Induced drag

[thez9zon]

Hey all

Am trying to work out the principles of induced drag. Can someone help me?

I understand that the effect of downwash from a wing is to tilt downwards the effective relative airflow and in doing so reducing the effective angle of attack. However i have a problem understanding how this is achieved and how downwash from behind the wing can affect the flow over the wing in the first place. Any ideas?

[Obidiah]

Hi thez9zon,

I'm not a test pilot and shouldn't really answer this one but am in the grey beard category and was happening past.

Maybe it is the up-wash you should be considering ahead of the wing.

Air at the lower velocities being incompressible (mostly) sends a forward pressure wave that influences the direction of the approaching airflow.

A visual representation of this would be the rising bow wave ahead of a large ship.

Hope that helps until you get a real answer.

[BOAC]

Not sure of what level of knowledge you seek and you may well need one of our experts here, but (like Obidiah), in simple terms, 'Induced' drag is that drag caused by the generation of a lift force, and a large amount of it is due to the energy 'wasted' in making the vortices which trail from the wing, rudder and tail tips. This has to come from somewhere and represents itself as a 'drag' force. Likewise the 'energy' required to change the direction of the air over a lifting surface to generate the lift is part of the 'induced' drag.

Depending on the level you seek you may not need to worry about the detail of up/downwash etc.

[Brian Abraham]

thez9zon - see if this answers your question.
Induced Drag Coefficient (http://www.grc.nasa.gov/WWW/K-12/airplane/induced.html)

[clangfo1]

With respect to induced drag and down wash it should be noted that induced drag is lessened when the aircraft in in ground effect. The down wash (from the wing) on the horizontal tail surface is less and this requires more elevator back force as the airplane enters ground effect, in order to maintain a given pitch.

There is a characteristic up wash ahead of the wing followed by a down wash behind the wing. These up and down washes are in a sense 'flattened out' as the airfoil enters ground effect.

:hmm: