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General control line discussion => Open Forum => Topic started by: Bob Reeves on December 14, 2012, 09:00:24 AM
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Another club member and I purchased a Bobby Hunt Lost Foam wing jig for a Geodetic version of the Legacy wing. This is the wing that is in my Latency and in my opinion it's as good a wing as anything flying. I know it's the lightest, straightest and strongest wing I ever built. I'm thinking if we could get laser cut ribs it would also be a fairly easy build, the real time consuming part of building a Lost Foam wing is cutting and sanding the ribs to the forms..
If I could get someone to volunteer to scan the rib forms and somehow get them into a CAD file we could get one of the laser guys to cut ribs for anyone that wanted them. I don't have a scanner or the expertise to be able to draw accurate ribs in CAD or I would attempt it. You would still need to buy the jig from Bob but having laser cut ribs would sure make building the wing easy.
Anyone want to take on a project? I'll be more than happy to box up the rib templates and ship them to you.
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Hi Bob,
I guess it is really a good idea, but the extra expense of laser cut ribs would not be worth it to me. By the time I ordered that ribs and they were shipped to me, I could have the ribs already made. Everything has been so simple to build an excellent wing, and quick, with the half dozen or so Lost Foam wings I have built.
Bill
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That's what John Henry said about the steam drill. If you know what you're doing when you specify laser-cut ribs, you compensate for that. A swipe of the sanding block with 400 paper and you're in business.
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If I was a master builder like Bobby, wouldn't need no stinkin laser ribs ;D
In reality it took me two full days just to make the ribs for the Latency and I hate doing something more than once. When I worked as an R&D tech at Hughes Aircraft making ribs is what we use to call pukity-pukity work.. If we had a redundant project we pawned it off on the girls in assembly. I can see Bob's point but agree with Howard in that if the ribs are cut to the high side a few swipes with sand paper would be all they need.
Have received a couple email messages and will reply to you guys shortly..
Thanks,
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I have to confess, I spent 1 day with Bob hunt in his workshop - During that 1 day : I was given a comprehensive rundown on how to make a lost foam wing - after only watching the DVD a few years ago and thinking " Phfft to complex.. "
Bob showed me in that 1 day :
Building a new foam core cutter to his design.
Making templates
Cutting the cores
Sanding
Alignment
Assembly
Changed the way I build wings forever - there was very little communication after that - Its so simply even I was able to do it...
Its so easy, so quick - extremely accurate and you don't need to be a master builder - to Master the building technique.
Sure you can buy them pre-done but the Joy is in BUILDING it yourself - from the foam cutter to the templates ; he will give you all the information you need !!!!
Thanks Bob!
(http://i1115.photobucket.com/albums/k554/pjaussie/P1020685_zps7bf1ff96.jpg)
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Don't have to sell me on the Lost Foam wing I just don't like making the ribs.
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I cut foam wings for a few years. Purchased a professionally manufactured wire cutter. Nice booklet, Instructions and all.
Eventually E bayed it!
My bow cutter was the type where you needed another individual to assist in the actual cutting.
Obviously my wings and customer's wings were for R/C. Always in two halves and in most cases each rib template was different, tapered cord, tapered thickness, wash out, stuff like that.
So, how do you cut a foam wing without the help of another individual, viewing his side of the foam and rib template?
Charles
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So, how do you cut a foam wing without the help of another individual, viewing his side of the foam and rib template?
Fix one end of the cutter to an aircraft rod end (ball joint). It works best with a female template on either end of the foam and the fixed end a tad farther from the tip end than you'd figure. That way the wire rides lightly on the tip template when you guide it around the root template.
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Besides it's called "model building." I like to put the emphasis on the "building" part. A set of ribs takes a few hours to make, but they can be made to fit perfectly with little to no experience. If you've never tried this method, you are missing out on a true building experience.
Good point. We should pass a new BOM forbidding laser cutting. Each contestant must cut his own ribs. No outsourcing.
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I made my own foam core cutter.
Howard : I'd have no issues with you making your own laser cutter.
Charles : You cut both templates yourself - Ours have different sizes : Root/Tip ect.. Its a speed change from one template to the other, with practice you can do it yourself.
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One year i found myself way behind and no new stunter for the next season. I needed to build a wing, and fast. I love the lost foam method. But I didnt want to make the ribs either. I called a local laser cutter and faxed him the root and tip tracing from my lost foam jig. Gave him the specs, spacing and span. Then I cut and molded the sheeting. Cut the trailing edge sheeting and the spars and set the jig up. Over the next two days I built the bell crank, tips, and slider. On the third day the laser ribs showed up. Two sets for $35.00. I proceeded to lay up the wing and about 6 hours later all but the cap strips were on. It was a snap!!!! It was a straight rib wing but it flies awesome. The other one I built flew great too but it was lost to a bird strike.
One of those wings is in my red Riff Raff, it flies good.
So there is a way to use a laser cutter and the lost fowm but you dont get the angle. One thing I did was I scanned every sanded geo rib from that jig into my PC. Then I sent to the cutter and he converted the images to dxf. But then he went out of business. He sent me the dxf file. But I have never tried to get a laser cutter to cut them out. He said it should work fine. Next time maybe I will try it.
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Charles
Like you, my experience cutting foam wings goes back to 1967 or 68, and I always had my buddy do one end of the wire on his template while I did my end of the wire on my template while I called off the stations marked on both templates as the wire came up to each mark. But recently I saw first hand a guy cut foam cores all by his lonesome. And his cores were as good or better than any I (we) ever did with two guys in the old days. Of course this guy I saw do this recently, probably has cut more foam wing cores than anyone I know and could probably do it in his sleep. But after seeing him do it alone, I can see how even I could learn to do it by myself. Just takes some practice and the reality that you will make a few pieces of scrap in the learning curve. :)
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Like you, my experience cutting foam wings goes back to 1967 or 68, and I always had my buddy do one end of the wire on his template while I did my end of the wire on my template while I called off the stations marked on both templates as the wire came up to each mark.
I remember the story of one of you asking the other whether he was on the top or the bottom, and the resultant laughter messing up the wing.
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So there is a way to use a laser cutter and the lost fowm but you dont get the angle.
There are two ways I can think of of getting the angle ribs. The way I did it was to first make equations for the root and tip ribs, then calculate a zillion coordinates for each with Excel. Then it's just some tedious interpolation to get the coordinates for the zigzag ribs. The other way is to take slices with a 3D CAD program. I don't know how to do this, but it looks easy. You about have to do the calculation yourself or carefully specify the LE and TE spanwise location of each zigzag rib so it will be just big enough to get to the 3D shape Bob mentions with a sanding block swipe. Here's a piece of the drawing of my wing. It's at the front. The upper line is the LE. The line just below it is the inside of the sheeting. You can see that you need to pick for calculation the chord that's on the short side of the wood. You sand off what sticks out.
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I was thinking of a 3 axis laser cutter to put the angles on the edges and spar slots, but that might not allow cutting stacks of ribs at the same time. I seem to recall that SOP was to cut a stack of sheets about 1/2" thick.
Pete P. told me about how to make the ribs with the lost foam system. Seems to me like there'd be a degradation of the foam after a half dozen wings, ya know...just not good enough for those combat boys known only by initials. LL~ Steve
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There are products that can be sprayed over foam that dry to a hard brittle finish. Seen this in the sign industry, although generally brushed.
An allowance could be made in the production of the foam jig to allow for the thickness of two coats of this chemical. Easily determined.
With this process, repeated when the coat gets thin from sanding, the foam, not coming in contact with sandpaper at all, even ever so fine, will have an unlimited life span.
Possibly?
Charles
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The other way is to take slices with a 3D CAD program. I don't know how to do this, but it looks easy.
It's not.
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When I made my lost foam wing I took a few things into consideration.
I took into account the extra .8 microns of thickness the Titebond used.
Took into account the extra .15 microns of burn down of the foam as I cut it slow.
All you need to do is measure your template, and add .6 microns of thickness to the template prior to cutting.
Its not quite the ball point pen trick but it saves a bunch of headaches in the trimming stage.
*rolls eyes*
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It's actually rather simple with the lofting program I use to lay out ribs from either straight, to several forms of "Geo" style angled ribs. I can even generate "Eggcrate" interlocking style ribs, with elliptical wingforms, if desired.
Bob is right that perfectly good ribsets can be cheaply made from his system, and building in the foam cradle assures a straight wing. I believe what is being missed by some, and alluded to by Doug, are the benefits coming from marrying the two systems, "Lost Foam", and Laser Cutting . Sure, it's at an increased cost, but accuracy, ease, and speed are the results of such a merger. We already are willing to pay a decent premium for speed when we go to using the often heavier foam wing.
One also has to consider that once the outline at the rib station has been achieved by hand cutting, the internals, such as lightening and bellcrank clearance holes must be laid out and cut. A set of ribs cut to work with the foam cradle can save time and some frustration, though at a cost.
National Balsa is one company I've worked with, that will sell you the balsa, and laser cut it to your files. The price is reasonable.
If I can find where I stored the 4 digit airfoil files for the Legacy, I might give it ago myself.
Bob, as innovative as you are, I cannot see how you aren't all over this, as a speedy alternative to grace, and inhance the user ability of your already excellent "Lost foam" system.
It seems like a win-win situation to me.
If I can be of help, drop me a line.
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When we start talking in terms of microns of thickness, aren't we getting a little too technical? How much do you sand off the surface when finishing a plane or how much do you add when you put the paint on. I still say a well built plane that is straight and light does not care if it's laser cut or lost foam.
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Although I have always enjoyed building an I-Beam wing. The first time I used a Lost Foam set up to build a wing I was just blown away! It doesn't appear to be any configuration of wing lay out that Bob can't cut a fixture for.
I have a special project that I have talked to Bob briefly about and I will be getting a Lost Foam system to build the wing. It will need to be in three sections due to the wing plan form, but that causes no problem. The only thing simpler is a pre-sheeted foam wing!
Bill
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Bob
I think it is more a matter of the CAD person/software rather than the capability.
A wing that is properly drawn, lofted, and sectioned, with an accurate laser cutter, will give you "dead nuts on" ribs. And compensation for the kerf is also very simple.
Perhaps Walter and I can convince you otherwise someday, my old friend... :-)
V/r
Bob Kruger
Hi Doc: I'm pretty sure PJ was being facetious with the microns comments... ::)
I do think that the important thing to remember - no matter what construction techniques are used - is that the model must be built straight and accurate; it must be rigid, so that accuracy is maintained during flight loads; it must be light (or at least within the acceptable wing loading specs for the wing used); it must have a consistent, reliable, repeatable and understandable power system that has enough power to pull the model easily and properly; and it must have a robust and adjustable control system. If all of the aforementioned attributes are present, the plane will fly well! If any one of these attributes are missing, well, then you have a caricature of a stunt model, not the real deal…
Hi John: How are you feeling? Our prayers and thoughts continue to be with you during your recovery. To your point about the laser cut ribs... Well, I did try that. I have a friend who owns a very high-end laser with fantastic optics. The parts he cuts (lasers?) have little to no brown color (burn) on the edges of the wood. He has produced a number of extremely easy to build kits and has received a lot of favorable comments on the accuracy of his laser cut parts. Having said that, when I supplied him with accurate rib profiles from ribs actually made in the Lost-Foam process, the resulting laser cut ribs did not fit the Lost-Foam fixtures to my satisfaction. Oh, they were very close to perfect, but my thought was, "Why compromise when I can achieve the accuracy I desire from making the ribs in the system's normal process?”
Admittedly it was a number of years ago that I tried that laser cut rib experiment. Perhaps it is time to give it another try. I still like the fact that the Lost-Foam process of rib making yields ribs that are not only perfectly accurate in profile, but also in top and front view taper. I like to make as perfect a wood-to-wood fit as I can. It cuts down of the amount of glue required, and it yields a strong joint and hence a stronger airplane. I’m not trying to be obstinate here, I just believe in the process as I’ve used it for nearly 25 years. Guess I’m just an old fashioned model builder…
In any case, whenever someone orders a Lost-Foam Wing Building Fixture from me (Robin’s View Productions), they will receive the foam rib templates cut up and ready for building along with the form-fitting fixture in which to build the wing. If they opt to buy laser cut ribs, that’s fine by me.
Later – Bob Hunt
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Kerf? Thickness of a hair? Worth considering?
I never asked my laser cutter, I can't now because he's off planet, but, I don't believe he has control of the thickness of the laser beam?
I will ask him.
I could be wrong, but the "vector" drawing or the "line art" is where all adjustments must be made. In CAD.
Including the rib overall measurements.
I.e. So, lets say, just for the sake of math, if the desired final rib thickness is 2.25" after sanding in Bob Hunt's foam jig.
Adding just .03125 would be pointless, especially if "titebond" was to be used.
There HAS to be rib material above Bob Hunt's foam jig to sand away for rib accuracy. Cannot cut the rib so close. The possibility of rib material being below the foam surface?
Even .0625 is close. The excess amount doesn't matter because it gets sanded down to the foam with it's layer or layers of titebond.
Charles