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Spitfire GT6 and Spitfire aerodynamic drag coefficient

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Beavis

Beavis

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I own an MkII GT6 and I've never been able to find any hard data on its drag coefficient. I'm interested in this number since I'm building an electric car out of it, and aerodynamics are the single largest energy eater it will face. With less power needed to go a certain speed, cruising range gets extended.

Anyway, I've heard from others that the per Mk III GT6 has a coefficient drag of .32. Does this at all seem accurate?

One must keep in mind that the MkIV Spitfire, which is a convertable and inherently will not have as good aerodynamics as a coupe, has a .42 Cd according to this page:

https://www.teknett.com/pwp/drmayf/triumph.htm

Given that number, .32 doesn't seem that unreasonable since it is not a convertable. However, I found a simulation of a GT6 MkI being run that had the Cd at .47, this not being hard data:

https://64.233.179.104/search?q=cache:Qdz..."GT6"&hl=en

Any aerodynamic data on the Mk I and Mk II GT6, and out of curiousity, the Mk I, II, and III Spitfires?

I'd really love to know. Thanks.
 
I can't help you with the GT6 coefficient, but I once saw a table for different cars which listed the coefficient for an E-type Jag (with the top down) being higher than for a VW bus. :>0

Warren
 
That doesn't surprise me about the E-Type, considering its top was down. A car with its top down or windows open could have its coefficient drag increased to .5 or .6.

I guess the figure that I'm looking for is unpublished? Any resources someone here could point me to?

The only figures I could find were by word of mouth, where neither of those stating .32 could remember where they read it from.

With a .32 coefficient drag, putting on a LeMans bonnet would lower that to like a .30. Covering the grille(No need for a huge amount of cool air for an electric motor), making a full smooth underbelly, taping up any seams, shaving the door handles down, removing the antenna, and covering the top third of the rear wheel wells, assuming that .32 is a real figure and the bonnet reduces it to .30, could potentially be reduced to about .26 or so, making this car very efficient.

Of course, I can't know for sure if no one knows the figure. /ubbthreads/images/graemlins/frown.gif
 
Anyone know of any books that may have this figure published? Any people I could email that might know it? If no one here knows it, it could be beneficial to find out. I've always figured racers with race-modded Spits and GT6s have known this figure.
 
Still haven't found the figure, but from a fellow LBC enthusiast at my university, I heard that .32 figure again, with no reference of where it came from that could be recalled.

With .32 stock and the possibility of lowering that to .25 or .26 through the techniques I mentioned earlier, such a coefficient drag would allow me to reach about 160 MPH or so at motor redline with 14 inch wheel rims on 185/70R14 size Nokian NRT2 tires(low rolling resistance + good handling, having a measured .0085 coefficient rolling resistance) with the TR6/s gear ratios and drive axel ratio(TR6 tranny/diff) according to simulation.

An electric powered GT6 theoretically capable of 160 MPH. Imagine that...
 
[ QUOTE ]
I own an MkII GT6 and I've never been able to find any hard data on its drag coefficient. I'm interested in this number since I'm building an electric car out of it, and aerodynamics are the single largest energy eater it will face. With less power needed to go a certain speed, cruising range gets extended.
Any aerodynamic data on the Mk I and Mk II GT6, and out of curiousity, the Mk I, II, and III Spitfires?
I'd really love to know. Thanks.

[/ QUOTE ]
I was also curious about air drag vs H.P. on an actual vehicle. In this case, an RV. You can come quite close by measuring the coast down time between two given speeds. I set up a spread sheet with formulae & plugged in the stop watch times to coast down at various speeds. Transmission in neutral to remove engine drag effects. This has proven to come pretty close to known numbers. I have attached a pic of the spread sheet & typical numbers. You should be able to work back to drag coefficient from there.

There are some dashboard dyno gadgets available that will give similar information & more.
D
 

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I am VERY skeptical of the .32 figure, or .42 for a Spitfire. I remember reading that a 1978 Datsun 510 I once owned had a drag of about .50, and was typical of small family cars of that era.
Since no effort was made to smooth flow beneath the car, no flush headlights or door handles, relatively vertical windshields and so on I think this figure is a misprint or a bad guess. Small frontal area helps reduce overall drag but has no effect on the aero figure.
Note that this is just my opinion, I don't have facts to back it up..
Simon.
 
i seem to remember reading somewhere that the saab sonnett had the best drag coefficient of any production car and (if my memory remembers correctly) the drag coefficient stated was .32. of course like batting averages the difference might be between .322 and .325.
 
Can't be true for the Sonnet. The Lotus Europa AND the Lotus Elite had it beat at .29 for each. Plus there are plenty of Imp cars that had bested the Lotii, even.

I'll keep looking. Any idea what racers who have extensively modified the GT6 have gotten coefficient drag down to? Estimations?
 
The TRUE aero drag coefficient of a vehicle is a very elusive thing. Advertising hype & wishing often substitute for real numbers. A small error in this number can result in a very large error in "required horsepower". Just because it is in vogue with magazine & advertising writers doesn't mean that the numbers quoted are significant.
D
 
The .32 figure rears its head again! Referenced!

Apparently the Spitfire is .39 and GT6 about .32. Should this be the case, this is very good news for me. I'll be able to build a 100+ mile range per charge electric car on inexpensive lead acid batteries and one that will also top 140 mph. Joy!

Posted by Roger Fenton on 4/28/2005, 9:12 pm, in reply to "Re: GT6 and Spitfire aerodynamic drag coefficient"

The aero subject has got my attention especially the GT6. The aero potential is sitting there waiting to be un-tapped. The best books I have come across are Road Vehicle Aerodynamics by AJ Scibor-Rylski, Streamlining and Car Aerodynamics by Jan P. Norbye, HPBooks Aerodynamics for Racing and Performance Cars by Forbes Aird, Competition Downforce by Simon McBeath, Race and Rally Car Source Book by Allan Stanforth and finally Race Car Aerodynamics by Joseph Katz. The most productive book for your needs would be Norbye's book followed by Scibor-Rylski. Scibor takes some hard reading but is a gem of a book. It has lots of math, probably deeper than most racers would venture but is full of pertinent info. As you mentioned there are 3 things you need for speed; more power, small frontal area and smooth bodywork. Looking at existing Cd's for comparison (Spitfire is 0.39) I would guess the GT6 to be around 0.32 which is not bad. Finding Nrobye's book could be a challenge but could be located by searching the web. Your comments are on the right track, you just have to follow the air behaviour all the way to the back, top and bottom. Take out all the bumps such as the gutters, and window molding. Dont forget to add lightness.

https://members.boardhost.com/GT6-Spitfire/msg/10863.html
 
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