Module 2, Lesson 3 - Understanding Lift

Module 2, Lesson 3 - Understanding Lift

Understanding Lift

Air is made up of several gasses but also has the properties and behaviors of fluid, can be compressed and expanded, and while flowing has viscosity and pressure attributes. The Bernoulli Principle is applied when moving air encounters the airfoil.

Multiple Choice

The Bernoulli principle states that an ____________ in the speed of a fluid occurs simultaneously with a ____________ in the pressure exerted by the fluid.

• increase, decrease

• decrease, increase

Multiple Choice

What's the first step that occurs when lift is created?

• Faster - moving air above exerts less pressure on the wing than the slower - moving air below

• Air speeds up, pressure goes down

• Area in which the air is moving narrows or widens, then air speeds up or slows down

Multiple Choice

What's the second step that occurs when lift is created?

• Air speeds up, pressure goes down

• Faster - moving air above exerts less pressure on the wing than the slower - moving air below

• Area in which the air is moving narrows or widens, then air speeds up or slows down

Multiple Choice

What's the third step that occurs when lift is created?

• Area in which the air is moving narrows or widens, then air speeds up or slows down

• Air speeds up, pressure goes down

• Faster - moving air above exerts less pressure on the wing than the slower - moving air below

The tilt of the airfoil is a major contributing factor to lift. When the wing tilts up, lift is increased, and the airfoil creates an incidence angle. Because the airfoil or wing, is tilted, when the airflow accelerates over the airfoil, it pushes on the bottom of the airfoil and is diverted down, creating what is called “downwash”.

Multiple Choice

Which of Newton’s laws is the above an example of?

• Newton's first law of motion. (every object will remain at rest or in uniform motion in a straight line unless compelled to change its state state by the action of an external force.)

• Newton's second law of motion. (the velocity of an object changes when it is subjected to an external force.)

• Newton's third law of motion. ( for every action ( force ) in nature there is an equal and opposite reaction.)

The lift of a wing is proportional to the amount of air diverted down times the downward velocity of that air. 

Lift induced drag is produced when resultant force is up and aft of the center of pressure of the airfoil, causing a divergence of vectors that work against the forward motion of the airfoil. 

Multiple Choice

How can this lift induced drag be overcome?

• By increasing the speed of the airfoil.

• By decreasing the speed of the airfoil.

• By stopping movement of the airfoil.

The tilt of an airfoil in a fixed-wing aircraft is controlled by the elevator position, which increases the Angle of Attack (AOA) and subsequently increases the forces of lift and drag. 

Multiple Select

Check everything that happens if the AOA is increased too much:

• Turbulence occurs

• Aircraft stalls

• Lift increases

• Lift decreases

• Aircraft goes faster

A UA can move through 3-D space with six degrees of freedom.

Multiple Select

What are the axis of rotation of an aircraft? (Select all that apply)

• Longitudinal

• Lateral

• Lateral

Your UAS should be designed to return to a state of equilibrium after a deviation in the flight path and achieve longitudinal stability. When a UAS is flying in a state of equilibrium, the airfoil must create enough lift to equal the weight of the UAS and any downforce generated by the horizontal tail and elevator.

Multiple Choice

More lift

• Aircraft climbs

• Aircraft descends

• Airfoil generates lift

• Systems returns to equilibrium, thrust equals drag

• Aircraft accelerates

Multiple Choice

Forward Velocity

• Aircraft climbs

• Aircraft descends

• Aircraft generates lift

• Systems returns to equilibrium, thrust equals drag

• Aircraft accelerates

Multiple Choice

Less lift

• Aircraft climbs

• Aircraft descends

• Airfoil generates lift

• Systems returns to equilibrium, thrust equals drag

• Aircraft accelerates

Multiple Choice

Forward vector

• Aircraft climbs

• Aircraft descends

• Airfoil generates lift

• Systems returns to equilibrium, thrust equals drag

• Aircraft accelerates

Multiple Choice

Thrust is greater than drag

• Aircraft climbs

• Aircraft descends

• Airfoil generates lift

• Systems returns to equilibrium, thrust equals drag

• Aircraft accelerates

Multiple Choice

Glide Ratio: To maximize the system’s available flight time you must fly at an airspeed that has the ________________ drag and ________________ lift.

• lowest, greatest

• greatest, greatest

• lowest, lowest

• greatest, lowest

Changing the RPM of quadcopter propellers enables the vehicle to pitch, roll and yaw, or move in a 3-D space. 

Multiple Choice

Roll

• The aircraft rotates around the vertical axis, causing the UAS to change direction.

• The aircraft moves laterally and rotates around the longitudinal axis.

• The aircraft tilts up and down.

Multiple Choice

Pitch

• The aircraft rotates around the vertical axis, causing the UAS to change direction.

• The aircraft moves laterally and rotates around the longitudinal axis

• The aircraft tilts up and down.

Multiple Choice

Yaw

• The aircraft rotates around the vertical axis, causing the UAS to change direction.

• The aircraft moves laterally and rotates around the longitudinal axis.

• The aircraft tilts up and down.

At this point, you should have a good understanding of the basic laws of physics and aerodynamics for quadcopters and fixed-wing aircraft. 

Below, fill in the blanks for each type of platform:

Assume a symmetric quadcopter is hovering directly above a stationary point on the ground in a state of equilibrium, meaning the sum of all vertical forces equals zero. To maintain this equilibrium in the three axes, the sum of all moments around each axis is also zero. To move the quadcopter, create a moment around any of the axes. 

Use this image to answer the next question.

Multiple Choice

Increase rpm of F2 and F3

• Moves the quadcopter forward

• Move the quadcopter laterally to the left

Multiple Choice

Increase rpm of F3 and F4

• Moves the quadcopter forward

• Move the quadcopter laterally to the left

M1+M2+M3+M4=0 denotes that the magnitude of moments is equal, but if at any time the equation is not true the resulting moment around the yaw axis will allow your vehicle to change direction, this movement is referred to as yaw.

Multiple Select

What two ways can you make this quad yaw to the right?

• Slightly decrease M1 and M3

• Cease movement of all motors

• Increase M2 and M4

• Slightly increase rpm of all motors