FT-style Mighty Mini B25 Mitchell Swappable
The Mitchell has significant history behind it and designing a scale model, especially at this size, was a daunting task. The B25 isn’t hailed as the “Jack of All Raids” for no reason, and I wanted this small foam board design to reflect that versatility in its flight envelope. After about a year and a half of deliberation, design, prototyping and beta-building, today marks the official release of my first ever original FT-style swappable design! If you haven't already, check out the release video below.
I’ve only been in the hobby for less than a couple of years, but I’ve had a passion for aerospace design and aviation as far back as I can remember. I bit the bullet to commit to this design around the middle of last year. The design process has been long and difficult with several occasions when I was very close to quitting completely. The main source of inspiration that motivated me to get back to the design table was FliteTest and their wonderful community, especially the wonderful beta builders, some of who are recognized at the end of build video. Words cannot do justice to the commitment and passion they showed in pushing this design to success by chiseling away at its weak points.
As always, there are free plans and a full build video that I prepared over the course of several months to assist potential builders in the processes necessary to assemble this plane. The Mini Mitchell is a standard mini swappable built out of less than two sheets of foam board and one 11”x14” sheet of poster board, all from Dollar Tree. The B25 is a great performer but a strong intermediate build and flyer. Read on to find out whether this could be your next build!
Plans:
B25 Release AIO Plans.pdf
Specs and Materials:
Center of Gravity: 1.25 inches from leading edge at wing root
Control Surface Throws: 10 – 14˚ deflection, 30% expo all around
Wingspan: 32 in. (813 mm)
Motors: Two 1806 size 2280 – 2400 kv miniquad motors (Twin Engine A-pack)
Prop: 6*3 two or three-blade
ESC: 12 – 20 amp
Battery: 3S 800 – 1200 mAh
Servos: 3 servos for 4-channel control ; 2 additional servos for cargo bay (5 - 9 gram servos)
Power Y-harness: ≥ 6 on each side
Accessories: BBQ skewers and Craft knife
Build Process
This FT-style build video walks you through virtually every step in the procedure to assemble this ship and pack in the appropriate electronics. As this is an intermediate to advanced build, the process has been divided into several components for clarity. I highly suggest that builders, as with all other FT build videos, please watch or at least skim through this video once before beginning the build process.
https://sketchfab.com/models/3c7fee4e527345c7838ccb572e09f103
A digital 3D model of this design is provided in the link above, to help builders better understand the structure of the airframe.
Scale Design
This B25 has been designed with attention to scale proportions and details. The design is based off of original blueprints of the Mitchell obtained online.
The tapered wing sports an authentic gull wing with inboard dihedral and outboard anhedral. The box spar inside along with doublers at the joint between wing sections provides tremendous strength to sustain high speeds and loading. The presence of the spar also eliminates the need for any dihedral gauge in constructing the wing. Located under the wing, the nacelles of this plane are built with the Rounded-Approximation-Method (RAM), using several molded rings of foam board to approximate the compound curve. The thin rings both provide a scale appearance and make the molding process very easy.
Functional Cargo Bay
This design features a unique mechanism that can add scale to the mighty mini experience! The Mini Mitchell has an optional functional cargo bay that can be operated by two stock Emax 5-gram servos.
The mechanism is immensely robust in carrying weight even during aerobatic flight. Servo speed can even be adjusted to provide a scale appearance. Note: Please do not use this mechanism to carry items that may harm the plane or people/animals below. The cargo bay is perfect for backyard target challenges with small Nerf darts or even the mock shells provided on the plans.
Flying Characteristics
My flying buddy Dominic Peluso painted and flew the final pre-release prototype of the Mini Mitchell and provided some pointers for pilots out there. Despite a couple of years of experience flying RC planes, this was in fact his first ever twin engine model. However, he got the hang of this ship within three successful flights, which are compiled in the release video.
As with the FT Mini Cruiser, the elevator on the Mini B25 will have generous control with minimal deflection. Use lots of expo to filter out the nervous finger-jittering that is bound to occur on the first few flights. The ailerons will behave similarly but the plane will respond in a more scale manner, with a slight delay in the order of half-a-second. Dominic warned not to panic and provide too much aileron input during this delay period as it may cause the B25 to over-roll into an inverted orientation. As long as you plan your turns and take care to use the correct ratio of speed, aileron and elevator, the B25 will turn solidly.
Lacking a function rudder, the key to scale flight with this bird is differential thrust. Again, the rates must be set relatively low to avoid entering a descending spiral, but when combined with elevator and aileron, differential thrust will provide a much smoother coordinated turn, pulling the leading wing around. 
The B25 has more than enough power to go vertical on the stock A-pack with a 3-cell battery, but the plane shines in slower flight with scale low passes. It resents snappy aerobatics and prefers long smooth lines, whether slow or fast.
This is definitely not a beginner plane to build or fly. However, if built, balanced and dialed in correctly, in the hands of a strong intermediate pilot, the Mini Mitchell can be a wonderful addition to your fleet of scale mini warbirds. I flew my FT mini mustang (post-crash pic below) with Dominic’s silver Mitchell (above) and the match-up was glorious to witness. I hope that this design becomes a solid performer at your field and adorns your hangar for years to come.
Words aren’t enough to thank FliteTest for the encouragement and support they provided through their show and their community for me to pursue this design in an economic and educational manner. Thank you for reading this article and happy flying!!!
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