Weight & Balance

[Tom McCutcheon]

Probably should have done this in the RV-4 thread but wanted as much input as possible.

Question 1. When doing a weight and balance on an RV-4 what do you level? The top rail of the cocpit? Or, some other measurement?

Question 2. If weighing the plane with full fuel, does anyone have a spreadsheet with computations to figure the empty weight on each main and tailwheel? I know that it can be done by calculation because we have the arm measurement of each of these locations. But, if someone else has developed the calculations it would save me some time. Thanks everyone in advance for your help.

Tom McCutcheon
tommccutcheon@msn.com

[GrayHawk]

I have a 6A but will take a stab.

Weigh in the normal level flight attitude. For the 6, that is with the top longerons, cockpit area, level in all directions, maybe double check level at other points. I would guess it is the same with the 4. Make sure that canopy is in closed flight position.

Probably best to weigh with empty fuel (unusable fuel only), as the density of the fuel varies with its temperature.

[dan]

Originally Posted by Tom McCutcheon

Question 1. When doing a weight and balance on an RV-4 what do you level? The top rail of the cocpit? Or, some other measurement?

From Section 14 of the RV-4 construction manual (thanks to Gary Sobek for the PDF):

"11. Leveling Datum - A point or surface on the airframe where a level can be placed to determine when the aircraft is in level position for weighing. For the RV-4 the Level Dataum line is the fuselage top longeron at the cockpit."

Originally Posted by Tom McCutcheon

Question 2. If weighing the plane with full fuel, does anyone have a spreadsheet with computations to figure the empty weight on each main and tailwheel? I know that it can be done by calculation because we have the arm measurement of each of these locations. But, if someone else has developed the calculations it would save me some time. Thanks everyone in advance for your help.

I definitely advocate weighing the plane with the tanks drained & empty if you can. But if you can't do that for some reason (why not?), then as long as you know exactly how much fuel you dispensed into the tanks, I can help you calculate the empty weight & CG. Data points needed:

- Distance datum to the center of the left main tire where it contacts the scale
- Distance datum to the center of the right main tire where it contacts the scale
- Distance datum to the center of the tailwheel where it contacts the scale
- Scale readings for each wheel
- Exact quantity of fuel in the tanks

If you want to take a stab at it yourself, Van's published the arm of the fuel to be 70" aft of the datum. The datum on the RV-4 is 60" forward of the leading edge of the wing.

Make sure that the scales are level, as well as the airframe, when taking your scale readings.

Ok...I think this post entitles me to a shameless plug: http://www.weighmyplane.com