The Stephens Akro is a single engine

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 ...

designed in the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

for aerobatic competitions. It first flew in 1967 and proved very successful, leading to several developments of which one won seven US Championships and one World Championship between 1975 and 1982. The

Extra EA-230 __NOTOC__ The Extra 230 was a single-seat aerobatic aircraft developed in Germany in the early 1980s. Designed by aerobatic pilot Walter Extra based on the layout of the Laser 200 he was previously flying, the Extra 230 was a conventional (if sh ...

and

Extra EA-300 The Extra Flugzeugbau EA300 is a two-seat aerobatics, aerobatic monoplane capable of Unlimited category Competition aerobatics, competition. It was designed in 1987 in aviation, 1987 by Walter Extra, a German people, German aerobatic pilot, an ...

were also Akro developments with over two hundred built.

Design and development

The Akro was designed as a

homebuilt Homebuilt machines are machines built outside of specialised workshops or factories. This can include different things such as kit cars or homebuilt computers, but normally it pertains to homebuilt aircraft, also known as amateur-built aircraft or ...

aircraft for pilots who competed in

aerobatic Aerobatics is the practice of flying maneuvers involving aircraft attitudes that are not used in conventional passenger-carrying flights. The term is a portmanteau of "aeroplane" and "acrobatics". Aerobatics are performed in aeroplanes and gl ...

competitions. It was the first U.S. aircraft design to be guided by the Aresti Catalog of manoeuvres for such events. The structure absorbs high stresses, +12/-11g. The Akro is a

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 ...

mid wing monoplane with a wooden, two spar

mahogany Mahogany is a straight- grained, reddish-brown timber of three tropical hardwood species of the genus ''Swietenia'', indigenous to the AmericasBridgewater, Samuel (2012). ''A Natural History of Belize: Inside the Maya Forest''. Austin: Universit ...

skinned wing built in one piece, its forward spar passing unbroken through 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 ...

and the rear spar in two parts. The plain, statically balanced

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 ...

s have steel spars with

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'' ...

ribs and

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. ...

s ; they are fabric covered and carry ground adjustable

trim tab Trim tabs are small surfaces connected to the trailing edge of a larger Flight control surfaces, control surface on a boat or aircraft, used to control the trim of the controls, i.e. to counteract hydro- or aerodynamic forces and stabilise the ...

s. The tail unit is a fabric covered steel tube structure, wire braced and with swept, straight tapered surfaces. Like the ailerons, all the rear control surfaces are statically balanced. The

rudder A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, airship, or other vehicle that moves through a fluid medium (usually air or water). On an airplane, the rudder is used primarily to counter adverse yaw ...

has a ground adjustable trim tab. The

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 ...

is mounted at the top of the fuselage, with variable incidence and a flight controllable trim tab in the

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 ...

. The Akro has a 180 hp (134 kW) Avco Lycoming AIO-360-A1A air-cooled

flat-four A flat-four engine, also known as a horizontally opposed-four engine or boxer engine, is a four-cylinder piston engine with two banks of cylinders lying on opposite sides of a common crankshaft. The most common type of flat-four engine is the box ...

engine in the nose, driving a two blade metal fixed pitch

propeller A propeller (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 a working flu ...

. Its fuel is stored in a fuselage tank between the single seat

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 ...

and the engine. The cockpit has a fixed screen and a rearward sliding bubble

canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape), aboveground portion of grapes Religion and ceremonies * Baldachin or canopy of state, typically placed over an a ...

. In addition, there is a large window in the forward cockpit floor. There is 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 Ter ...

, with the mainwheels under

glass fibre Glass fiber ( or glass fibre) is a material consisting of numerous extremely fine fibers of glass. Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the inventio ...

fairings on cantilever sprung steel legs.

Hydraulic Hydraulics () is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counterpart of pneumatics, which concer ...

disc brake A disc brake is a type of brake that uses the #Calipers, calipers to squeeze pairs of #Brake pads, pads against a disc (sometimes called a

rake Rake may refer to: Common meanings * Rake (tool), a horticultural implement, a long-handled tool with tines * Rake (stock character), a man habituated to immoral conduct * Rake (poker), the commission taken by the house when hosting a poker game ...

rotor) to create friction. There are two basic types of brake pad friction mechanisms: abrasive f ...

s are fitted. The tailwheel is steerable. Two slightly different models were designed specifically for the first two customers. The Model A design, begun in July 1966 was for Margaret Ritchie, the winner of the 1966 U.S. Women's Aerobatic Championship and first flew on 27 July 1967. The Model B had less tapered wings of greater area (6%) and bigger ailerons, though of unchanged span, slightly heavier (8%) and with windows in the fuselage sides below the wings. The B also carried 16% less fuel but had a lubrication system adapted to prolonged inverted flight. It first flew on 9 July 1969.

Operational history

The Akro and its developments were one of the most successful aerobatic competition aircraft. Amateur builders began from plans of the Model A or B variants. The 180 hp Lycoming remained the most popular engine but Akros with up to 230 hp motors were produced. The Haigh Superstar is one of several Akro developments as are the

and

single seat aerobatic machines. Leo Loudenslager's Akro Laser 200 was a particularly successful development with a 200 hp (150 kW)

Lycoming IO-360 The Lycoming O-360 is a family of four-cylinder, direct-drive, horizontally opposed, air-cooled, piston aircraft engines. Engines in the O-360 series produce between , with the basic O-360 producing . The engine family has been installed in ...

engine; initially a standard Akro apart from the engine, it later acquired a different wing airfoil, lightened fuselage and revised, lowered canopy with the decking behind it raised. Flying this aircraft he won the U.S. Aerobatics Championship seven times between 1975 and 1982 and won the World Aerobatics Championships in 1980. Several Lasers have been home built by others.

Variants

Stephens Aircraft issued plans for two models: ;Model A: as described ;Model B: Larger area wing and ailerons, reduced tankage, better inverted lubrication system, extra cockpit windows. In the amateur tradition, builders introduced their own variations such as bigger engines. Stand out variants/developments were: ; Haigh Superstar ; Akro Laser Z-200: Multiple US and single World Championship winner, adapted, built and flown by Leo Loudenslager between 1975 and 1982. ;

:Further adaptation of the Akro Laser by Walter Extra of Extra Flugzeugbau in Germany. ;

:Over 200 of the -230 and -300 produced.

Specifications (Model A)

References

External links

NACA 23012 airfoil
{{Aerobatics Single-engined tractor aircraft Aerobatic aircraft 1960s United States sport aircraft Mid-wing aircraft Aircraft first flown in 1967