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Hi everyone,
Expanding on discussion thread about 747 engines and some questions presented by one of our A/C members, i thought the time would be right to present a technique i’ve been using for a while.
As a competitive model builder, i’ve always been focused on cleanliness of construction and adherence to the basics like seam filling, paint/decal application, and alignment. One bothersome issue that vexes Civil and Military modelers alike, is how to handle sharp, 90-degree joints where components come together….. more specifically, when they don’t come together particularly well.
I present to you, the case of the fuselage-mounted engine nacelle.
Now, speaking as a pilot and something of an amateur aeronautical engineer, i can say that fuselage-mounted engines offer all sorts of aerodynamic and structural benefits. However for model builders like us, fuselage mounted engines can be a pain. They’re usually mounted exactly where fuselage cheat lines run, and that usually dictates painting and decaling the model before the engines can be attached. That has always been the accepted method but it runs up into the issue of nacelle-pylon-fuselage integration often looking amateurish which to some will detract from the overall quality and visual appeal of the model.
Now for this demonstration, i’m using the Roden Super VC-10, but this technique would be equally applicable to a Revell 727, an F-RSIN Trident, or an Airfix DC-9. Any installation where the engine nacelle is molded integral with the pylon, and especially if there is a clunky looking “Pad” molded to the fuselage sides.
In the photo below i’ve laid out our test subject and some of the tools. The left hand nacelle is done, so we’re using the right nacelle for our demonstration.
For the first step, we need to remove the raised “Pad”, or “Boss” that mates with the butt end of the engine nacelle pylon. Badly. By priming the area with a high contrast paint, it makes it a lot easier to see when the boss has been fully removed from the surface.
Some people have asked why i remove this. In short, these things tend to hurt cleanliness of assembly rather than help. Now in this case, i’ve made no effort to restore the loss in thickness of this pad onto the engine pylon. I did not consider this really noticeable. On VC10 number 2, i restored this loss of material with a slab of .030 styrene bonded to the butt end of the pylon, and now having done it, to my eye it does not make a lot of visible difference. I adhere to the philosophy of “Keep it Simple, Stupid” in situations like these.
With this step done, we apply a strip of clear, thin packing tape to the mating surface of the fuselage. I know that some people prefer to use Bare Metal foil and that works perfectly fine, But it can be hard to get off the backing sheet without tearing it, and the longer it remains on the model, the more difficult it is to pull off completely. Packing tape represents a good compromise, because it’s extremely thin, clear, sticks well and is extremely cheap.
So, when the packing tape is applied to the model, obviously it needs to go on perfectly flat with no wrinkles or puckers, and it needs to span the entire area where the pylon touches the fuselage.
Next, you will want to carefully slice the hole where the tongue of the engine pylon slots into the fuselage.
At this point, slide the nacelle pylon onto the fuselage, and look at the joint to determine where the big gaps are. Also check the alignment of the pylon to make sure its jiggered up at exactly the angle you want. In the case of my VC10, the mounting tongue and slot were a tight fit, so there was no problem with setting the angle of incidence or the dihedral when viewed from front. Effectively, it was a friction fit, which is a good early sign.
The next thing you want to do is apply just a few drops of CA to the mating surface of the pylon and “tack” the engine/pylon in place onto the tape/fuselage composite. This is your last and best chance to get the alignment “nailed” before getting deep into the process.
With the nacelle successfully attached, its now time to backfill the gaps between pylon and fuselage with CA. On this build here, i used medium-viscosity CA just by itself, but on a subsequent set of VC10 nacelles, i’ve been mixing in Dentists acrylic resin. Getting the mixing ratio at first takes some experimentation, but once that’s figured out, the powder gives the CA a lot more “body” and i think it might reduce the CAs tendency to crumble when its sanded very thin.
In the case of the VC10, the pylons have a significant angle of incidence and actually wrap down and around the lower fuselage rear undersides to where they almost come together. The whole subject of the VC10, and its engine pylons is an article unto itself. Trust me on this.
Its on the underside here where you can see the majority of the CA is needed. Mind you though, the engine installation is an extreme case. You can sort of see the magnitude of the gaps down here, and see why some sort of filler added to the CA would be beneficial.
So, once you are satisfied that you have enough CA laid in to fill all the voids and gaps, its a matter of drying it. I prefer to let my CA outgas and set up naturally for maybe an hour or so, and then hit it with accelerator, applied with a small disposable micro brush.
Once the CA is dried, i sort of shotgun the area with a paint or primer that offers a high contrast to the plastic. In my applications i like to use Mr Surfacer Black, or Mr Color H8 Silver. The purpose here is, just like with the mounting pads on the fuselage sides, you’re gonna be taking most of this stuff off and you want to see if there are any low spots adjacent to where you sanded away excess CA. Because you know if you missed them, they will DEFINITELY become visible when your bare metal finish of choice goes on….
And now the fun part…
In this instance, the tape came away from the fuselage and away from the pylon exactly the way i wanted it to.
What we now have is a gray, plastic, black, partly crystalized, engine pylon shaped mess.
Now what we do is we break out the rigid backed sanding sticks and proceed to sand/file away everything that’s not an engine pylon. You will probably need to start with a 180-grit stick for initial bulk reduction, then switching to 320-400 grit sticks as the last of the excess material is removed and you “zero-in” on the final contours.
Why rigid backed sanding sticks?
Because what we’re aiming for is an extremely sharp, 90-degree corner, and if you try to sand this by hand, you cannot apply pressure evenly and more likely than not you will round out or “chamfer” the corners, which defeats the whole purpose of this exercise. For the finer sanding i switch to Tamiya sanding sponges, but any hand sanding towards the end with a piece of sandpaper is done only with very fine grits mainly to work out any sanding scratches.
I didn’t take any photos of the nacelles halfway through the sanding process,, but here you can see what they look like when all the black primer and excess filler has been sanded away.
It doesn’t show well in the photos, but if you did it right, the CA filler should appear as a semi translucent, darkish sliver between the kit pylon and what will be the side of the fuselage; it sort of looks like smoked glass. This CA should have hardness characteristics identical to the adjacent plastic and there should be few if any air bubbles visible.
I mentioned “Crumbling”. CA is brittle stuff and it can sort of disintegrate if its been sanded to near knife edge thickness. I’m experimenting with adding dentists acrylic resin as i mentioned, and adding this in seems to mitigate the crumbling tendencies.
At any rate should you find some crumble, or air bubbles, or someplace where the CA didn’t quite go in… Simply repeat the process; apply a new piece of tape, slide the engine pylon on, apply the CA filler where necessary, take if off again and sand to final shape.
Now, it is important that you keep paint off the mating surfaces of the pylon when painting them, but they can now be painted up and decalled separately as conditions warrant.
The paint thickness on the fuselage sides i have found to be negligible with respect to affecting the fit. If everything goes perfectly, you will have a very neat, tidy joint that allows for a near friction fit of the pylon, requiring only white glue to attach permanently that can be easily rinsed away…and of course dries clear. You will have something which if not absolutely, technically accurate, looks aesthetically much more pleasing and certainly fulfills the requirements of IPMS judging criteria.
So, that’s it. I hope this demonstration gives you the modeler an additional technique to add to your arsenal of tricks, and perhaps gives you the confidence to tackle an aspect of model building that perhaps you wanted to get better at…. but didn’t exactly know quite how.
As always, comments, questions and critiques are welcome for follow up study.
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Hey, i had meant to add these photos to the original post, so you can see the process evolving from an assembly process, through painting, decaling, and installation.
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Blimey! Amazing work. I don’t think I have quite the skill for that level of finish. But amazing all the same!
George
AKL NZGreat work, thanks for the writeup! Is there a way to turn this into one of the articles? Might be worth chatting with Ahmed about how best to do that.
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Your timing on this post is serendipitous. I was just thinking about using this technique on a Minicraft 727 I’m working on. I’ve done it with a couple of Sergey’s kits and it’s a solid technique. Thanks for such a detailed write up!
Matt
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I am perfectly happy to do that, but it’s entirely up to Ahmed.
Thanks, BTW!
david
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Friends don’t let friends build bad models, badly.
LOL
-d-
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I am perfectly happy to do that, but it’s entirely up to Ahmed.
Thanks, BTW!
david
Yeah, absolutely, that would be great! If you want to take a whack at it, I can give you the Author role and you can give it a try. Otherwise, I can create it, and since all the images are in your Media Library already, it will be very easy. Would it be an exact copy of what’s above or would you like to add more to it, David?
Thanks,
ahmed
KSFOI’ve used the same technique but with conventional filler putties and catalyzing body putty. They sand much easier than hardened CA, which, if you wait too long to sand, becomes too hard to sand.
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Ahmed, at this time there’s no other photographs to be added. However, one important caveat that i’m not sure i elaborated on enough, is that its important to sand the cured CA withing maybe 12 hours or so. As you know CA gets harder than the surrounding plastic if its allowed to sit undisturbed for too long. However in its early stages it carves and sands nicely.
-d-
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You bring up a good point, that i know i mentioned to Mark, but i forgot to include in the article.
CA needs to be carved and sanded in maybe the first 12 hours or so, before it sets up steel hard. However, some CAs do not set up quite that hard… it’s highly dependent on the formulae the given manufacturer used.
Mixing CA with resin acrylic powder seems to help the sanding and filling characteristics, but i’m still new to using this technique and i want more experience under my belt before i endorse it in a written article.
Up to this point CA has been the preferred medium because it can be polished to glass smoothness and it takes scribing tools okay.
-d-
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Do you have any photos depicting your technique with putties and where you’re using it?
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Ahmed, just this one time, why don’t you go ahead and make it an article.
Not sure what, or when my next article would be but i’d be happy to take the authorship role next time around.
david
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Do you have any photos depicting your technique with putties and where you’re using it?
No, I don’t. But they would look much like yours, but with cured putty instead of superglue. I’ve generally used this technique on vacforms to attach fins and tailplanes to fuselages. Next time I’ll try it with superglue mixed with dental resin, which is a filler I’ve been wanting to try anyway.
By the way, regardless of what you used for filler, your VC-19 model is one of the best airliner model I have seen in years.
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Ahmed, just this one time, why don’t you go ahead and make it an article.
Not sure what, or when my next article would be but i’d be happy to take the authorship role next time around.
david
Sure, I can create the page but it might be a while before I can get to it.
Thanks,
ahmed
KSFONo problem with that, since it seems the people who are finding it the most value are naturally gravitating to it.
-d-
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Thanks!
Since you mentioned attaching vertical fins to fuselages, may i present “Exhibit A”, M’Lud.
-d-
Finally, this is worthwhile viewing…
-d-
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Anyone have a good source for the Dentsply Free Flow acrylic mentioned in the video? I am interested in trying out this technique.
Also, for you more experienced builders using CA for filling gaps and seams, how do you feel about using a kicker? Does it adversely affect the plastic or is it safe to use? I love CA as my go to filler but would like to use a kicker to set it on curves where it wants to flow away from the area I’m filling but am nervous I’ll wreck my models…
Matt
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I did a deep dive on the dental acrylic after seeing that video…seems to be discontinued and suppliers don’t like selling to non dentists.
I’m considering trying with acrylic nail powder, it’s a fraction of the price and easily available from amazon or beauty stores…haven’t got around to it though.
scott
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I’ve been using an accelerator, but i’m applying it with a one shot disposable micro brush, not the spray bottle.
I’m doing more experimentation and testing on an Atlantis CV-990…..
-d-
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Wonderful!
You never really know for sure how good a technique is, until somebody else tries it and duplicates the results. Glad to hear it worked.
-d-
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I’ve been using this stuff for awhile now: Liquitex Modeling Paste. At Michaels (for us folks in the states) is selling a store brand, Artist’s Loft Modeling Paste. It has properties like PVA (poly-vinyl acetate, most popular brand is tacky-glue) when wet, but dries to a hard & smooth surface. What I do is use a tiny spatula, usually a bit of scrap sheet styrene 2-3mm across, and “putty knife” it into the gap. I recently filled the gaps on the horrid Minicraft 1/144 707-320b engine pylons to wing join. Then using a wet cotton swab, wipe the excess away. Keep wiping & using new wet swabs until ALL of the excess is gone. Do not let any dry the model surface, it will dry hard as a rock. Not sure what the chemistry is, but this stuff acts like toothpaste wet, and is as hard as the surrounding styrene when dry. Accepts paint just like the styrene.
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It sounds similar to, but not the same as the Mig AMMO white acrylic glue that i use.
Does the excess glue change colour when you get it wet, and will the excess rinse away with a wet paint brush, before dry?
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Not really a glue. It starts out white, and stays white. Professional acrylic paint comes in a wide range of viscosities, from liquid in a bottle, through pure tint in tubes, to this stuff, which I believe is used two ways, applied directly to the canvas, board, or statue/carving and then painted a color, or tinted prior to application. And yes, the idea is you smear this stuff across the model in the location of the gap. Then using a wet cotton swab, or a paint brush, remove the excess until only the gap is filled, and the surrounding plastic is visible. I don’t recommend a paint brush, because unless you clean the brush extremely throughly, the modeling paint will ruin the brush. This stuff dries “rock” hard and won’t shrink or crack. Multiple applications will work, if the gap is exceptionally deep, or your first application did not adequately fill the gap.
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