OV9

We have a front wing!



The end plates are just temporary - I've got plans for some fancy carbon fibre pieces with curved footplates and deflectors to help guide the air around the outside of the tyres.
For the more technical readers, the triple-plane centre sections are at 27 degrees attack, and the outer singles at 11 degrees. All wing sections are an 'Eppler' E423 profile. I will add gurney flats to the single plane sections to generate a bit more downforce and help guide the air up beyond the wheel centreline.
My fag-packet sums suggest 45kg per side (not including the forthcoming endplates). I'm hoping that once those endplates are on, the whole arrangement will be roughly drag neutral.
Roll on the first test!

Interesting stuff aero, I look forwards to the results of testing

Neil is pure gold, isn't he

Unfollow.

What does drag neutral mean? (In stupid speak).

The drag reduction by better controlling the air around / over the wheels cancels out the drag created by sticking a wing on the front to work the air.

So overall the car has more downforce but no more drag than before.

Maybe.

integrale_evo wrote: Wed Sep 19, 2018 6:50 pm The drag reduction by better controlling the air around / over the wheels cancels out the drag created by sticking a wing on the front to work the air.

So overall the car has more downforce but no more drag than before.

Maybe.

Pretty much what I assumed - how would you know though?

It looks like the frontal area has increased a fair amount - particularly where the number plate is mounted?

There’s a simpler way to do this, close the front wheels and stick a massive flat floor on. It’ll look shit though.

Rich B wrote: Wed Sep 19, 2018 6:53 pm

integrale_evo wrote: Wed Sep 19, 2018 6:50 pm The drag reduction by better controlling the air around / over the wheels cancels out the drag created by sticking a wing on the front to work the air.

So overall the car has more downforce but no more drag than before.

Maybe.

Pretty much what I assumed - how would you know though?

It looks like the frontal area has increased a fair amount - particularly where the number plate is mounted?

Yeah, pretty much that. When I said drag neutral, I meant relative to the previous set-up (so with the centre dam and splitter).
In effect, the frontal area hasn't really increased very much - the sections between the wheels and the body are so 'dirty' with the suspension components that they are worse than brick walls. The triple plane sections should guide a lot of air away from those sections and reduce turbulence further back. The sections in the front of the tyres will have a beneficial effect on drag, because they're pushing the flow above the squish area (below the wheel centre-line). With the new endplates, there should be a significant reduction in flow over the tyre front face, so hopefully drag reducing (although all the theory around vortex creation and its interaction with linear flow makes my head hurt)

Rich B wrote: Wed Sep 19, 2018 6:53 pm

integrale_evo wrote: Wed Sep 19, 2018 6:50 pm The drag reduction by better controlling the air around / over the wheels cancels out the drag created by sticking a wing on the front to work the air.

So overall the car has more downforce but no more drag than before.

Maybe.

Pretty much what I assumed - how would you know though?

Hire a wind tunnel and corner scales to determine the downforce would be a way to determine the downforce created. I guess the before/after of a speed run with measured fuel consumption would determine drag. Lots of work involved for a road car but quite intriguing.

Carl.

Pretty much what I assumed - how would you know though?

Sorry missed that bit.
We'll test it on a Trackday at Knockhill with the data logging gear onboard. Vmaxs at the end of the two main straights gives the effective drag measurement, apex speeds through the two fast corners measure down force, comparative improvement through one slow corner gives an indication of variation with speed.

I could build strain gauges, measure damper movement with linear potentiometers and various other things, but I'd only end up with some (fairly unreliable) figures in Nm and kg.
I may try some of that as an academic excise at some point, but the first priority is to make the car go faster, so measuring in time gain and lost seems the most direct approach.

Nefarious wrote: Wed Sep 19, 2018 10:59 pm

Pretty much what I assumed - how would you know though?

Sorry missed that bit.
We'll test it on a Trackday at Knockhill with the data logging gear onboard. Vmaxs at the end of the two main straights gives the effective drag measurement, apex speeds through the two fast corners measure down force, comparative improvement through one slow corner gives an indication of variation with speed.

I could build strain gauges, measure damper movement with linear potentiometers and various other things, but I'd only end up with some (fairly unreliable) figures in Nm and kg.
I may try some of that as an academic excise at some point, but the first priority is to make the car go faster, so measuring in time gain and lost seems the most direct approach.

Sounds good fun! Yep, it’s all about speed, that’s the only numbers you really need to know.

Intriguing. So why three sections on the inner bits, not just one? At why 27 degrees and 11 outside - I guess there's more to divert around in front of the main body than the tyres.

JonMad wrote: Thu Sep 20, 2018 7:18 am Intriguing. So why three sections on the inner bits, not just one? At why 27 degrees and 11 outside - I guess there's more to divert around in front of the main body than the tyres.

It's all about compromises - compromise between lift and drag, between effectiveness and packaging, between direct effect and downstream effects.

Those three tiered centre sections are the most effective (most downforce for a given span) and efficient (lift/drag) I could design, and in an ideal world, would have just gone for 250mm span sections of those, but I didn't want just a massive wing slung out front (the car is still road-going!), and it wouldn't have been able to do the wheel-flow vortex bits (which I haven't done yet). So there's a packaging problem - the last solid bit of chassis to mount the whole thing to is the upper front wishbone mounts (level with the headlights), but that's the widest I could go without fouling the tyres on full lock.
So I added the single plane sections in increase the span. Single planes can only tolerate a much lower angle of attack before they lose efficiency (and ultimately stall), hence why its only at 11 degrees. It might not produce as much downforce as the narrower sections of 3-plane, but it comes with the benefit of being able to mess about with flow around the tyres.
Also, I suspect if I'd just gone for the two 250mm sections of three plane, it would have robbed underbody flow, which would make the venturis and diffuser less effective.

Oh, and finally, the single plane sections needed to be raised relative to the 3 tier bits. I wanted the 3 tier bits as low as possible to take advantage of any ground effects, but if I kept the longer bits at the same height, they might touch the ground in full roll. Raising them might reduce effectiveness and efficiency of the wing, but because they move the wake higher up the tyre centre-line, there should be greater benefits on tyre drag reduction.

Really appreciate the explanation Neil. What are the bits sticking out horizontally further up the bodywork?

JonMad wrote: Thu Sep 20, 2018 8:56 am Really appreciate the explanation Neil. What are the bits sticking out horizontally further up the bodywork?

Canards. They produce a tiny amount of downforce in themselves (c.100g per side!), but are designed for air management (downstream effects). They should help keep high pressure areas on the sides further up the bodywork, and reduce the tendency for air to want to spill back under the sides. The little upturns on the edges should create vortices to help the air through the suspension/headlight bits (think rifling on a bullet), and reduce flow separation close to the body after the 'dirty' bits.

Interesting work. Not sure if it was in Adrian Newey's book or a Chris Stephens article that was talking about pushing the air away from the squash under the tyres and the benefits. I'll be interested to see what effect that has.

How are you predicting what the downstream effects will be? I'm assuming back of a fag packet at best and guestimate at worst. A

How will you prevent the vortices from going under the car and increasing lift or is that something they won't do?

Have you got yourself a tin of flow-viz? That'll show you what's going on along the sides etc.

Fascinating project! My work with Lotus/Caterham/WhateveritWasThatWeek F1 was with the aerodynamicist boffins. Trying to replicate all that work they were doing effectively in a shed is teh awesome.

The empirical testing I've done so far is:
Photos and video of the car (and other people's cars) in the wet - spray pattern tells you quite a lot about flow patterns (as does the pattern of dirt left on the body)
Wool tufts with go-pro - helps finding high-flow, dead and turbulent areas
Smoke (smoke detector test kits) and go-pro - good for identify localised flow patterns (only really works at low ish speeds though.

Most of the flows are fairly predictable e.g. firing vortices up and out is only going to be beneficial in terms of guiding flow where you want it (or more specifically, NOT where you don't want it!)

I'm not an Aerodynamicist, but I spent many years as an analyst, so I'm a magpie - I read other people's research and nick the conclusions relevant to me, without necessary fully understanding all the detail and complicated maths of the theory that goes behind it.

I put up a shelf once.


It was wonky.