Taxi Test

Posted on by Neal

Today I arrived at the airport early to prepare for and conduct a taxi test. In my test card, I planned to check steering operations on the ground – braking action, differential braking, and tail wheel steering. I also planned to calibrate the magnetometer on the compass rose. Everything went well, and I learned a few things along the way.

The compass rose is at the other end of the runway, and I am trying to minimize the amount of engine run-time at low RPM. Because the engine is brand new and needs to be broken in, the recommendation is to run it at high power for the first few hours of it’s life. Since I can’t do that on the ground, I don’t want to be running the engine longer than I need to before it’s flying. However, I need to calibrate the magnetometer, and it’s a sensitive instrument. Calibration requires slowly taxiing in a circle in an area free from any magnetic interference, which is what the compass rose provides. I decided it was worth the extra 5-6 minutes to taxi there and back to give the calibration the highest chance of success.

The engine started nicely, and I started the taxi test right away. Since the tower was operating by the time I was ready, I also had a chance to test my Com1 radio, tower gave me a 5/5 rating – loud and clear. With the cowling on I could check my visibility while taxiing. By sitting up straight I can see over the top of the cowl, although the first 200 feet in front of the plane is obscured. Moving my head to the left I had a nice view down the side of the cowl, and I found that to be the easiest way to monitor the taxi way ahead. Engine instruments showed the engine was running well – consistent CHTs, EGTs, and oil temp & pressure.

Arriving at the compass rose, I positioned the aircraft on the left side, facing due north, as described in the Garmin manual. I needed to boot the PFD into Calibration mode which required shutting down the G3X system, and booting it back up. I shut off the standby battery first, then the main battery. For a moment I was surprised that all the avionics were still operating. Then I remembered the alternator was still on, and was powering the system. I shut off the alternator, and the engine started to shut down! I immediately realized what had happened, but didn’t have the reaction time to stop it. I pulled the mixture to complete a normal engine shutdown. The e-mag ignition system depends on main buss power at low RPM. The mags have internal Alternators to provide power, but only about ~1200 RPM. I was idling the engine when I shut off the power, and the ignition system stopped igniting.

While the engine was shutdown I booted up the G3X into calibration mode and get the magnetometer test ready to go. The engine started right up again, and I followed the on-screen instructions to slowly turn in a circle to the right, holding position every 30 degrees. The whole process took about 10 minutes, and thankfully passed at the end. I taxied safely back to the hangar and shutdown. The total engine run time was 18 minutes, a bit longer than I hoped.

Analyzing the engine data again, everything appeared normal.

Post taxi inspection. Exhaust is starting to change color. No sign of oil leaks, a track of splatter from the exhaust joint lubricant.

Here is some of the engine and flight data. Note, the data between the vertical bars is interpolated, since I only had data from the beginning and end of the test, and not while performing the magnetometer calibration (the time between the bars).

Not sure why the airspeed is indicating 18 MPH before and after the test, and why it’s so much higher than the ground speed. There was approximately 5 knots of wind, and no other reason I can think of that would cause it to read high. Prop blast could be a factor after engine start, but the pitot tube is well outside the prop blast area.

First Engine Run

Posted on by Neal

Today was a major milestone – the engine ran for the first time! My friend Donnie met me at the airport at 7am to help advise and provide a second set of eyes on the process. It was early enough to be very quiet, allowing us to focus. After a few preparatory steps, we pulled the airplane out onto the taxi way and started the test. I had a test card written that covered everything I wanted to test – engine instruments, ignition, prop governor, alternator etc.

Everything performed completely as expected, and I was very happy and relieved to complete the test successfully. After verifying everything engine-related, I also took the chance to test the brakes. Donnie removed the chocks and I rolled forward a couple of feet and confirmed the brakes worked well.

After shutdown, I did find an oil leak. I traced it back to a loose oil hose fitting, and was able to torque it up and resolve the issue. It was one of the oil lines connecting the oil cooler, and I must have just plain forgotten to torque it. I added torque seal and checked all the other fluid fittings on and around the engine while I was at it.

The engine ran well. I let it idle for several minutes until the oil temperature reached 100 degrees F, then performed a run-up by slowly increasing RPM to 1800. That’s where I checked the mags, cycled the prop, and double-checked the alternator output. I collected the engine data from the G3X system and uploaded into an analysis tool on my laptop. There was nothing that looked out of the ordinary to my untrained-eye.

First start!
First start from inside the cockpit
CHT data
EGT data
Fuel flow data
Oil temp data
RPM data

Fuel Calibration

Posted on by Neal

Today I worked on calibrating the fuel tank senders. This involves booting the G3X system into Calibration mode, and then running the fuel calibration steps while filling the fuel tanks a few gallons at a time.

I built a stand to place under the tail wheel to keep the airplane in level flight attitude. Because it’s a tail wheel airplane, the fuel level reads differently between level flight and when operating on the ground with the tail down. The stand worked well for getting the plane into level flight attitude.

The first step is to perform the fuel calibration in level flight, then the process is repeated in the ground attitude. The system simply reads a set of datapoints and then computes a curve to interpolate all the in-between values. It’s up to the operator to decide what values to use, and how many points.

I coordinated with the fuel truck driver, and he helped by pumping in specific quantities of fuel while I entered the data points in the cockpit. We started with the right tank, filling in 3 gallon increments, and one final 1 gallon increment to the full 25 gallons. Everything went well, and the process was painless.

When we switched to the left tank, the sender value being read by the G3X was stuck on the same value, even as fuel was added. We stopped the process and I started troubleshooting. I quickly found the sender wasn’t grounding correctly. I was able to fix this by slightly torquing one of the sender screws.

I called the gas truck driver again, and we attempted to complete the process. Unfortunately the sender reading didn’t change when we added fuel, so we stopped again.

At that point I switched focus back to the right tank. I took the tail stand out, and set the tail down on the ground. I was startled to hear a splashing sound, and quickly realized the excess fuel was pouring out the right tank vent. I quickly placed a gas can under the vent and caught some of the overflow. Note: the tail low ground position means a practical limit of fuel capacity of about 24.75 gallons.

Rather than draining the fuel, I realized that I could calibrate the fuel level as I remove fuel, not just adding fuel. I decided to siphon gas out into canisters, as I could transfer the fuel much faster than via the vent opening. It also allowed me to control how much I was removing, which made the calibration process for the second time (the ground configuration) super easy. The gas cans were all 5 gallons, so I set points at 5 gallon increments. I left 5 gallons in the tank because I ran out of gas canisters, and the zero point reading will be the same as the in-flight value.

With that done I had run out of time, so will have to come back to troubleshoot the left tank sender.

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.

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.

Oil change

Posted on by Neal

Last night I drained the engine preservation oil and added 6 quarts of mineral oil. I ran out of time to set the engine timing, but that is a quick job I can accomplish next time I’m at the hangar.

While I was changing the oil, I took the time to replace the oil drain plug with a quick drain fitting, and put some RTV between the starter solenoid and the snorkel.

I started by removing the snorkle and inspecting the fuel servo. Sure enough, some preservative oil had drained down the intake pipes and collected in the bottom of the servo. Rather than removing the servo, I was able to suck the oil out using a small piece of flexible plastic hose, and the wiping up the residue. There’s still a film of oil, but no pooling of oil at all.

View down the fuel servo’s air inlet. A small amount of oil had pooled at the back of air intake

Then I removed the bottom set of spark plugs, and rotated the prop a few times to push out the remaining oil. A lot of oil came out of cylinder 2, and just a small amount from the other cylinders. I leveled the airplane to help drain as much as possible. I also used a borescope to check the cylinders and take a few pictures, just because.

A small amount of preservative oil leaks out of the lower spark plug hole on one of the cylinders
Oil from the spark plug hole ran down the exhaust pipes and dripped all over the place. The red bucket caught most of it

With that done, I removed the oil drain plug and let the rest of the oil drain out the bottom.

The original oil drain plug, safety wired to the oil screen cover

After consulting a number of threads from Vansairforce, I left the oil filter alone. This is a new filter added by Lycoming, so I’ll just keep it on for the first 10 hours of engine time. At $40 per filter, no need to waste a new one.

Once all the oil was out, I cleaned and installed the quick drain fitting. I used some loctite to seal the threads, and torqued it to 14 foot pounds, per the table of limits for a 1/2-14 pipe fitting. The quick drain should make future oil changes a lot easier – just push on a drain hose, and push the fitting up and rotate to release all of the engine oil.

Preservative oil draining from the sump. By the time I thought to take a photo, most of the oil had drained out
Oil pan and a bucket collected most of the oil.
The quick drain fitting (finished in blue)
The underside of the quick drain fitting showing the safety wire securing it to the oil screen cover

I then cleaned and reinstalled the spark plugs. After wiping off all the oil, I used some acetone to clean the threads and carefully wiped the spark plugs down. I added some copper based anti-seize and reinstalled, torquing to 35 foot pounds per Lycoming’s spec.

Then I put the snorkle back on, adding a bead of RTV to help protect it from the starter. There’s plenty of clearance, but the RTV will help reduce any chance of rubbing and damage as things heat up, shift around and vibrate etc.

With that done, I poured in 6 quarts of straight mineral oil.

I’m adding Aeroshell 80 straight mineral oil which is SAE-40 oil, and is good for a wide range of outside air temperatures
Oil change complete

Prop safety-wiring

Posted on by Neal

Tonight I finished safety wiring the prop attach bolts. I had previously wired two of the 6 bolts, but had left the others so I could move on with other tasks. At the time I was working towards a deadline – moving the fuselage to the airport – and didn’t want to spend more time on the task. The first two bolts had been a real pain, and I had redone the wiring several times before I was satisfied that it didn’t suck too badly.

For the remaining four bolts, I started by practicing with the thinnest safety wire I have, which is much easier to work with. After figuring out the routing, the length required, and any other relevant details, I switched to the large diameter wire and completed the task. The bolts are wired in pairs, and each bolt has a hole through the center where the wire passes. Because of the varied orientation of the bolts, each one presents a unique challenge in getting the wire through the hole. I was lucky that only one bolt needed loosening and reorienting, and I was able to get all the others to work without adjustment.

In the end I was quite happy with how it turned out, and found that a little practice and lots of patience definitely helps.

A pair of wired bolts. The wire acts as a fail safe in case the bolts vibrate lose and start backing off
Another pair of wired bolts

EarthX Battery

Posted on by Neal

Before completing the aircraft wiring, I decided to switch to a Lithium battery, and EarthX seems to be the most popular brand for RV builders. The difference in weight between the original lead acid battery and the Lithium battery is substantial. I didn’t have the original battery specs, but it must be 3-4 times heavier than the Lithium battery. There are some other benefits too, such as a longer period of output, longer store of charge, and a battery health indicator output wire.

The EarthX 1200 series is an almost exact match in size. It’s slightly deeper, slightly narrower, and the top is shaped differently. The battery came with some foam to help make up for the narrower shape. I added a washer on each side to account for the wider shape, and added some aluminum strips with foam to the hold-down bar to ensure a snug and secure fit.

The battery terminals are basically the same, so once I had modified the hold down bar and charged the battery, it was ready to go.

Original Vans supplied battery. This is a few years old now.
Side by side comparison of Vans batttery (right) with EarthX battery (left)
Test fitting. Not the gap under the hold down bar
Added some aluminum strips and foam to the hold down bar
Final installment. Note, the ground is disconnected since I’m still running on ground power at this point