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Discussion Starter · #41 ·
Here's how the diffuser will look under the car.

You'll note that each channel has it's own vortex generator so each strake will create a vortex along with the generator on the frame. You'll also note that the strakes go full length, half length, full length. The angle of the strakes is a total of 1.5 inches.

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Discussion Starter · #42 ·
The first full episode of TOS is done. Diffuser design discussion, example of how to make strakes from ABS plastic, strake mounting methods and pointless information.

Next episode will be mounting the diffuser to the car, mounting the bargeboards and updating the front air dam since it's getting ratty from whacking stuff like squirrels, old ladies, some clown with a little yippy dog that wouldn't shut up, several beer cans, the driveway, that one neighbor, etc..

The design is turning out as I had hoped. There are some fine tuning things I want to do, perhaps make the strakes thicker for more vortex generation, possibly painting the end in a bright color for sporty effect. It's been a PITA doing the work in cold weather - it's taken several weeks longer than I wanted but numb fingers won the argument.

Youtube description:
EPISODE ONE - DIFFUSER WALKTHROUGH AND STRAKE MAKING

AIRTAB LINK IN VIDEO INCORRECT. SEE BELOW FOR CORRECT LINK

Links:
Amazon abs 12 x 12 sheets

Amazon abs 18 x 21 sheets

Amazon abs 24 x 48 sheets


 

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Discussion Starter · #43 ·
V1.0 of the diffuser is done.

I've finally mounted the diffuser to the car. Needless to say, it needs fine tuning. After a drive with it on the car (behind the "today is the day I'm going to drive 25 in a 55" crowd all the way ),

I did some clearance tests, hitting 4 of the steepest parking lot and driveways I ever go to. The strakes scraped (say that 4 times real fast) on two of them, so obviously I need to pull it off the car and shorten the strakes, probably by 1 1/2 inches.

Another issue that you can probably see in the top photo is that 5 pieces of the mounting hardware is resting on the bumper cover, causing the ripple you see in the frame. Haven't decided what to do about that as yet.

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hmmm, i have an aftermarket backup camera on my car that can be "turned on" all the time, though it's distracting when on all the time, perhaps next summer I could tape up some yarn and go for a highway rip and see what happens at the back of the car and then do the same with a diffuser :)
thanks for the diffuser idea!
 

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Discussion Starter · #45 · (Edited)
hmmm, i have an aftermarket backup camera on my car that can be "turned on" all the time, though it's distracting when on all the time, perhaps next summer I could tape up some yarn and go for a highway rip and see what happens at the back of the car and then do the same with a diffuser :)
thanks for the diffuser idea!
I can give some pointers right now.

$50 @ Amazon, Akaso Brave 4 - wifi sport camera, 1080p, 60fps. Comes with all this. I've got 20 adhesive mounts under my Stealth in various spots. Using an extra pistol case I had to hold it all. Spent $20 on a suction mount like what they use on television shows. Protip: Use the camera app on your phone when you're driving up on your ramps as a spotter.
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First, subscribe to kyle.engineers on YouTube. He spent a lot of consultant time with me working out the aero on these cars. At lot of our discussion is proprietary but I can give generalized help.

You've got a ton of dirt and gravel in your rear bumper cover because that thing is a sail up under there sucking in road dirt.

Think about vortex generators for the banana wing. They woke up the aero with my wing a lot. If you do go with a diffuser, getting air moving correctly back there is a must.

Also, the bargeboards I designed are a must if you have you have an air dam. Certainly if you're after real downforce, going after ground effects is a good idea simply from a safety POV, so you'll want an air dam.

One thing I insisted on is being able to take it off easily. 4 screws and it pops right off. I may use a 2 part system or a dzus screw system if it turns out I take it off a lot.

We'll be posting instructions fairly soon. That way people can avoid pitfalls. The ABS plastic is certainly a good direction - make it modular so WHEN you break it, it's easy to fix.
 

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Interesting post. I'm a bit of an aero guy myself with a bit of race testing trial and error on these cars of the years. Cool to see that your diffuser pretty closely resembles mine. I cheated and did mine in CFD though. What was your final angle of attack for yours?
 

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Discussion Starter · #47 ·
Interesting post. I'm a bit of an aero guy myself with a bit of race testing trial and error on these cars of the years. Cool to see that your diffuser pretty closely resembles mine. I cheated and did mine in CFD though. What was your final angle of attack for yours?
On my Stealth, there is a steel shield over the gas tank. The front of the main frame fits between the shield and tank and then the bumper cover. This makes the angle 8 degrees which is opimal.

Having a Mercedes F1 aero engineer helping is more valuable than I can say. I don't think I'm violating the NDA with this protip: yer outboard strake (and others) benefits from a 5 degree angle (side to side) which increases the venturi effect. That is, the end towards the front is where the 5 degrees starts.

While I'm at it, here's an update. The strake design called for a 4 inch tall strake with a 1.5 inch drop from rear to front to accommodate the angle. I mounted the diffuser with the intent of initial testing with the following goals:

1. Pavement/ driveway strikes
2. Will it hold up if #1 happens

With the strake height, it did strike the pavement but not enough to do any damage.

Thus, the strakes need to be adjusted. I'm adjusting them to 3 inches so there's plenty of clearance.
 

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Discussion Starter · #48 ·
I haven't updated the build in quite a while. After I sliced my finger to the bone, I had to wait a few weeks for that to heal and by that time, it was time for January cold to set in. 15 degree weather ain't the best for doing mods..

But, I've got a tank of propane for the heater (50,000 BTU) so I can get back at it.

The diffuser is up to version 2.0 now. I've decided to re-design the strakes - they were dragging on the ground going into/out of driveways and parking lots, so we've decided to reduce them by an inch.

It will affect the downforce but not by that much. The consultant (Kyle Forster) is heavy into prep work for the racing season working with various teams so he's busy as a one armed paper hanger but we did speak last week on the number of and angle of the strakes (side to side not height) to achieve the best flow which I'll incorporate into V2.0
 

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Watched the video. And have a couple of suggestions that address the criticism of booting vs gluing the layers together and another suggestion for resolving the being issues when you hear the flat sheet to make the 90° angle.

For those that are Aerocdynamically neurotic, why not use round button headed screws/bolts.

As for preventingxthe warping of the plastic when heating it up to bend it, clamp a 2" length of 1/4" flat steel " on top of the sheet you're heating. That will do two things; act as a heat sink for keeping the top sidet cooler AND provide uniform pressure for the length of the seam or bend getting you a more crisp uniform line. Regardless well done! ..."measure once cut 3x" lololol!!!
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Discussion Starter · #50 · (Edited)
START OF V2.0 DISCUSSION
From this point on, I'm developing a wiki article about aerodynamics


For those that are Aerocdynamically neurotic, why not use round button headed screws/bolts.

As for preventing the warping of the plastic when heating it up to bend it, clamp a 2" length of 1/4" flat steel " on top of the sheet you're heating.
Peace
Here's the rule: anything other than a flat or smoothly curved surface increases drag. So yes, round headed screws will induce drag. Even that tiny bit over a long length of time will make a difference in drag and downforce. That said, you can use round head screws if you cover them with a flat surface. Two words: Gorilla Tape.

Remember, we're not making a Formula 1 car here, we're just using a Formula 1 engineer. Getting into the deep weeds, if you take your rear wing and decide it's getting just too many chips in it and decide to put a tape on the leading edge to prevent your chips, what you've just done is introduced a stepped wing which will create lift and makes the wing useless. Many times even .01 inches is enough to make a difference - the area where the flow is attached is decreased by that piece of tape, reducing the theoretical width (front to back) of the wing.

The entire idea behind aerodynamics is that you want the smoothest surface possible which is why most teams and designers do the slot and glue technique (where you cut a slot in the material, slide the base the strake in and glue it. That's a very simplistic explanation but for this discussion suffices. The reason I'm not doing that is that I expect damage and to do modifications. More than likely, I'll do the slot and glue technique once I'm satisfied with the design and whether or not it gets damaged easily.

Almost none of the videos are done so while your suggestion is excellent about clamping the steel to the product, that's exactly how the strakes are formed. A simple flat piece of steel will bend up in the center when it's clamped which makes it's use....er....useless. What you want instead is a length of angle that will hole the strake solidly. The warping isn't actually that bad to begin with because as the plastic cools, it flattens out.

I happen to have a handy length of formed steel. As in the steel crossmember under the plastic nose of the car that I removed for the splitter just happens to be perfect for that. And, don't forget that the strakes should not be straight, there needs to be an angle built into them to achieve maximum effect - that's one of the major reasons why a bolt on solution isn't a solution.

Also, the diffuser is up to V 2.0 at this point using the 3 inch height for the strakes. Yes, that's going to reduce the downforce a LOT but as opposed to ground strikes, it's preferable in my opinion. However, the frame of the diffuser is still longer (height) than the strakes so the air that's captured is still there.

After some more testing and discussion with the consultant, we both agree that a secondary vortex generation solution will increase the downforce, so what I lose to the 3 inch strakes is made up for in that part of the design.

The crossmember clamped to a piece of ABS before cutting and forming.

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Discussion Starter · #51 · (Edited)
So it's time to start figuring strake angles which is where pi, tangents and degrees come into play. Or you can do what I did and use an online calculator which is the point where you realize that apparently all those classes were a total waste of time.

At any rate, the calculations tell me that over a 21 inch length to get the strakes angled at 5 degrees, I need to have one end 53/64 closer to the side of the diffuser. The good thing is I did all the legwork on this so if you're following my plans, you only need the 53/64 figure.

So, the strakes need to be angled so that the entry end towards the front of the car is shorter than the back end at the rear. The idea is to keep the strakes perpendicular to the ground (as much as possible). This is difficult because the difference between the front and rear of the diffuser is well over an inch. Since the highest the strakes are is 3 inches, it's difficult to form that small of a piece of plastic - so I've cheated and made the strakes to that there is a 1/2 inch difference from front to rear. Another issue is that the ends of the strakes at the front would be so short (height wise) that the purpose of helping with tire squirt would be pointless. So I've reduced the angle (front to rear).

The other change I'm making to the production process of the strakes is how the angles are achieved. For previous versions, I was forming the strake and then cutting them to get the angle.

In this version, when I draw the line where the strake is formed (the line along which it's heated to make the 90 degree angle), I'm drawing the line crooked so that the angle is built right into the strake.

The new strakes have been cut and formed and they turned out better than I thought. As I discussed in the last post, keeping the center of the strake from rising or warping during the forming process as suggested by LaughnJar, I use a formed steel piece that normally sits under the nose of the Stealth - which I had to remove for the air dam.

Protip: place your C clamp OVER the plastic
to prevent the metal piece from bowing as well.


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For heating the strake, I'm using a propane
torch instead of a heat gun because I can
pinpoint the heat better.


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The circle shows how the plastic looks at
optimum heat (loses the pebble finish).

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Discussion Starter · #52 ·
So, I'm getting ready to mount the strakes for version 2.0 and applying what the consultant has been suggesting which is a curve to the outboard edges of the diffuser.

As I understand it, this adds to the venturi effect. A lot of our discussions get into a lot of technical verbiage that would probably muddy the waters for most people (myself included) - the whole exercise has sent me to cracking open online textbooks and formulas that I haven't thought about in years.

The gist is a 5 degree curve which I talked about in the previous post. Getting the exact angle correct is highly difficult in a home workshop. 53/64 of an inch. But somewhere between 3/4 and 7/8 will get me in the neighborhood. I haven't crossed the bridge of how to curve the entire length of the strake which I suspect isn't going to happen unless a eureka moment hits me.

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One of the physical design aspects is achieving the angle of the diffuser (front to rear). When I use the crash shield in front of the gas tank as the forward mounting and the bumper cover as the rear, the angle is perfect. However, with the strakes installed, the diffuser becomes very stiff so that I now have to account for the gas tank itself. Mounting it without this consideration puts a ton of pressure on the crash shield (downward) so that I have to create an angle at the front of the diffuser to accommodate this issue. This of course will have the effect of shortening the diffuser so that mounting it means have to move the mounting holes in the bumper cover forward by approx. 1/2 inch.

Here's a couple of our exchanges to help everyone understand the process. Keep in mind the intellectual property and NDA we have keeps me from posting a lot of the information.

It is of my opinion that the higher centre, lower outside is the superior loading distribution, for three reasons:

1. The loading distribution is naturally more elliptical, which will inherently be more efficient if the edge vortices are not providing significant suction.

2. The lowered outer portion will decrease diffuser expansion near the tyre, reducing tyre squirt ingress.

3. In the event that we are getting significant edge vortex suction, the ground proximity in this portion is lower, and therefore we will get more induced load.


So with respect to the curved diffuser question, there is no reason you cannot curve the diffuser in the manner you propose, it is in fact quite a common thing done on racecars. Often we have the leading edge as all flat, but then the trailing edge could be either of those examples. For example, F1 cars have a higher centre than outside

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Discussion Starter · #53 ·
Just came across some photos of the NASCAR next generation car. With a diffuser, similar in design to mine. They've got a wider center section.

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I haven't crossed the bridge of how to curve the entire length of the strake which I suspect isn't going to happen unless a eureka moment hits me.
Well the ABS is pliable enough to be bend to the angle, the problem is just getting to hold the bend, correct? So why not slot the base of the diffuser itself, and then put the strakes through from the backside? Using a compass(or pen and string if you are going super low budget) you should be able to get your curves pretty uniform, then just cut out the slots using a rotary tool or something similar. You might have to step up the thickness of the base to support the pressure the curved strakes are causing, but it shouldn't be too bad. This slotted style would also reduce drag pretty significantly I'd think since it would get rid of all the bends and rivets from the surface that actually sees airflow.
 

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Discussion Starter · #55 ·
Well the ABS is pliable enough to be bend to the angle, the problem is just getting to hold the bend, correct? So why not slot the base of the diffuser itself, and then put the strakes through from the backside? Using a compass(or pen and string if you are going super low budget) you should be able to get your curves pretty uniform, then just cut out the slots using a rotary tool or something similar. You might have to step up the thickness of the base to support the pressure the curved strakes are causing, but it shouldn't be too bad. This slotted style would also reduce drag pretty significantly I'd think since it would get rid of all the bends and rivets from the surface that actually sees airflow.
Those suggestions actually rattled around in my cranial cavity recently. But the slot and affix method won't really work at this point for two reasons. First, the metal brace that runs across the back to induce the convex curvature and second, the strakes will more than likely need ot be moved around once we do tuft testing with them attached. I take that back, they will have to be moved. There is no possible way I can get lucky enough to have 6 strakes in perfect position the first time around.
 

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Well I mean for the prototype it might not make sense, but for the finished product it might? I mean with all the effort you've put into this I'm sure you are hoping to get something out of it. Whether that be actual financial compensation from selling the plans, or just general praise for publishing the plans or whatever.
 

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Discussion Starter · #57 ·
Well I mean for the prototype it might not make sense, but for the finished product it might? I mean with all the effort you've put into this I'm sure you are hoping to get something out of it. Whether that be actual financial compensation from selling the plans, or just general praise for publishing the plans or whatever.
Well, I'm retired and well off so I don't need the money. Paying the consultant really isn't a big deal for me. Neither is doing the research. There are reasons why I'm doing this without expecting financial gain. I don't think at this point that I would patent or claim intellectual rights at this point either.

I can actually answer. It sounds flippant but I assure you it's not: Esprit de corp.
 

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Well, I'm retired and well off so I don't need the money. Paying the consultant really isn't a big deal for me. Neither is doing the research. There are reasons why I'm doing this without expecting financial gain. I don't think at this point that I would patent or claim intellectual rights at this point either.

I can actually answer. It sounds flippant but I assure you it's not: Esprit de corp.
Well yea that's what I meant by "general praise". I mean if you are willing to actually publish how to make the finished product I'd be ecstatic. I'm going to start road racing my vr4 here soon and most "street" classes only allow for a diffuser or an adjustable wing, not both. And seeing as I have working active aero(but heavily leaning towards finding an OEM combat wing), having an actual functioning diffuser might help me skirt the rules a bit.
 

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Discussion Starter · #59 ·
Well yea that's what I meant by "general praise". I mean if you are willing to actually publish how to make the finished product I'd be ecstatic.
Most of the cars out there are like bars of soap - there's millions of them, all looking the same. But, if you've got something that's unique, there's a balance in that car that gives it an elegance and feel that is unique. Something that creates pride. A classic car doesn't become that overnight. Only time will do that.

The past cars, both the famous and not so much deserve respect. The respect of their legacy, of the people that designed and built them. Each carries their own history, their own personality.

But you have to move them on to the next level, so that becomes the future legacy for future generations to enjoy.

I love looking at the past, the past cars, the ones with personality, with their individual looks, their own little quirks. But at the same time, I want to make them better, to fulfill their purpose of bringing enjoyment.

This is why I do what I do with my vehicles. To bring joy and satisfaction to myself and others. It's stimulating, like remastering a piece of music, to put modern technology into it, to use what we've learned and developed from the past in order to make them better than they were, to make them achieve so much more.
 
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Just came across some photos of the NASCAR next generation car. With a diffuser, similar in design to mine. They've got a wider center section.

View attachment 292751

AND THEN AFTER ALL THE EFFORT, METICULOUS ATTENTION TO ACCURACY OF H, W, L, ANGLE, SLOPE, OFFSET, AERODYNAMICS TO THE MICROMETER, ETC AND EXQUISITDLY PERFRCTLY ALIGNED INSTALLATION... I DONT SEE THAT SPEEDBUMP JUST ONE TIME AND THAT SOUND FROM MY UNDERBODY IS 100 TIMES WORSE THAN NAILS DOWN A CHALKBOARD...NEXT THING I KNOW THEYRE CHECKING ME INTO BELVUE PSYCH WARD, LOLOLOLOLOLOL!

But liksly more truth to that than Id like to admit were this my project!

AD ASTRA PER ASPERA

From a native Kansan!!!

And the best of success to you realizing the fruition of the dream for all you've invested!!!

Peace
 
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