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Old 02-24-2008, 11:56 PM   #1 (permalink)
Join Date: Dec 2007
Location: Bay Area
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The Miata - '01 Mazda MX-5 Miata
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Building an HPV Fairing

It's that time of year again! It's time to make our fairing for this year's competition. We've been designing for the better part of 6 months, now it's crunch time and time to manufacture. I'll keep updating this post as progress is made.

I'll put a better into here eventually... For now, here's some history...
2006 Model

2007 Model

The 2008 Model shares characteristics of both previous models (moreso the 2007).

If you ever want to make a fiberglass or CF or Kevlar etc. fairing for your car - the process will be very similar

2/24 - Foam Cross Sections
Today we sketched out cross sections of our fairing onto 1" 4x8' sheets of foam.

This section looks squid like : D

Here's a bunch of the top sections on one sheet of foam.

What does done do with foam cross sections? You cut them out, glue them together and make a male plug. More on that later.

Careful Details: There's 2 or 3 keys. A quarter inch PVC pipe will be put through these holes with align the entire thing. The rectangle thing you see is a 5" by 24" index rectangle extruded through the entire model. We used this to make sure the projector was calibrated to 100% scale. How did we get sections? We just used the cross section view in Solidworks directly off our 3D model and projected it on a wall.

2/28 ish - Vendors and Models
Timing is critical. Ideally, we would be much further than we are. But predictably, we’re right where I thought I would be.

Composites Order In? Check - Pickup Friday March 7 from S. Florida
Home Depot Supplies? Check - Got the last (for now) items today and delivered to workshop
Frame Team? On Track - manufacturing begins Saturday

Rose, from UCF’s ASF budget office has been really great this year (ALL of our order must be signed by three people, the approved by someone in Rose’s office, then Rose has a PO made and she submits the order to the vendor). She was out, sick, for the past two days and the pile up of paperwork was obvious - a lot of people depend on her (and she does a great job). I visited her today to follow up on some budget requests, and she moved us to the front of the line - I had a phone call from one of our vendors within 30 minutes to work out a pick-up date (it’s a really big and fairly complicated order).

Tomorrow, I will start around noon on cutting foam and gluing together. Hopefully, the plug foam can be finished (glued).
Saturday, I am going on Catrike’s annual ‘bent rally. I don’t own a Catrike (I wish) but I’ll be riding my Challenge Distance.
Sunday, I hope to have the plug sanded and an initial coat of joint compound applied (so it can have a nice long/slow cure). To save on Bondo costs and sanding time, we’ll be using wall joint compound. I currently have a few samples curing at the moment to test for dry times/conditions. It’s cold right now, so hopefully that doesn’t cause problems.

So right now, I’ve got some compound curing on a rough scale model (testing surface finish of this stuff). This model will need a lot of compound to reach the proper shape… Oh, and because I’m hinting on shape here - material hint: think graphite and bullet proof material - no paint and light weight : D

3/02 - Plugging Away!
Friday, here's what we look like....

Foam sections were cut, then glued together.

The next step is sanding... To speed the process up, a cheese grater did the bulk of the material removal. We then followed up with sand paper and drywall screens.

Once we finished sanding.... Joint compound was applied. While it takes longer to cure - two 5 gallon buckets cost the same as 1 gallon of Bondo. Additionally, if we used Bondo - we would have needed to apply a layer of epoxied fiberglass as Bondo will melt styrene foams. Lastly, we can wet sponge sand joint compound and get super smooth finishes.

Details - be sure to apply enough joint compound as not to expose any foam. Polyester resin + styrene foam is a very bad combo.

3/7 - Materials Pick Up

I drove to West Palm Beach to pick up some materials. 10 gallons of polyester resin, a mess of epoxy and a whole bunch of other materials : D Heres some stuff in my car - theres four more boxes that you cant see : D

3/10 - Bottom Job

The interesting thing about wall mud Apply a thick coat, and its difficult to get bubbles out. So much so that we spent about a day of labor filling bubble holes, re-sanding - then discovering more holes.

Oh, we made some samples today... This is a preliminary first test...

Combos include base fabric alone. Base, coremat (1.5"), fiberglass (3" wide). Base, Foam (1"x.125"), glass. Base, Foam (1"x1"), glass. Base, Kevlar.

3/11 - Bondo Epiphany

To fix all those air bubble holes... Bondo! And the surface finish is very very smooth (ideal). So a thin coat for the entire plug! Sanding comes soon...

And we did more sample testing....

Foam is much lighter than the coremat as it doesn't soak up much/any resin. It's also much stiffer (or seems to be). I cut cross grain and with the grain of the foam (2 samples each) using a jig on a band saw (for uniformity). They're currently on my patio under vacuum....

The plan is to get into the materials lab tomorrow and do some testing... Thus far, I've worked out an Izod impact test - tensile testing and potentially a bending test. I'm designing an abrasion experiment now.

3/14 - Woo Glass!
In the past three days -
First round of material testing
Finished Plug
Third round of sample making
Built a plug frame/table
Cut table and sealed plug to table with Bondo
Applied mold releases (wax and PVA)
Laid up a tool (1 of 2)

Tool Table

Cut Table

Edge of Plug bondo'd to table surface

Wax applied - then PVA sprayed (which is why it has a green tint)

First Tool as we left it today

So - materials testing - we did Izod impact testing with some surprising results. We had some samples with a layer of glass, 1/8" foam, layer of carbon/Kevlar. We impacted the carbon/Kevlar side and a curious thing happened. The foam/glass broke and the carbon/Kevlar just bent out of the way. In one case, the carbon/Kevlar de-laminated from the foam. I'll have more info on this later.

We prepared some samples for tensile testing. To do this, we made our normal samples but laminated a metal plate on each end between the layer of carbon/Kevlar and a layer of fiberglass. This metal plate allows metal gripper jaws to clamp down while a machine pulls the sample apart. Oh, the vacuum pump seized up while making these samples. I tore it down today (3/14), applied some oil to the bearing and vanes and the thing spins again! I think the heat got to it as the oil level is correct...

The plug was placed in that table to make a perfect 1/2 waterline plane in which 1 of the 2 tools could be laid up. Bondo sealed the edges (to keep resin from leaking down) - the plug was waxed at the waterline so the bondo can be separated later.

The plug is prepped with paste wax #2 (by hand) and PVA #10 sprayed on with an HVLP gun.

We only had three people today, so it was a scramble. The tool structure isn't perfect (should work though), but we applied a gel coat like layer of resin first to ensure a good surface finish. To make this gel coat substitute, mix cab-o-sil (aka aerosil aka fumed silica) into polyester resin until you can remove the mixing stick and nothing drips off (and it holds peaks). Then add a little more as the MEKP catalyst will thin it out a little. Mix in your hardener (MEKP) then apply the resin to the surface with a brush (careful not to tear the PVA). It's thixotropic - this means when you apply a force to it, it becomes thinner - but only while applying a force (this is why hitting the ketchup jar makes it come out). Smooth out the entire surface with long strokes. You may have to work the same area with several brush strokes so the resin thins out and flows enough to coat smoothly (when you let it sit, it will gel up until moved again).

4 layers of 1.5oz chopped fiberglass mat was applied. The edges were also glassed to make ~2" flange for use later.

The temperature swings today were quite insane - it was really cold, followed by pretty warm. Enough to totally screw up my hardener measurements which caused some areas to start smoking : eek : I'll use less hardener tomorrow (but it's supposed to be warmer anyway : D).

3/15 - Glass Take Two
Today we popped the plug/half tool out of the grips of the table
Cut the flange down to size (somewhere between 2 and 3 inches)
Cleared the table of excess bondo
Put the plug back into the table
Fixed the gashes in the foam from cutting the table
Covered any exposed foam (packing tape - it works awesome as a barrier)
Sprayed PVA
Applied resin/glass - four people today : thumbup :

To pop it out - scrape around the flange with a putty knife. Then, shake the table. Lift the plug with a jack (throw some foam under to protect it) - bang on the table a little more... Enough banging will get it to pop out. You don't want to separate the tool from the plug just yet...

Flange trimmed with a jigsaw.

By the end of the day - the result... The fourth person really helped. We had one person dedicated to cutting glass, one person dedicated to mixing and pouring resin and two people dedicated to wetting out (and they always worked the same areas so they know exactly how to handle challenges of those particular curves).

Oh, the wind wasn't with us today - so we didn't have as good of ventilation. We got a little stoned by the end of it - I made sure everyone sat outside in fresh air for awhile before we went back in to clean up... Yesterday, the wind wasn't giving us problems - and there were no side effects from the styrene...

3/16 - Birthday Problems : (
Today is my birthday! I'm 22 : eek : Today was clean up and mold separation day. So the entire plug+tools weighs somewhere in the realm of 300+ pounds. It was only two people today, and lifting was quite a task. The workshop was cleaned up, organized, swept, etc.

Then came mold release time... Mixing sticks were used as wedges to split the tool flanges apart. One tool came off in 30-45 minutes of labor. The other half (the first one we laid up) didn't go so easily. Eventually, we drilled 7 or 8 small holes to hit it with compressed air - and that didn't even work. We then dumped water in there - to try and liquefy the PVA release agent and soften the joint compound. That didn't work. We tried several other methods over a period of 3-4 hours....

Sadly, here was the scene....

A Chainsaw and crowabar... The mold release failed - in epic fashion. This plug is officially done... But, the good news is - the tooling surface is good! I love how well that cheap gel coat alternative works : D

So comes to an end the spring break work week. Hours tallied - 76 by me alone... I gotta see how many everyone else did (I think it's somewhere around 200-250 this week alone)...

3/17 - This... Is a Tease

It's not done... It still has another hour or so until it's finished... And then it needs some post processing... But here it is.

I'll show you what it is when it's done and cleaned up : D

3/18 - Here It is!

After several meetings and model revisions (to save on material) - this came out of a machine... Rapid prototyped in 9 hours - the material is ABS and the process was fused deposition : thumbup :

So we spoke wit another professor who controlled the measurements lab - which has a water tunnel.... Basically, he said go do it - do it now, just figure it out and get it done... My kind of attitude!

This shows the stagnation point at the front of the model...

Flow over the model - sticky all the way...

Iso view... Some turbulence due to surface finish (ridges that haven't been fully sanded down)

Smoke screen - basically, pump the dye tank pressure up and open the valve all the way....

More sticky flow

So we also did some sample testing... These were tensile tests - ripped apart until destroyed...

I'll tell you the forces later : thumbup :

And... At the end of the day, my friend on the swirl burner design project was doing some cold flow tests with compressed air and a fog machine... Here's some CFD (compressor fluid dynamics) with smoke...

That's all for today - we've also been working on our design report... All engineering type stuff, not so much with the actual build... But the extra cure time for the tools is a good thing...

3/20 - Doors!

And that's all I have to say at this time....

Cars have not created a new problem. They merely made more urgent the necessity to solve existing ones.

Last edited by trebuchet03; 03-23-2008 at 01:09 AM.. Reason: updates!
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