44 replies to this topic

[Andrew aka Stuwy]

re light my fire

[manus]

Have anyone done any measurement on a VX and looked for gained downforce with different aero mods? BR, Per

Reverie has published on their website a number of tests on similar cars like Noble and Exige. Probably those numbers will apply with some margin to the VX as well. http://www.reverie.l...est_Session.pdf

Edited by manus, 01 November 2014 - 11:37 AM.

[Nev]

Test 9 looks the most significant point to take away, but I don't fully 100% understand the mod. Are they saying they increased the depth of the leftmost and rightmost diffuser vane downwards to stop air getting into the rear wheel arches ?

Edited by Nev, 01 November 2014 - 12:22 PM.

[jamiewillson]

Test 9 looks the most significant point to take away, but I don't fully 100% understand the mod. Are they saying they increased the depth of the leftmost and rightmost diffuser vane downwards to stop air getting into the rear wheel arches ?

 

When we went in the tunnel with my car with Simon McBeath, we closed the outer diffuser strakes right down to the floor (as we did down the sides of the car), but for some reason this actually resulted in less downforce than with them removed.

 

The thing that's very worthwhile doing which I told Lee/TurboToaster to do on his car, is to fit an extra strake at each side about 100mm from the ends. These in effect act as sacrificial tunnels to catch the turbulent air from the wheels etc and allow the rest of the diffuser to do it's job properly. Without them, the airflow gets very, very messy towards the outsides to the point where some of the airflow actually turns back on itself. i.e loads of drag. Very simple mod to do really. Check out this picture of how bad it is and look at where the smoke from the wand is going directly out of the tip:-

 

 

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[jamiewillson]

This is what it should look like in one of the tunnels that's actually working:-

 

 

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[turbotoaster]

yep, i did what jamie said from his aero tests, here you can see the 100mm end sections

 

The basic aero principles will apply to a VX220 just like a lotus

 

A larger splitter will give you more surface area of low pressure to create downforce

reduce wheel arch pressure front and rear to reduce lift

run a diffuser to allow the low pressure to equalize with the static pressure at the exit point

running rake increases underbody downforce.

if running a stock vx220 rear clam with a wing, test that the air is staying attached on the underside as there is a step change in height moving from the roof to the clam and that will effect what the air is doing.

[Aerodynamic]

Of course are the basic aero mods the same for VX220 as for Lotus Elise and many more cars and since we are daling with basic aerodynamics I wll stck to this. But I belive the Speedster/VX220 have different basis compared to the Elise. Speedster/VX220 turbo I think had 20kg downforce in front an about the same in upforce in rear. (I´m not sure what Elise have) This makes me want to add around 50kg dowforce in the rear to make it aerodynamically neutral for street use and then for track days add an extra splitter and canards for the front and a big rear wing a maybe gain Another 30ish kg downforce in front and maybe a littltebit more in the rear. But what can be expected from rear diffuser and a small rear wing? What to expecte from different mods at all. Like big rear wing and a splitter? BR, Per

[turbotoaster]

downforce isnt just a case of bolting a part on that will give a certain amount of downforce no matter what, i wish it was that easy!!

 

with regards to adding downforce, how much downforce your wing makes is dictated by the angle its set at, the type of end plate and how much clean free air it can get.

 

a good place to look at is reverie website at there wing data as that gives some basic information to get you started off to decide what size of wing you would want.

 

 

[Nev]

Thanks for confirming my question Jamie.

[Aerodynamic]

downforce isnt just a case of bolting a part on that will give a certain amount of downforce no matter what, i wish it was that easy!!   with regards to adding downforce, how much downforce your wing makes is dictated by the angle its set at, the type of end plate and how much clean free air it can get.   a good place to look at is reverie website at there wing data as that gives some basic information to get you started off to decide what size of wing you would want.

True, but there is simpler and more advanced aerodynamic. Placing a big rear wing high up is a safe way to gain downforce for example. If you can get data from supplier what downforce you will get at a certain speed with a certain angle this is basically what you will get. Placing the wing lower down to the body could increase or decrease downforce depending on how much free air it will get and how well it works with the diffuser. This is more advanced downforce. And the diffuser itself seems to be a very hard one. BR, Per

[Nev]

The problem with wings is that they rob you of a LOT of power. When I am running at low power setting it is really noticeable how the wing slows down acceleration from approx. 100 leptons upwards.

[Scuffers]

The problem with wings is that they rob you of a LOT of power. When I am running at low power setting it is really noticeable how the wing slows down acceleration from approx. 100 leptons upwards.

ie, lift to power ratio becoming the defining factor.

 

under-floor stuff usually wins on this scale, although thing to remeber here is that things like diffusers themselves do not generate downforce so much as drive the floor of the car to generate downforce.

 

other bit to remember is that adding aero will usually lead to an aero COG that's different from the physical COG and quite often, moves with speed, which usually is less than helpfull

[manus]

The problem with wings is that they rob you of a LOT of power. When I am running at low power setting it is really noticeable how the wing slows down acceleration from approx. 100 leptons upwards.

Active aero could be the answer. Air-brake and adjustable donforce-drag. If my Spexige project is back on the road, probably march 2015, it will have adjustable wing to play with. Drag will be easy to measure but downforce I wouldn't know how. A lot of cars have it in some form these days. Hypercars all have it but also the more modest cars. Even the old Crossfire I have pushes out the small wing when driven over a certain speed. Love the work these guys have done www.aeromotions.com

Edited by manus, 02 November 2014 - 06:19 PM.

[Scuffers]

Even the old Crossfire I have pushes out the small wing when driven over a certain speed

 

that's not a wing, it's a spoiler.

 

several cars have similar because their basic shape promotes rear end lift at speed so a spoiler is needed to break the airflow and cancel the lift.

 

Active aero can be the optimum, but it's nothing like as simple as you think.

 

before you start with that stuff, you need to have a petty decent aero profile to start with and you also then have to consider that any active change in aero on the move will have impacts on balance, and this may not be such a great thing!

[Bargi]

Its

[manus]

Even the old Crossfire I have pushes out the small wing when driven over a certain speed

that's not a wing, it's a spoiler. several cars have similar because their basic shape promotes rear end lift at speed so a spoiler is needed to break the airflow and cancel the lift. Active aero can be the optimum, but it's nothing like as simple as you think. before you start with that stuff, you need to have a petty decent aero profile to start with!

Agree, thats why I will start with the proven GT3 profile and will only modify the angle of attack while driving. Tell tales will show at what angle/speed airflow is lost. Video-vbox camera to capture the tell-tale movements and speed readings. The free-wheeling-speed-decrease-rate will indicate air-brake effects. If I can't feel or measure the effect of changes in AoA, then I will stop the experiment. If I do see results, next step to automate the controls. Rough setting could be: brake pedal --> max angle, max downforce, max drag full throttle --> min angle More complicated setup with G-force, speed, steering angle etc could be final step.

Edited by manus, 03 November 2014 - 05:10 PM.

[Nev]

I found the VX to be very rake dependent, ie lowering the front as much as possible had a BIG influence. Sub 8 CM at the front will probably give you markedly good down force on the front if my experiences are anything to go by. Unfortunately this is too low for the road in practice

Edited by Nev, 03 November 2014 - 06:05 PM.

[Scuffers]

automate the controls. Rough setting could be:

brake pedal --> max angle, max downforce, max drag full throttle --> min angle More complicated setup with G-force, speed, steering angle etc could be final step.

 

you might want to re-think this logic....

 

still think your barking up the wrong tree...

 

using a proper profiled wing, you can get 200Kg's of downforce without significant drag, any more than this you then have the issues of how you balance the front with this.

 

Look at the AOA on Jamie's car, then consider what downforce that generated.

[manus]

automate the controls. Rough setting could be: brake pedal --> max angle, max downforce, max drag full throttle --> min angle More complicated setup with G-force, speed, steering angle etc could be final step.

you might want to re-think this logic.... still think your barking up the wrong tree... using a proper profiled wing, you can get 200Kg's of downforce without significant drag, any more than this you then have the issues of how you balance the front with this. Look at the AOA on Jamie's car, then consider what downforce that generated.

No. When braking from high speed I want max downforce on the rear to get the best 4wheel load/grip to counter the weight shift to the front and an air brake (max drag) to support the braking. When in corners I want max balanced downforce to attack G forces. A bit more on the back to support understeer. When at the straight I want minimised drag and dont care about downforce at all. So that alone might require 2-3 different AoAs. The angle of force is at 90 degree to the wing. Changing the wing angle changes the drag/downforce ratio. Most important to know for me first is at what angle and airspeed the wing stalls. From there I can work with rough estimate on Force and direction of that (down/reverse).

[Aerodynamic]

So is there anyone that know good wings and if there are some numbers to be found on them? BR, Per