912 ULS Overheating and Surging
in 912 / 914 Technical Questions
9 years ago
On first flight of my Sinus Motorglider, the engine repeatedly surged on climbout. The RPM varied between 5400 and 4200 without any input, with a period of about 2 seconds. It was smooth, like I was moving the throttle. Actually reducing the throttle below 4000 stopped the surging, and I made a normal landing.
I subsequently conducted fuel system checks and verified a clean gascolator screen and 20 GPH gravity fuel flow. I did see air bubbles coming down the clear drain tube, but they stopped after about a gallon and did not occur in the next gallon. I found no other problems, including checking the variable pitch prop control, which remained in the minimum pitch position.
The same surging occurred in a subsequent ground after about 45 seconds at 5400 RPM, matching the first flight experience.
I also have had some overheating - CHTs both high and a boilover at shutdown. I had attributed this to a too-long taxi test and too-long ground running on a hot day. Overheating did occur in the ground run mentioned above.
None of the experts I have talked to can explain this, or offer a connection between the two problems - except maybe that the engine is somehow running lean....
Anyone else come across this?
I subsequently conducted fuel system checks and verified a clean gascolator screen and 20 GPH gravity fuel flow. I did see air bubbles coming down the clear drain tube, but they stopped after about a gallon and did not occur in the next gallon. I found no other problems, including checking the variable pitch prop control, which remained in the minimum pitch position.
The same surging occurred in a subsequent ground after about 45 seconds at 5400 RPM, matching the first flight experience.
I also have had some overheating - CHTs both high and a boilover at shutdown. I had attributed this to a too-long taxi test and too-long ground running on a hot day. Overheating did occur in the ground run mentioned above.
None of the experts I have talked to can explain this, or offer a connection between the two problems - except maybe that the engine is somehow running lean....
Anyone else come across this?
