The Airplane - Jay Spenser [43]
Most airplanes, past and present, have a few degrees of dihedral to reduce pilot workload. High-wing designs generally require less dihedral than low-wing ones because of the position of the airplane’s center of gravity relative to its wings.
Some airplanes have no dihedral, and some even have negative dihedral or anhedral. A downward tilt to the wings, anhedral makes an airplane inherently unstable but highly maneuverable. The Wrights chose to build with anhedral that was obvious when the Flyer was on the ground but less so in flight, when aerodynamic lift brought the wings almost level. This design decision made their airplanes less sensitive to gusts of wind from the side as well as more maneuverable.
The next time you’re at an airport and see a jetliner, take a look at its wings. You’ll notice this slight upward tilt and know why it’s there.
Scientists may discover the physical universe’s secrets, but engineers are the ones who change our world. In the early days of flight, these disciplines frequently overlapped, to aviation’s great benefit.
Francis Herbert Wenham was a theoretician with a foot in each camp. Born in London in 1824, this mechanically gifted son of a British Army surgeon grew up building and flying kites. Pursuing university studies, he emerged with a degree in engineering and wide-ranging interests.
Wenham’s face was jovial and his eyes observant. His beard and hair were often in wild disarray. Energetic, fascinated by the natural world, and keen on science, he would contribute in his lifetime to fields as diverse as photography, instrument design, microscopy, and high-pressure steam engines.
On a trip to Cairo in his thirties, this Englishman found himself enchanted by the birds that flocked noisily overhead and alighted to feed in the Nile wetlands. Egypt’s location at the crossroads of three continents made this river’s verdant course through the desert a migratory corridor for millions of birds. There were swifts, kites, bulbuls, kingfishers, swallows, gallinules, and other species Wenham couldn’t identify.
Francis Herbert Wenham.
National Air and Space Museum, Smithsonian Institution
The engineer in him marveled at the marked differences in how various kinds of birds flew. Even as his eyes assessed their abilities, his mind began equating them with the shapes of their wings. Back in the British Isles, Wenham undertook studies in this area. He was reportedly an excellent shot and collected specimens while on upland bird hunts.
Wenham was familiar with the work of George Cayley. Building on the latter’s advocacy for cambered lifting surfaces, Wenham observed that all bird wings are thicker near the leading edge. To engineers such as Wenham, thicker also means stronger. This led him to theorize that wings derive most of their lift toward the front. Why else would nature construct them this way?
This key insight dovetailed with Wenham’s observation that the birds with the longest wings were the strongest fliers. Short wings afforded birds greater maneuverability, but long ones kept them aloft longer and with less effort.
To test his insight, the enthusiastic Englishman decided to design and build a manned glider. Beyond Cayley’s insights and configurational advice, however, he could find virtually no information to help him with this self-appointed task. It was only the start of the 1860s; another three decades would pass before Otto Lilienthal would solve similar challenges.
Wenham ended up constructing a glider with five sets of wings mounted one above the other like slats on a venetian blind. He felt he needed this many wings because each was so narrow from front to back. He built them that way on purpose so that proportionately more of the