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SEPECAT Jaguar GR3A


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It's been a while since I started a proper build thread. So much of my time has been spent on projects for others - I haven't had time to build something for myself. So after finally clearing off everyone else's "to do" lists, I have actually started cutting some plastic. This has been a long time in the making. Some of you may remember the original computer work I posted some time ago. Old Jag Thread. I have since completely redrawn the computer model and finished the exterior details. After some close scrutiny the plans I used to start the model just were not up to snuff and a redo was in order.

Here are the shots: Keen eyes will find some missing fillets and blends in the surfaces (gun shrouds and engine to fuse join - come to mind). These fillets are really difficult to create on the computer model, but much easier on the physical one - so I opted not to duplicate them.

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The primary purpose of the 3d model is make sure the parts fit together - for example the flaps - I may even make them posable on the real model.

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These are the forms that will make up the internal structure.

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After a long days work - computer pictures turn into real model pieces.

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Edited by Timmy!
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To me these are like watching sausage being made - ugly! Anyway I have a couple more bulkheads to add more balsa sheet filler and auto body filler and sand the whole thing to shape. It was suggested that I include some items for scale - that's why there's a 1/48th scale F-4S and an X-acto knife in the pics.

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I filled the frame with pieces of 1/16" balsa sheet to fill most of the empty space, leaving about an 1/8" or so to fill with putty. (Think plaster and lathe walls). Originally I planned to use body filler but I found a stash of Apoxie Sculpt and decided to try it. Body filler is tougher to work with and requires application, sand, fill gaps and bubbles...repeat...ad nauseum! The Apoxie Sculpt can be applied and formed to the rough shape and sands about the same. It should save time in the end compared to body filler. Here are the shots after application - rough I know - but you can at least see the rough shape. Even though I boxed out a lot is space with the balsa it still took 4 pounds of Apoxie Sculpt to cover the fuselage.

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Also my photo etch work I just received from the etcher. This will be the motivation to keep the project moving - can't wait to play with the stuff!

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So these are shots of the first day's sanding effort. Couple of notes you should be able to see the cross-sections beginning to show through. I previously ran a Sharpie (permanent marker) along the edges to that they would show through and I can better control the sanding process. Really it helps prevent sanding too far and losing the integrity of the cross-section shape.

The Apoxie his hard stuff and sand like porcelain, so I'm using 80 grit paper, and unfortunately dry as lowest grit wet paper I could find was 220 and that sanded too slowly. One of the shots you can see my arsenal of sanding weapons. Next I'll fill the voids where I didn't put on enough putty and then finesse the shape further.

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Got the shape about 90% there, now the last 10% is to get it just right and keep both sides symmetrical. To do that I needed to get the build board ready. The build board is a piece of 1" thick table / desk top I found at a local lumber yard. It's pretty dense particle board with a plastic veneer - I confident to will stay reasonably flat and resist warpage. On top of that I screwed on Phenolic Resin Sheet, approx. 1/8" thick and 24" x 48", this is the smooth rigid base which I can mark and easily slide tools on.

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I made up a couple of stands from 1/2" brass angle. These hold the fuselage up off the build board, such that main panel lines are either parallel or perpendicular to the build board. I have scribed a center-line and reference line forward of the nose, the tip of the pitot tube to be exact. From these lines I can start plotting panel lines on the model. I'll use these to ensure the shape is symmetrical.

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Here are the tools I'm using, a height gauge for vertical measure and right angles and steel ruler for fore and aft measurement. The last shot is the first plotted line, this where the windscreen will join the fuselage.

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As with the rest of the 3d model I decided to re-draw the seat. These are shots of the 2d drafts, that I will turn into 3d drawings soon. Notice I have also been working on the decal art as I go. Really just for fun and to keep interest up.

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Granted not a lot of visually appealing progress, but important work to true up the model. This is how I'm checking progress and adding fillets and structures. Essentially I am laying out points with horizontal and vertical measurements taken from the drawings. This shows the intake splitter and the measurements for the point of the splitter.

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The measurements are transferred to the model (the little penciled in cross).

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Horizontal measurement method - Long rule, set on a point that matches the end of the pitot, and measurements from there give me distance to vertical planes on the model.

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The height gauge gives me parallel horizontal lines on the model.

Laying out the plastic form you can see it's close but not quite perfect, a little massaging will be necessary. This may look a little extreme but with a model this big these little errors will magnify to larger misalignments later. Plus when I build the rest of parts they may not fit - which kills the whole purpose for all the computer work.

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Even though I have been careful cutting out and "precisely" laying out the cross-section forms, the double checking of the model has revealed a few problems. Here's one that's pretty obvious. I noticed while I was rough sanding that the nose looked a little bent up. All the forms revealed nicely and evenly, but when I checked the profile shape with a little plastic profile you can see the big gap!

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Putting the fuse in the jig you can see that the third cross-section measures out fine.

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But once I got to the tip of the nose you can see it's much higher than it should be. The tip of the height gauge should be even with the top of the tube where the pitot tube fits. I'll cut off the nose, reposition it and then reshape it.

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Filleting has begun as well. The gun port fillet is in progress - you can see the horizontal lines scribed in - they represent panel lines nearest the fillet. Using photos I can judge where the fillet should start and end. This is a feel process really - sand until it looks right.

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Same is going to happen here at the engine area. Angled panel lines have been laid out and I'll start finessing this area.

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When I couldn't take the sanding anymore, I started the intake forms. These will be key to getting area where the intake blends into the fuselage. I pulled cross-sections from the 3d model, two each horizontal and vertical and printed them out. Just likes these, which happen to be forms for the windscreen. The print outs have been glued with Elmer's Glue Stick to 0.040" plastic sheet.

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The sheet came from signs I got at the hardware store. Cheap and more importantly big sizes!

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They are then cut out and fit together. I cut interlocking slots into each part so they slide together, just like those old wood dinosaur skeleton models.

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And last but not least, when I haven't had access to the build, I've been going a little nuts on the 3d seat model.

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The fillets are essentially done and I got the gun ports in place. Next up, spine will be built up and the windscreen forms are to made.

Intakes are attached with foil barriers. The splitter area will need to be shaped with the intakes off - I'll post shots of that when it happens. I needed to get the joints and fillets married up to the separate intake sections first that’s why the temporary attachment of the intakes.

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After expending a bunch of brain cells trying to finger out how I was going to get the gun ports done, I think I finally got it. At first blush I thought the interior shape was a square oval, but after finding some good photos I found it was a simple circle. So after contemplating complex drilling methods, I found some styrene tube just the right size. After grinding out the fuse with a Dremel armed with a sanding cylinder, I glued in the tube. Filler applied and some sanding and trimming, I think I got the opening really close.

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While I was at it with the Dremel I got the exhaust area worked out too.

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Finally, I chopped out the section where the windscreen will fit.

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As for the model I did fill in and shape the spine and windscreen. Also made a plaster form of the windscreen to vac form an acrylic part. Photos of that progress soon.

In the mean time, while away from the shop, I made progress on the seat. As I may have mentioned before this is more a test of my CAD skill than useful effort toward the model. It does make for some half good renders and continuing motivation to push forward.

Here are some shots.

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Good progress on the clear parts over the last few days. These parts will help me finish up the final contours of the forward fuselage. The next immediate steps will be to polish the interior of the clear parts and add interior structure and detail. Then blend and fair in the clear parts per the prototype.

Here are the forms in place, they are 0.030" smaller to account for the clear material. The plugs were then quickly cast in plaster of paris to make new heat resistant plugs. The Acrylic must be heated way beyond the melting point of styrene and if formed directly over the master plug the acrylic would melt the plug.

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Here is the formed clear windscreen. As you can see it's not perfectly smooth - the slight rough texture on the plaster transferred through - but not to worry it will polish out nicely.

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A little more progress, this time I been able to do some detail work that has been a nice change of pace.

The windscreen has been polished out and is nice and clear and smooth. I have added framing on the inside made from 0.005" plastic super glued to the acrylic. The center frame is 0.010" sheet glued to the outside and creased to form the proper angled or faceted appearance. There is also fastener detail embossed on the frame, unfortunately it doesn't show up well in the photos - I'll work on that. Little more framing to go and then I'll temporarily attach it to the fuse and work on the fairing. Still puzzling exactly how that will go down.

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One last shot of a new tool. Sharks with laser beams on top of their heads! Ok just one and without the shark and it's actually a laser level. It's working well so far and quicker, here I'm using it tell recheck the placement of the windscreen.

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Finished up the framing on the windscreen. Starting with sheet aluminum outer sections and fore and aft running frames on the inside.

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Then the bird bits keeper outer.

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The fairing process has begun. This is Apoxie formed to shape. The areas on the lower sides of the windscreen will be faired in next. (Hang on Scratcher - you'll see - I promise!)

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These ones were a little tricky but they look pretty good and even the bends around the windscreen fairing worked out well. Hope it portends the future of the paneling process.

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Windscreen temp attached and the roughed in the fairing. Again this is Apoxie Sculpt.

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Just about finished up the windscreen fairings. Still a little work to do but the windscreen is just about read to get popped of so I can finish the detail work. There wasn't much to do here just smooth out the Apoxie Sculpt and add some fastener detail. Also I added the curved ramp structures at the corners of the windscreen where the canopy seal will fit.

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While the Apoxie was setting I tackled the intake separation. A grove was cut to allow a 0.040" strip of styrene to be fitted. The aft edge matches the panel line where the real thing separates from the airframe. The strip was then glued to the froward portion, then sanded flush and the intake snapped off.

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On the bottom edge an angled piece was made to capture the fillet at the bottom of the intake. A notch was cut into the forward portion to allow everything to fit back together.

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Took a bit of puzzling to get it all to work but the fit is nice and tight and hold together pretty well without glue.

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accomplished some more work - mostly mundane stuff - but I did get the windscreen 99% complete. Lots of screw retainers added on the inside and a few other details.

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Also I finished off the intake joints. This involved getting the other intake carved out and the joint roughed out. I tuned up the joints by re-attching them with a foil barrier and filling the remaining gap with JB Weld (aluminum filled two part epoxy). This left a nice hard edge that left a super tight joint and a press fit of the parts.

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Last but not least the canopy has been vacuum formed.

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So after attempt 5 (probably 6) I finally got the chisel nose correct. In fact, I rebuilt the whole thing including acrylic sheet at the window locations. In the photos the acrylic is covered by white vinyl tape - i chose the acrylic so I'm assured a clear section when the casting is done. With the new nose in place I did a little sheeting. I use paper templates taken from the 3d model where possible, print them out, glue them to aluminum sheet cut out and apply. The larger piece was created with partial patterns printed from the plans and masking tape to make a pattern to transfer to the aluminum. A good bit of trimming and test fitting and I got it to fit. More on this process in the next update when I have more photos to share.

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The aluminum work continues. Although it started by the ripping off the panels fwd of the windscreen. Turns out the skin was is not symmetrical (from left to right) on the prototype, as I assumed is was when I drew up the pattern in the computer. So as is so often the case with scratchbuilding a "do over" was in order. Most of rest of the panels, applied so far, needed some a good bit of fussing, planing and tweaking to fit to with model with proper joints. There are few flat surfaces that allow panel sections to be taken directly from the plans. Some follow up work at the joints is still needed in order to differentiate hatches and doors from skin to skin joints. I probably run some paint it the skin to skin joints to fill and unify them a bit. I know this the will doom the model's chances at an IPMS event for uneven panel lines but it will look more like the real thing. Also note the triangular holes that will receive NACA ducts, which have been built just not photos for proof just yet.

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Here's a shot of some of the pattern work completed on the computer (note wing structure patterns a done).

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...more computer work while I'm away from the bench. I am still surprised how accurate the method of relative scaling works; that is the process of guessing the size of smaller parts by judging their relative size from larger known ones. For example, I found the actual tire and rim sizes online, fed them into the computer model and they were almost dead on to the size I guessed! Yea Me! This is empirical proof that if it looks right it is right!

Anyway on to the update. I drew up the nose gear and forward doors. Through a bit of trial and error and a little geometry I have managed to make the gear "retract." The trick was to find all the pivot points and the right lengths of the arms on the main leg and doors. I was initially approaching the retract experiment just to see if I could do it, but the process also helped make the gear more accurate. I found that the gear doors were slightly misplaced when retracted. (Good thing I didn't get those in place on the model yet). Now wether I build them to be retractable remains to be seen.

On to the photos...er renders.

Gear Down

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Gear Up.

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Today's update is more foil work plus some detail work.

Let's start with the detail work. This is the external canopy jettison handle and it's enclosure. The hardest part was the clear frangible panel. This was made from 0.030" acrylic sheet scribed, rounded slightly and polished. The shots show the first two reject parts. A "bezel was made from a few layers of clear 0.015" sheet that were cut such that the frangible clear part snaps in. Finally a layer of aluminum was fit on to get the fastener detail. These two parts will be permanently joined and cast in clear resin later.

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The rest of the assembly is a square oval tub that holds some interior detail, that represents the cable and pulley system that activates the canopy jettison system. Finally the "D" ring. All these parts will be cast as separate pieces and used on the left and right sides of the model.

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Some panel shots - they speak for themselves - note the hole started on the left side.

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More soon!

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Timmy,

Very inspiring work! :thumbsup:

Two quick questions if you don't mind. I know your OV-10 took a few years to complete, what's the timeframe for this build? Second, I see you are building a computer model for pattern work. During this build, are you going to have any data from the computer model printed(or grown) via 3D printing or SLA?

May the Force be with You!

Steven L :wave:

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