Take-off and Landing Gear
Take-off and landing gear has a surprisingly significant impact on the design of an aircraft. The total mass of such elements can be a noticeable fraction of overall weight, and the drag caused by unretracted wheels can be greater than that of the lifting surfaces combined. Also, when landing on grass runways, significant structural loads arise - we have measured accelerations of 20 g on undercarriage elements and have seen main landing wheel axles fail as a result
Figure 2.9 A typical UAV wiring diagram.
Figure 2.10 The SkyCircuits SC2 autopilot (removed from its case).
Figure 2.11 University of Southampton SPOTTER UAV with under-slung maritime flight releasable AUV.
of low-cycle fatigue. It is generally important that the undercarriage provides some form of compliance to cushion ground forces from passing unattenuated into the main airframe, either by the use of slightly flexible structural elements or through spring/damper systems. Some part of the system will also need to be steerable. If high flight speeds are important, some form of drag mitigation will be needed, either via wheel spats or by retract systems (typically electrical or pneumatic). We generally seek to buy off-the-shelf units for undercarriages for all but the very largest aircraft and mostly do not bother with the added complexity of retractable systems.