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Discussion in 'Mid Power Rocketry (MPR)' started by James Duffy, Apr 21, 2017.
Glad you're back at it James, this is a great thread.
We're going to transfer the forward hatch details to the nose cone next. Let's start by taking a look at the tools we'll be using.
The tool on the left is a panel line scriber, used in plastic modeling to refine or add panel line details to plastic models. As one nose cone is just a big hunk of plastic, it is ideal for our purposes. I was once told that it is essentially a dental tool that has been reworked for optimal use for plastic models, and that makes sense to me. It is available at most quality hobby shops (if you still have one), or direct from Squadron.
On the right you'll see a #11 blade and holder, and the tip has been broken off. The back side of the blade will be used after the scriber to refine the shallow trench created by the scribing tool.
More in a bit,
The first panels to be detailed will be the hatches found in quads 1 and 3. Masking tape is used to define where the lines need to go, and pencil lines representing the panel lines are then drawn directly onto the part using the tape as a guide.
With the lines in place a strip of Dymo labelmaker tape is aligned next to a panel line location. The Dymo tape will guide the tool as we scribe the line. Note that this is the old school, thick tape used with a "clicky-clicky" acoustic label maker, not the new electromogrified digital label maker products. It's thick enough to provide a robust guide for the tool, and is great for this application. It can also be peeled up and reused a couple of times.
Three or four passes with the scribing tool should be plenty for each line. If you do it right, you'll end up with long curls of plastic thread emerging from the trench after the last couple of passes.
After the lines are cut with the scriber, and single pass with the back of the X-acto tool will refine the profile of the scribed line, and you'll end up with a part that looks like this...
Note that we're reusing the cone from an earlier project, and that most of the paint from that project has been sanded away. There's still some residual paint left though, which accounts for the funky surface look. That will all go away when we finish sand and prime the cone.
The two remaining quads will be done next, using a different technique. On the actual V-2 vehicles quads 2 & 4 seem to be antenna panels, as evidenced by what appears to be a border of insulating wood. Here's a shot of the V-2 on display at the Imperial War Museum in London:
We are going to simulate this frame with a raised detail cut from .010" styrene sheet. To do that, a printed copy of the quad drawing is attached to a sheet of styrene with clear tape.
Using a fresh #11 blade, the inside frame line is cut first, followed by the outside frame line. The resulting part is a thin, delicate representation of the insulating frame.
Next, tape strips are used to define the lower and side edge positions of the frame on the nose cone. The bottom edge of the frame is carefully attached to the cone by wicking Tamiya thin plastic cement into place with a fine brush. Working in small sections, the remainder of the frame is attached in a similar fashion.
Eventually we end up with an accurately placed insulator frame detail.
I should pause to mention the tape that I am using. Years ago I went down a non-rocketry hobby rabbit hole and began building ukuleles. That nasty little habit is supported by tools and supplies from a company called Stewart-MacDonald, who are essentially the Apogee Components of the lutherie trade. They recently began offering a nifty little desktop tape dispenser, which you can see here. I opted for the version with three tools of vaguely defined "orange tape," which you see here. This stuff isn't masking tape, as it is far too tenacious for that purpose. On the other hand, it is a great all-around utility tape, and the assorted widths are handy.
Where are you getting your Dymo tape these days? I haven't been able to find any for a while now.
I have a stash that is many years old, but it is readily available on Amazon.
Next, sections of the quad drawings will be used to locate the various rivet/bolt/fastener locations found on these panels. The drawing bits are taped into place on the model, and a small awl is used to punch lightly through the paper into the plastic below.
Once all of the locations are marked the paper is removed, and the rivet locations can be lightly drilled with a tiny bit.
Note that we are not drilling through the plastic, just cutting into the top layer. This is the exact same technique used for the large rivet fields found elsewhere on the cone, and documented earlier in this thread.
After the antenna quads are done we can move on to the "barn door" hatch quads.
The hatch details on the #2 antenna quad are next. The large hatch detail is cut using a copy of the drawing as a guide, and the hinge line is scribed into the part.
The hatch is glued into place with Tamiya thin cement, and the three screw details are added.
The small hatch is then cut out and glued into place.
Our next task will be to add the little latch details to the barn door hatches as well as to the access door on one of the antenna panels. These will be fashioned from strip styrene, and it is critical that each little segment be exactly the same length. A tool called the "Chopper" will be pressed into service, which I grabbed 20+ years ago from the railroad section of my local hobby shop. It appears that it still available direct from the manufacturer, Northwest Short Line.
I tend to make many more parts than are needed, as I always seem to screw up a couple. Also, parts tend to go missing in action when they are this small.
The locations for the latch details are added using a section of a quad drawing as a guide.
The parts are positioned and tacked into place with a tiny bit of Tamiya thin cement.
Here's a quick look at the status of a couple of the quad panels after all of the parts are in place. The next step will be to clean up our work, sanding away a few rough spots and taking care of a couple of glue squeeze-outs. I also need to add some sort of detail separating the Bumper transition section (the bit with the fin slots) from the rest of the cone.
A couple of quick updates...
First, I decided that I wanted to locate the rivet line divisions between the hatch quads. Studying several drawings it appears that these divisions have either 23 or 24 rivets. I settled on 23, and whipped up a quick rivet drawing in Illustrator. These drawings were taped into place on the nose cone, and used as a template to punch the rivet locations.
With the rivet locations marked, we do the little trick with the drill bit to enlarge each marking. Here's the result.
Next, a strip of .040" half-round styrene stock is used to define the joint between the warhead/WAC section and the instrumentation section. As the strip is slowly wrapped around the cone Tamiya thin cement is wicked into the joint.
Here's what the joint looks like with the half-round strip in place. There's a great deal of clean-up that needs to take place, such as refining the fin slots for the WAC sustainer.
After a few days off to work on some other non-rocket projects, we're ready to add the airframe join covers to the V-2. As mentioned several posts back, the cylindrical portion of the V-2 missile plus a bit of the nose taper was produced in two lengthwise halves. The aluminum fuel tanks would be inserted in one half, then the other half added. The seams would then be covered with a long aluminum strip. You can see some of these details in this video, starting at the 3:30 point:
The strip installation can be seen at 3:37. Fun fact: the insulation being installed is simply the common household variety. During Operation Paperclip US forces gathered and shipped home several boxcar loads of the stuff, thinking that it was some sort of exotic application-specific material. When the boxcars were unloaded back at Ft. Bliss, Paperclip officials were told by their German "guests" that they simply could have gone to a local hardware store to buy the stuff.
Our model will have two strips 180º opposed from each other and 15º out of phase with a fin location. The strips are cut from a piece of .010"-thick styrene sheet, and are 5mm wide. A Great Planes 33"-long sanding bar is used as a straight edge to guide the cut. This tool was an old Hobbico product, and unfortunately disappeared from the market when that company went kaput.
One strip location will cover the joint on our rolled G10 fiberglass tube, and the other location is marked on the opposite side of the tube. The locations for the strips are masked off with tape to make installation quick and accurate. The strip will extend from the base of the G10 tube to the top of the rivet section on the cone. After it is glued in place and the adhesives cure we will cut the strip at the tube/cone joint.
With the positions of the joint strips defined we can glue them in place. This is slightly complicated by the fact that we have some dissimilar materials in play. We start by sanding the masked strip location on the G10 glass with a coarse sanding stick, as well as the back of the styrene strips.
A thin line of 5-minute epoxy is applied along the masked portion of the G10 tube, but not on the nose cone section. The styrene strip is then pressed into place.
There is a tiny bit of epoxy squeeze-out, but that is fixed by pulling up the tape masks on the tube section. The masks on the cone section will remain in place for now.
After the epoxy has set up for a few minutes we can use Tamiya thin cement for the styrene-to-styrene joint. After that cures for a few minutes we can pull up the tape masks on the cone. (Sorry, no photo.)
Here's how the join strip looks in place. Once the glue cures we'll repeat the process for the other side of the model.
Our next task is to carefully cut through the strips at the nose cone/airframe joint with a fresh #11 blade. (No photo, sorry.)
With the join strips in place and the glue cured, we can add some screw head details. Inspection of photos of the strips show that they are mounted in place with two parallel rows of screws.
These screws are far too close to the edge of the strip to replicate with 100% accuracy at our small scale, so we're going to fudge by nudging the locations a little closer to the centerline of the strip. A drawing of the screw locations is attached as a PDF.
The screw head locations are punched with a small awl.
...and the detail locations are drilled out lightly. I should note that I am using a finer drill bit for these particular details, a #73 bit from a jeweler's drill index.
The strips look really good at this point, and the model is beginning to come together nicely. It will look much nicer when we get it sprayed with some primer soon.
The prototypical V-2 has four shroud details at the base of the airframe centered between each set of fins. Two of these are long shrouds, one of which covers a liquid oxygen vent line on one side of the rocket, while the one on the opposite side covers a turbine exhaust vent. One of the two short shrouds covers five quick-release pneumatic connections, and I have no idea what is contained in the other short shroud.
Steve Kristal ("Gus" on this forum) was kind enough to snap a few photos of the four shrouds last week while visiting the Flying Heritage and Combat Armor Museum in Everett, WA last week. The V-2 on display there is a strange example of the rocket, as it is essentially a hybrid of original components finished out with recent custom new-build parts. In one sense, it is effectively a 1:1 scale model of the V-2. Here's one of the short shrouds from that display.
That distinctive rivet pattern is repeated for each of the four shrouds, so we're going to add that to our model. Fortunately the shroud shapes on the old Estes V-2 part are reasonably accurate.
Note that I used drill bits of varying sizes to add a bit of variety to the model.
Next, we're going to drill out the two long shrouds so that lox and turbine exhaust details can be added later. We start with a small drill bit, then move up until a section of 5/32"-OD styrene tube stock fits in the hole.
This approach isn't entirely prototypical, but it will do for our purposes.
Our next task will be to dress up the aft end of the V-2. Let's take a look at the nozzle area of the V-2 on display horizontally at the Royal Air Force Museum Hendon.
Three things to note:
1) The nozzle on a V-2 is much wider than the motor mount tube on our model. Not much we can do about that, at least on this model. (I do have ideas for potential future models.)
2) There is a distinctive square thrust structure that surrounds the nozzle.
3) There are several neat little bolt/fastener details that we can replicate.
I'm not using an engine hook on this model, and did not include the aft-most centering ring in the build. Instead, we're going to close out the aft end by replacing that centering ring with a styrene sheet. We can use the paper centering ring as a template.
A quick and simple pattern for the square trust structure is whipped up in Illustrator, taped to a sheet of .020"-thick styrene, and cut out.
After sanding the rough edges off of these two styrene pieces we are ready to attach them to the model with Tamiya thin cement.
Note that the edges of the square thrust structure extend over the aft edge of the tail cone. To trim that off we can use a special high-tech trimming tool. A bit of work with a sanding stick finishes these cuts.
The fastener details are simulated by creating four faux bolts from short sections of 3/32"-diameter styrene tube attached to a length of 3/64" rod.
Holes are drilled for the bolt details, then inserted and glued into place.
With everything in place here's what the aft end of our model looks like at this point.
After painting is complete we will be adding nozzle vanes to the fin roots, along with antenna details that will slide into the holes on the trailing edges of the fins.
It has been a few weeks since my last update, as progress will remain at a standstill until temps rise enough to prime the model. (The time has been used to work on my latest ukulele project, which uses exactly the same skill set as rocket construction, intriguingly.)
I did have the opportunity yesterday to add some detail to the exhaust vanes, the basic construction of which was covered back in this post a few years ago. We're going to add some simple nut and bolt details to the vanes, similar to what we can see in this photo of the RAF Hendon V-2 display.
The carbon vane assemblies on the V-2 were incredibly fragile and expensive. The vanes were transported along with the rockets in a special handling crate, and were added only at the end of the preflight process to reduce the possibility of damage. The installation of the exhaust vanes can be seen at the 28:33 point of this British-produced documentary of Project "Backfire," a V-2 demonstration program that took place just after the close of WWII.
Step One was to purchase some 00-90 brass hex nuts off of Amazon. .025" styrene rod will be used to simulate the threaded bolt section, albeit without the threads.
Next, the bolt locations are embossed into the assembled vane part.
A tiny drill bit is used to create a socket for the styrene rod bolt section. Note also that I have added a styrene tube "collar" to the vane axle to add a bit of visual interest.
The styrene rod is anchored into place using a drop of medium CA. Each bolt segment is much longer than it needs to be to make mounting them easier.
The nuts are mounted on the styrene rods, again using medium CA as an adhesive.
The styrene "bolts" are then cut slightly longer than the intended final length, after which we sand them down to the final size using a sanding stick (sorry, no picture).
After sanding each bolt has a bit of mushroom-shaped plastic flash on the tip. We can get rid of that by touching each bolt with a tiny drop of Tamiya thin plastic cement, which will immediately melt the excess plastic into oblivion (no photo).
Here's a quick shot of the completed vane assemblies. After priming they will be airbrushed with the final color coats and then lightly weathered to bring out the detail we just added.
These are tiny little boogers! As a reference each square on the cutting mat in the photos is 1/2".
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