Geodetic Ribs

[Motorman]

How did you make geodetic ribs before the lost foam method? What's the reason to use them, less ribs, less weight, looks cool?


MM

[Tim Wescott]

Lots of triangles = more rigidity for the weight.

[Randy Cuberly]

How did you make geodetic ribs before the lost foam method? What's the reason to use them, less ribs, less weight, looks cool?


MM

Mostly what Tim said.  Before the lost Foam method was put forth by Bob Hunt very few people used them.  A few appeared on constant chord wings and some with egg crate type construction.  The layout of the individual ribs for a tapered wing is very time consuming and tricky.  Certainly a CAD program could be written to produce them but once again, time consuming!  By far the easiest method is cut the wing in foam then slice it up at angles to the chord then trace the ribs.  They come out perfect and the cradle makes a great Jig for positioning that can be reused many times.  The cradles insure a straight wing with no built in stresses.  Using tube or wire jigs for ribs can build in stresses because the holes in the ribs need to be elipitical to accomodate the round rods at an amgle without forcing things.
The Geodetic wing can easily be built using significantly less wood and still be as stiff or stiffer than a conventional layout.  Hence, all things equal in terms of wood quality, significantly lighter.

Randy Cuberly

[Tim Wescott]

Certainly a CAD program could be written to produce them but once again, time consuming!

These days, someone who's a professional designer with a 3D CAD program could basically do the lost foam thing inside the CAD program -- make a solid model, slice it up, get tracings, etc. -- and then go straight from there to rib drawings.  I suspect it'd be fairly quick.

I'm not that guy, and can't do that job, but I know what job title to look for...

[RC Storick]

one way you can do it is just as I did in the 90s when I made a XXX wing double taper. Lofted each rib out. Pain in the rear. I only made one wing like that.

[Motorman]

So how do you do it without foam or CAD? I have paper, pencil and a calculator.

I guess I could measure the length, the high point and the thickness and draw each one by hand. Then build the basic frame and sand them together with a long block. Then back each rib with cardboard from a cereal box and trace a set of templates. Would that work?

MM

[Tim Wescott]

So how do you do it without foam or CAD? I have paper, pencil and a calculator.

I guess I could measure the length, the high point and the thickness and draw each one by hand. Then build the basic frame and sand them together with a long block. Then back each rib with cardboard from a cereal box and trace a set of templates. Would that work?

MM

That would work.  Why do the tracings?  Why not just build it up on a jig, sand it down to "correct", do the same on the other side, then call it good?

I would like to observe at this point that a straight-rib wing with leading edge sheeting and shear webs is going to be almost as stiff and light as a wing with geodetic construction.  So geodetic construction is getting into pretty rarefied territory.  If you're willing to go there why not learn how to cut foam, or buy a lost-foam jig, or otherwise use a method that's been proven?

[RC Storick]

If I were to do a XXX wing again I would make a plywood root and tip rib and locate the on the ends and place rectangle XX ribs to space on a LE and TE and sand to shape with a long bar.

I guess you said the same ting. The first one I made I laid out on a grid and measured the rib at each station made and mark on the grid and connected the dots with a french curve. Kinda had to explain and pretty hard to do.

[RC Storick]

I'm not that guy, and can't do that job, but I know what job title to look for...

John Miller

[Chris Wilson]

You could try and email Graham Swallow for South Africa as I seem to recall he made a nice geodetic stunter -
gswallow@global.co.za

Here is a link that should prove interesting -

http://stunthanger.com/smf/index.php/topic,20721.0.html

[Target]

I think you might be able to do it in profili2 or one of his other design programs.
R,
Chris

[Steve Helmick]

Profili will do it, but it was decades ago that I did it as an experiment.

If you have a grasp of the old fashioned way of rib plotting (graphically), it's not difficult, but you need to plot a rib for each chord length and lie to it about the % of thickness.

I recall reading about Graham Swallow's lovely elliptical stunters. He glued up all the ribs and carved and sanded it to shape, much like a HLG or any other solid wing plane. Looked really cool, and I reckon that as long as the LE is about right, everything else would be fine, maybe with a few VGs added.  Steve

[Randy Cuberly]

Good Grief....It's so easy with a Lost Foam Jig.  Order one or cut one from foam!

Bob Hunt does them so well it's a total waste of time to do anything else.

I have one for the GEO XL and the Saturn you could borrow for the cost of the postage.

The picture below shows a modified Saturn wing (flaps and tips modified) for my Whitely Shoestring 655 sq in.  Very similar to Werwage's P47 wing.

Randy Cuberly

[Steve Helmick]

And here I thought the OP wanted to know if there were other ways to do it! I'm still wondering about this "lofting" method that Robert wrote about. Is that yet another method, or a different name for plotting them the old fashioned way?  Steve

[Howard Rush]

Didn't anybody take math in high school?

Robert described how to do it.  Excel makes it easy.  To be accurate, you should account for rib thickness and laser kerf.   

[Motorman]

I was tryin' to get laid in high school  . Anyway, I have a kit I can trace and take to the printers to make different sizes, no need for math.

MM

[EddyR]

I built a lot of these ,they are very easy to do.

[Gerald Arana]

I built a lot of these ,they are very easy to do.

WOW! That sure is purdy......

I built a 12' R/C glider (My own design) that I called the
"Rhombus" because I had equilateral parallelogram ribs behind the "D" tube LE. This meant an intersection at eack rib.  Real fun to build...

Worst part was, it hit the ground (I lost the thermal) on a cross country (try) 10 KM run and shattered all the ribs on the RT wing. And NO, it didn't hit that hard. I said "Never again will I build this kind of wing". It was TOO stiff and that is the problem with this kind of construction AFAIC.

Tight lines, Jerry

[RC Storick]

I built a lot of these ,they are very easy to do.

Very nice. Good Job!

[Rick Campbell]

Larry Cunningham had a program called StuntRib. You could specify the root and tip airfoils, then ask it for a rib who's LE was 1" from the Root and the TE was 3" from the root giving you perfect angled ribs. Steve Yampolsky and I did a couple wings this way. We dropped all the rib plots into some CAD program and added all the cutouts for LE, leadouts and spars. Sent the files to a laser cutter and the rest was easy!

[peabody]

I remember that Tom Niebuhr did a Frisky Pete....which had a 1/16" spar running crosswise across the chord.....I got to thinking about it and realized how tough a job it was and what a nice job Tom did on the thing.
Soon thereafter, Bob Hunt showed up with a Frisky Pete that he had used his "lost foam" technique on......made me appreciate that method, and Tom's work even more....

Have fun!

[EddyR]

Here is another one about 10 years ago.

[MikeyPratt]

These days, someone who's a professional designer with a 3D CAD program could basically do the lost foam thing inside the CAD program -- make a solid model, slice it up, get tracings, etc. -- and then go straight from there to rib drawings.  I suspect it'd be fairly quick.

I'm not that guy, and can't do that job, but I know what job title to look for...

Hey Tim,
I did just that when I designed the G-Force all in 3D Cad in the early 90's.  What I wanted was a wing as stiff and light as possible.  The rib angles were set as close as possible to 45° and stay with in the wing area I wanted (720 sq.in.).  Going over my notes, the finished G-Force wing including bell-crank, lead-outs, pushrod, flap horn, flaps, wing tips, and landing gear blocks weighted 12-1/2 ounces  ready for covering.  All parts were laser cut and didn't require any foam what so ever.  Just for fun, I told Bob it was my no foam required system (LOL).   

later,
Mikey