14 replies to this topic

[soubriquet]

I have always loved the shape of the C-Type and D-Type Jaguars, but I know little of their technicalities. One thing I would like to know about is the purpose of the vertical fin on the D-Types. I am not aware of any similar feature on contemporary competitors.

Did the fin actually serve any useful purpose? Did they evolve during the competitive life of the cars? Does anyone care?

Cheers

[Ray Bell]

I have read that the fin-like rear mudguards of the early Lotus Sports Cars was to help create understeer (flavour of the month in the fifties...), something to do with air pressure on the rear of the car.

But the D-type, I suspect, had it more as a straight line aerodynamic appendage for the long Le Mans straights.

[soubriquet]

Thanks Ray. That begs the question, was there a vestigial fin/no-fin option for circuits-other-than-Le Mans?

And yes, I had forgotten about the Loti. I like them too, but at risk of my life, they lack that essential aesthetic ingredient, the Jaguarness of the Jags. IMHO.

[xkssFrankOpalka]

Fins, my XKSS didnt have one of course. I have heard the thoery is it moves the center of pressure towards the rear on a side wind. This moves the back end of the car and allows the driver to correct by steering into it. Fact or fiction? who knows.

[soubriquet]

Thanks Frank, or should I call you xk? I suppose moving the centre of pressure back would have helped counteract the aerodynamic lift of the front at speed. If so, why didn't other manufacturers follow suit?

[Garagiste]

I'm sure I've seen D-types without the fin and / or various configurations of it.
Frank - do / did you have a genuine XKSS? My absolute all time dream road car, I'm really very jealous!

[Holger Merten]

Ohhh, I thought you are talking about the Auto Union Typ D (and I could learn something about the streamlined body), but it's only Jaguar?

[Roger Clark]

Preesumably the tail fin has the same effect as feathers on an arrow, or the tail fin on an aircraft. they move the centre of pressure towards the rear and so improve straight line stability.

[TEJ]

It is a basic engineering principle. If the centre of pressure is aft of the centre of gravity (in a car as viewed from the side) then in yaw (when the car starts to rotate around its verticle axis), air pressure on the side of the car tends to straighten the path. In contrast, if the centre of pressure was forward of the centre of gravity, yaw would cause immediate swapping of ends.
I know this because of a testing accident with one of my cars which swapped ends at full chat after cresting Deers Leap at the old Westwood circuit. Feathers on an arrow and Airplane tail fins do indeed offer this function.

Interestly, modern fighter aircraft tend away from having this directional stability to allow then to change direction more quickly. The result is that the pilots need computers to help fly them as a man cannot react quickly enough.

[oldtimer]

Originally posted by Holger Merten
Ohhh, I thought you are talking about the Auto Union Typ D (and I could learn something about the streamlined body), but it's only Jaguar?

But Holger, the D-type is a real Jaguar.

[Holger Merten]

Oldtimer, yes drove a XJS froma friend for some month. And enjoyed it. I like Jaguar.... but D-type? There I prefer the AU.

[xkssFrankOpalka]

Yes, my XKSS was a real one, it was the last one made #769. They were renumbered D types with 700 series numbers instead of 500 series of the D types. When Jaguar had some D types left and were not selling well, Mr. Lyons had bumpers and windshields put on them and sold them for $5600 to clear the stock. I had mine 20 yrs, extremely exciting to drive.

[xkssFrankOpalka]

TEJ, your very correct, its a matter of yaw and center of pressure. Thanks.

[D-Type]

All very interesting.

Several other fifties sports cars had fins. From memory: Phil Hill's Ferrari in the Carrera Panamericana, the Ecurie Ecosse Tojeiro-Jag, the Cunningham C6R (I think), the Bristol 450 coupe had twin fins.

Also the '57 and '58 Indianapolis winning Belond AP Specials.

Most D-Types didn't have fins they just had a headrest. In Touch Wood, Duncan Hamilton mentions removing the fin from one of his cars but doesn't say why.

Regarding aerodynamic underteer, there was a thread on this either here or on the Technical Forum a month or two ago. I think the theme was that as the tail went out in a drift the air pressure would tend to straighten the car out.

[scags]

extremely exicting to drive, I'm sure! One of my friend's father's had a XK-SS in the garage from the mid- sixties to the late eighties, in Teaneck, NJ. Unfortunatly, it wasn't running, but it looked great, and I think he did alright when he sold it....