U.S. Army buys first Chinook Block II aircraft without advanced rotor blades

By Dan Parsons | October 12, 2021

The U.S. Army recently awarded Boeing a $136 million contract for the first four CH-47F Chinook Block II aircraft, but the service has no intention of purchasing the problematic advanced rotor blades at the center of the upgrade package.

“There is not an intent, right now, for the Army to proceed at all with the ACRB,” short for the Advanced Chinook Rotor Blade, Brig. Gen. Rob Barrie, the Army’s top aviation procurement official, told Vertical Oct. 12 at the Association of the U.S. Army’s (AUSA’s) annual conference in Washington, D.C.

Through various component upgrades, Block II is designed to increase the CH-47F’s maximum gross weight to 54,000 pounds (24,500 kilograms). Improvements include an enhanced drive train and rotor system — delivering 10 percent more torque capacity — designed to operate with a more powerful drop-in engine that is in development. The aircraft’s fuselage, fuel system and wiring also are upgraded with stronger, more reliable parts. 

Perhaps most important is the introduction of Boeing’s ACRB. The all-composite blades feature a swept-tip design that should provide an additional 1,500 lb. (680 kg) of lift.

The new blades hit a snag during testing when Army pilots reported that they produced excessive vibrations on the ground, in hover, and forward flight that an Army report determined “may cause a safety of flight risk.” Barrie said the composite blades also created stall on the aft rotor system during testing.

“Because of those two things and the additional work that would be required and the additional cost and additional weight of a vibration system, the Army said we’re not going to proceed with the ACRBs and that’s why it wasn’t included in the configuration” of the recently purchased Block II aircraft, Barrie said.

Boeing insists there is no safety of flight risk and continues to test the aircraft with the ACRBs installed in Mesa, Arizona. Technically, the Army has the option to fund the new blades if and when it decides they are worth the effort and cash.

The recently awarded Lot I contract includes the four aircraft themselves and unfunded options for ACRBs pending a limited user test by the Army initially scheduled for March. That testing, in which Army pilots and Boeing engineers would address the vibration issues specifically, has not been rescheduled. If the Army does not fund the new blades in time for delivery of the first four Block II Chinooks, they would be equipped with standard fiberglass blades, said Andy Builta, Boeing vice president and H-47 program manager. 

“The ACRBs would be a different award, an exercise of an option at a later time,” Builta explained. 

Boeing has completed 800 hours of testing on the three engineering and manufacturing development (EMD) Chinooks built in Philadelphia and flown to Mesa, Arizona, where they continue to fly. Most of that testing and the cross-country hop was performed with the ACRBs installed, Builta said.

If and when the Army decides to launch limited user test of the new rotor blades and then fund their production, the service and Boeing will still have to work out a solution to the vibration issue, which Builta said was not a surprise. When designing a new helicopter or a new rotor system for an existing helicopter, it is usually necessary to collect vibration data before developing and tuning a dampening system to the specific airframe-rotor configuration, Builta said. 

“That vibration issue was tied to a difference in vibration resonance and frequency associated with ACRBs and the new airframe,” Builta said. “To get the Army moving forward with ACRBs, that would still need to be addressed. It’s a dampener, so just like any other helicopter that has a vibration-dampening system, you need to develop a dampening system tuned to the specific frequencies based on the vibrations we’ve captured throughout flight test.”

After years of back-and-forth with the Army, the recent production contract is “a huge milestone for the program,” Builta said. Block II has for several years been in limbo as the Army ironed out its heavy lift requirements for the next several decades and seesawed with Congress on whether to fund the upgrade program for the 400 CH-47Fs in the active force. 

“Going into production on the CH-47F Block II is key to being able to get that aircraft and its capability out into the field in terms of its ability to deliver more payload faster, farther and smarter,” Builta told reporters at the AUSA conference.

Deliveries should begin in late 2023 or early 2024, Builta said. The $136 million contract is for the first four CH-47F Block II aircraft for the active service, with options for a fifth and ACRBs for all five. Separately, the Army awarded Boeing a $29 million advanced procurement contract for the second production lot of CH-47F Block II aircraft.

“We are starting to look at not just the Lot I deliveries, but starting to put the industrial base on order for Lot II,” said Heather McBryan, Boeing’s director of global sales and marketing.

Boeing already is on contract to build 24 MH-47G Block II aircraft for U.S. Special Operations Command and continues to deliver those helicopters “on a regular basis,” Builta said. The first was delivered in September 2020.