Swappable Messerschmitt ME262 - The “Schwalbe”
UPDATE - NEW FLIGHT VIDEO ADDED, AND REVISED VIEW OF FLYING CHARACTERISTICS
I have been tempted for some time to make a swappable EDF, but I am honestly not that interested in modern jet airplanes. I am more interested in the classics and things that look like “planes” and not like arrowheads.
I also don’t know anything whatsoever about EDFs, except they are noisy and I gather not very powerful. So as far as experimentation goes, better make one has the advantages of a nice airfoil and a shape like a normal plane. Maybe if I make one that can even glide I have reason to hope it will fly ok.
All of this brings me to the Messerschmitt ME262, which is probably because that’s what I wanted to do in the first place. As far as classics go, it’s hard to beat the ME262.
Towards the end of WWII, germany began developing a lot of scary technology. The ME262 is often cited as one of these desperate “secret weapons”, but work on it actually preceded WWII. It was not, however, produced in numbers until 1944. Apparently they learned from a captured allied pilot of the development of the British Gloster Meteor, the second jet powered fighter (that never saw combat in WWII), and this led to speeding up the program and the ME262 being put into service as a fighter, bomber, and night fighter.
It was a formidable aircraft - faster than the Gloster and other fighters of the day and hard to beat in the air, so allied pilots really focused on destroying them on the ground and when they slowed down to land. Incidentally, there is an excellent interview with Luftwaffe ace Franz Stigler that describes flying the 262 here (http://109lair.hobbyvista.com/articles/pilots/stigler/stigler.htm). He is also the pilot of the famous “Charley Brown” incident, who refused to shoot down a crippled B17 and actually escorted it home. It is interesting to see how he recounts flying in the 40s.
Here are a few photos of the ME262 at the RAF museum in Colindale. This is an interesting place to see one since they also have a cut-away Junkers Jumo 004 engine on display (which had a remarkable 12 hour life expectancy since by then Germany did not have access to many metals), and the 262 is sitting right beside a Gloster Meteor (the plane behind with the yellow underside). Pretty interesting to see them side by side.
Anyway, this is an iconic plane and a natural choice to make the leap into EDF building, so I gave it a go (fools rush in, and all that).
Here is a flight video that I hope is entertaining, but also shows it actually works. It has on board and ground footage from the first couple flights. I test flew it before it was painted both with props and EDFs. Thanks to Chad for additional footage.
Here is a second video with a lot more flying so you can see how it looks in the air. I also have to revise my views of it after about an hour flying in windy conditions - it did just great.
Because I needed to make a system to hold the EDF, and I thought I might as well make it a swappable one. This was partly for fun, but also because if EDFs turned out to be awful, I thought it would be worthwhile to make the plane in such a way that the EDF units could be swapped out for prop units, while keeping the overall appearance. Read on and you will see this was a good idea, so if you are scared of EDFs, or hate them through experience (like I do now), then no problem, you can make an ME262 with props that looks very nearly identical.
I posted the instructions for the EDF Powerpod separately. I chose 64mm EDF because that was the right size to keep the jets close to the scale of the Junkers Jumo 004 units on the 262. I figured better make them as big as I can.
Instructions for the EDF Powerpod can be found here:
I consider this to be a pretty advanced plane to build. There are lots of tricky bits that may be important, so probably best to try it once you have built a few other planes (I recommend the FT Spitfire, and the Messerschmitt Bf109 I posted since they are basic and fly great).
The 262 wing is very iconic, narrow and swept back, with the huge engines hanging down very low. Being scared of tip stalls, the wing design has plenty of under-camber at the tips, but is essentially the same design as the FT Spitfire. The actual wing is cut out and folds up the same way, the major exception being the spars do not extend between them because the angle of the sweep is too extreme. Instead, trim the spars flush and use two short joiner-spars. When you are ready to join the wings, glue these into one half and then test fit. If the joint is tight and the sweep and dihedral look good, then glue them together and tape after the glue has set. To get the dihedral, raise one wingtip 100mm while gluing the wings together. Lastly, I cut off the tip so it fit into the hole in the fuselage more easily.
Double joining spar between the wings.
The fuselage is a bit different, because in the 262 had a distinctive triangular cross section. To achieve this, I stuck with a traditional ‘box’ design, but made the top face smaller so when it folded up it made the correct angles of the side panels. The rounded top of the triangle was finished with formers and posterboard. This worked well, it is very strong and light, even given its large size. The tricky part in the build is that the sides of the fuselage taper to the tail, but also go from being angled to vertical, so you have to ease the foamboard into this shape carefully so it does not buckle. I put a couple supports in the back to help this too (see tail section instructions).
The fuselage has sloped sides to eventually get the triangular cross section
Fuselage with wing holes cut out.
Wing installed, and detail of large interior bulkhead
To taper the nose to a point, and allow for a longer fuselage than a single foamboard piece allows, it has a separate nose. This is also where you access the electronics and battery, and, I learned, becomes part of the landing “gear”. By making the nose breakaway easily, you soften the blow of landing. I am not sure how durable this plane is going to be...
Anyway, to make the nose first make the fuselage joiner piece, which fits tight inside the fuselage, and glue it into place. Now take the nose piece and glue it together just like the fuselage, up to the point where the taper begins. Once set, test fit with the adaptor - the joint should be clean as possible. Now bend the four sides of the nose together and test fit so the taper is symmetrical on both sides, and the nose should terminate so it is about 1.5cm across on the top and 4.5cm across on the bottom. Note that the bottom and top panels may be too big (overhang), that is OK as it will be trimmed at the next stage. Now glue the four joints together in an A-fold (butt against top and bottom), and when the glue is set trim the excess foam from the top and bottom with a sharp razor at a bit of a bevel to smooth the hard edge a bit. This trimming also allows some error in how you fold this up.
detail of the paper bottom of the nose, before the formers and top decks are added.
The horizontal stabilizer sits well above the fuselage, so can’t be used to stabilize the assembly as it does in many similar planes. Instead I made the vertical stabilizer go right down to the floor of the fuselage, and put two supports in the tail that keep it level, and support the sides of the fuselage at the same time.
The first step is to join the two stabilizers. To do this, cut the bevel hinge on the rudder, and then cut the rudder off. Now slide the horizontal stabilizer into the now exposed slot in the vertical stabilizer, so the two should fit tight together. Glue into place, checking the right angle is maintained, then tape the rudder back on. Now glue the bottom of the horizontal stabilizer to the floor of the fuselage so the rudder hinge lines up with the end of the fuselage sides (this should be dictated by the tabs). Keep this vertical while the glue sets. Now glue the two small supports to the sides of the horizontal stabilizer and the floor of the fuselage so they are flush with the edge of the floor. When this is all set, glue the fuselage sides to the floor, the supports, and the horizontal stabilizer, making sure to keep the tail straight with respect to the wings (this can be adjusted with hot glue by sliding the fuselage sides up and down as the glue sets, but once set is pretty much fixed).
Tail assembly, and detail of how it attaches to the fuselage and supports the sides.
Formers and top decks.
Once the nose is done, stick it into place, and glue the formers to the top at the positions indicated on the plans.
Now it’s time to add the top decks and finish the triangular look of the fuselage. Start with the tip, and glue the hourglass-shaped paper board (see plans) to the bottom from about 5cm back, and right around the tip and on to the top. When set, trim the sides with a sharp razor. Next, take the back top deck and test fit with the tail and formers, so that it lines with the rear-cockpit former and tail. When you are happy, glue/tape into place and trim the front parts so they end at the “seat” in the middle of the cockpit. Now test fit the front top deck, with the nose attached to the fuselage. Line up the bevel cuts with the position on the nose when the sides begin to taper and make sure everything lines up (it should go from close to the nose all the way back to past the seat). If you are happy, glue it down to the formers up to the two spanning the nose-joint. Then do the front (otherwise it’s too long to hold it all down). Glue and/or tape the sides and taper cut, and when it is all done, very carefully take a very sharp razor and cut the top deck where the nose/fuselage meet in a single clean line. This makes the joint very subtle.
formers glued into place
rear deck added
First do the rear portion of the forward deck (up to the joint), then do the top of the nose last.
When the decks are done, carefully cut the paper around the joint to make a seamless breakaway nose.
I initially attached the nose with a skewer, but found this cased damage on landing. So the nose is now intentionally made to break-away somewhat easily (not too easily, since the battery will be in there!). In the final version is is attached with velcro on the bottom. Do this after paining.
The nacelles have to be attached after the wing is inserted in the fuselage, so do that first. Make sure you trim a small bit off the tip of the wing joint first, so it fits into the holes in the fuselage. Once they wings are attached, measure out from the fuselage sides XXcm and XXcm and mark two lines at these points, parallel to the fuselage. Now take the nacelle piece, and remove the paper from one side as indicated on the plans. This is the inside. Gently pull this back and forth over the corner of your bench to induce the curve (paper side up). When it is nicely rounded, line the inside edge up on the inside wing line so the front of the nacelle is even with the leading edge of the wing, and mark where the tabs are. Cut the tab holes, and glue this side of the nacelle into place. Now bend the other side over to the other line, and repeat (the front of the nacelle will be well in front of the leading edge, but the sides should be parallel with the fuselage). Test fit your powerpod, and if it’s good, cut the outside tabs and glue the outside edge of the nacelle into place.
To give the nacelles the look, I also put two paperboard cones on the front and back (see plans). For the back, simply cut out the cone piece, fit the large end of the cone to the curve of your nacelle and make the small end so the diameter is about the same as the intake of the EDF, then tape the cone together (inside and out). Tape the cone into place so it is flush with the back of the nacelle - the top will not be attached to anything, and you may way to trim a little gap for the wires coming out of the powerpod. When doing the second one, line it up with the finished cone to make sure the openings are the same size.
For the front nacelle, do the same except make sure the large end of the cone fits just over the nacelle. At the top it should project back over the top of the leading edge of the wing and hide all the powerpod attachment stuff. When you are happy with the size and shape, tape it together (inside and out again). I attached it to the nacelle and top of the wing with velcro, since this needs to be removable to get the powerpod in and out.
A lot of people underestimate the importance of a good paint job in my opinion. Even be most amazing foamboard replica can look like foamboard, but then paint it and suddenly it totally changes and makes up for a lot of the downsides to cheap, flat building materials. Anyway, now is the time to paint if you are going to (and remember to do the one paper canopy piece too (see below - I forgot to paint this and it was a nuisance). Varnish everything with an oil based varnish (I am very sloppy here, takes a couple minutes), paint with acrylics, and then varnish with water based varnish again to protect the paint. I put some markings on that I just printed on my b/w printer and glued on with carpenters glue before the final coat of varnish, and they look fine. I did the bottom grey and the top darker to help with perspective in the air. Probably some coloured wingtips and/or tail would have been good, but I forgot.
The canopy is in four parts, all of which are in the plans. The main and rear glass parts are cut from the straight sides of a 2L pop bottle, the front from flat clear plastic packaging, and the rear from paperboard. Cut the main section first, test fit so it should go from where the cockpit hole begins to round at the front to a little behind the seat. Glue one side into place (glue the paper, not the plastic or it melts) and then tape both inside and outside with clear packing tape. Now test fit the rear glass section and do the same, also clear taping it to the main section and gluing it to the rear cockpit former. Lastly, tape the front glass panels together, then test fit and tape to the main section, and around the front. Now add some “ribs” with dark tape strips. Lastly, add the rear paperboard section, which should just cover the rear cockpit former, and the tips should just reach the joint between the main and rear glass sections. Make sure you paint this piece before putting it on.
Back and main canopy pieces installed
Front canopy piece installed.
Black tape for details.
Test Flights - Did it work?
EDF Flight - a comedy of errors.
To balance this plane I put an 1800 4s right in the nose. The receiver was behind this (plenty of room in the fuselage). I don’t know where the best CG is, but I balanced it at the wing spar half way between the fuselage and the nacelles. The ESCs are in the nacells to get some air, and the wires to the ESCs come out under the trailing edge of the wing where they are accessible. I made a Y-splitter for the power. The EDFs are 65mm, pretty cheap ones, and I hope the plastic housing holds up to landings (since it lands on the nacells). Here are the exact specs used:
EDFs: HobbyKing 64mm EDF units with ADH300 motor (4300kv)
ESCs: Turnigy Plush 45A
Battery: Turnigy Nanotech 1800mAh 4S
I test flew this prior to painting the plane, and it flew fine. It was a quick flight because it was really windy that night, but it launched ok, did a circuit around the park and landed. However, once the plane was completed, things started to go wrong. Chad agreed to throw it for me, but the tail got caught on his hand and it whet nose down. On the second toss one of the EDF units went funky, turning on and off, and it went into a flat-spin right away - smash. This was a re-occuring theme, if you watch the video it seems likely one of the two EDF units was bad and died sending the plane into a slow flat spin a few times. This was also early morning and the field was wet, so it began to get damp at this point. The next two tosses were equally bad, I finally realized because the wet nacell cones were floppy and one was being sucked into the EDF, so it had no thrust. Coupled with the funky EDF going off periodically. Smash, smash, smash. A total disaster. At that point, I put it aside for a couple months.
Adaptor for propellor flight.
Some people might like the 262, but not want to muddle with EDFs: I can relate to that. This plane was always designed so that a normal powerpod could be attached to the wing - in fact I test flew the airframe with the powerpods from my B25 bomber months before I finished the plane. If you wanted, you could just stick your favourite powerpods to the wing skewers and tape them to the underside of the wing firmly, then insert a skewer through the nacells and powerpods to finish holding them in place. This is how I tested the airframe (see the arial footage in the video), but without the front cones on the nacells it was a bit ugly. So when I ditched the EDF units, I made a quick and dirty prop powerpod adaptor to attach to the wing skewers and provide a new attachment site for the traditional powerpod that is further forward (just so the prop is right in front of the nacell cone). The motor is centered at the mouth of the front nacell. I put my B25 powerpods back in and tried it again. The maiden for this was also awkward because I had too little throw on my aileron and failed to notice the rudder was reversed. But with this corrected and lots of aileron (I would give it >100% because they are pretty small), it does indeed fly.
I had a nice windy day and a big open field and did 4 batteries for about 1h flying time the other day. Once I took the time to set it up properly it flew great. I gave it 125% aileron and mixed 30% rudder and it was smooth as can be. Even in a strong wind it was quite sound. It is still a heavy twin, so don't expect the agility of a smaller plane. I was flying with my B25 power pods (Turnigy 2217 1050kv motors, two 35amp ESCs and 9X4 SF props - See more at: http://flitetest.com/articles/swappable-b25-mitchell-twin-enginehttp-www-youtu#sthash.v0VTyeDQ.dpuf). If I were doing this again I would put higher kv motors and APC props to give it more zip, but overall I was a bit hard on it because of my bad experience with dud EDFs.
Re-configured with the prop adaptors. Looks almost identical to the EDF, and when they spin you can't really see them.
This was a hard plane to make, looked great in the air. The EDF version was plagued by problems, many of them were bad luck and bad EDF quality, but it is also clear that I was right on the edge of flyable to begin with, so small problems led to bad outcomes.
Why the EDF test flight worked, but the finished plane did not is unknown. It is possible it was just bad luck on the first couple throws, with faulty EDFs or whatever. It is also possible the strong wind of the first test flight was necessary to get the lift to get into the air. But it is also possible that the front nacell cone was limiting airflow to the EDF to the point it would not fly with them. I realized I don’t care enough about EDFs to find out.
The prop flight was actually very good - I would upgrate the motors and props to make it fly more like a fighter and less like a bomber, but the airframe really performed well when it was given enough throw on the control surfaces.
I hope someone makes this plane and flies it with props, it is pretty in the air and set up right flies nicely, even in windy conditions. But even more I hope someone that actually understands EDFs rescues these plans by making modifications that allow it to actually fly as a jet - it was impressive to see, briefly, and I would like to see it again.