aircraft testing[′er‚kraft ‚test·iŋ]
Subjecting a complete aircraft or its components (such as wings, engines, or electronics systems) to simulated or actual flight conditions in order to measure and record physical phenomena that indicate operating characteristics. Testing is essential to the design, development, and acceptance of any new aircraft.
Aircraft and their components are tested to verify design theories, obtain empirical data where adequate theories do not exist, develop maximum flight performance, demonstrate flight safety, and prove compliance with performance requirements. Testing programs originate in laboratories with the evaluation of new design theory; progress through extensive tests of components, subsystems, and subsystem assemblies in controlled environments; and culminate with aircraft tests in actual operational conditions.
Instrument testing, in controlled conditions of environment and performance, is used extensively during the design performance assessment of new aircraft to avoid the costly and sometimes dangerous risks of actual flight.
A wind tunnel is basically an enclosed passage through which air is forced to flow around a model of a structure to be tested, such as an aircraft. Wind tunnels vary greatly in size and complexity, but all of them contain five major elements: an air-drive system, a controlled stream of air, a model, a test section, and measurement instruments. The drive system is usually a motor and one or more large fans that push air through the tunnel at carefully controlled speeds to simulate various flight conditions. A scale model of an actual or designed aircraft is supported inside the test section (see illustration), where instruments, balances, and sensors directly measure the aerodynamic characteristics of the model and its stream of airflow. Wind tunnel tests measure and evaluate airfoil (wing) and aircraft lift and drag characteristics with various configurations, stability and control parameters, air load distribution, shock wave interactions, stall characteristics, airflow separation patterns, control surface characteristics, and aeroelastic effects.
Aircraft components are integrated into subsystems, system elements, and complete operational systems to help resolve interface problems. Integration tests establish functional and operational capability and evaluate complete system compatibility, operation, maintenance, safety, reliability, and best possible performance.
Rocket-propelled sled tests evaluate crew ejection escape systems for high-performance aircraft. A fuselage section, mounted on a sled, is propelled by rockets along fixed tracks. When a desired speed is reached, the ejection mechanism is automatically triggered, firing rockets that propel crew seats (containing instrumented mannequins) clear of the fuselage, and activating parachutes to limit the free-flight trajectory of the mannequins and allow safe descent to the ground. Water-propelled sled tests study landing gear systems and runway surface materials. Other dynamic ground tests include acceleration and arresting tests of aircraft fuel system venting, transfer, and delivery, which are evaluated while the system is subjected to flightlike forces and attitudes.
Proof load tests of actual aircraft are usually done on one or more of the first airframes built. An airframe, mounted in a laboratory, is fitted with thousands of strain gages, the outputs of which are recorded on an automatic data-recording system. Simulated air and inertia loads are applied to airframe components, which are loaded simultaneously, in specified increments, to simulate loads encountered during takeoff, maneuvering flight, and landing. Loadings are increased to design limit and then to ultimate failure to locate possible points of excessive yield. Component parts and system subassemblies are also tested with various loadings while operating under expected extremes of temperature, humidity, and vibration to determine service life. See Airframe
Aircraft flight and systems characteristics are represented with varying degrees of realism for research, design, or training simulation purposes. The representation is usually in the form of analytic expressions programmed on a digital computer. Flight simulation may be performed with or without a human pilot in the loop. The pilot imposes additional constraints on the simulator such as requiring a means of control in a manner consistent with the means provided in the aircraft being simulated. Flight simulation requires representation of the environment to an extent consistent with the purposes of the simulation, and it further requires that all events in the simulator occur in real time. Real time is a term which is used to indicate that all time relationships in the simulator are preserved with respect to what they would be in the airplane in flight. See Real-time systems
Simulators range in size and complexity from actual aircraft, outfitted with special flight decks that can be reconfigured to test different systems, to desk-top simulators that can test individual or integrated components.
Simulators may be classified by their use in research, design, or training. Research simulators are usually employed to determine patterns of human behavior under various workloads or in response to different flight instrument display configurations or different aircraft dynamic characteristics. Design simulators are used to conduct tradeoff studies to evaluate different design approaches in the aircraft. The most pervasive use of flight simulators is for training operators of the aircraft and its systems and maintenance personnel. The simulator is in many cases a better training device than the aircraft. This is true because of the safety, versatility, and speed with which critical maneuvers may be performed.
Flight testing can be considered the final step in the proving of a flight vehicle or system as capable of meeting its design objectives. This definition applies whether the concept is a complete vehicle, a vehicle subsystem, or a research concept. Flight testing can be categorized as research, development, and operational evaluation. These categories apply both to aircraft and to spacecraft and missiles.
The purpose of research testing is to validate or investigate a new concept or method with the goal of increasing the researchers' knowledge. Many times, the vehicle used is a one- or two-of-a-kind article designed specifically for the concept being investigated.
A new vehicle or subsystem enters development testing after it has been designed and the basic concepts proven in research flight testing. During this phase of testing, problems with the design are uncovered and solutions are developed for incorporation in the production aircraft.
Operational testing involves customer participation to evaluate the capability of the fully equipped vehicle to meet its intended mission objectives. Testing is performed to determine system reliability, define maintenance requirements, and evaluate special support equipment. Military vehicles are also tested to determine weapon delivery techniques and effectiveness, including target acquisition capabilities, ability to perform in all weather conditions, operational behavior in battlefield conditions, and, in the case of naval aircraft, carrier suitability. Commercial aircraft are tested for blind landing-approach systems, passenger services, baggage and cargo loading, noise levels, and safety provisions. Crew training simulators, handbooks, and procedures are also tested in this phase to demonstrate the ability to maintain and operate the aircraft effectively.