41 replies to this topic

[998dave]

Hello All,
I'm currently putting all my degree theory work to practice and planning to build a performance simulator for mini's. Taking aerodynamics, power and gearing into account to predict theoretical top speeds and accelerations for mini's. (Maybe getting into the effect of lowering/body kits/etc, etc, if the information is available.

Lastly finishing in predicting 'perfect' quarter mile times, maybe...

Now, I need to know the drag coefficient and frontal areas of mini's, anyone know? Using the values I got at the moment:

Drag Coefficient, Cd = 0.51
Frontal Area, A = 16.5 sq.ft = 1.533 m2
Air density, Ro = 1.23
Mass of a mini, m = 630kg
g = 9.81
transmission efficiency, you = 0.85
engine power, Pe = 37bhp = 28kW
f = 0.015 (coefficient of rolling resistance)

Pa = Pe.you = Cd.A.Ro.V3 + f.m.g.V
2

Pa = 23.8

Therefore V = 35 m/s = 126 kmh = 78.75 mph, which is a bit low...

I think Cd or A is too large, but neither seem unreasonable, anyone spot my mistakes? or know of any good values?

Dave

[MiniMoi]

I do not spot anything at is too much out of line. Just that the mass should be a bit higher since you are also in it. On a Mini that makes quite a bit of a difference. Mini's just are not that fast.

Arthur

[Guess-Works.com]

I always thought that the aerodynamics of a Brick Privvi was about right..

other than that, far too technical for me !

[Jammy]

Nah, a mini has the aerodynamics of a 92 year old lady going around Sainsburys on her pension day. Nothing gets around those old ladies, not even air!!! I may have a book at home with the drag coefficent and frontal area in it since I'm sure I've read what they are somewhere, it its not in the book I'm thinking of it maybe in Vizard's Bible!

[998dave]

I do not spot anything at is too much out of line. Just that the mass should be a bit higher since you are also in it. On a Mini that makes quite a bit of a difference. Mini's just are not that fast.

Arthur

ah, must remember to add a driver weight variable in, thank you!

but 78mph isn't as fast as it should go, that should run at about 90-95 ish.

(remembering this is being calculated on a perfectly horizontal road with no wind).

Dave

[998dave]

Nah, a mini has the aerodynamics of a 92 year old lady going around Sainsburys on her pension day. Nothing gets around those old ladies, not even air!!! I may have a book at home with the drag coefficent and frontal area in it since I'm sure I've read what they are somewhere, it its not in the book I'm thinking of it maybe in Vizard's Bible!

I got CB's copy of Vizard's books here, and Bill Sollis too, may have to take a peek in a bit.

Dave

[Bungle]

Nah, a mini has the aerodynamics of a 92 year old lady going around Sainsburys on her pension day. Nothing gets around those old ladies, not even air!!!

You just cant get TC out of you mind can you ?

[Jammy]

Ouch!!

by the way, those figures aren't in the book I was thinking of, must be the Vizards Bible

[Bungle]

is there a number for when you are following a merc sprinter ? that makes you go faster :grin:

[psycho mini driver]

havnt done physics for a while now, and never touched on aerodynamics really, but surly the fact that ther is some shape to the front of the car helps it, ie makes it more stremlined. i may be rong, but surley you are sugesting that the frontal area is a flat surface, which it isnt. this could account for the loss of 20ish mph. i remeber readin that when the mini was first being tested it was widened by 3" horizontally, this increase in width decreased the top speed by 10 or 15mph!! imaging the mph we are loosing through wide arches!lol

[Jammy]

I think thats what the drag coefficent takes into account.

[psycho mini driver]

o yeah, good thinking

[Dan]

Deseamed cars have 12 square inches less frontal area, you could add that into the mix.

[mattvallins]

I've done a little bit of aerodynamics. The arches HELP, because they keep the airflow off the wheels and stop it getting whisked by the minilites. Also, the worst bit is the SEAMS. They are terrible for drag.

[bluebottle]

i was chatting to one of the chaps who run DSN classics about frontal area etc.....he was quite amused at the trend these days to put on huge 13x7 wheels and the ammount of people that think this is a performance mod!

what with the increased rolling resistance and the increased frontat area, they sap off a suprising ammount of performance.

thats why my mini jem has a much higher top end than a mini with the same engine in, the frontal area is much smaller and it weighs a lot less(suprising many a boy racer over the years!)