mitchilito

My Feedback: (7)

I did a search of this forum using the words "surging" and "popping" because my Titan SE is doing just that on acceleration. Come to find out that seems to be a very common problem with these engines (but nobody has had an answer that I could find). It has mostly been an unpleasant inconvenience because it just happened on the ground. But today, after a gear pass I throttled up to finish my landing pattern and instead of the thrust I needed I got a bunch of surging and popping and a totally hung acceleration. I was VERY lucky to get it back on the ground in one piece. It has flamed out on the ground under these very same circumstances

Several important facts:

EDIT: I've already set "very slow" in the ECU for low throttle ramp time.
It's very hot and humid here.
I inspected the internals of this engine last week and found everything looked fine, including a flow check of the fuel manifold.
If accelerated VERY slowly to midrange, from there it will accel and run fine.
Starts great and puts out tons of power.

I really need help to figure this out because as of now I can NOT use this engine to power an aircraft.

KC36330

Hold Manual on the GSU and slowly advance thrust while continuing to hold it down and continue holding about 30 seconds. It will reset the PID loops and should clear up the issue.

mr_matt

My Feedback: (10)

Is this the turbine that you changed the NGV on? Are you sure you got the right one? There were many differences with guide came configurations and some are subtle.

mitchilito

My Feedback: (7)

Matt, yes this is the same engine that had the cracked NGV. I TIG welded and annealed it and reinstalled. All the internals are stock and look good.

KC, with the method you describe, would I actually be programming into the ECU the rate that I'm moving the throttle stick?

Mitch

mitchilito

My Feedback: (7)

One more question:

I have a suspicion compressor efficiency is down causing compressor stall on these older engines. Is it possible erosion has etched away compressor shroud contour opening a gap and causing inefficiency? If so, is it possible to re-shim the compressor closer to the contour and if so, how?

I really have a suspicion this would fix this problem.

Mitch

KC36330

No, it only resets the PID loops. Atmospheric conditions (determined with algorithms during previous runs) are stored and used by the ECU, sometimes when the turbine has sat unused this algorithm can cause surging, inability to reach full RPM and sometimes even flame outs. Resetting just allows the turbine to run "open loop" till it reaches full RPM and stores the new data.

mr_matt

My Feedback: (10)

OK my mistake I thought you got a replacement EGV. Kyron's hint is a good one at this point.

mitchilito

My Feedback: (7)

Had the chance to try the "PID reset" procedure today. Held manual button, slowly accelerated to 100% for 40 seconds and released. Next acceleration seemed much better. Nice and slow from idle to 50% then on up nice. Bad news is, next accel was bad and all the rest were same as ever.

I have "very slow" idle to 50% ramp time selected but it's almost as if the ECU is ignoring this setting. Upon accel you can hear it ramping too fast, loading up (popping), ramping back down then repeating over and over. I haven't tried slowing down my throttle channel servo speed yet although I'm quite sure I could slow it down enough to prevent the popping cycle. I just wanted to try to fix it right first.

Could there be a failure to communicate with the ECU via the GCU? I now really think it's ramping too fast and won't accept the command to slow down. Just FYI: Problem is from 32K to 50K. After 50K it accelerates fine. Hangs (popping) right around 40 to 50K, EGT doesn't climb, pump pressure stays pretty low, RPM hangs.

EDIT: Just came in from a test run. Tried slowing the throttle channel down but no luck. Believe it or not, even slowing throttle-up response to 30 seconds(!) had no effect. I took over "manual ramping" with the throttle stick and could actually get a very decent throttle response - but it takes very careful stick jockying at the critical rpm around 40 to 50K. My ECU is NOT accomplishing the needed ramping in that critical rpm range. Interesting because other than this little (albeit serious) quirk it's a great running engine.

Anybody have a suggestion? Pleeeeeeeeeese. . . . .

Thud_Driver

My Feedback: (1)

Ok, this may help or likely not.

Back in the early days of the P-70, I had a similar problem.  Even had a flame out on the ground during takeoff at a meet because of it.  I was told by JetCat the problem was caused by the fuel needles not being shaped correctly and/or positioned incorrectly.  They thought it wouldn't happen in the air but it did and so does a P-120SE I'm flying now.

John Redman eventually fixed the engine (when I got around to sending it in) by re-bending the needles and such.  Don't know the specifics but since he owns the place now, you might call and discuss your problem with him.

toolmaker7341

I have a P-80SE that pops on acceleration and continues very mild popping at full throttle. What should I do? It has only 40 minutes run time since new.

Thud_Driver

My Feedback: (1)

Generally, those are tiny droplets of fuel that weren't completely atomized and so they give that "pop" when they light off. I wouldn't expect them at full throttle. So you might call JetCat and discuss it with them and see if it's a real problem.

toolmaker7341

Does anyone have a picture of how the fuel needle are suppose to look. This thing popped on acceleration from day one. I called them and some kid said that was normal and they couldn't do anything about it. Unfroturnatly it was purchased 4 years ago and it has been sitting till now. It has 39 minutes run time since new.

Thud_Driver

My Feedback: (1)

There's a pic in the first post but it might not help much for shaping and position.