tangent ogive
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nick
Jun 26, 2012, 10:08:09 AM6/26/12
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Does anyone know how to create a tangent ogive? I don't seem to be able to get it right.
Thanks in advance
Nick
Rob McDonald
Jun 26, 2012, 10:57:13 AM6/26/12
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Nick,
There isn't an immediate 'Tangent Ogive' button in VSP. And, VSP
doesn't really support construction of one the way you would on paper
(with a compass and ruler). However, you can do a pretty good job of
making one with a little work.
The description and equation of a tangent ogive can be found here:
http://en.wikipedia.org/wiki/Nose_cone_design#Tangent_ogive
From which, I took the derivative of the 'y' equation with respect to
x. I evaluated that equation at x=0 (the nose). I haven't
double-checked, but I think the result is...
y' = 2LR/(L^2-R^2)
The nose angle will be the arctangent of that derivative theta=atan(y').
So, I then added a 'Fuse2' component to VSP and changed the cross
sections to circles. At this point, we have a circular fuselage with
radius 1.5, length 30, and the first critical cross section is at
station 7.5. I'll make the tangent ogive go to that station.
For the equations above, this means
R=1.5
L=7.5
Running the numbers
rho=19.5
y'=0.41666
theta=22.6 deg.
The slope at the circular section (Section 1) is already set to 0.0 --
this will enforce the tangency required.
You can easily change the slope at Section 0 to match 22.6 deg.
Because of the sign convention used, VSP expects a negative angle.
This still leaves the spline curve strength undetermined. To estimate
this, I made another fuselage with a circular cross section of 19.5
radius. This is the constructing circle and plays the role of a
compass in the generation of a tangent ogive. I rotated and
positioned this circle so when viewed from the top, it is in the right
place. I then adjusted the side tangent strength until it 'looked
about right'.
I've attached my result. For best results, 'View' 'Top' and 'Geom'
'Modify' 'Sel All' 'Shade'.
This is probably good enough for most purposes. If, on the other
hand, you have some detailed results and you want to compare an
absolutely perfect tangent ogive, I would recommend you use the above
equations to build a spreadsheet of x,y points along the ogive shape
and then enter multiple cross sections across the nose to model the
ogive.
Hope this helps,
Rob
There isn't an immediate 'Tangent Ogive' button in VSP. And, VSP
doesn't really support construction of one the way you would on paper
(with a compass and ruler). However, you can do a pretty good job of
making one with a little work.
The description and equation of a tangent ogive can be found here:
http://en.wikipedia.org/wiki/Nose_cone_design#Tangent_ogive
From which, I took the derivative of the 'y' equation with respect to
x. I evaluated that equation at x=0 (the nose). I haven't
double-checked, but I think the result is...
y' = 2LR/(L^2-R^2)
The nose angle will be the arctangent of that derivative theta=atan(y').
So, I then added a 'Fuse2' component to VSP and changed the cross
sections to circles. At this point, we have a circular fuselage with
radius 1.5, length 30, and the first critical cross section is at
station 7.5. I'll make the tangent ogive go to that station.
For the equations above, this means
R=1.5
L=7.5
Running the numbers
rho=19.5
y'=0.41666
theta=22.6 deg.
The slope at the circular section (Section 1) is already set to 0.0 --
this will enforce the tangency required.
You can easily change the slope at Section 0 to match 22.6 deg.
Because of the sign convention used, VSP expects a negative angle.
This still leaves the spline curve strength undetermined. To estimate
this, I made another fuselage with a circular cross section of 19.5
radius. This is the constructing circle and plays the role of a
compass in the generation of a tangent ogive. I rotated and
positioned this circle so when viewed from the top, it is in the right
place. I then adjusted the side tangent strength until it 'looked
about right'.
I've attached my result. For best results, 'View' 'Top' and 'Geom'
'Modify' 'Sel All' 'Shade'.
This is probably good enough for most purposes. If, on the other
hand, you have some detailed results and you want to compare an
absolutely perfect tangent ogive, I would recommend you use the above
equations to build a spreadsheet of x,y points along the ogive shape
and then enter multiple cross sections across the nose to model the
ogive.
Hope this helps,
Rob
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