"So, you found a Sympo article full of someone's theoretical suggestions,
but it didn't prove correct when compared with your flying notes."
"John A. Gard, designer of Monarch, Lazy Bones and Supreme...builder since
the thirties...USAF WWII...FAI enthusiast since '54...1st '62 Nats Wake...5th
'69 Wakefield WC...written articles on rubber model performance and conducted
research and controlled flight testing to correlate measured with predicted
data...BSAeroE, StL U '48...thirty three years structural analysis aircraft,
helicopters, missiles and spacecraft..." it says in the Sympo. He used
flight data provided by George Batiuk, Jack Brown, Joe Foster, Chris Matsuno,
Robert Piserchio, Jim Quinn and Robert White to calculate prop efficiencies. The
study focused on Wakefield propellers, which require a high efficiency
during the initial power burst to maximize altitude. We have a slightly different
problem. I independently developed the same method, but put a warning flag
next to one of the assumptions. When I got my flight test data, I went
beyond just the propeller efficiency calculation, used the data to check that
assumption and found it was not good. The aerodynamic characteristics of the
wing were not the same in glide and under power. In particular, the lift
coefficient was much higher than I would ever expect it to be. This can
significantly alter the sinking speed, violating one of the (unstated) assumptions of
the method.
"BTW, any official times I report will be timed by someone else. This is
not part of the Postal rules, and obviously I can't insist on you doing the
same, but it would be nice."
I intend to ask someone else to time my flights.
"BTW, would be interesting to see a picture of your foot stooge/cuphook
model holder hooked around the prop spar of your LPP while you stretch out the
rubber for winding, if I understand your system correctly."
I was intending on doing that, too. I uploaded pictures of the stooge and
its use in winding the Dandiflyer to the Tools file of the Photos section.
Using a cup hook is a good idea. They would be a lot easier to make that way.
"How many strands do you intend to braid for your LPP motor?"
I intend to use a two strand motor. The exact details must await initial
flight performance tests of the airplane and propeller. I was going to test
braided motors on the Dandiflyer, but I might as well do it here where I
suspect it will have a stronger motivation. My current Dandiflyer motor is only a
bit more than twice the hook distance, and indications are that the next
iteration will be about an inch shorter. The LPP motor looks like it may be a
lot longer in proportion. The decision whether to use braiding or not will
come after the flight tests tell me the best section and length of motor to use.
I expect I will be making a full written report after the contest.
Gary Hinze
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Received on Sun Mar 25 2007 - 13:22:33 CEST