Date:01 Dec 96 04:08:54From:inet@intellisys.net (brian whatcott)Organization:Telepath

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There is a 'rule' now percolating onto the rec.aviation groups which supports the suggestion that at 50% of takeoff roll, you should have 70% of required takeoff speed. It seems to me that this must have originated with jet operations where a constant thrust takeoff roll leads to this kind of figure. I have enquired of AF heavy pilots - who do not in general use this rule. A correspondent tells me the rule is advocated by a DOT and FAA office in Alaska, but for GA operations. When I work the numbers for constant speed props, I see that if I assume constant efficiency at constant horsepower, the relationship is much more like 80/50 to take care of the fact that a 25% of airspeed increase sees the prop thrust drop by 20% ( for these idealized assumptions). I would like very much to learn where this rule of thumb originated- I can only assume in airline operations? Regards brian whatcott <inet@intellisys.net> Altus OK