Any math teacher in the house? draw shape for weapon lines

[red Dog]

Hey guys,

 

Is there a formula of some sort to get the length and curvature of yellow bomb lines depending on the shape of the model bomb you want to use?

 

When the weapon is cylindrical that's easy enough

But when you want to draw a mask or decals for a bomb head, it's getting a little bit more complicated

 

I'm working on a triple yellow line on a GBU-31 and I'm losing my hairs

[themongoose]

red Dog here is my solution!

 

Now if you really want to do it yourself you can use a compass for the simple circles; draw 2 circles that are separated by the width of the yellow line you want to draw around the circumference of the bomb. I think that's probably what you need if you are doing a standard bomb.

 

For others you would use the equation for an ellipse or a parabola. I would do them on graph paper and then transfer with tracing paper to your final medium.

ellipse:  x^2 / a^2 + y^2 / b^2 = 1 where a is half the length and b is half the width of the ellipse you want. graph paper is your friend here if not doing this in CAD or Excel.

parabola:  way more complex. If you want to try this I need a few pages and some graph paper ;-)

 

For reference if you want to know where these apply to, the ellipse and parabola would be used if you are dividing a nose cone along it's length instead of around the circumference. The projection is generally a parabola. I've never done it with equations. I was trained as a draftman many many years ago and we learned how to do these by drawing 3 view diagrams. Now it's all done in CAD.

[scvrobeson]

11 hours ago, themongoose said:

.

parabola:  way more complex. If you want to try this I need a few pages and some graph paper ;-)

 

Shouldn't be too difficult, y= (x-h)squared + k.  But I think a bomb nose would be more of an ellipse than a parabola, since it should be an equal diameter curve all the way around

 

 

Matt 

[themongoose]

Almost all the bomb noses will be the circles. I can’t think of any that aren’t as the stripe is generally straight around the circumference but I’m leaving an opening for the exceptions that are probably out there as I’m not familiar with everything  

parabolas to me are harder because it’s tough to get the info needed to get the shape right. Circles and ellipses are closed shapes, whereas parabolas are open. So, trying to draw the curve with an equation becomes harder to guess at the slope of the line as it changes with both the width and length of the legs. So to me drawing them from your shape is easier then trying to fit a curve to it, especially in 3d where it’s harder to find all the coordinates in x, y, and z for it. I googled a drawing to see if something was out there to help with this thought…

 

hopefully that helps show the complexity I’m trying to present in creating a parabola for a 3d object like a nose cone where there isn’t already a cad drawing done that we can take the info from. 

[scvrobeson]

Yeah, measuring a bomb nose is almost like trying to measure a slice out of a sphere, since it's a constant diameter on a curved surface. Definitely not parabolic, that'd be more like trying to mask and measure around an F-16 intake. Definitely way too much math for my brain to handle on a Sunday morning.

 

I know that some guys have had success masking bomb noses by placing a pencil on the bomb nose, and then tracing it around the bomb at the fixed points you need. That might be the way to do it.

 

 

Matt 

[Rainer Hoffmann]

Lot's of complex thinking here.

 

For the purpose of painting narrow stripes it is quite sufficient to approximate the shape of the bomb as a cone. Then it's quite simple. Here is a  website for the calculation of cones and truncated cones: https://www.omnicalculator.com/math/truncated-cone

 

Just put in the numbers ...

 

However, for small scales like 1:32 you would need very exact measurements of the two diameters to get a good result. Good luck with that 

 

Cheers

Rainer