There is no magic in a Kamm tail!
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- Опубліковано 16 жов 2024
- For low aerodynamic drag, a long tail with attached flow is better than a Kamm tail. Here's the latest tech information from a new SAE engineering paper. My two books - www.amazon.com... and www.amazon.com...
Thank you so much for his wonderfully clear explanation. I've been reading up on aerodynamics the last few days, and as my general understanding increased, so my understanding of the Kamm tail decreased. Thanks to you it all makes sense.
You're very welcome!
It's not uncommon for people to re-imagine history to fit a narrative. Thanks for the info. 👍
Glad you enjoyed it
What I think of as the "modern" iteration of Kamm's tail started, I believe, in the early to mid Sixties on racing cars like the Ferrari 250 GTO, the Aston Martin DP214 and DP215, the Shelby Cobra "Daytona" coupe, etc. They adopted a modified version of the Kamm tail for solid aerodynamic and packaging reasons, it being a good compromise for those cars in terms of weight, length and drag performance. Since it worked well in that context it was also adopted by car stylists designing _production,_ mass-manufactured sports and sporty cars as well, often more as a visual cue rather than as an aerodynamic drag-reduction tactic. In other words, to look cool or sporty. (Likewise "ducktail" spoilers, which survived all the way through even the "wing" era of automotive styling.)
Of course there's no magic in the Kamm tail. It's a compromise. If you can get the benefit of _most_ of the drag reduction of a tapers-to-a-point teardrop tail without having to make your vehicle heavier and nearly twice as long to accommodate it, the Kamm tail might be the right compromise for your design and it shouldn't be ignored.
But you don’t get *any* the drag reduction of a “tapers to a point teardrop” - the more you truncate the tapering tail, the higher the drag, no matter what name you give it.
Hello from Wales, Julian. Thanks for the videos, most informative.
Glad you like the videos! I enjoyed Wales, especially Pendine and that historic beach.
@@JulianEdgar Thanks for the speedy reply. The reason your videos are so interesting for me is I build cars in my spare time - it was my business 38 years ago. I am about to modify one this year, so will be incorporating some of your findings. I have sent you a contact on facebook. If you accept, I can send you some photos of my last car. Regards, Hugo.
I drive a honda CRX, been looking for ideas on areo mods for it when I found this
they sure as heck look good though!
@julian... I find this super fascinating. What is your take on a kamm tail vs a round tube that is half the width of a kammtail as used on "aerodynamic" racing bicycles? They claim a significantly reduced draf vs round tubes...
The daytona race car was a classic example of this
My 1983 K5 BLAZER needs a tail pointing down ward like your box car you had. LOL
Thank you for sharing this. Currently, the use of Kamm tail virtual foils are all the rage in aerodynamic bicycle frame design, a departure from more traditional NACA airfoils from about ten years ago. The problem is, nowadays manufacturers and pro athletes don’t make their aerodynamic testing a available to the public, they just make marketing claims about their bikes. It’s nice to know that there have been studies done on the actual effectiveness of the kamm tail airfoils.
Part of what's driving this design decision might be the UCI rules. I believe there's a rule about tube dimensions designed to prevent the use of teardrop shaped tubes. A Kamm tail might be the best trade-off under the rules.
3:1, which has been scrapped... With new dimensions allowed. However, kammtails in IND windtunnel tests, show significantly faster than teardrop/naca foils. Could be a variety of factors such as external bottles, cyclist on top with moving legs, exposed wheels disrupting the air. Etc.
Old habits are hard to change even in the aero world too.
Funny, you never see Kamm tails on aircraft.
I like what you're pointing out here. I like it because not only do elongated, tapered 'boattail' designs work better but they LOOK better!! than some
Great channel! Just discovered it!
Welcome aboard!
The magic of the Kam tail is in the balance between the drag coefficient and lugging around an extra hundred kilograms or more or awkward sheet metal that you cannot possibly see to avoid backing into things.
What, like sedans have?! I think the Kamm tail has been massively over-rated for a long time, and still is.
@@JulianEdgar . The principal behind the Kamm tail is the heart of most automotive design features.
Compromise!
If you want the most aerodynamic vehicle possible you just need to compromise by not having wheels and engine or a cabin or control surfaces or be large enough to actually carry passengers . You just need to lay down maglev tracks everywhere and it will be perfect.
I don't know why you say that the principal of a Kamm tail is the heart of most automotive (aerodynamic?) design features. That's simply not true. But then again, a lot of people don't really know what a Kamm tail is, so maybe that's the problem?
@@JulianEdgar . Julian you need to take your sense of humour out for a walk it’s getting flabby.
You need to not read most of my comments as if I’m being serious.
I don't see it as humorous - I see it as more spreading of misinformation, of which there is a massive amount around on car aero. To suggest that a "Kam tail is in the balance between the drag coefficient and lugging around an extra hundred kilograms or more or awkward sheet metal" is a classic case of leading people astray. I don't really want to be part of that. I see too many people waste their time and money following such misinformation.
I had a Kamm tail VW......it was a slug. I don't think Kamm used Julian's testing techniques. While we're talking about nice rear ends , let's talk about McLaren speed tail .
Julian. I was looking at some images of the old Shelby Daytona coupe. The Kamm tail on it is concave. with sharp edges. Would the air swirl more there? or would the sharp edges flow together off the back of the tail do you think. Some of them had Wings. so don't count those.
Pic link please?
@@JulianEdgar this may be what he means - images.app.goo.gl/vgVsVHrwYu6HQA1i8
@@samctanner If that's it, it's just a Kamm tail with a rear spoiler. The spoiler provides a pressure increase on the back slope and gives a clean separation edge for the flow. Both are good (although that spoiler is a bit high for reduced drag as well, I'd guess.)
That extension of the body on the Jaray Design could be helpful along with modern diffusers? I mean, when Kamm proposed that it did nothing, it was a time when undersides where pretty much ignored when it comes to aerodynamics. With our modern conception of the play of the underside when it comes to drag, couldn't we use that tail as benefit to lower drag?
I am not sure that I understand you. The video argues that a long tail reduces drag, and of course that long tail can incorporate a diffuser.
I doubt a diffuser would prevent the flow separation on the topside. But I imagine a diffuser could reduce the "drag penalty" of a truncated tail, by reducing the size of the wake.
@@JulianEdgar the hole concept of the Kamm back is to chop that prolongation of the Jaray Design, right? How about make those a thing again, with better underside aerodynamics in mind
What i mean is, take that air that's running under the car and release it after the trunk, in the middle of the wake
@@heitorbernardes7977 The flow won't stay attached to the upper surface of the Jaray design, so the wake area will still be large with any normal diffuser that retains attached flow.
Sorry. I meant to say that if those did not have the wing. would it work better?
Julian. Sorry I was looking at images of Shelby Daytona coupe in wind tunnel. and Shelby Daytona coupe in the the rain. good images of the tail both with and without rear wing. and also rain coming of the rear. even a wool tuft pic. cool.
Link to pics please
No Magic? but the proof exists. Look at the Mini Jem for example. This little cars aerodynamic design incorporates a Kamm tail. It was tested and found to be stable up to 170 Mph in a aeronautical wind tunnel even though it could never achieve this speed with its Mini mechanicals.
Did you watch the video?
@@JulianEdgar Yes - I rather follow the proven science.
Well I am sorry but the proven science is as I covered it. Shortening a decreasing area tail that has attached flow increases drag. Doesn’t matter what the tail is called!