Some special-purpose airoplanes
Some aeroplanes do not fit into any of the broad classifications of the preceding chapters—or if they do they require so much qualification as to cut across the general theme—and yet are of too great an importance to be omitted entirely. Naval aeroplanes and types developed specially for the needs of the army are cases in point; good examples, for in each high performance is subservient to other requirements.
Naval aeroplanes have two inevitable handicaps, the extra weight of their deck landing and take-off equipment and the restrictions on size caused by lift dimensions and hangar height. The folding hinges and jacks for the wings, and sometimes for the fuselage, add their quota of weight, while the harsh decelerations of deck landing have to be catered for by stronger fittings and reinforced skins. Even with the help of the carrier's 30-knot speed, plus any headwind that may be going, stalling speed must be reasonable in order to be able to take off from, and land on the relatively short deck.
In addition to these stringent requirements, the naval aeroplane has to have a good range, for its base may move a hundred miles while it is in the air and allowance must be made for looking for the carrier. Radio equipment has to be rather more comprehensive than average and, of course, there must be search radar. Add to this guns, ammunition and dropable "stores" and the total is formidable. As if this were not enough the naval authorities, particularly those of the Royal Navy, have a habit of adding extra items in case of need, oblivious of the diminishing performance of the aeroplane.
It is easy to find examples of naval ill-treatment of aeroplanes—in fact each of the representative types mentioned hereafter has suffered. The Blackburn Firebrand started life in 1940 as a naval fighter specification and eventually went into service as a torpedo-fighter after the War. Admittedly there had been other difficulties, such as a shortage of the Napier Sabre engines originally wanted for it, but most of the delay was due to repeated alterations in requirements. To lift an 1,850 lb. torpedo, as well as four 20 mm. cannon and a multitude of equipment, including miniature search radar, the Firebrand has a large wing, so that even the cleanly cowled
2,500 h.p. Centaurus gives a maximum speed of only 350 m.p.h. Note the very large fin and rudder necessary to give directional stability and full control against engine torque for take-off from the narrow confines of the deck.
The American equivalent of the torpedo-fighter is the attack-bomber, of which the Martin Mauler is an example. With a 3,000 h.p. engine, loads of as much as 4,000 lb., under wing and fuselage, can be lifted. The deep fuselage is typical of American naval aeroplane design, as is the continuation of this depth at the rear with a large dorsal fin to supplement the side areas.
Naval adaptations of land fighters have already been mentioned, but there are special naval fighters, too. Because of the difficulty of locating a carrier after the hurly-burly of action, two-seater fighters have several times been mooted, that is, fixed-gun fighters with a navigator. Two examples have been the Fairey Fulmar and the Firefly. Even in their original form with standard fighter armament, the long, deep fuselage for the navigator increased the drag so much that the performance was well below that of contemporary land fighters. Because the Firefly is a delightful aeroplane to fly, it was adapted for fighter reconnaissance, then for night-fighter duties and, finally, as an anti-submarine aeroplane. The engine, a Rolls-Royce Griffon of 2,000 h.p. in the Mark 1, was installed with a radiator under the spinner. In the F.R.Mk.IV a two-stage Griffon 74 of 2,250 h.p. was fitted and the larger radiator and intercooler were mounted in ducts in the centre-section leading edge to keep the c.g. in place. This model had clipped wings, but with the extra power two 1,000 lb. bombs, sixteen 60 lb. rockets, or extra fuel could be carried. On the starboard wing was a radar • blister and on the port one a fuel tank—to balance the drag. The A.S.Mk.7 has a large "beard" radiator duct because extra cockpit equipment and a new large tail balance the weight, the rounded wingtips have been replaced to increase area, and almost the whole of the under part of the wing is festooned with bomb and sonobuoy containers, radome, and fuel tank.
During the War, the naval "heavy" was the torpedobomber , originally exemplified by the Swordfish and later by the Fairey Barracuda. The attempt to combine all requirements within the dimensions dictated by the carrier lifts was almost impossible from the start. To give both upward and downward view in the Barracuda, a shoulder wing layout was . adopted, with a long canopy above and bay windows below. A
crew of three and a torpedo were carried. It was largely the difficulty of combining so many needs in one aeroplane that led to the abandonment of the torpedo-bomber in favour of the torpedo-fighter.
After the War, strategic emphasis was on anti-submarine aeroplanes since the U.S.S.R. has prepared for an undersea war. Typical of the new class of aeroplanes is the Fairey Gannet A.S.Mk.1. Although it does not look like it, this is a twinengined aeroplane, since it has the Armstrong Siddeley DoubleMamba which consists of two axial-flow propeller turbines mounted side by side and driving counter-rotating airscrews. This arrangement eliminates torque and also allows the Gannet to cruise on one engine when the other airscrew is feathered. Another important feature is that the Mambas can be operated on ordinary ship's fuel oil.
The extremely deep fuselage of the Gannet is a hold-all for many things: in the nose are the engines from which two long fat jet pipes run aft under the wing to come out clear of the trailing edge; below the wing is a capacious bomb bay; aft of the wing is a retractable A.S.V. dustbin; while the crew of three, radio, and radar sets occupy most of the top deck. Originally the crew was to have been two, but the Admiralty altered its requirements. A large fin, recently supplemented by two small ones, ensures directional stability under all conditions. There are several reasons why the wing is cranked down and then up again. The mid-wing juncture with the fuselage allows the crew to be above and the bomb bay below, but would have made the wing too high when folded. The downward cranking has the advantage of shortening, and thereby lightening , the undercarriage. The wind has dihedral on the outer portion for lateral stability. Even with the crank, the wings have a double fold to keep them within hangar height. The folding is done hydraulically by jacks.
With its huge Midway class aircraft carriers, the U.S. Navy can afford to have larger fleet planes. In addition to their Grumman Tigercat fighters, equivalent to our Sea Hornet but rather larger, other twin-engined types are being developed. Because of the large load in a small compass these aeroplanes tend to grossness—like the North American A J Savage. Sideby -side seating for pilot and bombardier make the fuselage wide as well as deep. The nose contains a radome and the tail a turbojet engine to give extra power for take-off and combat. The normal engines are radials totalling 4,800 h.p. and the jet gives a further 4,600 lb. thrust (which suffices for a top speed
of 425 m.p.h.) so that it is scarcely surprising that the tip tanks are permanent fixtures. The outer wings fold and so does the top of the fin and rudder. A later version of the Savage has two double propeller turbines totalling 11,000 h.p.—which makes one wonder what can be got into the fuselage besides fuel.
Another special-purpose aeroplane of maritime significance is the long-range general reconnaissance landplane. During the War the coasts of Britain were patrolled by landplanes such as the Bristol Beaufort and Lockheed Hudson. The former was an effective, but rather cramped, development of the Blenheim. The latter was a modified feeder airliner and what it lacked in military virtues it made up in crew comfort. This lesson was learned and since 1939 adequate crew accommodation has been a feature of reconnaissance types. Liberators, Fortresses and Lancasters were fitted with the necessary search radar and the last is in use to this day with A.S.R. squadrons. The large bomb bay of the Lancaster was the first to take the airborne lifeboat (developed by the M.A.P. and Saunders-Roe and dropped by G.Q. parachutes), yet another all-British achievement and one that has saved many fives.
After the War a special general reconnaissance version of the Lincoln was projected, which gradually altered so much that it was renamed the Shackleton. The wing, tail plane and undercarriage are the same and the nacelles are similar; but the fuselage is much fatter, to make room for extra equipment and to give the all-important crew comfort. In the Mark 1 the radome is under the nose, in the Mark 2 it is in a retractable dustbin. Armament consists of a twin 20 mm. top turret and twin 20 mm. nose barbette, instead of a tail turret there is a lookout post; 2,450 h.p. Rolls-Royce Griffon 67 engines replace the Merlins and drive contra-rotating airscrews. Very large fins and rudders give the necessary directional stability to counteract the higher power.
American thought centred on large twins for long-range reconnaissance—a job which comes under the Navy in that country. One example, the Lockheed Neptune, is typical of several designs. The large clean fuselage is nearly the size of the Shackleton, but the span is less. Typically American are the radome on one wingtip and the fuel tank on the other. Very high-powered submarine detection equipment is mounted in a huge dome under the fuselage. Once again we have the huge fin, in this case to provide directional control in single
engined flight. The engines, which are in rather long nacelles, are Wright Turbo-Cyclones, giving 3,500 h.p. each. The TurboCyclone is a large radial engine with three exhaust turbines which feed back power into the crankshaft through fluid drives. This reclamation of otherwise waste exhaust energy greatly reduces fuel consumption.
Like the Navy, the Army wants an aeroplane for observing terrestrial activity, only in this case long range or endurance are not necessary. For many years the Army co-operation squadrons of most air forces were palmed off with adaptations, usually obsolete ones like the R.E.8. A few years before the War, attempts were made to meet Army needs with specially designed aeroplanes in the thousand horsepower category. The British contribution was the Westland Lysander, an aeroplane with numerous special features. Automatic slots and flaps gave it very short take-off and landing runs. A high wing, with the pilot in front and the observer behind, gave an exceptional allround view and, of course, the essential clear sight of the ground. The fixed undercarriage was rigid, with internally sprung wheels, and to it small winglets could be attached for the mounting of bomb or supply racks. Fixed front and movable rear guns were fitted. Naturally, with so large a fuselage and a fixed undercarriage the Lysander had no great speed. Owing to the collapse of France the Lysander had little chance to prove itself in action, since for years thereafter production was concentrated upon fighters and bombers. It was used, however, for taking agents into occupied territory, where the low stalling speed was a great advantage for hazardous night landings in rough fields.
The aeroplane that, perhaps, most completely represented army co-operation ideas was the Fieseler Storch. This highwing monoplane had all the attributes of the Gugnunc built into it. The wing was of ample area, with a thick section, permanent slats and slotted flaps and ailerons. A low wing loading of a little over 10 lb./sq. ft. resulted in a stalling speed of only 32 m.p.h. A very long-stroke undercarriage was fitted to absorb high vertical rates of descent and the tail surfaces were very large so as to give full control at low speeds. The rather gawky fuselage had a queer glazed "conservatory" that bulged over the sides of the fuselage, so giving the occupants a vertical downward view. The roof was also glazed for upward vision. The inverted vee engine developed 240 h.p., the crew was three, and yet the top speed was only 109 m.p.h., cruising speed 60 to 80 m.p.h.—a clear example of the penalties to be paid for slow flying and good view.
During the War both the R.A.F. and the U.S.A.A.F. discovered that most of the needs of Army co-operation could be met by good high-wing light aeroplanes of about a hundred horsepower. The familiar Auster—it was originally an American Taylorcraft type built under licence—is an excellent example.
As a cheap light aeroplane it was simple and its welded tube fuselage made it easy to increase the view by substituting perspex panels for the fabric. Army aeroplanes are usually arranged as emergency ambulances and this gave the Auster designer the idea of adapting his aeroplane on the pod-andboom principle. Queer though it looks, the Auster B.4 has quite a good performance and yet fulfils its military duties to perfection. With the Korean War, the U.S. Army found itself short of larger liaison planes capable of using small rough fields. To fill this need they turned to another special-duty type, the Canadian bush aeroplane. After their success with the Chipmunk , The de Havilland Aircraft of Canada Ltd. made a sixseater for their home market. The bush operator needs above all a rugged aeroplane, capable of carrying a good load at a fair speed, with little maintenance. The all-metal Beaver was designed to do just this. The high wing rises clear above obstructions and its strut bracing avoids the weight penalty of a full cantilever. The fuselage is a sturdy metal box. The cabin has large doors on each side and a very strong floor. The undercarriage is of welded steel with rubber block springing and is very strong. Slotted flaps give a low landing speed and the flying qualities are very good. To guard against turning over on rough ground the main wheels are far ahead of the c.g. Except for the lack of rear view the Beaver fills the need of the Army co-operation aeroplane, but this one failing restricts it to flights behind the lines. Like most bush types the Beaver can be fitted with floats or skis.
The success of the Beaver led to a larger version, the Otter, being built. In this the main features are repeated, but double- slotted flaps are used to obtain even better lift characteristics. The Otter, although it has but a single engine of 600 h.p. has a cabin and load capacity about equal to that of the Dove. It is illustrative of the importance of fitness for purpose that while the Otter sells as fast as it can be made, the Dove is not much used in Canada because it is too refined for bush needs—although in the U.S.A., where smart executive aeroplanes are in demand, it is very popular indeed.