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Sep 13, 2019, 11:12 PM
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Build Log

RFB Fantrainer v2 Build Log (with Free Plans)

hey gang!
so, it's been over a decade that i posted plans for an RFB Fantrainer based upon Spaceman Spiff's design. here is the link to the original RFB Fantrainer build thread:

back then, i was primarily a designer and builder and not a flyer, so i was afraid to fly the plane for fear of crashing it and not being able to tell if the plane flew poorly because of poor design or poor piloting skills. since then, i started flying 3 years ago and have become much more proficient. i finally dusted off my original Fantrainer, yanked out the ancient FM Rx and replaced it with a DSM2 Rx. i left the original brushed 64mm EDF in place and tossed her into the air and she flew fantastic! she was a bit slow, but handled beautifully even in winds up to 10mph on the maiden. she flew so well, i wanted to go back and redo her with a brushless motor and at that point, i decided i may as well redesign the plans to make her more scale. so, hence this current v2 of the Fantrainer.

i got her built and flew her with a 3s 64mm brushless EDF and though she was faster, she still didn't have the speed i was looking for, so i decided to upgrade to a 4s 64mm brushless 11blade FMS system. i made some changes on the fly on the build, so i decided to incorporate those changes into the plans and take pics of the build steps along the way as documentation in case anyone else is interested in building one.

here is a shot of the original Fantrainer as well as the new more scale planform. the original was a yank and bank and the new version is 4 channel.
the plans are also posted here. if there are updates, i'll change the plans on this first post. currently the most up to date plans are v2.4 (2019-09-13).

update: 2019-10-14:
-added picture of the v2 with upgraded wings and canopy
-will work on modifying the plans with updated wings and canopy if there is enough interest, otherwise, not worth my time
Last edited by beanie; Yesterday at 10:13 PM.
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Sep 13, 2019, 11:18 PM
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first step is working on the rudder. cut the rudder free from the 2 upper vertical aft fuse sections. then glue them together. i use Beacon 3-in-1... very similar to FoamTac, but much cheaper.
i used FFF for this build, so if you do, peel off the plastic layer on the outer sides and then sand a 45 degree bevel into the hinge. then sand a taper into the aft section of the rudder. i trimmed off about 1/8" from the top to give the rudder better clearance.
Sep 14, 2019, 07:32 AM
I Look, Listen, and Learn
Timbo383's Avatar
Looks cool and simple enough for someone of my skill levels to build, I'll be watching this and adding it to my build list.
Sep 14, 2019, 08:26 AM
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rajazo's Avatar

RFB Fantrainer v2 Build Log

Great work Beanie, nice to see you with a “new” design!
Last edited by rajazo; Sep 14, 2019 at 10:25 AM.
Sep 14, 2019, 09:54 AM
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timbo383- yes, this is an extremely simple build, but much less boxy than the original version. this version is based upon the 3-view planforms and i tried not to deviate from the overall shape. i included some tabs to help with the alignment of pieces. the hardest part is just cutting out all the pieces. on the plans, i always try to intentionally position pieces so the least amount of cutting of paper and taping is required.

thanks rajazo! its been a while since i've done designing, but doing this re-design was fun, so i'm getting the creative juices going again. i'm thinking of first going back and retrofitting my MiG-25 and MiG-21 and MiG-23 swing wing designs to 64mm EDF instead of pusher prop.

here is the next step. working on the upper aft vertical fuse. first glue the 2 upper aft vertical fuse pieces together. then hinge the rudder. i used 2 hinges, one near the base and one near the top. note that given the shape of the rudder and upper aft vertical fuse, if you put the base hinge too close to the base, it will be hard to slide the rudder into place. you can see from the pic of where it worked out well. another option would be to hinge the upper aft vertical fuse instead of the rudder first.

on my first v2 Fantrainer, i used a tape hinge, but the lower hinge failed. i originally tape hinged the rudder to the just one side of one upper aft vertical fuse and then used that one side as the middle of the 2 pieces in order to centerline the rudder. but when it failed, it would be hard to repair. i think using the hinges will be stronger. i try to keep my designs as cheap as possible and so one could either use tape hinges or not cut out the rudder at all and simply make it a 3 channel bird. v1 of the Fantrainer was a 3 channel bird and flew just fine. as i have gotten to be a better pilot, i appreciate having a rudder so that i can make fine corrections on final and do stuff like knife edge (not that this airframe yields a very satisfying knife edge).

after i inserted the hinges into the rudder, i then attached the rudder to the upper aft vertical fuse. i used a #11 blade to slice into the centerline of each part. i used a sharpie to mark where to slice into the upper aft vertical fuse for the hinges to line up.

note: be sure there is enough clearance at the bottom of the rudder so that it can swing freely. this is why i sliced off about 1/8" of the upper rudder in the post above.
Sep 15, 2019, 11:01 PM
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next step is completion of the rudder.
first install the rudder control horn. i cut a little flat surface for the base of the control horn on the rudder. also, be sure the horn is perpendicular to the hinge line.
then complete the rudder servo with your favorite linkages. this time i opted for a z-bend in the piano wire and EZ-links at the servo horn side. center the servo before securing everything. glue the rudder servo into place. i added some scrap foam to form a little cradle around the servo for more support.

next, trace a path for the servo wire. it will be routed to the lower aft fuse into the main fuse to make the upper half look cleaner. a servo extension will be needed. after cutting a shallow path for the servo wire, i went back and traced that path with a small screw driver.
after the path is deep enough, seat the servo wire into the path.

rudder with linkage is now done.
Sep 18, 2019, 12:53 PM
still goin if glue is flowin
100mph's Avatar
Lookin good! I love the sleek design. Here in Nebraska it's always breezy, I might have to make one of yours just to have fly on windy days. I might upscale it a bit too just for fun.
Sep 18, 2019, 11:28 PM
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thanks 100mph! she’d be a breeze to increase in size. on my original plans and build, some guys increased the wing by 1” all around and she became even more of a floater. i’m looking for more speed so i’m gonna try 4s this time. please post pics of your build! i’m outta town for an rcgroups fly-in, so the build is on pause til i get back next week.
Sep 29, 2019, 09:25 PM
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next step is to work on the elevator and horizontal stab.
first cut the elevator free. trim about 1/16" from the diagonals so that nothing binds with elevator actuation.
sand a 45 degree bevel to prevent binding.
use your preferred hinge method and attach the elevator.
install a CF tube to stiffen the horizontal stab.
dry fit the vertical stab to the horizontal stab and position the servo to help determine where to install the control horn. be sure the servo is on the opposite side of the rudder servo.
Oct 03, 2019, 10:59 PM
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the next step is working on completing the tail feathers.
first glue the horizontal stabilizer to the vertical stabilizer. the tabs should automatically align the parts. but make sure the horizontal and vertical stabs are perpendicular to each other.
for added strength, i added some scrap pieces of foam at the joint. just make sure the length of this support foam doesn't interfere with the movement of the rudder.
next, position the elevator servo so that the output arm is in line with the control horn to optimize movement and efficiency. be sure to position the elevator servo forward enough that you can access the servo control arm from above. in my first build, the servo was 'under' or 'covered by' the horizontal stab. this makes adjustment of the elevator servo much harder.
once you have determined the appropriate location, glue the servo in place. then add scrap foam as support on 2 sides.
Oct 04, 2019, 08:27 PM
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time to work on the ailerons.
first cut the aileron free of the wing.
i shaved off about 1/16" off the end so that the aileron would not rub up against the wing and strain the servo.
then i sanded a 45 degree bevel to allow freedom of travel. i bevel is such that the top of the aileron is flush with the top of the wing. be sure to sand the correct edge! (don't ask how i know... stupid me, i sanded the wrong edge, so i had to cut a new aileron).
again, use your favorite hinging method and finish the aileron and then repeat for the other side.
Oct 05, 2019, 12:33 PM
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Oct 06, 2019, 11:49 PM
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thanks ksqm!
ok, now time to finish up that wing.
first cut a shallow v-channel for the spar. i put the spar on the bottom of the wing so that she looks purdy from the top
i then run the end of the CF tube through the slot to make it the right size. if using something like Beacon 3-in-1 (my go-to glue)... be careful not to put too much because it can eat through the foam. i think it is better to put the glue on the spar, then lay the spar in place, then remove the spar for about a minute, and then place the spar into place.
now, on to the ailerons. version 1 used a single aileron servo, but the angles and geometry were strained. i decided to put 2 separate aileron servos in the new version. servos also sit on the bottom of the wing. i try to position the servo as close to the fuse side of the aileron to try to avoid needing a servo extension. glue in the servo so that the movement of the arm is perpendicular to the hinge line.
then help secure the servo by using some scrap foam to make a tiny support enclosure on 2 sides.
then tack down the servo wire.
next, glue the aileron control horn in place and hook up your control wires. i used EZ Links at the servo side and a Z-bend for the control surface.
repeat the process for the other aileron.
Oct 08, 2019, 08:50 PM
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ok, time to move on to the fuselage.
first take the bottom fuse piece and curve the forward and aft portions. i first peeled of the plastic covering where i expect glue to contact the foam. then i place the dotted line of the lower fuse against a straight edge, like a table edge. gently push down and then pull the fuse piece downward and it will yield a gentle curve. the harder one pushes, the more it will curve.
do the same for the aft portion. use the side fuse portions to determine how much to curve the lower fuse piece.
next, glue in the lower bulkhead using the tab system.
now glue one fuselage side into place. cut some scrap foam strips about 1/4" wide and make doublers where ever the fuse and the lower or upper fuse pieces meet. this will allow sanding a nice curve to the pieces.
Oct 09, 2019, 11:56 PM
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now repeat the same steps for the other side.
then glue on the front nose top.
place the canopy bulkhead right above the fuselage bulkhead, but don't glue it to the fuselage. then grab the canopy side and attach it to the canopy bulkhead. while still positioned over the fuselage for guidance, glue the other canopy side to the canopy bulkhead.
now remove the canopy assembly and then glue the aft canopy bulkhead. next, attach doublers of scrap foam strips to the aft and front canopy. now glue the top canopy in place.

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