Harrier Carrier

I am of course referring to the Harrier Carrier orojects which not only offer us the opportunity to build our own 8000 to 12,000 tonne ships but to equip them with the remarkable and advanced Sea Harrier. To this end the RAN could afford to deploy three such carriers during the ’80s and early ’90s. Furthermore the RAN could purchase three of these vessels with equipment and support for probably com­ parable cost of one 25,000 tonne conventional flat top.

It is to this encl that Australian Aviation & Defence Review would like to introduce Mr John Fozard, Executive Director and Deputy Chief Engineer of the remarkable Sea Harrier programme to fully outline the advancement of the Vosper Thornycroft Harrier Carrier and RN Sea Harrier programme and what it offers a navy like our own.

There are a number of smaller navies currently operating carriers, who, undoubtedly, have a current and future con­ cern for the Sea Control role. Australia, India, Argentina, Brazil and Spain all have a fixed-wing airpower capability at sea. None of these navies could afford to procure or operate a new conventional carrier when their existing aircraft-carrying ship is retired.

The other first-level navy has revealed for the first time its future intent for fixed-wing airpower at sea with the VTOL fighters aboard the Kiev. This ship carries enormous future implication for the navies of all independent nations. The Kiev and her forthcoming several sister ships could be the card which sends the maritime poker players away from the table to reconsider their resources and priorities. Clearly to be seen as an instrument of Soviet policy, the Kiev class has powerful capabilities in both the Projection and Sea Control roles.

Harrier capability

But, to return to specifics, what are the maritime air tasks, and how do the assets of the Harrier rank in terms of effective accomplishment of these roles and missions? Bear in mind the unclassified information that, like many subsonic fighters, the Harrier can cruise at altitude for well over an hour on internal fuel, that it cruises at M = 0. 8+ high, and between 350 and 450 knots low, and is capable of 600 knots.

Due to its very high thrust-to-weight, the Harrier enjoys many of the characteristics of a supersonic fighter, such as rapid climb rate and high acceleration. In addition it can make use of its unique thrust Vectoring in Forward Flight Page 38(VIFF) feature. USMC Harriers have outfought F14s, one v. one, below 20,000ft (6000m). All this is possible for a very modest fuel consumption, the Pegasus turbofan requiring a maximum fuel flow of order 250Ib/min (110kg/min) at low altitudes, compared with at least three times this rate for a reheated conventional fighter.

Possible roles and missions at sea

1. Fighter/Intercept/Patrol. The Harrier is cleared to carry 30mm guns and Sidewinder. Later-generation AAGWs are possible. Potential targets: large subsonic patrol aircraft and other fighter/attack aircraft. Intercept radius uo to 400nm (750km). Reaction time for a VTO off-the-deck in­ tercept: 2 min.
2. Reece. Electronic and visual surveillance. In an hour, flying at low level, a Harrier can survey the order of 20,000 sq. miles of sea (70,000 sq. km).
3. Strike. All of a wide range of standard UK/USN/NATO stores can be delivered – rockets, free-fall and retarded bombs. Preliminary clearance flying completed with Martel-type and Harpoon ASGW.
4. Close air support of land forces. This is the chief role of the Harrier in both USMC service and in the RAF. A future Sea Control mission in second-level navies must include this Projection aspect of airpower from ships in the amphibious assault role for which the USMC specifically procured their Harriers.
5. Anti-submarine. The Harrier cannot usefully come to the hover, dunk and listen. Helicopters do this better. But its rapid VTO-off-the-deck reaction to a call to lay a sonobuoy screen, or to carry airdrop torpedoes to a contact point, is unique. Total time from scramble alarm to a 30 mile (55km) distant drop point is under six minutes. This use could relieve AS helicopters of the need to carry armaments in addition to their detection gear, thus giving them a better capability for Sea Control duties.
6. Defence/Offence in Port. All the above missions could be flown from VTO (and with limited STO) from the ship when at anchor or alongside. With these capabilities in mind, we may now turn to the Sea Harrier itself and outline the changes being made to the standard RAF Harrier GR Mk. 3 to provide the Royal Navy with flexible and economic fixed-wing air power at sea.

As is normal in these days of austere defence budgets, the Sea Harrier Programme was approved in May, 1975 on the basis of high confidence that time, cost and risk would all be minimized. The extent of commitment in terms of each of these crucial yardsticks had been assessed in earlier Design Study and Project Definition phases.

Sea Harrier: significant changes from GR Mk.3

The basis of the design was the Harrier GR Mk. 3, allowing only those changes which were essential to meet the RN mis­ sions and shipborne requirements, together with modifications shown to be cost-effective in terms of maintenance and reliability costs over the life cycle; i. e. total final spend reduced. Whilst the aircraft (airframe, powerplant and mechanical systems) is some 90 per cent common with the GR Mk. 3, the nav-attack system and operational equipments are, by con­ trast, about 90 per cent new. This reflects primarily the new roles and missions of the Sea Harrier which (overlooking the fact that it will fly from ships) is really a multi-role Fighter/Reece/Strike weapons system (hence FRS Mk. 1 the designation).

The weapons system

Figure 15 shows the functional arrangement of the new avionics. The orincipal new equipments are:

1. A new (larger) Head-Up Display from Smiths Industries, driven by a 20,000 word digital computer which not only generates display symbology but also functions as a very flexible air-to-air and air-to-surface Weapon Aiming Com­puter.
2. A self-aligning attitude reference platform from Ferranti. This equipment is not truly inertial (because of the RN wish to avoid alignment problems at sea) but will attain previous-generation inertial nav. accuracy. It is controlled by an 8000 word digital computer which also performs the navigation and endurance functions. The platform is cross­ referenced to a Doppler radar from Decca.
3. The principal external sensor, the Ferranti Blue Fox radar. This is derived from the Seaspray Fox radar used in the RN Lynx helicopter, but much modified for the air-to-air and air-to-surface modes demanded by the Sea Harrier operational tasks. The radar display is a TV-raster daylight­ viewing tube which will convey flight information, as well as the radar data, to the pilot.

has been entirely revised to give the single crew of this multi-role weapons system the best operational efficiency. Early in the Design Definition studies, it became clear that the RAF cockpit (no lar_ger than the original P1127 cockpit, first flown in 1960) could in no way accommodate the equipment needed for these multi-mission naval iOles. At HSA we hit on the simole idea of raising the pilot as shown in Figure 16. With the pilot some 11in (280mm) higher, and without needing to alter the front fuselage overall width (and thus invite newintake problems), the cockpit quickly became ordered and workable. As the diagram shows, more panel space became available, and more console width; there was more space (now unpressurised) under the floor, anda large nose cone was available for the radar.

Maintenance access also has everywhere been much im­proved.

The better rearward view for the pilot was accepted by the Service with great composure. Forward and downward view is also improved over the GR Mk. 3, since internal en­ croachment by cockpit additions in RAF Harriers over thepart of his HUD porthole. The layout of the new raised cockpit ensures that no internal cut-offs deny the deck­ landing pilot the best forward and downward view through the unaltered but vertically displaced transparencies common with the GR Mk. 3.

“Navalisation” is an outmoded term since conventional naval aircraft now need to be specifically designed for ship use and cannot be converted (as in the past) from land-based fighters by adding, hook, catapult hardpoints, lashing lugs, etc, plus the prefix “Sea” to their name. The Harrier is the first exception to this rule for more than 20 years. The engineering changes for deck and sea compatibility have added the sur­ prisingly small total of about 0. 5 per cent to the aircraft’s operating weight empty.

Since the Harrier was originally designed (in 1965-7) to be operated for periods of intensive use dispersed away from normal main base facilities, existing maintenance rules and procedures, and the provisions for rapid servicing, have been easy to adapt for shipboard deployment. This is, after all, only operation from a hard-surfaced and mobile dispersed site which has less space than a wood or a field. New airborneequipment in the Sea Harrier has been designed with sea deployment in mind. The changes to existing equipments and to the airframe in order to satisfy RN maintenance policy have been relatively few.

During field deployments on land the Harrier/AV-SA has often shown its ability to fly intensively with a maintenance/servicing workload of well under 10 man hours per flying hour. The biggest servicing task afloat (as when operating off-base on land) is the engine change. Revised handling equipment is being designed for the Sea Harrier to allow this task to be done more readily within the limited deckhead height, and on the all-moving working surface of a ship’s hangar.

There are no grounds for believing that either servicing or maintenance will prove any more limiting in use of Sea Harrier from ships, than they have with existing Harriers in their many field deployments. RAF and USMC experience shows that the aircraft can average up to eight sorties per day for a week or more. One RAF Harrier flew more than 40 sor­ ties of 30 minutes’ duration in a three-day field exercise in which 12 aircraft completed 364 sorties. Under peacetime flight safety rules the RAF find that they need two pilots for each Harrier to exploit its military productivity to the full in a working day in the field.

The ski-jump jet

This remarkable advance in the art of flying jet V/STOL aircraft off ships was first published in conceptual form by Lt. Cdr D. R. Taylor, RN, in a thesis written at Southampton University in 1973, Ref. 4. His Ski-Jump launch proposal took an ancient and very familiar notion – that of increasing the time of flight of a projected body by imparting an initial up­ wards momentum and applied to the short take-off of a jet V/STOL aircraft from a deck.

Taylor perceived that, given an aircraft having enough thrust to accelerate in an initial upward tr;ijectory, the in­ creased time of flight thus made available would enable the vehicle to be launched at a lower speed and with a deficiency of lift relative to weight. By building airspeed through all the part-ballistic trajectory (on the upward as well as the downward path) the aircraft could be arranged to fly, fully supported, by the time it had lost height to a level ap­ proaching the initial launch point.

After his return to duty within MoD, early in 1974 Taylor gave a formal presentation of his ideas to an audience from the Service and MoD. HSA were also invited and expressed their early qualified support. There followed a period of silence whilst the authorities took stock of this new situation. Not only was the concept bold – even startling, and with a distinct “something-for-nothing” flavour – but also the Sea Harrier progrnmme at this time was unapproved and hanging by a thread in the turbulent economic aftermath of the world oil crisis. The Navy and the fixed-wing flat-deck Establishmentunderstandably needed to be extremely cautious.

Shortly after this, limited further in-house work increased HSA’s understanding of the potentialities of the Ski-Jump launch technique, and, from about mid-1974, we effectively espoused the cause. The active support of a few far-sighted men in MoD PE and MoD Navy was aroused and small study contracts were then placed with HSA Kingston who were by late 1975 championing the concept, convinced of its eventual practicability and the prize it offered. These vastly more detailed later investigations, utilising the expertise and com­ puter aids available at HSA – but clearly not to Taylor in his original work – have shown no flaw in the basic principles he advanced. These remain essentially valid and are integral to the comprehensive mathematical modelling and simulation going on today.

• MUCH reduced deckrun at given weight
• Increased payload frorn given deck
• Cons.iderable “built-in” WOO
• Ship endurance extended
• Launch independent of deck pitch motion

Hawker Siddeley Sea Harrier F.R.S. Mk.1 Rolls-Royce Pegasus Mk.104

Ski-jump benefits

The most dramatic and immediately evident gain is in the shorter deck run consequent upon the greatly reduced launch speed which the Ski-Jump permits.

It is also obvious that, for many launches at gross weight less than this extended maximum, the Ski-Jump ship need not steam at high speed in calm weather because the ramp provides the equivalent of about 30 knots WOD. Thus, on average, a significant economy in the use of ship fuel is realisable.

In fact, in a flat calm, the ship cruising at 15kt with a 20 degree Ski-Jump on its foredeck has the Harrier launch capabili­ty of a 45kt flat-deck carrier, if one can find such a ship credi­ble (HMS Inconceivable?). Any fixed-wing aircraft launched from a pitching deck during the bow-down half of the cycle requires extra launch airspeed to curve the flight path away from the sea. In a con­ventional naval catapult launch the boost (taking only a few seconds) can be timed to take place during the bow-up swing – in effect a mini-ramp. A Harrier STO deckroll takes several times the catapult boost time. It is on average, therefore, more difficult to forecast ahead and predict ship response (to the extent of about one complete pitch cycle) so as to ensure that the Harrier leaves the deck during the bow-up part of the motion. The consequences of getting this prediction wrong, due to say bow-down dwell in non-regular seas, can be very serious for deck pitch motions exceeding +2 deg. , and wet wheels would be highly probable in the worst case. Clearly, departure on an upward trajectory of order 20 deg. slope will permit a Harrier to leave the bow at any point in the pitching cycle, almost regardless of the amplitude of the deck motion, within the constraints of practical aircraft handling on deck. For comparison, large conventional carriers cease peacetime flying when deck pitch exceeds about +1½ deg. ; i. e. bow and stern vertical motions of order +10ft (3ml (recovery is motion-sensitive, too, in conventional naval flying). Independence of ship motion for launch, whilst not readily appa•ent, is therefore a real and very important asset Page 42of the Ski-Jump.

Av-8B Characteristics

Recollecting that deckrun, to the first order, is a linear function of launch kinetic energy, it is possible to relate STO endspeed to decklength for a particular launch weight. The reducing incremental gains as Ski-Jump exit angle is successively increased are immediately obvious. At STO weights closer to VTO weight than in the examples covered so far, the reduction in deckrun for the first 10 deg. of ramp is startling.

HMS Invincible

We can turn, firstly, to the non-contentious Harrier ships to come. In the broad SCS class the only ship at present building is HMS Invincible. This ship is termed a cruiser, variously qualified by the description Through-Deck or, latterly, Anti-Submarine. Invincible is also a very sophisticated Command and Control ship, and is intended principally for RN ASW operations in European and North Atlantic waters as part of the UK commitments to NATO.

HMS Invincible was conceived and designed for use by a rotary-wing Air Group, and was already under construction before the Royal Navy obtained approval for the Sea Harrier. The influence of the jet V/STOL aircraft on the ship overall has therefore been minimal. She offers a conventional flat deck for Harrier and helicopter operation. No flight deck machinery is provided but the deck is sufficiently large to provide for full-load Sea Harrier STO missions as specified bythe RN. They plan for a class of three of these ships.

Aircraft complement is planned at up to 12 Sea King size helicopters plus up to five or six Sea Harriers. Clearly the ship is large enough to carry more, if necessary. With a displace­ ment of about 20,000 tons, Invincible will provide a very satistactory Sea Harrier/latform. She probably represents the upper limit of size (an hence cost) for any navy, other than those of the USA and USSR, with aspirations to provide or re­ tain fixed wing airpower at sea.

The Harrier Carrier

The first ship ever to be conceived and laid out specially for the Harrier is the project of Vosper Thornycroft Ltd, known as the Harrier Carrier. This ship project has evolved from 16months of joint discussions between VT and HSA, and is now at a stage of design where customer participation is necessary to make the next phase meaningful.

The ship can be summed up as the smallest and hence the most economical vessel able to provide a full andeffec­ tive Harrier capability at sea.

Harrier Carrier is essentially sized by the flight deck. Deck beam is determined by the Harrier runway width plus the width necessary to park aircraft clear of the starboard wingtip safety line. The length results from the need to provide for full-load Sea Harrier STO. The forward flight deck has a six degree ramp built in, andthere is a turntable at the aft end to increase deck run without the need for aircraft to be pushed backwards thereby prolonging the launch interval. Use of a turntable also avoids the need for across-deck taxiing – reportedly the most daunting experience that USMC Harrier pilots have undergone when flying from the USS Guam in bad weather. (This LPH class has round-bottomed, non-roll stabilised, single,screw hull. ) The Harrier Carrier has a maximum design speed of 25kt. Since this is augmented by the 15kt effective WOD provided by the ramp in the bow, in still air this speed will allow the 420ft (128m) STO run to yield the same Sea Harrier mission capability as is provided by the deck of Invincible.

This flight deck forms the roof of a hangar which turns out to be capable of housing 10 aircratt. This size of Air Group, whilst modest by conventional carrier standards, forms an effective, viable and flexible multi-role weapons system for the ship. The aircraft complement can range from eight Harriers plus two Sea King/Lynx helicopters to eight Sea King plus two Lynx. This fully flexible grouping (dependent on the ship task and mission) could be extended to a total complement of 14aircraft by using the deck park on a 24 hour basis whilst at sea, and not just during flying operations.

Two lifts are provided and there are some aircraft maintenance compartments at hangar deck level. However, it is planned that squadrons will embark with their aircraft plus their main special-to-type maintenance facilities housed in fitted-out containers (portable workshops) which will be stowed in the hangar and provided with power, etc, by the ship. This solution gives the minimum cost and complexity in Page 43the ship, and facilitates changes between aircraft type and hence in ship role.

It emerges that the flight and hangar deck provisions made for the 10-unit Air Group can be carried on a frigate­ sized roll-stabilised hull of some 400ft (120ml waterline length. Of course the beam is larger than a conventional high-speed frigate, and the ship has a full-load displacement approaching 8000 tons. If my VT friends will excuse me – some frigate! But what’s in a name or label, except largely emotion and stereotype thinking? The tact remains that this ship 1s a completely etfect,ve Harrier/helo carrier at a size and weight (and hence cost) dramatically and, to date, uniquely less than any other ship which currently provides a comparable seaborne airpower capability.

Propulsion power is provided by 8x5000hp (3. 7MW) gas turbine driven generators housed at hangar deck level for easy maintenance and for minimal installation difficulties with uptakes and exhausts. One additional similar GTDG provides domestic electricity. The eight GTDGs are coupled electrical­ ly, a pair at a time, to variable frequency motors, one on each shaft.

This gives cruising flexibility with a high propulsive efficiency, as well as providing substantial redundancy against failure/damage.

In peacetime the ability to serve as a tloating power sta­ tion in disaster areas must be a considerable national asset. This ship can feed 30 megawatts of power outboard. One of the most meaningful (and popular) duties a fighting service can provide in normal times is to bring relief and aid in civil emergencies. Think of the RN role with HMS Hermes in Cyprus in 1974, or of the immediate aid needed in Darwin, after the disaster on Christmas Day, 1974. Containerisation of medical facilities could turn a hangar deck into a mobile hospital. No other type of fighting ship but the carrier canfulfil these roles.

Perhaps the most astonishing feature of the VT Harrier Carrier is the reduction in manning compared with the present-day norm. A “seaman” crew of some 250 is suf­ ficient to run the ship – not very difforent from a modern frigate. The Air Group would bring aboard between 120 and 150 more officers and ratings, the larger number correspon­ ding to a predominance of helicopters in the Group, since they need multiple crews. The design provides a high stan­ dard of accommodation for over 400 men.

Contrast this with a ship such as HMAS Melbourne (an old design, but carrying not many more aircraft) with a com­ plement of some 1600; HMS Ark Royal with 2500 men, and any US Navy CVA with 4000 to 5000 men aboard. Manpower consumes a large fraction of the running cost of a modern Service, and hence also of the direct operating cost of a fighting ship.

No doubt the future will see other ship designs promoted as Sea Harrier platforms, including modified merchant ships. This Vosper Thornycroft project, however, has confirmed most emphatically the reverse trend in fighting ship size, manning and cost which Harrier jet V/STOL capability will permit compared with present-day conventiona fixed-wing aviation at sea. The smaller navies of the free world – par­ ticularly since the emergence of Kiev – no longer have an excuse on economic grounds to shrug their shoulders when the future of seaborne airpower is under discussion.