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F-18 Mold Line Surfacing

F-18 Mold Line Surfacing

(OP)
Hello Everyone!

I have a part that I'm working on that requires a surface to be created by using the mold line data points supplied in the Northrop Data book. This part is for the F-18 and the part will be on the exterior of the aircraft. Has anyone worked on or is familiar with creating a surface from this. The data book is from 1989 and most of the people that I worked with in the past that knew how to interpret this data is no longer in the industry.

If anyone could point me in the right direction of a person that may be able to help me on this would be great!

Scott

RE: F-18 Mold Line Surfacing

The book should state what the data is, and how it would be used to create a surface.
Points (xyz) are usually for driving splines (or other types of smooth curves), and then the splines would be used to sweep a compound surface.
Point-vectors (xyz, ijk) are usually for driving lines, and then the lines would be used to sweep a ruled surface.
And of course, there are all kinds of variations on that, I.E.; hyperbola & parabola data, true arc data, actual hand drawn loft data, etc.
However, I wouldn't use a Data Book to hand key in surface data. Takes too much time, and is error prone. A lot of us have many horror stories about days of keying in data back in the old days.
Request from your buyer the digital dataset of the surface. Most all of the major aerospace manufacturers have converted their old Loft and Data Book information into digital datasets. I am surprised and happy about how many of the really old surfaces that have been converted.
Some buyers (who don't know) will say that the digital dataset doesn't exist, or, they can't get it.
Remind them of the time & error costs, and offer to procure the data yourself.

Harold G. Morgan
CATIA, QA, CNC & CMM Programmer

RE: F-18 Mold Line Surfacing

(OP)
Thank you for the information! I understand how error prone it would be having to manually enter in the surface data for the curves. There are equations and with all the inputs a mistake can easily be made. I will have to contact the customer once again and request the electronic dataset. Unfortunately this customer is slow at getting back to supplier's request. We don't want to make an error on the surface and change the drag to the section of the aircraft.

Scott

RE: F-18 Mold Line Surfacing

Be careful which F-18 variant you are looking at. the early A, B, C, and D are completely different than the E & F and G.

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