By Geoff Fein
The Navy is making design changes to its CH-53K heavy-lift helicopter to adjust the center of gravity and to switch to a new rotory damper that will continue to provide increased reliability for the aircraft, a Navy official said.
Additionally, the Navy is continuing to trim down Sikorsky‘s [UTX] CH-53K, looking to remove weight where it can, Capt. Rick Muldoon, CH-53 program manager, told Defense Daily in a recent interview.
“First of all, weight is an issue that every platform ever designed has to deal with and we have been struggling with the weight issue for a year or more,” he said. “We are making continuous progress. I get a weight update every week, and we’ve been whittling away at the planned value profile, getting closer all the time.”
There are still a couple thousand pounds of weight improvement planned, Muldoon added. “If I can get a quarter of that, I am probably in pretty good shape. So, from that perspective, I think we are headed in the right direction.”
Even if the weight reduction efforts fall short, Muldoon pointed out that the helicopter has some inherent performance, beyond what was planned for, because of the General Electric [GE] 381B engine and rotor blades.
“So when, and if, we feel we are up against a wall on weight, we could execute some changes in that regard and basically up the performance of the aircraft against the ORD (operational requirements document) requirements,” Muldoon said. “So there is some inherent capability we didn’t anticipate, which is a good thing. So we’ve got some margin there from the aircraft performance perspective.”
One area that crept up on engineers was a center of gravity problem. Muldoon noted, however, that it’s better to discover this now than later when an issue like that becomes harder to fix.
The center of gravity issue first surfaced during a January review. “It was enough that it set off some alarms for us and we were concerned, and we’re working it.”
The center of gravity shifted aft with the fuel burn on certain mission profiles, Muldoon explained.
“It wasn’t all missions, it was just a small subset of the missions where, as you burn fuel, the center of gravity started progressing aft to the point where it was outside our comfort zone,” he said.
What the Navy did was stop its efforts and focus on what, from an engineering team perspective, Sikorsky and the Navy could do together to remedy the issue before it got worse, Muldoon said.
“Because when you are constantly making weight changes it effects the center of gravity,” he added.
The Navy and Sikorsky took several steps resulting in a number of things going into the final answer. A couple of big ones, however, were changing the main mast tilt and moving some avionics forward, Muldoon said.
The main mast in the CH-53K design has a 5 degree tilt to it, he said. “So we are taking some of that tilt out and what that is going to do for us is both help the attitude of the aircraft and the center of gravity.”
“Additionally, we are moving some avionics from aft positions to the forward end of the sponsons on both the port and starboard side,” Muldoon said. “Those two are the big movers. There are a number of smaller activities that in total get us back in the box.”
Muldoon said the Navy was very pleased that the collective engineering team was able to come up with design changes that everyone is happy with. “I am convinced we are going to get that thing back in the box. For a while there, before we came up with the mast tilt, we were concerned.”
While most of the technologies on the CH-53K, such as the rotor blades and the split torque design of the gear box, have gone through successful testing, Muldoon acknowledged there were some critical technologies the Navy was worried about. In particular the rotary dampers, he added.
“We were working through all the risk reduction activities to come to a design on that and unfortunately when it came down to trade space, that damper grew in size over time to the point where it was going to cause a significant weight growth on the platform,” Muldoon said. “So we opted to take a lower technology approach and go with a linear damper, akin to the S-92 damper, only scaled for the 53-K.”
The change will cause a minor hit in reliability, he acknowledged.
“The rotary damper was supposed to give us at least four times the improvement in reliability and [linear] damper will give us a little over twice the reliability we have in the current system,” Muldoon said. “But it still falls within the numbers we need to meet our reliability KPP (key performance parameters).”
Actually, even with the change in dampers, there is still a net gain in reliability, Muldoon pointed out. “It’s twice the reliability as the current modeling indicates.”
“It’s just that we weren’t able to go with the next generation technology. It just wasn’t going to pan out,” he said. “Again, that’s why you do trade studies during SDD (system, design and development)…to make sure you have the right combination of technologies to deliver the capabilities to the warfighter. And it’s all about the Marines that are going to operate this.”
The issue with the larger damper was that it was going to require a redesigned sleeve assembly to accommodate the bigger damper and a bigger spindle assembly.
“That’s what drove the weight to a point where it was not a viable alternative,” Muldoon said.
The CH-53K will replace the CH-53E, currently in use by Marines. The new heavy-lift helicopter is expected to enter into preliminary design review before the end of the fiscal year, and into critical design review 12 months after that, Muldoon said.
Initial Operational Capability is slated for 2015.