41 replies to this topic

[Cooperman]

There are a lot of threads on here about increasing the performance of the Mini. In most cases the replies, including mine, are concerned with improving engine performance and getting better road-holding, handling & braking.

But today I was in my workshop talking with my grandson about speed & fuel consumption and we measured some Mini stuff relating to aerodynamic drag. 

A Mini with 3" wide wheel arch extensions and the late-type large mirrors has a lot of extra frontal area. As an example, the forward facing profile of the arch extensions are 3" x 11" each side, which is 66 sq, inches and the mirrors are around 6.5" x 4" which is 26 sq. ins. per side = 52 sq. ins.

As only one small mirror is legally needed at 3.5" x 3" = 10.5" the frontal area could be reduced by 107.5 sq. ins.  

Then with, say, 175 x 13" tyres, the extra width over a 145 x 12" (or 10") tyre is 1.3" each side and around 10" of tyre profile is exposed as frontal area, so that is another 26 sq. ins..

So the total frontal area could be reduced by a maximum of 133.5 sq. ins.

That is a heck of a lot of frontal area and at around 70 mph takes around 5 bhp (7% to 8% of total standard power!) just to push that 133.5 sq. ins. of area along. It's the same as driving along with a board fixed to the roof facing forward of 13.5" x 10". 

One might wonder how much fuel at normal cruising speed is used just to push the arch extensions, mirrors and wide tyres along the road.

 

[Alex_B]

I still want to get a CAD model of a mini through some aerodynamic testing and see what modifications can be done to improve the CD, flat under floor and thing. Ultimately the shape doesn't lend itself to ultimate aerodynamic efficiency but there must be some improvements to be made.

You could also modify the mirrors and such to reduce the CD, someone on my degree for his main project investigated mirror design and found pretty impressive improvements to drag by extending the shrouding of a standard rectangular motor sport mirror back past the glass, if you then made the shape more aerodynamic like a bullet mirror or such you could still run a pair of mirrors with a lower overall CD 

Edited by Alex_B, 12 July 2014 - 10:42 PM.

[BronkoMini]

Interesting, didn't realise it was that much.

[Cooperman]

Nor did I until we measured it today. I was surprised even though I have long realised that reducing the frontal profile area would significantly improve both top speed, acceleration above about 50 mph and fuel consumption.

If Alex can evolve a CAD model and do some dynamic simulation it will be very interesting.

[Dan]

The body seams add a square foot.

[zinzan]

That's really interesting...had no idea it'd be that much additional frontal area. Would surface "slickness" make much difference in this case to facilitate airflow?

 

 

 

But how do you account for all the go faster stripes and stickers?  Pretty sure a Monster Energy decal on the window adds 10bhp over this way...

[Island Mini]

I would have thought you would see air flow would actually be diverted from a lot of these areas like the rear arches for example. I don't know how much benefit would be gained by simply smoothing bodywork and large front facing profiles to reduce the turbulance and eddies.

I would love to run and see some simulations on the bodywork of a mini. Who knows what you could create! You've only got to look at the current formula student cars to know you can never have too big of a wing at the moment!

[sixtyeight]

this thread desperately needs minisprint.

 

no arches, no seams, no mirrors!

 

[mk1coopers]

It would be interesting to see how much the drag is reduced on the Sprint

[BronkoMini]

What if you put a kind of splitter just infront of the arches?

[The Matt]

An ex-colleague of mine did model it all for a project.  He did a load of FEA and CFD design analysis work on a standard Mini shell versus a GRP Sprint shell that he designed.

 

The difference in drag coefficient was pretty impressive and that was just comparing the standard archless Mini shell against it, never mind the Sportpack option.

[The Matt]

I still want to get a CAD model of a mini through some aerodynamic testing and see what modifications can be done to improve the CD, flat under floor and thing. Ultimately the shape doesn't lend itself to ultimate aerodynamic efficiency but there must be some improvements to be made.
 

 

You'd be just as well using a point cloud from a laser scan for assessment.  It'd save a lot of work if you're just looking at aerodynamics.  I did a 205 GTI shell, but haven't scanned a Mini.  I know how and know where to hire a scanner...could be a decent project to do now I'm retired!

[Tamworthbay]

Having used CFD and a wind tunnel extensively when developing our electric cars I can tell you that the whole subject is a dark art. Cooperman is right regards reducing frontal area generally, but what works and where is subject to a range of effects, some are predictable, some not so. We use tiny mirrors (70mmx20mm) but placing them 100mm forward of where we would ideally put them reduces drag significantly, even though both locations are in free air. Another area that always surprises me is a little gurney no more than 10mm high in front of the drivers helmet. It reduces the overall drag of the WHOLE car by 18%. So even small changes can make massive differences. I am surprised more race minis don't do simple things like taping up seams, perhaps the mini is so inefficient that it makes it little difference. One thing I can gaurantee 100% is that all the spoilers/ splitters and other 'aero mods' that companies flog are a waste of time and money.

[mab01uk]

It is interesting to look at the fastest lap times posted by Nick Swift in his Swittune  built Longman 1275GT Replica racer and his Swiftune Appendix K Historic Mk1 Mini Cooper S at the recent 72nd Goodwood Members meeting.

The best time in the 1275GT was 1m 32.556sec for the 2.4 mile circuit, while the best time in his Appendix K Mk1 Mini was 1m 32.926sec. With the extra power the GT has under the rules (1330cc overbore /split Webers, etc allowed) over the Appendix K Mk1 the 0.37 second difference shows just how much better the original round nose shape Mini goes through the air compared to the square front GT. The 1275GT racer also runs on the bigger wider wheels and tyres permitted in the 1970's while the Mk1 racer is on narrower 10" wheels with CR65 tyres as used in the 1960's.

 

Swiftune Quote:-

"The 1275GT engine will be on our dyno in December 2013. I expect it to give an extra 10% power over our pre '66 engines as we can run to Group 1 regulations, and we will use some of our new 2014 spec parts, mind you we will need the extra power, the Mini Clubman aerodynamics are even more like a brick than the Cooper S!”.

http://www.swiftune....t-goodwood.aspx

[carbon]

It would be interesting to see how much the drag is reduced on the Sprint

 

Not sure about the Minisprint, but I can give you an idea for the Mini Marcos. In 1966 one of these entered the Le Mans 24hr race and was timed at 146mph down the Mulsanne straight. And it finished.

 

This was using a Abingdon built 'rally specification' 1275 unit, probably putting out somthing like 100-110 bhp at crank.