cuoremia

I'm interested in lofting some detailed three view drawings, to get the fuselage sections. Can anyone recommend a cad program or text that would perform or explain the technique

Chad Veich

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Dave Platt's "Scratch This" series of videos will teach you what you need to know.  A CAD program is simply a tool for designing and cannot teach you how to design any more than a T-square and a pencil could.  I have never Googled "lofting" but I imagine if you did there may be some tutorials about the subject online somewhere.  Good luck with it!

Chad Veich

cuoremia

Thanks Chad,

I did lofting in college,45 years ago in engineering graphics, but never used it since.I'll look into the videos you've suggested.

Mike

dreadnaut

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I use AutoCAD to loft with. Like you, I learned iton drawing boards, as part of ''descriptive geometry". A lot of people will tell you that AutoCAD is horrble for doing 3d, but I dissagree. If you have an engineering background, and are comfortable using cartisian, and polar coordinate systems, it is very straight forward.

There is quite a bit to learning the program, but it is not to bad if you learn to use typed commands. There is a text box at the bottom where you type commands. Type ''line'' if yiou want to draw a line, then it will prompt you for input. An important command for 3d is ''UCS''. This stands for ''user coordinate system''.

The important thing to understand is that all CAD programs, including AutoCAD, are not 3d; they are (2+1)d. This means that by default, eveything you do is in the x.y plane. If you want to do a circle that is not in the global x.y plane, you will need to define a UCS with an x',y' for it. When lofting in 3d, I draw a profile of the top view in the global CS (AutoCAD calls it the ''World CS'' to be different). Then I set a new UCS by typinf ''UCS'', then at the prompt I type ''Y'', enter then ''90'' enter. This creates a UCS by rotating the WCS around the y axiz, by 90 degrees. Then I draw the side profile in thes UCS. Now type ''UCS'' enter, ''X'', enter for a UCS that you can start lofting formers in.

Read the command line. When it prompts you for input it will list options like rotating about an axis, or redifining the origin etc. Play with it, if you use this aproach, and have pretty strong geometry skills, you should be able to work it out.

ppljr

My Feedback: (94)

Give Rhino 3d a try.  It is very easy to get going.  Go to their website and download a free trial.

BMatthews

Er... just checking.  You do realize that you need a few sections shown first before you can loft the ones in between?  Sorry if this is basic but some folks seem to think they can get accurate sections from a little 4x6 3 view that has coarse line widths.

dreadnaut

My Feedback: (5)

Er... yeah.

The last I did this it was on a Yak. The first few formers are round. If the first tracings I made of the profile don't fit they need to be tweeked.

I think that cuoremia meant ''lofting'' in the old fasioned ''compas and scale'' way. If I have two profiles (top and side) and a decent Idea of what the thing looks like, I can draw sections. It won't make top grades in the Scale Masters, but it works for me.

Avaiojet

I never heard of "lofting."

Charles

tasesq

I am a serious NEWBIE when it comes to any CAD program, however i think i know what you are trying to achieve.

I am doing it at the moment with a 3 view of an aeroplane using Google's free program - sketchup. I was able to pick this basics of this program up very quickly with ZERO CAD usage before hand.

I downloaded Rhino andgave up after a couple of hours because it was just way too hard!The thing with Sketchup is that you can search hours and hours of tutorials online and for sure you will find one addressing the particular outcome you are trying to achieve. I reccommend it. A friend of mine has actually designed a new pergola/deck with it!

http://sketchup.google.com/

Here's a screenshot of the nose of the aircraft 'lofted' from 3 views - this will be to fill the voids with foam and make a plug.

Also - i was able to take the wing formers from Profili, add building tabs and build the wind 'virtually' to iron out any problems - great program.

dreadnaut

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Most in this forum will say that lofting is something done on a computer, and this is true, but it is derived from teqniques from the manual technical graphic area of ''Descriptive Geometry''. For example if you have a wing with a root section of one airfoil, and a tip with a different airfoil, and wanted intermediate ribs that blended from one to the other, you would ''Loft'' them on a drawing board with a compas, dividers and a scale (ruler).

The sample shows a loft of two intermediate ribs. The profiles are divided into 12 equal segments. Lines are drawn between corresponding divisions, then those lines are divided and the ribs are are lofted. I show this partialy done.

This is a simple case. The ribs are evenly spaced and parralell to each other. Most CAD programs have a feature called ''lofting''. It works, but has limits. In the Jet example posted above sections are lofted between several sections. The problem arises around the windscreen, which are flat sections, with are not reflected with hte simple computer generated loft.

I like lofting the old fasioned way, modified by the ability to use stick models in AutoCAD as a 3d ''drawing board.

CAD_Flyer_321

try using AutoCAD Inventor Professional Suite 2010, it includes AutoCAD and Autodesk Inventor, plus its an almost $8000 program free to anyone that has a .edu email address. students.autodesk.com has all the info plus tons of tutorials on it. You get the educational version which is completely full featured, only thing different is it prints an "Produced by an Autodesk Educational Product" watermark around the outside of all drawings.

cuoremia

My Structural analysis professor always stressed learning the pencil and paper method of analysis, so when a computer analysis is used, you can interpret the results as being correct or garbage. I would like to learn the manual method of lofting intitially,then progress to one of the programs you've all recommended.I'm a retired aerospace engineer, and haven't dealt with descriptive geometry since 1965, when I received my degree. that's why i appreciate your responses.

I notice when purchasing plans of an aircraft,i.e. the FW190, they vary with respect to scale accuracy, in overall layout and structural components,bulkheads,ribs,formers,etc. I have a wealth of information on this aircraft,some drawings include bulkheads,but not the airfoil stations. I'd like to be able to take any 3 view drawing and accurately determine the sectional profiles. I have the lofting drawing from Focke Wulf,showing he fuselage cross sections, and also the geometry table to plot each airfoil.

I'm one of those guys who has to "know how it's done",I appreciate your suggestions and recommendations, you've provided me with a lot of information this forum is terrific, I thought I was the only geek interested in this stuff.

Mike

jonastecknare

Whatever you decide to do, get the very best 3-wiev you can get. It will ease the pain! B`cause pain it is! Then again some people like that......... I have done it so much i am numb all over:Jonas

Avaiojet

3-Views can't always tell the story when entered into a software program.

The cross sections could be generated to be much different from the actual aircraft.

Jets with intakes would be an example. How would the program recognize them as areas that protrude from the fuselage?

Charles

dreadnaut

My Feedback: (5)

I think that CAD is the greatest thing since sliced bread, but you hit on the dark side of it. The thing I see wrong with the whole computer revolution is the desire of a lot of people to have the computer do the thinking for them. My laptop has on it the Educational Version of ACAD 2000 I got when I was teaching it at that ''Technical Instutute'' that shall not be named. I use 2007 at work, and have worked ont he Beta version of 2009. I have no desire to upgrade. I think that AutoCAD is being ruined by theattempt to make it so freindly ''For Dummies(r)'', that it is getting overloadedwith gimmicks and fluff.

What is happening in the software industry is what happened to the American Auto industry in the '50's and '60's. Planned Obsolence. They made a radical change to the user interface by replacing pulldown menus with someting called a ''ribbon''. Now you have to loose a month of prodictivity to learn to use a new device that really does nothing any better than the old way. It is just a new look. It is like putting bigger fins an a Cadillac. The only good it does is let your neigbors know that you aren't driving last years Cadillac.

Now, new software releases are on a one year cycle, when it used to be two or more years between new releases. Autodesk is now toying with the idea of a six month cycle. That means that they have to struggle to come up with new stuff twice a year. We have the choice of struggling to keep up with the changes, 90% of which are as useful as bigger fins on a Cadillac, or forget about it, and get to work.

I am a strong advocate of teaching the underlying principles; the a b c's, and the x y z's of descriptive geometry. The place I used to teach had ''Counselors" (high pressure sales people) who would tell prospective students what they wanted to hear to get them enrolled. I had to deal with irate studens, suffering from buyers remorse (a junior college education at a Harvard price) who expected it to be easy. One of the things that they were told was that our program would prepare tham for a career with Pixar (it didn't). They couldn't understand why they had to learn about cartisian coordinates, right hand rules, and descriptive geometry, and why I wouldn't just cut to the chase and show them ''how to draw Mickey Mouse''.

Sorry for the rant, but I am interviewing for a part time gig at a public CC, and this stuff has been on my mind, and your comment opened it up.

dreadnaut

My Feedback: (5)

Mike,

I have concluded that If you want to build scale you will have to make compromises. I suspect the accuracy of all three view drawings. If I were inclined to make the most true-to-scale model ever built, nothing short of climbing over a full scale example of the subject in a museum with a tape measure would do.

Even then, I would not try to be too faithful to the airfoil. What works with a 5 foot chord might not work well with a 1 foot chord. That Yak in the above example will get an airfoil like the symetrical section in the other sample. It was copiedfrom a 2meter pattern plane, and there is a lot of eyeball engineering involved. The airfoil on the full sized Yak is more like a FunFly. I am not inclined to ''over think'' the airfoil.

The Yak I designed is not absolutely correct, but it is probably closer to it than half of the ARFs on the market. Thisseems to bemore true for WWII fighters.

cuoremia

I can understand your sentiment. I've encountered engineers during my career, who needed a program, to design a small frame, composed of channel cestions under a concentrated load, one guy used it for a cantilever,because it spit out the stress results. Like you I feel learning the classical methods of analysis, should be a pre-requisite to using a computer program. Garbage in garbage out was the sentiment of my professors at the time, and when I was in college, programs were few and required key punched cards and a mainframe.

Boy I feel old.

dicknadine

Again I say the ruler,calculator- addition and multicplacation- compass, triangles, pencils and ERASERS, calculator for simple multiplicationwill acomplish the job a lot quicker and almost as accurate. I know it's an OLD story that I Must repeat over and over. you still need a large enough building board - so why not use it to draw your plans on it. I will keep saying this with a SMILE. believe me I am NOT demeaning the computor, its a fantastic tool.I spendmy money on Balsa, CA andother stuff, dick

Villa

Hi cuoremia
You and I seem to be about the same age. I graduated with a Mechanical Engineering degree in 1960. Drafting was always a big thing with me, during high school, college, and in my career designing air compressors. I must confess that I have no idea what "lofting" means. Is that term used in certain industries, such as perhaps the aircraft industry or perhaps the ship building industry? The term "projection"seems to fit the descriptions I have seen above for lofting.

cuoremia

Hello Villa,

Lofting came from designing ship hulls, the old timers were able to determine the cross sections of the entire vessel, by laying out the design in a loft at the shipyard. It was then applied to the aircraft industry, I read somewhere,that the most recent method was used in the design of the P-51 Mustang.As I said earlier,my engineering graphics program was in 1965,the pencil and paper method using a drawing board,but I've never used it since. I gathered a a large number of original of Focke Wulf FW190 drawings,including the lofting done on the fuselage, to get the fuselage templates. My curiosity became challenged, and I wanted to learn more about the method.

F86_SABRE

I am enclosing a write-up on lofting featured in one of the British magazines. Hope this helps