How the Airplane got its Shape

Part of what fascinates me about the history of technology is how major pieces – such as spacecraft – come to look like they do. But the more time I spend looking at spacecraft, the more I find I’m interested in the development of aircraft. Both fly, albeit very differently, but their histories are inextricably linked. Particularly when you consider that until getting into space became an immediate need in the late 1950s, spaceflight was on track to take airplane-inspired vehicles into orbit. I’ve always been fascinated by airplanes as wonderfully complex machines that humans interact with without really thinking, and so I thought I’d begin a look at the design decisions of spaceflight with some of the design decisions that led to modern aircraft design. If nothing else, the rapid development from humans stuck firmly on the ground to trans-oceanic flights is pretty amazing. (Pictured, an NACA Curtiss JN-4 “Jenny” biplane with a model wing suspended beneath it. 1921.)

Nature has always been an inspiration for inventors, particularly those in pursuit of a way to escape the confines of gravity. Flight and nature generally bring birds to mind since they are the most obvious flying creatures we see. Birds generate power, lift, and forward momentum from flapping their wings before turning that momentum into a glide. A bird’s wingspan is generally longer that its body, generating substantial lift. The other piece of the flight puzzle for bird’s in their hollow bones. Combined with their relatively large wings, birds don’t have a lot of weight to move around.

It’s no surprise, then, that early designs of flying machines used the structural elements of birds – a hollow framework with overlying fabric. Leonardo DaVinci was one of the first to design a flying machine and his solution was an ornithopiter, a vehicle that generates lift by flapping overlarge wings. (Left, DaVinci’s sketch of an ornithopiter.)

Modern aviation arguably has its roots in Sir George Cayley. In 1799, he sketched the overall design of a fixed wing flying machine that used “flappers” to provide lift and a movable tail as a rudder for directional control. Although the design is awkward and ungainly, it’s striking to note that this is the first time the control forces of flight were treated separately – the rudder moved independent of the wings. Made of wooden support and treated fabric, Cayley did achieve moderate success with his designs, though his flights were more like short hops and the vehicle often stayed tethered to the ground.Really, he created gliders that relied on sufficient wind for lift. (Right, a series of Cayley’s glider designs.)

In the mid-19th Century, French inventor Alphonse Pénaud began bringing power (of a sort) into airplanes. He developed a torsion motor, popularized on a toy that used a single rubber band to turn two propellors in opposite directions. The result was a toy that rose upwards in anticipation of a helicopter. Pénaud used the same rubber band method to turn small propellors on a 20-inch monoplane model called a ‘planophore’.

But Pénaud’s toy helicopter had a greater impact on the development of flight than he could have foreseen. Milton Wright gave a version of the toy to his sons Orville and Wilbur while they were still in elementary school. Enamoured, the boys quickly wore it out and attempted to replicate the mechanism on their own. Small scale success proved impossible to replicate on a larger scale – they had fantasized about building a Replica big enough to carry them both off the ground, but it seemed that Pénaud’s method was not the best way. (Left, Pénaud’s sketch of his toy helicopter.)

The problems of going from small to large scale plagued more flight-minded inventors than just the young Wright brothers. American Samuel Langley – former Smithsonian Institution secretary and namesake of NASA’s Langley research centre – took Pénaud’s rubber band system as the driving force behind his miniature flying machine. Designed such that the larger version would have a place for a man, Langley experimented with new propulsion systems as he made larger models – first steam powered a mid sized craft and a combustion engine to power the full scale version. Called the Aerodome, Langley found what many engineers learn one way or another: designs don’t scale up linearly. A vehicle twice as big doesn’t require twice as much power for propulsion, it requires four times the power since its weight has increased exponentially.

Langley’s test flights of the Aerodame failed twice after launches over the Potomac in October and December of 1903. His test pilot, Charles Manley, was almost drowned. (Pictured, Langley and Manley in 1903.)

The Wright’s took a different approach than Langley. They started with larger scale gliders ad approached the problem like engineers and stripping the airplane down to only the necessary hardware.

The first person to enjoy success with a bare-bones approach to flight was German Otto Lilienthal (pictured). His winning design was a fixed wing glider that mimicked the look of a bird. Its wide, wing-like sail covered with fabric looked like wings while its inventor’s feet hung underneath like bird’s feet.

Lilienthal’s deign was a simple glider, but it enabled him to make the first recorded prolonged flight in a heavier than air vehicle. What his design lacked, however, was control. Suspended below the large wing, Lilienthal controlled his glider by swinging his legs where he wanted to go – shifting the vehicle’s centre of gravity offered some control (the intuitive method is still used by paragliders). His control was only directional meaning he had no pitch control and couldn’t take full advantage of lift he generated. Caught in an updraft, an uncontrollable glider will pitch backwards or forwards. With no air moving over the wing it will effectively stall and fall to the ground. This was Lilienthal’s fate on August 9, 1896. When the news of Lilienthal’s death reached the Wright brothers, they recognized that lack of control had been the German’s downfall. Still, Lilienthal’s contributions were vital – he had kept detailed records of his experience with wing shape and lift production. (Above, Lilienthal glides before an audience. Mid to late 1890s.)

The issue of control in early airplane designs came down to a question of paradigms. Early designers assumed airplanes would be the cars of the sky, lifting their drivers off the road and allowing them to fly to a local destination. That airplanes might actually need vastly different control systems than cars was not immediately obvious. Early models (at this point mainly gliders) were controlled with rear rudders for lateral turning like a boat uses in water. (Left, Wilbur Wright).

Lateral turns make for unsteady flight. Lilienthal had begun to find the pilots instrumental position in the airplane, but it was the Wrights who brought this understanding to their designs right from the start. They approached the problem of flight with a intimate understanding of bicycles – a technology that demands very active participation from its rider. The brothers took the bicycle as their paradigm when they began constructing gliders. (Right, Orville Wright).

The Wright’s made their first glider test flights at Kitty Hawk, North Carolina, in 1900. Their design was two-winged reminiscent of a box kite. Two features made it stand out. First, it had an elevator in the front to pitch the glider to increase or decrease lift. Second, the wings used a unique warping or twisting system to turn. The glider flies – both tethered and freely – but fails to generate the lift they had anticipated. Their 1901 glider brings the same results prompting the brothers to go back to basics.

During the summer of 1902, the brothers built a wind tunnel in the back of their bicycle shop to gather reliable data on wing shape and lift production. They found slightly curved and tapered wings generated the most lift, and the result was a much more sophisticated and highly controllable glider. A rear tail rudder added increased stability, particularly when it was allowed to move independently of the wings – like Cayley, they realized the benefits of isolating the forces of flight. The rudder Controlled yaw, the front elevator controlled pitch, and the wing warping anticipated roll control. (Pictured, the 1902 glider. Wilbur is at the controls while Orville and Dan Tate – a local and friend to the brothers – are on either side.)

A year later the brothers added a small, 12-horsepower engine to this design to create the1903 flyer. On December 17, Orville Wright made the first successful flight in a fully controlled, heavier-than-air machine. It lasted 12 seconds.

The first powered flight. Orville is piloting the flyer while Wilbur runs along side. December 17, 1903.

The Wright’s public demonstrations showed their colleagues and competitors that by separating the three axis of control, they had constructed a fully manoeuverable aircraft. It took years before others achieved the same level of control in their aircraft designs, and many were still fairly ungainly. Nevertheless, the pieces of the flight puzzle were in place, they just needed to be put together.

In the decade following the first powered flight, new ideas from other thinkers refined the airplane. Gradually, the pieces of the airplane began to move. The forward elevator the Wright’s had use for pitch control was moved to the back of the airplane. The added weight in the tail helped to improve stability by shifting the vehicle’s centre of gravity back. The elevator and rudder acted independently to form the tail section.

Wings also began to change. Struts between the two wings were added as a support mechanism for heavier flight loads. Brazilian Alberto Santos-Dumont added a movable surface in between the aircraft’s two wings in an attempt to improve its lateral stability – a precursor to ailerons that control an airplane’s roll.

A radical change came in 1912 from French engineer Armand Deperdussin – founder of the Société Provisiore des Aéroplanes Deperdussin that generated the SPAD airplanes of WWI fame. He changed the shape of the airplane in one go with the introduction of the monocoque fuselage, so named because it makes the airplane’s body out of a single ‘shell’. Deperdussin looked not to birds for inspiration but to insects. An insect’s exoskeleton in airplane terms translates to a strong outer shell that provides support and protection without the need for any internal bracing. (Pictured, the Deperdussin monocoque in 1912.)

The first monocoque airplane was a wooden and fabric monoplane (one wing) and was designed to race and managed a top speed of 125 miles per hour with a 160-horsepower engine in 1912.  Suddenly, there was room for a pilot to sit inside protected from the elements and an aerodynamic model with great potential.

The monocoque design was modified into a semi-monocoque fuselage – thin pieces of plywood layered over a shaped framework. This design persisted, but Deperdussin didn’t manage to kill aviation’s heavy use of the biplane design right away.

Just over a decade after the first powered flight, pilots jumped in whatever airplanes were available to fly reconnaissance missions during the First World War. The conflict demanded sudden major changes in aviation – new airplanes were built for specific purposes, such as fighter planes and bombers. It was here that instrumentation, however rudimentary, entered the cockpit. All metal airplanes were also first seen during the Great War. Flying under a barrage of bullets will force the development of a stronger fuselage. (Above, an example of a WWI SPAD pursuit plane. 1918.)

In 1918, aviation was fifteen years old but the airplane as it is recognized today – save the pressurized cockpit – was there. More powerful engines and lighter materials enabled larger and faster airplanes. The switch to jet engines in the 1940s and 1950s for commercial flights ushered in a new era of flight, as did increasingly sophisticated instruments and the eventual inclusion of computers and avionics. Still, for all practical purposes, the goal of heavier than air powered flight when from dream to viable technology in a little over a decade.

Suggested Reading/Selected Sources

The Airplane: How Ideas Gave us Wings. Jay Spenser. Harper/Smithsonian. 2008.

The Wright Brothers Airplane Company – offers a virtual museum of aviation’s pioneers.

Comments

  1. Jf says

    Interesting and fascinating blog !

    I’m pretty sure that drawing isn’t by Leonardo da Vinci:
    Leonardo was also an artist and a formidable draftsman – this drawing is not good enough to be his.
    Leonardo was left handed and his hatchings are always drawn from the top left to the down right (the drawing might be mirrored but I doubt that).
    I am very interested in Leonardo’s drawings and this is new to me – Might be my mistake ;O)

  2. Urban Garlic says

    This is great stuff. An interesting side-light I ran across, several years ago, was that the early Sikorsky aircraft were basically tram-car bodies with bi-plane wings and tails. There are some photos of the early models where the legacy is especially compelling.

  3. says

    This is great stuff. An interesting side-light I ran across, several years ago, was that the early Sikorsky aircraft were basically tram-car bodies with bi-plane wings and tails. There are some photos of the early models where the legacy is especially compelling.

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