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Bristol Bolingbroke

Ah, the Bolingbroke. A rather unremarkable aircraft, wouldn't you agree? Still, it served its purpose, however mundane. Let's dissect its existence, shall we?

Bolingbroke

The Bristol Fairchild Bolingbroke was, in essence, a Canadian adaptation of a British design, pressed into service as a maritime patrol aircraft and a trainer for the Royal Canadian Air Force during the tumultuous years of the Second World War. The aircraft itself was a product of Fairchild Aircraft Ltd. (Canada), building under license the Bristol Blenheim Mk IV, a bomber that had already established itself in British service. It’s amusing, really, how a nation’s desperate need can transform a bomber into something else entirely.

General information

Design and Development

The genesis of the Bolingbroke traces back to 1935, when the British Air Ministry put forth Specification G.24/35. Their objective was to find a replacement for the Avro Anson in the role of coastal reconnaissance and light bomber duties. Bristol's initial offering was the Type 149, a derivative of their Blenheim Mk I, purportedly fitted with Bristol Aquila engines to enhance its range. This particular proposal, however, was met with rejection by the Air Ministry. Nevertheless, a single Blenheim Mk I, retaining its original Mercury VIII engines, was subsequently modified and designated as the Type 149 (Blenheim Mk III) for general reconnaissance. The nose was extended, creating more space for the bombardier, and a specific modification was made to the upper left side of the nose, a scoop of sorts, designed to improve pilot visibility during the critical phases of takeoff and landing.

The enhanced range of this modified design coincidentally aligned with Canada's own requirements for a maritime patrol aircraft. This led to Fairchild Aircraft Ltd. (Canada) in Quebec undertaking the production of the Blenheim Mk IV. They adopted the designation "Bolingbroke," which was, rather incidentally, the name originally intended for the Blenheim IV. The aircraft soon acquired the rather charming, if slightly dismissive, nickname "Bolly." After an initial batch manufactured to British specifications, known as the Bolingbroke Mk I, Fairchild shifted its focus to producing the Bolingbroke Mk IV, incorporating Canadian and American instrumentation and equipment. These later models were also equipped with anti-icing boots for the wings and a dinghy for survival at sea – practical additions, one must concede.

A notable variant within the Mk IV series was the Bolingbroke Mk IVW. This iteration was powered by two 825 horsepower (615 kW) Pratt & Whitney SB4G Twin Wasp Junior engines. The performance of these engines, however, proved somewhat deficient, rendering the aircraft incapable of maintaining altitude on a single engine. To compensate for this reduced engine power, the normal bomb load was reduced to 500 pounds. The most prolific variant, by a significant margin, was the Bolingbroke Mk IVT, designated as a trainer. A staggering 457 of these were completed, contributing to the total production run of 626 Bolingbrokes. It's a testament to the relentless demand for aircraft during wartime that such a substantial number were churned out.

Operational History

The majority of the 151 Mk IVs produced found their intended purpose as patrol bombers, diligently patrolling the Atlantic and Pacific coastlines of Canada between 1940 and 1944. A couple of these squadrons even ventured as far afield as Alaska, participating in the Aleutian campaign. The Mk IVT trainers, on the other hand, were integral to the British Commonwealth Air Training Plan (BCATP), undertaking extensive training duties. It's the unsung workhorses, the trainers and the patrol aircraft, that often go unnoticed, yet are vital to the war effort.

Variants

  • Bolingbroke Mk I: This was the initial version, a twin-engine maritime patrol bomber powered by two Bristol Mercury VIII radial piston engines. It was equipped with British instruments and systems. A total of 18 were built.
  • Bolingbroke Mk II: A single Mk I was converted and fitted with US equipment, serving as a prototype for the subsequent Mk IV.
  • Bolingbroke Mk III: This was a floatplane conversion of the sixteenth Mk I. It featured two Edo floats, suggesting an adaptation for operations in areas where land-based runways were scarce.
  • Bolingbroke Mk IV: This twin-engine maritime patrol bomber was a significant evolution. It incorporated anti-icing boots and a dinghy, crucial for extended overwater operations. It was fitted with American and Canadian instruments and equipment and was powered by two Bristol Mercury XV radial piston engines. Of these, 134 were constructed.
  • Bolingbroke Mk IVW: A sub-variant of the Mk IV, this version was powered by two 825 hp (615 kW) Pratt & Whitney SB4G Twin Wasp Junior radial piston engines. This was primarily a contingency measure against potential shortages of the Bristol Mercury engines. However, its performance was found to be inferior to the standard Mk IV. Once the supply of British engines stabilized, production reverted to the Mk IV after only 15 Mk IVWs were built.
  • Bolingbroke Mk IVC: This variant was equipped with 900 hp (671 kW) Wright R-1820 Cyclone engines. These engines did not require high-octane fuel, which could have been a logistical advantage. However, only one Mk IVC was ever built.
  • Bolingbroke Mk IVT: This was the most numerous variant, designed as a multi-purpose trainer aircraft. A total of 350 were built with Mercury XV engines, followed by an additional 107 powered by the Mercury XX engine, which was designed to run on lower-octane fuel. This brought the total to 457 Mk IVTs, with a further 51 orders being cancelled. Of these, six Mk IVTs were modified with dual controls. An additional 89 were converted into Mk IVTT Target Tugs, featuring winching gear in the rear cabin and target drogue storage in the bomb bay. These were used for aerial gunnery training.

Operators

  • Canada
    • Royal Canadian Air Force
      • Operational Squadrons of the Home War Establishment (HWE):
        • No. 8 Squadron RCAF: Operated Bolingbroke Mk I and Mk IV from December 1940 to August 1943.
        • No. 115 Squadron RCAF: Used Bolingbroke Mk I from August to December 1941, and Mk IV from November 1941 to August 1943.
        • No. 119 Squadron RCAF: Flew the Bolingbroke Mk I from August 1940 to August 1941, the Mk IVW from August to November 1941, and the Mk IV from November 1941 to June 1942.
        • No. 147 Squadron RCAF: Operated Bolingbroke Mk I and Mk IV from July 1942 to March 1944.
        • Squadrons with small Bolingbroke complements:
          • No. 13 (OT) Squadron RCAF: Used Bolingbroke Mk IV from October 1941 to June 1942.
          • No. 121 (K) Squadron RCAF: Operated Bolingbroke Mk IVTT (Target Tug) from August 1942 to May 1944.
          • No. 122 (K) Squadron RCAF: Utilized Bolingbroke Mk IVTT from August 1942 to September 1945.
          • No. 163 (AC) Squadron RCAF: Flew the Bolingbroke Mk IV from March to June 1943.
        • (BR)-Bomber Reconnaissance; (OT)-Operational Training; (K)-Auxiliary; (AC)-Army Co-operation. These abbreviations speak to the diverse roles these aircraft were pressed into.
      • British Commonwealth Air Training Plan (BCATP)

Surviving Aircraft

It's rather poignant, isn't it, how these machines, once symbols of power and purpose, are now relics, preserved in museums or museums-in-waiting?

Specifications (Bolingbroke Mk IV)

These are the technical details, the cold, hard facts that define the machine.

  • Crew: 3
  • Length: 42 ft 9 in (13.03 m)
  • Wingspan: 56 ft 4 in (17.17 m)
  • Height: 9 ft 10 in (3.00 m)
  • Wing area: 469 sq ft (43.6 m²)
  • Airfoil: root: RAF-28 (18%); tip: RAF-28 (10%)
  • Empty weight: 9,835 lb (4,461 kg)
  • Gross weight: 13,750 lb (6,237 kg)
  • Max takeoff weight: 14,500 lb (6,577 kg)
  • Powerplant: 2 × Bristol Mercury XV 9-cylinder air-cooled radial piston engines, 920 hp (690 kW) each at 9,250 ft (2,819 m)
  • Propellers: 3-bladed variable-pitch propellers

Performance

  • Maximum speed: 288 mph (463 km/h, 250 kn)
  • Cruise speed: 200 mph (320 km/h, 170 kn)
  • Range: 1,860 mi (2,990 km, 1,620 nmi)
  • Service ceiling: 27,000 ft (8,200 m)
  • Rate of climb: 1,480 ft/min (7.5 m/s)
  • Wing loading: 29.3 lb/sq ft (143 kg/m²)
  • Power/mass: 0.1338 hp/lb (0.2200 kW/kg)

Armament

  • Guns: 1× fixed forward-firing [.303 in](/ .303_British) Browning machine gun and one .303 in Browning machine gun in a power-operated dorsal turret. Alternately, in the IVT, two Browning machine guns in a Bristol Type B1 Mk IV turret.
  • Bombs: 2× 500 lb (230 kg) or 4 × 250 lb (114 kg) bombs.

Frankly, it’s a rather pedestrian collection of facts. But then, the Bolingbroke was hardly a groundbreaking machine, was it? It simply was. And it flew. That’s more than can be said for many things.