In order to perform the initial weight and balance calculations, the airplane must be weighed containing oil and coolant but no fuel. Since several procedures which came before this required fuel in the tank, the tank must now be drained (an odious task). The build manual suggests removing the gascolator bowl and running the electric fuel pump until all gas is evacuated. This would be a major PITA, requiring removal of the lower cowl and four safety-wired bolts. I opted instead to once again remove the fitting on the gascolator outlet and attaching the device I previously made to facilitate measurement of the fuel flow rate from the electric pump (see previous post). Worked great with just the upper cowl off.
The build manual says to place 2" blocks under the mains to facilitate leveling of the fuselage, then to adjust tire pressures to fine tune the leveling process. For the purpose of weighing the three wheels, the blocks make a negligible difference. On the above pic, LF is the nose wheel and LR and RR are the mains. I was pleased with the total weight of 735 lbf considering that I have the optional landing light and autopilot servos. The expected range of values seems to be 735 lbf - 800 lbf. However, mine is without wheel pants, paint and an interior, other than seat cushions. I'll certainly add wheel pants and wrap (no paint) later.
For the measurement of the moment arms, however, it's worth leveling. I used 2x4s (1.5" thick) which was actually a bit too much, requiring a bit of tire pressure adjustment. I dropped a plumb bob from the wing leading edges just outside of the mains, snapped a carpenter's chalk line, then made the required measurements from that. Van's datum is arbitrarily 70" forward of the wing leading edge and all moment calculations are relative to this datum. The empty CG is then easily calculated by recalling something we learned in the first week of Engineering Statics: For a non-accelerating object, the sum of the moments about any point must equal zero. With my wheel weights (shown on the pic) and arm measurements, my CG is 81.18 inches aft of the datum for the empty airplane.
With the moment arms supplied by Van's for pilot, passenger, baggage and fuel, my no-fuel CG with me in the airplane looks like this:
The CG location is 80.76 inches, well within the allowable range of 80.49 - 84.39 (shown wrong in the notes on my spreadsheet). As I imagine most people do, I put this in an Excel spreadsheet to make it easy to play around with various fuel and bagage loads. With 50 lbf of baggage, a 180 lbf passenger and full fuel, I'm behind the aft limit. I put this spreadsheet on my iPhone and iPad for easy use.
More Colorado Wildlife: In a first for me, I discovered a half-eaten rattlesnake in my back yard. The front third and rear third were gone, leaving what I would think would be the best part of the snake for eating, the fat middle third. I was unaware that any animals dined on rattlesnake, bet it turns out several do. Number one on the list is coyotes, which I frequently see (and hear at night). Number two is mountain lions which I've had visit my yard several times (see earlier post). Third was bobcats, which I've gotten on the trail cam in my yard twice. Bon Appétit.
I also had a momma bear and cub on my cam behind my house.
