Lockheed Martin Desert Hawk III
5.2 United Kingdom
5.2.2 Civil Systems
The EASA was formed in 2003 to take over responsibility for the airworthiness, certification and regulation of all aeronautical products manufactured, maintained or used by persons within the European
Design Standards and Regulatory Aspects 79
REQUIREMENTCOMPLIANCEGUIDANCE ……which should contain a summary document such as an “Operating Limits and Loads”report. f. The UAV shall employ flight control devices of sufficient effectiveness to achieve the required control authority demanded during each operational phase defined in 4.3.1.a.
(1)In determining the required control effectiveness, the UAV Design Authority shall take into account the flight envelope for all build standards of UAV, and the most adverse environmental effects that can reasonably be expected in operation such as turbulence and airframe icing. (2)The effectiveness of the flight control devices shall be fully predicted by the most appropriate means, then validated by simulation and/or test throughout the flight envelope for each build standard of UAV.
The UAV flight control devices, whether operating aerodynamically or by other means, should be of sufficient power to produce the required control response (such as a rate of rotation about a reference axis) for all conditions of mass, CG, load factor and airspeed in the defined flight envelope. It is implicit in the term “required control authority”that means should similarly be embodied to limit such control devices from exerting excessive force on the UAV in other parts of the envelope, such as at high speed, where extreme structural loads or adverse aerodynamic characteristics could arise. In consideration of control effectiveness, full account should be taken of installation aspects, such as structural flexibility, local aerodynamic effects and flutter. g. The design shall take into consideration the operating characteristics of the power plant in order to ensure that the performance and controllability of the UAV are not compromised
All power plant related effects shall be considered in the UAV performance and control/handling prediction and validation process, for each applicable flight phase.
The UAV power plant may exert variable or asymmetric effects on the airframe, such as propeller slipstream, rotor downwash, jet/rocket efflux and gyroscopic precession. These should be fully considered in the structural design, aerodynamic design and control system design of the UAV. 4.3.3 FLIGHT ENVELOPES a. The permitted operating envelope for all given build standards and role configurations of the UAV shall be declared.
The basic flight envelope shall be defined graphically, without ambiguity, in a recognised format.
(1) The Basic Flight Envelope, conventionally of the form shown in Figure 1 of Clause 4.4. should be expressed in…… Figure5.1Compliancedocumentation
80 Unmanned Aircraft Systems
n1
Acceleration Coefficient n2= 1-0.3n1
n3 1-1)
VA= Stall Speed at maximum positive acceleration (n1g) VB= Stall Speed at maximum
negative acceleration (n3g) VC= Maximum Level Flight
Speed at
Limits (or equivalent) VD= Maximum Dive Speed
(= 1.25VC)
NOTE The basic flight envelope is the design envelope for the UAV. It shall be based on the design / maximum All-Up Mass (AUM) of the UAV and should encompass actual flight performance under all conditions.
In the case of differing design, AUMs arising from variations in build standard, an envelope should be produced for each.
Normal Acceleration
0 1 +n
n1
n2
n3
n1= Maximum Normal Acceleration Coefficient n2= 1-0.3n1
n3= -0.6(n1-1)
VA= Stall Speed at maximum positive acceleration (n1g) VB= Stall Speed at maximum
negative acceleration (n3g) VC= Maximum Level Flight
Speed at Weight/Altitude/
Temperature Limits (or equivalent)
D= Maximum Dive Speed (= 1.25VC)
NOTE The basic flight envelope is the design envelope for the UAV. It shall be based on the design / maximum All-Up Mass (AUM) of the UAV and should encompass actual flight performance under all conditions.
In the case of differing design, AUMs arising from variations in build standard, an envelope should be produced for each.
Normal Acceleration
0 1
V
IG (LEVEL FLIGHT)
EQUIVALENT AIRSPEED
VB
VC VD
-n
n1
n2
n3
Figure 5.2 Basic flight envelope
Reliable UAV System
00 Control
Documents 01 Support
Equipment 02 Control
Station 04 Aircraft
01 Structure Module
02 Power-plant Module
03 Electronics Module
04 Payload Module A
05 Payload Module B
01 Module Structure
02 Low Light Level TV
03 Gimbals System
04 Actuators
05 Power Supply
06 Signal Processor 01 Module
Structure
02 Thermal Imager
03 Gimbals System
04 Actuators
05 Power Supply
06 Signal Processor 01 Module
Structure
02 Power Conditioning
03 Vertical Gyro
04 Directional Gyro
05 Air Data System
06 AFCS Computer 01 Module
structure
02 Fuel tank
03 Fuel pump
04 Carburettor /Injectors 01 Fuselage
02 Main Wing
03 Empennage
04 Under-carriage
05 Control Surfaces
06 Navigation Lights
05 Basic Engine
06 Ignition System
07 Control Actuator
08 Cooling System
09Alternator
07 Radio Receiver 1
08 Radio Receiver 2
09 Radio Transmitter
07 Connectors
07 Connectors
08 High-power Lamps 07 Radio
Antennae
08 Cooling/
dehumidifier 02
06
20 331
03 02 01
04 31
01 05
20
03 12 03
02
0
15
03 01
03 04
12 10
11 08
10
09
02 07
06
12 08
01 111 61
19 46
11 83 237 XXXDefects per 100,000 Flight hours
XXXDefects per 100,000 Flight hours
Figure 5.3 System hierarchy and reliability model
Design Standards and Regulatory Aspects 81
Union Member States. Whilst building up its resources, the Agency relies on national aviation authorities who have historically filled this rˆole and concludes contractual arrangements to that effect.
In the United Kingdom this is the Civil Aviation Authority (CAA) with documents covering different types of aircraft and bearing the title of the British Civil Airworthiness Requirements.
Within Europe, an EASA Regulation (EC Regulation 216/2008) makes provision for implementing rules dealing with aircraft certification and continuing airworthiness. These rules, however, do not apply to aircraft engaged in military, customs, police or ‘similar’ services. These aircraft are known as ‘State Aircraft’. EU member states must, however, ensure that such services have due regard as far as is practicable to the objectives of the EASA Regulation. (The words and phrases shown in italics are extracted directly from Reference 5.3.)
Certain categories of civilian aircraft are also exempt from complying with the EASA Regulation.
Those relevant to UAS are:
r
Aircraft designed or modified for research, experimental or scientific purposes and likely to be produced in very limited numbersr
Aircraft whose initial design was intended for military purposes onlyr
Unmanned aircraft with an operating mass of less than 150 kgTherefore any UAV of mass greater than 150 kg which is not experimental or a ‘State Aircraft’ will be required to have an EASA airworthiness certificate. Those aircraft (including UAV) which are exempt from EASA regulation must, instead, comply with their national regulations for airworthiness certification and continuing airworthiness. Their equipments, personnel licensing operation within aerodromes and compliance with air traffic, must comply with national regulations.
A process of certification, similar to that for the military, therefore may be required for UAV systems for civilian use (but not for recreational model aircraft) and overseen in the United Kingdom by the CAA with documents covering different categories.
Virtually all UAV systems in use today in the United Kingdom are, however, military which operate on test ranges, or are very light aircraft operating within the restrictions placed on the use of model aircraft.
(No airworthiness certification is required for model aircraft except in certain circumstances – see below.) Perhaps for this reason, although detailed design requirements and certification specifications exist for military aircraft in the UK, no such formal requirements currently exist for civil UAV systems.
The CAA, whilst accepting the worth of the available SBAC document, has not adopted it as ‘it did not conform to the format’ of CAA documents. The CAA has not, itself, prepared an appropriate document since it has, as yet, no funding to do so. There are consequently no defined detailed requirements covering the design and construction of civil UAS within the UK. This situation may change with the future issue of Chapter A8-22 of BCAR section A.
Instead, a document which is advisory only (Civil Aviation Publication 722 – ‘Unmanned Aerial Vehicle Operations in UK Airspace – Guidance’) has been issued by the CAA and is listed as Reference 5.3.
CAP 722 recommends the use, where applicable, of the appropriate manned aircraft design require-ments. It has no legal backing and any contravention of its guidance can only be pursued in the courts if the infringement may be seen to contravene any article in the Air Navigation Order (ANO). The ANO is reproduced as CAA CAP 393.
However, the major hurdle which prevented deployment of UAV systems for civilian uses, even within segregated airspace, in the 1990s and since, and which has still to be resolved, is that of airspace usage.
This aspect is also referred to within CAP 722.
The European Organization for Civil Aviation Equipment, EuroCAE, responsible to EASA, has established a Working Group WG73 UAV to start addressing the standards required for civilian UAVs
82 Unmanned Aircraft Systems
to fly in nonsegregated airspace. The group is currently focusing principally on UAV having an AUM greater than 150 kg, even though many, if not the majority of, UAS seen as serving future civilian operations may have an AUM far less than that.
Airspace may be considered to be divided under four classifications:
a) that which may be used by model aircraft which meet certain required rules and criteria, b) segregated airspace,
c) uncontrolled airspace, d) controlled airspace.
Model aircraft and UAV are divided into four categories by the CAA for regulation. The categories are:
1. Model aircraft of less than 7 kg mass when unfuelled.
2. Model aircraft of between 7 and 20 kg mass when unfuelled (alternatively referred to as ‘small aircraft’.
3. Model aircraft and ‘light UAV’ of between 20 and 150 kg mass when ready for take-off.
4. Aircraft of mass greater than 150 kg. These are referred to as ‘UAV’ and are not regarded as model aircraft.
The CAA see the military broad equivalent of category 1 as being Micro Air Vehicles of up to 5 kg mass and category 2 as Mini Air Vehicles of up to 30 kg mass.
Operation Restricted to Airspace of Category (a)
Aircraft category 1. The regulatory provisions for models (small aircraft) of less than 7 kg are less proscriptive than for those of greater mass but are currently the subject of a further review by the UK CAA.
Small aircraft of less than 7 kg unfuelled mass, if used only for ‘sport flying’, are currently not required to be built to any standards of airworthiness, but must comply with the following minimum operational constraints:
r
clear of controlled airspace, unless with ATC permission,r
clear of any aerodrome traffic zone, unless with ATC permission,r
at less than 400 ft above the point of launch, except with permission as above,r
within 500 m of the operator at all times,r
not within 150 m of any congested area of a city, town or settlement,r
at least 50 m clear of persons, vessels, vehicles or structures. This can be reduced to 30 m for take-off or landing. Other model operators and any assistants or officials may be within this distance; as may vessels, vehicles or structures under their control.However, if the small aircraft are to be used for commercial operations, i.e. ‘for hire and reward’ the would-be operators are required to request permission from the CAA to operate. The point of contact is given within Reference 5.3. It is possible that the CAA will then impose a system build standard and operator qualification requirement in addition to the same operational restraints, but this was still under review at the time of publication of this book.
Aircraft category 2. For small aircraft with mass 7–20 kg when unfuelled, further operational constraints, in addition to those listed for small aircraft of category 1, are imposed to ensure adequate safety. As
Design Standards and Regulatory Aspects 83
listed in Reference 5.4, these include:
r
a serviceable ‘fail-safe’ mechanism shall be incorporated to terminate the flight following loss of signal or detection of an interfering signal,r
it must be ensured that any load carried on the model is secure,r
flights must comply with any conditions such as byelaws,r
CAA permission is required for any commercial flights, i.e. using the model for ‘hire and reward’.Aircraft category 3. In the United Kingdom, ‘light UAV systems’, categorised by the CAA as those employing an aircraft with a mass at take-off of no more than 150 kg, may be approved and operated under model aircraft rules, i.e. not be required to meet requirements for formal airworthiness certification, but would be required to be operated under the same restrictions as applied category 2 small aircraft.
For many years the UK CAA has issued exemptions from most provisions of UK national regulation for larger model aircraft that fall outside the definition of a small aircraft. Whilst these exemptions have included relief from the need to comply with airworthiness certification requirements, the granting of the exemption has been conditional upon the CAA being satisfied that the model is designed and built to a satisfactory standard and that operational controls are in place, including the choice of a suitable rural site to preserve adequate separation between the aircraft and third parties, and flight is undertaken under the ‘control’ of a recognised model association.
For existing large models, the CAA has been satisfied regarding the design and build standards on the basis of recommendations provided by the Large Model Association (LMA), an organisation recognised by the CAA as providing expertise in this field. The process for recommending acceptance starts with the LMA inspecting an aircraft during construction and satisfying itself that it has suitable integrity of design and construction as represented by accepted good practice.
Then, following the granting by the CAA of an ‘exemption for flight testing’, the LMA will oversee a programme of ‘function and reliability’ flight trials (at least six flights totalling at least 1 hr for each named pilot). When satisfied that the aircraft has completed this testing without modification or mishap the LMA will normally provide a positive recommendation to the CAA that a renewable exemption should be issued.
For light UAV systems the CAA has concluded that UAV systems that are ‘equivalent’ to existing large model aircraft and have no greater capability, may be allowed to operate without obtaining airworthiness certification, subject to the UAV system complying with similar limitations and conditions to those applied to large model aircraft.
However, the LMA has advised the CAA that it exists for the benefit of recreational model aircraft enthusiasts only, and will not support commercial UAV systems. Consequently, it will be necessary to establish a body of similar competence to the LMA that will be able to provide similar recommendations on the basis of procedures acceptable to the CAA. In the absence of such a recognised body, the CAA has in the past accepted assurances given by a learned body with aeronautical engineering expertise, such as a University Aeronautical Department, in lieu of a recommendation.
Until such time as an accredited body is established, the CAA may, on an ad hoc basis, assess each application, taking into account the experience and knowledge of the applicant/operator in lieu of a recommendation, provided it can be assured that the standards applied are at least as demanding as those applied by the LMA. This absence of such an accredited body should present no problem to a company with the appropriate aeronautical expertise in-house.
To provide a measure of ‘equivalence’ to a large model aircraft, the regulatory concept developed by the CAA uses impact kinetic energy as a basic criterion. Impact kinetic energy is directly linked to the ability of a UAV to cause damage and injury. It provides both an absolute measure for the showing of compliance and a relative standard for identifying ‘equivalence’ with model aircraft. Kinetic energy is also an all-encompassing criterion applicable to all aircraft types, is easy to determine and can be readily
84 Unmanned Aircraft Systems
estimated during the design process from the product KE=1/2mv2, where m and v are in kg and m/s respectively (see the discussion on setting kinetic energy limits below).
To maintain comparability with models in other respects, the UAV system will be subject to design, construction, and flight testing scrutiny at least as demanding as that carried out for large models by the LMA.
A key feature of the involvement of the LMA in the safety of large models is their requirement for
‘function and reliability’ flight testing of significant duration. It is considered that it is this activity that provides, in the absence of formal requirements, the necessary safeguards against the presence of poor stability, control and performance characteristics. Under these provisions, a light UAV may be granted the necessary permission and exemption to operate commercially in the vicinity of persons and property, (subject to defined minimum separation distances).
To protect these persons and property, it is appropriate to set a safety level somewhat higher than that associated with recreational flying. Also, it is recognised that any flight assessment may be essentially qualitative, and therefore it is considered prudent to supplement the assurance gained through the function and reliability testing with some additional quantitative constraints to address the possible consequences of poor handling qualities.
The proposed additional constraints are as follows:
(a) A light UAV will not be granted an exemption, regardless of its mass, if the maximum speed it can sustain in level flight exceeds 70 kt. This addresses the issue of higher pilot workload inherent in operating at higher speeds, (a problem that increases as aircraft size reduces), and also supports the maintenance of separation from third parties. In common with model aircraft exemptions, those issued for light UAV systems will specify minimum acceptable separation distances from third parties and their property. Imposing the 70 kt limitation should provide a reasonable time period for the pilot to take recovery action in the event of his UAV unexpectedly heading towards a third party. (Note: it is envisaged that compliance with this speed limitation will be demonstrated during flight testing by flying the UAV straight and level at full power and measuring the steady velocity achieved.)
(b) To reduce the possibility of a high kinetic energy impact following loss of control, aerobatics will be prohibited.
(c) The conditions of the exemptions will prohibit tasks that involve aerial inspection of, or flight close to, any object or installation that would present a risk to safety in the event of damage due to any impact by the UAV (e.g. chemical/gas storage areas).
(d) The conditions of the exemptions will prohibit participation in any public flying display (except with the written permission of the CAA).
To set kinetic energy limits for UAV on the basis of equivalence with current large model aircraft, the CAA looked at their previous experience of models operating under exemptions.
Some 94% of large model aircraft carrying out aerial work within line-of-sight restriction, were seen to be within the mass range 20–75 kg. Combining the upper value of 75 kg with 1.4× 70 kt maximum speed gives a kinetic energy value of 95 kJ. This value is stipulated to be the maximum acceptable in a crash situation for whatever form the crash takes, i.e.: (i) a free-fall from 400 ft; or (ii) a high-speed impact.
The former would include the results of a complete structural failure, a separation of the rotor from a rotorcraft or the rupture or complete separation of the gas envelope of a lighter-than-air aircraft. On the basis of negligible aerodynamic drag, an object of 80 kg dropped from 400 ft is calculated to have a kinetic energy on impact of 95 kJ.
If the UAV is shown to have a significant aerodynamic drag in free-fall and a lower maximum speed in flight, then a proportionally greater maximum AUM (than 75 kg) would be allowed. Examples of mass and speed combinations which fall within these criteria are given in an appendix to Reference 5.3.
Design Standards and Regulatory Aspects 85
A light UAV system complying with these criteria and operated within the constraints listed in (a)–(d) above, could be eligible for exemption from formal airworthiness certification. UAV systems that do not comply with the criteria or are intended to operate outside the constraints imposed, including beyond 500 m from the UAV pilot, will not be eligible for exemption and will therefore be subject to formal airworthiness certification in accordance with the UK CAA previously published policy, even though no formal civil UAS airworthiness requirements yet exist.
Aircraft category 4. As previously noted, this category of aircraft is required to have an EASA Airwor-thiness Certificate.
Operation in Segregated Airspace of Category (b)
This is a designated volume of space, beneath a nominated altitude, in which no aircraft is allowed to operate without the express authority of that airspace controller. In the United Kingdom, with the exception of the facility at ParcAberporth in Mid-Wales founded with the support of the Welsh Develop-ment Agency (see Appendix A-5, UAV Systems Organisations – Test Site Facilities), the only available segregated airspaces are those owned by the UK MOD. They are all essentially military ranges for testing military equipments for the Navy, Army and Air Force.
UAV systems developers, on application, may be provided with facilities to test their systems at these sites, especially if the systems are under development for the MOD. The systems will be expected to be designed to achieve full military certification and to comply with the range safety requirements.
The same facilities may be made available to assist in the development of civil systems which would be expected to comply with CAA standards, when known, for full civil certification. However, there is currently no provision, in the United Kingdom, to nominate segregated airspace to allow the regular operation of UAV ystems in civilian roles such as, for example, agriculture or power-line inspection.
The situation may be less restricted in other countries. For example, there are more than 1000 Yamaha R Max VTOL UAV carrying out crop-seeding and spraying in Japan on a regular basis.
Operation in Uncontrolled and Controlled Airspace of Categories (c) and (d)
For UAV systems to be operated in either controlled or uncontrolled airspace, full certification, either military or civil, is required. For either operation, it has been ruled by EASA and the FAA that the ability of an aircraft to sense the presence of another aircraft in the vicinity, and to manoeuvre to avoid a collision, is required.
This ability in a UAV must be at least as good as that currently expected in a manned aircraft. The problem may be less acute in controlled airspace as, with the aircraft mounting a transponder, it will be under the watchful eye and intervention of an air traffic controller.
It is probable that, although not indicated in the announcement by Northrop Grumman (see Chapter 16), the Global Hawk aircraft is restricted to controlled airspace.
It is also required that the system maintains control of the aircraft following a total power failure on the aircraft.
Sense and Avoid
This is now usually referred to as detect, sense and avoid (DSA).
Some UAV, such as the Global Hawk, already have a forward-looking video camera dedicated to an operator looking ahead for other aircraft. In uncontrolled airspace it is very difficult for light aircraft pilots to spot another small aircraft approaching if it is on, or nearly on, a collision course. The ‘head-on’
image that each pilot has for only a few seconds (with a closing speed of about 500 km/hr) is quite small.
The view that a pilot may have of a UAV ‘head-on’ is likely to be even smaller. It may be expected,