What's Your Angle?


One of the more difficult concepts for the student pilot to grasp is the idea of angle of attack. I pulled The Student Pilot's Flight Manual, by William K Kershner, off the shelf and found that Kershner uses words like "confusing" three times in his description of angle of attack. Kershner starts with a simple definition: "The angle of attack is the angle between the relative wind and the chord line of the airfoil." He then immediately cautions the reader to avoid confusing angle of attack with the angle of incidence. A short time later he says, "the student is also confused concerning the angle of attack and airplane attitude." To help clarify matters, he reccomends the reader look at a diagram with lines showing the fuselage reference line, angle of incedence, angle of attack, relative wind and wing chord line, "before this gets too confusing." HOwever the diagram itself can be pretty confusing! Wouldn't it be nice if an instructor could actually show a student an airplane in flight with arrows coming out of the wing to indicate the impact on lift as he maneuvers the airplane? Even better, let's make those arrows show the relationship to angle of attack. While we're at it, let's throw in the thrust, weight and drag vectors, lift on the horizontal stabilizer and the instantaneous flight path. Tom Schefchunas, a corporate pilot and instructuor with over 15,000 flight hours, felt that one way to reduce the number of stall/spin accidents would be to help pilots understand the whole idea of angle of attack better. He sketched out some ideas and eventually came up with a cardboard model with various moving parts that could be used to demonstrate these concepts. Tom called his model the AlphaTrainer because alpha is the scientific designation for angle of attack. Chuck Bodeen saw a review of this cardboard AlphaTrainer in a magazine and ordered one. He liked the idea but immediately saw the possibility of greatly enhancing its value by writing a cumputer program to do the same thing. He contacted Tom and offered to write the program. ANother programmer, named Tom Wilson, also got involved in the project, and they spent a year working to develop and refine the program. They flew various types of stalls and other maneuvers on a flight simulator and recorded the data necessary to produce an animated representation of what happens during those maneuvers. The final result was a two-dimensional program that could demonstrate how the various vectors operated during 15 different maneuvers. Tom Schefchunas liked the result, but wanted to take it one step further to a three-dimensional representation that the pilot could actually fly just like an airplane rather than just watching canned scenarios that were not very realistic. Chuck is an X-Plane simulator aficionado, so he put a request on the X-Plane website asking for help. He soon was contacted by Sandy Barbour, who lives in Scotland and was one of the co-developers of the X-Plane System Developer's Kit (SDK), which allows programmers to write "plug-in" programs that will work with X-Plane to make the various vectors, protractors and even a real time data box show up on the screen with whatever airplane was being flown, while Chuck modeled the airplanes. To make it all work, Austin Meyer, the author of X-Plane and owner of Laminar Research, agreed to let the AlphaTrainer team make an abbreviated version of the X-Plane program available on the AlphaTrainer disk for a nominal fee. The result of this team effort is impressive. The original cardboard AlphaTrainer is now a three dimensional program using the most sophisticated flight simulation software available for personal computers. It allows a pilot to fly a number of different airplanes, including a generic single engine retractable gear model, a Piper Cub, a light twin, a Citation Excel, and a high performance acrobatic airplane. Angle of attack, lift, thrust, drag, weight, stabilizer lift and instantaneous flight path are all represented by different colored arrows that instantaneously change length and even direction, if necessary, to show the effect of the pilot's input on the controls on that vector. The instrument panel has a G-meter and angle of attack gauge along with a standard array of flight instruments. The pilot can select any angle from which to view the action.

Because of the sophistication of this program, it is not quite a plug and play affair. The AlphaTrainer program has to be loaded on the computer, after which a second disk is inserted that unlocks the X-Plane software. Two versions are available: a basic version with just two types of aircraft and scenery for Florida, and an advanced "Pro" version with all the aircraft listed above, along with scenery for the entire United States, including Alaska and Hawaii. The AlphaTrainer program will obviously be very useful in helping students understand the forces working on an airplane, especially the concept of angle of attack. What was formerly a two dimensional diagram with various lifeless vectors coming out of it is now a colorful active representation showing how everything works, such as what happens if the pilot pulls back too fast on the control wheel and how the angle of attack can ge into the red zone even though the airplane is in a nose low attitude. Even for a pilot with over 40 years experience like myself, it was fascinating to watch the lift vector on the horizontal stabilizer shift from negative to positive as i transitioned the simulated airplane from cruise fight to a climb. I was aware of how that worked but it made it much more meaningful to actually watch it happen in real-time simulation. There are other applications for this program. Last month I wrote about the Instrument Recovery Training program available at FCI in Mesa, Arizona. Using the aerobatic aircraft on the AlphaTrainer program, the student could practice the various maneuvers and recovery techniques before the flight while observing the reaction of the angle of attack, G meter and other vectors to his control inputs. IN fact, the aerobatic airplane in the ALphaTrainer program purposely has a very sharp break at the stall, similar to the Extra 300. An aerobatic pilot could use the program to practice aerobatic maneuvers. You can also do a VMC demonstration in the twin and even a V¹ cut in the Excel, all the while watching the effect on the lift and angle of attack, which are shown independently above each wing. Tom Schefchunas's motto is, "From red to green is our dream." - that pilots will keep their angle of attack in the green and avoid an inadvertent stall/spin accident. I believe the program Tom and his team have developed can go a long way towards achieving that dream by making the effects of control movements on angle of attack visible to the pilot in real time. For more information about the ALphaTrainer, go to www.alphatrainer.com or call 877/542-1112