HeliTrak has created a Federal Aviation Administration (FAA)-approved aftermarket device to help pilots react to an engine or driveline failure in a Robinson R22 or R44. The Collective Pull Down (CPD) lowers the collective independent of pilot action when a low-rotor rpm situation is detected. According to the Flight Safety Foundation, it takes pilots two to three seconds, on average, to recognize a problem, and then an additional four to six seconds to react. The CPD is designed to virtually eliminate this delay.
It works by sensing a low-rotor rpm occurrence using the aircraft’s existing low-rotor rpm warning system, and activates in less than a second to reduce the collective to the full down position — achieving this in less than three seconds.
Vertical was recently given the opportunity to complete a demonstration flight in a CPD-equipped Robinson R44 with Ray Debs, HeliTrak’s demonstration pilot and vice president of engineering, to experience firsthand how the device works.
At first glance, the installation is very well integrated into the aircraft. In the cockpit, there is a small toggle switch forward of the collective to select and reset the CPD, and an amber caution light on the panel to signal whether it is on or off, much like the governor light. On the aft end of the collective, there is an anchor for the actuating cable that links the CPD to the collective lever and collective friction arm. The rest of the device is located underneath the panel below the collective and is hidden from sight as well as interference from any loose objects in the cockpit.
Testing the system before takeoff showed that the CPD activated normally in conjunction with the low-rotor rpm system check that is standard in a Robinson product. Purposely drooping the rotor rpm to test the system resulted in the CPD lowering the collective completely to the down stop in less than a second. The force the CPD employs for this is adjustable from 5.5 to 10 pounds; the demonstration aircraft was set on the heavier end of the range at nine pounds. After a CPD activation, you have to manually reset the device before it can be considered “armed” and ready for use once again. This check is part of the preflight procedure. The CPD does not manipulate the throttle in any way — that task is still accomplished by the pilot.
In level flight, normal autorotation entries were done manually to demonstrate the autorotational characteristics of the R44 under prevailing conditions. On the day of the flight test, slight aft cyclic input was necessary to set the proper glide pitch attitude, along with an increase in collective to maintain rotor rpm in the green arc. With the CPD armed and ready for activation, rotor rpm was drooped by throttle manipulation to the point of warning system activation (97 percent rpm). At this, the CPD activated, lowering the collective to the down stop. With the slightly heavy nine-pound pull, it felt as if the CPD was an attentive flight instructor helping you initiate an auto; not strong enough to pull the collective out of your hand, but positive enough to not be confused for something else. CPD activation was demonstrated from an out of ground effect hover up to 90 knots indicated airspeed. In all cases, rotor rpm was maintained on entry to the auto, with pilot input then being needed to manage airspeed and rotor rpm during the glide portion. A maximum glide distance autorotation configuration was demonstrated as well. After entry, rotor rpm was stabilized at 90 percent. The CPD activated for three seconds, then stopped. Counteracting CPD activation was a simple matter of holding the collective up while putting the aircraft into a max glide configuration.
In hover operations, the CPD can be overridden easily when necessary. While in a two- to three-foot hover, rotor rpm was drooped down to activation of the low rotor light and horn. At CPD activation, it was a simple matter of holding the collective up to prevent ground contact for the three-second timeframe of CPD activation. During hovering autorotations it was again a simple matter to counteract CPD down collective motion while timing the up collective pull to cushion the touchdown.
Overall, the CPD should prove to be a very useful device for safety. It is light (less than two pounds installed), does not take up any storage space, is very low maintenance, is relatively inexpensive (under US$10,000 for the R22 and under US$15,000 for the R44, plus installation), and easily overridden by the pilot when necessary. HeliTrak worked very hard for a simple design, ending up with something the company characterizes as a “1/2 axis autopilot.” After experiencing the CPD firsthand, it felt very similar to the stick shaker/stick pusher devices found in the fixed-wing world; safety devices that work to assist the pilot while being unobtrusive during regular flight regimes.
In addition to the CPD, a future product to look for from HeliTrak will be an autopilot for the Robinson R44. Initially planned to be two-axis, it will support expansion to three- or four-axis and include low-G detection and upset recovery. It will also be linked to the CPD, allowing further integration for safety of flight. Certification is expected by the end of 2018.
