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Aviation History
1956
1956 - 0081.PDF
SHORT SEAMEW 1—The Design Philosophy By DAVED KEITH-LUCAS, B^., MJ.Mech.E., F.R.ACS.* JT was in 1951 that die Naval Staff, from considerations of theanti-submarine warfare of the late war, concluded that therewas a need for a simple, yet fully effective, light aircraft for anti-submarine duties. An aircraft with proper search equipmentwhich could be operated in almost any weather from small carriers would have been of very considerable advantage in the battle ofthe Atlantic and might have made a great difference to our losses. At the time of the Naval Staffs conclusion, development of radarequipment was tending to outstrip the development of aircraft capable of carrying it and yet of operating from small carriers. Short Brothers and Harland soon became engaged in designstudies of a simple and rugged anti-submarine aircraft, carrying a crew of two (a pilot and a navigator /radar operator), for all-weather operation from carriers of the smallest type. It was to be suitable for production and use in large quantities in time ofemergency and therefore the general design-philosophy was one of simplicity, ease of maintenance and low first cost, yet without inany way compromising the military performance which was con- sidered necessary. For example, it was decided that a large typeof radar scanner should be fitted, that the bomb bay should be capable of carrying large stores, and that a long patrol perform-ance should be provided. This initial work eventually resulted in the formulation of aMinistry of Supply specification which was issued to the industry as the basis for a tender design competition. Shorts won the com-petition with the design which then carried the company's num- ber S.B.6 and is now known as the Seamew. An Armstrong Siddeley Mamba ASM.6 engine was chosenbecause the high efficiency of this propeller turbine gave the neces- sary speed, endurance and small diameter which suited the type ofairframe Shorts wanted to design. The ability of the engine to operate on any fuel is a considerable advantage as it does notrequire the availability of high-octane petrol: and high-octane petrol is never popular on board ship. Incidental advantages of the propeller turbine engine are thatthere is no ignition system to cause interference on the radar screen and that the low band of vibrations allows the pilot to beplaced on top of the engine, where he gets the best possible view. Great attention was paid to the field of view of both pilot andnavigator. All pilots who have flown the aircraft have commented on the remarkably fine view, wh'.ch is so necessary both for searchoperations and also for deck landing. To enable the Seamew to operate from the smaller carriers it was given very short take-off and landing runs. Indeed, it will take off in a 12 kt wind in about 500ft. The stalling speed is correspondingly low and the approach speed for deck landing is very reasonable. Pilots who have flown the aircraft are delighted with the way it flies on to the deck and with the way it can be landed at all speeds. , A fixed and simple landing gear was chosen, as it was thoughtthat a retractable unit was not necessary at the operating speeds. A nosewheel was not used because it would interfere with theradar scanner, but Shorts evolved a system of extending the tail wheel for deck landing so that aircraft could land tail-up andwould not have a tendency to "balloon" off again once the wire was contacted. The unit subsequently sinks down to its normal position. The undercarriage was given a very long travel, inorder to accommodate a high landing velocity, and this enables landings to be made on the deck in the roughest of weathers.As the aircraft may possibly have to ditch in the sea in emergency, a main-undercarriage jettison system was evolved to avoid anydanger of nosing over on contact with the water. It has the inci- dental advantage of enabling undercarriages to be changed easily. Although originally it was proposed to have only manual wing-folding, power folding was eventually fitted because the complica- tion and weight penalty was small, and because it is an opera-tionally attractive feature, allowing aircraft to be struck down more quickly. As mentioned above, the bomb bay is large. The internallength is 14ft and, for an aircraft of this size, very big stores can be fitted. Although no details can be given of the radarequipment it is obvious from the size of the radome that the scanner is of large proportions and obviously able to search withthe greatest efficiency. Short's philosophy of designing for simple maintenance hasbeen used throughout the aircraft. An outstanding feature, made possible by the type of powerplant installation, is the speed withwhich an engine can be changed. During an official demonstra- tion we have changed an engine and run it again in a total time of1 hr 20 min, including inspection. There are many access panels and die standard of accessibility is high.As a result of the programme of strength tests and the results obtained from the Seamew it has actually come out slightly underthe original target weight of 14,000 lb with the originally specified stores load. Now, however, the Naval all-up-weight has beenincreased to 14,400 lb, which is still below the specification figure, to enable die stores capacity to be increased. The R.A.F. versionhas gone as high as 15,100 lb by eliminating the deck-landing requirement. This enables die aircraft to operate with the maxi-mum of stores and fuel without restriction. The target was a four-hour patrol at 120 kt, and this has beenachieved. As mentioned above, the take-off performance in a 12 kt wind is 500ft and even in still air it is only 300 yd. Thetotal stores load is in excess of 1,800 lb, with some stores carried on the wings, and several combinations are possible, includingmines, sonobuoys and torpedoes. The normal level speed of the aircraft is about 200 kt, but itis cleared to the relatively high diving speed of 325 kt; diis is to enable attacks to be made from altitude by diving on the enemy.It is of interest to note that the speed range between stalling speed and diving speed is unusually large for an aircraft of diis type.The forward position of the radar scanner ensures that, even in a steep dive, the target is always in the radar view and neverblanked by the nose of the aircraft. The first Seamew was flown 17 months after the order wasplaced wirn the company, and the production line is now in full swing. Ten aircraft are now flying. I would like to pay tribute todie staff concerned widi the project at the Ministry of Supply. Their co-operation was a real factor in getting the Seamewdesigned and built in so short a time. *Director and chief designer, Short Bros, and Harland, Ltd.
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