Quote:
Originally Posted by Xist
I replied to as many comments as I could.
Does anyone use Discord?  I want him to see my diagram! 
https://discord.gg/b7BfHq2QJM
I haven't done one of those in years!
The roof looks pretty close to the template. I moved the bottom forward to line up with the bumper.
He said that he tried to match the body curves, but those probably detach at the front of the bumper.
I am not sure that the length is wrong, just too much taper in the front, and then not enough in the rear.
Hey, do you guys remember fanfold foam boards?
Do you think that he could use individual layers of that to build up the front and then either use a longboard to sand it down, or fill it in with 2-part foam?
I am sure that he would want to remove the foil first.
How hard would that be?
It was a pain to remove the perforated film from my fanfold foam.
I am sure that the foil is fine--until a rock or grocery cart hits it, but after he adds to it he would need to fiberglass it.
There were some questions about how much benefit different lengths of tail would provide.
Does anyone remember where those tables are?
Aren't there rules of thumbs for major mods, like 5% for an air dam, 10% for an undertray, and 20% for a boat tail?
Are those first two high? Maybe 3 and 5%, respectively?
I hope he isn't planning on leaving the license plate on the car. He talked about it and in one shot it was gone, but it sure seemed like he drove around with a boat tail and the license plate on the car.
I was trying to figure out what year his Imprezza is.
It seems like most comments were the same assumptions over and over--and some people really don't like making a small car longer.
How long do you think his goop will keep the wheel covers attached?
If he makes a proper boat tail, should he remove the hatch? |
1) it's about wake area.
2) if you reduce wake area by half, you've reduced drag by half ( Variable trailer design drastically cuts aerodynamic drag,' SAE International Paper 2013-01-2414,' by Mario Hirz and Severin Stadler, Graz University of Technology.
3) before you boat-tail though, one wants to accomplish all the optimizations upstream of the tail, to provide fully-attached onset flow, or you risk compromising the tail's performance.
4) the tail itself must be 'streamlined.' At no point, top, sides, or bottom may the pressure increase exceed that seen in a 'streamlined' surface.
5) the 'top' is the easiest part, as the carmaker has already 'begun' to reduce the cross-section there, and the flow is typically attached until the rear edge.
6) the sides, while cambered, are typically not as 'boat-tailed' as the roof. And the flow on the sides of the vehicle is typically 'slower' than on top, is at a higher pressure already, is less 'displaced', has lower kinetic energy, and cannot survive as much cross-section reduction as on top without separation.
secondly, as you're creating a 'fastback' form, the fastback requires the highest degree of tumblehome, of the basic three body types.
7) The underbody has the most feeble flow, and asking a diffuser to position a separation edge at a 'higher' elevation than that from which the underbody flow originated at the front is a recipe for disaster.