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UAS FLIGHT TEST for SAFETY and for EFFICIENCY Seamus M UAS FLIGHT TEST FOR SAFETY AND FOR EFFICIENCY Seamus M. McGovern, U.S. DOT National Transportation Systems Center, Cambridge, Massachusetts Abstract (e.g., SAE International technical standards and recommended practices) but also takes advantage of Manned aircraft that operate in the National competitive racing in order to evaluate new Airspace System (NAS) typically undergo technologies and materials (as it turns out, this may certification flight test to ensure they meet a have applicability to UASs as well with the advent of prescribed level of safety—dependent on their several organizations and sanctioning bodies category—before they are able to enter service [for including the European Rotor Sports Association and example, Federal Aviation Administration (FAA) the Drone Racing League). Other aviation-related advisory circular (AC) 25-7C is the flight-test guide tests and test formats not discussed here include the for certification of transport-category airplanes]. typically Department of Defense-focused With the integration of unmanned aircraft systems developmental test and evaluation; operational test (UAS) into the NAS, in the future some type of and evaluation; and research, development, test, and certification flight test may ultimately be required, evaluation structures. however, even lacking such a requirement UAS manufacturers can find value in flight testing UASs In terms of flight test, the military services have using familiar experimental and certification flight- their own criteria for evaluating their various aircraft. test procedures, the results of which can enhance the These requirements are often bound by contractual safety of the design, the safety of the operation, agreements between the service and the vendor, and/or the efficiency of the operation. In this paper, however these agreements often default to FAA selected applications of flight-test procedures to the norms. development and operation of UASs are Maintenance flight testing (also known as or demonstrated using a rotorcraft UAS (a multirotor) related to production, acceptance, or functional and a surrogate for a fixed-wing UAS. The limited, checks) is performed for new aircraft acceptance, selected flight tests shown here reveal areas for post-maintenance performance confirmation, or for design improvements to potentially enhance safety, in-flight malfunction diagnosis. Maintenance test provide insights into UAS and manned-aircraft flights are designed to determine whether the equipage differences, enable potentially safer airframe, power plant, accessories, and other items of operational flight profiles, and facilitate more- equipment are functioning in accordance with efficient flight regimes (e.g., optimal flight profiles to predetermined standards while subjected to the maximize a UAS’s flight time). These sample studies intended operating environment. Military show promise for the use of conventional flight-test maintenance test flights are performed after 100-hour techniques in the design of UAS flight procedures inspections and after replacement or removal and and in the design of the UAS itself. reinstallation of any flight controls or surfaces, engines, engine controls, or gearboxes [2]. They may Aircraft Certification and Associated also be performed in some form to diagnose a performance discrepancy noted by an operational UAS Test Options pilot or for data collection. Guidelines also exist for A wide variety of tests exist for evaluating commercial-aircraft functional-check flying [3]. aircraft [1] many of which can be similarly applied to UAS. These include: regulatory agency certification Operational flight maneuvers can be used for testing, maintenance flight testing, pilot evaluation of an aircraft for use in its intended examinations, pilot operating handbook (POH) purpose (e.g., flying instrument approaches, comparisons, and experimental flight testing. Other shipboard interface, etc.). As such, the types of industries also have a variety of ways to evaluate evaluations performed on pilots can be used in their vehicles, for example, the automotive industry providing a test sequence and format for similarly not only makes use of various industry standard tests used UASs. Examples of typical pilot evaluations (also known as examinations or check rides) include training syllabus flights, annual pilot proficiency Flight Testing evaluations (normal procedures and emergency The numerous tests available in aircraft training), tactical checks (tactical or special certification/experimental flight test can be procedures), and instrument checks (pertaining to generalized into two categories: performance and instrument flight rules or IFR). Evaluation using handling qualities. Unlike manned aircraft or radio- operational flight procedures can be augmented with controlled (RC) aircraft, the computer system the Cooper-Harper handling-qualities scale. [commonly referred to as the flight controller (FC), Various regulatory agencies are involved in flight controller board (FCB), or autopilot] onboard a determination of aircraft standards. These agencies UAS is constantly providing for the aircraft’s static have well-established criteria for certifying various and dynamic stability. In a manned or RC aircraft the types of aircraft. Some of these agencies include the airframe primarily provides inherent stability which FAA [4] in the U.S., the European Joint may be augmented by the pilot; the level of stability Airworthiness Authority in the European Union, the is then measured during flight test. As a UAS’s Civil Aviation Authority (CAA) in the United computer provides acceptable stability with no effort Kingdom, the CAA in Australia, Transport Canada in on the operator’s part, stability testing—while Canada, the International Civil Aviation Organization potentially beneficial during a UAS’s development— (ICAO), and the Royal Aeronautical Society. may not need to be performed on a developed or operational UAS and will not be discussed here (for In a certificated aircraft, the POH typically more information on stability testing, the reader is contains various data, charts, and tables developed directed to [5]). The understanding that any UAS that from testing. Individual datum and data found in is being flight tested for the purpose of improving the tables typically includes airframe limitations (e.g., safety of its design or operation, or for the purpose of aerodynamic limitations such as airspeed, enhancing the efficiency of its operation, allows for acceleration, altitude, and gross weight limits), best- significantly reducing test planning, conduct, and angle-of-climb airspeed VX, best-rate-of-climb analysis through the elimination of all handling- airspeed VY, stall speeds VS at differing qualities tests. The level of testing performed has a configurations, and center of gravity (c.g.) dramatic effect on the time required to complete any limitations. Data found in charts is typically flight-test study as certification testing [5] includes performance-oriented and includes takeoff, climb, data collection at many test points (e.g., varying range, endurance, descent, landing, mission planning weight, c.g., airspeed, etc.) and test-point (e.g., turn rate versus airspeed, turn radius versus combinations for each test, as well as extensive data airspeed, etc.), and emergency operation (e.g., glide). reduction (e.g., to compensate for aircraft weight This data is a result of test flying, common to changes, an imperfect atmosphere, etc.). Thorough certificated and military aircraft, but often lacking in UAS testing can also be performed with significantly UAS, especially smaller UAS. less effort than is required in a full aircraft Experimental (also known as engineering, certification program and without compromising developmental, or certification) test flights are rigor through the use of limited testing. This may be conducted to determine or demonstrate critical appropriate as UASs typically possess protected operating characteristics of an aircraft. flight envelopes, excursions beyond which are not As typical POH data is often missing from UAS allowed by the onboard computer. Restrictions on the manuals and due to the accepted and rigorous nature size of the operating envelope of the UAS would in the way POH data is collected, experimental- eliminate the requirement for tests to be repeated at, flight-test procedures are proposed, not necessarily for example, various speeds, altitudes, weights, and for UAS certification, but at a minimum to determine c.g.s (though there is nothing that prevents this; these what a conventional flight-test program could types of tests are commonly referred to as “spot provide to a UAS manufacturer. checks”). Flight-Test Procedures Some level of taxi tests can also be performed on rotary-wing aircraft that are equipped with wheels for Performance experimental test-flight procedures landing gear rather than skids. as described by the FAA [6], the Society of Experimental Test Pilots [7], the Society of Flight Test Engineers [8], the National Test Pilot School First Flight (Fixed Wing) [5], and Askue [9] were studied for determining how Using VS (clean, and also for gear down, full these may enhance UAS safety and/or efficient flaps), 1.3VS, and VO at a given test weight, flight-test operation. An overview of some experimental-flight- procedures include: maneuvering climb to test test procedures is provided, which is then followed altitude, maneuvering flight characteristics and stalls by three specific
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