Falke Biplane 60 build
 

This is my first attempt at a build thread. The biplane in the pdf below is my own design drawn on ancient modelcad software. Let me give a little background. About 8 years ago I was part of a National Guard unit that was transitioning to air defense artillery. We inherited a huge stack of target dronesthe Mig-23 floggers and it was decided to get rid of them. I rescued one and gave it a home. Unfortunately, I didn't have space at the time for the airframe, but each plane came with a K&B .61which I saved from a certain death. Ever since, that engine has been waiting for a home. This design is my attempt. I suspect that I have too much wing for it, but I am looking to build a light as I reasonably can. I hope for a flight envelope similar to my Big Stik .40not full 3-D, but relatively gentle landing characteristics.

I have also drawn a full set of templates. My son's junior high shop teacher has a laser cutter at the school. Wood should be here this week, then we will cut as soon as possible after that. The local copy shop was able to print two sheets for a total of 8 dollars.

I am fairly confident that it will fly. This is my second biplane I have designed. The first died due to pilot error, but some of the lessons I learned from it have been incorporated into this one. But this is not a ARF fan's plane. There will be plenty of sanding and carving and careful work required. I really enjoy the building process; for me it is at least half of the joy of the hobby. I have never owned an ARF because seeing an idea develop into a plan and then into a creation that actually flies is so much more rewarding than paying for immediate gratification, that I cannot see the point.

So much for my soapbox. I hope I am among friends here. Tell me what you think.

RE: Falke Biplane 60 build
 

My wood has arrived. I hope to get it laser cut sometime in the next week. Some of the wood is good quality, some is a little warped (normal, not too bad) but some of it is really heavy. Balsa seems to get more and more like basswood every year. I guess I could have spent extra to have the stock hand-selected, so I can't complain. Since my tail is relatively large, it may be good to have stiff wood.

RE: Falke Biplane 60 build
 

You designed a neat looking biplane. Im right there with you about building your own planes, I think that is the best part also. Do you do your own laser cutting or are you sending your plans out and having someone else cutting your parts? Up until now I have always cut my airplane parts using a scroll saw and bandsaw. I have autocad and Pro-e and minimal experience with a laser cutter. I have been wanting to buy one so I can start cutting parts out on it.


David

RE: Falke Biplane 60 build
 

My son's shop teacher has a laser cutter at the school. I am going to take my wood to him and he will help me cut it. This will be my first attempt at a laser-cut plane as well, so I am curious to see how it turns out. Normally I use my scroll saw.

By the way, I teach German in my day job, so Falke is German for falcon.

RE: Falke Biplane 60 build
 

today was cutting day. I almost succeeded in cutting out all the parts on the laser cutter. We had a few issues with the scaling for some reason. Pretty sure I got them solved, but I will have to order a new sheet of 1/16 ply.

These ribs are not for a tapered wing. They are supposed to be all the same size.

RE: Falke Biplane 60 build
 

Keep it coming.  I love building also and look foward to seeing how your plane comes out.
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RE: Falke Biplane 60 build
 

I made a fair amount of progress this weekend. But since I spent my time building instead of posting, the pictures will come later. I got the tail feathers cut out, the fuse sides, and attached the fuse doublers to the fuse sides. The laser cutting has already saved a bunch of assembly time, and I think it will help in building a straight plane.

I have the plans in PDF format and I have been trying to decide what to do with them. I don't have great aspirations of making any money by selling them, but am not very excited to just set them loose in the internet. I don't even know if anyone would be interested in them. I kind of like the shareware concept, where people can pay what they think they are worth.

RE: Falke Biplane 60 build
 

Here are some pictures of my progress on the fuselage sides and doublers. It took an extra two trips to the copy shop for the template, because when I printed one out on my home printer, it came up more than half an inch shorter than the copyshop plans. The first trip back I had my own print sizing mixed up, but the second time was perfect. Luckily the local shop is much cheaper than kinkos. My full sized plans on two 36x48 sheets was only 8 dollars. the templates were $1.60 each.

For the doublers, it is important to put in the alignment lines first, as there is a top and a bottom doubler ( I suppose these could be connected without too much trouble, but I didn't think about that when I was drawing the plans). The bottom doubler aligns with the airfoil cutout, and the top is 1/8" above that. There will be a top and bottom former that are inset flush with the top of the sides, so care has to be taken to keep the spacing even. F-4 and the firewall can be used to help set up the alignment.

I also cut dove-tail notches in the bottom of the F-4 former so that it interlocks with the bottom former. This was something the laser cutter could not do, since the dove tails are at an angle.

RE: Falke Biplane 60 build
 

Here is the template for the fuse. Both sides are held together with adhesive spray and tape

RE: Falke Biplane 60 build
 

and some more pictures of the fuse in progress. I had to resort to an old-school exacto knife for some of the cutouts, because the jigsaw could not reach.

RE: Falke Biplane 60 build
 

Here are the pictures of the stab and fin. Like I said before, the wood is hard and heavy. I have planned to cut lightening holes in them, but I want to wait and see how it balances. I would be interested if any one knows of a website that can calculate balance points. I know how to figure cg, but how do I calculate where it will balance given known weight for motor, fins, wings, etc as a product of the moment arms between themie given a 1 pound motor 9 inches ahead of the cg, will a 7 oz tail balance it with a moment of 39 inches to the tail? does anyone understand what I am trying to ask?

I also wonder if a standard servo will be strong enough for the large control surfaces on this plane. On the plans I have a large and a small elevator drawn. I went with the large here, but I am not sure if standard servos will be overtaxed.

RE: Falke Biplane 60 build
 

I have three dimensions now. Before assembling the fuse I decided to reinforce the last section of the fuse with some carbon fiber, because the cross grain seemed likely to break out. Originally I had planned to build the sides upside down over the top former. this proved to be impractical for a couple of different reasons, mostly that it was too hard to align everything. Instead, I glued in the central formers where the box is untapered. Then I glued in the top former and brought the trailing edge of the fuse together. the center former can then be slid into place.

RE: Falke Biplane 60 build
 

The bottom former also has a dovetail tab built into it like the top former. I had to design the top former in two pieces just because it wasn't practical to buy a single piece of plywood that long. (and it would not have fit on the laser cutter). But this also means I had to cut in a dovetail on the bottom of F-4. It is a silly thing, but I like the way this part turned out. the fit is good and it feels like it ties everything together nicely.

The 3/8" triangle stringers on the back of the fuse are there so that I can round off the bottom of the fuse. Unfortunately I didn't account for the ply doublers and so I had a gap under one of the formers that I had to adjust.

With the main parts of the fuse put together I can start adding the mounting blocks. I always like to put in the blind nuts before I glue in the parts. Both the landing gear block and the firewall are reinforced with 3/8" triangle stock. Altogether the laser cutting has allowed the fuse to go together very straightbetter than a number of other planes I have put together in the past. I have a tendency to build bananas that I have to try to straighten out with a sanding block.

RE: Falke Biplane 60 build
 

Good looking work.
I am looking foward to seeing the progress and finnish.
Keep up the build thread. I have one on this site that is also my first. I really enjoy doing the thread. Started another build thread on another site today.

Ken

subscribed

RE: Falke Biplane 60 build
 

I have spent some time cutting wing pieces. this is where I begin to question the swept wing design. If I had a flat wing, I would need half as many pieces since they could reach full span. Instead, I have to make a left and a right of everything, plus a top wing and a bottom wing. I count 28 span-wise spars and stringers between the top and bottom wings.

I was also able to get the ribs laser cut today. It went much smoother today compared to last time. Everything looks pretty good

RE: Falke Biplane 60 build
 

Here are pictures of the wing tube and sleeve. The tube is a replacement part for some airplane on tower hobbies, and Extra, I think, but I don't remember now. But it didn't come with a sleeve, so I had to make my own. I am sort of proud of how it turned outsilly, I knowso I am going to explain what I did: I started by wrapping the tube in plastic wrap so that the sleeve would release after it was glued. I cut the paper from a grocery bag by spiraling the cut around and around the bag until I had a two-inch wide strip about ten feet long. This I wrapped diagonally around the wing tube and plastic while soaking the paper in wood glue thinned with water. I wrapped it a second time in the opposite direction. When it dried, the paper tightened up around the tube, but it came out relatively easily. Then I had to sand the outside smooth, and of course it was still too thick for the holes in the ribs by just a little bit, so I wrapped a drill bit in sand paper and put it in the drill press (poor man's drum sander) and sanded it until everything fit just right. Total weight was 7 grams.

RE: Falke Biplane 60 build
 

More progress on the lower wing. The first thing I had to do was assemble the trailing edge/ ailerons. Because of the shape of the airfoil, any single piece of stock even if I had been able to find one the right shape would have been very heavy, so I chose to design a built-up TE. I was about 10 shy of the little triangle pieces somehow, but they were easy to make without the laser cutter, so it wasn't a big problem. the main spar of the TE has to be tapered on both sides so that it forms an isosceles triangle, which will allow the final angle of the piece to sit straight on the back of the wing. What you don't see in this picture is the solid balsa filler needed for the wing bolts or for the clevis mounting. I got all excited about gluing them together, that I forgot to add them before I put the top on. Instead, I had to cut open each spot and add filler and then sand back smooth.

There is also a 1/16 x 1/2 plywood strip between the top and bottom sheet to harden the TE after everything is sanded to shape. The top sheet should probably be sanded before it was glued on, but it seemed a little easier to glue it on firstwhich caused a big flat spot on the last 1/2 inch. Most of that can be quickly sanded out. If the ply were set back from the TE by 1/16" or so, then the sanding would go even better.

RE: Falke Biplane 60 build
 

You would think that I could learn to keep my thumbs out of the way. when trimming the filler stock, my knife slipped yet again and I sliced into my thumb. Good thing we humans have evolved thumbnails to stop x-acto blades with. I wish I had a dollar for every knife scar on my left hand.

Assembly of the wing was fairly straight forward. Due to the sweep, each spar slot has to be sanded a little to account for the angle. Each rib is tabbed to keep it at the correct alignment, and I shimmed the LE and the TE to keep them straight across the entire span. Everything else is standard D-tube construction. Sheeted front section top and bottom, vertical sheer webbing butting against both ribs in each bay across the full span and cap strips on top of each rib. I decided to extend the plywood spar that holds the wing pegs out an extra rib bay for added strength, since the sweep makes it hard to reinforce the center joint. I extended the center sheeting for the same reason.

With the wing mostly framed (I still need to add the bottom sheeting) I can start to get an idea for the overall shape of the plane. Things are starting to look a little like an aircraft. The tail still looks big, but I don't think that will be a bad thing.

RE: Falke Biplane 60 build
 

One more not today on weight So far I am under my weight expectations. I did calculations for wing loadings between 18 and 22 oz/sq. ft. The low end would mean a weight of 7.3 lbs, and the top end would be 8.9 lbs. My fixed weights (wheels, engine, battery, etc.) plus the rough (unsanded) parts built so far come out to 5.5 pounds. If the top wing is about the same weight as the bottom, the frame without covering will be just about 6.3 pounds, which means I just might be able to get this bird in under 7 pounds. Since I don't believe the K&B .65 is going to be a real powerhouse, and since I would like landings to be gentle, the lighter it ends up being, the better.

RE: Falke Biplane 60 build
 

slow but important progress. I sheeted the center section of the lower wing, glassed it, and added the mounting pegs. I also installed the mounting block to the fuse, and drilled the bolt holes and tapped them for 1/4-20 nylon bolts. Next I sanded the wing tip blocks to shape and hollowed them out to save weight. It looks like I that may save me all of 5 grams. It doesn't hardly seem worth it, but I suppose it all adds up. there is a 1/32 ply insert at the TE to keep it strong. I also did some work on control surfaces. I cut out the ailerons from the TE and tapered their LEs. The elevator halves are joined with 1/8" music wire.

RE: Falke Biplane 60 build
 

for the next section, I need some advice. I built the N-struts and reinforced them with carbon fiber, But they look a bit tall in real life as opposed to the plans. The goal was to get the top wing one cord-width above the bottom wing, or about 9 inches, to reduce interferance between the two wings. Aesthetically, I don't think I like it that high, and I worry about an upward pitching moment with the top wing so high above the thrustline. I think with some semi-major surgery, I can lower the top wing an inch or so (probably closer to 3/4 of an inch) by cutting off the bottoms of the N-struts, but it would also mean cutting my already laser-cut wing struts in half and taking a chunk out of the middle. Do I make the change, or leave it as-is?

RE: Falke Biplane 60 build
 

I have a taped together plane now. After I roughed in the top wing, I cut apart the center section. I also cut down the wing tube by 2 inches, since it extends past the ribs, and therefore adds weight, but no strength. I saved 3/4 ounce. Next comes attaching the trailing edge, cutting out ailerons, and more fun with wingtips.

RE: Falke Biplane 60 build
 

Sanding, sanding, sanding. Not much to show, but a lot of work done over the weekend. Wing tips are hollowed out, balanced, and sanded to their final shape. I hope balsa dust isn't carcinogenic. I wrapped the wing struts with carbon fiber tow and epoxied them with finishing resin. The stuff sands pretty well, without fraying like fiberglass does. I am not sure how much strength it will add, but maybe it will reduce side-to-side flexing. Adding wire cross bracing would keep things perfectly rigid, but also add to set up complexity, which I would like to avoid.

All up weight is approaching 7 pounds.

Views of my thread have now passed 1000. Comments would be appreciated.

RE: Falke Biplane 60 build
 

Plan looks cool.. will be following your progress..

RE: Falke Biplane 60 build
 

some pictures of my progress. I installed the carbon fiber wing joiners, attached the wing tips and sanded them down. After giving the cabane struts an airfoil shape, they were wrapped in carbon fiber tow and impregnated with finishing resin.

RE: Falke Biplane 60 build
 

More pics. the interplane struts have been glued together, lightened, and sanded to airfoil shape. then it was time for the turtle decking. One end of the two hatches (one for the fuel tank and the other for the radio/servo compartment) are held down with magnets from a defunct brushless motor. The other end is held in place with a pin latch constructed from pen springs and pushrod wire. Sorry for some of the repeated pictures, but I can only see where to upload pictures, not where to remove them. does that delete link delete individual pictures, or the entire post?

RE: Falke Biplane 60 build
 

I have been working on hinging and lightening the tail of the plane, since it looks like it will likely be tail heavy. I have managed to shave a couple of ounces off, which may also help me keep the overall weight under 7 lbs. the servo hatch/ cockpit and the turtle deck are now done, although my son thinks I should sheet the rear turtle deck too.

RE: Falke Biplane 60 build
 

This is a really nice build you have going on Jeff. Thanks for sharing. Subscribed.

Bill

RE: Falke Biplane 60 build
 

I agree,

Bill

RE: Falke Biplane 60 build
 

Thank you. I am enjoying building the plane, but as an original design, I worry about how well it will fly. There are so many unknownsare the angles right? do I have enough down thrust? do I have enough power? will the engine even run? All I can do now is cross my fingers and keep building.

RE: Falke Biplane 60 build
 

I am having to post using my phone which is a pain but how is your build coming? I have one design-build but not a bipe and no swept wings. Seventy eight inch span with a converted 31cc Ryobi. Both the plane and the engine conversion were firsts for me. It has not been flown yet and I can't find the memory stick with the pics. Sorry for the rambling, lol. I will post more when I can get on a computer.

Bill

RE: Falke Biplane 60 build
 

BTW, I for one am following your build with a great deal of interest.

Thanks again,

Bill

RE: Falke Biplane 60 build
 

Bill,

Progress has slowed a little because I had to start teaching class again. That and I am a little stuck on the the cowl. Stayed up way too late last night trying to work it out. There are some complex curves and tight spaces that have to be accounted for. I also realized that my CG calculations were way off when I was first designingwhich was good, since the previously calculated CG would have left the plane very tail heavy. After double checking my numbers using several different methods, I realize that the CG should be further back than I thought, which puts me in a much better situationI shouldn't have to add any lead, which I always hate.

I would love to see some pictures of your project. It sounds interesting

RE: Falke Biplane 60 build
 

More pictures. I have finished the cowl. It is a clamshell style, split horizontally, with both sides removable so that I can access the engine. I use the masking tape to protect the parts I don't want to sand down. I really hope balsa dust is not carcinogenic.

On the advice of my oldest son, I also sheeted the rear turtle deck. It is only 1/32" thick, so it will be delicate, but the 1/8 balsa longerons were also really soft, so it won't be any worse.

RE: Falke Biplane 60 build
 

On the tail you can also see the fairings over the fin and stab. They are also hollowed out behind to reduce weight. the bottom of the lower wing has also received a fairing to blend it in with the belly of the fuse.

RE: Falke Biplane 60 build
 

Here we see the mounting of the top wing center section and the cabane struts. I borrowed an incidence meter for this one. Normally I am good with leveling the fuse and measuring the LE and TE of the wing to get it right, but aligning the top and bottom wings with 1 degree of decalage wasn't possible without a meter. Everything is glued in with epoxy and held with clamps until it sets. I also chose to cover the underside of the top wing center before attaching it, since it would be hard to do afterward. It feels good to start the covering process, and have some color on the plane. I like the contrast of the dark blue and the yellow.

RE: Falke Biplane 60 build
 

Covering continues slowly. I started on the wing struts, but ran into trouble because they are plywood and have a lot of compound concave curves on it. The covering did not want to stick to the edges at all. I had to rip off my first attempt and start over by covering the edges first and then the sides. The final result is adequate, if not particularly remarkable. Some people just seem to have a talent for covering, and the rest of us just muddle through the best we can. I would like to sit and watch someone cover who is really really good some day.

The pilot is also now installed in the cockpit. I found the bear at a garage sale. He is old and ratty, and has lots of character. He also now has a wooden stick up his neck. My son enjoyed watching me cut his legs off. The cockpit lining is split fuel tubing. If I can find a workable material, I may also add some leather stitching to hold it on.

RE: Falke Biplane 60 build
 

Having trouble getting on to the site. my virus protection software is blocking the site from homeFrom work, no problem. anyone know how to solve the problem?

update on the plane: I covered the rudder and the other wing strut, but work has put a real cramp into my building timethat and I helped my son put together his foamie nerf-trainer I never had anything like that to learn on.

RE: Falke Biplane 60 build
 

Here are some new pictures. Work is still getting me down, but at least I am back on the forum. The checks are sealed together on a glass plate first and then attached to the wing. the top of the bottom wing is also covered. I am having a hard time finding an extended period of time to do the big chunks. It could be a while.

RE: Falke Biplane 60 build
 

More extremely slow progress. covered some bare spots on the ailerons, and added the starburst stripes. Not shown in these photos, I have also glued in the fairings between stab and fin. Next week I am in Colorado, but after that big project is done, I should have a little more time for building.