Air Brakes

[maguromic]

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

[saltfever]

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. 

[saltfever]

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. 

[hotrod]

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

[jdincau]

Here is Marlo's

http://www.target550.com/gallery/08_speedbrake/index.html

[maguromic]

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

[Stainless1]

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 
 

[saltfever]

It is still in front of the CG . . . not a good thing! It is best to be on the CG or behind it.