Aircraft in Motion
Explain the four forces when an airplane is straight and level unaccelerated flight.
The sum of the forward forces equal the backwards forces and the sum of the lifting forces equal the forces contributing to weight.
How do Newton's Third Law and Bernoulli's Principle work together to explain lift?
Lower pressure above the wing and the upward reaction force caused by air being pushed downward combine to help the wing develop lift.
Why is it beneficial to minimize drag? Name 4 reasons.
Higher airspeed, faster acceleration, greater range, and better fuel economy.
How does a pilot correct for left turning tendencies?
What is CG?
CG is the point along its longitudinal (lengthwise) axis where the aircraft would balance if it were placed on a fulcrum.
What is a vector? What do they represent?
A quantity with both direction an magnitude. Vectors can be used to represent lift, thrust, weight, and drag.
Why is the Equal Transit Time or Longer Path theory incorrect?
The essential problem with this theory is that it is based on the false idea that molecules of air arriving at the leading edge (front) of the wing at the same time must also arrive at the trailing edge of the wing at the same time.
What is parasitic drag?
What are the three types?
When is it most prominent?
Drag caused by any surface of the aircraft that deflects of interferes with the smooth airflow around the plane.
Form drag, interference drag, and skin friction
Most prominent at high speeds.
What are the five stages of a turbine engine?
Why, in terms of thrust, is a turbine more efficient than a propeller?
intake, compression, combustion, turbine rotation, and exhaust
Although jet engines seem more complicated, they perform the task of generating thrust more simply since the thrust comes directly from the engine. A propeller driven by a piston engine is using the combusted fuel to drive pistons back and forth, which turn a crankshaft, which is connected to a propeller, introducing complexities and inefficiencies at each stage.
Define reference datum, station, arm, and moment.
Reference datum - an arbitrarily chosen point from which all other locations are measured in inches fore (forward) or aft (behind); considered “station zero”
Station - a location along an aircraft’s longitudinal axis (e.g. the front seat station, the fuel tank station)
Arm - the distance between the reference datum and a given station, measured in inches
Moment - the product of weight (measured in pounds) and arm (measured in inches); a measure of the tendency of a mass to create a rotating force around a fixed point
Which Newtonian law dictates the speed at which an aircraft would move in the direction of an unbalanced force?
Newton's Second Law
F=ma
The greater the unbalanced force, the faster the plane would move in the direction of the imbalance.
What are the five factors that affect lift production?
Which can a pilot control? How?
angle of attack, airspeed, camber, wing area, and air density
What is induced drag?
When is it most prominent?
At the tip of the wing, high-pressure air underneath the wing tries to move around the end of the wing to the low-pressure air on top of the wing. This creates a swirling vortex of air at the wingtip. The energy needed to move the air in the vortex is taken from the movement of the airplane, creating induced drag.
Most prominent at low airspeeds and high angles of attack.
How do designers and engineers overcome thrust production variation along a propeller blade?
They add a twist to the propeller blade, vary the camber, and vary the size of the blade along its length.
How might weight and balance change during flight?
Fuel burn, moving passengers, moving baggage
Define each of the four forces.
Lift is the force caused by airflow around the wings, supporting the aircraft in flight.
Thrust is the force caused by the engine, propelling the airplane forward.
Weight is the force pulling the airplane towards the center of the earth.
Drag is the force trying to slow the airplane down.
How is the coefficient of lift created? When is the coefficient of lift true?
It is based on the shape of the airfoil and determined through experimentation in a wind tunnel.
The coefficient of lift is constant for each individual wing shape, but only at a constant angle of attack.
What is ground effect? How does it affect take off and landing?
Ground effect, which makes the airplane seem like it’s floating on a cushion of air when near the ground, is an example of how reducing the amount of induced drag changes aircraft performance. As the airplane gets close to the ground, the vortices produced at the wingtips strike the ground, which interferes with the swirling motion and reduces the amount of induced drag produced.
Take off - ground effect may cause early lift off
Landing - ground effect may float the plane down the runway and delay landing.
What are the four turning tendencies?
Corkscrew Effect, Torque Reaction, P-Factor, and Gyroscopic Force.
If an aircraft is overloaded (over weight limitations), how will it perform?
Need to travel faster for take off - require more power, greater fuel burn, more fuel. If those conditions don't exist or impossible, an airplane may overrun the runway.
State each of Newton's laws of motion and describe an impact on aviation.
1. Newton’s First Law: “An object at rest stays at rest and an object in motion stays in motion unless acted on by an outside force.”
For an aircraft flying at a
constant altitude and at a constant airspeed, lift and weight balance one another and so does thrust and drag. In
this scenario, there is no net force on the airplane (or acceleration) and it travels at a constant velocity in a straight line. If the pilot increases the engine power, thrust and drag are no longer in balance and the aircraft will accelerate and increase in velocity.
2. Newton’s Second Law: “When an object is acted upon by a force, its resulting acceleration is inversely proportional to the body’s mass and directly proportional to the force acted upon the object.” Impact on Aviation: One of the effects of the second law is that large aircraft require large engines. It also means that light aircraft are more affected by turbulence than heavier ones.
3. Newton’s Third Law: “For every action, there is an equal and opposite reaction.”
Impact on aviation: It helps to explain the generation of lift for a rocket. Hot exhaust gases are produced inside the rocket which are accelerated as they pass through the engine's nozzle. The accelerated hot gases produce a thrust that propels the rocket in the opposite direction.
How does weight affect lift?
Weight does not affect lift. The magnitude of lift must be greater than the magnitude of weight for it to fly.
Why is it important to determine L/Dmax? What scenarios is it especially useful to know L/Dmax?
The ratio of lift to drag (L/D) is the measure of how efficiently an aircraft produces lift. It helps us find (at ) the most amount of lift for the least amount of drag. is useful in determining the angle of attack at which to fly an aircraft in order to get the greatest range for the least amount of energy. This is useful for conserving fuel or gaining distance in an engine-out scenario.
Describe some advantages and disadvantages of a fixed pitch propeller.
Advantages - Less mechanical parts - easier to maintain
Disadvantages - not always efficient because the pitch cannot be adjusted.
How does an aircraft that is loaded with a CG aft of its rear CG limit?
When the CG is aft of limits, the aircraft: will fly faster, will stall at a lower airspeed, and will tend to pitch nose up, which could make it impossible to recover from a stall.
a “rapid decrease in lift caused by the separation of airflow from the wing’s surface, brought on by exceeding the critical angle of attack. A stall can occur at any pitch attitude or airspeed.”
How can manufacturers mitigate the onset and/or effects of a an aerodynamic stall?
Wing washout, wing planform, wing camber, and vortex generators.