Aerodynamic Principles Flashcards
What is the relationship between lift and angle of attack?
Imagine an XY graph with lift as X (up the side) and AOA (along the bottom)as Y.
Now imagine a diagonal line from left to right starting from lower left of graph. As the AOA increases so does lift.
This relationship continues until there is a sharp drop in lift. This is essentially where the COA is. It is important to note that there is still some lift and it continues to decrease in the backside of the curve. This is where spins come into play.
What is a spin?
How to recover?
Simply put, a spin occurs when one wing is stalled more than the other. An aggravated, uncoordinated stall.
Imagine the graph that shows the relationship between lift and AOA. There is a region after a wing has exceeded the COA where aerodynamics react the opposite. As the AOA is increased lift gets worse. In a stall, both wings are at the same place in this reverse region. In a spin, one wing is more stalled than the other. And since increasing the AOA in this region decreases lift, if you try and use your ailerons opposite of the spin, you will actually worsen the spin! This is why you simply keep ailerons neutral and use opposite rudder. Ultimately breaking the uncoordinated stall condition with forward elevator.
Cessna 172 Flight Manual
P-power idle
A-ailerons neutral
R-rudder opposite direction of spin
E-elevator forward
What can happen if you enter a spin with an aft CG?
The further aft your longitudinal CG is, the more dangerous a spin can be. An aft CG can lead to a flat spin because the centrifugal force forces the weight to the outside of the spin diminishing elevator control.
What is a stall?
When smooth airflow over a wing is disrupted rapidly. This happens when a wing exceeds the critical angle of attack COA.
A stall can happen at any airspeed and altitude. Many factors such as weight, CG, load factor and speed can change when an airplane reaches it’s COA.
Describe the relationship between Drag and Airspeed.
Picture an XY graph with drag up the x side and airspeed along the Y bottom.
There are two types of drag depicted: parasitic (all the stuff hanging off the airframe: rivets to antennae) and induced (the turbulent air produced behind an airframe or air foil due to AOA)
As airspeed increases, parasitic drag increases and induced drag decreases. The two lines create an X
Best glide speed, or maximum coefficient of lift occurs at the intersection of parasitic and induced drag. Imagine a U shaped line which represents total drag sitting inside the top of the x the two types of drags created. The bottom part of the U is where best glide occurs.
