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Old Feb 24, 2013, 12:17 AM
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GeorgeG97322's Avatar
United States, OR, Albany
Joined Jun 2007
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Okay... 7.7 grams. might be able to shave off a tenth or two with a balsa propeller, however, I don't build props very well.

George
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Old Feb 24, 2013, 01:09 AM
Torn 'twixt buildin' and flyin
TheNightowl's Avatar
United States, TX, Austin
Joined Oct 2007
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At one time, the Bostonian record flight time (Don't remember it exactly, but it was in excess of 7 minutes) was held by Dave Aronstein and his "Ultimate Lifting Machine" (published as a full plan in Flying Models, in May 1994). Joshua Finn has a build log of his here: http://adhillon.com/smallflyingarts/...32-what-is-it/
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Old Feb 24, 2013, 12:08 PM
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smokey point, wash.
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I flew with Dave in Seattle in the 90's, and have several of his planes in boxes in my garage. I remember the lifting body well, and his ducted fan peanut scale jet.
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Old Feb 24, 2013, 01:50 PM
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USA, IL, Wheaton
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George
Great looking Celtic. The weight is really good too.

Is that an Ikara 150 mm prop? I have one and it weighs about a gram, somewhat less than the props with Sprite 2L bottle blades on my recent Bostonians. The blades are a bit narrower on the Ikara, and might work better with 3/32 rubber. I've used 1/8 rubber to pull the bottle bladed ones. Have you figured out a motor for it yet?

Is the wing covered on the bottom? From your structure, I'm figuring that the diagonals make a flat bottom for the wing once they are covered.

Have you checked the CG yet? With its relatively small tail, I don't think the CG can be as far back as on a Bostonian Patriot.

Good luck with you maiden flight

Joe
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Old Feb 24, 2013, 08:29 PM
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GeorgeG97322's Avatar
United States, OR, Albany
Joined Jun 2007
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Well, Where to begin... It not fly so good. I set up for a righthand circle, and I did not check the CG. So... first flight was a very step stall, I mean like VTO on takeoff (hand launched for testing) So I added more down thrust. Next launch better, but not by much. Added nose weight, several times to get a better pattern. I was fighting a natural lefthand circle. So I did not get an offical flight recorded. I will reset rudder and nose block for lefthand circle and try again next contest (late April).

George
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Old Feb 24, 2013, 09:03 PM
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GeorgeG97322's Avatar
United States, OR, Albany
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I have also got my hands on a copy of the Ultimate Lifting Machine plans and article. I was dumb-founded to see that David used a 49" loop of .090" rubber for the motor. Wow that's a lot of rubber... Oh yeah, with 4500 turns on it...

George
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Old Feb 24, 2013, 10:15 PM
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smokey point, wash.
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I remember him stretching that out to wind it.... I used 4300 turns in my Centurion profile to get a 4:35 flight
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Old Feb 25, 2013, 09:53 AM
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Nightowl
Thanks for posting the source on Aronstein's Nat's winner. I see that Carsten's/Flying Models still has the May 1994 edition available on their back issues list. Was that 98 inches total rubber for the 49 inch loop? Isn't that about 7 grams of rubber?

I've seen folks at the Bong eagles' contests at Racine getting 2 minutes out of 30 inches total of 0.080 inch rubber turning a Delta Dart prop on their Double Whammys (which have flat plate wings). When I try it, I get about 70 sec for 1500 turns in a 14 inch loop (28 inches total) of the same tan rubber. The pop bottle blade prop on my Bostonian gets 60 seconds out of 1080 turns but needs 1/8 inch for takeoff power. I've got to make my plane lighter to take on more than a 12 inch loop.

George
What width rubber are you using? The Ikara prop might be turning too fast in the power burst giving you that excess torque.

Hope you can figure it out. I went back to square one with my planform after fighting the Celtic. I've seen a great video of one flying at Marin County, so at least one Celtic flys well though.

Enjoy

Joe
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Old Feb 25, 2013, 12:03 PM
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GeorgeG97322's Avatar
United States, OR, Albany
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Joe,

I was testing with a 16" loop of .075 tan II. Usually about 900 turns so I don't think too much torque at this point. I really think I was chasing the lefthand circle and the CG. I might just build a new Ultimate Lifting Machine anyway

Would be nice if I had access to someplace I could test fly once in a while.

George
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