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