If designers sat down at their computer screens on the first day of the 21st century and started work on a new combat aircraft - a follow-on to the Eurofighter or the Joint Strike Fighter (JSF) - what would it look like?
For certain, first on the list of customer requirements would be affordability - in development, production and operation. That overarching requirement would influence all the designers' decision.
It is already happening in the JSF programme, where unprecedented co-operation between the customer services - and between government and industry - has resulted in performance being traded off against cost to an unheard of degree.
A glimpse of one possible direction for fighter development is provided by studies conducted under the US Air Force's Future Aircraft Technology Enhancement (FATE) programme. The objective of FATE was to meet a phased set of increasingly demanding affordability and performance goals by developing a series of unmanned technology demonstrators.
Although FATE has yet to progress beyond those initial studies, it provides an insight into the thinking of industry as it looks beyond the JSF at the "generation after next" fighter.
The independent studies by Boeing, Lockheed Martin and Northrop Grumman identified a remarkably similar set of technologies needed to meet the FATE Phase 1 goals of a 20% reduction in cost and a similar increase in performance for an aircraft to enter service after 2010. The picture that emerged was of an agile tailless fighter that was smaller, lighter and cheaper than today's Lockheed Martin F-16 or tomorrow's JSF.
Turn the clock back, and the aircraft that emerged from FATE Phase I bears a remarkable resemblance to designs Boeing and Lockheed Martin were working on in the very early stages of the JSF programme. Today's JSF designs are more conventional because many of the more advanced technologies, such as tailless configurations, were deemed too immature and risky to be used.
Tailless feasibility
A designer starting with a blank screen today might take a different view. Certainly tailless designs, with their reduced weight, drag and radar cross-section, are considered feasible following Boeing's successful demonstration of the X-36, a subscale model of a highly agile tailless fighter which used thrust vectoring and split ailerons for flight control.
Fluidic multi-axis thrust vectoring, another FATE-identified technology, is maturing. By injecting engine bleed-air into the nozzle, the throat area and thrust vectoring can be controlled without the need for moving parts. The resulting fixed nozzle is lighter, can be shaped for lower radar cross-section and cooled aggressively to reduce infrared signature.
The FATE studies identified the "lambda" wing as offering weight and performance benefits. Compared with the trapezoidal and diamond wings favoured for current fighters, the lambda wing provides increased aspect ratio and improves aerodynamic efficiency.
There are weight penalties, but the planform has been used successfully on the X-36.
Some FATE concepts combined the tailless configuration and lambda wing with advanced flight controls, such as all-moving wingtips and continuous aerodynamic surfaces. The latter uses flexible structures between the wing and control surfaces to minimise flow separation. Neither technology has been flight tested.
Other key technologies outlined in the FATE studies, and at various stages of development towards maturity, include: active flow control; active aeroelastic wing; reconfigurable "damage adaptive" flight controls; unitised (welded or cast) metallic structures; integrally stiffened composites; power-by-wire; and fly-by-light.
Taken together, all these technologies promise to reduce take-off weight and flyaway cost by about half compared with the latest generation of US fighters. The JSF programme will take a significant step towards those goals, but FATE shows there is still room to improve the affordability of fighters.
Source: Flight International
