aerdoynamics: forces & aerofoil (academic knowledge base)

7/30/2019 Aerdoynamics: Forces & Aerofoil (Academic Knowledge Base)

1/14

Academic Knowledge Base

www.aviationsimulationservices.co.uk

AERODYNAMICS

FORCES & AEROFOIL


2/14


Welcome to our Academic Knowledge Base video presentationseries.

In each presentation we aim to increase your knowledge and

understanding of key complicated aviation related subjects.

If you have any questions or wish to share feedback, you can e-mail

[email protected]

Find out about more of our services at




3/14



Forces acting on aircraft in flight.

The key forces acting on aircraft in flight are:

Drag Thrust Lift WeightWhen thrust and drag forces are in equilibrium, an aircraft will maintain a steady

speed. For the aircraft to accelerate then the force of thrust must exceed the force of

drag.

Therefore by the same definition, you would deduce that when lift and weight are

equal, an aircraft will maintain a steady level altitude. For the aircraft to climb, lift must

exceed the weight of the aircraft.


4/14



Forces acting on aircraft in flight. (Cont.d)

Thrust (T)Drag (D)

Weight (W)

Lift (L)

NOTE: In a banked turn, our force for weight is constant, but our force for lift is lost dueto the reduction of effective wing span. Therefore, to maintain a steady altitude in theturn, the forces acting for lift must be restored by increasing speed and/ or the angle ofattack (we cover angle of attack later)


5/14



Climbing and Descending

What is Rate of climb / descent?

RATE OF CLIMB or RATE OF DESCENT is the vertical component of the velocity of

an aircraft and is the time it will take to either climb or descend from a given height.

N.B. This is usually expressed as Feet Per Minute.

Example:

A Boeing 737 airliner is descending from 35,000ft to 27,000ft to avoid rough weather

conditions. The aircraft is descending at a rate of descent of 1,000fpm (feet perminute).

Therefore we can can deduce it will take 8 minutes to descend in this scenario.


6/14



The effect of weight on Rate of Descent

Simply: The heavier the aircraft, the greater its rate of descent.

Why

Well generally a heavier aircraft would fly at a higher airspeed for a given angle of

attack and so its rate of descent will be increased.


7/14



Glide Range

What would produce the maximum glide range?

Aircraft being flown at its optimal angle of attack and corresponding minimum dragspeed (VIMD).

What is the effect of weight on the glide range of an aircraft?

Contrary to what you may think: the glide range doesnt actually vary with weight,

provided, however, that the aircraft is flown at the optimal angle of attack as stated

above.

This is because the glide range is proportional to the lift-drag ratio which doesnt vary

with weight.


8/14



Glide Range (Cont.d)

A Quick Example to explain

A Boeing 747-400 (Heavy Aircraft) is flown at the correct angle of attack and speed. A Cessna 182 (Light Aircraft) is flown at the correct angle of attack and speed. Both aircraft will glide the exact same difference! HOWEVER, the heavier aircraft would have a higher airspeed than the light aircraft

and therefore, although it would be the same glide range/ distance, it would take

less time to do so.


9/14



An Aerofoil

What exactly is an aerofoil?

An aerofoil is a body that gives a larger lift force when compared to its drag forces

when set at a small angle to a moving airstream. (Think of a wing as generating lift)

Aerofoil Chord Line

A chord line is the straight line which leads from the leading edge to the trailing edge of

an aerofoil.

The mean chord line

Using the mean as we did in secondary school mathematics, it is simply the wing area

divided by the wing span. N.B. This is sometimes known/ referred to as standard

mean chord.


10/14



An Aerofoil

(Cont.d)

The mean chamberline

The mean chamberline is the line which goes from the leading edge to the trailing edge

of equidistance on the upper and lower surfaces of an aerofoil.

Angle of Incidence

Is the angle between the aerofoils chord line and the aircrafts longitudinal datum. It is

a fixed angle for a wing but may be variable for a tailplane. N.B. It may sometimes be

referred to as rigging incidence

See diagram next for an example of this remember think of an aircraft wing!


11/14



An Aerofoil

(Cont.d)

Source: U.S. Centennial of Flight Commission


12/14



THE ANGLE OF ATTACK

Weve already mentioned Angle of Attack quite a bit in this presentation but heres the

definition:

The Angle of Attack is the angle between the chord line of an aerofoil and the relative airflow.

Source: U.S. Centennial of Flight Commission


13/14



Additional Info you should know

Washout on a wing

This is a decrease in the angle of incidence from the wing root through to the tip. This

compensates for the early stall due to the higher levels of loading experienced at the

wing tips.

Diherdral

Dihedral is the upward inclination of a wing from the root to tip.

Anhedral

Anhedral is the exact opposide of Dihedral, it is the downward inclination of a wingfrom the root to the tip.


14/14


We hope you have found this presentation interesting and useful.

If you have any questions or wish to share feedback, you can [email protected]

Aviation Simulation Services. All rights reserved. Apart from any permitted use under UK copyright law, no part of

this presentation may be reproduced or transmitted in any form or by any means, electronic or mechanical,

including photocopy, recording, or any information, storage and retrieval system, without the express permission inwriting from Aviation Simulation Services.


aerdoynamics: forces & aerofoil (academic knowledge base)

Documents