Zweipanzerflug
A fantasy semi-
By John Miller
Imagine the early days of WW2, after the Nazis have invaded Russia. The concept of a heavy fighter, to act primarily in the close air support roll was in its infancy.
Suddenly, descending from the skies, the German Panzers encountered the infamous
Stormivik IL-
Axis planners became extremely aware of the need to have aircraft of similar abilities on their side. To fill the gap, the Stuka was pressed into service in that role, but it was slow and vulnerable to enemy fighters. The Zerstroyer, a modified heavy fighter, a version of the ME 410 had the firepower, but its size was a hinderment. Still, it was pressed into duty on the Eastern Front.
A search began for a new fighter, a fighter that could carry the munitions, and guns needed for the dual role of ground support, and air superiority. It needed to be powerful, yet agile enough to excel in both modes.
2 engines were desired for speed and reliability, as well as redundancy in a difficult environment.
It would be armed with a unique combination of weapons. A pair of 7.9mm machine guns, a pair of 20mm machine guns, and finally, a pair of tank busting 30mm machine cannons.
Thanks to the Nazi spy network, which had successfully stolen the plans for the Grumman X5F from the United States, the door was open for their designers and manufacturers to adapt the Grumman X plane to their own use.
That’s the fantasy behind this different and unusual stunt design. It was fun to play with. I enjoyed the research needed to make it look like it came out of the Messerschmitt design bureau. The ME 210 and later 410, designs that were actually used for these missions at times, heavily influenced me.
OK, let’s start the build
First item of business is the planning stages. Here’s where you study the plans, figure the types and grades of wood, as well as what bits and parts you’ll need
There are 2 options for builders. First would be a laser cut short kit. It would include the shaped cut parts. Parts, which are straight cuts, or sheets, such as the flaps, blocks, and sheeting, are not included. Neither are the bits and pieces. Laser cutting is precise, and accurate, but unfortunately, comes at a price.
The second option is using a pattern sheet to cut your own parts. I’ve gone to great lengths to give the scratch builder as much help as possible so he can create very accurate parts, and save material doing so.
I’ve a tutorial on using the pattern sheet. It only took me about 2 hours to cut all the parts for this design. Basically, I used some of my time to cut the parts, and saved considerably, which allowed me to have my new plane with less investment of my monetary recourses.
Building the rudders, stab, and elevators
I usually start with the smaller assemblies, such as the rudder, stab, and elevators. It helps get me into a building mood, while prepping and gluing up these smaller parts. One advantage for me, over starting with the larger assemblies, such as the wing, and fuselage, is that when I do build those assemblies, the smaller ones are already done. It makes the build go faster for me, with less discouragement at various stages.
The rudders have the grain going on a diagonal for strength and warp resistance.
Sand the joint area clean and square. If you use Ambroid, Sigment, Aliphatic resin, or a similar type of glue, it will make a much less noticeable joint when finished.
Once the glue is dry, sand the surfaces smooth, and round the edges.
The stab and elevator will be the next sub assemblies to construct.
I will build right over the plans. The plans are tacked, with a misting of 3M77 spray on glue, onto a large enough piece of 5/8” sheetrock, placed onto the workbench.
I’ll mist on some more 3M77 over the area showing the stab and elevator prior to placing a piece of wax paper to protect the plans.
Once the wax paper is in place, another misting of glue, and I stick the parts into their proper locations.
The 3M77 will hold the parts in proper alignment allowing hands free gluing.
I like to use a pipette style of glue applicator to control the amount of glue applied, and help limit the weight build up due to glue.
Careful cutting and alignment of the internal ribs can now be done without worrying about the main supporting framework moving.
Once all the ribs are in place, I’ll use the pipette loaded with thin CA and glue them all into place.
A few swipes with sanding block will clean up the surfaces, insuring they are flat and true.
The gluing and assembly is finished. Carefully lift the assembled stab and elevator from the wax paper. Next lift the wax paper from the plans. If you simply misted the glue on, the parts, and wax paper should release easily.
It’s desirable to sand a taper in the elevator. I’ll use a 1/2 “ dia. rod at the elevator leading edge. I want a ¼” sq. trailing edge, so I’ll use a 3/8” dia. rod at the trailing edge when making the first side taper.
The rods act as gauges to help maintain the thickness at their respective locations.
Once the first side is sanded to the correct shape, change to a ¼” dia. rod, and turn the elevator over, and sand this side to the correct shape. Once completed, use a soft pencil, and mark a centerline on the elevator’s leading edge.
While holding your sanding block at a 45-
This side view shows the shape we desire. Notice that I’ve drilled a hole in the side of the elevator. This hole goes all the way through to the solid center section.
The holes function is to allow air, heated by the sun sitting on the ready line to escape rather than swelling the covering.
The stab is treated in a similar manner.
Here’s another view, showing the finished elevator.
The Flaps are shaped using the rods in a similar way.
The fuselage
As you can see, I use a home built jig for building my fuselages. You can also see that I’ve transferred lines to the inner fuselage sides to align the bulkheads.
Using the jig, it’s easy to align the bulkheads, and hold them in place prior to gluing.
Once,all the bulkheads are in place, I use the pipette and CA to glue them in place.
Notice the centerlines marked on the bulkheads., used to align the fuselage so both sides are even. If you look close, you can see I’ve used 1/8” sq. balsa to reinforce the angled bulkheads.
I’ve also installed the 45 degree balsa reinforcements. You should also see that I’ve made some slices in areas where the balsa has to curve more than the shape will let it.
Below, you can see the tail wheel plywood mounting has been glued into place.
Another look at the bottom of the fuselage.
Here’s a view, looking down at the top of the tail wheel mount. Notice the 1/8” sq. reinforcements for the mount.
Building the Nacelles
I can’t believe that I didn’t take any pictures while building the engine nacelles. Not to worry though, as they build just like the fuselage. Notice, that there’s 1 degree of down thrust built into the engine thrust lines.
Weight conservation is always important, and even more so with Twins. The first two nacelles came out too heavy. I built two more and saved almost 2 ounces with the new ones. I went to using RC style bulkhead mounts which saved most of the weight. I now show these style mounts on the plans.
The Wing
It’s always a good idea to use some kind of jigging while building the wing. It is, after all, the heart of the entire system. Build it crooked, and you may just feel that you better start over.
You may notice that I’ve made my wing jig adjustable so it will work with almost
any type of wing layout. I call this fixture a “Combo-
One of the first chores to perform when setting up this style of wing jig, is getting everything leveled out. I use a long straight strip of Aluminum to align all the bottom clamps pieces.
Here, I’ve installed the trailing edge 1/8” x 1/2” balsa strip. Sighting down from each end shows me that all is straight and square.
I’ve used the plans to cut, and join, the leading edge 1/8” x ½” strips to the correct angle.
I’ll use the first, and last ribs to set the leading edge sweep. The ribs are not glued at this time, just used for setting the spacing.
I like to use my incidence meter, to make sure that the leading and trailing edges are level in relationship to each other. I don’t want to build even the slightest twist, or warp into the wing.
Once the jig is set, and the strips check out relative to each other, it’s time to install the ribs. I measure the first rib location, then use a piece of balsa I’ve carefully cut to match the rib spacing. Since this wing has no offset, only one gauge is required. If there was offset, there would be separate gauges for each half of the wing.
Make sure the spacing is correct, and the ribs are aligned fore and aft, then use the pipette with thin Ca, and glue each rib into place before moving to the next one.
All the ribs have been placed. It looks straight and level, but lets take a look from a different angle, just to make sure.
This angle will confirm that the wing is straight.
The spars inserted easily, also showing that the wing is properly squared up. A touch of thin CA at the spar rib joints will secure them proper.
The Bellcrank mounts Are epoxied into place. They fit flush with the top of the ribs.
Here, only the top one is in place. A second one is installed on the bottom. This will allow a suspended bellcrank to be installed later.
I’ve installed truss style shear webbing. Some prefer solid webbing. Either style will suffice.
The webbing extends to the ribs just outside of where the nacelles will mount.
Here’s a close up of the trailing edge treatment. Notice the 1/16” strip glued tight to the trailing edge of the rib. Carefully sand the taper to match the angle of the ribs.
In both views, you can see that the bottom trailing edge sheeting has been installed.
It also has that 1/16” strip that has been sanded to match the rib angle. In my case,
I loosened the top clamps on the jig, placed the trailing edge, and then re-
Again, I loosened the top clamp, set aliphatic glue onto that 1/16” strip, installed
the top trailing edge sheeting, and re-
I like to install my wing tip while still in the jig. The particular style I’ve used with this design lends itself easily to this technique. Here, the outboard tip is installed. Notice that the trailing edge sheeting has been pinched into place, and glued with Ca. This helps insure that the tips are straight and aligned properly.
The same thing is done at the inboard tip.
Now’s a good time to install the bellcrank, by first drilling a 1/8” dia. hole straight through the mounts. Use your favorite method to install the suspended bellcrank. It’s also advisable to install your measured, and built up flap pushrod assy.
I installed the top leading edge sheeting while the wing was in the jig, paying attention to getting the front edge of the sheeting as tight as possible to the 1/8” x 1/2” strip. Use aliphatic, or Ambroid, Sigment, or similar glue to the rib tops, and top of the spar. Then, bend the slightly dampened sheeting around the ribs. Pin or clamp the sheeting in place, after making sure it contacts all the ribs smoothly. Let the glue dry completely.
Loosen the top clamps on the jig, and turn the wing over, re-
Install, bottom leading edge sheeting, in the same manner. Let this sheeting dry completely. While we are at it, after the sheeting is dry, let’s install the bottom center sheeting. Use your choice of glue here.
After all the glue has dried, you can remove the wing from the jig.
Trying the fit
I couldn’t help myself, Most of the parts where ready, so I fit them together with pins to get an idea of what the finished project will look like.
Installing the tail wheel
Alignment, alignment, and then,
Alignment
I like to use a removable tail wheel whenever possible. Here’s one taught to me by Allan Brickhaus.
It’s built like a hairpin and held in place with a pair of Allen head screws. First, I have to prep the location. Notice that I’ve sharpened a tube and cut a hole in the balsa along the centerline.
Here, I’m cutting a second hole. I am only cutting to the surface of the plywood underlying the balsa surface.
The tube cuts a clean hole, and now it’s only necessary to use the exacto knife, and then remove the balsa, as shown in this next photo.
Use your bent up tail wheel wire to locate, and drill the proper sized holes for the size of Allen screws you plan to use. Enlarge these holes for the blind nuts. Use some Ca, or epoxy to make sure the blind nuts can’t fall loose later.
Use a washer to help keep the tail wheel in place.
Getting it together
Once all the major sub-
Incidences, and alignments is likely the most important item to pay attention to.
It becomes doubly important when building multi-
In the picture above, the nacelles have flat bottoms, and the mounts have been checked
to make sure that the designed in down thrust is there, and proper. They both checked
out good, so now, I’m checking that the wing is set at 0-
Once I’m satisfied that the wing incidence is at 0-
The plans are laid out so we can use them to help us lay out our plane within the designed parameters.
I’ve taken some scrap pieces of balsa, pieces with at least one 90 degree angle. I laid a 3 foot long aluminum yardstick along the flap line, drawn on the plans, and glued them to the work surface with Ca.
I can now set the wing/nacelle assembly on top of the plans. Take the time to line up the wing fuse centerline, and move the enire assembly tight to the scrap balsa uprights.
Notice, the incidence meter is still in place. Incidence meters are worth their weight in Gold, once you learn how to use them. In this case, I’m going to set up and install the fuselage. If I do this right, it will be straight and level to the wing.
I’m using the centerlines on the parts and plans. I’m using a scrap block of balsa to raise or lower the fuselage at the rear. I’ll use a small “torpedo” level to get the top surface of the fuse as close as possible, to matching the incidence of the wing. The incidence meter has a bubble, and getting both of them as close as matching as possible is a simple process.
Since I use at least 2, if not three incidence meters at a time, I can make the final adjustments using a second meter.
When I’m satisfied that all incidences, including fore and aft, are correct, I’ll glue an additional set of scrap balsa uprights to hold the wing assembly, and the fuse in correct alignment. Tack gluing, once again with Ca. I’ll final glue with epoxy, and the wing and fuselage are now one piece.
In the picture above, the stab is not yet glued, it is just set into place. I will need to set the incidences for it before I glue it in place.
I’ve replaced the incidence meter onto the wing. Notice that I’ve also placed scrap balsa with one 90 degree side, glued with Ca along the stab hinge line on the plan.I’ve placed the stab backed up tight to the uprights so they will be in line, and in proper relationship to the flap line.
I’ve cut and placed supports at the stab tips to establish and maintain the stab as level.
The second incidence meter is used to establish the, in this case, 0-
Once I’m satisfied with the stab’s relationship to the other parts of the plane, I’ll tack glue with Ca, and later final glue with epoxy.
Having the support pieces of scrap balsa in place, it was much easier to install the dual vertical stabs square and true.
The elevator pushrod has been installed, and finally, the fuselage top has been installed.
A final check for thrust line incidences, with the engines installed, is made. There should be only minor adjustments needed, if you’ve spent the time to do this right.
Time spent at this point is much better than time spent trying to trim in a crookedly built plane.
Since there are no “off the shelf” canopy's available for this design, we will need to make our own.
Building the canopy,
The first task involved in forming the canopy, is to carefully make a plug. The plug should fit the space properly.
After the plug is shaped and sanded, seal it with a coat of epoxy, and let it cure completely.
I’m going to make mine out of a green 7UP 2 liter bottle. I wanted green to go with the camoflage color scheme I had in mind.
Cut the bottom off the empty bottle, shove the plug as far into it as you can. Add some scraps or, as in my case, enough to make a handle to hold it all when heating.
Forming is accomplished using a monokote heat gun with the spreader tip in place.
The bottle will shrink readily when you add heat to it. It can take a fair amount of heat, but be careful, you can burn through it.
Once formed and cooled, remove the balsa, and the plug. Trim to size, and you now have a canopy that fits.
I’m not going into great detail over finishing our models. Just a basic overview.
First, let’s look at the base coats.
I cover the model completely. Not just the open bays, but the wood as well. It works best if the wood beneath the covering is sealed, and if you’re doing a paint finish, sealed with a sanding or filler coat.
A few , 3 or more coats of clear dope, then a coat of sealer, or filler then sanded.
Apply the covering, then seal with 3 to 6 coats of clear dope.
Sand with 3 or 400 wet or dry, and apply a primer coat.
Beginning the final painting steps
The first primer coat will be wet sanded until most of it is gone. A second primer coat will suffer the same fate. Finally look at the surfaces under good light, at an angle. Note, and fill, or fix any major problems.
A light coat of polar gray has been sprayed as a blocking coat. Very lightly sanded,
and it’s time to begin applying the final colors. Seen above, the light gray-
Below, the green base color for the “splinter” style camouflage scheme has been applied. So far there’s not been a need to do any masking, but that’s about to end.
A bit of masking, a bit of airbrush work, and some decals, it \’s looking like it may have actually fought and existed.