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CG question

Old 05-20-2014, 04:27 PM
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I have a GP Giant Big Stick with a OS 155 4 stroke! Checking the CG with a CG machine im way tail heavy!!! I hung 8 ounces of wheight to the tip of my spinner and that wont even do it!!! Moving my battery forward wont put a dent in it, what is the deal ?? Any clue from anyone?? I cant put a pound of wheight in the fuselage where gas tank is can I !! Always something with this plane!! Any thought people????
Old 05-21-2014, 06:58 AM
michael wood
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What I did with mine is to move the fuel tank back to the cg ( if you look you will see a secondary place to mount the fuel tank behind the first bulk head not shown in the instruction manual) then I went to dollar store and got a metal playing card box and used that to melt lead in it it gave a nice flat bottom after I pulled the tin way from the lead and the I used it to adjust it to get the C.G. then I glued it in the tank compartment. The engine I am using is an MT35 and the ignition and battery in the fuel compartment. Don't worry about the weight the big wing wont know it there. The giant stik takes a lot of weight in the nose at least the two I've built Michael
Old 05-21-2014, 10:36 AM
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When all else reasonable fails, move the wing to the rear!
(I ended up doing that on an Alpha 40 electric powered trainer!)
That's far better than adding gobs of weight.
Remember that the approximate correct CG is located at about 25%-30% of the distance
from the leading edge to the trailing edge on a straight wing A/C.
You also have to consider the empty vs. full fuel tank effects.
Empty obviously applies to landing, and full to takeoff.
Trying to land or takeoff with a tail heavy condition was one of the big causes
of full size A/C fatal accidents for quite some time.
Old 05-23-2014, 09:06 AM
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I have the Giant Big Stick and originally had an OS 120 4 stroke on it. It took 2 1/2 lbs of lead on the firewall to balance it. It flew well that way but was under powered. I replaced the 120 with a Zenoah G-26 and it required no additional weight at all. I love the way it flies now. I've seen them with bigger engines.
Old 05-23-2014, 12:30 PM
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Any way you can slide the engine forward? I would start there with this kind of weight needed. Moving the wing works also but requires a little more work.


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