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Old 04-03-2010, 01:34 AM   #161 (permalink)
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Actually, that was a 2°-7° upward angle of the underside of the tail. The shoulder should begin at 0° and gradually fall away.

I was thinking about applying pinstriping paint to the tail to illustrate airflow. Hmm, it probably wouldn't have the intended effect.

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Old 04-03-2010, 02:13 AM   #162 (permalink)
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Your boat tail project should try to also address the aft vortices caused by the tires. Even MetroMPG's elegant tail extension, as shown by the underside boattail vids, easily show the turbulences caused by them. Your boatail project should address these concerns & add tire spats to clean up up these disturbed flows. I tried to cleanly integrate them, look OEM & match them with the black colored finishes.
Underside vids, another observation...maybe another project but fully optimized belly pans could use full length strakes for better longtitudinal flow, front to back.
As for the modest tail, think of it as the 'Short-Tailed' (as in the famous Aerotech ST) version of the project. Your plan as the LT version.

Last edited by botsapper; 04-03-2010 at 02:20 AM..
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Old 04-03-2010, 09:18 AM   #163 (permalink)
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Quote:
Originally Posted by botsapper View Post
Your boat tail project should try to also address the aft vortices caused by the tires. Even MetroMPG's elegant tail extension, as shown by the underside boattail vids, easily show the turbulences caused by them. Your boatail project should address these concerns & add tire spats to clean up up these disturbed flows. I tried to cleanly integrate them, look OEM & match them with the black colored finishes.
Underside vids, another observation...maybe another project but fully optimized belly pans could use full length strakes for better longtitudinal flow, front to back.
As for the modest tail, think of it as the 'Short-Tailed' (as in the famous Aerotech ST) version of the project. Your plan as the LT version.
Just studying your rendering, which are superb, I have a couple of comments. First, looking at the top view, the taper of the lower shoulders looks excessive, if I understand the aero principles. Your tail tapers about 30 degrees referenced to the centerline. Will flow be smooth at that angle? It seems to me that you could use a slightly lower taper and achieve better results, but I'm just guessing.

Second, you could be a bit more agressive with the spats behind the rear wheels if you are going to add those aggressive front wheel spats anyway. The clearance/drivability issues would not change and I think it would actually look better - a matter of taste.

This is all JMO of course. I don't have any modeling SW so some of it is guessing. I want to build a boattail, but I'm kinda waiting for smarter folks like you and Robert to get it "right."

Last edited by jime57; 04-04-2010 at 12:54 AM.. Reason: spelling
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Old 04-03-2010, 06:13 PM   #164 (permalink)
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J,
The concept proposal was an effort to not only satisfy the boat tail aerodynamic benefits but to also accommodate some aesthetic balance. There are compromises with the existing contours & angles of the base vehicle. I had to 'grow' organically the proposed boat tail extension and 'follow' the resultant flow shape. Another design compromise that would be faced is when creating the rear light assemblies. Using trailer/aftermarket LED light assemblies would afford the easiest fabrication but incorporation (Honda) OEM rear lights would be project 'appropriate' & could be nicely done. On my commute home recently I was behind a 2000 Accord coupe with these tri-lamps that might work. The tail section may need to be larger though. There are still CHMSL, plate illumination & backup lights required. I've seen, combi antenna/third brake light, for some 'cool' factor.
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Old 04-03-2010, 09:12 PM   #165 (permalink)
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I see where your are comming from and I fully appreciate you intent. Certainly you have produced an aestheticaly pleasing rendering. I think it is also a practical design for the street. I also see what you mean about choosing the proper tail lights. The triangular lights in the model make the rear very pretty and almost "factory" like. Well done!
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Old 04-03-2010, 11:40 PM   #166 (permalink)
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I was leaning toward second-gen Saturn S-series taillights, which are three-colored and about 6" tall. But I might go with the 9" tall Insight taillights. Making the transom 3" taller increases transom area from 1ft² to 2ft² (compared to the car's frontal area of 20ft²), and shortens the tail extension by about 6". I am willing to give up a few counts of drag in exchange for a few points of cool, since this is my daily driver, after all.


I taped a ruler to my wheels, set my camera to "timer", and measured the deflection of the suspension with me sitting in the driver's seat and without. My 150lbs weight deflects the front left suspension by about 8mm, and the rear left by 12mm. This reduces ground clearance on the left side by 7%, and changes the angle of the body as presented to the wind by 0.1°. I will ignore this angle while building the tail extension.
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Old 04-06-2010, 02:03 AM   #167 (permalink)
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Reduce effective frontal area and restrict underside airflow. Your suspension height data should also include lowering the overall ground clearance. On the concept, I've lowered the model ride height. Inexpensively, you could use Eibach lowering springs (Honda Civic?) Pro-Kit 25-30mm drop or Sportline kit for a deeper 30-50mm drop. Springs rates are kept reasonable & lowers your center of gravity. The additional weight of your boat tail will shift your CG towards the back, adjustable (adj. coilovers) ride height & dampening might be required. May be cost prohibitive.
You might also plan backup sensors with your longer & out of your line of sight boat tail dimensions. Take your pick. Parking Sensor Backup Sensors Wireless Parking Sensor Kit
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Old 04-06-2010, 07:00 AM   #168 (permalink)
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If you extend the interior of your car into the boattail, so you can distance reference by comparing the back wall of the interior to the distance to the front of the parked vehicle behind you as you back up, then parking sight lines aren't a problem. My car's interior extends to within 2 feet of the tip of the boattail and have haven't found parallel parking to be any worse than with any other car of similar length. It certainly has a lot less hidden length than on a car with a long low trunk when looking out of the back window.
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Old 04-06-2010, 01:03 PM   #169 (permalink)
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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.
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Old 04-06-2010, 03:14 PM   #170 (permalink)
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A back-up camera that mounts to the license plate may be another option.

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