The Fokker D.XII was a Dutch single seat, single engine

fighter aircraft Fighter aircraft are fixed-wing military aircraft designed primarily for air-to-air combat. In military conflict, the role of fighter aircraft is to establish air superiority of the battlespace. Domination of the airspace above a battlefield ...

designed to an

American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, pe ...

specification which called for the use of a

Curtiss D-12 The Curtiss D-12, sometimes identified with the military designation Curtiss V-1150, was an aircraft engine of 18.8 liter displacement. It was a water-cooled V12, producing 443 hp (330 kW) and weighing 693 lb (314 kg). It was ...

engine, designated PW-7. Despite considerable efforts to improve the airframe, Fokker failed to win the USAAS competition.

Design and development

The D.XII owed its existence to the Fokker D.XI, even though they had no design overlap; the connection was that the earlier aircraft had some success when submitted to the USAAS's call for entrants in its PW-7 specification competition, an order for three resulting. The D.XII was intended from the start to meet this specification and was designed around the required

engine. Initially, the D.XII was, like the D.XI, a

single bay A biplane is a fixed-wing aircraft with two main wings stacked one above the other. The first powered, controlled aeroplane to fly, the Wright Flyer, used a biplane wing arrangement, as did many aircraft in the early years of aviation. While ...

sesquiplane A biplane is a fixed-wing aircraft with two main wings stacked one above the other. The first powered, controlled aeroplane to fly, the Wright Flyer, used a biplane wing arrangement, as did many aircraft in the early years of aviation. While a ...

but its wings were different in plan and construction. The upper wing was straight edged with some sweep on the

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, ...

, it had a thinner

aerofoil An airfoil (American English) or aerofoil (British English) is the cross-sectional shape of an object whose motion through a gas is capable of generating significant lift, such as a wing, a sail, or the blades of propeller, rotor, or turbine. ...

section than that of its predecessor and was

fabric Textile is an umbrella term that includes various fiber-based materials, including fibers, yarns, filaments, threads, different fabric types, etc. At first, the word "textiles" only referred to woven fabrics. However, weaving is not the ...

rather than

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. Overhung

ailerons 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 Flight dynamics, roll (or ...

were used, their ends projecting outboard of the squared

wing tip A wing tip (or wingtip) is the part of the wing that is most distant from the fuselage of a fixed-wing aircraft. Because the wing tip shape influences the size and drag of the wingtip vortices, tip design has produced a diversity of sha ...

s proper, acting as aerodynamic balances. The lower wing, which lacked ailerons, was both much shorter in span and smaller in chord. The early D.XII had a V-form

interplane strut In aeronautics, bracing comprises additional structural members which stiffen the functional airframe to give it rigidity and strength under load. Bracing may be applied both internally and externally, and may take the form of strut, which act in ...

on each side; another strut leant out from each wing root to the upper rear

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, ...

, assisted ahead of it on each side by a short V-form pair linking the two spars to the upper

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 ...

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 ...

, acting as N-form

cabane strut In aeronautics, bracing comprises additional structural members which stiffen the functional airframe to give it rigidity and strength under load. Bracing may be applied both internally and externally, and may take the form of strut, which act in ...

s. The fuselage of the D.XII was flat sided and deep from nose to tail. Initially it had the same 300 hp (224 kW)

Hispano-Suiza 8F The Hispano-Suiza 8 was a water-cooled V8 SOHC aero engine introduced by Hispano-Suiza in 1914, and was the most commonly used liquid-cooled engine in the aircraft of the Entente Powers during the First World War. The original Hispano-Suiza 8A ...

V-eight engine as its predecessor, but this was soon replaced by the USAAS-specified 440 hp (328 kW) V-twelve water-cooled

. Both were enclosed by a metal cowlings, though of slightly different shapes, and drove a two blade

propeller A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...

. The single, 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 ...

was well to the rear, about midway down the fuselage. Its horizontal tail was braced and the

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 ...

was small, carrying a

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 ...

that extended down to the keel. The D.XII had a fixed

conventional undercarriage Conventional landing gear, or tailwheel-type landing gear, is an aircraft undercarriage consisting of two main wheels forward of the center of gravity and a small wheel or skid to support the tail.Crane, Dale: ''Dictionary of Aeronautical Term ...

of the single axle type, supported by V struts. There was a small tail skid. The first flight under Curtiss power was made on 21 August 1924. Flight testing followed, resulting in major modifications. The upper wing was given an unswept leading edge and hence had constant chord and the small lower wing was replaced by one with the same chord as the upper plane and a span almost its equal, mounted with marked stagger. No longer a sesquiplane, the splayed V interplane struts were replaced with more rigid N-form ones. Another bracing strut ran from the forward foot of the interplane strut to the top of the root to upper wing inner strut, to further improve torsional strength. At the rear, the little fin was remove and the rudder, still balanced, reshaped. Two more aircraft with these modifications were built. Despite Fokker's efforts, the aircraft was still not to the liking of the USAAS who did not buy any of the three D.XIIs; further development was abandoned.

Specifications (Curtiss D-12 engine)

References

{{Fokker aircraft D.XII 1920s Dutch fighter aircraft Biplanes