Ch. 2, 3, & 4 Aerodynamics; Rotor Blade; Helicopter Basics Flashcards
What are 3 characteristics of an airfoil?
- Rounded leading edge: ensures smooth flow
- Sharp trailing edge: keeps wake behind airfoil small
- Specific shaping: reduces turbulence & separation of the layer of air immediately around the surface of the wing (this layer is aka boundary layer)
Resultants are two _____ combined.
Vectors
Vectors have both a magnitude (size) & direction
Ex. resultant airflow, resultant relative wind
What is induced velocity?
The speed of air being pushed down by the rotor
Don’t confuse this with induced flow.
Define induced flow
The mass of air accelerated downwards by the rotor.
Aka downwash
Induced flow is at its greatest during what condition?
At a hover with no wind.
This is because there is no horizontal air flow affecting the rotor disc.
Induced flow _____ (increases/decreases) as the AOA of the rotor blades increases.
Increases
Resultant airflow is made up of what?
The horizontal component from blade rotation & vertical component from induced velocity.
When the AOA becomes too high, about _____ to _____ degrees for most airfoils, the wing produces less useful lift because the airflow has separated from flowing smoothly over the top surface of the airfoil.
14-15 degrees
The airfoil is said to be stalled & the airflow on the top surface starts to separate away from the skin of the wing.
What is coefficient of lift?
A measure of the amount of lift a particular airfoil shape will produce.
As the airflow meets the segment at steeper & steeper angles, the blade segment produces more & more lift until it reaches the stall AOA. Lift produced decreases rapidly beyond the stall AOA.
What is the spar on a rotor blade?
The main longitudinal bean of an airfoil.
Many helicopters’ rotor blades are attached to the hub at a small positive angle. What is this called?
Pre-coning
This is built into the rotor hub to reduce stress on the blades & the hub
The _____ degree position on the blade has the minimum blade pitch angle and AOA.
90 degrees
Aka advancing side and it’s descending towards the lowest position at the front-“falling down through air”
The blade on the retreating side (270 degrees) is at a very high pitch angle & AOA & is climbing towards the highest position at the back of the disk.
As the blade flaps up & down, the blade _____ moves closer to & further away from the center of the blade.
Center of gravity
The _____ requires the blade to speed up as the CG moves towards the center of the hub & slow down as it moves out.
Law of Conservation of Angular Momentum
The momentum of the rotating blades can’t change so the velocity has to change to compensate for the change in location of the mass.
What function does the swashplate serve?
Transmits the commands of the pilot’s inputs to the rotor blades.
