

01312010, 03:37 PM  #11 
RCC Master Contributor
I am: Daren M.
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Re: Weight distribution
Hi Len, using individual scales is how we weigh the big ones as well.
Or, you could jump on your bathroom scale with your plane, then without, and do the math there as well. But, if you do weigh the plane this way, you have to include pictures. Take care, Daren
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01312010, 09:00 PM  #13 
RCC Senior Contributor

Re: Weight distribution
If you are using this to do your CG you are going to wreck your plane unless you can do the math. There is no blanket answer because it depends on:
Landing gear location Tail gear location Wing Tube location in Fuse Wing tube location in the Wing By the nature of your question, you should be sticking to CG the old fashioned way... please. If you insist and are a touch math savy, here is a good description of the proper way to do this... it's all about moments. http://www.acrodesigns.com/ratsrepus...07212001.php
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02012010, 06:27 AM  #14  
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Re: Weight distribution
Quote:
A way to observe the results of this weighing method is to use this method with a plane that I know is properly balanced and see what the result is. I have to wait though till CTA has those scales on sale again as I only have one at the moment. 

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02012010, 07:26 AM  #15 
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I am: robert j
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Re: Weight distribution
the old stand by of balance on the spar which by measurement is usually in the 1/3 of the length of the total, tip to tail .scaling a truck will tell where the center of the weight in the load is.if the tail wheel weight is more than roughly a third of the total of the two wheel weights on your model maybe take a garbage bag to the feild. not scientific but it is a way of visualizing what is going on. flying with weight centerd on the spar is usually a neutral responce to control input. both real and model. weight and balance calculations are simpler if ya can visualize what the numbers say

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02012010, 08:00 AM  #16 
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I am: Chris K.
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Re: Weight distribution
You can do the measuring with one scale. What you need to do is get the plane in the proper/normal flying atitude and then put the scale under one wheel at a time. When weighing one wheel you need to make sure that the other wheels are supported such that the plane maintains it's normal flying attitiude. This is discussed more in the "Balance that giant scale aircraft" thread http://www.rccanada.ca/rccforum/showthread.php?t=99938.
Chris 
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02012010, 09:27 PM  #18  
RCC Noob

Re: Weight distribution
Quote:
Prop up the tailwheel of your airplane so the airplane is at a straight and level attitude with the spinner against the wall. Place a mark where the CG is (or where you think it should be). Measure the distance of the mains to the wall. Measure the distance to the tailwheel to the wall. Skip the physics lesson and the mathematical derivation and you get these two equations... m1 = mt / ( (d1 / d2) + 1) m2 = mt x d1 / (d1 + d2) Where... m1 = Mass on BOTH left and right main gears. m2 = Mass on tailwheel. mt = Total mass of aircraft = m1 + m2 d1 = Distance from CG to main gear = wall_to_CG  wall_to_main_LG d2 = Distance from CG to tailwheel = wall_to_tailwheel  wall_to_CG In your case Len you know mt, d1, and d2 (or at least have a good guess). You can use the two equations above to estimate what m1 and m2 will be. Using the example from the "Balance that Giant Scale Aircraft" thread... mt = 9 + 9 + 5 = 23 d1 = 32.43  22 = 10.43 d2 = 70  32.43 = 37.57 m1 = mt / ( (d1 / d2) + 1) = 23 / ( (10.43/37.57) + 1) = 23 / (0.2776 + 1) = 23 / 1.2776 = 18 (on BOTH left and right main gears, or 9 on each main gear) m2 = mt x d1 / (d1 + d2) = 23 x 10.43 / (10.43 + 37.57) = 23 x 10.43 / 48 = 5 It doesn't have to make sense, but it works. 

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