Some added tables for AS'Template' Part-C

[aerohead]

I put these tables together from the original streamline body of revolution table to demonstrate how the drag will vary as it is brought down into ground proximity as a half-body,then what happens when wheels are added,and finally assigning a drag value to the wake itself.
NOTE: These values are only valid for the 12% thickness streamline body,although how the value percentage changes as a function of truncation percentage will be common to all bodies.



Here is a 2-D flow drag table I morphed from two in Hoerner's book.Remember,it's not 3-D,but you can see the effect of gaps and attempts to 'cheat' the air compared to 'ideal' teardrop forms.



Here is a table for 'J-form' wing/strut sections.Cd for the section is at left,and Cd of 'missing' portion is within yellow area

[freebeard]

Are your Photobucket albums public? (Answered my own question: Yes)

...the drag will vary as it is brought down into ground proximity as a half-body...

Uniform proximity in these examples. What is the distance, some % of the width?

[aerohead]

Originally Posted by freebeard

Are your Photobucket albums public? (Answered my own question: Yes)

Uniform proximity in these examples. What is the distance, some % of the width?

Paul Jaray discovered the effect and published about it in 1922.He found that when you brought an airship body down into ground proximity its drag would rise,reaching a maximum of 2X when pushed halfway into the ground,creating the half-body.
Walter lay took an airship body of Cd 0.04 and found that at a standard automotive ground clearance the Cd would be 0.08,or 2X.
Ludwig Prandtl and Edmund Rumpler continued the research,and later Stollery got into it as well as Rolf Buchheim,one of Hucho's associates at VW.
Hucho published a drag table illustrating the drag deviation as a function of ground clearance and uses it to flesh out the concept of "Effective-Bluffness or "Effective -Fineness Ratio" as it's one of the most important concepts in road vehicle aerodynamics.
I tried to illustrate the concept at the A.S.Template Part-A,B,C,maybe D.
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Since pictures are working better than text,I'll try 'n get that posted unless someone else with Hucho's book would like to do that post.
At the time of Kamm and Koenig-Fachsenfeld's research at the FKFS they were using 25 cm as a 'standard' automotive ground clearance.Their 'reproduction' of Lay's 1933 model suggests that 25cm was kinda what Lay used and got 2X drag increase.No dimensions are given for Jaray's 'pumpkin seed tested by Klemperer.It would be straight-forward to do a non-dimensional G.C. as a function of % overall height as a reference datum.
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Essentially though,whatever ground clearance we have on our 'store-bought' cars is what we're gonna have to work with.
If we
mirror-image our cars and look at their effective bluffness,we can compare to the relatively 'ideal' L/D= 2.5 in reflection,or L/H = 5 as the half-body.
Let's get the image going!

[aerohead]

I've edited the 1st permalink and added a drag table for machine gun barrel fairings morphed together from two in Sighard Hoerner's 1951 book,'Aerodynamic Drag'.
It's 2-D flow,although you'll easily see what gaps and shortcuts do,compared to 'ideal' teardrop forms.
The Cd 0.08 form is an instance where frontal area has been increased and results in overall lower drag.

[sendler]

The last three are interesting to me. The .08 is the shape we should be going for with our motorcycles and shows how good a short fineness airfoil can still be with the right curvature.
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The last two show what I have been trying to point out in the other threads about truncation. With a super long airfoil, by the time you truncate 30%, you have chopped off most of the part that is tapered. You are left with nearly straight sides already. And poor numbers. These long airfoil shapes do not satisfy the rule of thumb where the width at the truncation must be less than half the maximum width. The results of truncating a super long airfoil are clearly not representative of what can be expected for "all' airfoils. As shown by the second to last shape. If truncation is planned, the shape must be designed with a shorter fineness to retain an 11% slope leading up to the truncation.

[sendler]

Although, it looks like even a fat foil such as 0040 will measure half max width for a truncation of only 24%.
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[aerohead]

Originally Posted by sendler

Although, it looks like even a fat foil such as 0040 will measure half max width for a truncation of only 24%.
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I'm working on a table for symmetrical wing sections from Hoerner's book.
The table he has illustrates the drag curve for the wing section as a function of the truncation percentage of chord length.
Also,the mathematical formula is provided for calculating the drag for any % truncation.It requires an entry-level scientific calculator which can handle cube-roots and Y-to-the-x power.A few memory caches are handy.
It will be next Saturday at the soonest before I'll have it ready to scan/Photo-Bucket/and transfer over.
I think you'll like it.
Hoerner says it can be used for any conventional wing as long as the maximum thickness is located around 30% of chord.The math is based on the section thickness only.It doesn't matter what the thickness ratio is.
You are going to be alarmed at how quickly the drag rises as you chop away the trailing end.
Overall,the aft-body of the wing is responsible for over a 900% (9-X) drag reduction of the wing.
And also,the Kamm chop does not work with wings as it does with bodies of revolution or half-bodies.I'm working on a table for that as well.But I would advise you to wait before you lock in any design until you see this material.
If you can find access to the book,'Aerodynamiks des Fraftfahrzeugs' by Baron Reinhard von Koenig-Fachsenfeld,1951,you'll have access to a gold mine of data.Also 'Aerodynamic Drag' by Sighard Hoerner.

[sendler]

Thanks to you and everyone here for all of their hard work. I don't mean to be so contrary. But it is just that I tend to challenge things I am told until I grasp the information and understand it from the inside. I am not formally trained so I can stand outside the box and look in.
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The above charts with the snow cone shapes is exactly what I was looking for in the other thread. I am already slightly dissatisfied with the straight taper tail I have started. I can see now that a true foil made from glass over a mold will be worth the trouble. I am also working on trying to make a contact at the Cornell wind tunnel so I can do some testing. I believe that 150 mpg at 65 mph is possible with an aero and engine/ gearing optimized Honda CBR250R.

[freebeard]

I don't mean to be so contrary.

You are cranky but nobodies here to point fingers.

I am already slightly dissatisfied with the straight taper tail I have started. I can see now that a true foil made from glass over a mold will be worth the trouble.

[aerohead]

I've completed the wing/strut section tables and they're scanned,but I can't get into Photo-bucket.Perhaps summer-vacationers have overwhelmed the site.
I'll keep an eye on that window and if the green arrow ever stops spinning,try 'n get the new stuff down-loaded and linked over.
Hurry up and wait!