Conformal fuel tanks (CFTs) -- those sexy aerodynamic
bulges gracing the upper fuselages of most leading current combat
aircraft -- are the in-thing these days, despite expanding air-refueling
roles in most recent major campaigns.
Flexibility is among the main assets of these tanks, in extending
available trade-offs between range and payload. Apart from greatly
reduced drag compared with drop-tanks, CFTs allow unrefueled range
increases of up to 50% or more, without compromising stores pylon
availability.
Their weight, of course, results in corresponding reductions in
available weapons loads. But for smaller air forces they represent
far cheaper alternatives to air-refueling tankers. In fact, they
also offer additional operational capabilities from possible use
as tankers with buddy-pod systems
Optional CFTs, flanking only the fuselage, were first introduced
in the USAF's multirole Boeing/MDC F-15E Strike Eagle, dating
back to the mid-1980s, and also fitted to export versions. Each
tank contains 723 U.S. gallons, and supplements maximum internal
fuel capacity of 2,019 U.S. gallons. Requiring extensive wind
tunnel and design research to establish their optimum shapes,
CFTs can achieve relatively small degradations of performance,
and require only a few engineering changes in core structure and
systems modifications for anchor points and plumbing in retrospective
installations.
CFTs avoid the significant moment arms that affect outboard pylon
tanks and impose limits on combat maneuvrability. They are also
favourably placed to minimise CG problems, but cannot be jettisoned
to reduce operating weights, cross-sectional area and drag when
empty. While designed for fairly rapid field installation or removal,
they may not readily lend themselves to such operations on a mission-to-mission
basis.
Sixty Block 52+ multirole F-16C/Ds now being delivered to Greece
were claimed by Lockheed Martin as the first production aircraft
with over-wing/fuselage conformal fuel tanks. "These hold
a total of 450 U.S. gallons, or about 3,060 pounds of fuel, for
a significant increase in mission range and patrol times",
said John Bean, Lockheed Martin VP F-16 Programs. The CFTs, he
added, also allowed F-16s to carry a larger weapons payload by
freeing-up two stores pylons. Eighty UAE F-16C/D Block 60 Desert
Falcons will also be delivered from 2004 with CFTs.
Export Dassault Rafale Mk 2s will be offered with CFTs of 607
U.S. gallons capacity for a 20-25% range increase, following flight
development from April 2001. For the Eurofighter Typhoon, new
792 U.S. gallon conformal tanks developed by Australia's GKN Exchange
company were shown last year in mockup form at the Farnborough
Air Show. Their shape apparently required "a huge amount
of wind-tunnel optimisation work," the effectiveness of which
has not yet been flight-tested, to increase Eurofighter Typhoon
internal fuel capacity by nearly 50% when required. With the necessary
plumbing and attachment points in place, field installation or
removal is reportedly possible within a specified 75 minutes,
for rapid role changes.
The RAF has shown some interest in the Eurofighter Typhoon's CFTs,
which might be introduced as an option on Tranche 2 production
aircraft. With its Eurofighter partners BAE Systems is still looking
at technical solutions and operational benefits for possible future
development, in recognition of changing requirements.
