# Aluminum Tube & Gusset Airbike / Legal Eagle / Parasol Thread

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#### Victor Bravo

##### Well-Known Member
Putting my mouth where my mouth is (not a significant philosophical upgrade, btw), I am proud to herewith launch a thread for the discussion, renderings, slings 'n' arrows related to the recently rekindled interest in aluminum tube and gusset method for small high wing and parasol designs.

My belief is that this is far far far more relevant and promising than it may seem at first... because...

The original Graham Lee and Baslee tube and gusset designs have proven to be successful, fairly safe, easy to build, and my favorite... fairly cheap. They are easy enough to engineer, and require few specialized parts. The basic structure can be adjusted back and forth to make numerous different designs. Stock, mass-produced tube sizes in 6061-T6 and 6063-T8 are likely to be available in a lot of areas at a low price.

Importantly, the recent developments in CNC mahcines for cutting, coping, and drilling tubing can allow a cleco-ready fuselage structure right out of the box.

The airplanes using these fuselages have all been WW1 replicas, for no good reason whatsoever. The advantages of this type of construction for a small, light E-AB in the 30-80HP range have been artificially limited to WW1 airplanes because of designer preference. Let's have a thread that removes that artificial limitation because the basic concept is viable for many other uses:

It seems clear to me that the advantages of tube & gusset would be every bit as valuable for aircraft of the same size/shape/mission as:

Airbike / Legal Eagle
Texas Parasol
Flitzer Biplane
Baby Ace
Pietenpol / Sky Scout
Heath Parasol
Cracker Jack
Fisher Koala
LMA cub/T-craft

For this specific discussion, my intent is to limit this to high wing, conventional layout fuselages that will be paired with similar aluminum tube (UL style, or Zenith style, or Kolb style) wings. Yes, you could talk about a tube and gusset SR-71 or Supermarine S-6 replica, but that is far outside of what I envision this thread to be about.

So... what say ye, o Lofty Guild of HBA SolidWorks artisans?

#### ScaleBirdsScott

##### Well-Known Member
I've been batting for something like this for a few years now, so I certainly see the merits. I really like the idea of those Legal Eagles and airbikes and Kitfox Lites and Badland types. But I want one that can be mostly cut from aluminum and riveted with a puller; no gluing wood or hot-gluing steel. A few limited steel brackets and bolts where needed, and I'd even take some wood floorboards or similar. But in general, a tube-n-gusset job with an all-alum wing.

Ideally light enough that it could fly gud on a Verner 3V, and maybe in some form meet P103.

For some non-WWI examples the Murphy Renegade has a similar sort of aluminum tube and gusset construction, though they're a fair bit more advanced with custom extrusions and so-on. And of course I'm finishing up our WWII replica using a similar frame under all the hubbub.

#### rotax618

##### Well-Known Member
Perhaps a Stewart Headwind re-engineered for alloy tube/gusset construction would make a good candidate, the wing could be optionally built from wood, alloy tube or hotwired foam/glass depending on the builder’s preferences .
I used glass/kevlar ribs on my Boorabee, construction is pretty simple.

##### Well-Known Member
Log Member
VB,
Your more than welcome to build a 20% larger version of the skylite in tube and gusset and put Petes engine in it. Its a parasol so should fit the bill. That was my general plan but unsure if I will get to it anytime soon.
Marc

#### flywheel1935

##### Well-Known Member
Go to Tube & Fabric, you'll see my LMA build, tube /gusset/hysol glue, airframe.
Its quite labour intensive, and my next build will be welded 4130 instead.

#### litespeed

##### Well-Known Member
Gets my vote.
The advantages for many will outweigh the time building if done well. Alloy and rivet plus CNC can be a great time saver and easy to replicate quality wise.

A well optimised design can be cheap and fun to build. Baslee has the right ideas, we just need a built for substance not style design.

Parasol sounds perfect.

#### GeeZee

##### Well-Known Member
HBA Supporter
First off, thank you VB for starting this thread! I’ve been thinking of just buying a Airdrome Fokker D VIII fuselage kit as a starting point then putting cub gear and empennage on it. Maybe use his wing but adjust the cabanes to a more “modern” angle. Preferred engine would be the verner but a budget build could use the Briggs. I’d also like to add the Zing to the list of candidates for tube and gusset conversion.

Log Member

#### FritzW

##### Well-Known Member
Log Member
If I understand it correctly, which isn't likely, Graham Lee's designs fish mouth/cope all the tubes and Baslee doesn't. If that's the case that's a huge ΔPITA (difference in PITA). I think a good tube and gusset parasol would be designed for square cuts: hacksaw, table saw, miter saw, pipe cutter(?), etc. Keep it all "hacksaw and hand drill" simple. ....+ tin snips for the gussets.

So "how to get away with square cut tubes" would be the first question to answer (you gotta know that before you start drawing).

>>>>>>>>

...and a cut and paste of my standard rant

I can also see where a simple, *purpose built CNC machine would knock out all the tubes, gussets, ribs and fittings pretty quick. (if building a $500 machine saved$1000 on the cost of a kit or 6 months of build time it'd be something even the Ludites would have to consider)

*a 12" wide **MPCNC (Mostly Printed CNC) that's long enough to handle the longest tube on the airplane. ...Bill-Higden saw how the Facetmobile guys did it.

**One of these but ~12' long (total build ~$300) Bolt one of these to the table to cut the tubes ($200 on ebay)

#### Victor Bravo

##### Well-Known Member
+1 on the increased PITA for cope cuts, if done by hand. But a significant part of the original idea for this thread is that CNC will eliminate 75% of the tube cutting and fabrication, which would include cope cuts. The extra cost of CNC would be more than compensated by the time saved, and the accuracy of the build.

The Mike Sandlin gliders are demonstrating that these aircraft can be built at the "hacksaw level", and I understand many of the Graham Lee airplanes have been built that way too. BUT... the current "garage level" tooling like Fritz has shown in his post make it a no-brainer to do this on CNC. Someone like Fritz and several others on this forum could set that stuff up in their shop and knock out a cleco-ready fuselage kit for something this size very very quickly if it made financial sense.

(actually I suspect it would be a small-scale but viable money-maker, but it also would allow a clever guy to write off or depreciate buying all the machinery, the shop costs, etc.... when in reality it's all for his own nefarious uses) I know Fritz doesn't want to be in business selling kits from previous threads. But the concept itself is potentially valid. I'm still working on addicted2climbing for this, but he's got much bigger fish to fry right now.

I have no calculated basis for this, but I would SWAG guess that there's maybe $200-250 in aluminum tube and sheet in a Baby Ace or Legal Eagle size fuselage, and maybe 3 or 4 hours of machine time to cut the tubes and holes. Someone might be able to sell a basic fuselage kit, at a modest profit, for$995.00 that yields a safe and predictable structure. That's pretty attractive. I'm sure that many people on this forum can create a more accurate fact-based estimate - perhaps Fritz, or Scott, or one of our other smart/experienced folks would kindly validate (or napalm) my SWAG on this one portion of the aircraft?

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#### Victor Bravo

##### Well-Known Member
"Getting away with square cut tubes" might be accomplished with a second equal or half-size gusset on the inboard side of the joint, eliminating the "wobble" axis of movement, and constraining all the fasteners essentially to pure shear. I'll bet that would extend the life of the structure beyond even what a "cope cut" single-gusset design would do. This might only have to be half the size and thickness of the main outboard gusset??? Very easily done with the CNC.

#### GeeZee

##### Well-Known Member
HBA Supporter
What about square tube and gusset? No coping required. Something like the Honey bee and Pegasus structures (only not welded).

#### ScaleBirdsScott

##### Well-Known Member
As for CNC gusset work the challenge will be size of machine and speed of machine and number and size of the gussets. And volume of kit sales. You might find the best bet is a simple 2'x4' router table and get dozens of equivalent size plates and create cutting paths for all your parts to fit said table. Reduces the unknowns to a degree. At the same time maybe it's better to go all in if you have the space and get a 4x4 or 4x8 unit where you can gang up more plates and/or bigger plates and take more advantage of packing efficiency and less tool changes.

That will all affect cost and process greatly.

For tube cutting you probably would set aside a day or two and come up with a schedule of tubes to put into inventory for 5-10 kits and just stay cutting however many of each length until you've got piles and piles stacked into a cart or shelf.

That method doesn't even truly require CNC. Just some 80/20 and an adjustable end stop. Set your stop manually, bust out 20 tubes, then re-adjust with a master template for the next tube length. The precision is probably +/- 1/8 here so its well within minute of eyeball.

#### Aerowerx

##### Well-Known Member
As for CNC gusset work the challenge will be size of machine and speed of machine and number and size of the gussets. And volume of kit sales. ....
I thought the idea was to have the "kit" be a thumb drive with the CNC files, digital prints, and material list.

#### FritzW

##### Well-Known Member
Log Member
Another argument in favor of CNC is making all the fittings that get cut from extrusions. Knowing the design is going to be cut on a CNC machine opens up a lot of design options you wouldn't have with a bandsaw or a hacksaw (too fiddly and tedious).

ie...

#### ScaleBirdsScott

##### Well-Known Member
I thought the idea was to have the "kit" be a thumb drive with the CNC files, digital prints, and material list.
Maybe in another thread but I diddn't get that impression for this specific project. If there's a forum meta of people designing kitless plans using CNC as the "kit" then I'm out of the loop on that.

But at least for me, I'd never call plans on a thumb drive a kit. IMO a kit should include at a bare minimum some amount of physical tangible materials or componentry that is particularly provided to result in the final product. A box full of wood strips and plans is a kit. A simple box full of all the rivets, bolts, hinges, and other stuff from Aircraft Spruce, plus some plans, is a kit. Plans, regardless of how complete or in what format, are still plans.

I'm all for stretching the definitions and qualifications of what it means in the digital age to make the business model work for everyone, but still if I am in the market for a kit, I hope that it comes with at least the raw materials that are hard to source, or maybe at least the hardware or some custom brackets, or something. Something that takes a bit of the burden off my shoulders as a customer in terms of gathering and fabricating every part of the project.

But I'm still going to argue a thumb drive does not qualify as a physical tangible piece of materials/hardware, because that data could just as easily be sent via dropbox or hosted online, the need for a physical media transfer is simply a matter of medium vs message. And drawings, gcode, bits and bytes, is all "message". The thumb drive does not end up in the final product and is superfluous once the message is received. The thumb drive is akin to the crate a kit comes in. It's packaging. At best you could upsell it as a "fixture"

So I'm going to still consider any concept of CNC-ready design work, gcode packages, templates, whatever else that leaves the end user to source the actual materials, hardware, etc on their own, and where the user starts from nothing and doing all fabrication and so-on, as being "plans."

If the goal for this project is to be plans-based with an assumption of the end-user developing some sense of CNC capabilities, that's pretty good, and still worth discussion.

But IMO when VB is talking about,

the recent developments in CNC mahcines for cutting, coping, and drilling tubing can allow a cleco-ready fuselage structure right out of the box.
I'm imagining that box being a crate full of parts that have had said CNC work done to them already, with the main impetus for this project being a guy can quite literally do everything needed to provide said kits in a modestly sized basement.

As well, Baslee/Airdrome being mentioned here offers kits. He doesn't even offer plans-only best I can recall. If you want his plane you buy his kit and get a pile of tubes, gussets, specialty hardware, and then the drawings with it. So that seems to be at least part of the assumption here.

I, for one, like the idea of offering said design as a quick kit but also selling the plans-only version maybe via something like Patreon or another online platform that ensures subscribers get constant updates and so-on. It's the type of design that would really lend itself to easy kitting, leaving the creator with a relatively low barrier to entry in terms of tooling, and thus the cost for a kit should stay quite low and attractive. Meanwhile a maker who already has the tools and so-on would be easily able to take the plans and have a go on their own time. Win-Win.

#### Aerowerx

##### Well-Known Member
I guess what I was thinking was that some on HBA want to build their own aircraft, and some want to provide a kit/plans/whatever to those who want to build their own aircraft. And there are also some who design and build with no thought of making a business out of it. I don't know what percentage of each exists.

There was a thread not too long ago (Fritzw was involved, IIRC) where it was mentioned that a "kit" would consist of a stack of plywood and a thumb drive. Take them to your local maker shop, and in a few hours you have all your major parts ready to assemble. This was Fritzw's "slot and tab" idea, I remember, with all laser cut flat panels.

The same idea could be applied to tube and gusset construction. A stack of 6061 and a thumb drive. And, yes, the thumb drive would be redundant in today's digital age, as you mentioned.

Now, to apply the same concept to, for example the recent idea of a scale ME-262, an all aluminum aircraft with aluminum bulkheads, ribs, etc.. THAT would be something!