Taxi Tests

So far, four taxi tests of 15-20 minutes each have been completed. These were just slowly around the parking area and runup bay, getting a feel for the plane. I’ve also calibrated the magnetometer so the ADAHRS has stopped showing error messages.

I have been at the front of the hangar for a change so able to get the plane out. The weather doesn’t matter for these tests.

The last test was with the cowls on. When the engine starts I get a general coolant pump warning, low coolant pressure warning, low pressure from the oil and so on. This tends to inoculate a person to these messages and given I’m not above 1300rpm I pretty much ignored them.  The pump warning did go off and come on again so I turned on the backup water pump just to be sure.

When I stopped the engine back at the hangar there was a LOT of coolant on the ground. It turns out I’d blown a Welsh plug! This was the one we replaced that was leaking from when the engine was delivered. Clearly the installation technique needs improvement.

Of course I was not going to get of lightly. This failure in the air would mean I’d have to shut down the engine or wait for it to seize. On the ground it meant the engine just got hot… but the coolant temps were constant as there was nothing to show the sensors with no water present. I didn’t know. Given the water pressure is zero at start-up with a warning, then it slowly climbs towards 15psi. I missed any message that it must have dropped from that.

So the engine got hot and the cowls hot enough to blister the paint both top and bottom. <sigh> At some point these cowls will need a complete repaint. You can see the marks above like a case of the hives. Review of the engine logs showed nothing catastrophic so I really got of lightly if you consider the big picture.

These glorified bottle tops are cheap but losing an engine isn’t.

I googled how to put them in, I watched five videos and each one had its own method. After a bit I understood what to do rather than follow the instructions like a robot. Every single person also had a favourite sealant too. The more I looked, the more options were presented.

I went for the anaerobic sealant I have used on the water system sensors. This has worked well where others have leaked, so more of the same seems a good thing to try.   The important part seems to be getting the plug in via the edges and not touching the middle. The wedging holds the plug in under pressure, not the sealant.

With that sorted out, the next day I drained the coolant which was only about 2 litres despite the sight tube level indicator showing full!  I filled again with the 50:50 fresh green stuff by pulling a vacuum at the cap this gives me a much better chance of having no air pockets in the liquid.

What to do about these CAS messages that are false on start-up? It turns out that with recent software changes to the G3X you can make messages ‘conditional’. We have set things up so many of these messages happen after the engine has been started and running for a bit. This should make them appear when they are REAL warnings, not false ones so I’ll take more notice.

We also reconfigured the fuel level system to now display on the G3X rather than the AG6 annunciator button that I had spent a huge amount of time and money on. When taxi testing it seems stuck on low sump despite there being 60 litres of fuel in the plane. It’s just been a PIA to program and hook up.  With software updates to the Garmin G3X it can now  accept different voltage levels for fuel annunciations.

Here’s the AG6 button which is currently disconnected and dark. I’m thinking maybe it could be a Master warning for all the major CAS annunciations but I’m reluctant to go to my long suffering avionics guy right at the moment!

Next up is getting the exhaust pipes tweaked again so the sit in the middle of the cowl openings. This is a cut and shut procedure. Then its back to the engine fuel tuning issues which are not yet resolved. I also have to stiffen the top cowl. I’ll do a separate blog entry on all that. Its a bit of work.

My Long-EZ build moved under its own power for the first time, November 1st 2024. It has been 12 years and 11 months since this marathon began and over 16,000 hours of logged build time.

We had finally found the cause of the latest engine problem which was the fuel mapping and with a little difficulty the engine started.

Here’s a link on my YouTube channel with slightly better resolution.

Since then I’ve done 4 runs in total of around 18 minutes each. The steering was quite stiff which was a concern but that only needed some lubrication on the nose gear and now it really turns well and feels much better in the taxi. It is extremely sensitive so I need to be on my game on the runway.

I also found that with about 2mm off the nose gear cover and one AN size shorter bolt down there with a washer removed I can now rotate the nose wheel 360 degrees on the ground. This makes pushing it backwards where the nose must rotate 180 degrees much easier.

The cowls are not on yet so that will effect the temperatures in a negative way. We are starting on a cut and shut for the exhaust pipes today. The ends are too near the top cowl for my liking and I have found a gun welder to do the job.

The temperatures hasn’t reach maximum at low RPM after 20 minutes so that’s going in the right direction. However the Delta T is only 6 degrees. I need this higher. That’s the difference between the coolant temp from the engine and then measured after the radiators before it returns to the engine.

The only control I have with the Coolant temperatures in the cockpit is a switch to turn on the second water pump. This is why I will try setting the fans a bit lower for when they cut in. Mind you, we have no airflow over the radiators really at taxi speeds so its just when the fans cut in and I don’t know how effective they are yet.

There is an issue with the rudders not returning to fully closed. This is easily fixed by pulling the pedals forwards in the cockpit with my feet. The problem is that the angle from the pedals to the cable run is too severe to allow the rudder springs to pull back into line. It is likely that the airflow in flight will fix this but I will have a look at dealing with the angle involved. Its a bit of work and would need a new bracket on the pedals a bit higher and perfectly set up so I don’t have to alter the cable length. I wish I’d picked this up earlier, I thought it was paint too thick on the rudders preventing full closure. At least I know exactly what’s going on now.

There is also an issue with the fuel level electronics giving a false indication, so that’s another one. I need to adjust the squelch levels in software too. Its always open which is really annoying! That needs a borrowed laptop unfortunately. My old one is pretty much toast.