Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Victor Bravo, Oct 8, 2019 at 7:02 AM.
yes but you have to stay focused....diversion and noise will kill a project in my opinion.
If for any reason Fritz stops working on the Ranger project because of this tube and gusset discussion, I will personally throw him off this thread The Ranger is now an actual aircraft project, which is just a marvelous thing.
The hook I'm trying to set in him with this thread is actually for the third project. The Ranger is happening now, then we lock him in the hangar with the Piojo... then we can walk into his shop with an armful of 3/4 or 7/8 aluminum tube and a bucket of Avex rivets!
I wouldn’t rely on fishmouthing for any sorting of real loads in a non-welded joint. If you’re intersecting at close to a 90 degree angle you might take up some compressive axial loads but that’s it.
Fortunately a well-designed truss should minimize bending moments at the joints so that the only loads are along the axis of each member, either tension or compression. In those cases a gusset plate is perfectly sufficient since it would be loaded in tension along its plane.
Obviously gets tricky with multiple joints at a single point, also when you get into real world non-idea geometries you get loads beyond the textbook truss design.
We're just talking concept stuff here, no one's picking out china patterns. Besides, ...I'm in a happy, committed relationship with the Ranger.
The hook was set a long time ago with the TnG 3/4 scale Curtis Robin
Square cut tubes wouldn't bother me a bit, especially with 3D printed cluster aligners. But even if the tube ends aren't going to be CNC'd I still think CNC'd rivet holes (tubes and gussets) are the only way to go.
That's getting interesting now... A CNC tube laser machine cuts all the rivet holes, laser marks the part number on each section of the tube, and laser marks the cut lines (square cut) for the tube sections.
Minimum machine running time and cost.
The builder just puts the tubes on his little chop saw, set at 90 degrees, cuts on the lines, and has the tubular parts for the fuselage DONE in lesss than an hour.
A laser CNC can also cut, mark, and drill the gussets.
And why not just... also cut the tubes?
Save machine time. ImI assuming it's expensive?
It would cost the same either way.
Out of curiosity, is it possible to get a WAG on the cost of those 3D printed joiners you proposed that would add strength and hold each joint/cluster in precise alignment while the builder affixed the AL gusset(s)? I know they have been rejected, but what could a builder expect them to cost?
Nothings rejected. When I get around to a building a TnG airplane you can bet it'll have be 3D printed joiners.
Depending on the size of the joiner and what they were printed with they would probably cost somewhere between .10c and .50c a piece. If there were about 25 of them on the fuselage it'd be around $10 to print them with regular PETG filament. Double that if they were printed in carbon fiber filled PETG. (CF PETG would be gilding the Lilly but I'd probably use it anyway)
Right, I meant rejected for use in this building concept, as proposed by VB.
I read the below as closing the door on further consideration of the 3D printed joiners/jiggers for this concept:
So, about $20 in materials cost for all the junctions in a small plane. Obviously, if we add machine time and setup, it would cost more (i.e. if our homebuilder takes the thumb drive to a local Maker, or if the daddy rabbit for the plans makes the CF PETG joint "framing aids" available as part of a small kit for those who would rather not mess with printing the parts). For this investment we get self-jigging joints where all the tubes in a cluster exit at the proper angles and are held in place at those angles so the builder can rivet on the gussets. And we get some stay-in-place redundancy at each joint. Also, if the design does use square/rectangular tubes (they do have advantages in some applications), these joiners also index the shapes so everything is aligned right. Got it--super. An efficient, new approach to accomplishing a fundamental part of the build.
Here is a example of tube and gusset from here in Aus. but this is a low wing and using round tubes. The higher performance version has a square tube version and looks the same.
One of these is famous for flying into a badly placed Ferris wheel. No injuries, rebuilt and flying two weeks later.
Here is a video of the square tube version, it is yet to have all gussets and skins on the outside added. To me it looks very strong and easy to build as a process.
sorry about video quality
Thanks. Those angle cuts aren't coped, but they do seem to be butted tightly.
Looks like an aluminum KR2. Quite a line of interesting designs. http://www.morganaeroworks.com.au/cheetah.html
But if the cleco holes are already located in all the parts, what does the printed assembly aid alignment tool do?
3 things I can see:
1) Unambiguous assembly guidance. If our builder is standing there with 3 pieces of cut tube that andcome together orthogonally, a few pieces of (flat?) metal with holes in them, it is not clear how the thing goes together, with or without holes and labels. If he has a labelled plastic fitting, a 4 year old could put the tubes in the correct orientation in 20 seconds.
2) It provides a fixture to hold the parts while the gussets are put in place. Our builder could "dry fit" major assemblies or even the whole frame together before setting a single rivet. Then, the gussets can only go on one way, any problems are immediatly apparent, and the thing is rigid and self-supporting so he doesn't need a third hand to hold pieces while he sets the rivets.
3) It provides another thing holding the tubes together.
On the Zigolo many of the round tubes are only predrilled on one end and match drilled to the mating gusset on the other. This was only done when one side of the tube mated at an off angle. To predrill every tube would require a jig for each tube or if done CNC it would require a fixture each tube sits in and references the same end stop for all tubes. This fixturw would need to be trammed in to match the long axis of the CNC router and hopefully left in place. If the belt driven CNC router comes out of alignment between both sides of the long axis than your tube fixture is no longer aligned with travel of the machine. That might get annoying. On a large flat part that is cut out of a large sheet this issue is not much of a problem but when trying to hit the tangent point on a tube to avoid the drill waking it likely would be.
I had started a similar thread about making a tube and gusset fuselage and keeping the same construction on the wings but for a cantilevered fabric covered wing seemed the Ercoupe method of angled ribs was my only alternative. would prefer to avoid that.
Badly placed? Near an airport?
Separate names with a comma.