# AOPA ePilot Flight Training Edition - Volume 8, Issue 21AOPA ePilot Flight Training Edition - Volume 8, Issue 21

 Volume 8, Issue 21 • May 23, 2008

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 Training Tips HORIZONTAL LIFT What force makes an airplane turn? Expect that question on the private pilot knowledge test or flight test, and be able to answer it for yourself when deflecting the controls to practice turns in flight. The basic idea is that the same force that sustains an airplane in flight—lift—enables turns. A thorough answer also recognizes aerodynamic forces and piloting demands created when an airplane enters turning flight. How does lift turn an airplane? Banking the airplane allows some wing lift to act horizontally. "An airplane, like any moving object, requires a sideward force to make it turn. In a normal turn, this force is supplied by banking the airplane so that lift is exerted inward as well as upward. The force of lift during a turn is separated into two components at right angles to each other. One component, which acts vertically and opposite to the weight (gravity), is called the 'vertical component of lift.' The other, which acts horizontally toward the center of the turn, is called the 'horizontal component of lift,'" explains Chapter 3 of the Pilot's Handbook of Aeronautical Knowledge. Wait a minute. If lift is "borrowed" to turn an airplane that was flying straight and level, won't the aircraft descend? Good question. Total lift must increase to maintain altitude during a turn; how much depends on how steep the bank angle. Here's how it all works, according to "All types of turns" on AOPA Flight Training Online: "Total lift, composed of vertical and horizontal components when banked, still acts perpendicular to the relative wind and to the wingspan. And backpressure on the yoke then increases G-load and total lift. It's the growing horizontal component of lift that forces the airplane away from a straight flight path. As the flight path bends in the direction of this force, the tail assembly continually weathercocks the nose into the changing relative wind, resulting in a smooth, sweeping arc." Clearly there's much more to turns than the terse answer to questions on a knowledge test. And as a query about turns from a novice pilot revealed to retired airline pilot Barry Schiff [see "Proficient Pilot" in the July 2002 AOPA Pilot ], understanding the nuances of how they work is a continuing process, even for experienced pilots.
 Your Partner in Training Warm weather is upon most parts of the nation, and student pilots need to understand density altitude and how it affects aircraft performance. Conditions that result in high density altitude are high elevations, low atmospheric pressure, high temperatures, high humidity, or some combination of these factors. Your airplane likes dense air best, and its performance deteriorates gradually as density altitude increases. On a hot day at high elevation, you'll notice this particularly on takeoff, where you may need twice the runway to get off the ground compared to what's needed in cooler temperatures at lower altitudes. At high density altitudes you also can expect the aircraft to climb very slowly. Find out more in AOPA's subject report, " Density Altitude," and take the AOPA Air Safety Foundation's interactive online course on mountain flying. As an AOPA Flight Training Member, you have access to all of the features within AOPA Online and AOPA Flight Training Online. Login information is available online.