Insight 1 Rear Diffuser

[jimepting]

Joe's(cwrv892) nice Mini diffuser here:

MINI Cooper S rear diffuser w/ underpanel

has gotten me to thinking of building one for my Insight 1. I think I can achieve the near perfect angle of 2.8-3 degrees. I have a couple of questions to toss out for the experts, neither of which Hucho addresses.

First, does anyone have any good reference material for why one adds longitudinal "dams" to the diffuser, like Joe did? I see it done on Formula 1 diffusers, but we are hardly going 200 mph, so the effect might not be the same.

Second, should I extend the diffuser beyond the bumper? The Insight 1 rolls up the under bumper rapidly at the end and a strange "undercut" area in the underbumper midsection. I don't understand Honda on this, but I'm tempted to extend the diffuser past all that and close in the strange bits, making an abrupt termination.

Any thoughts appreciated.

[aerohead]

Originally Posted by jimepting

Joe's(cwrv892) nice Mini diffuser here:

MINI Cooper S rear diffuser w/ underpanel

has gotten me to thinking of building one for my Insight 1. I think I can achieve the near perfect angle of 2.8-3 degrees. I have a couple of questions to toss out for the experts, neither of which Hucho addresses.

First, does anyone have any good reference material for why one adds longitudinal "dams" to the diffuser, like Joe did? I see it done on Formula 1 diffusers, but we are hardly going 200 mph, so the effect might not be the same.

Second, should I extend the diffuser beyond the bumper? The Insight 1 rolls up the under bumper rapidly at the end and a strange "undercut" area in the underbumper midsection. I don't understand Honda on this, but I'm tempted to extend the diffuser past all that and close in the strange bits, making an abrupt termination.

Any thoughts appreciated.

Jim,I'm going to 'guess',as I have no real scientific data.
In the race car,the diffuser is operating as a down-force device.
In a wing,'lift' is spoiled if there is any spanwise flow.Some aircraft wings ( especially military)have utilized 'flow-fences' to control spanwise flow.
My guess is that this is the purpose of the 'dams' on the diffuser.
If the race car is overtaken and passed by another race car,the bow and stern waves from the overtaking car will be less likely to destroy down-force in the diffuser if the dams ( fences) are buffering the interference.Without them it could mean loss of rear traction within a curve ,potentially disastrous.
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As to extending the diffuser beyond the rest of the body,it seems that it would become immersed within the turbulent wake and cease to function as a diffuser as it is assailed by turbulence from all sides.

[jimepting]

Originally Posted by aerohead

As to extending the diffuser beyond the rest of the body,it seems that it would become immersed within the turbulent wake and cease to function as a diffuser as it is assailed by turbulence from all sides.

Actually, I misspoke here, leading to some confusion. I'm thinking of extending the diffuser just to the rear edge of the bumper, not into the wake area. On the insight, it looks like taking it out that far would clear several areas that just don't look right. Underneath the bumper, the stock "diffusing" section rolls up rapidly in the last 8-10 inches. In addition, there is the little underbumper tricky section in the middle, where the bodywork is undercut, which I do not understand. Looks to me like the entire diffuser section would be a lot cleaner aero wise to get the back edge just at the point of the rear bumper edge. Obviously some guessing going on here.

I'm thinking I'll give it a try, take some pictures and ask for comment. I certainly like the way Joe's came out, and he claims an improvement. I'll also try to do some testing, though that is a tough task on an Insight.