Singer ducktail rear opening

[WCN621]

Question, what function does the opening on the backside of the ducktail on a Singer actually provide for the car? My impression is that it would reduce the amount of downward pressure on the back of the car.

The reason why I ask, is that I’m having excessive heat buildup underneath my ducktail and it has twice changed the color of my Grand Prix white paint (yellowed). I still have the air-conditioning installed in the car as my better half desires that feature. My guess is the condenser is not allowing enough air to increase the flow through the ducktail to the engine, allowing it to cool better.

I am wondering if I cut an opening in the rear side of the ducktail, to allow excess heat to escape, would I lose down force and sacrifice performance? Any thoughts?

[john walker's workshop]

Low pressure area to suck road dust and exhaust into the engine compartment.

[kgieg]

A few months ago I made one, (hope they don't have a patent , and just got the car back on the road. I'm not sure it sucks in air. After a 900 mile shakedown run the rear of the tail was covered with a light oil film. I'm running a 2.7 and they seem to be a little leaky so I assumed exiting air. It does run cooler. Are you running a duck tail now?
OK I see you are running a tail.

[shoooo32]

Originally Posted by WCN621

I am wondering if I cut an opening in the rear side of the ducktail, to allow excess heat to escape, would I lose down force and sacrifice performance? Any thoughts?

Before you hack up your tail, have you tried adding any shielding? Either aluminized or gold foil adhesive backed heat shields work awesome for protecting paint.

https://www.pegasusautoracing.com/productselection.asp?Product=1828

[kgieg]

+1 shoooo32

Not sure if possible but could you lower the condenser to allow more air around and then test for improvement.

[PeteKz]

FYI, ducktails do not create downward force. They are "spoilers", not wings. Spoilers do what the name implies--they spoil airflow to prevent lift.

To know for sure what that screen on the back of the Singer does aerodynamically, you would have to put it in a wind tunnel or build a CFD model. My engineering sense suggests that its location does not change the spoiling function of the ducktail appreciably. But as John W noted, it probably increases the amount of crap that will end up in the engine bay.

[Ian Comerford]

It may not be too bad as it’s a low pressure area….? Lots of muck/dirty air swirling around in that tumblehome there so who knows.

[PeteKz]

Now that Ian mentions it: I live up a 1/2 mile gravel road. When I had a ducktail on my car, it collected a lot of road dust on the deck behind the spoiler.

[WCN621]

Yes, I’m running a ducktail now and when I ‘ve done long events, I’ve noticed the collection of grime on the rear of the ducktail. Will try the reflective heat shield.

I’ve also decided on replacing my grill, which may help also. Just don’t have much time to work on another project right now. This is the type of grill I plan to make. Currently running with a stock grill.

[pmax]

Originally Posted by WCN621

Question, what function does the opening on the backside of the ducktail on a Singer actually provide for the car? My impression is that it would reduce the amount of downward pressure on the back of the car.

The reason why I ask, is that I’m having excessive heat buildup underneath my ducktail and it has twice changed the color of my Grand Prix white paint (yellowed). I still have the air-conditioning installed in the car as my better half desires that feature. My guess is the condenser is not allowing enough air to increase the flow through the ducktail to the engine, allowing it to cool better.

I am wondering if I cut an opening in the rear side of the ducktail, to allow excess heat to escape, would I lose down force and sacrifice performance? Any thoughts?

At high speeds, that's a low pressure area.
I suppose at lower speeds, it could serve as a vent.

Is the heat buildup from running fast or slow ?

[WCN621]

It’s primarily occurred with spirited driving in the mountains, winding out and running 3500-4000 RPM, and I’ve noticed the temp on the engine tends to be higher in warm weather (55+) with daily driving (2500-3250 RPM) than what it used to.

[3literpwr]

Seen a few rally cars do this overseas. They are not doing for downforce, but keeping oil coolers high and tidy.

[Kemo]

i just love ducktails

personally, i dont think the hole adds anything to the looks.

[GG Allin]

Happened to get a picture of the rear of a Singer last week at a local car gathering. Look at all that salt on the ground.

[stownsen914]

Originally Posted by PeteKz

FYI, ducktails do not create downward force. They are "spoilers", not wings. Spoilers do what the name implies--they spoil airflow to prevent lift.

"Reducing lift" is the same thing as "creates downforce." It's just an absolute value thing. A ducktail doesn't bring the overall downforce at the rear to net positive, which may be the point you are highlighting.

Edit - Never mind - I think Pete may have been saying that a ducktail doesn't create a net downforce. Not that they don't create downforce. Please ignore my comments.

[Walter_Middie]

"Reducing lift" is the same thing as "creates downforce." It's just an absolute value thing. A ducktail doesn't bring the overall downforce at the rear to net positive, which may be the point you are highlighting.

PeteKz is 100% correct, and I was pleasantly surprised to see that someone actually understands this - and no, PeteKz is not saying anything about the difference between lift and downforce, which as you correctly point out are the same thing.

The ducktail is a spoiler - without the ducktail, the airflow over the top of the car will turn the corner at the rear of the top and start to flow down the rear window and onto the deck lid. This creates a low pressure area and suction on the back window and deck lid - or increased lift.

With the ducktail, the airflow over the top of the car can essentially see that there is an airflow blockage coming up and the airflow will separate off the back window. Now there is just turbulence and high pressure over the back window and deck lid caused by the duck tail "spoiling' the smooth airflow. It's the high pressure on the back window and deck lid that produce downforce (or a decrease in lift if you prefer it written that way).

It is not very efficient to expect ram air on or around the duck tail to help improve cooling. There is mostly turbulence. It is more effective to open areas into the engine compartment to allow the high pressure air in - but probably not as good as just improving the sealing inside the engine compartment to help direct the high pressure in.

[stownsen914]

I wonder if we are mixing topics. A ducktail of course is not a wing - it's a spoiler. Properly implemented spoilers do create downforce.

I was responding to the statement that ducktails don't create downforce. Edit - actually I think Pete may have been saying that a ducktail doesn't create a net downforce. Not that they don't create downforce. Please ignore my comments.

[PeteKz]

We're getting bogged down in semantics. However, I stand firm in asserting that spoilers do not create a force downwards. They only spoil lift. If there is no lift at that part of the car, a spoiler will not do anything appreciable--probably just add drag.

As a practical matter, a spoiler prevents the car from "getting light," or unweighting. A wing, however, will push the car down onto the track with more force than the car's weight alone. A spoiler can't do that.

[Bill Verburg]

A duck creates a high pressure aewa in front riht where the stock grills are and a low pressure area behind, this low pressure area sucks surrounding atmosphere onto the back of the lid, most of the oily residue is from the exhausts, those w/ center exhausts get it worse.

w/o a duck the low-pressure area is down in the license plate area








w/o getting bogged down in semantics a duck can create down force when all else is right, a single aero device needs to be part of a well designed system

note below a 2.8RSR w/ duck has measured -14# of lift front and -60#s of lift rear @~125mph

that said a wing is a far more efficient tool for creating down force, When I went from the stock 993RS aero to the 993RS/CS aero package the change was remarkable and eye opening.

[Bill Verburg]