MAN V

Introduction

The Man05 was the first entry into the Formula Student Competition from the new University of Manchester. Our strategy was to implement simple designs; our aim was to produce a light and effective proto-type.

There are nine key sections below; Suspension, Uprights, Steering, Chassis, Brakes, Drivetrain, Engine, Ergonomics and Bodywork.

Suspension

An unequal length double wishbone system is employed front and rear of the car for its ease of manufacture and high strength to weight ratio due to the natural triangulation of the wishbones. The kinematics of the system were first investigated using Solid Works. This enabled easy visualisation of the system through the full wheel travel. The technique involved starting from the known dimensions; a chosen wheel track and modifying the geometry until minimal roll centre height variation was achieved. Consideration was also given to camber gain in cornering but it was necessary to make various assumptions since no previous data was available and experience in the team was minimal.

The wishbones are constructed from mild steel tube and have been tested by FEA for extreme lateral and longitudinal loads.

The actuators are pull-rod (at the front) and push-rod (at the rear) which enable the shocks to be mounted vertically and horizontally in-board of the chassis respectively for greater resistance to loading and lower unsprung mass. Fox Vanilla RC damper units with coil over springs were chosen as they provide sufficient actuation and adjustability for the minimum weight.

Uprights

The rear uprights are fabricated from 5mm thick steel plate and are a very simple design with nominal manufacturing time involved. Other alloy designs were considered, yet the expense incurred from CNC machining could not be justified by the minimal weight saving. In employing aluminium it was found that the uprights would need to be a substantially larger volume to account for the lower stiffness than steel. FEA testing made these results clear.

At the front however, the aim was to reduce the unsprung weight to maintain ease of steering and this was achieved by constructing the uprights from cast alloy block. By implementing cut-outs in perceived non-critical locations, the structure is extremely light whilst still stiff enough to avoid affecting the suspension geometry.

Steering

The steering geometry has been designed for 100% Ackerman. The rack is mounted to the floor of the car to lower the centre of gravity. Additionally, the track rod pivot points are positioned in the plane of the wishbones pivot points to avoid bump steer.

To transfer the rotary motion from the height of the steering wheel to the floor a transmission box is normally employed. To save weight and for simplicity a Universal joint provides the necessary link.

Chassis

A steel space frame connects the vehicles major components and was selected in order to exploit the basic manufacturing/fabrication methods required, the relatively low construction time and generally that it is appropriate to use a simple design for a first entry given previous chassis data (construction and testing) was not available.

A plastic tubing model enabled different driver positions to be investigated; the driver’s comfort is high in the chassis specification. However, achieving high torsional stiffness was considered the main priority and was calculated through FEA employing Patran. The calculated torsional stiffness of the chassis is 1907 Nm/degree (1913 Nm/degree with suspension). Triangulation in all planes optimised the load paths passed from the tyre – ground contact patch, through the suspension pick-up points and into the chassis and the engine is used as a load bearing structure. Chassis deflection was also tested at loads of 3.5 g bump, 1.5 g braking and 1.5 g lateral acceleration to ensure that the suspension geometry is not affected in extreme driving conditions.

Brakes

Disc brakes are positioned front and rear of the car. Callipers are a product of AP racing and were selected for there application to Formula Ford Racing; they are lightweight and provide adequate braking resistance.

At the front, a brake calliper is mounted each side of the car to the front uprights and the brake discs are standard parts.

Because less braking power is required at the rear and thus to reduce the cars (unsprung) weight, one central calliper is mounted on the rear axle. The disc is of a larger than standard diameter to increase the braking force achieved and as such was tailored from a cast iron billet. Also, efficient biasing at the pedal box allows adjustment of the braking distribution.

Drivetrain

For compatibility with the Ford hubs and bearings installed at the rear, the outer CV joints are taken from a Ford Fiesta Mk5 ’96-’00. The inner CV joints are similarly taken from a VW Golf. The differential is an automatic torque-biasing model purchased from Quaife. These parts are readily available, adding advantage to the manufacturing goal. The axles are of solid section and custom built from High Tensile Steel EN24T which has a large tensile strength of 850MPa and are driven by a standard chain and sprocket arrangement.

Engine

The car is powered by a 1999 Yamaha R6 engine which was selected for its excellent power to weight ratio, reliability and affordability. Whilst originally designed to be fuelled by four 37mm carbs, the engine required modification in order to comply with the regulations. With the 20mm restriction on the air intake between the carbs and the engine the power output was severely limited. In order to increase the power output whilst restricted, a custom Electronic Fuel injection system was developed to improve controllability and quality of the fuel-air mixture entering the engine.

The ECU selected was a DTAfast E48 EXP for reasons of ease of use, after sale support and excellent feedback from other in the racing industry.

The system comprises four injectors in simultaneous operation and a tailored plenum chamber and fuel rail. Adjustments to the timing wheel were necessary before functionality due to the requirement of the new ECU of a tooth at most every 240.

Significant effort was devoted to creating a dynamometer test rig with the aim to develop the EFI system. Once created, attempts prevailed to complete the mapping of the engine. Unfortunately, the dynamometer available was designed for higher speed applications meaning that the final mapping procedure was performed externally by a professional.

The exhaust system is tailored from the standard Yamaha manifold to cut cost and requires minimal metal work to complete fabrication.

Ergonomics

The pedal box was purchased as a standard part from Car Builder Solutions and was chosen due to its simplicity and affordability. It has been modified to become movable down the length of the car to be in accordance with the rules and the range of drivers that will be driving the car. The pedals are the optimum distance apart to give the driver the best chance at driving the car to the maximum of his capability using all available room in the front of the chassis. This was equipped with the necessary brake light and brake-over-travel switch to comply with regulations.

The driver safety systems have been designed in accordance with the shape and size of our drivers and also the regulations, combined together a 6 point harness and arm restraints; these fastening to the chassis via 6 points on 5 different cross members on the chassis.

The steering wheel and dashboard combine with minimal instrumentation, a neutral light, change light and power light to give the driver the correct and sufficient information to drive the car. A rev. counter was deemed to be excess information, those people who intend to drive the car saw it as more information than was required.

Floor close out panels are required to meet the regulations and were cut from light weight aluminium sheet. The seat was also bought as a standard part from Tillet.

Bodywork

Due to the limited time to create the bodywork, simplicity was the main aim. Since racing at the track in Bruntingthorpe is at relatively low speeds and drag is heavily reliant on speed, aerodynamics are not of great importance. The bodywork is therefore shaped to fit the chassis, not to direct airflow in a particular way. The engine is not covered, as this would complicate matters and restrict engine cooling. Nevertheless, the body is quite long and the centre of gravity is rearward, so concern was raised about the moments that may be produced due to lift on the nose. For this reason aerodynamics were considered for the nose only. The nose was designed, with the aid of the Computational Fluid Dynamics program FLUENT to give a lift coefficient of approximately zero. A lift coefficient of approximately zero gives practically zero moment irrespective of the speed. Aesthetics were also taken into account and fibreglass was the chosen material for this reason. Although labour intensive, it provides the quality finish highly desirable in a market environment. Also, it was important to have the ability to reproduce sections of the bodywork if a part is damaged and this is possible by having permanent moulds as a product of the manufacturing process.