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MG Midget and Sprite Technical - spoilers and splitters

Hi all just a question to any who have competted with spidgets , any advivce on positioning of rear wing and front splitters etc ?? oh and do they work cheers , Dal
Darren 2 litre frogeye

for them to be effective you got to knife blade the carb butterflys so as to get that extra 150hp then you can hit those high speeds where a big ol whale tale on the rear, and a sporty front spoiler will come into there own. LOL

seriously, I got a front spoiler, its more for looks then anything, I cant tell any differance, I think if your serious about ground effects id look into monthy website about williams-preitchard front clips and do one of those arrow dynamic shapes

Prop
Props Black Hole

Have a look at William Smallridge's class A midget Challenge car - I reckon that car is fitted with about the best aerodynamics I have ever seen on a racing Spridget... and yes aerodynamics do work on racing Spridgets - but at speeds far in excess of those legal on the UK highway... and you will need to remove the windscreen...
J A Bilsland

With the Spridget once you get over 90mph it's worth considering aerodynamic improvements.

However, you need to now what improvements you are looking for. Fitting a rear wing will slow the car down because while it creates downforce it saps power to do so. It's useful in racing where cornering speeds are more important that top speed insofar as you spend more time cornering than at maximum speed. You also have to consider that once you get over 125mph it takes double digit increases in bhp to go 1 mph quicker whereas that same double digit bhp 'driving' a rear wing might generate more than 1-2mph through several corners. I can't see the need for a rear wing on a road car or any racer except those on slicks.

A front spoiler is always worth having. I haven't seen any off the shelf spoilers that incorporate a splitter. It's on my list of projects to make one and test various splitters. It's likely you need to have a very low ride height for the splitter to work so may not be of any use on a road car.
Daniel Thirteen-Twelve

I found that a front spoiler made a HUGE difference.
My car is gutless and so it every little helps, but it was very noticeable performance improvement at 60+....err like it had some with the dam and none without it. I'd guess that the effect is probably less pronounced without a lower ride height though.

'Fitting a rear wing will slow the car down because while it creates downforce it saps power to do so'

I agree that a down force configured rear wing won't reduce the Cd (quite the opposite in fact), but wouldn't a closer approximation to a Kamm tail (with out without a lip spoiler) help, especially with a fastback hardtop, giving a reduction in lift and hence Cd?

Having said all that I'm not sure the theory applies at all though since the bodywork/screen/air intake/headlights/huge back axle plenum+fuel tank/big arches all conspire to cock things up for the amateur student of aerodynamics!

Anyway this is mine. (bits of Sh*troen AX nailed on)
rob






robnrrugby

Interested to understand how fitting the front spoiler made a difference in performance.

Does it simply tidy up the airflow underneath and reduce drag?

Max max-at-midgetmax-dot-com

As I understand the theory there are two basic effects, the one that you describe of reducing the amount of air that is 'in shear' beneath the car...the other is more subtle but equally important, by changing the shape of the pressure wave ahead of the car (the bow wave)which, if your lucky, decreases the drag....aerodynamically it is similar to extending the nose section forward (ish)

Adding a splitter to a chin spoiler has very much the same effect...since it prevents air from diving underneath so it has to que up ahead of the car and take it's turn to be diverted around the nose...usually adding a little bit of DF on the way....but maybe not on a blunt nose spridget with an air intake 4 times larger than necessary.

By experimenting with ride height and spoiler depth on my car I found that at more than around 3" ground clearance it stops working as well. The spoiler is made from flexible bumper plastic (ABS?) so ground contact isn't a big issue in the same way as it would be with GRP....it just flexes and grinds a bit more off.

I have often wondered how much better in terms of Cd a decent shape would be, faired headlights with a small air intake, and more importantly a very low bottom leading edge.

Rob
robnrrugby

Are there twenty people with a £100 interestd in finding out.......
Daniel Thirteen-Twelve

I'd be in for that
may be we need to rais some funds at next years silverstone?
Onno Könemann

Interesting Rob, I'm not doubting you in the slightest but to be convinced want to see some definitive figures - lap times/speed gun/anything other than "it just feels better" (I raced a car once, did some mods that "felt much worse" but went 2 secs quicker)

My modsport Midget had a vertical air dam "because it was on the front end I bought". I thought I was learning about aero so I fitted a splitter. Just a strip of ally coming out horizontal just above floor height. It was so much at first that the steering went really h-e-a-v-y and I had to halve the size, and it definitely turned in quicker than without it. Can't remember the lap times, but I suspect it was an improvement.

That was for racing at Combe with high speed corners and was done to improve the handling, no thought at all to top speed. Will try and dig out/scan a pic.
Max max-at-midgetmax-dot-com

Competition Car Downforce by Simon McBeath ISBN 0 85429 977 7 is a useful book on aerodynamics and one of the better books on the subject (I have most of those written including some out of print).

Looking up spoilers I'm reminded once again that the subject is relevant to the Spridget and in Simon McBeath's book he has a picture of a Frogeye on page 40 where he discusses spoilers! The car looks like it might be Simon Page's car (pre turbo and black paint).

The front spoiler reduces drag and reduces front end lift - so beneficial to top speed and cornering speeds.

Adding a splitter improves front downforce while reducing drag though the emphasis appears to be on improving the downforce without creating drag.

The chapter goes on to include roof flaps to prevent take off on NASCAR cars when they spin and if you're sharp enough and watched Disney's 'Cars' often enough you'll see they deploy on 'Lightning McQueen' - proof enough the film was made by real enthusiasts who paid attention to detail.
Daniel Thirteen-Twelve

A quick look at the Le Mans Sprite may shed some light on this.With very modest power output this car was able to achieve very impressive top speed figures but I imagine it was pretty scary in the fast corners. It is very difficult to get a road car to produce any downforce,you can really only hope to reduce the lift generated by the original shape of the car. If you have an excess of power then you could reduce lap times for a given circuit by adding wings etc to improve the CL (coefficient of lift) but with more modest HP figures I would of thought your time would be better spent reducing the drag. Take a look at the rear wings on the F1 cars at Monza this weekend! Fast straight plus slow corners equals tiny rear wings equals a fast lap time.
Just my thoughts before setting of for another night working in the wind tunnel!!

Cheers Carl


C Bintcliffe

What about reducing service drag to go a couple of miles an hour quicker by having some really neat wing vents. I'd certainly buy a pair?
Daniel Thirteen-Twelve

At the risk of being picky Daniel, isn't it: 'Competition Car Aerodynamics' by Simon McBeath?

If so, it's a very good read.

I fitted a splitter/diffuser to my TF160 and testing at Mallory showed improvements of 0.7 - 0.9 secs a lap. Might not sound like much but that's around 25-25 YARDS per lap. Next will be a flat floor / rear diffuser mod from a Lotus Elise.

Whether you'd get much benefit on a Spridget I don't know. It's moot for us because Class B regulations ban the use of aero.
Deborah Evans

I am trying Daniel! I will let you know as soon as I have a few sets made. I need to try and get some idea as to cost but it shouldn't be too much.

Cheers Carl
C Bintcliffe

daniel,
i'm designing some at the mo after the success of fitting some landy ones, the front end lift was much reduced.
If you have any particular fav designs then email me & i'll see what i can do in Lada land,

cheers
Brad
Brad (Sprite IV 1380)

Deb,

The book I have is:

Competition Car Downforce by Simon McBeath ISBN 0 85429 977 7

I haven't checked if he did another book. Maybe he revised the book and had it re-titled? Does your book have the Frogeye in it?
Daniel Thirteen-Twelve

This thread was discussed between 31/08/2009 and 09/09/2009

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