That is spectacular in it's own way...even bothering with an old truck like that deserves a "bow"...
|
It from the book Race Car Aerodynamics by Joseph Katz with an excerpt on this website. Here is an excerpt if you don't want to read the whole thing:
Quote:
|
Thanks for the Bow. Well as of right now barely into the first tank. Even though it is quitter and the wake is less turbulent (much less snow being kicked up). This project will come to a close. About an hour ago I bought a beater car. 1988 Buick Century 3.8L Auto has only 40K original miles. The guy I bought it from (my father) just bought it and did the run through, parts replacement. Best of all $1100, for 28mpg highway. It should be quite a change from the 15/17 I am used to.
Depending on how long it takes to process and insure the truck may see another tank or two. And when the truck needs some "exercise" |
Quote:
Hey, so I have a question for you. I am planning on making a fastback for my pickup come spring, after reading this I took some measurements and found out if I make a fastback from the top of my cab to the back of my truck (top of the tailgate while up), it creates an 11.36 degree slope, so that sounds perfect. But my original thought was to open the tailgate up and create a fastback from the top of the cab to the very end of the tailgate while down. As you can imagine this will increase the slope, it calculates out to exactly 18 degrees. Will flow stay attached at that angle? Basically is it better to have an almost optimal slope (11.3 degrees) and THEN a 20" flat/drop off where the tailgate is while up, or would it be better to eliminate the flat surface of the tailgate by making an even bigger fastback but having it only be 18 degrees? |
|
I would say that it would be better to have the tailgate up and the smaller angle as you would have less turbulence at that angle and smoother flow. A boat tail with the end chopped square is called a kammback, here is a quote from wikipedia:
Quote:
|
Hmm, I don't know about the Kamm's theory. It seems widely accepted by the general public though, but I always felt that was more for looks.
If what you're saying is true than basjoos would do better with his two piece tail. I guess I can always try both but it's really hard to compare improvements with my horrible MPG. Anyway it's an experiment for the future. |
I am sceptical that the friction forces would be greater than the added turbulence that must occur at the cut off but I am pretty sure that the 10 degree angle will work better than the 18 degree one because there will be less turbulence where the sides and top meet. It would make a good simple experiment with some A-B-A testing, empty bed vs kammback vs higher angle boat-tail, all you would need is a large sheet of ply and something to secure it with and a loop of highway...
|
I was under the impression that a Kammback was a compromise. Where the Kammback cut-off is dictated by the utility of it. While a complete teardrop is the most aerodynamic it is also somewhat unpractical. Especially on a truck or any tall vehicle. Because a teardroped truck would have a very long tail, 14 foot. Assuming two 11 degree slopes with a 6' tall cab. This long tail would swing out in turns. I think that the Kammback was developed to get similar CD decreases( similar but not equal) while being much shorter -> more practical to drive with one equipped.
I hope that makes sense. |
Update
I know , I know one tanks means nothing. But for the past couple weeks during my lunch breaks from college. I have been running scrap metal loads. This whole tank has been 1/2 metal loads and 1/2 3 mile city trips (my dd needed repairs). The scrap runs were anywhere from 1000 - 3500 lbs of metal. Then empty on the way back.
This tank averaged 22mpg. Which is better than the previous best. 20 mpg I got last fall 100% highway. |
All times are GMT -8. The time now is 10:53 AM. |
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.