"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
And not just the "ebay diffusers"... but every mainstream car, truck and suv that has a bottom edge of bumper cover "diffuser" because marketing (often located below fake exhaust outlets for same reason).
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 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.
Yeah, but better again to measure on the actual car you're working with, and measure the differential between below- and -above hood pressures at various points. All cheap and easy - and covered in the book!
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.
@@JulianEdgar I guess it pays to lose weight then. 🪰 you would think their wing to weight ratio would keep them in the flow. That is why a fly in your car doesn’t smack off the windshield when you brake hard. But that is quite a quick direction change with windshield at highway speed.
comming from aviation im eating this up as breakfast. With my current focus on autosport this makes for great stuff! Thanks Julian. Subscibed imidiately
If you're really interested, buy the book. The videos are very superficial. www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country.
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
If you want to learn about handling, buy the book. Vastly better than any of my superficial CZcams videos. www.amazon.com/Vehicle-Ride-Handling-Modification-Development/dp/B0D7327WSB or Amazon in your country.
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).
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.
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.
Drag reduction techniques for all car shapes are covered in my book - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or your nearest Amazon
Hey if you are from Portugal you surely remember the good old days when the Galaxy was built by Autoeuropa and it was the same as the VW Sharan and the Seat Alhambra. That generation was my absolute favorite Galaxy! It’s a damn shame the Sharan won’t be build anymore, it was my absolute favorite car by VW besides the way to expensive busses from the T1 to the T7 series. The bigger caddies are also fine.
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.
Yes, but much better than rules of thumb like "more surface area you have perpendicular to the direction to travel will cause more aero resistance and inefficiency" is to look at the pressures and understand *why* this is the case.
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.
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.
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?
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!
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.
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?
No one chases increased lift to reduce fuel consumption - rolling drag at any speed over about 35 mph is lower than aero drag (and lift causes drag), and the downsides of aero lift are too great anyway. Re the number plate, it's a tiny area, but a curved number plate would reduce drag.
@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?
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 😁
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)
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?
I have covered wheel and tyre drag on this channel, and in detail in my book. However, most pressure drag (about 70 per cent) comes from the body shape as discussed in the video. A modern wind tunnel measurement takes into account cooling air flow and (most of) wheel drag.
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
Go have a look at tunnel cars like old F1 cars, Time Attack cars, and the Lucid Sapphire. Lucid, if you weren’t aware, doesn’t have a flat battery pack under the car like most EVs. It “bends” upwards starting much earlier than a conventional rear diffuser.
@@JulianEdgar Thank you! Is there a reason that modern EV's dont use a large curved underbody to act like an airfoil, instead of flat? Im sure that racecars would have to make undesirable compromises like increasing ride height to compensate for this, or are there other reasons that this is never seen, aside from the very front occasionally as you had mentioned
@@Ayane13b czcams.com/video/emkj_fOBovY/video.htmlsi=MKkxlWuf7v6F-Z1- Lucid Air Sapphire underbody aero, with front and rear vortex generators designed by former Red Bull F1 dude. Start at about 33 minutes in.
On a discussion group I once put up a graph of the top and bottom aero pressures of a car and asked people to guess what car it was. It was of an ultra low drag solar race car... so very hard to identify!
You can easily measure it for yourself - the technique is covered in my book. www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country.
If you're interested in that car, why not make the measurements yourself? Simple and easy. Covered in the book - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country. (Incidentally, isn't that the car where the video floating around on the web, and purportedly showing airflow, is utterly wrong?)
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 😀
Yes, it's not a cheap book. Full colour, nearly 500 pages, information you'll find nowhere else. You will save more than its purchase price on the first aero modification that you do that works.
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?
What I think is that it is very easy to test intercooler scoops - how well they work in standard form and how much difference modifications work. No need to guess - just make some very simple and cheap aero measurements. www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country.
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?
Just measure front and rear lift/downforce directly on the road - easy, and much more accurate than trying to calculate it from the pressure vectors. And yes, the depicted vectors are accurate (except for none beneath the car of course :).
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.
Why simulate when you can measure the real thing far more accurately? Unless you are building a new car from scratch, much better to measure the real thing with various changes.
@@JulianEdgar I'm a game developer. I'm thinking about this being used in a game/simulator context where CFD is computationally way too expensive. In a game where the players are allowed to design their own vehicles, out of parts, like Legos, this sort of approximation is exactly the type of thing I look for. Robust enough to work given only the data available to the game (no manual tuning for each vehicle is possible), but fast enough to run in real time.
It could be done at that level, but this video doesn't cover much about flow separation, which will change all the pressures. Read my book if you want a good overview that would provide justification for the approach you take. www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country.
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.
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?
Maybe. I actually tend to be more interested in road cars: getting the balance of lift/downforce versus drag is much harder than just going for one or the other.
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?
No digital version - they get pirated within days. My book has detailed coverage of truck aerodynamics, including tractor trailers. www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8
And Tatra and Porsche and the Tropfenwagen. All in my book on the history of car aero - www.amazon.com/Century-Car-Aerodynamics-science-airflow/dp/B095RLP52B or Amazon in your country.
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.
Yes I remember, and all I can say is what I said before. The lip is not to "direct air through the cooling system" but to create a low pressure area behind it, thus drawing more air through the radiator. However, such an approach is well outdated - it is simply not the best way of achieving low drag, low lift and good radiator airflow. If you regard that as a condescending lecture, so be it.
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?
You can think of it like that but unfortunately that idea gives you a lot less than half the picture (low pressures are more important than high pressures).
Yes, covered in my book with the measured results for multiple different cars - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country.
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 book covers drag reduction techniques that can be applied to any vehicles - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country.
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?
@@JulianEdgar Well you have to admit that getting a negative number after adding all the arrows together isn't exactly intuitive. Is the same type of drawing available for a less complex shape? Like, say, a VW bus? Or better yet a bowling ball. Sorry for the duplicate, my earlier reply was in the wrong thread.
Why would you want a diagram for a less complex shape? This is about cars, so we want a car shape. The commenter's mental model was quite wrong where they said of the air above the bonnet "... seeing as the car is pushing into the air and getting 'bundled up' slightly creating higher pressure area".
Fibreglass bonnets have hood pins as a safety factor due to issues with them lifting from lack of weight. They can only lift if pressure above the hood is negative, otherwise if positive pressure, the hood would stay in place and not need pins.
@@JulianEdgar Do the laws of aerodynamics apply to cars or do the laws of cars apply to aerodynamics? Anyway, to answer your question, the reason I requested a simpler shape is because understanding how complex shapes behave is easier if you understand the more basic principles first. It's about grasping the fundamentals. Don't worry about it. The authors of "Aerodynamics For Naval Aviators" thought it made sense to use it even though the book is about navy jets and the shape isn't a navy jet. It's the first illustration in the streamline pattern and pressure distribution section (pressure distribution on a cylinder, considering friction effects (viscous flow), page 15). P.S. Technically speaking, a Volkswagen Bus is a car.
The whole point of my aero writing and videos is to get away from guesswork and to test. So, especially when testing wheel covers is so easy, and wheel behaviour is specific to the car, I am not going to guess.
@@JulianEdgar thanks but easier said than done for the average working class joe. currently my wheels sit flush to the fenders of my EV. to test the aero i'll have to either buy new sets of the exact wheel with more offset, or grind down my wheels and put spacers and then do the tests. i'll be content with my set up i think. i'm sure the wheels being flush to fenders is the least of my aero concerns on the Kia EV6 haha
"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
And not just the "ebay diffusers"... but every mainstream car, truck and suv that has a bottom edge of bumper cover "diffuser" because marketing (often located below fake exhaust outlets for same reason).
😏
@@bradkerr2798Unfortunately, all these new body element designs are mainly for appearance and cosmetic design allowances.
Spot on comment! 👌
Gazing over at all the “cool cars”, both on and off track, with the back of the bonnet raised… 🤐😫
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
Thank you. Don't forget to leave a detailed Amazon review!
May I ask if it also helps with unusual or rather racecar design?
Yes of course. The techniques and concepts covered are applicable to any vehicle.
I used to own this rx7. That thing was super smooth.
Same '87 TII
Haha, i clicked on the video because i saw the FC
....after how many blown seals? lol
I used to love the FC. Almost bought one
@@leafboy3967 I was about to post the exact same sentence hahaha! God I loved that car! Sold it when I began to have coolant issues.
I had the convertible, even with the top down that was an amazingly nice vehicle.
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.
Yeah, but better again to measure on the actual car you're working with, and measure the differential between below- and -above hood pressures at various points. All cheap and easy - and covered in the book!
I saw the thumbnail of an RX7 I was obligated to watch 🤣
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 agree rock solid car, mine has been tested so many times 🏎️
That's my car!
that's the savanna one?
It needs a paint job. and I think there might be something wrong with your tires. But at least paper cars don't rust nor need maintenance.
Jealous
me too 😁😁
Keep it forever❤
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.
Bugs have greater mass than air... so usually not a good guide to what is happening.
@@JulianEdgar That makes sense! Thanks for your response.
@@JulianEdgar I guess it pays to lose weight then. 🪰 you would think their wing to weight ratio would keep them in the flow. That is why a fly in your car doesn’t smack off the windshield when you brake hard. But that is quite a quick direction change with windshield at highway speed.
Love the series 4 Rx-7
Love that you covered this with the FC RX7
comming from aviation im eating this up as breakfast. With my current focus on autosport this makes for great stuff! Thanks Julian. Subscibed imidiately
If you're really interested, buy the book. The videos are very superficial. www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country.
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
Great material! Thank you, Julian!
Bernoulli’s principal! Great video explaining aerodynamics on a car.
principle
Nice video very helpful! make more video's about suspension for handling in rwd or awd
If you want to learn about handling, buy the book. Vastly better than any of my superficial CZcams videos. www.amazon.com/Vehicle-Ride-Handling-Modification-Development/dp/B0D7327WSB or Amazon in your country.
Imma most definitely watch more videos on this channel. Wish school had taught me shit like this.
Now you need to read the books...
Bought most of your books... You explain physics of the automobile so everyone understands 👌🏼 love it
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).
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.
You should see the book! www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country.
I see RX7, I click like👌
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.
Thank you for this as I have an rx7 makes me understand it even further
This channel is such a discovery! Followed! :)
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.
Drag reduction techniques for all car shapes are covered in my book - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or your nearest Amazon
Hey if you are from Portugal you surely remember the good old days when the Galaxy was built by Autoeuropa and it was the same as the VW Sharan and the Seat Alhambra.
That generation was my absolute favorite Galaxy!
It’s a damn shame the Sharan won’t be build anymore, it was my absolute favorite car by VW besides the way to expensive busses from the T1 to the T7 series.
The bigger caddies are also fine.
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.
Yes, but much better than rules of thumb like "more surface area you have perpendicular to the direction to travel will cause more aero resistance and inefficiency" is to look at the pressures and understand *why* this is the case.
Most people buying SUVs and Pickups aren’t buying for their great efficiency numbers.
Williams and Kick Sauber engineers are watching this video on repeat and scratching their heads
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.
Just measure the aero pressures on the real car on the road. Then it's easy and accurate.
@@JulianEdgar Absolutely!
I clicked on this video just because of the FC RX-7 in the thumbnail
Great video! Thanks for creating informative content like this!
Glad it was helpful!
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.
Obviously the pressure distribution depends on the shape of the car. But this video shows the fundamental concepts.
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?
No. The downsides of lift outweigh any advantages. No car manufacturer chases lift.
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!
Glad you enjoyed it. www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country.
Nice video. I wished we had different cars to see how design changes the air pressure
Plenty of examples in the book.
@@JulianEdgar Ah ok thank you!
Interesting
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.
I'm a simple person. I see RX-7 FC3S, I like.
absolutely brilliant! thank you very much sir!
I am sure you'd enjoy the book - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country.
It would be really cool to see this graph for the Aptera.
It would be really cool to see *any* aero data on the Aptera. Oh, wait... they haven't released it...
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?
No one chases increased lift to reduce fuel consumption - rolling drag at any speed over about 35 mph is lower than aero drag (and lift causes drag), and the downsides of aero lift are too great anyway. Re the number plate, it's a tiny area, but a curved number plate would reduce drag.
Always nice information 👌
@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?
Could be for a whole variety of purposes. I prefer not to make guesses - so much aero misinformation comes from guesses.
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 😁
No, most cars have a lot of low pressures on top.
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)
Modern cars do - look under any current EV. And both lift and downforce are bad for drag.
a lot of them do. The oldest ive seen is E60 M5 but I am sure there are older.
The oldest is a 1921 Tropfenwagen - a bit , older than a BMW E60 M5!
the underside view of my 2nd generation MR2 is almost all plastic. No diffuser though.
Someone pls send this to the Williams team
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?
I have covered wheel and tyre drag on this channel, and in detail in my book. However, most pressure drag (about 70 per cent) comes from the body shape as discussed in the video. A modern wind tunnel measurement takes into account cooling air flow and (most of) wheel drag.
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
Yes, your theory is reversed.
Go have a look at tunnel cars like old F1 cars, Time Attack cars, and the Lucid Sapphire.
Lucid, if you weren’t aware, doesn’t have a flat battery pack under the car like most EVs. It “bends” upwards starting much earlier than a conventional rear diffuser.
@@JulianEdgar Thank you!
Is there a reason that modern EV's dont use a large curved underbody to act like an airfoil, instead of flat?
Im sure that racecars would have to make undesirable compromises like increasing ride height to compensate for this, or are there other reasons that this is never seen, aside from the very front occasionally as you had mentioned
Packaging and clearance.
@@Ayane13b czcams.com/video/emkj_fOBovY/video.htmlsi=MKkxlWuf7v6F-Z1-
Lucid Air Sapphire underbody aero, with front and rear vortex generators designed by former Red Bull F1 dude. Start at about 33 minutes in.
now I want to learn how to recognise cars only by their air preassure graph 😀
On a discussion group I once put up a graph of the top and bottom aero pressures of a car and asked people to guess what car it was. It was of an ultra low drag solar race car... so very hard to identify!
@@JulianEdgar hehehe, that's a bit mean 😛
Danke!
Thank you.
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.
You can easily measure it for yourself - the technique is covered in my book. www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country.
Next, do the MKI MR2
If you're interested in that car, why not make the measurements yourself? Simple and easy. Covered in the book - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country. (Incidentally, isn't that the car where the video floating around on the web, and purportedly showing airflow, is utterly wrong?)
@@JulianEdgar booooo.....I want you to do all the work for me.
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 😀
A higher number - more negative if you like. It's always hard to get the terms right in this area.
In the UK your book retails for £85.82 which seems expensive to me.
Yes, it's not a cheap book. Full colour, nearly 500 pages, information you'll find nowhere else. You will save more than its purchase price on the first aero modification that you do that works.
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?
What I think is that it is very easy to test intercooler scoops - how well they work in standard form and how much difference modifications work. No need to guess - just make some very simple and cheap aero measurements. www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country.
My pressures 😈
What if you used high pressure air on the front to deflect high pressure. Like air guns or fans
Every force has an equal and opposite force.
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?
Just measure front and rear lift/downforce directly on the road - easy, and much more accurate than trying to calculate it from the pressure vectors. And yes, the depicted vectors are accurate (except for none beneath the car of course :).
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.
Why simulate when you can measure the real thing far more accurately? Unless you are building a new car from scratch, much better to measure the real thing with various changes.
@@JulianEdgar I'm a game developer. I'm thinking about this being used in a game/simulator context where CFD is computationally way too expensive.
In a game where the players are allowed to design their own vehicles, out of parts, like Legos, this sort of approximation is exactly the type of thing I look for. Robust enough to work given only the data available to the game (no manual tuning for each vehicle is possible), but fast enough to run in real time.
It could be done at that level, but this video doesn't cover much about flow separation, which will change all the pressures. Read my book if you want a good overview that would provide justification for the approach you take. www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country.
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.
Yes it covers the developing and testing of undercar modifications in detail.
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?
The hood vents aren't to increase the pressure above the hood; they're to flow air out from under the hood.
No no that's not a pressure diagram, that's the optional "mowhawk" sports trim kit!
You might appreciate the extremes that time attack and european hill climb cars have gone to.
Maybe. I actually tend to be more interested in road cars: getting the balance of lift/downforce versus drag is much harder than just going for one or the other.
2nd gen rx7 4 life.
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?
No digital version - they get pirated within days. My book has detailed coverage of truck aerodynamics, including tractor trailers. www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8
@@JulianEdgar I was hoping to put it up on the big screen
Citroën & SAAB
And Tatra and Porsche and the Tropfenwagen. All in my book on the history of car aero - www.amazon.com/Century-Car-Aerodynamics-science-airflow/dp/B095RLP52B or Amazon in your country.
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.
Yes I remember, and all I can say is what I said before. The lip is not to "direct air through the cooling system" but to create a low pressure area behind it, thus drawing more air through the radiator. However, such an approach is well outdated - it is simply not the best way of achieving low drag, low lift and good radiator airflow. If you regard that as a condescending lecture, so be it.
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?
You can think of it like that but unfortunately that idea gives you a lot less than half the picture (low pressures are more important than high pressures).
How does one produce such a diagram?
I’d like to see one for my 1966 Lincoln.
Measure it yourself - easy. All covered in my book - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8
Can you do the same air pressure analysis video for the under/belly of the car?
Yes, covered in my book with the measured results for multiple different cars - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country.
🤔 hmmmm!! Indeed indeed!!🤔🤔
Is the car in the thumbnail a Mazda Rx-7 or a Porsche 944 (/S?)?
Watch the video!
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 book covers drag reduction techniques that can be applied to any vehicles - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country.
That diagram is one of the most logical I've ever seen😐
... and here I thought it was my explanation...
Is there suck a diagram available for the Mark I Mazda MX5?
You can make your own. Very cheap and simple to measure.
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?
The whole area over the bonnet is a low pressure area on this, and on most, cars. Your mental model is wrong!
@@JulianEdgar Well you have to admit that getting a negative number after adding all the arrows together isn't exactly intuitive. Is the same type of drawing available for a less complex shape? Like, say, a VW bus? Or better yet a bowling ball.
Sorry for the duplicate, my earlier reply was in the wrong thread.
Why would you want a diagram for a less complex shape? This is about cars, so we want a car shape. The commenter's mental model was quite wrong where they said of the air above the bonnet "... seeing as the car is pushing into the air and getting 'bundled up' slightly creating higher pressure area".
Fibreglass bonnets have hood pins as a safety factor due to issues with them lifting from lack of weight. They can only lift if pressure above the hood is negative, otherwise if positive pressure, the hood would stay in place and not need pins.
@@JulianEdgar Do the laws of aerodynamics apply to cars or do the laws of cars apply to aerodynamics? Anyway, to answer your question, the reason I requested a simpler shape is because understanding how complex shapes behave is easier if you understand the more basic principles first. It's about grasping the fundamentals.
Don't worry about it. The authors of "Aerodynamics For Naval Aviators" thought it made sense to use it even though the book is about navy jets and the shape isn't a navy jet. It's the first illustration in the streamline pattern and pressure distribution section (pressure distribution on a cylinder, considering friction effects (viscous flow), page 15).
P.S. Technically speaking, a Volkswagen Bus is a car.
Can you please do books in french !
No, but all my books use a very large number of images, and looking at them and their captions will give you 80+ percent of the content.
@@JulianEdgar ok thank you
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?
The whole point of my aero writing and videos is to get away from guesswork and to test. So, especially when testing wheel covers is so easy, and wheel behaviour is specific to the car, I am not going to guess.
@@JulianEdgar thanks but easier said than done for the average working class joe. currently my wheels sit flush to the fenders of my EV. to test the aero i'll have to either buy new sets of the exact wheel with more offset, or grind down my wheels and put spacers and then do the tests. i'll be content with my set up i think. i'm sure the wheels being flush to fenders is the least of my aero concerns on the Kia EV6 haha
How much of an effect on this with lowering the car in downforce
You don't chase downforce by lowering a car alone. You do that in conjunction with undercar modifications. Easy.
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
A mezda? I drive a mezda mieata
80-90's Dodge Daytona?!
Nope. That’s an FC Mazda RX-7.
He tells what car it is in the video