After the killer New Year holiday the I-want-a-big-twin-engine bug bit me hard into really building it.

Thank God, I’d gained a bit of skill...
Гадкий утенок+116
15 ноября 2014 года в 20:10 | Андрей Скворцов Новосибирск
Статья http://www.parkflyer.ru/blogs/view_entry/9968/

I did it based on my experience with the field-tested little Twins cargo plane.

Characteristics:
1. BIG SIZE (consist of 4 elements)
Pros: lots of free space, good weight-lifting ability
Cons: storage, transportation and assembly inconveniences

2.horizontal stabilizer with a lifting profile
Pros: high tail-unit stiffness, an opportunity to shift the normal centering back by 15-20% (in fact – by 50%)
Cons: none

3. two-fin tail
Pros: good propeller blowing (a smaller surface area is ok).
Cons: two servos are required

4. Rigid fastening of the wings and the tail (polyethylene bolts with captive nuts).
Pros: clear geometry, simple and reliable fastening.
Cons: 5kg of total weight can contribute to destruction in case of hard touchdown.

5. All these pros and cons are typical of twin-engine planes.
6. Сlark - Y15 wing profile (just the right thing for a cargo plane).

All my planes have names, and the name Little Monster stuck to this one; there are no drafts for it, I just made a life-size sketch on a piece of paper based on proportion.

I started with the tailboom and used lightweight balsa.






To glue balsa, I used white glue and cyanoacrylate.


The captive nuts turned out to be a complete shit. Happily, I had too few of them to use on the wing, so I cut a few ones out of a piece of caprolactam



the tail was great....
except I had to place the servo on the top due to specific structure

I built the fuselage frame from 10Х10 balsa

I made three lobes for better wetware mounting

I tightly covered the sides and the bottom with 4mm EPP

I pivot-mounted the front hatch to the battery compartments and bolted two readily removable ones at the rear with self-tappers


I'd planned to fix all four batteries in the nose

I reinforced the bottom of the nose with a 3mm piece of plywood



and covered the sides with balsa

I hand-cut rbs in the wings and tail using plywood templates. I took a terrific amount of 4mm balsa

I made this sandwich piece just for better geometry

each wing consists of two halves and 10-12mm long/4-6mm thick carbon tubes as primary structural members



There is a cable conduit all the way along the trailing edge.




Each wing features a distribution board made of a piece of fabric-based laminate.

So does the engine mount.

A servo mount

The wing halves are joined by wood strips at the top and at the bottom, and the leading edge is covered with 1.5mm balsa.

I filed the servos down to flush the wire and soldered the loop directly to the servo without using connectors.



The motor mount...

Two small inspection hatches.

I also made air-scoops with an output slot in the rear hatch.





Now let's discuss power supply:
since the "duckling" had given me a lot of interference trouble, I decided to reap the benefits of the BIG SIZE and provide separate power supply for everything.
video transmitter - 1,000mA\h
two power accumulator batteries paralleled to controllers only - 8,000mA\h
receiver, autopilot and mechanics - 1,000mA\h
All servos are powered by BEC 5a; the receiver and autopilot are powered by a 7805 parametrical stabilizer, since they do not require much voltage.
As I checked the SBEC controller on the simulator, I was dismayed at the thermal behavior and crazy pulses, so I followed recommendations - increased capacity and extended the wiring.
Even at this point 5A is freaking bad, while 3A is way to go!



The first test-flight revealed excess noseheaviness with batteries placed as suggested by the layout, so I had to move them backwards (for the first time in my RC hobbyist career...). Moving the two 1,000mah batteries back proved to be the simplest solution, and that was a huge advantage!

I placed the ARKBIRD on a cushion.

Here is an accumulator battery for the video transmitter.

I had to reshape the video transmitter (see a link below), since its case was as heavy as the transmitter itself; i made the radiator out of a duraluminum plate. Later I had to add a radiator from my old PC and therefore lose a bit of space, because the transmitter would heat up too bad during autopilot setup.

My DIY 1080mHz stainless steel clover-leaf antenna.

My first ride to the field raised a transportation issue, because the fuselage would in no way fit in my father's UAZ jeep's passanger compartment except if placed diagonally, and the thin tape got scratched. My dad said: "This is the last time I'm riding it this way, you should build crates." Building crates took two weeks of my vacation... Here are the crates built from 4mm plywood, all laquered and lined with 10mm foam on the inside.





This is how neatly I stashed the crates in my garage.






This is my personally owned ejector!


Simulation revealed a 2kg thrust with a 10Х7 prop and 60A current rate; the thrust-weight ratio allowed for a hand-launch. The plane turned out to be very nice in terms of control, and it flies in a laid-back manner and not for quite so long - about 15-20 minutes. My plans for the coming winter include a little trim-up for the fuselage, an upgrade for the landing gear and a little do-up for the wingtips (putting on balsa and black tape)






Here are the basic parts:
Nylon & Pinned Hinge 16x28.5 (10pcs)
Product http://www.rcfair.com/en/product/8282/
Nylon Screws 6.25x55mm (10pcs/set)
Product http://www.rcfair.com/en/product/8597/
Nylon Blind Nut M6 (4Pcs/Bag)
Product http://www.rcfair.com/en/product/537653/
Turnigy 5A (8-26v) SBEC for Lipo
Product http://www.rcfair.com/en/product/10312/
Mobius ActionCam 1080p HD Video Camera Set With Live Video Out
Product http://www.rcfair.com/en/product/1199918/
FrSky FSH-01 Telemetry Sensor Hub
Product http://www.rcfair.com/en/product/185806/
AeroStar™ AS-170MG Micro MG Servo 3.5kg / 0.11sec / 17.5g
Product http://www.rcfair.com/en/product/1127208/
Turnigy D3542/5 1250KV Brushless Outrunner Motor
Product http://www.rcfair.com/en/product/115070/
(3pcs) Rctimer Sport 10x7E Precision propeller
Product http://www.rcfair.com/en/product/1466959/
ZIPPY Flightmax 8000mAh 3S1P 30C Lipo Pack
Product http://www.rcfair.com/en/product/1520540/
Arkbird Autopilot System w/OSD V3.1020 (GPS/Altitude Hold/Auto-Level)
Product http://www.rcfair.com/en/product/691352/


The 8-channel video transmitter:
http://www.ebay.com/itm/191369590553?_trksid=p2060353.m1438.l2649&ssPageName=STRK:MEBIDX:IT

The ESC:
Hobbywing SkyWalker 40A Brushless ESC Speed Controller With UBEC
Product http://www.rcfair.com/en/product/1685262/

That would be it...
Sorry for the little yarn, guys, and these are only the most informative part of the whole load of pictures that I have.

This is the translated version. You can read the original Russian article here.