Aerodynamics ... or not!

[Alex Birtwisle]

Just a thought.... has anyone (and I am sure they have) experimented succesfully or not with aerodynamic modifications to the car?

 

I have seen the odd Elise with a rubber skirt and a diffuser and the odd westy with full aluminuim undertray and ducted radiator.

 

Is there any tangible benefit to this kind of thing?

 

As I said ... just a thought!

 

Cheers

Alex B

 

[edmandsd]

I've recently done some aero mods to my Caterham, namely alloy panelling the underside all the way to the rear of the car and adding Westfield carbon front arches fitted tight to the tyre with quick release wing stays.

 

With the alloy panelling I left it open directly beneath the engine and also left a 1 inch gap where it connected to the very back of the car. This was done deliberately to allow air out that was travelling through the tunnel. I know some people have vented air through the top of the nosecone (after the rad) which would allow you to seal the entire underside.

 

The idea with the front arches was to stop air getting underneath them and cover the top front half of the wheel. The Westfield ones allow this as they are the right shape and length and are also very rigid - They are not however the best in terms of quality.

 

I know Caterham themselves did a lot of work in a wind tunnel not so long ago with the main objective being reduced front end lift - something inherant with a Caterham. After a lot of work I think they finally managed to get a small amount of downforce although the car didn't look much like a Caterham when they finished.

 

I know there's a Caterham Hyabusa with a reverse fin underneath the nosecone to try to create more downforce.

 

The old 'black brick' BD powered Caterham racer had a purposebuilt hardtop with other aero mods that proved very successful and was far more aerodynamic than a standard Caterham.

 

When I used to drag race with my Sylva Phoenix I got Mike Barnby who makes the R500 wheels to make me a set of 4.5 inch wide front ones to which I fitted 145/70/13 tyres pumped up to 40psi. The objective was reduced drag/friction, and in the Sylva which had all enclosed bodywork it probably was worth a few 100th's if not a 10th of a second and maybe 1 or 2 mph extra terminal speed. When I bought the open wheeled Caterham I tried these and if anything the performance declined as it meant the brake disc and caliper were all exposed actually creating more drag than if they were covered by a wider wheel. All my quarter mile times are therefore now recorded with a standard set of R500 rims (6.5'' front, 8.5'' rear)

 

I reckon the alloy panelled underside and front arches did make a difference to my car over the quarter mile but not as much as some would expect........and only really over 100mph or the second half of the course...........it all help though !

 

 

 

 

[V7 SLR]

Interesting Dave. If I could get a flyweight panel (cf naturally) I'd be tempted to panel the floor all the way to the back of the car. Anyone know if the cost of cf is related to the complexity of the design or the amount used?

 

I'm interested in whether people believe there is notable lift in a Se7en at speed, particularly during cornering. We've all seen the extreme Westies with full wings-packs at hill climbs, but these are presumably intended to create lots of downforce at relatively lower speeds. I'm curious as to what speeds the Se7en achieves for what amount of lift and whether some small "aids" could be employed to cancel those. I've seen the little wingletts on the sides of nosecones before, and wondered if there was anything to it.

 

Anyone got a windtunnel with some spare time in the bookings...???

 

Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours

 

[caterhamnut]

ISTR a recent article in Autosport concerning a new Caterham Endurance race series, which mentioned that Caterham were working on some aerodynamic modifications. Don't think there are any details yet though.

 

😬24,000 miles in 1 year!

[Laurence Wilson]

I know there's a Caterham Hyabusa with a reverse fin underneath the nosecone to try to create more downforce.

 

It wasn't so long ago that there was a link to an image on the forums. IIRC it also had front wheel arches that wrapped around the circumference of the wheels so as to reduce turbulent air.

 

Cheers! 😬

Laurence 'LOZ' Wilson

[Joe 90]

Is anyone interested in a collaborative wind tunnel test. I read in Racecar Engineering that MIRA offer a service aimed at club racers (i.e. affordable, but I would have to check). If we could get a few modified cars together we could try them out to see which mods make a difference. From what I have heard, aero screens make the biggest difference. One of the regulars at the Penn Se7ens has cut his screen right down to give a similar affect, but it all depends on whether you go out in the rain. I am also very interrested in the tight fitting cycle wings, as they should look good.

 

98,000 miles so far

[sjwb]

I am certain that a car mag did exactly that some time ago. EVO perhaps 🤔

 

Steve B

[Richard J Darnell]

there was an article in Autocar a while back

i'm sure there was a thread on Blatchat about it - worth a search of the archives if interested

 

me? i just accept the aerodynamics are c**p and just enjoy the unique look of the car!

[Old Septimus]

The Cd is about 0.65. Why bother?

[Geoff Johnson]

One area that I have also been wondering about is wheels & wings. My understanding is that wheels act like a fan, which I assume that means there is a pressure difference between the inside & outside of the wings, has anybody tried cutting vents into the wings to diffuse this? How does it affect the behaviour of the car? I have flares & I am convinced that much about 100mph & I am suffering from front end lift (at least the steering lightens).

 

Geoff

J392PPD

VX & Flares how untrendy can I be?

[Dannyboy]

Richard is right.. have got a paper copy of the article somewhere........If you want a copy let me know!! If you're really adventurous can 'TRY' to get it scanned....

 

Dannyboy

 

he's a cheesy geezer

[aph]

don't forget though the cd doesn't give you the total drag! you still have to multiply by the frontal area I think.

[cdg]

If one is overly concerned about aerodynamics, perhaps one has bought the wrong car...

[Jason Plato]

I recall about 18month or 2 years ago that Tim Sieple ( sorry if I spelt your name wrong Tim ) did some work on his caterham at MIRA , this resulted in a very interesting article that was on the net ............ does any remember where its published ??

 

He then turned up at our next sprint meeting with a front wing and underfloor mods and little strips along the chassis sides - the scruntineers stopped play however before any benifit could be measured . Sure did look trick though !!!

 

Dave

[Jason Plato]

I found this in the archives .............

 

Take a look at the extract from the Curborough sprint web site , Tim has been doing some work in the MIRA wind tunnel with his 7 . Makes for interesting reading .

"A Blustery Evening……

Earlier this year MIRA (The Motor Industry Research Association) kindly made their Full Scale Wind Tunnel Test facility available for a Shenstone Club evening, which due to safety and security reasons was limited to 10 members only. Tim Seipel who sprints a Caterham 7, tells us about the evening…

"I was lucky enough to have my car selected for the test session. Following various conversations with Graham Kendall, who not only manages the Wind Tunnels at MIRA, but also competes with daughter Claire (yes that Claire) in the rapid Metro, I prepared a few add on devices in readiness for the limited time available for the structured tests in the Wind Tunnel, whilst some other lucky club members had a tour around the facility. Apart from the obvious Caterham design I had added a full flat floor under tray and rear diffuser. Previous theories on airflow meant that I already raced with the front number plate mounted low down on the front of the nose cone.

Yes I know you are all asking, "Why on earth would you want to do wind tunnel tests on something as unaerodynamic as a Caterham 7?" Well even though it has the aerodynamics of a brick, there are still very useful things that can be accomplished using a test facility such as the Full Scale Wind Tunnel at MIRA. Armed with a multitude of cardboard cut outs and tank tape I was aiming to reduce lift on the front axle to balance the car and hopefully improve the drag at the same time.

The first series of tests consisted of a splitter below the number plate, an additional spoiler below and blending. I won't bore you all with the full technical results but in summary these changes actually reduced aerodynamic drag and lift at the front. The action of reducing front lift actually increased rear lift by pitching the car around its centre of gravity.

The next areas of attention were the front cycle wings. The theory was that air flowed both above and below the wing surface acting exactly like the wing of a plane. This caused a depression on the top surface relative to the air below causing lift. Blanking off the gap between the wheel and the wing did indeed reduce lift and drag, but without increasing rear lift. These results were further enhanced with the addition of a low sharp edge towards the back of the wing in an attempt to trip the air up and not follow the contour causing depression.

At this stage CD (drag) had been reduced by 3% and front lift decreased by a whopping 14kg.

How could I not resist looking at the front suspension? Now obviously I couldn't remove it all so I made covers for all the exposed round section tubes to change them to pear drop section. Although improvements were made, they were nowhere near as big as the effort in making the new sections!

Another few kilos of rear lift were lost by adding wheel deflectors to the lower edge of the rear wings in front of the rear tyres, but at the expense of a little drag. Then came the addition of side skirts to the car. I set these to give ground clearance at all times under racing conditions. These had an overall reduction in lift of 9 kg but a slight drag increase.

As I stated earlier I had already fitted a very pretty carbon fibre rear diffuser. However the shape of this was wrong based on textbook theory. The MIRA experts decided it was not long enough and the diffuser angle was nowhere near the optimum range. Copious additions of very stiff cardboard went some way to correcting this situation. But no matter what we tried, the best solution was to consign it to a very large skip! (The diffuser, not the car!)

From a suggestion by one of the group present, we also added additional blending profiles to the windscreen posts. Although not strictly legal in my racing class, it did improve drag very slightly.

Lastly for amusement I removed all of the weather equipment (roof and doors). This increased the drag force through the proverbial roof requiring a further 10bhp at 100 miles/hour, but actually created some more rear down force.

I would like to thank Graham Kendall, Ivan Starkey & Paul Atkin for making this very interesting visit happen and for the opportunity to complete these tests, which sadly I have not had chance to convert into road/race-worthy modifications." "

 

Hope the Shenstone Club doesnt mind me lifting this onto our site .

 

Dave

 

[Old Septimus]

Why not go and see Colin Chapman at the works in Hornsey and enquire about his new aerodynamic model - I think it's called the XI.