nascar roof flap ???

[chota]

I know a few of you are using them. I have an opportunity to buy one nascar roof flap. I will be building a '30's coupe. Is one benificial? or do I need two? If I only have one, should it be placed at a 180 degrees of centerline or 140. What is the most common position at which you guys have seen lift in a Model A coupe, or older non fendered coupe? Thanks for the help.
Gary

[Sumner]

I know a few of you are using them. I have an opportunity to buy one nascar roof flap. I will be building a '30's coupe. Is one beneficial? or do I need two? If I only have one, should it be placed at a 180 degrees of centerline or 140. What is the most common position at which you guys have seen lift in a Model A coupe, or older non fendered coupe? Thanks for the help.
Gary

We have just one and the car has been backwards over 220 and didn't go in the air, but we can't say for sure that the roof flap prevented that, but we will keep it:

http://purplesagetradingpost.com/sumner/hooley/hooley-construction-2006-1.html

c ya,

Sum

[angryyouth]

I have been stewing over the benefits of said "Nascar Flaps" myself. I have seen them starting to be used in other motorsports as well and wondered if there was any formula or rule of thumb to their use? Are there manufacturers of them out there where they can be purchased or are they built by race teams for there specific application.

[Dynoroom]

A few teams like Hooley, John Rains, & Terry Hunts Guam Bomb run "roof flaps" at Bonneville. I think it's a good idea but there is a lot more to them than a flap and a hinge. You can buy them on E-bay from time to time or you can buy them new from Roush Racing the only manufacturer of roof flaps for NASCAR.

[chota]

Is there a name for those horizantal ribs on the roof designed to spoil the air when sideways? Winfield has them on his coupe. Can they be used in conjunction with a flap? How tall should they be?

[RichFox]

Roof Rails.  Page 40-4.X        1/2 to 3/4 high. Required where the record is above 200.

[AB-1]

Is there a name for those horizantal ribs on the roof designed to spoil the air when sideways? Winfield has them on his coupe. Can they be used in conjunction with a flap? How tall should they be?

You are correct, The roofs rails should be 1/2 inch tall for low drag, I can get you a set a roof flaps for cheap. I would highly recomend them.

Ab

[chota]

Sent you a IM AB-1, very interested.
Gary

[interested bystander]

What bout "roof rails" or longitudinal rails on the tonneaus of roadsters-  they seem to be the "BIG SPINNERS" maybe we oughta call em lottery cars!

What a GREAT day at El Mirage 2-day!

[Chicane]

Chota (and all): I have a copy of the original engineering abstract of, "The Development And Manufacture Of Roof Mounted Aero Flap Systems For Race Car Applications" authored by Gary Nelson (NASCAR), Jack Roush (Roush Industries), Gary Eaker (GM) and Stan Wallis (Ford). I recieved the doccument from Roush Ind directly while studying this very subject. Send me a message with your e-mail address and I will forward you a copy of this doccument. It explains a fair amount without going into engineer speak.


Angryyouth: As Dynoroom stated, Roush Ind is the only manufacturer of this device and it is available only through very few suppliers. One of those said suppliers is Hutchern-Pagan, an old school chassis manufacturer in NASCAR. This link >> http://www.hutch-pagan.com/roush_pg_219.htm will take you to their web page, specifically for this device. There are more designs available than what is shown here... but this is what they have displayed. They are not cheap in "new" form... which is why most try and find them used off of older NASCAR chassis.

[Dean Los Angeles]

When the car has spun around 140 degrees, its shape is very similar to that of a wing.

It seems that you would need two to kill the lift over the entire roof. The 140 degree angle, at least on NASCAR race cars, is critical.

Roof Flaps
In 1994, NASCAR introduced roof flaps -- a safety device designed to keep cars from going airborne and tumbling over the track. Before this, when the cars spun out at high speeds (more than 195 mph / 324 kph), they would often fly into the air once they had rotated about 140 degrees. At this angle, the car takes on a shape that interacts with the wind very much like a wing.

If the speed of the car is high enough, it will generate enough lift to pick up the car. To prevent this, NASCAR officials developed a set of flaps that are recessed into pockets on the roof of the car. Through wind-tunnel testing, NASCAR determined that the area of lowest pressure is at the back of the roof, near the rear window.

When the car reaches an angle at which it generates significant lift, the low pressure above the flaps sucks them open. The first flap to open is the one oriented at a 140-degree angle from the centerline of the car. Once this flap opens, it disrupts the airflow over the roof, killing all of the lift. An area of high pressure forms in front of the flap. This high-pressure air blows through a tube that connects to the pocket holding the second flap, causing the second flap to deploy. The second flap, which is oriented at 180 degrees, makes sure that the car continues to kill the lift as it rotates. After the car has spun around once, it has usually slowed to the point that it no longer produces lift.

The roof flaps keep the cars on the ground as they spin. This allows the skidding tires to scrub off some of the speed, hopefully allowing the driver to regain control. If not, at least the speed is reduced before the crash.

The 140/180 angle seems to assume that you are always going to spin towards the wall, but at Bonneville you could spin either way.

Notice how the roof flaps have deployed saving this driver from injury!

[Chicane]

 Within current technology and body shape, roof rails and rocker skirts do their job between -70* to -110*... and the flaps do their job between -120 *to -160* with maximum lift occurring at -130*.

Closed windows, 12.7mm roof rails and side skirts effectively reduced the aerodynamic lift to 65% of the original value, averaging right side lift and rear lift between -130* and -150* yaw. The addition of the roof flap reduced that number even more substantially between -150* and -180*.

I have been doing modeling for a two flap system... one flap at 140* and the second at 220* to address the possibility of a spin in either direction. The shallow rear spoiler angle of a chassis set up for LSR not only helps in the reduction of drag but also to disrupt the 180* lift leverage.

[Bob Drury]

I know one thing, after watching that 70's Camaro spin and go airborn on YouTube you better keep the ass of that car low to the ground.............watch it and see...............maybe that roof flap should be on the deck lid..........

[chota]

great info, thanks folks.

[Lynchy]

We're building an XJS to race at Lake Gairdner here in Oz and have 3 x flaps. One will go on the boot (trunk) lid and 2 will go on the roof. The two on the roof will be angled to cater for a left or right hand spin.

Do they work? They cost under $500 to buy so it doesn't cost the earth for extra insurance.

Lynchy