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Old 04-06-2010, 08:59 PM   #171 (permalink)
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Here's a 40" extension & your streamline pinstriping. I've added an aero no-no but there has been discussions that front canards work, not for front downforce, but as VG's prior the open wheel wells. You could substitute a Gurney flap or lip on the front wheel well edges instead. It also worked 'graphically' on the model.

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Old 04-06-2010, 09:07 PM   #172 (permalink)
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Edit: here's the model I'm taking dimensions from, for comparison. This is the 6" transom variant.



I think your render is very attractive, but what will the motoring public think?



I thought of a construction technique that might allow you to lay up a composite monocoque tail extension without any downtime for the car.

Build a wooden frame in the shape of the tail extension, on a wooden stand that puts it at the right height. Attach styrofoam boards to the frame and sand them to shape. Park the car in front of it whenever you want to work on it. You'd probably want to leave the rear bumper cover off, and take the taillights off when you need to. Would it work?
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Old 04-06-2010, 09:49 PM   #173 (permalink)
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Old 04-06-2010, 09:52 PM   #174 (permalink)
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Quote:
Originally Posted by botsapper View Post
Great to hear from basjoos. You have actual daily driver experience of living with a boat tail. I'm curious of the driving (handling) dynamics of the added weight of your tail. But I presume that the other aero additions may have counter balanced the rear weight bias of the added tail.
As for cutting out the rear bulkhead just for interior visual 'referencing' may structurally weaken the monocoque shell. Crash worthiness compromised. Structural tube cages add weight. Exhaust gases has to be completely sealed out. An alternative is to keep intact the existing rear hatch (accessible by power actuator locks) and add another lockable hatch to access storage in the new boat tail space. Rear sensors are beneficial & easily integrated to any 'tail'.
Especially for many 'new' (auto bloggers & reporters) drivers who wanted to test drive this boat tail.
My boattail didn't add any additional weight. I removed a heavy steel and glass hatch and replaced it with an aluminum monocoque and lexan boattail using strong but lightweight homebuilt aircraft construction techniques. The added side area made the car a bit more sensitive to crosswinds than it used to be. I didn't cut out any of the car's main monocoque structure when building the boattail. I just removed the tailgate and built the boattail around the opening created by the missing hatch. My muffler has a long fairing to release the exhaust about halfway up along the bottom of the boattail. The crash worthiness of my boattail was been tested in real life and its crush space saved my car from being totalled by a rear end collision. It was much cheaper to rebuild the boattail than it would have been to repair the car's stock bumper.

Wayne Gerdes is the only auto reporter who has driven my boattail and he said it coasted better than any vehicle he has ever driven.

Last edited by basjoos; 04-07-2010 at 02:48 PM..
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Old 04-06-2010, 09:53 PM   #175 (permalink)
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Hi Botsapper,

Very nice rendering.

Top trailing edge of the tail will end about six inches lower than your view.

And the underside of the tail will be about six inches lower as well.

Other than that, it is amazing to see what it will look like when done.

Thanks, Jim.
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Old 04-07-2010, 03:26 AM   #176 (permalink)
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I liked this Home Depot foam buck shaping process. Especially the rear section buildup. Trial fit of rear light assemblies could be done at this point. Equally spaced out mdf sections guide the cutting & shaping process. There are a lot more helpful techniques & details of the entire foam buck construction. A boat tail is a simpler process compared to their complicated design.
http://www.youtube.com/user/BaileyBl...25/xdsFLRmEtpI

Last edited by botsapper; 04-08-2010 at 12:30 AM..
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Old 04-08-2010, 06:06 PM   #177 (permalink)
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basjoos got me to thinking about the exhaust. There was some talk about venting the inside air into the rear of the proposed boattails, but what about creating a surface grill work and internal exhaust routing to "spread" the exhaust out across the boattail bottom. There would be more volume than the internal air would ever provide. I think it would be safe so long as smooth rearward flow was maintained underneath and the hatch seals were in good shape. We vent underneath small race cars. Sports Car Club of America(SCCA) only requires that exhaust exit behind the driver. Comments?
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Old 04-15-2010, 09:19 AM   #178 (permalink)
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Quote:
Originally Posted by jimepting View Post
basjoos got me to thinking about the exhaust. There was some talk about venting the inside air into the rear of the proposed boattails, but what about creating a surface grill work and internal exhaust routing to "spread" the exhaust out across the boattail bottom. There would be more volume than the internal air would ever provide. I think it would be safe so long as smooth rearward flow was maintained underneath and the hatch seals were in good shape. We vent underneath small race cars. Sports Car Club of America(SCCA) only requires that exhaust exit behind the driver. Comments?
I've been hoping that someone, Aerohead, RobertSmall, 3-Wheeler, Metro, botsapper, someone, would respond to this. The idea would be to use the high volume exhaust gases to help get addition flow under the boattail. Bad idea - good idea - unknown.

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Old 04-15-2010, 11:19 AM   #179 (permalink)
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Since you have gotten no bites on this in over a week I'll offer an opinion. Basjoos vented his exhaust in the stock location and faired in the muffler. I would suggest that is all that's necessary. IMHO the volume of exhaust gas is minimal compared to the airflow around a vehicle at highway speed. That said, it may be slightly better to exhaust to the bottom and out the back than to the side like some vehicles. May as well add some hot gasses to a low pressure area even if the difference is too small to be measured.
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Old 04-15-2010, 02:14 PM   #180 (permalink)
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IMO, would agree with COcyclist.

There is not enough volume & steady pressures from the exhaust of your small-ish powerplant to greatly affect any effective gains. Plus there would be materials expense in plumbing the hot, toxic & caustic gases. Specialized fabrication and stainless steel would be required to handle that exhaust medium. Have seen complicated ideas using compressed air, supplemental turbines/fans, and even turbochargers just to blow higher gas velocities/special plenums just to prevent flow separation, vortex roll-up and hopefully to reduce drag. Jim Hall-like.
Just sculpt the optimal aft shapes integrated w/ clean belly pan. Safe exhaust outlets & terminate rear section with clean Gurney lip edges.

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