LSA140 Build

[lsa140]

I appreciate the ideas, experience, and resources that the Bearhawk community shares with each other. I will be posting my experience building the LSA in this thread, and hope fellow builders find it enjoyable and useful.

The fuselage will be constructed using the Bearhawk tubing kit.

Build Table:
I already have a 4'x8' table available from a previous project. I didn't want to take up shop space with another full size table at this time, so I decided to build a tapered extension table for the fuselage build. It is constructed using two full length 10' 2x4s. The wide end is 3' and the skinny end is 1'. The top of the fuselage will be tacked together with the extension table flush with the 4'x8' table. Once this is completed the tapered extension will be set on the end of the 4'x8' table and angled to match the bottom longeron up sweep. The bottom fuselage tubing will be assembled in blocks, but not tacked - to allow adjustment as the side tubes are added. (thanks BTAZ) Internal plywood top fuselage supports will then be added one at a time and the vertical fuselage centerline will be marked using a laser. The tacked top fuselage tubing will be centered on the support marks, secured, and fine tuned. The connecting tubes and diagonals will then be assembled and tacked.

The tapered table should allow good access for assembly and tacking. The internal supports will give unobstructed access to assemble the fuselage tubing.

I built the tapered table this afternoon and will be fine tuning the combination tomorrow. I hope to receive the tubing kit early February and will be brushing up the welding skills until if arrives.

LSA140

[BTAZ]

While waiting, you might want to make a bunch of blocks to screw to the tables to hold the tube in position. Perhaps 1x1" and a few larger or of varying shapes, maybe 30 total or so.

If you are going to wait to tack the bottom like I suggested, you will want it well blocked into position.

The planned plywood verticals are different and probably would work but I would think it would be easier to just clamp 2x4's of the appropriate length to your table legs as verticals and then clamp 2x4's as horizontals to support the top frame.

The tubing fits together incredibly well so you want your jig to easily adjust to the tubing fit. Not sure the plywood verticals will allow this..

[lsa140]

Great input BTAZ, I appreciate the thoughts. I'll run by HD today and pick up some material for blocks. Previously I have used 1x2 pine with undersized pilot holes and 1-2 screws depending on the location. I would leave the screws in the blocks and move them around as needed. The soft wood worked well for squeezing against the tubing and screwing to the table.

I will make sure to secure the bottom tubing well. I am glad to hear things fit snuggly. Having previously built a fuselage from strait tubing, I appreciate the good value of the pre notched kit. I think you mention in your log as well that building with a notched tubing kit the jig needs to fit the tubing, not the other way around. Being able to firmly secure things, but move them around seems to be the way to go. Tighter gaps make welding easier, especially with .028 wall.

The 2x4 method looks like a good and established way to suspend the upper fuselage. I may end up using it when the time comes, or a combination of the two. On a previous build I used the plywood and was pleased with the results, but it was constructed by tacking the sides on the table (rather than the top and bottom).

I see you suspended the upper fuselage in three locations, did that work well? It looks like the furthest forward support was just behind the rear spar carry through. Did that provide enough stability around the cockpit?

[BTAZ]

To support the top, I clamped the verticals both to the table and to the rafters. Three sets because that's how many rafters I could clamp to and not block the garage door opener.

The trickiest part was getting the various tubes in the firewall area in place all at the same time to be tacked. I think the firewall itself could be built flat(I didn't) but jigging it to the rest of the fuselage took some creative jigging and clamping.

I used left over MDF scraps for my blocks but I think pine would have been better because it doesn't give off noxious fumes when you scorch it while welding.

Use wood that smells nice burning......

Still, definitely can't complain about having a tacked fuselage after just a couple weekends.

[lsa140]

That is definitely great progress for a couple weekends. I'm impressed by how much you have accomplished in a couple years of work. I was wondering about the firewall area. I ordered the Continental engine mount from Mark to help align and locate the mount bushings on the fuselage rather than trying to adjust factory mount later to fit my fuselage. I was wondering if I could tack the firewall area flat on the table and then jig at the proper angle in relation to the rest of the fuselage. Maybe even clamp the firewall tubes flat in some type of plywood jig and then mount that to the table. It looks like all the firewall tubing is all 5/8", it might be simple to jig that area up together. Did the engine mount bushings that get welded to the fuselage come with the tubing kit? It looks like a couple of them get sandwiched between the lower firewall corners and diagonals.

I have some scrap cedar around, that would make for some good aroma...

[BTAZ]

I don't remember about the bushings but the tubing is notched for them.

I knew I would be building my mount(this weekends project) so wasn't as concerned about exact bushing placement. If I was buying the mount, I would probably wait on the bushings until I had the mount.

With the bushings, make sure they extend far enough on both ends that you don't melt them. My bottom ones were just a little too short on the inside so took some creative work to square the ends so the engine mount bolt head/nut would sit flat when installed.

I can't remember where I saw it, but after I had done mine I saw that the firewall could be tacked flat(like I did the gear truss) and then put in place. Might even be in the LSA book that came with the plans.

[lsa140]

Those bushings look like a challenge to weld. I will make sure to leave them long enough. I've seen other designs put small corner gussets on either side of the firewall tubing at each mount location. The front and rear gussets are then drilled to the bushing OD. The gussets weld to the firewall tubing, and the bushings insert through the gussets and are welded front and rear. It looks a little cleaner, but adds to the weight and part count.

It looks like the LSA book mentions tacking the firewall frame on page 39.

I ended up taking my table height down this evening after realizing it would put the tail post through the ceiling sheetrock, and the upper tubing more difficult to reach. My existing table was 36", and I planned on using it as is, but things are easier to work on with a 30" table height. Everything will clear with 9' ceilings.

The tables were leveled quickly using shims and a self leveling cross line laser. I highly recommend one of these tools. I purchased one a number of years ago for a boat building project, and use it frequently. It will be mounted several feet in front of the table on the fuselage center line, shooting through the firewall and towards the tail.

http://www.amazon.com/DEWALT-DW088K-Self-Leveling-Cross-Laser/dp/B009O94W3E/ref=pd_sim_469_4?ie=UTF8&dpID=41cBeRv8gIL&dpSrc=sims&preST=_AC_UL160_SR160%2C160_&refRID=1FFG1ZGWWAX5KGMCHDSS

[BTAZ]

I too had ceiling height limitations so used a truncated tail post through most of the build until it was time to add the vertical stab.


Side benefit is it makes the fuselage much easier to rotate during the welding process.

[lsa140]

I went back to your build log, and saw the short, temporary tail post you used for assembly alignment and left tacked place for rotisserie welding. It looks like you left it place until vertical stab construction, fit the full length tail post to the tail spring socket, assembled the tail on a bench, welded, and then aligned - welded the entire assembly to the fuselage? That seems like a good way to go, were you pleased with the results? Your post reminded me of doing something similar on a previous fuselage. The tail post was not used as an alignment reference on that design, and I left it off until after welding the fuselage. After the tail post was welded on the fuselage was a lot more awkward to move around.

[lsa140]

Laid out the tubing centerlines for both the top and bottom fuselage sections.

I decided to go with oversized holes and small fender washers for the tubing blocks to allow easy adjustment to accommodate the pre notched tubing. The blocks are pine 1x2 with a half inch hole. 1-5/8" Gold screws, and 1/8" x1" fender washers. This setup allows the blocks to move side to side a max of 5/16".

Constructed internal fuselage jigs to support the tacked upper tubing. The front support captures station N cross tube and the rear support captures station L cross tube. The setup allows easy vertical adjustment. The supports are hinged at the table and an adjustable diagonal provides fore and aft movement while holding center. Now that everything is built, I will pull it off the table until I'm ready to assemble the upper and lower fuselage halves.

Started brushing up the TIG welding skills, and working on torch setup.

[lsa140]

All ready for the tubing kit. Set up a fence and drilled all of the block holes together. Used stop in the chop saw to quickly cut everything to length. Most of the blocks are 2" long with a few 4" and 6".

I enjoyed watching this video Bearhawk Aircraft posted of jigging/tacking a lower fuselage section, placing it in the main fuselage jig, and putting the bends in the lower longerons:

https://www.youtube.com/watch?v=-HhqY90kKXM

Played around with paint schemes last night. Will likely go with some variation on red, grey, and deep charcoal.

[mswain]

What software did you color that in? Looks great.

[lsa140]

That was colored using Adobe Illustrator.

[BTAZ]

Looking forward to seeing it go together!

I just finished my last large weldment today(the engine mount) and was basically where you were about seven months ago(except I already had the landing gear struts and the tail feathers done) so I can pretty confidently say that if you follow the plans all will work out.

However, it is still a large welded assembly so once the main frame is assembled, everything else needs to be built to fit it with plans dimensions more as a "guide" then the rule.

[lsa140]

Thanks BTAZ, its good to hear you where able to finish up your engine mount. Are you going with a small Continental? I look forward to seeing more BLSAs in the air.

[BTAZ]

In the beginning, I toyed with using an 0-320 but Bob talked me out of it.

I have a C-90 project engine that I am planning on using.

[lsa140]

I hear that. The climb would be incredible with that much power, light weight, lower drag, and high aspect ratio wings. It would likely take it right up against the 140mph VNE?

[lsa140]

On a previous project I gas welded 4130 with the Meco Midget torch and ultra light weight hoses. I have some training and experience with both TIG and gas. I would echo Bob's recommendation to utilize gas welding, for the reasons he stated in his build manual. For this project I will be going with TIG, because I enjoy the process and am confident it will produce an airworthy product.

I have a Miller Diversion 165 TIG and have converted the torch to a CK FL1325SF FlexLoc with a 25' SuperFlex lead. Installing this torch required removing the cover of the welder, and installing an adapter from Arc-Zone. USA Weld sells a nice metal foot pedal that plugs into the RJ45 connector used on the Diversion. I am currently experimenting with different torch setups, and enjoy using CKs pyrex cups/gas lenses.

I conducted some informal testing to better my understanding on how heat impacts thin wall 4130 tubing. The tubing used is USA 1/2"x.035 4130. Both samples were welded with ER70s-2 filler rod. The shop was just bellow 60 degrees. I wanted to observe how the colder air temps impacted the tubing.

(see attached photos)

The sample on the left was preheated to 400-500 degrees, TIG welded, and immediately brought up to around 1600 degrees with a gas torch. I slowly pulled the flame away and let the tubing cool in still air. This sample (pre and post heat) bent back and forth in a 20 deg arch around 10 times before any cracking appeared. I was very impressed with how tenacious the heated sample was.

The sample on the right was TIG welded with no preheat, and left to cool in still air. This sample (no pre or post heating) bent to around 10 deg and cracked abruptly.

This is a very informal test, but it does illustrate the impact heat can have on 4130 tubing. 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.