Building the Sig DO 217 kit (1)

Cutting balsa is in fact the first thing you’re going to do building this kit. Each of the two wing panels is built separately, flat on the plan, and they are joined later. The construction sequence is a bit unusual in that the entire lower surface of each panel is assembled in place on the plans…leading edge sheet, capstrips, trailing edge sheet and lower main spars…all cut to exact dimensions per detailed drawings provided in the instruction book, edge-glued as necessary, then pinned in position per old time model building practice. The ribs are glued on top of them, followed by the various upper surface sheet components. This kit is interesting in that you get precise measurements for making up the wing skins before they go together to make a wing. In this shot I have finished adding the top leading and trailing edge sheets and I’m beginning to fit the capstrips. The outboard end of the top L.E. sheet has yet to be trimmed to match the curvature of the wingtip assembly.

This is the right wing panel as seen from the bottom. The two round holes have been pre-cut for power and control cable access from the fuselage to the engine nacelle. The white tube (rolled from paper) will carry the aileron servo cable within the covered wing. With that in place my next step will be to add the lower center sheet balsa skin, which will also serve as a mounting base for the nacelle.

This happens to be the bottom of the left wing, but the game’s the same. I have added all the sheet covering, along with another section of sheet at rib W-6 which becomes part of the aileron servo installation. I departed from the plans at this point. The design originally calls for surface mounted aileron servos and provides two plywood mounting plates for this purpose. I think surface mounted servos on scale models are ugly, so I included an internal mounting plate which you can see down inside what has become the servo bay. More on this later.

I’m jumping ahead here. I finished joining the wing panels without telling you, since the instruction book does a fine job and you don’t need my help there. This is the horizontal stabilizer frame assembled in place over the plan. Later it will be closed in, top and bottom, with 1/16″ balsa sheet.

The next step was to build up the two separate elevator halves. These will remain fabric covered open structure.

Exactly per the kit instructions I have added the elevator joiner/control horn which is built up from furnished hardware components. This assembly looks somewhat unusual but it works just fine…there’s no need to change it.

I began fuselage construction exactly by the book by laying out and glueing the various reinforcements and doublers.Here F-11, F-12 and the 1/4″ sq. balsa doublers on the nose are in place.

Actual fuselage assembly begins with joining the two side assemblies parallel to each other at F-4 through F-6. I’m lining up F-4 (the wing leading edge station former) here.

Now the fuselage sides are joined all the way from F-1 to F-6 and the wing hold-down comprising all those F-20’s laminated together has been added ahead of F-6.

Now the fuselage sides are joined at the tail and the stabilizer support rails have been glued in place.

The stock kit makes no provision for landing gear. On this model I’m going all-out with a retracting main gear installation which requires changes to the engine nacelles and their assembly sequence and is the subject of a separate article. The tailwheel assembly becomes part of the fuselage and I’m describing it here. On the full scale DO217 the tailwheel retracted. Replicating that on a model this small would have risked adding too much weight in the worst of all possible places, so I kept it simple. I made up a mounting plate of 1/8″ plywood to fit between the fuselage sides between F-8 and F-9 and added a Sig tailwheel mounting bracket and a simple bent wire strut. Here it’s ready to ZAP in place along the bottom edges of the fuselage sides.

More changes…  As the instruction book mentions, this model is a close-to-scale conglomerate of several marks of the DO 217 including the -J-1 and -2R22, which included a prominent ventral (belly) rear-facing gun mount. As designed, the standard kit fuselage offers only a tentative curving bulge beneath the nose to suggest this feature. Here’s what the structure looked like per the kit before I decided to add some changes to represent that distinctly odd-looking ventral gun.

I removed the doubled F-13 belly sheet and added extensions to the bottom of F-2, F-3 and F-4 to define a deeper nose profile derived from 3-views I found online. I then replaced the “double F-13″ belly skin with new 1/8″ balsa sheet and followed that with new, deeper 1/8” sheet sides. This is a view from above and behind showing the extensions to F-3 and F-4 with the new belly skin in place.

This is the new right hand lower nose sheeting in place before being trimmed off and sanded to blend with the primary fuselage sides and the new belly skin.

Now I am departing completely from the kit design. The rear facing belly gunner’s window demands some complex shaping. I decided to eliminate some of the potential difficulty here by designing in a simple block that can be sanded to shape in place. This is the opening I created between F-4 and F-5 where the pre-shaped block will go. F-24 is already in place on the rear belly.

The stock F-23’s are now in place along the center corner contour of the tail. These finish the job of defining the opening where the block will go along with the finished outlines of the belly window.

I used a handy chunk of polyurethane foam for the filler block. Balsa would have worked just as well. If you’re going to use another modeling foam, remember that the white stuff won’t stand up to the solvents in any paint you might use later.

Now I have the foam block trimmed roughly to shape.

This is the cockpit/hatch area looking to the rear…the angled face is F-3T. I’m holding one of the two F-25 top/side pieces close to where it’s going to fit.

This is the nose as seen from the left. The curved face at the bottom is the new lower side sheet I added in step (14) where it meets the gunner’s window block. This will be sanded to a rounded, finished contour once the top of the fuselage and the cockpit hatch are closed up.

Now I’m building up the hatch assembly. HB-1 and HB-2 are joined and pinned in place between the nose block and F-3T and I’ve added the HS hatch sides and HR, which must be beveled to fit. The plastic wrap keeps the new assembly (which will be removeable) from being glued to the rest of the fuselage.

All the cockpit/base hatch parts are sanded to match the contour of the rest of the nose. The molded canopy comes later.

I have added F-4T, and then the wing bolt mounting plate which consists of 3 laminated F-20’s, and then drilled the single centerline hole for the 10-32 blind nut and screw. (This assembly is inside the fuselage.) The top/rear wing fairing has been assembled from WFS (side) pieces and a single WFT (top). I then beveled all the exposed edges and added the WFC (corner) sheets…these have not yet been rounded off.

This is the wing center section as seen from the front with the flat section where the nacelle former N-2 will fit, cut and sanded in.

Let’s work on the tail now. I have hooked up the transverse rudder actuating rod that runs spanwise through the horizontal stabilizer (per the instructions) to the push-pull wire-in-tube that leads to the rudder servo, and the elevator push-pull to the elevator servo. The foward ends of both these connections are still free to move around as necessary up front in the servo bay.

Now I’m sliding the entire horizontal tail assembly, with the elevator hinged in place, forward-and-down into its final position on the stabilizer saddle. This will be my last chance to access these control connections, so it’s important both that I know the tail assembly already fits the saddle perfectly and that the control connections are safetied and have full freedom of movement.

I’m using a drafting triangle to ensure that the stabilizer trailing edge is exactly parallel to the fuselage centerline. ( I have already squared the tail assembly to the fuselage in the roll axis in the same way.)

I cut out the tail assembly opening in the fuselage top per the instructions to install the tail, and now I’m fitting it back in place. I’ll use thin (fast) ZAP once I’m sure it’s exactly where I want it to be.

When it’s back in place it should look like this. There’s some finish sanding left to do before it blends smoothly into the rest of the fuselage top.

I made some changes to the vertical tail surfaces (fin-rudder assemblies). VS, RU and RUT are furnished as 1/8″ balsa sheet parts. There’s no reason the airplane wouldn’t fly just fine that way, but 1/8″ thick vertical surfaces are way too thin for correct scale appearance. I chose to cut out FOUR new sets of parts from very light 1/8″ balsa sheet…cross-grained to each other…and laminated them into two sets of 1/4″ thick surfaces that could be sanded to a more realistic cross section. Between the lightweight material I chose and all the shaping I did, I could not detect any significant effect on the balance of the finished model.

The original 1/8″ thick vertical tails are to be butt-jointed to the horizontal tail tips. I took advantage of the extra thickness and cut mortise openings to fit over each tip for additional structural strength.

Assembled into place with thin ZAP, the left vertical fin looks like this.

Here’s a look at both fins in place.

This shows a comparison between one of the rudders sanded to shape and the other part before I worked on it.

These are various nacelle skin pieces (N-4, N-5 and N-6) in the process of being wet-formed into a permanent curvature prior to assembly. The instruction book provides detailed explanations of how this works. Here the balsa parts have been pre-soaked in an ammonia solution and are drying under weights. I’ll leave this arrangement overnight before moving anything.

I’m closing up the bottom of one nacelle by adding both N-5’s. Right now the nacelle is on its side…the narrow sheet balsa strip partly obscured by the wider parts is N-6 (the nacelle bottom). There’s a lot of trimming and sanding left to do here.

This is the left nacelle, already glued in place along the top edges of both N-4’s where they meet the bottom wing sheeting. I have added both N-7’s, sanded a bevel into their top edges, and now I’m fitting N-8 to close up the assembly. You can see the right nacelle in the background.

Now N-8 has been ZAP’d to the top front of both nacelles, and the entire surface structure of both nacelles has been sanded to final shape. I used 80-grit production paper on a long flat block for this job…the balsa surfaces will be sanded smooth with progressively finer grades later.

This is the front of the left nacelle (the left firewall). You can see where the 1/8″ plywood RLG mounting plate protrudes through F-1 flush with the front surface. (I described those nacelle modifications, including the making of that part, in the RLG sidebar portion of this feature.) The cowl ring I’m holding is furnished with all those cool lightening holes pre-cut.

I used a pencil to mark the location of each cowl ring inside its respective molded cowl and now I’m using ZAP-A-GAP to create a neatly radiused glue joint all the way around each of them.

I built up a shallow fillet of Hobbylite filler and let it dry thoroughly. Now I’m using another of those custom sanding blocks (a length of brass tube with some 100-grit production paper this time) to shape the fillet material into an even radius that fairs neatly into the surrounding balsa surfaces.

Here’s another departure from the standard kit. I’m going to add scale exhaust stacks that exit beneath the rear edge of each cowl, and they’re going to need shallow (about 3/32″) recesses to fit properly. Here I’m marking one edge of the top center recess/cutout.

I’m using a razor blade to open up the cutout .

Another job for the sanding block…I’m creating a smoothly tapered ramp in the cutout I just made which will transition into the nacelle surface about 1.25″ behind the firewall.

The Sig kit provides molded nylon aileron hinges, which I am going to modify for improved scale appearance. As presented, the primary horn is mounted to one side of the control surface by two screws that extend through to a backing plate on the other side. This works just fine but looks clumsy in my opinion. On a model of this size, weight and speed I have found that mounting the horn as an inset to the aileron provides more than enough strength for safe flying. Here I’m holding the entire horn assembly molding as supplied in the kit next to one of the ailerons, which has already been trimmed and sanded to finished shape.

I am marking the aileron where the horn is going to be mounted.

Here I have already cut the edges of the horn mounting slot about 1/8″ deep with a No. 11 blade and I’m using a miniature wood chisel to complete cutting the opening.

You can see how the horn is going to fit into the cutout I’ve made.

I bedded the nylon horn into enough ZAP-A-GAP to flood the slot and form a smooth puddle across the top of the horn and extend smoothly out onto the surrounding balsa surface. In this case I want the ZAP to penetrate well, so I did not use any Zip Kicker accelerator.

The kit includes Easy-Hinge material which is intended to be fitted into place and then secured by wicking thin ZAP into each hinge installation. For this technique to work properly it’s necessary to make hinge slots in each of the mating surfaces into which each hinge tab will slip without binding, but also snug enough that there will be no gaps between the hinge material and the balsa structure next to it. Here I’m using a No. 11 blade to open a hinge slot in the wing trailing edge…I previously drilled two 1/32″ diameter holes to define the ends of the slot.

It’s supposed to look like this. At this point I’ve completed the job of covering the airplane and applying the base finish. On a small airplane like this I prefer to install the control surfaces/hinges before spraying the final color coats to avoid having to keep small loose parts under control while I’m painting. (I’ll talk more about that in another blog.)

The nose gets another modification in the interest of scale detail. Some DO 217’s had as many as eight guns installed in the nose. Using scale drawings I found online I’ve located and marked the position for each of the gunport openings.

I drilled out each hole to accept a length of 3/16″ diameter ordinary hobby shop aluminum tubing and fixed a piece long enough to extend beyond the front contour into each hole with plenty of thin ZAP.

The next step was to cut off each protruding tube end with a sanding block. I started with 80-grit production paper, worked on down to 320-grit to get a smooth surface, and then used the tip of a No. 11 blade to pare out any remaining flash from the inner end of each tube. I’ll show you the finished gun installation in a bit. (Sorry ’bout that focus.)

At this point the airplane has been painted with the overall light blue-gray German camouflage scheme base color. (I’ll talk more about that in the finishing blog.) I have installed the rudders and the elevator with Easy-Hinges (just like the ailerons) and now I have locked those control surfaces into a neutral “trail” position using clothespin clamps and short pieces of scrap balsa to serve as surface protectors. This will allow me to fit the forward ends of the rudder and elevator control rods into their respective servo outputs with the assurance that the surfaces will be aligned properly when I’m done.

Here I’ve got the rudder and elevator servos installed on mounting rails per the kit instructions and plugged into my Airtronics Rx-600 receiver’s servo connector ports…including two short extension leads that will connect to the aileron servos when the wing is in place for flying. The receiver will end up riding on the bottom of the open space to the right (ahead) of the servos.

I’m fixing the left aileron in neutral the same way. The Airtronics 94761 aileron servo is in place on double-sided tape inside the servo bay I built earlier and I’m checking the length of the aileron push-pull rod that’s nearly ready to install.

I made an aileron servo bay cover plate from more of that .007″ aluminum sheet I like to use. Here the plate is cut to shape, the corners are rounded, and the edges are polished smooth.

I drilled end holes and cut a slot for the servo output arm. When it was ready, I attached the cover plate with a drop of canopy glue at each corner (so I can remove it later if I have to) and held it in place to dry with some masking tape.

While the glue was doing its thing I hooked up the aileron pushrod made from the standard kit components.

This is one of the fun parts I’ve been waiting to do. With the cowls fitted and all the finish painting done I can make and install the dummy engine exhaust tubes. I discovered from those same drawings I used to research the guns that there are twelve exhausts per engine and that the portion that is visible behind each cowl trailing edge is a slightly flattened round tube. I cut lengths of 1/4″ aluminum tube to match the drawings (and fit within the cutouts I made earlier) and made up a jig from scrap lumber to add the slightly flattened coutour.

I squeezed JUST ENOUGH with the vise to do the job.

The individual tubes get ZAP’d to the inside of each cowl trailing edge like this.

While the cowl is off we get to take a good look at one of the Cobra 2213/18 brushless motors from Innov8tive Designs. I’m running a Master Airscrew 3-bladed 8-6 prop on each one, powered by a Venom 2100 mAh 3S LiPo pack. The LiPo’s are mounted beneath the cockpit cover, one per motor with its own Cobra ESC.

This is what it looks like all put together.

While we’re at the putting-together game, here’s the look I promised you at the finished gun installation. I cut a length of aluminum tube one extra size smaller than the outer tubes that were already installed to provide a clearance around each “gun barrel” and then used more thin ZAP down each barrel to lock them in place.

What d’you mean, “Does it fly?” It’s a real winner. Erick will include more flight shots with the FLY RC Magazine print version of the review.