more CRX aero (insight actually)
07-27-2005, 12:25 PM
#1
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more CRX aero (insight actually)
taken from some insight blurb.
"At the very back of the Insight, the teardrop shape is abruptly cut off in what is called a Kamm back (a distinctive design feature also shared by the Honda CRX). The Kamm back takes advantage of the fact that beyond a certain point there is little aerodynamic advantage to be gained by rounding off or tapering and extending the tail section of an automobile, so one might as well abruptly truncate it at that point. The Kamm back is a design feature that has been incorporated into many high-performance automobiles and racing cars over the years."
just fyi.
"At the very back of the Insight, the teardrop shape is abruptly cut off in what is called a Kamm back (a distinctive design feature also shared by the Honda CRX). The Kamm back takes advantage of the fact that beyond a certain point there is little aerodynamic advantage to be gained by rounding off or tapering and extending the tail section of an automobile, so one might as well abruptly truncate it at that point. The Kamm back is a design feature that has been incorporated into many high-performance automobiles and racing cars over the years."
just fyi.
07-27-2005, 12:36 PM
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Re: more CRX aero (Tyson)
Interesting. Now if you can tell me the best functional rear wing to go with a front splitter for the CRX for track work, I will be even happier.
Barry H.
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07-27-2005, 12:49 PM
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Re: more CRX aero (Tyson)
sounds like a marketing statement. Kamm is very catchy word, too. after all who's going to buy a car with a pointed, tear drop-like rear end. But, i'm sure Honda would like to lead us to believe it's not that beneficial 
07-27-2005, 12:56 PM
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Re: more CRX aero (chad)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by chad »</TD></TR><TR><TD CLASS="quote">a triple stack ebay wing!!</TD></TR></TABLE>
You mean a local stadium bleacher on some aluminum sticks?
You mean a local stadium bleacher on some aluminum sticks?
07-27-2005, 12:57 PM
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Re: more CRX aero (Dave_B)
Kamm Back
Named for the German aerodynamicist W. Kamm, who discovered that drag begins to increase after the rear of a car's cross-sectional area is reduced to 50 percent of the car's maximum cross section.
Named for the German aerodynamicist W. Kamm, who discovered that drag begins to increase after the rear of a car's cross-sectional area is reduced to 50 percent of the car's maximum cross section.
07-27-2005, 01:24 PM
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Re: more CRX aero (JHill)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JHill »</TD></TR><TR><TD CLASS="quote">Kamm Back
Named for the German aerodynamicist W. Kamm, who discovered that drag begins to increase after the rear of a car's cross-sectional area is reduced to 50 percent of the car's maximum cross section.
</TD></TR></TABLE>
Is there a desirable aspect ratio if one can't have a pointed rear end? If so, what percentage of the total front cross section?
Named for the German aerodynamicist W. Kamm, who discovered that drag begins to increase after the rear of a car's cross-sectional area is reduced to 50 percent of the car's maximum cross section.
</TD></TR></TABLE>
Is there a desirable aspect ratio if one can't have a pointed rear end? If so, what percentage of the total front cross section?
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07-27-2005, 07:36 PM
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Re: more CRX aero (YeahRight!)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by YeahRight! »</TD></TR><TR><TD CLASS="quote">sounds like a marketing statement. Kamm is very catchy word, too. after all who's going to buy a car with a pointed, tear drop-like rear end. But, i'm sure Honda would like to lead us to believe it's not that beneficial </TD></TR></TABLE>
Look at the Viper GTS, Corvette C5/C6, Saleen, etc... a lot of the mid 90s+ exotics/performance cars used this.
Jon K
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</TD></TR></TABLE>Look at the Viper GTS, Corvette C5/C6, Saleen, etc... a lot of the mid 90s+ exotics/performance cars used this.
Jon K
http://www.seat-time.com
http://www.racerjon.com
07-28-2005, 05:33 AM
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Re: (genxguy)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by genxguy »</TD></TR><TR><TD CLASS="quote">I always thought that abrupt cutoff in the back actually creates drag by producing a vacuum in the air as it moves forward.</TD></TR></TABLE>
The question you gotta ask yourself is "creates drag compared to what?". Yes, a chopped off back will create drag compared to the ideal airfoil-like shape, but that kind of shape isn't practical for an automobile.
What a sharply chopped-off rear end lets you do is control where the airstream separates from the body.
Consider a VW bug for example. The air flowing over the roof will start to come down the back, but it can't make a very sharp turn, so it won't be able to follow the roofline the whole way down the back. It will probably separate somewhere around the back window. When airflow separates this way, you get big, energy-consuming vortices and an area of disturbed air behind the car that's actually larger than where it separated from the car.
On something like an Insight or CRX, on the other hand, the roofline slopes gently down in back. The airstream is able to follow this kind of shape, so it stays attached right up to the point where it's chopped off in back. This creates a much smaller area of disturbed air in back, and the rest of the airflow acts as if there were in fact a long tapered tail. It isn't as efficient as if there were actually a long tapered tail, but it's closer than a more rounded shape.
Yes, a boat tail on boats and bullets is the same general idea.
That Vega is a good example of "Kamm" being used strictly for marketing. Have you ever seen the engine in one of those things? Weirdest valve cover I've ever seen.
The question you gotta ask yourself is "creates drag compared to what?". Yes, a chopped off back will create drag compared to the ideal airfoil-like shape, but that kind of shape isn't practical for an automobile.
What a sharply chopped-off rear end lets you do is control where the airstream separates from the body.
Consider a VW bug for example. The air flowing over the roof will start to come down the back, but it can't make a very sharp turn, so it won't be able to follow the roofline the whole way down the back. It will probably separate somewhere around the back window. When airflow separates this way, you get big, energy-consuming vortices and an area of disturbed air behind the car that's actually larger than where it separated from the car.
On something like an Insight or CRX, on the other hand, the roofline slopes gently down in back. The airstream is able to follow this kind of shape, so it stays attached right up to the point where it's chopped off in back. This creates a much smaller area of disturbed air in back, and the rest of the airflow acts as if there were in fact a long tapered tail. It isn't as efficient as if there were actually a long tapered tail, but it's closer than a more rounded shape.
Yes, a boat tail on boats and bullets is the same general idea.
That Vega is a good example of "Kamm" being used strictly for marketing. Have you ever seen the engine in one of those things? Weirdest valve cover I've ever seen.
07-28-2005, 05:42 AM
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Re: (Agent Smith)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Agent Smith »</TD></TR><TR><TD CLASS="quote">T
Consider a VW bug for example. The air flowing over the roof will start to come down the back, but it can't make a very sharp turn, so it won't be able to follow the roofline the whole way down the back. It will probably separate somewhere around the back window. When airflow separates this way, you get big, energy-consuming vortices and an area of disturbed air behind the car that's actually larger than where it separated from the car.
On something like an Insight or CRX, on the other hand, the roofline slopes gently down in back. The airstream is able to follow this kind of shape, so it stays attached right up to the point where it's chopped off in back. This creates a much smaller area of disturbed air in back, and the rest of the airflow acts as if there were in fact a long tapered tail. It isn't as efficient as if there were actually a long tapered tail, but it's closer than a more rounded shape.</TD></TR></TABLE>
You also have to balance reduction in separation drag (like you discussed) with the friction drag of adding more surface area. If you made a tapered tail, you add a LOT of surface area for the air to create friction on... At some point, it's LESS drag to chop it off than to finish the taper. Separation drag is coming down as the tail gets tapered but friction drag is going up... where those two curves cross is the optimal (Kamm) drag configuration.
Consider a VW bug for example. The air flowing over the roof will start to come down the back, but it can't make a very sharp turn, so it won't be able to follow the roofline the whole way down the back. It will probably separate somewhere around the back window. When airflow separates this way, you get big, energy-consuming vortices and an area of disturbed air behind the car that's actually larger than where it separated from the car.
On something like an Insight or CRX, on the other hand, the roofline slopes gently down in back. The airstream is able to follow this kind of shape, so it stays attached right up to the point where it's chopped off in back. This creates a much smaller area of disturbed air in back, and the rest of the airflow acts as if there were in fact a long tapered tail. It isn't as efficient as if there were actually a long tapered tail, but it's closer than a more rounded shape.</TD></TR></TABLE>
You also have to balance reduction in separation drag (like you discussed) with the friction drag of adding more surface area. If you made a tapered tail, you add a LOT of surface area for the air to create friction on... At some point, it's LESS drag to chop it off than to finish the taper. Separation drag is coming down as the tail gets tapered but friction drag is going up... where those two curves cross is the optimal (Kamm) drag configuration.
07-28-2005, 08:04 AM
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Re: more CRX aero (MMsportsRexSi)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by MMsportsRexSi »</TD></TR><TR><TD CLASS="quote">IF that is the best aero shape, then the EF hatch would have the "advantage" over the crx in the aero dept. </TD></TR></TABLE>
I seem to remember that is does have a lower Cd than the CRX...
I bought a new EF hatch in 91 and the sales brochure listed the Cd as lower than the Cd for the CRX. Frontal area for the hatch is still larger, thus still creating more total drag, but it is a more efficient shape. At least according to the Honda sales brochures of the day.
I seem to remember that is does have a lower Cd than the CRX...
I bought a new EF hatch in 91 and the sales brochure listed the Cd as lower than the Cd for the CRX. Frontal area for the hatch is still larger, thus still creating more total drag, but it is a more efficient shape. At least according to the Honda sales brochures of the day.
07-28-2005, 08:11 AM
#18
Re: more CRX aero (thawley)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by thawley »</TD></TR><TR><TD CLASS="quote">
I seem to remember that is does have a lower Cd than the CRX...
I bought a new EF hatch in 91 and the sales brochure listed the Cd as lower than the Cd for the CRX. Frontal area for the hatch is still larger, thus still creating more total drag, but it is a more efficient shape. At least according to the Honda sales brochures of the day.</TD></TR></TABLE>
swap the crx front end on it
and call it a day! *i know its not legal*
I seem to remember that is does have a lower Cd than the CRX...
I bought a new EF hatch in 91 and the sales brochure listed the Cd as lower than the Cd for the CRX. Frontal area for the hatch is still larger, thus still creating more total drag, but it is a more efficient shape. At least according to the Honda sales brochures of the day.</TD></TR></TABLE>
swap the crx front end on it
and call it a day! *i know its not legal*
07-28-2005, 08:23 AM
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Re: more CRX aero (MMsportsRexSi)
Also consider the flow coming from the underside of the car, though most productions cars don't. You gotta have at least enough tail for the upward sloping diffuser on the underside. 
07-28-2005, 09:03 AM
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Re: (Agent Smith)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Agent Smith »</TD></TR><TR><TD CLASS="quote">
That Vega is a good example of "Kamm" being used strictly for marketing. Have you ever seen the engine in one of those things? Weirdest valve cover I've ever seen.</TD></TR></TABLE>
I'm going to dissagree on your analysis of the Vega.
If you look closely at the picture, you will notice that the roof extends a little past the start of the hatch, and the sides of the car extend past the hatch a little too.
That Vega is a good example of "Kamm" being used strictly for marketing. Have you ever seen the engine in one of those things? Weirdest valve cover I've ever seen.</TD></TR></TABLE>
I'm going to dissagree on your analysis of the Vega.
If you look closely at the picture, you will notice that the roof extends a little past the start of the hatch, and the sides of the car extend past the hatch a little too.
07-28-2005, 02:44 PM
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Re: (fireant)
a lot of this stuff is discussed in books such as Race Car Aerodynamics by Katz, although hes doesnt mention Kamm from what I can see.
another good one only for production cars and drag reduction is the General Motors Research Laboratories symposium 'Aerodynamic Drag Mechanisms of Bluff Bodies and Road Vehicles' edited by Sovran, Morel, and Mason (1978). This one shows well how relatively small changes to shape can produce big changes in drag.
another good one only for production cars and drag reduction is the General Motors Research Laboratories symposium 'Aerodynamic Drag Mechanisms of Bluff Bodies and Road Vehicles' edited by Sovran, Morel, and Mason (1978). This one shows well how relatively small changes to shape can produce big changes in drag.
07-28-2005, 03:39 PM
#25
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<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by sporkcrx »</TD></TR><TR><TD CLASS="quote">Just another reason why the crx is superior</TD></TR></TABLE> 
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by MattP »</TD></TR><TR><TD CLASS="quote">My favorite Kamm back car:
</TD></TR></TABLE> MMMMMMMMMM.......
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by MattP »</TD></TR><TR><TD CLASS="quote">My favorite Kamm back car:</TD></TR></TABLE> MMMMMMMMMM.......