Aerodynamics Flashcards
Why can a swept wing aircraft go faster?
Imagine you’re running through a swimming pool filled with water. If you run straight ahead with your arms outstretched to the sides, you’ll feel a lot of resistance from the water pushing against your arms. This makes it harder for you to move forward quickly.
Now, think about what happens if you angle your arms backward, close to your sides. The water flows more smoothly around your body, and you feel less resistance. This allows you to move through the water more easily and faster.
Swept back wings on an airplane work in a similar way. When an airplane flies, it encounters air resistance, similar to how you feel water resistance. Straight wings would hit the air more directly, creating more drag (resistance). However, wings that are angled backward help the air flow more smoothly around the airplane, reducing the drag. This reduction in drag allows the airplane to fly faster, just like how you can move faster through the water with your arms swept back.
What happens to the center of pressure/lift as we enter mach tuck?
Mach tuck is an aerodynamic effect, whereby the nose of an aircraft tends to pitch downwards as the airflow around the wing reaches supersonic speeds. The aircraft will be subsonic, and traveling significantly below Mach 1.0, when it first experiences this effect. As the wing becomes more affected by the shock wave the center of pressure will continue to travel aft, thereby causing a significantly higher nose-down force and requiring a nose-up input or trim to maintain level flight. Although Mach tuck develops gradually, if it is allowed to progress significantly, the center of pressure can move so far rearward that there is no longer enough elevator authority available to counteract it, and the airplane enters a steep, sometimes unrecoverable dive
What is a coffin corner?
Coffin Corner is the edge of an aircraft’s high altitude operating envelope - Marked by the speed margin between the High Speed Buffet (Mach Tuck) and Low Speed Buffet (Stall). At very high altitudes this difference may be just a few knots. A small increase in bank angle or turbulence could induce a dangerous stall that may not be recoverable.
What is Mach Buffet?
It’s a vibration caused by reaching the critical Mach number and it’s caused by the formation of a shockwave over the wings
What is Dutch Roll?
A dutch roll is a combination of rolling and yawing oscilaltions when the lateral stability is more powerful than than the directional stability. A dutch roll may be set in motion when an airplane is disturbed in a roll or a yaw. Aircraft that operate above 25,000 are required to have a stablity augmentation system, yaw damper, to combat these oscillations
Why do airliners all have swept wings?
Swept wings reduce airflow acceleration over the wings and delay crit mac. The airflow is divided into span-wise flow and chord-wise flow. As airflow acceleration is now reduced over the wing, the airplane can now go faster before you experience shockwave and the resultant drag.
What is chord-wise flow vs span-wise flow?
Chord-wise flow is air moving along the chord line of an airfoil as you would experience in many GA aircraft with straight wing design. Span-wise flow is the product of a swept wing design where the airflow has two components. One is the familiar chord-wise flow and the other follows the “span” of the wing moving outward towards the wingtip. Span-wise flow allows higher speeds before reaching critical Mach when supersonic shockwaves begin to move the center of lift rearward on the wing and begin inducing Mach tuck.
What is mach tuck?
As an aircraft flies faster and approaches the speed of sound, the air pressure distribution over the wings changes. The shock waves that form can cause the center of pressure (the point where the aerodynamic forces act) to move backward. This backward shift creates a nose-down pitching moment
What to do if you find yourself getting closer to coffin corner?
Request lower
What type of wing does a Cessna have?
Straight Wing
What are wing tip vortices?
Wingtip vortices are spirals of air that form at the tips of an airplane’s wings as it flies. They occur because of the pressure difference between the upper and lower surfaces of the wings.
How does a winglet work? Draw it.
it directs the wing airflow up and away from the upper wing surface reducing induced drag
What is area rule?
The “pinched waist” – there is an indentation in the fuselage near the wing, which reduces the drag at transonic speed, allowing the airplane to fly faster and farther without increasing power
Describe a Delta Wing.
A delta wing is an airfoil shaped like a triangle, it is swept back and tapered, it helps increase maneuverability and proficiency at supersonic speeds.
What is Shock Stall?
A marked increase in drag, loss of lift and control on an aircraft approaching the speed of sound.
