# Answers - Aerodynamics, Assembly and Rigging

## Fill in the Blanks

1. Force, dyne
2. Hg or inches of mercury, barometer
3. Increases, increases, increases
4. Inversely, directly
5. First, inertia
6. Increase
7. upper surface
8. AOA or angle of attack
9. Longitudinal
10. Fluid, pressure
11. High, low, outward, vortex
12. Static
13. Ailerons, elevator, rudder
14. Free‐spinning, upward
15. Down
16. Left, all
17. Dissymmetry
18. Clutch
19. Right, left
20. “Go” and “no‐go”
22. Turnbuckle, left‐hand
23. Position or angle, wing tips
24. Dihedral, incidence
25. Double‐twist, single‐wire

## True or False

1. true
2. true
3. false; faster at higher altitude
4. false; inversely
5. true
6. true
7. false; lift to drag ratio
8. false; drag, not weight
9. true
10. false; center of gravity
11. false; vertical axis
12. true
13. false; wing fences
14. true
15. true
16. false weight added fore or aft of hinges
17. false; manufacturer provides instructions for fabrication
18. true
19. false; issued by FAA
20. false; flexible and used for pulleys
21. false; not used
22. true
23. true
24. true
25. false; never re‐used

## Knowledge Application

1. It is a substance that has the ability to flow or assume the shape of the container in which it is enclosed.

2. Atmospheric pressure is the force exerted against the earth’s surface by the weight of the air above that surface. It is measured using a barometer in “Hg.

3. Density varies in direct proportion with pressure and inversely with temperature.

4. Absolute ‐ the weight of water vapor in a unit volume of air;
Relative ‐ the ratio (%) of the moisture actually in the air to the moisture it would hold if it were saturated at the same temperature and pressure.

5. The law of action and reaction states that for every action (force) there is an equal and opposite reaction (force).

6. The top part of the wing has a greater curvature than the bottom. This requires the air above the wing to travel farther than the bottom. The air therefore, has a greater velocity and a decreased pressure. The pressure differential creates lift. The high pressure on the bottom of the wing tries to equalize by rising to the low pressure area.

7. There is an area of negative pressure behind the resultant force when AOA is 0°. As AOA increases towards its critical point, the resultant force moves forward. Once critical angle is reached the resultant force falls rapidly until the wing stalls.

8. Drag is the resistance of the air to an object moving through it. There are 3 forms of drag: Parasite drag occurs when an exposed object offers resistance to the air. Profile drag is the parasite drag of the airfoil. Induced drag occurs as lift is created and the air flow spillage over the wing tip creates a vortex. This vortex constitutes induced drag.

9. Control is the pilot action of moving the flight controls, providing the aerodynamic force that induces the aircraft to follow a desired flight path. Controllability means that the aircraft responds easily and promptly to movement of the flight controls.

10. Sharp disturbances generate shock waves that affect lift and drag as well as airflow downstream of the shockwave. A cone of pressure which moves outward and rearward from the shockwave. Also, the energy of the object moving excites the chemical bonds of the oxygen and nitrogen.

11. Each blade can move back and forth in plane, lead and lag; and flap up and down through a hinge independent of the other blades.

12. As the engine turns the main rotor in a counterclockwise direction, the helicopter fuselage tends to turn the opposite direction. The action of the main rotor blade creates an equal and opposite force that turns the fuselage clockwise.

13. It is a mechanical connection between the collective lever and engine throttle. When the collective lever is raised, power increases and when lowered, power is decreased. This system maintains RPM close to the desired value.

14. Loose elevator linkage at swash plate horn, loose elevator, or tail rotor balance and track.

15. The gas producer (compressor turbine) is essentially disconnected from the power turbine. When the engine is started, there is little resistance from the power turbine allowing the gas turbine to accelerate to normal idle without the transmission load dragging it down.

16. Pulleys are used to guide cables and change cable direction. Pulley guards prevent jamming or the cable slipping off when slackened due to temperature changes.

17. Positioning the flight controls in the neutral position and locking them in place. Adjusting the cable tension and maintaining control surface neutral. Adjusting the control stops to the aircraft manufacturer’s specifications.

18. To make minor adjustments in cable length and for adjusting cable tension.

19. Trim tab systems. As the trim tab control moves, the cable drum winds or unwinds to actuate the trim tab cables.

20. Annual, 100‐hour inspection, progressive.

## Multiple Choice

1. a
Air is considered a fluid because it fits the definition of a substance that has the ability to flow or assume the shape of the container in which it is enclosed. If the container is heated, pressure increases; if cooled, the pressure decreases

2. c
At sea level, when the average atmospheric pressure is 14.7 psi, the barometric pressure is 29.92 "Hg, and the metric measurement is 1013.25 mb.

3. c
If the wing has a high fineness ratio, it is a very thin wing. A thick wing has a low fineness ratio. A wing with a high fineness ratio produces a large amount of skin friction. A wing with a low fineness ratio produces a large amount of turbulence. The best wing is a compromise between these two extremes to hold both turbulence and skin friction to a minimum.

4. c
When the AOA increases to the angle of maximum lift, the burble point is reached. This is known as the critical angle.

5. b
Controllability is the quality of the response of an aircraft to the pilot’s commands while maneuvering the aircraft.

6. c
The axes of an aircraft can be considered as imaginary axles around which the aircraft turns like a wheel. At the center, where all three axes intersect, each is perpendicular to the other two. The axis that extends lengthwise through the fuselage from the nose to the tail is called the longitudinal axis.

7. c
A Dutch Roll is an aircraft motion consisting of an out-of-phase combination of yaw and roll. Dutch roll stability can be artificially increased by the installation of a yaw damper.

8. b
Winglets are the near-vertical extension of the wingtip that reduces the aerodynamic drag associated with vortices that develop at the wingtips as the airplane moves through the air. By reducing the induced drag at the tips of the wings, fuel consumption goes down and range is extended.

9. a
High-speed aerodynamics, often called compressible aerodynamics, is a special branch of study of aeronautics. It is utilized by aircraft designers when designing aircraft capable of speeds approaching Mach 1 and above.

10. b
Supersonic conditions occur for numbers greater than Mach 1, but less then Mach 3 (760–2,280 mph).

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