LSA140 Build

[lsa140]

Bdflies Your Patrol is looking great! Thanks for checking in. I chose to hit pause on the LSA build around a year ago after encountering a couple concerns with the project. I'm just now revisiting the build and deciding how to proceed. A big thank you to bway for the excellent flight testing reports on the LSA. It's been good to get caught back up on the forum and see everyone's progress.

[Bdflies]

Thanks about the Patrol! I enjoyed every minute spent building and now enjoying flying it!
Very cool skis. I can see many possibilities with that router...
"couple concerns"?

Bill

[lsa140]

I was disappointed to discover quite a few of the small parts I had fabricated developed surface rust over the last year despite being inside and dry. After some research I went by O'Reillys and found a can of Rust-Block from the same company that makes Evapo-Rust (great stuff). It is a non toxic indoor rust inhibitor that dries to a clear mat finish. The product can be rinsed off with warm water when you are ready to continue fabrication or paint. I tested it on one of my axles and expedited the dry time with a heat gun. It sprays out clear and dries to a non tacky surface.

[lsa140]

I found a 3D model of a C-90 and imported it into Rhino. It has some dimensional error but will work for what I need.

https://grabcad.com/library/continental-c90

[lsa140]

*Note: Deviation from plans. Changes to the LSA shown here have not been approved by the designer.

Working to wrap up a couple projects to make room for the fuselage coming down off the shop ceiling this week. I've taken some time in the evenings to dial in the extended gear design. It was interesting to run tubing load calculations on the stock LSA landing gear and cub gear. The rear tube on the Bearhawk gear carries a tremendous amount of compression when the gear is loaded. The shallow angle between the gear strut/landing gear leg on the Bearhawk loads the strut quite heavily when compared to cub type gear. This is evident when looking at the cub's small single tube external landing gear cabane vs the Bearhawk's much more heavily constructed internal truss that carries the gear strut loads.

I've opted to move the gear strut loads to an internal inverted pyramid truss centered on the axles. This drops the strut attach point down, increases the angle between the gear leg/strut, and allows a wider gear stance/additional gear travel. This also splits the compression loads evenly between the two gear leg tubes when loaded. The belly will be slightly deeper to accommodate the truss. It has taken a significant design effort to be comfortable with making these changes and I do not advocate or suggest doing so. In short, follow the plans! I have some specific and unique needs that warrant the time/effort.

[jim.mclaughlin924]

I like your modification. It reduces the gear leg and strut loads, simplifies maintenance and opens up a congested area where the struts attach per plans. Are you going to go with a softer spring and increase the strut travel?

[lsa140]

Yes, to get comparable travel/rate to the stock gear I would need a slightly longer/softer spring because of the geometry change. Dayton and Danly both have a very extensive catalogs with detailed specs. I'd like to gain a little travel and have a larger margin before the travel bottoms out in an extreme drop. The big tires help as well.

[lsa140]

*Note: Deviation from plans. Changes to the LSA shown here have not been approved by the designer.

Spent some time this evening really digging into the spring specifications, gear geometry, and load calculations. I found this video of a Cessna 180 clearing some pylons and coming down hard on the gear! It looks like he tried to come in with power to slow his descent and the engine was loaded up from the slow approach. It's impressive the Cessna gear can handle a hit like that... I wonder what the gearboxes looked like afterwards.

[lsa140]

The fuselage descended from on high and landed in the rotisserie this afternoon. Unfortunately I found the tube in front of the spar had been damaged and needed to be replaced. I had one side of it fully welded so it took some creative slicing with the 2" cutoff wheel to extract the it. After some grinding and fitting the new piece is in place and it felt great to have the TIG torch in hand again.

[Chris In Milwaukee]

Youch! How did that happen?!

[lsa140]

Youch! How did that happen?!

Not really sure what happed but it ended up being an easier fix than expected. The tubing had some damage mid span and needed to come completely out. The cuts shown in the picture are part of the extraction process. Back to welding clusters!

[Chris In Milwaukee]

Torch, tungsten, and filler size, if you don’t mind?

[lsa140]

Torch, tungsten, and filler size, if you don’t mind?

The torch is a CK FL1325SF FlexLoc 130A 25' Superflex lead and I couldn't be happier with it. If your going to weld an airplane fuselage get rid of the big torch/fat lead that comes with most TIG machines. The superflex lead makes a world of difference. The 25' lead allows work up and down the fuselage without dragging your machine around. I make a wrap around my arm with the lead and leave a small loop of slack to allow torch movement. I initially used 1/16 and 3/32 tungsten but now use 3/32 exclusively. 028 and 035 are thin but when you get a cluster with a bunch of tubes it often requires a little more heat than I like to run with 1/16. I keep a tray of .045 and 1/16 ER70S-2 filler rod on hand with several sharpened tungsten. It's easy to keep the tungsten clean while bench welding but I occasionally get some filler metal on the tip while doing gymnastics inside the fuselage. I change between .045 and 1/16 filler rod depending on where I'm welding in the cluster. Sometimes it's difficult to get 1/16 into a small puddle deep inside a complex cluster without disturbing the arc. Other times the 1/16 helps keep the puddle cooler and requires less hand movement to feed the weld. I use a large diameter #10 cup/gas lens. You can dial up the gas a little and get quite a bit of electrode extension when needed. The large cup stays cool, shields to arc nicely, and the back of it makes a great handle.

I've been looking around for where I purchased the gas lens kit. I think it was around $30 for a kit containing 1/16 - 1/8 lenses and #8-12 cups. Some of the large gas lens setups are very overpriced.

[Bdflies]

Do you weld with that much tungsten extension? I consider myself pretty gang-ho with stick out, but you've got me there!

Bill

[lsa140]

Not often, only when I’m trying to get at the root of a cluster with shallow intersecting tubes. In that scenario the tubes contain the gas pretty well. The gas lens with the long tapered cup seems to put out an even stream of gas.

[Chris In Milwaukee]

Thanks for the info. I have the stock #17 flex torch still, but did get a stubby gas lens kit from Jody at Weldmonger. Haven't yet had a chance to do anything with it yet, though.

[lsa140]

Good progress this week. I've been cleaning surface rust from the fuselage and small parts. The fittings were soaked in Evapo-rust, rinsed with water, and sprayed with Rust-Block. The product is very thin so it will likely need a couple coats for parts being stored inside.

Welding clusters and more clusters... nearly to the firewall.

[davzLSA]

beautiful welds

[lsa140]

Thanks Dave! It's great to see you progress on the LSA.

[davzLSA]

Thanks for all the documentation you have posted it is a great help.

[lsa140]

You are very welcome Glad it has been helpful!