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 designed to attack ground and naval targets by dropping air-to-ground weaponry (such as bombs), launching aerial torpedo, torpedoes, or deploying air-launched cruise missiles. The first use of bombs dropped ...

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

Blériot 127 __NOTOC__ The Blériot 127 (or Bl-127) was a French bomber aircraft of the 1920s and 1930s, developed from the Blériot 117 escort fighter. It was a large monoplane A monoplane is a fixed-wing aircraft configuration with a single mainplane, ...

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 planes. A monoplane has inherently the highest efficiency and lowest drag of any wing confi ...

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 planes. A monoplane has inherently the highest efficiency and lowest drag of any wing confi ...

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 supported at only 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 canti ...

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 material manufactured from thin layers or "plies" of wood veneer that are glued together with adjacent layers having their wood grain rotated up to 90 degrees to one another. It is an engineered wood from the family of manufactured ...

-covered. Each outer panel was built around two

spruce A spruce is a tree of the genus ''Picea'' (), a genus of about 35 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal (taiga) regions of the Earth. ''Picea'' is the sole genus in the subfami ...

, ash and ply

spar SPAR, originally DESPAR, styled as DE SPAR, is a Dutch multinational that provides branding, supplies and support services for independently owned and operated food retail stores. It was founded in the Netherlands in 1932, by Adriaan van Well, ...

s 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 around ...

at its tip. The

fuselage The fuselage (; from the French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds crew, passengers, or cargo. In single-engine aircraft, it will usually contain an engine as well, although in some amphibious aircraft t ...

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

longeron In engineering, a longeron and stringer is the 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 ...

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, usually near the front of an aircraft or spacecraft, from which a Pilot in command, pilot controls the aircraft. The cockpit of an aircraft contains flight instruments on an instrument panel, and the ...

at the wing

leading edge The leading edge of an airfoil surface such as a wing is its foremost edge and is therefore the part which first meets the oncoming air.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 305. Aviation Supplies & Academics, ...

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

Lorraine-Dietrich 12D The Lorraine 12D, also referred to as Lorraine-Dietrich 12D, was a series of water-cooled V12 engines produced by the French company Lorraine-Dietrich. The first variant began production in 1917, and the engines were used to power bombers for the ...

V12 engine A V12 engine is a twelve-cylinder piston engine where two banks of six cylinders are arranged in a V configuration around a common crankshaft. V12 engines are more common than V10 engines. However, they are less common than V8 engines. The fi ...

s cooled with Vincent André

radiators Radiators are heat exchangers 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 s ...

mounted on the

undercarriage Undercarriage is the part of a moving vehicle that is underneath the main body of the vehicle. The term originally applied to this part of a horse-drawn carriage, and usage has since broadened to include: *The landing gear of an aircraft. *The ch ...

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. Human anatomy Part of the functionality o ...

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

nacelle A nacelle ( ) is a "streamlined body, sized according to what it contains", such as an engine, fuel, or equipment on an aircraft. When attached by a pylon entirely outside the airframe, it is sometimes called a pod, in which case it is attached ...

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 stabiliser, is a small 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 and gyroplane ...

mounted a little above the fuselage and carrying unbalanced

elevator An elevator or lift is a wire rope, cable-assisted, hydraulic cylinder-assisted, or roller-track assisted machine that vertically transports people or freight between floors, levels, or deck (building), decks of a building, watercraft, ...

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 elevators and ...

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. Fin ...

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