Wednesday, 9 May 2012

Wheel Spats Part I

My idea for the spats is to try and make a single oversize mould, and then make four mouldings that can be cut down and stuck on to Quattro. I don't want to spend too much time on them, I just need something rough and ready that I can test on the track.
I have tried to compare Quattro with and without spats in Solidworks CFD and there seems to be little difference in the drag figures. This is actually quite encouraging from the point of view of adding the spats as I have not modelled in the gaps around the wheels, there is no rolling road and the wheels are not rotating.
If they work well, I want to incorporate them in my Quattro re-design. My idea is to have the major portion of all four spats as part of the bottom moulding. There would then be a lower removable section that can be taken off to change a wheel or access other components. By doing this, I am hoping that I can get rid of the removable panels underneath; they are heavy, the thin edges are prone to chipping and they make the mouldings rather complicated.
The quick and dirty mould is made from two MDF female formers with a thin sheet of plastic expanded and clamped into position. The formers are simple aero shapes, the top one 900mm x 180mm and the bottom one is 300mm x 60mm and they are 225mm apart. This will make oversize, conical and symmetrical parts that I can trim to fit around all four wheels.

Wheel Spat Mould
The aerofoil section I have used is simply an elliptical nose and a radius tail section. The radii are tangential to the ellipse and where they meet at the tail, they have an included angle of 32deg.

Aero Section
The main body and head fairing of Quattro are designed using similar “homemade” sections. I experimented with more sophisticated NACA profile but couldn’t measure any significant difference in CFD.

First Moulding as Template
I moulded a couple of wheel spats that I am using as templates but then ran out of cloth, so my moulding man is making me six. Four are for Quattro and two for experimenting on Beano.
I am locking my suspension at the moment for the spat test, I have pushed the front wheels out a bit further to match the rear wheels and should end up with a ground clearance of about 125mm, with a horizontal bottom. There are three 5mm section O-rings fitted on each of the suspension struts to give a little cushioning.
The reason I am locking the suspension is so that I can bring the spats right down to the ground to get maximum benefit. If there are any benefits that is, hopefully we can get to Reading Velodrome at the end of this week or early next week to give them a try…..

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