Bill Freeman wrote:

Bunch of snips.

" Redesign of the 16-series propeller with greater blade area and for
higher tip-speeds might produce a propeller with much better take-off
characteristics with little sacrifice of efficiency at high speed. "

So, we could probably go to a 16-5XX with wide chord blades to
make up for the lower CLmax of the 16-series - probably gaining
back any losses at TO & climb.   This is what the Reno guys have
been going towards - extremely wide and thin blades, it is also what
Jon Roncz used for the Rutan twin racer - the tips were literally
sharp as a knife - they kept rubber boots on them when static, big
paddle blades.  Probably 3% sections or so.

My guess is that a Clark Y will be fine for a first cut.  If we
really want work at chasing the last 3 percent, it might be worth
rewriting the Cd function in Perry's program to include four
coefficients, and probably a higher order function for the CL,
which is linear (Cd is a CENTERED(!?) parabola, i.e. no "X"
term for offset).  This will let it accomodate the more nonlinear
response of the 16-series airfoils.  Clark Y apparently has a
very linear CL vs alpha and symmetric parabolic Cd vs alpha.

more snips..

BTW the latest hot tip is to put a fixed flap on the first third of the
prop blade where it is going the slowest. A plain fixed flap should
give a C sub L of about two. I notice Jeff has these on the Predator
props. Also if you look closely at the prop PowerSport is pushing
(some sort of pseudo constant speed flex prop) it too has a flap.
Picture in a minute relative to Mike's muffler mount.

Paul Lamar
 
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