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And<
completed flight training in 1975 and was assigned to in Barbers Point, Hawaii. He was subsequently accepted
0-:
.01
at the
Navy Test Pilot School, from which he graduated in 1980 an' ^ Com' worked as a project officer at the Naval Air Test Center. In ^ group
2,000 sorties at 95% aircraft availability and accounted for 32 aircraft destroyed with nine losses of their own—an operation waged 4,000 miles from the nearest friendly base. The ease of operating the Harrier at sea was shown by the successful embarkation of RAF GR Mk 3s with no at-sea experience and the qualification of each RAF pilot after only one successful ski jump takeoff.13
The lessons of the Falklands have not been lost on the rest of the world. Although both Spain and India had purchased AV-8A/GR Mk 3 aircraft in the 1970s, both countries have since ordered more AV-8B/GR Mk 5 aircraft, and each has either built another aircraft carrier (Spain), or bought one (India purchased the Hermes from the United Kingdom in May 1986) to enhance their seagoing operational aircraft capabilities.
Despite its unconventional development path, the Harrier has survived its many critics and it is flying high—and low, and vertically, and ....
publish
4Bill Sweetman, Harrier: Janes Aircraft Spectacular (London: Jane Company Ltd., 1984), p. 9.
5Gunston, Aviation Fact File, p. 20. . •te(j) 19^’
6Alfred Price, Harrier at War (Shepperton, Surrey: Ian Allen Litfi
P- 31- „ • ,, crephen ^
7Francis K. Mason, Harrier (Second Edition) (Cambridge: Patriot ited, 1983), p. 109.
8Ibid.
9Price, Harrier at War, p. 53. l0Gunston, Aviation Fact File, p. 50.
"Mason, Harrier, p. 151.
12Flight International, 22 February 1986, p. 11. .. ^
,3Rodney A. Burden, et al., Falklands, the Air War (London: Bn >
Research Group, 1986), pp. 189-223.
A 1974 graduate of the U. S. Naval Academy, Commander g comdeted flieht training in 1975 and was assigned to Patrol 9 ,i $•
wv/ir\.v_vj uo a piyjvvi at ixavai rui itai ^ ^
mander Anderson was assigned to the staff of Cruiser Destroy ^ ^ Twelve as Electronic Warfare Officer, completing two crU1a(tend tl>{ Mediterranean and Indian Ocean before being appointed to aUtical Royal Naval Staff College in 1985. He was selected as an jngas Engineering Duty Officer in February 1985, and is presentpMA'2^* the Manager of the London Office of the Harrier Project ( ^va) Air and F402 Engine Technical Representative in London for the Systems Command.
larly in the vertical motion axis. Landing and ta^e°rrjed
til IliUtL, n n/.tiinll. > A’. ffl n. ■ 1 * t / 1 f A llv /'
of
therefore, while not actually difficult, tend to be
The evolution of the aircraft carrier has been driven by advances in defense technology. Aircraft and weapons have grown in performance and hence in weight and complexity; this has been matched by an increase in size and cost of the carrier. But only the United States, France, and—soon—the Soviet Union can carry the burden of the conventional carrier in its full flowering.
The advent of the Harrier family of jet vertical/short takeoff and landing (V/STOL) attack fighters has had a different effect. The Harrier’s short takeoff performance has made catapults redundant and vertical landing has similarly eliminated the arresting gear. Thus, the launch and recovery needs of the carrier’s aircraft no longer have to dictate the size of the flight deck, and hence the ship.
The Harrier, in principle, is capable of operating from decks as small as a frigate helicopter deck. It is feasible to configure a ship little larger than a frigate to be capable of supporting two Harriers. It is then possible to provide a degree of air cover for formations of ships much smaller than those warranting cover by a full-blooded aircraft carrier, whether 90,000 or 20,000 tons. British Shipbuilders made studies of vessels of less than 6,000 tons displacement capable of operating a mix of six fixed-wing vertical takeoff and landing (VTOL) jet aircraft and helicopters. This would be a handy force for brushfire conflicts and would leave the precious CVAs, LHAs, LPHs, and CVSs free for their primary missions.
Operating jet VTOL combat aircraft from small vessels offers considerable tactical advantages. However, it will
be effective only if any additional operating li*1® „
incurred as a result of moving away from the wls(iip spaces of the attack carrier deck are acceptable- ve0; envisaged could be as small as 4,000 tons, and he 0f lively. Indeed, in sea state six, the vertical m°ve® et_ an aft helicopter deck in such vessels could be 33 j,at 0 The problem is: How do we operate jet VTOL co ^ craft safely from small decks in extreme con^‘t'Pnucopter' Remember, a Harrier does not behave like a he^£ the Certainly, it can arrive and depart vertically, hut ^ resemblance ends. A helicopter is optimized for nacCu- and can do so for many minutes on end with gre jglit racy. It has a low density, low “wing loading \ ^ t0 divided by jet nozzle area), and is highly susceph turbulence. The stored energy in the rotor system^-1 a good standard of vertical-axis maneuverability- ^ rier, by contrast, has a high density, a very high (,a> loading,” and is thus relatively unaffected by guS ^jcU- Iess maneuverability in hover than a helicopter, P ^
out with commitment, the pilot embarking on a c°,)(]jljst' action from which it is difficult to diverge. Thus, ^ ment of hover height and position to accommodate ^ a movement is not normally feasible. Though the us^cts, raised or gridded platform can minimize ground e ^ the cross-coupling between aircraft attitude and tn ^ for vector can still cause problems: lower a wing to a a]l roll of the ship and you move sideways. That may
60
Proceedings
/ Novel"1
,bcr ■
Jjsht ^
i ifcraft ^°U davc a respectable amount of air between nUre, bu, Cxtremities and the nearest bit of ship struc- ‘8ht Prove embarrassing on a frigate’s helo
) ^ er, the response time of a jet engine,
'"'Id-up *’ ls such that a few seconds is required for full
dun'„°r decay, of thrust. Always there is a short pe-
UnS taU------- rr ... . J . . . ■ ■
l< ntact vitake°ff or *and'n8 when the undercarriage is in i °* ^c‘ni>' . ^lc dec'k but the full weight of the aircraft is >fncienMrncd ^ b- Even with brakes on there may be j Vcnt r>.. ateral force between the tires and the deck to
huT°,r.Cment- This, coupled with a wet, heeling
on [1dle elements for disaster. Harriers routinely ^Ser vessels within a few feet of a designated
^rcd in S^'P operation would require accuracy mea- e°Pter jsc ,es- However, even the less demanding heli- $ aSsistaSS'sted on occasion, by the U. S. Navy’s recov- °Val Navv^CUtr*n® and traverse (RAST) system or the ' ” " rpoon system, for instance.
AU|<-'h "ne of reasoning that led to the SkyHook, l)Cr°sPace Cen concePtually developed jointly by Britisl l^hier 0nand 'be Dowty Group. In normal recovery of a °ver r,., .’1 sbip the aircraft is flown to an established
was.X s Harpoon system, for instance.
js line of reasoning that led to the —j-------------------- ,
been conceptually developed jointly by British
1Ve to the ship—usually alongside, but some- /'Qn p(). Fn- In fact, the pilot aims to hover relative to the
is ^ Used*011 °k S^*P> w*dl s*ze vesse* nor" t S|hall tL **1C amount °f ship motion in most sea states
to>n
5 tv,..’ ranslates the jetborne aircraft, usually laterally, ( °n above the designated spot and carries out a "nchdown. The basis of the SkyHook concept is
November 1986
BRITISH AEROSPACE
that the two later stages are dispensed with and that, while in hover alongside the deck, the Harrier is captured by a ship-mounted crane which can then place it precisely in position on the deck. The pilot’s task is greatly eased: he has merely to establish a normal hover. There are zero concerns about relative attitudes between ship and aircraft when they make contact. This crane is SkyHook.
Wave-induced movement will be more significant on the smaller vessels wc are considering than on a carrier.
Hence, to make capture possible, it will be necessary to isolate the head of the crane from this motion. This can be accomplished with high fidelity by using an active control system which detects excursions of the ship relative to its mean path and articulates the crane to counteract them in such a manner that the head moves smoothly along the ship’s directed velocity vector with extraneous perturbations removed at the crane head. The state-of-the-art in control engineering is such that at normal ship passage speeds, SkyHook head “space-stabilization” can be achieved with considerable accuracy.
Capture of the aircraft will be done automatically. The aircraft is brought to the hover within the “capture window,” which is a ten-foot cube positioned 15 feet below the crane head (Figure 1). Sensors mounted on the head determine the position of the aircraft and the capture control system guides the lock-on jack to engage and lock on to the aircraft pick-up point (Figure 2). Similar systems are employed on many industrial robots. Up to this point, the aircraft has been weightless as far as the SkyHook is concerned, although it has mass and “windage.” After
61
SkyHook reduces the workload and increases
safety
cause the crane is digitally controlled, it can Pos'ta,a
Be-
the
issible.
aircraft precisely where required. It becomes Pos- [c. therefore, to lower the aircraft with its undercarnag ^jy traded on to a prepositioned cradle or trestle locke ^ to the deck. This cradle could also carry the stores next mission, positioned correctly below their des' |Luj|t-in stations. Thus, it would be simple with the use o ^ jacks to offer the stores up to the aircraft. Connec ^ cradle to a transportation system mounted flush deck would enable it, with the aircraft, to be mo the hangar when required. Aircraft can thus bepa5> more closely inboard and with decreased damage .^fl cradle could be armed for the next sortie while t ^ was away, thus considerably reducing turnaroun c0l). Refueling could be carried out through a self-sea i #aS nection mounted on the SkyHook head. Indeed, * ^
the only service required—perhaps to prolong a eo ^ air patrol (CAP) mission—it could be accompli the aircraft still positioned over the side, hanging ,jo0|;.
engine at idle on the deployed, space-stabilized j
The launch sequence is, essentially, the capture^ aI1J
quence reversed. First the aircraft is swung _
the engine started. The pilot opens up the engine ® |(lCk- ciently to give effective reaction control power. ^ on jack is extended to put the aircraft in the centeovVer capture window: when ready, the pilot increases P ^ until hover is achieved. The lock-on jack then sea^ and removal of weight, automatically releases the aircu|ltjl i' rapidly retracts. The jack cannot release the aircr^ enia- experiences zero weight, thus obviating the risk 0^ ^ ture release. The aircraft is now in free hover, a transition to forward flight. nllS.
Launching a Harrier in this manner confers a ^ oUnd Because the Harrier does not have to climb out effect, it can be launched at a somewhat higher .s than in the case of vertical liftoff from the deck- same small but significant performance bonus als ^ c0n- in recovery. The need to allow for a power marg y,0t trol vertical velocity plus the loss of thrust °vVin^j or gases recirculating into the intakes from the gr°u jnts deck jet flow pattern reduces by a few pereentng®) Fj, aS the weight that can be safely and consistently lan distinct from carried in a steady, free air hover. pilot
Critical to the entire concept is the ability of (
hover the Harrier with sufficient accuracy. In |hfi P^ there had never been reason to determine Precise(jnle of accurately the aircraft could be positioned, and sc' „j the Harrier design team thought the task would a
ffi-
the
lock-on is achieved, the pilot will reduce power slightly, still maintaining aircraft attitude using the reaction control system, as in a normal free hover. The lock-on jack senses the unsupported weight and pulls the aircraft up against the docking cradle. An internal lock is engaged and the engine may then be shut down. To recover the aircraft, the SkyHook is then swung inboard. During this maneuver, space-stabilization inputs to the crane’s articulation system are progressively reduced so that as the aircraft nears the deck, it is moving in consonance with the ship, giving no relative movement between the two—but also constraining the aircraft against motion relative to the ship until it can be secured.
Securing an aircraft after it arrives on board a small vessel in a high sea state provides its own hazards, as also does subsequent refueling and rearming. Here again,
62
_ _ d by
too much of a pilot. No such doubt was express^ to
company test pilots. A series of trials were carrie settle the point. The trials used a simple paraHeX. ujgb- mounted on the side of a “cherrypicker” hydraL1__^ peet lift platform. The platform was positioned some above the ground, and tests to position the aircra the aid of the sight were recorded by cine carnera^^ capture window dimensions had originally been lf«l p“t being within the capability of a moderately .... rjzaUofl In fact, the trials showed that, after a short fam>1 j period, aircraft movement in the hover was contalS(,at within a two-foot cube. Both single-seat and tw° |e(j up u’ riers were used; three pilots took part. Winds gus ^o0k 25 knots. Further tests used a mock-up of the bW ^,as
■aft’
head mounted on a mobile crane so that the a'rcrjngly positioned in hover underneath a somewhat daunt't|1j, solid object. The judgment of the pilots was that
Proceedings
/ Novo"1
^as Wcjj • i •
indeecj wWlt^ln t*lc capability of the average pilot and Precise s3S eas'er 'han the task of vertical landing on a onlv Ko^01, even if that spot was on land and moved at ,J 3 Per hour.
Cancelin2^eC^e<^ lPat t*le SkyHook should be capable of a 29-foot °Ut l^C rnovement of a 4,000-ton ship owing to by approWave (Figure 3). This wave height is exceeded 'he c0rreX‘matel-v one wave in 300 in sea state six, and 4eNrP™di»g ship movement for 1.5% of the time in 0rth Atlantic-
c°Urs<
this
-that is, 131 hours per year. This, of
- anto<u°eS n0t mean that recovery is not possible for $kyH0oknt t'me eacb year, only that the head of the l°n?'Period',8ht m°Ve to some degree. This small and “ ° niovement of the head would be interpreted by
the
•he “tar„rj,fs a m°vement of the aircraft and, provided rec°Verv Stayed inside the ten-foot capture window,
A preiiC°Uld Pr°ceed.
*° CaPturrtUnary design study examined a crane’s ability ^°ve ni(f an aircraft hovering approximately 50 feet to he n rn sea level. The base of the crane was assumed btin
17 , M me oase or rne crane was assumeu
hasp66* a,'30ve sea level. The total weight of the ro-
alth°UghSe and crane structure proved to about nine tons, «te design is judged to be rather conservative and
a?ed Usescould be reduced. The hydraulic system envis- “°Us p0wenergy regeneration to keep the required contin- ^ade to less than 500 horsepower. This is
°ne-half 0p le ky the cyclic nature of most ship motions:
^ other h i cyc'e takes power from the system while down” Puts ‘t back. Thus, extending a jack on the ri'°torj but 6 0p a wave takes power from the hydraulic s'de 0f subsequently the jack is closed by the “up” "'Put, y0^ Wave feeding power back in. If you store this >t of j, Can use h to power the next extension—or j’ign detail -S*nCe *osses are inevitable. Of course, the delation 0f jy°uld depend on the actual ship used and the ^ring kat le SkyHook on the ship, but sufficient engi- v'able sas been carried out to convince us that we have a Llntdevelo?m„Morethan that’ we believe that no signifi- lent’ off.th°Pme"* are required, and that, to a large ex. The p0e,s.belf components can be used.
■ and SS,b’ilities raised by small ship operation are man- jbpect of excding. Consider the air defense problem. The 'Shter wPcrT«rmancc which, to a large extent, forces up tk^at if'8htis lbe need for longer loiter time. The F-14 V carrj es'8ned for an extended CAP loiter time and > Of fi ? a hefty load of fuel. Suppose we were to base 'heSe8htr
aj° ters on the distant antiair warfare screen ships.
’> WOUlH thpn pffprtlvplv fv* “nn PAP nn thp
h°ok,’> k”dI‘ would then effectively be “on CAP on the p’igue ^ut quiescent: no fuel being consumed and pilot I' 'v°uld IIT1UP d be need to carry excessive amounts of rn d'saPPear and the resulting aircraft could be P*cket shi0re uimble, and cheaper. If we consider the Ratine qP uierely as the sea-based equivalent to the U. S. j uld no. rPs s forward operating base on land, then it a w Carry the facilities to maintain the aircraft, but ‘ted capacity to refuel and rearm.
sioi
A CAP mis-
be ',,now be limited only by the time the aircraft
htiejj___ °Wed to sit out—fueled, armed, and, perhaps,
. Tht b0 °n the picket deck or SkyHook—maybe six to
■Ha,
Ndfl8- .
Suit Sb °Ut h°m the “main base”—the amphibious • T PicfCj ^0 relieve a similar machine in nnsitinn (
Then, three or four times a day an aircraft
relieve a similar machine in position on result: less fuel used, less engine and reduced pilot fatigue, and continuous 'ewer aircraft. Such SkyHook ships in a group offer emergency dispersal/operating bases if the
'"gs /
November 1986
flat-topped small carriers were hors de combat.
Although the Harrier, as the only practicable Western V/STOL aircraft, has featured prominently in this discussion, the SkyHook is equally suitable for use with future advanced short takeoff and vertical landing (STOVL) aircraft, including future supersonic developments. Since the engine is only at full power when the aircraft is suspended over the sea, problems of ingestion of hot gases or deck heating from plenum chamber burning, or reheated engines are entirely avoided. It is likely that the existence of SkyHook could modify the preferred line of development of such aircraft, since the relative importance of the various powered lift performance parameters would be changed. “Footprint,” a characteristic of much concern to those who design or who will have to operate high-energy jet supersonic STOVL aircraft, is rendered meaningless by SkyHook. Mission profiles would also be correspondingly substantially altered by forward basing, this too having an effect on VTOL configuration choices.
SkyHook has the potential to increase greatly the flexibility of organic tactical air power at sea. The large carrier will remain for some decades the keystone of naval aviation, but the ability to operate aircraft from a multitude of smaller ships could transform the picture. Imagine the uncertainties raised in an aggressor’s mind if any naval ship larger than a frigate, or virtually any merchantman, could be carrying a fighter laying in ambush. Or, conversely, consider how the security of Western airborne, antisubmarine, and airborne early warning (AEW) screens— and our transoceanic civil air transports on military missions in emergency—could be maintained if the Soviets deploy a SkyHook first.
If SkyHook had been deployable during the Falklands campaign, it is interesting to speculate how the effectiveness of the air campaign could have been changed. Yet the many who blindly articulate, of the Falklands, that “it won’t happen again” or “it doesn’t apply in NATO” miss entirely the point that survival, flexibility, surprise, and concentration—prime elements of military success—are epitomized by jet V/STOL operations on land and at sea.
SkyHook can extend these merits by providing the key element essential to all warfare—timeliness. The fighter or attack aircraft can be Sky Hook-based at, or much closer to, where the action takes place. No matter the sheer power and capability of today’s carriers with their unmatched command, control, communications, and intelligence functions, their predictability, lack of stealth, and inflexibility will frequently limit their use.
The mold has become too set and rigid. We need to release tactical naval airpower from its straitjacket. Jet V/STOL’s capabilities are being demonstrated by several of the free world’s navies. SkyHook can open the possibilities even further.
Dr. Fozard has been Divisional Director of Special Projects for British Aerospace (BAe) since 1984. Before, he was Marketing Director for Harrier and Hawk (1978-84), and from 1963 to 1978, Chief Designer, Harrier.
Mr. Frick is Deputy Chief Test Pilot for BAe at Dunsfold and has flown Harriers since 1969. He has been with BAe since 1978 and spent seven years test flying for Rolls Royce. He flew Fighters in the RAF from 1960 to 1972.
Mr. Mottram has been Engineering Project Manager for SkyHook since 1983, following 30 years as a test engineer at BAe Kingston, including the period 1971-78 as Head of Structural and Mechanical Test.
63
'Bill Gunston, Harrier (Shepperton, Surrey: Ian Allen Limited, 1981), p. 8.
[2]Bill Gunston, Aviation Fact File: Harrier (London: Salamander Books Limited, 1984), p. 5.
[3]“Summary of Pegasus Development 1959-1982,” Rolls Royce Limited, 1982.