NASHVILLE, Tenn. — The U.S. Army has decided to shelve its Advanced Chinook Rotor Blades it was developing as part of the Boeing-manufactured CH-47F cargo helicopter’s latest upgrades due to issues that cropped up during testing, according to Brig. Gen. Robert Barrie, the program executive officer for Army aviation.
In 2020, the service was dealing with excessive rotor blade vibrations from the ACRBs as it headed into a limited-user test scheduled for early 2021, so the service decided to cancel that test until it had worked through the issues.
A report from the Pentagon’s chief weapons tester noted vibrations present in ground, hover and forward flight that could pose “safety of flight risk.” Boeing pushed back against the claim it posed a safety risk, but the company did acknowledge vibration issues.
“We’re working closely with the Army on a mitigation system or an adjustment to existing mitigation systems to account for that different vibration frequency,” Andy Builta, Boeing vice president and H-47 program manager, told Defense News a year ago. “It is in no way a safety of flight risk, but it is an issue that needs to be addressed going forward.”
The company may adjust or add dampeners to address the problem, he said. “This is a low-risk, well-known activity that we’ve done across multiple platforms.”
The Block II variant returned to some testing in the spring of 2021 and began to log flight hours. The company said the new rotor blades proved the aircraft can handle an additional 2,500 pounds of lift.
But last fall, the Army decided not to move forward with ACRBs. However, the service is proceeding with the rest of the planned upgrades for the helicopter, Barrie said at the Army Aviation Association of America’s annual conference on April 4.
“As we began developmental flight tests on the blade,” Barrie said, “there were two issues that we had. There was a vibration issue and then there was an aft rotor stall. So as the retreating blade on the aft rotor system swept back, there were stall issues that were created, which increased the stress on the rotor system.”
The two issues combined “and the inability to have an affordable way through — that led the Army to make a decision to stop … and shelve that portion of the development,” he said.
The new rotor blades would have given the Chinook another 2,000 pounds of lift at high altitudes in hot temperatures, “so without that there is some detriment in our ability in the high/hot configuration to meet that specific part of the requirement,” Barrie said.
The remainder of the upgrades are on track, such as the improved transmission — which gives the Chinook an extra 4,000 pounds of lift capability and a 10% increase in torque — some reliability improvements on the rotor head, and an integrated single-fuel system that adds another 100 gallons of fuel capacity.
“The Block II brings a lot of capabilities to the warfighter even without the ACRBs,” Heather McBryan, Boeing’s director of business development for cargo and utility helicopters and future vertical lift programs, said at the AAAA event during a media roundtable.
The Army is working to fully qualify the remainder of the Block II upgrades through engineering and manufacturing development, and the efforts are resourced through 2023, Barrie said.
“Our focus is on qualifying the Block II system,” Barrie added, “without the blade.”
The Army is also continuing to field the Block II version to Army special operations units. The service decided in 2018 not to buy the version of the aircraft for the active force in order to focus funding toward future vertical lift modernization efforts.
But Congress disagreed with that move, funding five Block II variants for the active force in its fiscal 2021 appropriations. It continued to provide additional advance procurement funding in FY22 as well.
The Army awarded Boeing a $391 million contract to build the first lot of five CH-47F Block II aircraft for the active force in the fall of 2021, as the service and the company continued to address technical issues.
Boeing announced Monday it had begun production of the first Lot 1 aircraft with the start of a teardown process of a Block I Chinook to salvage reusable parts that McBryan said is a cost-effective method.
Deliveries of the first aircraft under contract will begin in 2023, she said.
If the current timeline stays, the Army would field the first unit with CH-47F Block II aircraft in 2025.
The Army did not fund the CH-47F Block II for the active force in the FY23 budget request released March 28. The service has said it plans to make a decision on whether it will buy Block II for the regular Army in 2023.
Jen Judson is an award-winning journalist covering land warfare for Defense News. She has also worked for Politico and Inside Defense. She holds a Master of Science degree in journalism from Boston University and a Bachelor of Arts degree from Kenyon College.