What angle creates MAXIMUM air deflection?

I'm not a physicist, so please forgive me if my vocabulary is faulty
here. I really need this information, though; any feedback would be
greatly appreciated.

A flat surface, AB, is moving through the air, with the surface
exactly perpendicular to the direction of movement. In the graphic
below, the surface is moving downward. Point X is behind and slightly
to the inside of B.

X

A___________________________________B
|
|
V

As the surface moves through the air, the air "curls" around B and
hits X. To help eliminate this, we need to change the angle of
surface AB so that it deflects the oncoming air outwards and away from
X. In other words we need to move B "upwards" in the graphic above.

The question is, how many degrees does AB need to move to produce the
MAXIMUM amount of air deflection?

What happens at the A end is irrelevant. B really just pivots around
it.

For what it's worth, this is a fairly thin surface, about 1/4" thick.
The speed is typical highway driving speed, say 60-70 mph. Don't
worry about air temp, density, etc. It doesn't have to be that
precise.

A whole lotta thanks in advance. Please reply to the newsgroup.

Bill S.

On 27 Jan 2007 17:06:37 -0800, wrote:

....
A flat surface, AB, is moving through the air, with the surface
exactly perpendicular to the direction of movement. In the graphic
below, the surface is moving downward. Point X is behind and slightly
to the inside of B.

X

A___________________________________B
|
|
V

As the surface moves through the air, the air "curls" around B and
hits X. To help eliminate this, we need to change the angle of
surface AB so that it deflects the oncoming air outwards and away from
X. In other words we need to move B "upwards" in the graphic above.

The question is, how many degrees does AB need to move to produce the
MAXIMUM amount of air deflection?

What happens at the A end is irrelevant. B really just pivots around
it.

For what it's worth, this is a fairly thin surface, about 1/4" thick....
Bill S.

Airfoils develop max lift at an agle of attack around 15 degrees

Beyond that drag starts rising dramatically, though lift does not
vanish until much higher angles often.

In your diagram line AB would be 15 degrees away from vertical.
But airfoils expect air to flow along both sides - so if you are
masking the side where X lives, ignore this note.

Brian Whatcott Altus OK

On Jan 27, 7:31 pm, Brian Whatcott wrote:
On 27 Jan 2007 17:06:37 -0800, wrote:

A flat surface, AB, is moving through the air, with the surface
exactly perpendicular to the direction of movement. In the graphic
below, the surface is moving downward. Point X is behind and slightly
to the inside of B.

X

A___________________________________B
|
|
V

As the surface moves through the air, the air "curls" around B and
hits X. To help eliminate this, we need to change the angle of
surface AB so that it deflects the oncoming air outwards and away from
X. In other words we need to move B "upwards" in the graphic above.

The question is, how many degrees does AB need to move to produce the
MAXIMUM amount of air deflection?

What happens at the A end is irrelevant. B really just pivots around
it.

For what it's worth, this is a fairly thin surface, about 1/4" thick....
Bill S.

Airfoils develop max lift at an angle of attack around 15 degrees

Beyond that drag starts rising dramatically, though lift does not
vanish until much higher angles often.

In your diagram line AB would be 15 degrees away from vertical.
But airfoils expect air to flow along both sides - so if you are
masking the side where X lives, ignore this note.

Brian Whatcott Altus OK

Thanks, Brian. No, this has nothing to do with airfoils or lift. The
"airplane wing" model doesn't hold here. Drag, lift, etc. are not
relevant. The ONLY effect we need to produce is to deflect the
oncoming wind as far outward as possible.

Bill S.

On 27 Jan 2007 18:22:44 -0800, wrote:


Thanks, Brian. No, this has nothing to do with airfoils or lift. The
"airplane wing" model doesn't hold here. Drag, lift, etc. are not
relevant. The ONLY effect we need to produce is to deflect the
oncoming wind as far outward as possible.

Bill S.


Got it. Lift isn't relevant - just deflecting as much air mass as
possible. :-)

Brian Whatcott Altus OK

On Jan 27, 9:52 pm, Brian Whatcott wrote:
On 27 Jan 2007 18:22:44 -0800, wrote:

Thanks, Brian. No, this has nothing to do with airfoils or lift. The
"airplane wing" model doesn't hold here. Drag, lift, etc. are not
relevant. The ONLY effect we need to produce is to deflect the
oncoming wind as far outward as possible.

Bill S.Got it. Lift isn't relevant - just deflecting as much air mass as
possible. :-)

Brian Whatcott Altus OK

OK, don't make fun of me here!!! Lift also requires convex curvature
on the top, doesn't it? That's not the case here. This is just a flat
piece of Lexan, nothing else. Also the deflection isn't vertical,
it's horizontal. You're looking DOWN on it in the graphic above. That
"surface AB" in the graphic is looking down on the plastic "edgewise."
I just want to know what angle to set it to maximally deflect the air.
Can you tell me, or not?

Bill S.

Bill, you're going to get a vortex at that edge, air will curl around
it. Remember what you see at the edges of wings when there's hig
humidity?

So, for most cases, there's going to be air moving to the right along
that upper surface, and then at some distance from it, it will be
moving to the left.

I think this is counter intuitive, but if you want what an engineer
might call a stagnation point at b, you're actually going to have to
tilt the b edge downward, into the stream, to induce air to want to
flow right to left close to the aft surface..

Take a piece of wood, tape a piece of yarn -- a 'tell' -- on it, and
take it for a ride with a partner holding it out of the window. You'll
learn very quickly what the correct angle is,

Sometimes experiments are the best way to truth!

Good luck, and when it's the right thing to do, tell us what the h***
you're trying to do!


On Jan 27, 8:06 pm, wrote:
I'm not a physicist, so please forgive me if my vocabulary is faulty
here. I really need this information, though; any feedback would be
greatly appreciated.

A flat surface, AB, is moving through the air, with the surface
exactly perpendicular to the direction of movement. In the graphic
below, the surface is moving downward. Point X is behind and slightly
to the inside of B.

X

A___________________________________B
|
|
V

As the surface moves through the air, the air "curls" around B and
hits X. To help eliminate this, we need to change the angle of
surface AB so that it deflects the oncoming air outwards and away from
X. In other words we need to move B "upwards" in the graphic above.

The question is, how many degrees does AB need to move to produce the
MAXIMUM amount of air deflection?

What happens at the A end is irrelevant. B really just pivots around
it.

For what it's worth, this is a fairly thin surface, about 1/4" thick.
The speed is typical highway driving speed, say 60-70 mph. Don't
worry about air temp, density, etc. It doesn't have to be that
precise.

A whole lotta thanks in advance. Please reply to the newsgroup.

Bill S.

wrote in message
ps.com...


On Jan 27, 9:52 pm, Brian Whatcott wrote:
On 27 Jan 2007 18:22:44 -0800, wrote:

...
OK, don't make fun of me here!!! Lift also requires convex curvature
on the top, doesn't it?

No. It doesn't.

That's not the case here. This is just a flat
piece of Lexan, nothing else.

That will work fine to generate lift - the problem is your "maximum
deflection" would be maximum lift and would involve flow on both sides.

Also the deflection isn't vertical,
it's horizontal. You're looking DOWN on it in the graphic above. That
"surface AB" in the graphic is looking down on the plastic "edgewise."
I just want to know what angle to set it to maximally deflect the air.

I assume you want to "shield"? Which will be different than maximum
deflection.

Can you tell me, or not?

Likely not.

You want a flat plate with no turbulance behind? I ain't got a clue.

--
Geoff
The Sea Hawk at Wow Way d0t Com
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