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Flight Report: UL Power 350 In The S-7s



After a very successful show at Mt. Vernon Illinois, I headed to Telford Tennessee where Sam Kite had just started test flying an S-7S Courier with the UL Power 350. With a claimed 130 HP and a 68" Whirlwind prop, I was looking forward to validating their claims of increased performance.
Sam has a plush grass airstrip located just outside Telford; I noticed the Smoky Mountains off to the south would provide a scenic reference point. From the air Tennessee looked like a random scrambled of roads, small towns, and farms. It would be easy to loose track of Sam's grass strip in the sea of lush green turf. Thank goodness for GPS, but I think the local pilots thought my concerns for reference a bit amusing.
Within minutes of arrival, which was late in the day, I was taxing in out in the 350 equipped S-7S. The rumble of the engine was encouraging. It makes an impressive deep sound, and smooth at idle. I hoped this would be true at full power. My past experience with this engine was not encouraging; at full power there was a pronounced spike in the vibrations. Applying full power I learned the spike must have been specific to the airframe/prop combo (it was a competitors all metal low wing). Take off roll was short, the big 30" Alaska Bush wheels rolled easy on the soft grass. Airborne in less than 200 feet, I climbed aggressively, mostly because it felt right, and the VSI rang up to 1200 then settled on 1000 FPM till established at 3500 MSL. Watching the temps, everything was well under the limits, as Sam has said during the briefing, there was no heating issue.
Throttle response was instant, a trait of fuel injection and small displacement. Another delight was how steady it held RPM at various angles of attacks and in turbulence. It reminded me a lot of a larger Lycoming, where the torque is ample to hold RPM at a given throttle setting regardless of the prop loading. Smart throttle action, steady RPM, and a nice deep rumble made this a pleasant engine to fly. It was noticeably louder than a Rotax 912ULS, but well within what a good ANR head set can handle.

To call the 350 a true 130 HP engine in my opinion is a stretch. The reason is the torque flattens out at 2800 RPM and around 115 HP. Having maximum torque at 2800 is actually a good thing. It means you could go to larger props, 70" would be nice, 72" better. The engine could actually still turn these up to 2800, then you would see more performance, as much as another 40 FPM ROC perhaps. Flying against a factory built S-7LS proved out that engine does out climb the 100HP Rotax. It compared to the difference we saw when flying the 80 HP Rotax against the 100 HP. The gains in climb also support a 15 HP increase, which computes out to 24% increase in climb rate (800 FPM to 992 FPM at gross weight). No real speed increase was measured, mostly because we were not apples to apples on the test planes. The good news it was doing 102 MPH, with the 30" Alaskan Bush Wheels. There could be a decent cruise speed gain with the stock 6x800 tires.
Over all the engine may be a winner, it is now in the engines corner to prove its reliability. That sort of testing takes time. Our standard practice is to reach 200 hours without issues, once that is achieved then we feel comfortable about recommending an engine or creating a factory supported option. The following is a brief account of the testing done at Telford.

  • Service Ceiling: Climbed to 14,800. Average rate 525 to 10,000 with a gross of 1250 lbs. No heating issues, little RPM drop off, around 200.
  • Climb at Vx: 60 MPH IAS rate was 1200 lightly loaded, no heating issues.
  • Climb at Vy: 75MPH IAS rate was 800 to 1000, no heating issues.
  • Minimum power to maintain level fight: 3500.
  • Fuel Consumption: 5.8 GPH, this needs much more testing to be reliable.
  • Hot restart: NO issues.
  • Cold start: Notice cranking power of battery needs to be up, possible issue in cold weather.
  • Aerobatics and fuel injection: No power interruption experienced, or oil starvation, no sustained inverted flight performed.
  • Confirmation of Head Cooling: Covered cylinder heads and noted 25 to 30 degrees increase in CHT, still well within range, no oil temp increase. Note: design cowling to circulate some air over heads in final cowl.

Rans Designs Inc‎
4600 U.S. 183 Bypass
Hays, KS 67601
(785) 625-6346