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Seems to me that at the top of the roll, he would have had to be rolling at
a rate sufficient to have centripital force equal to 2 g; such that when you subtract the normal downward 1 g, there's a resultant 1 g left acting in the conventional direction You're mixing force and acceleration. First of all, it is not possible to do a barrel roll with a constant 1g, simply because an airplane is "pulling" 1g in level flight. A barrel roll involves a climb, so at the instant of departure from level flight, the "g" increases a bit, regardless of how gentle the manouver might be. Similarly, near the finish of the barrel roll, the nose will be down and must be brought back to level flight; that takes more than 1g, since level flight itself is 1g. That being said, the "g" the pilot talks about is what he sees on the "g" meter, which measures the force resulting from acceleration in the direction of the "z" axis. If the plane is inverted (and level) and showing 1g positive, the actual acceleration toward the earth is, as you've surmised, 2g's, or 64 ft. per second per second. But the resulting apparent force on the pilot and on the g meter is (the result of) 1g. So, the g meter really measures force resulting from acceleration, rather than acceleration itself. You clearly know how to analyze this, so now that you know how a g meter works, it'll be easy. Obviously, an airplane in level flight, at which time its g meter indicates 1g, is NOT accelerating toward the ground at 32 ft. per second per second. Nor is a g meter sitting on my desk, indicating 1 g. BTW, the g meter reads zero when flying a vertical line up or down, and it reads -1 when flying straight and level inverted. This brings up an interesting observation that I made an evening or two ago while practicing snap rolls and trying to snap with the minimum possible stick pull (thus, minimum energy loss). When snapping on a 45 degree up line, more stick movement is needed than when snapping on a level line. Why? Well, the stick is pulled to load the wings to a critical angle of attack close to a stall, so that when the rudder is kicked, one wing stalls (or nearly so) and the other grabs a chunk of lift to autorotate the airplane. When on a 45 degree upline at a constant airspeed (it's almost possible), the g meter reads only ..707 g (got my bifocals tuned up for that observation). Hence, it takes more stick pull (motion, not force) to load the wing to the critical angle of attack, since the angle of attack was less to start with. Nuff said, maybe someone who is actually an expert will chime in... Doug Sowder |
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