Roof Flaps

[Sumner]

I've been going to B'ville for the past 14 years, but don't remember ever seeing NASCAR style roof flaps on any cars there.  
 
 I'm wondering if we installed roof flaps on a '53 stude we run in competition coupe if that would be acceptable under the rules? Does anyone have any thoughts on this?
 
 NASCAR orientes one at a 140-degree angle from the centerline of the car on the right side since they feel most cars spin in that direction (not maybe the case at b'ville). 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 above was taken off of a site explaining the flaps.  I'm wondering at b'ville if it might be better to have 3 flaps.  One pointed towards each side and one facing back.
 
 After seeing some cars become airborn at b'ville over the years it looks like this could maybe improve safety there.  I'm not saying I would like to make it mandatory, but optional if the crew desired to do it.  Maybe even in the production classes if the roof flap installation showed no improvement in aero over a stock roof.
 
 c ya, Sum
 
  <small>[ October 12, 2004, 02:23 PM: Message edited by: 1FATGMC ]</small>

[Chad]

John Rains has them on his super fast fire bird set up on an angle like the nascars

[Sumner]

Thanks, you don't by any chance have pictures of the car?  Did he angle both sides or just one side?
 
 Anyone know how I could contact John?
 
 c ya, Sum

[Justin]

My car has two roof flaps and I would be interested in reading more about about the design and layout of nascar flaps.  Could you give me the site that you pulled the information above off. Thanks.

[Sumner]

Here are two sites:
 
 http://auto.howstuffworks.com/nascar-safety1.htm
 
 and,
 
 http://www.motorage.com/motorage/article/articleDetail.jsp?id=88747
 
 These aren't great articles and don't go into much detail.  I've considered trying to contact a NASCAR team and see if I can get a few more details.
 
 I would be interested in any photos of what you have done and your ideas on the subject.
 
 Thanks,
 
 Sum

[Lucky 7]

Whatever became of this subject?  Any conclusions?


.....Rip Van Winkle

[hotrod]

Thanks, you don't by any chance have pictures of the car?  Did he angle both sides or just one side?

I have some pictures of John's car, but won't be able to post them until morning when I get home from work.


Okay here is a roof picture from the rear of his car at 2007 speedweeks impound.
The NASCAR entry that spun also was as expected running roof flaps and the depoyed during the spin and it stayed on the ground at about 200 mph. (although that did not keep the windshield in the car)

I posted pictures of the spin in the NASCAR thread.
http://www.landracing.com/forum/index.php/topic,2936.0.html



Larry

[RidgeRunner]

Lucky,

     Believe they put a flap or flaps on Hooley's Stude, just checked my pics from this year's speedweek and couldn't determine if they are still on it or in what configuration.

     Believe Sumner is at the big shootout this week so will prob be awhile before he gets back to his 'puter and gives us the latest.  Meantime you might click on his link above in his post,"my Bonneville pages", and check around, should be some info there.

     Good question, I have been wondering lately how they might work for other body styles, liners, lakesters, etc.

                       Ed

[A2WindTunnel]

If someone really is interested in reading a technical paper about this subject.  Here is the SAE paper on the development of the roof flap ($14).  A2's very own Gary Eaker was heading up the GM wind tunnel when they came up with the idea and was one of the authors of the paper.

http://www.sae.org/technical/papers/942522

Author(s):
Gary Nelson - National Association of Stock Car Auto Racing
Jack Roush - Roush Industries, Inc.
Gary Eaker - General Motors Corp.
Stan Wallis - Ford Motor Co.

Abstract:
This paper describes the effort initiated by the National Association of Stock Car Auto Racing (NASCAR), and joined by General Motors Corporations (GM), Ford Motor Company (FORD) and Roush Industries, Inc. (Roush) to develop and manufacture a roof- mounted, aero flap system (referred hereafter as "roof flaps") for race car applications. This system addresses the problem of how to greatly reduce the severity of accidens involving spinning race cars by means of preventing aerodynamic lift-off. There were several NASCAR race car accidents in 1993 that involved cars which became airborne.

A variety of tests and procedures, both inside and outside the wind tunnel environment, were conducted to evaluate and consider possible solutions to this problem. Ultimately, a roof flap system was produced that has significantly reduced extreme yaw lift in race cars. The proof of success of this system has been the virtual elimination of aero lift-off in NASCAR race cars since the introduction of roof flaps, when coupled with previously mandated anti-lift devices, in February 1994.

[Stan Back]

How does having the left side windows open in NASCAR translate to LSR cars?

[A2WindTunnel]

If you are talking to me.  A left side window open would not, but roof flaps is the subject.  I was simply putting info out there so people could go to the source of the exact science behind the flaps, how they were tested/developed, and then put to use.  There might be someone interested in the technology.  Instead of people asking the question... how can we find out more about the roof flaps?  I am putting the info at their finger tips.  Relevant to LS or not.. there is an SAE paper on roof flaps for anyone to read and learn about the technology.

[Stan Back]

I guess what I was trying to ask is -- Do they work on an enclosed cockpit?

[hotrod]

They should work on a fully enclosed passenger car body, or the typical open window application as used in NASCAR.
If you look closely at John Rains car you will see two small air ports on the sides of the vehicle behind the doors. These provide slight suction to the roof flap boxes when the car is at speed in normal attitude, but when the car yaws excessively they would pressurized the roof flap box to help open the flap into the air stream.

I would think the same design could be made workable on open cockpit cars like the roadsters and cars similar to the Bocar that blew over this year when it got sideways. Likewise even a streamliner. You would need to do some model tests to find best placement for those applications.

I think it would be a good idea to allow applying the NASCAR roof rail concept to other body styles by allowing builders to put 2 four to five foot long, by 1/2 - 3/4 inch high strakes on the largest top surface of the car to spoil lift if the car gets sideways and induce down force if it is in significant yaw angle to the air flow.

This would be no issue on the special construction cars since their body design is unlimited but for the open cockpit modified sports etc. it is not clear to me if it would be legal to put a NASCAR roof rail like strake down the top of the hood to spoil lift of the car if it spins.

Larry

[A2WindTunnel]

They should work fine on an enclosed cockpit.  However, there are several things to think about.

-time + money to install the flaps.  It could be very difficult and expensive to install correctly. (It is hard to put a price on safety)

-They are configured for a stock car/truck turning left and spinning left, so how do you configure them for a LS car without development?

-testing the roof flaps.  There is a good chance that they will not work the same on all type/styles of cars.  If you wanted to test the flaps you would need a wind tunnel with high yaw capability.  Lockheed, Langley or the Manufactures are $2000+/hr.  Or, go out at high speed and spin your car to see if they deploy and work.    (I’m sure there are not too many people crazy about that idea)

-Not all cars become airborne in a spin at Bonneville, so witch cars install them?

-It might be a better use of time and money to work on the aerodynamic balance of your car to help the stability at high speeds so you don’t spin out.

[hotrod]

-They are configured for a stock car/truck turning left and spinning left, so how do you configure them for a LS car without development?

Good point, John canted both roof flap boxes symmetrically unlike the typical NASCAR install that places the right hand roof flap at an angle and the left flap in line with the car. When I was talking to him he said he had never needed them but thought it better to have them and not need them than need them and not have them. As you mentioned in an untested install you mostly have a "good faith" safety measure that you trust is more likely to help than it is to hurt the cars spin behavior.

Although untested is a gray area, wing spoilers and the principles for spoiling lift are pretty well understood, and even very simple measures to spoil flow over a wing like structure will disrupt the airflow, killing lift and building pressure on the surface in front of the obstruction. The FAA also has some guidance on low tech wing spoilers you can strap to a planes wing while it it is parked on the ramp to kill lift in high wind situations so the plane does not try to fly on its tie downs. Living in a high wind area I have actually seen light planes hovering 3 inches off the ground on the ramp at the airport down the road during chinook wind events where wind speeds were 90-110 mph.
It does not take much of an obstruction (like the NASCAR roof rails) to cause total flow separation and turbulent flow over the upper surface.

If I were doing it, I would certainly spend some time with some car models to get at least some basic testing data to see what the air flow is like over that car body style at 30*, 60* 90* and 120* yaw angles so you had some clue where to best place the devices.


As mentioned in the FAA circular AC 20-35C  (page 14) all it takes to spoil lift on a wing is a 2x2 board on the front 25% of the cord of the wings top surface. Applying that rational to a car roof or hood should be a fairly simple task looking at the car body as a wing section and placing an obstruction that would deploy at high yaw angles in that first 25% of the cars roof or upper body, to spoil the airflow and build induced pressure on the roof section on the upwind side of the obstruction.


http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/3121C979AF8A048C862569D60074B3B3?OpenDocument

Larry