A flight test technique (FTT) is a tool for answering common or frequently asked questions in flight test. It is a maneuver building block consisting of procedures for accomplishing the maneuver together with an objective and metrics.
FTTs are the “questions” that we ask to investigate various characteristics of airplanes.
For example, we may wish to know about the stall characteristics of an airplane. Since aircraft stall is a complex and non-linear phenomenon, one that is not well-understood, we must approach this boundary in the flight envelope in a very methodical, incremental, intentional, and safe way.
Pictured here is a portion of the test card used for gathering data about the stall characteristics of an airplane.
A FTT is in some sense a description of an experiment. It is a key element of the scientific method applied to aerospace sciences, engineering, and aviation.
#FTT Friday
Each Friday, @FlightTestFact will deliver examples, definitions, and explanations of flight test techniques for the entire day. You can view these tweets by searching for #FTT and #flighttest as depicted below. You can also click on the picture below to be taken to the twitter search results.
Here is a test report from Edwards AFB, Air Force Flight Test Center detailing the findings from high angle of attack X-29 research.
There are some interesting lessons learned in this X-29 Forward Swept Wing Flight Research Program Status Report.
The NASA Technical Reports Server has many (thousands) more technical reports and photos of the X-29 here.
Check out @FlightTestFact on Twitter for more flight test safety references, videos, and information daily.
This X-29 research aircraft at NASA Dryden Flight Research Center allows us to see a very unique wing as we wrap up this month long review of aircraft wing design characteristics with three more: dihedral angle, sweep, and twist.
Dihedral Angle
The angle between the aircraft’s xy-plane (parallel to the horizon when viewed from the front) and the wing is known as the dihedral angle. However, the position of the wing relative to the vertical center of gravity also results in a dihedral effect. High wing aircraft have a higher effective dihedral than low wing aircraft as a result of the fuselage’s effect on airflow. Dihedral has a significant impact on directional stability.
The X-29 has little or no dihedral angle, but since it’s wings are mounted low on the fuselage this gives it an anhedral (or destabilizing) effect.
Wing Sweep
The shadow cast by the aircraft in this photo clearly highlights the unique wing sweep characteristic of the X-29, with its forward swept wing. Some gliders have wings that are swept slightly forward as well.
Wing Twist
Close examination of this photo reveals the X-29′s wing twist. The root of the wing angles down, while the wing tip has a more positive angle of incidence. The X-29 was also uniquely designed with a special composite laminate that affected the twist of the wing caused by aerodynamic forces. The forces would have caused the wing to have a divergent twist, but the composite laminate reduced this.
Click here to read more about this airplane on the NASA Dryden website, or view more NASA photos of the X-29 here.
Airplanes by Design features photographs of aircraft from a test pilot perspective, highlighting aeronautical engineering characteristics and flight test facts. To see all of the these pictures (and many more of this aircraft and it’s unique design characteristics), click here. You will always be able to access any of these pictures by selecting the Flickr icon in the top menu bar.
Send a message to @FlightTestFact on Twitter to share your Airplanes by Design stories and photos.
