Engine ground runs [1.0 hours]

After several months spent finishing the engine installation, on May 3, 2024 I finally attempted some engine ground runs.

In preparation for this, I tried to pre-oil the engine by removing plugs and cranking with the starter motor, as is commonly done. After four 15 second cranks, I still didn’t have any indication of oil pressure. I tested the sensor, EFIS display, and the oil sensor restrictor fitting on the engine, they were all OK. It may have come good with continued cranking, but I felt this was simply the oil pump being totally dry (=> unprimed) after years of storage – with air gaps between the teeth and pump walls instead of retained oil held in place by surface tension – so I decided to give it some help. Not having a pressure pre-oiler, I removed the oil filter (which is on a 90 degree B&C adapter), and with a cheap new oil can and extension tubing, squirted engine oil into the filter inlet gallery until it filled up. I then had a helper gently wind the prop backwards, one blade at a time, and kept refilling the space with oil. This sucked oil back into the oil pump, and coated all 360 degrees of the gears.  With the oil filter re-installed, I then cranked the engine for 15 seconds, with still no indication of oil pressure. That’s not surprising, the sensor pickup is at the end of a chain which would include filling the oil filter and galleries after the oil filter outlet with oil. Sure enough, about 5 seconds into a second 15 second crank, the oil pressure came up and by the time I was done indicated in excess of 30 psi. After that I reinstalled the plugs and prepared the engine for first start.

To do these engine runs, I had heavy rubber chocks on the main wheels, and tied the tail down (with weights). And of course I had my feet on the brakes. I also had two helpers on the ground, with fire extinguishers handy. In the videos you’ll see me talking, apart from checklist items I had a phone link open to one of the ground helpers in case they told me to stop!

The first run was simply to confirm the engine goes, get oil pumped throughout the engine, and test each ignition system without going above 1200 rpm. It took a fair bit of cranking to get started – I think I did not have it sufficiently primed – and I was about to give the starter motor a rest when it fired. After this the run went fine, for a total of around 3 minutes and the CHT’s never got above 220F. There was a normal RPM drop when I disabled the left ignition system, and one backfire when I disabled the right ignition system, but then a normal RPM drop so something to look into there. Here’s a shortened video of the start and finish of this run:

After inspecting for leaks etc. and taking a break, we did a second engine run. This second run was to get the governor and propeller pitch control going. These won’t work until oil has been forced through the governor and into the propeller hub, and that takes more time and some sustained oil pressure at higher rpm. To do this, after a short warmup I took the engine up to around 1900 rpm, pulled the propeller pitch control back to a course setting, and waited. It took around 35 seconds for the propeller pitch to kick in, but I must admit I was expecting it to take longer and was slow pushing the pitch control forward again. As a result the transition to course pitch was a bit more severe than one would normally do for a ground test. I followed this with two more propeller pitch tests, again at 1900 rpm, before pulling the throttle back and ending the run.

A day later I downloaded the EFIS log data, and came up with the following plot for this run. It shows how I did the ramp up to ~1900 RPM cautiously in a few steps. The oil pressure drops before each propeller pitch event (as the governor becomes an oil sink), and along with the RPM drop there is an accompanying increase in manifold pressure. These changes are all as expected. Also on this plot are the primary and secondary alternator currents. The primary alternator current peaks at its rated 60 Amps not long after startup, but the battery was fully charged to begin with so the primary alternator only had to replace capacity lost due to cranking, which it was clearly able to mostly do across the short duration of this engine run. The secondary (vacuum pad) mounted alternator did some work as well, mostly at higher RPM’s, this type of alternator tends to have poor output at low engine RPM.

At the end of the test, fuel pressure drops to zero because I turned the (SDSEFI) fuel pump off. The engine RPM increased momentarily before stopping. This happens because as the fuel pressure drops, the engine sees a leaner mixture. Leaning from a rich mixture, the flame front propagation speeds up – i.e. the mixture burns faster, efficiency improves, and RPM momentarily increases. At some point we cross best stoichiometry (ideal mixture) after which the RPM will drop, the remaining residual fuel runs out and the engine stops.

Very happy to get these tests completed, and to have some good data confirming the test results. A special thanks to my neighbor Dickie and wife Kerrie, for ground assistance and camera work.

There are a few things to tidy up in the engine and cowl installation, then I need to install all the seat belts, a few inside panels, etc. before doing the weight and balance measurements, some more ground and then taxi tests, avionics certification and paperwork leading up to approval to commence phase 1 flight testing.