JP_Jets

I have an old P60-SE (propane start) fresh back from JetCat after the starter motor wouldn’t spin with a certain ECU and generally throttle response performance felt like it was degrading. It had been ~7 hours since the previous service. Verdict from JetCat was new electronics board, new ECU, new starter motor o-ring, and new fuel pump. While the engine was at JetCat I replaced the entire fuel system in my jet, since the original was 10+ years old.

After getting the engine back, I have not been able to get the engine to run properly. Engine idles fine and throttle response is great below ~30% throttle. Above 40% throttle, then engine stops responding to throttle increases. The engine tone drastically changes from nominal. It sounds more similar to the woosh/puff sound you hear during initial ignition on a propane start turbine (Imagine repeated low frequency pops). The exhaust also becomes noticeably smokey above 40%. Once throttle is commanded back to idle, the engine returns to nominal performance. Additionally, it seems like 50% of the time, the engine won’t start (see details below). I’m stumped on this and could use some help.

Relevant Information/Observations

• Running 1-K Kero with JetCat Turbine Oil
• GSU reads max RPM of ~90k RPM for the run (even when full throttle is commanded)
• The engine starts have been inconsistent since getting the engine back. Frequently I’ll get Low-RPM or LowTemp failures within <10 seconds of starting the engine, before propane ignition can occur. Sometimes the starter motor only spools up for ~3-4 seconds before shutdown.
• Even when propane ignition occurs on startup, the acceleration is rough during transition to kero. The RPM fluctuates noticeably and repeatedly and the starter motor appears to make a loud vibration sound for much of the acceleration profile. Once the kero lights and RPM increases, the vibration goes away and idle is fine. In the past, the engine would very quickly pass through the RPM range with the vibration sound, but now it seems to dwell at the vibration RPM during acceleration for >10 seconds.
• This engine used to be rock solid on startups (started every time and very quickly got to stabilization), now it seems like 1 in every 2 starts gets to stabilization.
• After shutdown, the starting motor frequently doesn’t spin during the cooldown cycle. Smoke comes out of both the exhaust and inlet if the motor isn’t spinning.
• Starter motor does respond to GSU commands (ignition/starter button) and seems normal with GSU commands.

Any advice is appreciated. I’m really hoping to avoid sending it back to JetCat again after just getting it back.

Dave Wilshere

What is the idle throttle response set to? If it’s Fast make it Normal, if it’s Normal make it slow.
if it’s not that hold the stick full power and press and hold (Red) Manual button on old GSU or Set on new type wait until it says pump stored.

Dave

JP_Jets

Thank you Dave! Idle throttle response was set to “normal”, setting it to “slow” got the engine running beautifully.

I did some more experimenting this afternoon. As for the failed starts, I think the propane solenoid is contributing to the problem (maybe going bad?). I bypassed the solenoid for a test run and the engine started the first time. This was after multiple failed attempts with the solenoid in the loop, sometimes I didn’t even hear the solenoid clicking during the failed starts.

The engine was still a little sluggish on the acceleration, but was able to reach stabilization.

The last remaining unknown is why the starter motor isn’t spinning on cooldown. After the most recent run, the starter motor did one spool up to cool down the motor, but then nothing. Taking off my ear protection, I did hear a quiet high frequency buzzing coming from the starter motor (I think) that was constant until temp got below 100C. I was able to manually spin the compressor wheel during the cool down sequence and it spun freely (thinking maybe the starter motor would be applying torque because of the buzzing). I can use an external blower for the cooldown moving forward, I just want to make sure I’m not frying the starter motor for some reason.