2G Rear Diffuser Design

[AngelOfPassion]

Wow. That looks really good. Keep up the good work dude. I think a carbon fiber version would look absolutely amazing. Do you have any pics of what the fiberglass looks like along with the carbon fiber? I don't expect pictures of them actually made but do you have any of the materials laying around so we can see the texture/look of them side by side for comparison?

 

[Atuca]

I do not, the materials I will be purchasing are not cheap (going high quality here, no more HD specials ), and the difference in ordering one diffuser worth of materials, and 5, is almost twice the amount per diffuser. Hense the magic number 5 testers If you have a specific carbon fiber pattern you want (2x2 twill, plain, or w/e you want) I can order that, but PM me about that stuff.

The fiberglass version would just be a black gel coat top (to help with painting as I'd assume most people would paint it black), 1 layer of fiberglass cloth, and 3 or 4 layers of 1.5 oz fiberglass chopped matt. Haven't decided how much thickness it will need exactly yet; I will have to actually build one to evaluate that.

Carbon fiber can be just one top coat layer with a clear coat/UV coating with fiberglass matt under it, or if you are feeling really baller I can do it all carbon fiber. Since I am not a vender mass producing these, I am just gonna build to order.

I can make it look however you want, that's easy. The hard part was designing everything, expecially that mounting panel!

I have one tester already who wants a carbon fiber one, and I assume I'll get a cheap DSMer to come through for a fiberglass one, so by the end of the year I'll have finished versions of each.

Taking this back on point, need more testers still, and still very open to any design suggestions (like that back plate?) before this gets molded and ready to go!

Since I have been asked a few times: testers will be getting a diffuser to keep (not a free hand out) that will be identical to the ones open publically there after, assuming nothing is wrong with them. I just want the first 5 to make sure everything is perfect, and can be installed by DSMers both mechanically inclined and not, and to help collect data on wether or not all this design and math I have been doing is worth anything or just for looks. More details via PM, but I am making being a tester worth your time if you want one of these now.

 

[Atuca]

Any thoughts on the strake back plate? Needed or not needed? Or is everyone thinking washers on some rivets be good enough?

Still looking for testers, want to choose them by Monday, PM me!

 

[greengoblin]

I think that if you build the main plate properly there will be no need for the strake baker plate.

 

[Atuca]

The diffuser panel = main plate?

And by building diffuser panel correctly, you mean as far as thickness is concerned? Would you happen to have your suggestion on the thickness of the panel? I was going to build it up until it was stiff and not flexible any longer.

We decided to go a full 1 inch for the mounting surface on the strake, with holes drilled every 7" (I think it was). He had the metal laying around and figured make a backing plate just in case, hense I figure I ask.

 

[ed1380]

The added weight is negligible but it spreads out the force much evenly. The diffuser plate is the most expensive and washers and rivets will cause small concentrated areas of force on the fiber, and we know fiber is strong but brittle.

 

[greengoblin]

I would lay it up with a thin core to keep it light. and make it super ridgid. The strakes are going to have VERY little forces acting on them unless there is impact. Why not use counter sunk or dome head bolts with large washers and nuts.

DIVINYCELL FOAM PVC from Aircraft Spruce

 

[ed1380]

How much force will be on the actual flat panel?

 

[Atuca]

I just did a quick google search and it looks like 50 lbs is what was recorded after some wind tunnel testing on a 997 Carrera. The image of the diffuser makes it look like the panel isn't as large of an area that mine is, and I can not verify the angle of the diffuser, but I am going to guess 50-100 lbs might be what is expected on mine.

Rear Diffuser - Page 2 - Corvette Forum


There might be other data out there to say more or less, but the 50 lbs doesn't sound unreasonable to me, and the presentation of the data (actual wind testing data) makes it look to be valid.

 

[Atuca]

Still looking for testers! If you PMed me but never confirmed you agree to the terms, please get back to me! Next Monday, Novemeber 12, I will be looking to reach out to 5 people who have said they were ready to go.

<- Excited

 

[dradernh]

If this were true, then the length (depth?) of the splitter would not have an effect on downforce, but boy does it! Why? Because you're increasing the surface area that the high pressure air on top of the splitter can push down with. Of course, there's a point where extending the splitter does not produce additional downforce, as the high pressure zone at the nose of the car only extends out so far (dependent on speed and front nose design). I've been a subscriber to Racecar Engineering for a few years now and this was covered in an issue a while back while doing wind tunnel testing on a Mini Cooper racecar. I'll have to dig up the article and scan it.

Beau

If you find it, please do scan it & post it as it would be useful to know. The article was likely penned by the aerodynamicist I hired, Simon McBeath, who edits the aero column for RE. As part of his service, Simon provides follow-up support, and one of my "winter questions" for him this year is how long is too long for a splitter, practical considerations aside. My guess is that a splitter is too long when/if it, along with other front aero, overwhelms the rear downforce, which is why adjustable splitters made of MDO/plywood/whatever are so useful during testing. (Mine is now 6-1/2", starting to get in the way and, despite dive planes & a vented hood, the car still has a slight push due to a very high downforce rear wing.) BTW, Simon's Competition Car Aerodynamics book is excellent basic training for us armchair aero practitioners (and not so armchair, OP! .

I believe that the longer splitter will create more downforce principally because the area of maximum downforce is further away from the front axle, thereby increasing the length of the lever operating on that axle; that is, same downforce + longer lever = greater effect, just as it is for rear wings or lifting the Earth a la Archimedes. I continue to think that the high pressure zone above the splitter is doing most of its work pushing against the lower front of the bumper, rather than pressing down on the splitter. Always happy to be straightened out by facts, however, as practical considerations far outweigh having to be right. I just want to go fast - efficiently.

OP: again, my apologies, and this is my last post in your thread on your diffuser. Best of luck on your journey.

 

[KeelesKustome]

I just read this from page 1-5.

You sir are doing a great job. I could easily see your design being dismantled, taken to a alluminum sheeting shop and have the entire thing duplicated in a lightweight race application, and easily mass produced from their.

I would be very interested in the lightweight version myself.

Be carefull who you send your product to without signing some paper work, f you can't afford a patent, This is how someone becomes a millionair off your hard work.

 

[H@xtGSX]

...can I "borrow" one?

 

[Atuca]

I sent an email to the first 5 potential testers. If for some reason of those those 5 are unable to commit now, I will reach out to some the others that expressed interest.

Feel free to send me a PM if you want to be a tester still until I say the search is officially over, but hopefully by next week, I can order some materials!

 

[AngelOfPassion]

I just sent payment. I guess I am officially a tester. Can't wait to see this thing first hand.

 

[AngelOfPassion]

So were you able to order the materials on thursday?

 

[Atuca]

No sir, and I realized that this next Thursday is.. well.. yea.. hmm.. oh yea.. Thanksgiving!

I'll have to put this on the back burner for about two weeks, but I did make some type of progress!

 

[ed1380]

Came across this awesome video today

Formula 1 Aerodynamics with Martin Brundle - YouTube

 

[KeelesKustome]

I love those types of videos, and the possiblities that they share.

 

[AngelOfPassion]

Any small updates bro? How has the move been?

 

[Atuca]

I just sent you your weekly email yesterday, but as for the public note:

I walked into work and was told I lost my job the week of Thanksgiving, so as I had no family in GA, took the opprotunity to move back to Cali; I just got up and went. Being a contractor sucks.. 13 months and then bam, that was it.

I am in with my parents temporarily, who's residence has no garage. They have some sheds though, so I plan to clean up and fix one of them up, and figure out a proper floor so dust is not an issue while creating the diffusers.

I have two confirmed testers, the first "other" 3 didn't go through. Instead of asking 3 more people as secondary choices, I chose to not involve anyone else due to the delay. I offered a refund to the first two testers, but they both chose to stick with me through the delay while I get back on my feet. Since I only had 2 of the 5 testers I wanted, I'll have to front some of the money for materials, which is fine by me, just means that I had to wait til I got a job.

I interviewed for a new job this past Monday, and I start the new job next Monday. It is a work from home Software Engineering position, so it will be perfect to continue this diffuser project with as I can pick my own hours.

All in all this hick up put a good 3-4 weeks delay on the diffuser project, but it is still happening. I can be forced to move across the country, but nothing can take from me the love for my DSM

 

[AngelOfPassion]

Yeah I saw your email about the job and all that stuff. (sucks dude) I was just wondering what has been going on lately and I wasn't at work to get the email. I'll see it on Monday haha.

Glad you are starting your new job though!

 

[ViciousLord]

Wow, dude. I'm happy you found something so quick!

 

[Atuca]

It was decided it was in both my employer's and my best interest to receive my first paycheck after the start of the new year, so the delay is officially over next week.

I wanted to bump this thread and see if anyone had some ideas on what they would want to see as far as collected data is concerned, and if anyone had any ideas on how to measure results.

As of now, I am looking into buying a few gopro cameras, and one of my other testers intends to as well. Capturing airflow data won't be hard with tuffs, but what do you guys think about as far as specifically capturing drag and down force data? If we are talking about 50 lbs of downforce, how would you capture hard data like that, especially when the amount is small enough I don't think measuring car height would work, or spring tension maybe? I don't know, I'm open to ideas and suggestions!

 

[AngelOfPassion]

Here is a good thread on measuring downforce yourself. A couple posts won't help us but there is some good info and some ideas on how to do it without a wind tunnel:

How do you measure downforce? Ferrari Forum

Overall though I think if you want to measure the downforce you are going to need to rent a wind tunnel...