Developing an active rear wing on a hatchback

[@indopleaser]

Been subscribed for a couple years now, one of my favorite newer subscriptions. Wish there were more channels like your

[@Automotivesquid]

Thank you so much! Love the video! Can never find info about wings of hatchbacks so I was pleasantly surprised when I found this.

[@nemoismyson]

Excellent video, only thing is I wish you showed the preasure differentials when the wing was in its low downforce +8 configuration. Looking forward to buying the book before I start my next project

[@JulianEdgar]

My memory is that in the low position there was no measurable pressure difference in the base area vs having no wing.

[@kalui96]

I'll take note of it

[@jasonrivers7518]

I once used a fixed aerofoil, to counteract the inherent tendency of my Charger, to break traction, at around 80, if you booted it. The pedestals I used were 75mm tall, so I'm guessing were well and truly out of the attached flow, as it certainly cured the cars nefarious tendencies. The angle of approach that I used was rather steeper, at 26 degrees, but I can't say I ever experienced any flutter. Its' tendency to break traction, at speeds below 80, I tamed with a set of trailing arms, and an XF Watts' linkage. LC Torana rear springs allowed me to remove all but two, of the leaf-springs, as I considered the axle to be adequately braced, mate. Excellent video, and I like the way you quote sources for parts. Just realised that I mentioned this in an earlier comment, as I ultimately cut the wing up, and fitted two sections of it under the car, which was only marginally less effective, but was actually quite noticeable, when I tested the car without it. The leading edge would have been 100mm from the floorpan, and the trailing edge was about the same distance, due to the kick-up, where the stock fuel tank had been. Just wish that I had known about diffusers, back then.

[@JulianEdgar]

The aerofoil would have been acting as a spoiler at that angle of attack.

[@jasonrivers7518]

​@@JulianEdgarAbsolutely, mate, that's exactly what I was after. This car was somewhere between skittish, in the dry, and virtually uncontrollable, in the wet, to feeling lovely, and planted. The very first parts I fitted were ex-Volvo four-piston calipers, which really helped, no end.

[@draguroyalty5045]

Well explained, straight to the point, no maybes, no it might, 👍

[@JulianEdgar]

Yes, testing takes away all the aero guesswork.

[@blainerawdon6545]

You are creating an excellent series of videos. Your approach is both rational and methodical. Thank you for your hard work and for sharing. A comment pertaining to the flutter experienced by your wife described at 18:00: This effect may be exacerbated by a couple design decisions that are easily addressed. 1) You are actuating the wing in the center of its span but supporting it at its tips. This provides the potential for wing deflection in the middle to result in a change in incidence angle. 2) You are actuating the wing behind the pivot axis. A downward deflection of the wing center results in an increased leading edge down (LED) incidence and, at speed, increased downforce and downward wing flexure. This feeds back into the actuation to further increase downforce and flexure. When the wing reaches its dynamic limit it may spring back and the cycle may repeat in the opposite direction. The result may be flutter. I can see at least four possible methods to address this behavior. 1) Actuate the wing pitch using a horn projecting ahead of the wing leading edge. This will reverse the process above, resulting in stable behavior: Downward deflection results in upward pitch, quickly cancelling the oscillation as opposed to exacerbating it. 2) Move the actuation point on the wing much closer to the trailing edge and using increased actuator deflection. This will reduce the unfavorable coupling between wing deflection and wing incidence. This may raise the speed at which the wing flutters. 3) Leave the actuator as-is, but install a gooseneck with a mass balance well ahead of the wing leading edge at the span center. This may tend to damp the oscillations by inertia and may raise the flutter speed. 4) Move the actuator to the side and actuate the wing near to one support. This may reduce or eliminate the coupling between wing deflection and wing incidence, increasing flutter speed. My favorite is the first method. Alternatively, Method 4 combined with Method 3 may also produce solid behavior. A parenthetical remark: This behavior may be most pronounced with the wing at low incidence because the variation in lift percentage per degree is much greater at low incidence. I hope these comments are helpful and/or interesting!

[@JulianEdgar]

Thanks for your thoughtful contribution but the wing never flutters if the driver sets it correctly!

[@maelradec6766]

You gonna learn today!

[@jzxtrd337]

Yeap, Julian Edgar is brilliant. All of his old books still hold relevance today.

[@JulianEdgar]

Thank you - but his new books are even better!

[@BrodeyDoverosx]

@@JulianEdgarlol.

[@nikolaisarnytsky2714]

Currently builing a similar system for my Toyota using a dual element setup where the top setup opens and closes using a DC motor rather than a linear actuator but what a useful video, will make sure to watch more.

[@JulianEdgar]

Buy the book - it will inform you far more than any of my videos... and you can see how to properly test your wing design (and the rest of your car's aero).

[@user-ih7gc7dt9l]

Wish I’d known about this when I tracked an old saab 900 that loved lift off oversteer!

[@robair67]

That's what left foot braking is for- no need to lift! (Mind your nose on the dashboard, first time you try it...)

[@D0zer122]

GOE Göttingen…remember these from reading Model Aircraft Aerodynamics as opposed to paying attention in physical science class !

[@10weslleynereu]

Amazing information as always! I wish we could see practical track measurements on before and after mods! (Like maybe a circuit timing, a top speed, tires temperature during a corner (maybe to measure increased pushing force of tire on the road), etc)

[@JulianEdgar]

Well, I don't drive on the track but if you're interested in that, you could do those measurements yourself.

[@10weslleynereu]

@@JulianEdgar There's no tracks around where I live, traffic would maybe get in the way of accurate measuring. But I'll definitely make the measurements Im able to when I fit the spoiler I'm projecting Thanks!

[@tiitsaul9036]

Very inspiring. Thank you.

[@narancs5]

I always like to see your clever and inexpensive testing methods. You give lots of great ideas. E.g. the downforce meassuring with the open tailgate and the spring. How would a simple Gurney-flap on the factory spoiler fair vs the added active wing on this car in your opinion?

[@JulianEdgar]

A Gurney flap is used only on a wing. Adding a spoiler to the spoiler would improve its effectiveness - covered in my book, complete with measurements.

[@nthk4u]

Excellent; thanks. I was thinking, attach to speed sensor voltage and calibrate to full wing when speed achieved. Also, full on brake switch.

[@JulianEdgar]

Yes, except sometimes at 110 km/h I want it up, and at other times at the same speed I don’t. Also, as covered in my book, air brakes don’t work well at normal speeds.

[@qwerty2010601]

For refference what thickness of aluminium you using for mountings?

[@theshed8802]

Just bought your book Julian. Looking forward to receiving it. Now, ignoring aesthetics, would moving the wing further backwards have reduced its influence on the drag behind the vehicle? Regards Greg

[@JulianEdgar]

Yes it probably would have but doing so increases front lift as the wing gets further behind the rear axle line.

[@theshed8802]

@JulianEdgar agreed. So by my understanding, if the wing was moved further back, reducing the angle of attack would reduce the total downforce number of the wing, whilst maintaining effective rear wheel downforce, and hopefully reduce drag at the same time.

[@JulianEdgar]

My actual preference, as covered in my book, is to develop nearly all the downforce under the car, primarily within the wheelbase. Just thought I'd do something different on the Note.

[@moritzm2143]

@@JulianEdgar Interesting! Is this only true for road car application or do you think so about track-/racecars as well? Isn't the car going to feel sensitive to bumps and curbs if there isn't sufficient top-car-downforce? What ratio of top-car vs below-car downforce do you aim to achieve?

[@JulianEdgar]

I am a road car specialist but I guess if you fly through the air off a curb it might decrease undercar downforce. I like undercar downforce because (1) it's easy, (2) cosmetics don't matter, (3) there's a lot of area to work with, (4) it's typically within the wheelbase (or close to it) so it doesn't adversely affect aero balance.

[@thomassavage2150]

14:09 why is it -12 deg and not -15 deg ?

[@JulianEdgar]

One is reference angle, just taken with the level lying across the top of the wing. The other is true attack angle, from the leading point of the profile to the trailing point of the profile. With this profile, trivial difference anyway - see airfoiltools.com/airfoil/details?airfoil=goe222-il

[@stigastondogg730]

We need to build you a wind tunnel my friend!!!!

[@mattdirks7896]

Any tips for looking for finding/evaluating NACA profile wings? (or is that covered in the book?) Thanks!

[@JulianEdgar]

My preferred wing profiles for low drag but good downforce are covered in the book, yes.

[@ELJ666]

I drive a 2007 Ford Focus ZX3 would a rear wing work for my car now I'm going for fuel economy basically working with airflow not downforce I'm looking at wings for cars that you buy online if I can adjust it to work if so should I go short mid high or does it matter. I love your page I really learn a lot

[@JulianEdgar]

How to reduce drag is covered in a detailed chapter in my book. You'll save more money buying it than buying a wing that doesn't do anything to reduce drag! www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8

[@BrodeyDoverosx]

Check the anniversary edition of the Abarth. It’ll change from a spoiler for wake reduction to a spoiler that disrupts flow (for downforce), increasing drag. I experimented with a cheap spoiler extension and wow. Great downforce at the track, but terrible on fuel mileage.

[@PatrickAndrewsMacphee]

Interesting, thanks. Generally we want large downforce and low (aero) drag. How do you deal with the extra rolling resistance caused by increased downforce? Is this simply insignificant?

[@JulianEdgar]

Yes, extra rolling resistance is minor unless downforce is massive.

[@PatrickAndrewsMacphee]

@@JulianEdgar Thanks!

[@Daniel-hy3xp]

Question. Im thinking about a big wing for my 2 door coupe cuz i love the look. And im wondering does a wing actualy increase drag on a coupe? Lets say its adjustable and i can change at how it sits tilted forward, backwards or perfectly horizontal. Wats the best position for it to not get any drag? Any mods i can add to help the wing reduce drag or anything like that? Like vortex generators or a lip on the top of the rear window

[@JulianEdgar]

All covered in detail in my book - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8

[@SDKRacingOfficial]

Does the Vehicle Aerodynamics book encompass other titles you've published in the past? As in is there a '"must have" list for track aero modifications and info. getting really stuck in on a build and want to take a more granular approach to the aero than most tend to

[@JulianEdgar]

The current vehicle aero book is a very major update and expansion on my previous aero books, yes. It also does have a 'must have' (key takeaways) listing for aero modifications - Appendix 2, including for gaining maximum downforce.

[@2103i]

Julian, are the endplates paralel? Would you try the endplate to change to aerofoil, to increase speed "inside" ie. under the main profile? Hence even lower pressure under the main wing/profile. Silly idea....

[@JulianEdgar]

The end plates are parallel. End plates stop 'spillage' / recirculation around the ends of the wing, they don't increase airflow speed under the wing.

[@2103i]

@@JulianEdgar Sure, this is the basic function. But what if we try to further reduce the pressure with a relative low "cost" of drag.

[@JulianEdgar]

Testing always beats guesswork, and with wings so easy to test, why would you guess?

[@megamonkey56]

Are you in a car club? if not join HDCC, we've got a supersprint coming up soon at Marulan on dec3, all cars of any speed are welcome! the Note would look epic blasting around!

[@vanishingpoint808]

Hi Julian, when will the book be available in the UK?

[@JulianEdgar]

It is available now from UK Amazon.

[@vanishingpoint808]

@@JulianEdgar I may have to wait until prices drop -currently £85!

[@JulianEdgar]

It will never be a cheap book, but you will save more than that the first time you do an aero mod that works really well.

[@vanishingpoint808]

@@JulianEdgar I have several of your books (and they are all great), but will have to wait until the UK prices drop.

[@06howea1]

I love you dude

[@ThomasStockinger-bn9yu]

Nice content as allways, but i think your angle-of-attack-meassuring is flawed. The negative pressure at the hatch counteracts the downforce and therefore decompresses the spring ( also due to the long lever). Couldnt you just meassure the pressures above and below and multiply it with the area of the wing?

[@JulianEdgar]

Matched well with the published AoA data for the wing profile.

[@TheJcman72]

I was wondering about one thing you said: With the first wing over the roof, the low pressure bellow the wing will be on top of the roof. That's clear no discussion about that. Now, regarding the effect on the car behavior, since the wing is stick to the roof, none of them can move relatively to the other one. At most, the wing would bend due to the force. So I can't see how that could create a lift to the car. Did you test the ride height with that solution? Eventually that could bring more drag, since that creates kind of a trap for vaccum that can't easily be filled with air ( although there a lot of it just in front ). Am I wrong?

[@JulianEdgar]

Lift and downforce depend on the pressures. Any low pressures on the upper surface of the car will create more lift. If the wing, because it is mounted close above the bodywork, develops low pressures on the upper bodywork, it will create more lift than if those pressures were not created there. An equal area of low pressure on the bodywork beneath the wing, and on the lower surface of the wing will, in terms of developed forces, cancel each other out, greatly decreasing the effectiveness of the wing.

[@TheJcman72]

I understand most of what you say, but my mind have some trouble to visualize one thing. The closest the wing is to the bodywork, the least effect it would have because the forces will cancel each other, and it acts more as a tube or tunnel inside the car volume where air flows. If you put the wing much higher, the farther the wing will be from the bodywork the more independent they will become. I suppose that might have been the idea behind the first F1 wings that were much higher than the car. In the second case, I can visualize a load coming from the wing, through the wing structure into the car, but in the first one, I can only visualize a neutral effect in terms of load of lift.

[@JulianEdgar]

Well, if it has a neutral effect on lift/downforce, the closely-mounted wing is no longer working, is it? You've answered it yourself.

[@TheJcman72]

@@JulianEdgar exactly, it has a neutral effect but not a negative one, as I understood at first from your video and your first answer.

[@JulianEdgar]

I said the pressures would cancel each other out, greatly decreasing the effectiveness of the wing. That's a negative if you want a wing to work!

[@LochyP]

19kg doesn't sound like a lot. Is it really noticeable? Im not sure i'd notice anything less than about 100kg.

[@JulianEdgar]

Hell yes. It's a downwards force with no extra mass to laterally accelerate around corners.

[@patcash1265]

Hi everyone. Do you plan to determine a function between wing position and speed for example to actuate your motor ?

[@JulianEdgar]

No, because when I want the wing active isn't just speed-dependent. For example, on the freeway at 110 km/h I don't want the wing providing downforce, but on a tight and twisty road at the same speed, I do.

[@kieranjamieson]

@@JulianEdgar You could keep the manual control but add some automated functions, e.g. maximum downforce and maximum drag under braking would be trivial to implement presumably? And maybe a DRS like function under full throttle with no steering angle?