The Blind Apex Podcast
The Blind Apex Podcast
Episode 53: Aerodynamics 101 - The Basics
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Most of us don't have a wind tunnel or even access to computer aided aero design... yet our classes allow for aero. I sit down with AJ Hartman (www.ajhartmanaero.com) to talk about the basics and get a better grasp on where the grassroots racer should be concentrating. AJ spends a lot of time using CFD and actual wind tunnel time and he was happy to share his knowledge with us!
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Welcome to the Blind Apex Podcast. Where amateur club racers tune in to get faster.
SPEAKER_01:I'm your host, Con John Turk, and on this episode, we're talking aerodynamics. Joining me is a carbon fiber wizard, a Mustang guy, YouTube star, wind tunnel nerd, and aerodynamic consultant. AJ Hartman. Welcome to the show.
SPEAKER_03:Thanks for having me. I appreciate it.
SPEAKER_01:Uh-oh. Something already occurred. Nope. It's it's giving it's showing me the download stuff. So we're both having fun here. Um I'm recording from the back of my pickup truck, hanging out, waiting for a football game. Um, so I I really appreciate you joining me, AJ. Um, I know we've been in the same paddock area for probably 20 years. Uh off and on, I've been in the tech shed, you've been racing. Um, why don't you give us a little bit of a background on your racing and the AJ Hartman aerodynamics and consulting business you have?
SPEAKER_03:Yeah, sure. Um, I started racing with NASA uh way back in 2010. Um feels like an eternity ago now. Um even back then, I was kind of interested in you know the aerodynamics around a car, built myself a splitter. Uh back then, um, just had to buy like an off-the-shelf wing. Um around 2014 is when I really started tinkering with composites. Uh, a company from Texas called Fulcrum Motorsports, um, they made what is currently our Fulcrum 14 wing. That guy kind of just got tired of it. Um, so I purchased, I'll say I purchased the company, but it was kind of like the wing mold, and that was about it. Um and that's when I really went off the deep end of you know aerodynamics and composites. Um since then, uh a few years after that, we ended up working with um JKF Aero. Uh most people listening to this, if you're interested in aerodynamics, you've probably seen Kyle Engineer's videos on YouTube. Um I reached out to him, had him do a bunch of CFD and design work for us on um our Apex 8 wing, our dual element wings, um, our diffusers, splitter tunnels, canards. Um I might be missing a few things there. Um but anyway, so so working with him in the design stages, and then we took we you know did our manufacturing and started producing all of those parts. That was in the 2018 time range, I think. Um 2017, because I think I think Kyle went to Mercedes in 1819 and 20. Um, and then since then I've worked with him on a handful of other projects, um, you know, d designing and developing CFD for us, and then we do the manufacturing. So um, yeah, the business in a nutshell, primarily aerodynamic parts for um we'll say like closed body sedan cars, um, Mustangs, BMWs, Corvettes, that type of stuff. Um and then during all of that, 2018 is when I took my first trip to the A2 wind tunnel in Mooresville, North Carolina. Uh, I've been there probably about a dozen times now. And certain times we've actually double, tripled, quadrupled up on cars. So we probably have 15, 16 cars, probably a couple hundred uh wind tunnel runs. Real quick, can you still hear me? Because I just got a network struggling thing across my screen.
SPEAKER_01:Yeah, you're you're good.
SPEAKER_03:Okay, no, no, no. Um so yeah, so the wind tunnel, uh been there a bunch of times, um, pretty much every single time with Al Watson from Race Louvers. Um, he's doing a bunch of awesome stuff with uh race or I'm sorry, with hood louvers and fender louvers on cars. Um and in 2022, that's when him and I kind of joined forces and we're half we're 50-50 partners in a company called Track Arrow Consulting, where people will come to us and say, you know, hey, here's my car, here's the class we want to race in. You may or may not already have a bunch of stuff on your car, and we'll just kind of guide you through changes you should make without having to get as deep into it as you know, CFD or taking your own car to the wind tunnel, uh, which we would go with you if you wanted. Um so so that way, you know, you're you're you're not way off in left field on your aero setup of your car. Um so yeah, I mean, pretty much 90% of what I do is based around uh aerodynamics and composites, and that kind of brings us to where we're at now.
SPEAKER_01:Yeah, so your SN95, it's a still SN95, right? Yeah, technically gnarly. Technically, yeah. I don't think there's actually a Ford panel left on that car. Uh quarter panels are the rear quarters, right? Yeah, yeah. Yeah, yeah. So everything else is pretty much a composite piece. It's gnarly looking. And now you uh you've started messing around with the GT350. Um that's the newer body style, right?
SPEAKER_03:Yeah, that's the S550 chassis.
SPEAKER_01:Okay. Yeah, so um you're a big Mustang guy. I I've perused your parts and you've you do BMW and Mustang stuff, basically. Um I can't twist you and twist your arm into Honda stuff, which is fine. But um a bunch of us Honda heads, we've we've definitely checked out your videos. So um online, YouTube, you're I think it's at AJ Hartman Aerodynamics, I think is the name of your YouTube.
SPEAKER_03:YouTube is just AJ Hartman Aero, just like the company. Yep.
SPEAKER_01:Okay. Yeah. So um, you know, I drive a production car. Most of us drive production cars. We're not in the MPO1 world, we're not in a formula car kind of thing. And unfortunately, there aren't a lot, at least for my car, there's not a lot of bolt-on parts. And so I went down a rabbit hole. I know Ryan Bradfield, he has a newer TSX that he's built uh for Honda Challenge H1. There's not much left out there for him. He and I have been collaborating. He and I were while we were collaborating, we're like, hey, have you checked out AJ's stuff? And I'm like, Yeah, have you? And we traded videos and sent videos that he hadn't found yet. Um so you've been really helpful. Just because you make mustang and BMW parts doesn't mean you can't be helpful for other folks. So especially in the consulting part and the and the free stuff that you've put out so far on YouTube has been excellent for me anyway.
SPEAKER_02:Yeah, yeah.
SPEAKER_01:Um, but in the in the world of production cars, we all have challenges, right? Yes. Um everybody has to fit into a rule book. Some rule books, you know, like the the NASA spec three, those poor E36 guys, they get a they get the M3 facelift if they want, but they don't really get anything else. They don't they have arrow, right? Every production car comes with some sort of factory arrow factor to it, right? But they don't get extra arrow. So in the as we talk, I want to talk both about the production side and the bolt-on side. Um because I think that's a really big issue. Um I don't know how to approach this exactly, but there's there's OEM design issues, right? So a lot of us, and they they sort of go hand in hand with the rules. So uh, and I'm focusing on the front of the car because that's the problem on my car, where we have these things, the rules say you have to look at um the the the shape of your splitter can only cannot protrude from the front bumper when looked at from above or something like that. Right, right. Um, but we have these big pudgy bumpers, and then we leave these little one and a half inch splitters on there because that's all we have. Right. Um so there's a lot of design issues. I personally had mounting issues. I think all of us have these types of issues, right? Um we're trying to balance theoretically, because we don't go to wind tunnels like you do, we don't have CFD models like you do, generally speaking, um, to balance our drag and downforce. You know, and so we're we rely on information that you provide on possibly different chassis to get some sort of idea of what's going on. What kind of challenges do you see production cars providing in the aerodynamic world?
SPEAKER_03:Um, kind of like you already alluded to, just about every car is going to be different to some degree. Um you you mentioned kind of talking about the manufacturing aspect where um we we do quite a quite a lot of splitters for people, but it's just like the splitter blade, you know, the flat part. Um you can add splitter tunnels to it. You know, we have we have three different size modular splitter tunnels. But depending on your bumper, um, I'm a Mustang guy, so I'll reference Mustangs here. You know, if you have a 15 to 17, that's a different shape bumper than the 18 to the 23s. So you need a different mounting solution or the air dam that goes from the bumper down to the splitter blade needs to be different. So it's really hard to make something work, uh, I'll say off the shelf for a wide range of stuff, you know. Um, so I think that's where a lot of the custom fabrication comes in. You know, a lot of people might just do like the uh the garden edge stripping and make like a little air dam to fill that gap. And you know, it's a race car, it works well enough, they're happy with it, you know. Um, but that that leaves a lot of, I guess, variables or people's abilities to fabricate stuff can vary wildly, you know. Um, so kind of having one solution for everything just isn't really possible. Um, and like you mentioned, that that H1 car, there isn't really much off-the-shelf stuff for it, um, probably because the amount of like time and RD that goes into developing a new part can't really be recouped. And from a business perspective, that's kind of a losing strategy. So that's kind of that line. Um, you know, I I and other companies need to walk walk is you know, what what will work well enough? What can we sell enough of that still provides good performance but doesn't take too many compromises into account? Um so yeah, that's kind of one of one of the tricky bits with with aerodynamics for sure, is just every car is gonna be a little bit different, and how do you account for all of that?
SPEAKER_01:Right. And it it's Mustangs, BMWs, Hondas, Yattas. Right, right, right. And and then every time they do a facelift, like you said, your Mustang, the facelift changed, you had to change the the air dam molds and things like that, and and even the blade shape probably changed a little bit. It's yeah, yeah, it becomes tricky and it's hard for companies like yours to justify, hey, I need to make there will be profit if I make this part. So we get stuck a lot of the time with doing it ourselves.
SPEAKER_03:Correct, yeah.
SPEAKER_01:Uh most of us are doing it ourselves to a to a certain degree. Now, you and I talked at VIR earlier this year, and uh we talked specifically about the back end of the car. And I I think that's the place where we don't really have to do it ourselves, right? So yeah, if you want to jump in on that, that's fine.
SPEAKER_03:Uh yeah, because the the the rear end, anytime we've been to the wind tunnel with a car, they're almost always front arrow limited. Wings uh if you get them high enough in clean air, it's like it'll make roughly the same down force uh no matter what car it's on. Um there's some variables there, but not getting too deep in the weeds. Um it's easy enough to make a wing make plenty of down force. Um yeah, so the rear end is usually the easier, uh, easier end to make down force. Um uprights, you know, we we have complete chassis kits for several cars, um, but even if uh you know a company doesn't make a complete kit, you know, probably half of the wings that we make go out the door is just the wing. And then the customer will kind of cut out their own uprights and figure out how to you know hook it to their car. Um yeah, so rear rear ends are relatively easy. Um back to the whole rules thing, you know, you you obviously have to take um rules into account if there's a cord or a span limit or a setback height, all that stuff. Um but yeah, they're they're usually the the easier end for sure.
SPEAKER_01:Yeah, and that's just on the wing side. But it that's what everybody sees, right? Everybody sees the errors, they have a wing, they don't have a wing, they have this kind of wing, they don't. It's a swan neck, it's a bottom mount, it offsets off the bumper, it comes off the true trunk lid. You know, people see all of that. But you're right. Basically, you need to know the rules so you know how wide your wing can be. Then you need to have a ballpark on what your trunk width is or how you're gonna mount it, and then they could provide the multitude of wing manufacturers. Well, I need the mounting points on the wing at this width, and that's about it, right? And then the rest is up to you. Yeah. And and you're right, it's there's angles involved, so it's not it's not super simple, but it's it's different than the front. You can make uprights and then trim some some metal off of both pieces to get the angle the way it needs to be to have a zero and then like a zero degree wing, and then to be able to do the adjustments from there.
SPEAKER_02:Right, right.
SPEAKER_01:The other thing, the other thing for the back of the car is there's a especially the more modern cars, they have these plastic pieces in the back, and they're almost factory diffusers. Right. Now, my car personally has one, and I've done I've taken all the steps possible to keep that stuff in the car because if I remove it, it just becomes a huge air pocket. Um you see a lot of that? I mean, I I know you're doing BMW and Mustang stuff, but um, how important is the rear lower part of the car in the grand scheme of things?
SPEAKER_03:It's the whole car as a package, it's probably the least. Um aside from going with like a real proper race diffuser, a lot of that factory OEM plastic, I'll call it, is kind of just drag reduction, if you will. Um, you know, they when they make that car, they have to hit a fuel economy, you know. So one way to do that is trimming out drag. So, you know, to it's it's best that you leave it like you have, you know. Um so yeah, in in in terms of like downforce generation, it's probably pretty close to zero, uh, but it's probably a a drag reducer for sure. Um but that's a little bit of a different ball game than you know if you were to slap on a huge diffuser real close to the ground, something you really want to make rear down force with.
SPEAKER_01:Right. Um another section of the car, let's talk about the middle of the car. Now, not many of us get to run flat panel bottoms or any of that stuff, but there's lots of pieces in the middle of our cars. Um, your exhaust hangs low, your some people have mud flaps front and rear. You know, uh my car actually has a little piece of plastic in front of my wheels, my rear wheels, and I'm assuming it's to help deflect air from being on the wheel. I I'm not sure. It actually looks like it would actually produce lift, but um what should we in a production car be looking at in the middle of our cars?
SPEAKER_03:Um if rules allow it, like you mentioned, a lot of a lot of rules just say like nothing in between the axle center lines or something like that. Um but definitely if you can smooth it out, there's there's a little bit of an advantage there. Um it's a little bit tricky because you definitely want some rake to it. Uh when I say rake, you kind of want the front a little bit lower than the rear. Um, but how much can you physically do that with all the other stuff under the car? Uh heat management with flat floors is probably the biggest issue. Um like you said, you got your exhaust, your transmission, all that stuff under there. That heat needs to get some amount of ambient air across it and it needs to exit somewhere, you know. Um my own car, I don't even have a flat floor on my own race car. I I call it like a three-quarters floor. I left like a probably about a foot and a half gap down the center of the floor just to let some air in and out. Um, funny enough, I run my exhaust down the quarter panels on the side of the car. So I I could maybe do it. But even yeah, it's a project I don't even really feel like getting into, if I'm being honest. Um yeah, there's a gain there, but I don't think it's substantial. Um and that's probably one of the areas it's a little bit easier to get wrong than right. Um, so yeah, that that's a tricky area. The um those little um deflectors that you just mentioned hanging in front of your rear tire, uh you said you think it looks like it would produce lift, uh, which you're probably right. There's probably a little bit of a high pressure zone built up in front of it, but the way it probably shapes the air around the tire and the wheel well, it's probably a net gain of reducing lift a little bit, if that makes sense.
SPEAKER_01:Yeah. I mean, that's why I left it. I I figured if I can get if it's there and it's there to move air around the wheel and tire, then I'll leave it where it is because I'm sure I'm I'm getting more downforce in other places. Right. Um so the rear seemed easy, right? We just buy a wing with certain dimensions that we need to know where to where our mounts are, how wide it needs to be. Leave as much of the plastics in the rear as you can if you have them. If not, you know, it's it's the least consequential portion. And then the heat management on the middle of the car, people don't take into account. And I'm glad that you said that. Because if you look on production cars, now I know when people are flat bottoming, they move a lot of stuff, but if you're trapping your exhaust underneath that flat bottom and all your brake and fuel lines are in there, it's not helping them at all, you know.
SPEAKER_03:No, yeah, yeah. Funny, funny story, real quick. The first flat bottom I did, uh, this was a customer back in shoot, this may have been 2013, 10 years ago. Um, he wanted a flat bottom. I said, okay, and we just like literally flat bottom the car. If I remember right, I think we used some of that like uh exhaust wrap. Um, but his first time out was at LimeRock, did a handful of laps, it got so hot under there, anything rubber just melted. Like the car was smoking like crazy. Like we got lucky, it wasn't worse. Um, so then we ended up cutting a bunch of like holes and putting some like you know, like louvers and ducks and stuff in there to make it manageable. Um, but yeah, that that was like 10 years ago, that was a way.
SPEAKER_01:Yeah, I'm sure you could put I mean if you knew where what needed to be cooled and it was in a certain line, you could knack a duct from the flat bottom, maybe. Um I don't know.
SPEAKER_03:That's the tricky part because there's probably like a high pressure between your floor. So say you flat floor the car, in between the flat floor, and I guess the floor pan of the car would be let's say your exhaust and all that stuff. That that there's a good chance that's a higher pressure than the flat floor facing the ground. So if you put a knack a duct in it, you know, there's a chance you'll probably get little flow, potentially even reverse flow out of it, you know. So it's right, it's a little bit tricky dealing with pressures uh to get airflow uh in a situation like that, you know.
SPEAKER_01:Right. Yeah, so it it's it's tricky. That flat bottom setup is very tricky. I'm sure when you start looking at really doing a flat bottom, you're gonna have to be you're gonna have to look at doing wind tunnel work.
SPEAKER_03:Uh probably, yeah. And moving a bunch of stuff, and yeah, like I said, heat management. You definitely want coolers on your transmission and diffuser if it's under there and all that, yeah.
SPEAKER_01:Yeah. So let's get to the meat and potatoes of what most of us have to deal with and when the struggle is, even that you pointed out, the front of the car. Okay. So what type of how hard should splitter mounts be? How rigid?
SPEAKER_03:Good question. Strong enough that it doesn't rip itself off. Um like I I have a guys of bent frame rails.
SPEAKER_01:Oh, if they go if they go off track.
SPEAKER_03:Yeah. Yeah, yeah. I've seen that where they go off track and rip the splitter off when you have frame rails bent. So that that's obviously too strong.
SPEAKER_01:Right. So there's a balance in this in this game. So one you need to figure out some people have it easy, right? Their car can roll up on the trailer with the splitter attached. They can they they have it designed. This is stuff that some people don't think about, right? They're designing their splitter, and then they go, Well, how the heck am I supposed to strap this thing down in my trailer?
SPEAKER_03:You know, right, right.
SPEAKER_01:Uh, and then they go, Well, I didn't build it to go on and off the car quickly, right? So these are things we have to account for. Quick disconnects if you need them. If you don't need them, God bless you, good for you. I definitely need them. Um, my car won't get on the trail, barely gets on the trailer without a splitter, so it'll never get on the trailer with the splitter on there. Right. Um, but these are all considerations before you look at the aerodynamics, right?
SPEAKER_03:Right, right. Quick uh quick solution there for the splitter if it's too low. Um, I just did a video on it on my GT350. Um, I just 3D printed, or I I actually cut mine out of a sheet of ABS um spring, I'll call them like spring lockouts. So what you do is you kind of like lift up the side of the car, jam these lockouts in the coil spring, so the car will end up being two, three inches higher than normal ride height, and it makes it a lot easier getting on off the trailer. So that's that's a solution potentially for some people if you want to go down that path.
SPEAKER_01:Oh, and then you just jack the car up when it's off in the paddock and rip the spring wedges out essentially.
SPEAKER_03:Yep, and then you just like pop them out of the spring and you're good to go. Yeah.
SPEAKER_01:All right, I'll have to look at that video. I don't think I caught that one yet.
SPEAKER_03:So I'll send it to you after this.
SPEAKER_01:Yeah, I'm d I'm definitely gonna need it because uh, I mean, I my car barely gets on without them, so I'll have to look into that for sure. The I got a lot of people were like, oh, you're gonna do an arrow one? Let I have a lot of questions. And I'm like, okay.
SPEAKER_02:Go for it.
SPEAKER_01:But they all basically are are are sort of similar. Okay. Okay. So um let's talk about the height of the blade off the ground and where what zone does it need to be in. I know every car is a little different, right? So they have rake. This is where your rake starts, right? So potentially, yeah. Yep. Yeah. You you talked about rake in the car, and then there's angle on the splitter blade. So let's talk about uh angle of the splitter blade and height off the ground for the splitter blade and what seems to be optimal.
SPEAKER_03:Um yeah, generally three to three and a half inches static. So your car just sitting there. If you're above three and a half, like you're losing a ton of down force. Um now, granted, yeah, some people, if you're just doing like track days and you don't want to rip your splitter off and you're not, you know, that that's a higher priority to you. Yeah, put it wherever you want. Um, but in terms of down force generation, closer to the ground the better, up to about the I'd say like the one, one and a half inch range. Now, obviously, when you hit the brakes and the car, you know, the the front of the car weight transfers gets closer to the ground, you can't be scraping your splitter to death either. Um, so like anything in race cars, that there's always a balance, you know. Um, how can you kind of keep that splitter in that zone? Um, but we have uh CFD and wind tunnel data where if the splitter is at uh we'll say like three inches, if you go up to four inches, you're losing like half of the down force on the front of the car. Um you go down to two inches, you you pick up a ton of down force. Um and that and let me preface all this by saying like the splitter, assuming that the rake of the splitter is correct. Uh what I mean by that is like the leading edge of the splitter should be a little bit lower than the trailing edge of the splitter. Um a lot of people, I I see this floating around on time all the time online where people look at like um like a GTD car where they say the splitter points up, and it's like the very are you familiar with kind of what I'm referencing here? Yeah, and it's like it's not that the splitter points up, it's like the leading edge has a radius, kind of like the leading edge of a wing, you know. If you looked at the first, let's say one inch of a wing, it it would effectively be pointing up, you know. Um, but the whole thing is not pointing up. I hope I hope that kind of comes across. Um so yeah, as as long as you have that splitter rake down and you're around that three-inch range, it's like that's a very good baseline to get you started.
SPEAKER_01:Okay. Yeah, uh everybody wanted to know what seemed to be the optimal. Now, I want to go back to that leading edge question because I get I've read a lot of different things. So I know folks who radius, all right. Most of us are building plywood splitters, right? Right. We're not all we don't have composite money all the time, we don't have the ability to make composite, and then I believe making a composite splitter, I would leave that up to the pros anyway, like you, because there's a lot of things that get taken into account, um, especially in the process. But part of that is the front leading edge. Now we you talked about that uh GTD car being designed like the front edge was part of a wing. I've read and seen a lot of people, and they take two two uh counts. One group will radius the top and bottom edge of their plywood splitter, and one group will only radius the bottom edge.
SPEAKER_03:Right. Uh put me in the group of radiusing the bottom edge.
SPEAKER_01:Okay. Yeah. Well, I'm splitting I might have read or listened, watched your video on radiusing the bottom edge.
SPEAKER_03:So okay, yeah, yeah. Um that just kind of helps squeeze more air under the splitter. And if you have that rake, like I mentioned earlier, um, you know, you're you're not building up a high pressure, you're actually accelerating the air, making a lower um dynamic pressure under the splitter. So yeah, radius just the lower.
SPEAKER_01:Right. And and we don't have that wind tunnel data where we can shape the front lip to be like a wing, right? Right. So we need to do the simple pieces that work with physics, right? That that's sort of my take on it. Yes, the GTD car has it, it looks like it's pointed up, it looks like it's radius top and bottom, but that car was designed very, very differently than we're able to do in our garages. Right, right, exactly. Yep. Yeah. So I have another question. I and there's there's a lot of data out there. I know like Johnny at Nine Lives and some other folks have produced some of this data, mostly it it's around a Miata, but the air dam height to lip ratios, or when does the lip get too long that it comes with diminishing returns? Can we talk about that a little bit?
SPEAKER_03:Um yeah, that one that one's always a little bit tricky. Um because like the the the top of the splitter is kind of like the least important. Um because if people say you get high pressure on top, and you do, but low pressure underneath of a splitter can happen at a multitude of high pressure on top. Uh I hope that kind of makes sense. So the air dam on top, it's uh you could you can kind of I would almost just put it where it's like the easiest to mount your splitter, you know, um or or fill that gap, however you you want to do it. Um as far as length, usually most classes have a role that's like reasonable, you know. Um so making it longer, yeah, you do start to get diminishing returns, but looking at the whole package, um, you know, my my race car, that one's uh uh it's 11 or 11 and a half because ST uh 2 allows 12 inches, which is huge. Um mounting it can then become an issue with that much you know, stick out. Uh you definitely need like some rods and stuff. Um, but if you take surface area into account, low pressure across the larger surface area obviously gives you a lot more down force. Um, so uh that's kind of a tricky question. It's like I would look at the whole package, um going back to rules. You know, I've I've seen rules where it's like they're allowed some huge splitter, but only a little tiny wing, or or the reverse of that, it's like they're they're allowed like a little one or two inch splitter, but there's like no wing rule. You wouldn't want to then put like a huge dual element wing on it if you're only allowed a little tiny splitter, you know. Um so yeah, uh you definitely get diminishing returns. The air dam on top, I I wouldn't get too hung up on exactly where that lands.
SPEAKER_01:Okay. So so the but what you're saying is for the splitter blade itself, right? It's the entire length of the blade that does the work, not just the lip that sticks out. Everybody's like, oh, I want a big fat splitter lip. Right, right. They're they're looking for that extra one or two inches where that if your blade is already 24 inches going to 26, there there will be some gains in that two inches of of making that all that surface area, but it won't be the same as making it a 34-inch blade over a 24-inch blade.
SPEAKER_03:Yeah, right, right. That that surface area is what the low pressure acts on and you know then makes the down force. The other thing is it'll push your center of pressure a little farther forward, um, which depending on what car you have, um E36s, E46s kind of suffer from this. If you look at the front axle center line to the front of the bumper, it's a very short overhang, right? Um, so if your center of pressure isn't that far forward, but you have a wing sticking way off the back, you'll end up with like a you know, an arrow imbalance there because the center of pressure is the leverage ratio of the down force to the axles ends up getting a little bit funky as well, you know. Um so something something like that, you would probably want to push your splitter out as far as you can. Um so yeah, that that's a consideration as well.
SPEAKER_01:So the splitter's not the only thing that people do to the front of their cars. I'm guilty of it. Your car is vented everywhere. Um let let's talk about venting a little bit. Um I I want to get out of the the math on the cooling part, but how let's just keep it in the aerodynamic realm because I don't I don't want to go down the thermodynamic ratio path that necessarily always agreed upon. But right, so some of us still have our our plastic inner liners for our front fenders, and some of us they ripped out of the car and we never put them back. Right, right. Um, I want to touch about that too. So let's talk about first hood venting and what type of uh downforce we can get there, and then let's talk about fender venting, which isn't legal in every class, but then also how um, like these spec guys, they may or may not have fender liners left in their cars, and maybe they don't need them, or maybe they do need them. So right.
SPEAKER_03:Um, yeah, that's uh so a couple couple uh points in there to unlap unload. Yeah, hood hood louvers for sure have always made down force in the wind tunnel. Um, like I mentioned earlier, um, 5050 partners with uh Al Watson at Race Louvers, he's doing a ton of cool stuff with the shape of the louvers. Um yeah, they make down force, they make cooling for sure. Um fender louvers, they're they're a little bit of a twofer where you'll alleviate that under uh wheel well pressure, kind of just like the hoods. But if you have splitter tunnels in your car, generally the gains are a little bit more than if you don't. Um, but all that kind of like you mentioned, it's like the the front end, multiple components um and how they're set up go to the total front down force. Um you mentioned removing the fender liners uh on like the spec three guys. Um personally, I would probably leave them in if you could. It just kind of seals you know the engine bay from the wheel well and all that turbulence and everything. And that that's a test we did in the Aerodyne wind tunnel, which is the one where the wheels and everything actually rotate um and not getting too deep in the woods. I would probably leave them. Um so yeah, there's a bunch going on to the front of the car that make the total down force. Um, quick, quick story again, um mentioned in the spec three guys, we were in the wind tunnel with an E36. Um, I did a video on this if anybody wants to hop on my YouTube later. Um the hood, the very first run we did, the hood latch, the hood pins allowed the hood to kind of like move up and down quarter inch, three-eighths of an inch or so. And we were we were sitting there watching the video, and all of a sudden you see the hood just kind of pop up that three-eighths of an inch or so. So, like, okay, you know, we'll we'll fix that for the next run. The car ended up losing like 40 pounds of down force at 100 miles an hour just from the hood lifting up that little bit, you know. So the front end, little tiny odds and ends like that can equal a large result, you know. Um, so yeah, there's the the front end, definitely a lot more is going on for sure. Um canards, um, I make canards for a ton of different cars, I love them. They obviously make front down force, believe it or not, they actually help cooling a little bit. Um, like when we're in the wind tunnel with pressure probes front and rear, um, they will help cooling. If you're having a cooling issue and you already did um you covered all the bases, you got hood louvers, you make sure your radiator isn't blocked, it's ducked, that all that stuff. Removing your fender liners, you actually allow air out the engine bay a little bit easier, so you actually get a little bit of cooling, but you will lose like down force and pick up some drag and stuff. So um, you know, there again, there's always that balance between all the options of what you are allowed to do, what you can do, you know, what's available to you, stuff like that. So yeah, front end, front end's definitely trickier.
SPEAKER_01:Yeah, and that's that's where we it I we we race at VIR. So when you can clean up the front end at VIR, you will see a difference. You know, I I think so anyway. Um I race against a guy with a hunter's got a rocket ship of an accord wagon, and the front end is all jacked up, and I'm afraid he's gonna fix it one day. Because he's impossible to catch as is, and if he cleans up that front end, it's gonna be even worse. Right, right. Yeah. Um you know, it's there, it's definitely there. I've my my poor car, uh, the front end's been beat up on it uh already. I've only had it for two years. And you know, I dropped it off the trailer in the wet. I bump drafted somebody with a uh metal toe hook in the back that's a faux pag. Don't ever put metal tow hooks in the back of your car. Um I punched like eight holes in my in my bumper from it. So I've I've I've had I've done a lot of work to the front end, and I've always tried to make sure that it's straight, sealed, clean, and ready to go because it makes a huge difference. Yeah.
SPEAKER_03:And you definitely are so many factors. Yeah, yeah.
SPEAKER_01:You know, fender liners, no fender liners. Where you where did you put your hood uh louver? You know, fortunately for me, they don't make much for my car, but for whatever reason, a bunch of folks nerded out and did the pressure tests on the hood, you know, with the pressure probe driving down the street on six inch by six inch squares and then mapped it all out. And there's four or five guys who've done it. That all came up with the same results. So it's pretty solid now. Um you know, that's where we all put our vents. So yeah, at least I know that part. But right, right. The the front end is very tricky because you're right, there's a lot that comes into play. And we're not really gonna get into the thermodynamics part, but that's part of it, you know? Yeah, so that becomes a real big issue. Um, let's see. I'm looking around at my notes. Do you see any benefits to smoothing front bumpers? So some of us have like faux uh faux fog light holes. Right. Um do those I could put a piece of sheet metal over it, you know, right and just make it flat so there isn't that little one and a half inch recessed cubby. Is that worth doing to a production?
SPEAKER_03:Is that cubby open or closed?
SPEAKER_01:It'll be closed.
SPEAKER_03:Like um, like the the fog light comment tracking.
SPEAKER_01:It doesn't exist and it's it's solid. They you can't keep yeah, yeah.
SPEAKER_03:So yeah, so so if that let's say it's like a scoop, but the back of that scoop is blanked off, so it's not letting air into the engine bay or the wheel well or something, versus just smoothing it to the I'll say the leading. Edge of the bumper, it's probably almost immeasurable. Um, because you have high pressure on the front of your bumper there, and you'll just get like a little high pressure pocket in that um we'll call it the faux fog light.
SPEAKER_01:Okay.
SPEAKER_03:Cubby. Um yeah, that that would be such a low-hanging fruit thing that it's if you want to smooth it because you think it looks cool, as long as there's not any like real sharp edges or anything, um it's like that, yeah, that's yeah, that that's such a minor, minor thing.
SPEAKER_01:Okay. Uh yeah, I I just I've been staring at the front end of my car after I made my splitter. You know, I don't have much of a lip, but I have plenty of blade, you know, surface area, and I'm like, where can I clean this up some more? Uh some of it is, you know, I need I'm I'm going to duct my radiator, um, mostly to just help concentrate air, uh not let it go through.
SPEAKER_03:The front or the back? Yeah, yeah. Yep.
SPEAKER_01:Yeah, just just to help concentrate the air towards the radiator, but also there's a lot of dead space behind my bumper in general. Gotcha. Um I'm just trying to work that out this year, and I was staring at you know the faux faux fog light pockets, and I was like, I could I could sheet metal over this or whatever and smooth that out. But if juice isn't worth the squeeze, why do it? Yeah.
SPEAKER_03:So it's it's easy enough, like you mentioned, just put a little piece of sheet metal or sheet aluminum or something. If you can then cut out all that plastic behind it and trim a couple ounces, hey, it's a small win, you know. Um, but yeah, as far as aerodynamically speaking, uh, as long as that fog light, you know, like we mentioned, is closed and not letting air just willy-nilly into the engine bay of the wood with the wheel well, yeah, it's it's almost almost no no change there.
SPEAKER_01:Okay. So we did talk about it a little bit, but the balance of your car we talked about, where you got a little splitter, big wing, or little wing, big splitter. Um some of that has to do with people are like, I'm just gonna put this stuff on my car because I own it, it looks cool, whatever. Um, without working the mechanical grip first. What's your position on when to bring aerodynamics into the game?
SPEAKER_03:I'm probably the worst person to ask that question. Um, it's fine. Because yeah, my GT350 again, prime example. Um, since we do aerodynamics, you know, we have a splitter kit, wing kit, canards. I threw all that on the car when it was on, it was on Ford Racing Springs, which are a little stiffer than stock, but not much. Um, and the splitter just scraped itself down to almost nothing. Um, but hey, I went uh I did a video on this one around VIR, picked up almost four seconds. Um I just arrow grip, it it'll it'll change how the car feels, just giving you a lot more confidence for sure. Yeah, I probably could have gone faster, non-arrowed, um, so that delta wouldn't be as large, but we've worked with tons of people now that have done complete arrow kits, and I'm talking multiple second lap time drops, you know. Um granted you don't end up in my situation where you just scrape the splitter down to nothing. Um so yeah, in in in practice, you you probably should have your suspension kind of figured out. If you're going from no arrow to what I'll call proper arrow, um not just like a little tiny splitter that hardly makes down force. I'm talking like real down force, you know, then you're gonna have to change springs. If you change springs, you're gonna have to change shock settings. If you change, you know what I mean? It just kind of re-leads you down that whole trail of the whole setup needs to work together. Um but yeah, generally speaking, you kind of want your suspension at least figured out to some degree. Um, but yeah, if you if you think your suspension needs to be like perfectly dialed in, and then you throw air on it and everything's gonna be perfect, then that's not how it's gonna work out.
SPEAKER_01:Yeah, so it's it's less of a balance uh of like front to rear, but it's balancing everything you're working on the car. Right, right. I think that's the I think that's the true balance, right? So you know you need more mechanical grip, you need more arrow grip, you need to work out how to do it, where to do it, which side of the car to do it, that kind of thing.
SPEAKER_03:Yeah, yeah. And certain certain tracks lend themselves to being able to do that because it it's a slow corner, okay, that's mechanical grip. Uh a fast turn, arrow grip will kind of play a much larger role. So you can kind of um the like yeah, you you can kind of tune both together at the same time. Um, VIR is a little bit tricky because there's no really fast, fast turns. I guess up the S is a little bit, but there's a lot of elevation change. Um but my my old home tracks up at New Jersey, uh, Thunderbolt and Lightning, they were great because there was a couple slow turns and there was a couple really fast steady state turns. Um so you can kind of get your car set up a little bit easier depending on what your your home track may be as well.
SPEAKER_01:Okay. So sort of wrap this up a little bit, um, what are some best practices for us home aerodynamicists to do while we are in the garage staring at our cars?
SPEAKER_03:Um that's a that's a tricky one, I guess, because again, it kind of comes down to best practices based on uh your car, what rules you have to build to. Um that that's actually a really good question. One, uh make sure your splitter doesn't point up in the front. That's a huge one. Um, two, if you can like tidy up any uh gaps around the front end, don't let your hood pop up or anything.
SPEAKER_01:Um I'm gonna go home and check my hood tonight.
SPEAKER_03:Yeah, you and you and everybody else listening to this. Um if you're if you're going down the road of arrow, whatever your company you decide to go with, um me, whoever else, it doesn't matter, reach out to them and say, you know, hey, this is kind of what I'm allowed to do. Um what data do you have on your parts? We we have a lot more data than we post. We can't give away everything we have. Um but whatever company you work with should be willing to work with you on, you know, making sure you're at least like in the ballpark on setting up uh your stuff. Um yeah, I mean those if you follow those, I think you should be at le at least not way out in left field on on your arrow setup.
SPEAKER_01:Awesome. So where can people find you? Uh online, Instagram, YouTube, all that stuff. What's your website?
SPEAKER_03:Uh, website is ajhartmanaro.com. That's A-E-R-O, like aerodynamics. Um, same thing for Instagram, uh, YouTube. Um I do probably more YouTube than anything. Um, tons of old videos, uh, wind tunnel videos are all in a playlist if you're interested in that type of stuff. Um, yeah, so pretty much AJ Hartman Arrow, and I'll I'll pop up.
SPEAKER_01:It's a rabbit hole, guys, and you should go down it because I definitely did, and I learned a lot. So um thank you for sharing on the podcast. Thank you for all the sharing that you've done on YouTube because it's been Yeah, yeah.
SPEAKER_03:Thanks for having me and glad my videos helped out.
SPEAKER_01:Yeah, absolutely. Um, they really did, they were helpful for me and Ryan. If you can help both of us, I'm sure other people have been helped too. So uh, from all of us grassroots guys, we really appreciate it.
SPEAKER_00:Yeah, yeah, you're welcome. Until next time, keep working on yourself, keep working on the car, and let's get faster.