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Helicopter Flying Handbook > Aerodynamics of Flight (Chapter Two) > Flashcards

Aerodynamics of Flight (Chapter Two) Flashcards

1
Q

What are the four forces acting on the aircraft?

A

Thrust, Drag, Weight, & Lift

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2
Q

What is Thrust?

A

The forward force produced by the power plant/ propeller or rotor. It opposes and overcomes the force of drag.

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3
Q

What is Drag?

A

A rearward, retarding force caused by disruption of airflow by the wing, rotor, fuselage, and other protruding objects, Drag opposes thrust and acts rearward parallel to the relative wind.

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4
Q

What is Weight?

A

The combinded load of the aircraft itself, the crew, the fuel, and the cargo or baggage. Weight pulls the aircraft downward because of the force of gravity. It opposes lift and acts vertically downward through the aircraft’s center of gravity (CG).

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5
Q

What is Lift?

A

Opposes the downward force of weight, is produced by the dynamic effect of the air acting on the airfoil, and acts perpendicular to the flightpath through the center of lift.

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6
Q

What is Angle of Attack?

A

The angle at which the airfoil meets the oncoming airflow. In the case of a helicopter, the object is the rotor blade (airfoil) and the fluid is the air. Lift is produced when a mass of air is deflectedm and it always acts perpendicular to the resultant wind.

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7
Q

In a symmetrical airfoil will it produce lift at a zero angle of attack?

A

No, it must have positive angle of attack.

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8
Q

What is Bernoulli’s Principle?

A

Describes the realationship between internal fluid pressure and fluid velocity. It is a statement of the law of conservation of energy and helps explain why an airfoil develops an aerodynamic force. The example is running water through a garden hose.

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9
Q

What does the concept of conservation of energy state?

A

It states energy cannot be created or destroyed and the amount of energy entering a stystem must also exit.

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10
Q

What is Newton’s Third Law of Motion?

A

For every action there is an equal and opposite reaction.

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11
Q

How is lift generated?

A

When an object changes the direciton of flow of a fluid or when the fluid is forced to move by the object passing through it.

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12
Q

What is Newton’s First Law of Motion?

A

Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

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13
Q

What is a load factor?

A

It’s the actual load on the roto blades at any time, divided by the normal load or gross weight.

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14
Q

How is Lift generated?

A

By the rotation of the main rotor system. In a helicopter thrust can be forward, rearward, sideward, or vertical.

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15
Q

What are the three types of drag?

A

Profile, Induced, & Parasite

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16
Q

What is Profile Drag?

A

Develops from the frictional resistance of the blades passing through the air. It does not change significantly with the airfoil’s AOA, but increases moderately when airspeed increases. Profile drag consists of form drag and skin friciton.

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17
Q

What is Form Drag?

A

Form Drag results from the turbulent wake caused by the separation of airflow from the surface of a structure. The amount of drag is related to both the size and shape of the structure that protrudes into the relative wind.

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18
Q

What is Skin Friction?

A

Skin Friction is caused by surface roughness. Even though the surface appears smooth, it may be quite rough when viewed under a microscope. A thin layer of air clings to the rough surface and creates small eddies that contribute to drag.

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19
Q

How is Induced Drag generated?

A

Induced Drag is generated by the airflow circulation around the rotor blade as it creates lift.

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20
Q

What is Induced Drag?

A

Drag caused by the same factors that produce lift; its amount varies inversely with airspeed. As airpseed decreases, the angle of attack must increas, in turn increasing induced drag.

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21
Q

What is Parasite Drag?

A

Is present any time the helicopter is moving through the air. This type of drag increases with airspeed. Non-lifting components of the helicopter, such as the cabin, rotor mast, tail, and landing gear, contrbute to parasite drag.

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22
Q

What is an Airfoil?

A

An airfoil is any surface producing more lift than drag when passing through the air at a suitable angle. Airfoils are most often associated with prodcution of lift. Airfoils are also used for stability (fin), control (elevator), and thrust or proplusion (propeller or rotor).

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23
Q

What is blade span?

A

The lenght of the rotor blade from center of rotation to tip of the blade.

24
Q

What is Chord line?

A

A striaght line intersecting leading and trailing edges of the airfoil.

25
Q

What is Chord?

A

The length of the chord line from leading edge to trailing edge; it is the characteristic longitudinal dimesion of the airfoil section.

26
Q

What is Mean camber line?

A

a line drawn halfway between the upper and lower surfaces of the airfoil.

27
Q

What is flightpath velocity?

A

the speed and direciton of the airfoil passing through the air. On helicopters is equal to rotational velocity, plus or minus a component of directional airspeed. The rotational velocity of the rotor blade is lowest closer to the hub and increaes outward towards the tip of the blade during rotation.

28
Q

What is Relative wind?

A

Defined as the airflow relative to an airfoil and is created by the movement of an airfoil through the air. Relative wind moves in a parallel but opposite direction to movement of the airfoil.

29
Q

What is Resultant relative wind?

A

Relative wind modified by induced flow.

30
Q

What is Induced Flow?

A

The downward flow of air through the rotor disk.

31
Q

What is Angle of Incidence?

A

The angle between the chord line of a blade and rotor hub. It is usually referred to as blade pitch angle. For fixed airfoils, such as vertical fins or elevators, angle of incidence is the angle between the chord line of the airfoil and a selected reference plan of the helicopter.

32
Q

What is Center of Pressure?

A

The point along the chord line of an airfoil through which all aerodynmic forces are considered to act.

33
Q

What are the two types of airfoils?

A

Symmetrical and Nonsymmetical.

34
Q

What is a symmetrical Airfoil?

A

Is distingusihed by having identical upper and lower surfaces. The mean camber lind and the chord line are the same on a symmetrical airfoil, and it produces no lift at zero AOA.

35
Q

What is a Nonsymmetrical Airfoil?

A

Has different upper and lower surfaces, with greater curvature of the airfoil above the chord line than below. The mean camber line and the chord line are different. Also, can produce useful lift at zero AOA.

36
Q

What is Blade Twist?

A

Because of lift differential due to differing rotational relative wind values along the blade, the blade should be designed with a twist to alleviate internal balde stress and distrubute the lifting force more evenly along the blade. Blade twist provides higher pitch angles at the root where velocity is low and lower pitch angles nearer the tip where velocity is higher.

The change in blade incidence from the root to the outer blade.

37
Q

What is a hub?

A

On the mast is the center point and attaching point for the root of the blade.

38
Q

What is a Blade Root?

A

The inner end of the blade and is the point that attaches to the hub.

39
Q

What are the two rotor blade angles?

A

Angle of Attack and Angle of Incidence.

40
Q

What is In ground Effect?

A

Is the increased efficiency of the rotor system caused by interference of the airflow when near the ground. The air pressure or density is increased which acts to decrease the downward velocity of air. Ground permits relative wind to be more horizonatal, lift vector to be more vertical, and induced drag to be reduced. These conditions allow the rotor system to be more efficient.

41
Q

How do you achieve maximum in gorund effect?

A

Maximum gorund effect is achieved when hovering over smooth hard surfaces. When hovering over surdfaces as tall grass, trees, bushes, rough terrain, and water maximum gorund effect is reduced.

42
Q

What is Out of Ground Effect?

A

The benefit of placing the helicopter near the ground is lost above IGE altitude. Above this altitude, the power required to hover remains nearly constant, given similar conditions. Induced flow velocity is increased, resulting in decrease in AOA and a decrease in lift.

43
Q

What is Translating Tendency (Drift)?

A

During hover flight, a single main rotor helicopter tends to move in the direction of the tail rotor thrust. This lateral (or sideward) movement is called translating tendency.

44
Q

How do we compensate for Translating Tendency?

A
  • The Main transmission is mounted at a slight angle to the left so that the rotor mast has a built in tilt to oppose the tail rotor thrust.
  • Flight Controls can be rigged
  • The transmission is mounted so the rotor shaft is vertical with respect to the fuselage, the helicopter “hangs” left skid low in the hover.
  • The helicopter makes small angles with the wind when the rotors are level and the slip ball is in the middle. This is called inherent sideslip. For some larger helicopters, the vertical fin or stablilzer is often designed with the tail rotor mounted on them to correct this side slip and to eliminate some of the tilting at a hover.
45
Q

What is Pendualr Action?

A

Since the fuselagfe of the helicopter, with a single main rotor, is suspended from a single point and has considerable mass, it is free to oscillate either longitudinally or laterally in the same way as a pendulum.

46
Q

What is coning?

A

The upward sweep of the rotor blade as a result of lift and centrifugal force.

47
Q

What is Centrifugal Force?

A

The apparent force that an object moving along a ciruclar path exerts on the body constraining the object and that acts outwardly away from the center of rotation.

48
Q

What is Coriolis Effect (Law of Concervartiotn of Angular Momentum)?

A

States that the value of angular momentum of a rotating object does not change unless an external force is applied. Angular momentum is the moment of inertia multiplied y the speed of rotation. Example is the figure skater. Slow with arms out and as bring them in she speeds up.

49
Q

What does the adavanicing blade do?

A

As the relative wind speed of the advancing blade increases, the blade gains lift and begins to flap up. It reaches its maximum upflap velocity at the 3 o’clock position where the wind velocity is the greatest.

50
Q

What does the retreating blade do?

A

As relative wind speed of the retreating balde decreases, the blade loses lift and begins to flap down. It reaches its maximum downflap velocity at the 9 o’clock postion, where wind velocity is the least.

51
Q

What is Dissymmetry of Lift?

A

Is the differential (unequal) lift between the advancing and retreating halves of the rotor disk caused by the different wind flow velocity across each half.

52
Q

How do we compensate for dissymetry of lift?

A

With blade flapping.

53
Q

What is Translational Lift?

A

Improved rotor effiency resulting from directional flight. The efficiency of the hovering rotor system is greatly improved with each knot of incoming wind gained by horizontal movement of the aircraft or surface wind.

54
Q

What is Effective Translational Lift (ETL)?

A

While transitioning to forward flight at about 16 to 25 knots, the helicopter goes through effective trsnaltionsl lift (ETL). The rotor system becomes more efficient as forward airspeed increases.

55
Q

What is Translational Thrust?

A

Occures when the tail rotor becomes more aerodyamically efficient during the transition from hover to forward flight. As the tail rotor works in progressivel less turbulent air, this improved efficiency profduces more antitorque thrust, causing the nose of the aircraft to yaw left and forces the pilot to apply right pedal in response.

56
Q

What is Transverse Flow effect?

A

As the helicopter aaccelerates in forward flight, induced flow drops to near zero at the forward disk area and increases at the after disk area. These defferences in lift between the fore and aft portions of the rotor disk are called transerse flow effect.

57
Q

What are the three regions of the rotor disk?

A
  • Stall region 25%
  • Driving region 45%
  • Driven region 30%

Helicopter Flying Handbook (7 decks)

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