Aerodynamic drag and lift of different car body shapes

[@Tarex_]

The fastback having the highest lift reminds or brings back the Audi TT that had to get the spoiler lip because of how unstable it was

[@anidiotinaracingcar]

The Audi TT is basically an airplane wing. Had it had a decent engine, it would have taken off

[@Tarex_]

@@anidiotinaracingcar we would've had mainstream flying cars sooner if it had a better engine xD the R36 wouldve been better suited than the the 1.8 Turbo xD

[@anidiotinaracingcar]

@@Tarex_ Hahaha. The first flying cars I can remember were GT1s (The 911 and CLR)

[@Tarex_]

@@anidiotinaracingcar sadly investments went towards keeping them on the ground instead of using ground effects to hover

[@BouncingCow]

If I remember correctly the problem was a bit more complicated and related to shear flows within the region during conering that finally lead to separation at higher velocities.

[@DanielinLaTuna]

The Volkswagen Bug (or Beetle) was scary to drive at high speeds for various reasons, but one of them was how light the car became at those speeds; this demonstration explains the lift it’s body shape provided.

[@JulianEdgar]

Yes, high lift shape indeed

[@thebrowns5337]

Thankfully the engine hanging onto the back of the chassis kept it down though.

[@quentagonthornton49]

@@thebrowns5337 The engine being at the back is worse than having it at the front as it will pitch up the car, increasing the amount of lift it produces, at least until an aerodynamic stall, but that is a huge number of degrees for a car to pitch up and the front wheels would be well of the ground at that point.

[@cdw3423]

I'm not sure VW Bug and "high speed" should ever be in the same sentence. :)

[@tommybronze3451]

I though that most scary thing about driving VW Beatle was that if indicators failed (and they did a lot) you would have to indicate turning by essentially saluting through the window 😆

[@AIRDRAC]

This corresponds extremely well with my personal experience on the Autobahn. My old Saab 9000 CS Aero had a frightening tendency to get very vague and loose in the rear above 250 km/h, whereas my VW Passat station wagon just had a lot more wind noise, but stayed stable at similar speeds, despite the Saab having a lip spoiler and vaguely venturi tunnel-like shapes underneath, and the Passat just being a slightly rounded box. Fascinating to see such a detailed study with such high quality data!

[@Tore_Lund]

One winter night 15 years ago, when it was snowing and the conditions just right with the wind blowing steady along the travel direction of the parked cars in my street. There was one car, a hatchback (square back), which collected snow on the rear hatch in the wake zone, where the snow was capable of sticking. It formed a perfect boat tail: slightly curved sloping extension of the roofline, 10-15 degrees, as science tells us and the sides sloping similarly but at a somewhat steeper angle. What surprised me was that the edge between the sloping sides and roof line buildup, was a sharp perfect 90 degree edge. This must mean that the air from the sides and the roof stayed attached and didn't mix, i.e. no turbulence sideways across the snow cone! So it was a shame I didn't photograph it, but this is an example of real life simulation not based on moddeling. And thank you, your channel is brilliant. Nb.: the sloping sides of the snow cone met in the middle forming a sharp stump vertical edge there, so the buildup overall ressembled the stern of a round bottomed wooden boat.

[@JulianEdgar]

Interesting. If the airflow had wrapped from the sides onto the top of the extended tail there would have been lift and so drag.

[@Tore_Lund]

@@JulianEdgar Yes it is interesting as usually people who refit boattails to their cars, round the edges at the corners, at an increasing radii to approach a circular cross section at the far end. Guess Mercedes figured it out too with their boxfish bodyshape, which had the roof edges extend all the way without rounding. I presume the snow was slightly warmer than the air at ground level, so the flakes were sticky, but refroze once they settled. It would have been an incremental process also, as the snow at first had few places without fast air to settle, but as the buildup progressed, it gradually improved aerodynamics and extended the attached flow, giving room for the cone growing lenghtwise.

[@jwalker7567]

My ford fiesta once was covered in about 2 inches of snow, I left it there as I drove on the highway for 3 hours for my journey at night, when I arrived I was amazed most of the snow was still there. Interestingly the leading edge of the hood and the roof were down to ice, yet they both mounded in the middle. I also noticed how they had random wavy patterns in the snow and it was no longer uniform (similar to the sand on beach after the tide goes out). I logged the MPG figure for the journey as it was the same journey each week and unsurprisingly it dropped from what would normally be about 45mpg to 41mpg. There was no snow on the roads and it didn't snow during the journey, so this was likely purely due to the snow on the vehicle.

[@Tore_Lund]

@@jwalker7567 I think we are onto something: Sticky substance natural forming aerodynamic fairings.

[@brokenrecord3523]

Check out the back of a Honda insight, especially the older ones with the narrow rear footprint.

[@Rob-Müller]

I ride a motorcycle and am always amazed at how various vehicles create turbulence as I follow behind. It is not necessarily what one would expect. For example, smaller vehicles such as a Rav4 create quite a bit of turbulence as a result of the square back even though it is not large. A larger SUV with a rounded back is sometimes less turbulent. Many cars can't be felt at all.

[@ProrokC2]

You saying that RAV4 is a smaller car tells me you are an American

[@Rob-Müller]

@ProrokC2 ​Close, Canadian, but we drive the exact same vehicles as Americans. Yes, a Rav4 is small here. A Nissan Pathfinder would be medium and GMC Yukon would be large. Also, more than half the people where I live drive large trucks. It is kind of ridiculous.

[@ProrokC2]

@@Rob-Müller Interesting, here in europe a RAV4 is a large car, something like a corolla is considered medium, and small is something like yaris/aygo. Even right now I'm looking at buying a Fiat Tipo (1.6 diesel, automatic transmission - not so easy to get around here) and it's a medium size car. Most people here drive compacts like peugot 308 or medium sized peugot 508, skoda octavia, vw passat etc, and them all mostly station wagons, but hatchbacks are popular as well. Interesting point of view. Come over here to europe, I fell as you'd get a small culture shock :). But something like GMC Yukon is absolutely ridiculous, it won't fit anywhere in european cities, literally not even at a shopping mall, not to even mention underground parking etc. Why would anyone need such a huge car?

[@Nimrawid]

rav4 as small vehicle xD

[@wills.5762]

I wonder if youre getting caught in the SUVs slipstream vs hanging out in the turbulent edges of say the Rav4s slipstream. How do you find it following a semi trailer?

[@SDH-g8g]

And that is why lots of sleek FWD cars still have rear spoilers! Another great video, thanks!

[@jmi5969]

They have space to place them to begin with... a boxy hatch or minivan doesn't.

[@julianbrelsford]

​@@jmi5969I've seen some US market minivans with a spoiler-like thing. Basically extends the high roof another 5 or so inches, possibly with a gap where some air can flow directly down against the rear window. Dodge Magnum station wagon (sometimes at least) came with a similar thing.

[@NikolaTesla-nb5nm]

yes, FWDs have terrible handling

[@rainretribute9852]

​@@NikolaTesla-nb5nmwrong. Don't speak if you don't know

[@MrSirGiuseppe]

​@@NikolaTesla-nb5nm absolutely not 😂

[@rohesilmnelohe]

I have '15 Corolla sedan. The flow separation on back widow in the centerline is a thing. Very well seen during winter when it is the only place where snow wants to stay. However the airflow reattaches itself really fast from the sides. Only place where snow accumulates and stays is top center of the back window and bottom edge of rear hatch. I'd say it is really well designed.

[@alexandervanwyk7669]

Still fascinating, from a retired engineer, spending my life in a wind tunnel. It will be awesome if you can present a series of basic tutorials (again) for us car enthusiasts. My first car was a 1930 Chevrolet. This car had almost zero drag but then it also had very little speed. (Pun intended) My latest car is a Porsche. With speed, aerodynamics became really an important issue also as it directly affect fuel economy. So referring to basics explain again the basic shapes, ie a square compared to an aerofoil shape has almost 25 times higher drag for the same projected area. The exponential phenomenon of drag vs speed. Tyre width and tyre pressures. Open windows vs closed etc. Basic practical principles that already assist in saving money before vast monies are being spent on attachments. As it is still a specialized subject with lots of 'confidential' results, it will just be great if you provide basics for the next generation. Thanks for your dedication and passioin. Love from Africa.

[@brokenrecord3523]

It looks better. It makes the car worse. - I can see the designers and engineers having this argument all over the world. As the manufacturing engineers and workers say "I can't build either one." and the mechanics: "That oil filter is where!!!"

[@qx4n9e1xp]

Please do a video showcasing the various types of wings/spoilers affecting lift & drag. I want to fit a spoiler on my notchback vehicle for cosmetic purposes, but I'm interested in seeing the airflow effects. Thanks again!

[@JulianEdgar]

Yes I can do that

[@Aengus42]

Reminds me of when Volvo wanted to get into Touring Car Racing and before they built something slippery to get into the series quickly (you had to have a certain number of production cars before you could race that type) they went through their entire fleet to find the car with the best aerodynamics. Which is why, in all it's glory, the Volvo 850 Estate appeared on the starting grid in 1995 (with a production Cd of 0.32 I think). That has a lot to do with my Toyota Corolla Hybrid Estate outside!

[@K03sport]

loved the 850R platform. not to mention, the wagon ethos stayed true to Volvo and it got noticed (a lot) I regret never buying an 850R...of course now, they are super difficult to find (in good condition)

[@Aengus42]

@@K03sport I loved my Volvo. I was offered a 240 automatic saloon (sedan) for £100 because my aunt had decided to stop driving. It was slow but with two young kids it was perfect for us. A huge amount of room, massive boot (trunk) built like a tank! It felt like driving a boat, mind you. But it never let us down and we went all over the place in it.

[@K03sport]

@@Aengus42...strange...had a (hand me down) '80 240 (244) GL non-turbo in 90-91 w/crank sunroof and automatic. only problem was the throttle and trans kick down. when pressing the go pedal, there would be no acceleration and no kick down for a lengthy 5+ seconds. and the issue was intermittent so you never knew when it was going to fall on its face. a friend in high school had the exact same car/color, but hers was a manual

[@Aengus42]

@@K03sport Mine would make all the right noises. I'd hit the throttle, the revs would climb and make a helluva noise! But absolutely zero acceleration! Nothing! Edit: On the motorway. Doing a steady 75. The kids would yell "Warpdrive in three! One, two, WARP!" I'd hit the throttle, you could hear Warpdrive engaging but absolutely nothing happened to the speed and we'd all collapse into giggles 😆

[@jakecole7447]

Worked for Toyota as a Technician - Good choice in that car ! Havent seen anything major break there yet. super reliable, nice drivability (Pulls no corvettes but so much better than previous generations hybrid) great looks and i've had customer cars that got 60 Miles per Gallon in mixed traffic (Europe).

[@Chris.Davies]

I am very lucky to own a 1997 Tommy kaira M20b wagon, with a custom made TK roof spoiler, which was experimentally set for minimum drag in the wind tunnel. The custom TK parts all have little metal plates with the TK signature on them. Tommy Kaira were engineers before all else, and they recognised the frailty of the Subaru 5-speed box in the JDM WRX the car is based on, and so they created two massive braces which go straight through the 'box hold it together, preventing it performing a RUD (Rapid Unscheduled Disassembly) at high boost and high RPMs. :)

[@Crysmatic]

Makes sense why Germans love their fast station wagons :) I see that bubble on my notchback every winter. Snow just sits in the bubble and doesn't get cleared away.

[@daszieher]

The worse drag is just compensated by more power. Enter RS6

[@oldskool235]

I have a 1995 Saturn sw2 doch 5 speed manual and I love it. It's built, stanced and riding on 16x8 high offset. Handles like a dream and super solid feeling at high highway speeds. I live in the Detroit area, so even though it says 70 mph speed limit, it's closer to 85/ 90 cruising speeds. If you're doing 70, you better be in the slow lane.

[@gregorykusiak5424]

Fantastic! Wonderful find - thank you for sharing! Nice to finally see someone has confirmed with research what I’ve understood from driving my squareback: when I’m driving and have a significant enough wind to fill the wake from behind, in the same direction I’m travelling (a tailwind or rear quartering crosswind), my fuel economy improves (not insignificantly). So now, it seems I have to get the air from over the roof and underneath the car into the wake sooner to reduce it, and hopefully drag along with it. I’m going to make an educated (from this channel’s videos) guess that it will take an undertray with a rather serious rear diffuser bringing the air from underneath upwards, as well as a roof extension lip curved downwards towards the road to fill in the wake area.

[@pedrobrito8080]

Nice. Good work.

[@brianvanwyk9878]

Did you make the undertray and diffuser? If so, what was the outcome? When you designed the diffuser, did you keep in mind that the wake is a 3D shape? If yes, how does the diffuser look like and did it make an impact?

[@gregorykusiak5424]

@@brianvanwyk9878 I only did an undertray as far as the rear axle- a diffuser was more complex from a design/implementation aspect due to exhaust and suspension issues. But just that on my SUV made for a quieter ride and made highway cruising much smoother and slightly (maybe 1-2mpg) more efficient.

[@CannonballCircuit]

could you also add a vortex generator on your roof?

[@gregorykusiak5424]

@@CannonballCircuit a roof extension is a better way to go I think- the air from over the roof needs to meet back up with what’s flowing underneath to minimize the wake by filling it up.

[@op3l]

I drive a van with basically a 90 degree tail. Any amount of moisture or dust, and the back is covered in crud due to aerodynamics.

[@JulianEdgar]

It's a topic I cover in my latest book - and how to stop it happening. www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8

[@xXZ31t6esTXx]

Can you please make a video about the airflow around the tires? I see different ways in which manufacturers try to deflect the air before the tire

[@JulianEdgar]

It's a really tricky area with quite lot of contradictory information. I'll think about how to best cover it.

[@jzxtrd337]

The Julian Edgar, 21 century performance was a stellar book mate

[@JulianEdgar]

Thank you.

[@poptartmcjelly7054]

The SAAB NG900 had to get the small spoiler added because of stability issues at speeds above 170kph.

[@AIRDRAC]

The Saab 9000 CS Aero had it's top speed limited to 250 km/h for the same reason, despite having both a lip spoiler and vaguely venturi-tunnel like shapes under the car. Speaking from experience the rear suddenly go VERY light and unstable over 250 😅 (I had a Hirsch with slightly more power than stock (~315 at the wheels) and the limiter removed - it was amazing right up until you reached 250)

[@334trax2]

Very interesting my hatchback "square back" has less lift. It never feels like it is light or floating at high speeds, that is suspension also.

[@JulianEdgar]

Yes, I learned a lot too!

[@roscius6204]

I have an A6 Avant (so a Sqaureback) It's stability at high speed (tops out at 250 kph) is amazing. Just planted. I've had other wagons and always suspected this. Conversely an RX2 I had in my youth was like piloting a skimming stone

[@spottersworld3135]

I had a b7 RS4 avant and a series 1 RX2 sedan in my youth and had exactly the same experience

[@linkskywalker5417]

So you can use it as a station wagon is intended to be used, as in, transporting stuff and an entire group of people, and going fast while doing so without worrying too much about rear lift.

[@roscius6204]

@@linkskywalker5417 The faster you go, the more planted it gets. So yes I guess. People have the visual idea of aerodynamics wrong , I think largely because sports cars have always been sleek looking. But reality is if you want to keep it on the road at high speed you have to push the tail down. Rockets don't have pointy tails either.

[@rogerking7258]

This is really interesting, although these figures can only be generic because of the significant detail differences between different vehicles. It would have been interesting to see figs for a true Kamm tail as well. And what I would _really_ like to see would be CD figures for the sleek E-type jag and the extremely boxy Austin A40 Farina. Rumour has it that the A40 is actually slipperier.

[@JulianEdgar]

There’s no magic in a Kamm tail. You’d be interested in my book on the history of car aerodynamics - www.amazon.com/Century-Car-Aerodynamics-science-airflow/dp/B095RLP52B or Amazon in your country.

[@racketman2u]

This reminds me of a photo I saw of a Datsun 240Z at speed, lifted right up on its suspension; no wonder mine felt much better once I added the rear bobtail and front airdam! It actually increased its top speed by about 15km/h too, so the drag must have dropped.

[@JulianEdgar]

These days, you'd gain vastly better results with a full length undertray and no front spoiler.

[@timothymoroney3561]

It would be interesting to see this study for semi-trucks, pickups & the Aptera !

[@JulianEdgar]

The Aptera doesn’t exist except as a prototype. The other vehicles are covered in my latest book - check Amazon.

[@jooky87]

Awesome, thank you for your enthusiasm, too makes it more interesting. I’m wondering if a spoiler like a ducktail or those small wing tails actually make a difference too.

[@JulianEdgar]

They certainly can, depending on the car. For example, see kzbin.info/www/bejne/h6i2eaJuirV3qbM

[@zeroelus]

Stumbling on this video years after it came out, but it's nice to see data that matches what I see in real life. Having an extreme squareback (minivan) it just confirms my suspicions as to what I've seen when driving: I've seen leaves picked up from the road just move around horizontally in the rear glass and just stay there floating, and living in the dusty desert, the rear hatch of the car is always covered in dust/sand, no matter how often I wash or what wax products I use, I can mitigate it but I've resigned myself to always have some dust collecting there. My other car (a wagon, Subaru Outback specifically) also see this but to a different degree: Years of being exposed to this same dusty environment and about an inch long lip on the rear hatch near where the rear wiper is now at this point sans clear coat, no matter my efforts at trying different coatings.

[@JulianEdgar]

My latest book has some material on reducing rear soiling on squareback vehicles - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8

[@FairladyS130]

Looks like both the fast and notch backs would benefit significantly from a modest bob tail spoiler. Likely to bring them up to square back figures I wonder.

[@JulianEdgar]

Yes

[@michaelbuckers]

Cool to see that hot hatch is actually the best body type aero-wise, it generates a bit of downforce without any additional aero.

[@JulianEdgar]

Generally the case, but not all hatches develop downforce. See Appendix 3 in my new book - lnkd.in/g88vC8qj

[@michaelbuckers]

@@JulianEdgar Well a car can only really approximate 3 shapes: a brick, a wedge and a wing. Making the tail end smoother makes hatchbacks' wedge shape closer to a wing shape. And car's angle of attack cannot be made zero or negative because that requires free flowing air under the body, same as over the roof.

[@JulianEdgar]

With all respect, I strongly suggest that you buy my book and read about lift/downforce. Your mental model is way over-simplified eg in your model, how can a fastback-shaped car develop downforce? Because it can (even without an added wing). And as I already said, plenty of "brick shaped" vehicles develop lift, especially on the front axle.

[@michaelbuckers]

@@JulianEdgar I know it's oversimplified, mainly in "all else equal" department which is never the case. It's just a youtube comment.

[@K03sport]

what I learned - wagons (hatchback) rule; other cars can drool (oh snap, Prius be damned) And it looks like my '19 WRX is hamstrung from the get go, not only being a Subaru, but also being a notchback (w/a trunk or boot). Might need to add one of those gurney flaps to the low profile trunk lip spoiler to push that air higher off the back of the trunk (as I do not have the big STI wing). Wonder if those vortex generators will reduce that high pressure on the rear glass area?

[@craigchamberlain]

Really interesting video - thank you!

[@jgonzalesm6]

There is a device on cars called a rear diffuser when properly applied i.e. the vanes have to start almost at the rear axle of the car. This rear diffuser or vanes create small vortices that "suck" the rear of the car back to the ground. The faster the car goes, the more suction is created. You will also see this rear diffuser in motorsports like F1 or WEC in the GT-Pro cars.

[@JulianEdgar]

Most EVs have rear diffusers at the end of their flat floors. They don't need vanes (strakes) to work.

[@jgonzalesm6]

@@JulianEdgar - And most, if not all, upper high end production cars have the vanes on their rear diffusers for them to work....just like in motorsports.

[@JulianEdgar]

If you want to see what measured difference strakes make in diffusers, refer to figure 6.22 in my book - it's very little.

[@jgonzalesm6]

@@JulianEdgar - not in motorsports nor in higher end production cars. F1 has videos of how much downforce the floor and rear diffusers(with strakes or vanes) produce...it's over 60%. The faster the car goes, the more downforce the floor and rear diffusers produce(with vanes or strakes). Look at an airplane wingtip under heavy humidity when taking off or landing and you can see the vortices. Imagine those little tornadoes underneath your car sucking the rear end of your car downward at speed (the higher you go at speed).

[@jgonzalesm6]

@@JulianEdgar - Adrian Newey has a book called "How to build an F1 car." I suggest you read it regarding rear diffusers with strakes or vanes and their purpose.

[@Nordic_Mechanic]

The notchback is the winner overall. The higher front lift counterbalance the rear lift and makes it stable at high speed

[@Joerg1One]

Thanks for your explanations. Drag and lift is a very very interesting topic. I have seen a lot of conclusions in the comments in regarding to stability. But I would say, the stability difference between the body shapes are very low in modern cars. More important for non track used cars are the speed of air flow, because of effiency. Thats why sportback shapes are faster in accelaration, espacially at higher speed, producing higher top speed and less fuel consumption. You can really good obeserve that at the German Autobahn. Anyway, I would love to see the effects of rear and front spoilers in regarding of different body shapes. Thank you in advanced!

[@JulianEdgar]

Stability is actually very important, and varies a lot between different current cars!

[@Lordosvk]

Looks like the combi (squerback) is best for normal driving.

[@aNaturalist]

That's what I gather from this video too, but I'd have to watch it again.

[@TheSaltFlatInterceptor]

Have any information on pickup truck aero? Interested in the effectiveness of cab spoilers and tail gate spoilers.

[@JulianEdgar]

Easy enough to measure for yourself.

[@TheSaltFlatInterceptor]

@@JulianEdgar perhaps for you it is haha

[@JulianEdgar]

@@TheSaltFlatInterceptor No, easy for anyone. All covered in my books.

[@TheSaltFlatInterceptor]

@@JulianEdgar oh! So you do, in fact, have information specific to pickups in your book! Excellent!

[@JulianEdgar]

@@TheSaltFlatInterceptor The aero testing techniques can be applied to any vehicle. Doesn’t matter what it is.

[@fredrickmillstead2804]

Wish I could see a presentation from above the 3 vehicles, that would prove interesting

[@rodin-06]

Interesting video YT threw at me. I ride a motorbike and when on the motorway, some cars create the most awful turbulance i just can't figure how modern cars would be so bad. So I was curious to see what this video revealed. To be fair, the distance I travel behind other vehicles means this video doesn't quite cover my query, but it remains interesting. What i have leant in general is that on the motorway, estate cars seem better, with a cleaner, less turbulant wake. But it's not obvious, as some slippery looking cars generate awful wakes. This wake turbulance is effective at 150-250m behind the vehicles. I tend to overtake these and get ahead, but sometimes people cut in front of you at much shorter distances and the wake can be a real pita!

[@JulianEdgar]

Interesting comment. Love to hear your best/worst cars.

[@rodin-06]

@@JulianEdgar I have actually thought to make a list, with a brief description of the body type. I'm in a long run on a few weeks, I might finally make that list and report back 😊

[@stefanomarchi3542]

This video is pure gold! Thanks a lot

[@JulianEdgar]

Glad it was helpful!

[@Nordic_Mechanic]

I found my book suggestion for this christmas :)

[@Russell_and_Rosko]

I'm curious how the coefficient of lift averages over the entire vehicle depending on ride height, and after you add a chin spoiler to the front then a gurney flap in the rear across the three body types. I'm interested in reducing lift without increasing drag. A chin spoiler along with the gurney flap should reduce lift at the expense of drag. Maybe wind curtains for the front wheel wells with a diffuser out back so theres less drag while still minimizing lift. Excellent video. I've watched it through several times. Squarebacks are the best 👌

[@JulianEdgar]

The answers to all your questions are covered in detail in the book - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8

[@Russell_and_Rosko]

@@JulianEdgar Awesome! Thanks for all of the valuable info 🖖

[@ehsnils]

As noted the aerodynamics considered is partial, so the actual lift and downforce values may be a bit different. What did seem to be left out is the airflow below the vehicle and for anyone familiar with Formula 1 these days the floor plays a vital role for the car. Just slight changes in the suspension geometry could give different result on downforce due to the changes in airflow under the car.

[@JulianEdgar]

The undersides of all the models are the same.

[@amduser86]

@@JulianEdgar not, they are not. that just to large a generalization. the aerodynamic desgin of the underside of a bmw 3 series is already different/worse than that of the alfa guila and those are fairly exepsnive cars. if you consider more afordable cars stuff get's even worth. the is no need for aerodynamic optimazation of the underside in most asian markets, since they are not allowed to drive at any speed the car would benefit from it ...

[@alexeysafronov6447]

It should be possible to transform turbulent flow into laminar flow by changing the shape of the hood and roof, making it go through a tight space for compression and separation and then gradual and linear compression. What is presented here is just a result of the front side of the car going through the air. It's also interesting to take a look at a side profile to create gaps that would smoothen the airflow or the car's wheels as well as making it more droplet like shape overall. Its well known to design the bottom of the car with aerodynamic splitters that both create directed airflow providing cooling and creating less lift, so there less downforce needed to be compensated.

[@JulianEdgar]

Quite a bit of confusion in what you have written here - maybe read my book?

[@2810Mad]

Toyota Corolla touring sports. It has ample space, great mileage with its hybrid drivetrain, is gorgeous and decently fast with its ~200hp. Best car I've ever owned.

[@nunyabidniz2868]

Would love to see visual representation of how adding some vortex generators across the roof affect the lift and the blue bubbles behind the body shapes.

[@JulianEdgar]

Vortex generators don't work as you seem to think they would do: neither lift nor the wake behind the car is likely to be impacted by vortex generators on the roof of these shapes.

[@tigerseye73]

Hi Julian: If you could break this down into a tiny nutshell, which shape would yield the highest MPG at 100 km/h? I always assumed the fastback/kamback shape was lowest drag overall. Your channel is much appreciated.

[@narancs5]

Lowest drag = highest MPG

[@OgamiItto70]

The lowest drag overall (for the same volume enclosed) is a teardrop shape. The "fastback" or "Kamm tail" is used on cars to reduce their size and/or weight and/or cost to manufacture, as well as making them more practical for use on public roads, parking lots, garages, in traffic. Wunibald Kamm, an aerodynamicist, discovered that _most_ of the aerodynamic benefit in reduced drag of a teardrop shape could be enjoyed even if the shape was "chopped off" at the rear at a point where the cross-section area was 50% of the cross-section area of the widest part of the teardrop. The Kamm tail's "missing" area also contributed to a reduction in (but not elimination of) aerodynamic lift generated by the long sloping profile of the back part of the teardrop shape.

[@marielizysurourcq]

@@OgamiItto70 I checked and it's all true. I just add that this low effect of chopping there in terms of drag is that there is a vortex at the rear that mimics a solid shape, i.e most of the flow does not enter this region. In terms of lift, it's lowering at the rear, so all good.

[@elionh4532]

Notchback is 0.5 liter per 100 km less fuel consumption in comparison to squareback

[@arrindaley3714]

Am I correct to think that there are no separation edges on particularly the squareback model? If there were, the offset airflow diagram might suggest they aren't that effective, 19cm is not far offset from the centre line. Interesting that the slow moving air seems to extend further out to the sides and low down on the notch and fast backs compared to the squareback.

[@arrindaley3714]

Sorry I was forgetting it was a 1/4 scale, so closer to 76cm at full scale which makes it more like I'd expect...

[@JulianEdgar]

I don't have detailed pics of the rear of each model, only those pics in the video. However, all the shapes look like they have side separation edges on the lower half. I don't think the pressure/flow measurements would show the effect of these edges as my measurements show that sep edges act on a very small areas, and these areas aren't really covered in the shown model measurements.

[@m_a_t_t6098]

If the front of the car is the same what makes the Clf so different between configurations? Is it because of the lift occurring behind the rear wheels and leveraging the front up (or down)?

[@JulianEdgar]

Yes I would think so. The pressure diagrams show that the pressures are certainly acting behind the rear axle line.

[@lindsayoosterwaal6338]

Great video. I have a flat bottom drag car that travels over 300km/h. Would ducting from front floor to the tail lights reduce pressure under the car and reduce drag at the rear? Thanks for the great vid

[@JulianEdgar]

No it wouldn't, to both questions.

[@WarriorOfEden3033]

So if you got a notch back get vortex generators & a spoiler. Fast back just get vortex generators because most already have spoilers

[@Blue-God]

Just what I was looking for

[@jimspc07]

I would like to have seen the Kram theory rear used also. The hollowed out rear seems to have the reported push in real life. A good example of this is the Chrysler Australia Charger, it was a fast back with a Kram theory shape below the boot lit. When these cars were used in outback Australia they got lots of dust embedded in the hollow of the rear end in the dry and a mud coating when it was wet.

[@JulianEdgar]

Do you mean Kamm?

[@3800S1]

My sedan rear window stays dry in the rain while driving and some lines of water comes around the side in a curve that is a partial shape of the side vorticies. This confirms my observations.

[@JulianEdgar]

Sounds about right.

[@3800S1]

@@JulianEdgar Do you know what effect rake or nose up vehicle level has on those parameters mentioned in the video. I know a lot of old vehicles from 70s and prior had the nose up level, ie. raised at the front and lower on the rear. My cars being 90s and late 80s German based chassis design but re-engineered and manufactured in Australia have a minor rake, slightly lower at the front than the rear. around 25mm lower. My intuition tells me that the rake is more stable and may create some ground effect if that's the term? I can hit top speed of about 210km/h and it's not much different than normal highway speed which only required one thumb on the wheel, the caster keeps the car tracking straight very easily. Years ago I used to have late model VW type 3s, squareback, fastback and the notchback and they were always raised up front from factory, at speeds over 100km/h the car felt very tippy toed. Could the level angle explain this effect?

[@JulianEdgar]

Speaking *very generally*, a lower front than rear ride height gives reduced drag and lift. But it really depends on the shape of the both the underside and upperside of the car. All in the book - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country.

[@3800S1]

@@JulianEdgar Thanks for the quick reply. The car's shape, angles and dimensions, especially the rear is very close to that of a mid 2000s BMW 325. The underside is not at all flat or enclosed so it probably be quite turbulent under there.

[@BLARNEYBLARNEY]

From 8:22 … would love to see this pressure map from above …. Looking down on the airflow. Excellent Stuff !

[@JulianEdgar]

It's only the pressures on the vehicle surfaces that matter, and you can work them out pretty well from the diagrams.

[@pudermcgavin4462]

I drive a mk7 golf hb and it's super stable at 100+mph where my old 90s civic hb was horrible darty and light feeling at even lower speeds! Than I lowered it and it made a world of difference but still felt very sketchy at the top speed for it limits 100-110mph

[@JulianEdgar]

Plenty of ways of overcoming high-speed aero instability - even gaining downforce in a road car. All covered in my most recent book - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8

[@MrPaw45]

Just had this video appear in my recommendations, very interesting it is too. One thing, at 6:30 you mention the front stagnation region, in the real world this would be different with airflow through the grill.

[@JulianEdgar]

Yes, interesting point. In well designed cars, the radiator inlet is placed in the zone where there *would be* stagnation airflow (and so pressure), if the radiator airflow weren't occurring. But as you say, with radiator airflow, the pressure won't be as high. In practical terms, the front numberplate almost always has stagnation pressure on it.

[@MrPaw45]

@@JulianEdgar Thinking about it, electric cars (notably Tesla) have a solid front. Also the airflow through the grill is likely to increase front end lift.

[@JulianEdgar]

Re front lift, it depends on how the exhaust flow from the radiator is handled.

[@23DuDe]

I would like to see this same test done with roof rails installed to see what the disturbance and impact is.

[@JulianEdgar]

Very easy to do such a test yourself at zero cost.

[@Person-cv9dj]

Very interesting. Thank you for this very informative video!

[@JulianEdgar]

Glad you enjoyed it!

[@srh2301]

Why didn't you compare with a car of the new menace type, aka "SUV" or "light truck", which do have an aerodynamic drag like a barn door? Would have been more interesting than comparing fastback and notchback, which differ only in subtle nuances...

[@JulianEdgar]

Because the technical paper the video is based on didn't do so? And not all SUVs have drag like a barn door.

[@thecatofnineswords]

I got confused for a few seconds when you referred to colder/hotter colours, as there was no reference indicating which one was which. I come from radio and optics, where red is cooler than blue. A colour/pressure scale would convey this information better.

[@chehystpewpur4754]

a funny little tid bit about drag and aerodynamics. i daily an suv with a coefficient drag of .4 at the time it was made it was very aerodynamic amazingly. a few years later bmw released the most aerodynamic production vehicle ever. it had a coefficient drag of .24 thats not a very big difference between an suv and a car. the can and suv both had a v8 and i owned both. still have the suv bmw was a pos. i get 35 mpg city and country roads and 30 mpg on the highway. by having relatively low drag low weight lots of torque and gears to use the torque without turning a ton of rpms. i have a fun to drive cheap to drive racecar that i can load with things and haul them all over. proper planning can go a long way.

[@kennethjackson7574]

Do a search for Drogo-bodied Ferrari 365 P2 LeMans 1967, then look among the images for a white one bearing number 18. That one ran at LeMans with two rear stabilizing fins, while number 26 had a wing between the fins. In any case, they sort of defined “long tail.”

[@JulianEdgar]

Long tails date back to the 1930s....

[@AmirPomen]

@4:50 now i understand fully why volvo decided to race their 850 wagon in british touring car back then purely from aerodynamic point of view

[@k0walsk]

Beautifully consistent with theory. One thing: these two, I'll call them measurement planes, are only 20cm apart right?

[@sevenday365]

Note: Varies with your vehicle speed. If under 120km/hr, not much difference of those drag force or lift force will do.

[@JulianEdgar]

Varies with speed, yes. But it's a fallacy that aero is not relevant under 120 km/h.

[@peanuts2105]

My Jaguar XF has a little aerodynamic ‘lip’ just above the rear window. I don’t think it’s there to provide attached airflow, I think it acts as a high speed stabiliser

[@chrisbarrett2512]

Check out the Aptera, a Morelli shaped vehicle.

[@JulianEdgar]

Yes, if it is ever actually released.

[@caioronnau5226]

would this be the reason why volvo raced the 850R wagon in the British Touring Car championship??

[@thereisnospoon52]

48 million pickup trucks registered for the road in the United States alone. They should have included a truck in this test.

[@JulianEdgar]

Pick ups are covered in my latest book. www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8

[@kiereluurs1243]

I am waiting for the first that is able to tell how a pick up isn't a waste of taste, space and fuel.

[@milis4932]

Hi Julian,great video!how about the aerodynamic at bed on the pick up trucks with or without roll top cover on it?ive not find any video about it,also the sunroof,widly open or shark open?thanks for this awesome knowledge!

[@JulianEdgar]

Yes, covered in my latest book - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8

[@Inimbrium]

@JulianEdgar 6:20 are you sure you didn't mix up hot colour and cold colour? In science hot is blue and cold is red!! It also would make sense that there is a low pressure zone behind the car!

[@JulianEdgar]

No, no error. Airflow wrapping around the upper curves has a lower pressure than in the wake behind the car. As for the colours, nearly everyone uses hot = red and cold = blue, eg on hot and cold taps.

[@Inimbrium]

@@JulianEdgar fair enough, I thought I'd double check with you. You have a lot of these kinds of videos on your channel so I'd imagine you know what you're talking about. Best way to refer to the colours would be to say redder of bluer, rather than hotter and cooler, as a lot of people now use the concept of colour temperature such as in image editing and professional lighting where hotter is bluer and cooler is redder. That is scientifically correct and can cause confusion when you're referring to the old fashioned water faucet tap concept of hot and cold!

[@antoniopateas6839]

Very nice video... I have watched many of them... Ok with the hatchbacks... What about the coupés and the Roadsters?? I have a BMW Z3 Roadster Cd:0.42... Roof down 0.55... What could i do to improve these numbers?? Should i use a flat bottom??

[@JulianEdgar]

Yes

[@rotorblade9508]

I think lowering the suspension also a bit should work. Anyway the .42 although it’s high the drag area is small which more than compensates for the high cd. Sports cars usually have higher cd even without spoilers but very small drag area

[@tbthedozer]

If there was a book like this for motorcycle windscreens it’d probably sell like mini donuts during crazy day at the shopping center.

[@JulianEdgar]

All the test techniques in my book can be applied to motorcycles - airflow, lift/downforce, changes in drag....www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8

[@mainrig4981]

thats why on some cars you have sand papered licence plates in the back

[@ResizeFilms]

So hatchbacks have more downforce. Interesting.

[@JulianEdgar]

More accurately, less lift.

[@twoface8717]

it would have been interesting to see how those duckbill-style spoilers, almost all newer cars have, influence things, be it positive or negative

[@JulianEdgar]

Covered in my latest book, including with on-road pressure, flow and downforce measurements.

[@indopleaser]

wish you would make some more videos

[@flee4urlives]

underrated vid.

[@JulianEdgar]

You should see the book! www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8

[@metepack4872]

I appreciate your attention to flow and drag. An area that *should have been central to automotive design at least 3 decades earlier. Question though, wouldn't these comparisons be more useful with an attached flow fastback? I thought attached flow was the whole point of the fastback

[@JulianEdgar]

I am not sure I understand you. The fastback has attached flow, hasn't it?

[@metepack4872]

Ideally yes, but in this particular model the fastback has a big low pressure zone that would not be there if the flow was attached

[@JulianEdgar]

@@metepack4872 Yes, but look at the pressures - there's still plenty of flow attachment. eg 5:05

[@ReddThreee]

Co-incidence: Fastback Notchback Squareback: VW made cars with exactly those terms whereas other companies went sedan coupe hardtop wagon etc

[@JulianEdgar]

No coincidence: in aero, the terms originated from German aerodynamicists.

[@tomwocjik8925]

I have a question and would really appreciate if anyone knows the answer. Whats the best car body shape to carry pushbikes mounted on towbar(behind the car) most efficiently? Any help much obliged!

[@JulianEdgar]

My guess would be a wagon / squareback that has a low drag coefficient.

[@Bird-0]

This makes me wonder why higher end brands who make vehicles with self adjusting spoilers don't design systems with a split or two in the wing. Tucking the outter half or third in a corner could have tangible benefits while the inside half or third of the spoiler would be fully extended to apply as much downforce and aerodynamic braking to the inside wheels/suspension as possible.

[@JulianEdgar]

It's been done - covered in my latest book. www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8

[@jraja9145]

Fascinating topic. Well put mate. Sadly no data for hatchbacks

[@JulianEdgar]

Most hatchbacks can be treated as squarebacks in shape.

[@wyskass861]

How is the airflow under the body modelled here, to meet and integrate with the top flow as they would affect each other?

[@JulianEdgar]

Not sure what you mean - the underbody airflow is modelled to reflect the shape of the model (and is the same for all three shapes).

[@wyskass861]

@@JulianEdgar Ok. I was wondering how the top side body shape would affect pressures on the underside by affecting the exit flow from the bottom . And also what proportion of the forces are coming from the underside. As in a diffuser effect. I'm not sure if it's relevant for this comparison though, since you're showing measurements not cfd simulations. I'm mostly asking, because I was wondering how much model detail iI'd need to get an accurate CFD simulation. Specifically, assumptions for flow through radiator and out the back of engine, as well as roughness of underbody. And if ignoring these would still give a good result when just analysing particular area options as in your example. Of course I could also be wording or thinking about this wrong.

[@JulianEdgar]

Watch kzbin.info/www/bejne/h6bPn3iErtl9aqs

[@Kualinar]

Curious to see the results for a pickup...

[@JulianEdgar]

Yes, covered in my most recent book.

[@cenkaetaya]

How would this work on a large car like a 2008-2015 Nissan Armada. I have the running boards removed (the side steps) so the vehicle is very tall. I was wondering if covering the floor could help highway MPG, and I was also just wondering about the roof rack on it and if you had any opinions. The front hood does have one of those wings at the front tip. The car gets decent gas mileage going 70mph but once you hit 80+ it really takes a hit from wind efficiency. I was hoping I could get it to cruise at 80 with less force.

[@engchoontan8483]

Front Stagnation area = grill, fan, fan position = direct air-flow to the inside of the bonnet to the firewall and downwards to join the bottom of the car in a smooth flow with rear-bias(vector) (direction of travel) == disperse excessive back-pressures in any direction (especially for the front windscreen to be cleaned. Main force directed to just above the roof, use "ancillary"-forces Center line Rear windscreen wiper-dust 1 = rear windscreen cleanliness maintenance by auto-mechanical-forces is paramount 2 = air flow should combine together, sloping slightly downwards, relative to gravity(90deg) in halving-angles of surfaces - quadrant If roof is 180deg parallel to horizon and rear-windscreen is 60deg from-rear, air-flow in that region should be 60deg-50%(60deg)= max30deg with bias to gravity. Do the same for boot and rear-bumper. Smoothen the lines to check the flow Off center line and bottom of car = should fill in and compensate for that rear stagnation area Mud and water flaps should direct solid particles to the ground before reaching the rear-bumper Cold color = negative to the other regions, suction effect, vacuum effect, speed reduction DRAG LIFT = ignore The plan is to CONTROL air-flow before redirecting it to the tailgater. There is no power without control. Controlled RELEASE is not my fault.

[@engchoontan8483]

The center punch will disperse to the blindspots to enable too-quick to have a tactile-signal and non-tail-gaters to have a smooth ride while cutting in and out

[@jabuticaba2000]

what about the nickelback tho?

[@mr.wizeguy8995]

We have 2 different car roughly similar size is it possible that car 0,3 drag coefficient and car 0,23 that car with higher drag coefficient number have still better efficiency if body type in those are different. Or is it always lowest number win?

[@JulianEdgar]

Lowest number wins, at least for aero.

[@fredvonjupiter6061]

I still dont understan why bigger wake equals more drag. Since there are more particles with speed vectors in the direction of movement

[@JulianEdgar]

Lower pressure than atmospheric acting over a bigger area. Or, you can consider it like this: the more energy that goes into the wake, the more energy required to propel the vehicle forward.

[@jamesmedina2062]

On a 2017 Civic what would overall effect on Cd be with using panels to create a flatter floor in rear 1/3? The factory mufflers were removed and now I fear that the rear bumper acts as a parachute. The front 2/3 of car already has flat floor coverings.

[@JulianEdgar]

I don’t guess - I test.

[@carrotgod]

they should put you on the talk tuah podcast

[@poncetio]

Hello, how much the plastic tray under the motor would help ?

[@JulianEdgar]

If it's well designed, a lot.

[@ChrisLoew]

Single line input ve entire wall of input will have different results.

[@JulianEdgar]

Centreline measurements give a good overall picture - no need to make things more complex than they need be.

[@rdbrewer4]

What about hunchback?

[@jonniejlo]

Great knowledge! It would be awesome to know your thoughts/experience regarding momentum injection into the wake. Something I often ponder :)

[@cnclathe21]

Julian please help me... I got a Suzuki Ignis 2004 MH a quite blocke body shame of car... If I abb the factory rear spoiler will it help with the fuel efficiency any? I know it will give an extra downforce on the rear wheels but will it also help by redirecting the air with the fuel efficiency or will it a drag? thanks a lot

[@willyjimmy8881]

Maybe we'll see a few time attack cars on estate chassis after this? Maybe?

[@gotenianiki]

I would like to see a 3d visualization of this.

[@pranavradhakrishnan5871]

What software do we use to calculate these numbers? Can we use ansys for this?

[@JulianEdgar]

CFD software. The link to the tech paper is in the description.

[@HanYou2]

Very interesting, I wonder what effect 2 ducts from the rear wheel arches (or some area with known high pressure) to the back of the car would have, would they help equalize the pressure in the back and lower cod? Similar to a very aggressive rear diffuser but trying to keep the shape of the car, to preserve the practicality

[@JulianEdgar]

1) There will not be sufficient airflow through the ducts to make any measurable difference to drag. 2) An aggressive rear diffuser creates lots of drag.

[@GoldsmithsGarage]

Hello i have just purchased your latest book from amazon so on my way next with tuft testing Where would my car fit into this test as its non of the above shapes 1961 ford anglia 105e

[@JulianEdgar]

It's a notchback with separated flow from the end of the roof.