3D Viper-ST 100-120cc scratch build......it continues!

[Terryscustom]

Well, here we go then. I got some time today to cut a couple of fuselages and some partial fuselages to do some testing for carbon longerons vs spruce longerons. I'm also cutting from light ply that I have previously not used so I want to double check that for consistency and strength of materials. I got some super good quality poplar light ply that is clear on one side (no knots) and 95% clear on the second side. I also got some super good 3-ply Baltic birch that is very strong. It also cuts very clean.



So far the lite ply is the cleanest cutting I've ever cut and comparing weights on the birch of cut parts it is very slightly heavier but bending strength is stronger than the birch I've used previously. Not all parts, but here are a few shots of the parts cutting.



Also the spruce 1/4" sticks I got from National Balsa are not cut on a high precision saw so they are a few thousandths off. I am lasering parts to more accuracy than a few thousandths so what I will end up doing is supplying longeron material with the laser parts. Again, this is if the kit part of this all comes together. I can sand 30-40 sticks at a time with much more accuracy than their saw so it will work better for the kit builder.



So for creating longerons: They must be scarf-jointed for strength. There are a couple ways to make a scarf joint but I prefer the disk sander. If you don't have a disk sander you can simply clamp a block over the sticks at an angle and use a razor saw to cut them. Finish with a sanding block for a perfect fit if needed. Test fit by holding the sticks against a known straight edge like an aluminum angle. I like to glue with wood glue, let dry and chase with thin CA. Then sand with a block to smooth the joint completely. Joints should be .75-1" wide and tightly closed as shown. If there is a gap, sand further before gluing!

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[ericb]

Looks awesome.

 

[Terryscustom]

Couple things that are cheap and nearly indispensable to building:

1 - Syringes for glue. These are great for wood glue and can be washed, they are super for applying "goop" in all kinds of places in a nice bead of a controllable size. They are also super for epoxy and can be washed out with denatured alcohol and re-used after epoxy. http://www.amazon.com/dp/B00L9IALK6/ref=pe_385040_121528360_TE_dp_2



2 - Clamps!! One of the best smallest investment is a couple hundred of these clamps, for an occasional builder a box of 100 is cheap and easy: http://www.amazon.com/HTS-104S1-100pc-Metal-Spring/dp/B0009T65OM/ref=sr_1_18?ie=UTF8&qid=1411359783&sr=8-18&keywords=2%22+spring+clamps

 

[Robbins]

Dude thanks for the tristock and the syringe. I will have a box of 50 coming soon!

 

[Terryscustom]

First step is to lay out all parts and make sure everything is in order. No sanding of any joints is required because I have taken care to make sure the laser power and speed is set to just cut through and leave a slight tan. No "burn" is left at all. I have done tests with several glues and this has no effect at all on the joint integrity.



Step one is to assemble the parts that have the dove-tail joints. I have designed these joints to have an interference fit. They tap together with few "light" taps of a hammer or rubber mallet working form one end to the other. These joints are very tight and hold together with no clamping pressure (notice pic that no light shows through). These joints get glued with thin CA after assembly as shown. They will later get further supported with either fiberglass and resin or thin balsa, after fuselage assembly.



At this same time there are two hard-points for the canopy bolts that get tapped into the fuse sides and thin-ca'd in place. These should be installed from the outside of the fuse (flush with the back) and glued on the back. Then sand the outside flush.



The SFG's also have two parts made from birch and two from lite-ply. Install the hard-points in the light ply halves, glue with thin CA and sand flush.

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[Terryscustom]

Installing longerons. The longerons are all glued and set. All four are made from a 48" section and a 24" section. When installing, each fuse side should have the bottom longeron with the scarf joint towards the front of the fuse and the top longeron with the joint towards the rear of the fuse. This location uses the turtle deck sheeting and belly pan sheeting to further strengthen where these joints are located.



I like to use Gorilla wood glue for most of the basic plywood to plywood and plywood to solid wood joints. It dries fast for low clamp time, does not try as brittle as titebond and but is wet enough to soak into and grab plywood well. Apply glue to longerons but "more" is not "better"!!! You just need enough glue to smear along the longerons to get a thin coat of glue. Excess glue is just a mess and adds weight. There should be very very little squeeze out after clamping. I left the longerons long and will trim to fit just before the sides get installed.

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[Fibertech]

Terryscustom;19464 wrote: One other thing to look forward to on this thread in the coming months......I really really hate talking on a video or basically being video taped in person in any way. BUT, just for you guy's that are afraid of vacuum bagging I plan on doing a couple of vids on just how simple, easy and inexpensive it can be. Not to mention the awesome results that you get compared to other methods. I'm thinking a combination of video and time-lapse on the go-pro. FixedWing gave me grief for just shy of two years on FG before I tried it......now I have several bottles of poly glue on my shelf that I use only for weight and collecting dust.

I too didn't want to take the time to set up a vacuum bag system for years. Know that I did I won't do with out it. Much better results with vacuum bagging and doesn't take much time to do. When Terry gets to the vacuum side of things I'll mention some places I purchased parts to build a vacuum system when doing the Slick build on the other place.

 

[Terryscustom]

Now onto the fun part, getting a fuse assembled. For those that have followed my other builds you already know that I have designed my fuselage's to be a very strong but yet quick and easy to build item. I have labeled the main engine box sides with an L and R so that it should be easy to not get them backwards during assembly.



As with ALL parts, ALWAYS ALWAYS test fit and make sure there is a clean fit with NO GAPS!! Gaps in the joints can render a good structural joint as nearly useless. I've taken great care in designing these to fit together tight. Once F-1 is test fit I simply tip it back and apply glue with a syringe and wipe off excess after clamping.



This is also a good time to install HALF of F-2b (small former at back of landing gear area The other half will be glued in at the same time as installing the floor.

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[Terryscustom]

After that sits for a few minutes it's time to install the floor and the rest of F-2, F-3 and the external portions of the floor / side fillers.



First test fit and install the floor. There is a lot of glued parts of this that all have to go in and get clamped in a timely manner so it's a good idea to plan the clamping strategy and have the clamps all laid out and handy so it goes quickly.



Next is the install the F-3 former(s), these are basically just two caps that fit in against the floor and rear of the engine box sides.



Next is the F-3 former(s). Again, two pcs simply glued and clamped in place. If you are going to leave these for any length of time before installing the rest of the side floor fillers, make sure to use a square and square these up with the engine box sides so they dry at the correct angle. There is no need to wait though, simply go right into test fitting and installing the side fillers as shown. Again, TIGHT JOINTS are critical. This will ensure the F-1 is straight and F-2(s) are at the correct angle.



Let these parts dry before starting on firewall and engine box top / bottom.

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[Terryscustom]

BTW, I've seen a lot of people post comments about not building because they don't have the tools so I'm trying to build this one with as few "fancy" tools as possible so show it can be done easily with minimal tools.



OK, firewall.....where all the action happens. You don't even have to measure or use any fancy triangles or anything because the 2* right thrust is built right in and as long as you test fit and install everything tight it will all work out fine.



The engine box bottom and firewall get installed at the same time so it's important to test fit those together and install at the same time so that the sides can be spread apart enough to get them in place. For simple clamping just use some flat scrap wood and a single clamp if that's all you have. Make sure the clamps are perpendicular to the engine box sides though, and not clamping along the angle of the firewall.....and don't clamp down any more than is needed to close the joints. Too tight or wrong angle and you can distort the front of the engine box assembly. You can use epoxy for the firewall but I prefer standard wood glue for this part.



While that dries I cleaned off the glue from the back-side of the firewall and cut some 1/2" basswood tri-stock to go around the back. Starting with the bottom keep in mind to make a recess to allow for the blind nuts or other fasteners for installing the engine. Next cut the sides. A quick tip to get a good cut if you are using a power miter saw is to use a pc. of scrap and hold the tri-stock against that. It's much safer and you get a cleaner cut. The side tri-stock is cut to fit flush with the underside of the engine box top. Also the one on the right is actually a 47* inside corner so I modified the angle slightly with a sanding block to make it fit tight.



I install this tri stock with a liberal amount of trim and molding glue from Tirebond since it does not harden to the state of being brittle and is gap filling so it does not shrink excessively. I apply way more than needed and wipe off the excess before clamping. This makes sure there is no voids behind the tri-stock. Repeat for sides. Let this dry for a while before installing engine box top.

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