Landracing Forum
Tech Information => Technical Discussion => Topic started by: maguromic on June 18, 2010, 12:47:39 AM
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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
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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.
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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
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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. :-)
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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¤t=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. :-)
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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
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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¤t=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. :cheers: Tony
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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
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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.
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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.
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How about just adding an extra chute .
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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
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if your chasing a record over 250 you need 2 chutes anyway.
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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
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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.
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How about a flip-up '29 radiator on the front -- it sure works for us.
Stan
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How about a flip-up '29 radiator on the front -- it sure works for us.
Stan
naaa, they want to stop it not turn it around... :wink:
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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.
I totally agree with what saltfever quoted.
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Are you going to have brakes on all wheels? With road racing background you should no how useless rear brakes only are.
JL222
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Wings similar to this
http://www.motorsportsinnovations.com/Bvile-pics/rw-full.jpg
become air brakes when pitched downward .
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Saltfever,
My thinking is to design the brake like a flap on a cup car. The extra large flap would be allowed to go vertical if the car turns around. Thanks for the help.
POPS
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Pops, I think it's way too high and it will lift the front wheels. If you turn around backwards it will most likely fly like a kite. Tony
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Are you going to have brakes on all wheels? With road racing background you should no how useless rear brakes only are.
JL222
We don’t have brakes on the front wheels, and the rear brakes are Nascar speedway brakes. They are small and fit inside the wheel for better aero, but in my opinion not good for stopping a car above 100 mph if that. We do have three parachutes, but wanted to investigate adding air brakes as an added safety measure. Since this is a roadster we are limited by the rules and the design package on where we can put the air brakes. Tony
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Tony - You are absolutely right about the roof flap - once you are 180* to your previous forward direction, it increases lift like crazy. We tried this with a closed car in the A2 tunnel (put the car in backwards). Since we couldn't actually yaw the car degree by degree (no big $$ for the Lockheed tunnel), I can't say at what degree of yaw the deployed flap(s) starts to become a liability. It certainly needs to act early to be of any use. About air brakes, I got nuttin'. vic
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Burkland (Tom) once told me that his air brake is the only slowing system (chutes, wheel brakes and air brakes) he never had a failure with. Apparently they also provided an impressive ability to slow the vehicle.
Air brakes are definitely something I will consider in the future.
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Tony,
Just a thought, use the 27 T doors for air brake. Your body will probably have an outline of the doors , cut them out and make a hinged "door" that will pop out and act as an air brake. As they will be verticle they should not add lift and should work no matter which way the car is going.
Rex
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As long as there is no change in the contour of the body, may require some good stiffeners
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Rex, One of the options we were thinking is using the doors. We could use some sort of bell crank or watts link with a single ram to push both open at the same time. But I still think it’s a little too high. Also it would be pretty simple to fabricate the doors out of aluminum and put some sort of structure to attach everything with. This is going to take lots of thought and sacrificing some brain cells. Tony
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I think it might work with front hinged doors and a redundant style actuating system to ensure there are no failures. The thought of only one coming out or having them deploy asymmetrically is downright scary. A solid panel behind the doors and some sort of sturdy structure to mount the hinges and actuators should do the trick. A travel limiting device so that they could be deployed a small amount at first and then greater amounts later on could prove to be a safe method for testing.
Pete
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This idea sounds great, how fast do you plan on going again? :cheers:
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Troy, The first few years of running the car will have some of the vintage engines and will be used for system evaluations and adjustments. But I think any of naturally aspirated big motors or any motor from blown “E” on up should make the HP needed to get the car to 300. The aero package is going to be very important and I think with some adjustments on the aero and chassis, with time it should get there.
Pete, Thinking about it a little more maybe using a lead screw like on airplane flaps so they can only open together. I still think the roadster doors are too far forward, though. Tony
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Yeah, I agree Tony. Yours is a rear engine car and the CG is most likely further back from the doors. Putting the center of pressure in front of the CG (and that is what will happen when the doors are deployed) is an unstable event! If we look at Tom Burkland's streamliner we see the air brakes are behind both the CG and the center of pressure. You can't do any better than that. Yeah, its a streamliner and he was able to do that where in the MR you are more restricted. I'm just pointing out what a desireable design should try to accomplish and what you already know. :-)
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I just re-read what I posted. Come to think of it Tom's air brakes might become the center-of-pressure. They are at the farthest end of the car which is as good as it gets.
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You might want to investigate the dive brake designs used in dive bombers during WWII. They were not all flat panels, many had holes in them. An obstruction to air flow that is not solid can have more drag than a solid panel due to the airflow through the holes.
The cruciform parachute also has more drag than a solid chute of the same size.
http://en.wikipedia.org/wiki/File:Dauntless_bomb_drop.jpg
You could design the air brakes as a perforated panel that slides out of a slot in the rear of the body. It only has to be large enough to cause a major separation in the air flow and "spoil" the aerodynamic shape.
If you have ever stuck your hand out the window at 70 mph, you know that even a small flat surface can develop a surprising amount of drag. Since drag goes up at the square of the speed, a human hand sized object would have 4x the drag at 140 mph as it does at 70, and 16x the drag at 280 mph as it does at 70 mph.
The German Stuka Dive bomber used narrow slats on the outboard section of the wings as dive brakes, that rotated 90 degrees into the air stream under the leading edge of the wings. You can see them just outboard of the main landing gear in these photos.
http://www.wwiivehicles.com/germany/aircraft/dive-bomber/junkers-ju-87-stuka/junkers-ju-87-stuka-18.jpg
http://www.wwiivehicles.com/germany/aircraft/dive-bomber/junkers-ju-87-stuka/junkers-ju-87-stuka-captured-01.jpg
All you would need to do would be a flush mounted strip about 3-4 inches wide and a couple feet long that would rotate 90 degrees (along its short dimension) to stand perpendicular to the body and spoil the air flow creating a very large high drag wake behind the car. This sort of design would also tend to inhibit spins. If the body tried to spin the slat facing the direction of the spin would create high a pressure zone ahead of it on the side of the body, and the slat on the side of the car facing away from the spin would become less effective and dump the high pressure zone ahead of it on its side of the body. This would create an aerodynamic force that would try to return the car to a stable direction of travel with both air brakes equally exposed to the air flow.
Larry
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Here is Marlo's
http://www.target550.com/gallery/08_speedbrake/index.html
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These are all good ideas, but this is a roadster and the rules are pretty clear on what parts of the body could be modified and what parts of the body cant. One thing we can’t do is modify the body proper. That leaves very few areas that can be modified for the air brake. It’s a safety luxury we would like to have, but may be impractical in a roadster the way the rules are written. Tony
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Tony, since it is a REMR can't the airbrake come up out of the original cockpit area, maybe between the engine and firewall. Then the only modified panel would be the tonneau cover
OK, as we all know I am not a roadster guy, but it is just a thought
See ya on the salt 8-)
:cheers:
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It is still in front of the CG . . . not a good thing! It is best to be on the CG or behind it.