PAP Section G-8: Fuel System Calibration (Dynon)

 In order to calibrate the fuel system in the Dynon software, data points must be taken starting with an empty tank as fuel is added in two-gallon increments until the tank is full.  The software generates a table of gallons vs.voltage output from the rotary resistor hooked to a float which was installed in the tank when it was built (as I recall, construction of the fuel tank was the first thing in the build to earn the characterization Klöster Föken).  This float-type fuel quantity sensor is not to be confused with the mechanical back-up fuel gage (also with a float).  It made sense to do this now since the tank was already empty from the weight-and-balance section.

Step one was to get 20 gallons of ethanol-free mogas in cans. Fortunately, it's available from the FBO here at my home base at KLMO.  So with four five-gallon cans of fuel, I proceeded to fill a two-gallon can and pour it in the tank until all the data points were recorded.  The Dynon looks like this as the table gets populated:

The only problem occurred when I went past 12 gallons.  The system was recording the data points but wouldn't display them.  I tried every way I could think of to scroll down but no go.  I ended up continuing the process, unable to see the voltage values corresponding to the rest of the data points.  When it's all done, you can edit the table and see everything.  The right-most knob then allows scrolling.  The data looks like this:

 

Being an engineer I couldn't help myself so I did a curve fit of the data to be sure there weren't any wonky points.  Looks good.  Amazingly so considering that I filled a two-gallon container ten times, each time eyeballing the fuel level and the two-gallon mark on the container to be sure they aligned.

Next up is the carb sync, coming soon to a browser near you.  In the bigger picture, I've secured a DAR do to the airworthiness inspection but we're dead in the water due to the government shutdown.

PAP Section G7: Weight and balance

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.