Whatever may be said about the FAA, it produces some useful publications. One of them is Advisory Circular 90-109A, Transition to Unfamiliar Aircraft. Not to be confused with its sister publication, AC 90-89, Amateur-Built Aircraft and Ultralight Flight Testing Handbook, AC 90-109A is directed at pilots beginning to fly an airplane of a type with which they do not have prior experience—pilots, for example, who have bought an amateur-built airplane from someone else. The author makes clear that while the information in the circular applies to any transition to a new type, amateur-built or certificated, amateur-built airplanes are of particular concern because their handling and stalling qualities are unregulated and vary widely—not only from one type to another but, at times, even among different examples of the same type.
AC 90-109A is quite long and may tax spans of attention weaned on television, but it is full of pithy observations and good advice and is well worth reading. (It can be readily downloaded; just search for the name.) After a discussion of various kinds of flying characteristics and types of stability and instability, it supplies a multipage list of amateur-built airplane types and the broad categories to which they belong. Some of these categories are self-evident; for example, it is quite obvious that a VariEze has a nonconventional configuration. But one category stands out for the number of types in it, particular challenges that it presents, and the fact that it might have never occurred to you that it is a category at all: the “low-inertia, high-drag” airplane.
