When Sherpa’s design team set out to address some of the “small tweaks” as described by well known Alaskan bush pilot PAUL CLAUS, they had no idea the final results would be so rewarding. Sherpa’s flight test team had already pinpointed several flight characteristics that could use improvement, one which was accomplished when the turbine engine’s propeller cam was changed to a single engine version that allowed a more linear application of power. This issue was particularly important because spot landings depend on the ability to make instant power adjustments. Principal aerodynamicist, Gary Robinson of Leap Engineering, reviewed the airframe design and flight characteristics and advised the team that the existing design with the wing set with a 5 degree deck angle and monster size fowler flaps was producing excessive amounts of unwanted drag. His study concluded a need to change the flap air foil shape and nest it in a negative position when not deployed. This change would substantially reduce overall drag and make a major reduction of the disturbed air that was reaching the tail surfaces. His analysis also indicated that the cruise speed would increase and stall speeds would go even lower.
Preliminary results with the new flaps follow:
- True air speed increased to 155mph with a power setting of 393 HP at 4000feet
Estimate high altitude calculates at 184mph
The aircraft flew mid range on trim adjustments straight down the road and broke evenly when stalls were performed. Landing and take off distances were not measured but performance figures will exceed the outstanding numbers obtained before the new flaps were installed. Continued flight tests are scheduled this week; more accurate results will be posted and presented in video form.