FROM THE COCKPIT OF X-35B
Mr S. Hargreaves, BAE SYTEMS, STOVL Test Pilot.

25 May 2001

On November 22nd last year the X-35A, which was the LM/NGC/BAE SYSTEMS Conventional Concept Demonstration Aircraft, made it’s 27th and final flight to conclude a tremendously successful flight test phase which demonstrated the outstanding handling qualities, performance and reliability of the basic CTOL aeroplane. On that final flight, after a brief supersonic run, Chief Test Pilot Tom Morgenfeld brought the aircraft safely ‘home’ to the LM Skunk Works at Palmdale, California.

Since then the ship has undergone a metamorphosis and emerged from the hangar early this year as the X-35B – our STOVL Concept Demonstration Aircraft. In the cockpit virtually nothing has changed; only the addition of a Thrust Vector lever (TVL) outboard of the throttle indicates that this is now a revolutionary new tactical STOVL fighter. However, this small cockpit addition belies the changes that have occurred under the skin of the aircraft. The basic airframe has remained untouched and many sub-systems and the CTOL flight control system remain identical to the ‘A’ Model, but the P&W F119 engine has been augmented by addition of a shaft, clutch, gearbox and Lift Fan to become the first ever Shaft Driven Lift Fan propulsion system. This concept produces an enormous amount of STOVL thrust without great penalty to the ground environment and, crucially, provides a huge growth potential. This is an important factor in an aircraft that is likely to be in service for upwards of 30 years.

Since the aircraft has become the ‘B’ model, we have been working steadily and confidently toward the first flight – a Vertical Take-Off, hover and Vertical landing – which is now imminent. That’s right, the first ever flight of this aircraft will be straight into the hover from a VTO!

One of the myths we had to overcome was that a SDLF was somehow ‘too complex’ to ever achieve an acceptable level of reliability. Well, since the historic ground run on 22 February when the Lift Fan was coupled to the engine for the first time we have completed a further 40 engagements, at all power settings we will ever require in flight, and we have not had a single problem. I feel entirely confident that the system is now mature and reliable enough for us to start in-air conversions. Engine start and system checks are identical to the CTOL aeroplane and there is absolutely no sensation in the cockpit that the shaft is turning, which it does whenever the engine is running because the clutch is on the Lift Fan end of the shaft. The STOVL system is engaged by moving the Thrust Vector Lever out of a detent, although this will change in the production aircraft to further simplify the cockpit. The Lift Fan spins up with an absolute minimum of fuss or drama; the fact that it feels so unremarkable makes it, in fact, a remarkable event. With the Fan engaged the engine note changes slightly with the addition of a characteristic low whine, but other than that there is nothing in the cockpit to indicate that you are now sitting just in front of the most powerful single engined propulsion system ever incorporated into an aeroplane. There is no additional vibration, for example, and noise levels are unchanged. With the aircraft safely tied to the ground we have run the propulsion system at full power to measure the thrust achieved and complete all the necessary system checks before flight. The cockpit environment remains benign, even with the massive amount of thrust being developed just behind the canopy. The thrust vectoring nozzles move smoothly and predictably and, even though the aircraft is tied down you can feel it trying to move against the restraint system.

From all my time in the simulator and my few hours flying the X-35A and X-35C, I am confident that this aeroplane will have excellent handling qualities in Jetborne and Semi-Jetborne flight, and through the conversion process. From the first Hovers here at Palmdale we will rapidly expand the flight envelope to encompass conversions, decelerating transitions to the hover and landing and take-off at a variety of speeds. The ultimate mission for the X-35B is a STOVL take-off, accelerate to supersonic speed at altitude and return for a vertical landing. This event will demonstrate clearly the enormous potential of the LM/NGC/BAE SYSTEMS STOVL JSF proposal.