem with these numbers is that the plane would have had to outrun the prop/pitch speed by 50-60 mph...
Edit to correct transposed numbers!!! the forward speed figure was supposed to be 297.87 ft/sec not 443.08 ft sec (203.1 mph not 302.1mph) sorry about that.