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IS&S Autothrottle System for PC-12s and King Airs
by Dale Smith
available with dynamic VMCa protec- tion,” he continued. “ThrustSense for the King Air features our patented LifeGuard Protection system that dynamically adjusts the power set- tings on the ‘good’ engine based on the aircraft’s airspeed to help the pilot maintain directional control.”
As Grunbeck explained it, the ThrustSense Autothrottle controller collects all the aircraft’s current f light data, then automatically calculates airspeed, engine power and rudder- effectiveness during single-engine op- erations, and it can make its throttle adjustments. And it does it at up to five-knots-per-second intervals.
“Our real-time analysis of loss of control due to asymmetric thrust and sudden loss of airspeed showed that by modulating the remaining engine’s available thrust, all the pilot has to do is put their foot on the rudder on the side of the failed engine and the airplane will stay straight,” added IS&S Chair- man and CEO, Geoffrey Hedrick. “No matter how slow you go, the airplane will go straight and level to the stall. Of course, our ThrustSense Autothrottle will sense the loss of airspeed and
Okay, so you’ve lined your twin up for takeoff, ad- vance the throttles, V1, V2, rotate, and just after you’ve
stowed the gear, the left engine gives up. As you try to “rub your head and pat your tummy,” you reactively do your best to control the airplane and keep it flying. But, in your attempt to maintain altitude, the airspeed drops off and suddenly you’re on the wrong side of right-side-up.
Of course, this is the classic VMCa stall situation. As you’ll recall from your training days, VMCa stands for Velocity-Minimum Control (airspeed). That happens when a multi-engine air- craft suffers the failure of one engine. While trying to maintain altitude, the pilot pulls back on the yoke, dropping the airspeed to the point where they lose control of the aircraft.
In fact, when it comes to VMCa situ- ations, it can be easier to keep a piston twin right side up than a twin turbo- prop. Why? When you lose an engine on a piston twin, you pretty much are committed to an emergency landing.
But, with the turboprop’s added
power is a temptation to keep flying. So, when you lose power on one side and still have all that added horse- power lifting the opposing side, the asymmetric thrust makes the airplane that much more unstable in the roll axis. Even the best of us can easily get way behind the airplane in that situation.
Less Power to You
And if it’s a problem with a pair of 650 shp turboprops, it must be a huge issue with much more power- ful aircraft. And it would be if not for dynamic engine control technologies.
“I was an aerodynamicist on the F-14 Tomcat program for Grumman, which was one of the first aircraft to have dynamic VMCa protec- tion,” explained Tom Grunbeck, director of autothrottle programs for Innovative Solutions & Support (IS&S). “If you lose an engine on take- off, the ‘good’ engine will maintain a fixed limited power of approximately 25 percent of thrust so the pilot can maintain directional control.”
“Our new ThrustSense Autothrottle system is the only full-regime system
IS&S ThrustSense Autothrottle – modes of operation.
18 • TWIN & TURBINE / February 2021