Boattail the most aerodynamic car... an Insight

[SVOboy]

That was quick!

[Hermie]

To eliminate drag further, round out that rear end. Don't just make it flat!

[basslover911]

Well I wanted to make a sharp cut off, like the kammback designs- kind of like the corvettes rear end as well; just sharp and clean air separation.

You cant see it in the photoshop, but the side would come closer to the middle like basjoos, just not as "epic" in order to try keeping it looking somewhat "factory" looking

[basslover911]

I also lowered the car about 1" in that picture, makes it look MUCH better... looks like a real rocket now and not a 4x4 aftermarket machine.

[Hermie]

I'm thinking smooth it out so the flow stays attached longer and results in a smaller void.

Someone should test it with the flat rear then a round one.

[Bicycle Bob]

1. Yes, Kamm's principle still holds. You might be able to increase the slope on the back a bit, but for detail shaping, use a small lip on top and a concave rear panel, to get a single large, attached vortex. Rounding rarely helps that part of a bad shape.

2. Hermie, The flow should already be close to separating. Rounding only worsens the trailing turbulence. This was thoroughly tested by Dr. Wunibald Kamm, producing the most famous principle in automotive aerodynamics.

[aerohead]

Originally Posted by RobertSmalls

Though I haven't gotten my Insight out of the driveway yet, I expect the biggest gains vs EPA to come from driving technique. Conserving momentum, DWB, and EOC will drastically boost FE around town.

There are two reasons this car will be a P&G champ. One, it will roll very well due to low rolling and aero resistance. Two, check out the sweet spot on the BSFC plot. It's at 4000 RPM, and probably around 50HP! So it's not only okay to accelerate quickly, it's encouraged (as long as you put 100% of your newfound kinetic energy to good use). Google the Insight 1-2-5 shift.

An Insight's boattail can be much shorter than on most cars, because Honda already tapered the body down to a small area where the car abruptly ends. However, due to the small cross sectional area of the rear wake, the benefit of a boattail would also be smaller than on a Civic hatch. Still maybe worth doing.

Regardless of how small the wake of the Insight is,It's Cd 0.25,and potential for Cd 0.125 still offers a 25% MPG HWY improvement from the single boat tail modification.If you have Hucho's book,you will know that this is your only path to lower drag,since Honda did such a good job with the rest of the car.------------- How you accomplish it can take many paths.

[jime57]

Originally Posted by aerohead

Regardless of how small the wake of the Insight is,It's Cd 0.25,and potential for Cd 0.125 still offers a 25% MPG HWY improvement from the single boat tail modification.If you have Hucho's book,you will know that this is your only path to lower drag,since Honda did such a good job with the rest of the car.------------- How you accomplish it can take many paths.

Don't have Hucho, but do have an Insight. It is a little hard to see a Cd objective of .125 when the Aptera is only Cd=.15. A target of .20 might be achievable with a boattail.

No one is going to want to screw up a good Insight with holes and such, but I think I see attachment possibilities. The taillights could be removed for sound anchor points, and the bumper cover could of course be removed for additional anchoring.

But, really, what's the point? Honda did such a good job with the compromises that it hardly seems worthwhile. It would be an interesting experiment, but it harly seems like a good idea in view of the already wonderful FE of the car.

[aerohead]

Originally Posted by jimepting

Don't have Hucho, but do have an Insight. It is a little hard to see a Cd objective of .125 when the Aptera is only Cd=.15. A target of .20 might be achievable with a boattail.

No one is going to want to screw up a good Insight with holes and such, but I think I see attachment possibilities. The taillights could be removed for sound anchor points, and the bumper cover could of course be removed for additional anchoring.

But, really, what's the point? Honda did such a good job with the compromises that it hardly seems worthwhile. It would be an interesting experiment, but it harly seems like a good idea in view of the already wonderful FE of the car.

The GM Sunraycer was Cd 0.089 before they removed the wheel fairings.Honda Dream 2 was Cd 0.10.This is where the mother lode is.-------- Cd 0.2 will get a 10% improvement.That's 1950s technology.If that's your cup of tea go for it.

[jime57]

The Honda Dream 2 is a motorcycle, so that doesn't seem a particularly applicable comparison. It may have a Cd of 0.10 by itself but with an upright rider that seems doubtful. The GM Sunraycer is a pure teardrop PV research car, far less practical than an Insight for everyday use. I like modding as much as the next guy -did a lot of it on an Echo. But from my viewpoint, whatever is done must be practical from an everyday use viewpoint and cannot permantently damage my valuable car. So, I suppose my objectives are a bit different from those interested in pure research.

Still, I'm an engineer and would love to have a workspace to build an Insight tail for testing purposes. I think an attractive and practical Kamm back extension could be built using this technology:

Using Fiberglass/Foam Sandwich Composite

Front wheel fairings would seem attractive, but if one carefully studies the details of what Honda has already done, improvements may be only slight. Wheels which are already pretty smooth, front wheel stakes, aerodynamically shaped openings at wheel rear. Taking on the disadvantages of movable fairings for potentially small improvement doesn't seem very practical.