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-   -   Balancing heavy aircraft (https://www.rcuniverse.com/forum/giant-scale-aircraft-general-467/11684710-balancing-heavy-aircraft.html)

sweinhart 11-12-2020 07:44 AM

Balancing heavy aircraft
 
My large scale aircraft is nearly complete. I've never had problems balancing a model before, but this one presents a little challenge, its heavy. I'm estimating in the neighborhood of 30-35lbs flying weight. The balancing point on the wing does not have any support for say, attaching dowels for string to attach, and balsa sheeting isn't strong enough to support that much weight with out using a strong point. How do people generally balance a heavy model?

Tony Hallo 11-16-2020 06:10 AM

If your plane has a wing tube, 1/8" plywood drilled for the wing tube inserted between the wing and fuselage works well. If the cg is off from the wing tube the plywood \ can be drilled for the alignment dowel as well. Then a small 1/8" at the location of the CG will get it done. On my current 33% Champ build I am using a bathroom scale under the mains and a food scale under the tailwheel then calculating the CG from weights and measurements, looks like it will come it at about 40 pounds.

sweinhart 11-16-2020 07:45 AM

Thnx for input. No wing tube in this plane. Hopefully the wing joiner holds lol. I'm thinking about making a couple dummy ply wing ribs that will hold a dowel at the CG location and bolting them to the wing ends. The actual ribs just have a big lightening hole there

tedsander 11-16-2020 08:27 AM

Google how to do weight/balance/cg for real aircraft. The FAA has a comprehensive (and very understandable to us non-engineers) booklet available on line detailing how-to. Essentially block the plane up so it is level, weigh all the wheels, then using the distances do the math to find the current CG. Also details how to figure out how much to add where to get the cg where you want it. Very accurate.

sweinhart 11-16-2020 12:35 PM

I looked and it seemed quite complicated with things called arms and datum I've never heard of before in reference to aircraft. One pictured showed a calculus formula after weighing the three wheels. Plans already indicate location of CG. I was interested in finding out how people usually do this. The scale idea would work if I understood the concept, though I only have one scale. The other option would be easier, but I'm a little concerned about 1/8 plywood holding full weight of the aircraft.

tedsander 11-16-2020 02:03 PM

1 Attachment(s)
Here's a well written article about how to do it, step-by-step for a large scale RC aircraft....and the math is very easy.....

Attachment 2268678

sweinhart 11-16-2020 02:32 PM

thnx. Assuming the math/science confirms those calculations, it'll probably be the best method to apply given the size/weight of my model.

sweinhart 11-17-2020 07:44 AM

One other question regarding this. My plane is a c-130 which has 2 mains on each side. When taking measurements from front to wheels, would you assume the center point between the wheels as the measuring point, and would you measure perpendicular length or diagonal length (that is from a front center point) from front to mains as these will be different

tedsander 11-17-2020 10:24 AM

It has two wheels (fore and aft) on either side, not really completely separate sets of main gear. I would weight each set at the same time (fore and aft wheels on the scale at once). Maybe using a board to rest them on, just subtracting the weight of the board from the weight measured. Measure from the "datum" (the wall noted in the article) straight back (perpendicular) to the midpoint between the two wheels.

If using the board to weigh both, don't forget to put one on the other side to jack it up to the same level as the set on the scale. It's important to take the weights on all points with the plane level both front to back and side to side.

ForcesR 11-17-2020 08:51 PM

This is what I use for balancing heavy model aircraft, works like a charm. Sold by Legend Hobby https://www.legendhobby.com/product/vic-rc-cger-stand/

https://cimg1.ibsrv.net/gimg/www.rcu...efc494a2d7.jpg
https://cimg6.ibsrv.net/gimg/www.rcu...1940711ac1.jpg

tedsander 11-18-2020 08:29 AM

Or...you could buy this: https://www.chiefaircraft.com/xcy-cgcombo.html

DGrant 11-20-2020 10:12 AM

Study up on the the "Vanessa rig"... Simple, cheap, and very effective..


Britflier 11-20-2020 02:51 PM

+1 for DGrant. I have a Vanessa rig permanently set up in my garage.


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