Racecar Engineering – September 2019

H

aving previously raced his3.2BMW

M3 E46 in the UK’s KumhoBMW

Championship and theCSCCNew

Millennium series, after samplinga BritcarSprint

race late in 2018 Piers Reid has nowmovedinto

the Britcar Dunlop Endurance series.Wetook

the car to the MIRA full-scale windtunnelto

optimise its aerodynamic package.

As ever, the first runs in our sessionwere

illuminating. Planning, however,hadallowed

for most likely eventualities anda raftof

modifications were made. The owner’sprimary

objectives were to reduce the dragandalso

improve the aerodynamic balance.Bythe

session’s end we had achieved highdownforce

and low drag balanced set-upsthatcompared

well with the dry weather baselinesetting

evaluated at the start of the session,asTable 1

illustrates. Wing angle reductionandsplitter

end fences played key roles in earlyruns,aswe

highlighted in last month’s issue,andfromthere

we examined further front endchangesto

modify the aerodynamic balance.

Get it taped

There aren’t many aerodynamicdevicesthat

can increase downforce while simultaneously

reducing drag, but the humble roll of race

tape is definitely one of them. It’s just a case of

applying it in the right places. In this instance

tape was used (with a couple of pre-fabricated

aluminium offcuts) to mask off the front brake

cooling duct inlets; to cover an opening in the

centre, rear of the bonnet; to cover gaps above

the headlights; and finally to secure some

foam board behind the upper grille aperture

to improve the seal to the engine airbox. The

results are shown in Table 2 in ‘counts’, where

one count is a coefficient change of 0.001.

Covering the brake duct inlets, which simply

fed air into the front wheel arches, was a useful

drag reducer as well as an effective means of

increasing front downforce. Taping over the

aperture in the centre, rear of the bonnet

madenodifferencetodragbutcontributed

TECHNOLOGY – AEROBYTES

SEPTEMBER 2019 http://www.racecar-engineering.com 61

It’s just a case of

applying the race

tape in the right

places on the car

Table1: Baselineaerodynamiccoefficientsandoptimisedset-ups

CD -CL -CLfront -CLrear %front -L/D

Baseline 0.462 0.589 0.205 0.384 34.8% 1.275

Highdownforce

balancedset-up

0.477 0.722 0.351 0.372 48.5% 1.514

Lowdragbalanced

set-up

0.430 0.603 0.295 0.309 48.9% 1.404

A sticky end

Our britcar BMW M3 E45 wind tunnel study concludes with some

front end tweaks, rake changes and lashings of good old race tape

Table2: Thebenefitsof racetape

∆CD ∆-CL ∆-CLfront ∆-CLrear ∆%front* ∆-L/D

Brakeducts -5 +14 +13 +1 +1.1% +45

Bonnetaperture 0 +14 +13 +1 +1.1% +29

Headlightgaps -2 +1 +4 -3 +0.5% +19

Engineinlet -2 +23 +29 -5 +2.7% +55

Totalas% -1.9% +8.0% +22.4% -1.6% +5.4% +10.3%

* Changesin%frontareabsolute,notrelative.

The M3’s owner using the smoke plume. The objective of the session was to reduce the drag and find a better aero balance

Using the race tape worked very well once again. Here the BMW’s brake cooling ducts and its headlight gaps are covered

Illustrations: Simon McBeath

By SIMON MCBEATH