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an interesting question. Please answer. Thanks.
terry wrote in
: On Feb 19, 1:00*pm, Dudley Henriques wrote: terry wrote: On Feb 19, 10:02 am, "Bob Gardner" wrote: Back to basics. I have in my hand the POH for a 172Q. In section 5, Performance, there is a whole page of data on stall speed vs bank angle . For example, at aeight of 2500 pounds with flaps up, indicated stall speed is 50 with wings level, 54 at a 30* bank angle, 59 at a 45* bank angle, and 7 1 at a 60 degree bank angle. easier to remember a formula the load increase in a bank by a factor of *1/ cos( AOB) since lift required is proportional to Vsquared to maintain level flight the lift must increase in a bank by *square root of load thus it follows the *stall speed in a level bank *must increase over the unbanked stall speed by Square root ( 1 / cos (AOB) ) which will give the numbers you have quoted from the POH. At 60 degrees the load is 2g *stall increase by root 2, *after that the g's just take off. *75 degrees is 3.8g which is the limit of the average lightie. and a good reason why the timid types like Msx and me dont like stretching the evelope too far. Right Max? Terry PPL Downunder I am struck with this irrepressible twitch of unbridled American humor as I envision some poor CFI up here using this explanation to explain things to Mrs average housewife as she attends ground school preparing for the written. As Lord Kelvin once said ( or something like this ) if you cannot explain a thing with numbers, your knowledge is of a meagre and unsatisfactory kind . Now I am not suggesting for one minute that your knowledge is unsatisfactory Dudley, I am sure you know the physics better than me, but up to a point I think there is a lot of truth in what Kelvin meant. Whilst I certainly dont advocate quantum mechanics or Tucker equations, where you can explain something with high school level maths or physics I believe this should be done. . There are many things about flying which are extremely difficult to fully explain with maths and physics, but banking at constant altitude is not one of them. The poster wants to know what effect banking has on stall speed. Yes, but his question was phrased in such a way as to require an explanation from first principles. The math is incidental and not of a lot of use in flight. However, the formula for acceleration vs stall speed is to multiply the stall speed by the sq root of the acceleration. Assuming a constant altitude is kept, a bank angle of 60 deg wil give 2 G the square root of which is approximately 1.4. SO an airplane that stalls at 50 will stall at 70 in a 60 degree bank. about 85 in a 70 (2.9 G) about 120 in an 80 deg bank (almost 6 G) and so on. A 30 degree bank (about 1.15G) will increase the stall speed by about 1.07. Call it 1.1 to take in to account the vagueries of aircraft handling.. Bertie |
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