"It's not just a little thing that's 12 inches long, gotten from Ebay and stuck on the back, they basically do nothing." a lot of people need to hear this

I used this image about 10 years ago to determine the proper placement of hood radiator venting on a turbocharged MX-5, as the most effective venting HAD to be where the above hood pressure was the lowest, but still aft of the radiator. As the effectiveness of the radiator was directly related to the pressure differential between the front and the rear of the radiator. That single change made the difference between slowly headed toward overheating on the track in about 10 minutes to being able to complete a full 30 minute session without significant heat accumulation.

I bought your book and I highly recommend it to others. Unlike a lot of other books, it' provides you with real world, cost effective examples of how to do stuff. Likewise, even if you are studying in order to undertake a profession in this area, it will give you a very sound understanding of how aerodynamics actually work

I saw the thumbnail of an RX7 I was obligated to watch 🤣

I used to own this rx7. That thing was super smooth.

Funny, you have a series 4 RX7 as an example. I had one, and it was rock solid at high speed (250 km) . Not bad for a 1988 vehicle.

I just got home from a 4,000 mile road trip in my recently purchased 2013 Toyota Avalon hybrid. It was getting 38mpg on Appalachian mountain roads fully packed trunk with my two teenagers my wife and myself. I was a bit surprised by how many bugs ended up on the windshield, I thought most would stay out of the attached air layer, but there was a nearly even distribution from top to bottom. While many might find the shapes of modern automobiles boring, I think aerodynamic sedans are beautiful. I've been watching your channel for quite a while and I want to let you know how much I appreciate your efforts.

That's my car!

comming from aviation im eating this up as breakfast. With my current focus on autosport this makes for great stuff! Thanks Julian. Subscibed imidiately

fond memories of the windtunnel lab at uni, tasked to measure and plot a couple of pressure profile graphs around a NACA 2412 aerofoil. we were expected to do this with ruler and pen on an ancient photocopy of the aerofoil cross-section. "Not Good Enough!" I said, and set out to plot the data exactly on my PC. NACA 4-series aerofoils are mathematically defined, so I could generate a series of x,y points for the upper and lower surfaces. I could also differentiate the 4-series function to get the gradient, and rotate by 90° to get the angle of lines tangent to the surface. From that could plot the pressure lines at each measuring point. Finally a line joining the endpoints to get the overall profile. I did all of this in Excel, using x,y graphs for the plotting Oh, and I never got round to actually submitting that bit of coursework

Love that you covered this with the FC RX7

Love the series 4 Rx-7

Great material! Thank you, Julian!

Imma most definitely watch more videos on this channel. Wish school had taught me shit like this.

Bernoulli’s principal! Great video explaining aerodynamics on a car.

Nice video very helpful! make more video's about suspension for handling in rwd or awd

Very lovely explanation. One thing many times could notice is that a lot of family/daily (not sport-ish) cars often have some small spoiler ("bump") in rear end of car and natural question would be "why?" - initally one would take 'it looks good" (okay, many times it actually does) until you see this and - at higher speeds many bodywork types of cars (with curves) naturally would become more and more free on rear end (windshield pressure makes it more front "heavy"), making crashing more likely. But placing even small size bump can push this balance way over to back (leverage vs center of car for rear of car is longer so even small force at trunk can offset larger force at windshield).

Bought most of your books... You explain physics of the automobile so everyone understands 👌🏼 love it

Great high level explanation of fluid dynamics around a car. Most aftermarket add ons are not properly developed or tested and are, therefore, only cosmetic, indeed, some make matters worse. Undertrays have further benefit in deterring cat thefts.

Egad. That was more informative than I would have given credit for.

excellent explanation. only with this video im convinced that ill learn so many things with that book.... thank you so much for making this video.

I see RX7, I click like👌

I'd imagine 99% of SUV buyers have no concept of aerodynamics. Maybe I'm wrong, maybe 99% of most car owners have no aerodynamic education either. It's a relevant concept that doesn't get enough attention, imo. I mostly know some basics from research papers I wrote in college in regards to cycling. Either way, the more surface area you have perpendicular to the direction to travel will cause more aero resistance and inefficiency. Also, smoothing out the flow of air behind the vehicle to reduce negative vortices/vacuum effect will help, even if it adds a little weight.

This channel is such a discovery! Followed! :)

Thank you for this as I have an rx7 makes me understand it even further

I clicked on this video just because of the FC RX-7 in the thumbnail

Great video! Thanks for creating informative content like this!

Williams and Kick Sauber engineers are watching this video on repeat and scratching their heads

Hello Julian. Just wondering if in one of your videos you talk about monovolume cars or the aerodynamics of large people carriers. I noticed that between the Ford Galaxy 2010 and Ford Galaxy 2015 models, the later has on the edges of the rear glass vertical winglets that are built in to the glass. What does that offer ? Less wake? Thank you for the very easy to understand videos. Regards from Portugal.

That diagram puzzled me at first. I have always heard that the base of the windshield was a low pressure area. Watching the video I realized it was based on attached flow and many cars have what is effectively a small spoiler lip at the rear edge of the hood. I just went out and looked more carefully at my Lucid Air, a car reputed to have carefully designed areo features, and noted both a gap between windshield and hood and an unusually thick strip of trim along the rearmost edge of the hood. Presumably this would detach flow several inches before it reached the new angle of the windshield. I may need to get your book to see if it would be worth fitting a trunk lid spoiler. I have noticed a little lightness in the rear under heavy braking on less than perfect surfaces, but only at speeds above what normal people would call rational.

A simplified silhouette of the centerline of the car if you analyse the curvature with a vectoral drawing format such as a curve in rhinoceros 3d you get a very similiar area, however it does not account for the force so you may think as a vectoral force acting on the graph from left to right and anaylse the airflow pattern that way. Not an exact solution but enough to give an idea. It would be best to use a cfm algorithm in any case. This could only help you in sketching phase.

This video randomly popped up in my feed and I found it absolutely fascinating. Those vectors were not intuitive to me at all. I think I need to buy the book now!

I'm a simple person. I see RX-7 FC3S, I like.

absolutely brilliant! thank you very much sir!

Nice video. I wished we had different cars to see how design changes the air pressure

So well explained, thank you. I wonder as you mention the lift and how cars are not flying ('99 Mercedes CLR says hello), if some sort of active aero under the car could create enough lift to reduce tyre resistance when you're travelling in a straight line, and change it as soon as you touch the brake pedal or the car is turning. That could reduce overall fuel consumption? And another point you mentioned about the highest preassure point being in the front plates, It would be a good idea to have the number plate hollow so the air can go thru and use some sort of hologram image for the numbers to create the plate being fully readable but without the drawback of being literally a wall? And How much (on fuel economy) that will make a difference?

Why is it undesirable to have some lift at high speed? Surely this would reduce wear and tear on the running gear and tyres? Obviously you wouldn't want it to become unstable or take off, but wouldn't a small amount be helpful?

Interesting

It would be really cool to see this graph for the Aptera.

its so depend on the bodywork shape and the space underneath the car. that lines shown there could change according to the factors i mentioned. i rather simulates the car punching through a sitting air volume and simulates the energy exchange on all the relationships between the ambient air around the car. and then convert that informations to energy transferred to the car themselves. i cant have "formula" for that. since it will change depends on the shapes and the spaces around the car.

Always nice information 👌

I had no idea there was so much area experiencing low pressure on your car. I imagined almost all the top surfaces being pressed down but apparently not 😁

@JulianEdgar I noticed that Lucid Motors has a thin spoiler along the trailing edge of the hood just before the windshield on their Lucid Air Sapphire. Would that smooth the airflow and cause it to remain detached over the windshield and reduce drag or increase downforce on the hood or is it for another purpose?

By looking only at the side-view planform of the car, you're missing a LOT of drag coming from the wheels and wheel wells. (As well as the mirrors to lesser extent). Those open wells are big "drag buckets," plus the tire itself is traveling at double the vehicle speed at the top of its rotation. Also, does the front drag calculation only consider the vehicle planform, or is the drag from cooling air factored in as well?

Danke!

Why don't cars from factory come with a smooth under-tray. The smooth low pressure will help the car to have a better grip, isn't this much safer for general drivers? ( i mean, added grip never hurt anybody other than lower MPG ratings)

In the UK your book retails for £85.82 which seems expensive to me.

I would like to see this image for my YJ Jeep. My guess is that is would have a lot more drag but not as much lift.

Thank you for the great video you made, Julian. I'm a bit confused. At 5:30, you said that the low pressure on top of the car is much higher than under the car, so it creates lift force. But as I understand, pressure will go from high to low, so how can it create lift force? I thought it would create downforce. Sorry if my knowledge is wrong 😀

Does your book extensively cover the air flowing underneath the car? I want to make a flat surface with some duct for cooling in an attempt to reduce drag and increase downforce. I don't want to be flipping backward 360 degree if I go too fast like that leman car.

Julian, in the RX7 community there is aome debate that the intercooler scoop for the turbo models is located in a poor spot on the hood. It is located approximately above the front wheel. Do you think there is any improvements that could improve its performance in that location. Such as making the scoop itself taller, or a very small air dam in front of the location?

Teach us about tractor trailer aerodynamics. There's very little out there. I'd like to improve my fuel economy. Is there a digital version on the book available?

What if you used high pressure air on the front to deflect high pressure. Like air guns or fans

I have a theoretical question for you about undertrays. If we ignore the undertray components of vehicles, and focus only on the shell to make this even possible.. What would happen if you made your undertray bow upwards or downwards at the center of your vehicle? Think like starting at the front of your vehicle, and ending at the rear. If you could have it bowing up into your car, it would make the front have normal pressure, but the middle would be a large negative pressure zone, right? Or alternatively, bow it upwards and have the rear of the vehicle not bow back down much. Is my theory incorrect? It's hard for me to understand because I know that in open air, a U shape would have the air attach to the bottom, pulling it downwards like an airfoil almost, but the ground and high pressure at the front of the car are what are making me doubt that

How does one produce such a diagram? I’d like to see one for my 1966 Lincoln.

I'm imagining pressing the lubricated heel of my hand into the car from left to right and basically where i'd meet the most resistance seems to be where the high pressure is. Is this roughly accurate?

Next, do the MKI MR2

No no that's not a pressure diagram, that's the optional "mowhawk" sports trim kit!

now I want to learn how to recognise cars only by their air preassure graph 😀

This pressure curve looks a lot like the curvature comb for the shape... I suppose they are indeed very closely related. I wonder if it'd be a good enough approximation to use the curvature gradient for a real time simulation.

We always see track cars using hood vents to reduce that low pressure zone over the hood. Why don’t people vent the roof to reduce that low pressure zone?

Someone pls send this to the Williams team

It would be nice that starting from this diagram to calculate the equivalent forces per axis, and also on the front and rear wheels, because at the end that will be what will dictate the performances of the car. Just one question, are these vectors represented with their real amplitude, or is it just to provide a rough idea?

Can you do the same air pressure analysis video for the under/belly of the car?

Is there suck a diagram available for the Mark I Mazda MX5?

Is the car in the thumbnail a Mazda Rx-7 or a Porsche 944 (/S?)?

You might appreciate the extremes that time attack and european hill climb cars have gone to.

Thank you for providing explanations of aerodynamic principles, but maybe put a little effort into reading more carefully before responding with generalities. I'm quite sure you would not remember the question I posed a few years back, but, some American vehicles direct air through the cooling system by having a lip, (or dam) below the nose. I tried to initiate a discussion about what effect changes to under hood (bonnet) pressures might have on that system. What I got was a condescending lecture about how air dams are outdated technology. You don't owe me a solution, but if you don't have one, you shouldn't just take the piss.

I have a Jeep and a Land Cruiser on big tires and off road bumpers. Do you have any suggestions on something simple I can do to improve the aero on the highway?

My pressures 😈

Can you please do books in french !

Citroën & SAAB

🤔 hmmmm!! Indeed indeed!!🤔🤔

That diagram is one of the most logical I've ever seen😐

can you tell me how far out / in the wheel/tyres of the car need to be to have best aero? flush? tucked in slightly? how much?

2nd gen rx7 4 life.

How much of an effect on this with lowering the car in downforce

This diagram is just for the attached flow correct? Because I cant imagine that on the whole, the area at the front of the car over the bonnet would in low pressure, seeing as the car is pushing into the air and getting 'bundled up' slightly creating higher pressure area?

I see a 2nd gen RX-7 -> I click

I'm too dumb to understand anything here, I just clicked cuz dinosaur car in thumbnail

80-90's Dodge Daytona?!

A mezda? I drive a mezda mieata