Home Engineering Small Unmanned Fixed-Wing Aircraft Design. A Practical Approach
The performance section of the System Description will set out the specifications and performance of the aircraft in various modes of flight, but pay particular attention to takeoff and stall. It will also contain kinetic energy calculations for an unpremeditated descent (i.e., crash) or
Table 19.7 Typical aircraft performance summary in still air.
Figure 19.1 Typical take-off performance.
other loss of control to demonstrate that the total kinetic energy in such scenarios complies with the relevant laws (such as UK CAP722). Table 19.7 summarizes typical performance information, while Figure 19.1 illustrates take-off performance.
Avionics and Ground Control System
In our experience, provided the design team is reasonably competent and the aircraft under consideration is of a fairly conventional configuration, the regulators tend to be much more focused on the avionics and GCS of the UAS than the basic airframe of the UAV, since it is these aspects that ensure the aircraft avoids collisions, does not stray away from the designated flight area, and can be satisfactorily flown. If any form of autonomous operation is envisaged, the focus on the control system will be particularly intense. The regulator will wish to be satisfied that the pilot in command maintains full situational awareness and the ability to intervene if any mishap looks likely to happen. Our approach to this is based on a combination of using redundancy wherever we can along with as many mitigations as possible against causing harm. So, for example, we now choose to adopt twin-engine designs with duplicated control systems whenever possible on our larger UAVs.
When documenting the avionics, we always include a full set of wiring schematics and information on the radio links being used, see Figure 19.2 and Table 19.8. When using autonomous autopilots, we typically have separate radio channels for these in addition to those used for
Figure 19.2 Typical wiring schematic.
Table 19.8 Radio control channel assignments.
the normal manual radio control systems all our aircraft carry, typically both being duplicated on the airframe. We generally do not duplicate the pilot’s radio control transmitter since we consider switching transmitters during an emergency procedure to be more risky than having multiple receivers bound to a single transmitter. We generally do operate with two GCSs active at all times; however, since these are much more complex, we opt for a single radio link bound to the autopilots so that this can rapidly be switched between GCSs. Clearly, all of this must be documented in the manual and operational sequences set out in the OM.
Acceptance Flight Data
At the start of the flight trials program this section is blank, but as information on the airframe is recorded from flight tests, we add a series of standard sets of data to this part of the System Description since they document the capabilities of the airframe. To do this, we use an instrumentation kit that records air and ground speeds, altitudes, accelerations, attitude, and so on. Typically we include the results from standard radio control range tests plus take-off, climb, cruise, stall, and landing characteristics for the airframe, fuel consumption, idle, throttle change, and engine failure tests for the powerplant plus any tests carried out on the autonomous capabilities of the UAV such as communications range, auto-takeoff, auto-landing, way-point navigation, and so on. Together, these help inform subsequent operators of what can be expected from the aircraft.
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