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Jan 24, 2012, 06:11 PM
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2 cells 3D snowstang 20" for 6400


this is a 20" ws-100 sq in version for 2 cells motors of the original snowstang 18". the idea is to increase power, and a little bit of wing area, to compensate for the expected gain in weight.

as the original version for 1 cell generated no more than 60 gr of thrust (that is the top i got with 1 cell motors), i decided to give a try to 2 cells.
i had to go to a 2 cells brushless esc. the lightest i found was the turnigy plush 6a that weighs 5 grams with wires/conns.

i performed 2 cells bench tests of 3 outrunner motors. the HXM 14mm motor from hk (that weighs no more than the single cells motors) did only 60 gr on a 2x120 hyperion. with the park 180, that weighs only 2 grams more i got 120, and with the 1811-2000, that weighs 2 grams more than the park 180, i got 140. i choose the park. 120 gr thrust and 60 gr auw means a 2:1 ratio, that seems enough for the purpose. the auw is 60 gr, compared to 50 of the 18": 2 gr go for the increase in plane's size, 3 for the difference between the single cell esc and the 2 cells, 3 for the larger pack, and 2 for the motor. the area went from 90 to 100 sq in. same gws 6/3 prop. following details are about same as on the 18" version: foam is depron from rcfoam. nose is 3mm, ailerons and stab 2mm, rest 1mm. glue is beacon foam-tac that dries hard and fast. motor is mounted to a 1/8" plywood firewall. i used .6 mm cf rod on sides, top and bottom of fuse, and under left side fuse diagonals for stiffening; pushrods are .8mm cf. airfoiled wing is 1" thick at root and 5/8 at tip to make wing stiffer and create some drag to slow it down and has a spar but no ribs. airfoil is formed by making slots along span and carefully bending until getting the shape. i use a diode from esc to brick to drop volts.
field tests (well, gym tests, that is): i have been flying it and it has lots of power. i am looking forward for spring to try it outdoors and try that power without restrictions. i expect unlimited vertical.
>>>so far i have experienced problems controlling the plane so i went to a standard flat wing of 3mm and when tested maneuvering is just fine, so the conclusion is that thick airfoil even if slows down the plane, creates too much drag and blankets the control surfaces and makes impossible to control. back to flat thin airfoils. now for the final conclusions, go here to comments.
Last edited by phil alvirez; Apr 04, 2012 at 02:47 AM.
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Apr 04, 2012, 03:01 AM
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conclusions


with the 20" version i was able to reach the 2:1 power-to-weight ratio, so i can get unlimited vertical with this kind of plane. great! so what? do we really need that? for 3d purposes, it is not necessary, and to get that i have to have a plane not large enough to handle that power. for that kind of power, the airplane is too small. it has 100 sq in and weighs 60 grams. the mod to use 2 cells provides twice the power, but it is too much for that plane. with same components i have the 24" epp version that is just 18 grams heavier but with 50 sq in more area. with this wing loading the plane can do all the maneuvers needed for 3d and is controllable-and slower. it was an interesting experiment that allowed me to understand the potential of the 2 cells on that size plane.
>>>change of mind: april 14: i must add that after more flying, i think this concept has a place. the plane is mighty, and once i learned how to deal with all that power, it gives me that feeling that i can ask for any power i need at any moment, and that gives a different feeling. doing snap rolls, loops, whatever, as quick as i want, is an exhilarating experience. as you can see from the video, even if my son just couldn't catch up with the fast changes in direction, the launching is uneventful and the plane behaves fine because i used the right amount of thrust, and no more. it is like riding a motorcycle with all that power at my disposal-just if i want or need it. so i will keep flying it now and then, whenever i am in the mood for that.
Last edited by phil alvirez; Apr 14, 2012 at 10:38 AM.


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