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How NAVAIR (Naval Air Systems Command), which is responsible for material support for aircraft and airborne weapons systems command of the US Navy, in mid-December reported a number of challenges in the integration of the CH-53K engine could be solved. For this, a civil-military team of experts NAVAIR and Sikorsky had met engineers. The Sikorsky CH-53K "King Stallion", is the new heavy transport helicopter of the US Marine Corps (USMC) and in Germany one of two candidates to succeed the CH-53 in the army.

The aim of this team was to solve existing challenges as soon as possible and to bring together the aircraft modifications on the cutting edge of technology in order to optimize the entire system. Here diverse methods and programs used, among other modern computer modeling techniques, risk management systems, flight test data and various instruments of the aircraft system technology came.

Colonel Jack Perrin, at NAVAIR PMA-261 (Program Manager, Air) responsible for the CH-53K program manager: "The civil-military team of experts to bring together, is a very good example of the importance and purpose of an integrated test team. It was great to see how the team straightforward a solution to an existing problem has found. This was the priority for NAVAIR, Sikorsky and the US Marine Corps (USMC), and the team has literally hit the nail on the head! "The NAVAIR Program Office is both the located for years in the use of CH-53E" Super Stallion, "and the new standard USMC helicopter CH-53K responsible. The Sikorsky CH-53K will enable the USMC more payload and greater range and faster transport of troops and material. the helicopter of three new General Electric / MTU is driven T-408 engines. These are considerably more powerful and more efficient than those currently installed in the CH-53E T-64 engines.

The integration of the three engines presented the team with challenges that have now been solved thanks to the common approach. The most important was the problem of exhaust intake (Exhaust Gas Re-ingestion - EGR).

For the visualization of air currents and wind effects at the rotor plane, colored oil mist is used while the surface flow is added to the cell structure by video recordings of flow threads for this experiment. This flight test was used among other things to the applied changes to solve the (EGR) exhaust Ansaugungsproblems the new aircraft of US to confirm Marine Corps. (Photo: US Navy)

EGR occurs when the hot engine exhaust gases, for example, be sucked in again by the underlying engine on the ground or in flight. This can even lead to failure or shutdown of the engine to a variety of problems, such as increased life cycle costs, reduced engine performance, shorter operating times, overheating.

The expert team started work in April of 2019. Here came experts in engine power, computational fluid dynamics, modeling and simulation, materials science, airframe structures, logistics, system safety, reliability and maintainability, flight testing, fire protection and survivability together. There were more than 30 tests carried out and digitally evaluated 135 possible design solutions for engine integration.

Various approaches have been developed in parallel to the problems of finding exhaust suction and off. The solutions found in the modeling were then confirmed by iterative flight tests and then promising applied to the aircraft. Then, components were designed for one of the test aircraft and included the corresponding data in a number of other flight tests, so this approach could be fundamentally validated.

In December 2019, the result could now be presented and the overall design change will be implemented for the entire fleet.

These modifications relate to: changes in the geometry of the exhaust duct, increasing the air flow into the Triebwerklufteinlässen and coverings, adding heat shields and minor changes to the engine FADEC (Full Authority Digital Engine Control) software.

Steve Schmidt, the Sikorsky CH-53K chief engineer, explained further to the fact that the original assumptions for the simulation at first, had not agreed with the results from the real flight. "We won the recognition in this flight test that the engine exhaust gases from the engine 1 and 2 (On the left side of the aircraft)Stagnate in hover, just below the center of the main rotor, and were ultimately drawn back in by the engine. 2

Computer-aided simulation of the flow conditions at the rotor plane of the Sikorsky CH-53K in various hover heights and different wind conditions (Video: NAVAIR)

In previous assumptions only the engine 1 was drawn to this problem into consideration. The modeling of appropriate simulation, as well as the data of the flight test, have contributed significantly to this understanding of the system and the final solution. In this area, the advantage of digital design of the CH-53K comes into its own. Many of the data could be evaluated as before flight testing in different approaches and adjusted accordingly.

The Sikorsky CH-53K fleet is currently in flight service at the Naval Air Station at Patuxent River, Maryland (NAS Pax River), while the technical and logistical operational test conducted at the Marine Corps Air Station New River, North Carolina (MCAS New River) becomes. (Photo: USMC)

This change and the fleet-wide implementation will support the USMC in the field testing and the planned year 2023/24, the first CH-53K mission contingent.

André Forkert