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-   -   Boattail without boattailing (https://ecomodder.com/forum/showthread.php/boattail-without-boattailing-19929.html)

Gone2 12-30-2011 06:11 PM

Boattail without boattailing
 
Is there a way to boattail a small sedan without doing a full on boattail?

spacer 12-30-2011 06:19 PM

Mount a force field generator in the trunk, and tweak the "shell" until it's about the right shape. Another effect is that the tailgater who doesn't stop in time may be vaporized by the field, but that's his own fault, right?

;)

CigaR007 12-30-2011 07:01 PM

1 Attachment(s)
I have been pondering an inflatable decklid extension for my Toyota Echo sedan. It could be controlled manually by a switch or automatically depending on vehicle speed. That way, it is less imposing (size-wise) when deployed and easily hidden when not needed. I believe that would be a good compromise and yield interesting results.

Here is what my car should look like when fully done ! :cool:

Gone2 12-30-2011 08:32 PM

I think I will remove the bumper and turn it into a pan that flows to the trunk. I may shave the edge of the trunk lid down a little and see about shaving the sides of the car. I don't mind doing the boattail, just seeing if there were any other options.

duffremle 12-31-2011 09:35 PM

I've kind of wondered about the feasibility of a windsock style boattail. Something along the lines of a sea anchor, but fitted to the rear end of the car with just enough of an opening to fill it with air at speed.

aerohead 01-03-2012 05:53 PM

Is there
 
Quote:

Originally Posted by Sentraguy (Post 276971)
Is there a way to boattail a small sedan without doing a full on boattail?

Kamm and Korff recommended cars with enough boat-tail such that the wake would be 1/2 the frontal area of the vehicle.That occurs at about 50% of aft-body boat-tail.Thie recommendation is based on 'practical' length for operating in traffic,negotiating streets,turns,curbs,ramps and parking.
Your design drag coefficient will determine how much you add.
I looked over my materials and it looks like a car with 'no' aft-body streamlining at all would be limited to a Cd minimum of 0.20.An extreme example would be the Blue Flame rocket powered land speed record car.It's rocket ship body has a higher drag than the blunt and 'stubby' Renault Vesta II.
It would basically be impossible to achieve lower drag without extending the rear.

KamperBob 01-03-2012 07:37 PM

Quote:

Originally Posted by aerohead (Post 277673)
Kamm and Korff recommended cars with enough boat-tail such that the wake would be 1/2 the frontal area of the vehicle.That occurs at about 50% of aft-body boat-tail.Thie recommendation is based on 'practical' length for operating in traffic,negotiating streets,turns,curbs,ramps and parking.
Your design drag coefficient will determine how much you add.
I looked over my materials and it looks like a car with 'no' aft-body streamlining at all would be limited to a Cd minimum of 0.20.An extreme example would be the Blue Flame rocket powered land speed record car.It's rocket ship body has a higher drag than the blunt and 'stubby' Renault Vesta II.
It would basically be impossible to achieve lower drag without extending the rear.

Half wake sounds pragmatic. :thumbup:

Sven7 01-04-2012 05:11 PM

Quote:

Originally Posted by duffremle (Post 277139)
I've kind of wondered about the feasibility of a windsock style boattail. Something along the lines of a sea anchor, but fitted to the rear end of the car with just enough of an opening to fill it with air at speed.

Wouldn't this work like a parachute, sucking energy from the car?

Here's how I see it. To inflate the sock it would have to have at least equal pressure inside than out. This would mean it's got to pull in a lot of air. So, to keep it from deflating or rippling at speed it might add more drag to your car than it actually solves. If you closed off the back and had small intakes at the cant rails like a Ford RS200's air intakes you might be able to keep it inflated. But I still doubt the real-world viability. Venturi intakes, perhaps?

Gone2 01-04-2012 08:23 PM

I noticed today as the cold air made it where vehicle exhaust was visible, that the air behind certain vehicles is very violent. Awesome to see first hand that all this is true. Is there a template for the perfect boat tail design?

California98Civic 01-04-2012 10:53 PM

Quote:

Originally Posted by Sentraguy (Post 277923)
I noticed today as the cold air made it where vehicle exhaust was visible, that the air behind certain vehicles is very violent. Awesome to see first hand that all this is true. Is there a template for the perfect boat tail design?

Check this link for starters: http://ecomodder.com/forum/showthrea...tml#post116392

drmiller100 01-04-2012 11:42 PM

thanks for the link. fascinating read, and explains how to think about things.

A different outlook. If we look only at the car from the side, we think about modifying the trunk.

If we look from above the car, and down, we think about modifying the sides.

We can only modify the top once, but we get to modify each side. So, twice the benefit in working on the sides of the car.

also, there is not a successful racer of any kind in the entire world who thinks undercar air is a good thing, except those who can legally run ground effects. When you run ground effects, they are playing games with 10mm ground clearance, so they do want very much air at all under the car.

EVERYONE else thinks air under the car creates drag.

aerohead 01-05-2012 06:16 PM

1/2
 
Quote:

Originally Posted by KamperBob (Post 277700)
Half wake sounds pragmatic. :thumbup:

yeah,50% would work pretty well in the real world.
W.A.Mair (the boat-tail man ) recommended truncating at about 52% aft-body.
Some cars which are at or near 50% are:
*1937 Tatra 87
*1938 Schlor car
*1948 Tucker Torpedo
*1964 Ford GT 40
*1965 Ford Mk IV
*1968 Ferrari 330 P4
*1981 VW flow body
*1982 Western Washington Univ. Viking-V
*1984 Chevy Citation IV
*1992 EV-1 LSR (Ft.Stockton,Texas)
*1994 Bugatti EB110
*2006 AeroCivic
*2009 VW 1-liter car
*2009 Koenigsegg CCXR
*2009 Lamborghini Sesto Elemento
*2011 Bugatti Veyron 16.4 Super Sport
*2010 Lamborghini Murcielago

aerohead 01-05-2012 06:21 PM

windsock
 
Quote:

Originally Posted by duffremle (Post 277139)
I've kind of wondered about the feasibility of a windsock style boattail. Something along the lines of a sea anchor, but fitted to the rear end of the car with just enough of an opening to fill it with air at speed.

There's a fella in Lubbock, Texas who's been 'inventing such a thing for 18-wheelers.
Texas Tech University did model wind tunnel experiments for him.The concept is fairly mature now.


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