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Military equipment

Code one: Cold Stops

With the exception of serial numbers and other surface markings, one F-35A tends to look like the next F-35A. Soon, however, a small, aerodynamically clean bump on the upper surface between the two vertical tails will distinguish Norwegian F-35As from other F-35s.

The bump, more accurately called a pod, will contain a drag chute system for rapidly decelerating Royal Norwegian Air Force F-35s after landing on the country’s short, icy runways. While Norway will be the first country to receive the pod, Canada and the Netherlands are also considering adding the capability to their Lightning IIs.

“All three countries currently use supplemental systems to slow their fighter aircraft during landings in icy conditions,” explained Suku Kurien, the Lockheed Martin program manager for the Norway drag chute system. “Norwegian and Dutch F-16s use drag chutes. Canadian CF-18s use arresting hooks.” In general, drag chutes are used for fighters that operate from shorter runways or from short, wet or icy runways in extremely cold climates.

Since none of the baseline F-35 configurations required a drag chute, the system represents the first modification to the F-35 design to come after the System Development and Demonstration Phase. “The drag chute system is the first new capability to be contracted for the F-35 by one of the original eight international partners,” added Kurien.

The drag chute program was born from a Lockheed Martin study funded by Norway, Canada, and the Netherlands in 2010. “We reviewed many alternatives with Lockheed Martin, including thrust reversers and larger wings,” explained Lt. Col. Christoffer Eriksen, former F-35 Norwegian Assistant National Deputy who led the study for Norway. “We have used the drag chute regularly on our F-16s with ease and success. When this concept was proposed, we were comfortable with it as were our Dutch teammates who also fly F-16s.”

The biggest challenge for the program was to develop a pod that did not degrade the F-35’s stealth capabilities and aerodynamics. “We put a lot of effort into optimizing the fairing shape to provide sufficient volume for the drag chute and mechanism while minimizing drag and signature impacts,” according to Adam Minks, the Lockheed Martin lead for the study.

Norway further challenged Lockheed Martin by moving up the delivery of its first two aircraft to 2015. “We requested the drag chute internal capabilities be included even though the final requirements were not complete,” said Eriksen. “To save time, the development program began with reengineering the aircraft structure while simultaneously defining the program requirements,” said Kurien.

Representatives from Lockheed Martin, the F-35 Joint Program Office, and Norway began developing the drag chute system in 2012. The basic goals were defined early on including the specified minimums for runway length and defined icy conditions, flying qualities, and operational life for the drag chute and structure. Maintenance needs were also defined. The methods to verify and certify the system were established. Norway is expected to procure a total of fifty-two F-35s and associated drag chute systems.

Structural changes involved adding a load fitting onto an upper fuselage bulkhead near the aft portion of the wing and redesigning the skins in the wing and aft fuselage. The tool fixtures used to manufacture the wing carry-through and aft fuselage structures were modified to allow for the change. These changes were made on the production lines in Fort Worth, Texas, and in Marietta, Georgia, for the wing and in Samlesbury, UK, for the aft fuselages that are produced there.

The drag chute system itself consists of a removable, or missionized pod. While Norway will likely operate with the pod installed full-time, other countries have the option of installing the pod as needed. The system is being designed much as a wing pylon so that the pod can be installed and removed with minimal time and effort.

To deploy the chute, the pilot flips a switch up on the upper left side of the instrument panel. The switch activates hydraulic actuators that open the pod to release a Kevlar parachute. Once the aircraft is slowed sufficiently, the pilot flips the same switch down to release the drag chute as the aircraft comes to a stop.

Besides developing the pod and modifying the structure to accommodate it, the design team is evaluating the effects of the pod in terms of flight performance, signature, and sensor interaction, to ensure the aircraft capability is not degraded.

“The pod acts as a fin that, from analysis and wind tunnel testing, has little to no adverse effect on the aircraft’s capabilities,” explained Kurien.

To verify the wind tunnel tests and certify the overall design for operational use, the drag chute system will go through a flight test program at Edwards AFB, California, beginning in 2017. “We are currently planning to use the SDD F-35A test aircraft designated as AF-2,” said Kurien. “AF-2 is a loads aircraft and has the best instrumentation to support the tests.”

Initial tests will confirm aero performance and flying qualities predictions. These tests will be followed by a series of landing tests with chute deployment on a dry runway surface with various crosswinds and aircraft configurations. The final tests at Edwards will involve wet runway landings with chute deployments.

AF-2 will move to a cold-weather location for the final tests, which will involve ground handling maneuvers and landings with chute deployment on an icy runway. The location for this test has not been finalized, though the test team is considering JB Elmendorf-Richardson in Alaska.

“Designing the drag chute system is truly a collaborative effort. Not just between Norway and Lockheed Martin but also with the F-35 JPO,” according to Jeff Mohr, the chief project engineer for the drag chute program. “Our success to date with such an aggressive schedule would only be possible with the trust and collaborative relationship among all three entities. Norway is involved directly with the engineers at a very detailed level. This level of involvement assures Norway that Lockheed Martin is incorporating its requirements to its satisfaction.”

“The drag chute system is a significant capability for Norway and for other F-35 customers,” said Kurien.“ Getting this design off the drawing board and into the F-35 fleet for the Royal Norwegian Air Force is important for Norway’s national defense plans. And it will be a major accomplishment for the F-35 program. Everyone involved will feel a huge sense of accomplishment when we see the system being used in an operational environment.”

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Source: Code One
Author: Eric Hehs
Photo: Lockheed Martin / Doug Moore

Autor: Redakcja Świat

Redakcja Świat