Posts: 2308
Joined: 10/27/2002 From: Woodstock, GA, USA Status: offline
Ok guys, you asked for it, so here it is.
Finally, an american built wood/foam/composite kit that is easy to build and has a flight performance that is second to NONE at the time of this writing. No it isn't perfect, but it's about as good as it gets!
The flight characteristics and testing have been covered extensively elsewhere, so I am going to focus on the building of the plane in this thread.
The weight is easy to make IF you follow my instructions to the letter. If you have better or more aggressive iseas, feel free to chime in, I certainly do not have all of the answers, I only know what has worked for me so I am going to share it.
First and foremost let's talk about weight management. You can NOT build a legal electric VF3 without an accurate gram scale. Unless you're the luckiest guy alive. Weigh EVERYTHING. if you can find a place to shave a few grams without sacrificing too much strength, by all means do so! But I can tell you right now, the 2 easiest ways to control the final weight of the airframe are with the sheeting and the finish.
The majority of sheeting on the VF3 uses 1/16x4x36" contest balsa. DO NOT use any piece of sheeting that weighs over 12 grams! The same goes for the capping and blocks....weigh and hollow everything. Even the leading and trailing edges, blocks for wing tips, tail blocks etc need to be hand picked contest balsa. The lighter, the better. To hedge your bets, get more wood than you need and only use the best pieces. if none are good enough, simply save them for another project and try again. Trust me on this one, this plane flies awesome so it's worth being patient and doing it right.
I'll go into specifics on the finish and sheeting in thier respective sections, but in general, just know that on a plane like this, with a LOT of surface area, you simply can't afford to get lazy. If you do it right and are careful in your execution and equipment selection, you can come out with a 10 lb plane with batteries. The plane was designed for the AXI outrunner (24-26 ounces) and 3 lb packs. it will make weight in this configuration, but you need to follow the directions. It's not hard at all, just don't get complacent.
As a general note, this plane is draggy and has a long tail moment. I strongly suggest using a DEPS system for the elevators and mini servos for the ailerons etc. You need to be thinking of an electric set up with a higher pitched prop. If you install the old industry standard hacker C50-14 and 22x12 prop, you can go have lunch during a downline. This is neat, but wait until that Nats wind comes up....not so neat. but personal preference.
Posts: 2308
Joined: 10/27/2002 From: Woodstock, GA, USA Status: offline
Items needed:
This is what you need to complete the framing of the kit.
-PBG C/F 7/8x30" wing tube and socket -PBG C/F 7/16" stab tube and socket -2 gator style wing adjusters -2 Gator style stab adjusters -landing gear of choice (ES long gear works best, alternative is Comp ARF Integral or Impact gear) -Wheel pants (small) -2 BVM style hatch latches -motor mounting system (Esprit/cambria or "X" mount) -36 pieces 1/16x4x36" contest balsa (LIGHT!) -2-3 pieces of 1/16x4x48" contest balsa (LIGHT) -3 pieces 1/8x4x36" contest balsa (LIGHT) -2 pieces 1/4x4x36" contest balsa (LIGHT!!!!) -2 pieces 3/8x4x36" contest balsa (you get the idea) -1 piece 1/2x4x36" contest balsa (ditto) -1 piece 1x4x36" contest balsa (getting the picture?) -1 piece 2x4x36" contest balsa (this one can make or break ya) -1 piece of 1/8" light ply for misc stuff -West system 105/205 resin for sheeting OR -polyurethane glue (You BETTER know what you're doing with this stuff!) -various CAs (mercury adhesives makes some really good stuff for composite bonding, M100XF) -Straight, flat table -72" straight edge (available at any hardware store) -various sanding blocks, permagrit files, etc -Fuselage jig (optional, but VERY nice!)
Now that I have been using the perma grit files, I don't know how I ever did without them. Especially the round and flat files. They can REALLY make life easy. I use a small hard piece of 3/4" MDF board wrapped in sticky back 80 grit paper for general building, as well as various blocks, bars etc. use the hard 80 grit blocks and the flat perma grit file for general fitting. For sanding sheeting, I use 220 grit paper on a 3m block. I also have a special 90 degree block I use for truing the edges of the wing and stab cores. I'll show you this later....
Ok we'll start with the cores as this is easily almost half of the work.
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Team Cool Power, YS Parts and Services, Mercury Adhesives, Dragonfire Customs, owner Custom Airframes of America
Posts: 2308
Joined: 10/27/2002 From: Woodstock, GA, USA Status: offline
Prepping the cores
Foam is a funny thing. it has internal stresses and 'wet" spots that make life difficult. All you need to know is that the cores were cut weighted on a flat table bottom side down, so always do sanding, weighting etc with this in mind.
When foam is cut, a hairy melted foam crap is left on the surface and the surface is glazed. This needs to be sanded off, but not yet.
First prep the Wing, stab and rudder cores by marking and cutting away the TE 1/4" back and sanding it flush (CAREFULLY) with a sanding bar.
Now install the false ribs and run the wing/stab tube inside and check to be sure the hole is centered and clears the tube. Sometimes the hole for the socket is a bit tight, so wrap some sandpaper around the tube (not the socket) and twist this inside the hole until the hole clears the socket. it should slide freely, but not really sloppy.
Now locate the balsa insert point for the hard points. Cut them out and install pieces of balsa to fit.
Now glue on 1/4" contest balsa strips for the TEs, glue in the false ribs, and glue in the balsa inserts with polyurethane glue. This stuff needs to be FRESH and thin. Wipe off the excess with a paper towel. It should only appear damp. tape the TE in place with masking tape and let dry overnight (or while you're making the skins.)
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Team Cool Power, YS Parts and Services, Mercury Adhesives, Dragonfire Customs, owner Custom Airframes of America
Posts: 2308
Joined: 10/27/2002 From: Woodstock, GA, USA Status: offline
On to the wings.....
On an electric, every gram counts. You don't have the vibration of an engine to worry about, so you'd be suprised what you can get away with.
I like to honeycomb my panels on electrics. I use a different technique on my glow planes, but for the electrics I build, honeycombing the panels saves at least an ounce per panel and shows no ill effects. I know some who swear they can feel the ing twist in flight (I'm not saying they can't, but this plane doesn't seem to care). At any rate, I think it's worth doing.
We can do this for before we ship for a small fee, but it's easy to do yourself if you're well versed with it. Basically you use poster board templates and a small hot knife and just cut away voids in a geodesic pattern. You need to leave at least 3/8" at the edges, and don't get over into the load bearing areas like the wing tube or spars. A little acreful planning though and it's not too bad.
Next, sand the TEs flat with the foam core. be VERY careful and patient with this step so as not to dish the foam surface. What I do is use an 80 grit bar and get it close, then sand it flush along with the entire core surface with a hard 220 grit block. This is the point to sand all of the cores. just break the glaze and get it even, don't go crazy.
The spar slots should be marked. The easiest way to do this is to use a straight edge guide (like the side of a level) and a dremel with a router cage. Use a 1/8" router bit set a hair deeper than the 1/4" spar and just guide it down the straight edge. be careful and patient when you hit the false rib. After this is done, use either your perma grit file or better yet a standard 1/8" steel file from the hardeare store and run it down the slots. Test fit the spars and they should be snug but flush with the top pf the surface.
Sand ALL cores with a 220 grit block and then blow them off with an air hose or vacuum. Keep them clean for the sheeting process.
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Team Cool Power, YS Parts and Services, Mercury Adhesives, Dragonfire Customs, owner Custom Airframes of America
Posts: 2308
Joined: 10/27/2002 From: Woodstock, GA, USA Status: offline
Making the sheeting
True up the edges of the sheeting. I ususally use a long straight edge and trim the edge straight with a new (very sharp) Xacto blade. Do this to all edges.
Next with a block sander (or preferrably an edge sander if you have one), stack the sheeting about 6 pieces at a time and sand the edges true.
Using the atached drawings as a guideline, trim and glue the sheeting together.
Place a piece of sheeting on a flat table. Lay out a piece of masking tape sticky side up and place the edge half way onto the tape.
Next, lay the glued piece onto the tape, taking care working all the way down the seam to ensure a tight fit with no gaps.
Lay the seam over the edge of the table, so the exposed piece drops over the side and exposes the seam like a hinge.
Run a small bead of elmer's white glue down the seam and make sure there are no dry spots.
Close up the seam on the flat table, and wipe off excess with a paper towel. The less glue left on the surface of the wood, the better.
Repeat until the skin is completely glued. Weight down the skins with whatever you have available so it doesn't bow up and open the seam.
Let sit for about 20 minutes, then sand the seams LIGHTLY with a 220 grit block. This creates dust as a fliier to close up the seam. Do NOT try and sand the skins perfectly flush at this time, only create dust and work into the seam if needed.
After the skins sit for about an hour to an hour and a half, carefully remove the weights and flip the skin over. Carefully peel back the tape.
Place the blocks down again, and after about 10 minutes, dust sand this side as well.
Let the skins dry overnight before final trimming and sanding.
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Team Cool Power, YS Parts and Services, Mercury Adhesives, Dragonfire Customs, owner Custom Airframes of America
Posts: 2308
Joined: 10/27/2002 From: Woodstock, GA, USA Status: offline
After the sheeting has dried, trim to final shape and sand flat.
Sometimes thicknesses vary, so you have to match this. The side the tape was on should be down against the table, and sand the exposed side first. Only then flip the skin and sand the other side.
After you have sanded the skins smooth, blow them off with an air hose or vacuum, but get all of the dust off the skins.
Next, spray the skins with aqua net hair spray (just regular old hair spray in an aerosol can). Don't spray them soaking wet, just damp. The skins will curl up and bow like crazy, this is normal so don't freak. let them dry for at least 3-4 hours or longer.
Block sand the sprayed side with a 600 grit block just enough to be smooth to the touch (only knocking down the high spots). After cleaning the dust off the skins, you're ready to sheet the cores.
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Team Cool Power, YS Parts and Services, Mercury Adhesives, Dragonfire Customs, owner Custom Airframes of America
Posts: 2308
Joined: 10/27/2002 From: Woodstock, GA, USA Status: offline
Sheeting the cores
Once this step is complete, you're almost halfway to a framed VF3!
There are a zillion ways to do this. The only things you really need is a hard flat table that won't bow under a few hundred pounds of weight, and some weights. you need at least 200 lbs for the wings. Various clamps and such are nice for the turtle decks too, just use your imagination here.
Here is the simplest way to sheet a honeycombed foam wing core.
Use a good, low viscosity laminating resin like west systems fast or slow cure.
Use a glue syringe for the honeycombed section.
Lay the core on the skin, and mark where the solid section begins. This is the only area you will apply glue to the skin. Always do the bottom skin first.
Glue in the spars with polyurethane glue. You don't need them more than damp.
When you are ready, mix about 18 grams of resin for the solid section per skin, less is better, but this is aceptable.
using a playing card or something similar, spread the resin on the skin in the marked area. To hedge your bet, next roll the skinn area with a foam roller to get it even and soak up the excess resin.
Using a glue syringe, apply a bead of resin to the honeycombed structure. You shouldn't need more than a 1/16" wide bead. on the LE, TE and Tips, apply 2 beads side by side to ensure adequate bonding. Do NOT get crazy here.
Also add a small bead to the tops of the spars, false rib and hinge line area.
Place the skin on the core carefully. Now flip the core, place it in the bottom shuck and repeat for the top side.
When both skins are in place, install the top shuck and begin weighting the core. Take care to align all corners.
As you apply weight, check the LE and TE with a traight edge to make sure the panel is not bowing under the weight.
200lbs is what I would consider minimum. The more weight you can use, the less glue you have to use. The amount of resin you can get away with would scare you.
Later I will demonstrate a vacuum/ carbn veil technique that I have been using.
Let the cores cure in place for at least 24 hours before removing.
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Team Cool Power, YS Parts and Services, Mercury Adhesives, Dragonfire Customs, owner Custom Airframes of America
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