In the last few days, I’ve often written about the F-35B. I have explained that the STOVL concept could not be abandoned and that, hopefully, USMC, Italian Air Force and Italian Navy, will most probably get their Harrier replacements sooner or later. However I forgot to complete the previous sentence: “hopefully, USMC, Italian Air Force and Italian Navy, will most probably get their Harrier replacements sooner or later provided that Lockheed Martin will be able to solve the heating management issues. Over the last couple of years, the US Navy has in fact discovered that the engine exhaust from the F-35B (and also from the tilt-rotor MV-22) was too hot for the deck plates on some on the carriers and that high temperatures could deform the deck plate’s understructure.
Below is an interesting article published on Aviation Week’s blog Ares by Bill Sweetman that clearly explains the type of problem the F-35B users could be facing because of the high temperatures and high jet exhaust speed of the STOVL variant of the Lightning II. If the heating problem is not solved, the F-35B will not be able to operate from unprepared strip or aircraft carrier, becoming almost useless (at least for the requirements it was expected to satisfy).
About That Austere-Base Thing…
Posted by Bill Sweetman at 3/11/2010 6:45 AM CST
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.
More from The Aviationist
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.
