LSA140 Build

[dcstrng]

This is a very informal test, but it does illustrate the impact heat can have on 4130 tubing. Again, I am in no position to make welding recommendations (other than agreeing with the designer). This is simply one of the steps I took to better inform my own approach to welding.

Wow, that's pretty dramatic -- my welds don't look as good as yours, but I've beat the *&%&$ out of `em... When my shop is below about 55-deg, I'll preheat my test welds with propane, now I'm not so sure... early on I had the weld fail, but maybe I'm not pushing the tubing enough for the failure your getting... I like TIG, but I'm just a weekend hack and sometimes I just grab O/A for the comfort...

[lsa140]

My observation is that both TIG and gas produce quality welds that will hold beyond the surrounding metal. They do however impact the surrounding tubing differently because of how each process applies heat. Understanding and controlling heat is a big part of any metal fabrication, and even more so when it comes to lightweight aircraft components.

[lsa140]

More welding practice/informal testing this evening. I tested one sample, using the same 1/2x035 tubing, with 400 deg preheat and no post heat. It held longer and bent further than the non pre/post heated sample, and broke in a perfect fish mouth contour just off the weld.

After testing a few more samples I realized that I may be taking the tubing slightly towards the annealed condition with my some of my post heating. It was bending easier than a piece of non-welded normalized 4130. The tubing would wrinkle in several spots under load, and I could bend it back and forth nearly a dozen times without cracking. I don't think it is necessarily a bad thing to have the tubing near the clusters a little softer. A little ways up the tube and out of the HAZ it remains in its normalized state. (how it arrives from the factory)

It is interesting to note that an annealed piece of 4130 tubing is still quite a bit stronger than a piece of 1025 that you find in some Piper fuselages.

I'll order a high temp IR gun from Amazon this evening to check my post heating temperatures. I'm hoping that if the post heat is dropped to 1200 deg and allowed to air cool the results will be better. The vast majority of the fuselage joints would never incur this type of loading (except in a crash). One of the only ones that comes to mind is where the axle tube welds to the gear legs.

[lsa140]

There is endless debate on pre and post heating 4130 online in various forums. I came across a thread that was getting a little "heated", and someone tried to lighten the mood with the following stress relieving method:

"I have used this process quite a few times with mixed results. First I start with some gangsta rap with the deep bass hits (NWA or Snoop Doog works well) and I use at least a pair of 15" subwoofers, then after about 30 minutes I alternate to some heavy metal such as Pantera or Metalica. For an extra bit of treatment you can step it up to Slayer or Seplutura, but only for 4340 and 300M. Last but not least finish with Kenny G to slowly bring it back to sane tempature, but too much Kenny G. will make the weldment weak and spineless, and lower the tensile strength."

It had me laughing hard enough that it got my wife's interest, and I had to try to explain welding humor... Time to throw out the torch and break out the Pantera.

[whee]

Great to see someone else doing some weld testing; I did similar testing. The fuselage (4 place) I bought was welded with TIG and I have continued to weld on the fittings with TIG only because I am much better with the TIG than I am with O/A. Once I complete the welding and it is warmer here I will stress relieve most of the clusters. Nothing like a tailpost failure to make you rethink the welding process...

IMG_1298 by Jon Whee, on Flickr

[Chris In Milwaukee]

Ouch! That hurts just a little!

[lsa140]

Garage door catch it? Better to find that weak point during building than flying... Some tail surfaces shake pretty hard under high power settings on tube and fabric aircraft, though the Bearhawk has another measure of bracing with the rigid horizontal stab strut. Watch the tail during takeoff on some of the high horsepower cubs, or when they drop the tailwheel; the surfaces shake quite a bit.

[lsa140]

I believe concave welds put the surface in tension as it cools and can lead to cracking in the weld, or where the toe of the weld meets the base material. I've been working on adding enough filler to form a strait, or slightly convex surface shape on welds. This shape also increases the ratio of ER70s-2 filler to 4130 in the weld and contributes to a more ductile weld. The smaller concave weld also cools at a more rapid rate due to having less mass, which can lead to more brittleness in the weld. I could see where a large, hot, concave puddle could put quite a bit of stress on the weld and tubing as it cools.

[rangermorton]

Has anyone compiled a bill of material for the LSA wings?

[lsa140]

I haven't seen one, you could try starting a new topic in the LSA plans built forum to see if anyone else has.

[lsa140]

Made a set of four tubing clamps this afternoon. I used some 1"x1"x1/8" angle and 1/8" flat bar that was on hand. The hardware is 1/4-20. I had a left over bag of rubbermaid shelving end caps that make nice little pads on the end of the clamping bolt. Max capacity using these materials is 1", though you have to pull off the caps to back the bolts that far. 3/4" (shown) slips in nicely.

[lsa140]

It is great to have a community of builders to exchange ideas with, I'm glad you are finding some useful things to incorporate into your shop and project. Some of these tools that we fabricate to build our aircraft, are very enjoyable projects in themselves. Best of luck on the welding practice and project.

[Chris In Milwaukee]

I've been terrified of bringing my O/A welding gear into the basement, lest I blow up the house. I've heard it's fine, but I'm not sure I'm falling for it just yet...

[lsa140]

I hear that, I always try to stop welding 1/2 hour before leaving the shop just to make shure nothing is smoldering.

[lsa140]

I don't plan on putting the LSA on floats until several years after the plane is flying, but I want to put provisions on the fuselage during construction rather than cutting into the fabric down the road. Bob mentions in a video interview on youtube that he wouldn't see a problem putting the LSA on floats from a design standpoint, but other than that I haven't seen anything discussing floats for the LSA. It doesn't look like many Bearhawks of any type have been put on floats. https://youtu.be/mwenTHwJs00?t=5m56s

There is discussion in the Patrol forum on which station the rear float strut would attach to (D or E). http://bearhawkforums.com/forum/bear...ting-locations Looking at the LSA, station E is around 10-12" further aft than the Patrol due to there being fewer stations aft of the rear door post. (which places more spacing in between the rear stations on the LSA)

I roughly scaled a set of Zenith 1450 Amphib floats, and very roughly placed them under the LSA. It looks to me that placing a rear float attach fitting at station E on the LSA would result in a very steeply angled rear float strut. At first glance stations B-D (45-1/2" apart - Cubs are around 43") seem like a possible option to attach floats to the LSA. I'm curious if anyone has discussed this with Bob?

Patrol%20floats_zps7lwipmjw.PNG

[lsa140]

Picked up the tubing package this afternoon. The shipping company had cracked the PVC shipping tube in several places, but overall it arrived in good shape. No tubing appears to be damaged. A big thank you to Mark Goldberg for his quick email responses, and help. I'm sure he answers the same questions a thousand times, and he does so kindly.

I loaded everything into the tubing rack except the top fuselage tubing. The tubing kit comes wrapped in several groups that correspond well to the build process. Top, Bottom, Left Side, Right Side, etc. I jigged the top tubing upside down, this allows the change in transition that occurs in the top longerons (when viewing from the side) to lift slightly off the table. Looking both at a 3d drawing based off of the plans, and how the tubing set in the blocks, this puts the furthest forward top cross tube (P) centerline right around 1" above the table. The rest of the tubing lays flat on the table surface. This will make more sense with some pictures tomorrow.

The longerons are coated with a thick yellow paint from the factory for QC purposes. As Mark points out, and others are following, the areas around the clusters can be cleaned for welding and the remaining paint blasted off when the fuselage is being prepped for paint. With welding, and torch post heat, an area 8-10" either side of the cluster would need to be stripped of paint to avoid burning paint fumes. Stations being around 36" apart, this would mean stripping 16-20" of that distance, so I just decided to remove all of the paint. The area around the cabin will receive various tabs/etc welded to the longerons, and I would rather be rid of the paint than pulling out the acetone every time to clear a small area.

All the best.

[lsa140]

Tacked the upper fuselage tubing together and pulled it out of the blocks this evening. Much of the afternoon was spent cleaning the tubing of paint and oil. I removed all of the tubing labels once their location was established. A 50/50 mix of acetone/lacquer thinner and a mild abrasive pot scrubber work well for paint removal. 320 emery cloth was used to remove scale from each joint area and denatured alcohol to wipe down.

Overall the tubing fit was decent. I felt that some of the diagonals were a little on the loose side. With the cross tubes placed precisely on plan layout/square and the longerons tight against them, a few of the diagonals in the tail section had a bit of play. I shifted things around best I could to accommodate, and split the play on either end. The gaps are acceptable, but there. 028 is a much bigger challenge to weld with gaps than 035, at least for me.

Assembling the top tubing upside down worked out well. Make sure you rotate the longerons to get the bend angles headed in the right direction. The tubing blocks with the oversize hole and fender washers are the way to go on a pre cut tubing kit. It really allows you to shift things around easily, highly recommended.

My wife picked me up this little ruler for my birthday, and it is awesome. Get one. Slip it in your breast pocket, and it is always on hand. I used it constantly today to check how the tubing matched the perimeter layout marks. Also, these magnetic vice jaw inserts are great for tubing. Both items are off of Amazon, and are worth every penny.

[lsa140]

Unwrapped the rest of the tubing today. Stripped that white paint off of the lower longerons, glad to be done with that. Tacked the firewall together. Assembled it with the front facing down to allow proper alignment of the lower joints. (It is a rather complex joint.) I used some 1/2 tube to leave the proper clearance for the engine mount bushings. A short piece of 3/4 x 035 was cut that mirrored the end of longeron to make sure all the merging tubes lined up. I think it is put together right, we will see tomorrow. I'm starting to get used to building from the tubing kit. As others have said, is a little backwards of what is familiar. I had the firewall drawn out, but the kit tubes where off from plans a little. There was a little moment of debate on making the tubes fit the template, but then I realized I just needed to roll with the kit. Variations are to be expected.

I've been using the TIG to tack everything, it takes longer but results in nice strong little tacks that are easy to weld over. It also provides a little more practice. Stitching the ends of some of those small tubes down in a joint is rather dedicate, but it is getting easier.

Separated the rear tapered table, and placed it in position to block up the lower fuselage. The laser continues to come in handy for quick alignment. Tacked the gear truss up, but left the outer diagonals off until mating it with the rest of the fuselage.

[lsa140]

Got the bottom tubing all aligned, and firmly blocked in place. 3/32" holes used sparingly in the longerons under joints to allow passage of air and prevent weld blowout. The fit of the lower tubing was excellent. I'm planning on float attach fittings at station D. Looking over PA-18 plans, 1"x049 is used at that similar location. (where the cub attaches the rear float strut.) Other tubing sizes in that general area are very similar to a cub. The LSA calls for 7/8"x035. I had some extra 7/8x049 on hand, so I got out the tubing notcher and swapped out for the thicker wall. The two vertical internal jig supports hinge at the table. Moving the diagonal on the front support allows for fore and aft movement of the tacked top fuselage tubing. Tomorrow I have a large stack of side tubing to clean and prep before jigging in place.

[Wayne Massey]

Looks great! After cutting and fitting tubing for my scratch build 4-place its nice to see it coming together so quickly!

[lsa140]

Thanks Wayne, much appreciated. Tubing kits are a great value, and a kick to build. Best of luck on you LSA project.

[lsa140]

Most of the fuselage tubing in place and tacked today. There are several more tubes to go in around the firewall/cockpit and some overheard structure around the wing attach area. It is nice to see the stack of tubing shrinking. Small pieces of aluminum foil tape work great to temporarily secure tubing at cluster locations. The wire feed came in handy for one hand tacking. Spent most of yesterday cleaning and prepping the remaining tubing. I noticed on a previous project that sometimes a small amount of oil rests just inside the tubing ends. Once in a while it can cause contamination in the weld. I filled a small container with about 3" of acetone, and dipped each end repeatedly/wiped down with a rag. The acetone ended up brown from the grit and oils, and the tubing ends came out clean. My cross line laser is mounted several feet in front of the fuselage, shooting a horizontal and vertical line at fuselage C/L. It has been handy for checking alignment.

[Bdflies]

Your attention to detail, fabrication innovations and progress, are commendable! Don't for a minute suspect that I'm discounting any of that. But I'm absolutely impressed with the pre-cut tubing! Are the tube ends cut on a CNC high def plasma or laser system? A customer, of mine, had a Trumpf Tubematic that could spit out the most amazing tubing fitments that I'd ever seen. It would make sense for Mark to employ such a system, but it took an awful lot of volume, to justify that equipment, at the time. If Mark is reading this, how are the tube cuts made? I spent 40 years, around metal fabrication and this impresses me!

Bill

[lsa140]

Thanks for the encouraging words Bill. I believe each piece of tubing has its own steel marking fixture, see the video bellow. Is this still how the factory notches the tubing ​Mark Goldberg?

https://www.youtube.com/watch?v=SQZKVPMwPNc

One of the major reasons I chose to go with the Bearhawk is their approach to offering many different paths to aircraft completion. It supports and honors the spirit of the homebuilding community. Many companies (understandably) withhold selling plans, and only offer kits.

I previously built a tubing fuselage from scratch, and knew right away the value a tubing kit would bring to the project.