Downen Scaled Replicas Posted August 6 Share Posted August 6 When I first saw photos of the General Atomics Predator C “Avenger” I was impressed with the design and the “mean” look of the vehicle relative to many other uncrewed aerial vehicles (UAV). No kits have yet emerged for the Avenger, so many, many months ago I began tackling the design. With complex curves that seem to shift and change with every new reference photo, it’s been an off-and-on project which, finally, is approaching completion. The Predator C first flew on 4 April 2009 employing a turbofan engine and incorporating stealth features, both of which were perhaps firsts for a General Atomics vehicle (?) At least two versions of the vehicle have been developed to date; the first was initially referred to as the “Predator C” and later “Avenger”, while the second, larger, vehicle is known as the “Avenger ER” and has recently been referred to as the MQ-20A in press releases issued by General Atomics. See The WarZone (https://www.twz.com/42906/this-is-a-great-comparison-between-general-atomics-avenger-drone-configurations) article dated 28 Oct 2021 for a comparison of the two models. Reports indicate that several Avengers (although it’s unclear which version) have been sold to an unspecified United States government entity and perhaps deployed in the Middle East. Foreign sales have been mentioned in the media but no actual sales or deliveries have been confirmed. See another great The WarZone article dated 1 December 2019 for more speculation regarding Avenger deployments (https://www.twz.com/26791/pocket-force-of-stealthy-avenger-drones-may-have-made-returning-f-117s-to-service-unnecessary). My design represents what may have been an early Avenger ER configuration with the longer forward fuselage but lacking winglets. The above photo has been used to baseline the major external features of the vehicle including lack of winglets, location of various antennae, presence of EO/IR targeting system, etc. Although great efforts have been taken to develop an accurate representation of the Avenger, the model has been designed using only materials available in the public domain and may, therefore, inaccurately represent certain details that would otherwise be available only via proprietary information. With CAD work (mostly) complete, it’s time to lay out the parts for printing. I’ve already done one rough prototype to work out major issues; this will hopefully be the final prototype prior to production. The parts fill one complete build plate on a Saturn 3 Ultra. I use Siraya Tech ABS-Like Navy Grey since the darker pigment tends to capture fine details and the resin is easy to sand and not overly brittle. This print will take approximately 13 hours at 20 microns layer thickness. There is a second build plate for the display base. Time to go get a cup of coffee while the printer works! POSTSCRIPT: This will be released as a kit in the very near future. Visit the website (downenscaledreplicas.com) and join the mailing list for updates on this and other kit releases. Quote Link to post Share on other sites
ST0RM Posted August 7 Share Posted August 7 Well, this will be interesting and exciting. -Jeff Quote Link to post Share on other sites
Downen Scaled Replicas Posted August 7 Author Share Posted August 7 Just saw this posted by Aviation Week on July 31. We’ll see what develops… MQ-20 Emerges As New Candidate For Adversary Air Surrogate A new U.S. defense project is devoted to converting two General Atomics Aeronautical Systems Inc (GA-ASI) MQ-20 Avengers into air-to-air adversaries for training fighter pilots. The jet-powered uncrewed aircraft systems won the $98 million contract for Project Red 5, a prototyping effort led by the Test Resource Management Center (TRMC), an arm of the Office of the Secretary of Defense. The contract calls for GA-ASI to modify the Avengers with new sensors, data links and advanced mission systems, allowing them to role-play as air-to-air threats during training missions. The full article… https://aviationweek.com/defense-space/light-attack-advanced-training/mq-20-emerges-new-candidate-adversary-air-surrogate?elq2=6b804e55867f4b78b049e921bc1ca824&sp_eh=1c91113b7532da927b56289a29644387b80451a62f7bd88895f72f34c1bd7495&elq2=6b804e55867f4b78b049e921bc1ca824&sp_eh=1c91113b7532da927b56289a29644387b80451a62f7bd88895f72f34c1bd7495&utm_campaign=47081&utm_emailname=AW_News_DefenseDigest_NL_08072024&utm_medium=email&utm_rid=CPEN1000000178681 Quote Link to post Share on other sites
Downen Scaled Replicas Posted August 10 Author Share Posted August 10 All parts printed, most still with their print supports intact in this photo. Everything seems to have printed well, although there are a few edges that need more supports so that the edges aren’t quite so ragged. I find that 3D printing is almost as much an art as it is science. That’s why 2 or 3 prototypes are typically required before all the issues are worked out with a new design. Even then, I still tend to find small issues that require design tweaks months or years later. Note the 3D printed display base and the 3” long brass rod for displaying the model in flight. More on this later… Layout and assembly is broken into three major parts for the fuselage (forward, mid and aft) with “plugs” for alignment and a firm join, and also a separate inlet “cap” and S-duct on top for the engine. Wings are separated into inboard and outboard sections. The model is broken into all of these different parts to yield the best possible 3D print with minimal print lines and the fewest areas that will need cleanup. Still, there will be work to be done… (this ain’t Tamiya… Ha!) I find a combination of sprue cutters (“nippers”) and a micro saw work best for removing print supports. For example, gently drag a micro saw across the attach points to avoid breaking off part of the model with the support, just as you would with a sprue gate on a plastic injection molded kit. A neat trick is to use a hair dryer or heat gun (carefully) to warm the print supports. This will make them “rubbery” and much easier to break off the model. It’s a fact of life (a fact of 3D printing) that anywhere a print support attaches to the model, there will be “nubs” remaining that need to be cleaned up. Another “art” in 3D printing is learning how to hide as many of these nubs as possible, and where to locate those which can’t be hidden so that cleanup is as simple as possible. On this design, most have been placed on flat surfaces away from details and panel lines. The good news is that this resin is easily sanded using 320 to 400 grit wet/dry sandpaper. Use the paper wet to control resin sanding dust, sand gently and check progress often. Note that panel lines are in evidence on the full-scale vehicle at the wing roots, along the sides of the inlet and numerous other locations. Many of these panel lines have been used as natural locations for parts to be joined on the model kit, so check references before filling and sanding joints. Now it’s time to dunk these parts in soapy water to remove sanding dust and prepare them for assembly. Parts will be left overnight to dry. More updates on the way… POSTSCRIPT: A Few Words on Water and Resin I’ve already heard the outcry through the Interwebs… “3D printing resin absorbs water! Don’t’ get it wet!” Well yes, but… If water (or isopropyl alcohol - IPA - which is often used to clean residual liquid resin from the surface of 3D printed materials) is left on the resin for an extended period, the resin will absorb the water (IPA), swell and perhaps crack. That can lead to a bad day depending on the extent of the damage. In my experience, it’s okay to get the resin wet during sanding and to wash it to get any residual sanding dust off the surface. And, of course, all parts get dunked in IPA for a “bath” immediately after they come off the printer so that residual liquid resin is cleaned from the parts. The key is to not permit the resin parts to sit with puddles of water (or IPA) for an extended period. After wet sanding and washing the parts, shake them out, blot them dry and position them on a towel or other absorbent surface so that trapped water can run out. Make sure they’re in a well-ventilated area so they can dry at a reasonably normal rate. Put a fan on them if you’re really worried about it; I have a small desktop fan to speed IPA evaporation after the parts have come out of their post-print wash. I will sometimes use a can of compressed air to blow out recesses where water collects. For the most part, if you practice common sense then you shouldn’t have problems. If you do find that water has been trapped overnight, for example, and an area on the model has swelled and/or cracked, first ensure that all residual water is now gone. Then go into “modeler mode” and practice your normal filling and sanding techniques to fix the damage. Quote Link to post Share on other sites
Da SWO Posted August 10 Share Posted August 10 This will be built as an in-flight model? Quote Link to post Share on other sites
Downen Scaled Replicas Posted August 13 Author Share Posted August 13 On 8/10/2024 at 3:02 PM, Da SWO said: This will be built as an in-flight model? Yessir. That's correct. I've designed a display base, which I'll start work on shortly & post here. Quote Link to post Share on other sites
Downen Scaled Replicas Posted August 13 Author Share Posted August 13 It’s a good idea for me to pause now for a bit of pre-assembly painting. It will be difficult / impossible to access the engine fan & mixer parts as well as the inlet and exhaust ducts after assembly. On the 1:1 scale Avenger prototypes the inlet color appears to be the base color of the overall vehicle. On this build I’m going to do a hypothetical Have Glass V operation paint scheme, so I’ll airbrush the inlet the lighter shade of gray FS36270. The boundary layer diverter will be airbrushed the darker FS36170 since it, too, will be difficult to access once assembled. I like Mr. Paint’s (MRP) Have Glass acrylic lacquers and will be using them for these two colors (MRP039 Haze Gray and MRP280 Camouflage Gray). The engine fan face and mixer will both be hard to see on the completed model without shining a flashlight into their respective ducts, so I won’t spend too much time on them. Tamiya TS-17 rattle can gloss aluminum for the fan face, and Alclad 113 Jet Exhaust for the mixer. The exhaust duct appears to be a dark, possibly soot-stained high temperature metal. I’ll use the Alclad Jet Exhaust again. Woo hoo! It’s FINALLY time to start assembling parts. My fourth favorite thing in the universe… It goes without saying (but I’ll say it anyway): Use only cyanoacrylate (CA, or “super”) glue or epoxy glue… Plastic cement WILL NOT work on resin parts. A couple snapshots of the inlet assembly. The lower S-duct is attached to the upper S-duct part, then the fan face is put in place and thin CA glue is run around the edges. Refer to that assembly guide / exploded view earlier in the thread and you’ll see how most of this thing goes together. I am focusing first on the fuselage so that I can do any general cleanup of joints without risking damage to the outboard wing and tail parts. Here it is joined together and ready for work on the joints. Note that panel lines are in evidence on the full-scale vehicle at the wing roots, along the sides of the inlet and numerous other locations. Many of these panel lines have been used as natural locations for parts to be joined on the model kit. At 1/48 scale the fuselage length overall is a little over 11 inches, and the wingspan should be just shy of 17 inches. It’s now that one begins to get a sense of how large this vehicle is… It’s impressive considering that it’s a UAV! These aren’t the RC airplanes I used to play with as a kid. Time for a breather before filling and sanding those joints. Quote Link to post Share on other sites
Da SWO Posted August 13 Share Posted August 13 I buy one if you decide to sell these. Quote Link to post Share on other sites
Downen Scaled Replicas Posted August 13 Author Share Posted August 13 Cruise over to my website (noted in my signature) and add your name to my mailing list. I'll be sending out a notice once the kit is ready. Thanks. --Troy Quote Link to post Share on other sites
Downen Scaled Replicas Posted August 19 Author Share Posted August 19 A brief pause while I check seams on the fuselage… A display base approximately 4.75 inches in diameter has been designed to accept a 5/32” brass rod for mounting the Avenger in “flight mode”. The base has raised detail representing a stylized Avenger. My process for painting display bases such as this is summarized in the accompanying photo. After priming, the base is sprayed overall in Tamiya’s TS-26 lacquer gloss Pure White. Tamiya’s rattle cans have never let me down; they atomize well and the paint self-levels to a smooth, tough finish. The vehicle is intended to be gray, so all text and raised edges are masked to keep the gloss white clean before two shades of lacquer gray are put down on the Avenger. It is important that these initial coats of paint be impervious to the scrubbing with Windex and isopropyl alcohol which will follow. All masks are removed. Sometimes I’ll complete the lacquer coats with one final clear coat just to tie everything together. Tamiya TS-13 Gloss Clear is my lacquer of choice. The recessed areas of the base will be dark blue, approximating General Atomics’ corporate colors. The entire base is given several coats of acrylic (important note: ACRYLIC!) blue paint. In this case, Tamiya’s X-4 Blue seemed like a respectable match. After about 15 minutes of drying, the process of removing the acrylic blue paint from the raised areas begins. (Yeah, Step 3 in the photos above shows blue paint removal on a different display base… I forgot to take a photo of the Avenger display base at this stage.) A combination of cotton swabs and soft cloths (old, but clean socks) wetted with Windex are used to scrub the raised letters, outlines, and vehicle to remove the acrylic paint. Because the white and gray paints are lacquers, the Windex will not affect those paints. Removing the blue requires patience and some scrubbing as the Windex slowly loosens the acrylic paint. Change out cotton swabs often! For stubborn areas, isopropyl alcohol (IPA) may be used as a “nuclear option” but Windex is generally preferred as it’s a bit gentler than IPA and accidental swipes against areas where blue should remain won’t immediately mar the blue. Smaller details such as the exhaust and inlet areas are hand painted black, and the entire base is then clear coated with acrylic gloss (Tamiya X-22). Note that once the acrylic paints were laid down, I have avoided putting lacquers on top of them since the “hotter” lacquer solvent will attack the underlying acrylic. That makes for an unhappy day. Okay, back to the model itself… Quote Link to post Share on other sites
Downen Scaled Replicas Posted August 22 Author Share Posted August 22 Unfortunately, I failed to take a photo of my preferred process for filling joints (gaps) on 3D printed resin models. I use the same liquid resin which was used to print the model. The resin is siphoned off into a squeeze bottle with a needle applicator (20 gauge if I’m not mistaken). The resin is run into the joint in question, and then exposed to UV light for a few seconds to cure it in the joint. This should only be done in thin layers so that the UV light can cure the entire run of resin. Since it’s the same material, the filler basically becomes part of the model. Once sanded, the joint should disappear like it never existed. I have a small UV flashlight that I use for this. After much practice, I’ve developed a skill for holding the resin applicator in one hand, the UV flashlight in the other, and filling joints rapidly as I hold & rotate the model using spare fingers, palms of my hands, elbows and whatever else comes in handy. This is where I think chimps have the best of us… they have prehensile tails. Funny that I’ve never seen a chimp work a model, though… Now, that said, all popular hobby fillers are compatible with the resin in this kit, and if I didn’t use the resin filler technique, I would opt for CA glue as a gap filler, Tamiya filler putty or any other filler you might prefer. I’ll confess that I still find hairline cracks frustratingly difficult to fill, even when I throw Mr. Surfacer 1000 or a scratch fill primer at them. Curse you, hairline cracks! Okay, shake it off… move on… The outboard wing sections were joined to the inboard sections so that some time with 400 grit sandpaper could be spent on the wings without having the fuselage in the way. Just a bit of cleanup top and bottom to remove any last vestiges of print lines. On the 1:1 scale article there is a panel line where these two sections join, so I didn’t spend time with filler to make that joint disappear. I did, however, dab some Mr. Surfacer 1000 into the joint just to downplay it a bit. I vaguely recall reading that the outboard wing sections on the Avenger fold for more compact storage in hangars and for possible use on aircraft carriers. No reference photos have been located to confirm this, however. The inboard wing sections join to the fuselage via a large airfoil-shaped tab. This should ensure a good fit with correct dihedral and wing incidence angle. Again, there is a natural panel line on the full-sized vehicle at this joint so I elected to skip the filler (again). Tamiya Fine Surface Primer is my go-to for a robust and smooth first coat of paint on the model. I’m looking mostly for any residual 3D print lines that escaped my attention earlier, but none are really showing up. I’m still obsessing over a few panel lines that I’d like to clean up on the aft fuselage. It’s probably just time to let them go… I’ve debated whether my preferred black basing airbrush technique is really appropriate for these otherwise well-maintained and clean prototypes. Ah heck, I’ll go ahead and do it anyway. I go back and forth between Vallejo’s Surface Primer and Ammo MiG’s One-Shot Primer for my black base (or, in some cases, dark gray base). Frankly, I wonder if they aren’t the same thing. Both go down without thinning but will clog up my airbrush over an extended period of spraying. I was just able to complete one coat of the Vallejo Surface Primer here before enough of the paint dried in my airbrush nozzle to clog it. Time for a tear-down and thorough cleaning. It happens every time… By the way, both the Vallejo and Ammo MiG primers go down fairly smooth, but leave just enough of a rough surface that I’ll give them a light wet sanding with a 1200 to 3000 grit sanding sponge before proceeding to the base color coat. Okay, everything needs to sit and cure for a while before the first color coat goes down. Quote Link to post Share on other sites
Da SWO Posted August 23 Share Posted August 23 On 8/13/2024 at 4:22 PM, Downen Scaled Replicas said: Cruise over to my website (noted in my signature) and add your name to my mailing list. I'll be sending out a notice once the kit is ready. Thanks. --Troy I did, also looked at the other two models. Loos good, can hardly wait for them to be available. Quote Link to post Share on other sites
Downen Scaled Replicas Posted August 24 Author Share Posted August 24 I’m going to pivot on the color scheme for this model… yeah, I’m a flake that way… Rather than a Have Glass V scheme, I’m going to go with the flying prototype’s two-tone camo and use some Hataka Orange (lacquer) paints that have been sitting on my workbench for a few months. This will be my first experience using Hataka’s line of paints. Initially I assumed that the Avenger / Avenger ER test articles were in an F-16 style two-tone camo using FS36118 Gunship Grey over FS36270 Haze Grey (or variously Neutral Grey, Medium Grey, etc.). But once I sprayed paint chips for those two colors in the Hataka range, they both looked way too dark for what I was seeing in photos. I finally settled on FS36231 Dark Gull Grey over FS36375 Light Ghost Grey. The Dark Gull Grey created the contrast seen in photos which an F-18E/F style FS36320 Dark Ghost Grey just wasn’t revealing. Putting down the first coats of paint on a new model is where I really start having some fun. To help give the otherwise monotone light grey base coat a bit of character, I’m using a black-basing technique. I’ve already laid down the overall black base and given it a light rubdown with a 1200 grit 3M sanding sponge. The photo collage shows the results of the three painting sessions over which I applied a mottled grey color coat over the black base. In the first session I tried to create a stark light/dark random pattern over the aircraft. This was done freehand with the airbrush about an inch away from the model, air pressure at about 10 psi, and paint thinned approximately 50/50. Just squigglies… no masks or such. In the second session I add more thinner and back off from the model, trying to get more grey on the model without obscuring the light/dark pattern from the first session. Finally, in the third session I’m working with approximately 30/70 paint/thinner, still at about 10 psi, and just building color until I’m happy with the overall appearance. I try to stop just before I think I’ve reached the end because I find that I tend to over-due that final color coat. Given that the Hataka Orange paints are lacquers, they dry quickly and I can move from one airbrush session to another fairly rapidly. The camo pattern is lightly sketched with a No. 2 pencil using photos of the test articles as reference. The Dark Gull Grey pattern is first outlined with about a 40/60 paint/thinner ratio, then filled in over two different painting sessions. After staring at it for a while, the overall results seem satisfactory. The model gets a good coat of X-22 Gloss Clear thinned 50/50 with Mr. Color Leveling Thinner. Getting there... (!) Quote Link to post Share on other sites
Downen Scaled Replicas Posted September 2 Author Share Posted September 2 In addition to lines defining the control surface locations, photos of the flying test articles consistently show a handful of prominent panel lines on the vehicles. Those have been recreated on the model. To get the engraved panel lines to “pop” for photos, my darkest grey enamel panel line wash (PLW) was applied over a coat of Tamiya’s X-22 Clear Gloss acrylic thinned 50/50 with Mr. Color Leveling Thinner. Normally I would use a slightly lighter grey for this PLW, but this build is intended to be photographed for marketing the kit and the darker color will ensure that the engraved lines are evident. Waiting for the enamels to dry, time was well spent at the computer getting the box art for the kit put together. After many, many months of designing and test prints, I can finally see this project coming to a close! Quote Link to post Share on other sites
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