Swappable Lancaster Bomber with FPV bombsight

 A four-engine Lancaster with differential thrust and FPV bombsight for accurate remote bomb-dropping. And with a wingspan of 1000mm, it uses a single sheet of DTF.

Full instructions and plans below, plus removable landing gear, bomb-cam, and video.  

I love the classics, and the Avro Lancaster is maybe the classic WWII bomber. The Lancaster debuted in 1942 as a four-engine modification of the twin Manchester, and was quickly recognized as an excellent flier. It went on to become the workhorse of RAF Bomber Command, and over 7,000 Lancasters were constructed during the war, at one time employing over 1,000,000 people to make them in Britain and Canada. Below is one of the few remaining intact Lancasters at the RAF museum in London, and one of only a handful that completed 100 missions. Disturbingly, Lancasters survived on average only 21 missions. 

Lancaster R5856 at the RAF Museum in London

The Lancaster was powerful but surprisingly agile for such a big machine, and was used for a variety of strange missions. Maybe the best known was the famous “Dambusters” mission later made into the 1955 movie, which features several Lancasters brought out of storage for the film, and some wild flying that is worth a watch. Below is my less interesting film showing the swappable Lancaster in action. The first 2 minutes is a more polished movie with Dambusters themes just for enjoyment and includes a FPV bomb run from different perspectives. The last 3 minutes is raw footage of crashes, FPV, differential thrust and bomb-cam views for viewers interested in actually building or flying - they show how it works. The crash was due to getting into trouble going low and slow with a 2S battery - 3S has the power to get out of the same problems - but it took the nose dive like a champ and was back in the air in minutes. Thanks to Chad for some filming and Paul for arial filming and acting FPV bombardier.

A while back I made a fun twin-engine swappable Mitchell Bomber and I generally enjoy dropping bombs (see also my Stuka dive-bomber for greater accuracy and some g-forces that push the limits of foamboard). The Mitchell was also really popular (>30,000 views, thanks everyone!), so I have been surprised not to see a big FliteTest four-engine bomber, which seems the next step up, but also something a lot of people might be interested in trying (I know the Mitchell has been made quite a few times). So I decided to do a big Lanc and got the wing and fuselage partially built. This is a really big plane (60” wingspan - see picture). But partway through this I bought the electronics to build a 250mm racing quad. I got to looking at this stuff on my desk...and thinking…. “what if I used it to build a mini-quad Lanc instead?” A mini quad bomber! So I put the 60” plane aside and set about building a mini-Lanc with a totally different design, using the wing profile of the FT Scout. I did not set out to make this a single sheet of DTF, but it turned out that way as an added bonus. It uses 250 quad motors, props, and ESCs, and a 3S battery. For added fun, I made a FPV bombsight to better aim your bombs, a simple remote bomb-dropper (with bomb-cam of course), and a “dambusters” style altimeter with two LED spotlights for low-level night-time bombing. And to keep it light and simple, I use differential thrust in the rudder channel, eliminating the need for complex linkages the dual rudder demands. I also made removable landing gear. 

Complete plans are at the bottom of the page, and below are detailed build instructions. As I said, it’s a one-sheet build so if you have any 250 quad gear around, then you have no reason not to try this! 

Build Instructions:

Wing. 

The wing is a simple fold with the same cross-section as the FT Scout, but after wiring it up I used paper to cover the bottom for better airflow and a cleaner look (and this is installed later). Cut out two wings and ailerons as marked, and score-cut, bend, and glue the wing using FT Scout jigs. When they are both done, glue them together and tape the joint. I gave mine 100mm dihedral originally and no spar, as a test. But when it got damp from dew the wings began to flex A LOT, so I ended up jamming a CF rod through the inboard nacelles and fuse, laying it right up in the bend. This stiffened the wing tremendously, but lost the dihedral. It flies great without the dihedral, so I suggest you make a flat wing with a stiff spar. If you want to make a dihedral spar out of wood, that will work too. 

Fuselage, Nose, & Tail Assembly.

Cut out the fuselage, making sure you cut out the H-shaped bomb bay doors and score-cut the hinges on the inside, which you will want for access to the wiring and Rx later. Glue the box as an B-fold, leaving the tapered tail section to last. Now you can insert the wing into the wing slots, being careful not to rip your ailerons. When it is centered and flat, glue it into place with a bead of glue on the top and bottom, wiping the excess with scrap foam for a solid joint. The wing won’t be removable due to the nacelles, so glue it on. 

Inserting the wing is easier if you put the fuselage on the edge of your bench

Cut out a horizontal stabilizer, including the two mortises where it connects to the fuselage tabs, and cut and bevel the elevator and reinforce it across the centre of the hinge so both sides move evenly. Reinforce the leading edge with a skewer. Cut out 2X oval vertical stabilizers, and on each cut the mortise for the tab where it joins the horizontal stabilizer. Make sure you do not cut right though, instead leave the paper on one side of each mortise intact - this will be the outside and it looks cleaner. Glue the two vertical stabs into place, being careful to keep the right angle (I actually left this until later so they did not get in the way). Now test fit with the tabs on the fuselage, and if the angle looks good, glue it into place. 

Make sure the wing and tail are straight

Glue up the nose-connector as a U-shaped A-fold. Then cut out the nose and glue the connector into the nose so it sticks about 2cm out from the joint. Test fit with the main fuselage - it should be snug. Now glue up the sides and top of the nose around the connector. Remove about 1cm of paper from the walls and bottom of of the tip of the nose, then gently fold the corners together to make a circle. Run some paper tape over the top to hold the corners together and form the top of the circle where the bombardier dome will eventually be installed. 

Now glue the formers into place on the top of the fuselage and nose, including two at the junction between them (same as the Mitchell). At the rear, one former glues on top of the horizontal stabilizer, and two others glue in directly forward and aft of it, for more support.

Detail of the formers around the tail. 

When the formers are in place, start gluing down the paper top covering, starting from the back and moving towards the cockpit. Make sure the paper does not interfere with the movement of the elevator, and trim it if it does. Now insert the nose and glue the front paper covering down on the nose and the forward part of the main fuselage. When the glue is set, use a very sharp razor to cut the paper between the formers spanning the junction, so the nose is once more removable. Take your time with this because if you do a good job it looks very clean (I did not and now have a messy junction).  

Nacelles & Mini Power Pod.

Cut out 2 outboard (small) and 2 inboard (big) nacelle bodies. Remove the inside paper from the triangle that will form the bottom of the tapered rear, and gently roll this over the edge of a desk to get a slight curve. Glue the front portion with a A-fold. Now glue the tapered part together and then the curved bottom into place, rolling it over the desk to press the glued joint together.

Trailing edges are tapered and rounded on the bottom

I did not mark the position of the nacelles on the wing plan because it’s very important they are parallel with the fuselage, so it is better to do this after you install the wing to account for minor irregularities in your instal. Measure 80 mm and 120 mm from the fuselage at the leading and trailing edge of the wing, and mark a line at each position, as well as the centre point between them at the trailing edge. Line up the inboard nacelles between these lines so the notch on the nacelle sits at the leading edge and the tip of the taper sits at the centre line on the trailing edge. Test fit this and check it looks parallel to the fuselage. If it looks good, glue it into place and reinforce with glue on the joint wiped with scrap foam. Repeat the same with the small outboard nacelles, with lines 230 mm and 270 mm from the fuselage and the centre marked at the tip of the nacelle. 

Cut out 4 “air scoops”, remove the paper from the inside and round it slightly by rolling it on the edge of a desk. Then cut a bevel about 6mm wide into the exposed foam on both sides. Now when you pinch it to fit the two paper tabs to the sides of the nacelle, it should bow slightly, giving the bottom of the nacelle a nice shape. Test fit all 4 and glue the paper tabs and beveled bottoms to the nacelles so the scoop is flush with the nacelle. NOTE: my nacelles were originally just boxes and I cut the profiles after a test flight, but the plans have this nicer looking profile, so yours will look slightly different than the pictures. 

Detail showing the eventual look of the nacelles. 

Build your 4 mini power pods as usual (but tiny!). Mount your motors and test fit in the 4 nacelles - sliding the pod back until the motor (and propellor) just emerge from the nacelle giving the prop unimpeded motion. Mark this position on all four, and insert skewers. I would now number the pods 1-4 so they always go back in the same nacelle. 

Baby power pods - I tired alternatives, but these were the easiest way to install the motors.

Now cut out and glue together the 4 nacelle formers. Use a razor to bevel the horizontal part at about the same angle as the rounded former, and then glue them into place over the powerpod, 30 mm back from the end of the nacelle (make sure you don’t also glue your powerpod into place). 

At this point I would delay gluing the paper on the top of the nacelle to give you more access for wiring. But when it comes time to do it, simple cut out four of the paper nacelle tops, round them slightly by rolling them over the edge of a desk, and fold the sides tabs down at right angles. Then test fit them over the former so the tabs go to the leading edge of the wing - the triangle should naturally extend up the wing to its highest point. If it looks good glue it down first behind the former, then forward of the former pulling it down tightly at the front so it angles down a little and gives it an interesting profile. Trim the front if it is too close to the prop. 

Formers in place and paper cut out.

Glue down the back over the former first.

Then pinch the front down tight and glue it into place.

Control Surfaces & Wiring.

This plane has a lot of wires in the wings. If the holes through the nacelles and fuselage are not big enough for your wiring, enlarge them. 

First lay out your ESCs to see how long your power harness needs to be. For mine the outboard ESCs are attached to the bottom of the wing between the nacelles and the inboard ones are inside the inboard nacelle. With this configuration I needed a power harness with 170 mm leading to the battery, then spitting into four 200 mm leads to the ESCs. You will need some servo Y-splitters and maybe some extensions too. Lay these out to feed to your ESCs (remember to have only one provide power by removing the red pin from three), aileron servos (which will be in the outboard nacelles), and bomb-dropper if you install one. 

To install the power harness, open up the bomb bay doors and feed the wires through the holes in the fuselage, into the inboard nacelle, and one set right through the nacelle. Feed the servo wires through the same way. Now hook up all the ESCs, and the Rx, and test the motor direction. If you want differential thrust, put the right and left pairs of ESCs on different channels of our Rx. You Definitely want counter-rotation, so make sure the props rotate towards the fuselage at the top of the rotation. When you have that set up correctly, glue all the wires into the fold of the wing/spar as neatly as you can. 

The mess of wires.

After organising wires. Shove as many into the nacelles as possible.

Run the aileron servo wires on a Y-splitter up the same route, and cut out holes for the servos in the outside wall of the outboard nacelle with the wire going through the nacelle. Hook up the pushrod like normal. The elevator servo should be back as far as possible since this is a nose-heavy design. I put mine at an angle towards the horn to keep the angle of the force pretty even. 

Here is a wiring diagram by request. It appears unreadable, so I also posted a higher res PDF in the plans section.

When the wing is wired up and tested, you can cover it up using the bottom paper. Test fit, then glue the leading edge down and tape it. Then tape the trailing edge down, there should be about 5mm of wing surface behind it to tape to. If you need access, you can cut this tape and open the bottom of the wing.  Lastly, push the wires and Rx back in the bomb bay as far as possible, or behind the wing even, to help keep the CG back, then tape the front of the doors shut.

Tidied up with the paper wing bottom covering. 

Painting Cockpit & Canopies. 

A good paint job is never time poorly spent - it hides a lot of design flaws! I did mine with the classic black bottom (RAF did most of the night bombing) and camouflage top, and added some white bands for visibility. I also like a good set of markings. But I have given up on buying stickers, and now just print them on a colour printer. Cut them out, brush a good, thinned wood glue on the back, and place them and rub them flat. Easy, very durable, and free.

Bombers had a lot of glass bits, so start saving up interesting shapes of clamshell packaging now (I have a bag in my garage). You need to find a few semi-spherical bits to get a good effect, but you will find there is lots of this around in the garbage. I just hold pieces up to the plane and see how they fit. I cut out some bits to make the nose gunner and bombardier bubbles, which are very distinctive, and the tail gunner. I also cut out a circle in the top for a top gunner because I had a little plastic bubble of about the right size and shape. The main canopy was three bit of plastic but you can do without the rear bubble bit just by tapering the rear section. When you have these together and cut out, glue them into place (glue on the plane, not the plastic since it can melt it if it is too hot) and hold. Then use strips of black tape to cover up your mess. This is worth a bit of effort because it is surprising how easy it is to make a big difference in how it looks. 

 Packaging from a light bulb made into the forward gunner. Did the same with all the glass. 

Removable Landing Gear. 

Originally this was a hand-toss plane, but I wanted to put a camera on the belly, and the differential thrust was intriguing, so I made landing gear. At the rear a simple skewer pin was glued in. The front gear should be low and from the inboard nacelles (this is why they were bigger). I designed a simple and removable bent-wire set using common light wheels (e.g. from Hobbyzone Supercub). 

Bend two mirror image wires using 2 mm piano wire like the picture. The distances (mm) between the bends (from wheel back) are: 25, 30, 10, 10, 75, 10, 10. 

Bent wires ready to go.

Now hold the wire on the bottom of the nacelle so the front protrusion is flush with the front of the scoop and mark where the rear dog-leg positions. Tape-reinforce this position and poke a hole here. Insert the dog-leg and fold it down into place so the front is flush. Not stretch an elastic (I use bike inner tube - great stuff that never degrades) between the ends of the skewer over the leading edge of the wire, holding it down. Pop on the wheel and dap a little glue on the end of the wire to hold it on, and you are done. To remove, simple take the elastic off and swing the wheel up and out of the hole. These work fine for taxi, take off, and landing (see video), and look good too. 

To install, insert end in hole, lower into place, and stretch elastics over the front of wire. 

Extra Fun: FPV Bombsight and Simple Remote Bomb Dropping System. 

Why make a bomber and not drop bombs? I originally intended to make a bomb bay like the Mitchell, but when I saw the rats nest of wires and tiny space, I gave up on that and made under wing bombs instead. These are SUPER simple. Just cut notches into the inside wall of the inboard nacelles so a 5g servo can sit upright lengthways and put a long arm on it, centered so it is pointing just slightly towards the nacelle. Also cut a hole in the wing bottom to match. Run the wire into the fuse on a Y-harness. Now get an elastic and loop a hard plastic ring on one end, and loop the other end around this servo wire inside the bomb bay. Shove the plastic ring end through the hole to the outside of the fuselage so the elastic is anchored to the side of the plane and has a ring dangling from it. If you slip this ring over the servo arm, stretching the elastic over a bomb, then turing the servo arm towards the fuselage allows the ring to slip off the arm, releasing the bomb. Put this on a three way switch, so centre is centre, up releases one bomb, and down releases the other bomb. You may need to cut a small recess for the servo arm when it is full extended back towards the wall (when the opposite bomb is dropping). It is important to keep the arm and ring clean. If you spray paint as I did, scrape the paint off both since you need them to slide easily or your bombs won’t drop. Also, the bomb can’t be too small since you need tension on the elastic to release. Try a few set ups and just go with the ones that work. 

A look inside the bomb bay showing the bomb-release elastic (red) is anchored around the bomb servo wire.

Bombs installed, showing position of 5g servos.

Bomb-cam - don't use your good camera!

The FPV bombsight is something I always wanted to make. I took a mini FPV rig that I made for FPV combat (on my FT Scout - something I totally recommend since the Scout seems more like a Spitfire when you are using it for FPV combat), and simply mounted it in the bombardier window hole, or even over the front of the nose, pointing down and slightly forward. I shot footage through my goggles using a crap 20mW Tx, which I have since replaced with a 200mW one that is the same size. The footage is black and white because I replaced the standard lens on a ultra-cheap camera (i.e. not going to cry when I crash on it) with a 1.8 mm fish-eye that I got on eBay and it brings in so much light the sensor gets confused and most color is lost. Strange, but I love the 180 degree FOV. To do this, just release the locking screw and swap the lenses.

FPV bombsight installed on an early test flight. 

To use this for bombing, either get a bombardier to use your goggles (I had Paul calling bomb shots for me), or hook up a monitor like in the picture. You can fly LOS and use the screen to line up your shot. It has occurred to me that mounting this on the brim of a ball hat would be an interesting project, so you could flip your screen down like Luke Skywalker and his X-wing targeting computer, at least for those of us who can’t use the Force for this. 

An inexpesive car "backup" monitor can be used as your FPV bombsight. 

FPV Bombsight Specs:

Really cheap 200 mW Tx:

http://www.hobbyking.com/hobbyking/store/__76392__HobbyKing_8482_FT952_5_8GHz_32CH_200mW_Mini_FPV_Transmitter_with_Gopro_3_AV_Lead.html

Really cheap camera:

http://www.banggood.com/FPV-14-CMOS-HD-Color-Camera-Module-600TVL-120-Degree-Wide-Angle-p-944546.html

1.8mm Fish Eye Lens for M12 Camera (this is the thread size for standard micro camera, not pico):

To get one just go to eBay and search for “M12 lens” and “fish eye” or “1.8”. They are about $8. 

Really cheap Monitor:

http://www.ebay.ca/itm/4-3-TFT-LCD-Color-Car-Rearview-Rear-View-Monitor-Reverse-Backup-Camera-DVD-M2-/131425635458?pt=LH_DefaultDomain_0&hash=item1e99940c82

Power Specs:

This was all done with parts for a starter 250mm quad. 

Motors - Quanum MT Series 1806 2300KV

Props - Gemfan 5030 Multirotor Propellers

ESCs - Afro ESC 12Amp Ultra Lite

Battery - 2S works, unless you get into trouble. 3S is ideal, and I have tested as big as 1500mAh. I use 850mAh ideally as it leave space to move it around and include a low voltage alarm. This gives 10minutes or so. But don’t push it, this plane does not like zero battery power. 

Flight Characteristics: 

First of all, this is a bomber, so don’t fly it like a mustang. Having said that, I was shocked at how nimble it is. You can throw it or take off using the gear. It can carry a fair bit of weight (bombs, plus camera, pus wheels, plus FPV gear, etc.) and does not seem to mind, as long as you are using a 3S battery. 

Aileron turns require a fair bit of elevator, and power. I give it a little pulse on all turns. Slow turns low to the ground are asking for trouble. I did not mix differential into the turns but use thumbs for this. It will flat spin easily, and goes nose down soon enough, so keep the differential dialed way down, but it will turn nicely this way too, and if you ever loose a prop or motor, you will want that option. 

The design is a bit nose heavy. I did the CG at the spar as usual, and this required pushing some wiring back as far as possible. I also strapped a mobs back around the turret.

I did not have much luck gliding, but I think I tried when it was nose-heavy (with FPV gear). It won’t fall out of the sky without power, but it likes power so don’t push your battery. I think the differential thrust maybe is a problem when the battery is dying, since I did notice some strange behavior in such circumstances. So land before your battery dies. 

Plans.

 Ahh..the plans. I loaded a single PDF with all the foam pieces (updated April 7 because I forgot the scoop) and a single PDF with all the paper pieces. Let me know (kindly please) if there are any errors in my transcribing the plane to plans (sorry if there are - I don't think so). 

Lancaster Plans - All Foamboard pieces

Lancaster Plans - All Paper Parts

 Quad wiring diagram