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zackarybyrd
Well-Known Member
- First Name
- Zack
- Joined
- Apr 23, 2024
- Threads
- 10
- Messages
- 127
- Reaction score
- 90
- Location
- Columbus, Ohio
- Car(s)
- 2024 Supra Stratosphere 3.0 MT
- Thread starter
- #31
Here ya go. Some select text from the article…
“To quantify how these devices work the air, we employed a magnehelic gauge. It simply shows the pressure differential between two different sources. There are two ports on the gauge, one tuned for pressure above ambient and one tuned for pressure below. The unused port can measure ambient pressure wherever the gauge is located, so you’ll want to keep it inside the car and away from any pressure fluctuation–so, if possible, close the windows.
Now to measure stuff: Simply run a flexible tube from the gauge’s other port to wherever you want to measure a pressure difference. (You can also run two tubes to the gauge to measure the pressure differential across a surface, but we find that ambient versus whatever is plenty useful.)
Our new plan: Record the speed needed to pull 1 inch of water. For our 10-inch spoiler, this was a mere 50 mph.
Simple aero: Our flat-plane spoiler started off as a cardboard template that Shields Windshields duplicated in polycarbonate. We then used an inexpensive magnehelic gauge–one tube measures ambient, the other measures air pressure–to test the spoiler’s effectiveness: How much did the spoiler increase air pressure across the decklid? Photography Credits: J.G. Pasterjak
Now, we mentioned earlier that 1 inch of water equals about 0.03 psi–0.036 psi to be exact. This means the air pressure in front of the spoiler increased by 0.036 psi relative to the air around it. In other words, the air pushed down on the bodywork in front of the spoiler, creating downforce. It’s literally just that simple.
Now, 0.036 psi doesn’t sound like all that much, but let’s remember a couple things. First, there are a lot of square inches on a car. Second, aerodynamic forces do not scale linearly, they scale with the square of the speed. So at 60 mph, the forces are a third higher than they are at 50, and by 70 mph they’re nearly double the force at 50.
Still, the forces at a mere 50 mph weren’t nothing, so to find out just how large an area they were affecting, we started moving the end of the measuring tube toward the front of the car in 3-inch chunks.
At 3 and 6 inches away from the base of the spoiler, the speed needed for a 1-inch pull changed very little–too little to really be measured accurately on our analog gauge.
At the 9-inch mark we had to raise the speed by about 10% to get the same pull, and by 12 inches we had lost much of the high pressure that collected at the base of the spoiler.
If you’re getting a weird tingle in the math part of your brain, yes, the predominant area of trapped high-pressure air in front of the spoiler is very close to the vertical height of the spoiler. That’s no accident.
But what’s cool is that our Corvette’s decklid represents nearly 600 square inches. If we can raise the localized pressure by just half a psi, that’s 300 pounds of downforce from just a simple, flat piece of clear plastic.
The Wind Beneath Our Wing
Next, we installed our AJ Hartman wing, which offers a little more than 1000 square inches of area right up in the airflow. Based on suggestions from friends in the aero business, we positioned our sensor tube on the underside of the wing–about a third of the way back. We then headed back out to pull our inch of water.
Coincidentally, we pulled our first inch at the same speed as the spoiler: 50 mph. This means the wing and the spoiler were nearly as effective as each other in producing downforce at low speeds.”
Quoted from Grassroots Motorsports
“To quantify how these devices work the air, we employed a magnehelic gauge. It simply shows the pressure differential between two different sources. There are two ports on the gauge, one tuned for pressure above ambient and one tuned for pressure below. The unused port can measure ambient pressure wherever the gauge is located, so you’ll want to keep it inside the car and away from any pressure fluctuation–so, if possible, close the windows.
Now to measure stuff: Simply run a flexible tube from the gauge’s other port to wherever you want to measure a pressure difference. (You can also run two tubes to the gauge to measure the pressure differential across a surface, but we find that ambient versus whatever is plenty useful.)
Our new plan: Record the speed needed to pull 1 inch of water. For our 10-inch spoiler, this was a mere 50 mph.
Simple aero: Our flat-plane spoiler started off as a cardboard template that Shields Windshields duplicated in polycarbonate. We then used an inexpensive magnehelic gauge–one tube measures ambient, the other measures air pressure–to test the spoiler’s effectiveness: How much did the spoiler increase air pressure across the decklid? Photography Credits: J.G. Pasterjak
Now, we mentioned earlier that 1 inch of water equals about 0.03 psi–0.036 psi to be exact. This means the air pressure in front of the spoiler increased by 0.036 psi relative to the air around it. In other words, the air pushed down on the bodywork in front of the spoiler, creating downforce. It’s literally just that simple.
Now, 0.036 psi doesn’t sound like all that much, but let’s remember a couple things. First, there are a lot of square inches on a car. Second, aerodynamic forces do not scale linearly, they scale with the square of the speed. So at 60 mph, the forces are a third higher than they are at 50, and by 70 mph they’re nearly double the force at 50.
Still, the forces at a mere 50 mph weren’t nothing, so to find out just how large an area they were affecting, we started moving the end of the measuring tube toward the front of the car in 3-inch chunks.
At 3 and 6 inches away from the base of the spoiler, the speed needed for a 1-inch pull changed very little–too little to really be measured accurately on our analog gauge.
At the 9-inch mark we had to raise the speed by about 10% to get the same pull, and by 12 inches we had lost much of the high pressure that collected at the base of the spoiler.
If you’re getting a weird tingle in the math part of your brain, yes, the predominant area of trapped high-pressure air in front of the spoiler is very close to the vertical height of the spoiler. That’s no accident.
But what’s cool is that our Corvette’s decklid represents nearly 600 square inches. If we can raise the localized pressure by just half a psi, that’s 300 pounds of downforce from just a simple, flat piece of clear plastic.
The Wind Beneath Our Wing
Next, we installed our AJ Hartman wing, which offers a little more than 1000 square inches of area right up in the airflow. Based on suggestions from friends in the aero business, we positioned our sensor tube on the underside of the wing–about a third of the way back. We then headed back out to pull our inch of water.
Coincidentally, we pulled our first inch at the same speed as the spoiler: 50 mph. This means the wing and the spoiler were nearly as effective as each other in producing downforce at low speeds.”
Quoted from Grassroots Motorsports
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