AVIONICS
Helicopter Stability from Genesys Aerosystems
The most basic rule of flying a helicopter is to NEVER take your hand off the cyclic control stick. That is good advice since helicopters are generally not stable flying platforms. Today, however, there are many helicopters that have helicopter stability augmentation systems (HeliSAS®
autopilot systems that allow the pilot to do just that — take their hands off the cyclic stick and the systems work to hold the aircraft in the pilot’s desired flight attitude. Genesys Aerosystems in Mineral Wells, TX, makes many
different systems for the aviation marketplace, including HeliSAS and autopilot systems for helicopters. Earlier this year, it announced that its HeliSAS and autopilot systems were available to retrofit into the Robinson R-44 helicopter. Before taking a look at the Genesys Aerosystems HeliSAS and autopilot, let’s refresh our memories on just what these systems are designed to do.
HeliSAS
The engaged SAS mode supplies short-term attitude and attitude rate stabilization for use in hands-on flying. It stabilizes the helicopter against outside disturbances and augments or helps pilot cyclic control input. The SAS mode is designed so that pilot-controlled motions (pitch and roll) are enhanced while helicopter motions caused by outside disturbances are counteracted. This mode of operation improves basic helicopter handling qualities. When helicopter motion (a wind gust) is detected, a stabilizing control signal proportional to the amplitude and rate of the motion is generated in the SAS computer and routed to the appropriate actuators. SAS is generally used during low and slow maneuvering where the pilot might be making constant attitude changes. SAS is flown hands on by design.
Autopilot
As complex as some of today’s autopilot systems have become, they all can be narrowed down to providing at least one main function: stability. In essence, the autopilot takes care of the routine repetitive tasks and allows the pilot the ability to concentrate on other flight concerns. Today’s helicopter SAS/autopilot systems can be two-,
three- or four-axis systems. A two-axis system is typically just a SAS for cyclic pitch and roll control. A three-axis system provides pitch, roll and yaw axis stabilization around the pilot’s desired attitude and heading reference. In a four-axis system, there is also a collective axis, where the autopilot provides collective (power) control. These systems are considered to be limited authority systems in that for short-term external
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R. Fred Polak | Editor in Chief
disturbances, the cyclic control does not change position. For long-term disturbances (like change in CG or fuel burn), the cyclic control is allowed to move to a new position which extends the authority of the autopilot. With the autopilot engaged, the pilot can remove his or her hand from the cyclic control stick and the aircraft will maintain its position. Many helicopter systems today are a combination of SAS and autopilot applications in one flight control computer (FCC). Now that we have reminded ourselves about SAS and autopilot systems, let’s take a look at the Genesys Aerosystems HeliSAS. Our interview is with Robert DuRall, senior manager of product support with Genesys Aerosystems.
HMM – Since Genesys Aerosystems might not be a name
that everyone is familiar with, how about giving us some background on the company? DuRall – Genesys Aerosystems is a culmination of
two companies: S-TEC, a leader in general aviation fixed- wing autopilots for over 35 years located in Mineral Wells, TX, and Sierra Flight Systems, later named Chelton Flight Systems. Chelton Flight Systems is a leader in synthetic vision electronic flight instrument system (EFIS) and wide area augmentation system (WAAS) operations for over 15 years, and was originally located in Boise, ID. Both companies were purchased by COBHAM, and in 2008, Sierra (now Chelton) Flight Systems was combined with S-TEC and relocated to Mineral Wells, where both companies are co-located in the same facility. In April 2014, the combined companies were purchased through a management buy-out and became Genesys Aerosystems, Inc. Chelton Flight Systems began work with a former NASA
engineer in 2007 to provide an affordable, light-weight rotorcraft SAS with autopilot functions for the Part 27 VFR market. This work continued when Chelton was relocated to Mineral Wells and has resulted in STCs for the Robinson R44, Bell 206, Bell 206B/L, Bell 407, Airbus AS350/355 and EC-130 airframes. Additional airframes are proposed or are currently in the works as of this writing. HMM – What are the HeliSAS functions, and what size helicopter is it designed for? DuRall – It is called HeliSAS and is a fully-integrated SAS with autopilot functions designed for the Part 27 VFR market. That is the helicopter market for helicopters weighing less than 7,000 pounds maximum takeoff weight, and carrying less than nine passengers. The system is configurable to be SAS only (basic leveler) or can include an autopilot. Basically, the HeliSAS is intended for all small and midsized helicopters with hydraulic assistance.
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HelicopterMaintenanceMagazine.com December 2014 | January 2015
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