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- - Body plan taper and drag (https://ecomodder.com/forum/showthread.php/body-plan-taper-drag-33568.html)

aerohead

03-12-2016 03:26 PM

Body plan taper and drag

aerohead

03-12-2016 03:57 PM

Part-2

aerohead

03-12-2016 04:24 PM

Part-3

freebeard

03-12-2016 04:38 PM

Quote:

I'm just going to post 'em randomly and we can talk about them later

You have the power to go back and edit the posts to enumerate them. I suggest 1.1 through 3.26. So we can talk about 'em later.

Where's the Beetle?

aerohead

03-12-2016 04:43 PM

Part-4

aerohead

03-14-2016 04:20 PM

edit/Beetle

Quote:

Originally Posted by freebeard (Post 508944)

You have the power to go back and edit the posts to enumerate them. I suggest 1.1 through 3.26. So we can talk about 'em later.

Where's the Beetle?

*yes,I can add errant data.:)
*I only have a crappy,low res. plan-view of the Beetle and it probably wouldn't serve us well.:(

freebeard

03-15-2016 03:10 AM

To what purpose?

aerohead

03-15-2016 01:31 PM

Beetle

Quote:

Originally Posted by freebeard (Post 509139)

To what purpose?

Here's a link to a better image than what I have
http://car-blueprints.narod.ru/image...-1300-1963.gif

freebeard

03-15-2016 01:44 PM

I'm waiting to learn the bounds of discussion. Everyone else just Thanked you and moved on.

Old Tele man -- your joke lives on in email notifications.

Xist	03-15-2016 01:55 PM

Big words make me sleepy!

aerohead

03-15-2016 02:23 PM

what does plan taper mean to us?

*we're trying to reduce flow separation in the aft-body or eliminate it.
*streamline body-based bodies cannot trigger flow separation.
*the reason is that the gradual pressure rise along top and sides is so gradual and progressive as to not jeopardize the turbulent boundary layer's ability to tolerate it.
*it's an area rule/sectional density issue.
*since the published data infers that the profile of a 2.5:1 streamline body would be essentially ideal for an automotive body,then it's aft-body contour suggests a benchmark,or 'template' for a low-drag tail.
http://i1271.photobucket.com/albums/...itled11_18.jpg
http://i1271.photobucket.com/albums/...titled8_18.jpg
*W.A.Mairs' boat tail is the easiest to construct and is very similar to the 2.5:1 profile,so we might use it's cross-sectional architecture as a safe profile.
http://i1271.photobucket.com/albums/...ad2/WAMair.jpg
http://i1271.photobucket.com/albums/...ntitled324.jpg
*no element of the aft-bodies cross-sectional area would vary any more than that of Mair's tail.It could be square/round/'squircle' (freebeard),etc.,or morph from one to the other as long as it's overall cross-section doesn't violate the percentage difference from one position to another.
*Morelli appears to encourage oval or circular transom,due to his 'fluid tail' ring-vortex,phantom tail pheneomena.
Here,some members have done this with their boat tail extensions
http://i1271.photobucket.com/albums/...titled5_27.jpg
http://i1271.photobucket.com/albums/...titled4_29.jpg
http://i1271.photobucket.com/albums/...titled3_31.jpg
http://i1271.photobucket.com/albums/...titled2_34.jpg
*the plan-view taper defines the limits we can expect when designing the side body taper of our mods.
*you can go 'slower' with the curvature and pay a little skin friction penalty,but you should never go 'faster' than the curve unless you've got really good CFD or wind tunnel 'proof' that it will work.Hucho warns of velocity/pressure 'kinks' along the air's pathway that can trigger vorticity or separation,exactly what we're trying to eliminate.
*The longer the body the better.Only you can decide your 'limits.'
Kamm's full body car
http://i1271.photobucket.com/albums/...titled4_28.jpg
http://i1271.photobucket.com/albums/...titled4_18.jpg
Kamm's recommendation for an extensible highway tail
http://i1271.photobucket.com/albums/...titled2_33.jpg
Kamm's recommendation for the 'stowed-tail' urban environment
http://i1271.photobucket.com/albums/...titled3_30.jpg
Kamm's plan-view
http://i1271.photobucket.com/albums/...85x11Scan2.jpg

aerohead

03-19-2016 04:21 PM

bounds of discussion

Quote:

Originally Posted by freebeard (Post 509175)

I'm waiting to learn the bounds of discussion. Everyone else just Thanked you and moved on.

Old Tele man -- your joke lives on in email notifications.

*At the Aerodynamic Streamlining Template Part-C thread there were some questions about how the aft-body plan profile would be addressed for streamlining,when considering the AST.
*I felt that this topic deserved it's own dedicated thread so it didn't get buried at the other thread,which is running to many,many pages now.
*I wanted to plant the seed of the discussion with images of how this task has been approached by others,some of which include drag coefficients which elude to how successful a particular profile turned out.This will save me millions of words.
*I'll attempt an independent 'square-to-round' thread as well in the near future after I'm more confident about some of the geometry/area data.
-------------------------------------------------------------------------
*The major theme is that whether we stick with the original frontal/rearward vertical elevation profile of our candidate vehicle,or morph it from,say,square-ish,to more 'round-ish',we should not allow the cross-sectional area to ever vary any more than that of the streamline body of revolution of near fineness ratio 2.5:1,to protect the velocity/static pressure profile.(which protects the boundary layer from separating)
--------------------------------------------------------------------------
*keeping track of the areas may entail breaking each cross-section into elements of squares,rectangles,circles,and elliptical areas.Which should be easier than ever with online calculators.
-------------------------------------------------------------------------
*Most production vehicles have bodies which attain roof convergence before side body convergence and when viewed from above will have to respect the fact that the plan-view streamlining will have to lag behind that of the roof/greenhouse.

sendler

03-21-2016 06:41 AM

This shows clearly that when streamlinig a truncated shape that half the improvements can be lost at the back.
.
.
https://scontent-iad3-1.xx.fbcdn.net...46264019_o.jpg
.
.
.

freebeard

03-21-2016 11:56 AM

Quote:

*I'll attempt an independent 'square-to-round' thread as well in the near future after I'm more confident about some of the geometry/area data.

The transition from square to round is defined by the superellipse equation with 1<n<2. Just run the subset (not quite square to not round) solving for area backward for each % reduction in area at subsequent longitudinal stations.

Quote:

The area inside the superellipse can be expressed in terms of the gamma function, Γ(x), as:
\mathrm{Area} = 4 a b \frac{\left(\Gamma \left(1+\tfrac{1}{n}\right)\right)^2}{\Gamma \left(1+\tfrac{2}{n}\right)} .

gafhj

03-21-2016 04:35 PM

Quote:

Originally Posted by sendler (Post 509503)

This shows clearly that when streamlinig a truncated shape that half the improvements can be lost at the back.
.
.
https://scontent-iad3-1.xx.fbcdn.net...46264019_o.jpg
.
.
.

I keep looking at it and can't seem to read it otherwise: J-form is better than K-form.
This contradicts what I used to know. Can anyone explain what's up?

freebeard

03-21-2016 04:58 PM

"I try to think but nothing happens"

Maybe it's that the chart compares fineness ratio and truncation, in dimensionless numbers? Apple and oranges?

sendler

03-21-2016 06:08 PM

Quote:

Originally Posted by gafhj (Post 509548)

J-form is better than K-form.

If the chart is accurate it is showing that for any given total length, the J form has nearly half the drag of the K form until you get out to the last 10-20% where the Kamm truncation is not so much of a loss.

freebeard

03-21-2016 10:55 PM

The overall lengths are not equal, by about 5%. The diameters are. The shorter lengths are disparate.

Kt=60 has no analog in J and the J curve is incommensurate with the horizontal scaling.

Possibly you could say that, in general, the area between the curves represents the benefit from wake stuffing.

aerohead

03-22-2016 05:14 PM

truncated

Quote:

Originally Posted by sendler (Post 509503)

This shows clearly that when streamlinig a truncated shape that half the improvements can be lost at the back.
.
.
https://scontent-iad3-1.xx.fbcdn.net...46264019_o.jpg
.
.
.

Bear in mind that these structures are 2D airfoil sections,like the fuselage of AeroVironment's human-powered airplane.
For 3D auto bodies,Kamm's bread chop truncations would have an advantage except at fairly long lengths.

aerohead

03-22-2016 05:18 PM

J-form better

Quote:

Originally Posted by gafhj (Post 509548)

I keep looking at it and can't seem to read it otherwise: J-form is better than K-form.
This contradicts what I used to know. Can anyone explain what's up?

These are 2D wing section models.
For 3D auto bodies the Kamm truncation would have the advantage,unless at rather long lengths,where it's a 'wash' between the two types.

sendler

03-22-2016 05:20 PM

I am always thinking about these aero shapes as would be applied to the top view of a motorcycle streamliner. The J form looks to be much better than a Kamm for a reasonable length.

aerohead

03-22-2016 06:17 PM

motorcycle

Quote:

Originally Posted by sendler (Post 509632)

I am always thinking about these aero shapes as would be applied to the top view of a motorcycle streamliner. The J form looks to be much better than a Kamm for a reasonable length.

Definitely! The Kamm chop costs us in quite a drag penalty.
The closer you can get it to the ideal,4:1 aspect ratio the better,dragwise
http://i1271.photobucket.com/albums/...head2/8-24.jpg
http://i1271.photobucket.com/albums/...rohead2/-2.jpg
http://i1271.photobucket.com/albums/...2/HPIM1949.jpg
If there were stability issues,you might have to compromise on drag,if it couldn't be sorted out with other parameters
http://i1271.photobucket.com/albums/...2/HPIM1955.jpg

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