This paper introduces an altitude control technique on coaxial-helicopter. Unmanned aerial vehicle (UAV) has been widely used with high performance computer (HPC) so far. Generally, advanced mathematics is used for flight control of the UAV on the HPC. However. the HPC has several problems, such as increase of cost and processing delays in calculation. We present a technique that performs the same control performance by using a low performance computer. In order to implement this technique, the limited pole placement (LPP) control is used for a prototype of electrical motor driven helicopter. Then, it is able to find out the critical efficiency of the control system considering time delay. Finally, this paper presents the good validation results by the experiment of the altitude control of the helicopter.