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Which Esprit over the whole range had the best aerodynamics? Least drag? Best cd figure? - Esprit Chat - The Lotus Forums Jump to content
benjamincalleja

Which Esprit over the whole range had the best aerodynamics? Least drag? Best cd figure?

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The ones with the glass hatch. Per Fifth Gear.


Luke Colorado, Super Spy.   -  Lotus Owner No Longer

1987 Zender Widebody 560SEC | 1994 Lotus Esprit S4 | 2013 Honda Fit EV (#269)

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Yes, as Luke mentioned above the glass back version has a lower CD. Removal of the glass back caused all kinds of wind flow issues. The S4 wing went some way to reduce these issues but only by a small percentage.


Simon  (94 S4)      My Esprit will be for sale in late 2017

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It's hard to see through when it rains. Rearward visibility was the same reason they moved the spoiler up the hatch on the S4 too.


88 Esprit NA, 89 Esprit Turbo SE, Evora, Evora S, Evora IPS, Evora S IPS, Evora S IPS SR, Evora 400, Elise S1, Elise S1 111s, Evora GT410 Sport

Evora NA

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It's hard to see through when it rains. Rearward visibility was the same reason they moved the spoiler up the hatch on the S4 too.

As it says in the Gumball Rally movie "What is behind me is nota my problem"

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It would be interesting to see some real numbers from the factory.... I know the elite of the period of my 77 S1 esprit had lower drag...

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The cd figures for the Stevens 89 Esprit were published in the book "Driving Ambition" about the design of the McLaren F1. IIRC, the Esprit had the best figures for any of the cars that McLaren used for comparison...

However, I'm pretty sure that the aerodynamics of the later cars without the glass back, are superior to the glass back early SE's. I performed a simple CFD study on all of the Esprit shapes (SE, S4, X180-R, Sport 300, 97 V8, 98 V8, and Sport 350) and the SE with the glass back had poor separation of flow at the top of the glass on the hatch, due to the curvature change. That would have caused drag... The later cars without the glass had a recirculation zone that kept the flow attached, up the the wing. The higher wings were generally better situated withing the smooth flow. It was easy to see why Lotus progressed from glass back to notch back, to high wing...

To see what I am talking about you only have to look at the Kamm Tail design, which results in reduced drag for a chopped off tail, as opposed to a rounded body.

http://en.wikipedia.org/wiki/Kamm_tail

Or compare the half sphere to the fully round sphere.

200px-14ilf1l.svg.png


Travis

Vulcan Grey 89SE

My Lotus Photo and Projects Album

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From the book "Driving Ambition" about the McLaren F1, and Peter Steven's personal notes about the Esprit SE

Esprit SE

frontal area A= 1.68m^2

Cd = .336

CdA= .565

G-Esprit

A= 1.70m^2

Cd = .424

CdA = .721

just out of interest

McLaren F1

A=1.62m^2

Cd = .33

CdA=.535

Of McLaren' comparison cars, the Stevens Esprit was second only to the McLaren F1 (at the time)...

Well actually the Opel Calibra was better with a super low Cd of .280 and a CDA of .543


Travis

Vulcan Grey 89SE

My Lotus Photo and Projects Album

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Does this explain why Stevens Esprit's feel so stable at high speeds?


Amateurs built the Ark

Professionals built the Titanic

"I haven't ridden in cars pulled by cows before" "Bullocks, Mr.Belcher" "No, I haven't, honestly"

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no... cd relates to drag and top speed with a given power, not so much to stability. Big wings would aid stability, but also add drag and slow top speed.

So a slippery car would generally have less stability.

http://en.wikipedia.org/wiki/Automobile_drag_coefficient

Though that Wiki article lists the Esprit SE CdA a little high at .595m2, while Peter Steven's personal notes listed it at .565m2.

The wing on the early Stevens SE is not very functional, since it is too low and in turbulent air. The rake and wedge shape probably does ok with front lift, though not great above 140mph on an SE with no rubber air dam. The '91 X180-R feels much better at speed, with more rake, lower suspension, a deep air dam, and a high rear wing placed farther back.


Travis

Vulcan Grey 89SE

My Lotus Photo and Projects Album

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According to 'Lotus Since the 70s' by Graham Robson the drag coefficient of the G was 0,34 and the Stephens 0.35 (making the comparison that although the new car looked more 'streamlined' it was actually less so.

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Out of curiosity, have there been any significant examples of automotive "wings" employing the aviation world's known drag reduction effect of "winglets?" Not just flat right angled end plates, but the real deal compound curve aircraft airfoil type wingtip extensions.

winglet.jpg

To some extent my Esprit makes use of this design, though in an inverted manner.


Being second is to be the first of the ones who lose.

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That doesn't agree with Peter Steven's notes in Driving Ambition...

Though the cd figure is fairly meaningless without the frontal area (A). And then even then, drag due to frontal area alone is only part of the story... There is also drag caused by the spoiler, and the shape of the rear of the car, and whether the air under the car is effectively accelerated back into the main flow with or without a diffuser... It all adds drag.


Travis

Vulcan Grey 89SE

My Lotus Photo and Projects Album

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I have a Stevens carb turbo, with a glass back, S300 spoiler and S300 front lip I also have the smaller Ford mirror casings, I wonder what this is like? I read the spoiler is functional at 120mph+ I would think the Thompson revamped cars are more slippery.

I know the Sierra Cosworth had a big wing to aid its stability in cross winds.


Amateurs built the Ark

Professionals built the Titanic

"I haven't ridden in cars pulled by cows before" "Bullocks, Mr.Belcher" "No, I haven't, honestly"

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S1 - 0.34 Cd (source Jeremy Walton's book 'Lotus Esprit Mid-engined S1, S2, S3 & Turbo')

S2 - 0.335 Cd (source Jeremy Walton's book 'Lotus Esprit Mid-engined S1, S2, S3 & Turbo' stating this is a MJK quote)

S3 - 0.33 Cd (source Lotus sales literature)

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Out of curiosity, have there been any significant examples of automotive "wings" employing the aviation world's known drag reduction effect of "winglets?" Not just flat right angled end plates, but the real deal compound curve aircraft airfoil type wingtip extensions.

winglet.jpg

To some extent my Esprit makes use of this design, though in an inverted manner.

Yes, of course they did. You mean like this example!

post-4319-0-76437100-1350714354.jpg

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John, to your enjoyment and for curiousity .. see the Alfa-Romeo 'Bat' cars ..

As for the 'stability' effects, you can add a real functional wing, to create more vertical load on the tire patch, but with the given cost of drag, more or less ..that's clear

-but for stability in straighline orientation an simple vertical plate on the car, just like on a plane (see Jaguar old Le-Mans cars) would do the job as well ..without more wheight (in aerodynamical terms of wheight) on the wheels.


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to name the things if I see them, that's what I call integrity..

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as a additional note, to Travis allready good informations:

the ones with fog lights instead of brake/cooling ducts in the front will be more efficient, as for less internal flow and ventilation drag


*********************************************************************

to name the things if I see them, that's what I call integrity..

*********************************************************************

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