Longtail vs. Shorttail

[NewyorkKopter]

Hey, what are the advantages/disadvantages of a long-tail or a short tail car? Doesnt a longer tail give you more stability at high speeds like the Porsche 917 LH that went over 240, but then the McLaren F1 which barely has a tail at all does about the same 241 mph. thnks

[beef_bourito]

i believe you're right when you say that but just having a long tail wont necessarily give you better stability, it's all about overall aerodynamics. with a longer car you can make the air change more slowly and therefore flow better and give you more stability. a shorter car will make theair change directions more quickly and make resistances and vacuums and such. what i said may be incorrect, this is just the hypothesis that i came up in the 3 minutes that i wrote this post in.

[curtis73]

I hope this thread really takes off. I'm CLUELESS about aerodynamics.

[CBFryman]

it depends on how the vehicle was designed, there are other ways to get high speed stability besides elongating the body...
im no fluid dynamics expert and i wasnt on the design team of either vehicle so i couldnt give you a good explanation.

[Black Lotus]

2 effects that I know of.
--Lower Cd, due to a more streamlined shape.
--Better high speed stability, as the lateral area is shifted further aft, with the possibility that the center of pressure can be behind the neutral-steer-point of the vehicle. I.E., in a crosswind, the car can be designed to steer by itself into the wind, helping the driver. Usually you want the driver to provide all of the "trimming" necessary to keep the car going straight down the road, but LeMans had 3 different places where the 917 was exceeding 200 MPH (and this was at night, too) sooo....
Modern cars have much better and more sophisticated aerodynamics than the 917. People know so much more nowadays, and the knowledge just keeps accumulating. Ground effects weren't even thought of back then. If the car started to lift and get squirrely down the straight, they tacked some wings, tabs, or fins on if the rules allowed, and hoped that that would hold the thing on the ground. The original 917 was an aerodynamic disaster when it first came out. Nobody wanted to drive it. Porsche then fixed it, but only just enough to do the job.

[Moppie]

There are some AWSOME posts somewhere, most likely in the AF archive about aerodynamics.
Search for post by Texan and Fritz269, both automotive internet gods.

[NewyorkKopter]

lol tru, the 917 isnt aerodynamic but like in general for top speeds long tails are better right? because the 917 LH hit 241 while the 917K was doing like 230. I would use the 962 as an example buts its top speed figures are unknown to me so yea. i always thought that in general a elongated tail will give you more stability at high speeds, although I prefer short-tails like the 787B, McLaren F1, etc.

[Black Lotus]

Originally Posted by NewyorkKopter

but like in general for top speeds long tails are better right?

Pretty much, yup.

[NewyorkKopter]

got it

[NewyorkKopter]

are there any circuit racing advantages of a short-tail??

[Ridenour]

Originally Posted by NewyorkKopter

are there any circuit racing advantages of a short-tail??

Yeh with a shorter body / wheelbase, it probably would result in quicker / more nuetral handling.

[NewyorkKopter]

oo so its like

Short Tail: Provides more neutral precise steering at the cost of high speed stability

Long Tail: Provides more high speed stability at the cost of steering response


also is this why the 787B had a really short tail, while the Venturis underneath stuck out more. did that give it a long-tail like effect??

[2.2 Straight six]

i think the reason for that sticking out more is because of the rear drivetrain, you see with the engine in the middle you often have the driveshafts exiting the gearbox casing in the middle, like there's the bellhousing where it "joins" the engine then between that and the end of the gearbox there's the drive shatfs, its complicated how the mechanics inside the gearboxes work on this kind of application.

so the diffuser there is placed im pretty much the same place, and appears the same size as a long tail's one

its like, for example (and this is only an example, apart from the mclaren F1 i dont think this has happened) two cars use the same chassis, same engine an gearbox, drive shafts in the same place same length etc.. now the engineers cut part of the body work off an longtail, and make a short tail, but want the same size diffuser, hence it sticking out from the tail of the car.

i hope that makes some sense, if not tell/pm me an i'll sorta draw you an explaination of what my jumble of words is meant to mean.

its like the diffuser is the same size, it only sticks out because one's with a longtail cover it up.

[NewyorkKopter]

O yea I forgot, because the gearbox if not wrapped around with venturi's would be sticking out from the back of the car because the 787b has a really short tail. So they probably extended the diffuser to equal the length of a longtail's diffuser to get that high speed stability and the short-tails agility