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Aviation History
1945
1945 - 2157.PDF
472 FLIGHT De llavillantl Goblin Some Details of the Turbine~jet Unit Now in Production for the de Havilland Vampire THE engine-building activities of the de HavillandCo. have tended to become somewhat over-shadowed by the outstanding performance and war record of the Mosquito aircraft. Consequently, the recent release of the news that the company had devel- oped a turbine-jet unit for its new Vampire fighter came as a surprise to all outside " informed circles." It was in January, 1941, that the first discussions on the subject were held and three months later a decision was taken to commence working designs of a unit to develop a thrust of 3,000 lb. for installation in the pro- jected Varnpire. The first drawings were issued to the shops on August 8th, and on April 13th in the follow- ing year the unit was ready for its first run on the test bed. In less than two months it was operating satis- factorily on its full designed thrust. Production of the jet engine outstripped that of the aircraft, and to obtain flight experience two units were first flown in a Gloster Meteor aircraft on March 5th, 1943. It was not until September 20th that year that the Goblin was flown in a Vampire. It is interesting to record that Goblin units were shipped to America and flown in the Lockheed Shoot- ing Star. Both the Vampire and the Shooting Star by the spring of 1944 were exceeding 500 m.p.h., and it is claimed that these were the first aircraft in Britain or America to achieve that speed. In January, 1945, the Goblin successfully passed an official type-approval test and now- holds Type Certifi- cate No. 1 for a turbine unit for aircraft propulsion. Following the de Havilland tradition, a high degree of reliability has been one of the principal aims, and a Goblin unit has already been run for 500 hours under official type test conditions without the change of any- main component. The development throughout has been conducted in closest co-operation with the Air Ministry and Ministry of Aircraft Pro- duction. f>K The Goblin is a linear descendant of ' ' the early Whittle units. It comprises I a single-sided centrifugal compressor * delivering air to sixteen combustion chambers grouped symmetrically xS around the axis of the unit and leading to the nozzle of the single-stage axial turbine which drives the compressor. Compressor im- peller and turbine rotor are coupled by a tubular shaft fo form a single rotating assembly which is mounted on only two ball bearings. The maximum diameter of the engine, around the compressor casing, is 50m., and with a jet pipe of minimum length fitted the overall length is' about 8ft. Equipped with a jet pipe and all the neces- sary engine auxiliaries the dry weight of the complete unit is 1,500 lb. Fuel consumption is at the rate of 1.23 lb./hr. per 1b. thrust. Air Compressor Turning to the main components, the retention of a single-sided impeller for the centrifugal compressor aims to provide the maximum diameter of entry and to take full advantage of ram effect. It is held that the double- sided impeller is slightly less efficient as the air must first pass through what is in effect a balance chamber for the two intakes. Furthermore, there is some degree of preheating of the air reaching the rear intake. Within the dimensional limits imposed by the aircraft installa- tion it is possible to meet all requirements by a single- sided impeller; simple to produce and requiring a less complicated casing. Axial thrust is balanced on a double-sided impeller, of course, whilst a single-sided impeller has a positive thrust loading. There is, how- ever, an axial thrust in the opposite direction developed by the rotor of the turbine, and in the de Havilland design these two opposing forces are arranged to neutral ise each other. Actually, the compressor impeller tencfe Rear view showing propulsion nozzle, heat shroud and closely stacked combustion chambers. Note two cooling-air pipes for rear of turbine disc.
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