Race Car Aerodynamics and The Curious Case of Julian Edgar

[fe1rx]

If you are looking for information on race car aerodynamics with meaningful information that can be applied to a track car build you might try Race Car Aerodynamics by Joseph Katz. It provides a decent summary of aerodynamic theory but nothing that will really guide your build.

Competition Car Aerodynamics by Simon McBeath fares much better with information on the kind of things we are likely to interested in: airdams, splitters, spoilers, hood vents, diffusers, underbody rake, etc. with relatable examples. Some useful guidance can be found in there.

A few real aerodynamicists have a presence on YouTube:

AirShaper is selling CFD, and the videos tend to be short in duration and short on usefulness.

KYLE.ENGINEERS is selling consulting services has produced quite a few informative videos. He took a job in F1 so his videos stopped but is back at consulting and back at posting. A good example is:

Andrew Brilliant is selling consulting services but with his track record doesn’t need to advertise. He has done some good interviews. Any of the long-form interviews you can find online are worth a listen. One example is this HPA podcast:

https://www.hpacademy.com/blog/032-s...-aerodynamics/

Grassroots Motorsports is selling magazines and has had a few good pieces but lately they have veered off into the dubious territory of amateur CFD. Try this one for something good:

Engineering Explained is trolling for subscribers and is often interesting (if somewhat irritating), but his aerodynamic stuff doesn’t add much useful. Of the people who just pop up to offer their summary of aero, he is a high point though.

The manufacturers of aero bits like Professional Awesome and AJ Hartman are obviously selling their products. Personally I have found it hard to extract useful nuggets from any of the videos produced by vendors. AJ’s wind tunnel testing is interesting, but I have trouble keeping track of what he is doing and what he is discovering. Some serious editing would be helpful, but the videos are really a sales tool.

I found this long form tour of a NASCAR wind tunnel to be quite informative:

I could go on, but this gives a sense of the digging required to get useful and applicable aerodynamic information.

Julian Edgar is a prolific author, experimenter, inventor and YouTuber who has been experimenting with vehicle aerodynamics for quite a while. His emphasis has been on street cars, drag reduction in particular and “high-speed” stability. I associated him with the hypermiling crowd, but he recently moved into the realm of race cars with the release of his book Vehicle Aerodynamics – Testing, Modification & Development for Road, Racing and Alternative Transport and he has popped up on YouTube promoting the book. I found the book timely, given that my “Full Aero” project now has the ability to measure both downforce and dynamic pressure. I knew that Julian’s work included the use of surface pressure sensors, pitot-static tubes and ride height sensors, so I bought the book.

The book is substantial, at about 500 pages, with many very good photographs and illustrations. Essential aerodynamic theory is well explained. The value of surface pressure measurements is a fundamental focus of the book. The value of a pitot-static tube is acknowledged but underutilized, with only a cursory consideration of the value of aerodynamic coefficients, and no attempt at calibration of aero sensors. There is a strong emphasis on same-day back-to-back testing of simple mockups at moderate speed to discover the big picture, leading one towards an optimum solution. Durable data normalized by measured dynamic pressure to be relatable to different test days/conditions is largely ignored.

Drag measurements are acknowledged to be difficult, with coastdown test results having a large variability. He does present a clever means of estimating drag changes by observing terminal velocity while limiting engine power with a throttle stop. In a track car, observing maximum speed on a specific track does the same thing. Because he virtually ignores the benefits of normalizing drag and lift forces with the dynamic pressure, and working with coefficients, his methods are best suited to same-day back-to-back testing.

When questioned on this he indicated that “I prefer the simplest possible approach, as that is much more likely to be done by my readers. And it doesn't get much simpler than before/after testing on the one day using the pole-mounted pitot, surface pressure measuring patch and Magnehelic gauge!” Data logging approaches are acknowledged as an option, but their vast benefits are mostly ignored.

I have to admit, I am skeptical of surface pressure measurements as the universal cure. McBeath’s Figure 4-17 provides a good indication of how quickly pressures change with respect to distance aft of the leading edge underneath a splitter. How could a single or few pressure taps under the splitter help optimize its ground clearance, length or rake?

[I have removed a summary of my email interaction with Julian from this post because it feels bad to leave it there. Also, I think the book should be judged for what it is, and not for what I wish it was, or for my interaction with its author.]

[bbnks2]

Originally Posted by fe1rx

So when I installed my hood vents, I didn’t need to measure the pressures above and below to know that the vents would flow outward (and tufting has proved that they do, with and without wickers).

The only example I can find in the book of what I would call race car development is an example of carbon fibre front splitter/undertray with large diffusers from a Czech hill climb RX-7. No information is provided about the development process (mockups built, pressures measured) to get to the final shape, but Julian opines “Downforce would have been improved by the undertray curving downwards along the red lines, rather than being flat at this point.” (Meaning that the nose of the splitter should curve upward rather than being horizontal.) This statement is made without any empirical evidence, although there is a discussion earlier in the book about Porsche undertrays which have such a curvature (but no real forward splitter projection). No winning time attack cars have splitters like this. Without data to support the claim, I am skeptical. I think undertrays that run at road car ground clearances are different than splitters that run at race car ground clearances. All splitter examples in McBeath are flat and horizontal.

sorry to hear he was so rude. Sounds like he mistook an hpde car for formula 1 car development that spend hours every day in a wind tunnel lol...

In regard to hood vent placement... They look to be right about where most people put them... i placed mine in pretty much the same place after reviewing multiple different hood pressure differential charts. Left and right of the engine is the second best place to vent after right behind the radiator. Ideally we would drop the vent closer to the bmw logo by 2-3 inches but #1 the hood is reinforced there and #2 the intake snorkel in there blocking airflow anyway. Could you gain a bit by hacking more of the hood support away and removing the intake snorkel? sure. Is it really going to make a massive difference compared to what you have already? no. Especially not without direct radiator to hood vent ducting.

In regard to the splitter, I don't know the full context of the convo but yeah a flat splitter isn't "ideal." Ideally the leading first couple of inches should curve up and the top side being flat... This curve helps the airflow to accelerate under the car which is what creates the downforce (not air pressure on TOP of the splitter). Overall the splitter should slope a few degrees toward the ground. I have to stop at 3* of rake myself because of SCCA rules. To make this leading edge shape though requires splitter thickness at the leading edge... and your material is limiting since it's thin and flat. I used 1/2" plywood myself and chamfered the underside leading edge. that's not much at all and probably not worth anything. SCCA rules limit me to only being allowed to chamfer 2" back from the leading edge though. This rule helps keep the aero to basic amateur shit like flat pieces of plywood so we can run aero without needing a NASA space budget... so there is little to no gain from chamfering splitters in scca classing. You are already a step above most amateur's in that you placed splitter tunnels! Most people don't do that and that's another big way to create downforce from the splitter.

I've been following your posts for years and I thought your aero was spot on for this level of prep. Did he expect you to mock up a whole cardboard hood and cardboard hood vents to test a million difference sizes and placements since he claims it's so easy? Did he expect you to redeveloped the entire front nose of the car to incorporate in F1 level aero? weird expectations he had for your aero thread... and weird attitude he had about "rules of thumb" when he passes judgment on your aero with 0 data while simultaneously claiming you need data to make aero judgements...

[DRLane]

I too was thinking the splitter raise comment was like so -

[bbnks2]

Originally Posted by DRLane

I too was thinking the splitter raise comment was like so -

is that yours? but yeah that's the idea... upside down airplane wing or whatever... couldn't tell you if the shape in the picture is really what you want but it's likely what the guy was referring to when he said "flat is bad." Flat better than nothing especially when class limited

[DRLane]

Originally Posted by bbnks2

is that yours? but yeah that's the idea... upside down airplane wing or whatever... couldn't tell you if the shape in the picture is really what you want but it's likely what the guy was referring to when he said "flat is bad." Flat better sure than nothing especially when class limited

Yes - Zebulon.

That author seemed like a jerk, but to be fair the internet and these forums are filled with nonsense. I know more than one professional MS engineer that won’t touch us with a 10’ pole.

[bbnks2]

Originally Posted by DRLane

Yes - Zebulon.

That author seemed like a jerk, but to be fair the internet and these forums are filled with nonsense. I know more than one professional MS engineer that won’t touch us with a 10’ pole.

Once working in that space I think it becomes harder to separate what's realistic for the avg hpde driver and what a professional team chases to get on podium.

Shit look at 90% of aftermarket parts and they don't incorporate any of this shit. Theyre all flat splitters. Look at even the zebulon offerings you posted it's mostly all flat pieces of carbon fiber. It's good enough. Were not chasing hundreths of seconds. I'll take 150lbs of front downforce for a $50 sheet of plywood over nothing.

I also see tons of fundamental errors made by race teams. Especially in lower levels of racing...

[DRLane]

Originally Posted by bbnks2

Once working in that space I think it becomes harder to separate what's realistic for the avg hpde driver and what a professional team chases to get on podium.

Shit look at 90% of aftermarket parts and they don't incorporate any of this shit. Theyre all flat splitters. Look at even the zebulon offerings you posted it's mostly all flat pieces of carbon fiber. It's good enough. Were not chasing hundreths of seconds. I'll take 150lbs of front downforce for a $50 sheet of plywood over nothing.

I also see tons of fundamental errors made by race teams. Especially in lower levels of racing...

That’s absolutely fair. It’s less about competence and specialist availability and more spewing incorrect “facts”.

Btw I do not believe Zebulon sells anything that’s flat pieces of carbon.

[fe1rx]

I appreciate the comments on the center vents. The following image shows a typical hood surface pressure profile for a front-engined car. The low pressure extends well back on the hood. Image is from Julian's book.



The location of the vents relative to the stuff under the hood is not accurately apparent just by looking at the closed hood, so I have placed a tracing of each vent in its relative location in the engine bay, with top and side views showing the obstructions. I have retained my OE intake so the center vent starts just aft of that. The center is particularly obstructed.











I have looked at outflow using tufting and the less obstructed side vents flow better than the center vent.



I have added wickers to all the vents as a trial.




Both flow better with the wickers, but the center vent is particularly improved.



So, a little thought went into the location of the vents!

[DRLane]

Originally Posted by fe1rx

I appreciate the comments on the center vents. The following image shows a typical hood surface pressure profile for a front-engined car. The low pressure extends well back on the hood. Image is from Julian's book.

Attachment 3324000

The location of the vents relative to the stuff under the hood is not accurately apparent just by looking at the closed hood, so I have placed a tracing of each vent in its relative location in the engine bay, with top and side views showing the obstructions. I have retained my OE intake so the center vent starts just aft of that. The center is particularly obstructed.

Attachment 3324001
Attachment 3324002
Attachment 3324003
Attachment 3324004
Attachment 3324005
Attachment 3324006
Attachment 3324007
Attachment 3324008
Attachment 3324009

I have looked at outflow using tufting and the less obstructed side vents flow better than the center vent.

Attachment 3324015

I have added wickers to all the vents as a trial.

Attachment 3324011
Attachment 3324012

Both flow better with the wickers, but the center vent is particularly improved.

Attachment 3324013

So, a little thought went into the location of the vents!

I think anyone thats followed your threads, know more than “a little” thought and intent goes into your decision making.

It’s the upper 1% and probably not even fair to call it grassroots given your technical acumen and fabrication skills and tooling.

[fe1rx]

Attached is an excerpt from Julian's book where a Porsche aerodynamicist discusses curvature on the underside of of the undertray. The pressure map is particularly good.



Every authoritative person I can recall has indicated the benefit of a pronounced leading edge radius on the lower corner of a splitter. The degree to which that is carried at is the point of contention, I think. For a street car with large ground clearance there is room to carry it as far back as the front axle, as with Porsche's approach. Presumably as splitter heights get lower that ability is diminished. My current configuration has an added cuff/fairing to achieve a better leading edge radius. I am not concerned with the top surface because the flow velocity is very low.





The recent downforce numbers I posted included this fairing (and the vent wickers), and I haven't tested without them yet.

The RX-7 splitter discussed by Julian is shown below:

[fe1rx]

Julian's book contains some interesting comments from actual aerodynamicists. I found the attached from both Jag and Porsche engineers does a good job of describing why even the sportiest street cars don't generate much downforce. To summarize, a bit more downforce at the rear than the front, or a bit less lift at the rear provides the required high-speed stability. Significant downforce would result in a drag penalty not acceptable in a street car. Porsches can have spoilers and maybe wings, but Jags can't.



The book includes a 23 pages like the one that follows. I was perplexed at the lack of significant downforce an any of the cars, but the above excerpt explains it pretty well. It also highlights that the gulf between street car levels of downforce and track car levels of downforce is huge.

[raqidona]

Originally Posted by fe1rx

If you are looking for information on race car aerodynamics with meaningful information that can be applied to a track car build you might try Race Car Aerodynamics by Joseph Katz. It provides a decent summary of aerodynamic theory but nothing that will really guide your build.

Competition Car Aerodynamics by Simon McBeath fares much better with information on the kind of things we are likely to interested in: airdams, splitters, spoilers, hood vents, diffusers, underbody rake, etc. with relatable examples. Some useful guidance can be found in there.

A few real aerodynamicists have a presence on YouTube:

AirShaper is selling CFD, and the videos tend to be short in duration and short on usefulness.

KYLE.ENGINEERS is selling consulting services has produced quite a few informative videos. He took a job in F1 so his videos stopped but is back at consulting and back at posting. A good example is:

Andrew Brilliant is selling consulting services but with his track record doesn’t need to advertise. He has done some good interviews. Any of the long-form interviews you can find online are worth a listen. One example is this HPA podcast:

https://www.hpacademy.com/blog/032-s...-aerodynamics/

Grassroots Motorsports is selling magazines and has had a few good pieces but lately they have veered off into the dubious territory of amateur CFD. Try this one for something good:

Engineering Explained is trolling for subscribers and is often interesting (if somewhat irritating), but his aerodynamic stuff doesn’t add much useful. Of the people who just pop up to offer their summary of aero, he is a high point though.

The manufacturers of aero bits like Professional Awesome and AJ Hartman are obviously selling their products. Personally I have found it hard to extract useful nuggets from any of the videos produced by vendors. Such books are quite detailed, as they are based on physics, fluid dynamics and other scientific disciplines that describe the processes occurring in nature and technology. This is confirmed by expert tutors from https://edubirdie.com/physics-help who provided me with services for writing assignments in college. Thanks to detailed explanations, such books become a valuable source of information for researchers. AJ’s wind tunnel testing is interesting, but I have trouble keeping track of what he is doing and what he is discovering. Some serious editing would be helpful, but the videos are really a sales tool.

I found this long form tour of a NASCAR wind tunnel to be quite informative:

I could go on, but this gives a sense of the digging required to get useful and applicable aerodynamic information.

Julian Edgar is a prolific author, experimenter, inventor and YouTuber who has been experimenting with vehicle aerodynamics for quite a while. His emphasis has been on street cars, drag reduction in particular and “high-speed” stability. I associated him with the hypermiling crowd, but he recently moved into the realm of race cars with the release of his book Vehicle Aerodynamics – Testing, Modification & Development for Road, Racing and Alternative Transport and he has popped up on YouTube promoting the book. I found the book timely, given that my “Full Aero” project now has the ability to measure both downforce and dynamic pressure. I knew that Julian’s work included the use of surface pressure sensors, pitot-static tubes and ride height sensors, so I bought the book.

The book is substantial, at about 500 pages, with many very good photographs and illustrations. Essential aerodynamic theory is well explained. The value of surface pressure measurements is a fundamental focus of the book. The value of a pitot-static tube is acknowledged but underutilized, with only a cursory consideration of the value of aerodynamic coefficients, and no attempt at calibration of aero sensors. There is a strong emphasis on same-day back-to-back testing of simple mockups at moderate speed to discover the big picture, leading one towards an optimum solution. Durable data normalized by measured dynamic pressure to be relatable to different test days/conditions is largely ignored.

Drag measurements are acknowledged to be difficult, with coastdown test results having a large variability. He does present a clever means of estimating drag changes by observing terminal velocity while limiting engine power with a throttle stop. In a track car, observing maximum speed on a specific track does the same thing. Because he virtually ignores the benefits of normalizing drag and lift forces with the dynamic pressure, and working with coefficients, his methods are best suited to same-day back-to-back testing.

When questioned on this he indicated that “I prefer the simplest possible approach, as that is much more likely to be done by my readers. And it doesn't get much simpler than before/after testing on the one day using the pole-mounted pitot, surface pressure measuring patch and Magnehelic gauge!” Data logging approaches are acknowledged as an option, but their vast benefits are mostly ignored.

I have to admit, I am skeptical of surface pressure measurements as the universal cure. McBeath’s Figure 4-17 provides a good indication of how quickly pressures change with respect to distance aft of the leading edge underneath a splitter. How could a single or few pressure taps under the splitter help optimize its ground clearance, length or rake?

[I have removed a summary of my email interaction with Julian from this post because it feels bad to leave it there. Also, I think the book should be judged for what it is, and not for what I wish it was, or for my interaction with its author.]

I'm subscribed to Matt Brown's youtube channel, and it's pretty interesting. But I've been trying to read a few books, and it seems like I need to recall what they talked about in college, from which I remember slightly more than nothing.

[Besim]

This is tons of great information for anyone just starting to learn about aerodynamics on a track car! (me)

fe1rx would you happen to have any measurements of where you placed your vents on your cars hood? I am thinking of imitating what you have done as this setup would be legal for NASA TT5 as well. Thanks!

[Suprgnat]

Originally Posted by Besim

This is tons of great information for anyone just starting to learn about aerodynamics on a track car! (me)

fe1rx would you happen to have any measurements of where you placed your vents on your cars hood? I am thinking of imitating what you have done as this setup would be legal for NASA TT5 as well. Thanks!

Surprised you weren't on here sooner.