Posted Monday, November 28, 2011 @ 07:17 PM  

Midway through my fuselage recover/paint project I found a good inexpensive online source in the US for weight scales I could use for the RF4D, that is rated for up to 750 lbs.

Weight and Balance are very easy to do, as is the math to determine the new Center of Gravity

The new weight of my RF4D is 620.1 lbs and the CG is at 13.25" from the LE.
Wish I'd had the scales before hand so I could have verified the initial weight.

The acceptable CG range was ~11" to ~19" from the LE, so I am within the limits with an empty tank and no pilot.

I think I could move my battery further aft so I plan to create a battery box out of aluminum so that the battery is sunken into the storage area behind the pilot and flush with the top surface of that area.

I will use an Odessy Battery that weights about 7 lbs and make it's supports withstand 30 G's so I never find it flying about the cockpit.

I'll be doing the calculations with fuel and pilot load as well to make sure the balance is right in all scenarios. (ie Full fuel with pilot, no luggage & no fuel with pilot and luggage etc)

Posted Sunday, July 14, 2013 @ 02:52 AM  

Its pretty easy.

I just made the datum the tip of the spinner and measured to the main wheel axle, tail wheel axle and front of pilots belly .

I weighed with 50% fuel and level flight attitude so tail was up on some boxes about 3 feet.

Calcs are like below:

Distance to main axle x weight at mainaxle = a
Distance to tail axle x weight at tail axle = b
Distance to pilot x weight of pilot = c

Balance point distance CG= (a+b+c)/ (weight main + tail + pilot )

Then compare that to allowed CG range from manual.

I'll take a look to see if I copied it on my other computer tommorow.

If CG is near the rear limit then do calc with no fuel to confirm you are still ok.

[Edit by jb92563 on Sunday, July 14, 2013 @ 02:55 AM]