The endplate effectiveness decreases dramatically after a certain point.

 

[QUOTE=3312DC,Nov 7 2007, 04:59 PM] there is two types of drag

 

Interesting stuff.

 

 

Mike, question:

Is lift/drag measured in relation to the wing centerline or the airflow?

I always thought that lift & drag were relative to the chord centerline and that induced drag was from the effect of the lift vector not being at right angles to the airflow at angles of attack other than 0 degrees.

As a comparison for the original post, the wing I made last year calculated at 129 lbs lift / 9.1 lbs drag @ 100 mph (0 degree angle of attack). Re 920,000, chord 12", width 60", section NACA 7310-63. In practice the wing did not work that well but I believe that is from the proximity of the body.

 

The induced drag is due to the wingtip vortices. You can look at the question from many different types of analysis, but the bottom line is that before the airplane flew through the air was still. After it flew through, the air is spinning. That wasted energy comes from somewhere -- induced drag.

I'm not actually sure what the definitive reference coordinates for lift are. I think they are with respect to the free stream velocity vector, though. When you change the pitch of the airplane, you don't change the defined direction of the lift.

There are all sorts of ways to look at this stuff. Momentum and energy balances, force vectors, pressures on the body, etc. Each of the different ways of looking at it has to sum up to the same physical result. But people spend endless hours arguing about which way of describing the same thing is the *real* description. As if there were any such thing.

 

Mike,
I believe the 3D shape of the wing is essentially trying to keep a constant AOA with respect to the free air stream which is descending behind the rear window and relatively horizontal near the outer edges of the wing (angles and distances all related to mounting height and vehicle shape of course). It appears that the CFD was set-up with a simple horizontal free stream condition which would lead to stalling at the outer edges before center section stalling.

Theoretically, these 3D wings should work great when used at lower mounting heights and on cars whose flow stays attached to the rear window (EX, S2000 CR). I imagine a constant section wing would be more efficient (or at least easier to tune) if mounted up high in a free stream.

For the record, I use the GTC-200 and have tested multiple heights and AOAs using datalogging and oil traces to tune.

 

Beat me too it, exactly what I was going to say. I don't know about the GTC-200, but my GTC-300 certainly has a long enough span that the ends are not at the same AOA as the middle. From the diagrams, APR's CFD is obviously not taking this into consideration (as expected, since they are doing it for every GTC-200, not one mounted on a specific car).

This is, again, why I would love to get some real world test data.

 

So Gearhead,

1. Do you actually see clean air at the side elements of the wing? It looks to me like the side of the car is pretty dirty and the air flow would be highly disturbed.

2. Is there a sweet spot for height based on your observations? That would tend to validate the shape of the 200.

 

Considering the potential from your 300, you're obviously balancing it out with what kind of splitter in the front?