Design

Biplanes are a bitch to build, twice as many wings and a complex system to attach the wings to the fuse and each other. I tried to make the build as simple as possible but it did not turn out as simple as I would have liked. Still a lot of different parts to cut and quite a few different materials. I like to use as few different materials as possible to keep the setup for machine cutting simple but since this is going to be scratch built I guess it will not matter much. Easy to see why biplane kits are so expensive.

The wings are removable and attached to the fuse and cabane with two 6/32 bolts and T nuts. They can be permanently glued on if so desired. Both wings are identical and can be interchanged except for the servos. The preferred setup is to have two standard size servos in the top wing, but they can be in the bottom, or four mini servos can be used. A channel is provided for the wires to run inside the fuse between the wings. The receiver and battery can be located in either wing.

One of the unique features of this plane is there are no interplane struts. I have put a strut/tip plate at the end of the wings. This could be left off as the wings are self supporting but I think that without them the wings will flex up and down as the air gets jammed between them also a biplane with nothing connecting the wings looks a little weird.

There is a sequence to building the components that should be followed so that the parts can be fitted to each other. There may be a better way but this works so if you want to change it be warned.

Read through the entire build thread before starting construction. A text only version of the manual is posted but these are the only pictorial instructions you will get.

 

Plans

The plans set consists of four drawings. A full size drawing of the fuse and tail, one of the wing (both wings are the same), one half scale drawing that shows the material sizes and how it goes together and a full size drawing with the patterns for all the cut parts.

If anyone wants to build this thing full size printed plans on D size paper with patterns for all the parts are available, pm me for details.

Attached to this post is a zip file containing a material list and a printable version of the build manual most of which is already covered in this thread. You can print them out for reference if you like.

Consider this plane a work in progress and as I get feedback I will post any changes and updates to the plans and manual here.

 

Parts

Included with the plans is a sheet with all the parts laid out for each of the material sizes for parts cutting. Just cut off the strips and glue them to the correct material type and thickness then cut them out with a scroll saw.

There are a lot of parts to cut for this so if the builder does not have them already I would suggest they obtain a scroll saw and small drill press. A band saw is OK but the advantage of a scroll saw is that it has a greater throat depth for larger material and it will cut inside a hole, which is nice for cutting out lightening holes. Cheap Chinese stuff from Harbor Freight etc. is good enough for this and the cost is probably less than what a kit would be. Once you have good tools you have them forever and they always get used.

Note that I did not cut out the lightening holes in the front fuse parts. It is easier to do it after the nose and wing mount assembly is glued together. The holes for the servos in the ply servo trays are sized for standard servos, be sure to make the cutouts for the servos you are going to use.

 

Build

This plane is intended for the experienced scratch builder so I am not going to cover any minor construction details, however the front fuse and wing build sequence is critical so play close attention to how this all fits together.

[] Start with the 3/8" thick balsa engine/motor mount nose block. It has a minimum width cutout for Saito 100 and a minimum length cut out for an electric motor. The motor mount and engine mount rails are shown by a dotted line, decide what power system you are going to use then make the appropriate cutouts for the hardwood mounts. There is a square hole marked for the engine throttle servo, adjust the cut out size to fit the servo and location to suit your engine throttle location or leave it off you are going electric.

[] Glue the hardwood rails into the nose block.

Note that there is a square hole just in front of where the tube goes for feeding the servo wires through.

 

Front Fuselage

We have to build the front part of the fuse first so we can use it to make sure that the wings will fit into it and line up properly.

The weakest part of a biplane is the usual method of mounting the upper wing to the fuse with struts. When a biplane is dorked in the upper cabane and interplane strut mounts are usually the parts that are twisted or tore off first. These parts are difficult to repair and get lined up at the field so I devised this method of tying the motor mount, tube and upper and lower wing mounts together in one solid piece. If you hit hard enough to break this part then I do not expect there will be anything else left to repair anyways.

[] Lay the nose block on the fuse plan. Glue the 3/8" thick plywood gear mount block into it.

[] There are four parts that are cut from the 3/8" balsa sheet that make up the upper and two for the lower wing attachment. Lay them on the plan in their proper location and check that they fit together nicely.

[] There are three interlocking pieces of 1/16" plywood that make up the doubler for the front fuse wing mount assembly. There are two sets one for each side. Lay them on the plan and check that they fit together properly. When the fit is good glue each side together. If you have a sheet of plywood large enough this part could be cut out in one piece.

 

[] Place one of the doublers in its location on the plan. Place the nose block on the plywood. Place each of the 3/8" balsa parts in their location on the plywood doubler. Check that they line up evenly with each other. Note the channel for the servo wires. Check that the fuse tube fits in its slot but do not glue it in.

[] Glue the balsa parts to the bottom ply doubler then glue the top ply doubler on. Use some weights to hold them together.

[] When the glue has dried remove it from the plan. Cut out the lightening holes. Do not drill out the holes for the wing attach bolts, they will be drilled after the wing is built and fitted.

I expect that this part could be built from 1/8" liteply with a 1/4" balsa core or even a foam core just as easily. It would probably be an ounce or two lighter.

 

Stab and Elevator

While we have the fuse and tail plan on the building table we might as well build up the tail group.

[] Collect all the cut parts for the stab and elevator and place them on the plan, check that the parts fit together correctly.

[] Place the precut 5/16" stab trailing edge on the plan. Glue the two center pieces to the trailing edge. Glue the 5/16" x 3/8" stab tips and leading edges in place. Cut and fit the 5/16" square balsa ribs to length then glue them in place.

[] Cut the 5/16" square hardwood elevator joiner to length and glue it to the two precut 5/16" balsa elevator leading edge pieces. Glue the elevator tips, angled root ribs and trailing edges in place. Cut and fit the center ribs to length then glue them in place.

[] When the glue has cured remove the stab and elevator from the plan and glue the 1/4" triangle stock to the stab trailing edge and elevator leading edge.

[] Trim and sand as required. Cut the slots for the hinges.

 

Rudder

[] Get the precut 5/16" rudder leading edge and bottom parts and place them on the plan. Cut the rudder tip and trailing edge to length then glue them in place. Cut and fit the two center ribs to length and glue them in place.

[] Glue in the diagonal brace and corner gussets.

[] When the glue has cured remove the rudder from the plan and glue the 1/4" triangle stock to the leading edge.

[] Trim and sand as required. Cut the slots for the hinges.

 

Wings

If the wings are to be glued on, the plywood doublers on the root and tip wing ribs are not needed and can be left off. Skip to the next post

[] Find the four root ribs and the 1/16" plywood root rib doublers. They are the ones that have one hole marked on them. Glue the doublers to the root ribs being careful to line them up evenly.

[] Line them up in pairs and drill through with a 1/8" drill bit. Drill one of each of the pair set to fit a 6-32 T nut. You should have a left and right side, the ply doublers face towards the wing tip and the T nut is on the side opposite the hatch.

[] Find the four tip ribs and the 1/16" plywood root rib doublers. They are the ones that have two holes marked on them. Glue the doublers to the root ribs being careful to line them up evenly. Do not drill the bolt holes in these ribs. They will be drilled after the wings are attached to the fwd fuse and the strut is fitted.

 

At this point the builder should decide how many, what size and where the aileron servos are to be located.

If the wings are glued on and the servos and receiver are located in the top wing no hatch or servo trays are needed in the bottom wing otherwise a hatch should be installed in each wing as it makes it easier to feed the servo wires through.

The build is easier if 48" material is used for the main wing spars, trailing edge spar and the outside leading and trailing edge sheeting. If the builder is using 36" material the main wing spars and the trailing edge spar should be spliced in the location shown on the plans.

Note that the wing is normally built outside up, that is you are building from the top of the upper wing and the bottom of the lower wing. During the build the short sheeting is on the bottom and the full length sheeting is on the top.

[] Lay the main spar on the plans. Place the two root ribs on the spar. Be sure the ply doublers are facing inside the wing (away from the fuse). Use the fuse nose/wing mount assembly to set the spacing between the ribs. Make sure the rib with the T nut in it is located on the side opposite the hatch.

[] Place each of the ribs in their location on the spar, square them up and glue them to the spar.

[] Glue the 3/16 x 1/4" trailing edge spar and 5/16" square leading edge to the ribs.

[] Glue on the other main spar (top during the build).

[] Cut the spar webs to size from the 1/16 x 4" balsa sheet and glue them in place to the front of the main spars.

[] Cut a 3/8" wide strip off of the edge of the three inch 1/16" balsa sheet, this will give you a 2 5/8" wide piece for the leading edge and a 3/8" wide strip for the rib capstrips.

[] Glue on the trailing then leading edge sheeting in place. Note that the outside leading edge sheeting goes the full length of the wing. If using 36" material make the splice at the location shown on the plans.

[] Sheet in the center section and glue on the capstrips.

 

[] When the glue has dried flip the wing over and cut off the rib tabs.

[] Place the wing back on the build table and shim up the trailing edge of the wing with some 1/2" thick scraps.

[] Glue on the trailing edge sheeting. Note that this sheeting stops at the root rib.

[] Glue the two 1 1/2"x1/2"x1/16" ply spar doublers to the main spars between the root ribs.

[] Glue in the servo tray to the second and third ribs and to the main spar, angle it down a little so the servo follows along the top edge of the ribs.

[] Glue the hatch opening between the root and second rib and to the main spar.

[] Glue the leading edge sheeting in place. Note that this sheeting stops at the root rib. Leave off the center section sheeting until the wings are fitted to the fuse.

[] Glue the 1/4" tristock to the trailing edge.

This completes the upper wing. The lower wing is built the same. If the builder is using four servos and the lower wing is built the same the servos will be on the bottom of the top wing and the top of the bottom wing. If the builder wants the servos on the bottom of the lower wing he will have to adjust the build accordingly.

 

[] Trial fit the wings to the front fuse assembly. Mark for the wing attach bolts then drill out the holes.

[] Epoxy glue the T nuts into the root rib. This must be done before the center section is sheeted as you cannot get at them after.

[] Fit the wing tip struts to the tip rib, line them up and drill the holes for the attach bolts.

[] Sheet in the center section. Note that this sheeting stops at the root rib. Make the cutouts for the servos and the hatch.

[] Make the hatch covers from scrap 1/16" balsa.

I am really pleased with how this all fits together, the wings slide on nicely and everything lines up tight and square.

 

Ailerons

[] Place the precut aileron spar on the plan sheet. Cut and fit the 1/4" square ribs and trailing edge to length. Glue in place then cut and glue in the two angle braces.

[] When the glue has cured remove from the board and glue on the 1/4" tristock to the leading edge.

[] Cut the slots for the hinges in the ailerons and wing.

 

Aft Fuselage

[] Place the fuse nose/wing mount assembly back in its location on the plans.

[] Glue on the 1/2" balsa lower fuse chin and 3/8" x 1/2" balsa vertical support.

[] Glue on the 1/2" balsa top nose block.

[] Cut the fuse tube to length. Glue it into the nose block. There is a hole in the nose block in the front of the tube to pull the servo wires through, be sure not to install the tube so far forward as to block this hole.

[] Collect all the cut parts for the fuse and lay them on the plans, check that they match the outlines and they fit together nicely. Trim if required. Some pieces will almost fit if reversed so try them both ways.

[] Glue the 1/2" balsa precut upper and lower fuse stringers to the fuse tube and nose assembly.

[] Glue the tail post and stab mount block to the fuse stringers. Use a piece of 5/16" thick scrap balsa to set the spacing for the stab.

 

[] Glue the two 1/16" plywood tailskid mount pieces together to make a 1/8" thick piece. Glue it in place to the precut lower fuse part.

[] Starting at the nose block cut the 1/4" x 1/2" balsa verticals to length and glue them in place to the fuse stringers. Glue each of the precut 1/2" balsa lower fuse parts together working to the tail.

[] Starting at the nose block glue each of the precut 1/2" balsa canopy and upper fuse parts together working to the tail. Glue in the 1/4" x 1/2" balsa verticals.

[] Glue in the 1/4" x 1/2" balsa servo mount frame. Glue in the
1/4" x 1/2" basswood servo mounts setting the correct spacing for the servos to be used.

[] When the fuse has been completely glued together and the glue has dried remove it from the table and glue the 3/8" tri stock to the back of the fuse/fin post.

 

Trial assembly

[] Fit the wings on the nose/wing mount assembly. Attach the wing tip struts. Glue the 1/8" balsa precut wing tip parts to the tip ribs to fair in the struts.

[] Check that the stab and elevator slides into its slot in the fuse. Check that there is full elevator travel.

[] Check that the aileron servos fit in their locations then drill for the servo mount screws. Fit the wing hatch cover then drill for the screws.

[] Drill the holes for the landing gear.

[] If the builder is using Epower make the motor mount from 2 pieces of 1/16" X 3/4" X 3/4" aluminum angle approx 3" long. Drill the holes for the 6-32 bolts in the aluminum angles and the fuse nose block making sure the holes go into the location of the hardwood motor mount rails. Drill out the angles to suit the motor mount bracket.

I like to do all this before the fuse is covered.

The completed bare bones airframe. Weight is 36.4 oz. I had hoped to get it down around 32 oz. (the bare bones GBR was 31.5 oz.) but it became apparent early on that this was not going to happen, not with all the structure needed for the extra wing plus the fact that the wing area is 20% greater.

I had not planned on building another plane this winter so the wood I used was not very good. I think with better wood one could save about 2 to 3 oz. plus by using liteply for the nose/cabane assembly another couple of ounces could be saved, so it might be possible to get it down to 32 oz.

 

Covering

[] Sand smooth each of the main sub assemblies making sure there are no glue lumps or high spots as these will show clearly through the covering. I find it is best to drill all the holes now and cut them out after it is covered rather than drilling through the covering.

[] Mark the location of the glue lines on the stab. It will be 1/2" wide on the top and 1 1/4" wide on the bottom due to the two 3/8" pieces of tristock that are gusseted between the stab and the fuse tube. I like to cover to the glue lines (or slightly past) rather than having to cut out the covering later.

[] Mark where the covering should end on the forward fuse and cabane where the wings will fit. The wings should be a tight fit where they slide of the nose/wing mount assembly so the covering will have to stop at the edge of the wing.

The GBR-50 as an ARF. Weight is 43.6 oz.

It is traditional that biplanes have a gaudy color scheme but I might have overdone it on this one a little. Visibility should not be a problem. I used HK covering as I wanted to try some out. Nice colors and it went on fairly easily but it seems to be a bit heavier than the others. The covering added 7.2 oz. I would have expected it to be around 6 oz.

 

Final Assembly

I am going to use four servos on this one that way I can check how the wires will route through the fuse. I wanted to use four HS82MG's on it but I did not have four that were not busted. I have four HS225MG's so that is what we will use though they are a bit more servo than it needs.

The following description is for the use of four aileron servos. It is easiest if the receiver is located in the bottom wing. A Y connector will be needed for each side pair of servos.

[] Glue the ailerons and hinges into their respective wing panels. Mount the servos and aileron control arms, cut and fit the pushrods to length. It is easier to do this before the wings are mounted to the fuse.

[] Install the tail servos. The elevator servo is on the top and the rudder is on the bottom. You will need two 24" servo extension wires. Run the wires through the fuse tube into the square opening in the fuse in front of the tube then run them either up to the top wing hatch or to the bottom depending on where the builder wants the receiver located.

[] Two 12" servo wire extensions are needed for the aileron servos. Run them from the opening in the wing mount at the top of the cabane to the opening for the lower wing. Use the hole in front of the tube to guide them through. Be sure the ends of the wires are located correctly depending on where the receiver is located.

[] Run the throttle servo or controller wire into the opening in front of the fuse tube and to the hatch where the receiver is to be located.

[] Place the top wing flat on the build table and slide the fuse into it. Make a hook from a piece of 1/16" wire and use it to pull the servo extension wires into the hatch as the wing is slid on. Pull the wires from the top servos into the hatch.

[] Flip the fuse over and do the same for the bottom wing.

[] Pull all the servo wires into the wing hatch. Connect a Y connector to each pair of aileron servos. A battery and servo tester works well to sort out the wires. Mark the servo location on each of the wires.

[] Secure each wing with a 6-32 bolt.

[] Bolt the struts in place on the wing tips.

 

[] Slide the elevator into 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. Cut two pieces of 3/8" tristock to length to gusset the stab. Cover the wide edge with a piece of covering then glue it to the stab and tube with epoxy.

[] Glue the elevator hinges into the stab.

[] Hinge and glue the rudder in place.

[] Mount the elevator and rudder control arms, cut and fit the pushrods to length.

[] Mount the motor/engine.

[] Attach the main gear to fuse with 2 6-32 X 1 1/4" bolts and locknuts and the tail skid/wheel with a couple of small wood screws.

The completed GBR50 Bipe.

RTF total weight less batteries 77.4 oz (4 lbs 13.4 oz). Add about a pound for batteries and the all up weight is just over 5 3/4 lbs. A little over my goal of 5 1/2 lbs but not too bad for a plane this size I think. I am sure a more careful build could easily get it down to the 5 1/2 lb mark.

 

Power System

I decided to use a Turnigy SK 50-55/570Kv motor on this as my 500Kv motors are previously engaged. This is the same one I used on my MoAss and Sbach55 and it worked well on 6S with a 15x6 prop. I test ran it up with a JXF 15x6 before I went to the field and it pulled 83.2 Amps for a little over 1600 Watts or
about 266 Watts per lb. Should be lots of power. I only have 6S 3000Mah 30C batteries for this so at full throttle they are going to be stressed a bit.

I used an 85 amp 6s controller with a 6 volt BEC. With Align 610's on the tail and four HS225's on the rons the surfaces are plenty fast enough. Setting up the four aileron servos was a tricky business. Took quite a bit of effort to get them so they all had the same amount of throw both up and down.

I normally set my dual rates up as a high rate and a not quite so high rate. I have the throws set at 45 deg on all the surfaces (except the rudder which is set at 50 deg) for the high rate setting and 5 deg less on all the surfaces for the not so high rate, then adjust from there after the first few flights.

 

Flying

After waiting a few days we finally got a nice day. Cloudy, almost no wind and temps in the high 40s. The RC field was covered in snow and rutted and packed from snowmobiles, no place to take off or land. Trying to hand launch a biplane is somewhat risky as there is no place to hang on to it so that it balances. The full scale airstrip that I fly from has a roadway plowed that parallels the runway. Cannot fly off the airstrip as it is full of ridges from ski flying, so it has to be off the roadway, just have to stay away from the frozen snow banks on either side and not crash into any parked aircraft.

With the CG at the recommended 4" from the wing leading edge the plane flew dead level both upright and inverted, only required a couple of clicks of roll trim.

I first flew it with the dual rate set at the not quite so high rate which was good thing as this plane is super responsive to the controls, so much so that I was afraid to try it on high rates. It will do a pinwheel in its own wingspan and a flip in its own fuse length. Rolls and snap rolls are a blur. Not a loose airplane but it sure is touchy.

Some roll coupling to upright during knife edge, the rudder is so sensitive that it was difficult to hold at an even angle. Some negative pitch coupling during hard rudder turns and flat spins. Harriers had a small amount of gentle wing rock in high alpha, none in low.

Generally biplanes are wobbly unstable things that wander all over the sky but this one locks in solid, flies straight as an arrow. Pull it up into a hover and it instantly locks right in, so easy to hover that your Granny could do it. Because it tracks so well it is real easy to land, doesn't stall or drop a wing just does a nice predictable sink. Perfect airplane for spot landings at a Funfly.

It does the best elevators of any plane I have ever flown. It keeps its heading, no wing rock or wobble and just comes straight down, does not even require any throttle.

Half way through the second flight I noticed that it wanted roll to the right badly, I flew it in close and could see one aileron flapping in the breeze. I managed to bring it around and land it without hitting the snow banks. The gears on one servo had stripped. They were old and well used so I expect the gears were on their way out when I installed it, still I had tested them all with a servo tester and they seemed OK. This really pissed me off as I wanted to work a lot more on the setup. Biplanes typically require quite a bit of effort to get the setup right and this one is no exception.

Back to the shop to replace the servo and tweak the surfaces a little to try to reduce some of the control sensitivity.

 

Second try, snowed 3" last night and colder, below freezing but the weather forecast is not good for the next week and I want to get this done. The roadway was not plowed so I had to take off in the soft snow.

It flew quite a bit better this time, I think that servo acting up was causing some erratic behavior. Roll to gear during knife edge is gone and it tracks straight. With all that side area ahead of the CG it requires almost no rudder to hold the nose up.

Like most biplanes it rolls real well, I have trouble with my rolling circles but with this plane I can do them easily. Does torque rolls and anti-torque rolls like it's on a wire. Spins are brutally fast. It does great walls, half throttle level pass down the runway, cut the throttle, pull it up in a wall and it just stops and hangs there, no zoom up or wing drop.

The only minuses are the negative pitch coupling and the slight high alpha wing rock. I am hoping some more work on the setup and some fine tuning will get that fixed. Cure those two things and the GBR bipe will fly better than most 3D monoplanes out there, however it does fly differently than a monoplane so it takes some getting used to. The more I flew it the better I liked it.

I got three flights on it before my fingers got unbearable cold. We do not get many decent flying days here in February so it was lucky I was able to get to fly it enough that I am satisfied that it is going to be a great little plane. More flying on it is going to have to wait until the weather is warmer. At least I got to fly it, as I did not want to send the plans out unless I was sure it was going to fly OK. The drawings are done and available to any of the Bros that want a set.

 

Comments

This is not a beginner's airplane, neither in the build, setup or flying. If you do not have a lot of confidence in your flying and building ability then you may want to pass on this one. If you want a plane that gives you an adrenalin rush every time you fly it then this is definitely the plane for you.

Be very careful when covering the ailerons that you do not get any warps in them. Warped ailerons will drive you crazy trying to get the setup right. Consider building them out of 5/16" material if you are not handy with taking out warps with your covering iron. If one is using four aileron servos be sure to get a good selection of different indexed servo arms otherwise you will never get the throw the same on all the ailerons.

This is the ideal airplane for E power as without the wing in the way the batteries can be located anywhere on the nose so it makes it easy to adjust the vertical and horizontal CG just by moving the batteries around. If one is using glow there is room for the tank to be mounted right on the CG.

I thought it would be a lot bulkier than it turned out to be. It does not take up as much room as I expected. It easily fits in the back seat of my F150 pickup, my Mojo 60 would not come close to fitting back there.

I built this with removable wings but the reality is that removing and reinstalling the wings on a biplane is a real PITA. Start by removing the hatch covers (2), the wing attach bolts (2) and the tip strut attach bolts (4). Then one has to disconnect all the servo wires from the receiver in one wing, the servo wires from the extensions in the other then fish them all through the hole in the root ribs. If it can be transported with the wings on that may be the better way to do it.

By gluing the wings on, the wing attach bolts, tip strut attach bolts and ply rib doublers are not needed. It would probably save a couple of ounces. It really does not take up much more room than a large 40 size, it is higher of course and the fuse is longer but the wings are quite a bit shorter and narrower. Having said that, when you do dork it in it is a lot easier to repair by being able to remove or replace the wings.

 

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