Airframe from non-aircraft grade material.

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Tiger Tim

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Can’t be worse than the Gere Sport with the tube clusters held together with a bent over nails.
Be nice to the Gere Sport, it’s all welded like a real airplane and the build article goes so far as to advise hiring a pro for that job.

You’re thinking of the plans-built Heath Parasol being ‘riveted’ together with nails, which I’m convinced was only published to get people deep enough into a build that they’d buy a factory welded kit fuselage from Heath.
 

PiperCruisin

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At Airventure 2021 I stopped at an auto engine conversion booth (won’t say who).
My eye caught the mount tubing first. It was welded stainless.
The owner (engineer?) came up and I asked a bit about the stainless mount. Finally, I asked about “toughness” or ductility. He didn’t understand.

I'd say the toughness is more of an issue when you have an impact and cold conditions (think Titanic). I'd be more concerned with weldability. With an engine mount that experiences high cycles due to engine vibration, fatigue is a potential issue. Good welds help. Welded aluminum has about 1/3 the stress allowable vs welded steel. Never looked up the welded stainless curves to see if they were much different.
 

BBerson

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Stainless exhaust seems to crack more than mild steel (ref Bingelis).
I don’t know if a cold engine mount would be fatigue prone with stainless. The stainless weld is softer, but not as much lost as aluminum.
 

BBerson

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I don’t have documents other than AC43.13-1A 1972: “exhaust systems failures generally reach a maximum rate of occurrence at 100 to 200 hours' operating time and over 50 percent of the failures occurring within 400 hours.”
and “ changes in composition and grain structure of the base metal further complicate welded repair”.

Not so good is my experience, especially the rotted grain structure of stainless that is hard to weld repair.
 

PiperCruisin

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I'm not sure what the aviation community likes to use for designing for fatigue of welded structures. Industry uses AWS D1.1, Eurocode 3, BS 7608, or TWI. I'm partial to BS 7608. There is also a number of other techniques like Glinka, Battelle Structural Stress (see ASME VIII).

Eurocode 3 is one of the newer ones and treats steel and stainless the same as long as they meet toughness requirements.

So stainless vs steel, they should be about the same. It is load and design dependent.
 

stanislavz

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One more turn into this stress-boy madness.

This is a link to Russian forum thread with some pictures of FAR103 category ultralight beeing build Проект ультралайта «Zola»

And its "technology" is same as was used in this aerobatic one-off airplane : Laros-100 - Wikipedia Which was build, and was tested.

And the most "funny" part of this story - this technology is just square tube from 6060-T6 alloy with pulled rivets and some gussets. And yes, vertical and horizontal gussets are not-interconnected.

1653511330741.png

And more interesting - that 20x20x1.5 box is on par with our non-aircraft grade 18x1 tube from 1020 or aisi 444, but its lighter at 30% beeing 10% stronger. Which in fact is same as 20x20x0.5 box from steel, but with more rigid walls.
 

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stanislavz

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Mine reference from Skyranger/cheetah

1653519058961.png

1 mm in Cremona diagram = 10kg. 60.7059 * 2 * 10 = 1200 kg with Fos = 1.0. For 1.5 Fos - is still in 1.5 mtow range. Methodology and numbers looks to be in range. Tubes are 40x1.5 2024. Bolted connections, so pinned-fixed criteria.

Now from 20x1.5 square tube and with 3 times more gussets 56.5 * 2 * 10 = 1130 kg with Fos 1.0. Fos - is still in 1.5 mtow range. Lighter than base one, six gussets more to make. Fixed-fixed edges.

1653519645157.png
 

stanislavz

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Now some words on how to run that simple numbers., based on post #53.

1. You draw your truss. Scale is irrelevant, only angles have to be right.
1653521350951.png
2. Starting from load - in this case tail (100mm - 1mm=10 kg as per example) - we draw our force triangles/squares as per Sport aviation article. They can be drawn separately or in one pile as in my this example. If all done right - latest line will be equal to our reaction force * sine of truss member.
1653521432542.png
3. We delete our load vector constraint.
4. Using Buckling Calculator — Column Buckling and starting from your known tube length we enter critical load as a length of any element. I prefer to start from highly loaded one.
1653521477871.png
1653521501826.png

5. Now we need to check next members. From Cremona diagram we take load, from drawing - lenght. If all is ok - we go to next element. If not - we have to decrease length of element. And we have to go from our reaction point to the load.

6. If we see, that latest element is too long to hold necessary load - we have to redraw our truss and add new element or pick up next size of tube and start from first step.

7. If we have run out of space and our last element is very short - we can again take smaller size of tube or just delete/ignore it.

Repeat 5-7 till most of tubes (especially longest) are similarly stressed.
 

KeithO

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You can get all the stainless tubing you could possibly want here:
https://eagletube.com/wp-content/uploads/2017/12/Fractionaltubing2.jpg
Fractionaltubing2.jpg
 

stanislavz

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You can get all the stainless tubing you could possibly want here:
https://eagletube.com/wp-content/uploads/2017/12/Fractionaltubing2.jpg
Fractionaltubing2.jpg

Thank you. But - i am on the other side of the pond. We are really limited on size of tubes or its comes from USA with huge price and time tag.

Back to basis.. So that square aluminum tubes with blind rivet gussets have longer history and it wider spread than i though of it before. And it is none of new-new inventions. Some examples from this thread : Tube construction: Alternatives to conventional welding

And some of them - are acrobatic. Like Murphy Renegade. Now we big question would be only 6061 vs 6060. Both tempered.

That is possible to learn (it still kind of questionable one) - do 4 trusses connected at corners and forming one big box are rigid for torsion - having gusset separated for each plane. I have seen this on that Russian forum. It nicer and easier to make than trying to connect horizontal and vertical tubes at same point.
 

stanislavz

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That's a table of possibilities. The odds that the entire list and every alloy is in stock is zero, and close enough to zero for any given alloy.

I wouldn't begin to contemplate any 300 series in annealed condition.

Same is here. That we may have in stock - 6060 T6 in big variety of shapes ang gauges. Tubes, round, square etc, down from 1mm wall.

Ss - ok if we skip 300 series, we have some 400 series. But supply here is much more limited. 444 only in 15 18 22 od 1mm wall. Used for water pipes. 304 wider range, due to being used in chemical plants..

But - wenerable 6060 is totally ok on paper if we choose right gauge. 3/4 0.035 is nicely changed to square 25*25*1 made from 6060. In some length it is ok to use 20"20*1.5
 

Niels

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Is there somewhere one can read more about the AI-10 aeroplane?What engine?
 
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