CADH

Is the overall pressure acting at a point due to air

Total Pressure Formula

The air pressure due to the weight of the atmosphere, and acts equally in all directions.

Is caused by the motion of an airmass relative to an object and the “Density” of the air mass.

States that total pressure is combined of both static and dynamic pressure and total pressure will remain “constant” unless energy is added

A Specially shaped body designed to accelerate air, reduce pressure and so create lift when placed in an airflow.

Is a straight line drawn from the centre of a curvature to the “Leading edge” of an aerofoil to the centre of the “Trailing edge” of an aerofoil

Is a line drawn “Half way” between the upper and lower surfaces of an aerofoil.

Is the “single” airflow presented to an aerofoil after adding up all the smaller airflow components

Is the “smaller” angle between the chord line and the relative airflow

Is a point along the chord line of an aerofoil through which the total of all aerodynamic forces is said to act

Is the position on the chord line of an aerofoil in which gravity is said to act

Is the single resultant force of the pressure acting on an aerofoil and, as a vector, can be broken down into various component vectors

Is the component of total reaction that acts at “right angles” to the relative airflow

Is the component of total reaction which acts “parallel” to the relative airflow.

Is the axis about which the helicopter disc is said to rotate

Is at a right angle to the axis of rotation. It is the plane passing through the rotor hub, and parallel to the plane in which the blades rotate.

Is the path of the blade tips during rotation.

Is the area contained within the Tip Path Plane. The area actually swept by the rotor blades.

Is the Gross Weight of the helicopter divided by the Disc Area

Is the Gross Weight of the helicopter divided by the Total Blade Area

Is the ratio of the total blade area to the disc area

Is the component of Relative Airflow parallel to the plane of rotation, caused by the rotation of the blades.

Is the component of Relative Airflow at “right angles” to the plane of rotation. It occurs when air is being accelerated “down through the disc”

Rotational and induced airflow

Is the acute angle between Plane of Rotation and the Chord Line

Is the acute angle between Relative Airflow (RAF) and the Chord Line

Is the angle between Relative Airflow (RAF) and the rotational flow

Be sure to understand how to recreate this for different phases of flight

Is the component of the Total Reaction Force which acts along the axis of rotation.

Is the component of Total Reaction which acts in the plane of rotation, “parallel” to the rotational flow.

A

C

D

A

B

B

All bodies at rest or in uniform motion along a straight line will continue in that state unless acted upon by an outside force.

Force is proportional to Mass x Acceleration

For every reaction there is an equal and opposite reaction

Speed and direction

The rate of change of velocity

A state of zero acceleration

Newton’s first law states that bodies in motion travel along a straight line, and that a force is required when this straight line is to be changed to a curve. This force is called Centripital Force.

Is defined as that which has “magnitude” and “direction”

The moment of a force about a given point is the product of that force and the “right-angle distance from that point to the “line of action” of that force.

A couple consists of “two equal, parallel and opposite forces”

Pressure energy can be related to “atmospheric pressure”

Energy resulting from motion

The greater the atmospheric pressure (the number of air molecules per volume) the greater the air density.

Air Temperature and Air Density are “inversely” proportional

1) With altitude, pressure falls off, which reduces density 2) With altitude, temperature falls off, which tends to increase density Note: generally the pressure effect is by far the stronger influence, so we tend to say as altitude increases, density increases, but at a slightly reduced rate because of the opposing temperature factor.

AIr with water Vapor (humid air), will have greater mass than “dry air”. This will have an effect on air density.

The standard used for the “average days” atmospheric values. 1) Sea Level = 1013.2 hPa or 29.92 in/Hg, or 14.7psi 2) Sea Level temperature is 15 degrees Celsius or 59 degrees Fahrenheit 3) Temperature lapse rate is 2 degrees Celsius per 1,000ft of altitude up to 36,090 feet

A situation where the sea level pressure is less than 1013.2 hPA. So the air is less dense at sea level and the helicopter will perform as though it as a higher altitude (not as well).

If the temperature at any given “pressure altitude” is warmer than average this leads to a “High density altitude” because the reduced pressure will cause the helicopter to perform as if it is at greater altitude. Can act in reverse as well, “Low density altitude” and colder temps will cause increased air pressure. Leading to better than average helicopter performance.

The straight line axis between the root of the blade and its tip about which the blade can alter its angle.

The movement of the blade about its feathering axis (which results in blade angle, or pitch angle, changes)

Lift = Coefficient of Lift x 1/2 x Dynamic Energy x Surface Area of aerofoil

The angle of attack is the angle between the Chord Line of an aerofoil and the Relative Air Flow (RAF)

The Centre of Gravity of an object is defined as the point at which all of the weight forces are said to act

The Centre of Pressure is defined as the point (on the chord line) through which all aerodynamic forces are said to act

The point on the chord line about which no change in pitching moments is felt with changes in the angle of attack

Are considered the parts of the helicopter that do not contribute to lift. e.g. the cabin, tail boom, skids etc.

Is made up of “Form Drag” and “Skin Friction”

Can only be found in a region of decreasing air pressure (i.e leading edge of an airfoil). And is consisting of very thin layers of air molecules.

Consists of revolving and disturbed air molecules - produces more skin friction drag than the laminar boundary layer

Is the point where the laminar boundary layer changes to the turbulent boundary layer

Reynolds number relates the “inertial forces” to the “viscous (fluid) forces” in a flow, and is affected primarily by airspeed

Is the point where the turbulent boundary layer thickens and separates from the airfoil and where the “wake” commences

1) Surface Roughness - The rougher the surface, the more the skin friction (hence why aircraft components are as smooth as possible) 2) Shape of the Airfoil - The further back the lint of maximum thickness, the less skin friction (ignoring airspeed) 3) Airspeed - The higher the speed of air past a blade, the greater the skin friction drag.

Induced drag is a scenario where the “net downwash” component affects the relative airflow. An increase in the lift coefficient (AoA), will increase the induced drag; A decrease in the lift coefficient (AoA), will decrease the induced drag.

Is the circular motion of air around the tip of a blade caused by air movement from a high pressure region to a lower pressure region. Tip Vortices add to downwash behind the blade and an increase in the amount of induced drag.

Since induced drag is proportional to induced flow, and since induced flow decreases as airspeed increases (less air flow through the disc), induced drag decreases with an increase in airspeed

Is the ratio of the blades “span” to its “chord”

1) Wash out 2) Tip Design

The structural design of a blade that reduces the lift coefficient at the blade tips. It’s achieved by reducing the “blade angle” near the tips, hence a reduction in the AoA near the blade tips as opposed to the root of the blades. The effect is that it reduces induced flow through the disc.

Blade designers reduce the blades camber and/or chord toward the tip and taper the blade towards the tip in an attempt to reduce induced flow/drag

Is the angular difference between Lift and Total Reaction, and is determined by the L/D ratio

A

B

B

B

A

D

B

C

D

A

A

B

C

The resultant action or deflection of a spinning object when a force is applied to this object. This action occurs approx. 90 degrees in the direction of rotation from the point where the force is applied.

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

At high forward speed, the retreating blade stalls because of a high AoA and slow relative wind speed. Results are a nose pitch up, high vibration and a rolling tendency to the left (for counterclockwise rotor system)

Is a situation during transitioning a helicopter due to both dissymmetry of lift and transverse flow.

Is the result of improved rotor efficiency resulting from directional flight

Is a situation where as the rotor blades become more efficient as forward airspeed increases, the rotor disk essentially outruns its old vortices and operates within relatively undisturbed air. Generally between 16-24 knots.

Translational thrust occurs when the tail rotor becomes more aerodynamically efficient during the transition from hover to forward flight