Correct Rear Deck Spoiler Angles.

To really determine this you would need a wind tunnel to adjust it for maximum performance as each cars stance/shape would be different. The speed required to realize the benefits is high so it's more for the cool factor than functional. The goal is to keep the air flow as laminar as possible coming off the rear of the car and keeping the point where the air becomes turbulent as far back as possible. The point where the air becomes turbulent is where drag is induced and the further back from the car the better. Also the shape of the airfoil would make a difference. On a plane you want lift and on a car you want the force in the opposite direction to plant the car on the ground so the wing shape should be reversed. You could adjust the angle of the wing to create the downward force but you start to induce drag as the angle increases. I have never looked at our cars wing shape too closely to see how its really designed. Here is a video that explains this on a general level but it explains the concept. I had the opportunity to test wing designs in a wind tunnel long ago and its an interesting science. Maybe someone here works in this area now and can provide their thoughts here too.

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So I went out and checked my wing and its actually a reversed wing so in theory it would produce a downward force at speed. So based on that I think the proper angle would be level with the road surface and not with the slope of the car. Both positions would produce the downward force but the position that is level with the road should straighten the airflow to create the turbulence further back. Again the only way to maximize is to use a wind tunnel. That's why the racing folks test their cars with tunnels.

To really determine this you would need a wind tunnel to adjust it for maximum performance as each cars stance/shape would be different. The speed required to realize the benefits is high so it's more for the cool factor than functional. The goal is to keep the air flow as laminar as possible coming off the rear of the car and keeping the point where the air becomes turbulent as far back as possible. The point where the air becomes turbulent is where drag is induced and the further back from the car the better. Also the shape of the airfoil would make a difference. On a plane you want lift and on a car you want the force in the opposite direction to plant the car on the ground so the wing shape should be reversed. You could adjust the angle of the wing to create the downward force but you start to induce drag as the angle increases. I have never looked at our cars wing shape too closely to see how its really designed. Here is a video that explains this on a general level but it explains the concept. I had the opportunity to test wing designs in a wind tunnel long ago and its an interesting science. Maybe someone here works in this area now and can provide their thoughts here too.

Click to expand...

I agree that's what I surmised from the video and that's cool I can easily change that, not that I would ever benefit (at least not very often) from it as the Green Queen rarely hits the highway. Most of her time on the road is spent on back roads winding through the hills, but every now and then she gets to stretch her legs. Thanks again for your help.

Great Video !

One of the first things I did when I got the green 72 was to change the Angle of the rear spoiler..I knew from building flying designing r/c airplanes That having the spoiler even with the slope contour of the decklid or lower in the rear of the spoiler is NOT the correct angle.. Almost every car I've seen places it that way..Heres a shot of mine almost even with the body line of the quarter panel

wings are for airplanes and cool looking mustangs and other muscle cars...as for angle, think of it as an upside down plane wing...angle more down in front, more down force..and yes the downforce is inversely proportional to the speed..do they work?, without actual wind tunnel testing done its a hearsay..BUT, put your hand out while driving, at any speed past 30, and you will FEEL the forces as your hand changes angles..so whether it really works bellow 100mph, i myself dont really care..for if it makes my hardtop, or convertible or mach1 look good..then so be it..remember the mustang was made the way YOU wanted it..what? no pink on the paint sheet?...well i want that, if not im going to go buy that purple barracuda...so ya in them olden days you were king, if you wanted it, and had cash, you got it. (wasnt that Toyotas theme?...you got it,Toyotah)?

That's my understanding as well. If the spoiler is pointed up it will create low pressure underneath and create lift like an airplane. The opposite effect of using it to hold down the rear end..thanks to the posters of the articles and videos. Very informative

I am sort of the old fart here being 67 and I ordered my Mach 1 and drove it in a time when there was not a cop at every corner. I do not remember a day that I did not go over 100 mph on the way to work and usually got about 2000 miles out of a set of tires.

I remember when you would get about 120 the front end would feel light and the car would wander around on the road. I put one of the front spoilers on and it did actually make a noticeable difference the car was much steadier. As for the angle on the rear the old races that could not afford wind tunnel testing would put strips of yarn all over the car and take photos at speed to see how the air was flowing. If the spoiler does anything I agree with those about the turbulence being controlled better. Wind tunnel testing is why the spoiler on the superbird was so high up. They had to add the extra reinforcements in the trunk to keep it from bending. It was up high enough to pick up the air above the car coming off the roof.

The ideal shape for the rear of a car would be like a plane very pointed to bring the air around the car smooth with little turbulence.

My son built a scaled down wind tunnel for a school science project. He used an electronic scale and could show how changes in the model cars he place in would change the down force on the scale. You could probably do the same thing with a model of our cars and try with and without spoiler and see the difference. You can get over 100 mph wind speed from a leaf blower.

If you have ever been to the Dayton Air force Museum you can see the small wind tunnel that the Wright Brothers used to develop their wing designs. They didn't just build one and go to the Outer Banks and hoped it would fly. They knew it would fly from their wind tunnel testing with models.

Anyone got lots of time on their hands I sure don't you might build one.

They do look cool with them I had one mounted on top of my 1969 ford van back in the 70's.

I went to Aircraft School to get my A&P License, and there we studied airframe and airfoil and drag. What I believe some of you are confusing here, is lift vs. angle of attack. Any airfoil wing shape will produce the high pressure/low pressure simply by virtue of the teardrop shape. Once you alter the angle of any wing from directly into the wind, you will induce drag to some degree.

On our rear body mounted , upside down wings, we also get the reverse of lift ( downforce ), which is again, created by the airfoil shape, NOT angle of attack. If you angle the wing down in front like a SPOILER, which it isn't, you will add drag, which you don't want. The upside down wing on a mustang's rear should have it's angle of attack in line with the airflow, which IS NOT level with the road, but flowing even down the roofline, so that, the top of your wing should be in the same plane as the roof/trunk line.

Remember, an aircraft flying along at cruise altitude has it's wings directly into the airstreams direction, angle of attack is not keeping it in the air, Bernoulli's principal of low pressure above the airfoil is overcoming the aircraft's weight and holding it up by suction.

However, as others have alluded to, at legal road speeds, I'm not sure the angle of attack question will help, or hurt performance significantly. Maybe that's why our wings are adjustable rather than fixed from the Factory, giving the owners the opportunity to position it as they liked....