The AV-8B Harrier II v Sea Harrier

The AEW problem affects all the V/STOL carrier options, and was recognised long before the Falklands conflict erupted, with British planning for a major conflict being based on the availability of land-based RAF or carrier-based US Navy AEW aircraft. The fighting around the Falklands was a fundamentally different scenario, but it did emphasise the paramount importance of flexibility in naval air power. The Sea Harrier, which was intended to intercept Soviet maritime patrol aircraft operating as medium-level singletons, and to attack with nuclear weapons any major Soviet vessel threatening NATO sea lines of communication, was suddenly dogfighting (very successfully) with Mirages and A-4 Skyhawks at low-level, and performing airfield attack missions with iron bombs and BL755 cluster weapons.

An essential factor in the aircraft’s operational flexibility is the forward-looking radar that can be used in both the air-air and air-surface modes. It follows that, in the event of the RAN being approved to buy high-performance V/STOL aircraft for the new carrier, the two options would be the British Aerospace Sea Harrier as operated by the Royal Navy (and shortly by the Indian Navy) and McDonnell Douglas’ proposed AV-SB Plus, a radar-equipped development of the Marine Corps AV-SB Harrier II, which is intended purely for the air-surface role.

The following notes provide an outline of these two competing programmes, highlighting their advantages and shortcomings, and comparing their relative merits in an Australian context.

Sea Harrier

The BAe Sea Harrier FRS Mk I is a radar-equipped strike fighter, designed to operate from relatively small aircraft carriers in the air defence, surface attack, and reconnaissance roles. It is a straightforward development of the well-established Harrier/ AV-SA, with minor airframe and engine changes, and a completely revised nav-attack system and armament to suit RN requirements.

This new variant differs in appearance from its predecessor mainly in having a raised cockpit and enlarged nose, respectively providing an improved rearview and greater equipment space in the front fuselage, which houses the Ferranti Blue Fox radar. In order to reduce salt water corrosion problems, various airframe and engine components have been redesigned in aluminium alloy, rather than magnesium, the Rolls-Royce Pegasus accordingly being redesignated Mk 104 (as distinct from the Mk 103 of the Harrier GR3).

Whereas the land-based RAF Harrier has a pure inertial navattack system, the Sea Harrier has a Doppler-TGP system, to avoid the problem of levelling and aligning the inertial platform on a moving deck. The main components of the Sea Harrier system are a Decca 72 Doppler radar and the Ferranti NAVHARS (navigation, heading and attitude reference system), the latter consisting of a twin-gyro platform (TGP), a navigation computer controlling the erection of the platform, and a combined HUD/WAC (head-up display and weapon-aiming computer). The TGP can be aligned in two minutes, even at sea, and is stabilised in flight by inputs from the Doppler radar. The system stores the coordinates of up to ten reference points, and displays steering instructions, ground speed, track, and time/ distance to go, on the HUD. Navigation updates can be made by means of radar fixes, TACAN, or visual on-top fixes. In practice, navigation errors have averaged 1. 5 nm after a 50-minute flight.

The Sea Harrier also differs from the RAF version in having a radar warning receiver with an improved display, and various modifications to the flying controls system. The power of the reaction control system about the roll axis has been increased, and the aircraft is equipped with an autopilot to provide hold modes for pitch, bank, heading and height, in order to reduce pilot workload during radar operations.

Whereas the RAF Harrier is mainly used for the delivery of Hunting BL755 cluster weapons and 68 mm SNEB rockets against armoured vehicles, the primary armament of the Sea Harrier is its air-air missiles, with air-surface weapons taking second place. Initially, the AIM-9G Sidewinder was used, but the all-aspect AIM-9L came into use just before the Falklands crisis erupted, and by all accounts has served extremely well. On one occasion two Sea Harriers, armed with a total of four AIM-9Ls, intercepted four Argentine Mirages and destroyed them all. The Sea Harrier retains the two 30 mm Aden cannon of earlier variants, although this is clearly only a back-up armament to these new missiles.

The AIM-9L is probably the most advanced missile of its class, but it is nonetheless a short-range weapon with the traditional limitations of infra-red homing, i. e. it cannot be used in the cloud, and it may be decoyed by flares. The RN is therefore interested in the use of a medium-range radar-guided weapon on the Sea Harrier, the obvious candidates being the BAe Sky Flash and the Hughes AM RAAM (Sparrow replacement). There is currently no funded programme to add a medium-range missile to the Sea Harrier inventory, but it is generally accepted among those concerned that money will be made available in the near future. Exactly how these larger weapons would be carried has not been decided. In principle, the RN would like to retain its AIM- 9Ls on the outboard pylons, and 455-litre tanks on the inboard pylons for endurance in the CAP (combat air patrol) mission. One possibility is to mount the new missiles on the drop tanks, and the radar illuminator (if required) in the nose of one of these tanks.

For the air-surface mission, the Sea Harrier was initially cleared to use 450 kg bombs. Its ‘strike’ designation implies (in NATO terminology) a nuclear capability, although the RN has never confirmed this, nor indicated how this type of weapon would be carried or delivered. It is clear from accounts of the Falklands operations that the Sea Harrier is using standard RAF-type conventional weapons, including BL755 and 68 mm RPs. Under development, but not scheduled for service until the mid-1980s is the BAe Sea Eagle, a long-range’. Sea-skimming derivative of the long-established Martel. The new missile is believed to offer some improvement over Harpoon in ECM resistance and warhead design, although the American weapon could well be employed on some export Sea Harriers.

The Sea Harrier retains the wing of the land-based version, which has proved remarkably free from dangerous departures, even in the most violent combat manoeuvres. It has a span of 7. 7 m, an area of 16. 68 sq m, and an outrigger track of 6. 7 m. The new aircraft is slightly longer at 14. 52 m, but the nose folds for radar access and to facilitate the use of carrier lifts, reducing the overall length to 12. 72 m. Its height of 3. 7 m is no problem in the context of hangar stowage, the criterion being the clearance needed to remove the engine vertically from the fuselage for a powerplant change.

Due to additional equipment, the Sea Harrier is somewhat heavier than the GR3, with an empty weight of 5900 kg. Internal fuel is unchanged at 2290 kg, and the maximum take-off weight is 11,880 kg. Vertical landing weight is 7650 kg.

In a CAP mission with two AIM-9Ls, two cannons and drop- -tanks, the Sea Harrier can remain on station for 90 minutes at 100 nm radius. When STO is not possible, a CAP mission with the same armament can be flown from VTO, but time-on-station is then reduced to 30 minutes since disposable load suffers from the absence of wing lift at take-off. Given guidance from a radar picket vessel, the aircraft can fly a high-level intercept mission out to 400 nm radius. In a HI-LO-HI reconnaissance probe, the radius of action is increased to 450 nm, the aircraft in this case being fitted with two cannons and a starboard oblique camera in the front fuselage. In a HI-LO-HI strike mission with two Sea Eagle missiles and two cannon, the Sea Harrier can fly a radius of action of 280 nm, the missiles adding a further 20-50 nm (presumably depending on release altitude).

The Sea Harrier programme for the RN was initiated formally in May 1975 (ten years after the go-ahead for the RAF Harrier). with an order for 24 aircraft, which was later increased to 34, supplemented by four two-seat Harrier T4s. The first aircraft (XZ450) had its maiden flight on 20 August 1978, and the first delivery to RNAS Yeovilton took place on 18 June 1979. The original planning was done on the basis of equipping a training unit and three operational squadrons, but (following a failure to win support for a further incremental purchase) the British Fleet Air Arm decided to limit its operational force to two squadrons, despite the fact that three Invincible-class carriers were planned.

The Sea Harrier IFTU (intensive flying trials unit) formed as No 700A Sqn in May 1979, and in March 1980 it became No 899 Sqn, the headquarters and trials unit for the Sea Harrier, normally equipped with seven aircraft. The operational squadrons have a normal peacetime establishment of five aircraft each, No 800 Sqn (normally allocated to HMS Hermes) being commissioned in April 1980 and No 801 Sqn (normally aboard HMS Invincible) in February 1981. Due to the need for more RN fighters to serve with the Falklands task force, these two regular squadrons have been enlarged (and augmented by RAF GR3 Harriers), and a third squadron (No 809) formed specifically for this operation. As with all operational details, the choice of base for this unit has not been revealed, although it might be conjectured that it is on the larger ship, HMS Hermes.

To date the only export order for the Sea Harrier has come from the Indian Navy, which will use the type to replace the old Hawker Sea Hawks which were operated from the carrier Vikrant until 1980 (they are currently used for shore-based training). With the acquisition of the Sea Harriers, Vikrant will be fitted with a ski jump, and will thus no longer be able to fly the Alize ASW aircraft. The Indian order is for six Sea Harrier FRS Mk 51s and two Harrier TMK 60s. The single-seater differs from the RN aircraft in having the Matra Magic missile in place of Sidewinder, modified radar, different radios and IFF, and gaseous oxygen in place of LOX. Whereas the RN two-seaters are purely for flying training, the Indian T60s will have virtually the complete naval nav-attack system, except for the radar. Deliveries begin at the end of this year, and (in the case of the Mk 51s) will presumably be completed in the course of 1983.

Unless there is a repeat order from India, or a new export customer appears (e. g. Japan), then the best hope for linking an RAN order to another batch, and thus benefiting from a higher production rate, is a follow-on order from the RN. Aside from replacing Sea Harriers lost over the South Atlantic, there may well be sympathy for strengthening Britain’s Fleet Air Arm in the light of the remarkable flexibility it has demonstrated in the Falklands crisis. An order for anything from 10 to 20 aircraft might well result, when future needs can be assessed.

Sea Harriers ordered in 1983 for delivery in 1985-86 will presumably incorporate some advances over the current FRS Mk I, with provisions for Sky Flash or AMRAAM, Sea Eagle, and probably the modified engine of the AV-8B (which will be used by the RAF as well as the USMC). Some extra thrust would doubtless be of value to Sea Harrier performance in the context of vertical landing weight (which has always been a matter of some concern throughout the development of the Harrier family) and of specific excess power at altitude.

AV-8B

The McDonnell Douglas AV-8B Harrier II is likewise based on the Harrier/AV-8A series, but it is a much more radical development, aimed at achieving a significant increase in workload and radius in what the US Navy designates as the ‘light attack’ role, at present carried out by the US Marine Corps’ A-4M Skyhawkand AV-BA. Conceived specifically for the USMC, the AV-BB will operate both from aircraft carriers and from short beach-head airstrips, generally with support from aircraft such as the F-18 Hornet.

In order to achieve this warlord/radius improvement, the wing, air intakes and lift-improvement devices under the centre fuselage have been completely redesigned, and extensive use has been made of lightweight advanced composite materials, notably in the wing, flaps, tailplane, rudder, ailerons, forward fuselage, outrigger fairings, and engine access panels. Carbon fibre composites form approximately 26. 3 per cent of structure weight.

In striving to achieve much higher disposable loads, MDC increased the gross wing area by around 20 per cent, to a nominal 22. 4 sq m, although this figure does not allow for the leading edge extensions that have recently been added. The Harrier’s small, plain flaps were replaced by large single-slot flaps, which obtain considerable lift augmentation from the pumping action of the front jets. In addition, the air intakes were provided with a second row of suction-relief doors, and the front nozzles were redesigned with a zero-scarf cut-off to reduce the sideways spread of the jets (and hence the loss of vertical thrust component).

Take-off weight in the VTO mode (which is employed by the USMC for a deck-launched intercept mission) is increased by the use of enlarged longitudinal strakes under the centre fuselage, and a retractable cross-dam at their forward end. Combined with the presence of the main undercarriage to the rear of this area, the strakes improve the ground cushion effect and reduce the recirculation of hot engine exhaust to the intakes. Handling at low speeds is improved by the greater moment arm of the wing-mounted reaction controls, which are moved out from the outrigger fairings of the Harrier wing to the tips of the AV-8B’s long-span wing.

Other airframe changes include a new front fuselage, which provides more equipment space and improved rear view by virtue of the pilot’s eye position being raised 26. 7 cm (only marginally less than the 28 cm elevation of the Sea Harrier cockpit).

The engine of the AV-8B is the Pegasus Mk 105, or F402- RR-406, derived from the Mk 104, but with a revised intermediate casing to smooth the flow into the HP compressor, and with changes to the turbine to improve cooling and increase engine life. The emphasis has been on improving component life and reliability while reducing operating costs, but these same modifications could (if required) be used to increase thrust instead.

The AV-8B will have Litton ASN-130 inertial navigation, TACAN, digital air data computer, radar altimeter, a podmounted ALQ-164 ECM pod, flare/chaff dispensers, all-weather landing system (AWLS), and a Hughes angle-rate bombing system (ARBS). In the ARBS, laser- and TV-trackers use a combined set of optics, which can be locked on to a target marked by a laser operated by another aircraft or by friendly troops. In this mode, the system can be used in both day and night attacks, but daylight missions can also make use of a simple contrast-lock on visually-acquired targets. In either case, the slant range to the target is computed from the sight-line spin rate.

The design of the cockpit reflects earlier MDC experience with the F-15 and F-18. An up-front control (UFC) directly below the Smiths HUD groups together all essential communications, navigation, identification and weapons control functions, Below the UFC, the conventional flight instruments serve as backup to the HUD. On the left, a multi-purpose display provides pictures from the ARBS and Maverick missiles, plus navigation data, stores management and checklists, and on the right there is a digital engine display. As would be expected in an MDC combat aircraft, the hands-on-throttle-and-stick (HOTAS) design allows the pilot to make all the vital inputs to the weapon system (plus manoeuvre flap and stability augmentation) without removing his hands from the flight controls.

The systems of the British variant of AV-BB will differ in that there will be a moving map display (the Tornado front cockpit repeater unit) below the engine instruments, and that AWLS will be deleted, probably being replaced by MEL’s Madge (microwave airborne digital guidance system). The British aircraft will also have a panoramic reconnaissance camera in the front fuselage, a Martin-Baker ejection seat in place of Stencel, and stronger wing leading edges and intake lips to meet RAF birdstrike requirements. The RAF will retain the ARBS (existing Harriers use laser ranging, which is subject to peacetime training problems) and the new General Electric GAU-12/U Equalizer cannon. A five-barrel Gatling gun that fires 25 mm ammunition at 3600 rd/min and a muzzle velocity of 1097 m/sec, the GAU-12/U will be carried in the port ventral pod, complete with pneumatic drive, linked by a crossover fairing to the starboard pod, housing 300 rounds in a multi-layer linear magazine. The AV-8B can carry up to 4170 kg of ordnance on its seven pylons, the options including four Mavericks, 16 GP bombs (presumably Mk 82s), 10 laser-guided bombs, 12 cluster bombs, and 10 rocket pods.

The AV-8B is naturally a larger aircraft in hangar space requirements than the Sea Harrier, having a span of 9. 23 m and a nose that does not fold, giving a length of 14. 1 m. However, it is even less tall, at 3. 53 m, and the outrigger track is usefully reduced to 5. 2 m, which will facilitate deck handling. The empty weight of the USMC aircraft is slightly less, at 5780 kg, although the extra equipment of the RAF version may make it heavier than the Sea Harrier. Internal fuel capacity is increased by almost 50 per cent, to 3400 kg, due largely to the greater thickness of the AV-8B’s supercritical aerofoil. Maximum take-off weight is increased by 1610 kg, to 13,490 kg. In a HI-LO-HI attack mission, the AV-8B can fly a radius of 600 nm with 1500 kg of ordnance, or 3500 nm with 3630 kg. Ferry range is 2460 nm.

Many AV-BB features, including the composite supercritical wing, lift-improvement devices, modified intakes, and zero-scarf nozzles, were tested by modifying two AV-8As, which were designated YAV-8Bs, the first of which flew on 9 November 1978. This testing was followed by flight trials with the first of four full-scale development (FSD) AV-8Bs, which began hover tests on 5 November 1981. By the time these notes are published, all four aircraft will be flying. The second funded batch consists of 12 pilot-production aircraft out of the USMC total of 336 AV-8Bs. According to the production schedule, deliveries will take place over eight years, starting in October 1983. Britain’s RAF is to receive 60 slightly modified AV-8Bs, designated Harrier GR5s, starting in mid-1986.

From the outset of the programme, there have been some US Navy interest in acquiring an ‘AV-8B Plus’, which would retain the light attack capability of the USMC aircraft, but would also be able to function effectively in the air-air role, by virtue of a forward-looking radar such as the APG-65 developed by Hughes for the F-18 Hornet. It has been suggested that some form of radar (possibly the Blue Fox of the Sea Harrier) should be tested in one of the FSD aircraft, but there currently appears to be no work in progress on such a trials installation or on detail design of the AV-8B Plus, although limited studies are continuing.

Summary of Comparison

Although both the Sea Harrier and the AV-8B were developed from the same basic Harrier, they have different roles, somewhat different timescales, and probably different prices. From the outset, the primary role of the Sea Harrier has been air defence, with anti-shipping attacks using Sea Eagle or nuclear weapons as the second mission. The AV-8B is intended purely as a bomb truck, hence additional funding will have to be found if it is to have a radar in the nose, or to employ an anti-shipping GW such as Harpoon.

Although it is possible that MDC will develop some form of ‘AV-8B Plus’ at company expense, there is at present no commitment to such a programme, nor is there any stated intention on the part of the US Navy to operate such an aircraft. It follows that the RAN cannot know when (or even whether) the AV-8B Plus will be available.

Considering the two existing aircraft, the Sea Harrier entered operational service in 1980, whereas the first of eight Marine AV-8B units is to have an initial operational capability (IOC) in FY85, which could mean late in calendar ’84. The British aircraft will thus have at least four years more background experience, and will have been tested in war. An order for Sea Harriers placed early next year would presumably result in deliveries starting in late 1985, whereas the first export AV-8Bs would go to the RAF in mid-1986, and it seems unlikely that Australia would receive the aircraft before 1987. A radar-equipped derivative could easily delay this timescale to 1988-89, depending on when serious development work starts.

A proper comparison of unit prices is not possible at this stage, since Sea Harrier costs have never been published, and since there is a long way to go before annual AV-8B production brings costs down to a meaningful level. On the basis of DoD information released in February (‘Program Acquisition Costs By Weapon System’), the 12 AV-8B pilot production FY82 aircraft cost $US613. 1 m (or $US896. 0 m with initial spares, plus RDT&E), while the 18 aircraftrequestedforFY83were estimated at $US751. 0 m (out of the annual total of $US1059. 5 m).

However, it is no secret that the Sea Harrier is a minimum-cost development programme, and it seems highly unlikely that the RN paid more than $USS m for each aircraft. In contrast, the AV-BB represents a much more extensive modification, with large-scale changes to airframe and systems, and considerable use of costly advanced composite materials. The AV-8B programme has recently been reported as costing $US9100 m for 340 aircraft plus R&D. This may imply a unit flyaway cost of over $US20 m, although this is clearly related to a much later timescale than the first production Sea Harriers for the RN.

Perhaps the most reasonable comment that can be made at this stage is that the extensive changes and costly materials used in the AV-8B suggest that it is a significantly more expensive aircraft than the Sea Harrier, notwithstanding the Termer’s higher production rate. The cost of adding a nose radar, integrating it with the existing systems, and clearing the aircraft for new types of surface missiles, will clearly add to this price differential.

If the Sea Harrier wins in regard to timescale, cost, and certainty of availability, the AV-8B obviously wins handsomely on warlord-radius performance. According to testimony submitted to Congress very early in the programme, the AV-8B will be able to carry six retarded Mk 82 bombs for a radius of almost 750 nm, hence it should be able to go somewhat further with two Harpoons. It will be recalled that the corresponding Sea Harrier radius is 280 nm.

The AV-8B development effort has certainly paid off in terms of workload and radius, but performance is not improved in every respect. For example, vertical landing performance is crucial to the successful operation of any such aircraft but has received no special attention. In the case of the Sea Harrier, VL performance may be marginal under hot conditions, and an increase in thrust would probably be welcomed to ensure safe recovery with certain external stores. The AV-BB Plus with nose radar and appropriate tail ballast will be somewhat heavier than the Sea Harrier, hence VL performance may be of much more serious concern.

Initial flight testing of the AV-8B showed that the supercritical aerofoil was not performing as expected, probably due to the concave area of the undersurface toward the trailing edge. The associated drag increase resulted in a major loss of speed and acceleration relative to the ‘cooking’ Harrier and there were doubts whether it could ever be developed successfully into a combat aircraft. However, modifications to the wing root, inboard wing pylons, and intake cowls, coupled with revised engine limits have now reduced the maximum speed differential to acceptable figures.

The Sea Harrier is undoubtedly a faster aircraft, but the AV-BB has far better low-speed handling characteristics, and a more advanced cockpit, which reduces pilot workload. Due to its larger wing, the AV-8B is more manoeuvrable at low speeds, but it remains to be seen whether it has retained the original wing’s departure-free handling in high-speed combat.

The AV-8B also incorporates a large number of detail modifications to improve serviceability, although it might be argued that its extensive use of carbon composites may involve some degree of risk, conceivably leading to additional costs later in the programme.

To summarise, the Sea Harrier is less expensive, has plenty of background experience, and by the mid-80s will be fully developed for the air-air and air-surface roles that interest the RAN, although some additional expenditure would be necessary if different weapons (e. g. Harpoon in place of Sea Eagle) were specified.

The AV-8B in its simple bomb-truck form will be more expensive will lag in timescale, and will require a major development effort if a radar is to be added. Whether such a multi-role version will ever be available remains to be seen. The AV-8B is far better than the Sea Harrier at hauling heavy loads over long distances, in low-speed handling, pilot workload, and serviceability. On the other hand, its maximum speed is reduced, VL performance may need improvement, handling in high-speed combat may have been degraded, and there may be some risks associated with the large-scale use of advanced composites.

It follows that an RN decision in the near term would probably favour the Sea Harrier, but that the balance may swing in favour of the AV-BB if the decision is delayed until the second half of the 1980s and if the US Navy embarks on full-scale development of the AV-8B Plus.