Useless "Ducktail spoiler" on Guigiaro cars

[GTK]

 

Just read a snippet from an interesting feature in Evo mag from 2005 that compares an Esprit Turbo with an Exige 240R. Roger Becker is quoted so:

          "Chapman totally believed in Giugiaro's design for the Esprit Turbo, despite the shape being based on what Giugiaro thought looked right rather than hard wind tunnel data. Chapman said that we couldn't mess with the shape, even though we discovered that the ducktail spoiler destroyed the balance and stability. [...] if you look at the engine louvres you'll see that the top one has a small Gurney flap, which stalls the air before it reaches the ducktail. We couldn't remove it but no one said we couldn't render it useless."

I've been intrigued by the aerodynamics of the Esprit ever since I saw one, the idea that so much less was known at the time of the Esprit's design and that the rather decent C_d of the G car seems largely serendipitous. Looking at a modern Audi saloon with a C_d of .26 and comparing with the Esprit's .32 (or .34, the interweb is conflicted), how much of the latter is dialled in, how much is intentional drag, can drag be reduced in proportion to a vehicles weight?

What do we know about the Giugiaro car's aerodynamics? (Aside from the S2's front spoiler being an improvement on the S1's). I'd love to know at what point that Gurney flap comes into play?

George 

[Bazza 907]

George

Can't help on the speed at which the flap (ridge) comes into play but the red Esprit that was being used in that photo shoot (loaned by Paul Matty) has just been refurbished and sold by Bell & Colvill.

 

 

[JayEmm]

I read that recently too. I am quite interested because if you look at the side profile of the Ferrari 355, that has a similar spoiler at the back - and that was very much essential on that car. However, the 355 has all sorts of under-body aero going on, which I doubt the Esprit does.

[Bibs]

The Esprit is pretty much completely flat underneath with NACA ducts for air ingress into the engine bay. 

[JayEmm]

Interesting. I wonder what's so fundamentally "right" about this:

But "wrong" about this?

I'm no aerodynamacist but those two side profiles look extremely similar to me. Amazing given the fact the 355 is a much newer car and Ferrari no doubt did a lot of time in a wind tunnel. Okay, both of them can trace their design heritage to the 70s but I' interested to know more about the Esprits "problem" nonetheless.

The only major difference I am aware of is the Ferrari has a flat engine bay cover, where the esprit has the louvres. Now, the later Esprits also had a flat engine bay cover... a clue perhaps?

[Barrykearley]

The mr2 with a body kit looks nice !!

[GTK]

Hahaha! I can count on a high brow convo in here. I like it too Buddsy, it's very nice  and put the claws away Barry (355 does look a bit Noddy though)

I reckon what Mr. Becker was getting at was that the Gurney flap effectively means that everything aft of it is of much less concern. As I understand it, the gurney flap interrupts the air flow over the car which creates eddies directly behind it (the flap) so now instead of the airflow hugging the tailgate and running down and over the ducktail, it's held up off the car and misses both the louvres/flat tailgate and spoiler which are buffered by low pressure.

So a flat tailgate or louvres, or even if it was an uncovered tailgate, relative to the gurney flap it may not matter at all? This is the stuff I'd love to know about. I'd get my nerd on in a wind tunnel. With smokey sticks and such.

There aren't knacker ducts under my S2 are there!? 

Edit: I didn't realise the Turbo had a bigger rear spoiler than the earlier cars until I saw the above photo. So maybe it's not a factor on them. That plus they don't do 150mph?

[Andyww]

If you look at the airflow design of the G Turbo it seems they were putting engine bay cooling at the top of the priority list. The undertray has an upward slope on the rear edge of it. Air comes in through the ducts and the rear edge directs it upwards through the engine bay. The undertray extends to just behind the sill ducts.

So this airflow is only going to work if the air can escape through the louvres. The Gurney flap would likely help with pushing air flowing over the top of the car upwards to allow room for the louvre air to escape.

Overall aero probably came second to the necessity of dealing with a turbo engine encased in a small fibreglass box.

Many people at the time thought Lotus simply made up Cd figures. The Europa had a Lotus figure of 0.29 which nobody who actually tested it could get anywhere close to.  

Here is an example of a pointless spoiler on my 328. Nobody has ever been able to explain any benefit to these spoilers, which were a factory option, other than appearance.

[GTK]

Of course! The only louvres I ever saw in the flesh were on cheesy Escorts and classic Minis so I forgot the Esprit's are actually open. 

Is that spoiler open on the leading edge? Open rear deck on there too, and rear lip is minimal.

[Barrykearley]

my first car was a metro - always wanted a spoiler and louvre like the one above 

[The Pits]

As I understood it the Turbo was the first Lotus road car to be properly wind tunnel tested. The original Giugiaro design had a bigger front chin spoiler which was effective at reducing lift together with the rear ducktail. However the nose was so low it was impractical for road use so they reduced the chin spoiler to where it is today. In order to keep the car aerodynamically balanced the engineers advised getting rid of the rear ducktail but Chapman insisted on keeping it, understanding the importance of styling for his new 'supercar'. The solution was to stall the rear ducktail that we know and love.

I had read about the 'useless' ducktail but it turns out it was too effective!

[GTK]

Ah days gone by, I remember pushing a schoolmates MG Metro of a Friday home time Barry. My first road cars were Minis and I thought the louvred rear window cover was naff, but I have nostalgia for the '80's now and still have one Mini left

The whole area of fluid dynamics is amazing. The bottom, rails and fins of a surf board are just as tweaked as the body of a car these days for flow and drag characteristics. That bulbous protrusion you see under the bow when a ship is high in the water reduces resistance on the hull and gives significant reductions in fuel consumption.

I'd love to see an early Esprit in a wind tunnel, see whether the figures quotes by Lotus tally, but I suppose if the Turbo was the first car tested maybe not. There must have been some testing for the S2's revised front. 

 

[Andyww]

10 hours ago, Barrykearley said:

 

my first car was a metro - always wanted a spoiler and louvre like the one above 

80s tuning: Louvres fitted over a window and a bumper sticker marked FAST. Cant beat it

 

[JayEmm]

Sounds like the Countach story. The car was designed to work perfectly well without a rear spoiler, then 1980s fashion basically demanded it. So the engineers thought long and hard how to build a spoiler with absolutely zero downforce! It basically just creates drag, that's it. But it looked cool, so...

[Jenna'sEspritTurbo]

I have a love affair with my G car

[nello]

Aren't the rear louvres more to do with heat extraction than any kind of performance benefit?

Edited June 2, 2016 by nello

[GTK]

On 6/1/2016 at 09:30, Andyww said:

80s tuning: Louvres fitted over a window and a bumper sticker marked FAST. Cant beat it

The only thing that can defeat that kung fu is a front wing shopping list, or if you want to keep it strictly period - a "KEV & STACY" full with windscreen sticker

[Kimbers]

Just spoken to MJK:

"I agree the aerodynamics weren't good, because you mustn't forget that Guigaro was a designer not an aerodynamicist. It was about the Aesthetics not the drag factor, especially with the original car (S1). It's also true that Colin didn't want to change it's base design for the models that came after the S1 because that was what made it a success and different. What we did manage to do with the later models (S2/3 and Turbo) was add to the base design and add things that "helped" the Aerodynamics, like the front Spoiler. But also we added bits that were needed to keep it current, the spoiler, sills, etc. That was what was "in at the time". So when you ask why did we add this or that there can be several reasons dependant on what part it is."

I then asked him about Rogers comments: "Totally true. The back end was all over the place, the rear spoiler spoiled the stability, but that was what was required to look "modern" so we fitted a Flap that basically broke the air up before it got to the spoiler basically negating it's effect"

Dad's going to see Roger tonight and said he would chat to him about it and see if any other info can be remembered.

Here's proof that the original design did get Wind tunnelled, the original wind tunnel model:

 

[Bibs]

I remember seeing that at CC back in 2007...

[The Pits]

Good stuff but still quite a difference between wind tunnel testing a model and the full sized car.

[Bibs]

100% and then some! 

[Andyww]

On the subject of airflow, a great upgrade on a G car is to fit the Stevens window frame secondary seals. These reduce wind noise by a large amount.

[GTK]

I'm just home from seeing a new flame off on an unexpected three month trip that cut short a romance that had promise, sufficed to say I've been in better spirits. I've cracked a beer from the cool box here in Athens, and bummed a smoke (I haven't smoked in years) and was about to have a good time feeling sorry for myself when I find a message from one of the creators of a car I'm passionate about and ... well things aren't so bad

slainte TLF, MJK and the rest o'you.

Ah f&*k how'm I gonna light this thing!?

[Tocus]

 

thats why this is made, just because Colin Chapman wanted the ducktall spoiler so badly, and the car was very bad inside the wind-tunnel without this louver spoiler...

[pyropolymer]

On 5/31/2016 at 09:40, Andyww said:

If you look at the airflow design of the G Turbo it seems they were putting engine bay cooling at the top of the priority list. The undertray has an upward slope on the rear edge of it. Air comes in through the ducts and the rear edge directs it upwards through the engine bay. The undertray extends to just behind the sill ducts.

So this airflow is only going to work if the air can escape through the louvres. The Gurney flap would likely help with pushing air flowing over the top of the car upwards to allow room for the louvre air to escape.

Overall aero probably came second to the necessity of dealing with a turbo engine encased in a small fibreglass box.

Many people at the time thought Lotus simply made up Cd figures. The Europa had a Lotus figure of 0.29 which nobody who actually tested it could get anywhere close to.  

Here is an example of a pointless spoiler on my 328. Nobody has ever been able to explain any benefit to these spoilers, which were a factory option, other than appearance.

i wouldnt be so sure that 308 airfoil was pointless... just because the ferrari didnt explain its function dosent mean it didnt work (big debate on fchat).

 

pinninfarina built a new wind tunnel in the late 60's. the 74 boxer was the first production fcar to be extensively tested have one of these roof airfoils.  in 77 a car called the aerodynimico based on the 308gtb was unveil in geneva featuring many areo add-on also  had this roof airfoil.  many of these features ended up on the 308qvs and 288gto.

 

was it a fad or a styling gimmick? most likely yes. did it worked? most likely yes.  many station wagons had similar airfoils to guide the are around the back-light as well as rallye cars right up to the modern ages that were wind tunnel developed.  

 

lotus did have a habit of posting all sorts of numbers and spec that nobody can ever replicate back then.  if its anywhere near .32 cd its still amongst the slipperiest car of the 70's.  porsche 924 and the Renault Fuego went to great lengths to boast to the public when they got their cars down to .32-.35 cd