Lofting a fuselage

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Aerowerx, Jul 9, 2016.

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  1. Jul 9, 2016 #1

    Aerowerx

    Aerowerx

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    Raymer's "Simplified" book has a whole chapter on conic sections, lofting, and flat wrap.

    Although I understood how to draw a conic section, I could not grasp how to apply that to drawing a fuselage that could be flat wrapped.

    Today, however, I found this article from the Sept 1990 Sport Aviation. It is written by the guy that created the FLOFT program, which eventually became Loftsman. Unfortunately this program costs almost $300.

    This document is the user manual for the Loftsman program, and has even more discussion on the method.

    I need to study it a bit, but I am beginning to see how it all works, and thought that other HBAers that prefer pencil and paper instead of bytes and pixels would find it of interest.
     
    Last edited: Jul 9, 2016
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  2. Jul 9, 2016 #2

    Aerowerx

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    There is a demo version of the Loftsman program available here. (the one labeled PSW).

    Loftsman is described on their web page as:
    I just downloaded the demo. Although it does not save output, it might be interesting to play with, and may be possible to do a screen capture to get the output.
     
  3. Jul 9, 2016 #3

    mcrae0104

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    I find lofting really fascinating. A while back, to get a grasp of flat wrap lofting I worked up some arbitrary shapes using Raymer as a guide. These were worked out in 2D as a series of bulkheads (could've just as easily been done with paper & pencil) and then projected into 3D (just lines in space, not surfaces) to visualize and check the work. Fun stuff to play with. You guys that work in SolidWorks and Catia might find this a waste of time but it's fun to see how the old school manual methods really do work. I think if AutoCAD had slightly different spline controls you could skip all the laborious "shooting" of points and draw bulkhead shapes directly without constructing them manually. I recall searching in vain for a simpler method.

    loft 01.jpg

    loft 02.jpg

    loft 03.jpg

    Also, here's a look at the basic amount of curvature you get by varying rho.

    rho.jpg
     
    Last edited: Jul 9, 2016
  4. Jul 9, 2016 #4

    Swampyankee

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    If there's a boat builder or airframe company in the area, you may be able to find some of the older drafters who have done lofting. If they're bored, they may be willing to give lessons. I think hand-lofting was done, even in the big shops, into the 1990s, so it maybe a moribund skill, but it's not extinct.
     
  5. Jul 9, 2016 #5

    BJC

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    Boat designers have some skills that drectly correlate to aircraft design. I met a fascinating designer back in 1984. He was confined to a wheelchair, but was well known, and was workng on several contracts to design the hulls and structure of what are commonly called "mega-yachts". (All were being built in other countries. Remember the Jimmy Carter luxury tax, that adversely impacted manufacturing of boats and airplanes in the USA?)

    The designer had a computer that he had designed, built, and programmed. It was spread over a plywood table in his office, and occupied a space about two feet deep by eight feet long. And remember, this was in the early1980's.

    Fascinating, very talented man.


    BJC
     
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  6. Jul 10, 2016 #6

    bcguide

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    a fellow by the name of Kevin Morin on the welding web forum has a thread on boat building that has good info on lofting. search for [h=2]Welded aluminum skiff build[/h]
     
  7. Jul 11, 2016 #7

    Jon Ferguson

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    I've done a little paper and pencil lofting for a wood and glass boat I built years ago. It wasn't bad really. Ton's of boat building books out there can teach you how to do it.
     
  8. Jul 12, 2016 #8

    Kestas

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    There are described some ways of a fuselage lofting. Its my old article for Vilnius Technical University students. Sorry, it is in Lithuanian only, but the pictures may help, I hope.
     
  9. Jul 13, 2016 #9

    Gurney

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  10. Jul 13, 2016 #10

    fly2kads

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    Google's "translate a document" feature did a respectable job of translating the PDF from Lithuanian to English. Thanks!
     
  11. Jul 13, 2016 #11

    Aesquire

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    The first airplane I know of built with conic lofting was the P-51.

    It took a serious amount of math time, room full of gals with mechanical adding machines for weeks.

    But when done it was the first plane with a fuselage entirely defined by numbers.

    IIRC it was Irving Ashkenas who gets credit.
     
  12. Jul 15, 2016 #12

    Aerowerx

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    Didn't work for me at all.
     
  13. Jul 18, 2016 #13

    proppastie

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    funny this thread now....I did my rib profiles for my Horizontal Stab. and elevator in 3D. Basically a ruled surface between the tip and root rib, with lots of planes and intersections.....pain.....I did the Vertical Tail the old way (in Autocad) in about 1/5 the time.
    I did have to digitize, (arcs) the profile of the end and root rib, but you almost could see the ends of the arc on the paper so it was rather easy.
     

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