Aluminum Tube & Gusset Airbike / Legal Eagle / Parasol Thread

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Rockiedog2

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BJC said
If you want to analyze your indeterminate structure, look into the virtual work method.

yeah. That's what I did. No worries now.
 
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cavelamb

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Just a note to point out that the Texas Parasol does not use riveted aluminum tube in the fuselage structure.

The fuselage is built using extruded 6061-T6 aluminum angle - overlap joints and driven rivets.
While this may be a little heavier than pop-riveted aluminum tube, the weight difference is minimal.
 

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BrianW

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Lots of aircraft have indeterminate structures. Many are simply over-built, or copies / extrapolations of existing successful designs.

If you want to analyze your indeterminate structure, look into the virtual work method.


BJC
Reminds me - when rebounding from an aeromedical decline, I purchased a Loehle Parasol. The cockpit access involves sidling around the three wing struts (count 'em) then lifting a foot over the cockpit wall to place it on the seat, and rising in a crouch to avoid the overhead wing, then shuffling legs into position, remembering to confine the feet to reinforced structure - after fifty years of opening a door and stepping in (a Cessna 150). What I REALLY need is a sidewall cutaway. Toying with a square tube warren girder connecting the forward structure to the rearward structure, so I can step in more gracefully!
 

erkki67

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Reminds me - when rebounding from an aeromedical decline, I purchased a Loehle Parasol. The cockpit access involves sidling around the three wing struts (count 'em) then lifting a foot over the cockpit wall to place it on the seat, and rising in a crouch to avoid the overhead wing, then shuffling legs into position, remembering to confine the feet to reinforced structure - after fifty years of opening a door and stepping in (a Cessna 150). What I REALLY need is a sidewall cutaway. Toying with a square tube warren girder connecting the forward structure to the rearward structure, so I can step in more gracefully!
The Airbike is the answer for your request, or the Affordaplane and it’s derivatives.
 

Ollie Krause

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Hi Home Built Airplane Enthusiasts,

We're working on designing a gusseted aluminum truss frame which resembles the Legal Eagle and have been really struggling with some of the more complex joints (places where 3+ beams come together on separate planes. We opted to use a gusseted aluminum frame since we noticed many people have an unusually strong aversion to welding and using a gusseted frame would remove the need to cope all the beams. Throughout our design process, we've run into several gnarly gusset problems. We were able to solve most of them but there is one that we just can't figure out a way to connect. A gusseted aluminum truss frame isn't very uncommon so I would imagine it's possible to do but I was wondering if y'all could point us in the direction of some resources and documentation we can read which may help in this situation. We can adjust the truss layout however necessary and if we can't solve this gusset problem, we can use a welded 4130 frame. Even if we are able to solve this gusset problem, though, we want to strike a balance of simplicity and ease of construction. If our complex gusset joints become too difficult to construct, it may be simpler just to weld the frame despite people's aversion to it. Below I've attached some screenshots of some of our latest truss design and failed gusset attempts. Home Built Airplanes has been an invaluable resource over the course of our project and we are extremely grateful for all of the experienced advice and crucial insight you all have given us.

Thanks again,
Ollie
Annotation 2020-05-04 104206.jpg

Annotation 2020-05-04 104249.jpg

Justin's Gusset 2.jpgJustin's Gusset 3.jpgJustin's Gusset 4.jpgJustin's Gusset 1.jpg
Ollie's Gusset 2.jpg
Ollie's Gusset 1.jpg
 

addicted2climbing

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Hi Home Built Airplane Enthusiasts,

We're working on designing a gusseted aluminum truss frame which resembles the Legal Eagle and have been really struggling with some of the more complex joints (places where 3+ beams come together on separate planes. We opted to use a gusseted aluminum frame since we noticed many people have an unusually strong aversion to welding and using a gusseted frame would remove the need to cope all the beams. Throughout our design process, we've run into several gnarly gusset problems. We were able to solve most of them but there is one that we just can't figure out a way to connect. A gusseted aluminum truss frame isn't very uncommon so I would imagine it's possible to do but I was wondering if y'all could point us in the direction of some resources and documentation we can read which may help in this situation. We can adjust the truss layout however necessary and if we can't solve this gusset problem, we can use a welded 4130 frame. Even if we are able to solve this gusset problem, though, we want to strike a balance of simplicity and ease of construction. If our complex gusset joints become too difficult to construct, it may be simpler just to weld the frame despite people's aversion to it. Below I've attached some screenshots of some of our latest truss design and failed gusset attempts. Home Built Airplanes has been an invaluable resource over the course of our project and we are extremely grateful for all of the experienced advice and crucial insight you all have given us.

Thanks again,
Ollie
View attachment 96215

View attachment 96216

View attachment 96210View attachment 96211View attachment 96212View attachment 96209
View attachment 96213
View attachment 96214
Looks Great Ollie,

I am planning to redo the Skylite as tube and gusset eventually as well and will run into the same problem if I keep the tube interfaces and clusters the same as on the welded version. To fix your issue, maybe have a look at some of the Baslee Airdrome WWI fuselages to see how they get around it. My guess is they avoid multiple clusters intersecting other clusters in another plane. Also have a look at the Texas Parasol even though it uses angle aluminum. Maybe you will need to rethink your fuselage a bit now thta you have found a problem.

Marc
 

Hot Wings

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Some possible options:

A welded/brazed cluster 'stub' that the other tubes are socket-ed into/around?

Abandon the planer gussets in these areas and use a bent gusset that ties tubes in 2 planes together?

Use a second, overlapping gusset, to tie 2 intersecting "V" sections together?

overlap.jpg
 

TFF

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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.
 

GeeZee

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I saved these photos from a recent craigslist add that was posted on HBA the other day. these are the best photos I’ve seen of a Airdrome fuse. Sadly even Baslee’s site doesn’t show construction details.
 

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ScaleBirdsScott

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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.
 

addicted2climbing

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Ollie,

What is mass properties saying the weight is for the fuselage not including the tail feathers? Want to compare it to the Skylite in 4130 as this is on my list to change as well to help those not comfortable with welding.

Marc
 

Victor Bravo

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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.
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.
 

sigrana

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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.
 

sming

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Also maybe consider 3D printable fixture
I don't know anything about cast aluminium strength, but seeing guys on the interwebz casting with 3D printed pattern and "lost PLA" technique, you wonder what's possible nowadays? Not easy at all, but you can't stop wondering...
 

ScaleBirdsScott

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Well, I've been part of doing some prototyping of limited production gun parts using 3D printed molds for lost-wax investment casting, so there's something there. But lost PLA is also definitely possible now for small specialty items. Another thing is its possible to 3D print specialty "single use" forming dies for making specific bends. Might be an option to explore if a particular complex bent part is needed.
 

Vigilant1

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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.
If the tubes in the cluster all point to the same spot, the fixture might be composed of
1)a "plug" that goes into the end of every tube. They could be printed, but since there would be manu, many identical ones, maybe just mass produce them via injection molding, etc. The plug has a nub that extends out (2"?) and this plugs into a :
2) custom 3D printed sphere (1.5" dia?) with holes at the correct angles for that joint. Each hole can have a printed label identifying the tube end. If using square or rectangular tubes, the nubs and holes could be square/rectangular as well to assure the tubes are in the right orientation before the gusseting/riveting starts.

I'd just leave them in place after the riveting.
 
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BJC

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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.

Tie them together with a heavier-than-just-a-gussett plate.

Tie the upper longeron to the plate with angle brckets.

Ditto the lower diagonals.


BJC
 

Ollie Krause

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Looks Great Ollie,

I am planning to redo the Skylite as tube and gusset eventually as well and will run into the same problem if I keep the tube interfaces and clusters the same as on the welded version. To fix your issue, maybe have a look at some of the Baslee Airdrome WWI fuselages to see how they get around it. My guess is they avoid multiple clusters intersecting other clusters in another plane. Also have a look at the Texas Parasol even though it uses angle aluminum. Maybe you will need to rethink your fuselage a bit now thta you have found a problem.

Marc
Thanks for the references! I had been examining the pretty detailed photos on this guys' Nieuport 11 Bébé build log. It seems like a lot of WWI planes used aluminum tube and gusset. We'll do some more research and will keep working on that gnarly gusset!
 

Ollie Krause

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Some possible options:

A welded/brazed cluster 'stub' that the other tubes are socket-ed into/around?

Abandon the planer gussets in these areas and use a bent gusset that ties tubes in 2 planes together?

Use a second, overlapping gusset, to tie 2 intersecting "V" sections together?

View attachment 96217
We thought of using bent gussets and layered gussets but we had concerns they wouldn't be strong enough in compression (particularly the large compression load during landing). Do you think compression would be an issue? If so, could it be mitigated through the use of thicker gusset plates? We also thought of making a cluster stub through lost PLA casting or SLS 3D printing but were concerned about its strength without heat treating. Maybe we could use it in conjunction with some thinner gusset plates. SLS 3D printing (in steel or aluminum) would also cost hundreds of dollars which just wouldn't be worth it. Welding a steel cluster stub definitely is an option which we totally overlooked! I think we're going to try to avoid welding though unless we have no other option since it would deter people from using our frame and take away one of the main benefits of gusseted aluminum.
 
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