The NTF Alternatives

The innocent observer might be excused for concluding that the people at Canberra have now exhausted the possibilities of the American and European sections r-f “Jane’s”. and are about to thumb through the products of Mikoyan and Sukhoi! However, in the nick of time, a new batch of Western fighters has been announced in the marketplace. Some are brand-new designs, others are major developments of existing types, and a few are simply well-established and formerly expensive aircraft now offered at knock-down prices. Not all of these aircraft will necessarily receive serious consideration in the Russell offices, but they are nonetheless of interest in illustrating how the fighter business is developing and what equipment other air forces will be receiving during the early years of the RAAF’s Mirage replacement.

Placing these new aircraft in rough order of size, weight, and thrust, the lower end of the scale is represented by the Northrop F-5G. The F-5 family of fighters began life in the form of the N-156F, which flew in 1959 and led to the initial production of the F-5A with two after-burning J85-GE-13s of 4080 lb (1850 kg). At this stage, it was an outstanding exercise in lightweight fighter design and an affordable, harmless aircraft that America could give to impoverished friends without any real fear that they would kill anyone with it. With two Sidewinders on the tips it was a credible short-range defensive aircraft, but with larger external stores it lost any supersonic capability. It also got stuck with a bad reputation for FOO problems, partly because the tiny blades of the J85 were vulnerable to quite small stones, and partly because the air forces that operated the F-5A often could not afford to clean their runways. The USAF evaluated it in Vietnam but found that it lacked radius of action and warlord and that its take-off performance was badly affected by external loads.

The modest beginnings of the F-5 family are worth recalling, 1f only because of the staggering improvements that have since been made. The second major series is the F-5E Tiger II with two J85-GE-21s of 5000 lb (2268 kg), increased wing area, modified LEX, manoeuvre flaps, two-position nose gear, and more internal fuel. Although still not a front-line aircraft to· 1 major power, Northrop had produced a short-range dogfight aircraft that could hold its own against far more expensive fighters, and (through the operations of the Aggressor Squadrons) became a standard against which all other types were assessed. The F-5E may not be able to achieve a kill ratio of unity against the F-15, but, if their relative prices are taken into account, then the Northrop aircraft is far more cost-effective in close combat.

The third major series is the F-5G, which is now under development and will make its maiden flight in 1982. In this aircraft the two J85s are being replaced by a single General Electric F404 (as in the twin-engined F-18), giving 16,390 lb (7433 kg), ie, a 64 per cent increase in static thrust. Aside from the modifications directly associated with the powerplant change, the F-5G has an enlarged LEX (with zero leading edge sweep), duplicated fly-by-wire longitudinal control with mechanical back-up, graphite composite fin skins, a shark-nose front fuselage profile for stability at high AOA, a thicker wing skin permitting 9g manoeuvres, and heavy-duty wheels and brakes.

Empty weight has risen from the 9853 lb (4345 kg) of the F-5E only to 11,220 lb (5088 kg), and internal fuel remains unchanged at 4400 lb (1995 kg). Clean take-off weight is quoted as 17,11O lb (7760 kg), which probably means with ammunition and Sidewinder launch rails, but in any event gives a, thrust/weight ratio very close to unity. Maximum take-off weight will be 26,140 lb (11,855 kg), giving an ISA day ground roll of 3650 ft (1115 m). This weight permits a load of seven Mk 82 bombs to be carried over a radius of up to 360 nm (665 km).

Taking off clean, the F-5G will unstick in a mere 1450 ft (440 m) and will achieve an initial rate of climb of 50,300 ft/min (256 m/sec), reaching 40,000 ft (12,200 m) in 2. 3 minutes from brake release. The absolute ceiling is approximately 55,000 ft (16,770 m). The aircraft’s staggering climb performance is matched by acceleration times. With two Sidewinders and half fuel, flying at 30,000 ft (9150 m) it will accelerate from Mach 0. 9 to 1. 2 in 30 seconds, and from 0. 9 to 1. 6 in 80 seconds. Maximum level speed in the same condition is Mach 1. 1 at sea level and Mach 2. 0 at the tropopause. For comparison, the F-5A topped out at Mach 1. 4 and the F-5E at 1. 6.

Although small aircraft will always be somewhat limited in their operational capability, the severity of the restriction is decreasing as avionics and missiles become smaller and lighter. Northrop has already fitted F-5s with fire control radar, dual display, maverick missiles, inertial navigation, laser investigators and guided ordnance, and in-flight refuelling. What is less well known is that provisions have been made for ECM equipment and that the Emerson APQ-159 radar has growth potential for use with a missile such as the AIM-7 Sparrow or Sky Flash. In any event, the F-5G appears certain to end up armed with the AMRAAM Sparrow replacement.

The F-5G will not have the warlord-radius performance of an F-16 or F-18, nor will it have the radar range. However, it will provide a worthwhile performance across a broad spectrum of roles, and it will probably cost around half as much to buy and operate. Aside from limitations imposed by its small size, the basic drawback to the F-5G is that its wing area has not been increased to allow its thrust to be exploited fully in the air superiority role. Thus, its sustained turn performance in the clean configuration with half-fuel is little improvement over the F-5E until the latter begins to run out of steam at supersonic speeds. It appears that the aircraft has been “designed down” to achieve an exportable product that does not out-shine the F-16 in the dogfight performance. This eliminates the F-5G as a front-line aircraft for Australia, but it might make a useful proficiency trainer for the service if the F-18A or F-18L is purchased.

The advent of the General Electric F404 engine has made possible a whole new generation of light yet effective single-engine fighters. Of these, the F-5G benefits in low cost and short development timescale from its F-5A and F-5E forebears, but in terms of sustained turn rate and ceiling it suffers from an undersize wing of only 186 sq ft (17. 29 sq m). For the record, the F-5E is expected to reach 19. 3 deg/sec instantaneously at sea level and to sustain a turn rate of 11 deg/sec, yet new aircraft designed around the same F404 engine but with larger wings and canard surfaces will do significantly better.

One such project is Israel Aircraft Industries’ Lavi, which was touted around Farnborough last year as a basis for collaborative development, the desired partner being either European or American. No details have been published, but the work on the grapevine is that the Lavi is primarily an A-4 Skyhawk replacement, ie, a light attack aircraft with a well-developed self-defence capability. It is basically similar to an F-16 but with a wing and foreplane of delta or arrowhead configuration. The engine is expected to be the 16,390 lb (7433 kg) F404, although one possible alternative is the 20,000 lb (9070 kg) PW1120 projected by Pratt & Whitney as a smaller derivative of the F100 used in the F-15 and F-16. For improved radius of action in the ground attack role, the Turbo-Union RB. 199 used in the Tornado should be attractive, due to its very low sfc. With some development, it will give as much thrust as the F404, but its reputedly astronomical price may be a deterrent to the Israelis.

In planning the Lavi, IAI is essentially looking for a low-cost complement for aircraft in the F-16 and F-18 class. It is envisaged that R&D will cost in the region of $US 1000m, which is less than half the figure for the F-18A, and around three times the non-recurring costs for the F-5G. As a first estimate, if the F-5G contractual unit price (ie, with spares, GSE, documentation, contractor support, etc) runs out at around $US 8m, then a brand-new aircraft designed around the same powerplant will presumably cost at least $US 9m-1Om in current terms. To put these figures in perspective, the US budget figures for FY81 appear to indicate a unit price of around $US 1Om for the F-16 and $US 26m for the F-18A, these figures being distorted by the 3:1 rates of production (180 F-16s and 60 F-18s). In future export sales, the F-18 price will presumably fall as production builds up, while the F-16 price will rise as it passes its peak. Export prices are, in any event, higher than those paid by the US services: the Israeli F-16s, for example, appear to have cost around $US 16m each.

At the time of writing, there has been no announcement regarding the selection of a partner for the Lavi project. However, if politics are excluded, then the obvious choice is Saab-Scania, since Sweden has a requirement for an aircraft in roughly the same category as Israel’s A-4 replacement. Saab has received preliminary funding for project definition and initial development of this new JAS (an abbreviation for fighter, attack, and reconnaissance aircraft}, and a final decision by the Swedish Government is scheduled for 1982, following a firm proposal from the Swedish manufacturers in June 1981. First flight date has been reported as 1984, although this sounds optimistic.

The JAS will replace all Viggen models, starting in 1990 with the AJ37 attack version that was first delivered in 1971, then the SH37 and SF37 reconnaissance aircraft, and finally the JA37 fighter, deliveries of which began in 1979. Including the SK37 trainer, there are 329 Viggens planned for home use, and it is anticipated that they will be superseded by 300 JAS, costing approximately $US15m apiece. Broadly speaking, the JAS will use modern technology to combine the Viggen’s straight-line performance with dogfight capability at least as good as the F-16, while retaining the ability to use dispersed road sites.

The JAS is expected to be a canard aircraft with either the F404 or RB. 199 engine, a carbon fibre wing, a fly-by-wire system allowing direct lift control (DLC), and a synthetic aperture radar. Saab indicates that it will weigh approximately half as much as a Viggen, the JA37 version of which has a typical take-off weight of 37,500 lb (17,000 kg). Sweden is looking for overseas partners to assist in development. However, it seems unlikely that the JAS and Lavi could lead to a collaborative project in the JaguarfTornado sense, as Israel is intent on exports while Sweden is more interested in keeping its hands clean.

If the F-5G is in danger of being overtaken by the Lavi, then both the Lavi and JAS may equally well be outclassed and underpriced by a new fighter from America based on forward-swept wing (FSW) technology. Both Rockwell and Grumman have been working on FSW studies and research under DARPA funding, and there is now pressure for a technology demonstrator that could lead to a new lightweight dogfight aircraft within perhaps ten years. Rockwell showed a full-scale mockup of an F404-engined FSW project in Paris two years ago and is now advertising its X-FSW-Sabrebat in the aviation press. Rockwell’s position is strengthened by experience in developing the HiMAT unmanned research aircraft, with one-third of the structure·in advanced composites, aeroelastically tailored wing and foreplane, and modular construction permitting the use of an FSW in later testing.

Traditionally, the FSW has had two major drawbacks: the aeroelastic problem of wing divergence (as the wing bends upward, the tip effectively twists to increased AOA) and the aerodynamic problem of the wing-root stall. Advanced composite materials can now cure the divergence problem by having the fibres orientated to move the torsional axis of the wing. A foreplane has been found to cure the wing-root stall. The FSW offers the benefit of increased lift coefficient since it avoids the tip stall of the aft-swept wing. Rockwell also claims better internal volume distribution, lower supersonic drag, improved flutter characteristics, and enhanced wing bending moment relief.

The FSW thus appears to offer prospects for a fighter that is smaller and lighter than a conventional design. However, there is little experience in the use of advanced opposites for primary structure, and no recent full-scale experience of the handling characteristics of the FSW. Hence America will have to proceed by way of a technology demonstrator, and the development timescale will suffer accordingly.

Moving on to a rather heavier category of fighter, the General Dynamics F-16/J79 originally appeared simply as a down-market version of the standard aircraft. However now seems that, while losing out to the F-16A in transonic combat performance and cruise fuel consumption, this new model (which first flew on October 29, 1980), will probably be at least as good as its predecessor in terms of maximum speed and altitude. Whereas the basic J79 gives 17,820 lb (8080 kg) afterburning thrust in comparison with the 23,830 lb (10,800 kg) of the F100, the new J79-GE-17X has a “Combat Plus” emergency mode that boosts the static thrust to 18,730 lb (8500 kg). Supersonic thrust also benefits from the fact that GD, in narrowing the intake throat to suit the lesser mass flow of the J79, has introduced a compression ramp that reduces the shock losses and gives a higher pressure recovery.

Fuel volume is unchanged at 6972 lb (3162 kg), but the empty weight of the aircraft is up from 15,200 lb (6895 kg) to 16,800 lb (7640 kg), due to the longer, heavier engine and associated nose ballast. Most performance aspects undoubtedly suffer, but whereas the F-16A appears to be limited to the region of Mach 1. 7 due to its crude intake, the indications are that the F-16/J79 may well be a genuine Mach 2. 0 aircraft. Procurement cost has been quoted by GD as $US?. 7m, but rumours of the Austrian offer suggest a figure twice as high.

While GD is flying what might be described as a de-rated F-16, work is in progress on several up-rated versions. Aside from normal thrust growth for today’s P&W F100, funds are being provided to General Electric to develop a Derivative Fighter Engine (DFE). This DFE or F101X is a turbofan of 0. 87 bypass, and may well have flown in the F-16 by the time these words are published. Two further examples are due to fly in an F-14 later in the year. The core of the engine is taken from that used in the F101 in the 8-1 bomber, while the fan and exhaust nozzles are scaled up from those in the F404. The DFE is said to give a static after-burning thrust of 26,000-29,000 lb (11,800-13,150 kg), which would generally enhance F-16 performance, especially in high-drag configurations.

Another GD project team is looking at a supersonic cruise derivative of the F-16, designated SCAMP (Supersonic Cruise Aircraft Modification Program) or F-16XL. (See page 92, September 1980 AADR. ) This would have a lengthened fuselage, a cranked-arrow wing with 70° leading edge swap and graphite epoxy skin, an enlarged vertical tail, and a variable geometry intake, allowing sustained flight at Mach 2. 2 Fuel weight is increased to 12,750 lb (5780 kg), and empty weight is raised to 17,400 lb (7890 kg), implying a take-off weight carrying air-air missiles in the region of 31,400 lb (14,240 kg).

The company is proposing a two-aircraft, $US 40m program to test the concept, with the first flight 15 months from go-ahead. Although the product would have considerable technical interest, the supersonic cruise concept is so far removed from today’s operational requirements that series production appears unlikely, unless for the reconnaissance role. Its shape is far from optimum for air superiority and ground attack missions, and it could not cruise supersonically with external armament.

The Northrop F-1BL was ruled out of the RAAF shortlist because there was no existing customer. If the choice of a Mirage replacement is delayed much longer, this situation could change, since Northrop has a good chance of winning the Spanish Air Force order. To recap, the Northrop F-18L will be lighter, simpler, more reliable, and less expensive to operate than the US Navy/McDonnell Douglas F-18A. Because of its lighter weight, it will have a performance advantage in the region of 15 per cent in regard to acceleration times, turn rates; and fuel consumption.

Another aircraft that failed to make the shortlist was the Panavia Tornado. Since that stage, three prototypes of the Tornado F2 air defence variant have flown, and there has been a revival of interest in the aircraft in Australia. Although the Tornado is undoubtedly more expensive than the F-16, the very high price tag rumoured for the F-18 bid now makes the Tornado appear more competitive. Likewise, although the Tornado cannot compete with the F-16 and F-18 in dogfight capability it is equally true that these American aircraft cannot equal the Panavia product in a CAP mission against a high-performance bomber in a jamming environment. For long endurance on the station, there is no substitute for highly economical engines and variable sweep. Nor is there any substitute for a two-man crew to make full use of onboard systems, and four advanced radar homing missiles to provide something approaching 100 per cent kill probability. A case might therefore be made for the RAAF having some Tornado F2s, with an aircraft such as the Lavi coming in later to handle the dogfight and close support roles.

The McDonnell Douglas F15 was strongly supported by the RAAF as an aircraft with outstanding capabilities in interception and air superiority, though with some need for further development in the ground attack role. It was turned down only been of its cost, and there is no doubt that in going down-market the service had to accept a significantly reduced capability. It is therefore interesting that MDC is now proposing to the USAF a low-cost follow-on buy of F-15s, reportedly quoting a bargain-basement unit flyaway price of $US12m if 500-700 are purchased! Another report quotes an exchange rate of ten F-15s for the cost of thirteen F-16s. Even when allowance is made for all the problems of comparing costs, it seems that the RAAF could get F-15s cheaper than F-18s, if the USAF takes up the MDC offer. Coupled with the possibility of the F-15 Strike Eagle with improved warlord-radius performance and synthetic aperture radar eventually replacing the F-111 in both services, this option is clearly worthy of study, although operating costs for the F-15 would be far higher than for the F-18.

One potentially outstanding fighter that never got started with the RAAF was the Grumman F-14 Tomcat, although, given rules of engagement that allow firings without visual identification, it undoubtedly represents the world’s finest air defence system. The F-14 was far too expensive, and its dogfight performance suffered from the fact that the original plans for more powerful engines had not been put into effect. This situation has changed for two reasons: the (remote) possibility of acquiring F-14s cheaply from Iran, and the forthcoming DFE that will transform its performance. However, operating costs would still be even higher than those for the F-15. A mix of a small number of F-14s and a larger number of F-16s (both using the DFE) would produce an impressive fighter force, but this is unlikely to happen.

To summarise, within ten years there will probably be available new lightweight dogfight aircraft that will outclass the F-16 and F-18. In the shorter term, the F-16DFE, F-18L. Tomado F2 and F-15 will all bear watching.