Louver question...what is the point of...

[Deyomatic]

I know it isn't necessarily a GOOD question, but it bugs me when I see louvers on the TRUNK LID of a car. What is the point of this? Just for looks, or did the old timers used to throw their clothes in the trunk with a little laundry detergent when it rained and find a nice dirt "donut" track?

[MilesM]

It is for aero. the louvers break the air off the trunk lid.

[Petejoe]

opps sorry .. I misread. Here I was thinking hood and you were saying trunk Duh.

[MilesM]

Also I beleive they are usually blocked off on the inside.

[Bruce Lancaster]

Many old roadster racecars were stripped and gutted to the point that the trunk lid was actually an escape point for air scooped in at the cockpit or even the engine compartment. Some roadsters seem to have even run with unlatched trunklids, which were lifted part way open by air pressure venting at speed. On a car that's not just an open tunnel inside, it's just a styling statement referring back to ancient race cars. Some racers riddled EVERYTHING with escape vents, and the more sophisticated ones even identified positive pressure areas and ducted them to low pressure areas. '53 Studebakers at Bonneville had to be trained not to fly using this technology. Now, can streetrodders explain all those louvers on fake deuce gas tanks??!?

[Smokin Joe]

As stated above, to upset the air drag over the trunk.
Also hot rodder's version of flow thru ventilation.
Same reason NASCAR and NHRA have those panels that spill the high pressure air instead of alowing the car to become airborn.

And the number one reason....

<font color="red"> Because they're Cool </font>

[Deyomatic]

Sounds good to me. I just always wondered. The ones on the hood made sense-cool air in/hot air out. I just never thought of the 150+ MPH factor.
Thanks.

[Just Gary]

The Pierson Bros used aother approach to solving the same problem on their '34 coupe. They cut a big slot across the entire width of the body, just below the trunk lid.

[av8]

To add to Bruce's excellent post I'd like to add something about the swoopy '26-'27 roadster bodys that have been popular forever. In recent times we see the faster ones at Elmo and Bonneville with great protuberances in the form of 'chute packs on their deck lids.

Kent Fuller put me wise to this when he told me me that the latest of the T bodys have a significant low-pressure area off the tail that rises rapidly as speed increases. Punching louvers in the decklid to break up the boundry layer, and kill or reduce the lift, is effective only up to a certain speed. Beyond that, something more is needed to kill the lift, hence 'chute packs mounted on the deck. As untidy as they appear, with regard to aerodynamics, they actually keep the tail down and do it with less drag than a spoiler would. BTW, a spoiler is not permitted in many of the classes in which the early roadsters compete.

Finally, much of the efforts of venting the aft end of the car years ago had to do with not trapping air. Not only were decklids louvered, but the trailing edges of fenders on lakes and drag cars were liberally laced with holes to spill air. Gowd! we were havin' fun . . .

[sodbuster]

What ever happened to the old post (a year ago) that was in the "Tech" area? I tried to search for it and could not find it. Did anyone save it to bring it back to the top?

Chris Nelson
Kansas

It was a great read and it taught alot....

[flt-blk]

I was watching a Brookville A Roadster roll by at Goodguys this year in Ft Worth and his deck lid was louvered.

He hit his brakes and had a 3rd brake light behind the top center louver, I thought it was kinda cool.

Sorry kinda O/T, please resume your normal viewing
TZ

[Bruce Lancaster]

I remember reading an old HRM article on aerodynamics back about '61--one of the cars shown was a Bonneville Stude that looked more or less stock at a glance--the whole trunk and much of the interior was filled with big tubes past the ballast tanks dumping air from beneath the car through the decklid and elsewhere. I think it was all cut and try--it would be interesting to see a windtunnel test and find out how close this old-timers observe and cut aero work matched up to documentable flow. i bet they got real close to the truth keeping those things right side up and on their wheels at ridiculous speeds.

[gman]

It's so the people you sneak into the drive-in in your trunk can breathe

[CruZer]

Next time you watch an NHRA meet,look at the funny car taillights as they do a burn out or leave the line.The taillights are hinged to open so the air can escape.Just like the louvres of old.

[tokyo]

on the trunk...they look cool...on the hood...they look cooler..i don't know the real reason they did, just know that they did...plus Louvers are kick butt..i would louver everthing if i could...

[Roothawg]

Yeah whatever happened to the aerodynamics of a louver post?

[Bruce Lancaster]

aerodynamics??? We're discussing stuff that looks cool here.

[Digger_Dave]

[ QUOTE ]
Yeah whatever happened to the aerodynamics of a louver post?

[/ QUOTE ]

Roothawg; that post, "louver aerodynamics" ran for about six weeks over a year ago. (think it got to about 18 pages) carps (Toyota F1 boss &amp; HAMBER) had a lot of good pictures and drawings relating to race car aerodynamics.

Shortly after the post was slowing down, Ryan changed servers/computors and the thread was lost.

I saved the whole thread and would have posted it here; BUT, MY hard drive took a "nose dive" around the same time and I lost ALL of the TECH O-Matic stuff that I had saved up till then.

So if ANYONE saved; "LOUVER AERODYNAMICS"; PLEASE POST IT AGAIN!!!

[cheap-n-dirty]

here's a shot of a current el mirage roadster that uses louvers in the deck lid.
the louvers are on the top end a tube described above that ducts air from in just front of the rear end to the low pressue area on the deck lid.
also look at the parachute placement.
the car holds the blown fuel flathead roadster record at el mirage.

[cheap-n-dirty]

here's a picture of the car at speed .
look close to the dirt flow behind the car and at the dirt on the trunk lid in the first shot.

[Roothawg]

Yeah I remember the post...I just wanna know why it never made the Tech-o-matic? That post was so deep my head hurt...Made me rethink the average intelligence of a hamber... http://www.jalopyjournal.com/ubbthreads/images/graemlins/smirk.gif

[Carps]

[ QUOTE ]

Roothawg; that post, "louver aerodynamics" ran for about six weeks over a year ago. (think it got to about 18 pages) carps (Toyota F1 boss &amp; HAMBER) had a lot of good pictures and drawings relating to race car aerodynamics.

[/ QUOTE ]

I should be so lucky to be the TF1 boss.

FWIW, the Tojo F1 facility comissioned it's new windtunnel shortly after that thread died. The information gleaned from it has lead to a myriad of changes to the cars and pretty much a different aero package for every track that's raced during the season.

The facility is totally awesome covering about eight or nine acres and the entire tunnel is suspended so as to avoid disturbing the air flow within as a result of vibrations in the main structure. The amount of data that can be collected from a full sized car in the tunnel is incredible and moreso is the amount of change or gain from even the most minute adjustment of the car's body work.

[Digger_Dave]

Well Hello Peter!
Long time no talk to!

I refered to you as "Numro uno" cause the one pic I have of you shows you holding up the "one finger!!" (which everyone knows means "the boss!!" http://www.jalopyjournal.com/ubbthreads/images/graemlins/cool.gif)

Did you ever save the thread?

[Carps]

[ QUOTE ]
Well Hello Peter!
Long time no talk to!

[/ QUOTE ]

Yeah, has been a while hasn't it? I think I've been a bit busy at the office. http://www.jalopyjournal.com/ubbthreads/images/graemlins/crazy.gif

[ QUOTE ]

Did you ever save the thread?

[/ QUOTE ]

Nope, I have enough trouble logging in, saving threads is way beyond my vast knowledge of things computerised. I think I have kept some of the stuff I posted in a folder somewhere. And I do have a few F1 books here for you to make up for my speedy efforts on the Lake Gairdner story. http://www.jalopyjournal.com/ubbthreads/images/graemlins/blush.gif

[Digger_Dave]

Peter, seeing the car reminds me of this little piece....

Ferrari's F1 Team has fired its entire pit crew.

The announcement follows:

Ferrari has decided to take advantage of India's high unemployment rate, and hire unemployed Indian youths from Dharavi.

The decision to hire them was brought on by a recent documentary on how they were able to remove a set of wheels from a car parked in the street in less than 6 seconds without proper equipment.

Ferrari's erstwhile crew took more than 8 seconds with the right equipment.

This was thought to be an excellent yet bold move by the Ferrari management, and, as most races are won &amp; lost in the pits, Ferrari would have an advantage over every other team.

However, Ferrari's expectations were exceeded, as during the crew's first practice session; not only were 'da boyz' from Bombay able to change the tyres in under 6 seconds, but within 12 seconds had re-painted the car, filed off the chassis
number and sold the vehicle over to the McLaren Team!!

Sorry..a little off topic; but I couldn't resist! http://www.jalopyjournal.com/ubbthreads/images/graemlins/smile.gif

[hotrodA]

Looks only on a street car. Used to vent the pressure build-up on lakes/drag cars. I bought a Brookville skin, punched it, sealed the backside, sent it back to them and they mounted it on the inner panel and shipped it back.

[Phil1934]

I wonder if you punched a louver the width of the deck lid and about 3" high, do you think they would call it a spoiler? I remember an old tech article in a mag saying the rounded deck on these cars was horrible for lift and a flat pro mod type spoiler was needed.

[Digger_Dave]

Shades of "louver aerodynamics!" this is how it got started.

One of the items that got discussed was that certain classes at Bonneville NO LONGER permitted louvers on the trunk lid. (would need to check a current rule book to find out which one(s))

[Carps]

[ QUOTE ]
I wonder if you punched a louver the width of the deck lid and about 3" high, do you think they would call it a spoiler? I remember an old tech article in a mag saying the rounded deck on these cars was horrible for lift and a flat pro mod type spoiler was needed.

[/ QUOTE ]

It may have a positive effect but I'd argue against it being a spoiler on the basis that the shape is wrong. If the louvre was formed with an indented curve rather than a protruding radius, then I'd call it a spoiler. Finding the right spot for such a louvre would also require a great deal of trial and error... unless you have access to a wind tunnel. Then you could make it from styrofoam, apply it to the bodywork and test away until the location where it generated most downforce was found. Of course for the Bonneville racer we must remember that downforce reduces speed. Thus a more ideal aproach is something that reduces lift, like the neat little slot under the rear of the Peirson Bros Coupe.

If you look at a new LEXUS LS430 and compare it to say, an Audi A8, the immediate thought would be that the Audi must have a lower drag coefficient by virtue of it's sleek and low body with smaller frontal area by comparison to the bulk of the Lexus. Not so! The Lexus is a study in airflow management, every crease is designed to move the air where it flows best. The shutline gaps are minimised and sealed again for optimal airflow. But the real secret to the Lexus having a significantly lower CD is that it runs what is essentially a full belly pan with a series of small airfoils that direct airflow around and over the obstacles under the car. Even the mufflers feature rounded nose cones and spilers attached to the trailing edges for optimum airflow management. For going fast in a straight line, the full belly pan and slick body is a better deal. The real trick is getting the balance right. The air suspension in the Lexus, lowers the car at speed to reduce the drag cooeffiecent by a further one half of a point, further optimisisng high speed stability by reducing the volume of air under the car.

Another example is in the F1 car pictured. That vehicle was consistently faster in a straight line than any other F1 car during it's debut year. Why? Because it didn't have a good aero package in terms of downforce. Thus whilst it was fast in a straight line, it didn't have the cornering grip that downforce generates and was slow thru the bendy bits by comparison to the other cars. In F1 there's a very fine line between the perfect levels of lift, downforce and drag. Improving one can be to the detriment of the other. This is no different for lakes racing however, cornering grip is not so important as traction and straight line speed. However, one again the balance needs to be just right between downforce for traction, drag that might sap speed and lift, that will reduce traction and most likely soil the drivers underwear.

I've gotta go away again next week, but if you guys keep this one going I'll see how much data I can scrounge from the F1 Aero guys. FWIW what the teams knew back at the beginning of the season is now long since obsolete and they've moved on. As data logging and analysis systems improve, so does the aero package on the cars. For example, the rear wings have gotten smaller to reduce drag but without an advers effect on downforce as they learn more about air spillage and pushing the air around inside the wings to make better use of it.

[Carps]

[ QUOTE ]
here's a shot of a current el mirage roadster that uses louvers in the deck lid.
the louvers are on the top end a tube described above that ducts air from in just front of the rear end to the low pressue area on the deck lid.
also look at the parachute placement.
the car holds the blown fuel flathead roadster record at el mirage.

[/ QUOTE ]

This is a great photo and it suggests there potentially some more speed in this car without doung any more than changing the way it sucks air behind the driver's head. Notice how the dust has attached to the car? The driver it appears creates a low pressure area and there's enough suction here that it's ossibly pulling the car backwards.

So how could it be inproved?

I'd suggest as step one, lowering the driving seat and then reducing the height of the roll cage accordingly. This would also reduce the stess on the driver's neck as the air hitting the front of his helmet will be less and therefore reduce the stress on his neck.

A taller windscreen might be considered but that's going to create more drag and most likely increas the low pressure area. A better move might be to reduce the height of the windscreen and close up the gap around the driver.

Mike mentioned chute mountings as a means to manage airflow. Whilst it's not clearly visible here, there's possibly a good opprtunity to capitalise on that idea for this car.

Even in the best thought out race car, there's always plenty of scope for improved performance as a result of airflow management, just requires a great deal of thought and analysis, even for those with big windtunnels and powerful computers.

Shit! I should be outside working on my car. Who started this and got the gears in my head spinning again?

[Deuce Rails]

[ QUOTE ]
originally posted by av8:
Kent Fuller put me wise to this when he told me me that the latest of the T bodies have a significant low-pressure area off the tail that rises rapidly as speed increases. Punching louvers in the decklid to break up the boundary layer, and kill or reduce the lift, is effective only up to a certain speed. Beyond that, something more is needed to kill the lift, hence 'chute packs mounted on the deck.

[/ QUOTE ]

[ QUOTE ]
originally posted by Phil1934:
I wonder if you punched a louver the width of the deck lid and about 3" high, do you think they would call it a spoiler? I remember an old tech article in a mag saying the rounded deck on these cars was horrible for lift and a flat pro mod type spoiler was needed.

[/ QUOTE ]

The turtle deck of the Model T does create a significant low-pressure area, as av8 points out. I think that the SCTA rules want to keep it that way, which is why they forbid any changes to the turtle deck itself in the Modified Roadster class.

However, they do allow a wing, which, according to Phil's definition, is a spoiler.

So where would you put a wing--and at what angle, how high, and what shape--in order to get the best top speed?

And as an aside note: don't you think that the majority of SCTA roadsters would probably be more aerodynamic if they ran backwards? They would look more teardopped that way...

[Carps]

Back in the day, there were quite a few that did run that way. However, I think there's an issue of classification that would come into play here.

If you want to run in a street roadster class for example, the car has to be configured the right way around as there are limitations in repspect of body mods and turning the body around would make the car more a streamliner than a street roadster.

[Mel]

Tokyo said:
[ QUOTE ]
i would louver everthing if i could...

[/ QUOTE ]

Now I don't think Sarah would like it if you louvered the toilet seat!

~Melissa

[Digger_Dave]

[ QUOTE ]
If you want to run in a street roadster class for example, the car has to be configured the right way around as there are limitations in repspect of body mods and turning the body around would make the car more a streamliner than a street roadster.

[/ QUOTE ]

If you use a roadster pick-up (our '28 A for example) then some different effects come into play.

In the "other thread" I believe it was called the "Kambe (sp?) Effect" which allowed the high pressure air flowing off the body, to "curl" into the space behind the square tailgate.

[Rix2Six]

[ QUOTE ]
And as an aside note: don't you think that the majority of SCTA roadsters would probably be more aerodynamic if they ran backwards? They would look more teardopped that way...


[/ QUOTE ]

There was a Renault (I think it was an R17) that they wind tunneled backwards (don't ask me why) and found out that it had a lower drag coeffecient (sp?) thank facing forwards.

Just a wealth of useless information http://www.jalopyjournal.com/ubbthreads/images/graemlins/wink.gif

[56fordf100]

Louvers are cool where ever you put them, just don't over do it!

[ehdubya]

[ QUOTE ]
And as an aside note: don't you think that the majority of SCTA roadsters would probably be more aerodynamic if they ran backwards? They would look more teardopped that way...


[/ QUOTE ]

There was a Renault (I think it was an R17) that they wind tunneled backwards (don't ask me why) and found out that it had a lower drag coeffecient (sp?) thank facing forwards.


I seem to remember reading Harry Hartz drove a Desoto roadster cross country with the body mounted backwards to promote the 34 Airflow.