Mesa, AZ, USA
N85TL
ADAMS DRAGONFLY
The pilot reported that, shortly after takeoff, the engine power decreased from about 3,100 to 2,500 rpm. The airplane continued to barely climb until it reached an altitude of about 150 ft above the ground. At that point, the airplane was unable to continue the climb or maintain altitude, and it began to descend. The pilot landed the airplane onto a field where it struck vegetation and came to rest in a bush about 1/2 mile from the departure end of the runway. During postaccident examination of the engine, the No. 3 cylinder had noticeably less compression, and a hissing noise was heard coming from the exhaust pipe. The cylinder was removed from the engine, and the piston head had a tan, sandy-colored appearance. Also, a light yellow band was observed around one-quarter of the circumference of the exhaust valve. Additional examination of the valve and valve seat revealed no defects; however, it did not appear that the exhaust valve was seated with consistent uniform contact; inconsistent uniform contact between the exhaust valve and the cylinder head valve seat would decrease engine performance.
On June 12, 2014, about 0615 mountain standard time, an experimental Adams Dragonfly, N85TL, experienced a partial loss of engine power after takeoff from Falcon Field Airport (FFZ), Mesa, Arizona. The private pilot was uninjured and the airplane sustained substantial damage to the left canard and elevator. The airplane was registered to, and operated by, the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed, and no flight plan was filed. The pilot reported that shortly after takeoff, the engine power decreased from 3,100 RPM to about 2,500 RPM. The airplane continued to barely climb until it reached an altitude of about 150 feet above the ground. At that point, the pilot was unable to continue the climb or maintain altitude, and the airplane began to descend. The pilot landed the airplane onto a field where it struck vegetation and came to rest in a bush about one-half mile from the departure end of the runway. During a postaccident examination by a Federal Aviation Administration inspector, the Volkswagen engine was rotated by hand. The inspector observed that there was noticeably less compression, along with a hissing noise coming from the engine's right side exhaust pipe. The right side valve cover was removed and it revealed that the number three cylinder was making the noise. The number three cylinder was removed and it was noted that the piston head had a tan, sandy colored, appearance. Also, a light yellow band was observed around one quarter of the circumference of the exhaust valve. Additional examination of the valve revealed no confirmed defects; however, there was no evidence that indicated the exhaust valve was seated with consistent uniform contact. The airplane's most recent maintenance was completed on February 1, 2013, about 11 flight hours prior to the accident. At that time, the cylinder heads were removed from the engine and replaced with stock Volkswagen cylinder heads, valves, rocker shafts, and valve covers. Since the maintenance occurred, the airplane flew three short flights and underwent various ground runs.
A partial loss of engine power due to a reduction in the No. 3 cylinder’s compression as a result of the exhaust valve not having consistent uniform contact with the cylinder head valve seat.
Source: NTSB Aviation Accident Database
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