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Bil

1:16 Scale Scratch-built PT-17 Stearman

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Thanks everyone for the warm welcome, I really appreciate it.   :coolio:

 

hi and welcome, this is the perfect place for you. May I recommend you check out some of the scratchbuilt aircraft that others have made, such as Peter Castle's 1/18 Spitfire. Many of the techniques would be relevant for your build.

 

Here's his Spit build - a long read but well worth it:

 

http://forum.largescaleplanes.com/index.php?showtopic=61418&hl=+118%20+spitfire&page=1

 

Thank you, I had, of course, already found Peter's amazing thread on the Spitfire.. I am half way through reading it.. what a master class that one is.

 

FIN - A Swing and  Miss

 

I decided to work on this assembly first as it had only a few parts and I thought it should assemble fairly quickly.  Well I was right about the number of parts but it wasn't as straight forward as it seemed at first.

 

Below are the main structural components:
  • Front Spar - 1/16" aluminum tube
  • Rear Spar - 3/16" aluminum tube
  • Root Rib - aluminum sheet
  • Two Structural Ribs - 1/32" brass rod

This mix of metals is because i could not find aluminum rod in the smaller diameters that I could in brass.  It's going to be painted anyway, so I wasn't too worried about it.

 

The ruler in this image gives you a scale for these parts:

Main%2BStructural%2BComponents.jpg

 

The basic structure assembled:
 
The root rib was a fiddly bit of aluminum sheet that I created over a wooden form, then cut out the hole for the rear spar. 
 
The brass rod ribs were bent by hand over the plan until the curve was correct, then I added the little support pieces in the center of each.  Note that the ends were flattened, this is in accordance with the plan, as a strip of aluminum will be glued to them (it was riveted in the real aircraft).
 
The front and rear spars were cut to size, and the front spar was angled at the top to match the drawing.
 
All of the parts were epoxied together, the only trouble spots being the split ribs on the front spar, I reworked them several times until they were correct.
Main%2BStructural%2BComponents-Assembled
 
Looking at the plan above you can see that I am still missing some parts, the internal bracing for example.  The image below shows the (mostly) complete fin on the plan, and then with the plan shown next to it for reference.
Fin-Plan.jpg
 
The problem with this assembly was that it was a failure, it was too sloppy for my tastes as well... but more on that as I explain it in context with the rudder construction coming up next.  I do promise to show my dead ends, my failures etc. as I go along.. remember I am learning as I go so expect a lot of failures.
 
By the way I am using Poxipol epoxy to assemble these components, as when I discussed this with Guillermo Rojas Bazan that is what he uses... and if its good enough for him, well then, it should work for me too.  Problem is that at times the joins are weak or brittle and I have started hitting all my joins with a little CA as an extra safety measure... but I am going to start experimenting with JB Weld epoxy and the JB Weld SteelStik to see if I get better more reliable performance.
 
More anon.. Bil    

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RUDDER
 
After completing the vertical stabilizer I wanted to build the rudder so I will have constructed a complete assembly, something I thought would be a landmark for me on this journey.
 
This drawing shows the framework pretty well:
rudder_figure_14a.jpg
Laying out the basic components and building one half of the structure was pretty straight forward.  I am getting more comfortable with this manner of building and starting to get cleaner and better looking results.
IMG_0942.JPG
 
Note the ends of each rib have been flattened against a curved form (the shaft of a screw driver to be exact) in order to give me a curved surface where the rib meets the front spar.  Note also the different sized rods and tubes used in this construction... I tried to make them as close to scale as I could get.
IMG_0945.JPG
 
Unfortunately what I found is that the fin I built previously needed some modifications as it was not really square when aligned with the new rudder.  I think the rear spar is not aligned correctly.
IMG_0943.JPG
 
FIN - Rebuild
 
In order to match the rudder, I decided to totally rebuild the vertical stab.  The only parts that have been salvaged from the original fin are the front spar and the internal bracing parts (not yet added to this new build).. the rest has been trashed. 
 
With this rebuild I am matching the build quality of the rudder, and am also being very careful to ensure perfect alignment.
IMG_0962.JPG
 
RUDDER - Continued
 
I have completed the ribs on the opposite side of the rudder.  I still have some details to add to this part:
Internal bracing (top front section)
  • Rib cross supports pieces
  • Hinge support details (will match with the vertical stab)
  • Rudder horns
  • Light and wire
  • Trim tab
IMG_0967.JPG

 

I have found this next task to be very difficult due to the size of the parts and how fiddly it is to assemble them... in the following image I have circled all of the rib cross support pieces.  Those in red were completed earlier, and they took me a long time.  These small pieces of brass rod are between 1mm and 3mm in length, they need to be test fit prior to fixing in place. 
 
Carefully moving these pieces into position with a pair of tweezers, they have the tendency to snap out of the tweezers' grip and fly across the room, never to be seen again... believe me this happened several times.
 
I needed to come up with a more efficient and faster way to assemble these very small parts.
B-001.jpg
After thinking about it I experimented with placing the part on a small piece of tape (degummed a bit with my finger so it wouldn't be too sticky) and was able to do my test fits over and over again without the risk of losing the part.
B-002.jpg
 
Next I used the tape to attach them to the rib, here is the sequence:
 
1. After the test fit is complete and the part is scaled correctly, I file the inside of the rib where the cross support will attach:
B-003.jpg
 
2.  I then apply a little epoxy to the area:
B-004.jpg
 
3.  Pushing it into position from below I place the support piece into position.  Still on the tape I can rotate it gently and move it back and forth until it is perfectly aligned with the sharpie mark I made on the rib to ensure correct placement:
B-005.jpg
 
4.  I let it sit for a few minutes to give the epoxy some time to set (it only takes two or three minutes to get firm enough so I can continue work), I then remove the tape, being gentle so as to not pull the support piece off with the tape:
B-006.jpg
 
The completed rudder structure is shown in the images below (sans some of the details outlined earlier).  All that is left to do is to clean up my work with an x-acto knife to remove extra epoxy and make it prettier.. then I need to hit some of the edges with a file to improve the fit and form.
 
The larger cross supports at the front of each rib were 2mm in length, the ones in the rear of each rib were 1mm or smaller.. these in particular were fiddly and more difficult to size, test fit, and attach correctly.  Couldn't have done these small pieces without using the tape method.  Maybe you guys have smaller hands than I do, but I struggled with them.  ;) 
B-007.jpg
 
Rudder (before clean up work) - drawing comparison:
B-008.jpg

 

Enjoy!

 

Bil

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Cheering you on, Bil. What a terrific start!  Bravo. My 1/24  Fury Scratchbuild started with similar ambitions to build every spar but for me that just proved more than I could master and instead focused more on end result (surface detail)  learning such techniques as embossed plastic card. I still, one day want to build it all. My Bearcat is a bit richer in detail using 3D printed parts, so I'm making progress.

 

Great connect with Bazan. He's the Man 

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Luuuuurvly start Bil!

 

Great idea with the tape on those small parts - the carpet monster is unfortunately very well fed under my desk

 

Just a thought - have you considered soldering the brass joins for ultimate strength or do you think epoxy has enough purchase on such tiny contact points?

 

Torben

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Torben beat me to it Bil, but I second his motion; I think soldering would be very useful here..... You can get heat sinks from electronics shops that will effectively isolate the parts you are trying to solder so you can join them effectively. 

 

Here's a few examples of what soldering can do for you (and I am far from professional!)

 

17KRXfb.jpg

 

XKtj8cz.jpg

 

GBHPwol.jpg

 

It cleans up very easily with a file and is for the most part very strong. I see you are using a mixture of brass and aluminium though, so your epoxy solution is the way to go there......

 

In any case you're doing a bang up job, and it's definitely looking the goods!

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Thanks guys, 

 

Cheering you on, Bil. What a terrific start!  Bravo. My 1/24  Fury Scratchbuild started with similar ambitions to build every spar but for me that just proved more than I could master and instead focused more on end result (surface detail)  learning such techniques as embossed plastic card. I still, one day want to build it all. My Bearcat is a bit richer in detail using 3D printed parts, so I'm making progress.

 

Great connect with Bazan. He's the Man 

 

Torben beat me to it Bil, but I second his motion; I think soldering would be very useful here..... You can get heat sinks from electronics shops that will effectively isolate the parts you are trying to solder so you can join them effectively. 

 

Here's a few examples of what soldering can do for you (and I am far from professional!)

 

 

It cleans up very easily with a file and is for the most part very strong. I see you are using a mixture of brass and aluminium though, so your epoxy solution is the way to go there......

 

In any case you're doing a bang up job, and it's definitely looking the goods!

 

Jim and Brahman104, yes I considered soldering for this build, but 1) I wanted to keep it simple, 2) I have never soldered before, though there are some excellent tutorials online, and 3) as I said, Guillermo Rojas Bazan builds his models without any soldering, and his work is a huge influence and inspiration, so my intent was to emulate his techniques to a degree, though not slavishly.. so all options are of course on the table.

 

Brahman104, do you have a link to the model build in the photos you included?  Looks like it would be worth exploring.

 

Bil 

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RUDDER - Control Horns & Fin Test Fit
 
I have added the control horns to the rudder, these were made from a piece of 1/8" aluminum tube that was shaped and sanded into the correct proportions:
001.jpg
 
The two pieces were then carefully epoxied into position.  I used a jig made of wire to ensure I had the angle correct.
002.jpg
 
Then I attached the rudder to the fin with a couple pieces of tape to do a test fit of these components.  Much better fit than with my first attempt!
003.jpg
 
004.jpg

 

The control horns aren't as clean as I'd like (though they will paint up well) however the control horns on the original aircraft are even rougher, so I'm not obsessing about it:

IMG_1162.JPG

 

Enjoy! 

 

Bil

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excellent stuff. I was going to ask all the same questions about soldering, but I see others have answered them. I tried it for the first time recently, and although I made a complete pig's ear of it the resulting bond was unbreakable. You should give it a try... but the epoxy route seems to be working just fine!

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