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Gazoo
Joined: 01 Jun 2016
Posts: 3
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 Posted: Fri May 26, 2017 3:22 pm Post subject: On the hunt for one pesky gremlin |
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Well, my Yak season is off to a very slow start due to a phantom gremlin stuck inside my airplane.
1st start and attempted run-up
My first start of the season was a difficult one which required much coaxing but resulted in success after numerous attempts and nitrogen bottles. The first run-up was conducted with cowlings off to check for oil leaks following a compressor change-out. Given the ambient temperature at the time and no cowls, it took approximately fifteen minutes to come up to temperature.
The engine ran smoothly during the warm up at 40% except ran rough once about midway thru for about five seconds but then ran smooth once again after momentarily changing power setting.
Just as oil temp was approaching 40°C and CHT 140°C, the idle started to “hunt” between 40% and 35%. I glanced quickly at the fuel pressure and it was holding at 0.4. After three rapid increases and decreases in RPM, the engine just smoothly quit.
No restart was attempted because at first we suspected fuel blockage so a tear down of the fuel system was completed to find the issue, however, no anomalies were found. The fuel system was checked over during the annual and all fuel screens, which were clean, were checked at that time, however, we checked them again. All were clean and in good condition.
2nd start and run-up
After putting the airplane back together, engine started no problem this time and ran beautifully smooth for the entire warm-up and run-up. All engine parameters were normal. Engine was run for approximately 20 mins.
3rd start and run-up
Same story as the second, engine started no problem and ran beautifully smooth for the entire warm-up and run-up. All engine parameters normal. Engine was run for approximately 20 mins. Only anomaly found was a broken line from the compressor to the snot valve.
At this point, whatever clean-up and recheck of the fuel system we had done was leading us to believe that the issue may have been a one-time event, but with no hard and fast culprit in custody, we were suspicious that the problem was not corrected so more run-ups were in order.
4th start and attempted run-up
Engine started beautifully on very little prime and ran smoothly. It took about five minutes to get up to temp and just as oil temp was approaching 40°C and CHT 140°C, then engine again just smoothly quit despite adding throttle to compensate for the dropping RPM. Fuel pressure held steady at 0.4 throughout.
A few phone calls were made and we were advised to check for blockage in the fuel vents. These were checked and flushed these with compressed air.
5th start and attempted run-up
After flushing the fuel vents, we started up again. Smooth start and run but within the same timeframe and temps, the engine just smoothly quit. Fuel pressure again held steady at 0.4 throughout.
6th start and run-up
This time we elected to try another restart immediately so with only one shot of prime to the cylinder side, the engine again started right up and ran beautifully and continued to do so through the entire run-up. We ran it for 20 mins with no anomalies.
We are now officially, totally at a loss as to what could be the cause.
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Stefan Corriveau
stefancorriveau@hotmail.com |
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Etienne Verhellen
Joined: 13 Apr 2007
Posts: 141
Location: Belgium
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| Posted: Mon May 29, 2017 9:52 pm Post subject: Re: On the hunt for one pesky gremlin |
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Hello Stefan,
A few questions :
1. Did you do a high power run-up (before the engine quitting) ? 70% and above ?
2. Is it possible for you to do high speed take-off power run on your runway ?
3. When is the last time your engine was overhauled and by whom ?
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Yak-50 Display Pilot - Airshows - Яковлев Як-50
Yak-52 training anywhere - FI(A) Aerobatic Instructor - Specialised Yak-52.
https://www.yakoteam.com/
https://www.yakovlevs.com/the-team/pilots-and-crew/ |
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bwade154(at)yahoo.com
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| Posted: Tue May 30, 2017 9:14 am Post subject: On the hunt for one pesky gremlin |
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and If I might add did you try stroking the primer on Cyl as the engine started to quit, should tell you if its fuel or spark
From: Etienne Verhellen <janie(at)yak52.fr>
To: yak-list(at)matronics.com
Sent: Tuesday, May 30, 2017 2:04 AM
Subject: Re: On the hunt for one pesky gremlin
--> Yak-List message posted by: "Etienne Verhellen" <janie(at)yak52.fr (janie(at)yak52.fr)>
Hello Stefan,
A few questions :
1. Did you do a high power run-up (before the engine quitting) ? 70% and above ?
2. Is it possible for you to do high speed take-off power run on your runway ?
3. When is the last time your engine was overhauled and by whom ?
--------
Yak-52 training anywhere - FI(A) Aerobatic Instructor - Specialised Yak-52.
http://www.afors.com/index.php?page=adview&adid=25551&imid=4
To Fly To Serve ...
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Read this topic online here:
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