S-38 Restoration

[Builder 2010]

My modeling reputation has gotten out in Louisville, KY. There is a monument in the historic Bowman Field admin building commemorating a flier who was lost in 1937. A metal model of a Sikorsky S-38 seaplane sits atop of a bronze hemisphere and several years ago, when moving the very large object, the model fell off and was severely damaged. The members of the historical society patched it up with hot glue and it looks just as bad as that sounds.

One of the members of the Bowman Field Historical team had just joined the Military Modelers Club of Louisville of which I am a member, and the first meeting he attended was the one where I was running a soldering clinic. He came to the conclusion that I was the person who could restore this model.

The model is cast and is probably pot metal which makes it effectively non-solderable. I have restored some interesting models and took on the assignment. We're meeting next week to discuss particulars since this a paid endeavor. I will probably have to drill and use pins and epoxy to put it correctly together. It's missing one prop which I'll have to scratch-build. But since I now own a high definition 3D Resin printer, if I can draw it (or get the existing one scanned) I can make one. Here's the rest of the pictures I took today. Any input would be appreciated. I really don't know how much to charge for my services. We've agreed in principal that it would be a cost plus materials contract, but what the "cost" is I have no idea. I don't know how long it's going to take until I pull it apart and get rid of all the old hot glue. Hot glue is good for craft projects, but has no business on model restoration.

 

[MiTasol]

My modeling reputation has gotten out in Louisville, KY. There is a monument in the historic Bowman Field admin building commemorating a flier who was lost in 1937. A metal model of a Sikorsky S-38 seaplane sits atop of a bronze hemisphere and several years ago, when moving the very large object, the model fell off and was severely damaged. The members of the historical society patched it up with hot glue and it looks just as bad as that sounds.

One of the members of the Bowman Field Historical team had just joined the Military Modelers Club of Louisville of which I am a member, and the first meeting he attended was the one where I was running a soldering clinic. He came to the conclusion that I was the person who could restore this model.

View attachment 546080

The model is cast and is probably pot metal which makes it effectively non-solderable. I have restored some interesting models and took on the assignment. We're meeting next week to discuss particulars since this a paid endeavor. I will probably have to drill and use pins and epoxy to put it correctly together. It's missing one prop which I'll have to scratch-build. But since I now own a high definition 3D Resin printer, if I can draw it (or get the existing one scanned) I can make one. Here's the rest of the pictures I took today. Any input would be appreciated. I really don't know how much to charge for my services. We've agreed in principal that it would be a cost plus materials contract, but what the "cost" is I have no idea. I don't know how long it's going to take until I pull it apart and get rid of all the old hot glue. Hot glue is good for craft projects, but has no business on model restoration.

View attachment 546083View attachment 546084View attachment 546085View attachment 546086View attachment 546087View attachment 546088

Quite beyond me that is for certain.
Would love to see photos of the finished job

 

[Capt. Vick]

Good luck!

 

[Gnomey]

That repair job is interesting to say the least.

Looking forward to your efforts!

 

[TheRealMrEd]

It sort of appears that some of the metal plating has been damaged. If so, I doubt that you can plate over epoxy, etc. to repair the finish. Might have to go with some of the metal paste type repairs...

Ed

 

[Chris H]

That looks like a lot of stripping off the glue; cleaning and straightening the struts; followed by drilling and pinning with brass or steel rod. Then maybe use Bondo or Milliput to fill and strengthen the joints, followed by rubbing down and a re-spray with a metallic bronze shade.
It's not beyond the realms of a competent modeller, but it's going to take a lot of time and patience. If you have any other Club members who could help, it would be good!
Please keep us updated on this one and "Good Luck"!

 

[Builder 2010]

Thanks guys! I'll run this as an active thread. We agreed to a price (decent!) and I brought i home in pieces. The whole thing fell apart when we got it off the monument.

There may be a hitch in my agreed to price and I won't be starting until any misunderstandings are clarified. Meanwhile I came up with an elegant way to support the plane in proper configuration for reassembly. It turns out that the whole thing is either cast brass or bronze, not pot metal. That means once I get it cleaned up and down to base metal, I can use normal soldering procedures. It will be much stronger than going with any sort of glue. The thing weighs a ton with the main wing well over 20 pounds and the cabin and lower wing slightly less.

What I'm planning is this. I will install long threaded rods into the build board with nuts and washers above and below. I will then have nuts and washers at the level that the part to be suspended. This level will include a formed block of wood to support the wing and then another more flexible piece above and then another set of nuts and washers. I will have the lower wing upside down on the build platform with any level or padding to stabilize it, and the cabin and lower wing suspended upside down above it. This way I can fine tune the positioning by raising or lowering the nuts on the threaded rod.

Here's what the real plane looked like.

The model's wing span is 41" so the scale is an odd 1:21. That's just plain weird. I thought there was a prop missing, but it was laying on top of the model on it's pedestal. The mounting will have to be re-designed also since it was cobbled together with some 3/8" bolts. I'm going to copy and enlarge the drawing so it will be full size and use it for positioning and building any unrepairable spars.

If

 

[Wurger]

 

[Airframes]

A bit of a challenge, but I'm sure you'll manage it.
Looking forward to seeing the result.

 

[hainus]

Have you tried to use a fine blow torch and join them with silver solder ?
i use to make clutch and throttle cables for motorbikes and found silver solder was alot stronger than normal solder.

 

[Builder 2010]

Hey gang. After working on another model railroad extravaganza I'm now starting to do the S-38 restoration in earnest. The model is worse than I thought partially because I knocked the wing onto the floor and broke of the tail section and two more long struts. Regardless, everything had to re-soldered. Before doing that I have to strip all the paint and the residual hot glue that was used to patch it together four years ago. Stripping the paint is a messy, smelly job that got complaints from my wife upstairs when the air conditioning system was sucking the fumes and distributing them all over the house. I just striped the engines, the tail and all the loose parts. The Bowman Field Heritage Group thought it may be great to have the model in bare metal to match the bronze globe on which it's fastened. It may be possible, but there are some concerns. The model is actually three metals. The body and wings are bronze or something that looks like bronze, the long struts are brass and the short ones are steel. I was wondering why the short struts just weren't cleaning up and showing brass color.

This is the main wing surface. Not only was the paint to hide the hot glue, but it also hid some terrible soldering work. All of this needs resurfacing before I reassemble.

Today I was able to solder the nacelles back on their center strut. You can see the bronze color of them and also how mottled the surface is. I've suggested we get it media blasted to provide a nice, uniform surface after I put it all together. When I solder something it doesn't look like a mess.

I also soldered one vertical fin back on. I think it broke loose when I knocked the wing onto the cellar floor. Regardless, the tail metal is better than some of the other parts.

Here are all the struts after stripping, ultrasonic cleaning and some steel wool. You can see the steel vs. brass struts. I confused me at first as to why they looked so different. A test with a magnet solved my confusion quickly.

I'm going to strip the pain off the big parts in the garage so the smell won't get all over the house. The mass of some of these parts is so great that my propane torch had to heat them for minutes in order to reach soldering temperature at the joint. Patience was needed.

I'll start building the assembly fixture soon that will support the 50 pound wait of this beast. I've also selected some brass lamp parts to support the model on the bronze globe. Right now it was held with some bolts with pieces of copper pipe as decorative sleeves. I'm assuming the brass turned bushings and the threaded pipe will be able to support the weight.

 

[Builder 2010]

A lot has happened since my last post. I had the large parts commercially stripped using glass bead blasting to remove all the old paint, hot glue and most of the oxide. This prepared the model for soldering. I built the jigging that would hold the heavy pieces in alignment so soldering could proceed without too much handling. I started soldering the first set of main struts in place and ran into a brick wall. The bronze parts are so massive in relation to the pieces being soldered to them to make them almost unsolderable. I use "almost" because my problem was simply not generating enough heat to get the joint to solder temp before the bronze sinks all the heat away. I actually resorted to using two torches simultaneously; one a MAP torch and the other propane. This didn't do it. Then, one of the Heritage team members brought his acetylene/air torch and it's 2,700 degree flame was sufficient to bring the joint up to solder flow. I was still not satisfied. I talked to a tech service person at Harris Metals, a major solder and flux maker here in the USA and he suggested using 60/40 solid core solder and their high temp flux so it would stay put during the long heating session. I'm waiting for this new stuff to arrive.

Here's how the plane parts looked after glass beading; a far cry from how it looked before. At least now I had a chance to get it desoldered.

I constructed the jigging using 3/8" threaded rod, nuts and b body washers. The jig let me align all these heavy parts and not have to worry about them moving while I'm fitting up all these heavy pieces.

My first joints were decent, but didn't meet my standards.

The landing gear were missing. In the original installation, the landing gear were load bearing and held up the front part of the model. The rear was affixed with a 3/8" threaded lug. At some point after 1988, the gear disappeared and the model was supported with three lugs. I've re-created the landing gear using a hybrid of 3D printed parts and machined brass. I first was going to do the entire deal with 3D printing, but the long strut was too weak. So I designed the print with a 1/8" hole down its length which I would fill with a piece of brass rod. My first print had too much uncured resin in the bore and after hardening, formed a hardened plug that I attempted to drill out. The drilling out process destroyed that gear. For the next one, I drilled some tiny drain holes at the base of the strut so I could flush the recently printed resin out before hardening. This worked and I was able to insert a 1/8" brass tube down the entire length to reinforce it. I also reinforced the mounting lugs that would hold the gear to the fuselage wall by inserting a 3/64" brass rod into previously drilled holes. In the process of pushing this rod into a tight fitting hole I pushed too hard and blew the entire thing apart losing the reinforced strut. I still had the entire lower portion. I then made the struts out of brass and created the hybrid assembly. If this didn't work, the last resort was to print the parts in casting wax resin and have them investment cast in brass. We had a source to do this if necessary.

I didn't have much clearance to drill the 1/8" holes in the fuselage to accept the reinforced lugs on the gear legs. I was looking to buy and angle drill, but then remembered that I had a Dremel right angle drill attachment. I hadn't used it in years. Today it was worth the wait.

I measured twice before drilling the holes in the fuselage to accept the gear. I knew that the spacing was accurate since, even though the drawings were very rudimentary, I was able to at least got those details correct.

The last thing I did was drill out the wooden shafts from old props from the engine fronts and then bored out the props to accept machined hubs which I'm now in the process of turning on the lathe. Originally, it looked like the plane didn't have variable pitch props, but later iterations showed Hamilton Standard HydroDynamic props and their distinctive hubs. I'm going to make something in between. I was concerned that my drilling of the props could destroy them. I hand drilled a centered pilot hole and then used the drill press to open it up to a #2 drill. I was careful and was rewired with clean centered holes ready for the new hubs.

Once I get the new solder and flux, work should proceed fairly quickly. Until next time...

 

[Builder 2010]

I machined prop spinners and then covered them up with bronze paint. I also ordered lower melting temp solder and a high temp longer lasting flux. The flux arrived, but the solder has yet to arrive. I 3D printed a fixture to hold the main struts in place and at the correct angle so I can solder them more easily to the main wing.

After painting these are set aside until the end of the build.

I designed the fixture directly over the scaled plans I found. I did the design in SketchUp. My first version was too wide and I found that the brass struts are narrower than the steel ones. The steel struts are 1/4". I think they are made of common steel key stock used to make keyway keys in machining. The question I have is were the originally struts developed in 1937 steel or were they substituted in a rebuild sometime later. I know someone did some sloppy desoldering in the past. I had to refine the design to accommodate this variation. The UV resin is thermoset and will not soften as the metal heats up. It will most likely burn and I don't intend on getting the heat anywhere near it. I only have to use it two times.

 

[Airframes]

Lots of dedicated work going on - great job !

 

[Wurger]

Agreed. Well done so far.

 

[Gnomey]

Great work so far!

 

[Builder 2010]

Thank you. With the new solder (60/40 solid core) and the new higher temperature flux (Bridgit) and the acetylene/air torch I'm able to get solder to correct temperature and solder parts together. I used the fixture and got the main struts soldered to the big wing at a reasonable position so they'll successfully mate up with the smaller lower wing. I fixed the joint in the right engine nacelle so it's more correctly seated. The new torch is has some many more BTUs than the propane that instead of five minutes (or more) it now takes 30 seconds to get to heat. I then started fitting the missing engine support struts. I'm making these out of 1/8" square brass rod. I also substituted brass bar stock for the steel struts. I didn't like how the steel struts were soldering (or not soldering).

The engine struts were pinned to the engine. I'm doing this also. It helps stabilize the joint which is coming at an acute angle. I needed to cut and fit the outer two struts to measure for the third one that goes diagonally between these two. I couldn't measure it without simply building it and just fitting it up in real time. None of my drawings show details about these struts but they're there in photos of the plane and there's soldering residue in the previous strut's positions.

Once I get these struts fitted I will invert the plane and realign the filtering so it will be right side up and solder the struts to the lower wing and the long diagonal that runs from the main wing to the fuselage. One of those was also missing and I have brass for that too. I have one more work day and then we're off to Philly for a wedding. We'll return next week. I'm confident that the rebuild will be done by the end of the month.

 

[Builder 2010]

It was ridiculous trying to hold those struts still while I could solder them to the nacelles. I tried welding clamps, iron wire, and was unsuccessful. I then took the engine assembly off the plane and again attempted to use wire. Didn't work. Finally, I made a metal fixture to hold the three struts at the correct angles and position so I could solder them. The pins kept the top joint stable enough. It took all the heat I could generate to get those 1 pound bronze casting hot enough to melt the solder correctly.

I cleaned up the joints using cutters in the Dremel and then into the ultrasonic cleaner. I put the engines back on the wing and the angles are good. Next week I will solder the other end to the wing. This should be easier, but I'm not holding my breath.

Here's another view showing the solder joints themselves. Not pretty, but it will be painted. Thank goodness!

 

[nuuumannn]

Mate, you've got your work cut out for you there, and your perseverance is admirable. Enjoying your commentary on welding. Looking foirward to the fnished product, which I'm certain you'll get right.

 

[Wurger]