Control surface issues

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Jonny Gambell

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Mar 7, 2023, 9:27:13 AM3/7/23
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I'm having some issues modelling rudder control surfaces in OpenVSP. A start U of 0.35 is the smallest value I can select for the spanwise direction. I need the rudder to begin at a fraction of 0.15 of the span direction but this doesnt seem to be possible.

Any help would be very much appreciated.

Thanks,
Jonny
Screenshot 2023-03-07 142432.jpg

marco

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Mar 8, 2023, 3:43:27 AM3/8/23
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in the Plan tab,.. what are your root and tip cap settings?

Sehwan Park

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Mar 15, 2023, 6:31:00 PM3/15/23
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Jonny, I believe it will work as you wanted if you set root/tip cap setting as None.

Sehwan
2023년 3월 7일 화요일 오후 11시 27분 13초 UTC+9에 Jonny Gambell님이 작성:

Rob McDonald

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Mar 15, 2023, 6:35:43 PM3/15/23
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The U parameter of a wing-type surface includes the root and tip cap.  Each wing section (including the root and tip cap) gets an equal proportion.

So, for your vertical tail, the root cap runs from [0,0.3333], the main wing panel runs from [0.33333, 0.66666] and the tip from [0.66666, 1.0].

If you want a control surface to run from 15% to 70% of the main wing panel, then you want it to start and end at:

Ustart =0.333333 + 0.15 * 0.333333 = 0.38333333333
Uend = 0.333333 + 0.7*0.3333333 = 0.566666666

Rob


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Jonny Gambell

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Mar 16, 2023, 10:40:31 AM3/16/23
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Thank you all, I really appreciate the help. Do you know why the line representing the pivot of the control surface appears curved in the first screenshot I posted?

Thanks,
Jonny

Rob McDonald

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Mar 16, 2023, 12:37:17 PM3/16/23
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I've approximated your vertical tail in this image -- but instead of a shaded view, I've used the Hidden view...

VTail.png


The blue lines that run spanwise and chordwise are in U,V coordinates.  Those are the parametric coordinates that define the surface of the wing.

The SubSurfaces (including the control surface) are drawn in U,V space -- not X,Y,Z space.  Try treating the blue grid as graph paper and plot out a 'straight' line in U,V space -- you will find that it is not a straight line in XYZ space.

So, for control surfaces, I try to do a little better.  I calculate two intermediate points on each side and then draw three straight line (in UV) segments.  Usually, this does a pretty good job.  However, in situations like this where the UV coordinates are particularly warped (with respect to XYZ), the boundaries will appear curved.

Rob


Brandon Litherland

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Mar 16, 2023, 1:09:48 PM3/16/23
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We cover this a bit in the OpenVSP Ground School topic on Control Surface Refinement.  The relevant bit comes in at about 2:40.
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