Lift question

[flog]

The spilt flap thread got me thinking.

If you put an aerofoil (airfoil?) onto a flat surface so air can only travel over the top, and pass air over it (fan or similar artifical wind supply on top of the surface the wing is attached to), does it generate lift?

Flog

[tipsy2]

Yes...................................

[flog]

Yes...................................

So who can explain what the theory behind the whole "Air trying to move into the low pressure but the wing is in the way, etc."? No air moving under the wing in this example, but lift is produced.

I'm pretty sure we don't have qantam air masses and the whole gas pressure equalisation into the surrounding area means there's no localised cylinder of vertically upwards moving air that streches under the table.

Alternatively I'm living in 1965 and I've just not managed to find an instructor (or ask an instructor) that knows how to explain it properly.

djpil, if you read this remind me to ask next time I see you!

[Chimbu chuckles]

Take a dessert spoon, or other large spoon, and hold it under a running tap lightly between thumb and forefinger so JUST the curved surface is in the water flow. Water is not flowing down both sides of the spoon only the convex (cambered) side of the spoon...but strong 'lift' is generated.

The air under the wing is not 'high pressure' air but relatively high pressure compared to above the wing. The lower pressure area produced ABOVE the wing does the work. Depending on the shape of the wing the air traveling UNDER the wing will be likely LOWER pressure than local atmospheric pressure (it has camber too) but still higher pressure than that airflow above the wing.

RAF is accelerated under the wing as well as above the wing but that proportion going OVER the wing is accelerated a lot more. If the wing doesn't go up a vacuum will be produced and nature doesn't do vacuums.

[toolowtoofast]

Originally Posted by Chimbu chuckles

Take a dessert spoon, or other large spoon, and hold it under a running tap lightly between thumb and forefinger so JUST the curved surface is in the water flow. Water is not flowing down both sides of the spoon only the convex (cambered) side of the spoon...but strong 'lift' is generated.

The air under the wing is not 'high pressure' air but relatively high pressure compared to above the wing. The lower pressure area produced ABOVE the wing does the work. Depending on the shape of the wing the air traveling UNDER the wing will be likely LOWER pressure than local atmospheric pressure (it has camber too) but still higher pressure than that airflow above the wing.

RAF is accelerated under the wing as well as above the wing but that proportion going OVER the wing is accelerated a lot more. If the wing doesn't go up a vacuum will be produced and nature doesn't do vacuums.

coander effect though is not what the OP appears to be asking about (i'll stand corrected...) i reckon you're still describing the effect of the higher px wanting to move to the area of lower px, with a solid object in the way. the only difference is that the wing is not moving, just the air over the top, so the spanwise flow will be fwd, aft, sideways, all directions.

the effect of blowing air over the top of the wing to gain extra (ie STOL) lift is clearly represented in the Antonov AN-74

[djpil]

flog, I will be at the aerobatic contest this weekend. As usual we'll be discussing all of the topical subjects at Kelly's Pub.