Cd and frontal area of an Elan

[jcocking]

I was working (ok playing) with one of the programs that compares car
performance. The program asked for the Cd and frontal area. Has anyone
ever seen these numbers published for an Elan? If so, where and what were
they.

The program is Car Test and can be downloaded at
http://home.earthlink.net/~patglenn/ct.html

tia

jeff

[paul_adamson]

----- Original Message ----- > From: "Jeff Cocking" <[email protected]>

I have seem CD and Cda figures quoted for the Europa and possibly also for
the Elan
I think they were in one of the Brooklands portfolio books
(You know the ones, with reprints of magazine articles from the 1960's)

I'll have a look and (if I find them), let you know.....

Paul Adamson

-o^o-?

[lotustony]

I don't remember seeing drag coefficient figures for Elan but it is often
repeated that the original Elite had an astonishing ratio of .29! Costin is
supposed to have tweaked the final design but I've always wondered if this
.29 figure was based on anything more substantial than vivid imagination.
Tony Clark - Sherman, TEXAS
five slippery Lotus cars
Eleven S1 - Elite S1 - Elan S1 - 23B - 51A
[email protected]

[jcocking]

I have found the following to date:

CDa (frontal area):
S1-3 => 14.0 sq. ft.
S4 => 14.1 sq. ft. (bigger tires and fenders)
+2 => 16.6 sq. ft.

Gs
+2 => 0.757g

Cd
Have not found anything. An early Miata (Eunos or MX-5) has a Cd of 0.380.
It is as close as a car I could find, that is similar in nature.

If anyone has any other info, please forward on.

thanks

jeff

*-----Original Message-----
*From: Tony Clark [mailto:[email protected]]
*Sent: Thursday, August 12, 1999 1:56 PM
*To: [email protected]
*Subject: Re: [lotuselan] Cd and frontal area of an Elan
*
*
*From: "Tony Clark" <[email protected]>
*
*I don't remember seeing drag coefficient figures for Elan but it is often
*repeated that the original Elite had an astonishing ratio of .29!
*Costin is
*supposed to have tweaked the final design but I've always wondered if this
*.29 figure was based on anything more substantial than vivid imagination.
*Tony Clark - Sherman, TEXAS
*five slippery Lotus cars
*Eleven S1 - Elite S1 - Elan S1 - 23B - 51A
*[email protected]
*
*
*
*
*
*
*ONElist: home to the world's liveliest email communities.
*
*------------------------------------------------------------------------
*
*
*

[BrianMartley]

Hi all,

I have the Alan Staniforth "Race & Rally Car Sourcebook" which goes into
predicted performances, although it's a bit dated these days. He calculates
performance using basic formula derived fluid dynamics and verifies from
info on other cars of the period. The calculation shows the original Elite
to have a Cd of 0.345, reasonable I would have thought. Dennis Ortenburger
quotes 0.29, but this was for the Costin modified version - smaller front
intake, steeper windscreen, undertray, flush side windows, etc. So 0.345 for
a genuine road car seems about right. The Europa is often quoted as 0.3, but
I've seen mention that figure was obtained on the S1 with an extension over
the rear deck.

Anyway, using the basic info from road tests this gives a Cd figure of
around 0.45 on the calculated 14sq ft frontal area. Could get worse if the
engine outputs on the road-test models were tweaked. Disappointed ? Well the
E-Type Jag is often quoted at 0.44 for the S1, so I'll bet it's not too far
out. Underneath the Elan isn't that smooth and it doesn't have the modern
tweaks of flush windows, recessed door handles, windscreen wipers, etc, etc.

The Costin book - "Flying on Four Wheels" (Costin fans only) gives an
insight into how his mind worked and the early developments with Lotus, etc.
He points out that Cd is only part of the equation - frontal area is more
important as is the centres of pressure developed as something moves down
the road. Which I guess is one reason why the Elan, Elite were all tiny by
comparison to todays cars - MX5, etc.

Brian

[ozone.breath]

Brian Martley wrote:


I used a wild guess of:
Cd = 0.4
Cda = 14 sq. ft.
Ta = 70.00 degrees F
Pa = 30.00 inches Hg

and plugged in 150MPH for grins, into Bowlings Aerodynamic HP Calculator at:

http://www.bestintexas.com/cars/calculate/aero.html

The result was 157 rear wheel HP, which would correspond to about 185
flywheel horsepower. Wow. Gulp.

Comments, anyone?

Regards,
Erik Berg
Los Angeles

[rodbean]

"Erik V. Berg" wrote:


Flashback to one time at a vintage race at Riverside when I qualified the Elan
on the pole against tough competition, then, sort of routinely, had the rear
wheel horsepower checked by Dave Evans' mobile chassis dyno only to find that
the car, supposedly with about 175 hp at the flywheel, had only 105 to the rear
wheels! Turns out the head gasket had been leaking slightly under load for a
long time. He told me (not for publication) what another well-known Elan was
getting and I nearly fainted. I couldn't wait to fix the head gasket problem
but it made me love the Elan all the more for being so good even without a lot
of horsepower.

Rod

[JKING]

"Erik V. Berg" <[email protected] wrote:


Seems high.
Just running the numbers out long-hand:
Standard air density (ro) - .076 lb/cu ft
Acceleration of gravity (g) = 32.2 ft/sec sq
Conversion MPH to ft/sec = 5280/3600 = 1.467
Dynamic head (q) at 150 mph (V) = ro x V sq / 2 x g =
.076 x (150 x 1.467)sq / 64.4 = 57.1 lb/cu ft
Therefore at at 150 mph, using Cd = .4, and frontal area(Af) = 14 sqft
Drag force (Fd) = Cd x Af x q = .4 x 14 x 57.1 = 320.0 lbs
Work = Fd x V = 320 x (150 x 1.467) = 70417 ft-lb/sec
1 HP = 550 ft-lb/sec
Therefore the HP needed to propel the car at 150 mph = 70417/550 = 128 hp.
This number would ratio directly as Cf, i.e. a Cf of .45 would yield 144 hp.

There is, of course, no consideration of rolling resistance or any other
efficiency loss considered here.
J King S1
Pacific Grove, California

[ozone.breath]

I speculated:

J. King replied:

Thanks J., and actually I am impressed by how well your calculation agrees
with Bowling's algorithm. Aero Horsepower was 126, and rolling resistance
was 31, according to Bowling's page. Total was 157hp. I think this is a
pretty good validation of Bowling's aero equations!

185hp does seem pretty high though, and I think I may have made an
error in my assumptions. See if you agree? I believe I double booked the
rolling resistance, which is a substantial part of the loss hp difference
between engine dyno readings compared to chassis dyno readings.

Driveline losses might be 70% rolling resistance and 30% gear losses, and
I think I counted the rolling resistance portion twice.

I'm going to guess that gear losses would only be 13hp, and so the total
would then be:

126 + 31 + 13 = 170hp total

If the Cd is really 0.45, then the total would be 188hp.

Regards,
Erik Berg
Los Angeles

[BrianMartley]

Hi all,

I know this is an old topic, but I don't recall a definitive answer (unless
I just plain missed it).

Anyway I've just been looking up some info, and came across the original
press release for the Europa, dated 1966. It says "The drag factor of 0.3
(Elan 0.35) was originally 0.34 until...".

Sounds a bit optimistic, but it looks like Lotus were claiming 0.35 for the
1966 Elan - maybe the fhc model ?

Brian

[melvinhecht]

BTW, There's an s2 Europa unassembled with a rebuild engine for sale near
Baltimore, if anyone cares