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Unmanned Air Vehicles

The term “unmanned air vehicle” is broadly used to describe any flight- capable vehicle that has nobody on board during its flight - sometimes UAV is taken to mean “uninhabited air vehicle.” This encompasses an extremely broad range of systems, but generally does not include missiles or other guided weapons (though for cruise missiles the distinctions can be very blurred). Even so, it is useful to next set out a brief taxonomy of UAVs, indicating where in this space of potential designs the work described in this book primarily lies (noting that it was, of course, the aim of the research undertaken during the DECODE project to address wide-ranging issues that would apply to many complex design tasks).

A Brief Taxonomy of UAVs

Here we use five axes to categorize UAVs:

  • 1. Size. The maximum take-off weight (MTOW) is used to distinguish between micro: <2 kg, small: 2-20 kg, medium: 20-150 kg, and large >150 kg UAVs; this distinction also maps to typical Aviation Authority definitions and quite closely to cost, since air vehicle costs correlate quite strongly with MTOW.
  • 2. Mission. Six basic mission types are considered: surveillance, transport, combat, communications relay, support, and target.
  • 3. Capability. The performance of the UAV in terms of endurance, range, speed, payload mass, and operational ceiling.
  • 4. Degree of autonomy. Here this is based on the chart developed at the US Wright-Patterson Air Force Base, which uses an 11-point scale from simple remotely piloted vehicles through to those with complete autonomy, which are essentially indistinguishable from piloted vehicles to the outside observer (see Table 2.1) - note that most current systems operate at level 3 or lower on this scale.
  • 5. Aero-structural configuration. The absence of the need to accommodate crew on UAVs has lead to a range of unconventional configurations being considered, so this axis ranges from conventional fuselage/wings with traditional control surfaces though morphing and deformable structures and blended wing-bodies, to aircraft using things such as Coanda effect controls.

Small Unmanned Fixed-wing Aircraft Design: A Practical Approach, First Edition. Andrew J. Keane, Andras Sobester and James P. Scanlan.

©2017 John Wiley & Sons Ltd. Published 2017 by John Wiley & Sons Ltd.

Level

Level descriptor

Observe

Orient

Decide

Act

10

Fully autonomous

Cognizant of all within the battlespace

Coordinates as necessary

Capable of total independence

Requires little guidance to do job

9

Battlespace swarm cognizance

Battlespace inference - intent of self and others (allies and foes);

complex/intense environment - on-board tracking

Strategic group goals assigned; enemy strategy inferred

Distributed tactical group planning; individual determination of tactical goal; individual task planning/execution; choose tactical targets

Group

accomplishment of strategic goal with no supervisory assistance

8

Battlespace

cognizance

Proximity

inference - intent of self and others (allies and foes); reduced dependence upon off-board data

Strategic group goals assigned; enemy tactics inferred

Coordinated tactical group planning; individual task planning/execution; choose targets of opportunity

Group accomplishment of strategic goal with minimal supervisory (example: go SCUD hunting)

7

Battlespace

knowledge

Short track awareness - history and predictive battlespace data in limited range, timeframe, and numbers; limited inference supplemented by off-board data

Tactical group goals assigned; enemy trajectory estimated

Individual task planning/execution to meet goals

Group accomplishment of tactical goal with minimal supervisory assistance

Real-time

multivehicle

cooperation

Ranged

awareness - on-board sensing for long range, supplemented by off-board data

Tactical group goals assigned; enemy location sensed/estimated

Individual task planning/execution to meet goals

Group accomplishment of tactical goal with minimal supervisory assistance

Real-time

multivehicle

coordination

Sensed

awareness - local sensors to detect others, fused with off-board data

Tactical group plan assigned; real-time health diagnosis; ability to compensate for most failures and flight conditions; ability to predict onset of failures (e.g„ prognostic health management); group diagnosis and resource management

On-board trajectory replanning - optimizes for current and predictive conditions; collision avoidance

Group accomplishment of tactical plan as externally assigned; air collision avoidance; possible close ah space separation (1-100 yds) for automated aerial refueling (AAR), formation in non-threat conditions

Fault/

event-adaptive vehicle

Deliberate awareness - allies communicate data

Tactical plan assigned; assigned rules of engagement; real-time health diagnosis; ability to compensate for most failures and flight conditions - inner-loop changes reflected in outer-loop performance

On-board trajectory replanning - event-driven self-resource management; deconfliction

Self-accomplishment of tactical plan as externally assigned; medium vehicle airspace separation (100s of yds)

(continued)

Level

Level descriptor

Observe

Orient

Decide

Act

3

Robust response to

real-time

faults/events

Health/status history and models

Tactical plan assigned; real-time health diagnostic (what is the extent of the problem?); ability to compensate for most control failure and flight conditions (i.e., adaptive inner-loop control)

Evaluate status versus required mission capabilities; abort/return to base if insufficient

Self-accomplishment of tactical plan as externally assigned

2

Changeable

missions

Health/status sensors

Real-time health diagnosis (do I have problems?); off-board replan (as required)

Execute preprogrammed or uploaded plans in response to mission and health conditions

Self-accomplishment of tactical plan as externally assigned

1

Execute preplanned mission

Preloaded mission data; flight control and navigation sensing

Pre/post-flight bit (built-in test); report status

Preprogrammed mission and abort plans

Wide airspace separation

requirements (miles)

0

Remotely piloted vehicle

Flight control (altitude, rates) sensing; nose camera

Telemetered data; remote pilot commands

N/A

Control by remote pilot

The Southampton University SPOTTER aircraft at the 2016 Farnborough International Airshow

Figure 2.1 The Southampton University SPOTTER aircraft at the 2016 Farnborough International Airshow.

At Southampton, the design process has been focused on small and medium, 0.5-8 h endurance, medium range, low-speed surveillance- and transport-based designs, which operate changeable but essentially preplanned missions but can make use of unconventional control surfaces or morphing wings. The aim has been to keep MTOW below 150 kg to take advantage of the reduced certification requirements that are then typically applicable and also to keep the cost of a typical system below (often well below) $150 000 to make the entire program affordable while still allowing multiple airframes to be built and flown. A key aim has been to produce well engineered, rugged designs capable of many flights that could readily be used in a commercial context. Figure 2.1 shows our SPOTTER aircraft at the 2016 Farnborough International Airshow; Figure 2.2 provides a line drawing of the aircraft.

 
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