Barge Board / Flat Floor Design
 

Been meaning to ask this for a while and now finally have a proper sub-forum to ask the question. I'm planning on doing a barge board / flat floor / rear spat / vented front fender design at some point relatively soon. Hoping I could get some advice to guide my design and learn a thing or two.

• Is there a method to the madness on designing DIY barge boards without any means of CFD? It would seem to me that you are trying to control airflow without understanding the airflow as its difficult to visualize.
• I currently have front wheel spats where the outer edge of the spat is flush with the wheel face to cover up the front area of the tire. Does designing a barge board on the other side of the tire to come out just as far make sense?
• What is the drawback to designing a barge board that sticks out too far or not far enough? Drag vs downforce like a splitter?
• With the airflow behind the front wheel being disrupted, is 6mm alumalite still strong enough to use for the application or should 10mm be used like what's recommended for splitters? 6mm is a bit cheaper and lighter which would be preferred if possible.

I'm sure i'll have more questions to ask as the thread develops, but just wanted to get a start to get the creative juices flowing.

In my search for information on this I found that another big factor was cooling of the trans and the diff and how to get all the hot air out that is between the flat floor and the body.

Should be a good thread as it develops

There are two primary focuses; 1) vent all of the pressure out of the wheel well area and 2) prevent the travel of airflow that is moving down the side of the car from wrapping under the car

1 is all about reducing front end lift in the most basic form and in more comprehensive designs, other aero devices or heat exchanges may vent into the front wheel well and so venting the front wheel well serves an even greater purpose.
2 is a lift and drag reduction technique. Generally, airflow under the car is moving a bit faster than the air beside the car thanks to less obtrusion, and the faster that air under the car moves via smoothing the under-body etc., the greater the pressure differential between the air beside the car and the air under it. Thus, if left unimpeded the air will follow that pressure differential and wrap under the doors and increase lift and drag as it increases turbulence, hits the rear tire, etc.. The Miata's body shape along the side is particularly conducive to this negative effect. It's beneficial for any car to reduce this, but of utmost importance for cars with significant under-car aero as in those cases it's crucial to isolate the airflow feeding the under-car elements. Preventing that under-car flow can be achieved with a vertical skirt, but I prefer the barge board approach because it provides a surface area for the pressure differential to act on and create a bit of downforce.

Yes, 6mm alumalite will do the job here, that's what I use. Here is my current setup, with a new version of the front fenders to be coming sometime next year:

https://photos.smugmug.com/2018-Even...MG_9011-XL.jpg

Funny I was just pouring over this topic today ( https://www.miataturbo.net/race-prep...nderbody-60805 ) .. especially blackbird's post on the last page.

Re: the question about developing barge boards without CFD resources

There's certainly a point of development and complexity past which CFD is necessary to ensure you're doing any good. DTM/JGTC cars (they're merging in 2020) provide a perfect example of fender and barge board areas that are developed via extensive simulation. This level of complexity would be pointless without CFD (Photo is a 2017 GT500 GTR):

https://photos.smugmug.com/Miata-Aer...2017_10-XL.jpg

For contrast, and appropriately timed since WTAC is just a day away, I would submit the HKS TRB-03. This was also designed via substantial simulation, but (in the area that this discussion relates to) relies on basic principles to maximum effect. This could be replicated via DIY methods with good results:

https://photos.smugmug.com/Miata-Aer...ts800_4-XL.jpg

Another example for similar approach on Miata -

https://cimg0.ibsrv.net/gimg/www.mia...06c7fb2b45.jpg

Question for Ryan and Moti: Did you opt for a one piece floor/barge board combo, or are you using detachable barge boards?

Mine are bolted to each other and the car, I did not see a reason to make them a quick release design, this isn't a splitter that prevents you from loading the car onto a trailer.

I am not running a flat floor due to rule limitations in my class, the barge boards can only extend inwards to a certain point so mine do just that. Moti has a full flat floor (he's in Unlimited).

Thanks both for the replies!

Can someone explain why a flat floor works "without" using a skirt type flap on the outer edges between the wheels (sorry i cant think of a word for this)....

I would think a flat floor and no skirt (or edge) would encourage air from the side coming in to the underbody flow and that adding a vertical edge (skirt) would discourage that.....for ref see motis car versus Supe's rx7.

edit:: and common belief (currently) is that reducing or limiting side air to underfloor is a bad thing.

I am interested in this for 2 reasons,
- Like Ryan, a flat floor between axles is not allowed in any class we run but flat sides with/without side skirts likely are (grey area).

- The Video Chris Harris did on the Porsche 962 where the designer, Norbert Singer said that unlike F1 of the time, the tunnels on the 962 worked BETTER with air coming in from the sides than without. Specifically at 2.45 - 3.00 in the following video.

Maybe the difference is flat floor versus ground effects tunnels...but I would think it would be similar in theory, especially if your running a rear diffuser. So it seems like opposite arguments.

Anyway, posted for discussion, further contemplation.

The answer is flow control and pressure differential.
Comparing a prototype to a formula car is a bit like apples and oranges, especially without having the full contemporary specs of both classes.
What you want is to control the air flow in order to maintain / improve the pressure differential between the top and bottom.
As a rule of thumb for the Miata shape (if there ever was such thing..), the air would love to get under the car along the sides, and thus reducing your pressure diff and losing potential downforce.
Setting a barrier along the way is "a good thing".

I appreciate that, I just thought it weird and the opposite of what is "common understanding" that they would test the conventional way with skirts (as in F1 of the time) only to find that air from the sides improved the downforce...

Anyway, as per your comments above, is their a reason you didn't add skirts to your flat floor between the wheels to reduce the air ingress from the sides?


https://cimg0.ibsrv.net/gimg/www.mia...06c7fb2b45.jpg

Design, lack of time/development etc.

I am unsure of the reason as I am not Moti but the article on Morpheus by MotoIQ says that splitter creates vortices down the side sealing the ingress of air.
How much sealing is actually happening Moti would need to clarify but another thing is a skirt would be rubbed away making it a replaceable part which is not that desirable.
I always wondered if a thin wall of bristles would do the trick.

The horizontal extension of the flat bottom IS the barrier in my case.
Running lower you start risking damage, at the end of the day this is a Miata that deals with production car compromises, not a purpose design Porsche 962 with springs that have variable wire diameter and coil wind.
Ride height -
https://cimg1.ibsrv.net/gimg/www.mia...2c04de9dab.jpg

Keep in mind that the pic above was taken with the car running 1400/700 spring rates, it's not soft.

How are you guys attaching your barge boards on the bottom if you dont mind sharing pictures?

Fooking Hooning along :)

Cool thanks for the explanation.

on a side topic....1400 front springs Yikes! :)

Yeah, driving with so much spring is an interesting experience!
Choosing the rate was an educated guess I had to take before SLB because Creampuff was set to run with more downforce than any other Miata.
Emilio and Ryan were both running a softer setup but have since gone up to rates that are in the same neighborhood.

Bullet ran 1400/700 at VIR with an RB 1.25 front bar, 14 SPM rear.
Our starting point for Vegas is 1600/800 with Small Fortune 1.25" front and .625 rear three piece bars. Because aero platform

Appreciate the feedback and photos so far. I'm curious about the leading element question, but I have a gut feel that's too far into CFD land to have conclusive evidence that makes it worth the effort.

As far as mounting is concerned, what is the rough feel for the weight that a flat floor needs to support? I can stand on my splitter leading edge (175lbs) without issues. Is it safe to say you should design a flat floor with similar capabilities? My intention is to add the least amount of weight as possible which ties into hardware / bracket quantities and sizes.

Edit: I don't intend to be able to stand on my barge board

Personally I would consider ability to apply a human sized load to barge boards a decent test given the loads it will see are likely under such a force.
I would also imagine that such a test is not as necessary because the lower pressure areas will be near the pressure differential creating areas.
So the splitter and the diffuser and the parts near them will need the most support but how much depends on your efficiency and design.
A brief look through McBeth will show that the forces are not just applied at the devices and the devices design affects how much of that is on the central floor portion.

I would listen to Moti, Ryan and Emilio on this as they all have things upwind of theirs so will have tried creating vortices to seal the underside wrapping airflow.
In Moti's Morpheus MotoIQ article it is stated that his front splitter does this but I am not sure of the timeline and whether it actually worked.
Its also worth noting Moti runs aggressive spring rates so likely will have a different affect than people who have bounce in their shocks.

From your pictures I would also recommend shaping that rear flap some what to make it less abrupt. Sharp turns generally create drag by the bucket. Once again you can look to Moti (I think on Morpheus) for a single panel design that curves out allowing gentle change of direction.

I'd believe elements on the barge board would more care and work than the average person has resources for.
I would also assume that anything on the barge board would be preparing air for use by something further downstream (ie not the barge board). My assumption for this is that vortices and such take "time" (ie distance) to form so elements that aren't dive plates won't apply their effects until after. Those effects could also be unhelpful or far wider ranging than initially though without testing, CFD or both.

Any shots of how you're supporting the outside edge? Thanks!

I would avoid using Dzus fasteners for any flat bottom elements and highly recommend switching to something with positive retention like bolts and weld nuts.

I like the concept of using a flush mounting method, but I'm not sure I'd trust Dzus fasteners for a load bearing in that direction. I'm currently digging around hardware websites to find a combination with a bit more positive retention like Moti has mentioned. Most of what I'm finding is going to force me to give up having true flush mounting. Not sure a bolt head sticking <1/4" from the surface of the flat floor will give noticeable air flow issues.

Hat inserts with recessed bolt heads

In for pictures of how these things are mounted on other's cars.

For Street/StreetMod class TA cars, the bargeboard outboard edge may extend up to 3" past the body and the inboard edge may not extend past the pinchweld which removes the possibility of mounting it to the frame.

I'm looking for inspiration. Trying to come up with an incomplex way to mount the bargeboard to only the pinchweld that still provides sufficient support for the loading the board may see.

Materials:
I'm considering PVC trim board for ease of machining and price. (Can be purchased locally for cheap) A quick search says I can expect roughly 1.1lb per foot on the 8 inch wide board (might be too wide)

I used that stuff last summer and it needs a ton of support and it still was all wavy and sagging between supports. you would have to run a piece of aluminum angle along the edge of the whole thing to get it stiff enough.

Good to know, thanks.

That wouldn't be too big of a deal but is surely going to increase weight and cost... Will need to rethink that.

What about 1/2" Birch Ply like all our splitters for a cheap option?

No one uses "search"? :slap:
https://cimg3.ibsrv.net/gimg/www.mia...7aff6466a7.jpg


More pics in the Morpheus thread.
Is there interest in those pucks?

On the point of attachment of flat floors to the vehicle, I contacted a company here in the UK called Clarendon Speciality Fasteners with regards to my solitter design. Their aerocatches have a safe working limit of 270kg per catch! (Whats that like 500lb?) Meaning a set of two for ~$50 should be capable of supporting 1000lbs and still be quick release.

​​​​​​Certainly will be looking to utilise these on my splitter

Wilson

Do you have a link? and it is only 595lbs

Which rulebook is this per? Gridlife or others?

Edit: and Moti I was aware of your setup. Super nice. I just know that's not really an "off the shelf" design which is more where I was trying to direct ideas to. Do you have any rough estimate on sale price for pucks like that? I'd imagine they aren't the cheapest thing to turn out on the lathe and drill press.

http://www.clarendonsf.com/ is the manufacturer

This website links me to the likes of merlin Motorsports or demon tweeks to purchase .

If you're looking for a simpler version of what Moti did you can run a plastic flanged washer glued to the carbon, with a button head cap screw through it. Won't be quite as low drag, but significantly simpler to assemble. Parts can come straight from McMaster-Carr. They'll also be a lot more tolerant to mistakes gluing the parts up.

Woods good for splitters as an off track experience could be expensive with anything else. Barge board assemblies would seem pretty hard to damage. I'd look at carbon or S Glass with either aluminum honeycomb inside or a layer of balsa wood. McMaster also sells aluminum honeycomb with aluminum on the facing sides. Not super cheap, but could probably be assembled for $250 or so.

The Dzus fastener above is pretty scary as the load is really cantilevered out there. If you can't go beyond the pinch welds McMaster (again) sells screw on nut inserts and glue on nut inserts that could probably be used just outside the pinch welds if there's a flat enough spot (or one can be made).

Do you have a link or mcmaster part number? I know what you're talking about and I've seen them used on splitters before, but I've tried every search term I can think of and I've never been able to find them on mcmaster or google image search.

What would make it expensive? The fact that you have a very strong piece of material between two tires and bodywork?

Also post up a link or mcmaster p/n

Some links to alumalite suppliers. And Pat I think now i now what you meant. Alumalite in this application is most likely cheaper than the birch we use for splitters.

https://www.thesignchef.com/custom-s...lumalite-signs
https://8020.net/shop/2637.html
Alumalite


And then a picture of how its mounted on moti's car.
https://cimg7.ibsrv.net/gimg/www.mia...8c5819dde0.jpg

Close, but those aren't even deep enough to fully cover a button head. The ones I've seen had a full-depth counterbore to use with a socket head cap screw.

Downloaded the washer in question with a button head bolt and plugged into solidworks for a visual reference of how much it sticks up. The overall height of is 0.095"

https://cimg9.ibsrv.net/gimg/www.mia...540750abb0.jpg
https://www.mcmaster.com/mva/library...91255a541l.gif
https://www.mcmaster.com/mva/library...92856a105l.gif

Yep, I downloaded the cad and measured it too. Still not the specific product I've seen used in the past.

Personally, I've used carriage bolts on all of my previous splitters and undertrays and have no intentions of changing. They have smooth, large diameter, low height heads that should have minimal effect on airflow, and there's no allen socket on the bottom side to get worn down and make disassembly a pain. I've only used them with 1/2" birch splitters so far but I bet they'd work with alumalite too if you got the hole diameter just right.

https://www.mcmaster.com/93226A240

Might give these elevator bolts a try on my next splitter.
https://www.mcmaster.com/93226A240

Also a "fanged" version:
https://www.mcmaster.com/92963A655

Seems like a good setup for a splitter. How would you tighten then on the barge boards. What would you assembly process be since you lose access to the top side when mounting.

Yeah, I kinda forgot we were talking specifically about hardware for barge boards. Negcat for me. :hatecat:

Idea: Weld or bolt a set of pins onto the outside face of the v8r/FM frame rails, with the pins pointed outward toward the pinch welds. Bolt two longitudinal (parallel to frame rail/pinch weld) pieces of angle aluminum on the top side of the barge board using your low profile aero hardware of choice. The inner piece of angle aluminum has clearance holes on the vertical leg that slide onto the pins. The outer piece of angle aluminum has clearance holes for bolts going into the pinch weld, like in the above picture of Moti's car. This way the barge boards get installed and removed with tools from the side instead of from the bottom, and you potentially don't even have to jack the car up for install/removal.

Or instead of pins you could just have a couple pieces of angle welded to the frame rails that the boards just sit on top of, with a similar outer setup to moti.

Stumbled across those same cup washers last night and currently working those into my design to see if its feasible. My goal is to do ZERO welding. I'm picking up alumalite tomorrow. Will be making a plywood prototype first. Nice ideas getting tossed around here!

Yep, I just had that same thought while driving to lunch. :likecat:

You could use your frame rail bolts and bolt up a piece of angle with a hole then on your barge board have a hole with the below stud to act as an alignment pin



https://cimg0.ibsrv.net/gimg/www.mia...68fc7d65e5.jpg

https://www.mcmaster.com/mva/library...ed%20studl.gif

Or if you really want to duplicate my setup, save the weight of the angles altogether by drilling some holes and weld some weld-nuts directly to the frame rails :)

https://www.mcmaster.com/90563a660

The majority of force will be on the portion of the skirt outboard from the bodywork (pressure differential between top and bottom is greatest there). Therefore you need your inboard mounting points to be fixed, not just sitting on a shelf, because otherwise the outer mounting points will act as a pivot and the inner edge of the material will want to lift.

Makes sense. I added some stuff to my earlier picture and replaced it. For a non-weld solution for OP that should work shouldnt it.

Are you against welding because you can't, don't want to or don't want to impact the chassis.

If adhesive is okay: https://www.mcmaster.com/inserts