Swappable B25 Mitchell Twin-Engine Bomber

by ultramicrobe | November 17, 2013 | (60 Ratings) Posted in Projects

UPDATE -  I started a thread in the forum on this build if anyone wants to post upgrates or pictures of their versions that would be great to see. 

http://forum.flitetest.com/showthread.php?12028-Swappable-B25-Twin-Engine-Mitchell-Bomber&highlight=b25


The basic design of the FT Spitfire is readily adaptable to a number of other planes. I have previously posted adaptations of The Messerschmitt bf109 and P51D Mustang, both of which flew well and looked great (see links at the bottom of this post). The whole idea behind these was to change any parts needed to make it resemble the plane of choice, but not to change the joints between the parts so you know it will fit together. 

 

This basic configuration allows for almost any WWII fighter to be adapted, but there are two big exceptions the would also allow a lot of really fun planes from the same era to be made. The first is gull wings (e.g. Corsair or Stuka), which seems like it should be doable with only a few changes. The second is big multi-engine planes, like bombers. Here, I show how to make a popular bomber using essentially the same parts as FT Spitfire or the other planes I have designed. I picked the B25 Mitchell bomber for a few reasons. It is an iconic plane, its shape lends itself well to foamboard construction, and it was no sluggard in the air, having been adapted for a number of purposes beyond droning around and dropping bombs. I hoped this might be the case in a scaled up Swappable twin engine version, and this proved to be the case. The plane flies like a big plane, but is lots of fun and looks pretty good. 

Below are some videos of the maiden flights showing some of the main characteristics, and also instructions to build your own. I should say, this is not a plane for beginners. Both flying it and also building it requires some experience. I have not been quite so step by step with my build instructions, because I assume if you try it you have some experience under your belt, and already know the basics. Much of the design was made up during the build, and many of the parts I made up as I went, and built to fit. Still, if you know how to build a Spit or bf109, you could do this from the below instructions. 

But first, I recently got to go to the RAF museum in London (http://www.rafmuseum.org.uk) and I highly recommend it. It is an excellent museum, and happens to have every plane I have ever designed, and some I am just working on. So I have updated all my old posts to include picutres of the real thing, and where possible will do this in the future too. 

Here is a shot of the dintinctive cockpit and nose. 

This one has a different tail turret. You can also see the interesting partial dihedral on the wing (just past the nacells)

Here is a nice shot of the distinctive rudder. 

 

Here are two short movies showing how the plane flies and looks. The first one has a clip from the BombCam that we set up, which is kind of fun (the camera faces back so you can see the plane as it falls). The second on is from a friend Ed (thanks Ed), and shows a few clips from the prototype flight before it was finished. 

 

BUILDING INSTRUCTIONS (PLANS BELOW):

The first step is the wing. Where the wing meets the fuse is the same as the Spit and my other builds, and all I did was extend the length so that each wing half uses the whole length of a pieces of Adams foamboard, and extended the spar accordingly (did not bother making plan for this, just make it longer).  The overall shape is just estimated based on pictures of B25s. Ailerons were standard 1.5” X 10” and the servos were installed on the spar, as usual. The wing halves are attached like those of the Spit, but I reduced the dihedral by 50% since the B25 only had a bit of dihedral between the fuselage and nacells. This seems to be fine and did not affect the stability.

 

Next is the fuselage itself. You have to install the wings BEFORE adding the nacells (or the wing can't be forced into the wing holes in the fuselage). Again, the overall shape, including the height and width, is the same as the Spit, but the length is extended to the rear to use the whole length of the foamboard. None of the notches for the power pod need be cut in the top. The holes for the wings are the same, but raised so the wings emerge roughly half way up the fuselage (once the top formers are added).  I also inserted a triangle at the top rear because I made my whole tail assembly removable for storage, but this is optional. At the extreme rear the two sides are not glued directly to one another, but three small pieces of foam are glued between them as spacers (where the rear gun turret will be). 

Wing installed in fuselage

 

The motors are housed in two adapted power pods. The front end is identical to a normal powerpod, but at the rear they are tapered on the sides and bottom to form the trailing edge of the nacells. Paper was glued to top of the back 2”, which covers the part that shows behind the trailing edge of the wing. I cut a notch about 3” from the back to allow the wires to be fed from the powerpod to the fuselage (this is an extension of the servo wire, and I soldered a Y-connector for the positive and negative power wires with bullet plugs). I tucked them into the gap in the trailing edge of the wing to keep it tidy, and left all the connections outside the powerpod so they can be disconnected before removing the pod. The power pods are mounted under the wing in two A-fold boxes that fit tight to the power pod dimensions, which are glued to the wings (with notches cut in the wing bottom) parallel to and 5” from the fuselage (to easily allow 9” props). If you make this tight you don’t need the skewers at the front, just one through the side. 

 

Marking nacell positions

 

To make the nacells look more realistic, it would be nice to make them round. So to trick the eye, I made round covers for the front of each. These are easy. First take a short length (like 1”) of 3” foam pipe insulation. Then use these to form a tube from a length of something like thin plastic or paperboard (I used the packaging from a thermarest) that has been cut in the shape shown to allow them to fit over the leading edge of the wing when they are formed into the tube. Then I added some velcro to the back to hold them on the plane and put a little square of tape where the cover meets the top of the wing. It works well - the eye sees a round nacell. (this piece is included in the plans below)

Nacell covers, trick they eye into seeing a round nacell

These are removable (to take the pod out) and attached by velcro

 

The power system I used consists of two Turnigy 2217 1050kv motors, two 35amp ESCs and 9X4 SF props. This provided plenty of power. I used a standard 2200mah 3S battery, which is situated near the front of the nose to balance a pretty tail-heavy design.  

To finish the fuselage, formers are added as usual. Three former shapes were used. Formers are numbered from front to back on the main fuselage (1 & 2 forward of the cockpit, 3, 4 & 5 behind. Former 3 is repeated twice. Forward of the cockpit formers 1 & 2 set up a slight downward angle. The usual paperboard is glued and taped down over the formers to the rear of the cockpit, as usual. I just cut this to fit after the formers were installed and cut two slits at the last former to taper it. Leave the paperboard forward of the cockpit for now, it is cleaner to install that later. 

Formers and paperboad installation - Formers 3, 3 & 4 are already covered here

In the bottom I cut out a section to make bomb doors, and also provide access to the electronics. I aim to drive the bomb doors with servos at some point, but am posting this before I have gotten around to figuring out how. This proves to be a bit tricky. With servos with huge throws it would be simple enough, but if anyone has any good ideas to McGiver something with standard Hextronic 5g or 9g servos, I would love to see a comment. For now, I satisfy my want to bomb things with a simple bomb release mechanism on the gear channel (see picture). 

 Bomb Dropper

BombCam (the yellow loop attaches to the dropper - it is a slice of plastic hose which prevents hang ups - and there is a lot of lead weight added to the nose so it falls camera-up)

The tail is a bit tricky, because the B25 has a distinctive double rudder. To make this, cut out two rudders. They are mirror images, so cut the hinge and mortises on opposite sides (and leave the paper on the outside of the mortise so it hides the tenon from the horizontal stabilizer). Cut the horizontal stabilizer as shown, and attach the two rudders. To be honest, having now flown it I have come to the conclusions that this plane does not need rudders, so if you want, skip making them hinged and skip the complex problem of how to drive them. But if you DO want rudders, and like making things difficult for yourself, what I did was mount a single servo in the bottom of the horizontal stabilizer so just the double arm poked up. Then I cut notches in the vertical stablizers, just forward of each rudder, and inserted control horns in the foam of the rudders so they emerged into these notches (see pictures - its hard to explain). These were plastic strips from a hotel key card with a hole, inserted about 1.5cm into the rudder. Then two thin pushrods were inserted into thin flexible tube which arced to the servo arms and were held down with some glue and a couple small zip ties. The result of this is that the two rudders move together in the same direction. I tried a few variations of this, and ended up throwing them away, but this one seems to work. In retrospect, I would not bother with movable rudders.

Rudder Assembly

Rudder Hinge

The elevator is driven by a servo in the side of the fuselage, as usual. The trick here is to get both elevators to move together because they are separated by a bit of fuselage. I made a piece of wire to connect them and glued/taped it to the top, and this seems to work okay. My tail is held down with an elastic (bike inner tube, great elastics) at the back and a tab under the fuselage at the front so its removable, but again it would be simpler just to glue it down. 

By now you probably noticed the plane has no nose. This is because the foam board sheets are not long enough to keep the proportion right. To solve this, and at the same time make a  hatch to access the battery, you have to add a nose piece. This is a 3” extension of the fuselage lines that fits to the main fuselage using an inside tight-fitting coupler, basically a 3” box that is just smaller than the two pieces to be joined. Glue this inside the nose extension and this allows the nose to slid on and off (and put a skewer in to hold it, though it seems unlikely to ever fall off). The nose piece is a box just like the fuselage, and I cut the bottom at the same angle as the fuselage, so the lines are just extended.

Once you have the nose box built, install two formers on the top that continue the line of the fuselage top forward of the cockpit. I simply made them about right, then put the nose on and cut them down to match the angle on the rest of the fuselage. Now cover the entire forward section with one piece of paperboard, gluing it down on all four forward formers (attaching the nose to the rest of the fuselage temporarily), and taping down the sides, as usual. Once this has dried, take a sharp blade and carefully cut the paperboard between the fuselage and nose section to re-separate the nose. This ensures your two pieces form a perfectly consistent line from the cockpit to the nose, and looks very clean. 

  

The rest is optional decorations. I made cockpit canopy, top gun turret, rear gun turret, and nose-glass out of old pieces of clamshell packaging and black duct tape. I used coloured tape for the rudders and wingtips for visibility, and went with a British paint scheme with the black and white stripes on olive, and varnished and painted it. 

Tempting, but so many people gave me grief about the stickers on my Messerschmitt not being authentic...

Tail Turret - bit of garbage plastic

Front Canopies - more bits of garbage plastid (the main one and top of nose are given in the plans)

Battery hatch - I use a 2200mah 3S, which is velcroed onto the floor of the nose


I balanced the plane assuming a CG at the wing spar, and this worked well. The plane glides okay at speed, but does tip stall if you are underpowered. I saw this as I glided for landings, especially once with a tail wind. I now land under low power until the last second, then power down (see movie). Other than that it flies great, and since it is big you can get up pretty high for great bomb dropping. I would seriously consider skipping the working rudder on this build, its a lot of work and it does not appear to need it to fly well. Looks nice in the air - here are some stills from a movie during a nice early morning flight. 

 

Now I am asking myself, should I make plans for this? I actually hate making electronic files for plans and don’t think I do a great job because I hate doing it. But would be nice to have plans if people really wanted to make the plane, right? Unfortunately I can’t tell from previous posts I have done whether people are actually making them or just reading the post. All my friends told me I had to make plans, so I did, but I would ask one favour - if you actually do make this plane, can you please leave a comment saying so? I would appreciate it in case I am wasting my time with plans. Thanks.


BUILD PLANS:

Canopies

Formers

Fuselage

Horizontal Stabilizer (re-uploaded)

Vert Stab

Nose Coupler

Nose

Nacell

Nacell Covers

Powerpod

wing

COMMENTS

Joker 53150 on November 17, 2013
Wow, very nice work!
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Fly'n-V on November 17, 2013
Bravo!!! Great design and build...Thanks for sharing!
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LordVader on November 17, 2013
Can't wait to build this one. I have built your other two planes. They are awesome. I believe I have pics of them in the mad scratch-build forum. If not, I'll try to post them along with some of my other planes.
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Jaxx on November 17, 2013
You are an amazing designer. Thanks for sharing all your work!
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Flynn on November 17, 2013
Amazing job on all your planes! I will be building this one. Thanks for sharing!
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Good Kebo on November 17, 2013
What a nice job! Thanks
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alibopo on November 17, 2013
Very nice build - love how it flies. Bomb-cam - what next - great idea! :) Just a little bit of effort with the detail is all it takes - inspirational.
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ultramicrobe on November 17, 2013
I forgot to post the nacell cover plan, so when I did that I added a picture of the actual bomb if you are interested. I have dropped cameras from my supercub too, it is fun. I also made a ParachuteCam but have yet to try it (you don't want to do that on a windy day...)
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Dagger_117 on November 18, 2013
Very nicely done!
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onemoreflite (John Michaels) on November 17, 2013
Pure Awesomeness!
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Okie on November 17, 2013
great job love all them what is the best program to print them from

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ultramicrobe on November 17, 2013
All the pieces have a 5 inch scale bar - so you can just print with any PDF viewer and then put a ruler on it and make sure it is ok. If not, scale the printing accordingly. Sorry, but the files are made to scale but seem to change when other people use different programs and computers. As I said, I hate plans, but with the scale bar you can be sure when you have the right size.
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Trauma50 on November 17, 2013
Great work. Cant wait to build it. Thanks for taking the time to draw the plans up.
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Cortes Gary on November 17, 2013
Good attention to detail. Looks great in the sky. Very impressive.
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NewZee on November 17, 2013
Fantastic Job! I am very impressed at what you were able to create! I have folwed the same "design approach" on a Swappable J3 Cub and had good results as well! I feel like you do that formal plans are not required , however I also reconginize that others would benefit from these plans, regardless you are to be complemented on a great theme of an iconic WWII era airplane, Well done!!.
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Eduardo Fritis on November 17, 2013
Amazing plane Patrick! I am blown away by the looks and the way the plane flies! This job requires SKILLS! Congratulations... and when you are tired flying it I can "Storage" it for you!!
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Art on November 17, 2013
Nice build Pat - as far as bomb drop - can you have a servo operating a pivot arm that gives you the throw you need - I have seen those on some planes to operate ailerons from one servo as throw direction is changed 90 degrees - you would need room to do it though - keep building - keep sharing - later - art
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Michael763 on November 17, 2013
Awesome Plane. Thanks for the plans. I noticed in some of the video that the vertical stabs looked like they were not 90 degrees, was that due to damage or stress? Thank you for sharing your designs.
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ultramicrobe on November 17, 2013
They were banged up when I cartwheeled a landing. Did not seem to matter much. It is a weak point though, probably worth gluing little supports in the corner on the bottom or something like that.
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Michael763 on November 17, 2013
I was wondering if you thought pre-bent plastic gift cards might work as a good support?
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lracnolip on November 17, 2013
Really nice job, all your planes have a great finished look.
Always thought a foam board bomber would be cool, thanks for showing us it can be done.
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andre on November 18, 2013
Epic!
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Patnaude_av8r on November 17, 2013
Please post plans and continue to make and design outstanding scratch builds.
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andre on November 18, 2013
BTW what kind of run time do you get off 1 2200 3S?

Thanks.
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ultramicrobe on November 18, 2013
about 15 minutes at low speed (like the movies)
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andre on November 18, 2013
No kidding... That is great.
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andre on November 18, 2013
I was testing my bomber this past weekend as well but a nasty tip stall scrubbed the plane.
Like you based off the spit design. I'll have to revisit the wing and see if I can find a better solution.

Love the Canadian decals ;)
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andre on November 18, 2013
http://forum.flitetest.com/showthread.php?6259-New-twin-bomber
http://andrerousseau.wordpress.com/category/rc-flight/ajr-48/

Reading along yes same issues was excessively tail heavy.
I had a GoPro at the nose, x2 2200 3S's and had added a 1300 to counter the tail wait (bombpod removed) but on final I brought the speed down and lost the plane.

Still seeing yours makes me want to build a fresh plane try again.
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ultramicrobe on November 18, 2013
Maybe I overstated about stalls. Its not that bad. If you watch the video I do some pretty low speed turns, banking up and out of a low pass say. Not a problem really. Just when you are almost not moving at all, and I was landing with a tail wind. So, not a huge deal. Your plane sounds like it might have been very heavy. I just weighed this one and its 875g + battery (a single 3S 2200 mah), so that is really pretty light.
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andre on November 18, 2013
That is impressive.

With 2 3S, gopro and bomb pod + gear she was heavy.
I'll see what I can do to strip it down. That said I was trying to do all that with 48" wings. Again thanks for the inspiration.
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Art on November 18, 2013
Bomb bay doors - I didn't like my comment earlier so I built a dummy version of what I had pictured in my head - the door is like a control surface so put a control horn on it - the throw is from 2 'L' shaped 'control arms', one mounted on the side and one mounter on the top - the servo would also be mounted on the top - the length of the 'L' arms would determine the amount of output throw you get from a smaller input throw - my 'L' arms were made from coffee can plastic - one servo would control both sides of the door - you need a little room to do this but it might not have to be in the bomb bay itself - I have a picture of it but don't know how to load that into comments - I think other RC forums have discussed bomb bay doors also, probably with better solutions than mine.
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andre on November 18, 2013
Art this is what I came up with.

http://andrerousseau.files.wordpress.com/2013/11/img_7577.jpg?w=595&h=396
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Art on November 18, 2013
Looks really good and straight forward - but remember - no problem is so simple that it can't be made ALOT more complex with a little thought and imagination :) Mine may be like a Rube Goldberg Machine :)
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ultramicrobe on November 18, 2013
I like it. It exactly what I tried, but I did not make the servo arms long enough. Time to warm up the glue gun. I am going to hook them up to the flaps channel so I can slow the motion waaay down and have them open over 3-4 seconds. Then the bomb is on the gear channel, so you drop it separately.
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andre on November 18, 2013
I'm going to modify my pod to be a 1x4 setup vs 2x2. The idea is my son has his own remote to release the bombs.

Testing to see if a full wing plane will fit in the car.

Thanks for the inspiration.
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WarbirdFan66 on November 18, 2013
wow, if that isint awesome i dont know what is, great work man.... 8D...i hope you made some plans for that thing because a lot of guys in here want to build it too, im sure, cheers
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1959 cutter on November 18, 2013
you and josh bixler seem to be on the same wavelength with design!
great work!
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ultramicrobe on November 18, 2013
I was thinking of a fun challenge to propose: if the number of views of this post exceed my Mustang post, I will make a Bell X-1 to drop from the B25. What do you think?
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andre on November 18, 2013
That would be a big plane ;)
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nickhall55 on November 18, 2013
Wow, flies great, real scale speed!
Excellent job!
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RoyBro on November 19, 2013
What a great silhouette passing overhead. The attention to detail is awesome.
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FliteOmega on November 20, 2013
Really cool, i'd like to make it.
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808aerosquadron on November 19, 2013
This is absolutely awesome. Great job on a RCAF Mitchell.
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andy_spoo on November 22, 2013
Love it!
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Art on November 20, 2013
How about doing another twin engine bomber? Like the Gotha G. V :)
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ultramicrobe on November 20, 2013
ha ha. I friend of mine suggested this one:
http://fungur.blogspot.ca/2010/03/russian-tank-ship-plane.html
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Art on November 21, 2013
I didn't mean the Russian 'ekranoplan' but the German WW I twin engine bomber Gotha GV - engine nacells on the wings, kind of like the power pods - old biplane type, this:
http://en.wikipedia.org/wiki/Gotha_G.V
Yours still looks neat even if you don't build a biplane :)
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81zapper on November 20, 2013
What a fantastic job love it should of put the Canadian emblem on Makes her that much better.
Going to try the lancaster next ?
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ultramicrobe on November 20, 2013
I was actually thinking a Stuka would be cool. Very square, easy to do with foamboard, and I always thought they looked pretty distinctive. I also think its time to try a swappable EDF. Maybe its a stupid idea, but since I don't know anything about EDF that won't stop me. Avro Arrow, ME262, the Batplane, lots of possibilities.
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81zapper on November 27, 2013
oh ya an Avro Arrow is a must with plans hurry up can't wait
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Krivak957 on November 21, 2013
Like everyone else, I was blown away by this new design. At the rate you (Ultramicrobe) are designing warbirds, Josh and David better hurry with another F-T warbird, or you will beat them to the punch on all the popular models. In any event, you are doing a great job of staying true to the F-T building style -- and advancing it. In particular, I was impressed with your simple technique for making round nacelles. Obviously, this technique could be used for radial-engine (i.e., round-nosed) fuselages as well, e.g., Corsair, Hellcat, Zero, Sea Fury, etc. As you suggest, if the front of the element (whether nacelle or fuselage) is round, this tricks the eye to make the rest of the plane look okay, even if it is actually rectangular.
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ultramicrobe on November 24, 2013
Yes, I have been thinking of doing a Hellcat and Zero at the same time and posting them together. They are also a great pair to show how emphasizing just a few things distinguishes the planes. I have also considered doing a post to propose "Super-Swappables". The idea is to make a collection of a small number of interchangeable parts that can be recombined into many, many different planes (e.g. from a couple wings, a couple fuselages, a few tails, and several formers you could make a LOT of different WWII fighters).
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andre on November 29, 2013
I am working away on my twin bomber. Printed your wing template out as I noticed it does have a few differences in the design over the FT Spitfire.
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ultramicrobe on December 7, 2013
let me know how it goes. The wing is quite different from the spitfire - much bigger. I would suggest skipping the moving rudder for a start, and someone suggested reinforcing the rudder with a 90 degree - a good idea since if you land nose up you can bend them.
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Emeralaz52 on December 9, 2013
I think this is pretty awesome. If I had the materials and skill level, I'd build it in a heartbeat.
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flihghy on February 8, 2014
By-the way, the design is fantastic and I plan to start construction as soon as I finish the Versa Wing.
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flihghy on February 8, 2014
After printing out the horizontal stab It appears that the stab is skewed, one side is larger in area than the other. Is my printer going south or is the skew real? If real, what is the reason for the skew?
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ultramicrobe on February 16, 2014
hi, the h stab should be symmetrical, so no one side is not supposed to be different from the other. its possible my plans are slightly off (in which case it won't matter), but if it is way off then it is probably a printer problem and you should make your stab symmetrical. I had a look at the file, and for some reason it looks like it might have been truncated in the upload (i.e. its missing both ends). I will upload a replacement (right now) and you can see if that looks better.
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ultramicrobe on February 16, 2014
I found a couple files had their ends cut off so I replaced them all. Should be ok now. Has anyone made this plane?
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flihghy on February 18, 2014
Thanks for the updated stab. On my computer, printer combo the stab is missing both ends. I can redraw the stab because my computer view shows the full stab. This problem has resulted in my need to redraw the fuse in order the get correct dimensions. After assembling the first wing half I decided to taper the spar from 1/2" to 1/4". Makes for a better fit when folding the top over the bottom at the outer end of the span. Fuse is done and the nose and coupler are being redrawn to get a better fit. Was wondering what size servos you used for the ailerons? I am planning to use Turnegy TG9z servos with 1.6kg-cm torque.
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ultramicrobe on February 25, 2014
I just use Hextronic 9g. Sorry you are having problems with the files, I don't know why now since I have re-checked and they all look good on my computer. Its definitely an issue of the "artboard" size, but usually this is not a problem.Post some pics when you get the plane in the air - looking forward to seeing it.
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Yogenh on February 26, 2014
Ok I love it and do plan on making one. Now how about a B-17??? I think that would be great!!!
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ultramicrobe on February 27, 2014
I was tempted, but put off by the added cost of a 4X motor set up. This B25 already maxes out the wingspan and fuse size possible from a single sheet of foam board, so you would either have to scale it down or make the wings from a couple sheets. No reason it would not work well though.
Myself, I am more tempted to make a mosquito if I made another bomber. That would be more fun to fly.
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Yogenh on February 27, 2014
That would be a good one and I would like that too. I like the older ones. hehehehehe so when are you starting?? LOL

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Wojethebest on May 2, 2014
Im wondering How did you make the clear nose and the rear gunner
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ultramicrobe on May 5, 2014
Hey, its just a piece of clam-shell packaging (i.e. garbage). If you keep your eye out for interesting shapes, they are all over the place easily found. But, if not, look up at the pictures I just added to the post for an alternative tail, which is blunt with a little window up above (from a real B25).
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pdxflyer on May 5, 2014
Looks awesome, I want to try it out but I have yet to get the others up and flying. but thanks for sharing
PdxPete
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stingerbee on May 6, 2014
An excellent build, congrats on your achievement.
Was wondering if this could lead to a 4 engine build of the AVRO Lancaster Bomber, that is one iconic British aircraft.
I don't suppose you can guess I have a very close relationship with this aircraft. My late father decided to volunteer for the war effort in 1942, he was trained in Australia then onto Alberta Canada on twin engine aircraft then finally to Bomber Command in England he piloted two versions of the new Lancaster, he was in a split 15th squadron 1x Canadian 2x Brits and 4x Aussies of which he was one "The Pilot". Completed 30 missions, night bombing over Germany etc, After the war when I was born and a young teenager he wouldn't talk to much about the war, you would have to force any information and details of what he went through. My brother and nephew became pilots later on flying for Cathay Pacific etc. Hope you may give it some thought on a foam build of The Lancaster, just a slightly scaled up version of the Mitchell B25.

Cheers for now......stingerbee
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ultramicrobe on May 6, 2014
Strange timing, I just spent some time looking at a Lancaster at the RAF museum (where the pictures of the B25 above were also taken - the Lancaster is beside it out of view), and reading the horrifying statistics about what it must have been like working in bomber command (over a million people were employed making them because they only averaged 21 missions before being lost). A four engine bomber would be a real beast to make and fly, but it is an intriguing challenge. If one were to do one, I think the Lancaster is the obvious choice because it is so iconic, but also amenable to foam board methods, largely because it is so square (a B17, for example, would be hard because it is so obviously a tube). I am more inclined to make a twin that is more fun to fly, like a Mosquito (in fact, I have lots of Mosquito pictures from the RAF museum too, so maybe that is next for me). But I would love to see someone do a Lancaster, so you should adapt the B25 and do one. I would do wings in 4 parts - one board up to the aileron servo, and then have the under cambered tips an extension to get the extra wingspan. The fuselage could be done exactly the way I did it with a joiner to get a bit of extra length. It would not be so hard to do, but boy it would be a big plane and I am not sure I have anywhere to store one!
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stingerbee on May 7, 2014
Hi ultramicrobe
I may just try that foamy, probably build the B25 first to get a feel for it then adapt it to the Lanc.
I know that next year when I turn 65 and retire I will build a Tony Nijhuis Designed Lanc.- 72" wingspan electric. If you never heard of him check out his website here - http://www.tonynijhuisdesigns.co.uk/ an absolute genius model aircraft designer. - See more at: http://flitetest.com/articles/swappable-b25-mitchell-twin-enginehttp-www-youtu#sthash.sNSzu0ZM.dpuf
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DukeNukem on May 26, 2014
THANK YOU!!!

I love ww2 planes , and spent crap load of time and resources failing. But i took a night and built this plane , love it.... flys like a dream right off the table. I did scale it up a few % , and used larger motors , but still for a really new pilot made it really easy. Thanks again, and to all the Flitetest people. If it wasnt for them I would of prolly not made it long.

Very Thankfull,

Dukie

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ultramicrobe on May 26, 2014
Cool - bigger means bigger bombs, right? Hope you drop a few, that is fun.

If you like the WWII planes, I recommend the 800mm Messerschmitt Bf109 because it flies better than any of the other ones I have experience with - and you can use your leftover foam from the B25 to make it. Just a suggestion, but it's my main "go to" plane when I don't know what conditions are like or don't know what to fly.

Anyway, I was thinking that with the size of the 800mm 109 and your bigger B25, they might be about the same scale? You could get a buddy flying one and see who wins.
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epic on August 29, 2014
how do I tile the planes so that I can put it on foam board?
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RickDean on September 1, 2014
Hi everyone. I'm a late comer to the party. Only recently found the FliteTest site. Being an avid builder of RC planes all my life, I've become inspired once again by the guys here at FliteTest.

I downloaded the plans for the B25 and somehow printed them out at 150%. At first I started to reprint but then thought, why not an eight foot wingspan version of a foam board B25. I cut the wings out first and they looked rally cool. I purchased a couple of 1/2" wide carbon fiber spar strips and presto, I was on the road to an eight foot B25!

I'm taking photos along the way and will share them and a maiden flight video with you all when it's completed.

Thanks FliteTest for putting this site together for people like myself.

Rick Dean
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ultramicrobe on September 2, 2014
8'! Now THAT I would like to see. You can drop some massive bombs with that thing. Please do post some movies and pictures. Maybe we should start a thread about this build on the Forum page? I see a lot of people are reading it, and maybe making it too? I figure a plane that size will fly even better. Based on my experience, my main suggestions would be to reinforce the tail a lot (like put a CF rod under the horizontal stabilizer since it sags under the weight of the rudders, and something to keep the rudders at 90 degrees), and obviously big motors, likely a pair of 3536 or something like that (I use the Turnigy Aerodrive SK3 - 3536-1050kv on my fun cub and love it, I bet 2 of them with 10-12" props would be killer on an 8' B25).
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RickDean on September 2, 2014
I have the wings completed and did use carbon fiber spars. The horizontal stabilizer its self is 24" long (wide) so I'm building it up and using CF tubes to strengthen it. Thanks for the suggestion on the motors. I'll get a little farther along with plenty of photos then start a thread in the Forum Page. I've also built a P51 and F4U1A Corsair from FliteTest plans but couldn't leave well enough alone. I built both fuselages up using my own techniques to keep the foam board nice and curved instead of squared.
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fishermansteve on September 18, 2014
hi rick is there a chance you can give me the plans to the F4U1A Corsair i like to build one thanks steve
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ultramicrobe on September 5, 2014
I just created a thread in the forum on the B25

http://forum.flitetest.com/showthread.php?12028-Swappable-B25-Twin-Engine-Mitchell-Bomber&p=131178#post131178

If anyone has builds and flight pictures to show, please sign in and show them off. Modifications and upgrades would be great too.
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Flying Fox on September 9, 2014
Beautiful Plane Keep up the good work.
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fishermansteve on September 12, 2014
Beautiful Plane. I love ww2 planes in the middle of cutting out the fuselage. just one thing why don't anyone show the painting side of the planes i'd love to see that
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ultramicrobe on September 12, 2014
There are two good posts by flite test on painting, I basically do the same thing. Coat with oil based varnish, then paint with cheap acrylics, and then another coat of varnish (water based this time if you want). I don't use an air brush because they are too fiddly and slow, I use a cheap car repair touch up air sprayer. Can do a whole plane in a few minutes, and don't get gummed up with acrylics. Here are links to the FT posts and an example of a touch up brush.

http://flitetest.com/articles/minwax-on-your-plane
http://flitetest.com/articles/painting-foam-board
http://www.kmstools.com/vaper-hvlp-touch-up-spray-gun-10153

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fishermansteve on September 16, 2014
thanks for the reply will check it out now.or buy the way this plane is fantastic An excellent build, congrats on your achievement.and please keep up the good work it is thanks to you people like me can learn from and keep the hobby alive thanks Steve PS please consider the Lancaster build
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fishermansteve on September 20, 2014
is it possible for you to take some pictures of the undercarriage.and bomber doors please. wings done fuselage half done. but stuck on doors thanks Steve
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ultramicrobe on September 22, 2014
I actually got distracted with other things and never did the bomb bay doors. I just took them off, so there is just a hole for the bombs. Someone suggested a good idea, which is put a extender on the servo arm so it can push the doors all the way open (I think there is a link above and some comments here). You should do this right, and if you do post some pictures on the forum:

http://forum.flitetest.com/showthread.php?12028-Swappable-B25-Twin-Engine-Mitchell-Bomber&highlight=b25#sthash.kcBgk0Da.dpuf
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horacio monterroso on April 8, 2015
Great Job ! congrats, nice plane.
I have a question, I cannĀ“t find the wing spars detail in your plans.
Can you added ?
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ultramicrobe on April 13, 2015
It is just a folded over 0.5" piece like the other designed that use the spitfire wing. I just trim them at the joint and add a little joiner piece to bond them and set the dihedral, but I just made it from scrap.
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Soufiani on December 10, 2016
I'm planning on building this plane after my exams. The Turnigy motors look a bit expensive so could I use 2 emax cf2822 1200kv motors?Thanks in advance!
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ultramicrobe on December 10, 2016
Can't see why not, but I have never been able to predict motor/prop combos very well. It was quite powerful with the 1050kv motors (which are not special or even that good really). If the motor is good for the same size prop, then should work. If you build it post some pictures on the forum, I would love to see it. Blast from the past.

By the way, I would also consider hooking it up so you get differential thrust and then not bothering with the control on the rudder. I did this on a mini-lancaster (on flite test, so if you are curious look that one up too). It made the build way simpler and also keeps the weight up front. I would seriously recommend that here too.
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SlingShotRC on February 2, 2017
Hi. This B-25 is very nice and looks like something I could use. But If I build it, I will want to fly it like a fighter. Fully aerobatic. What sorts of mods will I need to beef it up?
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ultramicrobe on February 2, 2017
Honestly I would recommend just building a fighter if that's what you want. It is big and being a twin won't likely fly like you want if you want aerobatics. If you set up differential thrust you can do other things you can't easily do with a fighter, and they are fun. The flat spins for example are pretty awesome. I would look up my Lancaster article to see what I mean about that setup - it would be even easier with the twin than it was with that quad engine model. You can find that information here:

http://flitetest.com/articles/swappable-lancaster-bomber-with-fpv-bombsight

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SlingShotRC on March 13, 2017
Hey. I printed the plans and I am making the templates. I have a question about the fuse. Is the top a completely separate piece?
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SlingShotRC on May 4, 2017
Ultramicrobe: Check out the Forum thread for the B-25. It flew great at Flite Fest and it was a hit with the kids!
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ultramicrobe on May 4, 2017
Wow, blast from the past! I love the fact someone flew one of these at flite fest. I would like to go to that some day. Anyway, thanks for letting me know and also that people are using the forum page too. I see nearly 50,000 people have looked at this, so I figure someone must be building it, right? By the way, if you liked this I would recommend the mini lancaster I posted a while later. It is small, super powerful and easy to build, but has some crazy potential because of the 4 engines and the setup with differential thrust - means you don't need rudder and makes the build simpler (which I should have done here).
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SlingShotRC on May 6, 2017
Might have to try it! For now I need another B-25 that I can fly for a while. Solid as a rock and goes where you point it.
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SlingShotRC on May 8, 2017
I final word about the power plant used. When I got home and checked my motors I realized that I had been flying the B-25 with stock C-Pack motors. This contradicts what I told many people. I am sorry. I had some larger 80 gram motors that I had originally plan to use and I somehow forgot that I scaled back.

Also they were 9" props. 9050 three bladers that were pretty soft. I forgot to pack the ESC's so I bought some from the FT store. Next generation.....very small 30a.

All in all, the thrust, weight and drag combination was very fun to fly. If it cruised along at 45-50 mph it felt like it pulled hard straight up at about the same speed. Delicious torquey goodness.
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SlingShotRC on July 24, 2017
@ultramicrobe

Do you feel like adapting this to a 1/10 scale Mitsubishi G4M Betty? Or better yet, a Yokosuka P1Y Frances.

I want to launch an Ohka Cherry Blossom from it ;-)
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