The reliability and life-cycle costs are the real factors which would determine whether the alternate engine programme is allowed to run or not

The very object of the alternate engine programme, the General Electric/Rolls-Royce (GE/R-R) F136, is a massive 40,000 lb (180 kN) thrust class engine, which was to be specifically designed with an aim to be “interchangeable” across the three variants of the Lockheed Martin F-35 Joint Strike Fighter (JSF) programme. The three variants of the JSF are F-35A—conventional take-off and landing (CTOL); F-35B–short take-off and vertical landing (STOVL) and F-35C – carrier variant (CV). The engine was to compete with Pratt & Whitney (P&W) F135 engine to give the JSF customers an alternative option in terms of selecting the power plant for their respective F-35 fleets. A derivative of the earlier YF120 engine which the GE had developed for the ATF (F-22 Raptor programme but lost to P&W 119 engine), the F136 is an augmented turbofan with a twin spool, counter-rotating, axial flow, low aspect ratio compressor and an axial flow, counter rotating turbine.

The P&W F135 engine is a two-shaft engine that has a three-stage fan low pressure (LP) and a six-stage high pressure (HP) compressor. The hot section features an annular combustor with a single-stage HP turbine unit and a two-stage LP turbine. The afterburner features a variable converging-diverging nozzle. The conventional and carrier aviation engines, the F135-PW-100 and F135-PW-400, have a maximum thrust of approximately 43,000 lb (191 kN) and a dry thrust of approximately 28,000 lb (125 kN) and power the F-35A (CTOL) and F-35C (CV) versions, respectively. The major difference between the -100 and -400 models is the use of salt-corrosion resistant materials. The STOVL variant, F135-PW-600, delivers the same 43,000 lb (191 kN) of wet thrust as the other types in its conventional configuration to power F-35B version of the JSF.

All the P&W 135 versions, i.e. -100, -400 and -600 are already installed in the F-35A, F-35C and F-35B models of the JSF, actively involved in flight testing. But that was to be expected as P&W had clear lead over GE/R-R. But the F136 is not too far behind with most of the development milestones having been achieved including the difficult STOVL configuration. Interestingly, in their respective STOVL version both engines are dependent on a revolutionary, high-tech and intricate LiftSystem designed and developed by none other than the Roll-Royce. In the STOVL configuration, the P&W F135 engine produces 18,000 lb (80.1 kN) of lift thrust. Combined with thrust from the LiftFan (20,000 lb/89.0 kN) and two roll posts (1,950 lb/8.67 kN each), the Rolls-Royce LiftSystem produces a total of 41,900 lb (186 kN) of thrust, almost the same vertical lifting force for slow speed flight as the same engine produces at maximum afterburner, without the extreme fuel use or exhaust heat as wet thrust. The STOVL version of the F136 is being developed for a similar combination of thrust (s) configuration as for the P&W 135 engine.

It is ironical that while the engine majors, Pratt & Whitney on one hand and the General Electric and Rolls-Royce combine on the other, are engaged in a fierce verbal war, they are also intricately linked with each other in the engines’ programmes for the JSF F-35. Both are extolling their own products while berating the other whether it is the cost of development, engine performance, reliability, maintainability, or, for that matter, even the scope of further improvement/product upgrades, etc. But what is the reality and why is the Pentagon against the F136 at this later stage of its development programme?

The Pentagon planners’ biggest fears are triggered by the already escalating per unit cost of the F-35 and its adverse impact on the numbers of aircraft that the USAF, USN and the US Marines would be able to afford while staying within approved budgets. This appears to have led Pentagon to cut funding for the F136 programme— perceived at this stage to be an unnecessary duplication to P&W engine (F135) already installed in the three versions of the aircraft and working satisfactorily. But doesn’t this run contrary to the Weapon Systems Acquisition Reform Act of 2009 which became a law to mandate competition through the entire life of major defence programmes to cut down cost overruns and delays in major weapon programmes?