Rear diffusers
Discussion
I can recommend the excellent book by Simon McBeath, "Competition Aerodynamics" published by Hanes. Read several other books that confused me and then read this one which is written in English. Has a fair bit about Diffusers and smooth underbodies. Am planning something similar on the Griff but initially with plywood to see what happens. As I understand it to really see a benefit you need to get below the lowest sticky down bits which on the Griff are the anti roll bar drop links.
McBeaths Comp Aero is well worth buying and is, as has been suggested, written in english not techy geek speak. Simon McBeath writes a monthly column, Aerobytes' in Racecar magazine too.
Joseph Katz book is also well worth a look.
im no expert at all, but a few things ive picked up. every single aero element of the car is linked, so forget fitting a diffuser or a spoiler etc, it doesnt work like that. think of changes as a package.
A flat floor is pretty well essential for a diffuser to work anything other than a paddock pose. Ideally a splitter, running into a flat floor through to a diffuser will be whats required. some 'rake' in the setup is needed. This can be the floor parallel to the chassis and the front suspension lower than the rear to create the rake, or have the chassis parallel to the tarmac, and the aero flat floor raked, lower at the front.
As for diffusers, dont get too het up with pics of Le Mans or F1 stuff, those funny 'Bat cave' shapes are dictated by rules saying the cant have a normal diffuser design. ideally the diffuser should have a smooth transition from the floor (not a defined angle) and run up between 7-10degrees. the roof of the diffuser wants to have rounded corners down to the vertical sides rather than square angles. ideally it should be finish at least as long as the car in plan view (if your competing) or a tad more if your not. central vertical 'strakes' or 'vanes' will help to keep the flow straight and reduce the likelihood of the flow becoming detached and going all wobbly (techy term right there...)
that above will defo work to some extent. ive always used the assumption on my car, that negating a cars inherent positive lift at 100mph, is a positive gain, therefore if i can reduce say 100 lbs of lift at 100mph to zero lift, ive effectively produced 100 lbs of downforce (figs all for easy explanation purposes only). to create tru downforce, more time, effort and testing would be required in my opinion, although im still having a go.
measuring the differences and net gains is difficult (for me), but given a light powerful RWD car, this setup makes it hugely more stable at 100+. ask any westy coffin dodgem driver and they will tell you the open area behind and around the rear axle acts like a dragsters parachute, so just covering it with any old flat panel, stops this and make sthe car easier to drive.
HTH
CNH
Joseph Katz book is also well worth a look.
im no expert at all, but a few things ive picked up. every single aero element of the car is linked, so forget fitting a diffuser or a spoiler etc, it doesnt work like that. think of changes as a package.
A flat floor is pretty well essential for a diffuser to work anything other than a paddock pose. Ideally a splitter, running into a flat floor through to a diffuser will be whats required. some 'rake' in the setup is needed. This can be the floor parallel to the chassis and the front suspension lower than the rear to create the rake, or have the chassis parallel to the tarmac, and the aero flat floor raked, lower at the front.
As for diffusers, dont get too het up with pics of Le Mans or F1 stuff, those funny 'Bat cave' shapes are dictated by rules saying the cant have a normal diffuser design. ideally the diffuser should have a smooth transition from the floor (not a defined angle) and run up between 7-10degrees. the roof of the diffuser wants to have rounded corners down to the vertical sides rather than square angles. ideally it should be finish at least as long as the car in plan view (if your competing) or a tad more if your not. central vertical 'strakes' or 'vanes' will help to keep the flow straight and reduce the likelihood of the flow becoming detached and going all wobbly (techy term right there...)
that above will defo work to some extent. ive always used the assumption on my car, that negating a cars inherent positive lift at 100mph, is a positive gain, therefore if i can reduce say 100 lbs of lift at 100mph to zero lift, ive effectively produced 100 lbs of downforce (figs all for easy explanation purposes only). to create tru downforce, more time, effort and testing would be required in my opinion, although im still having a go.
measuring the differences and net gains is difficult (for me), but given a light powerful RWD car, this setup makes it hugely more stable at 100+. ask any westy coffin dodgem driver and they will tell you the open area behind and around the rear axle acts like a dragsters parachute, so just covering it with any old flat panel, stops this and make sthe car easier to drive.
HTH
CNH
steve-V8s said:
I can recommend the excellent book by Simon McBeath, "Competition Aerodynamics" published by Hanes. Read several other books that confused me and then read this one which is written in English. Has a fair bit about Diffusers and smooth underbodies. Am planning something similar on the Griff but initially with plywood to see what happens. As I understand it to really see a benefit you need to get below the lowest sticky down bits which on the Griff are the anti roll bar drop links.
Cheers will take a look at this book too. I am in a similar situation with the front ARB being the hanging down point on the chassis. Im sure smoothing over this with sheeting under the car, then running this all the way back to a diffuser starting aroung the diff case would see some benifits. Not worried about big style at the rear end, the more descrete the better. Looking at using the current number plate recess and relocating the plate as a vinyl version above on the boot. Will do some more reading first, then intend to give the underside a good clean up then cover over, and work on rear diffuser style. Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff