Alan Baxter was Roll Royce's Chief Flight Test Engineer at the Filton Works in Bristol. Here he looks back to his early days with the old Bristol Siddeley Company. This report takes up the story of XA903.
'With XA903 being retired from the Blue Steel programme, the modifications to the aircraft to permit carriage of a partially-recessed stand-off weapon were such as to preclude its use on any other MoD trial. It was therefore the ideal choice of vehicle when a requirement arose for an aircraft to be used as a flying test bed for the Concorde powerplant, and it was so allocated in December 1963. It was delivered to Bristol Siddeley's (now Rolls-Royce) flight test facility at Filton Airfield, adjacent to the Patchway works, on 3rd January 1964.
'Concorde is powered by four Olympus 593 reheated turbojets. These are developed from Olympus 320 for the TSR2, and were considerably improved in the process. In turn the Olympus 320 can trace its origins back to the Olympus 301 which powered the later versions of the Vulcan B. Mk 2, so in fitting an Olympus 593 to a Vulcan B Mk 1, we were keeping it in the family, so to speak.
'The Olympus 593 installation on XA903, consisting of one half of a Concorde nacelle, was slung underneath the bomb bay, fuel and water tanks plus instrumentation and control avionics filling the original bomb-bay space. A simulation of the Concorde intake's central splitter plate projected forward of the intake plane on the starboard side. The moveable front ramp, which on Concorde is used to control the position of the intake shock waves during supersonic flight was used on the Vulcan to close off the intake for take-off and landing, thereby preventing any engine compressor damage from foreign object ingestion. An auxiliary intake door, designed to permit extra air into the engines at low speeds or spill excess air from the intake at high speeds, or if the engine was shut down, was also fitted. In theory therefore the installation was representative of both a No. 1 and No. 2 intake.
'The Vulcan was found to be ideally suited to the role of FTB. Its considerable ground clearance made the job of fitting the test engine relatively straightforward, and its flight performance was more than adequate for the initial flight trials of the supersonic powerplant. The conversion took two years, the first flight, which was captained by Tom Frost, Bristol Siddeley's Chief Test Pilot, occurring on 9th September 1966 after some weeks of ground running. Strenuous efforts had been made to get the aircraft ready in time to be demonstrated at the SBAC Show at Farnborough, but the first flight did not occur until the Thursday of Farnborough week. With only four flying days left. Clearly the flying qualities of the aircraft with the somewhat rectangular nacelle underneath had to be checked for safety and controllability before the aircraft could appear at the show, and tests to check these items were scheduled for the first two flights. As can be imagined, considerable discussion had taken place to decide on the minimum level of testing consonant with safety to clear the installation for Farnborough, and to simplify the exercise, it was decided not to operate the test engine in flight until after the show.
'The first flight was to consist of a take-off and climb straight ahead to 10,000 feet, with the intake ramp closed, where the aircraft handling would be checked at high and low airspeed. Then the climb was to be continued at 250 knots to 30,000 feet where the intake ramp was to be opened, thus allowing the engine to 'windmill'. The aircraft handling would then be checked at low airspeed and high Mach Number. However in the climb, at about 27,000 feet, the ramp opened of its own accord, and a very heavy divergent vertical oscillation set in on the aircraft, caused by air spillage from the Olympus 593 intake, which did not stop until the Vulcan had slowed to below 200 knots. The ramp could not be closed using the normal controls, so the landing had to be made with the risk of foreign object damage to the compressor. Fortunately there was none, the installation was cleared on the second flight on the Friday, and we finally got to the show on the Saturday and Sunday.
'Because of doubts about the effect of the ventral test engine nacelle on the escape trajectories of the rear crew, dummy drops were made over the Larkhill bombing range on 1st October 1966 from a height of 2000 feet and an airspeed of 170 knots. Comparison with the escape trajectories from service Vulcan's showed no discernible difference, with the possible exception that the second parachute failed to open, and a very expensive dummy was written off. This exercise was mounted with the aid of the Airborne Trials Unit, based at Boscombe Down, and they were very upset with the Bristol Flight Test Department, until it was found that an incorrectly set barostat had been fitted to the parachute release mechanism.
'The difficulties of abandoning a Vulcan from the rear cabin were well known, as in approximately half of the Vulcans lost in flying accidents the rear crew had not escaped. It was therefore considered essential that escape drills were practised by all rear crew at least once a year, under as realistic conditions as possible. To achieve this, the aircraft was taken of flying status, and mounted on jacks with the under carriage retracted. The undercarriage was raised to simulate the most likely configuration for abandoning the aircraft. The possibility of successfully escaping with the nose leg down was theoretically possible, but in my opinion would have been extremely marginal in practice. The complete crew, all wearing flying kit, would strap in, and a wide variety of escape drills would be practised, ranging from complete crew abandonment on the ground. Because people tended to come out of the aircraft fairly fast, thick mattresses were liberally strewn around to minimise the risk of injury.
'Test flight tended to be very busy affairs. A crew of five was usually carried, each crew member having specific tasks. The aircraft captain flew the aircraft from the left-hand seat, used the radios and carried out any instructions from Air Traffic Control. The co-pilot, who was the engine project pilot, was also Vulcan qualified, and operated the test engine. The rear cabin had been completely transformed during the conversion, with a large instrument panel added to enable various aspects of the test engine to be monitored. The two flight test engineers, who occupied the Nav Radar and Nav Plotter positions, could both see the panel but had their own division of labour. The Nav Plotter controlled the instrument recorders, and kept the flight log for post-flight analysis. The Nav Radar acted as Test Controller, deciding with the project pilot the sequence of tests and in addition controlled hydraulic and electrical loads that could be applied to the test engine, and kept a general flight log. The final crew member was the AEO, who carried out limited navigational duties using ADF and TACAN, and also looked after the aircraft's electrical systems. This last was an extremely important duty, as the Vulcan B. Mk 1 was an all-electric DC aircraft, and several had been lost due to electrical problems.
'The aircraft could be comfortably flown on the thrust from the Olympus 593 alone. The main engines were never shut down, however, as they provided the electrical power necessary to operate the flying controls and other services. The Vulcan B. Mk 1 had quite substantial batteries, to be used in the event of a total failure of the generating system, but we never counted on more that 10 to 11 minutes of battery time - enough to abandon the aircraft, but not to get back on the ground. So we never deliberately switched off the generators.
'Most Vulcan test flights were accompanied by a chase aircraft, usually a Folland Gnat T. Mk 1. Because the endurance of the Gnat was short, 45 minutes as opposed to the Vulcan's two hours plus, the Gnat did not takeoff with the Vulcan, but was cleared for flight and kept on the ground. When the Vulcan approached that part of the test programme that required external observation, the Gnat was scrambled. ATC would vector the chase to the target aircraft in a very short time, although on one occasion ATC inadvertently vectored the Gnat to an RAF Vulcan, eliciting from the pilot the comment, 'Nice intercept but the wrong Vulcan, this one's camouflaged'. Sitting in the back seat of the Gnat ten feet below and perhaps twenty feet behind the Vulcan, seeing a huge white delta apparently hovering there in front of us, was an unforgettable experience.
'Very few airframe problems surfaced during the programme, potentially the worst occurring in 6th February 1970 on flight 167, when a hydraulic pipe fractured after two hours of low altitude flyovers at Filton. A total loss of hydraulic fluid ensued, and as the emergency power pack simply pumped the reserve fluid out through the same fracture, it also caused a total loss of hydraulic pressure. On a Mark 1 Vulcan the undercarriage and wheel brake anti-skid systems (Maxaret) are operated by hydraulic pressure. Without the Maxarets a long runway is required in order to avoid overheating the brakes, so the aircraft was diverted to A&AEE Boscombe Down, only to find that the airfield was closed, it being after 1600 hours on a Friday. A further diversion to RAF Fairford then took place, the undercarriage being lowered under freefall conditions, but the nose leg failed to lock down, and remained only partially lowered. On landing, the nose leg did finally lock down after the main legs were firmly on the runway, at less than 100 knots, when presumably the aerodynamic loads on the nose leg had dropped to a sufficiently low value. The braking parachute also failed to stream, and the subsequently heavy wheel braking, made without the benefit of the anti-skid system, resulted in a port brake fire. The final landing was made with all the fuel low level warning lights on. After landing the underside of the aircraft was covered in blood-red hydraulic fluid.
'The weight of the Olympus installation plus test gear was such that XA903, at what we regarded as minimum fuel, was above the normal Vulcan B. Mk 1 maximum landing weight. Every landing was thus made in a fairly flat attitude at a threshold speed of around 130 knots. Because aerodynamic braking - holding the nose high so that air resistance slows the aircraft - could not be used due to the ventral engine nacelle, the braking parachute was streamed on every landing. This technique necessarily caused a high turnover in brake parachutes, with the Safety Equipment section on occasions re-packing them like mad, but was inevitable consequence of the design.
'A further dummy drop trial took place on 12th March 1971, after the water spray grid has been fitted for the de-icing trials. Again, no effect on escape trajectories was noted. The de-icing trials was one of the more important tasks carried out by XA903. A water spray grid containing over a hundred nozzles was mounted ahead of the Olympus 593 air intake, and water was sprayed into the engine at varying concentrations with the intake de-icing system in operation. The ice built up around the intake, and the way in which it was removed by the de-icing system, was monitored by a series of television cameras. The variable not under the control of the test crew was ambient air temperature, and the Meteorological Office was of great help in predicting where the desired air temperatures could be found. The programme was extremely successful, so much so that a Special Category icing clearance for Concorde was issued, based entirely on the Vulcan results.
'On landing after the 219th and final Olympus 593 test flight on 21st July 1971, the brake parachute failed to deploy when streamed, and also failed to jettison. The Vulcan made several circuits of Filton with the parachute trailing in shreds behind it, before the 'chute finally fell away. This time however there was no brake fire on landing. During the 219 test flights, 417 flying hours were accumulated which included 248 engine test hours in flight.'
Copyright © Paul Hartley