Author Topic: Construction differences? (Read 3111 times)

Jim Pollock · « **on:** May 08, 2007, 05:52:16 PM »

Hi all!,

Are there construction differences between the strip I beam a-la the Ares and suspended spar/beam consturction
like the AAE or the Stingray? I find it interesting to speculate on how Bob Gialdini got his ribs placed on the wing spars
of the Stingray? Anyone know how? Shultzie, you had one, how's it done.....

Jim Pollock

Jim Pollock · « **Reply #1 on:** May 09, 2007, 08:30:40 PM »

Wow,

I didn't mean to ask an unanswerable question!

Anyone?

??

Jim Pollock

John Miller · « **Reply #2 on:** May 09, 2007, 09:19:57 PM »

I spent almost two hours this morning typing in a great, ( I can say that cause it didn't show up) article about the differences in the two styles of I-beamers.

When I tried to attach a few photos, things went bad. QApparently, I had to many bytes so I got kicked back out. After trying and getting a message saying I had already posted this message, the entire thing dissapeared. Sort of bummed me out.

There're differences, but they are minor. Strip ribs need more attention, and time to set everything. The system as used with the All American Eagle sets the ribs fast, and doesn't need to be flipped over to do the other side.

John Miller

Jim Pollock · « **Reply #3 on:** May 10, 2007, 07:54:08 PM »

The method used on the AAE doesn't need to be flipped over. A nice point John! I suppose the methodology used on the Sting Ray has similarities? Or do you just build the wing as a separate unit?

Jim Pollock

John Miller · « **Reply #4 on:** May 11, 2007, 06:51:55 AM »

I can't speak to the Sting Ray, as I've never built one, but the AAE's wing system, especially as modified by Gordan and myself, really works well.

The wing is built in a very similar manner to the typical I-Beamer. Fuse built first, tip plates, etc.

We found it helpful to make some spacing, and support jigs. These really helped speed up the build.

John Miller

Bob Hunt · « **Reply #5 on:** May 11, 2007, 09:10:40 AM »

The Novi and American Eagle wings, as well as the Sting Ray and Eclipse are naturals for the Lost-Foam method. Generate the ribs from the cut up core, mark and cut the spar slots in each rib, make the spar, slide the ribs onto the spar and position the ribs over their marked positions in the cradle, pin and glue!

I built the wing in the photos in one day!

Bob Hunt

PaulBowman · « **Reply #6 on:** May 11, 2007, 09:27:22 AM »

Bob, I know it's a little off topic but could you tell us about your work bench ? the blue surface ? what is it made from, etc.... ? thanks.

proparc · « **Reply #7 on:** May 11, 2007, 10:06:19 AM »

Bob,

Why do you have to make the individual foam templates from the internal cores in your lost foam setup. Cutting out all those separate foam rib templates seems like a lot of work.

Thanks again Mr. "slip on the secret prop 78".

Bob Hunt · « **Reply #8 on:** May 11, 2007, 01:20:44 PM »

Paul: The bench is made from flake board that is painted blue so that balsa parts will show up better in my video productions. Better contrast than the normal color of the flake board. Wish I could tell you that it is more technical than that, but it isn’t!

Milt: The inherent accuracy of the Lost-Foam wing is due to the fact that the cut up core provides absolutely accurate rib profiles at a given station. This doesn’t take long and it isn’t difficult. The wing pictured was built from scratch in one day. Does that sound like a too labor intensive process? The templates were made, the blanks were cut and marked for rib positions, the airfoils were cut, the surface sanded and the spar location was scribed on both the top and the bottom of the core, and than the rib profiles were cut yielding perfectly accurate rib profiles that had the exact spar location at that station. Then the templates were used to trace out ribs from 1/16 inch thick rib stock. The ribs were cut out slightly outside the line and then the ribs were pinned back onto the foam templates from which they were traced. The ribs were then sanded carefully to match the exact profile of the foam template. Voila, Perfect ribs that need no additional sanding or fitting. I added lightening hoes as space provided as air is lighter than balsa... The spar depth at each rib station on the spar was measured and transferred to the corresponding ribs and the resulting rectangle was cut out of each rib to allow then to slip up onto the spar. The whole mess was positioned in the form fitting lower cradler halves, which had the rib positions marked in ink. The ribs were pinned to the foam to hold them in position and the whole mess was glued while it was indicated absolutely flat and accurate on the bench.

Note that the Lost-Foam technique keys on the outside shape of the wing, not on each rib’s centerline. The accumulated error that results from working from the centerline induces stresses in the wing which relieve themselves when the rod is removed. The Lost-Foam system has no stresses built in, and the outside shape of the wing is perfect in every case, so long as your building board is flat to start with.

Let’s keep our eye on the ball about what we are looking for when we build a wing or any other part of a model – accuracy! Speed is not what we should be concentrating on. Having said that, again, the Lost Foam wing pictured was produced in one day from scratch. Isn’t that fast enough?

Bob Hunt

John Miller · « **Reply #9 on:** May 11, 2007, 04:20:31 PM »

I hold Bob's development of his "Lost Foam Process" in extreme high regard. It's one of several modern developments that have made our sport/hobby advance to the highest levels of accuracy and repeatability.

It's especially great for those who for lack of the ability to generate the files needed for laser cutting and such, to produce, in ones own shop, very accurate parts and then to assemble them to a very difficult to achieve, with other methods, extremley accuract wing.

On the other hand though, since I have the ability to generate the files, etc. and I'm basically too lazy to spend the time to generate the parts by hand, I use a different method.

Once the files are ready, I e-mail them to the laser cutting service. I usually have my parts in hand in a few days. If I did the job of creating the files correctly, the parts should be very accurate, and ready to assemble. The following pictures show the construction of the All American Eagle, using the slightly modified method Gordan and I came up with.

The first pic shows a few of the ribs. The designer, Dave Gierke used an I-beam made up of laminations. It's basically a thick rectangular spar, with inset plywood center section to mount and carry the main gear and it's load. What Gordan and I came up with, was a true I-beam consisting of 1/8" X 1/2" medium to hard balsa laid flat, top and bottom. After Gordan framed up his wing, he spent a lot of time setting in his shear webs. He did this during the week, while I was unable to work on mine. When I got to the shop the next weekend, he was telling me about all the time it took to set the webs. Not wanting to spend thet amount of time, (remember, I'm basically a lazy guy) I was immediatly struck, with the idea of making the cuts and sliding the vertical web into the wing after starting with setting the ribs. The middle rib is what we started with, the top rib shows how I modified it for the vertical web. The bottom rib, is the rib that fits next to the fuselage, that's why the strange hourglass shape. It's used to make sure the bellcrank clears.

The next 2 pics, show the initial setup and alignment of the fuselage, and the trailing edge, (hingeline) of the wing. Note that so far we are duplicating the normal sequence that's used in most I-Beamers.

The 4th. Pic shows the start or, setting the wing ribs. You can see the supporting jig we made, (laser cut) to keep from breaking any of the ribs while we were assembling them onto the spars.

The next 3 pics show the sequence, or progress, as the ribs are set. At first they are simply slid onto the spars, in the proper order. Later, after the tip ribs are in place, and located (spot glued) at their reference points, they are spread out a bit.

The next pic, shows me using the spacing jig we made to set the rib and half rib spacing.

The next 2 pics, show the wing, as it's completed to the point where the tip plates are removed, and, the fuselage is cut loose. Note also, that prior to this point the leading edge has been installed.

OK, 2 more pics show the ribs in close up. Look between the spars, and you can see the vertical web in place, having been slipped into place aqfter a few ribs where placed. Also, the view of the tip rib, shows the shape of the true I-beam. This setup has proven to be very strong, while being very light wieght.

The last 2 pics show the completed wing from above. The very last one shows the fuse and the wing on the digital scale.

As Bob said, accuracy is more important than speed. and his method surely provides both. But, if you have the laser cut parts, this method that is so close to the traditional I-beam method, is very fast, and if you are careful with your layout, very accurate also. The entire wing as you see it here was framed up in about 1 1/2 hours.

I expect that I'll use this method often in the future. I also support and recommend Bob's "Lost foam" wing system especially if you have to generate your own ribs...

proparc · « **Reply #10 on:** May 12, 2007, 11:21:11 PM »

John Miller,
Your laser rib I beam method is one of the most unique and interesting ways to frame up an I beamer yet. It appears as if you have pretty much solved all of the problems of doing an I beam.

If you could hit us with more pics of this build, I would certainly appreciate it.

proparc · « **Reply #11 on:** May 13, 2007, 12:36:28 AM »

Bob,
You are absolutely correct about the small amount of extra time being more than worth it in terms of the final result. You don't want to be "penny wise and pound foolish" when it comes to allocation of time in terms of building a straight structure. I once asked Gene Schaeffer, (my idol lol) just how important it was to build a super straight structure. His reply to me was " Milton, build them straight or don't bother".

You are also very correct about "internal stresses" coming back to bite you later. How many times have I heard cats tell me that the "wing developed" a warp. I honestly believe that these guys built their structures straight initially. But, these internal stresses had the final say as to the alignment of the wing.

Futhermore, the popularity of iron coverings like Monokote, can lend quite a bit of strength to an open structure but, these same coverings can exert considerable force on a wing and exacerbate already present-hidden potential problems. Mitigating these problems at the onset can go a long ways towards avoiding disappointment later on.

Bill Little · « **Reply #12 on:** May 13, 2007, 05:03:24 PM »

Quote from: proparc on May 12, 2007, 11:21:11 PM

John Miller,
Your laser rib I beam method is one of the most unique and interesting ways to frame up an I beamer yet. It appears as if you have pretty much solved all of the problems of doing an I beam.

If you could hit us with more pics of this build, I would certainly appreciate it.

Hi Milton,

What problems are you referring to??

it's te simplest way to build an airplane since everyting is "pre-aligned". All it relies on is the ability to cut straight and have a flat surface to build on.

proparc · « **Reply #13 on:** May 13, 2007, 05:48:39 PM »

Quote from: Bill Little on May 13, 2007, 05:03:24 PM

Hi Milton,

What problems are you referring to?? it's te simplest way to build an airplane since everyting is "pre-aligned". All it relies on is the ability to cut straight and have a flat surface to build on.

Johns method has integrated the ribs of a "regular wing" into an I beam configuration. The strip cutting and careful fitting of those strip ribs onto the I beam are eliminated. I have the video of Bill Werewage himself building an Aries, (correction HIS Aries lol). There was a gentleman selling very nice Playboy kits who addressed this issue by laser cutting the strip ribs with a notch under the ribs. John appears to have taken this to it's final stage-whole ribs.

John Miller · « **Reply #14 on:** May 13, 2007, 10:50:28 PM »

Thanks Milton, but I cannot claim all credit for this system. Like most advances in our pastime, it's the accumulation of small steps started by others that inspire.

First, Greats from the past, Like Dave Gierke and Bob Gialdinni, first worked out the idea to use full ribs into an I-Beam wing build.

In my opinion, this was a pretty good leap. It allows the designer to achieve a true airfoil, with the normal mods towards the tips. Hard to do with a strip rib I-Beamer.

Still, they used the standard style of I-Beam. This is often a rectangular, laminated structure. Where the weakness with this type of spar is, that the matterial is carried into areas where they contribute more weight than stregnth. The greatest stregnth comes from the material furthest from the center of the bending axis.

In steel work, the I-beam is used for load carrying because of the areas furthest from the bending axis, have the most material. In my design classes, the term "section modules" refers to the ability of the extreme structure to carry the load. The top and bottom caps places maximum section modules where it does the most good resisting the bending moment.

So, it was Gordan Delaney's idea to use a pair of flat spars, 1/8" X 1/2" as far out as we could place them. This put the largest section modules out close to the surface of the wing. We actually built Gordan's wing this way. He then had to place the shear webs between each rib. This turned out to be a time consuming task. After he told me about the hours he spent fitting and gluing in the shear webs, I made my contribution to this system.

It would be simpler to cut a 1/8" slot in the middle of the flar spar cutouts, and slide in a shear web as the wing was constructed. It only took about a half hour to manually add the slots to the laser cut ribs.

I'll mention that the fits, with the laser cut ribs, along with the shear web slots were very good. we set the kerfs up to allow a tight but smooth sliding fit. Once all the parts were assembled, and before they were glued, the stregnth was remarkable. we would push down on the spar, and experience almost no movement.

So the final analysis is that thanks to those who first showed the way, and following a few steps, we get to a pretty neat way to build an I-Beamer, very close to the traditional way, but better.

There are a couple of threads from the last building season showing the build sequences from both mine and Gordan's All American Eagles.

Bill Little · « **Reply #15 on:** May 14, 2007, 07:20:48 AM »

Hi John,

I have seen the full rib I-Beam before, but never built one that way!

n Some nice planes that use a similar set up like the NOVI I, and all.

As to "problems" building a traditional I-Beam that Milton referred to, I guess it all about what we get used to building. I never experienced any problems with the traditional style, but that's just me.

I have had three different people stay the weekend at my house, and armed with nothing but balsa sheets to start, we have framed up a USA-1 in each instance before they left Sunday afternoon. Not pulling all niters, either, and neither of the three had ever built an I-Beamer before. So they are quick and simple, and self aligning.

I really like you and Gordan's AAEs!!

don Burke · « **Reply #16 on:** May 14, 2007, 10:48:12 AM »

Shear webs.

The shear webs are to keep the spar caps from moving apart from or closer to each other when the beam is subjected to a bending load. In balsa construction this is usually accomplished with the grain of the web perpendicular to the spar caps. A "slid-in" shear web does not have the same strength since the grain is spanwise. However, the loads experienced in CL models are probably not enough to worry about the difference.

A compromise is to fabricate the slide in web from a least two layers of balsa with the grains at plus and minus 45 degrees. This would yield the best of both worlds, but would have some weight penalty.

Another way to do it is to use diagonals between the ribs in the normal plane of the shear web. I built a Cardinal wing this way with 1/8 x 1/4 diagonals between the ribs. The cutouts in the kit ribs left a small upright at the spar locations, but the ribs lacked any compressive strength.

John Miller · « **Reply #17 on:** May 14, 2007, 04:35:07 PM »

Quote from: Bill Little on May 14, 2007, 07:20:48 AM

Hi John,

I have seen the full rib I-Beam before, but never built one that way! n Some nice planes that use a similar set up like the NOVI I, and all.

As to "problems" building a traditional I-Beam that Milton referred to, I guess it all about what we get used to building. I never experienced any problems with the traditional style, but that's just me. I have had three different people stay the weekend at my house, and armed with nothing but balsa sheets to start, we have framed up a USA-1 in each instance before they left Sunday afternoon. Not pulling all niters, either, and neither of the three had ever built an I-Beamer before. So they are quick and simple, and self aligning.

I really like you and Gordan's AAEs!!

Hi Bill, say Hi to Aaron for me. We used to IM a lot a few years back. 'Hope he's still flying and progressing, or did the darkside get to him...

Last time we "talked" he was speaking about a pretty nice young lady....

Bill I agree with you on the simplicity and accuracy of building the traditional I-Beam wing. I like the fact that they are usually lighter, and very well aligned. I like the fact that when building one, you are also attaching the fuse, and in proper alignment.

The problems some might find with I-Beam construction are minor, but to some, they can be daunting.

Between the two methods, we're discussing here, the differences, though minor, alleviate some of the "problems".

For some, having never constructed an I-Beamer, the unfamiliar construction may seem much more difficult than it is, resulting in a "problem" for the builder.

By using the whole rib, the construction is more familiar and helps some builders make the jump.

By using a lofted rib, the designer can more effectively control the rib profiles from the root to the tip. Many feel that moving the high point forward a little, and increasing the percentage of thickness is a desirable thing to do. This is easier to do with a lofted rib. I'm not sure if there have been many designers of traditional I-Beamers that have factored in the airfoil for stall control.

Another problem for some is the common practice of setting the bottom strip ribs first, then cutting the alignment tabs loose, turning the assembly over, and readjusting the alignments, gluing the tabs back into place, and setting the top strip ribs.

With the whole lofted rib, this step is completely eliminated, making the build faster and easier.

Strip ribs can be quickly and accurately cut with the use of a home made stripping jig. Lofted ribs, as I use them really need to take advantage of the accuracy laser cutting can impart. This means you have to generate the files, send them to a laser cutter, and wait to begin construction until the cut ribs arrive. This step usually only takes a few days, what with e-mail. You can use this time to build the motor crutch and fuselage.

Strip ribs are not conducive to the use of removable gear blocks. Lofted full ribs are, allowing this feature of removable gear easier than with strip ribs. By not having to attache the gear to the I-Beam, allows a lighter I-Beam.

OK, so there are a few of the "problems" that are addressed with this method. As I said, nothing major, but it does make constructing the I-Beam wing easier for some folks, and faster than normal with strip ribs.

Speed isn't everything, especially when achieved at the cost of accuracy. The best of this system is that it shares the same potential for accuracy as the traditional I-Beam wing. So how fast is it?

I had the fuse framed up, and the laser cut ribs stacked and ready. By myself, I had the alignment and construction com[completed in an hour and a half. could have been faster, but I took my time, gabbed a bit with Gordy, and drank a few sodas while working on it.

John Miller · « **Reply #18 on:** May 14, 2007, 05:03:13 PM »

Quote from: don Burke on May 14, 2007, 10:48:12 AM

Shear webs.

The shear webs are to keep the spar caps from moving apart from or closer to each other when the beam is subjected to a bending load. In balsa construction this is usually accomplished with the grain of the web perpendicular to the spar caps. A "slid-in" shear web does not have the same strength since the grain is spanwise. However, the loads experienced in CL models are probably not enough to worry about the difference.

A compromise is to fabricate the slide in web from a least two layers of balsa with the grains at plus and minus 45 degrees. This would yield the best of both worlds, but would have some weight penalty.

Another way to do it is to use diagonals between the ribs in the normal plane of the shear web. I built a Cardinal wing this way with 1/8 x 1/4 diagonals between the ribs. The cutouts in the kit ribs left a small upright at the spar locations, but the ribs lacked any compressive strength.

Don,You are correct when you suggest what the function of the shear web is. In addition, the shear web also helps resist the slight sliding motion between the top and bottom caps. For instance, with the fuselage and tip supported, if you placed a weight at mid span of an I-Beam, the center will bow slightly down depending on the weight. This puts the "threads" (section modules) into compression on the top cap. The bottom caps "threads" will be in expansion, or trying to stretch. The shear web helps control the shear created when the I-Beam is loaded. This is that slight sliding motion I was referring to.

One of the problems I've encountered using vertical shear webs, ( usually 1/16" balsa) has been a splitting of the grain between the cap spars. I admit that this is rare, and a lot depends on how well the shear web is fitted to the ribs. This happening almost resulted in the loss of the plane. Never the less, even though the strength per weight is higher, between the spars, with the grain running vertical, by using a slightly thicker shear web, say, 1/8" thick, and slid into place, the strength is plenty good enough for our use. You're correct when you suggest constructing a spar made of biased laminations, but you're also right about the possibility of weight gain.

I also have used strips angled as in a Warren Truss arrangement with C tube style wings this has worked well for me also, but I'm not sure the resistance to bending was due to the trusses, or to the spars being located as far out as possible in the wing.

Jim Pollock · « **Reply #19 on:** May 16, 2007, 06:46:45 PM »

Well, Well

From this thread's humble beginnings I would say it's become the standard for how to build I beamers without strip ribs!
Thank you Bob, John, Paul and Bill for you excellent posts here.

I am very humbly honored by those posts.

Jim Pollock