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Old Oct 22, 2008, 08:27 PM
HMX Dave is offline
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Help!

CMP Yak 54 question


Hey guys....converting this plane to electric and nearly finished. It has a 52" span and the wing cord is 12.25" where it attaches to the fuse. The manual says the CG is 80 to 90mm (3.125 - 3.5") measured out from the fuse 150mm (6"). It seems very nose heavy. This point falls about an inch forward of the thickest part of the wing. Any experience here? My gut tells me that 4" or so would be more realistic....

I would like to nail this down for sure as it is going to determine where I build the battery box and hatch on this beast.
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Old Oct 22, 2008, 11:03 PM
SCALEFAN is offline
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Done it all
Dave,

Whenever I have doubts, I use this on-line calculator.

Remember CG is not absolute, it is a range that will allow the plane to fly safely. If you change the MAC % you will see the range in your results. I use the average % that is suggested on the screen for MAC.

http://adamone.rchomepage.com/cg_calc.htm

Al
Old Oct 22, 2008, 11:10 PM
HMX Dave is offline
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Thanks! I'll get out the measuring tape tomorrow and see where she goes.
Old Oct 23, 2008, 11:27 PM
HMX Dave is offline
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Well....it turns out the instructions are correct.

The most I can jam into the front is 2x 22004s (in parallel for 4400 4s) and I still had to add a few OZ's to get the CG .....but I got 'er. A bigger motor would probably be better for this plane...but I had everything laying around, so I'll try it this way for now. Should be 850w and 110 oz of thrust.....
Old Oct 24, 2008, 01:09 AM
Dbox is online now
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One Idiot is plenty...
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In saw this one in the air and up close.Beautifull plane with fiberglass fuse.
But I doubt I want to convert this particular one to electric------IT IS HEAVY.
Needs lotsa speed and WAY more then 850W .
Yuri.
Old Oct 24, 2008, 08:35 AM
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It's just over 6 lbs with a 52" wing .....I'm sure it'll fly.
Last edited by HMX Dave; Oct 24, 2008 at 10:50 AM.
Old Oct 24, 2008, 01:20 PM
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Gilbert, AZ
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Oh I'm sure it will fly. 140 Watt's per pound may not let you hover at 1/2 throttle but I'll bet the power will be more than sufficient.

The wing-loading works out to 27 oz/sq foot so it shouldn't be too much of a handful.

I just can't believe a CMP plane came in anywhere near the published weight, especially an e-conversion!!!

850 Watts on 4S seems like alot of amps (57 or so?). Hope you've got a good ESC & cooling!!! Also, as amps go up, efficiency goes down so your watts out may be 10% less than your watts in, depending on the motor.

Good luck! Let us know how it goes!!!

Chad
Old Oct 24, 2008, 03:50 PM
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Thanks for the calculations Chad! I hope its just one of those "nice to fly around in circles" planes for lazy afternoons. The plan from the start was to just have a nice looking scale-type plane. The plane fell in my lap as a buddy ordered one on-line...his computer froze and he accidentally ordered two. So I said I would build a e-version from spare parts. I'm pretty sure this baby was never intended to be a 3D Yak54....the manual's suggested throws are pretty short. I have an E-flite 60a switching ESC runiing the Scorpion 3026-12 motor. I've pushed these two items in my Ultra Stick 25e to a lot more than this....so I hope it'll be OK.
Old Oct 26, 2008, 01:30 PM
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Maiden this AM....she's no screamin' powerhouse....but she flys OK. Big loooong rollout on the grass field, up and out.....4 clicks of left,2 clicks of up...and she flew fine. Something amis in my power set-up though....when I went wide open, it would surge. 3/4 throttle was no problems, but as soon as you pin it, it would surge. Going to check my timing settings on the ESC.

Edit: and cooling was no problem: it was -4C (22 F) hehehe.
Last edited by HMX Dave; Jun 15, 2009 at 10:27 AM.


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