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Merlin 140XBL Full Throttle Problem

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Old 04-08-2017, 12:44 PM
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Default Merlin 140XBL Full Throttle Problem

I installed a new Merlin 140XBL in my Ultra Flash late last year. At first it seamed like a fire-breathing monster, but I soon adapted to it (Wren SuperSport was installed previously). However, recently I have had the feeling that it is not as potent as I was expecting, and especially so on the last couple of flights yesterday.

On checking the telemetry logs (Jeti DS-16) at the field, I noticed that the max rpms were in the mid 120,000's range, not the 130,000 maximum expected. On doing a ground run and watching the ECU status it showed that after applying full throttle and the ECU running through the calibration function, it was reporting that the pump was maxed out, even through the rpm's were in the low to mid 120,000 range. Suspecting a fuel blockage, I stopped for the day.

Checking back at all previous flight logs, I noted some strange behaviour, even from the first flight of the Merlin 140. See data plots below for a number of flights.





After initial application of 100% throttle, full rpms are reached and then starts to fall as the pump voltage increases. At times it looks like the EGT is climbing up and reaches a limit of around 700C. Subsequent full throttle during the flight does not reach 130,000rpm.

I'm not sure of the explanation - I've flushed my fuel system and no blockage was found. I'm running a MAP Air Trap with a paper filter just before the fuel pump.

I don't know if the pump is going bad, or if there is some FOD in the pump or engine.

Any ideas from the experts?

I plan to e-mail Gaspar to get his thoughts also, unless he responds directly to this thread post.

Thanks

Paul
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Old 04-08-2017, 01:33 PM
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Best way, is to contact Gaspar directly. He is a super nice guy, and will help you To me, it seems like some kind of restriction/blockage, maybe in the small filter inside the turbine (close to the internal valves).

Last edited by kimhey; 04-08-2017 at 01:35 PM.
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Old 04-09-2017, 05:55 AM
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Could it be a weak battery?
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Old 04-09-2017, 06:11 AM
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Sounds like you may be hitting the PUMP LIMIT.

What is your Pump PW at full throttle? Compare that value to the PUMP LIMIT parameter.
The recommended procedure is to set PUMP LIMIT to 1020 (no limit), run the engine to full throttle and note the Pump PW. Then set PUMP LIMIT to 10 - 20% higher than what the pump runs at full throttle.

Joe
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Old 04-09-2017, 09:59 AM
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ajp
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Try running the engine out of your 5 gallon fuel jug. This will bypass your fuel system, filter and uat. Compare the pw values
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Old 04-09-2017, 06:08 PM
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AJP,

Thanks, and that is exactly the suggestion I got from Gaspar this morning. He is suspecting pump cavitation on the inlet line, so he suggested starting from an external tank direct to the pump, and then start adding back in the shut-off valve, the UAT and the a/c tanks one at a time to see where the problem is.


As this is a brushless pump, the Pw adjustment is not available. It was topping out at around 2600, which indicates differently then the old brushed pump motor Pw readings.


Hopefully I can get a chance to try later in the week.


Paul

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Old 04-10-2017, 08:40 AM
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LimitDwn
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Paul,
I have two 140XBL’s and have experienced both of the sameissues that you described, and not on the same turbine.
First the high temperatureissue this was something that was seen during the startup process and yes myturbine reached these temperatures and higher. This was contributed to aninternal fuel leak, and me not diving into the issue sooner I ended updistorting the shape of the outside turbine casing and rubbing off the exhaust turbine wheel. One thing that I did see whenthis turbine had this problem was a small amount of fuel leaking from theexhaust cone during startup. May want to check if you can see fuel on startup, mine is in aReaction so its easy to see.
Second I also have a 140 in an Ultra flash and experienced thesame issue where I started to lose top end RPM and was told that the pump wasgoing away. I replaced the pump and the turbine was back to full RPM. Then itstarted again and was told to check the fuel system I did a complete clean andhave only flow it twice since then and no issue, so time will tell. One thing Idid do when I started having problems was to re-learn the RC and on couple of occasionthat fixed the problem. Would try tore-learn the RC and then see if there is any change in the top end RPM.
Good luck and please keep use all posted on how you make outthis is all good information for everyone.
Robert
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Old 04-10-2017, 04:45 PM
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So, it looks like Gaspar hit the nail on the head.

I removed the Air Trap and ran the main fuel tank directly into the shut-off valve then to the pump. On running the engine, the Pw dropped by half, to around 1300 compared to maxed out at around 2600 when pulling fuel from the Air Trap. It would hold 130,000rpm continuously.

This Air Trap has had 70 flights on it, and on dis-assembly it had no sign of slime or anything unusual on the paper filter.

My second 140XBL also runs a MAP 40z Air Trap with no problems, but it has half the number of flights on it.


I did notice that the brass fittings had some significant shavings remaining on them which could cause line restrictions, although the filter would prevent them getting to the engine.




I have another MAP 4oz Air Trap on order.

I'm considering setting a Pump Voltage alarm in my Jeti DS-16 to indicate when the Pump Voltage is approaching the maximum (6V) as an alert to fuel restrictions. Normal ops is around 4V, so that should give plenty of headroom.


Paul
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Old 04-10-2017, 06:58 PM
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Originally Posted by JSF-TC View Post
So, it looks like Gaspar hit the nail on the head.

I removed the Air Trap and ran the main fuel tank directly into the shut-off valve then to the pump. On running the engine, the Pw dropped by half, to around 1300 compared to maxed out at around 2600 when pulling fuel from the Air Trap. It would hold 130,000rpm continuously.

This Air Trap has had 70 flights on it, and on did-assembly it had no sign of slime or anything unusual on the paper filter.

My second 140XBL also runs a MAP 40z Air Trap with no problems, but it has half the number of flights on it.


I did notice that the brass fittings had some significant shavings remaining on them which could cause line restrictions, although the filter would prevent them getting to the engine.




I have another MAP 4oz Air Trap on order.

I'm considering setting a Pump Voltage alarm in my Jeti DS-16 to indicate when the Pump Voltage is approaching the maximum (6V) as an alert to fuel restrictions. Normal ops is around 4V, so that should give plenty of headroom.


Paul

Ew, these pictures are really scary.
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Old 04-17-2017, 12:58 PM
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Well, there's more to this than I first thought.

Where I thought I had found the issue, as Gaspar suggested, I installed a replacement Air Trap and performed a ground run. Yet again, I observed the rpm drop after initially reaching 130,000. After confirming that this was repeatable, I removed the air trap, and ran my overflow tank directly to the pump using 6mm fuel line all the way, for minimal flow resistance.

After holding 130,000rpm for approximately 10seconds, I again observed the rpm decay to around 126,000. I confirmed that this effect was totally repeatable.

I did observe that whilst running at 130,000rpm, the GSU would show ‘MAX’, but as soon as the rpm started to drop, this changed to ‘Running’. Pw stayed at approximately 1300 throughout at full throttle, both at 130,000 and 126,000rpm.



Even though the logs show 100% throttle, I performed a radio calibration, but it had no effect on the rpm drop after approximately 10seconds.

It is though the FADEC is automatically throttling back uncommanded,

I have sent the Jeti TM data and the FADEC download data to Gaspar for further advice. I am out of ideas.


Paul
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Old 04-17-2017, 03:06 PM
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Thanks, for the update, please keep us informed as you move further into trouble shooting. I only ask in case i have an RPM issue when i get things up and running again.

Robert
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Old 04-17-2017, 05:27 PM
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What battery are you using to power the engine?
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Old 04-17-2017, 06:44 PM
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Jeti 5200mAh Li-Ion, sitting at 7.2V during the run as shown in the plot above.

I can get at least 5 starts and flights from it before needing to recharge. This run was fresh off the charger.

I have exactly the same battery set-up with my other M140XBL, and it holds 130,000rpm indefinitely.


Paul
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Old 04-17-2017, 07:15 PM
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Originally Posted by JSF-TC View Post
Jeti 5200mAh Li-Ion, sitting at 7.2V during the run as shown in the plot above.

I can get at least 5 starts and flights from it before needing to recharge. This run was fresh off the charger.

I have exactly the same battery set-up with my other M140XBL, and it holds 130,000rpm indefinitely.


Paul

Right, just noticed the plot has that now, never seen these new ones and old ones did not show voltage.
Looking at the plot, it seems like the ecu is actually commanding the pump to slow down for some reason, so I wouldn't be looking for restrictions or pump problems. Seems to be either a software issue or some failsafe mechanism kicking in. Is that temperature level normal? It seems a little on the high side, but I don't know the m140 numbers. KT engines display 200 to 300 deg less than that at full throttle, but 700 is not that high either... When you figure it out let us know what the problem was!
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Old 04-19-2017, 07:10 PM
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Drill out your fuel clunks, and check every joint in the fuel system to see if it flows well, also check your vent.

I had a tank that everything looked ok, but it was doing the exact same with my 140.. It ended up being the Tank Vent, it had glue slag in it. I ended up replacing the vent.. problem solved.
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Old 04-27-2017, 06:03 PM
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Status update on the troubleshooting.

After sending Gaspar both the Jeti TM logs and the ECU data download, he suggested that there may be an issue with the ECU, so he shipped me a replacement ECU via 2-day UPS. On receipt I installed it, but no change, still getting the rpm drop exactly as before.

I then hooked up an external fuel tank, new receiver and ECU externally to the model and ran the engine, trying to isolate any installation issue and I saw the same rpm drop. Next, I swapped the turbine for another M140 from another model which I know runs fine, and again saw the rpm drop. At this point, the only remaining common item left was the fuel pump.

After sending Gaspar this latest information, he agreed that the pump was most likely the cause, and he shipped me a replacement pump, again by 2-day UPS from Spain.

Well, tonight, I swapped out the pump and did another ground run. No change!!, still getting the rpm drop exactly as before.

So, in desperation, I made a test stand where I could run the engine away from the model. With the old pump and direct fuel feed to the pump, the engine ran fine, holding 130,000rpm indefinitely. At least some progress at last!!

I've started to add back into the test stand individual parts of the system as installed in the model and I have again observed the rpm drop when using the model installed radio system and ECU, connected to the proven good external pump and engine on the test stand.

At this point I think I can prove that it is a model electronics issue, but I have yet to isolate the actual source of the issue.

More updates to some - I think I'm getting closer to solving it.

Paul

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Old 04-27-2017, 06:17 PM
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The other difference between in and out of the model will be the air path.

What is the distance between the tailcone and the pipe? Are there any obstructions preventing airflow to the intake? Are you running a bypass?

Do you have a photo of the installation?

(edit: ignore that - I have just seen that you have reproduced it out of the model. Very odd.)

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Old 04-30-2017, 09:17 AM
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Wow great service from Gaspar! Glad that my next turbine will be from them
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Old 04-30-2017, 10:09 AM
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Problem solved!!

After a couple of false leads, I ruled out any radio or installation issue, as I could reproduce the rpm drop on the test stand with a completely independent set-up.

Along with the replacement pump, Gaspar had sent yet another ECU, but with this one programmed with some custom modified settings. His suspicion was that my engine needed a higher fuel delivery pressure to achieve max rpm, and the pump was being current limited by the nominal M140XBL ECU settings.

So, after consistently being able to reproduce the issue on the test stand, I replaced the original ECU with the new, modified unit. That fixed it!!!

After running for about 2mins at max rpm with no sign of any drop, I replaced the ECU with the original unit and confirmed successfully that the problem returned.

I've now rebuilt my Ultra Flash with all the original parts except the modified ECU and a new Air Trap. Just now waiting on the weather to cooperate to fly it as final confirmation.

Many thanks to Gaspar for excellent customer service - he has gone above and beyond in helping me resolve this issue.

Paul
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Old 05-01-2017, 02:38 AM
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Paul,

Awesome trouble shooting, the work that you did here and the time involved is what gives everyone that much more knowledge and information when it come to issues with turbine powered aircraft. I know that I really appreciate it being a 140XBL owner.

Robert
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