Aluminum Tube & Gusset Airbike / Legal Eagle / Parasol Thread

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Ollie Krause

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Where is the fuselage on weight? It might be easier to convert to a four longeron fuselage. That or merge into three longerons after those cabane drag braces, keeping it four to that point.
It currently weighs 31.4# but a lot of the hinges and gussets haven't been added yet. Our target weight is 40#- We considered using a four longeron tail but we decided not to as it would add a substantial amount of weight due to the required cross web beams (or at least wires) within the tail in addition to the weight of a new longeron.

Note: weight calculations exclude wing support struts. Weight measured from everything highlighted in yellow below:

Annotation 2020-05-05 081051.jpg
 

Ollie Krause

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I'm really liking where this design is going. Please stick with the aluminum! Unless your only goal at the end of the day is to just get something going with the least energy.

I for one think an all alum alternative to the Legal Eagle would be great.

Your major joint there does look like a pain but I think breaking the cluster up into a few gusset plates would solve most of it. Also maybe consider 3D printable fixture that holds all the tubes in the exact right orientation for fixturing, at which point that block can be abandoned in place or removed/discarded.
Haha we'll keep working at it. We'd much prefer a gusted aluminum frame as well. Using a temporary 3D printed piece to hold everything together while the gussets are installed is a great idea!
 

Ollie Krause

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The picture is of a replica. The original WW1 planes were mostly wood.
🤭 I've been looking at too many replicas haha. It seems like a lot of replicas use gusseted aluminum truss frames. Is there any reason why people have shifted away from wood for replicas? I would imagine that gusseted aluminum is easier to construct and probably stronger but there's something to be said for the nostalgic beauty of wooden frames.
 

Aerowerx

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🤭 I've been looking at too many replicas haha. It seems like a lot of replicas use gusseted aluminum truss frames. Is there any reason why people have shifted away from wood for replicas? I would imagine that gusseted aluminum is easier to construct and probably stronger but there's something to be said for the nostalgic beauty of wooden frames.
There are still replicas made of wood. The Ragwing Storch is one example. It depends on how close to the original you want to get. And what type of material you are comfortable with.
 

Ollie Krause

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Ollie that's the idea of the day right there. Print a disposable plastic holding fixture that allows you to drill and rivet all the gussets in place easily, then break off or disassemble the printed fixture. A great use of CAD technology, modern fabrication methods, etc.

Several HBA discussions have involved printed fixtures and assembly aids. This project of yours would be a very good use of that capability, and it will yield an actually usable, viable airplane. Not a demonstrator, not a mock-up, not a school project... a viable airplane.
Yeah I really like the 3D printed fixture idea. Ideally, I'd like to be able to CAD the gusset before beginning construction to reduce the chance of any surprises but making up the geometry by hand is also a viable option. Maybe I purchase some tubes and create a mock up of just this joint before we begin construction. That way, I'll be able to bend the gusset by hand to visualize the required geometry so I can easily insert it into our CAD before beginning official construction.
 

Ollie Krause

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Having been in this situation several times (I designed, built and successfully flew 8 microlights and 10 hovercraft) I could suggest a solution: the gussets can be pre-formed into any desired shapes just making appropriate jigs and creating tridimensional gussets. It is not as difficult as it seems. It just requires some dimesticity with pattern design, panel beating and a little patience.
Great! I'm super glad to hear this has been done before. Do you have some examples you could direct us to? Thanks!
 

Victor Bravo

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Gusseted aluminum tube is 1000% the way to go for this. It allows aircraft developers and builders to take advantage of new technology that reduces cost, reduced build time, and increases accuracy. Designing for inexpensive commercially available tube sizes (6061-T6 or 6063-T8 x 1", 7/8", 3/4". and 1/2"), then designing the gussets for 6061-T6 sheet in .063, .040, and .032 is going to create a huge opportunity for practical small airplanes to be built. Please trust me (and others here) on this, there is a big need for this.
 

Victor Bravo

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Bending the gusset is possible, but creates a little more work in terms of fabricating the gusset after it is CNC cut. One of the things you might consider is having the gusset designed with very small sharp points or spikes on each side of the bend axis. That way, you are able to insert the gusset into a very inexpensive (HF) vertical press brake and make sure the bend is exactly where it needs to be. Once it is bent, put the gusset up against a small belt sander for 3 seconds on each side, remove the little spike, and it's safe to handle. The spike is a built-in fabrication jig that takes an extra two or three seconds of CNC cut time, but guarantees you a good straight fit on the tubes. The rivet holes should already be in the gusset, and all you have to do is clamp or tape the gusset onto the tubes, poke the drill through, and rivet. (de-burr and apply corrosion primer first if you want)

Also if you have not found it yet, see our previous discussions about a rivet hole alignment tool that uses the tube as a guide to center the rivet holes under the gusset. That will be a huge time saver.
 

GeeZee

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“GZ, that one looks like it's straight off of Graham Lee's plans.”
Well Cavelamb now you’ve done it. You’ve caused me to start searching for Graham Lee aircraft and I’ve discovered I can still buy plans? $139 seems like a bargain to reveal the mysteries of the tube and gusset construction method ;)
Is there consensus (well as much as there can be on HBA) that Mr. Lee did a proper stress analysis on his aircraft? In any case it seems like there have been quite a few built over the past 35ish years. Change the cosmetics from WW1 to something more “Hatz like”, slap on a little Verner radial and that would be ”it” for me.....
 

Victor Bravo

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GZ, I can't answer for Graham Lee's engineering and I certainly can't answer for Richard Lamb, but I can say for certain that we here on HBA have been enthusiastically discussing the viability of this type of construction for some time. Graham Lee and Robert Baslee had pioneered this (in the modern homebuilt era), but both of them were/are locked firmly into WW1 type aircraft. Several of us here are well aware that there are many other types of airplanes that could benefit form this construction method.
 

Ollie Krause

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One option:

Position the tubes that form an “X” between the wing’s rear spar and the lower longerons to be in one plane.
Wouldn't the tubes intersect then? Would you be able to do a 20 second sketch? I think I'm misunderstanding.
 

Hot Wings

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consider is having the gusset designed with very small sharp points or spikes on each side of the bend axis.
I like that idea!

@ O K:
With regard to the bent gussets at the joints I'd actually worry more about the tension than the compression. The gusset in compression is a massive short structure compared to the tube in compression. In tension the forces are putting the first rivet in tension as well as shear as the gusset tries to straighten out.

My favorite material to build planes with is ABS..........Anything But Spruce. Wood is just too hard to source in aircraft quality and getting expensive. If you don't live near the source the freight ads up fast.

Cast parts generally need and extra margin of strength compared to other methods because defects can be internal and undetectable with simple tests.
 

Ollie Krause

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Bending the gusset is possible, but creates a little more work in terms of fabricating the gusset after it is CNC cut. One of the things you might consider is having the gusset designed with very small sharp points or spikes on each side of the bend axis. That way, you are able to insert the gusset into a very inexpensive (HF) vertical press brake and make sure the bend is exactly where it needs to be. Once it is bent, put the gusset up against a small belt sander for 3 seconds on each side, remove the little spike, and it's safe to handle. The spike is a built-in fabrication jig that takes an extra two or three seconds of CNC cut time, but guarantees you a good straight fit on the tubes. The rivet holes should already be in the gusset, and all you have to do is clamp or tape the gusset onto the tubes, poke the drill through, and rivet. (de-burr and apply corrosion primer first if you want)

Also if you have not found it yet, see our previous discussions about a rivet hole alignment tool that uses the tube as a guide to center the rivet holes under the gusset. That will be a huge time saver.
I'm not quite sure what you mean by the spike method... Do you have some photos of an example? Thanks for all of the help!
 

TFF

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A real reproduction of a WW1 plane is very complex. Ten times as many parts even if you count the rivets of the alu. To build a real WW1 reproduction over a replica like is about purity. If it’s all about looks or simplicity, the aluminum is the way to go. If you want to fly a WW1 plane modernization is a cheat. This plane just flew last month. Here is the best thread on it My Fokker DVII Project
 
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Okay....Been lurking on the site and came across this thread and just had to jump in. I am a new member but my head has been filled with the tube and gusset ideas for a long time. I have just recently been getting serious about my first build. Anyhooooo...tons of questions but I will save them until I get a chance to read through the entire thread. I have read the first few pages and the last few. Olli...I love your idea and had the same kind of thing in mind for the Legal Eagle. Beautiful man...just beautiful. Keep going with it!!!
 
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I'm not quite sure what you mean by the spike method... Do you have some photos of an example? Thanks for all of the help!
Ollie...I think what he means is you would use the spikes to align the gusset in the "bend jig" so you get the bend axis perfect (each spike 180 degrees out from each other along the bend axis) Then once bent you would not need the spikes anymore and simply nip them off so to speak.
 

Victor Bravo

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Sorry, in too much of a hurry... "Bend Indicators", not Indicatotrs

Galaxy Engineer - I was hoping that little spikes like this would eliminate the need for a bend jig, since the shapes of all the gussets would be different. Just putting the spikes in the center of the press brake die should get the holes within .010 of the exact location, which is likely plenty good enough. The goal is to make sure the rivets are through the centerline of the alum. tube.

And yes, although my original idea was a belt sander, nippers would also be a perfectly viable way to remove the little bend indicators.
 
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