Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Victor Bravo, Oct 8, 2019.
Guys, calm the heck down, nobody should be getting snitty here.
While the Challenger Rony bracket issue is concerning, we're not talking multiple failures. The biggest issue was the inability to properly inspect it.
Challenger has a very long history and is one of the EAB and ultralight success stories in the industry.
That said - it is a 70s design that bears little resemblance now to its original configuration.
However it's not a T&G design...
How many Baslee designs have crashed due to structure failure? I've seen many go in due to engine failure only to be rebuilt and flown again but... I've seen most of them as flying machines (even if I wouldn't particularly want to fly some examples I've seen in the wild)
If you find elegance in simplicity...
The HiMax uses a 1 x 1 x 1/8 2024 C channel for the spar carry throughs and a 3/4 x 3/4 x 1/8 2024 C channel on the floor for the strut attach points. ...scarry to look at but it obviously works. (I've never heard of a HiMax falling apart).
Because of my size, and the size of the yellow stripe down my back, I'd look real close at that though.
The stress analysis for the Mini Max has the numbers for their 6061 brackets.
A friend of mine went 4 wheeling in his full scale T&G GL Nieuport 17. It was interesting to see how the structure failed during the "crash".
Some cable tangs bent and some thimbles (without Never Kinks) got stretched flat but none of the cables, or the structure they were attached to, actually broke. Some of the rivets started tearing out the rivet holes in the flimsy looking gussets but I think that just spread the crash energy out over time (crush zone in a car).
It gave me some real appreciation for T&G construction.
Miscellaneous thoughts; When NASA did crash testing on aluminum aircraft from the Piper flood they were surprised at how the would flex and pop back in a crash. If you look at the shear strength of a cheap pop rivet the numbers are in the hundreds. Once you design for tear-out your brackets will be very strong. I bet that Nieuport was bouncing along going boing, boing boing.
any designers out there this might help.....Please load test ....maybe test a sample to destruction.....this is from Peery. Spread Sheet is mine and is posted for educational purposes only. Do not use for actual structural design without load testing.
On my Minimax via 1992 plans it is a 6061 T6 channel thats cut down in the center. It gets bolted in so that helps:
Question: Legal Eagle and Airbike both used three tube longerons instead of four in the aft fuse, saving the weight of the fourth tube and diagonal tubes associated with the square vs. triangle cross section. Would the weight savings in three tube construction be worth the added complexity of designing gussets ( and maybe Fritz's printed widgets) that would work for that scenario?
I definitely am pro tri-tube. But there's arguments for 4, clearly.
But yes, tri-tube!
I like the four tube rear for looks but the three will weigh less.
No added complexity in designing the gussets. They would be the same, just bent to a 60 degree angle instead of 90 degrees.
FYI, the Aeronca / American Champion 7 and 8 series use a three longeron, welded 4130, scheme.
There are of course advantages to 3 and 4 tube tailcones, however I do believe it is worth mentioning that the number of 4 tube fuselages outnumbers the 3 tube designs probably 100-1. They gots to be a reason.
Note on the Aeronca designs the three tube fuselage has a pretty big pile of plywood formers and spruce or aluminum stringers to put the fabric in the final shape. All this plywood and spruce must certainly weigh nearly as much as one extra piece of tube. That extra wood is not necessary for flight on a small low-speed UL/LSA of course.
Also, I have seen an Aeronca 11 (Chief) fuselage up close without the fabric on, and I can say the forward half of the fuselage is a four sided rectangle, that morphs and transitions into the three sided tailcone behind the wing. That transition and alignment will not be easily done without a fair amount of jigging and fixturing off of the workbench, regardless of whether you're welding or riveting.
Because of all that, I will bet dollars to donuts that the four tube fuselage is some modest amount easier and less effort/time/head-scratching to build than the three tube fuselage.
The 4 tube makes it easier to contain a human form, but in context of this thread title, the human will straddle the fuselage, making a 3 tube viable.
Pretty sure people like 4-tube simply to simplify transitions and let you build left and right halves identical on a table and all the fixturing is done with a 90° square while tri tube a lot of work has to be done in 3D to some extent.
With proper CNC work beforehand it's not a huge issue, as mentioned.
My bad, I was suffering from an acute case of cranial rectalitis when I wrote the original title. My actual intent was to include all sorts of small single seat high wing airplanes, ALSO including the style of the Baby Ace, Sky Scout, Texas Parasol, Heath Parasol, etc.
Not by any means intended to be limited to "straddle" style airplanes. The thread idea was about using tube and gusset Graham Lee / Baslee construction style on something other than a WW1 replica.
The original thought was that the Texas Parasol was a wonderful idea for a quick and cheap and easily built structure, but using extruded or bent angle would create a risk of the truss members being more susceptible to twist and buckling than a tube.
I'd argue that a 3 tube fuselage is much faster and easier to build if you have the right jig.
...and before the naysayers jump in to say it's way too complicated and they can do it faster and better with a hammer and 2x4's, blah, blah, blah...
Once the fuselage model is done it only takes an hour or two to pull a jig off of it, and that only has to be done once. Another hour or two to cut the jig (less than an hour if it's XPS foam from the box stores). So, from fuselage model in CAD to a finished jig would take an afternoon. The second guy, who doesn't need to draw the jig, could do it on his lunch hour.
This one is a welding jig so it's beefier than it needs to be for a T&G fuselage.
T&G would be light enough that you wouldn't need castors, you could make one like this out XPS foam
It's fast, simple, cheap and works like charm
Once again Fritz from one SW user to another, how on earth are you so fast at cranking these out. Your jig looks amazing. I had a design for the Skylite for a jig, but it was not as nice nor refined as yours. I will once again follow your lead.
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