FA's at the Sprints

[Mike B]

The dough hardens rock-hard, and is specially formulated to be machined. The pattern is then re-machined with a very small step-over to produce a smooth, hard finish that needs only light sanding to be ready to pull a mold from.

Hope that helps.

Yup. I thought that the initial machined surface was all you needed. Didn't know you needed the added tooling dough step to get a good tooling surface. Are you using Renboard or some other media for the intitial, pre-tooling dough surface?

I suppose CNC routering time on your own machine is (relatively) cheap but is there a way to avoid that interim step?

How difficult is it to arrive at a CNC-able file from a SolidWorks file?

[Stan Clayton]

There are many choices in the initial tooling material, but in general the closer to mold-ready the more expensive the material. In view of our market we choose to use a less dense initial material and add the step of the tooling dough. As you note, once over the initial hump of purchasing the CNC center, machining time itself is relatively cheap.

Generating the tool paths from a CAD file is the second big hurdle, and the software to do that well in 3 to 5 axes is often as expensive as the machine itself. Not to mention that it has an even steeper learning curve...

Rennie has spent most of the past year breaking that particular code, and we are now at the point where every aspect of our new pieces is planned out in CAD to exploit the CNC capabilities. The pattern for the matched right and left inner endplate skins shown above is a good example, but our new sports racer rear wing and front splitter packages were done the same way, as was our new FA rear wing.

Our future projects will be done the same way as well. The idea is to bring the high tech solutions one normally sees at higher levels of racing to the average club racer. Of course, this process has been going on for a long time, and we are just continuing that tradition.

[Rennie Clayton]

Rennie:
I've toyed with the idea of trying FC wings on my DB-4 for Road America. Do you have data comparing the FA and FC wings? While we aren't front runners (old car & old driver) we had some of the best speeds on Arnie's gun at the Sprints. If we have anything going for us it's straightline speed, with 13" fronts, a very narrow cockpit, and trimmed out as much as we can. It would be interesting to see how far we could go in that direction and see what kind of results we could get. That is why I was so keen to see what the Stohr DB-4 would do.

Jim Gustafson
Swift DB-4

Jim,

Sorry, missed your question here amid the CNC hubbub.

We've got quite a bit of data comparing FA and FC wings, and the answer for "which is better" really depends on what your assumptions are. Target downforce is your biggest variable - and FC wings don't produce much of it. Neither do "standard" FA wings, proportionally, but at least they have ~30% greater surface area to get the job done with compared to FC bits. In order to get an FC wing to produce FA levels of downforce, you have to crank them up pretty good - well beyond their point of max L/D. Wings get less and less efficient, the more you try to get out of them - and since we're not (yet) hobbled with F1-style wing size restrictions, I'd prefer to stick to what's most efficient.

Trimmed out, FC and FA wings actually produce very similar drag numbers. Usually, FA stuff will still produce higher downforce for a given drag number, meaning their L/D is typically better, so in that scenario I would still go with FA wings. Because of other factors, you can never get an FA down to FC levels of drag anyway, and you might as well take advantage of some of those factors to generate as much downforce as you can, within your minimum drag envelope. FC wings just don't have enough juice to do that.

I think, in the final analysis, we will find improvements in four areas:

• More appropriate airfoil selection (don't get me started on current FA / FC airfoils...)
• Architectural design - how to make all the elements work together for maximum benefit
• Detailed optimization for specific flow conditions - i.e., the flow at the center of the wingspan is not the same as the flow at the tips
• Endplates - by the time we're done, the days of flat endplates in FA will be history. There is so much to find here...

Cheers,
Rennie

[bill gillespie]

What about the rollbar air intake????

[Rennie Clayton]

What about the rollbar air intake????

The logistics for a rollbar intake on the Ralt are pretty dodgy, especially considering the typical "club" seating position, which is pretty high in the car. I sit pretty low in the car for a Ralt guy, and even my bobblehead is kinda tall:



At least with the Toyota mills, anyway - the intake veers too far horizontal to keep everything under the engine cover without doing a lot of contortions. I think we'll end up going the same direction you have, with an F3-style intake, unless we convince Arnie to do something really unorthodox.

Other engines, other cars - who knows??


Cheers,
Rennie

[Rick Iverson]

Rennie;

I have just one weekend in a FC car, and that was four years ago (been quite busy lately). From a novice point of view, it would be my surmise this FC Aero package will require some fairly extensive testing. For those of us who aren't sophisticated in our thinking, is there a starting point for set-up? What about incremental changes: where; what to look for; signals you've gone too far.

I have a NEW Pennon Polecat diffuser. With your areo package, stick should no longer be an issue. I simply need to get book smart on the procedures. Got a CL?

Iverson

[Stan Clayton]

Sure! The pattern in the photo above is too rough surfaced to pull a mold from. To get it ready, I mix up epoxy tooling dough (like J.B. Weld, except in 5-gallon buckets) and roll it out in quarter-inch-thick strips. I also mix up a cup of slow adhesive epoxy resin. To bond the dough to the pattern, I paint a layer of the resin on the surface, then lay the strip of dough on top of the painted part. The epoxy in the resin and in the dough are compatible, and since the resin soaks a bit into the pattern, it bonds the two together.

The dough hardens rock-hard, and is specially formulated to be machined. The pattern is then re-machined with a very small step-over to produce a smooth, hard finish that needs only light sanding to be ready to pull a mold from.

Hope that helps.

Here is a photo of the process I was describing above. The pattern was first roughed out 1/8" undersize, and then a quarter-inch layer of gray tooling dough laid up over it. The dough was allowed to harden, and now the machine is cutting half way through the dough (at full height) to produce a smooth, hard surface. That surface will sill require a little work to get it ready to pull a mold from, but this process is a lot quicker and more accurate than doing it by hand.

[Mike B]

Here is a photo of the process I was describing above. The pattern was first roughed out 1/8" undersize, and then a quarter-inch layer of gray tooling dough laid up over it. The dough was allowed to harden, and now the machine is cutting half way through the dough (at full height) to produce a smooth, hard surface.

Does this require creating two CNC programs for the tool path?

That surface will sill require a little work to get it ready to pull a mold from, but this process is a lot quicker and more accurate than doing it by hand.

What is required, just some light sanding and buffing?

Neat stuff. Sorry for the continued threadjack!

[Stan Clayton]

Does this require creating two CNC programs for the tool path?

No, it requires 4...

Seriously, but it's worth it. All of the tool paths are generated from the same CAD geometry, though, so the process is *fairly* straight forward.

What is required, just some light sanding and buffing?

That...and perhaps some spot repairs if there are any voids.

[Rick Iverson]

Rennie;

How are the wings coming?

Also, may I draw your attention to the last comment here? It's analogous to going though your fanny to get to your elbow. But there are several considerations here, and the sooner all players are talking, the better it is for the consumer.

Regards

Iverson

Rennie;

Ever thought about FC aero packages? I should think the principles would be the same, just a little less of everything.

Might want to give it some consideration. With RSF raised noses and a thoughtful wing package both fore and aft, the mid-year Van Diemens could perhaps compete again. And there's about a zillion of them out there.

Iverson

[Rennie Clayton]

Rick -

Drop me an email - rennie@dauntlessracing.com - I've got a number of ideas about how to get everything connected.


Cheers,
Rennie

[Rick Iverson]

Rennie;

How's it going? Sure would enjoy meeting you at the Run-offs, but I have this rediculous re-integration crap to attend this weekend.

Iverson

[Rennie Clayton]

How's it going? Sure would enjoy meeting you at the Run-offs, but I have this rediculous re-integration crap to attend this weekend.

Rick,

Patterns for all the wing bits are complete - 19 patterns in all, between the front & rear wing assemblies - but of course now everything is on pause while we're all at the Runoffs. We'll start in on the moulds once we get back...

I'll be arriving at the track this Sunday, and leaving shortly after our race on Friday, or maybe Saturday morning if things go long on Friday. As is typical with the Runoffs, we'll probably be twiddling our thumbs most of the time, so if you get a chance to duck out to the track at some point, we're paddocked in the Toyota tent up by the start / finish line.


Cheers,
Rennie