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Old 03-10-2013, 08:38 PM   #1 (permalink)
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Drag figures for Kamm cut teardrops at various lengths?

Do you know of some drag (and maybe lift) tables for teardrop shapes cut at various lengths, Kamm style?

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Old 03-11-2013, 02:17 AM   #2 (permalink)
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Like this?



Or this?


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Old 03-11-2013, 11:54 AM   #3 (permalink)
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I thought I remember something like that, only it looked like the Template. I searched, I searched, but I didn't find it
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Old 03-12-2013, 06:20 PM   #4 (permalink)
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Quote:
Originally Posted by Big time View Post
Do you know of some drag (and maybe lift) tables for teardrop shapes cut at various lengths, Kamm style?
If you can find a copy of Aerodynamiks des Kraftfahrzeugs,by Baron Reinhard von Fachsenfeld,1951,it's packed with stuff like that.
I've been working with it slowly over a number of years now,converting the tables into smaller bite size visuals.
You'll see Kamm's actual wind tunnel model configurations with accompanying Cd for each 'slice.'
If you're in a hurry,get a local librarian to locate the nearest library which has a copy.You probably won't be able to do a inter-library loan,but it would be worth a trip.
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Old 12-12-2013, 12:11 PM   #5 (permalink)
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Drag of recessed truncated teardrop

Great to see the table on drag vs truncated lengths of teardrops as well as the graph on same subject -- I am interested in what is known as a "Camm Back" configuration as contrasted to the "Kammback" chopped off rear or downstream end. It appears that this Camm Back refers to a recessed rear face with outside thin or even knife edge shell extending out beyond this recessed face. Examples including the 1960 era Triumph TR6 with a sharp edge protuding further back beyond the vertical rear face of trunk. From what I have found, apparently this helps move the turbulent fluid back away from the truncated tail and reduces drag even further -- Does anyone know anything about this configuration and related data?? I am also interested in application of the truncated tail drag data as applied to water instead of air -- Does same data hold true for this much denser fluid or are some limits or adjustments necessary??
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Old 12-12-2013, 03:22 PM   #6 (permalink)
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"box cavity"



Colani:


Quote:
I am also interested in application of the truncated tail drag data as applied to water instead of air -- Does same data hold true for this much denser fluid or are some limits or adjustments necessary??
"Reynold's Number"
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Old 12-12-2013, 04:50 PM   #7 (permalink)
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Kamm's drag figures

Quote:
Originally Posted by Big time View Post
Do you know of some drag (and maybe lift) tables for teardrop shapes cut at various lengths, Kamm style?
*Kamm reproduced Walter Lay's research at the FKFS,along with Baron Reinhard von Koenig-Fachsenfeld in the late 1930s.
The models tested with K-form architecture represented five different lengths as opposed to Lay's four,adding an intermediate length between Lay's #3 and #4 position.
*The model terminated at 77.3% of the Aerodynamic Streamlining Template,with the rear contour terminating at 27-degrees.
*Length #1 was 37.5% AST.and measured Cd 0.25 with zero edge rounding,and zero plan taper.
*Length #2 was 45.5% AST and measured Cd 0.24 under the same conditions.
*Length #3 was 53% AST and measured Cd 0.24.
*Length #4 was 67.5% AST and measured Cd 0.22.
*Length #5 ,77.3% and Cd 0.21.
Here is the table

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*With Buchheim et al.' body side camber the full-tail Cd falls from 0,21,to 0.186.
*With Lay's 0.14% body width radius edge rounding the Cd falls from 0.186,to 0.151.
*With the full tail plan taper escalation the Cd drops from 0.151,to O.12.
I don't have any facility to analyze the intermediate positions but I did a breakdown at the AST Part-C thread.
*Essentially,the body drag varies as with the fuselage truncation,with the wheel/tire drag super-imposed upon that drag to reach the total.
*The fuselage drag doubles in ground reflection and it's half-body carries the entire drag of both 'above' and 'below' ground half-bodies.
*With wheel fairings the drag can go below Cd 0.12,as with the Cambridge University's 2013 CUER solar racer.
--------------------------------------------------------------------------
*I don't recall any lift tables for the FKFS work.Kamm wasn't interested in lift so much as with crosswind stability.All the K-cars suffered gust effect stability issues.Koenig-Fachsenfeld patented a split-fin stabilizer as a palliative.
--------------------------------------------------------------------------

*Typically,half-bodies do not generate lift in the general sense of how it is used.
*Proper truncated half-bodies produce no separation 'over' the greenhouse area.All the drag is behind the body chop,acting like a drogue-chute.
*Full-tail half-bodies have no separation at all and no wake as generally understood.As with barn doors,with enough horsepower and velocity they can be made to fly,but at 'normal' highway velocity it's not an issue.
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Last edited by aerohead; 04-05-2014 at 04:49 PM.. Reason: add image
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Old 12-12-2013, 04:53 PM   #8 (permalink)
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Recessed KammBack

The Box Cavity photo shows what I referred to as a recessed back KammBack configuration. And I realize that Renold's Number is involved -- but it has been many many years since my college fluid dynamics course and I need some help in learning whether a recessed KammBack would help reduce drag in a fluid denser than air (such as water) -- I am considering airfoil (hydrofoil) structures and plan to truncate as per the info posted above but would like to explore some calculations and am lost in the math. I don't have a clue as to how to mathematically treat or explore effect on drag (if any) as related to the recess distance back behind the outer projecting edge -- For that matter,
will the drag reduction of truncating downstream end of an airfoil (hydrofoil) in water have proportionally a similar effect as per info above for air as the fluid??
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Old 12-12-2013, 05:17 PM   #9 (permalink)
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water

Quote:
Originally Posted by jesdreamer View Post
The Box Cavity photo shows what I referred to as a recessed back KammBack configuration. And I realize that Renold's Number is involved -- but it has been many many years since my college fluid dynamics course and I need some help in learning whether a recessed KammBack would help reduce drag in a fluid denser than air (such as water) -- I am considering airfoil (hydrofoil) structures and plan to truncate as per the info posted above but would like to explore some calculations and am lost in the math. I don't have a clue as to how to mathematically treat or explore effect on drag (if any) as related to the recess distance back behind the outer projecting edge -- For that matter,
will the drag reduction of truncating downstream end of an airfoil (hydrofoil) in water have proportionally a similar effect as per info above for air as the fluid??
*3/8 th-scale automobile models have been tested underwater both by Ford and Mercedes-Benz.
*Water is 833X more dense than air and for proper Reynolds number 2-mph towing speed will represent 30-mph in air at full-scale,which gets your Rn above critical for turbulent boundary layer.
*As to the mathematics,model scale testing has been preferred to CFD in some instances do the the complex nature of the 3D flow.
*Kamm and his son tested cars underwater at the Stephens Institute at Hoboken,New Jersey.
*The David Taylor Model Basin,Maryland,operated by the US NAVY is the most famous of these laboratories.Some of the human-powered submarine competitions take place in their facility.
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Old 04-05-2014, 04:52 PM   #10 (permalink)
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visual drag table

I added an image of the K-form wind tunnel test model at #7 permalink above

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