Home Engineering Small Unmanned Fixed-Wing Aircraft Design. A Practical Approach
The “rushing through” principle involves designing for spending the least possible amount of time in unfavorable design conditions - for example, a gas turbine engine spooling up quickly past a rotor speed that could cause resonance. Consider the following conceptual layout design example: an unmanned glider is released from a high altitude balloon and is designed to deliver a payload (e.g., a scientific instrument or an aid package) to a target location on the ground. Along the way, it has to fly through several layers of the atmosphere moving in different directions at different speeds, some of which are unfavorable. A possible solution may be to tuck the wings away upon passing the upper level of the unfavorable wind altitude range and fall through it at the highest possible rate of descent; then, the wings can be redeployed for an efficient glide upon emerging into a favorable layer.
This is a pair of concepts that used to be at home in aircraft design to the same extent as it is in the design of laser eye surgery equipment or that of nuclear reactor control rod actuators. The advent of unmanned aircraft has, however, changed that. This is largely because the risks to life and limb are often much lower than in the case of manned aircraft. Take, for example, the case of a 1 kg maximum take-off weight (MTOW) aircraft designed to collect aerial imagery of fields of crops to assist precision agriculture. Holding the servos of such an aircraft to the same standards as those of a 400-seat transport aircraft operating in and out of large urban sprawls clearly does not make sense and therefore savings can be made. Additionally, the operating life of a small UAV tends to be orders of magnitude lower than that of a manned aircraft - how can we best take advantage of this? What concept design choices can be made under this philosophy? Semidisposable landing skids? A single-use payload bay made out of a cheap foam?
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