In our previous post we have discussed about what is aerodynamics and how its study with respect to air crafts is divided into two main categories; the subsonic and supersonic. In this post we will discuss about what is aerodynamic flight and how it affects the performance of an aircraft flying. But before going so deep into aerodynamics lets first understand how actually aerodynamic forces act on a body and how it affects an aircraft performance characters. There are two primary aerodynamic forces the lift and the drag, the lift is the component of the resultant aerodynamic force in the direction perpendicular to the air flow while the drag is the component of aerodynamic force parallel to the direction of flow. The lift is induced by the flow happening over an aerofoil inclined at an angle( angle of attack) to the flow direction. For flow to happen a forward pusher force is required which is the thrust provided by the engines of an aircraft. When an aircraft is flying steady level and straight then the aerodynamics forces hold the the following relations with the thrust and weight of the aircraft.
Thrust = Drag
Weight = Lift
These would be the primary fundamental parameters that would help us analyse the performance of an aircraft. All our discussions on aircraft performance in future will deal with these conditions i.e. straight, steady and level flight. Now that we know the elemental conditions for analysing the performance characteristics of an aircraft let us start to understanding how various aerodynamic parameters such as lift, drag, velocity, thrust required, etc. vary under various conditions. Before doing that we need to know how the lift and drag coefficients are related. They are given by the drag polar which is
Cd = Cdo + K(CL)^2
where Cdo is the drag at zero lift,
K is a constant given by 1/(3.141*Oswald efficiency*aspect ratio),
CL is coefficient of lift and
Cd is drag coefficient.
Now that we are done with some basics let us now try to understand what happens to the lift and drag when HIGH LIFT DEVICES(HLD)are used. The HLD's include the flaps and slats which changes the camber of
the wing aerofoil of an aircraft and hence generates a greater lift coefficient. but as we understand from the relation between the lift coefficient and drag coefficient, the drag coefficient increases with an increased lift coefficient. An increased drag would mean that the maximum distance the aircraft can fly under steady straight level conditions is now reduced because of greater fuel consumption to generate thrust which supports the increased drag. a natural question in any body's mind would be why do we need a device that will cause us a disadvantage??? Well don't think too much the answer is quite simple, the devices as their name suggests are high lift devices which means they generate a greater lift at a given velocity when deployed compared to when not deployed. This in turn means that we can generate the lift required for the aircraft to be airborne at a lower speed, which on ground means the length of the runway required for the aircraft to attain that minimum velocity to be airborne is reduced, because velocity is proportional to distance. Now you must be having a clear idea as to when and why these HLD's are used. YES!!! They are used only when an aircraft wants to take off and also wants to land. Wait a second!!! Why did I mention the landing distance???? Well the answer is again simple, in fact you have already read the cause for the usage of HLD's in landing. Still guessing???? remember that the drag increases when lift is increased...???? Yes the relation between the lift and drag coefficients is what causes the drag to be increased and hence reduce the landing distance.
Now that we have discussed about the performance of an aircraft when high lift devices are used we believe we have served our purpose of giving a small introduction to aircraft performance.Hope you enjoyed reading our blog for updates on our blogs please add us on +1 or follow the author on google plus. Do share it if you found the blog informative.
Thrust = Drag
Weight = Lift
These would be the primary fundamental parameters that would help us analyse the performance of an aircraft. All our discussions on aircraft performance in future will deal with these conditions i.e. straight, steady and level flight. Now that we know the elemental conditions for analysing the performance characteristics of an aircraft let us start to understanding how various aerodynamic parameters such as lift, drag, velocity, thrust required, etc. vary under various conditions. Before doing that we need to know how the lift and drag coefficients are related. They are given by the drag polar which is
Cd = Cdo + K(CL)^2
where Cdo is the drag at zero lift,
K is a constant given by 1/(3.141*Oswald efficiency*aspect ratio),
CL is coefficient of lift and
Cd is drag coefficient.
 |
| flaps |
 |
| slats |
the wing aerofoil of an aircraft and hence generates a greater lift coefficient. but as we understand from the relation between the lift coefficient and drag coefficient, the drag coefficient increases with an increased lift coefficient. An increased drag would mean that the maximum distance the aircraft can fly under steady straight level conditions is now reduced because of greater fuel consumption to generate thrust which supports the increased drag. a natural question in any body's mind would be why do we need a device that will cause us a disadvantage??? Well don't think too much the answer is quite simple, the devices as their name suggests are high lift devices which means they generate a greater lift at a given velocity when deployed compared to when not deployed. This in turn means that we can generate the lift required for the aircraft to be airborne at a lower speed, which on ground means the length of the runway required for the aircraft to attain that minimum velocity to be airborne is reduced, because velocity is proportional to distance. Now you must be having a clear idea as to when and why these HLD's are used. YES!!! They are used only when an aircraft wants to take off and also wants to land. Wait a second!!! Why did I mention the landing distance???? Well the answer is again simple, in fact you have already read the cause for the usage of HLD's in landing. Still guessing???? remember that the drag increases when lift is increased...???? Yes the relation between the lift and drag coefficients is what causes the drag to be increased and hence reduce the landing distance.
 |
| the flaps deployed for landing |
Now that we have discussed about the performance of an aircraft when high lift devices are used we believe we have served our purpose of giving a small introduction to aircraft performance.Hope you enjoyed reading our blog for updates on our blogs please add us on +1 or follow the author on google plus. Do share it if you found the blog informative.
No comments:
Post a Comment