Moog’s Genesys three-axis rotorcraft autopilot for the Sikorsky UH-60A Black Hawk helicopter will soon get a fourth axis that incorporates full control of the collective. This safety enhancement, expected to get an FAA nod as soon as May, would build on the Genesys GRC autopilot supplemental type certificate (STC) issued in October for the helicopter.

Moog partnered with XP Services, a specialty helicopter modification company based in Tullahoma, Tennessee, on the Black Hawk GRC-4000 four-axis autopilot STC, which Moog will own. The modified Black Hawk with a full Genesys IDU-680 avionics suite and autopilot can be seen this week at the company's Verticon static display.

Two- and three-axis autopilots or automatic flight control systems are common in the helicopter world and are generally a minimum requirement for flying IFR, helping pilots manage pitch, roll, and—with the third axis—yaw. Adding the collective as the fourth axis brings new layers of capability to helicopters and, to make a simple comparison, is like having autothrottles in an airplane.

A helicopter’s collective control is essentially a thrust control, enabling the pilot (or autopilot) to adjust vertical velocity. This means climbing or descending or speeding up and slowing down, depending on which way the helicopter is oriented.

Fourth-axis Modes

With the fourth axis, the Genesys autopilot adds more hover modes, envelope protection features, and a level button to recover the helicopter to straight-and-level flight in case of imminent loss of control. This is especially useful for inadvertent entry into instrument meteorological conditions (IMC) situations.

An automatic leveling function in the three-axis system is enabled by engaging the stability augmentation system (SAS) with the SAS button on the HeliSAS control panel (HCP) or pressing the force-trim release (FTR) button on the cyclic for 1.25 seconds. The four-axis system adds a level button on the collective, and this accomplishes the same leveling function while also engaging the collective servo, which provides friction to keep the collective in the position that the pilot selected.

In addition to the three-axis autopilot modes, which include altitude hold, heading hold, navigation signal tracking, speed hold, and approach guidance, adding collective control as the fourth axis enhances those capabilities by adding hover modes. These include roll/pitch geo-position, yaw heading hold, and collective above-ground height hold. The yaw damper adds turn coordination in forward-flight mode.

With collective control, the four-axis autopilot can also fly terrain-avoidance maneuvers and bring the helicopter to hover at a point in space after flying an RNAV or other instrument approaches. The three- and four-axis autopilots include search-and-rescue patterns that can be programmed into the IDU-680’s integral FMS.

Sikorsky’s S-92 was one of the earlier helicopters demonstrating the benefits of four-axis autopilots in civil rotorcraft, and they are now slowly but surely moving into more civil helicopters such as Black Hawks and lighter machines. Garmin’s GFC 600H is available in four-axis configuration and is approved on the Leonardo A109 Trekker.

Thales and StandardAero have developed a four-axis autopilot for the Airbus H125. Genesys HeliSAS and autopilots have been installed on more than 1,000 helicopters, including the Airbus H120, H125, and H130; Bell 206B/L, 407, and 505; Robinson R44 and R66; and UH-60. Along with Metro Aviation, Moog is developing a four-axis autopilot for the Airbus EC145.

Analog SAS

Legacy UH-60A and L Black Hawks come equipped with a SAS and a flight path stabilization computer, and the Genesys autopilot retains the original SAS but adds its own SAS, which flies on top of and in parallel with the original SAS. The SAS always stays on during flight and is never shut down, even for training purposes.

Because the original SAS is an analog system, Genesys provides a digital interface between the SAS and the GRC-4000’s flight control computer. UH-60M models have a Collins autopilot and aren’t covered by the Genesys STC.

Replacing all the old electromechanical instruments and gyros (some are fiber-optic) and wiring and installing the Genesys avionics suite with autopilot results in 80 pounds less weight in the nose of the Black Hawk. If the customer’s helicopter is equipped with radar or other nose-mounted sensor systems, the weight and balance work, but if not, stainless steel ballast plates may need to be installed.

Besides being more capable, the modern avionics are more reliable and repairable; the older instruments and gyros are almost impossible to repair, although companies such as XP Services do make removed and working equipment available to operators that still need those products.

In the demo Black Hawk, the Genesys avionics include four eight-by-six-inch IDU-680 displays, dual GPS/SBAS, dual ADAHRS, dual digital radios (navcom), a dual-channel data acquisition unit, an integrated engine and crew alerting system with system synoptic pages, and an L-3 ESI-500 standby instrument. Each IDU-680 is interchangeable and includes synthetic vision system, integral FMS, TAWS, and TCAS. Two of the IFDs are isolated and can run off the helicopter’s battery in case of a complete power failure, plus the ESI-500 has its own internal battery.

Flying in the Black Hawk

For a first-hand look at the Genesys GRC four-axis autopilot, I visited XP Services in Tullahoma and joined test pilot JD Williams for a flight in the company’s Black Hawk equipped with the autopilot and a full Genesys avionics suite. The weather was clear but cold on a mid-winter day, with temperatures hovering below 20 degrees F.

Williams, flying from the left seat, started the Black Hawk’s Honeywell 36-150BH auxiliary power unit and turned on the most welcome heater, then started the two GE T700 engines.

After a short taxi, Williams lifted the Black Hawk off and climbed about 50 feet, then turned back towards the XP hangars and demonstrated a hover hold. He pressed the ALT button on the HCP to capture the altitude and pushed the upper portion of the HVR switch to set ALT:AGL and NAV:HVR mode; then the radar altitude height captured at 46 feet.

Moving the cyclic and pedals, Williams showed how perturbing the set attitude and height just resulted in a return to the original location and heading. I tried adjusting the captured altitude using the beep switch on the collective and gradually moved the helicopter to 50 feet while maintaining the same position.

Pushing the go-around button, the Black Hawk began a climb that settled into 80 knots and 800 fpm. Climbs can be done to a target vertical speed or airspeed, and these can be adjusted with the beep switch.

During the climb, Williams shut off the autopilot and banked to the left. I pushed the SAS button and the Black Hawk leveled off. He then demonstrated speed changes with the beep switch during the climb.

In addition to audible and visual TAWS alerts, the four-axis autopilot can automatically pitch up and add power to prevent controlled flight into terrain using just the radar altimeter when the helicopter is below 200 feet and not in approach or SAS mode. We weren’t able to demonstrate this feature that day because the condition to activate it wasn’t enabled in flight, but we did get the alerts, with “caution, terrain” that changed to “warning, terrain” as we flew toward a mountain ridge. This feature will be integrated with HTAWS in a future release.

Our next maneuver was setting up the RNAV 36 approach into Tullahoma Regional Airport. Williams selected vector guidance and we flew towards the final approach course at 120 knots, then slowed to below 80 for the glide path. Williams likes to fly the final approach at around 80 knots to avoid an aggressive deceleration when it’s time to level off.

He set the decision height at 100 feet and set the speed target at 87 knots, and as we descended along the glide path, highway-in-the-sky symbology backed up the glide path guidance. The flight path vector was pointed right at the runway end, giving us a view much like that on a head-up display.

As the Black Hawk neared decision height, it slowed to a hover, then Williams dialed the helicopter down slowly using the beep switch, first to 10 feet, then to three feet, where we should easily be able to see the landing spot even in inclement weather, then touchdown on the Black Hawk’s wheels. “If you’re in thick fog and you can’t see the runway [at this point], then you’re in trouble,” he said.

The full Genesys IDU avionics suite and four-axis autopilot will cost less than $3 million. XP Services is modifying a second Black Hawk with the avionics and autopilot as well as putting together a VIP version for a customer. It also has several contracts for the avionics and four-axis autopilot as well as interest from operators of the civil Black Hawk, the S-70.