Rear Vents (again!)

General General Lotus Talk
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Guys,after all the talk about our pride’s fake vents, I decided to do something about it.First is the rear fake vents (the ones to the sides of the exhaust).I don’t think they will improve the engine compartment’s cooling that much, they would cool more the exhaust/catalyzer section (which in turn heats the engine compartment) and besides it’s easy to do. Therefore it gets done first.Have a look: http://www.bookatrack.com/isapi/bat.dll?7&pics&185&uldis&25824&3&d&54&6 (Admin5, could we have an “attach picture” button in this bb?)Second step will be the one behind the license plate ala Pesky. Third will be the front brake cooling [image]http://www.exiges.com/ubb/NonCGI/images/icons/grin.gif[/image]Cheers,Uldis [image]http://www.exiges.com/ubb/NonCGI/images/icons/grin.gif[/image]PS - It looks Nice !

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Aaargh no - big mistake, you’ve gone and made rectangular holes!!!Just wait until you get out on track - it will be fine round hairpins, but sweeping corners!!! [image]http://www.smilies-world.de/Smilies/Smilies_boese_1/BIGassault77.gif[/image]

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Huh ?! [image]http://www.exiges.com/ubb/NonCGI/images/icons/confused.gif[/image]What are you talking about?

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This looks similar to what I’m thinking of doing, but I’m worried about the lamps getting too hot. Let us know how you get on.Pesky, I’m thinking octagonal holes would be a good compromise. Does this sound right? I wasn’t sure whether triangles would generate a bit of negative lift.

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quote:Originally posted by Brendan:I wasn’t sure whether triangles would generate a bit of negative lift.Don�t be silly, everyone knows that triangular holes are perfect for banked circuits, but not for the more traditional layouts, and that they are therefore best avoided.Uldis, a word of warning regarding the front vents: they were designed in so that they could be opened up on the race cars if it was found that the brakes were running too hot in race conditions, but it turned out that even on the race cars the brake temperatures were fine without additional cooling. If you open them up you may over-cool the brakes to the detriment of braking performance (I looked at getting Lotus to do this ex-factory on mine when I bought the car new). FWIW… [image]http://www.exiges.com/ubb/NonCGI/images/icons/smile.gif[/image]

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Oh come on, Tony. Everybody knows that ovals are best for banked circuits.

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I now have perfect circles in my rear end…if you’ll pardon the expression…Lots of them,(12 in all) behind the grills, behind the number plate. (can provide pics if anyone is interested)Mike

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Circular is the best compromise - the square of pi (3.142)2, creates the least negative pressure, this affects the separation point to some extent, but the rear aerofoil drags the airflow past the holes and negates any adverse high pressure. On Anglesey, you would be better with square holes, but Donington is definitely a circular hole type track. Hope that helps.

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Uldis, nice one…Brendan, done that ages ago and no probs so far…Rob, can you send me some picis about your license plate job 'cause I want to do that during winter…cheers,Bruno

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erm…Mike…thinking about my rear end…he-he…so you can recommend the circles… [image]http://www.exiges.com/ubb/NonCGI/images/icons/grin.gif[/image] [image]http://www.exiges.com/ubb/NonCGI/images/icons/grin.gif[/image] [image]http://www.exiges.com/ubb/NonCGI/images/icons/grin.gif[/image] [image]http://www.exiges.com/ubb/NonCGI/images/icons/grin.gif[/image] [image]http://www.exiges.com/ubb/NonCGI/images/icons/grin.gif[/image] [image]http://www.exiges.com/ubb/NonCGI/images/icons/grin.gif[/image]Tonyas far as I know, Lotus did it in the second racing season, I did see it when vising the Motorsport dept. in Hethel…later,Bruno

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quote:Originally posted by Bruno:Tony as far as I know, Lotus did it in the second racing season, I did see it when vising the Motorsport dept. in HethelI remember the pictures, but were they from a one-off or was it done to all of them? [image]http://www.exiges.com/ubb/NonCGI/images/icons/confused.gif[/image]

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quote:Originally posted by RussT:Circular is the best compromise - the square of pi (3.142)2, creates the least negative pressure, this affects the separation point to some extent, but the rear aerofoil drags the airflow past the holes and negates any adverse high pressure. On Anglesey, you would be better with square holes, but Donington is definitely a circular hole type track. Hope that helps.So, for Oulton would you recommend one circular hole & one square hole? Which is better on the left? [image]http://www.exiges.com/ubb/NonCGI/images/icons/confused.gif[/image]Also, next year I fancy a blast round Spa - how will the change in altitude affect my holes?

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Tony, as far as I can remember, I saw the whole lot at Hethel being serviced and all of 'em had it done…later,Bruno

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Gentlemen, I think that the shape of the hole is in fact less important than the manner with which the air exits it. Therefore I have been designing an egg shaped funnel to attach to the back of the hole. This has two advantages, firstly it means the hot air can be move past the lights so they aren’t cooked and secondly, the use of a ball joint where it attaches to the car means it can be directed for any shape of circuit. I had considered automatic actuation, so it would move itself depending on each individual corner, but that just seemed a little silly (not to mention the added weight). The best shape to fit the funnel to is a circle, so I’m with Russ.Ian [image]http://www.exiges.com/ubb/NonCGI/images/icons/smile.gif[/image]

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Ahhh, Pesky, I see where you’re coming from.But it seems that you guys have settled on the old theory of the round holes.Since then, major advances have been made in Thermal aerodynamics, starting with convoluted and angular shapes (remember the Stealth Fighter?), which strong point was the clean adjoining of diffrenet laminar flows as to not create a shock, to a series of developments, head by Muckenshneiber in his book: Turbulent Chaos.In there you can see how a round port that act as an exhaust of hot gases into a turbulent zone with a temp. differential >= than 40 DegC (depending on gas viscosity, but for sismplicity’s sake let’s suppose normal air at 80% humidity) can create negative axial force derived from the subsonic velocities (nobody here is thinking that our beloved car can really break in the supersonic range, right?) which in turn would lead to drag, thermodynamic drag. Now having it on both sides of the rear of a car creates a balanced situation which will not do harm in a straight, but applies torque to the vertical axis of the car, exactly proportional to the speed you’re traveling, unbalancing the car in high speed sweepers! (easy to understand when you envision the normal forces in a Gyroscope, and exactly the opposite of your first statement).But this can be cured by elongating the holes and creating 4 vortex in the ex-circle, effectively cancelling the negative axial pressure and actually reversing it, that in turns creates a higher laminar flow from the rear of the car (compared to what flows beneath it through the diffuser), with the result of self cancelling torque effects, creating more down force and less drag, all benefitial to hi-speed sweepers.So, in reality the rectangular holes are really more suited to turns, (max benefit in high speed sweepers) and round holes would be better for straight line stability (if you have the BHP to counter the induced drag).PS- Brendan, this is the reason behind your logic. In fact, ovals are better than round !PS2-Russ, your comments are very valid, but they apply only to fluids, or you can consider them also valid while in the supersonic domain. Again, we are excluding supersonics here.Hope this finally clarifies (and unifies) all theories.Rgds,UldisAnd Tony, thanks for the tip, but don’t worry, I have considered that fact already.In Anglesey for example, my brakes were working perfectly. It’s just that last day at Knockhill the juddering appeared again so what I will do is have a small lid on the front vents, and only open them (nothing fancy, just velcro, or a quick release fastener) when on tracks like that. On the road everything is fine, don’t want to cool the brakes more than needed. [image]http://www.exiges.com/ubb/NonCGI/images/icons/grin.gif[/image] [image]http://www.exiges.com/ubb/NonCGI/images/icons/grin.gif[/image] [image]http://www.exiges.com/ubb/NonCGI/images/icons/grin.gif[/image] [image]http://www.exiges.com/ubb/NonCGI/images/icons/tongue.gif[/image]

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I’ll get me coat.

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UldisDing [image]http://www.exiges.com/ubb/NonCGI/images/icons/grin.gif[/image] [image]http://www.exiges.com/ubb/NonCGI/images/icons/grin.gif[/image] [image]http://www.exiges.com/ubb/NonCGI/images/icons/grin.gif[/image]

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Oi, Pesky,been trying to find black aluminum grille with the same hole size as the one you have in your car, but no luck. All the ones that I find are the really big/thick openings that they use on Hot Hatches [image]http://www.exiges.com/ubb/NonCGI/images/icons/frown.gif[/image]Would you happen to know where to find that one? maybe your mechanic?Cheers,Uldis

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UldisMesh (aluminium) for grills was painted black before fitting. Rumour (started by IDG, I think!!!) has it that you can buy the mesh in B&Q.

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Looked for it there already but at least in the B&Q here in Aberdeen they didn’t have it.I found some other one, in Checkpoint, but it was too… open.Well, will keep on looking.Cheers,Uldis