Custom ducktail -- input requested

[verticalflight]

We are working on our Rektor build of a high powered longhood with modernized suspension. Link on project here - REKTOR 911 Modernized Hot Rod Build

Planning to add a custom ducktail to the rear. Below is a mock up by Freddie. note the center dip in the tail is exaggerated here vs actual which will be more subtle.

- Is the purpose of the ducktail to create downdraft to increase road stickiness?

- Does the stock ducktail also help with cooling by directing the air into the engine bay? Where does the air exit in that case?

- We think it will look better visually to cut out the section on the underside of the tail so as to not look too blocky. If we cut out that area, and allow for air to exit on the underside, will that defeat the purpose of the downdraft / stickines effect?

[fanaudical]

The ducktail does indeed serve both functions of decreasing rear-end lift at speed and providing more air into the engine bay. Air entering the engine bay exits partially as exhaust but mostly exits below the engine for cooling (the cooling fan blows the air over the cylinder heads and engine case to remove heat).

There are several articles on the function of the ducktail here on the forums.

You absolutely need a sizable air intake on the engine lid somewhere...

[verticalflight]

Just to clarify, we would have a large intake on the topside of the ducktail, now we are just debating if the large long hole area on the underside will reduce the benefits of the tail itself.

[McLaren-TAG]

Something is not adding up on your rendering. How/Where is the air getting into the engine bay I don't really see where the opening is.

From a functional perspective I can't see what you're attempting being anything more than visual, when compared to a duck what you've got is minimal in appearance but it will also be minimal in function. The reason Porsche got rid of the duck was because the whale was better and the tea tray better still.

Looks like you may be going for something along the lines of the Singer stub but that tail lifts at speed, unless you're planning to also be able to lift the tail up at speed, what you've got there is pretty much functionally neutered.

[verticalflight]

Yeah the inlet is missing in the drawing. Good point on the minimal aspect of the tail.

Given all that though, what about the underside hole I was talking about -- we can either keep it or remove it...

[McLaren-TAG]

You wouldn't necessarily need it, i guess I'd need to see the inlet in order to understand the full picture of where you're headed. The tail's primary function was to reduce lift, the fan can suck quite a bit of air on its own.

I know I've seen some threads around here where folks have custom grills, there's an actual mathematical formula for the size of the inlet required.

[RSBob]

Originally Posted by verticalflight

Yeah the inlet is missing in the drawing. Good point on the minimal aspect of the tail.

Given all that though, what about the underside hole I was talking about -- we can either keep it or remove it...

I like it as a visual element but from a functional standpoint it defeats the purpose of the duck - reduced lift by air pressure against the tail as well as funneling air into the engine to increase cooling.

Love the renderings. Great skill.

[SCWDP911]

forgot about this project. thanks of the reminder! beauty

[RocketWrench]

Are you doing those renderings yourself?

[DanielDudley]

You can make the hollow without making the hole, since it is a visual cue. If you really want to know what it does, I would think a wind tunnel test would be in order.

Would it negate low pressure on the backside of the duck ? Intuitively it would seem so, but that is akin to making it up.

[wayner]

Visually one of the things that the duck tail does is interrupt the lines of the car as they flow to the back. The stripes help with that, but if you are looking for visual input, I would be conscious of that aspect.

Other than stripes I am not sure how to better integrate a duck into the lines of a 911, but it is that interruption that always bothered me.

(having said that I like my duck)

The other thing is that form the rear, the duck seems to present a big flat billboard when viewed from a few feet away. (The underside contours disappear and it just looks vertically flat.

That is another aspect that I would try to improve on

I find many times you don't actually have to modify something visually to look a certain was, but instead modify it slightly so that it suggests the new lines to the mind's eye.

This probably wasn't much help but maybe it will give you some ideas.

For me the notch doesn't do it, but I think you are onto something.
The rear vent seems to break up that vertical billboard nicely though.

P.S.
One of the strong styling elements of that car is the flat faced flares.
I wonder if focusing on that aspect while you stand back from the car, if that will give you some perspective on what to do with the tail?

[tirwin]

Just a thought, but what if you combined your idea of the mini ducktail with a motorized 964 so that it moved up at speed and behaved aerodynamically more like the tea tray or whale tail?

[wayner]

...or what about combining that idea so it is a duck at rest, but raises, unfolds and flattens out into a mini whale tail at speed (or on command using a switch for car show party tricks?)


...or vice versa

[75 911s]

I really like your concept. I love the center dip as is. You should make these in carbon fiber. I'd buy one. Has anyone tried a custom aluminum duck? would that be heavier than glass?

[verticalflight]

I really appreciate everyone's input here. Good thoughts and ideas all around! My takeaways are basically:

-- We should keep the hole on the underside visually
-- But not connect it all the way through to the engine (to maintain at least some of the downforce effect of the mini tail)
-- We should see if we can connect the design to the flares and also make it not so blocky from the back

BTW nobody commented on the recessed aspect of the decklid itself, we pushed that part in to make it look like the hood area with its recess...

[verticalflight]

Originally Posted by 75 911s

I really like your concept. I love the center dip as is. You should make these in carbon fiber. I'd buy one. Has anyone tried a custom aluminum duck? would that be heavier than glass?

We are doing the work in aluminum, but I think we might have to shape it in foam first to be sure...

[fhernand]

[wayner]

Here is how the mini duck converting to mini whale would work.

There would also have to be a short pivot at the front.
(The orange line is the car)

You could activate it using one of the power window motors and cables that they us to slide the rear sliding window on modern GMC pickup trucks. Shoten the cable and feed it internally through the dic tail attaching it at the tip.