Solution
2.4 Introductory Flight Test Concepts
2.4.2 The Flight Test Process
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range of aerospace vehicles, such as low-speed propeller-driven airplanes, unmanned aerial vehi-cles, vertical takeoff and landing vehivehi-cles, unmanned missile test beds, space access vehivehi-cles, and prototypes of advanced aircraft, missiles, and spacecraft. Despite their differences, the flight test of X-planes share the common goal of advancing the research and technology boundaries of aerospace engineering. The US X-planes, from the Bell X-1 to the present, are listed in Table 2.11. We refer back to many of the significant accomplishments of the various X-planes throughout the text.
k k Table 2.11 The X-planes.
X No. First flight Goals or accomplishments
X-1 25 Jan 1946 First manned supersonic flight, reaching Mach 1.06 at 45,000 ft on 14 October 1947
X-1A-E 24 Jul 1951 Continuation of X-1 high-speed flight research
X-2 27 Jun 1952 High-speed flight research aircraft with swept wing flight, 1st to exceed Mach 3
X-3 20 Oct 1952 Mach 2 research aircraft, but never flew faster than Mach 0.95 X-4 15 Dec 1948 Tailless (no horizontal tail) research aircraft designed for high subsonic
speed flight
X-5 20 Jun 1951 First variable-sweep wing aircraft
X-6 None Evaluation of nuclear propulsion using a modified B-36 aircraft (not built)
X-7 26 Apr 1951 Testbed for ramjet propulsion, fastest flight Mach 4.3
X-8 24 Apr 1947 Upper air research sounding rocket (highest to 800,000 ft), led to Aerobee rocket
X-9 28 Apr 1949 Testbed for air-to-surface missile technology
X-10 14 Oct 1953 Aerodynamics and systems testbed for intercontinental cruise missile technology
X-11 None Proposed test vehicle for original Atlas intercontinental ballistic cruise missile concept
X-12 None Proposed test vehicle for original Atlas intercontinental ballistic cruise missile concept
X-13 10 Dec 1955 Vertical takeoff and landing (VTOL) flight research with a jet aircraft X-14 17 Feb 1957 VTOL flight research using vectored thrust, data used to design the
Harrier prototype
X-15 8 Jun 1959 Hypersonic flight research, first manned hypersonic aircraft flight, flew to Mach 6.70
X-16 None Designed to be a high-altitude long range reconnaissance aircraft (not built)
X-17 17 Apr 1956 Multi-stage rocket used for hypersonic entry research up to Mach 14.4 X-18 20 Nov 1959 First tilt-wing vertical takeoff and landing (VTOL) aircraft
X-19 20 Nov 1963 VTOL flight research using tandem, tilt-rotor concept (similar to V-22 Osprey)
X-20 None Hypersonic “space plane” design, called the Dyna-Soar (not built) X-21 18 Apr 1963 Northrop laminar boundary layer control test aircraft
X-22 17 Mar 1966 V/STOL aircraft with dual tandem ducted-propellers and variable-stability system
X-23 21 Dec 1966 Lifting-body, maneuvering reentry test vehicle
X-24 17 Apr 1969 Rocket-powered lifting body, explored low-speed flight and landing of lifting bodies
X-25 5 Jun 1968 “Gyro-chute” concept for emergency egress capability using an ultralight gyrocopter
X-26 3 Jul 1962 Schweitzer 2-32 sailplane used as a Navy trainer and as a stealth observation platform
X-27 None Lockheed design for an advanced lightweight fighter to replace the F-104 (not built)
X-28 12 Aug 1970 Prototype of small, single-engine seaplane for reconnaissance use in Southeast Asia
X-29 14 Dec 1984 Forward swept wing flight research
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Table 2.11 (continued)
X No. First flight Goals or accomplishments
X-30 None Hypersonic, scramjet-powered, single-stage-to-orbit (SSTO) vehicle (not built)
X-31 11 Oct 1990 High angle-of-attack flight research, including post-stall region, using vectored thrust
X-32 18 Sep 2000 Boeing concept demonstrator aircraft for Joint Strike Fighter competition X-33 None Single-stage-to-orbit vehicle with linear aerospike rocket motor (not
built)
X-34 None Reusable access to space testbed; captive-carry flight in June 1999 X-35 24 Oct 2000 Lockheed concept demonstrator aircraft for Joint Strike Fighter
competition
X-36 17 May 1997 Boeing remotely piloted, 28% scale vehicle with no vertical or horizontal tails
X-37 22 Apr 2010 Orbital space plane to demonstrate reusable space technologies, operated by USAF
X-38 12 Mar 1998 Concept demonstrator of a crew rescue vehicle for the International Space Station
X-39 None Reserved for use by USAF for sub-scale unmanned demonstrators X-40 11 Aug 1998 80% scale version of proposed Space Maneuver Vehicle, became the
X-37
X-41 Unknown Classified DARPA common aero vehicle (CAV) maneuvering reentry vehicle
X-42 Unknown Experimental, expendable upper stage, designed to boost payloads into orbit
X-43 2 Jun 2001 Air-launched, unmanned, hydrogen-fueled, scramjet testbed; flew to Mach 9.68
X-44 None Tailless research aircraft concept (not built)
X-45 22 May 2002 Tailless, thrust-vectoring unmanned combat air vehicle (UCAV) demonstrator
X-46 None US Navy unmanned combat air vehicle (UCAV-N) demonstrator, (cancelled)
X-47 24 Feb 2003 Tailless, diamond-shaped wing planform UCAV demonstrator X-48 20 Jul 2007 Unmanned, sub-scale, blended wing body (BWB) testbed
X-49 29 Jul 2007 Compound fixed wing airplane-helicopter with vectored thrust ducted propeller design
X-50 24 Nov 2003 Canard rotor wing demonstrator vehicle
X-51 26 May 2010 Air-launched, unmanned, hydrocarbon-fueled scramjet testbed; flew to
>Mach 5
X-52 None Number skipped
X-53 8 Dec 2006 Active aeroelastic wing (AAW) technology demonstrator using highly modified F-18
X-54 Pending Reserved for Gulfstream/NASA supersonic business jet demonstrator X-55 2 Jun 2009 Advanced composite cargo aircraft testbed
X-56 26 Jul 2013 UAV to study high altitude, long endurance flight technologies
X-57+ Unknown Unknown
k k Theory or
hypothesis
Conclusions Prediction
Data analysis
Experiment (f light test)
Figure 2.43 The scientific method applied to flight test.
Define objectives and requirements
Complet hazard assessment Write flight test plan
Write test cards
Pass flight readiness review
Conduct post-flight briefing Conduct pre-flight briefing
Conduct flight test
Perform data analysis
Determine if objectives and requirements have been met
Figure 2.44 Example detailed flight test process.
measurements and instrumentation required, ground testing to be performed prior to flight, and any other test requirements. A critical element of the flight test process is the assessment of the potential hazards in performing the test. This hazard assessment may be included in the written test plan or it may be a separate document. The safety and risk assessment aspects of the flight test
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planning process are covered in a later section. After the test plan has been written, reviewed, and approved, test cards are written that specify the step-by-step procedures to be used to set up and perform the test maneuvers. Test cards are discussed in more detail in a later section. Prior to the test, there is usually a technical and safety review of the readiness to proceed to flight, often called a flight readiness review. This final, formal review is usually presented to technical, safety, and management personnel who are not associated with the flight test, so as to provide an independent, objective assessment and approval as to whether the flight test team is ready to proceed to flight.
Once this readiness review is passed, the flight test team is complete with the preparation phase of the test and is ready to move on to test execution.
On, or very near to, the day of the flight, the test team meets to brief the planned flight to ensure that everyone understands the test objectives, the flight test techniques that will be flown, test data that is required, and any flight restrictions or limits. The test cards for the day’s flight are talked through, as they will be flown. Finally, it is time to go flying, and the test flight is performed, following the briefed plan. The well-known adage for this process is to “plan the flight and fly the plan”. After the flight is completed, the test team holds a post-flight briefing to review the flight, discuss what went well and what did not go as planned, and to identify any issues or discrepancies.
The flight test data is analyzed by the engineering analysts to ultimately determine if the objectives and requirements have been met.