Strike Aircraft of the Nineties

It wasn’t too long ago that the argument for complex, high-technology systems was that they helped make up for being outnumbered (4 to 1) by less able threat aircraft. But the Soviets, while maintaining their numerical lead, have narrowed the technological gap to the point that the pursuit of still greater technological advantages may not be enough to offset the threat. We’ve got to start playing the numbers game, too.

The Soviets are currently introducing new tactical aircraft at a rate of better than one each year! This compares to one about every seven years in the US. Such proliferation has apparently allowed the Soviets to shift their design philosophy from basically defensive systems (relatively small, multi-role, fixed-wing fighters and other tactical planes) to a new emphasis on long-range offensive systems with variable-sweep wings.

Along with these first-line interceptors and strike fighters, the Soviets had excellent surface-to-air missiles and antiaircraft artillery deployed in great numbers throughout the Warsaw Pact nations of Eastern Europe. The vast Soviet-built air-defence network comprises the densest, most hostile electronic environment in the world for our tactical aircraft.

Today, Russian surface-to-air weapons are directed by a variety of sophisticated radars, electro-optical trackers, and infrared homing devices. These systems provide overlapping coverage over so broad a spectrum of the sky as to make penetration by our aircraft extremely hazardous most of these systems are mobile and thus capable of rolling forward with attacking spearheads. Minimising the effectiveness of electronic air defences will surely be a major concern in designing the tactical aircraft of the 1990s and beyond.

Quantity vs. quality: a necessary compromise

In addressing this ever-growing Soviet threat in numbers and sophistication of tactical aircraft and air-defence systems, we must place increased emphasis on quantity as well as quality. Within today’s budget constraints, where economics are as much a consideration in aircraft design as the projected threat, this means smaller, lighter, less-expensive new aircraft. It also means more emphasis on applying advanced technologies to existing aircraft to increase their effectiveness over a longer period of time, and to enhance their survivability.

This does not imply less quality or reduced emphasis on new technology. What it means is putting technology to work to meet parameters for affordability as well as high performance – to prove out new systems in today’s aircraft, and to be selective in determining what is really needed to do the job, as opposed to “wouldn’t it be nice to have”. It’s a delicate balance to be sure, and we have to do our homework to stay on top of it all in the most cost-effective manner.

Since early design decisions critically affect overall program costs, it may well be that the US will delay any new aircraft starts until a significant improvement in effectiveness and survivability can be assured by incorporating proven new technologies. So the emphasis at present is on pursuing those key technologies on which a future advanced tactical strike aircraft will depend. Toward this end, the US Air Force is manipulating joint USAF-industry air-to-surface and air-to air technology studies in which Grumman Aerospace has been a major participant.

The artist’s concepts displayed on these pages are not actual aircraft designs. Rather they are examples of the designs developed during our studies to demonstrate what technology could do, given a particular set of mission requirements.

Keeping size and weight down, while still fulfilling mission requirements, is probably the single greatest challenge. Generally, the heavier an aircraft, the more expensive. Our studies, wind tunnel tests, and production experience have shown that, by using a combination of lighter, stronger materials, advanced manufacturing techniques, improved aerodynamics, and smaller, more efficient propulsion systems, we can reduce the weight of new combat aircraft. For example, were we to design a future supersonic all-weather penetrator using today’s advanced technologies, the plane would weigh about half that of the 80,000-pound-plus F-111A. Furthermore, the life-cycle cost (the cost of operating and maintaining the plane throughout its service) would be cut by about 40 per cent.

Composites and other new materials will dominate

Advanced titanium and composite materials will probably dominate weapon systems of the future . . . the first significant change in fabricating aircraft skins and load-bearing structures since aluminium replaced fabric and wood more than 40 years ago.

In association with the US Air Force, Grumman pioneered the development of advanced composites, introduced boron/ epoxy in the F-14 fighter, and qualified graphite/epoxy and hybrids in producing the composite horizontal stabiliser for the B-1 bomber.

We have since automated much of the labour-intensive operations previously required in handling composites within our recently completed Integrated Laminating Centre. With computerised parts programming, the ILC production set-up automatically controls the entire fabrication cycle.

Titanium advances aimed at making this high-strength, lightweight material cost-competitive with aluminium include super plastic forming combined with diffusion bonding – a molecular interaction that provides a homogeneous piece of metal with built-in stiffeners – and hot isostatic pressing in which titanium is processed as a powder and forced into the shape required. These new processes are expected to improve the buy-to-fly ratio of titanium so we can finally make practical use of this superb material in the next new tactical aircraft.

A fighter that can attack or an attack plane that can fight?

Whether the next tactical aircraft will be a fighter with attack capabilities – which would ally it with conventional design – or an attack plane that can deal with any fighter has not been determined. It may well be the traditional concepts of “fighter” and “attack” as distinct, dedicated types will no longer apply in the tactical environment of the 1990s.

Grumman’s studies have examined both approaches at some length. The “all-around” tactical aircraft, for example, imposes obvious challenges in system versatility and automation.

Its weapons control systems, alone, would have to be better than today’s most sophisticated computers to handle both air-to-air and air-to-surface engagements.

Currently, we envisage three classes of tactical aircraft for the 1990s in support of ground operations in the critical Central European environment: close air support for our troops on the battlefield (the role of the recently-introduced A-1O tankbuster aircraft); short-range interdiction of mobile SAMs, armoured columns, highway bridges, and ground-controlled intercept centres; and long-range interdiction (hundreds of miles into hostile airspace) of fixed and mobile SAMs, air-defence command centres, railroad bridges, airfields, petroleum dumps, and resupply columns.

Future penetrators may go in high and fast

Strike aircraft tactics currently rely primarily on low-altitude penetration to minimise exposure to air-defence radars and enhance survivability. Our studies of Europe and other heavily defended areas show that, in the future, chances of survival may actually be greater at high altitudes and speeds. For example, at 50,000-60,000 feet, survivability is significantly improved because the penetrator is outside the length envelope of a large number of anti-aircraft weapons.

At medium altitude down to treetop level, strike aircraft face an awesome array of anti-aircraft defences. Shifting to high-altitude strike capability, however, imposes several technological challenges, not the least of which are new, longer-range fire control systems and air-to-surface weapons.

Giving the high-altitude penetrator supersonic cruise capability to enhance its survivability is equally challenging. Today’s tactical aircraft can dash supersonically only by turning on engine afterburners, and then for only brief periods because of the enormous amount of fuel consumed. What’s needed is the ability to cruise supersonically “dry”, that is without resorting to fuel-gulping afterburners.

It could be done aerodynamically, as with the supersonic Concorde airliner, which has a lift-to-drag ratio (UD) of about 8. In contrast, an advanced aeroplane like the F-14 has a UD about half that because it was designed to meet such diverse (and sometimes conflicting) requirements as reasonably short takeoff and landing distance, manoeuvrability for dogfighting, supersonic dash, moderate size and, of course, the ability to deliver weapons. For a future tactical aircraft to truly “supercruise”, we must give it a UD of between 6 and 8 and, more importantly, a “zero-lift” drag half that of current vehicles.

The propulsion required is well within the state of the art. Advanced engines will be smaller and lighter for given thrust levels, with fewer components and two-dimensional nozzles for cleaner lines (less drag).

Aerodynamic improvements are expected in several quarters. For example, the Grumman Supersonic Tactical Aircraft Configuration (STAC) model has achieved an UD of about 6. 5 at Mach 2 in the Air Force wind tunnel at Tullahoma, Tennessee. In this design, engine placement and design of the wing, fuselage, tail, and canopy are critical elements in minimising supersonic drag.

A wing for all missions

In addition, we are developing a mission-adaptive wing that can literally change its shape – in flight – to meet the performance required at a particular point. It also can vary this shape spanwise, even under the intense loading typical of high-performance aircraft.

It’s a wing for all missions. Computer controlled, it gets more lift without going to higher angles of attack, is less sensitive to gusts, and distributes wing loading so the aircraft can compensate for bending moments that exceed the design load limit.

Another aerodynamic concept that looks very promising is a close-coupled, canard-configured supersonic vehicle with low-mounted, swept-forward wings. Providing lower weight and higher manoeuvrability, the forward-swept wing can be made practical using composite materials. Through directional tailoring of composite laminates and high absolute levels of wing-cover elastic properties, previous aeroelastic limitations can be overcome. The relatively high aspect ratio, shorter structural span, and favourable stall characteristics have a powerful effect on reducing aircraft size, weight, and cost.

There’s little doubt that control-configured-vehicle (CCV) technology will be part of any new aircraft design. With digital flight control systems replacing today’s performance-limiting aerodynamic stability criteria, a whole new world of combat manoeuvres and improved agility is made possible.

The key is advanced electronic data processing: more information, available faster, using microprocessors. Hand-in-hand are fly-by-wire guidance systems and rapid-response actuators for highly loaded control surfaces. Taken as a whole, CCV also offers significant opportunities to reduce aircraft size and weight.

In terms of reducing aircraft weight through aerodynamics while also improving performance, super-critical wing technology offers both advantages.

Coupled with higher wing loading, the· new airfoil reduces drag while generating greater lift and manoeuvrability. In essence, less wing area is required for the same aircraft weight.

To help pilots handle the more manoeuvrable aircraft of the future, Grumman is developing a high-G, high visibility cockpit. During high-G manoeuvres, the seat tilts back to reduce G-loads on the crew. At the same time a simple, unified instrument panel slides forward to keep basic flight information in full view of the pilot.

“Low observables”, a new dimension of stealth

In addressing the challenge of survivability, especially in the hostile electronic warfare thicket of Central Europe and other heavily defended arenas, a number of factors come to bear. Size, in particular, takes on critical importance.

Reducing size and weight contributes to what is termed “low observables”, that is, making the aircraft less visible to the enemy, an extremely important element of survivability.

There are several other ways to impart the desired stealth: shaping the aircraft to reduce its radar cross-section, for example, and controlling its visual and infrared signatures. The latter can be “hidden” from heat-seeking missiles by shielding engine exhaust nozzles with parts of the aircraft structure.

Radar-absorbent coatings can also be used to make the aircraft harder to pick up on ground radars. Parts of future aircraft structures will actually be made of radar-absorbent materials. Frequency sensitive metallic radomes would also help by shielding the radar antenna from enemy radar waves.

Electronic countermeasures – jammers and chaff – will continue to play a major role in spreading confusion among enemy defences. However, because of their weight and cost, they must be balanced with these other means to enhance survivability.

Glint, or light reflections, from the canopy and other bright spots, can also give an airplane away. Flat surfaces that reflect upward are preferred to curved surfaces which can reflect in any direction. By the same token, properly oriented bright surfaces can be used to advantage by reflecting the plane’s background (the sky), thereby reducing the visual contrast- a sort of mirror camouflage.

Grumman is currently working with the Air Force in an experimental program aimed at determining how such visual cues could be used.

Standoff weaponry could reduce losses

Standoff capability, the ability to launch self-guided weapons at long ranges from the target, offers still another means for improving survivability in a high-threat environment. To stay out of range of concentrated terminal air defences, strike aircraft must be able to launch weapons accurately from many miles away.

The control functions for such critical weapon targeting could be achieved by several systems presently under development. One of these, the Grumman developed Radar Guided Weapon System (RGWS), combines an improved synthetic aperture radar with new angle measurement techniques for determining the exact angle between the target and a beacon in a missile, for example.

An almost photographic image of the target area is presented, allowing the aircrew to visually pinpoint and guide multiple weapons. Accuracy is 1 O times greater than with conventional systems. And ordnance cost is lower too, since the guidance system is safely integrated aboard the aircraft, instead of in the weapon itself. Possibly operational as early as 1982, RGWS can also use weapons already in the inventory, a further cost saving.

If our probing studies of standoff weaponry and other future tactical aircraft technologies have taught us anything, it is that the real challenge lies as much in designing and building to cost as in the technology itself. Pursuing the “ultimate” weapon is not the answer, but rather the best affordable weapon to do the job.

Considering that it takes about 1 o to 13 years to move an advanced aircraft from the drawing board to operational status, the time to start on the next century’s smaller, better tactical aircraft is now. At the same time, advanced technologies can be applied selectively to existing aircraft to provide them with the higher levels of mission effectiveness and survivability required to keep pace with the growing numerical superiority and weapons quality of our potential adversaries.