12.6.16(a) . total reaction (TR); 

TR:
This is a single vector line drawn to represent the combined effect of a number of vectors. The TR of the pressure envelope around an aerofoil represents the sum of the effect of the pressure envelope.

Terms
Define...
(a) . total reaction (TR); 


This is a single vector line drawn to represent the combined effect of a number of vectors. The TR of the pressure envelope around an aerofoil represents the sum of the effect of the pressure envelope.



(b) . centre of pressure (CP).


 
The centre of pressure is the point in the aerofoil which the total reaction (TR) is acting through.



 
        

         
    

12.6.14(b) . the pressure distribution around an aerofoil which is producing lift. 

A streamline airflow around an aerofoil behaves in the same way as the flow through a venturi
Air moving over the aerofoil shape must accelerate to pass over the top surface.
it therefore gainsdynamic energy and the static pressure in that area is decreased
At the same time air passing below the aerofoil is not deviated from its path – there is no change in velocity and static pressure remains the same
In this pressure distribution a small force is generated which tends to move the aerofoil towards the lower pressure area (image)

12.6.14(a) . venturi effect; 

A venturi is a a convergent – divergent duct.
When placed in a steady stream of air it enables a given volume of air entering it over any given time span to accelerate smoothly and pass through the restriction at the throat in the same amount of time
Once it has passed the throat the air then decelerates to pass out through the exit at the same speed it entered
‘++diagram++

12.6.14. With the aid of diagrams,explain:

12.6.12(b) . decreased. 

Whereever the speed of the airflow is decreased the air loses dynamic energy and it static pressure is increased

12.6.12(a) . increased; 

Whereever the speed of the airflow is increased, the air gains dynamic energy and it’s static pressure is accordingly reduced

12.6.12. Explain the changes which occur to dynamic and static pressure wherever the speed of the airflow is: 

–

(a) . increased;

(b) . decreased. 

–

12.6.10. Describe streamline airflow around an aerofoil.

Streamline airflow:
If succeeding molecules in the airstream follow the same steady and predictable path this can be represented as a streamline
No flow is across the streamlines only along them
–
– (image)

12.6.8. Explain Bernoullis Theorem in simple terms.

Bernoullis Theorem States that..
In the streamline flow of an ideal fluid
the sum of the

• energy of position
• plus the energy of motion
• plus the pressure energy

will remain constant

Energy of position will not change significantly for aviation proposes.
Leaving us with : Dynamic energy + static pressure = a constant.

Therefore, when the speed of the airflow is increased the dynamic energy of motion is increased and the static pressure will reduce to keep the total constant.(image)