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Conic Tool issue - Rho Value seems completely wrong
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sweboss  
#1 Posted : Wednesday, February 8, 2023 4:58:54 AM(UTC)
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When using the Conic Tool, whether it's the Two Point, Three Point or Four Point Tool, the Rho Value is not giving the expected result. As I understood the Rho Value is defined as A divided by B, whereas A is the top of the curve and B is the vertex.

When I change the Rho Value to 0.75 I got the curve I expected for Rho 0.5 and with Rho 0.5 as set value the curve is almost flat.

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specktech on 4/10/2023(UTC)
Tim Olson  
#2 Posted : Wednesday, February 8, 2023 9:53:20 AM(UTC)
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It looks good here.

This is how we checked/calculated Rho at Lockheed, which is also the same method used by Dassault for ACIS.

Rho of 0.707 with straight and equal distances to control point should yield an exact arc.
Rho of 0.5 with straight and equal distances to control point should yield a line.
Rho is ratio to shoulder point and control point.
Shoulder is intersection of diagonal and conic.

Where rho > 0.5 and < 1.0.

Tim

Edited by user Wednesday, February 8, 2023 7:17:45 PM(UTC)  | Reason: Not specified

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GARLIC on 2/8/2023(UTC), specktech on 4/10/2023(UTC)
sweboss  
#3 Posted : Wednesday, February 8, 2023 10:32:39 AM(UTC)
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Thanks, Tim.

It seems though that you are referring to another definition than what I once learned, which is as enclosed graph.
Anyway, now I know how it's calculated in TurboCAD.

Edited by user Wednesday, February 8, 2023 10:35:13 AM(UTC)  | Reason: Not specified

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specktech on 4/10/2023(UTC)
Tim Olson  
#4 Posted : Wednesday, February 8, 2023 11:29:11 AM(UTC)
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I am a fan of conics:) Conic and polyconic surfaces was the preferred surface of choice for exterior configuration design of the F-16, F-22, and F-35.

No inflections and they stayed tangent at edges as you changed the rho to increase/decrease cross sectional area distributions during advanced design phases.

For the F-16, most surfaces are polyconic with the remainder ruled. Even the most difficult surface being the lip of the smiley duct was created using polyconic surfaces and a spine:)

For F-22 & F-35 production we moved over to CATIA where conic surfaces were elevated to higher order to get certain curvature distributions, but were still based on the same core definitions.

Tim

Edited by user Thursday, February 9, 2023 3:33:01 PM(UTC)  | Reason: Not specified

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GARLIC on 2/8/2023(UTC), sweboss on 2/8/2023(UTC), specktech on 4/10/2023(UTC)
jlm  
#5 Posted : Thursday, February 9, 2023 8:17:59 AM(UTC)
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Originally Posted by: Tim Olson Go to Quoted Post
I am a fan of conics:)

Tim


I'm a fan of conics too.
My projects can't fly like F16, but sometimes they sell like hot cakes...

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specktech on 4/10/2023(UTC)
jlm  
#6 Posted : Thursday, February 9, 2023 8:35:30 AM(UTC)
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Originally Posted by: jlm Go to Quoted Post
Originally Posted by: Tim Olson Go to Quoted Post
I am a fan of conics:)

Tim


I'm a fan of conics too.
My projects can't fly like F16, but sometimes they sell like hot cakes...



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damhave on 2/9/2023(UTC), specktech on 4/10/2023(UTC)
Jean-Francois Jacques  
#7 Posted : Thursday, February 9, 2023 1:35:06 PM(UTC)
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Good to know! I did an upper part with conics, and now I want to do the lower part with an other conics (like an airplane wing). How can I do a continuity with the right part of my geometry. (tangent with an other conics) ??
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Tim Olson  
#8 Posted : Thursday, February 9, 2023 2:48:24 PM(UTC)
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You might try using TWO four point conics where the control points go through a shared line at the leading edge.

That will get you tangent continuity.

If you want rough curvature continuity, manually elevate the conic to order 5 and moved some of neighboring control points around. Use the verify : curvature circle at the leading edge for guidance.

I wish we had a curvature match tool available for curves. Our 2D DCM solver offers a curvature constraint, maybe I should explore hooking that up

Normally airfoils have curvature/camber distributions as part of their definition. Something else you can do is visit this site...

http://airfoiltools.com/airfoil/naca4digit

Create your airfoil and then copy the Dat file into a text file. Remove everything but the x,y points and then import this as a Spline file into Shark.


Tim

Edited by user Thursday, February 9, 2023 11:53:14 PM(UTC)  | Reason: Not specified

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GARLIC on 2/10/2023(UTC), specktech on 4/10/2023(UTC)
Tim Olson  
#9 Posted : Thursday, February 9, 2023 2:55:45 PM(UTC)
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>>>My projects can't fly like F16, but sometimes they sell like hot cakes...

I love that! Thanks for sharing those images.

Tim


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specktech on 4/10/2023(UTC)
Jean-Francois Jacques  
#10 Posted : Thursday, February 9, 2023 4:39:50 PM(UTC)
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Originally Posted by: Tim Olson Go to Quoted Post
You might try using TWO four point conics where the control points go through a shared line at the leading edge.

That will get you tangent continuity.

If you want rough curvature continuity, manually elevate the conic to order 5 and moved some of neighboring control points around. Use the verify : curvature circle at the leading edge for guidance.

I wish we had a curvature match tool available for curves. Our 2D DCM solver offers a curvature constraint, maybe I should explore hooking that up

Normally airfoils have curvature/camber distributions as part of their definition. Something else you can do is visit this site...

http://airfoiltools.com/airfoil/naca4digit

Create your airfoil and then copy the Dat file into a text file. Remove everything but the x,y points and then import this as a Spline file into Shark.


Tim


Thanks TIM !

Edited by moderator Thursday, February 9, 2023 11:19:16 PM(UTC)  | Reason: Not specified

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