Is there any kind of mathematical calculation to estimate the overall weight of the rc aircraft from the battery current rating and c rating?
  Actually if i want to use a lipo battery of 7.4v / 850mah / 5c , then what should be the aircraft size and weight?

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is there any kind of mathematical calculation to estimate the overall weight of the rc aircraft from the battery current rating and c rating?
  actually if i want to use a lipo battery of 7.4v / 850mah / 5c , then what should be the aircraft size and weight?
actually i could not any such kind of mathematical formula for this purpose. and the above battery could not provide sufficient trust for my cesna of 450gm .

You can draw maximum 7.4 volt x (0.85 x 5) A of power from battery
                                = 7.4 x 4.25 watt
                                = 31.45 watt

That mean, with efficiency taken care of every stage, 20 watt max. you can draw.
Therefore, 100gm maximum your plane AUW (not for acrobatics, just floater one)
and 55gm youu AUW(All Up Weight) for acrobatics if I am not wrong.

Details given in previous threads, Please search.

Where are you from Hooghy? near hooglyghat Station, Pipulpati Xing ?
Please contact me. I will be happy.

plz tell me what is AUW

yes i am from bhadreswar ---4 station before from hooghly

All Up Weight = Airframe weight + Electronics + Engine + fuel weight
or simply weight with everything.

my mob. no. is 8902229025. when you will come to your sister's home plz call me . i will meet with you.