Air Brakes

[maguromic]

Instead of posting on the build diary I thought I would start a new thread on the subject.  I have looked at all the old post and Freud’s comments on Marlo’s liner on the subject.

We are thinking of designing some air brakes for the rear engine roadster to use when it runs the big engines. Don’t know much about airbrakes, but I am a student of WWII aircraft that used them plenty. I know it would have to be on the centerline and apply the pressure below the Cg- that Cg issue is the real head scratcher…  I don’t want to pull the air brake and do a back flip to prove it really works.

I would like to hear others thoughts on the subject.  Tony

[Dynoroom]

I don't know anything but am thinking out loud.

Malcom & Donald Campbell ran air brakes on their cars. Malcom's 1935 car had them on each side of the car right in front of the rear tires, and they were different widths left to right and open upward on a hinge. This car ran 300 mph.

Donalds 1964 car had them at the very back. They opened outward. He ran 400 mph.

The space shuttle has brakes that open from the vertical stablizer.

The only point I'm making (I think) is that not all of these apply load below the Cg.

[maguromic]

Michael, Thanks for the info. I didn’t think of those examples. The air brakes would not be used all the time, just on the big runs and  as a  safety features we would like to add just incase of a catastrophic parachute failures.  The driver will be able to activate the  air brakes form the driver cell.

Eventually our goal is to go 300 with some tweaking on the chassis and the aero package with the big engines.  This roadster is just a tad over 21 feet (253”), it’s basically a lakester with a ’27 roadster body in the back.  Tony

[saltfever]

The most massive air brakes I have seen are on Burklands streamliner. They are configured so they both deploy perfectly in sync and it can't happen any other way. My guess is the middle may be on the CG. Meaning one half of them is above the CG and one half of them is below the CG.

Interesting Tony . . . you are always comming up with good stuff.  

[saltfever]

I don't know if this link will work. Supposedly it is on Ray The Rat's web site.
http://s445.photobucket.com/albums/qq178/RayTheRat_2008/burkland_wed_runs/?action=view&current=090924_0159r8.jpg

Assume the Z dimension of the CG is at engine cam height; then looking at the pic you might assume the CG is in the middle of the air brakes. But . . . ask Tom, he can could write a book about the engineering on the whole car. Come to think of it I wish he would. 

[maguromic]

The most massive air brakes I have seen are on Burklands streamliner. They are configured so they both deploy perfectly in sync and it can't happen any other way. My guess is the middle may be on the CG. Meaning one half of them is above the CG and one half of them is below the CG.
 

Tom sent me a PM with his thoughts. I am looking in the archives for some pictures of the car with the brakes open.  

Interesting Tony . . . you are always comming up with good stuff.  

It’s easy when you have a clean sheet of paper to start with.  One of our main design goals was to build in the maximum amount of safety we could (the seat is next).  The hard part is anticipating the events that might occur. Tony

[maguromic]

I don't know if this link will work. Supposedly it is on Ray The Rat's web site.
http://s445.photobucket.com/albums/qq178/RayTheRat_2008/burkland_wed_runs/?action=view&current=090924_0159r8.jpg

Assume the Z dimension of the CG is at engine cam height; then looking at the pic you might assume the CG is in the middle of the air brakes. But . . . ask Tom, he can could write a book about the engineering on the whole car. Come to think of it I wish he would.  

That helped a lot.   Tony

[hotrod]

Here is a picture of the clam shell air brakes part way open as they were rigging the chutes. They set up the chutes with the lines tied to the struts inside the air brake clam shell, with tape and thin string that would break as the chute pulled them out, controlling the lines so that they came out clean.


Larry

[Seldom Seen Slim]

Just in case you might not realize it -- the 411 car (as shown in the photo) was on the transporter/dolly at the time the shot was taken.  Don't assume that the air brake wings are really as high off the ground as Rex's tummy.

[desotoman]

Tony,

Where are you thinking you could put air brakes? In front of the cowl? Or would you consider having the doors open slowly, or the trunk lid? Just trying to think of the original body parts that hinge, that you would be able to use, and be considered legal.

Tom G.

[John Burk]

How about just adding an extra chute .

[maguromic]

Tom, That’s the problem we are grappling with.  I think it needs to be behind the rear wheels and below the Cg-, which is only going to be about 16-18” above the ground (from the ground to the top of the roll hoop is 33”) and if we use two they need to open evenly on both sides at once. It will have to be a clever system for that last part on this car.

How about just adding an extra chute .

John, We are limited at the back of the car.  Last year there was a rule proposal to limit the parachute and headrest fairing sizes, which failed.  But this year it will be back and I think they may have a consensus to pass it. The scuttlebutt is it will most likely be a percentage of the rear that can be covered.  Currently we are very close to the number that’s been thrown around.  Tony

[DallasV]

if your chasing a record over 250 you need 2 chutes anyway.

[POPS]

Thanks Maguromic for opening up this thread. 
All your thoughts would be appreciated.  Our lakester could easily be modified to install an air brake.  It would be impossible to make a split brake like the 411, but we could mount a horizontal one on top where the current vertical stabilizer is.  I envision the brake as a flat plate hinged in the front with an air cylinder pushing the plate upward from the rear.  I could make the plate with large spill plates to replace the vertical stabilizer.  Is there any handling problems that you can for see?
Thanks,
POPS










   

[saltfever]

Just remember that a wing or a air brake that adds downforce will truly act as a wing and fly you sky high in a spin. A downforce wing is great until you are going backwards and then it produces huge lift. An air brake should be designed to add only drag and absolutely no down-force or up-force of any kind regardless of car direction.