Js3 jet catastrophic failure.

On Monday, October 26, 2020 at 6:33:02 PM UTC-4, wrote:
I've been digging around trying to find out what the process has been for pilots that have added jets other than the MD-TJ 42. This group seems to have a lot of knowledge on this niche subject. The jets are coming down in price and getting a lot more reliable to start, so it seems it would be a more considered option for a lot of pilots. Are there many self-installs, or are there a handful of companies that specialize in the retrofit?

You didn't say where in the world you are but for the US, Bob Carlton in Moriarty would be my first choice to call, if I wanted to have 'my ride pimped out' with a jet.

Uli
'AS'

P.S.: Bob - as soon as that lottery thing works out for me, I'll be giving you a call! ;-)

I'm in the US and familiar with Bob. What he does is fantastic, but I'm more curious about some less expensive, less pimped out options. Everything I've seen of his so far uses PBS engines which are extremely expensive. The Jetcats and some other options are much more affordable and I know there are pilots that use them.. I'm wondering how they went about the retrofit.

a lot more reliable to start
mmm, on the RC side I'm not sure they are much better since I last posted on this thread couple years back. Since then:
-bad egt probe
-bad glow plug
-newish turbine had stiction on the starter motor but if you could reach in and spin the bendix by hand it would start.
-another with bad starter motor.

But no catastrophies. Above were all fixable for a price.
Darren

I've been operating the microturbines for about 15 years (only up to the 90lb thrust class) and all those problems have been addressed for much more reliability. The EGT probe sheaths were switched to much higher temperature materials and were moved internal to avoid being deflected in any way that would fatigue the material to a point of breaking. The glow plugs were horrible and failed all the time. They used to be the ones used in RC nitro engines but are now ceramic and have proven to last way beyond multiple service intervals. The starter motors have transitioned from high friction brushed motors to virtually zero friction brushless. Same with the fuel pumps. I'm just addressing Darren's list but there are a lot of other improvements. The biggest issue I ever found consistently with starting the microturbines is variations in the atmospheric conditions that don't jive with the programmed start parameters which are set for a most likely "window" of conditions. But there are operator techniques to remedy even this scenario on the fly.

Obviously I'm biased toward the jets but always looking for the failure stories because it motivates me to figure out how the potential for those situations can be minimized.

I'm actually reporting on turbines less than 5 years old and it was a ceramic "glow plug"(igniter) that failed. In the case of the Jetcat starter motor I was able to fix that myself which was nice.
Darren

I'd be curious to know which Jetcat models. The P300 and P400 have the ignitors situated differently than the smaller engines and I found that the wrong location contributed to faster wear. Also, the most typical reason for failed ceramic ignitors (that I've experienced) was from too much voltage. The ignitors that Jetcat uses are very happy with 6V and that's plenty for consistent starts but I know of a lot of guys that crank theirs up. Was the starter problem perhaps a jammed open bendix that was holding the o-ring against the compressor nut? Or were they disengaged and the motor itself was jammed up? The former is always an easy pre-flight fix but the latter is obviously the motor. If that was the case, is it brushed or brushless?

I'll admit I'm a bit of a jet addict and always trying to eliminate their nuances. Sorry if this is the wrong place to be posting the technical stuff but maybe it will help others.

I'd be curious to know which Jetcat models.

P120 and other brands through 320N. I think the starter motors are all brushed but the pumps are all brushless. My experience plus all others of my buddies is that turbines less than about 6 grand are expected to behave this way. So you bring a jet to fly and second one as a backup(essentially the same idea as a twin/redundant install). I can't speak for the class that are likely intended for large UAV in roughly the 10 to 20 grand range. I would expect better reliability out of those..