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Hi BBB,

Yes, I was talking about anti-dive as the postmodern tech-types consider things.

I had this diagram from another post, but is this what you mean about changing the training arm angle to resist dive? I had not considered the consequences of the geometry of the trailing arms in the lowered position.

What we do with our two road race Ghias is counter dive with a balance of braking effort, so that under hard braking, instead of going nose down, the whole chassis depresses fairly evenly front and rear.

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

If you watch this approx one minute clip of our 53 car (1970 ball joint rear IRS), on tall 70-series tires and with no suspension lowering at the time of the video on an AutoX course, you'll notice little nose dive with abrupt braking.

FJC

Hi Fj , great graphics, says it all really, thats exactly what i had in mind for the trailing arm inclination, whats your view on it?
Yer man in the Ghia was cheating tho', he was steering it on the throttle
Looked good, no alarming dive and it looked quite flat considering what you said about it, maybe the load transfer from being high was actually helping it grip more than if it was stiff and low, trouble with a good pilot is they cover bad thing up handling wise, almost automatically, so bystanders cant always see it. Looks like you remember the no1 rule tho; with the soundtrack etc, it HAS to be fun, too many people forget the fun bit. Regards BBB

I race a 69 ghia and we have hit @ 120 mph. we have a little nose dive under hard braking into the turns however i need the weight to transfer to the front end on mycar because I have a fg. front end and I am very lite on the front. as far as the straights were I am running wide open, the car feels very solid. I am not running any spoiler or air dams yet. we are going to run quite a few more races this year so we may have to use one before the season is over.

A friend told me he had a stock beetle that would top out at 90mph on the street. If he drafted his buddies 396 Chevelle hit a 100. They had to almost touch to do it. I always got a kick out of that story.

OK, this my story dealing with caster. I had built a drag fiberglass short WB buggy. Based on a 66 pan. Early on I had an adjustable beam cranked all the way down and one set of shims. Never checked caster. The first event was a 1/8 mil and all was fine. The next time out (complete with a fresh paint job) was a 1/4 mile. I was hitting just over 80mph (the Gene Berg magic number) and the thing felt like it was on ice through the traps. Very scary, steering input did very little and the rear wanted to pass the front. Well, I looped it on a bye run. Started in the right lane, got very close to that guard rail, crossed the center ine fearing the the other guard rail and came to a smokey stop facing the starting line. Thank god I was the only car on the track. I think the caster was at zero. For the next few races I added a 2nd set of shims. Over the winter we raised the frame head and built in 12 degrees of caster. Eventually the buggy would go 111-115 in the 1/4 with no issues.

Hey guys, after reading through this thread and stewing over a few ideas, I came up with an idea for a bit of street-aero. I wanted something for my car that has the benefits of the herrod helper without, well... looking like a herrod helper.

I've got a prototype of the shape cut out, which you can see taped to the car here. My idea is to attach it to the car using 3 clips made out of thin stainless flat straps that will be bent to fit in the window channel sheetmetal. No drilling, rivets, or glue. But, the window and rubber will have to be removed and re-installed to install the mounts. That, with a nice flat-black powdercoat and some rubber edge trim, should make this thing very low-key.

If there's any interest in this idea I might make a few more for forum members to beta-test, and if it does well then possibly make them for sale?

Does anyone have any input on the shape, size, attack angle, etc.? FJ?

Looks good to me. I like the shape and it should work well.

Hi ToRy70,

It will work as is, but work better if you give it just one more inch in extension. I have made a few sheet metal versions of this very design, inspired by the Audi and VW pop-up roof spoilers.

Maybe you could keep exactly what you have as the street version, and the extended as the racing.

Excellent work.

FJC

I think ToRy is trying to steal my idea...



See this page for more info & pictures: Gerrelt Spoiler

Gerrelt those are VERY cool! You beat me to the punch!

It looks like those install from the window-side edge of the rubber instead of the car side (if that makes sense). I don't have much experience with fiberglass which is why I'm leaning toward aluminum sheet. Can you install them without removing the window? Will they work with original (aluminum trim) window seals? If I can't get my clamps idea to work out I might want to jump on your waiting list.

FJ I couldn't decide what width to make them, I settled on 3 inches for this prototype cut but was thinking about making them fatter to 4 inches as well. I'm going to alter the drawing today and cut out another one to see how it looks. The NB popup spoiler is exactly where I got the idea from.

What do you guys think about angle? Mine is almost parallel to the ground but I see that Gerrelt's have a much more relaxed angle, which it seems that he did to decrease the chance of drag. It's funny, when viewed directly from behind mine is almost invisible. I wonder what the best angle is for vacuum breakup vs. drag.

Thanks!

ToRy 70 wrote:Can you install them without removing the window?

Yes, it slides under the window rubber.

ToRy 70 wrote: Will they work with original (aluminum trim) window seals?

Probably yes, but I haven't seen a beetle with the aluminum trim and my spoiler yet.

ToRy 70 wrote:What do you guys think about angle? Mine is almost parallel to the ground but I see that Gerrelt's have a much more relaxed angle, which it seems that he did to decrease the chance of drag. It's funny, when viewed directly from behind mine is almost invisible. I wonder what the best angle is for vacuum breakup vs. drag.

The angle of my spoiler is about 12 degrees. I was told by a guy who was into gliders (the planes without engines), that everything over 12 degrees becomes an obstruction instead of guider.

On a race car, this kind of spoiler not only looks good, but I think will work very good too:












Probably easy to create too.. but it is not as subtle as my spoiler of course...

Interesting. The race car tails are very cool, but like you said, not very subtle... I also don't want to drill holes in the body. My goal is to have no drilling, rivets, or glue.

I cut out a 4 inch wing today. It seems like it's moving away from subtlety too, it's a little too fat for my liking. I also worry about overextending the mounts' useful length without flexing.











Maybe I can compromise and make a 3.5" version, try to make them all uniform with one set of mounts and hardware rather than split up production.

Gerrelt, when you say 12 degrees, I assume that is relative to the surface it's mounted to correct?

Also, I've been noticing a lot of weird spoilers on cars lately, now that I have been obsessing over kamm tails. This particular style is so weird that I thought that it had to be one of a kind, but I'm seeing a LOT of them, particularly on snugtop trucks and SUV's. This one is from a late model Lexus SUV! Can anyone shed some light on it?



It might be hard to tell from the picture, but imagine a typical ricer trunk spoiler, except mounted to the rear vertical surface of the hatch, with about half of it sticking up in the airstream.

Hi ToRy 70,

The SUV (or minivan, etc.) type rear window spoiler as you've shown isn't for high-speed aerodynamics, but just to create a local vortex to break the partial vacuum created by the semi-Kamm tail that sucks dirt and dust onto the rear window glass.

And yes, that means the spoiler is working against the Kamm effect.

All aerodynamic aids are a trade-off. Aircraft designers have cheated at times with holes or slots in wing flaps or dive brakes to balance out drag vs efficiency. Look at the WWII Douglas Dauntless dive bomber flaps, for instance. I'm a little surprised automotive aerodynamicists havn't copied ventilated surfaces to reduce air resistance on spoilers or airdams.

FJC

hmmm, i like the look of those speed holes on the douglass! maybe i should cut some too!

unfortunately, i think the only way to optimize my wing idea is to cut a bunch of them out and then do the fillup/gas mileage test over and over again. i don't think my salary would pay for a set of four wheel scales and renting a wind tunnel!

i wonder if there's any online estimation software that lets you plug in a cross section of a car and then add shapes to see changes?

lastly, if i do make these, would people be willing to test them if i offered them for free? maybe a half-dozen testers who could contribute back-to-back mileage figures, trap speeds, wind noise decibels, rain visibility, etc.

I'll knock one up for me and you guys can have a look to see what you think.

The top of the rear window is already past the point of flow separation so your spoiler will be less effective. 10-12 degrees of divergence is about the max you can use and that puts the starting point for the spoiler at least 8 inches further forward than where you have it now. It could work that far back but it would have to be much longer to get it back into the good air. You'll notice those race versions are both mounted further forward and are much longer.

hi jhoefer,

i see what you mean in reference to the larger race wings, but i was under the impression that cars of this style had fairly good attachment until the area below the window; which is why the herrod helper has some sort of effect even if it is minimized by its location. also, my design is itself compromised because i want it to attach to the car with no glue, rivets, or drilled holes... and also to make it blend in with the car and not stick out like a giant race wing!