This paper summarizes problems that occur when engineers use the classic work-energy-theorem equation, climb gradient equals thrust minus drag over weight ( (T-D)/W), to predict climb performance. Over years of work in industry and academia, I noted that aircraft modeled using a rigorous set of equations of motion would climb at a different rate than otherwise predicted by the classic equation. In this paper, the reader can compare and contrast actual against work-energy-theorem predicted climb performance for a variety of aircraft configurations. As the thrust loading (T/W) grows stronger, the work-energy-theorem increasingly underpredicts the actual climb rate. Other factors like lift-curve-slope (dCL/da), climb speed, induced drag and zero-lift-drag impact actual climb performance. Because these factors are not negligible, the discriminating engineer should always solve the full equations of motion to predict even unaccelerated climb performance at modest flight path angles.
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