Experimenter is a magazine created by EAA for people who build airplanes. We will report on amateur-built aircraft as well as ultralights and other light aircraft.
Issue link: http://experimenter.epubxp.com/i/126719
F li g h t Te s t in g Te c hn i q u e s Figure 1 Flight Path Stability Test Technique Creating the stability curve By Ed Kolano Last month we introduced flight path stability, or how airspeed changes affect your airplane's vertical flight path. We described the intuitive expectations when flying on the front side of the flight path stability curve—and the perception danger of the back side. We completed our discussion by looking at different flight path stability curve shapes and how they influence the way we control glide path during final approach. The test philosophy is simple. We want to know how changing airspeed on final approach affects your airplane's descent angle. Because your plane probably doesn't have a descent angle indicator, you'll measure its forward speed and vertical speed. Then, after a little math fun…voilà…you'll have the vertical flight path angle (γ, pronounced "gamma"; see Figure 1). We'll do this for a range of discreet airspeeds, then literally connect the dots to create the flight path stability curve. This month we will describe the flight testing that will let you gather the data you need to create your airplane's flight path stability curve. The flight test procedure is straightforward; but it can be demanding because you'll have to keep your airspeed within just one or two knots of the test speeds to acquire meaningful data. Demanding, but it's certainly doable in smooth air. With a little practice, you'll collect the data you need in short order. Flight path stability information is most useful for final approach, so you'll probably want to perform the test with landing gear, flaps, cowl flaps, etc. set as they'll be on final. You can perform this test in any configuration you like, but the results will apply only to that configuration. In addition to keeping the plane's external configuration constant throughout the testing, we're going to EAA Experimenter 41