Technology Explained

V/STOL aircraft such as the Harrier may easily accompany ground forces, which helicopter equipped, and possess refuelling facilities or hand, their limited air-air capability should be adequate in disrupting any enemy air strikes directed against friendly ground forces. The roles of air superiority and interdiction could then be covered by the F-18A and F-111C, without the need to divert these aircraft to the above role.

Another very serious, yet often ignored role is convoy protection It is easy for the US to recommission a mothball carrier, deploy helos and aircraft and rapidly form a second-line naval air defence system to cover vital convoys to and from Europe or the Middle East, while front line Carrier battle Groups tackle hostile naval forces Nations such as Australia, Japan and Britain rely on shipping for most of their trade and as such are extremely vulnerable in times of war. Hostile submarines, surface vessels and aircraft will pose a serious threat to shipping (see TE June and Sept. 1983) This will demand that convoys possess an anti-submarine (ASW) capability, a limited anti-surface strike capability and above all, an anti-air warfare (AAN) capability. AAW means not only VTOL air defence fighters, it also means airborne early warning (AEW), to alert the fighters and SAM operators of the screening vessels. Without the above systems, it is unlikely the RAN could provide any protection to its shipping, let alone its own naval strike forces. Standoff weapons such as Exocet are becoming very common and may be operated by unsophisticated forces. Regional allies of hostile powers may operate short-range aircraft with such weapons, making life very difficult for shipping to and from Japan, for instance.

V/STOL aircraft have reached a point in capabilities, where they may be an effective defensive and offensive weapon, this should be further proved in the future. Current efforts in VISTOL development focus on two classes of aircraft- an air-ground fighter and a multipurpose transport assault/ASWAEW aircraft.

V/STOL Fighters

Currently, there are two families of V/STOL fighters in service, the established and proven Harrier vectored thrust family and the VTOL-only (hence limited) Yak-38 Forger aircraft of the Soviet Voenno- Morskiy Flot.

The Harrier family is represented by the Harrier GR 3/Sea Harrier FRS 1-8AV-8B aircraft, all built around the same powerplant, a single Rolls Royce Pegasus vectored thrust turbofan, delivering 21,500 lb (95. 5kN).

The vectored thrust turbofan exhausts via four nozzles, the fan via two forward “cold” nozzles and the turbine via two aft “hot” nozzles. The exhaust air gases may be directed, by pointing the exhaust nozzles, this being the key to VTOL operation. If the engine is conveniently situated in the aircraft’s centre of gravity, such that the forward nozzles are ahead of it and the rear nozzles aft of it, rotating the nozzles down will create four columns of thrust Given that the total thrust is greater or equal to the weight of the aircraft, it will hover (providing, of course, that the moments about the C. G. (moment-nozzle thrust distance of the nozzle from C. G. balance out, to avoid pitching up and down). This is the principle upon which vectored thrust aircraft operate. Once airborne, in hover, the nozzles may be slowly tilted backward, to accelerate the jet forward, as it accelerates, its wings begin to generate lift, eventually carrying the aircraft, when the nozzles are fully aft. At high speeds, control is provided by conventional control surfaces, as in any other aircraft. At low speeds, these are ineffective, in hover absolutely useless. Here is where the second control system comes into effect, that being the reaction control system. This system employs high-pressure air bled off from the engine compressor, this air is channelled via ducting to control jets situated in the nose, tail and wingtips, these provide pitch, yaw and roll control by varying the amount of thrust from each jet. The reaction control system is coupled to the control column and rudder pedals, so the pilot uses both sets of controls without the necessity to change over. This feature allows short take-off Manding operation (STOL), where the aircraft swivels its nozzles to an angle providing both lift and forward thrust, and carries out a rolling take-off, total lift being shared between the wing and engine thrust. This allows the total weight to exceed the maximum engine thrust and also allows fuel saving, as hover is very inefficient.

A ski-jump, as fitted to British carriers, further improves on this. as it imparts extra vertical acceleration to the Harrier, as it goes over the end of the flight deck, reducing necessary roll distance.

The Harrier family suffers serious performance shortcomings, if considered as a front-line weapon system. Firstly, its top speed is restricted by its powerplant, as the Pegasus must have a large fan and large inlet area, to provide adequate airflow for the forward nozzles. The Harrier will have difficulty in sustaining a speed above Mach 1. Though this may limit its ability as an interceptor, the high acceleration provided by its large thrust-to-weight ratio (better than 1:1) and ability to pull “square” turns, by vectoring engine thrust to augment wing lift while turning. make it an exquisite dogfighter, as clearly evidenced by the type’s combat debut over the Falklands (Argentine pilots nicknamed the dark grey Sea Harriers of 801 Sqn (Invincible) the “Black Death”. reflecting the 30:0 kill ratio of the Fleet Air Arm). Unfortunately, an air defence situation demands a fighter to intercept a target as fast as possible in order to stop it from launching missiles, this is where the supersonic dash is essential, cutting the enemy’s time at least twofold. The Harrier also suffers of severely limited endurance, as it is a very compact aircraft with little volume available for fuel, further restricted by payload limitations. If one also considers that these payload/space limitations cut severely into the plane’s radar and ECM capabilities, it is painfully apparent the type can successfully perform its air defence mission only against second-rate fighters or subsonic bombers. If the aircraft were to acquire a lookdown/shootdown radar with radar-guided missiles, together with a datalink to an AEW aircraft, of capabilities in the class of the E-2C, it could become more effective in its role, relying on AEW for target acquisition and vectoring into a head-on shot position to kill an incoming target. This is currently under investigation at the time of writing.

A substantial improvement in speed can be provided by the use of plenum chamber burning (PCB). A PCB derivative of the Pegasus would be fitted with revised forward nozzles, these containing miniature afterburners. During takeoff or supersonic dash, these would operate, vastly increasing the thrust available from the nozzles, in cruise the engine would perform as 1:1 bypass ratio Pegasus. The installation would require variable inlet geometry, to satisfy in-hover airflow demands and supersonic drag and flow conditions.

A PCB powerplant in the 30,000 lb (134kN) class is currently feasible. A possible disadvantage of the system may be the effects of the “hot” forward nozzles on runway surfaces and inlet airflow, as reingestion may occur.

At this stage, the US Navy has asked for preliminary studies on a future VISTOL supersonic strike/air defence fighter, this extending on earlier studies of a V/STOL “B” fighter. The USN would like a 20,000 to 40,000 lb gross weight (9000 to 18,000 kg) aircraft, reaching at least Mach 1. 6 and capable of a VTO deck launch followed by an intercept dash to stop hostile aircraft. This aircraft would be operated from LPHS, cruisers and destroyers, later presumably from surface-effect vessels.

Submissions have been offered by Rockwell, Vought, General Dynamics and McDonnell Douglas. Rockwell and GD would like to use augmenters, systems that employ high-pressure exhaust gases to generate a high-volume, low-velocity airflow. Both technology demonstrators, built some time ago, failed to perform, though it appears NASA believes the project will work. Vought’s submission is the tandem fan, which diverts fan airflow into a PCB nozzle, fore, the turbine exhaust nozzle, aft, deflects down to generate lift, drawing air from a dorsal auxiliary inlet. In cruise, the system behaves like a low bypass turbofan.

The fourth submission is by MDC, based on a PCB 34,000 lb (150kN) powerplant, the aircraft designated Model 279-3, would have an all-moving canard and could reach Mach 2. Of all the systems, this aircraft currently appears to have the most potential, though it will probably take another ten years before anything flies, this will obviously allow for a lot of changes, both in technology and requirements.

V/STOL technology places great demands on the powerplant, which must have an extremely good power-to-weight ratio and superb reliability, if the aircraft isn’t to become a death trap, something very important in a fighter, which will have a single engine. Minimum empty weight will necessitate the use of advanced composites, e. g. carbon fibre or Kevlar epoxy, both for major structural components and skins. The demands placed upon the electronics will also be massive. The radar will have to have performance as good as if not better than current systems such as APG-65, all packaged into a smaller volume/weight. Fly-by-wire control will be used, most likely employing optic fibre digital command links. ECM/EW systems will have to be extensive, this will necessitate a lot of compact computing power, a lot of that at an autonomous level to limit the amount of data that would have to be channelled through the aircraft will have to perform a multitude of strongly diverging roles, each demanding specific display formatting. Space limitations will force an extremely compact system, possibly even necessitating helmet projection visors. The lack of on-hand diagnostic equipment, when operating from forward bases or small ships, dictates a sophisticated sell test and diagnostic system, this together with maintainability would force increases in empty weight, something not permissible for the given role.

From the engineering point of view, this represents a considerable challenge (more likely a nightmare), though designers will be able to draw on a lot of experience gained in current projects such as the F-18, AV-88 and X-29A. Advances in HgCdTe array technology will allow compact and cheaper FUR, just as conformal radar array technology is coming of age, also allowing weight savings.

The next major class of V/STOL aircraft is represented by multirole derivatives of transport aircraft, such as the Bell Tiltrotor family and Grumman’s proposed Tiltfan. The Tilfan (see Design 698, March 1981) represents a subsonic V/STOL aircraft, powered by two high bypass turbofans, fitting into the 20,000 lb (9000 kg) gross weight class. This aircraft would come in two basic versions, an ASW and AAW/anti-surface version, complemented by an ECM jammer. Grumman proposes large-scale use of composites, conformal radar arrays, advanced display technology and distributed computer systems employing autonomous bit-slice processor-based subsystems.

At this stage, a technology demonstrator has not yet flown. Conformal arrays have not yet been incorporated in a large-scale production weapon system and of the newer display technologies, Honeywell’s helmet-mounted projection visor is in production for the AH-64 Apache, though flat panel displays are still moving rather slowly, only alphanumeric Light-emitting-diode (LED) arrays having found their way into production.

Grumman’s Tiltfan is a very ambitious project, unfortunately, it may never see the world in the form it is currently depicted as having. One of the harsher aspects of the real world is the endless series of problems any designer will encounter when marrying an immature airframe to untried electronics. In this sense, the Titan could be expected to have very sizeable teething troubles, till the bugs are removed (one of the nastier aspects of conformal radar, which is comprised of flat panel arrays flush with the aircraft’s skin, is its insistence on being tested on an airframe identical, mechanically and electrically, to that of the production aircraft. A testbed with a different shape will distort the antenna patterns, precluding the established practice of testing radar sets by fitting them to an instrument-packed executive class transport).

Another contender, for the multirole aircraft, is Bell’s Tiltrotor family, currently mature enough to become a viable system.

Having been rather successfully tested, the Tiltrotor is likely to become a major element in the Western military, for reasons which will become obvious shortly.

Bell’s involvement with Tiltrotor technology began with the early sixties XV-3, which did fly, but due to the non-existence of compact and reliable electronics, missed out on a stability augmentation system and as a result was rather difficult to fly, particularly in hover Bell Helicopters were patient, though, and exploiting this experience, developed an advanced technology demonstrator for a US Army NASA test program, the Bell Model 301 XV-15 Tiltrotor. The 301 has proved to be very successful, vindicating Bell’s support for the concept.

The 301 operates in two distinct modes, helicopter and aeroplane, with a transition mode termed conversion. In helicopter mode, both wingtip engine nacelles are pointed vertically up, and the rotors provide lift, in aeroplane mode, these are tilted forward (see photo) and perform as turboprops. As one may observe, the concept fuses a helicopter’s VTOL capability with turboprop speed and efficiency.

In hover mode, each of the three-bladed stainless steel rotors provides lift and control. Pitch control is provided by cyclic pitch on both rotors, yaw control by differentially applying cydic pitch. Roll control is simpler, by the differential application of collective pitch. The advantage offered by this configuration, in forward flight, is the lack of interference between the rotors, as neither lies in the slipstream of the other.

Control performance in hover in enhanced by a three-axis Stability Control and Augmentation System (SCAS), which damps attitude changes, improving gust response, which is fairly good, due to the higher disc loading, compared to a helo. A Force Feel System provides an artificial feel, proportional to speed, it also conceals SCAS inputs from the pilot. The aircraft may be flown with SCAS and FFS disengaged, though handling will degrade.

The cyclic and collective pitch controls are gradually phased out, during conversion, by a mechanical mixing box, which monitors nacelle tilt angle and commanded attitude change rates. In aeroplane mode, control is provided by purely conventional control surfaces, which operate all the time. Each of the engine nacelles contains a powerplant, a 1550shp (1156kW) Avco Lycoming T-53 turboshaft, a gearbox, control mechanisms for hover and a tilt actuation mechanism. Both gearboxes are linked by a drive shaft to synchronise the rotors and avoid a crash in the event of a single-engine fail, each engine has a 2 min. rating of 1800shp (1343kW). If failure occurs during transition, the extra power should allow the aircraft to pull through. Both SPECO tilt actuators are linked by a drive shaft, one alone should tilt both nacelles in the event of a failure.

The 301 has an empty weight of 10,250 lb (4640 kg) and a nominal VTOL weight of 13,250 lb (6000 kg) gross, allowing for 1100 lb (500 kg) of instrumentation, 400 lb (180 kg) of crew and 1500 lb (680 kg) of fuel. Including reserves, at this fuel load it will cover 400nm (740 km). At 13,000 lb (6000 kg), the aircraft has hovered at 6600 ft (2000 m) and at its 15,000 lb nominal STOL weight, it has hovered and transitioned.

In aeroplane mode, the 301 has clocked a sustained 300 kts (557 km/h), actually below expectations, due to excessive drag, it has descended at 345 kts (640 km/h). The aircraft has pulled -1 to +2. 7 g’s and it has flown at 25,000 ft (7500 m), apparently still climbing at 790 fu/min (240 m/min) and 14,300 lb (6500 kg) gross weight.

Though a Tiltrotor has lower hover efficiency (6 lb/hp) than a helo (typ. 7 to 8 lb/hp) this need not be a serious deficiency for a typically fixed wing mission, e. g. AEW, ASW patrol, where hover occurs only during the VTOVL part of the mission, on the other hand, the higher disc loading the (typ. 13 lb/ft3) reduces gust sensitivity, which is helpful at sea, under adverse weather conditions.

The aircraft is reputed to have a very smooth ride at low level, due to the high loading of the relatively small wing (effectively, the wing is “blown” by the rotor slipstream, in a fixed-wing mode). Interior noise is low, also externally, it is reasonably quiet, apparently first heard only 3 seconds out on a high-speed pass at low level (the low rotor tip speed, cca 600 ft/sec, is responsible).

The aircraft have demonstrated 99% availability, which is attributed to low vibration levels, significantly, the gearboxes must be designed to helo reliability specs, yet spend most of their lifetime operating as turboprops.

In 1982, the XV-15 underwent a series of mission evaluation tests. The Army’s SEMA Phase IA (Special Electronic Mission Aircraft) tests were carried out at Ft. Huachuca in early May. The aircraft was fitted with radar warming gear, APR-39, and chaff dispensers, to assess its survivability in the face of medium altitude SAMs (12 to 20,000 f/3. 5 to 6000 m), the aircraft performed equally or better (claim Bell) than currently fixed-wing aircraft.

The latter half of May saw the XV-15 undergo radar cross-section measurements at NAS China Lake, results were not released.

SEMA Phase IB continued at the same location as IA, in June and early July, the XV-15 received a desert camouflage overall and was pitted against short-range, low-altitude SAMs and radar-directed AAA (guns). Apparently, survivability was demonstrated as better than current fixed-wing or rotary-wing aircraft. Low altitude, low speed manoeuvrability at high gross weights was praised. The final set of major tests occurred in late July, early August, involving shipboard tests. Operating from NAS North Island, California, and the LPH (helo carrier) Tripoli, the XV-15 underwent its sea trials. The aircraft, repainted in a low visibility paint scheme, carried out 54 take-offs and landings (5 rolling take-offs, all landings vertical). In the opinion of the Navy test pilot, as quoted by Bell, the aircraft was easier to land than any other rotary wing aircraft he had flown. Deck edge effects were minimal, and downwash comparable to medium size helicopters.

The 301 demonstrator was built from off-the-shelf subsystems and little effort was focused on stretching performance. A production aircraft would employ carbon/Kevlar composite rotors, carbon wings and fuselage. This would reduce empty weight, radar cross-section and increase allowable g-factors. Where the Tiltrotor would demand refinement is in payload/range (it is rather thirsty, compared to a turboprop, but is more productive than a helo at anything beyond 32 nm (60 km), top speed could hit the 340 kts (630 km/h) mark and some of its unorthodox gust responses (typically yawing in cruise) could be ironed out with a digital fly-by-wire control system with more authority than the SCAS and FFS. The cockpit controls, resembling a helicopter’s in configuration (tilt initiation by a switch at the end of the collective), could probably be retained.

Potentially, Tiltrotor could fill a large number of missions, starting with assault from LPHS or shore bases, an anti-helicopter (Hind killer) and attack gunship, a SAR/combat rescue role, involving low-level penetration. The same type could also perform covert penetration missions, dropping and recovering commandos. Vertical replenishment and COD roles would be very useful for navies. AEW and ASW are obvious naval applications, over the horizon targeting and Elint are also feasible.

At the time of writing, the US DoD was issuing its Request for Proposals for the Joint Services Advanced Vertical Lift Aircraft Program or JVX. JVX is to be a 40,000 lb (18,000 kg) VTOL gross weight aircraft intended to replace current aircraft in the following missions:

Typical of these mission requirements would be carrying 24 troops (5700 lb/2600 kg) on a Lo-Lo-Lo profile for 200nm (370 km) and return. The aircraft is expected to sell-deploy worldwide, with additional fuel tanks it must have a ferry range of 2500 (4500 km).

On April 3, 1982, the US DoD JVX team announced it had selected the tilt-rotor concept in preference to Sikorsky’s Advancing Blade Concept (ABC) helicopter and Grumman’s Tilfan. Subsequently, on June 7, Boeing Vertol and Bell Helicopter announced a teaming agreement on the JVX, exploiting Bell’s XV-15 experience and Boeing’s heavy lift experience (Boeing had also dabbled into tilt-rotors).

The Bell-Boeing proposal for the program would be an enlarged Tiltrotor, cruising over 300 kts (560 km/h) at 30,000 ft (9000 m). Off the shell powerplants would be used, the GE T-64 would be a viable candidate, in an uprated form, as it is in widespread use throughout the US services. Wings and rotors would be most likely composite, to save weight and reduce radar cross-section. The control system would employ fly-by-wire. Perhaps a digital, software configuration system. Bell have suggested shipboard stowage where the blades fold inward, nacelles tilt forward and wing swivels in line with the fuselage, occupying an area comparable to the CH-46, rotors folded.

Of all the above roles, the Tiltrotor is exceptionally well suited to the USMC Assault mission and the USARUSN combat rescue/covert landing missions. Fitted with FLIR, Low Light TV and compact terrain following radar (TFR), the quiet, relatively fast Tiltrotor has a low IR signature, all of these factors would assist in the low level penetration of hostile territory. The aircraft would carry an in flight refuelling probe, and conformal fuel tanks would probably mount on the undercarriage sponsons. Radar warning and ECM would be necessary, defence suppression equipment would probably be comprised of GAU-2 Miniguns, tailgate and nose-mounted and perhaps the AIM-9L to counter hostile heloes or fighters. The USMC Assault ship would lack the more elaborate systems.

This basic airframe would be well suited to a tactical transport, for the Army (a very suitable candidate for the RAAF Caribou’s job) and a Navy Carrier On-board Delivery (COD) transport/Vertical Onboard Delivery (VOD) transport or tanker. In these roles it could perform very well, particularly as a tanker, it can be rapidly launched in emergencies and may refuel holes and jet aircraft. A further advantage for the CV role is the small rotor size coupled with the 14 ft+ rotor height above deck and the absence of tail rotors out of the pilot’s view. Bell’s suggested CODVOD could execute a VL after covering 900 mm (1600 km) with a 5000 lb (2250 kg) payload. Aircraft in this class, i. e. a multirole COD/VOD/SAR/tanker would be extremely valuable to services such as the RN or RAN, who cannot afford the luxury of dedicated aircraft on undersized carriers.

The question arises, how well-suited is the aircraft to the ASW and AEW roles? At 40,000 lb (18,000 kg) VTOL gross weight, it falls into the same category as the E-2C and S-2A, though it will fall behind them in terms of top speed, it does have better endurance. On the other hand, it would outclass the current Sea King (or ASW SH-3) in both the AEW and ASW roles. Given that the USN (or anyone else willing to pay the development costs) is willing to accept a loss in all-out performance in exchange for VTOL capability, an asset hardly appreciated now through sheer inexperience with V/STOL, the Tiltrotor could offer vastly increased operational flexibility and superior availability, as the airframe and dynamics would be designed to satisfy USMC Assault role maintainability and reliability under battlefield conditions.

The implementation of a dedicated ASW aircraft could really involve only the redesign of the fuselage and repackaging of the onboard systems fitted to the S-38 Viking, perhaps adding dunking sonar, e. g. Bendix HELRAS. A replacement for the E-2C would be more demanding, as a rotodome on top of the fuselage is hardly practical, Bell and General Electric have, in fact, established that a nose and tail-mounted pair of radomes (as the Nimrod AEW 3) would provide 360-degree coverage, without interfering with the rotors. An AEW aircraft of this sort is sorely needed by the Royal Navy, who have to rely on a lash-up AEW Sea King. Under these circumstances, one cannot help thinking of Marconi Avionics’ experience with the Nimrod, optimised for overwater low-flying target detection and fitted with fore and aft radomes. Marconi Avionics are, in fact, part of General Electric, this would create an opportunity for a joint US-UK development program, to satisfy the needs of the USN and RN. One could surmise, that were the aircraft available, the RAN couldn’t afford it, anyway. It appears nobody has yet examined the operational aspects of land-based VTOL AEW As this aircraft wouldn’t be ready till 1990, it could take advantage of a lot of progress in electronics, eg. smart flat panel, microprocessor driven, displays and faster, more compact computers. Onboard systems may communicate via optic fibres, increasing data rates by orders of magnitude above established buses as MIL-STD-1553. The aircraft’s passive detection system would probably employ conformal arrays, to provide finer angular resolution. The question of whether this aircraft will come into being depends on whether Grumman’s Tiltfan can establish itself. The Tiltfan is in the 20,000 lb (9000 kg) class and performs better, flying considerably faster, but one could question whether its advanced electronics would be ready, as discussed above.

One may, in fact, find the Tiltrotor assuming the AEW role from CVs and CVNS (counting in LPHS) and being used to establish operating procedures, with the newer Tilfan being gradually phased in, for use on smaller vessels (history shows us that the E-3A, Nimrod and Moss came into being when transports sprouted motorhomes or radomes – it is always a safer proposition to work with an established platform).

Bell suggested the COD/VOD, assault and tanker derivative could be available by the early 1990’s, and AEW and ASW aircraft in the mid-nineties.

The US Army’s SEMA-X (Special Electronic Mission Aircraft) rol covers the tasks of existing OV1 Mohawks and RU-21J, both i the 12,000 to 18,000 lb (5000 to 8000 kg) class, one can only assume that the JVX will have to carry much more equipment, possibly communications monitoring and jamming, aside from the IF surveillance equipment and synthetic aperture ground map radar.

The tiltrotor concept offers an extremely flexible aircraft, it is very likely that the 40,000 ib JVX will become as common a multipurpose platform as the current C-130, filling any one of a wide spectrum of roles. Smaller tiltrotor aircraft may however have to compete with advanced heroes in the gunship role, as they are not really suited to nap of the Earth operation.

It is unlikely that its most capable competitor, the Tilfan, car match it in its primary transport role, this alone will allow the type to establish itself.

V/STOL technology has reached the turning point in its development and is likely to become very common, in the future for all of its assets. Australia should not fall behind, in the development of V/STOL aircraft, as experience must be acquired before the new generation of aircraft appears. Whether the RAN Fleet Air Arm will operate from container ships or shore bases, it should not be denied the opportunity to acquire and operate WSTOL fighters such as the Sea Harrier. Failing to recognise the significance of this technology now may cost much more than a few hundred million dollars, in the future.

Tiltrotor for AEW and Missile Targeting?

It is one of the more disappointing aspects of current naval air defence, that most vessels tasked with fleet area defence cannot really protect themselves against low-flying sea skimmers, such as Exocet. Where these vessels are equipped with systems such as Phalanx (see TE, Sept. 1983), a self-defensive ability is present however these vessels are to provide air defense cover for unarmed convoy vessels (say requisitioned, as the RN gained the ill-fated Atlantic Conveyor, in 1982), the limited range of the gun will leave sizeable gaps in the defensive screen. It is unrealistic to assume that any navy at war will divert most of its destroyers to provide anti-aircraft screens for convoys. The result is likely to be carnage reminiscent of the WW PO convoys to Murmansk. As much as the Arapaho program may offer (Arapaho involves the development of a containerised rapid conversion kit to transform a container ship into a makeshift VISTOL carrier in a matter of hours) for convoy defence, the absence of a viable VISTOL AEW aircraft, coupled with the currently dismal lookdown/shootdown capability of the Harrier family means that a fast, sophisticated bomber as the Tu-26 Backfire, admittedly a pain for the USN’s current fought missile screen, would have little difficulty in getting close enough to launch a small sea skimmer (it is rather naive to assume that a weapon in the class of Exocet would not be in the V-MF inventory, particularly since this missile has been on sale to Third World countries) which could find its way through the screen, particularly if assisted by jamming from the Backfire (it does have enough size to accommodate powerful jammers), standing off beyond the range of the area defence SAMs. If Harriers are scrambled, it will still take them longer to intercept the Backfire, than it would take a fast missile to hit the convoy. The Backfire can exit the scene pretty quickly, once the sea skimmer has locked on. Backfires would find this situation a bit more difficult to deal with, if the convoy isn’t advertising its position with its shipboard surveillance radars, as it would have to get closer to acquire range/bearing from its own radars. Things may be even worse, if a decent lookdown/shootdown radar is carried by an airborne platform, as the Backfire loses its opportunity to get in close and undetected, beneath the horizon of the shipboard radars. Modern fighter radars, such as the ANAWG-9 (F-14 Tomcat) or AN/APG-63 (F-15) have ranges beyond 100 nm (it is impossible, for obvious reasons, to get accurate figures, but estimates place the AWG-9’s detection range well beyond 115 nm, as it will illuminate (Pheonix guidance and targeting) targets at 100 nm, in the presence of jamming), will track around 25 targets while scanning for others, ground map (including synthetic aperture fine resolution), accurately range and target or provide illumination for air-air missiles. These radars are the key to the lethality of these large fighters. One could, of course, further extend and suggest fitting such systems to a small, VTOL platform, such as the Tiltrotor. Given that the SAM guidance is compatible with the radar’s illuminating mode, this would allow area defence tasked vessels to launch SAMs at low-flying targets over the vessel’s horizon and therefore, not necessarily aware of the SAM launch. The ideal guidance kit for this type of missile would come from Hughes AMRAAM, after launch the Tiltrotor would continuously update the missile with the target’s position until it is close enough to activate its own active radar homing seeker and destroy the target. A further extension would be a containerised version of the Martin Marietta EX-41 Vertical Launch System, fitted with a launch command receiver, slaved to the fire control of the targeting aircraft. The targeting platform would detect, track and interrogate a target, if hostile, it could have a SAM launched and then guide it into the target. Alternately, it could vector AMRAAM carrying Harriers into a suitable launch position, via a datalink (say generate steering cues on the Harrier’s HUD head-up-display]). This would allow the Harriers to operate with radars off, a further advantage. Of course, this Tiltrotor radar would also have the ability to detect surface contacts or map the coastline, alternately operate as a Blint aircraft. If an improved version of the current XV-15 were used as a platform, it could probably enter service by the mid-eighties, as the radar equipment itself is well established. An aircraft of this type may be far more effective than a helo in over-the-horizon targeting, it could of course itself carry a limited amount of weapons, for self-defence (AIM-9L, AMRAAM?) or attack small surface targets, e. g. patrol boats. Carried by vessels such as the FFG-7, it would be a relatively agile reconnaissance platform, faster than established helos, and offering more range.

The conversion need not be as difficult as one may think, for instance, the APG-63 is completely modular, weighing in at 494 lb (224 kg) and could easily fit into the volume of the XV-15. The aircraft’s engines would require uprating and fitting with generators capable of coping with power supply demands to the radar. The aircraft could retain a two-man crew, the copilot’s station being fitted with the given CRT displays. Later models of the APG-63 are fitted with a Programmable Signal Processor (PSP), a fast digital computer which carries all of the radar’s functions a software in computer memory. This means that operating modes dedicated to the F-15’s weapons could be deleted without butchering the hardware, the system focusing on track-while-scan, range-while- -search and velocity search air-air modes and the various air-ground modes, e. g. synthetic aperture ground map or air-ground ranging. Passive detection mode software could be substituted, for the Elint role. The question arises, where to fit the radome with the planar array antenna? The electronics and gridded Travelling Wave Tube transmitter could be packaged into the fuselage aft of the cockpit, together with communication equipment. One option would involve a bulbous nose radome, the array fed by a waveguide through the lower fuselage, this providing forward hemisphere look-up/look-down. A reworked gimbal system and retractable ventral radome would offer a 360-degree scan but limited look-up (rotor interference may be a worry). A tail-mounted radome, as in the first instance, together with a nose radome would be most expensive, but offer best coverage (one must note that both gimballing and array control must be altered, aside from signal processing, to enlarge the scanned sector from cca 140 deg to 180 deg), it would though impose a drag penalty. In terms of overall performance, the aircraft need not suffer too much, the radar systems would weigh about 1000 lb (450 kg) as the test instrumentation of the SV-15. Weight could be saved with composites and fibreglass.

As much as one may regard the above as blasphemy, of sorts, it may be worth some thought. Helos are very common in targeting roles, but could hardly match the air-air, air-ground and Elint capability of such a system, opponents of which will basically cry – it is not survivable enough to justify the cost of the radar installation. Only the future can really tell us whether such concepts are viable.