Emira vs Elite

[richardw]

I recently saw on Facebook a picture of Peter Russell’s Elite next to an Emira, and thought how comparatively small his Elite looked. So, having a few idle minutes this afternoon, I did a quick comparison of the main dimensions:

Overall length
Emira: 173.7”
Elite: 175.5”

Width:
Emira: 74.6”
Elite: 71.5”

Wheelbase
Emira: 101.3”
Elite: 97.8”

Height
Emira: 48.2”
Elite: 47.5”

Kerb weight
Emira (V6): 3097lb
Elite: 2450-2550lb

Drag coefficient
Emira: Cd 34.9
Elite: Cd 30.0

So, apart from overall length, the Elite (and by extension the Eclat and Excel) are a little smaller than the Emira, lighter in weight, and more slippery!

Cheers, Richard

[TonyL]

& the biggest difference of all:

Wheel diameter
Emira: 20"
Elite: 14"

[bash]

I bet the difference in insurance and road tax is huge too.
Bash

[Alan_M]

Wow, didn’t expect Emira to be higher.

[rbgosling]

I'm quite shocked that, with all the advances in wind tunnel and CFD simulation in the last 50 years, that the Cd for the newer car is so much worse! Is this due to the need to create greater downforce, or just the impact of fashion over-ruling engineering (which would have ACBC turning in his grave)?

[Lotus-e-Clan]

It's the cDA that really counts. The Emira body design relies somewhat on porosity which helps reduce the frontal area factor A. The cd is a coefficient of surface slipperiness. Big SUVs can have a very low cd but the huge frontal area (A) destroys the advantage.

[richardw]

It's the cDA that really counts. The Emira body design relies somewhat on porosity which helps reduce the frontal area factor A. The cd is a coefficient of surface slipperiness. Big SUVs can have a very low cd but the huge frontal area (A) destroys the advantage.

That’s right Peter - I’d be interested to know what the CdA for the Emira actually is. Based on the vehicle’s dimensions, frontal area should be greater than the Elite but then, as you say, you would need to factor in ‘porosity.’ But then the Elite has an element of porosity - part of the airflow over the engine is directed through the central chassis box section to escape in the rear brake/differential area.

Just for interest, here is the Elite aerodynamics information from the press release pack:



Cheers, Richard

[richardw]

I'm quite shocked that, with all the advances in wind tunnel and CFD simulation in the last 50 years, that the Cd for the newer car is so much worse! Is this due to the need to create greater downforce, or just the impact of fashion over-ruling engineering (which would have ACBC turning in his grave)?

Oliver used to complain about heavily sculpted modern car designs - he called them ‘just bloody dents’ and stressed how important smooth surfaces were to uninterrupted airflow. Whether he would have made the same comments about the Emira I don’t know! I do believe that even the original Elise had a Cd in the same region as the Emira, but of course the frontal area was lower.

Cheers, Richard

[phoenix]

Cars these days seem to have got fat and bulging for dare I say it, no reason. As one person put it, Chapman would be rolling in his grave. More so elegant today, that’s why I love the pure sleek lines of the Lotus Wedges.

[Marten]

It's the cDA that really counts. The Emira body design relies somewhat on porosity which helps reduce the frontal area factor A. The cd is a coefficient of surface slipperiness. Big SUVs can have a very low cd but the huge frontal area (A) destroys the advantage.

That’s right Peter - I’d be interested to know what the CdA for the Emira actually is. Based on the vehicle’s dimensions, frontal area should be greater than the Elite but then, as you say, you would need to factor in ‘porosity.’

Nope. The 'porosity' hides in the Cd. You measure the force on the body in the windtunnel, divide by area of the silhouette and that's your Cd

[Lotus-e-Clan]

It's the cDA that really counts. The Emira body design relies somewhat on porosity which helps reduce the frontal area factor A. The cd is a coefficient of surface slipperiness. Big SUVs can have a very low cd but the huge frontal area (A) destroys the advantage.

That’s right Peter - I’d be interested to know what the CdA for the Emira actually is. Based on the vehicle’s dimensions, frontal area should be greater than the Elite but then, as you say, you would need to factor in ‘porosity.’

Nope. The 'porosity' hides in the Cd. You measure the force on the body in the windtunnel, divide by area of the silhouette and that's your Cd

So the porosity reduces the impact of silhouette area (A) and makes the published Cd for Emira look better than it would have been if the silhouette was actually solid? Or the porosity is baked into the Cd making the Cd worse than it could be?
Which renders the Cd (as a coefficient) a useless parameter for comparison purposes without considering silhouette frontal area A.
A tall, fat, blunt, non-porus SUV will always produce a lower Cd for the same air resistance measured in the tunnel as a small roughly surfaced wedge offering the same total air resistance. i.e. the Cd is used as a marketing tool and is only really useful to compare small wedges with small wedges with identical frontal silhouettes and big SUVs with big SUVs with identical frontal silhouettes. Or you can use the Cd to assess how much effort the designer has applied to the surfaces to reduced the impact of the frontal silhouette.
They should be made to publish actual wind resistance numbers and not try to hood-wink the punter.

[Marten]

A tall, fat, blunt, non-porus SUV will always produce a lower Cd for the same air resistance measured in the tunnel as a small roughly surfaced wedge offering the same total air resistance. i.e. the Cd is used as a marketing tool and is only really useful to compare small wedges with small wedges with identical frontal silhouettes and big SUVs with big SUVs with identical frontal silhouettes. Or you can use the Cd to assess how much effort the designer has applied to the surfaces to reduced the impact of the frontal silhouette.
They should be made to publish actual wind resistance numbers and not try to hood-wink the punter.

Cd tells you how much effort was taken to get an aerodynamic shape, but if you want to take a guess of the CdA topspeed vs engine power tells you more. But as with any spec, if it can be distorted for marketing it will happen. The most blatant I've come across was a Belgian bus manufacturer. The formula for resistance is something like 0.5 Cd*A* Rho *V^2. So the manufacturer quoted 0.5 * Cd, making his product twice as good .

[moriniman]

The Elite Cd figure was calculated from a drag force measured in an old static floor wind tunnel and without the wheels turning. Even if it had a propper boundry layer extraction duct (for example, the old MIRA tunnel didn't) the drag force will be significantly below what you'd get in a modern tunnel. So you really can't compare historic Cd figures.

It was really nice to see drag horsepower figures in Oliver Winterbottom's 'A Life in Car Design'.

[richardw]

It was really nice to see drag horsepower figures in Oliver Winterbottom's 'A Life in Car Design'.

Agreed - but the drag horsepower figures were also published in the Elite press pack document pictured earlier in this thread.

Cheers, Richard