POWER DURATION MODELS: GLIDING

Models which have only a small excess of power available for climbing, beyond that needed to sustain level flight, are necessarily trimmed to fly both under power and in the glide, at the maximum possible Cl’ VCd condition, and must be as light as possible if they are to climb at all. This also applies to many types of rubber powered model towards the end of their power run, since it is important that the climb should continue rather than the model, still under power, losing height After the power is exhausted, these models become soaring gliders, and the same design and trim requirements govern both flight modes. They may be trimmed for minimum sinking speed in the glide and this trim should be retained as far as possible for the later stages of the powered flight With a power assisted glider or an electric powered model the same rules apply.

Fig. 4.8 The spiral climb at high CL

Fig. 4.9 The straight climb at low CL

total

No power waste

low CL therefore low induced drag. ,

Small camber therefore low profile drag coefficient. High velocity therefore high parasite drag.