By William Pearce
On 12 September 1942, the Martin-Baker MB3 fighter crashed after its Napier Sabre engine seized. Company co-founder Captain Valentine H. Baker was killed during the attempted forced landing. James Martin, the aircraft’s designer, had already designed the MB3A, which was the production version of the MB3 that incorporated several changes to enhance the fighter’s performance. The second MB3 prototype was to be completed as a MB3A. After the MB3 was destroyed and Baker was killed, Martin wanted to further alter the aircraft’s design to improve its safety and performance. Perhaps the paramount change was to replace the Sabre engine with a Rolls-Royce Griffon.
The British Air Ministry doubted the quick delivery of the two MB3 prototypes still on order and was agreeable to a contract change. They authorized the construction of a single prototype of the new aircraft design designated MB5. The MB5 was given serial number R2496, which was originally allocated to the second and never-built MB3 aircraft. The third MB3 prototype was cancelled.
The Martin-Baker MB5 was officially designed to the same Air Ministry Specification (F.18/39) as the MB3. Also, the aircraft’s construction closely followed the methods used on the MB3. The aircraft’s fuselage was made of a tubular steel frame with bolted joints. Attached to the frame were formers that gave the fuselage its shape. Aluminum skin panels were attached to the formers, and detachable panels were used wherever possible. A rubber seal attached to the formers ensured the tight fit of the detachable skin panels, which were secured by Dzus fasteners. The large and easily removed panels helped simplify the aircraft’s service and maintenance.
The MB5’s wings were very similar to those used on the MB3, except that each housed only two 20 mm cannons with 200 rpg. All control surfaces used spring servo tabs; the rudder was fabric-covered, but all other control surfaces were metal-covered. The aircraft’s brakes, split flaps, and fully retractable landing gear were pneumatically controlled, and the air system operated at 350 psi (24.13 bar). The main wheels had a wide track of 15 ft 2 in (4.62 m). Two fuel tanks were housed in the aircraft’s fuselage: an 84 gallon (318 L) tank was positioned in front of the cockpit, and a 156 gallon (591 L) tank was positioned behind the cockpit. The cockpit was positioned directly above the wings and was enclosed with a bubble canopy. The cockpit had very good visibility, and its design was praised for the excellent layout of gauges and controls. The three main gauge clusters hinged downward for access and maintenance.
The MB5 was powered by a Rolls-Royce Griffon 83 engine capable of 2,340 hp (1,745 kW) with 25 psi (1.72 bar) of boost and 130 PN fuel. The engine originally turned a six-blade Rotol contra-rotating propeller, but by late 1945, a 12 ft 6 in (3.81 m) de Havilland contra-rotating unit was installed. A small scoop under the spinner brought in air to the Griffon’s two-speed, two-stage supercharger. The intercooler, radiator, and oil cooler were arranged, in that order, in a scoop under the fuselage. This arrangement provided some heat to the oil cooler when the engine was first started and prevented the oil from congealing and restricting the flow through the cooler.
The aircraft had a 35 ft (10.7 m) wingspan, was 37 ft 9 in (11.5 m) long, and was 14 ft 4 in (4.4 m) tall. The MB5 had a maximum speed of 395 mph (636 km/h) at sea level, 425 mph (684 km/h) at 6,000 ft (1,829 m), and 460 mph (740 km/h) at 20,000 ft (6,096 m). Normal cruising speed was 360 mph (578 km/h) at 20,000 ft (6,096 m). The aircraft stalled at 95 mph (153 km/h) clean and at 78 mph (126 km/h) with flaps and gear extended. The MB5 had an initial rate of climb of 3,800 fpm (19.3 m/s) and could reach 20,000 ft (6,096 m) in 6.5 minutes and 34,000 ft (10,363 m) in 15 minutes. The MB5’s service ceiling was 40,000 ft (12,192 m), and it had a range of around 1,100 miles (1,770 km). The aircraft had an empty weight of 9,233 lb (4,188 kg), a normal weight of 11,500 lb (5,216 kg), and an overload weight of 12,090 lb (5,484 kg).
Construction of the MB5 started in 1943, and some components (possibly the wings and tail) of the second MB3 prototype were used in the MB5. The work on the aircraft was delayed because of other war work with which Martin-Baker was involved. In addition, Martin continued to refine and tinker with the MB5’s design, much to the frustration of the Air Ministry. However, the Air Ministry decided that Martin was going to do whatever he thought was right and that the best course of action was to leave him alone; the MB5 would be done when Martin decided it was done.
Captain Baker was Martin-Baker’s only test pilot and was never replaced. As the MB5 neared completion in the spring of 1944, Rotol test pilot (Leslie) Bryan Greensted was loaned to fly the aircraft. On 23 May 1944, the MB5 was disassembled and trucked from Martin-Baker’s works in Denham to the Royal Air Force (RAF) station in Harwell. The aircraft was reassembled and underwent some ground runs. Later that same day, Greensted took the MB5 aloft for its first test flight. To disassemble, transport, reassemble, and flight test an aircraft all in one day speaks to the MB5’s impressive design.
Greensted was not overly impressed with the aircraft’s first flight, because the MB5 exhibited directional instability; in fact, he said the aircraft “was an absolute swine to fly.” Martin listened intently to Greensted’s comments and immediately went to work on a solution. The increased blade area of the contra-rotating propellers had a destabilizing effect when coupled with the MB3 tail that was originally used on the MB5. To resolve the issue, Martin designed a taller vertical stabilizer and rudder, which were fitted to the MB5. The change took six months for Martin to implement, but when Greensted flew the aircraft, he was impressed by its performance and handling. In addition, a new horizontal stabilizer was fitted, but it is not known exactly when this was done. From its first flight until October 1945, the MB5 accumulated only about 40 flight hours. Martin-Baker had been informed around October 1944 that no MB5 production orders would be forthcoming, given that the war was winding down, and any production aircraft would most likely enter service after the war was over.
Some sources state the MB5 was prepared for a speed run in the fall of 1945. The Griffon engine was boosted to produce 2,480 hp (1,849 kW), and the aircraft reached 484 mph (779 km/h) on a measured course near Gloucester. However, the speed record claim seems highly doubtful. On 29 October 1945, the MB5 was one of the aircraft exhibited at the Royal Aircraft Establishment (RAE) Farnborough. It was the only aircraft present that had contra-rotating propellers. While Greensted was demonstrating the aircraft before Winston Churchill and RAF officials, the Griffon engine failed. With his vision obscured by oil and some smoke in the cockpit, Greensted jettisoned the canopy. The canopy flew back and struck the tail, but Greensted was able to land the MB5 without further damage.
The MB5 had accumulated around 80 flight hours by the time it was handed over to the Aeroplane and Armament Experimental Establishment (A&AEE) at Boscombe Down. In March, April, and May 1946, the MB5 was flown by various pilots, and the aircraft’s performance and handling characteristics were well praised, but it was noted that the MB5’s acceleration and its roll rate were not quite on par with contemporary fighters. Overall, the tests showed that the MB5 was an excellent aircraft and that it was greatly superior from an engineering and maintenance standpoint to any other similar type. The MB5 was back at RAE Farnborough for an exhibition in June 1946. During the show, Polish Squadron Leader Jan Zurakowski flew the aircraft in a most impressive display and later stated that the MB5 was the best airplane he had ever flown.
The MB5 was flown sparingly until a number of flights were made toward the end of 1947. Wing Commander Maurice A. Smith flew the aircraft during this time and highly regarded the MB5’s layout and performance. From mid-November to the end of 1947, the MB5 was loaned to de Havilland at Hatfield for propeller testing. In 1948, the aircraft returned to RAE Farnborough, where it was flown by legendary pilot Captain Eric ‘Winkle’ Brown. Although Brown was slightly critical of the aircraft’s lateral handling qualities, he said the MB5 was an outstanding aircraft and that he had never felt more comfortable in a new aircraft.
On 5 May 1948, the MB5 was sent to the Air Ministry Servicing Development Unit at RAF Wattisham. There, it served as a training airframe until it was moved to RAF Bircham Newton around 1950. Reportedly, the MB5 was used as a ground target until its battered remains were burned in 1963—an inglorious end for such a fine aircraft.
The Martin-Baker MB5 is one of a handful of aircraft that demonstrated superlative performance and flight qualities yet never entered production due to the end of World War II and the emergence of jet aircraft. It is quite impressive that the MB5 was created by a small firm that produced a total of four outstanding aircraft—each being a completely different model. Despite the quality of Martin-Baker’s aircraft and their best efforts to enter the aircraft manufacturing business, the MB5 was the company’s last aircraft. Martin-Baker turned their attention to other aircraft systems and became a pioneer and world leader in ejection seat technology.
An MB5 replica has been under construction by John Marlin of Reno, Nevada for a number of years. Although not an exact copy, Marlin’s reproduction is a labor of love intended to commemorate one of the most impressive aircraft of all time and to honor all who created the original MB5.
RAF Fighters Part 2 by William Green and Gordon Swanborough (1979)
British Experimental Combat Aircraft of World War II by Tony Buttler (2012)
Wings of the Weird & Wonderful by Captain Eric ‘Winkle’ Brown (1983/2012)
Sir James Martin by Sarah Sharman (1996)
“The Martin-Baker M-B V” Flight (29 November 1945)
“M-B V in the Air” by Wing Commander Maurice A. Smith, Flight (18 December 1947)
“Martin-Baker Fighters,” by Bill Gunston, Wings of Fame Volume 9 (1997)
The British Fighter since 1912 by Francis K. Mason (1992)