Курсовая работа: Airfoils and Lift

It would be fascinating to know to what extent these factors were understood prior to 1918. I expect that the concentration of lift forces (as an intense negative pressure zone at the upper surface LE) was reasonably well appreciated by wind-tunnel investigators- if only by the application of Bernoulli's theorem to the visible flow patterns around test sections. Probably the effects of aspect ratio were understood- even if only qualitatively; but lift-grading would require much more complex investigation. Regarding the aspect-ratio issue; advocates of multiplanes (Horatio Phillips, for example) appear to have worked from the understanding that high aspect-ratio is a "good thing" (true) but not to have had evidence of the detrimental effects of interference between closely-spaced multi-plane wing systems.

But such is the nature of progress - the testing of ideas. It took the lives of airmen to drive the investigations which led to today's understanding of these matters and which allow our complacent and sometimes arrogant review of history.

A final thought. It is theoretically possible for the Fokker triplane to remain airborne on its 2 lower planes alone (of 9.9 square metres area). The stall speed would be about 64mph. No doubt, when both Gontermann and Pastor found themselves in dire straits, they did the natural thing: to pull back on the stick even though the aircraft was deeply stalled. Maybe if they had first pushed... ?

Forces Acting on an Airplane

The airplane in straight-and-level unaccelerated flight is acted on by four forces. The four forces are lift, gravity, thrust and drag.

The airplane in straight-and-level unaccelerated flight is acted on by four forces--lift, the upward acting force; weight, or gravity, the downward acting force; thrust, the forward acting force; and drag, the backward acting, or retarding force of wind resistance.

Lift opposes gravity.

Thrust opposes drag.

Drag and weight are forces inherent in anything lifted from the earth and moved through the air. Thrust and lift are artificially created forces used to overcome the forces of nature and enable an airplane to fly. The engine and propeller combination is designed to produce thrust to overcome drag. The wing is designed to produce lift to overcome the weight (or gravity).

In straight-and-level, unaccelerated flight, (Straight-and-level flight is coordinated flight at a constant altitude and heading) lift equals weight and thrust equals drag, though lift and weight will not equal thrust and drag. Any inequality between lift and weight will result in the airplane entering a climb or descent. Any inequality between thrust and drag while maintaining straight-and-level flight will result in acceleration or deceleration until the two forces become balanced.

Flight Control Surfaces

The three primary flight controls are the ailerons, elevator and rudder.