Innovative Solutions & Support (IS&S) announced new features to its ThrustSense autothrottle system today at NBAA VBACE, in addition to the news that Textron Aviation selected the IS&S autothrottle for the new King Air 260. The ThrustSense autothrottle for Pratt & Whitney PT6-powered airplanes is now a standard feature on the King Air 360 and retrofittable to the King Air 300 and 200 series. Other approvals include the Pilatus PC-12 (legacy and NG), and IS&S’s autothrottle and avionics suite are also installed in Eclipse Aerospace’s 550 very light jet, which IS&S continues to support.
The new autothrottle features will be optional for PC-12 and King Air installations and available next year in the first or second quarter, added via software upgrade. “We’re finding as time goes on and we’re flying with the autothrottle, [there are] additional features that further enhance it,” said IS&S founder and CEO Geoffrey Hedrick.
A new VNAV mode will allow vertical navigation using the autothrottle based on waypoint speed constraints in the Collins flight management system. If there is a speed restriction at a waypoint, the autothrottle will automatically reduce power to meet that speed when crossing that waypoint.
Guard mode protects against exceedances when flying with the autothrottle switched off. Some pilots might prefer to manage thrust manually, but ThrustSense will still monitor airspeed and engine performance. If the pilot chooses an airspeed or power setting that causes the engines to exceed a torque or temperature limit or the airplane’s speed to drop below a minimum, the autothrottle will automatically engage and set power to prevent the exceedance or to keep from letting the airplane fly too slowly. “You’ll never see it if you do the job right,” Hedrick said, “but it provides the safety protections that the autothrottle provides in automatic mode, in manual mode.”
Asymmetrical beta mode protection eliminates problems where in some situations a beta valve hangs up when both engines are at idle, causing high drag on the affected engine and a subsequent yaw at a critical time, for example, during landing. This protection feature monitors the engines constantly and if it sees asymmetrical thrust in this condition, it moves the beta engine out of beta mode and adds power so the two engines are again operating symmetrically.
With the torque matching feature, ThrustSense matches engine torque to eliminate asymmetrical thrust when the pilot sets power. This eliminates the distraction of trying to match torque when changing power settings; all the pilot has to do is set the power then leave the throttles alone, and in a few seconds ThrustSense balances the torque settings.
The clutchless design of the ThrustSense autothrottles allowed IS&S engineers to incorporate electronic detents at any point, and these can also “move” based on various parameters. For example, a detent set for a certain torque limit might switch to a temperature limit as the airplane climbs. Detents could also be set for overspeed, again, depending on the circumstances.
An “electronic brake” feature is available, and this acts much like a friction lock to prevent an uncommanded change in power setting. It can be overridden easily, but the value comes during busy times when an uncommanded movement of the throttles may not be noticed by the pilot.
A loiter and endurance mode will be available as an option, but this is targeted for special-mission aircraft and won’t be available for commercial aircraft. With this mode, the autothrottle optimizes the airspeed for minimum fuel flow to maximize endurance.
For multiengine applications like the King Air, the big benefit of the ThrustSense autothrottle is the LifeGuard Vmca mitigation, which automatically detects a failed engine in any phase of flight and manages the power on the good engine to prevent loss of directional control. IS&S has demonstrated this capability right down to stall warning in the King Air, with no tendency to roll thanks to the autothrottle’s management of power output on the operating engine.
Another significant benefit of ThrustSense in the King Air is automatic setting of power when engaged during takeoff. Typically a PT6 engine surges a bit as speed builds after the initial takeoff power setting, and pilots have to either pull back the power to avoid over-torquing or sneak up on the proper power setting, which is distracting and could end up making for a longer takeoff run. The autothrottle sets maximum power but then adjusts the throttles to maintain the correct setting as the ram air increases during the takeoff run, leaving the pilot to focus on flying the airplane.
To cut down on takeoff noise and improve relations with airport neighbors, some pilots reduce propeller rpm after takeoff, but it’s difficult to do so because the torque climbs when rpm is lowered, so a throttle adjustment is also needed. With ThrustSense, the pilot can simply pull back on the propeller levers and set a lower rpm, and the autothrottle adjusts power to stay within torque limits. This not only helps lower external noise but also makes for more comfort for passengers and pilots, especially because the precisely matched engines controlled by the autothrottles prevent any disharmonious noise from developing.