Since the beginning of the first prospects of aviation, daredevil test pilots have been at the forefront of expanding the technological development of the latest and greatest in the industry. In the old days, flight testing was mainly done by trial and error, and it often made or broke the company. In the modern day, all aircraft components are thoroughly examined through the use of extensive computer analysis, and rigorous flight testing of each aircraft system. The flight testing process of a new born aircraft obviously begins on the ground. The first stages of testing that occur on the ground mainly include things such as ensuring all of the electronic systems will function correctly, the hydraulic systems function correctly, the airframe can withstand an appropriate amount of stress, that the engines function safely and efficiently as per the engine manufacturer’s specifications, and also that the aircraft’s fuselage can withstand the pressures encountered at high altitudes. After these tests have been performed on the ground, a test pilot will take to the skies in the new prototype and ensure that each system is functioning correctly during flight, as well as performing a series of aircraft performance tests.
Ensuring that the aircraft’s electrical systems and hydraulic systems are functioning correctly is vital to the safety of the first test flight. The main electronic systems that would be looked at include things such as the functionality of the fly-by-wire systems in the flight controls. A very time-consuming project that all aircraft companies face is calibrating the computer sensors in the flight controls that the pilot operates with the hydraulic actuators that move the control surfaces. Other things such as the aircraft’s autopilot functions, flight instrument systems, navigation sensors, brakes, landing gear, flaps, spoilers, and everything all the way down to ensuring that the proper flow of electricity is being distributed from the aircraft’s generators in the engines need to be taken into consideration. The autopilot functions and flight instrument systems are usually quite easily tested as there is equipment to guide them through a self test. For the navigation sensors, a test pilot has to ensure that all navigation sensors are picking up signals accurately. Navigation censors on the aircraft would include the GPS(global positioning satellite) receiver, the ADF(automatic direction finding) censor, the VOR(VHF omnidirectional range) censor, and any other technology the aircraft might have to navigate or shoot an approach.
The flight controls are also ground tested while hooked up to computers to calibrate the sensitivity in the flight controls and how far each control surface will move. For the secondary flight controls, such as the flaps and spoilers, they must be checked in their increments to ensure that proper deployment is ensued when they are activated through their stages. The braking system in the aircraft also must be calibrated on the ground, and tests have to be performed to determine how safe the brakes are if an aborted take off has to be performed. The general aircraft safety standards for most aircraft manufacturers suggest that the aircraft must be able to perform an aborted take off, and not have flames on the landing gear for five minutes, which is enough time for emergency crews to react. Also, the landing gear must be tested with the aircraft elevated in the hangar to ensure that proper retraction is established. Further ground tests that are performed on the new airplane before it takes flight include the airframe stress tests. Computers are hooked up to a hydraulic stressing machine that applies stress on different areas of the aircraft most vulnerable to stress in flight, such as various portions of the wings, each control surface, and the vertical and horizontal stabilizers. These stress tests basically determine how much stress it takes to cause structural failure in these components of the aircraft.
With this information, the engineers in the designing team will determine mathematically if the aircraft can withstand a level of stress that would be more than safe enough for emergency situations. Next, the aircraft manufacturer must ensure that the engines function on the aircraft according to the specification supplied by the manufacturer of the engines. Each engine is run up in a special engine test cell, and computers are hooked up to many various censors in the engine. These censors will show compressor speed in the jet engine, turbine temperature, the amount of thrust being produced, and the fuel being burned. After it has been determined that the engines comply with the manufacturer’s specifications, they are assembled on to the aircraft, and further testing of the engines must be completed in a ground run up in the aircraft. The ground run up is to ensure that the bleed air systems and any hydraulic systems that are powered by the engines are working properly. The final ground testing involves performing a pressure test on the fuselage. This test simply pressurizes the fuselage to a value that will ensure safe operation of the aircraft at high altitudes. Once the aircraft has passed all of these tests, and the design engineers are satisfied that it is safe for flight, it is time for the flight testing!
This is certainly the most exciting part of aviation. The time where the test pilot gets to take the brand new prototype aircraft out to push its limits. On the several test flights that are conducted, many things have to be determined. The pilot will determine exactly how much fuel the aircraft burns during flight, what the safe operating speeds are, what the maximum speed of the aircraft is, how much runway the aircraft takes to accelerate to take off speed, and how long it takes to decelerate. The pilot also has to perform tests on the navigation equipment in the aircraft as well as the autopilot. He or she will simply try out each function of the autopilot to ensure that everything works correctly.
For the navigation equipment, the pilot will try the GPS, and determine if it is giving accurate readings, and will also try every other navigation system such as the VOR, ADF, ILS(instrument Landing System), etc. to ensure that each system is giving accurate information, and is safe enough equipment to be used in IMC(instrument meteorological conditions). Other systems that need to be tested include the flight controls, and the engine systems. In flight, the pilot has to provide an opinion for how he or she feels about flying the airplane. Whether it is too sensitive, or what have you. As for the engine systems, the pilot must make sure that the hydraulic systems that are running off of the engines are fully functional, and that any bleed air system from the engine(such as cabin heating, etc.) are also working fully. To determine if all of the systems related to the engine and flight controls are working correctly, most aircraft are equipped with an LCD indicating screen called the EICAS, which stands for “engine indicating crew alerting system”.
This is a brief look into the rigorous process of flight testing a brand new prototype aircraft, and there are usually very many hold backs in the production of a new aircraft. It can normally take two or three years from the time the aircraft is drawn out on paper until it is ready for its maiden flight with the test pilot. As a pilot, I think test pilots have one of the neatest aviation job in the entire industry, as they are always trying out brand new innovations, and always pushing the envelope for aviation advances.