Spoiler flap

[dw230]

When I was helping Keith Young with his roadster we used the air ducts behind the cockpit. The roadster was the old Quincy Auto/Brisette Bros. car that Keith found. LSR myth is that when the Brisettes added the ducts in back to back tests they picked up 18 MPH.

Don't know if that is the truth or just a good story.

DW

[Bob Drury]

  Dan, that's the problem.  Wouldn't it be nice if we had a wind tunnel on the West Coast available to the public.
  Believe it or not, I live within ten miles of a brand new one that Freightliner installed recently to test new truck design's.
  Maybe if I buy a new Mercedes they will throw in a free wind tunnel test.
  Here is another interesting tidbit.
  When Marlo tested his four foot model, the aerodynamisist had Jim Hume carve a mirror image of the bottom half of the car and mated the two wheel surface to wheel surface.
  This was supposedly to simulate how the air reacts flowing under the car at speed.
  At that point they are talking way over my head.
  This year at SpeedWeek I hope to aim a camera at ribbons on the deck to get a better idea of whats happening.
  It would be neat if a Stude with the vent's could do the same to compare.
  If I could afford all the sensor's and computer gadgets, it would certainly be neat to see how much effect that speed has on the downforce in the rear.
  One more note, as slippery as the nose of a 53' stude is, the shape of the rear is not really what is desired.  The way the trunk dives quickly is one more reason I feel that the spoiler help's on this car.                    Bob

[hotrod]

I'm not sure if you all remember the comments I posted a year or so ago about using oil tests to see the air flow patterns on a car body.

I did my tests on a 2002 Subaru WRX at around 70 mph and could clearly see the airflow over the rear window and rear deck of the car. The rear shape of the WRX window area is quite similar to the 53-54 studebaker bodies, so I think some of the information is applicable.

At speed the air flow along the rear quarter panels is flowing to the rear and slightly up ward as it tries to make the turn into the rear window area on the WRX. It fails to completely make the turn and separates from the body and as a sheet rolls into the void behind the rear window. Visualize this in three dimensions you have two sheets if high speed air flow dumping into the rear deck area off the rear quarters and they roll over and down toward the center of the rear deck on each side.

The airflow coming over the top of the roof does pretty much the same it tries to follow the rear window but fails and part of it forms a turbulent bubble behind the rear window, and the rest flows over the top of that bubble, gets pushed into the center by the air flowing off the rear C posts and "splashes off the center of the rear deck lid.

In the oil test, I placed a dozen or so dime sized spots of used engine oil on the rear deck, then drive at highway speed from one exit to the next -- ie about one mile. I then stopped and looked at what the oil streaks had to tell me.

Below is a picture of the studebaker I had in high school with stream lines showing what I believe the air flow does on that car body based on the WRX airflow.

[hotrod]

second image from the rear quarter showing the turbulent bubble behind the rear glass.

Now we get into the complicated part. The spoilers you guys are using are leaving that bubble of low pressure turbulent air unmodified, and extending the rear deck lid in the area where the airflow naturally tries to re-attach to the deck lid creating a high pressure area on the rear deck and spoiler top.

The low pressure in that bubble helps pull the air flow down and around the rear deck, but it also creates a large low pressure area on the top of the trunklid near the rear glass that is trying to lift the rear of the car.

If you put vents in that area just behind the rear glass, you reduce the pressure drop in that area, but the airflow will not turn quite so sharply in from the sides or top of the car to fill the zone behind the rear glass. That will reduce drag by making the low pressure bubble longer and more tapered, but will move the high pressure area where the air flow tries to re-attach farther back on the deck lid (maybe even missing the stock deck lid).

It is basically a choice of evils situation. Venting into that low pressure zone will reduce lift at the source but it might slightly reduce the effect of the spoiler if it is too short. Putting end plates on the spoiler and in the mid spoiler will help keep the airflow straight as it separates from the rear of the car.

What you really need it a method to help the air make that turn into the void behind the rear glass. One legal way to do that, is to put a slight forward rake on the car so that turn is not so abrupt.

The only way to know for sure is to do some tuft and oil testing to see what the air is really doing back there, and then try venting into that low pressure zone and see how it modifies flow.

To help visualize that bubble of low pressure turbulent air think about the bubble or air and foam that forms on the down stream side of a rock in a stream. Essentially the same thing is happening behind the rear glass in most any car at speed.

larry

[Bob Drury]

  Hot Rod, thank's for posting. 
  I wonder if my side spell plates would affect that side flow trying to wrap around the back glass? 
  I think I will try the oil and also attach ribbons to the top of the side spill plates.
  Unfortunately, my neighbor's frown on be driving down the street on 25%.........     Bob

[hotrod]

Take the car to a test and tune day at your local drag strip. You only need about 70 mph to get good data from tuft tests and oil tests.

Larry

[Bob Drury]

  That is certainly not a bad idea. 
                                                      Thanx, Bob

[NathanStewart]

Very interesting information hotrod.  I've seen a very similar situation with my late model four door sedan that is similarly shaped to your WRX.  After a car wash and with the car still wet, I'll zip down the freeway at 70 or 80 mph to blow the water off.  Starting out there are beads of water on the back window and as I increase in speed the beads start to disappear from very outside of the back window and the clearing path slowly works its way towards the middle.  Then, no matter how fast I go (still on the freeway mind you) there is still always a strip of water beads that are still stuck right in the middle of the back window.  They never blow off or go any where. 

BTW the Thompson Stude is severly chopped.  I actually saw the car in person recently and was very surprised to find out that it was not only still around but very near by in So Cal.  It's chopped so hard that I have a hard time believing Neil was able to see out the windshield. 

[Bob Drury]

  I punched in Wind tunnel test on you tube, and found two excellent examples of high and low pressure air flow.
  The first is titled A2 wind Tunnel Test All Generations Corvette.  The opening car is a 58-62 Corvette with the air wrapping around the roof just as Hot Rod theorized.
  The second is titled Mercedes Benz SLS AMG.  This one shows both a great shot of the air coming up over the hood and roof, and a great side shot of the air coming off of the roof.
  This particular car has a short rear deck and the video shows that the air stream cannot get back down to the deck surface.  The Krafty Kraut's solved this with a pop up spoiler that I assume rises at a given speed or possibly even for high speed braking.  Now that spoiler (or is it a wing?) looks like it would add a fair amount of drag...........  gotta love that damn internet.............. Bob

[hotrod]

I think the two you referenced are include in this group of 4 wind tunnel videos that show how the air flow tries to fill the dead space over the rear deck and behind the rear glass.

http://www.youtube.com/watch?v=FjwyUOq_goI

http://www.youtube.com/watch?v=B29ScK8tIwY

http://www.youtube.com/watch?v=eszhVxE_9-8

http://www.youtube.com/watch?v=jd71qpfUfEg

Larry

[Cajun Kid]

Bob and Hotrod,,,

FYI- I live less than 45 minutes from A2 Wind Tunnel... I have visited there often and helped on several test days with other cars.
I have done lots of research and also learned a lot.


So far I have not had the time, help or money to put my car in there (what a shame) as I don't mind sharring what I learn.  But right now I would need 3 to 4 helpers and $2,500 to do it right.

For now I am just adding HP to get my goals,, there will come a point where I have to tweak the areo,, and the tunnel will prove to be my best use of time and funds then..  for now pass me more HP...(there is only so much a NA 255 cu in motor on gas can do)

Charles

[Stan Back]

Has anyone ever considered that a Studebaker may not be the best choice to get the job done? (Blasphemy!!!)

Stan

[Bob Drury]

  That does it!   CRUSH THE ROADSTERS!!!!!
  I recently sold a 53 hardtop (project) at the Portland Swap Meet.
  I swear every other guy  with grey (or no) hair stopped and looked then told me his story about his uncle, brother, dad or best friend having one in high school.
  My own story is being a avid reader of HOT ROD Magazine starting in 1959.  I loved Beach Ball Sanchez's car from the first time I saw it.
  Over the year's, John Larson's car, the car's of Les Leggit, Joe Pisano, Bruce Geisler, The Burkland's, The Thompson Coupe (thank's T.B. for the pictures), all affected me greatly.
 My first trip to the salt in 1996 was to inocently spectate.............. MISTAKE!!!
  On the trip home I was planning the car build, and I knew it had to be a Studebaker! I could have had a comfortable retirement, but nooooooooo,  I am now in debt up to my eye ball's, and I LOVE IT...........     Bob