Complete undertray?

[bert]

Hi,

 

Haven't got a 7 myself (yet!) just looking at all the possibilities.

 

Has anyone tried, or come across, an undertray on the their 7? It seems to me that a simple, flat piece of thin Carbon Fibre would make a nice path for the air to follow under the car and keep the delicate metal bits nice and dry. This might also have the added function of increasing downforce.

 

What do you chaps think?

[dino ferrana]

I believe that the 7 doesn't generate any downforce. It does generate quite a lot of drag though and an undertray can reduce this as well as possibly reducing the lift.

 

WIth an undertray you have to decide what type you are going for.

you can either.

1. Seal the entire underside (probably except round the sump pan) and then you have to find somewhere for heat to go like venting the nosecone for the radiator.

2. Or leave some of it uncovered to allow some airflow for the engine.

[stevefoster]

I have a partial undertray to prevent stones from getting into my cam and dry sump pump belts.

I have heard of a plastic bag taking out a cambelt too.

 

It goes back to about half the sump pan. The angle means that should anything get in it will fall out (hopefully) at the bottom out of harms way. No difference in engine bay temp.

 

The tray is far from flat. It needed to allow for the oil feed into the sump pan (I am running the internal oil pump on the VX EX) and I wanted to be able to use the cross bars as a jacking point with my quick lift still. So a panel beaten (some what crudely) ali undertray was in order.

 

Can't say I'd noticed any reall improvement in drag reduction in laptimes but I did have a binding rear brake issue that is not fixed so maybe it did help.

 

 

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[V7 SLR]

Miraz has a rather snazzy ali flat floor on his SV. I think Arch will produce one if you ask them, although you'll probably either need to affix it to the car yourself or give them your car so they can install Dzus fasteners.

 

Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours

 

[Tony Whitley]

I found a thread elsewhere here and the bottom line seemed to be that there was no noticeable difference in drag (which surprised me) but that it did keep the mechanicals cleaner.

 

 

Tony

M1 7 SMW

1.4SS Green/yellow Cycle wings.

[bert]

Thanks all, I think I sort of mean't reducing lift. I was hoping that it would decrease drag as well.

 

I sort of found the 7 a bit wayward at higher speeds on my 'testdrives' and would appreciate a bit more confidence in the grip levels with less lift. Maybe my Palmersport day upcoming will increase my confidence levels 😬 😬

 

Hey V7SLR, who are Arch? Just showin' my ignorunce here...

[greg]

Arch are the manufactures of the Caterham 7 Chassis, they also made some of the Lotus Chassis along with a few other companies (I think lotus changed over the years).

 

They also do repanneling work and resprays etc....

 

Greg, Q 86 NTM (Green 185BHP XF)

[bert]

Doh!

 

I was thinking of setting up a leeetle experiment with my Tamiya 1/12 model that's coming soon, with a set of digi scales and a big fan, or maybe 1/12 is too small to measure the differences?

 

What do you guys think? Certainly sounds like it could be fun, I was going to use balsa and some sandpaper to get the shapes right under the body with a nice rear diffuser.

 

I'll let you know if anything comes of it.

 

Thanks again

[V7 SLR]

As Tony says, it has been tried for real in a wind tunnel. Someone wrote it up in Low Flying. Can't remember who, but he tried all sorts of things to both reduce drag and lift. Not much helped save perhaps having 270 degree cycle wings with parallel-to-the-ground flaps sticking out of the trailing edges.

 

Flat undertray made no difference to drag or lift.

 

Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours

 

[Nick M]

Just a couple of comments / observations...

 

I spoke with someone (can't remember who to be honest) who had done this to their Caterham (panelled the engine bay) and he used a sheet of aluminium held in place with cable ties round the chassis tubes, the logic being that if you need to remove the panel it was easy to do and didn't involve drilling holes in the chassis rails. I don't think the car ran any hotter and it was primarily done to protect the cam belt from stones, etc.

 

The other comment is in relation to a comment somewhere above about a rear diffuser. I'm sure people have seen pictures of Westfields with these fitted. There's some question about whether they give much (if any) downforce but the larger stepped ones do seem to help. Certainly one person who had one fall off noticed a big difference in the car's stability without it in place. What they do help with is cleaning up the airflow under the back of the car - a Westfield Megabusa at Snetterton ran 6mph faster down the long straight at Snetterton with a very simple diffuser in place. Basically the back of the car acts like a huge parachute and creates a lot of drag. Allowing the air to flow cleanly out the back of the car cuts this noticably.

[dino ferrana]

"High speed waywardness"

 

What cars have you driven before? I ask because this is usually to do with the very sensitive steering of the 7. Remember an R500 can do over 140 mph with the right diff without taking off. A lot of people who come from tin tops think that 7's are very twitchy but it is just a case of getting used to steering that you have to think your way round a corner.

 

One of the Caterham guys told me that most first time Caterham drivers will swerve when they change gear intitally because they are not use to the direct steering!

[stagecrew]

I think that an under try would be a good idea. In fact im looking into having one made just now.

I was quite concerned the first time I look at the location of the oil filer on the R500. Very close to the deck without any sort of protection at all.

 

While the car was on the ramp for the MOT I noticed that the previous owner must been running the car far to close to the deck as the dry sump casing has signs of grounding. A simple skid plate would at least give it some protection.

 

Greg

R500N

[V7 SLR]

It's generally accepted that you will wear the sump pan down, even on the dry sump which (to be honest) offers very little extra clearance over the wet sup pan anyway. Mine now has CATER... (or something) printed on the bottom.

 

Any skid plate will only make you lower to the ground.

 

The oil filter has never presented any problems to my knowledge. The problem is the oil pressure sender which is known to become unreliable over time owing to the environmental damage it receives being so low and at the front of the engine. The answer to this is a remote sender kit, available off the shelf.

 

I think the undertray idea is one to solve a problem that doesn't exist. Likewise the diffuser idea which has been disproven on a number of occasions. A better bet would be a tail-plane of the like found on planes. Attach that to the rollbar and you'll fly straight like a dart. Space for advertising and sponsorship too. 😬

 

Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours

 

[bert]

😬 😬 😬 LOL and thanks for your input.

 

I still think it's worthwhile to evaluate it so I@m going to for the helluvit and it's not down to my newbieness though I can understand what you mean dino. I managed to stay pretty straight during the redlight changes on the R400 I took for a (no) spin.

 

I actually just loved the steering, it was brilliant. I can't understand why we don't see these cars on the telly driving progs more often. They always seem to leave it out/ Take 5th gear, evaluating best sports car next week and not a 7 to be found. Plonkers. Most lardy modern lcars leave me cold now and I've got a brand new M3 sitting on the driveway, bores me to tears now 😬

 

I know the 7 is more 'motorcycley' than most casr, it just feels like it needs something covering it's tum and gluing it down a bit more, anyway, out with the balsa and a hairdryer...

 

 

[Nick M]

 

I think the undertray idea is one to solve a problem that doesn't exist

 

I guess it depends what you perceive the "problem" to be. If it's just something to prevent things getting in the cambelt or acting as a sacrificial skid plate offering, even if only a little, protection to some of the more exposed components then it might be worth considering.

 

 

Likewise the diffuser idea which has been disproven on a number of occasions

 

🤔 🤔

 

Granted the wind tunnel results may have shown little effect, but practical real world evidence suggests otherwise, certainly as far as Westfields go. A 6mph improvement in top speed (with no other changes to the car) suggests that the diffuser was offering some benefit, if not actually any downforce. Maybe the shape of the "cavity" behind the rear bulkhead is such that it's leff of an issue on a Caterham ?

 

*shrugs*

 

I'm fitting my one anyway (when I eventually get round to it !) - if nothing else it helps keep the back end of the car cleaner !! 😬

[V7 SLR]

If you place a board over the differential space, so as to offer a continuous run between the floor under the seat and the fuel tank you might benefit from a marginal recution in drag, which I would guess is the effect you noted on the Westfield. What I don't understand is why people go to the trouble to fit a diffuser-shaped board when it's not nearly large enough or close enough to the ground to actually act as a true diffuser. Seems like an excercise in styling rather than real-world engineering.

 

Everyone else I've heard of having fitted a diffuser (and I met a few Westfield guys having done so at Mallory a few years ago) claimed, rather good naturedly (if that's a word) that their diffuser kept the diff clean. That seems consistent with your desire to run a flat floor under the engine. Nothing wrong with it and I might be interested myself except I'd worry about cooling the engine. Those that have done so that I've seen have sculpted the flat floor around the sump so it's not completely sealed.

 

Good luck with the experiment though. To be honest, I love the look of diffusers. If they were proven to work I'd want one but things as they are, I'd rather spend my money on suspension next, or a new set of tyres. A carbon diffuser was going for about £200 or thereabouts last time I looked (a good while ago). That's 2 tyres for me.

 

Then again, a sheet of ali could be bought and fabricated for 1/10th of that. Worth thinking about as an experiment before you commit to carbon.

 

Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours

 

[EFA]

"Flat undertray made no difference to drag or lift"

 

Wrong. It moves the aerodynamic flatspot my car has from 127mph to about 135mph.

 

Acceleration at all speeds above 100mph is also improved.

 

Fat Arn

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[Miraz]

I haven't done any comparisons with my undertray yet, but will release the numbers when I have them.

 

The undertray is in three pieces attached with Dzus clips to the chassis - there is one panel which covers the engine bay, and runs within a couple of cm of the sump, oil filter and scavenge plumbing - the second panel cover the transmission tunnel between the gearbox and diff - the third is part of the A-frame.

[edmandsd]

Glad to hear you've been proving your claims in the wind tunnel Arnie 😳

 

I like others find that there's a terrible aerodynamic flat spot at around 761.50 mph which is often associated with terrible buffeting and booming noises

 

Home of BDR1200

[Nick M]

 

What I don't understand is why people go to the trouble to fit a diffuser-shaped board when it's not nearly large enough or close enough to the ground to actually act as a true diffuser. Seems like an excercise in styling rather than real-world engineering.

 

Granted - I don't think anyone has actually tried to measure any appreciable downforce from them, although some of the cars are running pretty low to the ground, especially with the stepped type diffusers that are available now. I think it's the drag reduction and "tart" factor which are the biggest benefits !! 😬

 

I got my diffuser (wet lay carbon and foam core - only a bit heavier than the pre-preg ones but probably not as stiff) made in a rather roundabout way for 100 quid, but that was really a one-off. At that price it was OK, but I'd probably baulk at spending too much on a pre-preg one which will inevitably get chewed to bits on the road anyway ☹️

 

As for the engine bay panelling, fortunately the dry sump pan (1.6 16v VX Ecotec) doesn't project below the line of the chassis rails - it's just slightly higher than them. I was going to panel it as far back as the bell-housing / flywheel which does protrude slightly (at least until I fit a smaller steel flywheel). Engine cooling shouldn't be an issue because I plan on cutting a hole in the side of the bodywork to fit a NACA duct to provide cooler air to the dry sump tank. Failing that I can always fit an oil cooler but oil temps, at the moment, aren't a cause for concern.

[Bare]

Undertray?? Just take a look at the Series 1 Seven ;-)

It had a full stressed skin undertray , several more chassis tubes.. AND a genuine 5 link rear axle system that didn't destroy the axle housing.

Seems that Version was a bit more expensive to manufacture .. so Lotus took out anything that cost $$.. regardless of the consequences..seriously degrading the structural rigidity..and claimed 'lighter weight' as a 'virtue' and incredibly lotsa people believed it ;-)

 

[Miraz]

Undertrays are very difficult things to test in a windtunnel as a key element is a speed differential between the ground and the vehicle - there are a few wind tunnels around that have a large belt for a floor to do this type of analysis but they are really hard to gain access to - afaik the MIRA windtunnel has a smooth, polished floor.

[Martin Plant]

There was an undertray on my Blackbird when I got it. It was pop rivetted to the chassis. As far as I could tell it did nothing except prevent air flowing properly over the oil cooler.

[Grim Reaper]

I have some pictures of a Seven with undertray and diffuser done by Fredy Kumschick,which looks rather tasty.

[dino ferrana]

I remember seeing a Kumshick car in a car magazine years ago. It was a picture piece from the Geneva show and they had their totally mad turbo cars there. They had vented noseconens and undertrays on. The top speed was alleged to be 160 mph IIRC!

 

Can you put the photos up Mr. Reaper?