Discussion in 'Tube and Fabric' started by Vigilant1, Mar 28, 2017.
One of the 2 major issues I'm rectifying.
The other of course is cost.
Get off the internet and into the workshop. You would be surprised the amount of progress you make with your head down and focused.
I think, your work speed can be increased with practice. Training can also help you to some extend. You could get anything you needed from the online but I say, it lacks in many cases. Once I was interested in welding, I used to surf google and youtube for the tutorials. I was a daily visitor of the youtube, especially for the WeldFever. Even though they have a detailed tutorial, I found it bit hard to learn since there is no interaction between us. Also, it is difficult to clear the doubts as I have to type my queries in the comment box below the video and wait till I get a reply. And my husband always says that I lack in welding. So, I decided to upgrade my welding knowledge in metal core welding techniques with regular courses rather than online.
But, it is a bit difficult to find time for welding when kids are around you. I agree with that.
(I was going to post this in a new thread, but it seems to go well in here.)
I don't think I would design a welded steel tube truss structure for a new design aircraft. I've been playing around with the Willford spreadsheet for tubing (column buckling) and aluminum always comes out better.
For example, a 0.75" dia x 0.035" wall x 24" long 4130 seamless steel tube has a column buckling strength of 2501 lb, a tensile strength of 7469 lb, and weighs 0.53 lb.
A 1.0" dia x 0.049" wall x 24" long 2024t3 round drawn tube has a column buckling strength of 2915 lb, a tensile strength of 9076 lb, and weighs 0.35 lb which is 66% of the weight of the steel tube. So even with gussets, rivets, and bolts the aluminum truss of slightly greater strength would weigh no more than 75% of the steel tube truss.
Because of the bolts and rivets, I chose the 2024t3 because it has a greater bearing strength than the 6061t6. Also, while the 6061t6 is only very slightly weaker in column buckling than the 2024t3, it has a significantly smaller tensile strength (67.8% of the 2024t3's tensile strength) and weighs 97% as much.
Even when the column length is reduced to 12", the 2024t3 aluminum tube is still slightly stronger then the 4130 steel tube (5162 lb vs 4918 lb) and still 66% of the weight while tensile strengths have not changed.
Fatigue cracking from vibration at drilled holes is also a factor. Don't see many engine mounts of thin aluminum tube or fuselage frames with 9000 hours.
Very true, you don't see many. But there are and have been some, and I think it could be designed for. The Potez 25 had a semi-monocoque motor mount made from extrusions and sheet metal shear webs: https://www.flickr.com/photos/aerofossile2012/3527946748
Tubes are different from plates. When a hole is drilled in a tube it tends to snap off at the hole when bent.
If I were doing a gusseted aluminum tube frame, I would consider bonding a 2" long tube doubler over each end to move the bending stress away from the last hole.
I don't think that is necessary....because; the gussets will increase the bending resistance in a plane perpendicular to the gussets so that the "I" of the tube at the section where the last hole is located is smaller in the fore and aft direction, putting the holes on the neutral axis where the tension/compression forces are smallest.
Fatigue cracks are very real on vehicle, not just aircraft, but this "bending" nonsense gets thrown around a bit. Everything "bends", that's a fixed foundation, but if anything on your fuselage is bending in a manner to promote short term fatigue failure, then it was designed to spread loads poorly in the first instance.
I am heading for commercialization of such a fuselage tube design, so I have a vested interested in calling you out on this, so while one would be silly to argue the engine mount point, in reference to your "fuselage" claim, could you show us some examples please.
Note I am not arguing that fatigue cracks occur, but hey, they occur in all materials, not exclusive to aluminium tube.
Easily obtained, high quality aluminium extrusions for the homebuilder, is a reasonably recent thing (relative) so I believe your going to be a bit short on showing 9000 hours examples anyway, I think you'll be struggling for 2000 hours, cracks or not. I guess BD4s might be the oldest, I don't profess to know the history of every BD4, but I've never heard of structural problems, Jay Kemp maybe knows?
Hey, lets take it one step further, does any one in the forum know of fuselage failures (not wings) on anything (light aircraft), be it made from chewing gum through carbon fiber?
I don't want to sound confrontational BB, but as I say, your claims affect me directly and I have to support my position.
I have no dog in this fight, but it's interesting to look at aircraft that have been around for a long time to see what we can learn. The New Standard pilot + 4 passenger biplanes were made with bolted and riveted aluminum angle, which I have heard some people deride as a construction method these days, yet they served for decades in hard use giving joyrides, cropdusting, and smuggling quite a bit of liquor during Prohibition. It would be interesting to get the details of a New Standard restoration to see how well the method has stood the test of time. There may be other, similar cases of production bolted and riveted aluminum tube designs you could examine.
Yes, but in a crash the bends are extreme in all directions.
Cheapracer- my comment about holes in tubes was for thin round tubes. It does not apply to your square tubes where holes are not on the extreme fiber like round. I am building with square tube also. You can read remarks from our late Mark Stull about cracks in ultralights. I don't have much experience with aluminum tube frames but I have inspected some and have found loose pop rivets. I did own a Taylorcraft with 9000 hours. But like I said, I can't find any old ultralights. The toughness of steel tube compared with aluminum tube is readily apparent to me. The aluminum tube frames are generally made with thicker walls than is usual for steel, so the weight isn't much different. Each material has advantages.
Matthew- interesting about the New Standard, I didn't know about the angle.
One still gives rides every year at Arlington Fly-in.
Angle isn't as strong in column buckling, but won't snap usually in a crash. It just twists and folds. Again, each material has advantages.
Agreed, crash is something to worry about. Ultralight style aluminum construction is not what I had in mind, and the elongated holes is why I would use 2024t3 and solid rivets instead of pop rivets; I was thinking more of the gusset designs used in the Boeing F4B biplane fighter. Granted, this is square section but it is aluminum and I would flatten the sides of the tube ends (or square them) to do the same thing (along with tube spacers for the bolts):
Here are some more pics of the F4B restorations, https://eaa1361.org/chapter-tour-roy-rehm-workshop/
Yeah, the square tubing is different than round, it won't crack at the hole in bending so much, in my opinion. I just edited my comment to Cheapracer about square tubes.
I will admit that it's much easier to design the welded steel tube truss; no gussets to design (well, some...), no fasteners to select for shear strength, etc., just assume pinned ends and fit and weld them together, nice and simple and economical, and only a little heavier as a percentage of empty weight so I can see why welded steel is attractive to manufacturers and homebuilders, but some people like to weld - I like to cut and drill holes.
Yup, I'd love to learn more about designing with angle rather than tubing as it seems like it would be very rugged and straightforward if you stick to simple shapes. For the scratch builder or low-volume kit you'd want to stick to existing mass-produced angle sizes, but for for factory production of a kit or ready-to-fly machine it's not hard to image a CNC machine cutting out flat shapes with pre-drilled holes that are then dropped in a power bending brake to create an angle customized for it's position in the structure.
Thanks for your reply BB, appreciated.
Is this spreadsheet publicly available?
Why can't you use 4130 tube and sheet with pulled steel rivets?
Errrr get a load of this !!!!
It does look nice.
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