Aerodynamics!

[phil allen]

I know this is a strange question about a seven, is there any thing that you can do to improve the aerodynamics of the seven. How effective would a flat smooth floor be worth?

 

Cheers

[old captain slow]

Only drive it in a vacuum?

 

 

Sorry!

[Number Six]

Phil - were you asking on another thread about number plates? If so, put it on the nosecone if you can get away with it - you can get a kit in Halfords. It's probably outlawed though - check the regs. You can get away with it on the road but I think it's technically illegal to Plod.

 

As for a flat floor, the 7 has the areodynamics of a brick so anything you can do to improve this area is worth experimentation. The latest Ferrari 360 Modena underwent extensive wind tunnel testing with a surprising percentage of hours spent in getting the underfloor Venturi? effect spot on. Check out the Ferrari web site for details.

 

just another idea - try and find out what the factory have done (underfloor) with the 38K Caterham 21 - if anything.

 

Arrival

Where am I?...In The Village.

What do you want?...Information.

Whose side are you on?...That would be telling.

We want information. Information. Information.

You won't get it!

By hook or by crook, we will!

Who are you?...The new Number Two.

Who is Number One?

You are Number Six.

I am not a number, I am a free man!

(Mocking Laughter)

Listen to Lotus 7 KAR 120C by Booting Accelerator

 

[Jason Plato]

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

 

Edited by - Dave J on 16 Dec 2000 20:47:10

[old captain slow]

Dave,

 

When you say you removed all the weather equipment did that include the screen? Seems an obvious air brake.

 

David

[Number Six]

Just another idea. I wonder why nobody (that I know of) has got around to making an FIA-type bar in carbon fibre. I don't have the RAC blue book in front of me - I daresay it's not allowed. (I once tried to get Safety Devices to make up a cage in air-spec alloy until the RAC banned it). If it *was* allowed in CF, and the CF was deemed up to the job, then couldn't aerofoil sections be incorporated in the design (like the old F1 wings) to provide more downforce?

 

Arrival

I am not a number, I am a free man!

Listen to Lotus 7 KAR 120C by Booting Accelerator

 

[Andrew Walker]

Dave J - that's very interesting I wonder if they would allow for it to be printed in Low Flying?

Were there any photos with it?

[Matt Prior]

Just for the record, a tube with a round cross section produces approximately 20 times more drag than an optimum teardrop cross section.

 

Meanwhile, on most normal cars, around 30% of drag can be accounted for by the underbody. I suspect it's less on a Seven because of the messy topside.

 

My ideas for smoothing a Seven - completely flat floor, new bodywork covering front wheels/suspension and continuing over rear wheels, hard tonneau, half doors, no screen at all, low-mounted driver with aero helmet and teardrop shaped cover for roll bar. Still wouldn't be the most aerodynamic car in the world (by some margin), but should be much improved.

 

Would be damned ugly though.

 

[Super_Rich_Bernie]

There is a Caterham 7 rebodied as a Lotus 11 lookalike featured in Classic Sportscar this month. That may give rather less drag, and looks gorgeous too.

 

 

[Andrew Walker]

Matt, your Seven will end-up looking like a 'Black Brick' before you know it!!

[Andrew Walker]

Incidently, the car on the front of this months Low Flying has a completely flat bottom.

 

[Jason Plato]

Sorry I can't answer any of your questions . Like I said at the start of my posting ....... I only lifted cut and pasted the article from the Curborough sprint web site for you folks to read .

 

:-(

Dave

[Richie]

Do you get less drag with a roof on? What about with half doors rather than full doors?

[Tim Sture]

Phil

 

If you are doing the Academy - you won't be allowed to make any mods to improve the aerodynamics (except for fitting sidescreens!), I don't think you're even allowed to run with a roof up ....

 

About all you can do is lower the ride height, play with tyre pressures, change the front arb, get the weight down to the minimum - all within the published regs (which you might not have been provided with yet). The basic rule is you;re not allowed to change anything unless the rules say you specifically can. A couple of people had their wrists slapped in 2000 for having non-standard gearknobs fitted - they had to find a standard one before running in the race later on the same day.