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 Titel: Principe van het vleugelprofiel.
BerichtGeplaatst: 01 Feb 2010, 09:06 
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Geregistreerd: 15 Mei 2009, 12:53
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Afbeelding
Spanwijdte vleugel

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Verschil in slankheid

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Vleugelvormen

Een voorbeeld van een vliegtuig met een vleugel met zeer grote slankheid is het zweefvliegtuig. Door gebruik van composiet materialen is het tegenwoordig veel gemakkelijker om een dergelijk vliegtuig te bouwen. Ook de GlobalFlyer, het toestel waarmee rond de wereld vloog, is een goed voorbeeld van een vliegtuig met zeer grote aspect ratio.

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Luchtwervel of vortex zichtbaar gemaakt met gekleurde rook

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Doorsnede van een vleugelprofiel

_________________
Greetzzz,

Yvin. :ugeek:

Afbeelding


PH-9S8



Afbeelding



Afbeelding

Skype Me™! Afbeelding


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 Titel: Principles of Flight
BerichtGeplaatst: 21 Feb 2010, 15:07 
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Principles of Flight


Here we will give an explination of some of the aeronautical terms used when talking about the 'Principles of Flight' and explain in brief how a wing works.

Aeronautical Terms

Angle of attack.


The measured angle between the airfoil / wing chord (explained below) and the direction of the undisturbed air in front of the airfoil / wing.

Aspect ratio.

This is the ratio of the span of the wing divided by the chord. The glider wings are usually high aspect ratio wings - the reason for this is that for a given amount of lift produced by a wing, the lower aspect ratio wing disturbs a shorter width of air, but it must deflect it more vigorously. the result is, the tip area experiences larger losses in the form of 'swirls at the tip' (Wing Tip Vortex).

Centre of Pressure.

The centre of pressure will move from the leading edge to the trailing edge depending on the angle of attack.

Centre of gravity.

The center of the forces from all of the forces involved in flying can be considered to be at the 'centre of gravity'. Centre of gravity can move by the poilot weight shifting. Center of Gravity can also be called the centre of mass or center of effort.

Chord

This is the straight line drawn from the furthest forward point on the wing (Leading Edge) to the furthest rearward point on the wing (Trailing edge) via the vertical center of the wing.

Washout.

A lowering of the angle of attack of the wing as it progresses from root to tip. Hang gliders have washout and the tips are held up by tip rods or other means.

Washin.

An increase in the 'angle of attack' from root (front of the 'Leading edge' to the tip.

Reflex Section

A modern airfoil section used in Powergliders / Paragliders. Innovated in to our sport by Mike Cambell Jones it has allowed us to fly faster, and safer. Reflex is the upward curving of the rear of the wing and is controlled by the pilot by using 'trimmers'.

Pendulum stability

Most of the stability with a Paramotor comes from the pendulum effect. The weight of the pilot is great compared to the weight of the canopy. The lift comes from the canopy and the weight from the pilot. This effect means it is extremely difficult to dislodge the pendulum stability that a paraglider has. Roll stability and pitch stability come mainly from the pendulum effect. Pitch stability can be influenced by the aerodynamic section used, some are more pitch stable than others. The curve of the glider (viewed from the front) also affects the roll stability due to the direction the lift is acting in relation to the position of the pilot.

Glide angle

Glide angle is not actually an angle but expressed as a ratio i.e. 8 to 1 glide angle. This means for every 8 units of length travelled across the ground, then 1 unit of length is descended. The greater the number, the better the glide angle.

Drag

Drag is result of us flying in a fluid (air) and cannot be totally removed. There are several types of drag.

'Induced' Induced drag is a by product of lift. The majority of induced is formed at the wingtips where the
wingtip vortices are shed, as the area of low pressure above the wing and the high pressure below the wing slide off the wingtip and mix in a swirling trailing tip vortex.

'Parasitic' Parasitic drag is a friction drag and varies with the square of the speed. i.e. doubling your speed quadruples your parasitic drag. There are a few types of parasitic drag

'Form drag' Caused by solid non-lifting items in the airstream. i.e. You, lines, Paramotor frame etc.

'Profile drag' Caused by the lifting surfaces. It consists of skin friction drag and leading edge form drag. The more streamlined the airfoil shape, the less profile drag.

'Interference drag' Interference drag is when the airflow around the aircraft interfere with each other. Not a big problem on paramotors.

Polar curves

The curve is a series of plots taken for a particular aircraft and for a series of airspeeds. At each airspeed the sink rate is taken and then it is possible to plot the polar curve. The sharp increase in sink rate at slow speeds is the point just before the stall.

Min sink is the highest point on the graph. Max glide in still air is obtained by drawing a tangent to the graph from the origin . The point of intersection can be read off in sink rate and airspeed.

So how does a wing create lift?

Afbeelding

A wing creates lift because the distance the air must pass over the curved top of the wing is longer than the distance along the lower surface this causes the pressure above the wing to be lower than the pressure of air below it. Lower Pressure Above the wing, Higher Pressure below the wing.

This result is lift being produced. The amount of lift depends on the airfoil design and the speed of the air over its surfaces.

Around 2/3rds of the lift is produced from the reduced pressure above the wing and 1/3rd from the increased pressure below it.

The majority of the lift being in the front top surface of the wing. The lift is proportional to the angle at which the airflow meets the wing, (angle of attack).

The Angle Of Attack also helps to create 'lift'

As the aircraft passes through the air it follows a particular level of flight.

The air passing over the surfaces of the wing in the opposite direction of travel is called the 'Relative Wind'. The angle which the wing chord meets with the airflow is called the Angle of Attack.

An increase in angle of attack increases both lift and drag. If the angle becomes to great, it will pass the critical Angle of Attack. This is a point where the airflow over the wing becomes so disturbed that the wing ceases to produce lift (this area is called 'Cavitation'). The wing is then Stalled.

The amount of lift generated is proportional to the speed' at which the airflow meets the wing and sufficient lift can be generated by high airspeeds with low angle of attack or low airspeed with high
angle of attack.

_________________
Greetzzz,

Yvin. :ugeek:

Afbeelding


PH-9S8



Afbeelding



Afbeelding

Skype Me™! Afbeelding


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