Forces on Aircraft

Question 1

Torque

Answer 1

As blade moves in one direction to create lift, it creates and opposite affect which is countered by the tail rotor to keep the helicopter stabilized. This type of lift is usually dealt with the size/type of airframe

Question 2

Drag

Answer 2

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

Question 3

Weight

Answer 3

the combined 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)

Question 4

Lift

Answer 4

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

Question 5

Factors of Lift

Answer 5

• Speed of the airflow
• Density of the air
• Total area of the segment or airfoil
• Angle of attack (AOA) between the air and the airfoil

Question 6

Angle of Attack (AOA)

Answer 6

The AOA is the angle at which the airfoil meets the oncoming airflow (or vice versa)

Question 7

Parasite Drag

Answer 7

Air resistance on the object as it moves; which increases with the surface area and the speed and is the basis why you want to streamline objects. Parasite drag increases with velocity squared and drag equation. Ex: if speed if doubled, drag is 4x

Question 8

Profile Drag

Answer 8

These correlate to the frictional resistance of the blades as they travel through the air

Question 9

Induced Drag

Answer 9

Result of producing lift. Results from higher angles of attack and generating more downward velocities, which increased your induced drag

Question 10

Bernoulli’s Principle

Answer 10

Describes how water input and water output would remain the same if you were to run water through a garden hose. If any of the areas of the hose were to compress, the water output would increase in order to maintain a constant flow-rate to match the needed water output

Question 11

Venturi Flow

Answer 11

Fluid flow pressure has two components: Static and Dynamic. Static pressure is the constant flow of water through an uncompressed water hose and only measures the flow but not the pressure associated. Dynamic pressure of flow is the component existing as a result of the movement of the air. As water flows through a constriction in a hose, static pressure decreases as velocity increases, which increases dynamic pressure. The sum of these two pressures is total pressure

Question 12

Solidarity Ratio (Thrust)

Answer 12

Ratio of the total rotor blade area, which is the combined area of all the main rotor blades, to the total rotor disk area; this ratio is used to measure the potential for a rotor system to provide thrust and lift

Question 13

Airfoil Terminology

Answer 13

Blade span—the length of the rotor blade from center
of rotation to tip of the blade.
• Chord line—a straight line intersecting leading and
trailing edges of the airfoil.
• Chord—the length of the chord line from leading edge
to trailing edge; it is the characteristic longitudinal
dimension of the airfoil section.
• Mean camber line—a line drawn halfway between the
upper and lower surfaces of the airfoil.

Question 14

Airfoil

Answer 14

Any surface that can create more lift than drag when passing through the air at an angle. They are also used for stability (fin), control (elevator), and thrust (propeller or rotor)

Question 15

Flightpath Velocity

Answer 15

the speed and direction of
the airfoil passing through the air. For airfoils on
an airplane, the flightpath velocity is equal to true
airspeed (TAS). For helicopter rotor blades, flightpath
velocity 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 increases outward towards the tip of the blade
during rotation.

Question 16

Relative Wind

Answer 16

defined as the airflow relative to
an airfoil and is created by movement of an airfoil
through the air. This is rotational relative wind for
rotary-wing aircraft and is covered in detail later. As
an induced airflow may modify flightpath velocity,
relative wind experienced by the airfoil may not be
exactly opposite its direction of travel.

Question 17

Trailing Edge

Answer 17

the rearmost edge of an airfoil.

Question 18

Induced Flow

Answer 18

the downward flow of air through the

rotor disk.

Question 19

Resultant Relative Wind

Answer 19

relative wind modified by induced flow.

Question 20

Two Parts of wind passing a rotor blade

Answer 20

Horizontal part—caused by the blades turning
plus movement of the helicopter through the air

• Vertical part—caused by the air being forced down
through the rotor blades plus any movement of the air
relative to the blades caused by the helicopter climbing
or descending

Question 21

Rotor and Hub Assembly

Answer 21

• Hub—on the mast is the center point and attaching
point for the root of the blade
• Tip—the farthest outboard section of the rotor blade
• Root—the inner end of the blade and is the point that
attaches to the hub
• Twist—the change in blade incidence from the root
to the outer blade

Question 22

Four Types of Friction (Newton’s First Law - Law of Inertia)

Answer 22

Sliding, Kinetic, Friction - results when the surface of one object slides along the surface of another object
Fluid Friction - is the resistance of an object when moved through either air or water (bird or fish)
Rolling Friction - it’s the same result as sliding friction, except the object must be rolling across a surface
Static Friction - it’s what keeps and object from moving unless an external force is applied

Question 23

Newton’s Second Law of Motion

Answer 23

when a body is acted on by a constant force, it’s resulting acceleration is inversely proportional to the mass of the body and directly proportional to the applied force