Absolutely excellent article (“Extreme-Altitude Hazards”) by Jim Lockridge in the May issue summarizing issues that confront pilots in the high-altitude environment. I cant recall ever seeing a better or more thorough summary of the topic, and Ive been reading aviation publications for a long time. 288 This subject has been of particular interest to me for over 30 years, after I flew a sailplane to 41,000 feet in a mountain wave west of Boulder, Colo. My hope that day was to earn a diamond altitude soaring badge (5000-meter gain above tow release). When the lift continued beyond that goal, so did I. Fortunately for me, I was flying a glider that belonged to a good friend and veteran of many high-altitude flights. It was equipped with both an A-14 pressure-demand system like that described in the article, and a completely independent constant-flow system available as a backup, plus terminal-velocity-limiting dive brakes. Jim was still suffering slight decompression sickness from a flight to 35,000 feet the day before, despite pre-breathing 100-percent oxygen for two hours, and he generously offered me his ship to try for my altitude badge. After getting a very thorough briefing, I will never forget Jims final words to me before takeoff: “If you feel any sort of problem, open the valve on the redundant oxygen, pull the dive brakes, wrap your arm around the handle and hope you wake up before you hit the rocks.” I happily confess that not-so-happy thought was foremost throughout the entire flight, and it helped me stay alert and thoroughly enjoy what I can honestly say was the “high” point of all of my recreational flying. Great article. Great publication. Steve Hopkins Yaw adversity Im writing to see if you can clarify something in Tom Turners article, “Five Exercises For Better Crosswind Landings” (May 2010). In his discussion of adverse yaw steering, I think there may be an error. The article states, “The left aileron will deflect upward. In many airplanes, this will cause the nose of the airplane to move to the right. Why? When the left aileron moves upward, it generates an adverse yaw force that makes the nose go to the right. The opposite happens when you move the controls fully to the right-the right aileron goes up, and adverse yaw moves the nose to the left.” My understanding of adverse yaw-which I define as a force in the direction opposite of that desired-is caused by the drag from the down aileron. So, one applies left (up) aileron, the right aileron deflects downward, adding drag out at the end of the right wing. This additional drag is what moves the nose to the right. I fly a T-6 and a Great Lakes biplane (with four ailerons) and I use stick correction on the takeoff roll all the time to keep the nose straight. If the nose drifts left, a little left stick adds drag on the right wing and it only takes a little bit of stick deflection to make it work. I of course also use rudders, but the adverse-yaw method of keeping or correcting the nose pointed in the right direction is just another item in the toolbox of tailwheel flying skills. Please let me know if you think my observations are correct, or if I am misinformed. Thanks! Mark Hutchins Tom Turner responds: “Adverse yaw causes the airplane to turn opposite the direction in which it is banked. In flight, when the wing is generating significant lift, the greatest contributor to adverse yaw is the higher speed the wing on the outside of the turn. Higher speed means higher drag and, therefore, a resistance to the turning force. At runway speeds, adverse yaw does not result from wing-movement (the airplane is not turning). It is instead the result of drag from the deflected ailerons, as discussed in the article. Whether this be spoiled lift on the wing with the upward-deflected aileron or drag from the downward-deflected aileron on the downwind wing, or a combination of the two, is debatable. Regardless, Mr. Hutchins technique is spot-on for dealing with the adverse yaw effect during takeoff and landing.”
Denver, Colo.
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