1434. JT9D-7R4 – A High Thrust-To-Weight Improved Efficiency Engine for the 80’s


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T L Davis: 1434. JT9D-7R4 – A High Thrust-To-Weight Improved Efficiency Engine for the 80’s. 1981.



The JT9D series of turbofan engines is Pratt & Whitney Aircraft’s largest aircraft powerplant family.
Variations of these engines cover a thrust range from 40,000 lbs. to more than 60,000 lbs., have inlets
eight feet in diameter, and weigh more than 4 tons each. The JT9D entered commercial service in January,
1970, on a Pan Am 747 and models of the engine are now aboard more than 400 aircraft.
In the early seventies, when revenue service began, airlines were paying eleven cents per gallon for fuel.
Today the price is approaching one dollar on contract and the spot market considerably exceeds that level.
Every facet of airline equipment, operation and service is being re-examined in response to the current
energy environment turbulence. Engine manufacturers have responded with successive model improvements
delivering higher and higher efficiencies. The changes necessary to produce these improvements offer a particular
challenge to the weight engineer, as many result in increased powerplant weight and thus reduced net
thrust-to-weight. Increased engine weight has a serious, multiplied and detrimental effect on the aircraft
gross weight and/or payload.
This paper discusses the background and weight development of Pratt & Whitney’s third generation of large
power plants, the JT9D-7R4 series of engines, scheduled to debut on the Boeing 767. Using a method of strong
weight control and weight reduction techniques, weight increases necessary to develop the specific fuel
consumption improvements required for todays energy environment were more than offset. This program thus has
resulted in the highest thrust-to-weight ratio of any Pratt & Whitney turbofan ever offered for commercial service.


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