Hi Tracy Hey that's excellent well that's made up my mind as to what size I wish to stick on, will keep al posted when I can get a whirlwind on the front and see what difference that makes.
Cheers Christian
Sent from my iPad Hi Christian, No problem with the 74" prop even on my early model RV4 with the short main gear. My home field is grass and 95% of my flying is on grass strips.
Tracy
Sent from my iPad Hi Tracy That's excellent results, I've heard that running the 74 " prop on a tail dragger rv isn't recommended, how have you found it on yours for ground clearance, would like to go the 74 over the 72 as I operate from a grass strip all year round.
Cheers Christian
Sent from my iPad Charlie is right. Consider that an airplane flying with the wing at 0 deg. AOA does not fall out of the sky :-)
My average speed in the 2004 Sun 100 race was 217.58 mph which includes standing start takeoff and climbout. Prop was a 74 x 88, RPM was 7250 with a 2.85 : 1 drive. If you calculate that out it comes to 212 mph with zero 'slippage'. Draw your own conclusions!
Tracy
Sent from my iPad
Ice sails, desert sails, and now, even
unlimited class sailboats can sail faster than the wind. 'Negative
slippage'. :-)
A more significant point might be that pitch numbers are virtually
meaningless, unless you're comparing two props from the same prop
maker with the same blade plan form. Even then, it just tells you
which has a finer pitch than the other.
Variables can be: whether the pitch is measured on the back side
of the blade or through the chord line, where along the diameter
the pitch angle is measured (due to blade twist), and no doubt
others I'm not smart enough to think of at the moment.
Bottom line is that unless there's an identical airframe flying an
identical prop, the pitch number isn't a reliable indicator of
speed.
FWIW,
Charlie
On 7/23/2014 7:45 PM, James Osborn wrote:
I don't know jack about slippage, but I think it is
the percentage difference between actual distance traveled and
theoretical distance traveled if your propeller corkscrewed
through the air with no thrust. I found a prop slip calculator
online and for 86 inch pitch, 2.85 gear ratio, 7000 rpm, 180
mph, I get 10% slip. Granted the calculator was for boat
propellers, but I don't think it matters as long as the units
are correct. There has to be some slip because there would be
no thrust otherwise. So what is considered a reasonable or good
amount of slip? Using Bill's numbers 86 inch pitch, 2.85 gear
ratio, 7000 rpm, 200 mph, I get 0% slip. That can't be right!
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