We've heard how the stealthy F-22 and F-35 are flying thermos bottles, struggling under the huge heat loads imposed by their powerful engines and systems. Well it seems the latest generation of vertical-lift aircraft is turning the flight decks of US Navy amphibious assault ships into frying pans.
Photo: US Navy
The initial culprit is the MV-22 tiltrotor, but the big concern is the STOVL F-35B, which is due on deck after 2012. With nacelles tilted and rotors turning, hot exhaust from the Osprey's engines is buckling the decks, and Navy studies warn repeated buckling will cause deck failure at 40% of planned ship life. F-35B exhaust plumes are expected to have a "severe thermo-mechanical impact" on the structure and non-skid surface of the flight deck.
That's according to a new solicitation from the Office of Naval Research, which is looking for new ideas for flight deck thermal management. The solicitation is looking for alternatives to a DARPA/ONR program that is already looking at "cooled heat pipe technologies" to overcome the thermal issues.
It's not a trivial problem. For the MV-22, where the exhausts are close to the deck when the nacelles are vertical, buckling has been observed after just 10min of sitting on the deck, rotors turning. The F-35B will be in STOVL mode for a fraction of that time, but is expected to cause even more heating of the deck.
ONR is looking for thermal management technologies that can keep the deck surface temperature below 300ºF when exposed to MV-22 exhaust plumes for 90 minutes before takeoff, and F-35B exhaust plumes for 2 minutes when landing. And cooling the deck is not enough - any solution has to be compatible with the deck's non-skid coating. It also has to be affordable and capable of being installed below deck or retrofitted above deck. Tall order.
Photo: Lockheed Martin
Based on measurements taken during recent hover-pit tests, Lockheed Martin does not believe there will be an issue with deck temperatures. One acknowledged area of concern is the combined auxiliary/emergency powerpack, or IPP, which exhausts downwards on the STOVL aircraft. (It exhausts upwards on the F-35C carrier variant to protect deck crew, but downwards on the F-35B and CTOL F-35A to save weight and gain fuel volume.)
The IPP has two modes: bleed and bleed-and-burn. In bleed mode the exhaust is relatively cool, Lockheed says. In bleed-and-burn, fuel is burned in the IPP to generate more power, and exhaust temperature rises. Because of operator concerns about surface heating, Lockheed says the pilot will have the ability to switch the IPP back to bleed mode if holding on the runway, or deck.