1955 - 0735
1
FLIGHT, 27 May 1955 733 A LTHOUGH the ground-work of American jet development A\ was largely laid by G.E.C., the first large American axial •*• - ^ design, the TG-180, was passed to the Allison Division of General Motors who were better placed to undertake large- scale production. Previously Allison had been noted for their range of l,710cu in V-12 piston engines. As the J35, the basic TG-180 has now been made by Allison in enormous numbers. During the past ten years, the company have also developed a family of turboprops which are beginning to reach military service and have also tackled the problem of developing a large turbojet to succeed the J35 on the production lines. This new turbojet is the Allison J71, the fact that it has an odd number indicating that the initial design was sponsored by the U.S. Air Force and not the Navy. The basic design of the J71 was virtually complete by 1950 and early examples of the engine were run in that year. Since then, considerable development has taken place, and present engines have the following features. The compressor has 16 stages, all mounted on the same shaft as the three-stage turbine. The combustion system is of the cannular type, consisting of a two-piece stainless-steel chamber housing ten interconnected flame tubes. Concurrently with the basic engine has been evolved an exceptional variety of auxiliary devices, including a variable- area tailpipe, an electro-mechanical control system, automatic intake screens to prevent the ingress of ice and foreign material, an integral oil and hydraulic system, and a comprehensive range of engine and airframe accessories including a power-pack driven by an air-turbine motor. The J71 is also available with at least two types of afterburner, both of which are completely cleared for service. One afterburner is employed for take-off and low- altitude boosting and another is specifically for increasing the performance of fighters at high altitudes. The principal bone of contention in the J71 design is that it is a single-shaft engine. According to Allison, the design was specifically intended to meet the need for "a single-compressor engine with high compression ratio which would match good fuel economy with maximum thrust"; Mr. E. B. Newill, general manager of the Allison Division and vice president of General Motors, recently stated that the J71 had "demonstrated thrust in excess of 10,000 lb with the highest pressure ratio of a single- compressor engine yet developed. In addition, this engine develops more thrust per square foot of frontal area than any jet engine ever produced." (The last sentence is incorrect, if Mr. Newill's statement is based on his company's published figures; the later Sapphire and Olympus can both achieve better thrust per unit frontal area, even on type-tested ratings.) The diameter is 39.5in, and the basic engine (without afterburner) weighs about J71 Allison's Big Axial Turbojet 4,100 lb and is 191.4in long. Several 150-hr tests have been run at 10,000 1b at 6,100 r.p.m., with an sl.c. of just under 0.91b/hr/lb. The mass-flow and pressure-ratio are, respectively, of the order of 172 lb/sec and 8.75:1, figures which are well up to the best values achieved by other type-tested turbojets. The establish- ment of a single-shaft pressure-ratio of this order (in an engine used by such aircraft as all-weather carrier-based fighters) is a remarkable achievement. After a lengthy incubation, Allison now seemed pleased with the engine and would, no doubt, strongly deny regret at the acceptance of such a layout. The illustrations show two representative types of engines at present in production at Indianapolis. The larger picture shows the J71-A-2, which is installed in the McDonnell F3H-2N Demon, a transonic carrier-based all-weather machine. A point of interest (apart from die engine's immense size and complexity) is the jungle of accessories between the bifurcated intake ducts. The — 2 engine has the long type of afterburner, which raises the thrust to 15,000 lb. Without afterburning the J71 gives 44 per cent more thrust than the earlier J35, also seen in the large photograph, which is of roughly The same diameter. The smaller photograph shows the J71-A-11 for the Douglas B-66 and RB-66 tactical and reconnaissance bombers. This engine is considerably shorter than the other, principally owing to the fact that it has no afterburner. It picks up at four points inside a single nacelle, one such power-installation being pod-mounted under each wing of the Douglas bomber. Accessories in this engine are spread around the lower half of the com- pressor; the starter is an air-turbine motor, which draws compressed air from a Solar gas- turbine/compressor trolley. In the photo- graph the nose-drive pad is not yet occupied and the intake fairing has not yet been fitted, in order to reduce the overall length for ship- ment. The retracted intake screens are visible. One type of J71 with the short afterburner is fitted to the Martin XP6M SeaMaster. These engines, designated J71-A-4, are mounted above the wing in two paired nacelles, the afterburners projecting behind the trailing-edge. Full afterburning thrust is employed in this aircraft for take-off and also to increase the performance at low altitudes during mine-laying or photographic missions.
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1955 - 0735
Transcript of 1955 - 0735
FLIGHT, 27 May 1955 733
A LTHOUGH the ground-work of American jet developmentA\ was largely laid by G.E.C., the first large American axial
•*• - ^ design, the TG-180, was passed to the Allison Divisionof General Motors who were better placed to undertake large-scale production. Previously Allison had been noted for theirrange of l,710cu in V-12 piston engines.
As the J35, the basic TG-180 has now been made by Allisonin enormous numbers. During the past ten years, the companyhave also developed a family of turboprops which are beginningto reach military service and have also tackled the problem ofdeveloping a large turbojet to succeed the J35 on the productionlines. This new turbojet is the Allison J71, the fact that it hasan odd number indicating that the initial design was sponsored bythe U.S. Air Force and not the Navy.
The basic design of the J71 was virtually complete by 1950and early examples of the engine were run in that year. Sincethen, considerable development has taken place, and presentengines have the following features. The compressor has 16stages, all mounted on the same shaft as the three-stage turbine.The combustion system is of the cannular type, consisting of atwo-piece stainless-steel chamber housing ten interconnectedflame tubes. Concurrently with the basic engine has been evolvedan exceptional variety of auxiliary devices, including a variable-area tailpipe, an electro-mechanical control system, automaticintake screens to prevent the ingress of ice and foreign material, anintegral oil and hydraulic system, and a comprehensive range ofengine and airframe accessories including a power-pack drivenby an air-turbine motor. The J71 is also available with at leasttwo types of afterburner, both of which are completely clearedfor service. One afterburner is employed for take-off and low-altitude boosting and another is specifically for increasing theperformance of fighters at high altitudes.
The principal bone of contention in the J71 design is that it isa single-shaft engine. According to Allison, the design wasspecifically intended to meet the need for "a single-compressorengine with high compression ratio which would match good fueleconomy with maximum thrust"; Mr. E. B. Newill, generalmanager of the Allison Division and vice president of GeneralMotors, recently stated that the J71 had "demonstrated thrust inexcess of 10,000 lb with the highest pressure ratio of a single-compressor engine yet developed. In addition, this enginedevelops more thrust per square foot of frontal area than anyjet engine ever produced." (The last sentence is incorrect, if Mr.Newill's statement is based on his company's published figures;the later Sapphire and Olympus can both achieve better thrustper unit frontal area, even on type-tested ratings.) The diameteris 39.5in, and the basic engine (without afterburner) weighs about
J71Allison's Big Axial Turbojet
4,100 lb and is 191.4in long. Several 150-hr tests have beenrun at 10,000 1b at 6,100 r.p.m., with an sl.c. of just under0.91b/hr/lb.
The mass-flow and pressure-ratio are, respectively, of the orderof 172 lb/sec and 8.75:1, figures which are well up to the bestvalues achieved by other type-tested turbojets. The establish-ment of a single-shaft pressure-ratio of this order (in an engineused by such aircraft as all-weather carrier-based fighters) is aremarkable achievement. After a lengthy incubation, Allison nowseemed pleased with the engine and would, no doubt, strongly deny
regret at the acceptance of such a layout.The illustrations show two representative
types of engines at present in production atIndianapolis. The larger picture shows theJ71-A-2, which is installed in the McDonnellF3H-2N Demon, a transonic carrier-basedall-weather machine. A point of interest(apart from die engine's immense size andcomplexity) is the jungle of accessoriesbetween the bifurcated intake ducts. The— 2 engine has the long type of afterburner,which raises the thrust to 15,000 lb. Withoutafterburning the J71 gives 44 per cent morethrust than the earlier J35, also seen in thelarge photograph, which is of roughly Thesame diameter.
The smaller photograph shows theJ71-A-11 for the Douglas B-66 and RB-66tactical and reconnaissance bombers. Thisengine is considerably shorter than the other,principally owing to the fact that it has noafterburner. It picks up at four points insidea single nacelle, one such power-installationbeing pod-mounted under each wing of theDouglas bomber. Accessories in this engineare spread around the lower half of the com-pressor; the starter is an air-turbine motor,which draws compressed air from a Solar gas-turbine/compressor trolley. In the photo-graph the nose-drive pad is not yet occupiedand the intake fairing has not yet been fitted,in order to reduce the overall length for ship-ment. The retracted intake screens are visible.
One type of J71 with the short afterburneris fitted to the Martin XP6M SeaMaster.These engines, designated J71-A-4, aremounted above the wing in two pairednacelles, the afterburners projecting behindthe trailing-edge. Full afterburning thrust isemployed in this aircraft for take-off and alsoto increase the performance at low altitudesduring mine-laying or photographic missions.
