Tail aerodynamics?

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rayce13
Posts: 26
Joined: April 13th, 2011, 10:46 am

Tail aerodynamics?

Post by rayce13 »

I have a citation that doesn't have the bottom rear cowling (around trans and back to exhaust end) that I have seen on other cars. I have a generic one that has never been fit to the car and wondering if there is any evidence that having the cowling on is a noticeable benefit vs. running with the bottom half open?
Russ Dykstra
FV '95 Citation #13
FV '93 Citation #31
brian
Posts: 1348
Joined: June 26th, 2006, 12:31 pm

Re: Tail aerodynamics?

Post by brian »

Don't really know if there's any data out there, but common sense indicates that closing up the bottom could help. Many of the vees at the Runoffs have some kind of closure or floor on the rears of the cars. Long tracks like RA promote aero projects. The long tails on CItations, Swift DB-1 and Caracals all have their origins at those kinds of tracks.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
FV80
Site Admin
Posts: 1195
Joined: June 27th, 2006, 9:07 am

Re: Tail aerodynamics?

Post by FV80 »

Russ,
From my (quite limited) experience, closing in the back can sometimes cause MORE trouble than not - with regards to head cooling and aero drag. I built my previous car to be (almost) totally enclosed at the rear. After 2 or so years of efforts to improve head cooling, I finally cut the bottom off the rear. I have to say that I could telll absolutely NO difference on the track .. but my head temps dropped about 25 degrees (not nearly enough, unfortunately).

Just a voice of experience. SEAT TIME is far more important than "improving" (changing) the car :P .

Steve, FV80
The Racer's Wedge and now a Vortech, FV80
billinstuart
Posts: 201
Joined: July 17th, 2006, 8:53 pm

Re: Tail aerodynamics?

Post by billinstuart »

Listen to Steve.

The case is just a big magnesium radiator. The more airflow around it, the better the engine cools. There was a guy who won the runoffs one year..Wayne Moore. Never ran an oil cooler. It took a while to realize that car had excellent airflow around the case and heads.
rayce13
Posts: 26
Joined: April 13th, 2011, 10:46 am

Re: Tail aerodynamics?

Post by rayce13 »

Thanks for the info. Exactly what I was wondering given the work it would take to put it all together.
Russ Dykstra
FV '95 Citation #13
FV '93 Citation #31
maurus97

Re: Tail aerodynamics?

Post by maurus97 »

I run a citation, and I used to wonder the same thing. I spoke with guys who were fast in Citations; some of whom ran a$$ pieces and some of whom didn't. Some swore by them, others didn't. One REALLY fast guy told me they matter pretty much at one track only (Road America)
I had/have one and I used to run it on the car. I don't anymore. So, I really don't know...never seen a citation in a wind tunnel.
But if you're losing sleep thinking about it, take some melatonin. I'm of the belief that on a trailing armed citation (ie not an XTC), the air is already fairly dirty and chopped up well before it reaches the frontal area of the transaxle (ie lower rear of the citation). With whatever bodywork you do [or do not] attach to the back of your citation, just try and be sure that the bodywork itself isn't creating drag or acting as a parachute of sorts. I think that with our cars, the main case to be made for running a lower tail would be to prevent the upper tail piece from slowing the car.

**Disclaimer: Reader acknowledges and agrees that all "information" listed, is worth .02 (non-refundable).
AJP
Posts: 41
Joined: February 20th, 2008, 9:10 pm

Re: Tail aerodynamics?

Post by AJP »

I tried the lower tail at Pocono last year. One session with and the next without.
My data gizmo showed no top speed increase or time to top speed but I did get much higher oil temperatures.

-Andy P.
Rmalcomb
Posts: 4
Joined: July 10th, 2008, 10:34 am

Re: Tail aerodynamics?

Post by Rmalcomb »

I have seen many inclosed tail sections, and from what I have seen they all seem to make the car run Hot. I have heard some people claim that it increases RPM but I do not know this to be a fact. Look at Rick Shields at the Runoffs, his VDF is not the enclosed tail section either.
problemchild
Posts: 901
Joined: June 25th, 2006, 9:34 am

Re: Tail aerodynamics?

Post by problemchild »

The one thing I can guarantee, that if you use an undertail, you will spend a lot of your time cleaning it .... or your car will look really scuzzy. You will have to worry about tech people and grid people seeing all the mess coming out of your engine/tranny compartment, and looking closer. I had a really tight, low oil-consumption engine ..... or so I thought .... until I extended the floor out with a nice white piece of aluminum. Looked like hell after each session. Lasted two sessions. Gone. If you must use an undertail, I would have it dark, certainly the inside surface.
Just a general PITA, IMHO. Not worth the bother!
Greg Rice
"Happy 50th Birthday"
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