The Blériot 117 or B-117 was a large, twin-engined French aircraft from the mid-1920s. Heavily armed with three gun positions, it was designed to defend

bomber A bomber is a military combat aircraft that utilizes air-to-ground weaponry to drop bombs, launch aerial torpedo, torpedoes, or deploy air-launched cruise missiles. There are two major classifications of bomber: strategic and tactical. Strateg ...

formations against fighter attack. It did not reach production but was developed into the more successful Blériot 127.

Design and development

The problem of protecting groups of day-bombers from fighter attack was recognised in the 1920s. One possible solution was, rather than arm individual aircraft with vulnerable gunners, to have heavily armed escorts. Blériot's analysis led them to prefer this conclusion and the bomber-like Blériot B-117 was the result. It was a twin-engined,

mid-wing A monoplane is a fixed-wing aircraft configuration with a single mainplane, in contrast to a biplane or other types of multiplanes, which have multiple wings. A monoplane has inherently the highest efficiency and lowest drag of any wing config ...

monoplane A monoplane is a fixed-wing aircraft configuration with a single mainplane, in contrast to a biplane or other types of multiplanes, which have multiple wings. A monoplane has inherently the highest efficiency and lowest drag of any wing con ...

with three gunner's position providing a wide field of fire. Its thick section,

cantilever A cantilever is a rigid structural element that extends horizontally and is unsupported at one end. Typically it extends from a flat vertical surface such as a wall, to which it must be firmly attached. Like other structural elements, a cantilev ...

wing was in three parts, with a centre section between the engines and twin outer panels. The centre section was rectangular in plan and the outer panels were straight-tapered, square-tipped and constantly decreased in thickness outwards. The centre section had a steel tube structure which carried the engine mountings and the outer wings and was

plywood Plywood is a composite material manufactured from thin layers, or "plies", of wood veneer that have been stacked and glued together. It is an engineered wood from the family of manufactured boards, which include plywood, medium-density fibreboa ...

-covered. Each outer panel was built around two

spruce A spruce is a tree of the genus ''Picea'' ( ), a genus of about 40 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal ecosystem, boreal (taiga) regions of the Northern hemisphere. ''Picea'' ...

, ash and ply spars and had an

aileron An aileron (French for "little wing" or "fin") is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll (or movement aroun ...

at its tip. The

fuselage The fuselage (; from the French language, French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds Aircrew, crew, passengers, or cargo. In single-engine aircraft, it will usually contain an Aircraft engine, engine as wel ...

of the B-117 had a rectangular cross-section defined by four spruce

longeron In engineering, a longeron or stringer is a load-bearing component of a framework. The term is commonly used in connection with aircraft fuselages and automobile chassis. Longerons are used in conjunction with stringers to form structural fram ...

s and was entirely ply-covered over its central part, though elsewhere the upper and lower surfaces were canvas covered. There was a flexibly-mounted machine-gun position in the nose, whose operator was also the navigator, radio operator and photographer. An open

cockpit A cockpit or flight deck is the area, on the front part of an aircraft, spacecraft, or submersible, from which a pilot controls the vehicle. The cockpit of an aircraft contains flight instruments on an instrument panel, and the controls th ...

at the wing

leading edge The leading edge is the part of the wing that first contacts the air;Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 305. Aviation Supplies & Academics, 1997. alternatively it is the foremost edge of an airfoil sectio ...

housed the pilot and mechanic side-by side. The B-117 was powered by a pair of water-cooled Lorraine-Dietrich 12D

V12 engine A V12 engine is a twelve-Cylinder (engine), cylinder Internal combustion engine#Reciprocating engines, piston engine where two banks of six cylinders are arranged in a V engine, V configuration around a common crankshaft. V12 engines are more c ...

s cooled with Vincent André

radiators A radiator is a heat exchanger used to transfer thermal energy from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in cars, buildings, and electronics. A radiator is always a ...

mounted on the undercarriage legs. Its engine mountings and square-sided nacelles were constructed from

and plywood. Under the wings, a pair of near-parallel

strut A strut is a structural component commonly found in engineering, aeronautics, architecture and anatomy. Struts generally work by resisting longitudinal compression, but they may also serve in tension. A stay is sometimes used as a synonym for ...

s on each side braced the bottom corner of the nacelle to the lower fuselage. The

nacelle A nacelle ( ) is a streamlined container for aircraft parts such as Aircraft engine, engines, fuel or equipment. When attached entirely outside the airframe, it is sometimes called a pod, in which case it is attached with a Hardpoint#Pylon, pylo ...

s extended rearwards just beyond the wing

trailing edge The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge meets.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 521. Aviation Supplies & Academics, 1997. ...

, where each housed a gunner with a flexibly-mounted machine gun. A corridor within the wing allowed access from the fuselage. The B-117 had a slightly tapered

tailplane A tailplane, also known as a horizontal stabilizer, is a small lift (force), lifting surface located on the tail (empennage) behind the main lifting surfaces of a fixed-wing aircraft as well as other non-fixed-wing aircraft such as helicopters ...

mounted a little above the fuselage and carrying unbalanced

elevator An elevator (American English) or lift (Commonwealth English) is a machine that vertically transports people or freight between levels. They are typically powered by electric motors that drive traction cables and counterweight systems suc ...

s. The twin broad-chord

balanced rudder Balanced rudders are used by both ships and aircraft. Both may indicate a portion of the rudder surface ahead of the hinge, placed to lower the control loads needed to turn the rudder. For aircraft the method can also be applied to elevator (air ...

s were on small

fin A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. F ...

s, mounted close together over the fuselage sides. It had a conventional, fixed, tailskid undercarriage. Under each engine there was a pair of mainwheels on a single axle mounted on two vertical V-struts from the nacelle. The B-117 flew for the first time on 19 June 1924. It did not reach production but was developed into the B-127, which had a very similar layout and dimensions though with more powerful engines and a single fin and rudder. Forty-two of these served with the Service Aéronautique.

Specifications

References

{{Louis Blériot aircraft 1920s French fighter aircraft 117 Aircraft first flown in 1924 Aircraft with fixed conventional landing gear Twin-engined piston aircraft