Air is considered a fluid. Below speeds of Mach 0.3 it is considered an incompressible fluid. Static pressure plus dynamic pressure equals the total pressure which is expressed as:
Ps + Pd = Pt
Pd = 1/2(PV2)
where P = fluid density and V = fluid velocity
Newton's Laws of Motion (paraphrased)
- An object at rest, tends to stay at rest. An object in motion tends to stay in motion.
- Force equals mass times acceleration or F=MA
- Any action results in an equal and opposite reaction.
Bernoulli's Principle (paraphrased)
For an incompressible fluid, an increase in velocity will result in a decrease in pressure.
Magnus Effect (paraphrased)
Creation of dynamic pressure around a spinning cylinder in a fluid. Very similar to the way a wing generates lift.
Coanda Effect (paraphrased)
Fuilds will follow a curved surface. This is what helps to create the boundary layer of air over the wing.
Lift
L = CL(1/2)pV2A
where:
CL = lift coefficient (calculated for each wing design)
p = air density
V = air velocity
A = wing area
Lift force occurs due to the creation of differential pressures above and below the wing. Lower pressure is created above and with the right configuration and speed, enough lifting force is generated to lift the weight of the aircraft.
Climb
The force vectors in a climb reduce the lift force and increase the induced drag. More thrust is needed to maintain a steady climb rate.
Wing Tip Vortices
All wings create wingtip vortices. The differential pressures that are created around the wing, collide at the wing tip and in doing so create a whirling of air that spirals down and away from the wing tips. This is a problem for planes that follow in the wake of other planes, especially during take-offs and landings.
High Lift Devices
High lift devices help create lift by changing the shape or the airflow over a wing. High lift devices are comprised of flaps and slats/slots. Slots are permanent holes thru the wing that allow high pressure air from underneath the wing to the top of the wing, helping to stabilize the boundry layer of air. Slats are slots with movable covers that are actuated under certain flight conditions.
Flaps are divided into four categories:
Plain - attached by a simple hinge, plain flaps change the curvature of the wing only.
Split - also attached by a simple hinge, split flaps drop from beneath the wing and increase drag as well as change the curvature of the wing.
Slotted - have a slot between the flap and the back of the wing.
Fowler - have a complex hinge that extends and lowers the flaps changing the curvature and increasing the area of the wing. Fowler flaps are what is outfitted on the C-150.
Ground Effect
Ground effect is caused by the wing vortices deflecting of of the ground and reducing the induced drag as a result. The effect generally occurs when the aircraft is within one/half wingspans length from the ground.
Stability
Positive Static - plane goes back to original flight path after you release controls.
Negative Static - plane does not go back to original flight path after you release controls.
Positive Dynamic - plane returns to flight path via a series of decreasing oscillations.
Negative Dynamic - diverges from original flight path via a series of increasing oscillations.
Three Axis of Flight
There are three axis of flight that each rotate around the center of gravity of the aircraft.
For an incompressible fluid, an increase in velocity will result in a decrease in pressure.
Magnus Effect (paraphrased)
Creation of dynamic pressure around a spinning cylinder in a fluid. Very similar to the way a wing generates lift.
Coanda Effect (paraphrased)
Fuilds will follow a curved surface. This is what helps to create the boundary layer of air over the wing.
L = CL(1/2)pV2A
where:
CL = lift coefficient (calculated for each wing design)
p = air density
V = air velocity
A = wing area
Lift force occurs due to the creation of differential pressures above and below the wing. Lower pressure is created above and with the right configuration and speed, enough lifting force is generated to lift the weight of the aircraft.
The force vectors in a climb reduce the lift force and increase the induced drag. More thrust is needed to maintain a steady climb rate.
All wings create wingtip vortices. The differential pressures that are created around the wing, collide at the wing tip and in doing so create a whirling of air that spirals down and away from the wing tips. This is a problem for planes that follow in the wake of other planes, especially during take-offs and landings.
High Lift Devices
High lift devices help create lift by changing the shape or the airflow over a wing. High lift devices are comprised of flaps and slats/slots. Slots are permanent holes thru the wing that allow high pressure air from underneath the wing to the top of the wing, helping to stabilize the boundry layer of air. Slats are slots with movable covers that are actuated under certain flight conditions.
Flaps are divided into four categories:
Plain - attached by a simple hinge, plain flaps change the curvature of the wing only.
Split - also attached by a simple hinge, split flaps drop from beneath the wing and increase drag as well as change the curvature of the wing.
Slotted - have a slot between the flap and the back of the wing.
Fowler - have a complex hinge that extends and lowers the flaps changing the curvature and increasing the area of the wing. Fowler flaps are what is outfitted on the C-150.
Ground Effect
Ground effect is caused by the wing vortices deflecting of of the ground and reducing the induced drag as a result. The effect generally occurs when the aircraft is within one/half wingspans length from the ground.
Stability
Positive Static - plane goes back to original flight path after you release controls.
Negative Static - plane does not go back to original flight path after you release controls.
Positive Dynamic - plane returns to flight path via a series of decreasing oscillations.
Negative Dynamic - diverges from original flight path via a series of increasing oscillations.
There are three axis of flight that each rotate around the center of gravity of the aircraft.
- Pitch - lateral
- Roll - longitudinal
- Yaw - vertical
Center of Gravity
All aircraft have a center of gravity (CG) envelope. When the plane is loaded for flight, the center of gravity must fall within the envelope for the plane to fly safely. If your CG is too far forward:
- aircraft nose will be heavy
- needs a longer take-off roll
- higher stall speed
- more stable
- may not be enough elevator to raise nose
If your CG is too far aft:
- aircraft tail will be heavy
- unstable in pitch
- elevator is less effective
Lateral Stability
One way that aircraft maintain lateral stability is by mounting the wings in a dihedral configuration. This means the wings are mounted in a shallow V. This adds lift to the forward wing in a side-slip - correcting the side-slip automatically.
Stalls
Stalls always occur when the critical angle of attack is exceeded, usually around 18 degrees. Usual recovery is to simply lower the nose.
- Power On - usually during take-off
- Power Off - usually during landing
- Accelerated
- Cross-controlled
- Secondary - too aggressive a stall recovery that results in a second stall
Next class: Spins and Flight Operations.
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