Weight and Balance - CG

[myrv]

Ok, I am toying with the idea of building a 7A.

I want to be able to do CG and Weight and Balance calculations for different Engine, Prop, Equipment positions. What is the best way to do this?

[Kevin Horton]

1. Download a spreadsheet that calculates weight and balance. A bunch of RV builders have created them, so Google should find them.

2. Measure an RV, or have someone else do it, to get the distance from the wing leading edge to the items of interest (centre of mass of prop, engine, battery, etc).

3. Find the empty weight and balance for an RV that is configured similarly to one of your configurations of interest.

4. Modify the spreadsheet to add several lines where you can add or subtract weights at the arms you found in step 2. You can also add the ability to modify the arm of the battery, to simulate moving it to fore and aft positions.

5. Spend hours playing around, looking at the effect of adding and subtracting weights.

[dan]

Or just go to http://www.rvproject.com/wab and play...

[Kevin Horton]

I knew that page was there, but I didn't realize that you could click on an N number and then play with loading scenarios. Neat. Is there a way to start with one of the aircraft, and then vary the engine and prop weight, and vary the arm of some heavy item (e.g. battery)?

Thanks for all the tools you have put on your web page Dan.

[dan]

Nah, unfortunately there's no way to do that with the WAB site.

[Pirkka]

Hmm... after looking Dan's page, noticed that the gross weight of the planes vary. Why?


I undestand that the gross can be easily set to be lower than Van's has specified, but in case like Dan has gross of 1950 lbs so is there structural changes and/or strenght calculations done that this piece of RV can handle 150 lbs more than the others?

[Mel]

Gross weight for an amateur-built is determined by the designer. If you want to change it, you may, but you will probably have to convince your DAR that your new limit is safe. As a rule of thumb, I generally look at the aerobatic gross weight set by the designer and extrapolate the numbers from 6 Gs (aerobatic category limit) to 4.4 Gs (utility category limit). This is the largest gross weight limit I generally allow.
Mel...DAR