Aluminum Tube & Gusset Airbike / Legal Eagle / Parasol Thread

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radfordc

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Let's say you take something like the Ragwing RW6 Parasol (just as an example, folks. So don't chastise me!), and wanted to build it in T&G instead of wood. The fuselage framework is made of 3/4 inch wood.

How would you go about sizing the aluminum tube for the equivalent strength?
You could look at the common T&G examples and copy them. Aerodrome is what I'm most familiar with and they tend to use 1" tubes in the aft fuselage and a larger size in the front.

I personally wouldn't go for "equivalent strength", I would go for stronger than needed by a good amount which is how I think Robert Baslee designs his.
 

FritzW

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Aerodrome...tend to use 1" tubes in the aft fuselage and a larger size in the front.

I personally wouldn't go for "equivalent strength", I would go for stronger than needed by a good amount which is how I think Robert Baslee designs his.
Just sayin... If Baslee overbuilt (overweight) his designs and Aerowerx uses his designs for "inspiration" and goes stronger by a good amount (more unnecessary weight) ...things are going to start getting pretty heavy.

There's a neat chart in the Evans Lightplane Designers Handbook that lists the "Properties and Allowable Ultimate Tension, Bending and Torsional Moments" for 2024 and 4130 tubes. It lists them by OTS sizes and you read the properties in the 2024 or 4130 side of the cart (you'd have to interpolate for 6061). The LPDH also has the column load curves from the Summerill charts.

The Summerill charts are available from a google search. I don't know which ANC the 2024/4130 comparison charts were copied from but they could be scanned and posted. It wouldn't be copyright violation because they were cut and pasted from a govt. pub to begin with.

Be careful with just copying the tubing size from another design, the geometry is just as important "The strength of a rectangular beam is proportional to its width times the square of its depth", and the fuselage is a rectangular beam.
 

FritzW

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Please don't tell me that. I have about 6 designs I would like to work on and build. The BeetleMaster is just one.
At my age I forget the new ideas I had a few months ago so when I have them again they count as "new".

P.S. I've spent many hours with a set of Skymaster RC plans trying to get a twin VW O2-A to look right. ...I can make it look right or I can get the CG to work out but not both ...yet
 

Tiger Tim

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I’ve waffled back and forth on whether my fantasy Verner Solocoupe should be wood (stealing heavily from the Hi-Max) or aluminum tube with a pile of inspiration from Graham Lee. I’m watching this thread with interest.
 

radfordc

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Just sayin... If Baslee overbuilt (overweight) his designs and Aerowerx uses his designs for "inspiration" and goes stronger by a good amount (more unnecessary weight) ...things are going to start getting pretty heavy.
I'm not suggesting you need a structure stronger than those designed by Robert....his are already more than strong enough. I'm saying that trying to build a T&G structure that matches the strength of a wood structure isn't necessarily a good idea. If you are designing to minimum weight and minimum strength you must be a good engineer and should probably test structures to confirm their adequacy. An overbuilt structure will always be heavier than it could be, but as long as it performs acceptably that isn't a problem.
 

ScaleBirdsScott

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I'm on board with the idea of a single-seater designed after the Monocoupe radial. It's along the same sort of lines I've been thinking.

I definitely would say for optimal lines on something of the aesthetic, I would... favor welded steel.

T&G would do it. But for T&G I would not get too fussed with trying to replicate the classic aesthetic as much. Definitely would aim for a more utilitarian package while keeping some clean lines in mind.
 

Aerowerx

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... I'm saying that trying to build a T&G structure that matches the strength of a wood structure isn't necessarily a good idea. If you are designing to minimum weight and minimum strength you must be a good engineer and should probably test structures to confirm their adequacy. ...
Did you read my post, to which everyone is responding?

I said match the strength of the wood structure as a starting point as to the T&G structure. And then also do the engineering calculations to confirm. Of course, testing after construction.

But if a wood structure is designed to fly at 'A' knots, with +/-'B' g load, and you pick your aluminum to match the strength of the wood, shouldn't the T&G design have the same characteristics?
 

David L. Downey

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...I am not getting testy. But as I stated in my comment, a career in structural test is perhaps more valid than the opinions of a sales or "engineering sales" rep at a fastener company. even our low and slow airplanes suffer from low cycle fatigue..and that is where these issues show up. People can indeed skip proper deburring as it is a pita, but the longevity and security of the airframe are compromised - every time. As someone said, Cogsdill makes lovely tools that are prices but last forever in aluminum. when properly set they deburr effortlessly. Another advantage of deburring in process when skinning with aluminum is less puckered skins on final assembly as the line length is not different between the structure and skin. I do acknowledge that deburring does add time to the task. I disagree that it is not worthwhile.
I also am one who has never been able to become a good welder in over 40 years of trying - and I own decent equipment in all the types of welds!
I will let this drop now as there is no place for antagonism in a help forum.

I had contact with 2 rivet manufacturers on the subject, and they suggest it is important yes, and sent me some guidelines, but not to the level that people report here. I have also done numbers of tests pulling rivets with different levels of cleanliness, cut them in half to see the results.

Oh don't get me wrong, I'm not disputing good practices in anyway, and it is that critical for Boeing, Airbus etc, and you said it yourself, you worked for a "Major", but most of our builds are no where near the critical stress levels they see.

For cleaning I use a 9/16" 14mm drill bit held in my hand, quick twist, surprisingly fast, followed by a quick rub over with 800 wet and dry, and a shortened, small allen key in a slow drill for the blind hole's inside. Works well and is fast. Of course I have inspected the results and as the rivet companies advised, the rivet forms into and fills any irregularities if pulled properly.

Posts like yours tend to give the folk an impression that horrible weeks will be spent detailing every single hole of thousands, when in fact it's a lot faster and easier than that for excellent, and safe, results.

There is some scientific articles on the subject on the Net, including hole edge differences between laser, water jet, plasma and drilling at microscopic levels. Interesting stuff (or maybe I need a life!)....
 

BJC

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But if a wood structure is designed to fly at 'A' knots, with +/-'B' g load, and you pick your aluminum to match the strength of the wood, shouldn't the T&G design have the same characteristics?
I would want to verify that the load carried by any plywood skins would be carried in the (presumably fabric covered) tube and gusset structure. That could require additional tube structure. I would want to verify that the tubes would not buckle under ultimate load. I would want to verify that the stiffness of the tube and gusset structure was adequate. I would want to verify that all hard points are adequate, with close attention to the control surface hinges. I would not assume that the tube and gusset fabric covered structure would have the same Vd as the wooden structure. I would be more concerned about fatigue in the tube and gusset structure.

Given all of those issues and concerns, I would consider that the tube and gusset structure needed to be a completely new design. That is not to say that a “copy” design will not fly; however, if would be pleasant coincidence if it was close to an optimum design.


BJC
 

mullacharjak

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The DSK Delta style of wing spar construction was a type of tube and gusset construction which has been forgotten.
Combined with the fisher style of fluted angle rib would result in a very nice structure.
We dont have aluminum tube/sheet here so I am just sharing my idea.I am sticking to wood as
that is all we have.
 

Tiger Tim

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What’s out there for wing and strut mounting options on an aluminum tube cabin plane? I’m picturing a square steel carry-through across the top and steel strips tying in the struts across the belly. Is there anything more elegant than that?
 

Toobuilder

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A heavier wall aluminum tube as one of the crossmembers on the bottom, with bolted or riveted attach tabs.
And taking a lesson from the Challenger (IIRC), that is one load path that needs to be engineered and fabricated very carefully. No second chances with that one.
 

cheapracer

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.I do acknowledge that deburring does add time to the task. I disagree that it is not worthwhile.
At no point anywhere did I say not to deburr, it is indeed quite important, and I mentioned the 2 methods i use to deburr above, i.e. a 14mm drill in my hand and a modified allen key for inside the tubes. Most intelligent people realise I use them for deburring.

What i am saying to people interested in this method of construction is that you don't have waste your time making love to every one of 5,000 to 10,000 holes, nor do you need special skillsets or tools.

As long as all major burrs are removed, and there is no raised surfaces to interfere with the 2 surfaces mating to each other, you're good to go.


a career in structural test is perhaps more valid than the opinions of a sales or "engineering sales" rep at a fastener company.
You have no idea who I was dealing with in those major rivet manufacturing companies, that is just consescending arrogance on your belief you are superior to others, for which you will now be put on my ignore list, as I don't want to see your self importance again. The irony here is all your practices came from those, or similar sources.

My purpose here, and the bulk of all my other posts around here are to encourage people that they can do it, and most things are nowhere near the stress and as hard as 'Experts', like you, make them out to be.

Bye bye.
 
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