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That looks very heavy :-) However, I have not seen this before so a little research is in order.
My long term plan is to run a series of wool tuft and pressure differential tests to see what I am actually dealing with.
The CFD pressure simulations have many caveats; it is 2D, no floor, no vehicle apertures etc so the resulting data is a ball park guide only and a bit of fun. However, I will add a floor and remove the wheels so I can get a better picture of the air flow over the centre of the car. I can then also play with rake.
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ndg
Part of things
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As your main focus is top speed (with stability), I'd focus on getting the pressure drag as low as possible. Imagine the car being sucked backwards by the low pressure behind it. I'd accomplish that by firstly keeping the airflow attached as far as possible (air guide on the roof), and then inducing a vortex deliberately to fill the vacuum behind the car (Kamm tail or vortex generators). This is a design I was heavily involved in. You can see that the taper of the body is smooth and gradual. We would have extended to a teardrop but we were restricted on length by the regs so decided to Kamm tail it at the back to try and reduce the pressure drag. It was good enough for 63mph round Molecomb with no push start and a win  . No invite to the drivers dinner the year after though  .  You're probably already planning a flat floor - this will make a massive difference due to the proximity of the ground. If possible a diffuser would help aero balance with minimal drag. 7 degrees seems to be the limit for plain diffusers without help from giant rear wings. I'm no expert, so hope I'm not teaching you to suck eggs . |
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Last Edit: Jun 9, 2016 11:44:02 GMT by ndg
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ndg
Part of things
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Last Edit: Jun 9, 2016 11:38:44 GMT by ndg
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ndg
Part of things
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Just remembered about Humster3D. They have a 3D scan of the elan:
humster3d.com/2015/07/08/lotus-elan-sprint-fixed-head-coupe-1971/
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jpr1977
Club Retro Rides Member
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Club RR Member Number: 18
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ste
Part of things
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Very interesting thread, love some of the progress and the history behind your ownership.
I'm very surprised at your predicted weight though. Maybe the YB is much heavier than I realised, and you obviously have a significant climbing frame inside it, but you seem to be predicting that the car will end up significantly heavier than when it left the factory.
I've done 'an amount' of lightening on my Elise, but nothing like you have yet from your predictions your car will be heavier than mine.
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Darkspeed
Club Retro Rides Member
Posts: 4,880
Club RR Member Number: 39
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Having built a 500Kg car I know how difficult it is - and compared to what I built the Elan is a big car. Plus a lot of factory, and pub, weight claims are well off the mark of actual. The YB is a heavy old lump fully dressed and there is a point where you need to consider that the chassis needs to be strong enough to actually control the power being put through it and, as nsl found, start adding weight back in. Bonus if it's a simplication and doubles up as a safety feature.
There is good reason why high power cars bolt the wheels directly to the engine and do not try to generate the power needed at the back from the other end of the vehicle! It's like trying to tighten a nut with a torque wrench - the RR has the socket on the wrench - the FR has three extensions on it and with a poor chassis it's like just holding the end of the wrench handle.
It's hard enough to get a car to handle well when you are just thinking about the components being static never mind that there is an engine in there trying its hardest to tear itself off its mounts and twist the chassis left to right whilst at the same time the diff tries to rotate itself out of chassis fore and aft. Engineers quickly tired of all that thinking and just stuck it all in one block in the back and gradually made all the casings and joins thicker until first the metal bits could not escape and then the liquid bits.
Engineering a well handling super high power lightweight FR is no easy task.
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I have no plans at present to enter competitions so there are no restrictions, other than those imposed by budget and aesthetics. I am reading that book at the moment :-) |
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As your main focus is top speed (with stability), I'd focus on getting the pressure drag as low as possible. Imagine the car being sucked backwards by the low pressure behind it. I'd accomplish that by firstly keeping the airflow attached as far as possible (air guide on the roof), and then inducing a vortex deliberately to fill the vacuum behind the car (Kamm tail or vortex generators). This is a design I was heavily involved in. You can see that the taper of the body is smooth and gradual. We would have extended to a teardrop but we were restricted on length by the regs so decided to Kamm tail it at the back to try and reduce the pressure drag. It was good enough for 63mph round Molecomb with no push start and a win . No invite to the drivers dinner the year after though . You're probably already planning a flat floor - this will make a massive difference due to the proximity of the ground. If possible a diffuser would help aero balance with minimal drag. 7 degrees seems to be the limit for plain diffusers without help from giant rear wings. I'm no expert, so hope I'm not teaching you to suck eggs . Actually, my main focus is the quarter mile ET. A top speed build would require different gearing and fewer mods (flappy paddles, sequential box, etc) I'm not convinced that an air guide would work, but I am looking into vortex generators for the roof. A Kamm tail wouldn't look right on the Elan :-) Floor is pretty flat as standard, but I have got to sort out the mess between splitter and rear of engine. With regard to a diffuser, this will be looked into once car is running and I can get some real world data. Neither am I, so we are both learning how to suck, which is quite apt when talking about aerodynamics :-) |
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I have seen this site and agree that it isn't quite right. The rear needs to curve down and in slightly, but it is pretty good and there is an AutoCAD file option so this could be addressed. However, until I have 3D flow software I am not going to spend $85 :-) |
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Very interesting thread, love some of the progress and the history behind your ownership. I'm very surprised at your predicted weight though. Maybe the YB is much heavier than I realised, and you obviously have a significant climbing frame inside it, but you seem to be predicting that the car will end up significantly heavier than when it left the factory. I've done 'an amount' of lightening on my Elise, but nothing like you have yet from your predictions your car will be heavier than mine. Thanks. I am a little disappointed with the predicted weight, but I guess my original predictions were through rose tinted glasses :-) Standard Elans weigh around 700Kg. Yes, the YB is known as a boat anchor, weighing in at around 140Kg. The 6 speed sequential gearbox and diff are also heavier than the standard items. The cage weighs 32Kg and the wheels and tyres are heavier than the originals. The original bare shell weighed around 95Kg and I have reduced that slightly. The chassis weighs 54Kg and I can't do anymore to that. I hope to keep it below the factory weight and as near to 650Kg as possible. There is still a little scope for weight removal :-) How much do you hope your Elise will end up weighing? |
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Having built a 500Kg car I know how difficult it is - and compared to what I built the Elan is a big car. Plus a lot of factory, and pub, weight claims are well off the mark of actual. The YB is a heavy old lump fully dressed and there is a point where you need to consider that the chassis needs to be strong enough to actually control the power being put through it and, as nsl found, start adding weight back in. Bonus if it's a simplication and doubles up as a safety feature. There is good reason why high power cars bolt the wheels directly to the engine and do not try to generate the power needed at the back from the other end of the vehicle! It's like trying to tighten a nut with a torque wrench - the RR has the socket on the wrench - the FR has three extensions on it and with a poor chassis it's like just holding the end of the wrench handle. It's hard enough to get a car to handle well when you are just thinking about the components being static never mind that there is an engine in there trying its hardest to tear itself off its mounts and twist the chassis left to right whilst at the same time the diff tries to rotate itself out of chassis fore and aft. Engineers quickly tired of all that thinking and just stuck it all in one block in the back and gradually made all the casings and joins thicker until first the metal bits could not escape and then the liquid bits. Engineering a well handling super high power lightweight FR is no easy task. Can't argue with any of that :-) We looked at making it rear (or mid) engined but the work was beyond my skill and budget. It would have also destroyed the essence of the car, IMO. The primary reason for the full cage was to stiffen up the chassis as it would have twisted like a liquorice stick otherwise. The safety advantages were secondary :-) |
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ste
Part of things
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How much do you hope your Elise will end up weighing? It was circa 690kg the last time I weighed it. Since then I've unfortunately had to remove the magnesium wheels (sprint regulations) and took a 6.8kg hit. I have however removed about 10kg of other weight (mainly more hole saw and angle grinder action). It should be circa 670kg when finished. Engine is a tuned NA K20 that currently makes 251bhp but should be circa 265 shortly. Current PWR is 364bhp/tonne. It's built to lap circuits though, not for straight line speed. I will however have it at Santa Pod next weekend for the RWYB. Would hope to see 12.x ET. |
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Jun 10, 2016 15:48:27 GMT
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How much do you hope your Elise will end up weighing? It was circa 690kg the last time I weighed it. Since then I've unfortunately had to remove the magnesium wheels (sprint regulations) and took a 6.8kg hit. I have however removed about 10kg of other weight (mainly more hole saw and angle grinder action). It should be circa 670kg when finished. Engine is a tuned NA K20 that currently makes 251bhp but should be circa 265 shortly. Current PWR is 364bhp/tonne. It's built to lap circuits though, not for straight line speed. I will however have it at Santa Pod next weekend for the RWYB. Would hope to see 12.x ET. You should run 12s with ease. I was running high 12s in the Elan back in the 80s with 168bhp at the wheels with no weight reduction and no real idea how to launch properly. Our cars will end up around the same weight, hopefully. 670kg I will be OK with. Not happy, but OK. |
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Jun 10, 2016 18:09:00 GMT
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This is a design I was heavily involved in. You can see that the taper of the body is smooth and gradual. We would have extended to a teardrop but we were restricted on length by the regs so decided to Kamm tail it at the back to try and reduce the pressure drag. It was good enough for 63mph round Molecomb with no push start and a win . No invite to the drivers dinner the year after though . Colin obviously knew about Wunibald Kamm's work as the rear is 'Kammed' :-)  |
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Jun 11, 2016 21:29:16 GMT
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Damper cover/hood tray/wheel tubs plug (which is covered in fibreglass to form the mould from which the carbon fibre panels will be formed) under construction.  |
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Last Edit: Jun 11, 2016 21:36:28 GMT by nalesutol
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Jun 12, 2016 19:48:39 GMT
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Experimenting with colour :-)  |
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Jun 18, 2016 16:36:45 GMT
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Mould finished, just need to get it out :-) To that end I have marked the cut lines. The centre section needs to be removable to allow access to dampers, etc. A few hours of mould surface preparation prior to laying carbon in my future :-)  |
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Last Edit: Jun 18, 2016 16:45:19 GMT by nalesutol
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Anglia68
Posted a lot
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Posts: 2,050
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Jun 19, 2016 16:04:59 GMT
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Lovely work.
I expect you've cut it all out by now but I've found that one of those cordless multi-tools with a fine blade is absolutely brilliant at cutting through fibreglass very precisely and creates hardly any dust which is a bonus.
I'm looking forward to see ing all in carbon fibre very shortly.
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Jun 19, 2016 17:45:24 GMT
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Yes, cut out today :-) I used a Dremel (lots of dust) but I keep looking at the non rotating cutters. After a fair bit of cussing I managed to extricate the mould sections. Next task is to trim and smooth them.  Whilst staring at the car I realised that there was a weak point in the cage. The rear suspension struts to which the roll cage is welded are not connected so there is no lower triangle. I will fix this with a tube as shown in the photo.  |
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. No invite to the drivers dinner the year after though 
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