Bristol Blenheim / Bolingbroke.

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Bristol Blenheim / Bolingbroke.

Berichtdoor Tandorini » 12 mei 2009, 19:59

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Bristol Aeroplane's Blenheim was a British high-speed light bomber used extensively in the early days of the Second World War. It was later adapted into a successful heavy fighter. A Canadian-made variant named the Bolingbroke was used as an anti-Submarine and training aircraft. It was the first British aircraft to have all-metal stressed skin construction and one of the first to utilize retractable landing gear, flaps, powered gun turret and variable-pitch propellers.

Design and development

The Type 135 civil twin design was on Bristol drawing boards by July 1933.

In 1934 Lord Rothermere, owner of the Daily Mail, issued a challenge to the British aviation industry to build a high-speed aircraft capable of carrying six passengers and two crew members. At the time German firms were producing a variety of high-speed designs that were breaking records, and Rothermere wanted to recapture the title of fastest civilian aircraft in Europe. Bristol had been working on a suitable design as the Type 135 since July 1933, and further adapted it to produce the Type 142 to meet Rothermere's requirements.

Blenheim cockpit. Note the asymmetry of the instrument console, which indicates the "scooped out" area of the nose in front of the pilot. The ring-and-post gunsight for the forward firing guns is also visible.

Blenheim cockpit. Note the asymmetry of the instrument console, which indicates the "scooped out" area of the nose in front of the pilot. The ring-and-post gunsight for the forward firing guns is also visible.

When it first flew as Britain First at Filton on 12 April 1935 , it proved to be faster than any fighter in service with the Royal Air Force at the time. The Air Ministry was obviously interested in such an aircraft, and quickly sent out Specification B.28/35 for prototypes of a bomber version of the Bristol called the Type 142M (M for "military"). The main changes were to move the wing higher on the fuselage from its former low position, to allow room under the spar for a bomb bay. The aircraft was all-metal with twin Bristol Mercury VIII radial engines of 860 hp (640 kW) each. It carried a crew of three – pilot, navigator/bombardier and gunner/wireless operator and was armed with a forward firing 0.303 inch (7.7 mm) machine gun outboard of the port engine and a 0.303 inch machine gun in a semi-retracting dorsal turret firing to the rear. A 1,000-lb (454 kg) bombload was carried in the internal bay.

To achieve its relatively high speed, the Blenheim had a very small fuselage. Pilot's quarters on the left side of the nose were so cramped that the control yoke obscured all flight instruments while engine instruments eliminated the forward view on landings. Most secondary instruments were arranged along the left side of the cockpit with essential items like propeller pitch control actually placed behind the pilot where they had to be operated by feel alone. Like most contemporary British aircraft, the bomb bay doors were kept closed with bungee cords and opened under the weight of the released bombs. Because there was no way to predict how long it would take for the bombs to force the doors open, bombing accuracy was rather mediocre.

Operational history

The aircraft was ordered directly from the drawing board with the first production model, known at the time as the Bolingbroke (pronounced Bolling-brook), serving as the first and only prototype[3]. The name then became Blenheim I with subsequent deliveries started in March 1937, with 114 Squadron being the first squadron to receive the Blenheim.The aircraft would prove to be so successful that it was licensed by a number of countries, including Finland and Yugoslavia. Other countries bought it outright, including Romania, Greece and Turkey. Total production of the Blenheim in England amounted to 1,351 Mk Is.

After France fell to Germany in June 1940, the Free French Air Force was formed at RAF Odiham in the form of Groupe Mixte de Combat (GMC) 1, consisting of a mixed bag of Blenheims and Westland Lysander liaison/observation aircraft, which eventually went to North Africa and saw action against the Italians and Germans.

By the start of the Second World War, fighter technology had eclipsed the Blenheim's speed advantage and it would only achieve moderate success as a bomber and coastal patrol aircraft. One of the greatest advantages that the Blenheim had over other fighter aircraft was its range. It could penetrate deep into enemy territory, that is provided that they did not come into contact with any other enemy fighters. With a top speed of only 263 mph (423 km/h) and cumbersome and slow in turning, it was soon eclipsed by other more modern types, nonetheless, the Blenheim continued in frontline service throughout the early years of the conflict.

The Bristol Blenheim was used by both Bomber and Fighter Commands. Some 200 Blenheim I bombers were modified into Blenheim IF heavy fighters with 600 (Auxiliary Air Force) Squadron based at Hendon, the first squadron to take delivery of these variants in September 1938. By 1939, seven squadrons were operating these twin engined fighters. In addition to the existing armament, an under-fuselage gun-pack consisting of four 0.303 Browning machine guns were installed. The Blenheim IF proved to be slower and less nimble than expected and by June 1940, daylight Blenheim losses was to cause concern for Fighter Command. It was then decided that the IF would be relegated mainly to night fighter duties where No. 23 Squadron RAF who had already operated the type under night time conditions had better success.

In the German night bombing raid on London, 18 June 1940, Blenheims accounted for five German bombers thus proving they were better suited in the nocturnal role. In July, No. 600 Squadron from RAF Manston had some of their IFs equipped with AI Mk III radar and with this equipment, a Blenheim from FIU at Ford airfield achieved the first success with this radar on the night of 2/3 July 1940, over a Dornier Do 17 bomber. More successes came and, before long, the Blenheim was to prove invaluable in the night fighter role. Gradually, with the introduction of the Bristol Beaufighter in 1940-1941, its role was supplanted by its faster, more modern successor.

Blenheims continued to operate widely in many combat roles until about 1943, equipping 26 RAF squadrons in the UK and in British bases in Egypt, Iraq, Aden, India, Malaya, Singapore and Dutch East Indies. Many Blenheims were lost to Japanese fighters during the Malayan campaign and battles for Singapore and Sumatra. By that point, most fighters could carry similar bombloads at much higher speeds and the surviving examples were relegated to training duties. Bristol's intended successor to the Blenheim, the Buckingham, was considered inferior to the Mosquito, and did not see combat.

In 1936, the Finnish Air Force ordered 41 Mk Is from Britain and two years later, they obtained a manufacturing license for the aircraft. Fifteen aircraft were constructed in Finland prior to the Winter War at the Valtion lentokonetehdas and a further 41 were constructed later on, bringing the total number up to 97 aircraft (75 Mk Is and 22 Mk IVs). The Finns obtained large supplies of ex-Yugoslavian spares from the Germans during the war.

The Finnish Blenheims flew 423 bombing missions during the Winter War, and some further 3,000 bombing missions during the Continuation War. Blenheim machine gunners also shot down five Soviet fighters. Half of the Blenheims were lost to all causes during the wars.

After the war, Finland was prohibited to fly bomber aircraft. However, some of the Finnish Blenheims continued in service as target towers until 1958.


Work on an extended range reconnaissance version started as the Blenheim Mk II, which increased tankage from 278 to 468 gallons, but only one was completed. Another modification resulted in the Blenheim Mk III, which lengthened the nose to provide more room for the bombardier. This required the nose to be "scooped out" in front of the pilot to maintain visibility during takeoff and landing. However both of these modifications were instead combined, along with a newer version of the Mercury engine with 905 hp (675 kW) and a second gun in the rear cockpit, to create the Blenheim IV. When it was introduced in 1939, the Mk IV (Type 149 to Bristol) was one of the fastest bombers in the world, second only to the Dornier Do 215. In total, 3,307 would eventually be produced.

The longer range also fulfilled a Canadian requirement for a patrol bomber, consequently Fairchild Aircraft Ltd. (Canada) in Quebec, started production of the Blenheim Mk IV as the Bolingbroke, irreverently nicknamed the "Bolly." After a small run of aircraft constructed to British specifications, as the Bolingbroke Mk I, Fairchild switched production to the Bolingbroke Mk IV with American instruments and equipment. These versions also included anti-icing boots and a dinghy. Some of these aircraft served as bombers during the Aleutians campaign, but most of the 150 served in the intended role as patrol bombers on the Atlantic coast. Another 450 were completed as the Bolingbroke Mk IVT as trainers and saw extensive use in the Commonwealth Air Training Plan. One of the final variants was the Bolingbroke Mk IVW which was powered by two 895 kW (1,200-hp) Pratt & Whitney R-1830 Twin Wasp engines. A total of 676 Bolingbrokes was produced.

Another modification led to a heavy fighter version. For this role, about 200 Blenheims were fitted as Mk IF variant, with an underbelly gun-pack with four 0.303-in machine guns. Some of them were also fitted with an Airborne Intercept (AI) Mk III or IV radar, being the first British fighters with radar. Their performance was marginal as a fighter, but they served before the advent of more sophisticated machines. A radar-equipped Blenheim Mk IF scored the first night fighter victory. About 60 of Mk IVs were also equipped with a gun pack as Mk IVF used by Coastal Command to protect convoys from German long-range bombers.

The last bomber variant was conceived as an armoured ground attack aircraft using a solid nose containing four more Browning machine guns. Originally known as the Bisley, the production aircraft were renamed Blenheim V and featured a strengthened structure, pilot armour, interchangeable nose gun pack or bombardier position and, yet another new Mercury with 950 hp (710 kW). The Blenheim V was ordered for conventional bombing operations, with the removal of armour and most of the glazed nose section. The Mk V or Type 160, was used primarily in the Middle East and Far East.

The Blenheim also served as the pattern for the Beaufort which itself led to the Beaufighter.

Specifications (Bristol Blenheim Mk IV)

General characteristics

* Crew: 3

* Length: 42 ft 9 in (13 m)

* Wingspan: 56 ft 4 in (17.17 m)

* Height: 12 ft 10 in (3.91 m)

* Wing area: 469 ft² (43.6 m²)

* Empty weight: 9,790 lb (4,440 kg)

* Loaded weight: 14,400 lb (6,530 kg)

* Powerplant: 2× Bristol Mercury XV radial engine, 920 hp (690 kW) each


* Maximum speed: 266 mph (231 knots, 428 km/h)

* Range: 1,950 mi (1,690 nm, 3,140 km)

* Service ceiling 31,500 ft (9,600 m)

* Rate of climb: 1,500 ft/min (7.6 m/s)

* Wing loading: 30.7 lb/ft² (150 kg/m²)

* Power/mass: 0.13 hp/lb (210 W/kg)


* Guns:

1× .303 in (7.7 mm) Vickers K machine gun in the nose

2× .303 in Browning machine guns in chin turret

2× .303 in Browning machine guns in dorsal turret

* Bombs:

4× 250 lb (110 kg) bombs or

2× 500 lb (230 kg) bombs internally, and

8× 40 lb (18 kg) bombs externally

Bristol Bolingbroke

Type: 3 Seater Light Bomber

Manufacturer: Bristol

Designation: Bolingbroke

Location : Canadian Warplane Heritage Museum

Powerplant : Two 920hp Bristol Mercury XV

Number of Engines : 2

Wing Span : 56ft' 4"

Length : 42ft '9"

Height : 12ft 10"

Horsepower : 920"

Speed : 266mph

Armament : One 0.303 Vickers K in nose, two 0.0303in Brownings in chin turret and two 0.0303in Brownings in dorsal turret. Four fixed brownings under fuselage. 1000lbs bomb load
NEC JACTANTIA NEC METU ("zonder woorden, zonder vrees")

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Re: Bristol Blenheim / Bolingbroke.

Berichtdoor Falco » 23 mei 2009, 16:41

De Bristol Type 142 maakte zijn eerste vlucht op 12 april 1935.Het was een snel tweemotorig transportvliegtuig,dat ontworpen was op verzoek van krantenmagnaat Lord Ruthermere.De prestaties van het toestel waren zo opzienbarend dat de Type 142 - en later Type 142M - aangepast werd tot lichte bommenwerper onder Specificatie B.28/35 van het Air Ministry.Het resultaat was de Bristol Blenheim Mk I,die direct vanaf de tekentafel besteld werd.De eerste exemplaren gingen in maart 1937 naar No. 114 Squadron in Wyton.Ten tijde van de Crisis van München in september 1938 vloog de Blenheim Mk I bij zestien squadrons van No 1,2 en 5 Bomber Groups van het Bomber Command.Al in januari 1938 werd de Blenheim Mk I in gebruik genomen bij No.30 Squadron in Habbaniya,Irak.Begin 1939 werden andere Blenheim Mk I's in India gestationeerd.De Blenheim Mk I had twee 626-kW Bristol Mercury VIII stermotoren.Zijn lichte bewapening bestond uit een 7,7-mm machinegeweer in de vleugel en een handmatig te bedienen 7,7-mm Vickers K machinegeweer in de rugkoepel.Er kon duizend pond aan bommen worden meegevoerd.Bristol,Avro en Rootes produceerden in totaal 1365 Blenheim Mk I bommenwerpers.Het Finse bedrijf VLT bouwde er 45 onder licentie en het Joegoslavische Ikarus zestien.De Blenheim Mk I,met zijn karakteristieke korte neus en rijk beglaasde cockpit,werd door de RAF ingezet in Griekenland,Maleisië en Noord-Afrika,daarnaast uiteraard ook in Groot-Brittannië.

Latere versie.
De belangrijkste productievariant was de Blenheim Mk IV met zijn sterke twee Mercury XV motoren en een langere,asymmetrische neus.Van dit type werden er 3286 gebouwd.De Blenheim Mk IV vloog tijdens het uitbreken van de Tweede Wereldoorlog in september 1939,bij zeven squadrons van No. 2 Bomber Group.De bewapening was aangevuld met twee 7,7-mm machinegeweren in een Bristol geschutskoepel op de rug.Ook kon een achterwaarts gerichte geschutskoepel met een dubbel machinegeweer onder de neus geïnstalleerd worden met een periscoopvizier.De Blenheim Mk IVs schreven geschiedenis in de eerste oorlogsdagen.Op 3 september was luitenant A. McPhersons Blenheim Mk IV van No. 139 Squadron het eerste RAF-toestel dat sinds de oorlogsverklaring het Duitse luchtruim binnendrong.Hierbij fotografeerde hij de schepen voor de kust bij Wilhelmshaven.De dag erna voerden Blenheim Mk IV's van No. 107 en 110 Squadron de eerste aanvallen van Bomber Command uit.De eerste vernietiging van een U-boot door de RAF vond plaats op 11 maart 1940 door een Blenheim Mk IV van No. 82 Squadron.Aan de stuurknuppel van dit toestel zat majoor M.V. Delap.De Blenheim Mk IV's werden veelvuldig ingezet boven Frankrijk,voor de Noorse kust,Duitsland,Griekenland,Kreta,Noord-Afrika,India ,Maleisië en Sumatra.In augustus 1942 werden de toestellen niet meer gebruikt.

Buitenlandse dienst.
Finland en Griekenland vlogen ook met de Blenheim Mk IV.Dit gold eveneens voor Canada,waar het type was omgedoopt tot de Bolingbroke.De Blenheim Mk V (945 exemplaren gebouwd) verscheen eind 1942.Deze variant was voorzien van twee 708-kW Mercury 25 of 30 motoren en werd ingezet in Noord-Afrika en Tunesië,en het Verre Oosten.Doordat de motoren van de Blenheim weinig vermogen hadden en de toestellen te licht bewapend waren sneuvelden er meer bemanningsleden in een Blenheim dan in welk ander RAF-toestel ook.

Mk IV.
Driezits lichte bommenwerper.
Motoren: Twee Bristol Mercury XV stermotoren van 686 kW (920 pk).
Prestaties: Maximumsnelheid:428 km/u op 3600 m ; Kruissnelheid:318 km/u ; Plafond:8300 m ; Vliegbereik:6537 kg.
Afmetingen: Spanwijdte:17,2 m ; Lengte:13 m ; Hoogte:3 m ; Vleugeloppervlak:43,6 m².
Bewapening: Tot vijf 7,7-mm machinegeweren (een vaste in de vleugel,twee op de rug en twee (optioneel) achterwaarts vurende machinegeweren),plus een normale bomlading van 1000 pond (454 kg).
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