jwxr7 -
Ha ha. While I was reading your mega air dam thread I was admiring your kammback. I noticed the vertical center brace. Nice touch. Thanks for the test. You made me add it to my todo list. CarloSW2 |
Thanks,
The results seem almost too good to be true. I'm probably not an awesome tester but there was an obvious difference with the first coast after I removed it. I thought, man that was way shorter distance and time. Anyone think .05 Cd improvement is feasable for a single aero appliance such as a kammback? |
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Looking forward to grill blocks on the MZ3 this fall and winter. psy |
Oh yeah bruce, I forgot to mention that I use "goo remover" from menards to remove residue left by the packing tape. I've also used mineral sprits and wd-40 with success. Duct tape can be a bit more of a B*^%$ due to the reinforcing grid that sometimes gets left behind and sometimes to goo hardens. Packing tape varies alote, most tear lengthwise when you go to pull it off, but the "duck" high performance I've been using seems tougher.
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your car starts to resemble a miniature version of the new renault senic
https://www.fuelly.com/attachments/fo...7a9e66c757.jpg looks like you're inventing a new car rather than modding an existing one :) there's been some positive report on kammbacks, yet i've noticed they're all with an open end, could the fact that they hold a pocket of non turbulent air somehow help them reduce the wake? has anyone ever rested open vs closed kammbacs? or for example, remove the rear hatch? |
Reading up on Kammbacks in wikipedia, it said they are like a teardrop shape (or a boattail, I'd say), just not coming to a complete point. You get most of the benefit of a complete taper without going all the way to a point.
Many of the cars designed with a Kamm back are also partially hollow - have a concave rear end. It looks like the air moves along the surface and then just keeps going, it apparently doesn't really care much whether the surface continues or not. Just my half-educated take on it. |
>>Anyone think .05 Cd improvement is feasable
>>for a single aero appliance such as a kammback? Seems high to me, but depends on your starting Cd. For example, .30 to .25? Pretty hard to believe. But a square back truck at .5, I can see that. My guess is if you tighten up your testing methodology, the delta will close more towards half of what you are seeing now.... just a guess, but I have played around with this stuff some. |
I saw a 5% improvement from my air dam, and sometimes I doubt that number, even though it is defensible.
.05 would be something like a 20% improvement, which seems pretty high. Still, it shows you are going the right direction. As always, running more trials with and without the mod helps you to be more sure of the results. |
jwxr7,
I saw a VW with a nicely manufactured, shorter version of your Kamm back yesterday. Top lip was maybe 3-4 inches front to back. It had little triangle side pieces that were also about 3-4". Didn't need the center support since they were able to make it out of something pretty strong. It was a hatchback type, sorry I didn't note which model. Maybe a Rabbit. |
6 Attachment(s)
I had the kammback off and decided some pictures may help others. Here are some shots with it laying flat. BTW I am replacing this one because the plastic has degraded and is cracking. The middle pic has a yard stick for reference and there is still old tape ragged around the edges.
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