The Lindberg Curtiss F11C-2 Goshawk
How to Make a Cowl Ring.
Once I found out that the Lindberg provides the builder with an undersize cowl ring, that pretty much killed the notion that I was going to put any time into dressing up the already-horrific engine. As I mentioned in my earlier installment, I decided to utilize an R-1820 engine from QuickBoost as a replacement. But what about the cowl ring? Hmmm.
My first thought was that I could vaccuum-form a cowl. However, early tests proved that (a) the plastic wasn’t real happy conforming to a cowl-shaped buck, and (b) if it DID conform, it was extremely difficult to remove the buck from the formed cowl ring without damaging it. In addition, it was very, very tricky cutting out the front opening with a compass. After much consideration, I decided to try casting the cowl in resin. This would require a two-part mold. How was it done?
First, I would need to make two bucks - one for the cowl’s outer surface, and another for the inner surface. The profile for the outer cowl was replicated by blowing up a side drawing from my Squadron publication “Curtiss Navy Hawks in Action” to 1:48 scale. The outer buck was made from white styrene on my Dremel Moto-Lathe, a recent Ebay acquisition. The inner buck was turned from a bit of large hardwood dowel, also spun on the Moto-Lathe. The inner buck should have no curved profile, just keep its profile straight and cylindrical. Notice that they both have the same size hole driled through their centers. This will be the pilot hole to align both mold halves later. Both bucks were sanded smooth. The wood buck was coated with sealer, and sanded again. We don’t want wood grain to show in our mold!
Now we make open-face RTV castings from each buck. After 4 hours, we’re ready to fill the smaller of the two molds with more RTV. Our objective is to cast a rubber buck, which, when dry, will fit into the larger of the two open-face molds we cast earlier. (Be sure to apply mold release agent to the open-face mold before pouring in your wet RTV!)
Here’s the RTV rubber buck after removing from the open-face mold.
Here, we can see how the two parts work together. The center post of the open-face mold fits into the center hole of the inner buck, maintaining the alignment. The gap between the two parts will be filled with resin. In about an hour, you got yourself a cowl ring. Notice the little goofy edge on the inner buck? This was added to make it easier to fill the mold with resin. You can sand the bump from the resin casting later. I like to use little squeeze bottles with pointy spouts for filling my molds, these bottles are available at beauty shop supply stores. My wife is a hair stylist, that’s how I came to discover these little gems. We do not need to apply release agent to the molds this time. I smeared a thin coating of white glue on the face of the inner buck before placing it face down into the open-face mold. This will minimize the tendency for the liquid resin to “creep” underneath the inner buck where the cowl front opening will be, thereby making a cleaner casting.
Here is the finished product, after removing the flash. It’s quite substantial.
Here it is again, with the QuickBoost engine set in place.
Here is the original Lindberg cowl/engine, next to our new cowl and engine. Which one would you rather have on your plane? Easy question!
It took me three tries to get the inner buck diameter and profile correct before the final resin cowl casting had sufficiently substantial thickness.
How to Vaccuum-Form a Windscreen
The windscreen that came with the Lindberg kit was also quite horrible. Too thick, and incorrect shape. Why not just make our own replacement?
You baby boomers will likely remember this toy from the early ‘60’s. It’s a Mattel Vac-U-Form, perhaps the single most deadliest toy ever made (besides the “Slip-and-Slide”!). I got mine off Ebay. Like the Creepy Crawler Thing Maker, this toy had an electric hot plate built into it. Hot enough to melt plastic, which was the objective of this toy! I think it even came with a street map to regional burn wards in the greater USA. However, this was sold before the era of ambulance-chasing attorneys, and I’d even go so far as to say people of earlier generations had a better understanding of the concept of personal responsibility.
The operation was simple: you place a styrene sheet into the clamp holder, then swing it over the hot plate. When the plastic starts to sag, you quickly pivot the clamp/plastic over a buck on the vaccuum table side, then work the pump handle furiously to suck out the air, effectively pulling the soft plastic sheet over the buck. Voila! Instant replicant toy cars, log cabins, jewelry items, and more! It was only some time later that someone discovered you could use these things to make model parts. So, how to make a windscreen?
First, we need the buck to form the plastic over. Working from photos of an actual Goshawk’s windscreen, I drew up a pattern on the computer. I then printed it, cut it out, and glued the pattern to thin styrene sheet. I cut it out, then scored along the fold lines (this is a 3-panel windscreen). Once I was satisfied with the shape, I glued it down to a small styrene block. I then filled all the gap areas with filler. We want to just be certain there’s no edges or ledges that may trap the buck in the vacu-formed plastic.
Since I hate waste, I quickly cast four copies of the buck, and glued them up to an index card “tree”.
And here’s the finished vac-u-formed windscreens. All that remains is to carefully cut them out.
Not only can one find Vac-U-Forms on Ebay, you can also find there pre-cut plastic sheeting in white, clear, and other assorted colors. Other accessories can be found at www.vac-u-form.com, however, I cannot endorse their plastic sheets, they use PVC and it does not work nearly as well as styrene. The PVC also smells disturbingly weird when heated up.
Hope you enjoyed this installment.
