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The Prospects for Safe Personal Airplanes
Commercial production in the United States of newly designed personal airplanes has been neglected for a number of years, the victim of high costs and liability suits. Kit – built airplanes have proliferated instead, with no apparent improvement in stability and control over the last commercial designs. Many kit airplane designs show inadequate tail lengths, spin resistance, and spin recovery features. This prevails in spite of the provisions of FAA regulations Part 21, which call for kit manufacturers to comply with the FAA Part 23 airworthiness requirements for light general-aviation airplanes.
U. S. amateur-built airplanes qualify as experimental under FAA Part 21 and are excluded from the Part 23 airworthiness provisions. A new FAA category of Ultralight Vehicles (Part 103) is also excluded from Part 23 regulations. Part 103 vehicles are VFR (Visual Flight Rules) airplanes weighing less than 254 pounds empty, with stalling speeds not more than 24 knots and maximum airspeeds less than 55 knots.
The hiatus in commercial production of new personal-airplane designs may bring about stability and control improvements. There are two key developments that make this likely: computer-aided design and satellite navigation. First, computer-aided design has been brought down to a level of cost and simplicity that makes it available to the general-aviation industry and conceivably to computer-wise kit builders. There are at least three such systems available.
The Design, Analysis and Research Corporation of Lawrence, Kansas, sells software called “Advanced Aircraft Analysis,” which allows users to size tail surfaces for stability, to compute stability and control derivatives, and to generate linearized dynamics. Another available computer-aided design scheme is that developed by Frederick Smetana, as a computerized version of the Perkins and Hage book Airplane Performance, Stability and Control. A third group of aerodynamic design and analysis computer programs specifically designed for personal computers is marketed by the Desktop Aeronautics Company of Stanford, California. Desktop’s “LinAir Pro” computer program can be used to generate a complete set of stability derivatives for an airplane of arbitrary configuration. Accuracy should be comparable with that for preliminary design handbook methods.
With the availability of personal computer design programs such as those mentioned and others sure to be developed there really is no reason for basic errors in stability and control layouts to be made by kit airplane designers, not to mention the designers of the commercially built personal airplanes of the future. As a last resort, if the machine resembles a well-known existing airplane, and has a center of gravity near 25 percent of the wing chord, it probably will fly and can be made reasonably satisfactory by control surface and other modifications based on flight testing.
GPS satellite navigation is within the reach of general-aviation airplanes, with consequences for stability and control. Many small airports should be able to provide approved, charted instrument approaches. If instrument approaches become more common in general aviation, there will be increased attention needed to handling qualities under those conditions. Simplifying navigation with GPS should allow pilots to pay more attention to airplane control.
