briansommers

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if i have a set of 3 views, does that give me enough of info to draw x-sections??

i dont think it does, so how does one do this, do you just kind of eyeball it?

any help would be great thanks

dicknadine

whats your level of building? beginner?, advanced beginner? do you have any drafting exoerience? need a bunch of info before we/I can help. are there any model builders, hobby shops in your area ?? dick

briansommers

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ive been into rc flying for 8 yrs, off and on, not straight through, ive taken the last year off and im planning on building a laser kit of the piper tri-pacer from mosquitobiteplanes.com

im a roof truss designer and have the cadd program (Fastcadd) and a nice big 24" plotter, so im familair with that end of things

ive got the itchens to design somethin'

and no i live out in the stix at 8000' msl

SoCal GliderGuider

Cross sections depend on the type of aircraft. If it has a built up fuse of steel tubing or wood then you can derive reasonable sections from a three view. If you are thinking of a modern jet fighter then many will buy a plastic model of the plane and cut it into sections. The sections are scanned into graphics files and loaded into the back ground of the cad program. You can then draw over them and scale the outlines as you wish.

Do you need sections for the Tri-Pacer?

briansommers

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no i bought a kit of the tri-pacer

im actually interested in old homebuilts, ultralights, GA type planes - that kind of thing

but yeah i had forgotton about the plastic model thing, i remember that now, i could buy one of those for common GA type planes

BMatthews

Often you can get a good idea from pictures and the shadows they have in them as to the general shape of things. But it's far from perfect.

Also the small 3 views are not often very accurate. You sure won't be using them as supporting documentation for any world champs scale event. But for "stand back and squint" scale they would be fine along with the picture and shadow estimate cross sections.

briansommers

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yeah, im not entering any contest, this is just for myself, so yeah it doesnt have to be square on or anything

just so it kinda looks like it - well more than kinda, but it doesnt have to be exact!

BMatthews

Exactly. As the old advert goes "only you and your hairdresser will know for sure"... Do a decent guess and most folks won't know the difference.

What rare old desireable design are you thinking of doing? Or would that be letting the cat out of the bag?

Edwin

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Well, since you have cad experience, you're half way there. I've done a few plans from nothing but 3-views and it can be done. It might take some iterations in the build process, I usually forget things like the wing to fuse fillet and such. I start with a center line on the 3-view. Then place your formers on the 3-view. At that point I measure the size box I will create for a former with the center line crosshairs in the box, has to match the 3-view center lines. I do this for all the formers and make them their own entity (group or what have you) and stack them on each other with all the crosshairs matching. I also make the reference point at the crosshairs. It makes it easier to snap to your reference lines when stacking. This is a front view. You will notice the boxes get smaller towards the tail and nose. Then I pull out a former and use the spline command to draw half the former, then mirror it. Put it in a new stack and get the next one and place it on the new stack. Once your done with the first one you will notice all the others start falling into place referenced off the first one. I know its not as simple as I make it sound. Just trying to convey a process here. You will have your own drawing method. Thats another whole longer discussion I try to avoid. Its just too hard to teach without showing. Attached is what you end up with. Each former is its own entity.
Edwin

briansommers

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nothing in particular, ..... maybe the rans Shekari looks cool

Rocketeer10

If you check out the April 2005 issue of MAN, I did a segment on plotting unkniwn cross-sections between two known sections from a 3-view. Page 112 in my Thinking Big column. It give you the basics for the method I have been using and I think it is pretty easy.
Good luck with your project!
GY

briansommers

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thanks i will be on the look out for that article

Mike James

I did a generic "CAD Tutorial" on my site, where this problem is discussed. The article is at http://homepage.mac.com/mikejames/rc..._tutorial.html

Technically, a 3-view simply does not contain the data you need for accurate cross-sections. But, using a combination of your eyeballs, photos you have on hand, and some simple extrapolation, you can get close enough that most people couldn't tell the difference. (unless it's a VERY complex shape )

If your CAD software will render reflections and shadows, that can be more helpful than you might think. Set up your model so you see it from a viewpoint, and with the same lighting conditions, as your photos the actual aircraft, and then can tweak the shape, until you see the same shadows and reflections.

briansommers

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wow thats intense there!

my problem is my cadd program is only 2D

so...........