Chap­ter III — Fly­ing Machines Con­struc­tion And Oper­a­tion explores the basic aero­dy­nam­ic prin­ci­ples that allow both birds and air­craft to achieve and sus­tain flight. Through sim­ple, observ­able exper­i­ments, it reveals how motion and air inter­ac­tion con­tribute to lift. These foun­da­tion­al insights form the basis of under­stand­ing why fly­ing machines behave as they do once air­borne.

A com­mon demon­stra­tion uses a flat cir­cu­lar piece of card­board. When dropped, grav­i­ty pulls it down imme­di­ate­ly. But when it’s thrown edge­wise into the wind, it glides for­ward, sup­port­ed momen­tar­i­ly by air resis­tance. This reveals how for­ward momen­tum alters descent, allow­ing objects to “ride” on the air. The sus­tained force in fly­ing machines comes not from a human throw but from a motor. Unlike the short burst of ener­gy from an arm, an engine pro­vides con­tin­u­ous thrust. This con­sis­tent propul­sion is what sep­a­rates a glid­ing fall from true flight.

Anoth­er illus­tra­tive exper­i­ment involves a flat card­board piece with a curved paper edge. Blow­ing across the con­vex side caus­es the paper to lift, demon­strat­ing the lift­ing effect of curved air­flow. When the paper is flipped with the con­cave side up, the same action push­es it down, high­light­ing how shape dic­tates air behav­ior. This result sur­pris­es many but is con­sis­tent with aero­dy­nam­ic laws. The cur­va­ture caus­es pres­sure dif­fer­ences above and below the sur­face. Low­er pres­sure above and high­er pres­sure below gen­er­ate lift. This same prin­ci­ple is built into air­craft wings, or air­foils, designed to pro­duce the nec­es­sary lift dur­ing motion.

Ear­ly exper­i­menters tried flat wings, but those proved inef­fec­tive. Flight requires not just resis­tance against falling but active sup­port from the air. Curved sur­faces turned out to be much more effi­cient. Planes designed with a con­cave under­side help trap air, enhanc­ing lift. Dif­fer­ent builders exper­i­ment­ed with how much to curve the wing—some using a one-inch rise per foot, oth­ers going up to three inch­es. This vari­ance reflects ongo­ing test­ing in pur­suit of the most effec­tive wing pro­file. Adjust­ments in cur­va­ture affect per­for­mance, influ­enc­ing sta­bil­i­ty, lift, and con­trol.

This dynam­ic close­ly mir­rors how birds gain alti­tude. A bird, before glid­ing, must flap its wings to pro­duce the ini­tial upward motion. Once air­borne, glid­ing uses min­i­mal effort as its wing shape sus­tains flight. A fly­ing machine, how­ev­er, can’t flap—it depends entire­ly on engine pow­er for both lift and for­ward motion. With­out speed, lift van­ish­es. This under­scores a key avi­a­tion prin­ci­ple: for­ward motion is essen­tial to stay­ing aloft. Air must con­stant­ly move across the wings to main­tain flight. This is why stall occurs when an air­craft slows too much.

The wide­spread use of the term “plane” in avi­a­tion comes from old­er lan­guage, though tech­ni­cal­ly, it’s a mis­nomer. In geom­e­try, a plane is flat, yet in flight, sur­faces are inten­tion­al­ly curved for bet­ter aero­dy­nam­ics. Despite this incon­sis­ten­cy, the word “aero­plane” has become embed­ded in lan­guage and avi­a­tion cul­ture. Its mean­ing, though not exact, is under­stood. Engi­neers and pilots alike accept the term while focus­ing on what matters—how the wings func­tion, not just what they’re called. The term now car­ries mean­ing through usage, not accu­ra­cy.

This chap­ter rein­forces the impor­tance of under­stand­ing air­flow and shape in flight design. Whether design­ing a toy glid­er or a full-scale air­craft, the prin­ci­ples stay con­sis­tent. The air­flow over and under a curved sur­face pro­duces lift, and con­tin­u­ous motion ensures it’s main­tained. This knowl­edge isn’t abstract—it’s test­ed, proven, and essen­tial. As flight tech­nol­o­gy evolved, these same sim­ple exper­i­ments remained rel­e­vant, remind­ing design­ers that even com­plex machines rely on basic aero­dy­nam­ic truths.

For those enter­ing avi­a­tion, mas­ter­ing these basics helps in both design and pilot­ing. A plane’s shape and motion aren’t just mechanical—they’re deci­sions based on nat­ur­al laws. By learn­ing how birds fly or how curved paper reacts to air, a builder or avi­a­tor gains an intu­itive grasp of flight mechan­ics. It’s not just about engines and frames—it’s about har­mo­ny with the atmos­phere. This har­mo­ny, under­stood through sim­ple exper­i­ments and thought­ful obser­va­tion, is what makes human flight not only pos­si­ble but reli­able.