Flight test
Flight test is a branch of
aeronautical engineering that develops and gathers data during flight of an
aircraft and then analyses the data to evaluate the flight characteristics of
the aircraft and validate its design, including safety aspects. The flight test
phase accomplishes two major tasks: 1)finding and fixing any
aircraft
design problems and then 2) verifying and documenting the aircraft
capabilities for government certification or customer acceptance. The flight
test phase can range from the test of a single new system for an existing
aircraft to the complete development and certification of a new aircraft.
Therefore the duration of a flight test program can vary from a few weeks to
several years.
Civil Aircraft Flight Test
There are typically two categories of flight test programs � commercial and
military. Commercial flight testing is conducted to certify that the aircraft
meets all applicable safety and performance requirements of the government
certifying agency. In the US, this is the Federal Aviation Administration (FAA);
in Canada,
Transport Canada (TC); in
the
United Kingdom (UK), the
Civil Aviation Authority; and in
the
European Union, the
Joint Aviation Authorities (JAA). Since commercial aircraft development is
normally funded by the aircraft manufacturer and/or private investors, the
certifying agency does not have a stake in the commercial success of the
aircraft. These civil agencies are concerned with the aircraft�s safety and that
the pilot�s flight manual accurately reports the aircraft�s performance. The
market will determine the aircraft�s suitability to operators. Normally, the
civil certification agency does not get involved in flight testing until the
manufacturer has found and fixed any development issues and is ready to seek
certification.
Military aircraft Flight Test
Military programs differ from commercial in that the government contracts
with the aircraft manufacturer to design and build an aircraft to meet specific
mission capabilities. These performance requirements are documented to the
manufacturer in the Aircraft Specification and the details of the flight test
program (among many other program requirements) are spelled out in the Statement
of Work. In this case, the government is the customer and has a direct stake in
the aircraft�s ability to perform the mission. Since the government is funding
the program, it is more involved in the aircraft design and testing from
early-on. Often military test pilots and engineers are integrated as part of the
manufacturer�s flight test team, even before first flight. The final phase of
the military aircraft flight test is the Operational Test (OT). OT is conducted
by a government-only test team with the dictate to certify that the aircraft is
suitable and effective to carry out the intended mission. Flight testing of
military aircraft is often conducted at military flight test facilities. The US
Navy tests aircraft at
Naval Air Station Patuxent River, MD (a.k.a. �Pax River�) and the US
Air Force at
Edwards Air Force Base, CA. 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
organisations, the
RAF,
BAE
Systems and
Qinetiq. For minor upgrades the testing may be conducted by one of these
three organisations in isolation, but major programs are normally conducted by a
joint trials team (JTT), with all three organisations working together under the
umbrella of an
Integrated Project Team (IPT)
Flight Test Processes
Flight Testing is highly expensive and potentially very risky. Unforeseen
problems can lead to damage to aircraft and loss of life, both of aircrew and
people on the ground. For these reasons modern flight testing is probably one of
the most safety conscious professions today. Flight trials can be divided into 3
sections, planning, execution and analysis and reporting.
Preparation
For both commercial and military aircraft, flight test preparation begins
well before the aircraft is ready to fly. Initially requirements for flight
testing must be defined, from which the
Flight Test Engineers prepare the test plan(s). These will include the
aircraft configuration, data requirements and manoeuvres to be flown or systems
to be exercised. A full certification/qualification flight test program for a
new aircraft will require testing for many aircraft systems and in-flight
regimes; each is typically documented in a separate test plan. During the actual
flight testing, similar maneuvers from all test plans are combined and the data
collected on the same flights, where practical. This allows the required data to
be acquired in the minimum number of flight hours.
Once the flight test data requirements are established, the aircraft is
instrumented to record that data for analysis. Typical instrumentation
parameters recorded during a flight test are: temperatures, pressures,
structural loads, vibration/accelerations, noise levels (interior and
exterior), aircraft performance parameters (airspeed, altitude, etc.), aircraft
controls positions (stick/yoke position, rudder pedal position, throttle
position, etc.), engine performance parameters, and atmospheric conditions.
During selected phases of flight test, especially during early development of a
new aircraft, many parameters are transmitted to the ground during the flight
and monitored by the
Flight Test Engineer and test support engineers. This provides for safety
monitoring and allows real-time analysis of the data being acquired.
Execution
When the aircraft is completely assembled and instrumented, it typically
conducts many hours of ground testing before its first/maiden
flight. This ground testing will verify basic aircraft systems operations,
measure engine performance, evaluate dynamic systems stability, and provide a
first look at structural loads.
Flight controls will also be checked out. Once all required ground tests are
completed, the aircraft is ready for the first flight. First/maiden
flight is a major milestone in any aircraft development program and is
undertaken with the utmost caution.
There are several aspects to a flight test program:
handling qualities, performance, aero-elastic/flutter stability,
avionics/systems capabilities, weapons delivery, and structural loads. Handling
qualities evaluates the aircraft's controllability and response to pilot inputs
throughout the range of flight.
Performance testing evaluates aircraft in relation to its projected
abilities, such as speed, range, power available, drag, airflow characteristics,
and so forth. Aero-elastic stability evaluates the dynamic response of the
aircraft controls and structure to aerodynamic (i.e. air-induced) loads.
Structural tests measure the stresses on the airframe, dynamic components, and
controls to verify structural integrity in all flight regimes. Avionics/systems
testing verifies all electronic systems (navigation, communications, radars,
sensors, etc.) perform as designed. Weapons delivery looks at the pilot�s
ability to acquire the target using on-board systems and accurately deliver the
ordnance on target. Weapons delivery testing also evaluates the separation of
the ordnance as it leaves the aircraft to ensure there are no safety issues.
Other military unique tests are:
air-to-air refueling, radar/infrared signature measurement, and
aircraft carrier operations. 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, so such programs are
typically flown by a specially trained
test pilot,
and the data is gathered by a
flight test engineer, and often visually displayed to the a test pilot
and/or flight test engineer using
flight test instrumentation.
Analysis and Reporting
Flight Test Team
The make-up of the Flight Test Team will vary with the organization and
complexity of the flight test program, however, there are some key players who
are generally part of all flight test organizations. The leader of a flight test
team is usually a
Flight test engineer (FTE) or possibly an experimental
Test Pilot.
Other FTEs or pilots could also be involved. Other team members would be the
Flight Test Instrumentation Engineer, Instrumentation System Technicians, the
aircraft maintenance department (mechanics, electricials, avionics technicians,
etc.), Quality/Product Assurance Inspectors, the ground-based computing/data
center personnel, plus logistics and administrative support. Engineers from
various other disciplines would support the testing of their particular systems
and analyze the data acquired for their specialty area.
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.
|
