By SS Collins

Date: 16th March 2007
Car: AHS Challenger R&D
Class: UK Formula Vee
Engine: Volkswagen 1300 (air cooled)
Driver: Jason Worthington
Weather: Cool, Sunny, Windy

Runs were conducted in a straight line at both 50 and 60mph

Introduction

First I should state that I’m not an aerodynamicist, or even a fully qualified engineer and this is a first attempt at writing something meaningful about developing one cars shape so its not exactly going to be reliable but I hope some of it will be useful. What is contained are my own observations of the Challengers performance on track (on a number of occasions), with some of the info gleaned from Richard. These observations are backed up with the visual data obtained on the 16th

Report - Front

The front beams are a clearly a problem, the cylindrical shape is clearly not ideal and could be given a better profile.

Not exactly a perfect example but the concept is clear

Steering arm, pushrod and ARB are all exposed to frontal airflow. The steering arm could all be brought into line with the upper beam and be faired in as one. This would give a significantly larger upper fairing than lower.

Moving the steering arm may mean that the rack may have to be moved lower in the car, perhaps by as much as 4cm, whilst this may lower the cofg it may create space issues in the cockpit, mechanical design may overcome this. Also the outer end of the steering arm is already notably higher than the inner and this may also create a problem.
However if this is achieved the frontal area should be reduced, which in turn reduces drag.

The push rod is also exposed to the airflow, a thinner design could be sought, perhaps using a composite material or aero section steel (if strong enough), the inner joint (outer end of the steering rack) could be build into the fairing, alternatively the joint could be faired separately.

The clip attaching the nose to the rest of the car is messy and increases frontal area, it could be included in the lower fairing but that could make servicing difficult. An alternative is the Aerocatch.

The region between the front beam and inside of the wheel is a real mess, and could be cleaned up. Formula Three style Inner wheel plates could be employed simply and effectively and could really clean up the flow in that area. Hubcaps could also be employed on the outer rim however current regulations ban bodywork outside of the inner edge of the front wheels. But wheel design seems to be free, if Reynard Champ Car style hub plates were welded to the rims it could give a drag reduction.
The brake line could perhaps be more strategically positioned on the hub and deliberately out of the airflow.

From the tests its clear that the flow is smooth on the front of the cockpit – more tufting on the front is needed but it seems likely that the flow is smooth in that area.

Wing mirrors – these are having a detrimental effect on the engine cooling ducts, and could be moved, though the effect is not as bad as first though. However

Roll hoop and rearward.

The roll hoop may suffer from the same issues as the front beam but perhaps on a smaller scale. It could be faired in with a secondary hoop (perhaps of a lighter material) in a similar style to that used on the LMP1 Pescarolo. Could the support bars be moved so that they are inline with the hoops vertical sections this may reduce the drag but if the drivers head and hoop was faired in then this would not be an issue.
The central cooling duct (behind the driver / above fuel filler) totally ineffectual drivers helmet could be more faired in.

The gap between the fuel tank and the front of the engine could be covered with bodywork, this again may reduce drag.

Flow going into the main cooling duct is less than idea and it seems that the duct shape needs to be redesigned. The top section of the duct bodywork seems to be creating a lot of drag – the tufts were flapping badly at both 50 and 60mph.
Ahead of the duct the flow seemed to be avoiding the lower 30% of the inlet whilst the central section appeared to be flowing reasonably though with a little turbulence. The tufts from the wing mirrors were influenced by the cockpit (could the sides be raised to the anti decapitation bars Sheane mk3 style?) but showed that flow was mixed around the top of the duct.

Perhaps the ducts could be moved into a different position higher up perhaps as a single central duct above the drivers head, or as twin ducts protruding from the car somewhat similar in design to a F3 airbox with the duct centre line in line with the drivers eyeline.

The airbox on the engine needs some serious work, recommend consulting Richard Adams. A short term fix may be to adopt twin F3 style airboxes. Currently the airbox/engine/carb layout is creating huge drag, to the point that the lower section of rear bodywork sees either no airflow at all or a vacuum sucking the tufts forward, the resultant drag is likely significant.

Power benefits of this layout should be compared to the inboard and tower outboar layouts to find the best middle ground between engine performance and drag – perhaps with a multi car tuft and coast down test perhaps at around 80mph as the average speed at our fastest track – Silverstone is that. Testing at higher speeds than that may be too hazardous to be conducted however Bruntingthorpe may be a good alternative.
Hub plates on the inner and outer wheels may be beneficial on the rear too.