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Old May 26, 2010, 10:49 PM
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twin pond master repower

I have a nice flying scratch built RCM Twin Pond Master: 51" wing span, 35 oz. ready to fly weight. Currently it is running with two Great Planes 7.2 v speed 400 brushed motors. I burned up the first two in ten flights!

I would like to improve the power by up grading to brushless but am having trouble deciding just what KV and voltage to go with. My problem involves the restricted area which limits prop diameter. On the other hand Hobby Lobby has long can 400s that are rumored to be a good up grade. They will cost me $40.00 with postage.

At present it flies sedately with 6.5" X 4" APC props. I have thought about extending the motor mounts upward to give clearance for 8" or 9" props that would work well with standard low cost out runners. Would inrunners with a higher KV work better of this kind of plane with its small diameter props?

Do you have any suggestions for brushless items that would work well and still provide decent run times. I like to fly 15 -20 minutes. Would the bigger higher position props be worth the effort or will they create torque issues? How about using three bladed props with the out runners to make up for the reduced swing diameter?

Would two 7.2v 2100mha batteries be better that the single 11.2v 2100mha I am using now. I use 7.2v 2100mha lipos on some of my other planes.
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Last edited by james.wood; May 26, 2010 at 11:25 PM.
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Old May 27, 2010, 12:18 PM
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Chicago, IL
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I wouldn't go through the trouble of rebuilding the motor mounts for bigger props. At 35oz (1000gr) you should easily be able to find a pair of small brushless motors good for 14oz-17oz (400-500gr) of thrust each on 3S. Looks like 1500-1800kv is a good range for turning a pair of 6" props. I'd shoot for 70watts/lb or better. So each motor should be able to handle about 7amps on a 3S lipo.

C-20 ~ 78watts

FC 28-05 ~ 75watts

C2226 ~ 70watts

"Blue Wonder" 1700kv
~ 75watts
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Old May 30, 2010, 08:00 PM
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Houghton Lake MI
Joined Apr 2008
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I am getting ready to do a RCM plans order. (Real Thing, Q-Tee, Arctic Tern, Showboat, and a couple others) I am pretty sure I want to add the Twin Pondmaster to my order.

Will I be happy with the Twin Pond Master for flying off of a large lake with a small bay to take off from? Are the ailerons effective enough to handle some crosswind flights? Does it do nice splash and go landings? Anything I should know about building or flying this beast. I would probably go with a pair of outrunners I bought a while back that have too high a KV rating for most sport flying. They should swing a smaller prop with a bit of zip on 3S lipos...

Thanks,
Dave
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Old Jun 02, 2010, 04:06 PM
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I would build the motor nacels slightly higher to acomodate bigger diameter props and standard KV out runner motors this would increase efficentcy and allow for longer flight times. The flat bottom on the fuse makes it difficult to control the plane, won't come into the wind, when taxiing on the water in cross winds. A vee bottom or a small directional fin would help. The fuse would be improved with a double coating of film on the wear surfaces or perhaps a light fiberglass. The boxy motor nacels look cheap I would rather see some cylindrical ones. My plane required alot of weight to balance the CG so I would move the batteries to the front where the hatch is and put the radio and servos behind. I would build this plane with bolt on wings as the rubber bands prevent the establishment of a water tight seal at the wing saddle. The pontoons would be more secure with bolt on attachment also as I have lost them in flight more than once. Brushed motors are barely capable of flying this plane I strongly recommend more powerful engines. The fight speed requires long take off and landing area. The plane is easy to fly, self righting, and might even run ok as a three channel set up. When it flips the wings suspend the motors out of the water so if the ESC was placed into the bottoms of the nacels/ wing pannel they would never be submersed.
Perhaps shaped foam blocks could be used to add the vee bottom and cylindrical nacels. I will try to get a picture of my plane for you.
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Old Jun 03, 2010, 03:05 PM
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Flat bottom hull should have little to do with how it taxis on the water... in fact, a flat-bottom should turn easier because it has less draught in the water. V-bottoms help a plane plow through waves more smoothly, because it splits the waves rather than ride over them. Same with landing... the V-bottom helps a plane settle-in more easily than a flat-bottom, which is more likely to "skip" if you come in hard and fast.

Sounds like it needs a water rudder if you have difficulty taxiing in a cross-wind. If you want it to weather-vane into the wind easier, add some fin-lets on the H-stab tips.

If you want a cheap solution for the nacelles, check out ParkFlyerPlastics... they have some wing-mount nacelles and round cowls that you might be able to modify. They might even sell you just the nacalles and cowls from their TwinStar kit.
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Old Jun 03, 2010, 06:20 PM
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It has a large water rudder that works greats in clam air. When the wind increases speed the bow slides on its flat high floating bottom preventing the plane from being able to come into the eye of the wind for take off.
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Old Jun 03, 2010, 08:17 PM
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Then it sounds like the tail finlets are the answer... with more fin, it would weather-vane into the wind. Take a look at the Drake II seaplane. It's a very similar plane, flat-bottom, points into the wind easily.
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