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Aviation History
1957
1957 - 0378.PDF
380 FLIGHT, 22 March 1957 BARRIER AKLA |UNDER ! SHOOT LANDING UREA PULL-OUT | | PARKING AND j PULL-OUTiCATAPULT AREA \ \ i S OVERALL LENGTH REQUIRED 1000ft-1100ft DEVELOPMENT OF THE AIRCRAFT CARRIER... any aircraft going too fast would bounce when it hit the deck, andthis was the source of many accidents. It was clear to the authorities that regardless of any respite thatmay have been achieved by the adoption of the standard system there remained a rapidly increasing problem which would soonrequire a new solution. Already new high-speed types of jet naval aircraft were coming along, with inevitably increased land-ing speeds. The first problem to be overcome was the straight- forward physical one of providing arrester gear capable of stop-ping these aircraft. This is, perhaps, an over-simplification, as the development of arrester gear takes just as long as, if not longerthan, the development of aircraft; and so the aircraft was designed just as much for the arrester gear as the arrester gear for the air-craft. Nevertheless, it is correct to say that the rapidly increasing landing speeds of naval aircraft were forcing a high pace on thedevelopment of arrester gear. In addition to the sheer physical development of the arrestergear (the required energy-absorption increases as the square of the entry speed, as well as proportionally to the all-up weight) anew problem began to be talked of. This was the impact of the hook on the wire, which above a certain engaging speed simplysnatches a piece out of the wire instead of picking up the wire in the normal way—and it makes no difference how thick the wire is.The particular problem even led to talk of switching to some other material, such as nylon, in lieu of the high-tensile steel wire nor-mally used. As yet mis problem is still in the offing, but it remains as a threat if entry speeds are increased too far. The improved arrester gears required an increased length ofpull-out. Simple dynamics shows that for the same aircraft deceleration (i.e., same aircraft strength) the pull-out lengthrequired increases as the square of the speed. Of course, this increase can be held down by increasing the strength of the air-craft; but since this would involve a weight penalty it must be kept to a minimum and, inevitably, arrester gear pull-outs areincreasing. This increase of pull-out high-lighted a problem of growingdifficulty. For high-performance aircraft it was impossible to design a conventional deck layout based on the existing carriersize. Equally, financial considerations precluded the building of a new carrier. Fig. 1 outlines the problem.Existing fleet carriers have flight-deck lengths of about 850ft, and the problem of getting everything in was already acute in thepiston-engine era. Some radical replanning was necessary, and it was in 1951 that Capt. D. R. F. Cambell, R.N., andMr. L. Boddington put forward a brilliant solution in the angled- deck scheme. This solved the problem completely by doing awaywith the necessity for barriers altogether, and at the same time overlapped the landing, the parking, and catapulting areas. Thenew plan was basically as shown in Fig. 2. One of the outstanding attributes of the angled deck arrange-ment is its flexibility. Flight-deck width becomes a substitute for length and the amount of parking space available is dependent onthe accuracy with which pilots can be expected to land down the angled centre-line. Operation of one catapult, or even both, whilelanding is in progress is dependent on the degree of angle and the clearance necessary between landing area and deck operating area.At present all British carriers in service are fitted with what is known as a half-angled deck. This term simply means that thedegree of angling has been kept down to that which could con- veniently be achieved without major ship reconstruction. It is,however, strictly an interim phase to obtain advantages as quickly as possible, and does not give the ships the full capability whichthe principle of angling has made available. The semi-angling was, in fact, largely achieved with the aid of a paint-brush—i.e., simply by painting-in the angled deck. Though it provides the main advantage of angling in eliminating the barriers andallowing the "bolters" to bolt, it seriously reduces the operational capacity of the ship by reducing the size of the deck parkingarea. The importance of this is seen when it is realized that no lift can be operated while aircraft are landing, and thus landingmust cease when the available parking space is full. It cannot be resumed until enough aircraft have been struck down to makeway for the rest. From the operational point of view it is highly Fig. 1. (Left) Lay- out of axial deck. Fig. 2. (Right) Layout of the angled deck. important that both launching and landing periods be as short asis humanly possible. Any increase in these periods seriously affects the "on the job" endurance of the aircraft, since extra fuelmust be allowed for the additional waiting time involved, and at the same time the freedom of manoeuvre of the carrier force willbe increasingly curtailed. The ideal angle of angling would be that which would clearboth catapults from the landing area. This would then permit launching and landing to take place simultaneously and reduce toa minimum the period during which the ship had to be into wind. At the same time, parking space would be required for the land-ing aircraft and the best way of meeting this necessity would be a lift, clear of the landing area, which could be used while landingwas in progress. The deck-edge lift—which has been such an important adjunctto efficient deck operations in U.S. aircraft carriers and the lack of which was at one time considered one of the greatest shortcomingsof British carriers—is not now in such great favour. It is extremely difficult to incorporate such a lift in a British carrier,owing to the fact that the flight deck is the strength deck; and there is a growing realization that a heavy penalty is paid in thereduced seaworthiness implicit in the large hole necessary in the ship's side at hangar-deck level and in the external structurerequired below this level. The original port-side position pre- pared for the deck-edge lift is rendered valueless by the intro-duction of the angled deck, and if such a lift was introduced now it would have to go into the starboard side. There is, however,the possibility of a normal lift (probably one offset to starboard) which would be clear of the landing area in a fully angled ship. It has often been asked why the angled deck did not comeearlier; but had it done so it might have been a failure, as it is completely dependent on pilots' ability to keep straight. Withmodern jet aircraft with tricycle undercarriage and an adequate forward view this is a very minor problem; but would it have beenso in a piston-engined aeroplane with a tailwheel undercarriage, an atrocious forward view, and the difficulty of torque and itsassociated swing? A danger exists that forward view will deterio- rate in future aircraft, and any tendency in this direction must bestrongly combated. Experiments soon showed that the angled deck was the begin-ning of a new era in deck landing. At last there was a chance to go round again—even after touch-down—if all did not goentirely according to plan; and at the same time practical deck layouts could be produced with the landing area where it shouldbe and with the proper undershoot distance. With the advent of the jet types and their high approach speedsanother near new problem became apparent. It lay in what now seems to be called the "servo control loop" of the approach.There was simply too long a time-lag between the batsman appreciating an error in the aircraft approach path and the pilotcorrecting it. Clearly, this lag could be much reduced by eliminat- ing the batsman and arranging for the pilot to appreciate anyapproach error direct. At the same time, it was also apparent that the landing flight-path implicit in the standard deck-landingapproach was becoming progressively more unpractical as speeds increased. The system required (in a jet aeroplane) two distinctmanoeuvres, first a slight push over from the cut point and finally a flare-out for the landing. Judgment of these two manoeuvrescalled for considerable skill, and while the penalty of flaring out too high was not serious in angled-deck ships, flaring out too latewas inclined to push the undercarriage up through the wings. Here again a radical breakaway from tradition was required.Consideration of a steady descending approach led to the con- clusion that an angle of descent could be chosen which wouldfulfil the conditions for a safe approach path and at the same time obviate the necessity for a flare-out while remaining inside theabsorption limits of the undercarriage. Fig 3(a) shows the after- half of a carrier in a calm sea and indicates the path followed bythe undercarriage of the aircraft in a perfectly steady no-flare approach. Fig. 3(b) shows the same carrier pitched bows-up in a heavy swell.The flight-path remains the same relative to the horizontal and the aircraft strikes the deck at the ship's pitch-angle plus thedescent angle. This combination must not overstress the under- carriage. Fig. 3(c) shows the ship pitched bows-down. The significantfactor in this case is round-down clearance. In both cases reason- able allowances must be made for deviation from the perfect onthe part of men and equipment; even so, it became apparent that the steady no-flare approach was practicable. [Com. on p. 381
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