Fuel flow test

Posted on by Neal

Today I tested the fuel system for the first time, running the electrical fuel pump and testing fuel flow. Everything worked well, and I was happy to see no obvious leaks.

I started by disconnecting the fuel line leading into the fuel servo, and redirected it into a large measuring jug. Then I poured approximately three gallons of gas into the left fuel tank, and turned the fuel selector to the left tank. I wanted to make sure I had fuel in the fuel pump before starting it the first time, so I used the shop vac and some clear tubing to prime the system – drawing fuel through the fuel lines, all the way to the fuel servo.

I powered up the panel and switched on the pump, and was happy to see fuel flowing into the jug. I ran the pump for a minute and measured 92 fluid ounces pumped, which translates to 43.125 gallons per hour. I repeated the test on the right tank, measuring 94 ounces pumped, about 44 gallons per hour. During the second test the fuel flow gauge was measuring 43.7 gallons per hour, which is very close to the amount I measured.

I repeated the test in a level flight attitude, and then tested for unusable fuel. With the plane in a level attitude, I pumped all the fuel out of the tank, and then drained the leftover fuel from the fuel tank drain port. I measured 6 ounces of unusable fuel per tank, for a total of 12 ounces.

Note the fuel flow of 43.8 G/H. Fuel PSI is low at just 1.5, but I expect that is because the fuel line is simply draining into a jug
Disconnected fuel line pouring fuel into a jug
Left tank test results after a minute of pumping fuel
Right tank fuel flow test
Total unusable fuel left, just 12 ounces

Blast tubes

Posted on by Neal

Today I added a couple more blast tubes to cool the battery, and the voltage regulator on the back of the alternator. I also reconfigured the fuel lines in the engine compartment and moved the fuel flow sensor to the engine mount.

The Earth-X battery gets a lot hotter than the standard battery, and benefits from a blast tube to direct cool air at the battery while in flight. I used a length of 1 inch SCAT tube, some hose clamps, and an aluminum flange to make the blast tube. I used a step drill to upsize the hole to the right size. I also added a lock washer on the back side of the flange, along with RTV to make it secure to the baffling.

I had bought a 3D printed fitting for the back of the alternator that directs air at the voltage regulator, but never installed it. Today I mounted it and hooked it up with a blast tube from the air inlet ramp on the right side of the engine compartment. Lots of RTV, another lock washer, hose clamps, and it was done.

Then I moved onto the fuel lines. I had previously loosened some of the fuel lines to test that my new routing would work. By switching the fuel lines either side of the fuel flow sensor, the sensor moves aft several inches, placing it right above one of the engine mount struts. Today I removed some of the old fittings, added new ones to streamline to fuel line routing, and mounted the red cube to the engine mount. It’ll be much more stable, and cooler, in this location, which should hopefully make for a longer useful life.

Battery blast tube, forward side of baffling
Back side of the baffling showing the new blast tube
Blast tube directed at the battery. The safety wire is holding the tube steady while a blob of RTV dries
Voltage regulator blast tube entry on the air ramp
Under side of the blast tube flange on the air ramp
The 3-D printed fitting for the back of the alternator. Note, this is high-temp material with Carbon fiber blended in
The new blast tube
The new location for the Red Cube (fuel flow sensor)
The fuel lines aft of the fuel flow sensor. I removed the 45 degree fitting from the red cube inlet, as this is not ideal. The straight fitting I replaced it with will allow for a smoother flow of fuel, and is actually the recommended configuration by the manufacturer. A single adel clamp is holding the sensor.

Red Cube (Fuel Flow Meter) Relocation

Posted on by Neal

Based on some advice from a few other builders, I relocated the “red cube” (the fuel flow meter) from the Vans recommended position to the engine mount. The Vans location is above the exhaust, and other builders have complained of excessive heat and vibration causing the units to fail. The fix is easy – switch the fuel lines – and the cube is perfectly positioned above the engine mount. By switching the fuel lines, I mean the line from the fuel pump to the red cube is switched with the line from the red cube to the fuel controller.

My mount is not the most robust, but I think it’s sufficient. A single bolt holds the unit onto a cushion clamp that holds the engine mount. If the clamp ever failed, the fuel lines themselves would keep it suspended. However, it would probably cause some damage in the process. A better solution might be designing a bracket that has two clamps, which is something I’ll look at down the road.

Weight and Balance

Posted on by Neal

Today Donnie helped me with a weight and balance. The airplane weighed in at 1257 pounds, which is right about what I expected. The center of gravity is a very important datapoint too, and after crunching some numbers the empty CG was 81.54 inches aft of the datum. The datum is a point 72 inches forward of the wing leading edge.

The process started by loading up the airplane with all the panels, screws, interior panels, carpet, literally everything that will be part of the airplane. I didn’t bother installing everything, in some cases I just placed the parts in their correct position.

With that done, the next task was to level the airplane. The weight needs to be calculated on level flight condition, so I needed to raise the tail up about 3 feet. To facilitate this I brought my standing desk from home, and was able to easily raise and lower the desk to find level. Using a desk instead of a saw horse allowed room for the scale to sit under the tailwheel. A digital level on the canopy rail was sufficient to identify level.

With that done, I moved the desk out of the way and Donnie set up the scales – one under each wheel with a WiFi controller giving a digital readout for each scale. We then rolled the mains up onto the scales. Then we raised the tail and positioned the desk and scale under the tailwheel. With that done we wrote down the weights, and the weighing exercise was complete.

To get an accurate arm for each scale, I used a plumb bob to make a mark on the floor identifying the wing leading edge. Then I carefully measured the distance to the center of each wheel. The plum bob came in handle at the tail too so I could measure the distance while the tail wheel was still elevated.

With those calculations done, I created a spreadsheet to plot W&B and played around with a few scenarios.

Configuring the standing desk to attain level flight attitude
The numbers. Interestingly, the right main wheel is a quarter inch aft of the left main wheel, relative to the wing leading edge.

P-Mag timing

Posted on by Neal

Following Dan Horton’s recommendations, I set the engine advance to a range of 19.6-28 degrees…

The process is very easy, just power up the electrical system, set the prop to the appropriate position, and blow a puff of air into the Manifold Pressure port on the mag. Conveniently I already have flexible rubber tubes connected to these ports, so it was a trivial task.

The black mark on the left was my reference point for setting the timing. The p-mag will operate ~30 degrees from this point.
Using a mirror was the only way to see the LED light on the mags. Green indicates the timing process has completed.