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  • About That Austere-Base Thing...
    Posted by Bill Sweetman 12:45 PM on Mar 11, 2010

    In operations around Marjah in Afghanistan, the Marines have been using AV-8B Harriers as they were designed to be used, flying the jets from runways that are too short or ill-prepared to accommodate a conventional fighter. Kimberly Johnson is reporting on this for DTI's April issue.

    The Marines say that the
    the AV-8B's replacement, the F-35B Joint Strike Fighter, will be able to do the same: “The flexibility that the STOVL variant of the F-35 will add to the contemporary Marine Air Ground Task Force is amazing,” Marine commandant Gen James Conway said when the first F-35B was rolled out, more than two years ago. “This generational leap in technology will enable us to operate a fleet of fighter/attack aircraft from the decks of ships, existing runways or from unimproved surfaces at austere bases."

    But a Navy report issued in January says that the F-35B, in fact, won't be able to use such forward bases. Indeed, unless it ditches its short take-off, vertical landing capability and touches down like a conventional fighter, it won't be able to use land bases at all without some major construction efforts.

    The newly released document, hosted on a government building-design resource site, outlines what base-construction engineers need to do to ensure that the F-35B's exhaust does not turn the surface it lands on into an area-denial weapon. And it's not trivial. Vertical-landing "pads will be exposed to 1700 deg. F and high velocity (Mach 1) exhaust," the report says. The exhaust will melt asphalt and "is likely to spall the surface of standard airfield concrete pavements on the first VL." (The report leaves to the imagination what jagged chunks of spalled concrete will do in a supersonic blast field.)

    Not only does the VL pad have to be made of heat-resistant concrete, but currently known sealants can't stand the heat either, so the pad has to be one continuous piece of concrete, with continuous reinforcement in all directions so that cracks and joints remain closed. The reinforced pad has to be 100 feet by 100 feet, with a 50-foot paved area around it.

    By the way, any area where an F-35B may be stopped with the engine running - runway ends, hold-shorts on taxiways, and ramps - also has to be made of heat-resistant concrete to tolerate the exhaust from the Integrated Power Pack (IPP), which is acting as a small gas turbine whenever the aircraft is stopped.

    This follows the revelation that the US Navy is worried about the exhaust damaging ship decks.

    Lockheed Martin pooh-poohs the report, saying that it was based on "worst-case" data and that "extensive tests" conducted with prototype BF-3 in January (after the report was completed) showed that "the difference between F-35B main-engine exhaust temperature and that of the AV-8B is very small, and is not anticipated to require any significant CONOPS changes for F-35B."

    What do "very small" and "significant" mean? In VL mode the main engine on the F-35B is producing some 15,700 pounds of thrust, while a Harrier's aft nozzles deliver about 12,000 pounds of thrust. (The fore-aft split is roughly equal.)

    But the F135's overall pressure ratio is almost twice as high, which would point to a much higher jet velocity (which LockMart doesn't mention), the JSF nozzle is much closer to the ground, and the Harrier has two nozzles, several feet apart. 

    So maybe the F-35B is not shaping up to be the best anti-runway weapon since the RAF retired the
    JP233. However, it may still not be what the Marines got when they first acquired the Harrier in the early 1970s.

    Having clung tenaciously to the WW2-era AU-1 Corsair until the late 1950s, because unlike early jets it could use minimally improved fields, the Marines had finally entered the jet age with the help of the Short Airfield for Tactical Support (SATS), an astonishing set of equipment that included a portable water-brake arrester system and (I am not making this up) a catapult powered by J79 jet engines.

    The original Harrier allowed them to get rid of this kit. While the first justification for land-based STOVL - that it provided a dispersal alternative when air attacks shut down major bases - has a Cold War feel to it, the idea of using STOVL as a more expeditionary force has remained somewhat valid, and has been used by both the UK and the Marines: the RAF's Harriers were able to operate from Kandahar when other aircraft could not.

    Again, the question is how well the F-35B will be able to do that, and what "significant " means. Worst case or not, there is a very big difference between a solid slab of high-grade concrete and the kind of surface you are apt to find anywhere ending in -stan.

    Tags: jsf, base-requirements, marines

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