FTFC'18 WWII Kalinin K-12


Building Fool-Flying Noob
After Your post, the racks might just have Exploding Bombs too!

I was planning to Iron-shape the reflex pieces... and connect them with Credit Card Standoffs, or BBQ skewer struts glued to skewers in the panel ends... then cut control surfaces. 'tsall good. My quick plans don't quite address things like servo placement, or battery bays or the like.

I'm also planning a Viggen-esque battery component bay under the cockpit. I'll be working that out when I confirm the CG etc.

Am I doing this backwards, or Does this method sound about right?


Building Fool-Flying Noob
The Small Build is
Wing Span: 42"
Length: 21"
Base Chord: is 9"
Tip Chord: is 3.7"
Weight: ~350g
Wing Loading: TBD
Motors: Twin A or F - Pack motors with Differential Thrust.
Prop: 6-x4.5 Propellers
Battery: 1.65 Ah 2S or 2.2 Ah 3S.
Servos: 5 to 6 - 9g .

I will also be equipping it with FPV Gear in the Nose.
C-Pack will be 167% -Info to Come.


Old and Bold RC PILOT
Must be great to be able to use the lightweight FB as I doubt I could build the wing alone for the projected 350g.

As for the control surfaces I would be concerned with the spanwise flexibility of the mount though at the projected weight I suppose it might be OK. Also the control surfaces were rigidly mounted, on the original design, with trailing edge control surfaces, are you maintaining this detail or making the whole surface movable in the small version?

I really love the detailed design of the original including the inverted aerofoil section for the control surfaces!

Keep up the good work!

Have fun!


Building Fool-Flying Noob
in short yes. The reflex wing will be fixed. I will cut in control surfaces like most planes

fix reflex wing with I will be trying a few things. the first is the ironed shape. the second is to shape it with exact-o knifes and finish skin it with DTPB (gluing the poster board/card stock over the shaped reflex wing). and gluing in skewers to stiffen. or in the C-pack version, make it two halves to fold over a stiffener like nerdnic's speed builds. and build the standoff to rigidly secure the stiffeners in the reflex wing.

I'm also thinking of ways to "set" the reflex properly. right now put in the struts, have the plane on it's top and place a section of dtfb along the bottom of the wing extending out the back. lay the reflex in place then glue. pull the spacer out.

I know I will have to increase the control surface areas but I definitely want them a sub part of the reflex.

I also want the front turret to be a unit to take out to hook up the FPV camera...

So the weight, i don't have a working scale right now, and I've never weighed a finished plane with or without the battery.
but here's my CG calculated with components... looks like weight estimate is about 415g... (with 225g battery)


Building Fool-Flying Noob
problem I'm seeing with the bombs is that the battery seems to be set right where the bay goes. cart before the horse. sorry.


Building Fool-Flying Noob

I have the engine mounts and cowl set and is looking great. I started fabrication the landing gear too. I'm doing a pool noo

I'm still working out the flap details. And the more I look into it, the weirder it gets. Pulling together some of the flap details. and figuring out how it's supposed to work.


The way I see it, is the reflex wing section is worked like flaps en mass, and the little control surfaces are for elevon and aileron controls. The wing tip flaps are for Yaw control. What I don't understand is when the flap is extended down the control surfaces will "reflex" up as the controls for them traditionally wouldn't move.

Is this right? and how is this going to effect flight?

(I'm building the flap/controls the weird was anyway, I'd just like to understand how it's supposed to work.) I'll post some update pics when I get home.


Elite member
I am trying to picture what you are saying. If I am understanding what you mean is that the flaps extend down, then the little rear sub surfaces pitch up,(e.g. elevator up) at the same time?

I would guess the flaps down puts the aircraft into a pitch down moment, and the air forced down by the flaps is redirected as a pitch up thrust angle by the sub surfaces to counter the pitch down moment without changing the main airfoil dynamics?


If I misunderstood, disregard post.


Old and Bold RC PILOT
From what I read using the plan view with the view you have posted the profiles shown for the control surface are all for the same control surface.

The section view K-K is the main incidence control by pushing/pulling the rod which comes from the wing to the bottom of the control surface around the bottom of the spar. The control surface pivot point, (Fixed), is shown in profile (inverted) V-V, as is the control surface trim tab. The pivot for the control surface is affixed to the wing using 2 braces which converge and connect to the control surface at the upper edge of the main control surface spar. Section, (Backwards), N-N shows the mass balance weight used for the control surface.

There is another section view, M-M, shown in the plan drawing which might be the inboard TE section which looks as if it might be for a flaps setup, with trim tab, but about this I am currently still unsure.

I hope this helps!


Old and Bold RC PILOT
I decided to do a quick drawing joining the 3 cross-sections together and also to post the Rudder, (sorry not flaps), diagram/cross-section as well. Sorry about the drawing quality but I did not want to spend too much time and the poor quality still gives the physical arrangement anyway!

The Elevons, (3 TE sections on each wing? Suspect any flaps mixed into inboard elevons!).


The Wing tip drag rudders, (Sorry not Flaps after all!).


Hope this helps!
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Building Fool-Flying Noob
@Namactual - That was what I suspect too. I know there are folks here that understand this stuff way better,
@ Hai-Lee - That helps immensely. Thank you. I especially with the the wing tip drag mechanism. Now I see it's on the other detail sheet I didn't think would be much help. I have the pieces mostly made with skewers and Popsicle sticks. I'll make the standoffs and the armatures with Popsicle and tongue depressors. Also have the wheels fabricated.

It's coming together and I'm encouraged.

I tried my own penny bombs - Penny for weight and inertia. I wasn't getting able to get the compression mechanism right. however a missing mid-section and crinkled paper, seemed to work-ish. I'll do it right with Poster board. if it works.. I'm using this in EVERYTHING!

Here's my original idea. Parts borrowed from Psyborg.
View attachment 93259


Old and Bold RC PILOT
Because of the age of the original design and the technology they had access to and due to my research on old RC and FF flying wings I do really wonder if all of the control surfaces perform the same functions.

I suspect that the outer control surfaces might have been ailerons only, the mid wing control surfaces possibly elevators and the inner wing control surfaces possibly flaps! Should you have any specific control surface mapping I would like you to share it!

Have fun!


Building Fool-Flying Noob
Me too!

I'll be figuring that out tonight I believe, I want to close up this wing (impatient) and give this a fly. However, I NEED the control surfaces figured out first.

When I do, I will post Pics, Diagrams Etc.


Building Fool-Flying Noob
Project Update

So I've been a bit busy this weekend working on the project.

I worked on the landing gear and it's structure.
one down in this picture, the cowl is making this... permant

Then I worked on the flaps, and reflex surfaces... I'm only going to say - Ug.
here's some pics, there are just a number of moving parts and pieces. not hard, just tedious. I'm not sure this will make it into the final - for-public-consumption-build-version... anyway enjoy.

Cutting the control tabs.

getting them ready from Popsicle stick and bbq skewer

gluing it in.

checking they are generally aligned.

setting up the reflex surface. I used bbq skewer and coffee skewer.

here the reflex in action

General Layout control decision:
I have connected the inner and outer outside flap. and I will be installing a servo each flap.
Have one servo for the inner elevator flaps by connecting them together. lastly have the wing tip flaps on a spring loaded thing so it only can be pushed out. these will track to one central servo. I will have on for bomb door/release, and one last one for fpv camera rotation.

I hope this helps. There's still so much to get done, but definitely good progress.
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Building Fool-Flying Noob
The previous posts' day it felt like a whole heap had gotten done. It had...ish. But I've looked back, and it took a LONG while for such a little set of parts. I understand it is complex, however, Is this something the general FT Population will look at and think, "Yeah I wanna try this one."?

I've been rolling around a simpler, more "FT" style method to do such a complicated thing. Please don't get me wrong - I'm really happy and proud of these reverse-hung or junker offset flaps and reflex flap-ettes. I'll use it, but the stick and wire construction is...involved, and don't believe the average beginner RC adventurist is up for that challenge.

So, I'm thinking a Vertical small extreme packing tape hinge. Like an unglued C-fold reinforced. I try out of few iterations tonight.

I'll let you know what comes of it.


Elite member
Man, that's crazy cool! I can't wait to see that in action.

Nothing wrong with making it complicated. Maybe make two versions so the builder can decide what challenge they would like to tackle?


Building Fool-Flying Noob
Here's the control surfaces set next to the wing ready for me to connect it up.

I mocked up a standoff method that's all DTFB. I Think it'll work. All these small pieces are fidgety.
DTFB ReflexFlap Trial noted.JPG
DTFB ReflexFlap Trial w CounterWt.JPG

The first method is Popsicle sticks and a LOT of little pieces/control horns and Small Z-bent-ish wires.
The second will be small foam bits with lots of burnt fingers. Hmmm.

hope the pictures help.

I think I'm going to do two versions to see how both build out. Mainly to tell how sturdy the foam version is during flight. (if it flies.)
I'd love to build out a K-12 RF 7.5 model, but not really sure where to begin. (a way to test out wonky tendencies.)


Building Fool-Flying Noob
Still more updates: Winglets and reflex.

Last night I spent longer than I thought - 3 episodes of Game of Thrones - building the second landing gear, trimming the control surface stand-offs to length (4 foam layers thick), and getting the wingtips reflex mechanism ready.

A while back I picked up this REALLY thin (22 ga.) galvanized picture hanging wire. Thinking, "control rods". Turns out they were way to flimsy, and very hard to straighten well. Except for lightly loaded short runs, or continuous support through a drinking straw. After looking at these reflex panels on the Junker style wing control fins I thought I could use it here... and i saw the 3 short control rods for the wingtip drag-fin reflex and realized this is the perfect application.

Wing-tip  DragFlaps.JPG

Trying to think up an easy push-out only scheme for the drag flaps. Right now I'm thinking a pen spring and guide track near the servo arm.

Anyone have idea?