AircraftPower is an Aircraft Engine Performance App. It uses a standard reciprocating engine performance model to calculate and display the sea level and altitude performance of sixty-three engines in the Lycoming -235, -290, -320 and -360 families. A graphic display shows the engine performance chart and illustrates the manual construction method for determining altitude performance that we learned in ground school (and promptly forgot). As the user moves the input sliders for manifold pressure, rpm, pressure altitude and outside air temperature, the power output and percent power are displayed, and dotted lines and colored dots in the graphic display follow the manual construction method. While the graphics aren't really necessary, they are instructive (and interesting) to watch.The user may choose english or metric units for altitude, temperature, manifold pressure and power output (however, the graphic always uses english units), and may select default values for the slider settings and the engine. The sliders used in this app have a special vernier mode that permits a much better setting accuracy than a normal slider.