C

Camillo

Well Known Member
I would like to add a second battery in my 9A in the tail cone, as per an old RV7 drawing (OP-16).

I know that this will move aft the CG (and this is the main reason for the installation) and I can obtain the new CG simply measuring the arm from the CG to the battery location (and multiplying it per the weight of the battery).

But since this is a definitive installation, I would like to simulate a new airplane weighting and obtain the weight data for the single wheel (without having to place the airplane again on the certificated scales).

Is there a formula to recalculate the weight per wheel starting from a known weight per wheel and the data of the new installation (arm and weight of the new battery)?

Thanks.
Camillo
 
Camillo,

You can do the same procedure as calculating the weight and balance, but do it laterally. Measure from some arbitrary point (say, the left wingtip) to the left and right wheel and to the battery position. Then you can add up the different weights x arms. With a little algebra, you can then calculate the redistributed weight on each wheel. Or you can put it into a spreadsheet and just change the numbers to get it to work out (the brute force method). Technically, you should also add in the weight and arm of the nose/tailwheel to the calculation as well, but I doubt that would make more than a few ounces difference.

I'm not sure if this is what your question is (lateral W & B). One can do a similar exercise from front to back if your concern is the fore-aft W & B.

cheers,
greg
 
Nose Wheel Weight

Camillo,

If you are trying to calculate the change to the nose weight by adding aft weight you can use the following formula:

Nose Force = Loaded Weight * (CG_Arm - Mains_Arm)/(Nose_Arm - Mains_Arm)

You will have to calculate a new CG_Arm and revise the Loaded Weight to reflect the addition of the second battery.

Hope this helps.
 
Thanks a lot.
Jim, yes, I was searching for that formula.
I made classical studies and almost no math. So, I wouldn't be able to do that!
Ciao.
Camillo
 
You must log in or register to reply here.