Julian’s book is incredibly helpful, both in correcting past assumptions about how I thought aero appendages worked, as well as the impression that you need a wind tunnel, CFD software, etc, to understand aerodynamics. Best part? It is so inexpensive relative to other possible car mods. Highly recommended.
I wanna know, on a scale from 1 to 10, how crazy these modified tuner cars drive Mr. Edgar when he sees them since the Fast & the Furious came out in 2001? 🤔😄
Hi Julian, given that the Mazda MX-5 has sold millions of units around the world, it would be great if you produced a short video on aerodynamic modifications for convertibles. Given that there is a lot of turbulent flow behind the windscreen with the top down, I would be curious to see how you approached designing a road car like that to reduce rear lift!
great channel and very great video there is very few channels in you tube specialized in aerodynamic i think two and this the best because it takes you very deep in this sience thank you very much mr.julian you're quite special
Beg to differ on the Porsche, as I was responsible for 981 exterior design. The “Spalt Fluegel” (gap wing) worked very well according to our extensive wind tunnel tests when developing the 981 Boxster and Cayman. it was specifically developed to be a wing and not a spoiler like the 986 and 987. We saw flow under the wing and the panel below It is also shaped aid this. It certainly wasn’t stalled in our tests as you claim. The “spoiler” part of the rear end is the lip on the tail lamps.
The rear 'wing' is definitely stalled, as on-road tuft testing clearly shows (photo in the book). It can hardly fail to be stalled with its angle of attack to the airflow direction. It is acting as a large spoiler, not a wing. Dr Thomas Wolf (ex head of Porsche aero) agreed with my analysis - his comments are also in the book.
I drive a big square van (a Ram Promaster High Roof), and have been thinking about ways to improve fuel economy. The biggest opportunities I can see would be making a flatter underfloor or possibly top and side flaps on the rear like you see on semi-trailers. Since there’s no back window to push, seems like the best strategy is clean flow underneath and clean separation out back. What do you think would work best?
Yes, they are good starting points. Reducing drag is a full chapter in the book (and also how you can test that you have in fact reduced drag is another chapter).
Hi, I love your work on aerodynamics. I am wondering if it is possible to install some supporting mechanism to keep my trunk lid half-open as a "makeshift spoiler" for some extra downforce in track, do you think that would work? I have some legal restrictions in my area that prevents me from installing wings/spoilers.
Question: isn't the role of a spoiler also to ensure a clean separation of flow when the rear slopes down in a rounded shape? I remember the terrible failure of the first Audi TT, where the rear would be lifted by the flow going downwards on the rear. They fixed the problem with ESP, anti-roll bars and a spoiler. Also, I've always explained myself the need for spoilers with the fact that cars are, more or less, wing-shaped. The upper part is longer than the underside: this leads naturally to lift, lift that in certain cases is better... spoiled.
Spoilers can be used to create clean separation, eg a roof extension spoiler on a squareback car. However, in terms of reducing lift, their primary purpose is to change pressures ahead of / on them. In part that can be achieved by causing flow separation. The Audi TT is mentioned in the video - did you watch it?
One day people will apply this principle to cars under yaw, where they actually need the most downforce. A car in yaw changes the effective free stream flow relative to the front of the car. One thing I've discovered is that the windward side of a car in yaw is always the most sensitive, and most likely to experience separation, vortex breakdown, and turbulence. This phenomenon seems to work across different scales, for example in large super cell thunderstorms, the windward side of the storm is very chaotic and turbulent, the tornadoes, and other flow structures happen on the leeward side of the storm. In aircraft this is also an issue, part of the reason why flying wings are so terrible aerodynamically in general is because of vortex breakdown under slip and moderate angles of attack. As shown in this video here ua-cam.com/video/8DH53XZbEOo/v-deo.htmlsi=y_kbewkVj18UyvkF
@JulianEdgar Mr. Edgar, great video! I own a Tesla Model X and want to make aero modifications that will increase the range to counter the loss of range due to the high voltage battery degradation that has occurred and is continuing to occur. Does your book discuss the importance and order of how to do that with the Tesla Model X or EVs in general? After watching several of your videos I'm tempted to start with the rear of the car then the partial wheel covers. Would a wing like this one which can be found on Amazon under this description "Carbon Fiber Rear Trunk Spoiler for Tesla Model X 2016-2022 75D 90D P90D 100D P100D Sport Utility 4-Door Rear Spoiler Boot Lid High Kick Wing Lip Factory Outlet (A Style)" be a good or bad start? Also, do aftermarket splash guards / mud flaps significantly disrupt the air alongside a vehicle? Thanks for your reply.
Yes my major book covers how to reduce drag, irrespective of the driveline. It doesn't specifically cover the Model X. No I think the appendage you named would substantially increase drag. And yes, mudflaps increase drag - how much depends on the mudflap design and the car. Plenty for you to read and ponder - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8
@@JulianEdgar Thank you for your response! I will order the book! Does it give details on how to make the wheel covers? I measured from the center of my wheel to about an inch from the openings edge and it is 7.5 inches so I would guess I would need a 15 inch diameter cover to leave an inch of airflow.
I have a question. I drive a Mini Coupe (R58) which has a spoiler that extends at ~70km/h (very similar to the Cayman you showed, but not as aggressive). I noticed that water drops stay on it when I drive on the highway. Does it have any aerodynamic effect? When I purchased the car I originally thought it was a similar situation to the original Audi TT, but after my observation I'm questioning its intent. Interestingly the car shows an alert when you manually pop the spoiler up but don't do so all the way and start driving, warning you not to drive too fast. What are your thoughts on this? Thank you for your excellent videos!
You sort of skipped over the most interesting part, the spoiler on the back of the yellow car. It looks like air could flow underneath it which would reduce it's air damming ability, a airflow diagram would be very educational. But I guess that it's 'in the book'.
Yes, in the book I have a good pic showing dirt deposition above/below an elevated spoiler of that type. Clearly shows that there is little airflow through the gap.
@@JulianEdgar Does the book contain details and flow diagrams of how those type of spoilers work? Because of all other aero devices they are the mystery type to me.
A garage door can work just fine as a wing, it's all about the angle of attack. Shapes of wings are more about how they behave close to, or beyond, the critical angle.
@@JulianEdgar This "wing" pull the air down along the rear of the car. i.pinimg.com/originals/be/78/00/be78006f303575d8899fc38a298dbff3.jpg Annonced by Renault as a real drag benefit.
That is a roof deflector to direct air over the back window and stop dirty build up. Very unlikely it decreased drag, but if you have evidence it did, I'd love to see it.
Intuition would have me believing that a spoiler would bring more drag since it has an higher vertical component than a wing. I understand why deflectors can reduce drag, because it will leave a higher volume of air to drive the flow, but can't understand how a spoiler (at least those seen in the video) can achieve it to. Is there any scientific explanation or is it just the result of measurements?
What does this mean: " I understand why deflectors can reduce drag, because it will leave a higher volume of air to drive the flow"? A spoiler can reduce drag because it can increase pressures acting on surfaces ahead of it that have a vertical component, eg a sloping rear window.
I wasn't sure... Still not sure. The wing at the Porsche are automatic and start lifting around 80 km/t. Picture must show the wing fully extend by "driver assist" or braking from high speed.
Now I'm wondering about the Aussie Charger. I wonder if anyone's got good data on how effective it's spoiler is, and also, how one would effectively fit a wing.
You can be pretty well certain the Charger's spoiler was for looks alone. Basically there was no aerodynamic testing of Australian cars of that era. Easy to work out how to position a wing for best results - covered in my book.
@@JulianEdgar Thanks. I'll keep that in mind if I ever do manage to get myself a Charger. It's good to have a dream. It sounds like some of the early factory turbo installations, just drop that compression ratio and call it good enough.
Isn't having a spoiler or wing better than having none for more of a race setup. I only think so because a spoiler is what helped solve audi tt's design flaw of the back side generating lift at higher speeds an killing people
For example, Subaru Impreza Wrx Sti 2004 has 2 in 1 - spoiler and wing in one solution. There are 2 parts, lower part on boot works as a spoiler, upper part works as a wing. Is that correct? :) And in 2006 there is also small spoiler on the rear window, that directs flow better to the rear wing & spoiler. Is that also correct? :)
@@JulianEdgar Why rear window spoiler is called spoiler? Imo it should be called something else. :) It has basically water drop shape and it is placed above the car in negative attack angle, creating a lift. In expense of that, flow under is directed to rear spoiler/wing, and flow above detaches from the car. Isn't so? Is this really can be called spoiler? :)
I don’t know if you can consider it a “2-in-1” since the platform isn’t changing. It’s a wing, and probably a pretty good one at that. End-plates massively increase efficiency of a wing by reducing turbulence and drag. Also almost all boots/trunk lids are designed to act as a spoiler in modern cars. It’s a safety measure to prevent lift at high speeds. Just ask Audi what happens if you dont.
What would you classify the Swing spoiler used on the S550 Shelby GT350 (base model) and Shelby GT500 (non CFTP)? I have a GT350 with the Swing spoiler and optional Gurnee flap installed. I was debating whether to add some Vortex generators to the rear part of the roof to enhance air flow attachment down the rear window. However, I don't know if that would be a potential benefit or detrimental to the function of the Swing spoiler and Gurnee flap. Here is a quick walk around video showing the Swing spoiler and Gurnee Flap. ua-cam.com/video/Zmm0C-8M1YM/v-deo.htmlsi=YYso_kpwo6ZF5hRK
It's just a very big spoiler. (And Gurney flaps are used only on wings - and what you've shown me is not a wing.) Re vortex generators, without first testing the flow pattern (zero cost and easy) it would just be guessing whether they'd make any improvement.
Hey, I am currently following a course about Aerodynamics at my University. Here we are dealing a lot with different equations to calculate forces on the airfoil, is the book also using calculations to find the forces on the wing or is it mostly conceptual design?
The book covers the equations for aerofoil forces, however most space is devoted to measuring the *actual* forces developed on a real car on a real road or track - far more accurate than using the equations alone.
Julian’s book is incredibly helpful, both in correcting past assumptions about how I thought aero appendages worked, as well as the impression that you need a wind tunnel, CFD software, etc, to understand aerodynamics. Best part? It is so inexpensive relative to other possible car mods. Highly recommended.
I wanna know, on a scale from 1 to 10, how crazy these modified tuner cars drive Mr. Edgar when he sees them since the Fast & the Furious came out in 2001? 🤔😄
probably depends on the angle of attack and if the wing has stalled or not lmao
It would make a great video that's for sure
Thanks for all the comprehensive knowledge!
Glad it was helpful!
Cheers.
I like the sound of a wildlife in the background too.
from a pilot, this is a fantastic video 👍👍
Thank you. You may enjoy the book - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country.
I'm getting into openFOAM because of this channel
I wouldn't - watch ua-cam.com/video/QulnENytJ4I/v-deo.html
Thanks for the video, very informative. I have your book on order, looking forward to reading it.
I hope you enjoy it.
I would love a comparison of a standard Cayman spoiler, vs the elevated wing of the GT4 model.
Sure. Lend me a GT4 and we can make it happen.
Wow this was some great info, I thought they were just 2 different words for the same thing. I'll definitely start a spoiler and not a wing.
I was going to explain how a well designed spoiler can also reduce drag. But then Julian mentioned it. 😎
Hi Julian, given that the Mazda MX-5 has sold millions of units around the world, it would be great if you produced a short video on aerodynamic modifications for convertibles. Given that there is a lot of turbulent flow behind the windscreen with the top down, I would be curious to see how you approached designing a road car like that to reduce rear lift!
Very easy: you work under the car. All covered in my book....
This video needs a _spoiler_ warning Julian! Great to see some quality content, almost like consuming Autospeed in video form.
Thanks, but the book is so far ahead of AutoSpeed it’s on another planet!
Im very excited to fill the gaps in my oem spoiler and see if it creates a little improvement
great channel and very great video
there is very few channels in you tube specialized in aerodynamic i think two and this the best because it takes you very deep in this sience
thank you very much mr.julian you're quite special
Wow, great video. Found your channel yesterday and glad I did; you make this subject easy to understand.
Glad it was helpful!
Beg to differ on the Porsche, as I was responsible for 981 exterior design. The “Spalt Fluegel” (gap wing) worked very well according to our extensive wind tunnel tests when developing the 981 Boxster and Cayman. it was specifically developed to be a wing and not a spoiler like the 986 and 987. We saw flow under the wing and the panel below It is also shaped aid this. It certainly wasn’t stalled in our tests as you claim. The “spoiler” part of the rear end is the lip on the tail lamps.
The rear 'wing' is definitely stalled, as on-road tuft testing clearly shows (photo in the book). It can hardly fail to be stalled with its angle of attack to the airflow direction. It is acting as a large spoiler, not a wing. Dr Thomas Wolf (ex head of Porsche aero) agreed with my analysis - his comments are also in the book.
Extremely helpful video. Thanks a lot!
You're welcome!
Awesome, you are back!!😊
Great video as usual Julian. Top man.
Thank you
I drive a big square van (a Ram Promaster High Roof), and have been thinking about ways to improve fuel economy. The biggest opportunities I can see would be making a flatter underfloor or possibly top and side flaps on the rear like you see on semi-trailers. Since there’s no back window to push, seems like the best strategy is clean flow underneath and clean separation out back. What do you think would work best?
Yes, they are good starting points. Reducing drag is a full chapter in the book (and also how you can test that you have in fact reduced drag is another chapter).
Hi, I love your work on aerodynamics.
I am wondering if it is possible to install some supporting mechanism to keep my trunk lid half-open as a "makeshift spoiler" for some extra downforce in track, do you think that would work?
I have some legal restrictions in my area that prevents me from installing wings/spoilers.
Probably. But why guess? Very easy to measure.
@@JulianEdgar Good idea! I will try holding the trunk lid open with a stick and measure it. Thanks!
p119 of my book has a test with a trunk lid held open on a BMW.
Great video ( as always )
Question: isn't the role of a spoiler also to ensure a clean separation of flow when the rear slopes down in a rounded shape? I remember the terrible failure of the first Audi TT, where the rear would be lifted by the flow going downwards on the rear. They fixed the problem with ESP, anti-roll bars and a spoiler.
Also, I've always explained myself the need for spoilers with the fact that cars are, more or less, wing-shaped. The upper part is longer than the underside: this leads naturally to lift, lift that in certain cases is better... spoiled.
Spoilers can be used to create clean separation, eg a roof extension spoiler on a squareback car. However, in terms of reducing lift, their primary purpose is to change pressures ahead of / on them. In part that can be achieved by causing flow separation. The Audi TT is mentioned in the video - did you watch it?
@@JulianEdgar Yes I did watch it but I missed the Audi TT ... will check again
One day people will apply this principle to cars under yaw, where they actually need the most downforce. A car in yaw changes the effective free stream flow relative to the front of the car. One thing I've discovered is that the windward side of a car in yaw is always the most sensitive, and most likely to experience separation, vortex breakdown, and turbulence. This phenomenon seems to work across different scales, for example in large super cell thunderstorms, the windward side of the storm is very chaotic and turbulent, the tornadoes, and other flow structures happen on the leeward side of the storm.
In aircraft this is also an issue, part of the reason why flying wings are so terrible aerodynamically in general is because of vortex breakdown under slip and moderate angles of attack. As shown in this video here ua-cam.com/video/8DH53XZbEOo/v-deo.htmlsi=y_kbewkVj18UyvkF
@JulianEdgar Mr. Edgar, great video! I own a Tesla Model X and want to make aero modifications that will increase the range to counter the loss of range due to the high voltage battery degradation that has occurred and is continuing to occur. Does your book discuss the importance and order of how to do that with the Tesla Model X or EVs in general? After watching several of your videos I'm tempted to start with the rear of the car then the partial wheel covers. Would a wing like this one which can be found on Amazon under this description "Carbon Fiber Rear Trunk Spoiler for Tesla Model X 2016-2022 75D 90D P90D 100D P100D Sport Utility 4-Door Rear Spoiler Boot Lid High Kick Wing Lip Factory Outlet (A Style)" be a good or bad start? Also, do aftermarket splash guards / mud flaps significantly disrupt the air alongside a vehicle? Thanks for your reply.
Yes my major book covers how to reduce drag, irrespective of the driveline. It doesn't specifically cover the Model X. No I think the appendage you named would substantially increase drag. And yes, mudflaps increase drag - how much depends on the mudflap design and the car. Plenty for you to read and ponder - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8
@@JulianEdgar Thank you for your response! I will order the book! Does it give details on how to make the wheel covers? I measured from the center of my wheel to about an inch from the openings edge and it is 7.5 inches so I would guess I would need a 15 inch diameter cover to leave an inch of airflow.
The book covers wheel drag in some detail, yes. It also shows how one set of wheel covers was made.
I have a question. I drive a Mini Coupe (R58) which has a spoiler that extends at ~70km/h (very similar to the Cayman you showed, but not as aggressive). I noticed that water drops stay on it when I drive on the highway. Does it have any aerodynamic effect? When I purchased the car I originally thought it was a similar situation to the original Audi TT, but after my observation I'm questioning its intent. Interestingly the car shows an alert when you manually pop the spoiler up but don't do so all the way and start driving, warning you not to drive too fast. What are your thoughts on this? Thank you for your excellent videos!
Tuft and pressure testing is your answer. Anything else is just guesswork.
You sort of skipped over the most interesting part, the spoiler on the back of the yellow car. It looks like air could flow underneath it which would reduce it's air damming ability, a airflow diagram would be very educational. But I guess that it's 'in the book'.
Yes, in the book I have a good pic showing dirt deposition above/below an elevated spoiler of that type. Clearly shows that there is little airflow through the gap.
@@JulianEdgar Does the book contain details and flow diagrams of how those type of spoilers work? Because of all other aero devices they are the mystery type to me.
Not sure what the issue is? As I said, very little air flows through the gap on most cars ie it just acts as a spoiler.
@@JulianEdgar What confuses me is that those separated spoilers are usually level and not tilted like an attached spoiler.
They are styled to look like wings, but they work like spoilers. Very common.
A garage door can work just fine as a wing, it's all about the angle of attack. Shapes of wings are more about how they behave close to, or beyond, the critical angle.
A wing has attached flow both sides. The Porsche appendage does not.
THANK YOU
Do you remember the "roof spoiler" of the Renault 16?
For me, a wing used to decrease drag.
A true wing is never used to decrease drag. How can it?
@@JulianEdgar This "wing" pull the air down along the rear of the car.
i.pinimg.com/originals/be/78/00/be78006f303575d8899fc38a298dbff3.jpg
Annonced by Renault as a real drag benefit.
That is a roof deflector to direct air over the back window and stop dirty build up. Very unlikely it decreased drag, but if you have evidence it did, I'd love to see it.
Intuition would have me believing that a spoiler would bring more drag since it has an higher vertical component than a wing. I understand why deflectors can reduce drag, because it will leave a higher volume of air to drive the flow, but can't understand how a spoiler (at least those seen in the video) can achieve it to. Is there any scientific explanation or is it just the result of measurements?
What does this mean: " I understand why deflectors can reduce drag, because it will leave a higher volume of air to drive the flow"? A spoiler can reduce drag because it can increase pressures acting on surfaces ahead of it that have a vertical component, eg a sloping rear window.
Interesting ; thank you
Glad you enjoyed it
I recently saw a subaru wrx with a wing behind vortex generators. I was wondering how this affects the downforce of the wing.
Depends if there was originally flow separation where the vortex generators are.
I wasn't sure... Still not sure. The wing at the Porsche are automatic and start lifting around 80 km/t. Picture must show the wing fully extend by "driver assist" or braking from high speed.
Doesn't change any of the points in the video, but the wing has been manually raised for the pic.
Now I'm wondering about the Aussie Charger. I wonder if anyone's got good data on how effective it's spoiler is, and also, how one would effectively fit a wing.
You can be pretty well certain the Charger's spoiler was for looks alone. Basically there was no aerodynamic testing of Australian cars of that era. Easy to work out how to position a wing for best results - covered in my book.
@@JulianEdgar Thanks. I'll keep that in mind if I ever do manage to get myself a Charger. It's good to have a dream. It sounds like some of the early factory turbo installations, just drop that compression ratio and call it good enough.
Isn't having a spoiler or wing better than having none for more of a race setup. I only think so because a spoiler is what helped solve audi tt's design flaw of the back side generating lift at higher speeds an killing people
I don't understand your point, sorry.
For example, Subaru Impreza Wrx Sti 2004 has 2 in 1 - spoiler and wing in one solution. There are 2 parts, lower part on boot works as a spoiler, upper part works as a wing. Is that correct? :) And in 2006 there is also small spoiler on the rear window, that directs flow better to the rear wing & spoiler. Is that also correct? :)
Yes and yes. In the book I measure the downforce of the Sti wing/spoiler.
@@JulianEdgar Why rear window spoiler is called spoiler? Imo it should be called something else. :)
It has basically water drop shape and it is placed above the car in negative attack angle, creating a lift. In expense of that, flow under is directed to rear spoiler/wing, and flow above detaches from the car. Isn't so?
Is this really can be called spoiler? :)
I don’t know if you can consider it a “2-in-1” since the platform isn’t changing. It’s a wing, and probably a pretty good one at that. End-plates massively increase efficiency of a wing by reducing turbulence and drag.
Also almost all boots/trunk lids are designed to act as a spoiler in modern cars. It’s a safety measure to prevent lift at high speeds. Just ask Audi what happens if you dont.
Would it be correct to characterize a gurney flap as a spoiler on a wing?
Yes.
🤓🤓nice video
Thank you.
do you sell ebooks of this book sir
No e-book. The book's Amazon page explains why.
@@JulianEdgar Now i understand the motivation behind it. Hopefully, Amazon will deliver to my country someday. thank you
1:31 That looks like a car attached to an aircraft. 😄
It's a mighty wing. Worked, too.
@@JulianEdgar Good to know. Thanks!
What would you classify the Swing spoiler used on the S550 Shelby GT350 (base model) and Shelby GT500 (non CFTP)? I have a GT350 with the Swing spoiler and optional Gurnee flap installed.
I was debating whether to add some Vortex generators to the rear part of the roof to enhance air flow attachment down the rear window. However, I don't know if that would be a potential benefit or detrimental to the function of the Swing spoiler and Gurnee flap.
Here is a quick walk around video showing the Swing spoiler and Gurnee Flap. ua-cam.com/video/Zmm0C-8M1YM/v-deo.htmlsi=YYso_kpwo6ZF5hRK
It's just a very big spoiler. (And Gurney flaps are used only on wings - and what you've shown me is not a wing.) Re vortex generators, without first testing the flow pattern (zero cost and easy) it would just be guessing whether they'd make any improvement.
Hey, I am currently following a course about Aerodynamics at my University. Here we are dealing a lot with different equations to calculate forces on the airfoil, is the book also using calculations to find the forces on the wing or is it mostly conceptual design?
The book covers the equations for aerofoil forces, however most space is devoted to measuring the *actual* forces developed on a real car on a real road or track - far more accurate than using the equations alone.