Page 10 - Volume 15 Number 1

Same with Blackhawk. That’s why you see our technologies displayed together; and you see us at trade shows together.”
Edwin Black of Blackhawk said that the PT6A-135A conversion “never hurts performance, in any corner of the envelope; and those engines increase performance over most of it, particularly in high- altitude ops and cruise. The Raisbeck props allow the extra performance
of the engines to be realized down low and even on the ground.”
The Raisbeck/Hartzell props are 93 inches in diameter (up from 90 inches), and provide a big portion of the short-field improvement, with greater thrust and better braking action. (Ski also went to Cleveland brakes as part of his upgrade.)
BLR’s Marone described the advantages: “Brakes locked, max
avail torque; brakes off – make short-field rotation speed and pull the nose up. You get a quicker response, and you’re quicker to a positive rate of climb. The winglets add an effective 3.5 feet to wingspan – so you get more lift out of the same airspeed. He rotates at the same speed, uses less runway, and starts climbing sooner. Increase angle of climb and take off sooner – that’s a big safety improvement.
“Additionally, his practical Vx improves: rate of climb increases by something like 250 fpm at sea level. (It’s as much as 400 at altitude.) You get to cruise altitude faster, as soon as you’re cleared.”
He cited some numbers from memory: “Flight test data show that time to climb (depending on altitude) can be reduced 10 percent to FL200; if to FL250, reduction is 21 percent. Fuel burn, of course, is directly related, so you can save 5-15 percent in climb.”
Ski purchased the six-year- old C90B with the Raisbeck wing lockers and body strakes (lower rear fins) already on it. He added the Raisbeck props and other aero bits, noting that ram air was increased to the Blackhawk XP engines. For better wing performance at all angles of attack and loading, he was convinced that the BLR winglets would be the way to go.
Marone pointed out that each modification Ski incorporated made the other modifications more effective. “Everyone can argue about the order in which these modifications should be made. The answer involves the phase of flight you wish to improve. To improve the overall mission profile, you do them all at once. Runway, cruise performance, and ride quality – everybody wants them all, in varying amounts. You get more stability in roll from the winglets; better yaw stability from strakes. The result is better ride quality. In cruise you get a reduction in drag from winglets and extra speed (or
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JANUARY 2011