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Part of your problem, re: feedback, is that everyone is concentrating on the launch of the F1 cars and the detailed analysis of those cars.

On my part (and as you already mention), I still think the diffuser on your model is much too big. As designed, it looks like the car will be very draggy (the huge upturned tail is like a parachute). Also, you have nothing at the front to balance the diffuser. I'd bet that the car would be horrendously understeery at speed. Indeed, the nose may end up being so light that steering authority is all but lost as speed rises.

Think about the Mercedes that took off at Le Mans. They had big downforce devices at the rear balanced by undernose diffusers and they still lifted off the ground at speed.

Just putting the biggest diffucer possible on a car isn't likely to be effective. Again, looking at Le Mans cars (which yours is most similar to), the early Group C cars had huge diffusers. Some nearly as big as yours. The problem is that they weren't that quick because the things couldn't drive the diffuser sufficiently. You need both base suction and mass flow - your design will likley have decent base suction because of the big tail 'spoiler' but I doubt you could flow enough air under the front end to allow it to work properly. The side inlets appear to be an attempt to ape the RB6 style double diffuser inlets but you don't need to do that. Start with a flat floor and a medium size diffuser, look at how the air will enter the underside of the floor too. How about looking at something like the McLaren F1, Ferrari Enzo etc. for inspiration / an idea of how the two ends of the underfloor relate to each other?

I do not think the diffuser is necessarily too big, it might needs its start further forward.

Note that most of the road cars dont rely on downforce but rather on stability. This car seems to rely on downforce with an enormous trag penalty. The front end is already an great explaination, this 'shovel' bodywork is far from efficient and was only used to max downforce. The crawford tried it once on their SCC2K car, the 1991-92 Riley and Scott GTP cars had it too. The Courage C41 tried it too. On all occasions it was utlised to just max out on downforce or when there wasnt enough front downforce(Courage C41 is an great example). As I said, an road car doesnt rely much on downforce but rather gets its focus to stability and lower drag.

An large diffuser might be a good idea though, but not in this utilisation and with the huge airbrake on the back of this car this car is going airborne, that is if it even is able to reach the speed of going airborne.

I really like the idea but maybe for front fender shape and such you need to look to the contemporary LMP's

Just_a_fan wrote:Part of your problem, re: feedback, is that everyone is concentrating on the launch of the F1 cars and the detailed analysis of those cars.

On my part (and as you already mention), I still think the diffuser on your model is much too big. As designed, it looks like the car will be very draggy (the huge upturned tail is like a parachute). Also, you have nothing at the front to balance the diffuser. I'd bet that the car would be horrendously understeery at speed. Indeed, the nose may end up being so light that steering authority is all but lost as speed rises.

Think about the Mercedes that took off at Le Mans. They had big downforce devices at the rear balanced by undernose diffusers and they still lifted off the ground at speed.

Just putting the biggest diffucer possible on a car isn't likely to be effective. Again, looking at Le Mans cars (which yours is most similar to), the early Group C cars had huge diffusers. Some nearly as big as yours. The problem is that they weren't that quick because the things couldn't drive the diffuser sufficiently. You need both base suction and mass flow - your design will likley have decent base suction because of the big tail 'spoiler' but I doubt you could flow enough air under the front end to allow it to work properly. The side inlets appear to be an attempt to ape the RB6 style double diffuser inlets but you don't need to do that. Start with a flat floor and a medium size diffuser, look at how the air will enter the underside of the floor too. How about looking at something like the McLaren F1, Ferrari Enzo etc. for inspiration / an idea of how the two ends of the underfloor relate to each other?

Yes at this point there is absolutely NO downforce at the front. I just started to work on the front bodykit, and this involves modifications to the front tubes structure which may be reduced by 50% in order to make room for ground effect at the front. I do not know however if ground effect would more effective than adding a front wing (more evolved than the Porsche 956 below of course), just as these examples (Jaguar XJR-14 at the top) :




I'm quite influenced by the group C era because they were not so limited on an aerodynamic point of view, and my target is to make a sort of Dauer 962-like which was homologated on the road. I know that a lot of the technologies at that time are outdated now, but still I'm sure there are lot of aerodynamic tricks which are more efficient than the todays' LMP cars.

Now I have to choose between ground effect and wing to create front downforce, the question is to know what can I expect from these 2 devices !

Funny that you mention the Red Bull because honestly I did not look at F1 cars to inspire myself ! I just tried to try to find a way to get some air to the venturis and the side of the cars came first to my mind. I do not know how much air will go inside the tunnels, I may have to use a curved monocoque on the side to guide air to the inside, and through the side opening channels.

machin wrote:That diffuser does look big... also, remember that the downforce isn't generated under the diffuser itself; its created in the area infront of the diffuser, where the air is at high velocity because you have a high mass flow and a small area, hence you get a small drop in pressure. Since its only a small drop in pressure you need to provide a large surface area for it to work on... so the air coming out of the diffuser should go under the front of the car so the low pressure acts over the whole floor... you seem to have it coming in from the sides....

I'm pretty sure Just a fan meant all that, but I didn't think it was all too clear...

Some nice modelling details though.. and your passengers in the later shots are amazing!

Yes the problem with closed sportscars is that you cannot (unlike open wheels seaters), having a nice clear front area to get air to the venturis. I might open channels from the front, but I will try this later ! Channels such as the ones on the Pagani Zonda R for example (which in this case are made to get air to the brakes).

This is why I opened the side of the car, and that I created channels from behind the front wheels in order to get some air there.

Here is a view underneath the car so you can see how the air goes to the venturis :



Thank you for the comment about my modeling, but I must say that the passengers were not designed by myself, tho. You can get them directly from inside Catia, through their HUMAN BUILDER feature. I must say these are the only 2 things which I have not done myself because I really wanted to get accurate dimensions, unlike the first ones I did which, although they were quite right overall, were not 100% right.

wesley123 wrote:I do not think the diffuser is necessarily too big, it might needs its start further forward.

Note that most of the road cars dont rely on downforce but rather on stability. This car seems to rely on downforce with an enormous trag penalty. The front end is already an great explaination, this 'shovel' bodywork is far from efficient and was only used to max downforce. The crawford tried it once on their SCC2K car, the 1991-92 Riley and Scott GTP cars had it too. The Courage C41 tried it too. On all occasions it was utlised to just max out on downforce or when there wasnt enough front downforce(Courage C41 is an great example). As I said, an road car doesnt rely much on downforce but rather gets its focus to stability and lower drag.

An large diffuser might be a good idea though, but not in this utilisation and with the huge airbrake on the back of this car this car is going airborne, that is if it even is able to reach the speed of going airborne.

I really like the idea but maybe for front fender shape and such you need to look to the contemporary LMP's

Yes the airbrake shape of the rear body is a bit too extreme. These are just sketches, I am trying things, so I really appreciate comments. I do not think I will need a rear wing, due to enough downforce made by the ground effect at the back, so just a small lip will be enough I think. I will continue to work on the bodywork later I think !

Thank you all 3 for your comments !


P.S.: Yes I just saw that people are 100% on the 2011 F1 cars !

Where does the flow to feed the inverted wing shape behind the front wheels come from?

Do you think that it is realistic to try to get the large amount of air required to turn sharply in to the side entry for the rear diffuser?

The likely air flow in to the space behind the front wheel might be expected to create a couple of vortices that will ruin flow to the diffuser.

Why do you need the lateral feed for the diffusers? Why not just use a flat floor with a moderate diffuser and then try to detail the edges to reduce flow from the sides of the car getting under the floor? Southgate did this quite simply with a longitudinal gurney along the edge of the floor.

Couple this to a nose diffuser discharging in to the front wheel well. Detail the exhaust from the front wheel well to ensure decent flow through the front diffusers. Look at using this flow to help seal the sides of the car.

Bear in mind that road cars don't want lots of downforce because if you lose the downforce for whatever reason the resulting accident is going to be huge and without the attendant emergency systems in place at race tracks. Also, huge downforce levels will result in higher drag (and hence fuel use) even though a well designed underfloor system is more efficient than wings.

Just_a_fan wrote:Where does the flow to feed the inverted wing shape behind the front wheels come from?

Do you think that it is realistic to try to get the large amount of air required to turn sharply in to the side entry for the rear diffuser?

The likely air flow in to the space behind the front wheel might be expected to create a couple of vortices that will ruin flow to the diffuser.

Why do you need the lateral feed for the diffusers? Why not just use a flat floor with a moderate diffuser and then try to detail the edges to reduce flow from the sides of the car getting under the floor? Southgate did this quite simply with a longitudinal gurney along the edge of the floor.

Couple this to a nose diffuser discharging in to the front wheel well. Detail the exhaust from the front wheel well to ensure decent flow through the front diffusers. Look at using this flow to help seal the sides of the car.

Bear in mind that road cars don't want lots of downforce because if you lose the downforce for whatever reason the resulting accident is going to be huge and without the attendant emergency systems in place at race tracks. Also, huge downforce levels will result in higher drag (and hence fuel use) even though a well designed underfloor system is more efficient than wings.

The flow comes from the wheels themselves but I doubt there is enough air to feed the channels, I will have to move the entry of the channel more inside the car and feed them with air from the front directly, maybe !

Your last paragraph is really interesting, I had not think about this really. But if you look at the current cars running, they can be quite extreme and have lot of downforce, such as the McLaren F1 GTR for example. Ok not many of them are driven on the road, and people owning them know what they have in the hands, and I expect the same attitude with my car (in the building process).

So dealing with relatively high downforce won't be a big issue I think. But it is right to search for a very pure design so the streamline are not that horrendous looking. So I will better shape the rear, make it go a bit lower to the ground, reduce the venturis at the back.

My biggest concern is to make the ground effect work with this car. Lotus did a twin-chassis car in order to have the advantage of the ground effect and good comfort for the driver. I won't go into such extreme solution for a non-100% racecar, so maybe using movable skirts is a solution but again the fact that the car "will be driven on the road" is a concern on the way that the road surface is really million miles from a race track, so the car may hit a bump in a corner, and lose all ground effect resulting in a crash.

I really do not want to get ride of the ground effect because the aim of my project was to try to use this technique, but now after having read your opinions and searched more on various sources, it is hard to find solutions to explore ! I do not have the aerodynamic knowledge that I would like to have !

The Lotus twin chassis design predated active suspension though. Modern powered suspension is better able to deliver comfort and grip. Also, don't forget that modern tyres give more grip than tyres of even 10 years ago. As for comparing modern road tyres with racing tyres from the 70/80s is folly really. Different things altogether.

I'd suggest you look in to ground effect before trying to design for it. All cars with a flat bottom and some form of diffuser are ground effect cars. They don't have the extreme skirts-assisted downforce of the F1 cars (Lotus 79 et al) but that doesn't mean they're not ground effect cars.

Look at the two pictures on
http://www.ferrari.com/English/GT_Sport ... amics.aspx
One is an F1 car - lots of d/f from the diffuser which needs a wing to counter it. The other is an F430 which uses front and rear devices to generate d/f. Both are ground effect vehicles.

I'd suggest looking at the F430 and playing (gently) with these sorts of devices. Whatever you stick on the back has to be balanced by what the front can generate.

For an extreme ground effect road car, look at the Caparo T1. This thing gives 3.5g cornering ability. Look at how small (relative to yours) the diffusers are. They're mad compared to other road cars though. Gordan Murray helped with the aero on that car...

MadMatt wrote:About the cooling, well I would say that I take dimensions of existing cars for the vents, which are a good way to start with, so I have a safe basis. A V6 engine doesn't require a lot of cooling, and as I take dimensions from V8 cars as basis, I think it is oversize. But that's the basis, then it will be possible to optimize everything.

Your cooling requirements have almost nothing to do with how many cylinders you're running. It's mostly about how much power your engine is handling.

There are several ways you can go about designing a car, but jumping around as you happen to think about a given part is not a very good one. One tried and true way to design is to start with the engine and transmission as a unit. Put these together, figure out what driveshaft angles you can live with, and that's the maximum you can move that combo around in your car. Now place your suspension in the available space, figure out if moving the engine a couple cm's helps your aero concept, and move to the passenger cell. That is mostly designed around ergonomic and safety related issues, so there's not really that much leeway. Once you have these 2 modules, join them together, figure out where you have volume left for fuel, place your front tires and suspension based on whatever design compromises you've chosen (longer wheelbase gives more room for cargo and aero, but big cars are much harder to deal with in the real world), figure out your CofG (balast is not a very good idea on a road car), cooling, brakes, passenger comforts (you're gonna need a heater and defroster at a minimum), there's a very long list of things.

You worry about aero after you've designed the entire car, not first on your list. Also, you're chassis as it's shown in your pics is unbuildable. Assuming you actually want to at least dream of making this thing some day, it needs significant changes.

Why marry yourself to a V6? Pick the power, efficiency, volume and mass you hope for, then shop around for the best compromise you can find, and could realistically afford if you're serious. I would advise you dump the supercharger, it adds weight, volume and complexity for nowhere near enough performance gain. The engine is the heart of a roadcar, it's by far the most important component. I'm sorry, but it seems like you've mostly ignored it to date.

Ground effect has no realistic place on a road car. The Daur 962 was changed to a flat bottom unless I've lost my mind, and the other cars you reference are all racing cars. As an aside, the McClaren F1 wasn't much of a ground effect car, even in race trim. There have recently a handful of so-called ground effect roadcars, but they measure their total downforce in the hundreds of pounds. The Comparo isn't a roadcar, it's a track-day car. And is it even in production yet?

Real ground effect requires a great deal of control over the airflow underneath the car. This in turn pretty much requires an extremely low ride height, which is just not viable on a road car.

You should have your car around 90% complete before you even begin playing around with your aero profile. But when you do start, you do so by figuring out where your C of G is, and where you need your C of Pressure to be in order to maintain stability. THEN, you start at the front of your car and work your way back. Anything you do to your aero has a massive effect on all the aero stuff behind it, so leaving the front till last is useless.

For nearly cars, and especially roadcars, rear downforce is easy to gain, but has a large drag penalty. Front downforce is very hard to gain, but is essentially free.

Personally, I think you've not only jumped into the deep end, but jumped off the pier into a hurricane without a vest. The vast majority of chassis designers who came up through the ranks built at least 1 spaceframe as their first car, nearly always with an available and well established engine/trans. Many of them also copied or used off the shelf suspension components on that first car. Even McClaren didn't try to design their first engine totally in house without expert help.

If I were you, I'd start with something like the Lola T70. You want a medium displacement turbo V6, so modify your car to accept that. You want a carbon chassis, so start with the survival cell, modifying the front and rear halves of the spaceframe to put their loads into your cell. You'll have a hard time finding a road engine that can work as a stressed member, and there are very good reasons to not use your engine as a stressed member in a roadcar, so you'll most likely find you're stuck with the rear spaceframe, though you could always redesign it in aluminum if you'd like to.

The front of cars sees the vast majority of accident damage, so there's a very good reason to keep your front chassis as spaceframe. It's a lot cheaper to repair and/or modify that way. Again, you can always redesign it out of aluminum, just bear in mind that it's tough to save much weight compared to a well designed steel spaceframe, and steel is much more forgiving of suboptimal design, especially in fatigue.

Personally, I'd give up permanently on ground effect, but if you're dead set on it you should design your car with a removable floor and start out with a flat bottom. You should really do this anyway, floors see a decent amount of accident damage as well. Build your car as above, and you'll have a running, testable car before you even start making body panels.

There is some good advice here about overall approach to car design. A couple things I'd like to throw in the ring:

Remember that the puropse of the diffuser is not to occupy volume, but to increase flowrate per cross-sectional area in the underbody. Inlets are as important as outlets, and yours don't match any accepted practice. Look for pictures of a Champ Car's underbody inlets (Panoz DP01, Lola B03, or Renynard 2KI); these are not restricted by a flat-bottom rule.

Toward the end of group C, the rear 'diffuser' became increasingly a 'wing.' Look to the Jaguar XJR-14 or Peugeot 905 for examples of where the ground-effect heyday ended up. A slot in your diffuser roof fed with high-energy air (top side or from a pressure source) will boost the diffusers performance. Consider a slot along the side walls as well, since they camber pretty significantly aft of the rear wheels.

Group C's implementation of the front wing was never optimal - accepted practice for about 15 years has been to let air flow aid out the sides, behind the front wheels (with a fairing, typically). Look at the Audi R15 or R18 for an idea of cutting edge front-end aero.

My advice on aero is to look at what existing race cars have done with their many billions of dollars and decades of development, and copy. I would look at modern LMP at the front, Group C at the rear, Champ Car for the center. If your ambition is to advance on what they were able to do, try to deduce what stopped their progress - what regulations are they trying to skirt?

'Active' suspension can significantly enhance on the performance of 'passive' arrangements, but the twin-chassis still has a lot to recommend it. It allows the dynamic movement of the main masses to vary while maintaining optimal position of the aero elements. This is part of the reason 'tuned mass dampers' were banned as an "aero" device in F1 - the logical path of progression is to a pseudo-twin chassis. The skirts era and 'flexible floor' development over the past 5-10 years are microcoss of this idea - aero surfaces needing to respond to road surface changes quicker and more precisely than the entire sprung mass can.

Endurance cars rarely use cylinder loadings over 100hp/cylinder. The AER 4-cylinder in the Lola Mazda does to mind as an example, though. For a long-life engine, RPM, piston speed (RPM and stroke), and individual cylinder loading are three key constraints.

Have fun.