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Flight testing is a branch of aeronautical engineering that develops technologies and equipment required for in-flight evaluation of behaviour of an aircraft or and reusable spacecraft at the atmospheric phase of flight. Instrumentation systems for flight testing are developed using specialized transducers and data acquisition systems. Data is sampled during the flight of an aircraft, or atmospheric testing of spacecraft. This data is validated for accuracy and analyzed to further modify the vehicle design during development, or to validate the design of the vehicle.
The flight test phase accomplishes two major tasks: 1) finding and fixing aircraft design problems and then 2) verifying and documenting the vehicle capabilities when the vehicle design is complete, or to provide a final specification for government certification or customer acceptance. The flight test phase can range from the test of a single new system for an existing vehicle to the complete development and certification of a new aircraft, launch vehicle, or reusable spacecraft. Therefore, the duration of a particular flight test program can vary from a few weeks to years.
Flight testing of military aircraft is often conducted at military flight test facilities. The US Navy tests aircraft at Naval Air Station Patuxent River and the US Air Force at Edwards Air Force Base. The U.S. Air Force Test Pilot School and the U.S. Naval Test Pilot School are the programs designed to teach military test personnel. In the UK, most military flight testing is conducted by three organizations, the RAF, BAE Systems and Qinetiq. For minor upgrades the testing may be conducted by one of these three organizations in isolation, but major programs are normally conducted by a joint trials team (JTT), with all three organizations working together under the umbrella of an integrated project team (IPT) airspace.
Many launch vehicles are flight tested, with rather more extensive data collection and analysis on the early of a particular launch vehicle design. Reusable spacecraft or reusable booster test programs are much more involved and typically follow the full Flight envelope paradigm of traditional aircraft testing. Previous and current test programs include the early of the Space Shuttle, the X-24B, SpaceShipTwo, Dream Chaser, Falcon 9 prototypes, OK-GLI, and SpaceX Starship prototypes.
The document used to prepare a single test flight for an aircraft is known as a Test Card. This will consist of a description of the Test Points to be flown. The flight test engineer will try to fly similar Test Points from all test plans on the same flights, where practical. This allows the required data to be acquired in the minimum number of flight hours. The software used to control the flight test process is known as Flight Test Management Software, and supports the Flight Test Engineer in planning the test points to be flown as well as generating the required documentation.
Once the flight test data requirements are established, the aircraft or launch vehicle is instrumented with a data acquisition system (DAS), or data acquisition unit (DAU) and sensors, to record that data for analysis. Typical instrumentation parameters recorded during a flight test for a large aircraft are:
Specific calibration instruments, whose behavior has been determined from previous tests, may be brought on board to supplement the aircraft's in-built probes.
During the flight, these parameters are then used to compute relevant aircraft performance parameters, such as airspeed, altitude, weight, and center of gravity position.
During selected phases of flight test, especially during early development of a new aircraft, many parameters are telemetry during the flight and monitored by flight test and test support engineers, or stored for subsequent data analysis. This provides for safety monitoring and allows for both real-time and full-simulation analysis of the data being acquired.
There are several aspects to a flight test program, among which:
Testing that is specific to military aircraft includes:
Emergency situations are evaluated as a normal part of all flight test program. Examples are: engine failure during various phases of flight (takeoff, cruise, landing), systems failures, and controls degradation. The overall operations envelope (allowable gross weights, centers-of-gravity, altitude, max/min airspeeds, maneuvers, etc.) is established and verified during flight testing. Aircraft are always demonstrated to be safe beyond the limits allowed for normal operations in the Flight Manual.
Because the primary goal of a flight test program is to gather accurate engineering data, often on a design that is not fully proven, piloting a flight test aircraft requires a high degree of training and skill. As such, such programs are typically flown by a specially trained test pilot, the data is gathered by a flight test engineer, and often visually displayed to the test pilot and/or flight test engineer using flight test instrumentation.
Introduction Aircraft Performance has various missions such as Takeoff, Climb, Cruise, Acceleration, Deceleration, Descent, Landing and other Basic fighter maneuvers, etc..
After the flight testing, the aircraft has to be certified according to their regulations like FAA's FAR, EASA's Certification Specifications (CS) and India's Air Staff Compliance and Requirements.
1. Flight Performance Evaluation and documentation
2. Reduction of Flight performance to standard conditions
3. Preparation and Validation of Performance Charts for Operating Data Manual (ODM)
Performance charts allow a pilot to predict the takeoff, climb, cruise, and landing performance of an aircraft. These charts, provided by the manufacturer, are included in the AFM/POH. Information the manufacturer provides on these charts has been gathered from test flights conducted in a new aircraft, under normal operating conditions while using average piloting skills, and with the aircraft and engine in good working order. Engineers record the flight data and create performance charts based on the behavior of the aircraft during the test flights. By using these performance charts, a pilot can determine the runway length needed to take off and land, the amount of fuel to be used during flight, and the time required to arrive at the destination. The data from the charts will not be accurate if the aircraft is not in good working order or when operating under adverse conditions. Always consider the necessity to compensate for the performance numbers if the aircraft is not in good working order or piloting skills are below average. Each aircraft performs differently and, therefore, has different performance numbers. Compute the performance of the aircraft prior to every flight, as every flight is different.
Every chart is based on certain conditions and contains notes on how to adapt the information for flight conditions. It is important to read every chart and understand how to use it. Read the instructions provided by the manufacturer. For an explanation on how to use the charts, refer to the example provided by the manufacturer for that specific chart.
The information manufacturers furnish is not standardized. Information may be contained in a table format, and other information may be contained in a graph format. Sometimes combined graphs incorporate two or more graphs into one chart to compensate for multiple conditions of flight. Combined graphs allow the pilot to predict aircraft performance for variations in density altitude, weight, and winds all on one chart. Because of the vast amount of information that can be extracted from this type of chart, it is important to be very accurate in reading the chart. A small error in the beginning can lead to a large error at the end.
The remainder of this section covers performance information for aircraft in general and discusses what information the charts contain and how to extract information from the charts by direct reading and interpolation methods. Every chart contains a wealth of information that should be used when flight planning. Examples of the table, graph, and combined graph formats for all aspects of flight will be discussed.
Interpolation Not all of the information on the charts is easily extracted. Some charts require interpolation to find the information for specific flight conditions. Interpolating information means that by taking the known information, a pilot can compute intermediate information. However, pilots sometimes round off values from charts to a more conservative figure. Using values that reflect slightly more adverse conditions provides a reasonable estimate of performance information and gives a slight margin of safety. The following illustration is an example of interpolating information from a takeoff distance chart:
Since many aircraft development programs are sponsored by government military services, military or government-employed civilian pilots and engineers are often integrated into the flight test team. The government representatives provide program oversight and review and approve data. Government test pilots may also participate in the actual test flights, possibly even on the first/maiden flight.
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