Downwash Concerns
Marines prepare to test effects of F-35B
engine and lift fan on the decks of USS Wasp
By DANIEL P. TAYLOR, Special Correspondent
Thermal Stresses
Navy spokesman Christopher
Johnson said the service is confident that the downwash will end
up being a non-issue.
“The thermal stresses imparted
to the deck steel by the F-35B have
been characterized by sub-scale
modeling and a representative deck
structure coupon, which was tested
at Lockheed’s hover pit in January
of 2010,” he said. “Initial results
show that the ship’s structure will
handle the thermal footprint for a
single landing, but further evalua-
tion is required to assess the impact
of how [concepts of operations] and the desire to have
unrestricted operations will inform NAVSEA of any
structural modifications that will be required.”
The modifications will come with a price tag. Lt. Gen.
George J. Trautman III, Marine Corps deputy comman-
dant for aviation, told the House Armed Services Com-
mittee early last year in written responses to their ques-
tions that it will cost at least an estimated $70 million to
modify each large-deck amphibious ship to accommo-
date the F-35B, a cost that covers mitigation efforts and
infrastructure modifications.
NAVAIR already has identified $27 million in “
cornerstone” modifications necessary for L-class ships to
handle the STOVL JSF, as well as another $43 million
per ship for alterations to deal with external environmental impacts, according to Trautman.
Last June, the Navy put out a source-sought notice
seeking potential sources in other countries to provide
ship deck lighting that could handle JSF STOVL
exhaust heat.
In the meantime, the Navy is working to solidify
exactly what modifications will be necessary, which is
what makes Wasp’s instrumentation and upcoming
F- 35 testing an important first step. Developmental
testing onboard Wasp “will include measurements for
The short-takeoff, vertical-landing variant of the F- 35 Lightning II
is intended to replace the AV-8B Harrier II jump-jet.
■ The Harrier creates lift by simply directing thrust from the
main engine downward by rotating exhaust nozzles.
■ The F-35B uses vertical propulsion from the main engine as
well as a shaft-driven lift fan.
■ The F-35B will have downwash that is two to three times more
powerful and hotter than that of the AV-8B.
As the Marine Corps works to bring the short- takeoff, vertical-landing (STOVL) variant of the F- 35 Lightning II strike fighter to the
fleet, the service is faced with one major question:
How will ship decks handle the powerful, super-hot
downwash from the aircraft?
The F-35B is a new aircraft that will be landing
aboard ships that have been around for decades. Those
ships have largely had to handle the AV-8B Harrier II,
a STOVL aircraft that is just about as old. The F-35B
will have downwash that is two to three times more
powerful and hotter than that of the AV-8B, so some
have raised concerns about the potential for the
exhaust to warp or buckle ship decks.
Marine Corps officials have taken a wait-and-see approach to the problem, and have been gathering data since
the program began testing on the effects of downwash.
The service will continue to do that when the F-35B gets
on a ship for the first time this fall.
In fact, the Joint Strike Fighter (JSF) joint program
office, Naval Air Systems Command (NAVAIR) and
Naval Sea Systems Command (NAVSEA) are all partnering on the effort, and NAVSEA in particular is
installing special instrumentation on the amphibious
ship USS Wasp to test downwash effects on ship decks.
