Poor Man's Aero: Building Your Own Wing (many pix)

[Duckworth]

It's some darn nice work for (let alone) a car nut - but you're into the territory of aircraft assembly here - which is impressive for a guy who tends to keep his hands clean.

However, I'm curious whether you really need or really want to keep expanding upon ground effects (downforce) since all of that technology doesn't seem to be of the period when RS or RSR models ran in early years. Meaning, that the more expert one becomes at the track - the more you will avoid mishap from a car getting loose in the turns. ???

Anyway, I'm wondering the desirablity of a pseudo 'Martini rsr' type of setup. ...you know, how the basic idea was to extend the ducktail laterally upon the back fenders in what looked like a very integral design. And a few shots I've seen where guys tried to imitate it by what appeared to be removable items that rigged left and right of the ducktail.

This may not be as feasible as I'm making it sound. And most likely would not generate quite as much downforce. But it would add more than a ducktail and the appearance would be outstanding for photo shots etc.

______________
(....not quite the rsr shot I had in mind)

http://mishami.image.pbase.com/o4/53/615153/1/52667194.MartiniRacing1973Porsche911RSR2.8literPho to2.jpg

[smarjoram]

How about skirts and a big fan to suck the car to the road. The car has a big fan already



Only thing is, people complained about getting sprayed with gravel when they were behind it and it got banned.

This looks like an interesting read..

http://www.bentleypublishers.com/gallery.htm?code=GAER&galleryId=768

[911pcars]

If the 911 engine sucked air like an Osprey (or was that Harrier jet) from the bottom, and spit it out of the fan like Jim Hall's Chapparal or the Brabham BT46, maybe we could harness that.

Sherwood

[smarjoram]

That's exactly what they said the fan was for on the Brabham - engine cooling. Didn't fool anyone though.

[rsa]

Maybe the only additional down force needed would be winglets on the bumpers. They can be adjusted to size and angle of attack at the track according to environment that day.

[Jack Olsen]

Here's the package for this weekend's testing. The 70-inch rear wing has better reinforcements where the uprights mount to the car, as well as a piece of cold-rolled steel stock inside the insert tube that connects the two halves of the wing. There should be no flex, now, even if the wing were able to generate 300+ pounds of downforce.

In front, I've made a new splitter that extends 5 inches out in front of the base of the bumper. If that makes the car tail happy, I can switch back to my old 3-inch splitter.

I don't think I'll be testing the front wing idea, since some of the posts here have got me reconsidering the best place to mount it, and honestly I don't think I have the time to get it all put together and tested before Satruday morning.



I'll post here with my subjective driving impressions (and/or reports of the wing's spectacular and catastrophic disintegration ).

[randywebb]

try using Yakima roof rack clamps to clamp the F wing onto the fenders

good luck!

[Peter Bull]

Nice work Jack!

One thing that might be interesting is that a rear diffusor actually adds downforce in the front of the car. This sounds a little counter intuitive, but measurements show that that is the fact. The effect can be increased if the diffusor is used together with a flat floor pan with "guard rails" stopping the air from going out sideways.

/Peter

[JohnJL]

Going to Bunnings tomorrow for materials...with the car in the suspension shop and paint, I'm climbing the walls. Not having something to wrench with is driving me crazy.

Jack, are you OK if I borrow some ideas?

[Duckworth]

Question I have for anyone who often runs at the track:

Do 911 owners always benefit from 'goundeffect' packages that add hundreds of Lbs. of downforce to their cars ? If the car becomes effectively 'glued' to the surface in the turns - something seems funny about that...

Doesn't a lot of the skill needed to drive the car go to the wayside if you've got an elaborate setup of groundeffects ?

Seems to take away control from what the driver should be involved in. Need more info please.

[Jack Olsen]

Originally posted by Duckworth
Question I have for anyone who often runs at the track:

Do 911 owners always benefit from 'goundeffect' packages that add hundreds of Lbs. of downforce to their cars ? If the car becomes effectively 'glued' to the surface in the turns - something seems funny about that...

Doesn't a lot of the skill needed to drive the car go to the wayside if you've got an elaborate setup of groundeffects?

Seems to take away control from what the driver should be involved in. Need more info please.

Aero doesn't change the way you drive the car at all, really. It just raises the threshold point where you're making your corrections. So instead of throttle-steering through turn 2 at Willow at 85 mph, I'll be doing it at 95-100 mph.

Viewed another way, any car is 'glued to the surface' right up until the point where its tires begin to lose adhesion. Aero mods simply raise the point at which that happens. You're still dancing on the edge, but you're doing it at a higher speed.

ABS, traction control, computer-controlled launch assistance and automatic transmissions are all driver aid devices that would be -- in my opinion -- in the kind of category you're talking about. They fundamentally change the driving experience. Aero would be more like wider or stickier tires (only cheaper) in that they don't do any work for you. They just change the point on the speedometer where the work gets done.

In fact, since they change the car's behavior in less predictable ways than an unmodified car, you could easily say they make the car more of a challenge to drive. You have the normal dynamics and characteristics of the car, and then also the dynamics and characteristics of your aero package.

As a side note, none of the mods discussed in this thread are ground effects. But trust me, that's a thread I hope to start in the coming months.

[Jack Olsen]

Originally posted by JohnJL
Jack, are you OK if I borrow some ideas?

No problem there, so long as you watch this space for the weak points I find in what I built.

The key ingredient if you're working in aluminum is the adhesive you use. I tested 2500 lb per square inch two-part epoxies that were terrible. I could peel two pieces of aluminum apart without any trouble at all. The Scotch-Weld DP460 is the one I finally settled on (after a number of others were tested). It's expensive (US$12 for 1.25 oz, and it took me four tubes to make the wing), but it's very strong.

Of course, we'll see how strong this weekend.

[Don Plumley]

I just drove into Lancaster. It's windy - if it keeps up should make the aero testing interesting...

[JohnJL]

Thanks Jack. I just got back from the supply shops with about 200 aussie in materials.

I bought from "pro" shops and asked lots of questions so I hope to have the right start. You should have seen the looks on the guys faces explaining to them I am building a`wing for the car. Of course that always led to a sad discussion on Brocky...I haven't seen it commented on yet on this board, but Peter Brock died in the WA Rally yesterday in his Daytona Coupe. A real gentleman, Peter was, and a hell of a driver.

One idea I had was to inject some lightweight expanding foam core into the structure...i'll try it without first. It sounds like the strength issues might primarily be in the mounting and brackets. If there is any flex at all in the wing I might drill out a few holes and squirt something like that "Great Stuff" you get in the US. That might add a few ounces, but its super-sticky, quite stiff while still retaining some relsiliance (sp?) and would seem to add rigidity and damping to the wing.

Ok...plywood, clamps, extrusions, sheeting, epoxy, rivet gun, 6-pack of Coopers Extra Stout, I'm ready to go!

BTW, how did you choose that exact wing cross-section? And how thick is your "skin" and internal braces?

One simplification I am making is to keep it one piece. This is a track-only car so I don't care about breaking it down, though that is a very cooll piece if additional engineering!

john

[JohnJL]

I am about to try "Aradilite Maximum Bond" with rivet reinforcements in the internal joins. I wish I had a TIG rig and knew how to use it...

Is that a "flap" on the training edge of the wing stencil, or just an extraneous line?

[Jack Olsen]

Construction:

A - Ribs are Alloy 3003 .02 inch, folded over to 3/4 inch tabs

B - Anchor rib: Alloy 6061 .9mm
Rear leg doubled up with same material
Front leg doubled up with 1.1 mm by 3/4 inch bar, L-shaped to meet up with 1/2 tube, secured with clamp and glue

C - Spars are 35" each Alloy 6061 T-Section 5/8" X 1/2" X 1/20" Thk
Spars are bridged with 4" rectangles of Alloy 3003 .02 inch

D - Main tube is Alloy 38.5" 6063 .625" Od, .527" Id,
with inserted 36" Alloy 6063 .500" Od, .370" Id

E - Rear tube is 14" 6063 .625" Od, .527" Id,
with inserted 7.5" Alloy 6063 .500" Od, .370" Id

F - Skin is '0.86 gauge' Aluminum flashing material

Also:

Gurney lip is made with 35" each 1/2-inch L-shaped Alloy 6063 1/16" thick

Where tubes meet ribs, the junction is reinforced with a snap-on piece of PVC pipe, about 1/3-1/2 inch, secured all around with adhesive.


What I would (will) do different next time? The core of my wing's strength is two-fold. The I-beam that runs the length of it provides its rigidity, and next time I might use thicker aluminum between the top and lower T-shaped pieces, maybe reinforcing those with rivets. The 'anchor' of the whole thing is a path that goes from one upright, to the cross tube, and back to the other upright. This is the part that shouldn't fail even if the wing kinks and bends. Next time, I may do two complete tubes to double this strength.

Also, the aluminum I'm using for the skin is probably too thin. I love that it's light (and was cheap, since it's roofing flashing (US$40 for 50 feet of 24-inch wide aluminum). It's not a structural problem, since it's strong. But it dents too easily -- almost like fabric on the old biplanse, but more prone to dents.

And here's a shot of some of the extra last-minute reinforcements I did.

[Jack Olsen]

Oh, and the line off of the tail end is a half-inch L-shaped piece -- it helps structurally and functions as a Gurney flap.

The Gurney flap is named for driver Dan Gurney, who tried to convince his competitors that it was only a structural reinforcement for his wings. In fact, it adds a vertical component to the air velocity at the trailing edge of the wing, deflecting the airflow up (like a spoiler, sort of) and increasing a wing's downforce with a surprisingly small drag penalty. It also slows the airflow over the top of the wing, which slightly increases the static pressure in that region, adding a little more downforce. The vortices it creates at the trailing edge of the wing also help adhesion on the underside the wing. You can run a slightly higher angle of attack on your wing with a Gurney flap before inducing stall.

On my wing, it also helps structurally. But then, that's what Dan Gurney used to say.

[Duckworth]

...Some interesting viewpoints. Got some rethinking to do.

The key ingredient if you're working in aluminum is the adhesive you use. I tested 2500 lb per square inch two-part epoxies that were terrible. I could peel two pieces of aluminum apart without any trouble at all. The Scotch-Weld DP460 is the one I finally settled on (after a number of others were tested). It's expensive (US$12 for 1.25 oz, and it took me four tubes to make the wing), but it's very strong. ...Jack Olsen

The Scotch-weld may be terrific. However, I always have had very strong bonds with JB Weld - provided one is willing to 'prep-sand' the aluminum first. If you use a 60 grit and cross hatch the sanding (X X X )- followed by a 40 grit - it's a surprise on how tough JB Weld can be. But with your thin sheet type of aluminum -you may have trouble scratching it up.



________________

'80 928
'82 Targa sold

[Jack Olsen]

I have JB Weld, but I didn't test it.

For prep, I etched the surface with a brass wire wheel and then cleaned it with denatured alcohol.

[cstreit]

Very impressive Jack!

Did you happen to do a writeup on the underbody aero/diffuser? I've been thinking about that for my car for a while and would love to get some more detail on that.

Did you do any quasi-science on outlets for cooling the engine?