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Discussion Starter · #1 ·
Stix3D 27" - Construction and Plans

Last winter I joined the local RC club so I could fly indoors during the winter. They rent half of the Sports Dome for club flying. During the last winter I built quite a few different foamys trying to get them to fly as best I could. By the time the winter was over I had developed a fairly good flying plane. While a foamy looks simple enough there is a lot that goes into it to get it to fly well.

But this year I decided I wanted to try something different. I keep wondering if a proper airfoil will fly better than the flat plate or KF airfoils on a small indoor size plane. I have tried to built full airfoiled wings from foam with less than ideal results so I thought why not just build a small balsa profile plane same as we do the larger ones. The question was could it be built light and strong enough.

It has probably been tried before, there is not much that hasn't, but I could not find anything here or on a few other sites.

I have been using the power system from my miniPBF for power.
This system will pull an 8 oz PBF around with good authority and the foamys were coming out slightly over 7 oz flying weight so if a balsa plane can be built at 7 to 8 oz it should fly good.

I decided to built in the typical build method we use for most of our slabs, it works for the bigger ones so there should be no reason it will not work on a little one. I am going to use a thick Funfly airfoil on it to try to slow it down and make it as floaty as possible. Same size, outline and moments as the foamy because I know they fly well with them.
 

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Stix27.JPG


Design Specs

Wing Span ----- 27 in
Wing area ----- 250 sq in
Length -------- 29.5 in
Flying weight - 7 oz
Wing loading -- 4 oz sq ft
Motor --------- 2122 (250 size) 1800 Kv on 2S, 1200 Kv on 3S
Battery ------- 500 to 800 Mah on 2S, 350 to 500 Mah on 3S
Prop ---------- 8x4
Servos -------- 4 5 or 6 gram
 

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Discussion Starter · #3 ·
Plans

Anyone wanting plans just pm me with your Email address and I will send you, at no cost, a zip file containing the drawings, builders manual and materials list for the Stix27 in tiled PDF format so they can be printed with home printer.

Seven sheets of legal (8 1/2 X 14) size paper will be required to print them out. I use legal size to keep the number of sheets to a minimum and make gluing them together easier.

If anyone wants a full size printed set, pm me and I will mail you a set for the cost of printing and mailing.

The plans are slightly different than is shown in the build. I made a few changes after the build to correct things that did not work out as well as expected.

For anyone having trouble printing out the plans.
Be sure the paper size is set correctly in Adobe. From within Adobe Reader select the print icon. Select printer properties and set the page size to legal 8 1/2 x 14". Set Page Scaling to none. No scale is needed as the pages are printed out full size. You must use legal size paper, 8 1/2 x 14". For some printers Adobe will not over ride the printer settings, in that case the paper size for the printer must be set in the control panel, select printer/properties/preferences and set the page size to legal.
 

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Discussion Starter · #4 ·
Video

Everyone wants to see a video, so between my mediocre flying, the wife on the video camera and my first attempt at video editing I managed to kludge together a video.


I dunno why but the video seems to have lost a lot of quality after I uploaded it.
 

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Discussion Starter · #5 ·
Materials

There is not much to this plane, just a bunch of stix (pun intended) and only two material thicknesses for most of it. 1/16" for the ribs and 1/8" for the fuse and tail. I found it best to just cut the strips off a 1/8" sheet with a balsa stripper.

Use a 6mm id x 4 mm od carbon fiber tube for the fuse, this is a 1mm wall thickness. Do not use the 1/2mm wall tube to try and save weight, it will break the first time you dork the plane in on one wingtip. Do not ask how I know this. Cutting a one meter tube in half will get enough for two planes.

Select the best wood you can for it, 6 to 8 lb balsa that is firm and straight grained. Do not use light, soft, punky wood in an attempt to lighten it, there is not enough wood in it to make a difference and we need it as strong as possible to stand up to the abuse it is going to get.

The nose of the plane and motor mount support is made of 1/4" EPP foam, the intention being that when it is dorked in the foam will absorb most of the energy and not have it damage the airframe. Lots of the dork damage comes from the spinning prop stopping and twisting the fuse, the foam should help with that as well.
 

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Discussion Starter · #6 ·
Construction

All of the patterns for the parts are in the second PDF file, glue them to the proper material and cut them out with a scroll saw or #11 blade, note that you will need two sets of wing ribs.

The fuse has to be built first to ensure the wing will fit into the fuse.

Fuselage

Select one of the root ribs and the two root rib doublers. Glue them together, use the cf fuse tube to check the spacing. Make sure the tube slides in easily but do not glue it in yet.

Place the rib and tube in their proper location on the plans. They are only there to act as a guide to keep the parts in alignment while the fuse is built around it.

Lay the nose and aft fuse 1/8" x 1/4" balsa stringers on the plans and glue them together being careful to not glue them to the tube or root rib doublers. The tube is glued in after the fuse is assembled and the root rib assembly is needed to build the wing.
 

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Discussion Starter · #8 ·
Starting at the nose cut and glue each of the fuse parts together working to the tail.

Take the tail post and lay it on the plan, mark where the turtle deck stringer meets the tail post. From this point up the tail post will have to be cut down to a 1/8" thickness to match the fin.

Glue the stab support block to the fuse stringers and the tail post. Use a piece of 1/8" thick scrap balsa to set the spacing for the stab.

If the plane is to be flown without the landing gear glue the doubler on to the lower nose stringer as shown on the plans. This will reinforce the fuse in the area that takes a beating when landing.

Glue in the diagonal bracing between the bays in the lower fuse.

Remove the root rib. Roughen up the tube with some fine sandpaper and glue it into the fuse with a light coating of epoxy. Make sure the tube is in its proper location at the slot for the stab.

Cut and glue together the four pieces that make up the fin. When the glue has dried glue it in place to the fin post and fuse top deck.
 

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Discussion Starter · #9 ·
Wing

The wing is built over the wing plan layout. This is a double taper wing so the top and bottom is the same, just be sure the diagonal bracing is up when the wing is glued in the fuse if you want the servos in the underside of the wing.

Find the other root rib and glue it on the opposite side of the existing root rib and doubler assembly to make a box that the fuse tube will slide through.

Cut the two 1/8" X 1/4" wing spars to length and place the lower one over the wing plan.

Take the root rib assembly and place it over the wing spar in the center of the wing, lining it up square with the spar

Place each of the 1/16" balsa ribs in its proper location on the wing spars, square them up and glue them to the spars. Check that the trailing and leading edges of the ribs line up, trim if required.

Cut the two 1/8" X 1/4" trailing edge spars to the proper length and angle. Glue them to the ribs in the notch provided.

Glue the 1/8" X 1/4" upper wing spar in the notch in the ribs.

Glue the two 1/8" X 1/4" leading edges in the notch in the front of the ribs.

Cut two balsa spar webs from the 1/32" balsa sheet to length and glue them with the grain vertical between the first two ribs as shown on the plans.

Cut and fit the 1/8" square balsa diagonal bracing as shown in the plans. The bracing in the first two bays goes to the top of the main spar and to the bottom of the main spar on the outer two bays to form a zigzag pattern.

Glue a small piece of 1/16" balsa to the root rib on the underside of the wing to guide the wing servo wires.

When the glue has completely cured remove the wing assembly from the table.
 

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Discussion Starter · #10 ·
Select the most flexible sheet you can find for the leading edge sheeting. Cut two pieces of 1/32" X 4" balsa 13 1/2" long then cut each one at an equal taper angle 3 1/2" on one end and 2 3/4" on the other for the leading edge sheeting.

Mark the sheet along the center where the wing leading edge will go. Lay the wing leading edge on the sheet in the location marked and glue it with ca. Now we have to fold the sheeting back for gluing to the ribs and main spars. Starting at the middle rib in the panel push the sheeting back over the rib to the spars with your thumb and forefinger, hold it tight to the rib and spars and hit it with some thin ca. Work your way from the center out to the tip and root gluing the sheet to the ribs and spars as you go. Do not glue it full length to one side then the other (top then bottom) as it will create a warp in the wing panel. Do not ask how I know this.

If the sheeting will not bend around easily spray a light coat of Windex on the outside of the sheet, let it soak in for a couple of minutes then try bending it around.

Sheet both wing panels, making sure a 1/4" gap is left between them at the root rib for the fuselage.

Cut the tabs off the ribs with a #11 blade. Bevel the trailing edge to 30 deg on both sides.

Trim off any spars or sheeting that may extend past the tip ribs. This completes the wing.

The wing is extremely ridged and strong torsionally, there is no way a cf reinforced foam wing could be made this stiff for the same weight.
 

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Discussion Starter · #11 ·
Ailerons and Tail

Not too much to say about this, the usual slab construction but with small pieces. Cut the sticks to length and angle and stick them together.

Cut and glue together the four pieces that make up the fin. When the glue has dried glue it in place to the fin post and fuse top deck.

Bevel the leading and trailing edges of all the hinge lines to 30 deg on both sides.

I cut down some ca hinges to 1/4" wide by 1/2" long and hinged them in the usual way but Blenderm tape would probably work just as well.
 

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Discussion Starter · #12 ·
Covering

If the plane is to have a landing gear use 1/16" music wire and bend the gear legs to the shape shown on the plans. Install the wheels and collars. The 1/4" lite ply mounts must be installed in the fuse to accommodate the gear leg attachment. The landing gear will add half an ounce to the plane.

I used Coverite Microlite on this one, goes on easily and does not shrink so much as to distort the airframe.

Sand smooth each of the main sub assemblies making sure there are no glue lumps or high spots. Do not over do it as it is easy to break the parts with the sanding block.

Mark the location of the glue lines on the stab. It will be 1/4" wide on the bottom and top. It is better to cover to the glue lines (or slightly past) rather than having to cut out the covering later.

Glue the aileron servos to the wing spar and second rib in the location shown in the plans with hot glue. You should have just the output shaft sticking up above the wing. If you are going to use them cheapy servos from HK or VH make sure they work and center properly before they are glued in. Do not ask how I know this. Cover right over the servos then cut a hole for the shaft. Do not cover the center section of the wing where it will glue to the fuse.
 

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Discussion Starter · #13 ·
Final Assembly

Now comes the tricky part of the build, gluing the tube, fuse and wings together. I seems to be easiest if all the parts are glued together in one shot instead of trying to do it a piece at a time. Do a trial fit of all the parts first.

Cover the tube, wing center and the edges of the fuse where the root rib goes with a very thin coat of slow drying epoxy. Use it sparingly, just enough to make a good bond.

Slide the wing on the tube and into the fuse. Clamp the whole mess together with some short pieces of wood and some spring clamps.

Slide the EPP nosepiece into the front of the fuse. If the lite ply landing gear mount is going to be used slide it in first between the front of the root ribs. The EPP nose piece will then have to be cut shorter to fit.

With a square on top of the wing at the spar check that the fuse is at right angles to the wing and with a tape measure the distance from the trailing edge of the wing tip to the rudder post on both sides, move the fuse until both sides are the same. Wipe of any excess glue and allow it to dry.
 

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Discussion Starter · #14 ·
Glue the plywood motor mount into the slot in the EPP nosepiece. Glue the two 1" square support pieces of 1/4" EPP to the mount on both sides. Use welders glue for this.

Glue the hinges in their location in each of the control surfaces.

Slide the elevator in the slot in the fuse. This must be installed before the stab as you cannot get it in after.
Slide the stab into the slot and square it up with the wing and fuse. Glue it in with epoxy glue. I put a bead of hot glue between the stab and the fuse tube on both sides.

Glue the elevator hinges into the stab.

Hinge and glue the rudder in place.

Attach the ailerons to their respective wing panels. Mount the aileron control arms, cut and fit the pushrods to length. Pull the right side aileron servo wire through the guide hole on the left side of the wing along with the left side servo wire.

I used Dubro #919 control horns on all the surfaces. They are easy to install, just mark where the pins have to go, drill a couple of 1/16" holes, push the pins on the control horn through the holes then lock in the pins on the opposite side with a dab of hot glue.
 

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Discussion Starter · #15 ·
Install the tail servos. You will probably need a couple of 6" extension wires. Tape or shrink wrap over the connection so it will not pull apart. The female plastic cover over the extension wire connector will have to be cut off to do this. Run the wires along the tube to the receiver. The elevator servo is located in the top mount location and the rudder is in the bottom. Mount the control arms then cut and fit the pushrods to length.

I found it best to install the tail servos and pushrods on the left side of the fuse. I put the receiver and the controller there as well and the battery on the right side. Stick a Velcro strip in the area between the motor and the leading edge of the wing. The batteries may be mounted anywhere there to obtain the optimum balance point.

Mount the motor with four small wood screws.

If you are going to install the landing gear bend the gear legs from 1/6" music wire as shown in the plans. Install the wheels and locking collars. Mount the hooked end of the gear legs in the top holes in the lite ply then secure them with a zip tie through the two lower holes.

Drill a hole into the triangle gusset at the bottom of the fin post for a tailskid. Use a piece of nyrod or similar plastic rod or tube.
 

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Discussion Starter · #16 ·
Final Setup

Check that the motor rotation direction is correct and that the throttle stick movement is in the correct direction with the propeller removed! Some controllers require that the setpoints for the throttle range movement be set before operation. Refer to the controller manual for this.

The airplane should fly neutral balanced at 3 7/16" back from the wing leading edge measured at the wing root. This is 33% of the wing avg chord. The plans show a 1/16" hole in the bottom of the fuse at the balance point. Make a hook from some 1/16" music wire and hang it upside down to check the balance.

The plane has large control surfaces to give good control authority at the low speeds required for indoor flying. Check that all the control surfaces move in the proper direction. Start with a 45 deg deflection on high rate with 30% expo for all the surfaces and then work your way up from there.
 

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Discussion Starter · #17 ·
Flight Testing

A link to the Video of the first couple of flights is on the fourth post of this thread.

I am pleased with how well it flies, it sure exceeded my expectations. For a plane running on only 70 Watts I think the performance is impressive.

The plane is very versatile in its flying qualities, low and slow with good control authority and more than fast enough for the high energy stuff.

While I intended this to be an indoor plane it really flies best outside in the back yard. Good in the wind and if you like high energy maneuvers this plane does them a lot better than the typical foamy.

Weight with 2S 500 Mah battery and no landing gear 7.2 oz. It is important that the all up weight be under 8 oz. when using the recommended power system otherwise vertical performance will suffer. A more powerful system will add weight and increase wing loading and flight performance will not be as good. There is a point of diminishing returns.
 

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Discussion Starter · #18 ·
Conclusions

For a small plane this one is a lot of work to build, one could almost build a 40 size for the same effort, however I think it makes up for it in excellent flying qualities. It is a lot more responsive and predictable than the typical foamy especially at the higher speeds that usually causes the flat plate airfoil to hunt and become very pitch sensitive.

Use decent servos. Nothing will make a small plane more difficult to fly than servos that will jump a gear tooth easily, do not center well and have throws that are not equal in both directions.

This plane will not stand up to dorking as well as an EPP or Depron plane, if you're the kind of pilot that crashes every flight you might want to pass on this one until you get more experience and confidence in your ability.

It is a lot stronger than it seems while building it. I have dorked it fairly hard with little or no damage, easy to fix with some ca. Landing it hard on the turf in the Dome without any landing gear doesn't bother it at all.
 

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So, when can I get ribs and plans? Im sold!
 

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TriFlyer3D said:
Stix3D 27" - Construction and Plans
Looks good Ron :tu:

Found the construction part, but can't find the plans yet :roll:
 
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