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Beyond P1
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Discussion Starter #1
Oh no, more moving parts to contend with, how will we cope. Would you be so kind No Lotus as to explain the ideology behind all of this. To be more specific the retractable twin chassis is the area of most interest. Cheers....??
Ok, here goes: :)
The twin chassis idea originated with Colin Chapman and Peter Wright, two of the most innovative car designer/engineers in automotive history. Among their innovations are the monocoque chassis, side pods, ground effects, active suspension, and the twin chassis. Did I even need to list those? :D

Chapman was extremely passionate about that last idea, seeing in it the ultimate solution to an otherwise necessary compromise between aero and mechanical grip (not to mention ride). Unfortunately, he and Team Lotus were never allowed to race using the technology and the idea effectively died with Chapman in 1982. He considered it to be useful for more than just F1, however, and patented the idea for road use. Of course, no manufacturer has since developed a car around the idea, but, given the extreme performance of current high-end sports cars, I think it's just a matter of time before that happens.

What a twin chassis gives you is essentially two separate suspension systems: one adapted to maximize mechanical grip and ride, and a second system that stiffly supports the underbody (or "aero chassis") so that the underbody follows the road closely. With it, you don't have to compromise between mechanical and aero grip and very high levels of the latter may be generated.

The problem with Chapman and Wright's twin chassis, however, is that the underbody is permanently coupled to the suspension of the car, which obviously limits its use for a road-going car. This is overcome by making the aero chassis retractable and able to be disengaged from the primary suspension. This gives a car two distinct modes of operation: 1) a normal street mode with normal ground clearance and a disengaged aero chassis that is fixed to the undersurface of the car and, 2), a track mode with lower ground clearance and a deployed aero chassis that automatically adapts to the road. Because of that last feature, the setup is also well suited for the use of ground effect fans to transform grip levels at lower speeds and it's low speed grip where modern supercars are most lacking, the Caparo T1 being an extreme example: http://www.youtube.com/watch?v=ZFcanpNarEg. Downforce fans, of course, were pioneered by Jim Hall and Gordon Murray, and have already proven their worth at the highest levels of motorsport. Beyond the performance aspect, though, a twin chassis setup with vacuum traction is a safety device that will allow, among other things, significant decreases in braking distance from any speed and allow the driver to more likely regain the car regardless of attitude and speed. And yes, it'll let you use all of your 600 bhp off the line.
 

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Fantastic! I thought the idea was gone with Chapmans' passing. Great to see something may become of it. Thanks for posting.
 

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Now you post pics? After I join the Noble site? lol

Nice work man - good luck!
 

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Ground effects downforce will increase until your clearance meets a critical limit. To be honest, your floor looks way too low

Do you have any numbers from CFD or a tunnel?
 

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Seems complex. Do u foresee reliability issues with twin system. Any weight penalty, if so would one need to go to CF solely. TIA for reply
 

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Chapman's twin chassis was one inside the other, permanently coupled as you stated. How do you go about decoupling/disengaging one from the other? has to be a pretty advanced software system. Can it be realistically applicable for a road car. from the photo not much ground clearance for inclines or speed bumps?
 

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This is the single best posting I've seen on the Site. Thank you. One quibble. I don't believe twin chassis with vacuum would be a racing safety feature. I believe it increases risks because if the vacuum system falters, the greatest effect would be approaching a turn and the driver would be doomed.

Also, I believe Colin got the idea for the twin chassis from Jim Hall's Chaparral 2E that attached the articulated rear wing to the suspension uprights rather than the bodywork which up to then was then SOP. Chapman, being a genius of the first order, saw that aero could be decoupled from other parts of the car and took it to its ultimate implementation.
 

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Beyond P1
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Discussion Starter #10
This is the single best posting I've seen on the Site. Thank you. One quibble. I don't believe twin chassis with vacuum would be a safety feature. I believe it increases risks because if the vacuum system falters, the greatest effect would be approaching a turn and the driver would be doomed.
Wow, that is quite a compliment. Thanks so much. :)

I think the issue with vacuum traction is how it is used. In my view, the point is to add grip at low speed where you otherwise have no downforce, whether that's on a slow hairpin on the track or on the street after a sudden loss of control. Let conventional aero give you downforce at higher speeds. I think 2g's at 130 mph is potentially a lot more dangerous than 2g's at 45 mph.
 

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Discussion Starter #11 (Edited)
Chapman's twin chassis was one inside the other, permanently coupled as you stated. How do you go about decoupling/disengaging one from the other? has to be a pretty advanced software system. Can it be realistically applicable for a road car. from the photo not much ground clearance for inclines or speed bumps?
Yes, the Lotus 88 had an outer body sprung directly from the uprights. In their patent, Chapman and Wright show another embodiment where just the underbody is connected to the suspension.

The retraction and decoupling of the underbody is straightforward and greatly facilitated by segregating horizontal and vertical loads. The latter are dealt with exclusively by the connection with the ends of the car's suspension and, because of this, we're able to measure precisely how much downforce is individually and directly applied to the four wheels using appropriate strain gauges. All horizontal loads are borne by linkages that extend from the underbody to the undersurface of the car body.

What is really neat about this system is that, while the mass and downforce load from the "aero chassis" is borne by the unsprung components of the car when the aero chassis is deployed, there is no addition to unsprung mass! The wheels are free to adapt to the road surface in rebound without "carrying" the aero chassis with them. At the same time, the mass and downforce load from the aero chassis naturally limits/controls jounce. We've got the aero chassis set particularly low in the front and with a fair amount of rake in that image just as part of testing. You don't want to go so low that you stall the undersurface, but, in terms of impacting the road, realize that the underbody cannot transmit upward jolts to the rest of the car. With an upturned inlet, the aero chassis simply rides over anything it encounters. For the road, of course, you just have the aero chassis permanently retracted where it forms the undersurface of the car.

As far as this thing being applicable for a road car, at least Chapman thought so and that was in an era of "limited" performance. My wife's 2009 Toyota minivan has more bhp than my 1981 Ferrari 308. I think today, with what's happening to performance and the manufacturers that are involved and the need to be the fastest, this idea can have a place. In my view, there's no doubt that if a manufacturer were to build a car around this idea from the ground up, they'd have something that would not be touched for the life of the patent.
 

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Yes, the Lotus 88 had an outer body sprung directly from the uprights. In their patent, Chapman and Wright show another embodiment where just the underbody is connected to the suspension.

The retraction and decoupling of the underbody is straightforward and greatly facilitated by segregating horizontal and vertical loads. The latter are dealt with exclusively by the connection with the ends of the car's suspension and, because of this, we're able to measure precisely how much downforce is individually and directly applied to the four wheels using appropriate strain gauges. All horizontal loads are borne by linkages that extend from the underbody to the undersurface of the car body.

What is really neat about this system is that, while the mass and downforce load from the "aero chassis" is borne by the unsprung components of the car when the aero chassis is deployed, there is no addition to unsprung mass! The wheels are free to adapt to the road surface in rebound without "carrying" the aero chassis with them. At the samtime, the mass and downforce load from the aero chassis naturally limits/controls jounce. We've got the aero chassis set particularly low in the front and with a fair amount of rake in that image just as part of testing. You don't want to go so low that you stall the undersurface, but, in terms of impacting the road, realize that the underbody cannot transmit upward jolts to the rest of the car. With an upturned inlet, the aero chassis simply rides over anything it encounters. For the road, of course, you just have the aero chassis permanently retracted where it forms the undersurface of the car.

As far as this thing being applicable for a road car, at least Chapman thought so and that was in an era of "limited" performance. My wife's 2009 Toyota minivan has more bhp than my 1981 Ferrari 308. I think today, with what's happening to performance and the manufacturers that are involved and the need to be the fastest, this idea can have a place. In my view, there's no doubt that if a manufacturer were to build a car around this idea from the ground up, they'd have something that would not be touched for the life of the patent.
Another great write up and explanation. Thank you!.....any manufacturer toying with the idea, say NOBLE. is the system cost effective enough to bring it to market. The advantages seem staggering, just surprised no has developed it further since chapman in the early 80s. Would it be to costly and complex (reliability) for road use. I guess at HYPERCAR prices the sky's the limit. The VENENO cost over $4mil for god's sake!:eek:.....the Lotus 88 was primarily made of CF just like the McLaren MP4/1?
 

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Beyond P1
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Discussion Starter #16
Another great write up and explanation. Thank you!.....any manufacturer toying with the idea, say NOBLE. is the system cost effective enough to bring it to market. The advantages seem staggering, just surprised no has developed it further since chapman in the early 80s. Would it be to costly and complex (reliability) for road use. I guess at HYPERCAR prices the sky's the limit. The VENENO cost over $4mil for god's sake!:eek:.....the Lotus 88 was primarily made of CF just like the McLaren MP4/1?
Yes, I think the advantages are staggering. Just consider the unique advantage of being able to use all your power off the line. It's something that Jim Hall remarked regarding the 2J and that car was 700bhp and only 2000 lbs. In comparison with what we've got, though, the Chaparral 2J had an absolutely terrible fan and skirt arrangement with an approximate 1/2 " gap all around. That required high cfm and big, bulky fans. With an adaptive chassis and folding skirts, there's literally no gap with the road and the fans we use are small electric ones, very powerful (2 x 10hp) that weigh a total of 10 lbs. compared with 200 lbs. for the chaparral fan setup.
 

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Absolutely. We've fitted simple ones, but will be trying an articulating arrangement that automatically folds up when the aero chassis is retracted.
Of course it will be more effective and simpler to have skirts on a twin chassis than a conventional one.

On a conventional chassis, ground clearance is going to be more problematic. However, do you think there is scope for reactive skirts?

I believe some car manufacturers have the tech to read the up coming surface of a road and firm/soften the suspension in order to react.

Could these sensors be used to help skirts avoid bumps in the road? It would be a pretty complicated job to engineer it, but if you can stop low pressure bleeding away the gains could be massive. I wonder what the P1's down force levels would be if it had a seal no more than a few millimetres off the tarmac?
 

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Beyond P1
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Discussion Starter #18 (Edited)
Of course it will be more effective and simpler to have skirts on a twin chassis than a conventional one.

On a conventional chassis, ground clearance is going to be more problematic. However, do you think there is scope for reactive skirts?

I believe some car manufacturers have the tech to read the up coming surface of a road and firm/soften the suspension in order to react.

Could these sensors be used to help skirts avoid bumps in the road? It would be a pretty complicated job to engineer it, but if you can stop low pressure bleeding away the gains could be massive. I wonder what the P1's down force levels would be if it had a seal no more than a few millimetres off the tarmac?
In fact, the aero chassis can be in the form of adaptive skirts alone, i.e. no plate, just skirts. I don't see any advantage to going with reactive skirts with the associated actuators and ride height sensors, ECU, etc. That's just more weight and complication, and will certainly not be as effective in maintaining a fixed ground clearance. You can look at it this way: with a twin chassis the primary suspension of the car functions as four already built-in actuators keeping the skirts, when deployed, at a fixed clearance to the road. I designed the setup on the Elise so that we can eventually fit actuators in the body of the car for a different purpose: to precisely control ride height and rake of the aero chassis while driving. This'll let us change downforce distribution front to rear. I can post a photo, but basically this involves a small bellcrank at the end of each of the upper A-arms that redirects the vertical load at the end of the suspension to the base of the suspension. For now, we've just fitted a strain gauge at each corner at that spot.
 

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Yes, I think the advantages are staggering. Just consider the unique advantage of being able to use all your power off the line. It's something that Jim Hall remarked regarding the 2J and that car was 700bhp and only 2000 lbs. In comparison with what we've got, though, the Chaparral 2J had an absolutely terrible fan and skirt arrangement with an approximate 1/2 " gap all around. That required high cfm and big, bulky fans. With an adaptive chassis and folding skirts, there's literally no gap with the road and the fans we use are small electric ones, very powerful (2 x 10hp) that weigh a total of 10 lbs. compared with 200 lbs. for the chaparral fan setup.
Very interesting stuff. Just a question if I could, would you not have issues with the fans blowing out huge amounts of dirt/debris behind and also would active suspension not be required to maintain downforce stability if the car is running that low to ensure there is no loss of downforce on a change of pitch/roll due to the road surface?
 

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Discussion Starter #20 (Edited)
Very interesting stuff. Just a question if I could, would you not have issues with the fans blowing out huge amounts of dirt/debris behind and also would active suspension not be required to maintain downforce stability if the car is running that low to ensure there is no loss of downforce on a change of pitch/roll due to the road surface?
I think dust is more of an issue where the skirts don't seal the road well and comparatively high cfm are required, as was the case with the Chaparral which could pick up clouds of dust. This didn't appear to be an issue with the Brabham which had a much better seal with the road, although Chapman had Andretti complain about rocks being picked up by the car in an effort to get it disqualified. As Gordon Murray pointed out, the efflux on that system was only 60 mph. One thing that might be done where it does turn out to be an issue, however, is use of a cyclonic dust trap before the fans.

As far as pitch/roll affecting downforce, understand that there is no pitch/roll of the aero chassis. It maintains a fixed ride height and rake. The level of downforce and downforce distribution is much less variable than in a conventional car, which is kind of the point. By decoupling the underbody, a consistent, comparatively low ride height with high downforce is possible. At the same time, the car is softly sprung leading to better mechanical grip and a far more comfortable ride. If you look at the P1 in those track videos, the thing is really bouncing along with a fairly harsh ride.
 
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