Finishing Those Foam ARF RC Scale Airplanes

FINISHING THOSE FOAM ARF RC SCALE AIRPLANES

Yes, this really is a foam ARF  airplane…with some extra time and effort invested.

If you love model airplanes, it’s pretty much impossible to ignore all those electric powered RC scale jobs made primarily of expanded plastic foam of one variety or another. “Almost-Ready-To-Fly”,  “RTF”, “Bind & Fly”, “Plug and Play”, whatever…you get them virtually all built, ready to go out of the box in a couple of hours using only basic tools and requiring none of those traditional model airplane building skills I write so much about elsewhere.  I am as tough a hard-case dyed-in-the-wool, build-it-from-balsa aeromodeler as you are ever likely to meet, but even I can’t help looking at them…especially those little scale warbirds with a disturbingly high “cute factor”. Have I flown any? Sure…to help other modelers get them trimmed and so on. Do they fly as advertised? Almost without exception, yes. Do I have any of my own? No…at least not the way they come out of the box. No matter how cool they might look on a low fly-past, up close they can’t help reminding me of squishy foam food packaging. For me, that’s a deal breaker, but for lots of people who want to do RC airplanes they are the solution to lots of problems. Like…you want to be an aeromodeller, but you don’t have all those refined skills (yet) or you don’t have time to build a plane or a place to work on models? I’d say that’s what those foam scale jobs are for…on a sunny Saturday morning that insists you go flying they don’t care who built them. But…what happens when the model flies so well you decide you want to keep it for as long as possible and then you realize the factory foam finish is seriously vulnerable to dirt, dings, and degradation from even minor impacts …and…no matter how well you fly it, the impression of all that neat surface detail sort of falls apart when you get close to the airplane.   I have an answer, and that’s where we get back to the finish part.  Aren’t those models finished right out of the box? Well, yes, they have a more-or-less smooth surface imparted by the foam molding process and they have whatever colors the designer chose to include pre-applied, as well as trim and insignia markings that may be provided to you as pressure sensitive decoration. Is that good enough? It may be, or it may not…that part is up to you. What I’m here for is to explain how you can “finish” the job of building a foam ARF model by adding a finish that that both strengthens the surface AND improves the appearance (especially up close) dramatically. How far can you go with this? There are indeed RC Scale competition categories designed specifically to encourage ARF planes (foamies included) . They are based on flight scores…no static (scale fidelity) judging or who-built-it? requirements. You might want to go for that, or perhaps just see if you can do a “clean-up” to disguise that pebbly foam finish. All that is up to you. Regardless, there are some heavy-duty questions hanging over the whole idea of “fixing” foam ARF’s. How do you do it? What materials actually work and how do you get the best results from them? How far does it make sense to go with “improving scale appearance”? And of course the big one…How much weight will that add? and Won’t that spoil the ARF model  by making it too heavy? Read on, please. I have answers to all those questions. And oh, by the way…does all this apply only to scale models? Of course not, but I doubt I could get you interested in doing all the work I’ll be describing on your boxy super-simple looking high wing trainer. However, when you’ve worked your way up to that super-cool P-47 or maybe a B-25, what I’m suggesting might start to look like a really good idea. Here’s how it all works.   I’m going to introduce this series of articles by describing the changes I made to an ARF foam J-Power P-51-D as advertised and distributed by Atomik RC (http://www.atomikrc.com/collections/almost-ready-to-fly/products/j-power-p-51-mustang-rc-airplane-pnp-silver-with-esc-and-servos) We’ll talk about the specifications of the box-stock model later, when I have some numbers from the modified version for comparison. You may be able to find this same model elsewhere, and there are others very similar to it out there as well. What I’m doing here applies to them all. In the course of “finishing” this airplane I’ll be talking about various products I’ve come to trust and recommend, as well as sharing techniques I’ve learned from other model builders and refined to suit my own preferences.   Where should we start? My standard answer to that question is always, “Read the directions!” That applies here, too, but it’s just a beginning. As with most ARF models, this instruction manual provides a list of the various parts/components and a sequence in which to assemble them. That’s not going to be much help here…doing a conversion like this means that you’ll go WAY beyond the printed instructions, make your own choices about LOTS of changes, and figure out the best way to make each of them work as you go along. With this P-51 I’ll describe every change I chose to make and explain how (and maybe why) I did it. If you are going to try this on your own, you’ll have two important decisions to make right away. First: How much are you going to change? You might choose to make ALL the “extra detail” modifications I have – like the improved cockpit and those control surface trim tabs – or you might simply want to put a new fiberglass-based finish on the ARF model as it comes out of the box, along with a paint-and-markings theme of your own. Second: You have to choose to start. I’m sure you’ve already figured out that once you make that first cut or sand away that first bit of surface color, you’re committed. That can be scary…and that’s OK. Check out the images of my completed conversion at the end, remember that I’ll describe every step along the way, and go for it.

 

Where did I start? After learning all I could about the way the parts in the box were designed to go together by studying the manual, I realized that my first task would be to cut free and “clean up” the control surfaces that are “pre-hinged” to the corresponding flight surfaces during the molding process. This results in a thin, flexible strip of compressed structural foam that connects each set of parts…like a horizontal stabilizer half and its corresponding elevator half… so they come out of the box as a module.

 

Those hinges work as designed if you’re flying the model as an ARF, but there’s no way to work around them and do an acceptable job of fiberglass-coating the individual parts …they’ve got to go. I’m using a steel ruler (straightedge) to guide my old-style model airplane tool/single-edge razor blade right along the center of the hinge joint.

 

Did you notice that I cut off part of the fixed stabilizer tip (the black part) right along with the elevator? Right away, here’s one of those decisions about how far to go with your changes. A check of a good P-51-D scale drawing will show you that the stabilizer-elevator break, or hinge line, extends all the way to the outside edge. The little squared-off-looking rear end of the fixed stab tip is supposed to be part of the elevator and move with it. Here I’ve cut it free and I’m using a sanding block with fine (320-grit) production paper to clean off any foam flashing and bevel the newly cut trailing edge to match the rest of the horizontal tail T.E. We’ll catch up with that cut-off tip in a bit.

 

Next, I’m going back to the manual to begin assembling things. I’m using Deluxe Materials Foam 2 Foam adhesive exactly per the instructions on the tube to assemble the tail module to the main fuselage structure. (Supplying the fuselage as two pieces that join here is a manufacturing/packaging process decision that has nothing to do with aircraft design…just stick ‘em together and let ‘em dry.)

 

I’m using Foam 2 Foam again to assemble each wing panel into the fuselage/wing base. (This part of the assembly is strictly by the book.) This model includes two carefully measured carbon fiber tubes that serve as wing center section reinforcements. I have already installed them per the manual and now I’m laying a generous bead of Foam 2 Foam into the open joint. (There’s some already on the bottom and the front and rear spar edges of the mounting stub, too.) When I push the wing into position,, the bead of adhesive will spread itself evenly across the surfaces to be joined. It’s best to make a joint like this with enough Foam 2 Foam to create a bit of “squeeze-out” at every surface of the finished assembly. This ensures that all the joining surfaces (that are now hidden inside) have been properly wetted. Leaving dry spots will weaken the assembly. Be sure to wipe off all those little beads of squeeze-out. Dried Foam 2 Foam is tough stuff.

 

With the wing panels in place, I cut off the flaps (and ailerons) just as I did the elevator. (Yes, I could have done that part before assembling the wing panels to the fuselage.)

 

More clean-up. There are simulated aileron linkage fairings molded into each wing panel. There’s no way they are ever going to look like anything but plastic bumps, so I’ll sand them off flush with the rest of the surface and decide whether to do them over – right – after the new fiberglass base finish is on.

 

Same game with the vertical tail/dorsal fairing. As with many scale ARF’s, there are places where it’s obvious that the mold designer didn’t pay much attention to his references for the full scale airplane. This P-51 is one of the better planes out there in this respect, but it’s not perfect. Remember the stab tip modification I just did? What’s happening here is that I’m using a custom sanding tool (sandpaper around a fat dowel) to thin the forward portion of the dorsal fin top/leading edge closer to the correct scale contour. This is one of those places where I have to decide where to stop in trying to get everything “right”. To sand back to the correct (thin) cross section I’d have to reshape the entire dorsal and end up with a weakened, vulnerable structure, or maybe replace the whole thing with new, built-up balsa…and then where would I stop?

 

Now it’s time to decide what to do about all those “scale” panel lines and door indentations. These are nearly always exaggerated, way too deep, wide and obvious. This sort of “detail” cries out FOAM ARF whenever you look at it, and it’s got to go. I’m using Deluxe Materials WonderFill (which is formulated to be used over a foam structure) to “plaster over” all those lines. Here I have chosen to fill over/seal/hide the flap and aileron servo cables that would otherwise be left exposed in channels molded into the lower wing surface. I had to make a choice here…leave them exposed on the chance a servo might need to be replaced, or do the job right at the expense of some extra work in the future if I have to change out a servo.

 

Same deal on the upper surface of the wing. I’m using one of my favorite tools…an old artist’s pallette knife…to push the WonderFill into every crevice and then smooth the surface to minimize the amount of sanding I’ll have to do next.

 

Here’s the entire airplane, without control surfaces and the fuselage top/cowl, all filled and primed with WonderFill. At this point it’s better to have too much filler than too little…you are about to sand away most of the material, but if you’ve left a depression or other flaw, no matter how small, you’ll have apply more WonderFill and wait for it to dry before you can go back and finish sanding.

 

Sanding out the surface looks like this. Here I’m using a long, flat sanding block with 100-grit paper to cut away ALL the excess, dried WonderFill right down flush with the surrounding surface.

 

I’m doing the same job on the vertical tail. At some point in working around that curved leading edge I’ll switch to a rounded sanding block to avoid gouging the surfaces with the corners of the flat block.

 

All that WonderFill on the upper wing surface has been sanded flush with the surrounding foam skin, and I’m experimenting with EzeKote by putting a pre-coat of it over the areas I’ve filled. It turns out that’s not necessary…follow the label instructions and brush EzeKote right through the fiberglass when the time comes.

 

Let’s work on the cockpit. The first thing you’ll notice about it is that TINY pilot figure, wearing a ‘60’s style jet helmet etc. We can do better…he has to go.

 

I decided to leave the black “radio area deck” behind the pilot as-is, and remove the undersized figure by cutting out the entire foam floor of what is essentially the pilot’s seat area…from the bottom because I discovered that there was no way to temporarily remove the canopy from above without risking damaging it. This is a good example of the “make it up as you go along” creativeness that’s necessary to do these ARF conversions.

 

The old stuff is cut out…you can see where I leave a nice new clean space to define a more realistic seat area for that neat new “Aces of Iron” 1/7 scale WWII pilot figure once I get him out of the bag and painted.

 

Back to where I left off with the control surfaces. When I hold the elevator and the cut-off tip in the correct positions relative to the stabilizer, you can see that my custom cutting has left me with a gap we need to deal with.

 

It turns out that a little piece of 3/16” balsa sheet cut to match the elevator cross section will do the job…here I’ve used Deluxe Materials Roket Max (cyanoacrylate) to stick it to the foam outer tip.

 

While you weren’t looking I assembled then whole elevator and set it aside for a moment to let the thick Roket Max cure hard enough to handle safely. What I’m doing here is using that same 100-grit sanding block to clean up the leading edge of one of the flaps where I cut it free of the wing.

 

Back to the elevator. I’m using a really coarse (60-grit) sanding block to cut the surfaces of the newly-extended elevator smooth. (Yes, I did the other half as well.) I’m sanding “against the block” to give extra support to the foam-and-balsa elevator, as bending the new assembly of dis-similar materials now would risk breaking it. This problem will go away once it’s fiberglassed. Extra background info: I could have avoided the mix-and-match stuff by making an entirely new elevator from sheet balsa¸ but I wanted to retain as much as possible of the original ARF model structure.

 

Here’s the elevator all extended and sanded…BUT…there’s another “detail decision” waiting for us. If you look carefully at the P-51-D scale drawing in the background you’ll see that there’s a rectangular balance section of the elevator that extends forward into a matching cutout in the stabilizer. While we don’t need those to fly our model, that feature is so characteristic of the P-51 that I have to represent it.

 

I scaled the dimensions of those outlines off the drawing and transferred them to the stabilizer and elevator parts with a soft pencil. Here I’m using a standard razor blade to start a cutout into the foam of the elevator leading edge. Wait a bit and I’ll show you why I’m cutting into the elevator as well as the stab.

 

I’ve also made the cutout in the stabilizer for the balance tab. Because that’s a narrow, potentially fussy opening to finish, rather than relying on being able to work fiberglass cloth around and into those sharp corners I’m using another great Deluxe Materials product, Foam Armour, to seal and surface those newly cut, raw foam surfaces. This is good stuff. On a smaller plane it would do a fine job of surfacing and reinforcing the entire model without the weight and fuss of fiberglass… that’s what it’s designed to do. Since this big (61” span) model will carry that small extra weight easily, I’m reserving Foam Armour for little detail applications like this one.

 

Foam Armour needs a few hours to dry properly. While that’s taking care of itself, I’m working on other parts. This is an aileron. It turns out that the aileron tips were (incorrectly) designed as part of the fixed wingtips (just like on the horizontal tail) so I’ve cut them loose and attached them to the outboard end of each aileron with more Roket Max adhesive. It turned out that I didn’t need to add sheet balsa spacers here as I did on the tail.

 

This time they got it right! The balance tab and cutout on the rudder was represented. However, there’s ANOTHER series of control surface details that deserve just as much attention if you’re investing so much effort in this model. Both elevator halves, both ailerons AND the rudder on the P-51 feature TRIM TABS, which on the full scale airplane are separate, adjustable mini-control surfaces cut into the trailing edges of the primary surfaces. You’ve already noticed where the tabs on the elevator and ailerons are represented by molded-in parting lines, and you can see it clearly here on the rudder. That’s OK for an ARF, but we can do better.

 

I’m using a steel straightedge again to ensure that I get a clean, straight cut when I separate the trim tab from the rudder.

 

Cut off, it looks like this. The white line near the bottom is where I sanded away a molded-in foam lump that was intended to represent the trim control rod fairing. I can’t think of a practical way to make that look like anything but a foam lump, so I got rid of it. Will I replace it with a custom built detail later? I’m thinking about it.

 

Back to the elevator. You can see that I cut away the “faked” trim tabs there as well. What’s going on here is that I have cut a rectangular piece of balsa about 5/16” thick to match the outline of the balance tab AND extend back about 3/16” into the elevator leading edge for a really secure glued joint. (That’s why I made that “extra” cutout a while back.) I have attached one tab with Roket Max; the other is all ready to be assembled.

 

Sanding isn’t always the best way to remove foam/structure that doesn’t need to be there. This is the belly radiator housing air intake. The leading edge “lip” is way too blunt and thick. While I can’t replicate the correct scale shape without replacing the foam entirely with some other material, I can come close. I began by carving away as much foam as I felt comfortable removing this way.

 

As I would have with any traditional balsa structure, I switched to a contoured sanding block for the final reshaping of the radiator intake lip. This is another of those places where you’ll have to make your own decisions about how much to change, again using your scale references as a guide.

 

Same game on the chin airscoop below the prop spinner…the intake opening was too small “as molded”. In this case I’m concerned with more than appearance. This hole is where the motor cooling air gets into the airplane. My first step was to carve out the opening to the approximate shape I wanted.

 

As with the radiator I’m using a sanding tool to do the final shaping.

 

Those tight compound curved surfaces would be really demanding to cover neatly with fiberglass cloth, so again I’m going to rely on Foam Armour to get a practical finish base on the newly exposed foam. I’m using a thick application and relying on the high surface tension of the product to hold it neatly around that curvature while it dries.

 

Now we get to play with the fiberglass cloth. I’m using Deluxe Materials 1.5 oz/sq. yd. material everywhere on this P-51-D conversion…it’s just thick/heavy/stiff enough to resist the handling loads a model of this size will be subjected to without risking building up too much added weight. Here I have cut a piece just oversize for the lower nose/cowl to extend and wrap around the transition from “bottom” to “side”. The critical thing here is to learn just how large a piece will allow you to stretch and fit it tightly to those curved surfaces before it gets too big and starts to pucker and lift.

 

Exactly per the instructions on the label, I’m brushing a generous, wet coat of Deluxe Materials EzeKote directly on to (and through) the glass cloth. You’ll know when you have filled the weave/put on enough EzeKote when the cloth becomes almost transparent and seems to disappear.

 

You’ll have to experiment with your model and the specific weight (thickness) of Deluxe Materials fiberglass cloth you are using, but there are going to be limits as to how tightly you can curve, stretch and press it to conform properly to the foam airplane structure without puckering and/or loosening and lifting at the edges. You’ll know it when you reach that limit. The 1 ½ oz./sq.yd. cloth I’m using on this P-51-D will accept being pushed and pressed around the inside of the chin airscoop opening. The further you can make the glass do what you want in a place like this, the more reinforcement and finish base you’re going to get. Remember, though that if the free ends of the cloth “get away” inside a closed space like this, you’ll have to do some tight “inside work” to get them cleaned up after the EzeKote hardens.

 

This curve…the bottom trailing edge wing root fillet/fairing… is a lot easier to get right. Don’t forget, though, to wet the cloth thoroughly, press it down aggressively everywhere, and be aware that pulling around the outer edges of a finished application is likely to lift “bubbles” of detached cloth nearer the middle of the job.

 

Time to work on the cockpit some more. What you see here is that Aces of Iron pilot figure after I finished painting him, an instrument panel image that I scanned from an on-line photo and printed, and a simple seat for my Ace to sit on. The seat back is 1/32” aircraft plywood, the base is ¼” balsa sheet, and the “google eye” is from my scrap box (when it’s painted it will do a fine job of looking like a headrest cushion.)

 

In the past I’d have used some clear dope to seal the wooden seat before painting it…now I’m using more of my EzeKote, which is reliably non-shrinking so it won’t bend/warp the seat, and seals the wood grain as well as dope…maybe better.

 

When I checked some measurements against my scale drawings, I discovered that the place where I cut off and removed the original foam cockpit deck was a bit too far BACK. In order to have structure to support the seat in the correct location I had to add a spacer made from scrap ¼” balsa sheet. I trimmed the insert for a tight fit and stuck it in place with Roket Max.

 

Rather than fool around with paint up inside that canopy I chose not to risk by removing it, I cut and fitted a piece of black craft paper and gave it a generous coat of Deluxe Materials Speed Bond.

 

Pressed carefully into place, that black paper patch looks as if it was always intended to be there.

 

This part might seem scary, but it doesn’t need to be. Once I determined that the shape of the windshield/canopy frames wasn’t right, I decided that the most practical way to get it acceptably close to scale appearance would be to redefine the windshield framing using good quality masking tape along where I wanted the new edges to be, build up several layers of tape to represent the distance the metal framing protrudes above/beyond the plexiglass on the full scale airplane, and then build up a generous base of a light, stable filler that I knew I’d be able to sand easily. My choice (that blue stuff) was Stits Lite Fill two-part epoxy, used exactly according to the label directions.

 

See how accurately I can shape the Stits Lite Fill once it has cured overnight? By sanding back so the surface of the remaining epoxy matches the outer face of the masking tape, I get a uniform build-up to the thickness pre-determined by the multiple tape layers.

 

I used a combination of flat and curved sanding blocks and free-held sandpaper to get the surface of the new framing exactly right.

 

Let’s glass it! I was so pleased with the way this framing job came out that I went right on to use the Deluxe Materials fiberglass cloth/EzeKote method to add the final outer skin surface/finish base to the canopy/top hatch structure. It’s easy to see how the glass cloth goes transparent in appearance once it is saturated with EzeKote.

 

EzeKote dries enough to handle in four or five hours, but I prefer to leave it overnight to ensure a good, clean job of sandpaper trimming like this. The fiberglass/EzeKote extends up from the lower edge of the part and across the transition to epoxy filler. I am trimming it against/along the slight ridge formed by the original canopy frame as molded into the ARF model.

 

Let’s cover/ surface some more smaller parts of the airplane. This is the rudder. I’m brushing EzeKote directly through a layer of more of that 1½ oz./sq. yd. cloth. Notice that I am wetting the cloth thoroughly, so that it becomes transparent, AND using my brush and the EzeKote to stretch the cloth JUST ENOUGH to ensure that it lies smoothly against the foam surface. Any loose spots I might leave now would become bubbled, detached cloth when the EzeKote dries.

 

I’m using a razor blade to trim the cloth flush with the edges of the trim tab cutout I made earlier. I can do this because I pre-coated the faces created by the cutout with Foam Armour to avoid having to fuss the glass cloth around those narrow edges.

 

This is the rudder with one side “glassed” and all the edges trimmed.

 

Here I have covered the opposite side of the rudder and I’m brushing more EzeKote into the wrapped-around glass cloth that overlaps the covering on the first side. These edge overlaps will be easy to sand smooth once dry. The extra strength they impart to all those flying surface edges is considerable.

 

I’m covering the first (top) side of the left horizontal stabilizer half just as I did the rudder. I have allowed the right end of the glass cloth to overlap all the way up and around that concave tail fillet/fairing…you can see how well a generous coat of EzeKote holds it to that compound curved surface.

 

Same as with the rudder, I’m trimming the dried EzeKote/glass skin flush with the edges of the balance tab cutout.

 

This time I’m using a loose sheet of 100-grit paper to freehand-trim the glass along the edge of the right stabilizer half.

 

There were a few extra bumps along the leading edge, so I chose to use a sanding block to be sure I ended up with a straight, true edge.

 

Now it’s time for the big stuff…let’s glass the wing. This is the top/right panel. You can see how I have left a generous working margin (overhang) all around. This image also gives you a good idea of how the limp glass cloth lies on the surface before you start with the EzeKote.

 

I cut a straight edge on the inboard wing root of the cloth. To keep it under control and in alignment where I want it to stay I’m starting the EzeKote application right there, With one end of the working piece of fiberglass held in place, I have a base against which I can pull and smooth the glass across the rest of the panel.

 

When I have done that it looks like this.

 

Same game along the forward half of the right fuselage side.

 

Remember the working margin/overhang? I made a generous overlap along the fuselage/wing root junction ( a high-stress area) as well as around and over the top edge of the fuselage side for reinforcement where the fuselage top cover/cockpit will go. Again notice that I have been generous with the EzeKote….if it doesn’t puddle, drip or run at this stage you have not put on too much. This is NOT a place to try to save some weight…the integrity of your fiberglass job depends on filling the weave/saturating the cloth.

 

I’m using a “store-bought” aluminum sanding block (from Great Planes) to true the fiberglass cloth even with the right wing trailing edge at the flap well cutout. Sometimes like along this straight edge/corner, a sanding block is better than hand-held sandpaper to ensure an even edge.

 

…and sometimes a “loose” sheet of sandpaper gives a better feel for specific spots on the airplane that demand extra attention.

 

With that done I’m back to my old reliable wood sanding block with 100-grit paper to knock down any high spots in the dried EzeKote /glass surface that I might not have detected visually.

 

Same game, different place. I’m making sure the front face of the rear fuselage deck is neatly squared off so the cockpit/top deck will fit against it snugly.

 

It’s very difficult to sand too much when you’re building model airplanes of any kind. Here I’m “just checking”, touching up the flap leading edge. Remember, we’re looking at the first coat of EzeKote that adhered the glass cloth to the foam surface and filled the weave.

 

More of the same with 100-grit paper on one of the drop tanks, which got the same EzeKote/glass treatment as the rest of the airplane.

 

Last chance…I’m using more 100-grit paper with the “calibrated fingertips” technique to run a last check for “ugly seeds” that I might have overlooked on the wing root fairing.

 

This part is kinda’ fun. I’m giving the entire airplane a second coat of EzeKote. If I put the first coat on wet enough, this isn’t needed to fill any cloth weave…it will give me a reliable surface on which to do some serious priming and wet sanding.

 

Sneak peek time! Here’s the whole airplane with some of the control surfaces taped in place after the second application of ExeKote has dried. You can still see most of the original marking scheme/decoration through the clear glass cloth finish, but we’ve already made the decision to move beyond that.

 

Remember those clumsy attempts at simulated trim tabs we cut away from the original control surfaces? Here’s how I replaced them with something better. I found a piece of scrap (soft) balsa that I could trim to fit the tab cutout (in this case, the right aileron). You can see how I have marked it for the final cut to the correct outline.

 

Off camera I cut out and shaped (thinned and tapered) all the tabs. These are the two for the elevators, with an extra piece of balsa sheet and one of the cut-off foam tabs for comparison.

 

Now I’m giving all five tabs (two elevator, two aileron and one rudder) a preliminary coat of deluxe Materials EzeDope (thinned about 50-50 with water) to seal the balsa so the silkspan (tissue) that’s coming next will adhere more easily.

 

With that pre-coat of EzeDope dry ( a couple of hours) I’m fine-sanding it with 320-grit paper to eliminate the “fuzz” that the first coat of any liquid finish product would have raised. This creates a really smooth, snag-free surface foe the covering that goes on next.

 

This is medium weight (“GM”) silkspan previously sprayed with water. I’m “doping” right through it with more thinned EzeDope and wrapping the tissue around the part to get generous overlaps front and rear. I’ll trim the overhang off the tips when it’s dry. (I’ll finish that part of the job off-camera).

 

Time to get ready for some control surface hinges. This is the left flap and the wing trailing edge it will hang from. I’m doing yet another last chance sandpaper check of what will become a hinge line joint.

 

I’m going to use ordinary pinned nylon tab hinges that are about ¾” wide. I have marked ¾” wide hinge slot locations on all the mating surfaces. This is the right flap. Because I want the “mating”/moving portion of each hinge to recess “back” into the tapered flap leading edge (to give me a really close flap-to-wing hinge joint clearance) I’m starting by cutting the ends of what will become 1/8” deep clearance cutouts in the flap using a razor blade to help ensure a neat, square cut.

 

I used a No.11 blade to cut those short lengths of foam free to form the cutouts and now I’m cutting the actual hinge slot using the same tool.

 

Two things are very important in installing tab hinges like these: getting them installed securely and getting them in alignment. There are lots of ways to do that, I’m going to install each hinge separately into its respective control surface (like this aileron), aligning it visually with the structural edge, . Later I’ll set the free/open ends of the hinges into the main structure all at once. Since I’m working with each hinge separately at this point, I’m using Deluxe Materials Roket Max (thick) to get the quick cure of a CyA adhesive (in comparison to epoxy) while ensuring myself about a minute to double-check the alignment of each hinge carefully before the Roket “grabs”. The first step in that process is to give the entire mating portion of each hinge unit a generous shot of machine oil to keep the adhesive from sticking there.

 

With that protection in place, I can give both sides of the tab I’m going to inset a generous shot of Roket Max…enough to get a bit of “squeeze-out” to guarantee I’m making a properly wetted joint inside the flap. The oil will keep the CyA from sticking where I don’t want it to.

 

With the hinge all lined up in place, I can let the Roket Max cure…ten minutes or so is enough. By flexing the hinge a few times that squeeze-out of adhesive that’s trying to foul the hinge in fact breaks away and falls off. I installed all the hinges in their respective moveable surfaces just like this.

 

Now I have each control surface with its hinges installed and aligned, all ready for the part that counts…final assembly. This is the left horizontal tail and elevator. I have already cut the hinge openings into the stabilizer trailing edge and double-checked that the elevator/hinge assembly will slip into place accurately. What happens next is that I’ll re-oil all those hinge joints and then use a medium-cure epoxy (in place of Roket Max) to guarantee that I’ll have enough time to insert and align the entire assembly (all the hinges at once) exactly the way I want it. I’ll hold it in place with masking tape and go work on something else for a couple of hours to be sure the epoxy is completely cured before I handle it any more.

 

Off camera I finished assembling all the pre-hinged control surfaces to their respective main flight surfaces. While that epoxy is curing, I’m going to work on the dummy scale exhaust manifolds that came with the J-Power kit. These consist of a pair of rectangular foam inserts (right and left) that fit into matching cutouts in the nose. Each includes what passes for a row of six exhaust stubs (pipes)…but they aren’t very convincing, even at a distance. This is a high-interest area of any P-51 and it’s worth the effort to improve. (You can see my reference drawings in the background). For a start I have cut all six pipes off the molded base. What remains will fit into the slot with what represents the long, rounded exhaust manifold shroud protruding from the side of the cowl.

 

I’m going to keep those molded bases…here I’m applying a layer of that 1.5 oz./sq. yd glass cloth with a generous application of EzeKote.

 

I let that dry really well (overnight) and then used my trusty old sanding block to clean up and square off the edges.

 

Now comes the good part…I cut a series of exhaust pipes (angled at 60 degrees) from some 3/8” K&S aluminum tube, positioned them carefully one at a time, and then used a generous shot of Roket Hot inside each pipe to hold them in place.

 

Next it’s the drop tanks’ turn. I cut away the little foam mounting nubs on the top of each molded-in pylon before I glassed the tanks. Now I’m drilling each of those locations for a length of 7/32” K&S tube. These tubes will be inserted about 1 ½” into the foam tanks.

 

The remaining length of tube that protrudes should be as long as possible to fit up into the wing at the marked location without risking breaking through the upper surface.

 

I used a liberal shot of (thin, penetrating) Roket Hot to lock each of these new mounting pins in place.

 

The next step was to mark exactly where the pair of mounting pins on each tank contact the lower wing skin when the tanks are positioned where they belong. I’m drilling holes to accept lengths of ¼” tubing, which allows a telescoping fit to the pins I just assembled to the tanks.

 

Now comes the part where you have to do neat work. I have cut those pieces of 1/4” tube to fit over the pins, but before I can do any assembly I’m using plenty of machine oil (just as with the control surface hinges) to keep my adhesive from sticking where I don’t want it to.

 

I slipped the ¼” outer tubes over the pre-oiled inner pins and then I used more thick Roket (this bottle happens to be some Foam- Friendly I was trying out) to coat the entire outer surface of each tube. The next part (off camera again because I was really busy trying to get it just right) was to align the pre-glued outer tubes with the holes already drilled in the wing and push each in turn gently but firmly into the wing until those molded-in pylon bases seat against the wing skin. If you fitted all this stuff accurately and were careful with the oil AND the CyA, once it’s cured you should be able to wiggle and tease each tank free of the wing with the outer tube still in place inside. There should be enough friction inherent in these assemblies to permit you to slip/press the tanks into place for flight and have them stay in place until you decide to pull them directly down and away from the wing.

 

More cockpit work. When I sanded all that blue Stits Lite Fill epoxy flush with the external cockpit framing I had defined with masking tape, I left a distinct edge where the finished epoxy meets the tape. If I finished painting the airplane now and then pulled the tape, I’d leave odd-looking blue lines along each cockpit frame edge. What I’ll do about that is to pull all the canopy masking that I used to define the framing, do any last-minute fine touch-up with appropriate sandpaper, and then re-mask the whole thing. Here’s the canopy with the original masking removed.

 

Now I’m using fine edge quality masking tape to re-mask it all. Here you can see where I have already done the main canopy…what you might not notice is that I left a very narrow (less than 1/32”) space clear along each tape edge adjacent to the frame. That leaves each of those exposed edges and a tiny strip of clear canopy plastic exposed to the final paint job to form a neat seal along each epoxy-canopy junction line. Right now I’m pressing down the tape right over the edge of the right windshield panel.

 

Now we can use a new (sharp) blade to trim along that joint line…just a hair away from the frame…where I want the finished paint edge to be. It takes care and some practice to press just hard enough to cut the tape cleanly without scoring or cutting the plastic. (You can do it…just take your time).

 

When the cut’s finished I can peel away the tape outside the area to be masked off. That looks like this.

 

Here’s the entire cockpit/canopy assembly re-masked and ready for painting.

 

Time to fix an oversight. When I removed the flaps for re-hinging, I should have compensated for the loose end clearance dictated by the molded-in ARF hinging scheme. That left me with gaps at each end of the flap that must be corrected or look sloppy. (The ends of the flaps and ailerons on a P-51 are supposed to match up closely). I have cut a piece of ¼” balsa sheet to fit the opening at the inboard end of the left flap that needs to be filled in.

 

I glued that insert in place, along with this corresponding one at the other end. Now I can use a sanding block (working carefully around all that surrounding structure) to finish the inserts flush with the original surface. (Yes, that would have been easier if I’d done it before the flaps were assembled.) Doing this kind of catch-up fix-it I’ve just been admitting to will be a measure of how important it is to you to get your model finished right.

 

The best way I have found to “blend in” a small balsa modification to a dis-similar structure (foam in this case) is to dope a piece of silkspan (tissue) over it. This will add strength to whatever joint I have created and relying on the silkspan to hide the wood grain will add less weight than the sanded-out filler/primer that it would take to get the same result. In this case I’m using EzeDope just as I did with the control surface trim tabs. I gave the raw wood a pre-coat of EzeDope, sanded it lightly when dry, and then wrapped wet silkspan around the area I wanted to cover, with generous amounts of EzeDope both under the silkspan to adhere it and over the finished work to help seal it. (Note: When all this had dried thoroughly, I sanded it again and added a second coat of EzeDope to bring the surface up to a standard of finish comparable to the surrounding structure.)

 

Off camera I added a generous application of surfacing putty (the balsa filler stuff is OK but I prefer using cellulose based autobody spot primer wherever I find any trace of rough spots, cracks, or any other depression in the surface, which at this point is fiberglsss cloth with two coats of EzeKote. When that was dry it was time for some aggressive wet sanding with 220-grit wet-or-dry paper. The goal here is to cut (sand) away everything that protrudes/sticks out above what should be turning into a uniformly smooth surface. You will learn to judge by sight just when you’ve sanded away enough material… the surface will begin to exhibit a uniform dull sheen through all that water and sanding dust mess.

 

The trick here is to sand down just to a uniform surface and no further. When you get to that point it should look like this. The darker gray areas are the original aluminum colored ARF finish showing through the EzeKote/glass surface and the lighter gray is where traces of that filler have been left in what used to be low spots.(Note: Right here your best tool for checking the accuracy of your sanding job is your fingertips, not your eyes. With practice you’ll be able to feel a rough spot that you might not see.)

 

I’m chasing down and fixing any remaining flaws in the surface I’ve created so far. This is the vertical fin/dorsal fin leading edge…there were some low spots I didn’t like, so I used more surfacing filler (in this case more red autobody primer) and then used a custom sanding block to blend it into the surrounding curved surfaces.

 

Time to add those new trim tabs. Holding these small parts separately for finish painting would be really fussy, but sticking them in place now would risk heavy paint filling all the narrow gaps that should be easy to see ahead of their leading edges. My solution on this model was to make stand-offs from cut-off straight pins inserted just deep enough to hold each tab near the corresponding surface so I’ll be able to paint it without getting that buildup. Once the final paint coat is dry I’ll push the tabs all the way onto the pins with a bit of Roket on each pin to keep them there.

 

Now it’s time for a serious coat of sanding primer. There are lots of products that will work here. I chose one that most readers might be familiar with…Rust Oleum Wet-Sandable Auto Primer from the local hardware store. Use this stuff per the directions on the can. Spray a generous, double wet coat (all the material you can put on the surface without getting sags or runs) and let it dry really well.

 

If you don’t spray on enough primer you won’t have enough material to sand away…but…if you don’t sand away most of that primer you’ll leave too much unnecessary weight on the model. The primer you leave should just fill the low spots…no more. Here I’ve gone to 400-grit wet-or-dry paper for a finer base finish in preparation for the surface paint coat.

 

Here’s an advance look at the airplane after that 400-grit wet sanding. I’ve wiped it all down and let it dry, then inspected it for any more stubborn flaws and spot-primed those with more autobody primer.

 

Here’s where I close up the trim tab assemblies I described a few steps back. We are very nearly finished with the surface prep work.

 

When all that last-minute fix-ups with red primer were wet sanded smooth, I gave the entire airplane another coat of that soray can primer. When it was completely dry (one way to tell is to feel the primer coat surface…if it is even a little cool, solvents are still evaporating. WAI T). This time I used more 400-grit paper and once again wet sanded aggressively. Most of the primer needs to end up on the floor. Don’t stop too soon…once you’ve done this you’ll recognize what “finished” is supposed to look like.

 

The purpose of your top/color paint coat is to add a uniformly colored finish…nothing more. When you have built up a base with primer and sanding that is as good as you want it to be, put on your color coat. In this case that’s Stits PolyTone Nevada Silver…close enough to a full-scale P-51’s finish for this scale-for-fun project. I’m using a DeVilbiss Automotive double action touch-up spray gun here. I lay on just enough silver to create a uniform color and flow out, and then I stop.

 

No more Big Beautiful Doll… this P-51-D is getting a new identity. The first part of adding to that aluminum base is to make the rudder red…I’ve masked off and airbrushed just enough Stits PolyTone Madrid Red to get a uniformly colored surface.

 

The spinner that came in the box gets to be red as well.

 

My subject airplane had the partial black and white “invasion stripes” that were used in the ETO during the summer of 1944 (after Normandy). I masked off the large areas on the bottom of the tail and both wings and sprayed a base coat of Stits PolyTone Insignia White. When that was dry I masked it off to define the black stripes.

 

On a competitive scale model there’d be intricate detail up inside the main gear wheel wells. I used some dark gray acrylic craft paint to fill them in and give a sense of depth that wouldn’t have been there if I’d left them “plain silver”.

 

Time for some real detail. I cut the original “foam lump” machine gun fairings off flat and resurfaced them around some 3/8” washers to approximate the shape of the full scale fairings. Those all got primed and painted right along with the rest of the wing. Now it’s time to insert the simulated .50 cal. muzzles I made using several different sizes of K&S tubing.

 

I used a custom set of 1/7 scale P-51-D vinyl markings from Callie Graphics…Callie has an excellent selection of warbird marking sets to choose from.

 

A delicate touch with my Badger Double Action airbrush and some Stits PolyTone mixed up to an exhaust/smoke/grime color creates gunsmoke smudges. I did the same treatment on the engine exhausts.

 

With all the paint and markings in place I gave the entire airplane a light coat of Stits PolyTone Clear with enough Stits Flattener added to produce a dull eggshell finish. The only exception to that clear coating was the cockpit canopy. The plastic would get cloudy and look odd if I sprayed it, so I waited until the clear was dry before I pulled off those final bits of masking tape.

 

And here she is…Capt. “Bud” Anderson’s “Old Crow: from 1944, all assembled and ready to head for the field. NOW I’m going to make you wait for a flight report. (Yes, she does fly, and well, but there are some things I want to say about the original J-Power ARF and ways you can improve it. Watch for that right here!)