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Old 06-11-2024, 05:54 PM   #1 (permalink)
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Supersonic Radial Ogive

This outside the typical Ecomodder remit; but perhaps aerohead will appreciate the historical insight.

The shape is double-ended with a straight center section, derived from a boat-tailed supersonic military bullet. None of the 30-70 forward bias one might expect.

He goes on for over an hour, but never gets to my favorite modern rocket, the Rocket Lab Neutron.


https://img2.cgtrader.com/items/3469...blend-gltf.jpg

This has a boat tail more similar to the 19th Century military supersonic bullet, plus tail fins with minimal frontal area.

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Old 06-13-2024, 10:47 AM   #2 (permalink)
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' 12.5 X diameter radius, double ogival body '

Awesome video!
For supersonic flight, ruled by shockwave drag, the 'pointy' nose allowed for successful flight, once Volkswagen got the sheet metal thick enough to survive max-Q.
Translated to subsonic operation though, the nose would demonstrate a distinct disadvantage, drag-wise.
Then you'd desire the 'bulbous' nose ( forebody ), constituting the ichthyoid ( fishlike [ cod's head ] ) 33.3%, and 66.3% ( mackerel tail ) aft-body; and ideally, the l/d = 2.5 fineness ratio, in mirror image ground reflection.
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Old 06-13-2024, 12:17 PM   #3 (permalink)
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I like their characterizing a curve as the radius of a hypothetical circle, rather than an angle as with The Template discussions.



The Hugo Award gets the ichthyoid part right.
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Old 06-17-2024, 11:29 AM   #4 (permalink)
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' angle '

Quote:
Originally Posted by freebeard View Post
I like their characterizing a curve as the radius of a hypothetical circle, rather than an angle as with The Template discussions.



The Hugo Award gets the ichthyoid part right.
Road vehicles don't have the luxury of the rocket's fineness ratio, and as 'bluff' bodies 'ARE' limited in the magnitude of all local tangent angles along the aft-body contour, such that they remain incapable of triggering the adverse pressure gradients that cause flow separation.
In addition, 'curves' are aerodynamically inefficient compared to a streamline contour.
I gave you the ROLEX, Big Ben 'template' over a decade ago. It is based on the 'curve' of the dimpled golf ball. It provides a separation-free aft-body, but at the cost of added length, friction drag, weight, etc., compared to the 'template', which performs the same task with the absolute minimum in material.
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Old 06-17-2024, 12:45 PM   #5 (permalink)
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Quote:
I gave you the ROLEX, Big Ben 'template' over a decade ago.
Citation? Or are we talking about Thee Holy Template?
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Old 06-20-2024, 11:34 AM   #6 (permalink)
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' or are we talking about...'

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Originally Posted by freebeard View Post
Citation? Or are we talking about Thee Holy Template?
1) The thread was presented as an alternative 'template' to the ASTs.
The aerodynamics of the sphere is so well known that, it's measured drag can serve as a calibration for Reynolds number.
2) If an analog 'clock face' is superimposed on the image of a sphere, in side elevation, and 'flow' is attacking from the 'left', we already know what the flow is doing, whether in a laminar boundary-layer ( LBL), or turbulent ( TBL ).
3) The forward's stagnation point will always be 3:00 O'clock.
4) With LBL, the flow will separate near the 11:00 O'clock location, before the flow ever reaches the maximum cross-section of the body.
5)'Dimpling' just the leading edge of a smooth sphere forces an immediate transition to TBL, which, without going into boundary-layer theory, has the facility to survive positive ( adverse ) pressure gradients that would trigger flow separation in a LBL.
6) With the dimpled golf ball, coming off the face of a club head @ 110-mph, the flow separation is moved from 11:00 O'clock, rearwards to 115-degrees behind the forwards stagnation point, adding pressure recovery, a smaller wake, of higher base pressure, lower total drag, greater distance off the tee.
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7) If you project a horizontal line from the new separation point, to the left, until it intersects a vertical line down from the 12:00 O'clock position, you've isolated an oddly-shaped 'pie-piece,' that can be used as a template for streamlining.
8) You'd 'double' the image, in mirror-image ground reflection, introduce whatever ground clearance you chose, leaving the separation point at the road interface.
9) Add a 'nose' and you have a separation-free shape.
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10) It will be 'longer' than the ASTs, so the friction drag will be amplified, but it will be free of pressure drag.
11) I've flown over London, but have never 'been' there, so I don't know how Big Ben actually is, but it's face would probably be large enough to create one of these crude templates for cars and light trucks. It's aerodynamics is a 'known quantity'.
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Old 06-20-2024, 12:19 PM   #7 (permalink)
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Quote:
2) If an analog 'clock face' is superimposed on the image of a sphere, in side elevation, and 'flow' is attacking from the 'left',... The forward's stagnation point will always be 3:00 O'clock.
Possibly 0900?
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Old 06-21-2024, 09:25 AM   #8 (permalink)
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Probably more than you cared to know: https://www.visitlondon.com/things-t...action/big-ben

The forward stagnation point is relatively fixed? Hmmmm. If true, learned something new today that slightly violated observational theory only because you cant change angle of attack on a clock tower.
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Old 06-24-2024, 10:12 AM   #9 (permalink)
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' 0900 '

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Originally Posted by freebeard View Post
Possibly 0900?
That's pretty funny!
We can add dyslexia to my repertoire now. If I could do images it might keep me square with the world. Oh well.
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Old 06-24-2024, 10:25 AM   #10 (permalink)
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' fixed '

Quote:
Originally Posted by Piotrsko View Post
Probably more than you cared to know: https://www.visitlondon.com/things-t...action/big-ben

The forward stagnation point is relatively fixed? Hmmmm. If true, learned something new today that slightly violated observational theory only because you cant change angle of attack on a clock tower.
Yeah, if the 'clock' is moving from right, to left, and not rotating ( for the sake of simplicity ), the location at 9:00 o'clock is technically the only one that would satisfy the requirement that all dynamic pressure ( 1/2 rho v-squared ) were impacting without any bleeding.

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