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I read the article and I don't agree with it. I think it's much
better to fly the minimum sink airspeed for the bank angle. Lets do the math. Bill Daniels With a little reflection it is *obvious* that it cannot be optimal to fly a given radius circle at a certain bank angle and airspeed if there is a different combination of airspeed and bank angle giving a lower sink rate for that radius of circle. If there is a different combination yielding the *same radius* and *lower sink rate* then all the higher sink rate combinations for that radius are not optimal. If we are optimized then we are at the minimum sink rate for the circle radius we are flying - period. Judah's beautiful graphs and Reichman's 70's vintage "Cross Country" both make it clear that the optimum will be found somewhat on the back side of minimum sink speed for the optimal bank angle. Severe mushing descent speed and sub-minimum controllable airspeed as potential solutions are exagerated straw men. But I did not understand from Reichman that the optimal speed actually decreases initially with increasing bank angle/decreasing radius. So this feature of the data in my ASW-20C pilot's manual was always a bit of a mystery to me. Thanks to Judah for graphing optimal speed versus radius directly for several types, making the situation clear. How to find the optimal radius though! Wouldn't it be a wonderfully convenient coincidence if at the optimal radius the overbanking tendency of the glider was exactly balanced by the lift gradient trying to unroll the glider? Would this work out for some particular span? I could probably notice when the stick was in the center, and it would sure be nice to know I was flying right. Someone please do the math and let me know. Jonathan |
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![]() wrote in message oups.com... I read the article and I don't agree with it. I think it's much better to fly the minimum sink airspeed for the bank angle. Lets do the math. Bill Daniels With a little reflection it is *obvious* that it cannot be optimal to fly a given radius circle at a certain bank angle and airspeed if there is a different combination of airspeed and bank angle giving a lower sink rate for that radius of circle. If there is a different combination yielding the *same radius* and *lower sink rate* then all the higher sink rate combinations for that radius are not optimal. If we are optimized then we are at the minimum sink rate for the circle radius we are flying - period. Judah's beautiful graphs and Reichman's 70's vintage "Cross Country" both make it clear that the optimum will be found somewhat on the back side of minimum sink speed for the optimal bank angle. Severe mushing descent speed and sub-minimum controllable airspeed as potential solutions are exagerated straw men. But I did not understand from Reichman that the optimal speed actually decreases initially with increasing bank angle/decreasing radius. So this feature of the data in my ASW-20C pilot's manual was always a bit of a mystery to me. Thanks to Judah for graphing optimal speed versus radius directly for several types, making the situation clear. How to find the optimal radius though! Wouldn't it be a wonderfully convenient coincidence if at the optimal radius the overbanking tendency of the glider was exactly balanced by the lift gradient trying to unroll the glider? Would this work out for some particular span? I could probably notice when the stick was in the center, and it would sure be nice to know I was flying right. Someone please do the math and let me know. Jonathan The original issue was that gains could be achieved by reducing bank angle and flying slower. More specifically, that the same radius could be achieved at a lower sink at a lower bank and speed. My point is that any gains are very, very small and likely to place the pilot at risk of a stall/spin in rough air. (If I know a pilot is attempting this, I won't be flying under him in a gaggle.) All I'm saying is that small reductions in airspeed below min sink have little effect on turn radii. Bank angle has a far larger effect. I've done the math and plotted the results to scale to prove it to myself. A small turn radius is good but it's best achieved with bank not reductions in airspeed below min sink. Accurate centering has a much greater effect on average climb rate than a tiny reduction in turn radius achieved by a small reduction in airspeed. Minimum sink is a solid airspeed that provides good control authority for centering the thermal and is a much better bet for most pilots. Almost any pilot will benefit more by practicing a "standard" 45 degree bank at minimum sink airspeed for that bank angle than by reaching for a few feet reduction in turn radius by flying slower. Bill Daniels |
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