Swappable Stuka JU87B
I can’t say why, but I always liked the Stuka. By many accounts, the Stuka was a pretty crap plane: it was kind of slow, not very maneuverable, and no match for anything like a Spitfire. But the Stuka could dive, it was actually really good at what it was supposed to do (accuracy) and it looked and sounded pretty scary. With its strange, pointy inverted gull wings, the off-set ailerons and flaps, fixed landing gear and generally boxy shape, it certainly was a distinctive plane - maybe one of the most distinctive of WWII. So I bought a foamy Stuka: it looked great, but I hated it. With a big motor and a 4S, it had to fly fast, which did not seem right, and was hard to keep it in a park. I suspect the weight to power ratio is a hard balance with the wing shape. So, altogether the Stuka looked like a perfect swappable project - boxy and square, better off light, and something that will probably crash a lot (dive bombing). Perfect.
The results are these build instructions, plans, and flight movies of my Swappable Stuka JU87B. I picked the JU87B because I liked the big front air scoop, and because it was the earlier models of Stuka that forged its reputation. Amazingly only two intact Stukas remain in the world (one I just got to see - see below), so I based my design on pictures from the period, and a few diagrams still around.
These pictures below are of one of two remaining intact Stukas, this one at the RAF museum in London (an excellent musem, and I have now updated my old posts to include other pictures of the real plans from a recent visit). This is a later model than the one described here, but they are similar.
This is detail of the aileron-wing connection - the large knob hanging down is a counterweight for the aileron.
This plane looks complex, but it was really a pretty easy build. I would say other than the landing gear, it was one of the easier designs I have done (only slightly harder than the Messerschmitt or Mustang, but considerably easier than the B25 and Pitts Special - see links at the bottom of the page). It actually flies really well - I was dreading it being a real dog in the air, but was quite surprised. It takes off better than any plane I have ever had (straight and scale), is super stable in the air (no aerobatics with this big plane though), and it is fantastic at diving. It is easy to keep in a park, and with the flaps (or without really) it can fly VERY slowly. Landing has not been so good so far, but I have only tried it on frozen turf, so maybe an unfair test. I think on a proper surface it would be OK.
First, here are a couple movies of its initial flights. The first one includes some wing-camera segments, some pattern diving, and the ever-popular bomb-cam. I made the bomb-cam for the Swappable B25 Mitchell post, but adapted it here for dive-bombing (i.e. it has a more robust release mechanism, and a better way to keep the bomb straight when flying). I will show how to make your own remote bomb-release below. The second movie is by my flying buddy Ed, which has some nice footage of low passes, and Ed’s usual excellent music and editing.
At the end of this post you can find plans for all the parts. Start with the wing, which is essentially similar to that of the FT Spitfire. First make all the spars (two angled wing spars, and one angled joiner spar) and cut out the two main wing pieces. Bevel the leading edge, and bend the airfoil as normal (and glue skewers into the airfoil bends if you want extra strength). Also cut a large bevel on the inside of the bottom trailing edge where it will join to the top of the wing. Now cut out the ovoid taper on the top of the wing that will form the joint when you bend it (make sure to cut this from the top to get a nice clean cut. Score the bottom of the wing on the same line to allow it to bend, and then carefully test-bend it up to get it into shape.
The wing will be assembled and bent at the same time, in three steps. First, glue the outer part of the spar into place on the lower wing surface as shown in the picture, making sure the angle sits on the bend-score. Test bend the wing around this spar to make sure everything fits, that you get a nice airfoil, and the ovoid cut in the top is large enough to allow the wing to bend fully. This is a lot of folding, so make sure you check it carefully and know what you are doing before putting the glue on it. Now install the servos. One at the end of the spar for aileron, and also if you want flaps put another in the position indicated on the plans (and cut out the slot for the servo arm). Once you are happy with the fit, glue the leading edge and the remaining surfaces of the spar (top and rest of bottom), and quickly bend the whole wing into place around the spar. Hold it in place securely for a while until the glue sets, making sure the spar emerges from the wing at the correct position in the airfoil. Once this is set, glue the entire trailing edge, and hold it until set.
Main wing cut out, beveled, pre-bent, and servos installed. Glue down long arm of the spar first
Test bend wing - make sure everything fits before gluing the rest of the spar or any joints.
Repeat all this with the other wing. When complete, trim the parts of the spar that are extending from the wing and test fit the joiner-spar (which is at the same angle as the wing bend) by placing one copy in front of the main spar and one behind (see picture), and insert into the other wing. Trim the wings at the joint if they don’t join up fairly cleanly (little gaps don’t matter). Also check the wing tips should be at about the same height when sitting on a flat surface. If all looks good, then make small hole in the top of the wing, pull the servo wires out of the the hole and tape them out of the way, then glue the joiner spar into one wing. Once set, glue the other side of the spar, and the entire wing joint, and hold the wings tightly together until set. Tape the joint well.
Make sure both wings are the same height and roughly the same angle.
Glue joiner-spars into one side, and test fit everything twice before gluing the actual wings together.
Finished wing, with servo wires for ailerons and flaps
Fuselage and tail
The fuselage is pretty standard, just assemble the box like the FT spitfire and other builds of mine, as shown in the above picture. Cut out the tail pieces, cutting bevels for the elevator and rudder. The little things on the end of the horizontal stablizers are just paper board glued on purely for the look. Assemble stabilizers as usual, making sure they are at right angles, and glue. Now attach them to the end of the fuselage, again, as usual, and make sure they have free movement and they are siting at the right angle with the fuselage. Glue a popcicle stick to the top of the elevator to connect the two halves securely. Elevator and rudder servos are inserted anywhere around the leading edge of the tail pieces in the side of the fuselage, as usual. The Stuka rear wheel was pretty far forward, so I made a bent-wire tail wheel that hooks up to the rudder servo. You could just make a skid, or a wheel on the rudder.
Glue tail at right angles
Install the wing
The wing should fit tightly into the wing-shaped holes in the fuselage. gently but firmly work the wing through the holes until it is centred, and at right angles with the fuselage. Check the wingtips are still at the same level too - they should be close to even with the top of the fuselage box. If everything looks good, then glue the wing into place. I would not make this wing removable if you plan to use this for dive bombing. I think it might fall off when you pull up really hard at speed (lots of momentum with the landing gear).
Wing instalation complete
Formers and Fuselage Covering
The formers are pretty simple, except the forward most one is double-thick since it will form the little air vent on the top. Once they are glued into place, attached the rear deck covering paperboard by gluing to the formers, and taping the sides down. Then glue the front deck down. Make sure the small slit sits exactly over the double former, so when you glue it down you can push down the deck forward of the slit so it forms the small air vent. Lastly tape the very front most part down at an angle, as shown (and the same as my Messerschmitt).
Detail of front-most former, which is 2X thick to form the air vent
When you install the fron cover, push paperboard down into the double former in the front - this makes the air vent shape
Remember to fit your power pod at this point. I always put a velcro strap over the fuselage top (below the paperboard and formers) to provide more stability for the battery - especially in a dive bomber
Install ailerons and flaps
The ailerons and flaps are of course a distinctive part of the Stuka, so I put some thought into how to do this, but keeping it easy and durable. The result is a nice off-set control surface that looks about right, and functions well. You need to get some little nylon hinges to do this, I used Dubro ones: 4 larger ones on the flaps, and 6 smaller ones on the ailerons. I did not make the small inner flap functional to save on servos.
First cut out the six parts (two ailerons and 4 flaps). Mark the leading edges and sides, and test them to make sure they fit your wings. Mark where the junctions are going to be with a pencil (the three segments from the tip inwards should be about 24cm, 20.5cm, and 12cm, respectively). Now cut out 10 small foam pieces the widths of your hinges and about 2cm long. Peel back 1/2 the paper on one side glue back together with a hinge in each (see picture). Insert the other half of the hinge into the leading edge of the flap or aileron at whatever position you want (space them evenly, 2 per flap, 3 per aileron, and that none of them line up with the servo arm since that would interfere with the horn), and make sure the hinge is on the top of the control surface such that the little foam piece is opposite (see picture). This is important to make the control surface sit well BELOW the trailing edge of the wing (see pictures). I put tape around the little foam bits and hinge, and beside the hinge insertion on the control surface, in case the paper ever separates from the foam this will give it extra strength.
Finished hing off-set spacers
Hinges and spacers installed on flaps and ailerons
Now test fit your flaps and ailerons onto the wing so the foam bits will be what actually attaches to the wing. When happy. mark their position, glue (the correct side) of the little foam bit, and glue into place and hold until set. The small, non-functional inner flap is the same, but rather than a hinge I glued a small piece of pop-bottle plastic in place. If you don’t want flaps, do this with the large flaps too.
Hook up your flaps and ailerons to the servos as usual, and make sure everything moves smoothly.
Finished control surfaces from bottom (above) and top (below). The hole over the flap servo is because I forgot to install it in one wing and thought two flaps would work better than one
Finished control surfaces. Note how the hinge is inserted in the top of the ailerons and flaps, and the bottom of the little spacer - this sets the control surfaces below the wing.
I hate landing gear, but it’s essential for a Stuka, unfortunately. So I took advantage of the fact that the wheels attach where the wing bends to attach them. I slightly bent a 2.3mm piano wire, and poked it through the bottom of the wing, so two short segments extended out either end. Then I made a bent-wire landing gear and scale sized wheel (2.5”), and used bike inner tube elastics to attached the gear to the wires inserted in the wing. This worked really well - it is secure, but also has some flex for hard landings. To keep the wheels in place, I poked the back sides of the landing gear wires into the wing too, which holds them into place well. The wheel pants I made by laminating many layers of foamboard. Cut out 4 of the end pieces and 10 of the inside pieces. Stack them up and glue two sets with an end piece and 2 inside pieces, and two sets with an end piece glued to 3 inside pieces (see picture). Cut out groves inside each for the wires on the gear. Make sure these fit over the wheels nicely (one 3-layer paired with one 4-layer). If they fit, then shape them by carving with a really sharp blade (straight razor is what I used).
When they are done, tape them together over the wheels (or glue them if you want, but I wanted to be able to remove mine). I smeared hot glue on mine and then put paper masking tape to smooth it out a bit. These would be better done from depron, the paper is a pain when shaping them.
Bent wire landing great and 2.5" wheels
Stack parts to form wheel pants
Then shape them with a razor blade and do your best to smooth them down.
To attach the gear, poke a wire through the wing centered on the bend
Then put two elastics over the base of the gear wires, and poke the ends of the gear wires through the wing so the base of the gear sits in the right place over the bend
Lastly, streatch the elastics over the ends of the first wire, protruding from the wing. This sounds absurd, but it really works well.
I wanted to be able to drop bombs, so I put a bomb release on the bottom. Put it around the CG (wing spar). I made mine with a servo inserted in the bottom of the fuselage and made the release from a couple layers of foam and a straw (see pictures). It is hooked up to the gear channel. I put a matching thing on the bomb so when you hit the gear switch the pin pulls out and the bomb drops. Works pretty well, but the paper delaminated in the foggy wet weather, so I would also tape this well.
Bomb drop mechanism. Very simple, but note it has already been repaired in the field with duct tape. I suggest making it waterproof
To finish up I added a cowling around the front air scoop. This is a 1/2 a piece of 1.5” pipe insulating foam glued into the inside of the fuselage (see picture) Then I glued a piece of paperboard over this, with cuts every 1” on the trailing edge, and bent these tabs back to give the look of the JU87B.
I added a canopy, made from garbage of course. I put plans for the front of the canopy with the other plans, but the main parts are all made from three pieces taken from 2L pop bottles. Simply cut the clear, flat part from the middle and make two pieces that are 4” long by 5.5” around. Cut the end of one piece at an angle on both sides, this will be the rear edge of the front section of the canopy (see picture), and tape the three front pieces to the other end of the same piece, fold them down and tape them together to form the front of the canopy. For the back section, cut out a rounded section of the bottle (the top, around the lid), and cut to fit this to the rear of the cockpit, and tape this piece to the rear canopy section (see pictures again). The Front and rear sections overlap, so tape whatever ribs you want with black tape first. Then glue the rear section into place and hold until set. Then glue the front section into place, overlapping with the rear section. When set, tape around the whole base. I also put “seats” in first from scraps of foam.
Lastly, varnish, paint, and varnish again. I did the yellow with tape, which gives good visibility when flying (even in the fog I never lost track of it). I added stickers too. I was ribbed pretty badly about my stickers on my Messerschmitt, so I tried to make these more scale. I could not find a small enough German cross, so I made it out of black and white tape (one of those things that was easier just to do it than fine one on the web). Here are some pictures of the final product.
I test flew the airframe without the finishing bits, and put 6-7 batteries through the finished plane over a couple days (I drenched it in the fog, and it stood up pretty well to the water). As I said above, it flies really well. It’s not a bank and yank plane, but flies really well slowly, especially with the flaps, takes off great - straight as an arrow, but the real fun is diving. There is a pattern for a Stuka to dive bomb, so I tried it and it is a lot of fun. In the movie I dropped a couple bombs with a camera on them, but it was too foggy to go high enough for a real dive bomb, but I can see this is going to be a lot of fun to learn properly - and will probably end in a really spectacular disaster.
The power set I use is as follows:
NTM 2826 1350kV
9X4.7 prop (9X6 APC would probably be better, but this one worked fine)
The battery installs through the air scoop and is pushed back roughly to the firewall. That should give you a CG right on the wing spars, which worked for me.
So, this is a fun plane, though a bit of a specialist. Great if you want a bomber, but not a boring slow lumbering monster.
Below are PDF files with complete plans (except for the simple pieces to make the air scoop and bomb drop, which are all squares and rectangles). The parts of the canopy with cut shapes (the front) are included, the rest are just fiting shapes of given dimensions cut from a 2L PET bottle. Hope some people make it and find it as nice to fly as I have. Post some pictures if you do. Thanks for reading.