Date: 202008
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 20
Light: Daylight
Aircraft: Ultralight
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Climb
Airspace: Class G ZZZ
Aircraft component: Reciprocating Engine Assembly
Component problem: Improperly Operated
Reporter organization: Personal
Reporter function: Single Pilot
Reporter qualification: Flight Crew Private
Human factors: Training / Qualification
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Maintenance Action; General Flight Cancelled / Delayed
Contributing factors: Equipment / Tooling; Human Factors; Incorrect / Not Installed / Unavailable Part; Procedure; Aircraft
Primary problem: Procedure

Narrative: I was conducting the first flight of Aircraft X; a type of aircraft that used to be known as a 'fat' ultralight. I had made extensive modifications; mounting a 37 h.p. 1/2 VW engine instead of a two-stroke type of engine; which is what this particular aircraft usually is equipped with. Due to my incorrectly setting the digital tachometer; I have no way of knowing what the actual takeoff and climb RPM's were; but once I was airborne; I quickly discovered that the airplane simply would not climb sufficiently. I was barely able to clear several low tree-lined hills and slowly make my way back to the airport at very low altitude. The airplane actually stalled once; but I was able to recover. A relatively routine landing followed; although I landed on the nearest available runway (X) instead of the one I had taken off from (Runway Y). Even though the wind was out of the south; it was light; so the runway change didn't create any additional problems; I just wanted to get on the ground as quickly as possible.Considering the many poor choices/decisions I made; the outcome should have been quite different and far more costly. Here are a few well-deserved self-criticisms: 1. In retrospect; I gave in to a form of 'get-there-itis;' in that I perceived pressure from the inside and the outside to make the first flight. I was definitely feeling quite a bit of apprehension in advance; as this would be the first time I'd ever flown an airplane I had never flown before (or; in the case of this particular airplane; anyone had flown before) without an an instructor alongside; and I put a lot of pressure on myself to just get the first flight over with and go from there. After initial high-speed taxi testing; I realized that several improvements needed to be made -- better brakes; an externally-mounted com antenna; and a better way to monitor the fuel system -- but these delayed that first flight several more weeks and increased my impatience. And; of course; the outside pressure came from others who were frequently asking me when the first flight would be.2. As soon as I realized that the tachometer was incorrectly configured; I should have returned to the hangar and taken care of that issue right away.3. I should have conducted a full-power ground test of the engine before the first flight; which I did not do. This would have alerted me to the tachometer issue mentioned above; and might have indicated precisely how much power the engine was actually producing; which; for whatever reason; isn't enough for this aircraft as it is at the moment. 4. I should have had greater knowledge in advance of the terrain along my flight path; and waited for another day when the winds would have allowed me to conduct the first flight in the direction of flat; open farm ground instead over more hilly terrain with trees.5. I let the fact that this particular airplane design is neither sophisticated nor high-performance lull me into taking 'shortcuts' in pre-first-flight testing. If there is anything even remotely positive I'll take away from this incident; it's that I was able to perform in the midst of the crisis itself. This was the most serious danger I'd even encountered in my flying 'career;' but I didn't panic; remembered my training and kept flying the airplane.




Synopsis: Pilot reported an incorrect tachometer and loss of power during initial climb; resulting in an air turnback and precautionary landing.