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Block 2 CH-47F to Tackle Payload Shortfalls

CH-47F

This article first appeared in Aviation Week & Space Technology.

Gaining weight with age is a familiar curse, and after 50 years of service the Boeing CH-47 Chinook can no longer carry the loads it did when the heavy-lift helicopter was first introduced. With weight growth averaging 100 lb. a year, the U.S. Army wants to reset the clock to take the tandem-rotor Chinook well into its second half-century.

Boeing and the Army are working to define a "Block 2" upgrade that would be introduced after 2020, once all of the service's CH-47Ds have been replaced by new-build and remanufactured F models. "We are really after payload improvements," says Col. Bob Marion, cargo helicopter program manager. The latest CH-47F has boosted international sales of the Chinook, and the Block 2 program could keep the line rolling into the next decade.

"The D to F upgrade introduces a machined airframe and digital cockpit [and flight controls], which are real game changers for the Chinook fleet," he says. "The new frame improves sustainment and the cockpit enhances controllability and situational awareness. The next thing is payload improvement -- we need to take weight out of the aircraft."

Work to define Block 2 is getting underway as the Army prepares to award Boeing the second and final multiyear procurement contract for the CH-47F. Expected to be signed in May, the five-year contract for 155 helicopters, plus 60 options for export aircraft, will save $810 million, or 19.2%, over year-by-year contracting, says Marion.

Many of the modifications added post-production to Chinooks built under the first multiyear award will be incorporated on the assembly line under the new contract. Additionally, the second multiyear agreement will see the introduction of the first upgrades planned for Block 2, including an advanced rotor blade that will increase lifting capacity by almost 2,000 lb.

"Block 2 would follow Multiyear 2, and we are looking at what [non-recurring development] work we need to start executing now," says Marion. "The key thing is the JLTV [Joint Light Tactical Vehicle, the planned replacement for the Humvee]. As it goes through development, we have to ensure that the CH-47 can carry a combat-equipped JLTV and crew."

The Army's goal for Block 2 is to make sure the post-2020 Chinook can carry a 22,000-lb. payload 50 nm., with 4,000-ft./95F high/hot hover performance. "We are still working toward that, and in the future will look to increase that to 6,000-ft./95F," he says. Today, the CH-47F can carry 16,000 lb. in 4,000-ft./95F conditions, "and we are adding 100 lb. a year [of airframe weight]."

airframe, cockpit and flight controls, it added empty weight. Other modifications, such as armor, engine inlet particle separators and exhaust infrared suppressors, as well as added survivability equipment such as laser missile jammers, have also increased weight. Block 2 will seek to "buy back" lost payload by both boosting lift and trimming weight, Boeing says.

"We are working with Tradoc [Army Training and Doctrine Command] on the requirements for the future Chinook and the lifting capacity needed after 2020," says Lt. Col. Joe Hoecherl, CH-47 modernization product manager. "We are also working with Boeing, doing initial development with the focus on payload, primarily JLTV." The upgrade is expected to be fiscally constrained, so trade studies are under way to identify potential changes and determine what will be affordable.

Because of budget limitations, the Block 2 is expected to involve remanufacturing existing F-model Chinooks, a process some airframes already have gone through twice, having been built as CH-47As then rebuilt first as D models, later as Fs. The D-to-F upgrade has modernized the airframe and avionics, so the Block 2 program is focusing on the dynamic system and other areas of the aircraft.

One of the first pieces of Block 2 is the advanced Chinook rotor blade (ACRB), which is already under development and planned to be cut into production during the second multiyear contract, in late fiscal 2016. Drawing on experience from the canceled Boeing/Sikorsky RAH-66 Comanche, the ACRB has new airfoil sections, increased twist and a redesigned tip. This increases lifting capacity by more than 1,900 lb.

Blade length is unchanged and no detrimental loads are introduced into the rotor hub or controls, says Boeing, allowing the hub to remain unchanged and enabling existing Chinooks to be upgraded, which is important as there will be approximately 400 aircraft in the field by the time the new blade becomes available.

It is expected the engines will be upgraded, with Honeywell's T55-715 turboshaft offering 20% more power than the 4,900-shp -714A now powering the CH-47F. "We are looking closely at increasing the power capability," says Hoecherl. This would require modifications to the combiner and nose gearboxes and, unlike the ACRB, would come at the cost of extra weight. So Boeing is looking for modifications that will remove weight from the Chinook.

Foremost among these is a new fuel system derived from that used in the special-operations MH-47G and Canadian CH-147F variants. Instead of three tanks per side -- forward, center and aft in the fuselage sponsons, each with their associated pumps and plumbing -- there would be a single tank. "There are two main and four auxiliary tanks, so there is potential to consolidate them as eliminate pumps and plumbing," he says.

While the MH-47G and CH-147F have "fat" sponsons housing extended-range tanks with twice the fuel capacity, Boeing is investigating a "skinny" single-tank solution for standard Chinooks -- with the potential that eliminating the extra tank hardware could allow the sponsons to be slimmed down to reduce download from the rotors and so increase lifting capacity.

Another expected element of Block 2 is the active parallel actuator system (APAS), a next-generation version of the CH-47F's digital advanced flight-control system. APAS would provide tactile cueing for pilots and improve rotor torque management. On today's Chinook, pilots do not know the exact split of torque, and therefore lift, between the fore and aft rotors so a safety margin is built in. APAS would reduce that margin and allow more of the rotor system's performance to be used.

"We have been flying with the same torque split since the Chinook was designed," says Marion. "In Block 2 we will measure torque precisely at the rotor head." APAS would use the sensors to provide tactile feedback on torque margin to the pilots via "soft stops" on the flight controls. The system is planned to be retrofittable by removing the existing force-feel pallet and installing the APAS.

Another potential change is incorporation of the redesigned electrical system developed for the CH-147F, a hybrid between the CH-47F and MH-47G now in flight-testing. The new system has increased capacity -- three 60 kVA generators -- to power additional survivability equipment and provide addition growth capability. "We always want more, and cleaner power," says Hoecherl.

By beginning work on Block 2 now, the Army is hoping to keep the Chinook line rolling beyond the end of the second multiyear contract. Current planning is for the last CH-47D to be modernized to an F in 2019, and the first aircraft to be inducted for Block 2 remanufacturing in 2019-20, budget permitting.

The second multiyear contract, meanwhile, will provide the Army with some flexibility to manage budget cuts. The base contract is for 121 remanufactured and 34 new-build CH-47Fs for the Army plus options for 60 aircraft, principally for foreign military sales (FMS). Deliveries are to begin in April 2015, but bridging a gap between the first and second multi-years is a contract for 14 helicopters, the first to be built in Multiyear 2 configuration, to avoid a break in production.

Only one of the Chinooks under the bridge contract is for the Army -- a "production-representative Multi-Year 2 aircraft" -- and will be used to reduce risk, says Marion. Configuration changes from the first to the second multiyear award center on incorporating on the assembly line approximately 30 modifications now performed post-production. These include installing the roller-floor cargo on/off loading system, an health-monitoring system and some rewiring to tackle avionics obsolescence.

Because any FMS aircraft built under the second multiyear contract will be in the same configuration as those for the U.S., the Army has the contractual flexibility, if there are further budget cuts, to move FMS helicopters into the base 155-aircraft program and still achieve the targeted cost savings, Marion says. Of the 60 option aircraft, 16 "are already spoken for by FMS customers," including Turkey and the United Arab Emirates, says Lt. Col. Reese Hauenstein, CH-47F product manager.

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