Collaboration enhances success of CH-53K flight control system

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A full-authority digital flight control system is one of the many impressive capabilities that sets the CH-53K King Stallion heavy-lift helicopter apart from any other heavy-lift aircraft.

“Full Authority” means that the FCS provides all aircraft movement – not just to supplement the pilot for stability.

A digital fly-by-wire FCS is an electronic flight control system combined with a digital computer that replaces mechanical control systems in an aircraft. It makes the aircraft easier to handle in degraded visual environments at gross weights up to 88,000 pounds. The CH-53K is currently cleared for 27,000 pounds of external lift, but will eventually be cleared for 36,000 pounds.

“The CH-53E/Ds were much harder to fly,” said retired Lt. Col. Lucas Frank, formerly of Marine Operational Test and Evaluation Squadron 1 (VMX-1). “And the ease of piloting, the flight control system is probably the biggest game changer for the 53 community. We’re not used to that kind of stuff.

The high performance of the FCS is a direct result of the ongoing collaboration and cooperation between subject matter experts within the Naval Air Systems Command Heavy Lift Helicopters Program Office (PMA-261), the Integrated Test Team and the engineers flight control system design from Sikorsky, a Lockheed Martin company.

For pilots, FCS provides more predictable and stable control responses to improve mission safety and efficiency.

For maintainers, FCS reduces complexity by eliminating conventional helicopter hardware like mixers, push rods and tail rotor cables, while improving diagnostic capability and maintenance time.

For members of the CH-53K ITT, the most impressive FCS advantage is how it can be used to achieve future capabilities and quickly correct identified deficiencies.

The CH-53K flight test program uses four CH-53K engineering development aircraft. In these four test aircraft, the fly-by-wire FCS allows the use of adjustable parameters called flight test variables, giving the test team the ability to improve the control characteristics of the aircraft. plane.

A CH-53K King Stallion aircraft plugs a refueling drug behind a KC-130J in-flight refueling tanker during a test over the Chesapeake Bay in 2021.

“FTVs are an extremely powerful tool,” said CH-53K deputy program manager for testing Craig Merriman. “It allows us to test design fixes on aircraft between major software releases.”

According to Merriman, this means the team can continually improve the FCS software. If a problem is identified during the flight test, the FTVs can be adjusted within a pre-approved range, providing pilots with the ability to assess the correctness of the aircraft in the intended environment. These FTVs are then integrated into the next major version of the FCS software.

“With every major FCS software update, baseline aircraft performance increases significantly due to the incorporation of these verified FTVs,” Merriman said.

The CH-53K FCS is a work in progress and a team effort. When issues were identified during flight testing that required rapid resolution, the entire team worked together from locations in Florida, Maryland and Connecticut.

An example of the team’s success was fixing air data flaws during in-flight refueling. During initial in-flight refueling tests on the CH-53K in 2018, the FCS showed flaws due to turbulent air data created by the tanker aircraft. The FCS air data computers were reading large pressure fluctuations, leading the FCS to believe that the air data computers had failed.

With the shortcoming identified by the flight test team, design engineers began developing FTVs and performing analysis. The FTVs were evaluated in the Flight Controls System Integration Lab, a Sikorsky-owned lab in Stratford, Connecticut used by ITT. FCSIL is a representative CH-53K aircraft laboratory and simulator with triplex redundancy – a representative flight control system.

The facility is used to simulate aircraft behavior and evaluate aircraft performance against newer FTVs. The facility is also used to verify the safe loading and unloading of FTVs to the software.

Following FCSIL testing, the NAVAIR Airworthiness Group reviewed the analysis and granted clearance to fly the FTVs. With this approval, the test team loaded the FTV onto the aircraft. The fix has been tested without degradation, enabling the fleet aerial refueling operations that are used today.

“It’s a very intuitive flight control system,” Frank said, “and it blends really well with the pilot and the computers. It lets you bypass the computer. And then the second you stop replacing it, the computer takes over without any further driver intervention. This is probably the biggest game changer for our community.

The use of FTV has been critical in addressing FCS shortcomings discovered during flight testing and will be used to enhance the already successful electric flight system as the CH-53K takes on additional capabilities in the future.

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