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Lead Sled Alley - April 2003

Welcome back for part two of the Me-109 construction series. Last month we covered the building of the basic plug. This month we will be adding all the various details and getting the plug ready for the mold.

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Me-109 Building Series - Part 2



The Plug is Finished!

Welcome back for part two of the Me-109 construction series. Last month we covered the building of the basic plug. This month we will be adding all the various details and getting the plug ready for the mold.

Gun Ports and Hatch

When I cut the gun ports into the fuselage, I ended up cutting through the blocks of wood that were there to accommodate them. This was not a big deal because the area would need to be glassed and filled anyway. After cutting out most of the wood, I used a 1/4" dowel with some sandpaper wrapped around it to finish shaping them. The tricky part here was getting the ports centered properly on the fuselage, and ensuring that they were the same depth and length. Actually, they are not perfect, but close enough for government work.

After cutting and sanding with a 1/4" dowel.

Here I have laid some glass in the ports. After the resin kicked, I trimmed the edges with a razor blade.

A little filler and we are good to go.

There are two challenges here - one, to build the hatch mold, and two, to build the stepdown section in the plug to accommodate the hatch. In order to make the stepdown the right size, we first need an actual hatch to use for test fitting, so we will build the hatch mold first.

I built the hatch mold right on the plug. To build the clay dam, I rolled out some long, worm-like rolls of clay, and then used the side of a spray can as if it were a rolling pin to flatten them out to about 1/8” thick. I sliced them down the middle using a straight edge and a razorblade to create a nice straight, clean edge on the clay. I then used this to create the dam that would form the edge of the mold.

Clay dam to form the edges of the hatch mold.

After the dam was in place, I coated the area with PVA, and then painted on a coat of jellcoat.

Once the jellcoat had kicked (but while still tacky), I laid up about five layers of 6oz cloth.

I let that cure for a day, and then popped it loose. The plug was still a little rough in that area, but a little wet sanding with some 600 grit paper smoothed the mold out nicely.

Finally, I PVA’d and waxed the mold, and then laid up a hatch.


Stepdown



I always kind of cringe at the thought of hacking a big chunk out of my plug, but it must be done in order to build the stepdown. However, if you do it methodically, it is not quite so scary. Having just finished building the mold over the very spot that I need to cut out, what better cutting template is there? I set the mold back on the plug and held it firmly in place while carefully cutting along the edge of it with a razor saw. After removing the cut section, I closed the hole back up with 1/32” plywood.

Removed section filled in with 1/32" plywood.


I then built the stepdown from balsa blocks, using the hatch I just made for test fitting.


With a little trial and error, I soon had the hatch fitting nicely.


Gun Blisters

Whenever I need to make symmetrical features, I will usually try to make a mold of one, and then make two parts from the mold. However, this would not work for the gun blisters because they are opposites of each other. The next best thing is to use formers. First, I marked the outline of the blisters on both sides of the fuselage. Then I made two identical crescent shaped formers from 1/8" plywood and glued them in place.

Crescent shaped 1/8" plywood formers in place.

The next step was somewhat tedious; I filled in the outlined area with small pieces of 1/4" balsa.

With that done, I block sanded the balsa down to the height of the formers.

Using a small sanding block, I chamfered on the edges down evenly.

A little smoothing and we have our gun blisters. I then glassed them with 1.5oz cloth.


Exhaust Pipes and Scoops

To create the exhaust pipes I decided to build a rough mold, then make two parts from that to use on the plug. After determining what the overall length should be, I divided that by six and made some marks on piece of scrap wood. Then I made what would end up being the individual pipes from some 1/8" x 1/2"  balsa strips. I sanded a wedge on the end of each one so they could overlap each other.

1/8" x 1/2" balsa strips sanded to a wedge on one end.

I glued the pipes in position.
I did a little shaping to give them a bell shape.


I tacked on some scrap balsa to simulate the side of the fuselage.


Then I filled in the gaps with filler.


I just wanted the basic shape of the pipes, so I did not spend too much time making them perfect. After coating them with PVA, I laid up the mold.


There are four small scoops on the nose (two on each side). Just before I built the mold, I decided to kill two birds with one stone and whipped out a single scoop to include with the exhaust pipes. Here are the first parts. These are just resin with Cabosil. I also laid a few strands of fiberglass in with the exhaust pipes to keep them from breaking. I will admit they are a little ugly, but it was quite easy to clean them up with a small sanding block.



To attach the pieces to the plug, I mixed up some resin and Cabosil until it was about as thick as peanut butter. I thought I would have to use tape to hold them in position until the resin cured, but they stayed put just fine.



Tail Bumps

To be honest, I am not sure exactly what these were. My guess is that they made a little more room for some part of the rudder linkage, or they could be the vestigial remains of the struts that used to support the horizontal on the eariler models. All I needed here was a couple of small, long, skinny bumps that were the same size. Again, I made a crude mold, this time by simply carving out a grove in a chunk of wood. I sealed it with some PVA and made two parts from resin and Cabosil.

Small resin and Cabosil bumps.

I attached them to the side of the plug the same way that I did the exhaust pipes and scoops. Then I put some filler around the edges to fair them into the fuselage


Supercharger Intake

This piece was surprisingly easy to build. After measuring the diameter of the intake on a small model I am using for reference and scaling up that dimension, I found that it should be almost exactly one inch. So to make life easy, I started with a piece of 1” doweling, and grooved out a chunk of balsa to fit it.

1" dowel with balsa block grooved out to fit it.


Using my disc sander, I shaped down the sides and back. I also angled the base so that it will protrude horizontally from the fuselage.


I chamfered down the corners using a drum sander on my Dremel.


Then I rounded the corners down with a sanding block.


Finally, I glassed it with 1.5oz cloth and smoothed it later with some filler. Here is the finished part in primer.


Primer/Wetsanding and Finish Details

The moment of truth came when I finally sprayed the plug with primer. Boy, was it ugly! Once it was all one color, I could see every little imperfection. There were pinholes everywhere, some big scratches that needed filling, and a few other details that needed a little more attention. Some lightweight model filler made short work of the pinholes and after fixing the other problems, I sprayed another coat of primer on and wetsanded the plug again. I repeated this process four or five times until the surfaces was smooth.

The last things to do would be to add some molded lines that would make it easier to see where to mask off spinner and rudder before painting. I also wanted the canopy frame to be raised for the same reason.

To create the lines for the spinner and rudder, I applied some narrow chart tape.


Then I sprayed multiple coats of primer over those areas and wet sanded them back down until the tape showed through. When the tape was removed, it left a groove in the primer.


I used aluminum tape to create the canopy frame.  Although the tape is not very thick, it will leave a deep enough impression in the mold that the frame will visible in the molded parts. Again, this will make it easy to see where to mask when it is time to paint. Other features such as the attachment point for the supercharger intake and the location where the horizontal goes through the vertical will be marked in the same manner.

Conclusion

Building all these little details took a little longer that I thought it would.  I think I spent about twice as much time on this phase as I did building the basic plug.  Before I wrap up this month, I'd like to talk about a couple of body filler products that I really like.

For filling large areas, I like “Evercoat Glazing Putty”. This is a lightweight body filler and sands very nicely, but is thick enough that, with a few layers, it can be used to build up thick sections such as wing fillets. Many of the heavier fillers could fill an area like this in one application, but some are much harder to shape afterward.

For doing finer work like filling large scratches, or for example, filling around the edges of the exhaust pipes and scoops where I want a very small radius, I use a 3M product called, “Piranha Putty”. In my opinion, this stuff is the greatest thing since sliced bread! It is about the consistency of pudding - very creamy and easy to spread. It also sands very easily.

Both of these products are available at most automotive paint supply shops.

Another tip for doing fine work is to use a razorblade as a spreader. I find that the large plastic squeegees are too thick and do not give me the control I want. The thin edge of a razorblade makes it much easier to see what you are doing and fits better into small areas. A razorblade also works well for scraping away any excess filler just after it kicks to minimize the amount of sanding you will need to do.

There is still much more to come on this project. Next month we will cover the building of the mold and laying up the first part. Stay tuned.

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