UL520T Crankshaft Failure / Investigation

In early May 2023, there was an accident with a Rans S12 powered by a UL520T.  Preliminary accident report available here.

As stated in the prelim accident report, the engine had been experiencing high CHT temperatures on one side of the engine and the builder had increased the size of the oil cooler and was working on overall cowling / cooling issues.  No reports of high oil temperatures are present in the prelim findings.

I have talked to the US Distributor and other builders about this accident - which is very concerning.  A crankshaft failure is not something to be taken lightly.

I am not going to get into relaying what I have heard about the circumstances around this incident - although there appears to be extenuating circumstances.  The crank failure was most likely a result, and not necessarily the cause.  But the nature of what started the failure chain are not yet known.

Bottom line:  I am going to wait for the 'final' report before making any decisions.  The week of June 19th, 2023 the NTSB is going to perform an detailed analysis of the crank and case with the assistance of the US Distributor.  The factory is fully cooperating with the investigation.

This is the first crankshaft failure of any UL engine.

More questions than answers at this point.

I am going to continue forward on the build, but spend as little money as possible on the engine side of the install just in case I have to abandon it.  I truly hope that is not the case, but a definite possibility.  Flying behind an engine you do not trust is not a happy feeling.

UL ECU Update and Issues

 Up until now, all of my interactions with UL Power have been excellent.  Super responsive (considering time zones), and reasonable.

UL changed a number of ECU parameters last year, and mine had to go back to the factory in Belgium for a software update.  So I packed it up in March, and UL arranged for everything else.

In May, I reinstalled the ECU.  Everything appeared fine... but the CANBUS feed from the ECU was now on lane B and not lane A.  I also thought there were a bunch of sensor failures (but that turned out to NOT be the case).

UL claimed that the CANBUS lane A / B decision is made via the cable.  After some sleuthing on the diagrams I found the pins and checked - no jumper.  UL then stated they were going to test with my version of hardware - and they found the issue.

The explanation given:  I have board version 63, and they are now on 64.  They added additional input ports, which shifted the CANBUS lane A / B jumper.  

The label on the ECU says

HW ver 1-63

SW ver 07-022

Based on my experience in over 30 years of dealing with hardware and software issues, there are more issues than what I am being told.  They GUARANTEE everything is fine, and no need to update the ECU software.

I do not agree.

I am trying to stay positive on UL as 1 bad experience should not taint all of the good things they do and have done.  But this has definitely left a bad taste with me.

90% done, 90% to go - be done on Tuesday

 It's a long list of what is left, but its getting shorter (last updated Sun, June 11).  This is to keep me focused and motivated.

Things to do at home

1. Complete intercooler air inlets, and finish brackets
2. Complete air cooler brackets, open hole in cowl, make mold, finish cowl
3. Modify cowl for larger spinner
4. Finish cylinder air inlets
5. Exhaust - from UL stubs 
6. Finish air outlet on cowl (exit air ramp)
7. Plenum tops
8. Plug wires, CHT and EGT
9. All windows
10. Brakes - from park brake valve to calipers
11. Finish pitot lines
12. Air intake / filter / alternate air source
13. Cabin heat plumbing - firewall side
14. Put doors on
15. Finish mounting hardware for rudder and cables
16. Fuel plumbing from gascolator to engine. Return line from engine to firewall
17. Gear leg fairings
18. Wing to fuselage wiring connector (fuselage side done)
19. Install interior
20. Glareshield upholstery
21. Tighten up tailwheel bolts

Things to do at airport (final assembly)

1. Strut to wing and strut to fuselage fairings
2. Hang wings
3. Finish hatches and flap fairings
4. Wing tips
5. Lights
6. Wing to fuselage wiring connector (fuselage side done)
7. Brake fluid / bleed brakes
8. Wing mounted antennas / coax cabling
9. Paint

I will probably keep this list updated as I think of more things and scratch some off.