Tale of Twinstar

by Finncopter | June 18, 2013 | (7) Posted in Projects

Twinstars story begins from crash of my first RC plane, Multiplex Easystar. Week after loss of the Easystar I decided to buy a new Multiplex Twinstar so I would have something to fly. After I paid the Twinstar, my old Easystar was found from a tree few hundred meters away from the flying field.

Content of the kit

GPS module, receiver and some servos installed. If I could build Twinstar again, I would put rudder and elevator servos inside that space where the GPS is now. Servos are now badly in the way of bigger batteries, that makes moving the CG backwards very hard.

Aileron servo (HXT900) of the starboard wing

ESCs prepared for installation. I had to cut the second ESC off and solder a XT60 connector in between to make the wing separate in two halves.

Motor and ESC installed on the starboard wing

Motor and Optical RPM sensor of the port side wing

Wings almost completed

I finished building the Twinstar on December 2012 and it flew for the first time on 2 December. Maiden flight was really horrible because thrust angles were too high and the plane was barely visible on cloudy sky. After the flight I corrected the thrust angles and painted the Twinstar with red spray paint.

Fuselage masked with tape and plastic wrap

GoPro installed on the wing

Twinstar flying over the frozen sea. Painted wing is very visible on cloudy sky.


Testing how much payload Twinstar can carry. I mounted old Ni-Mh batteries of my Easystar on base of GoPro with some zip ties. Twinstar carried the payload of 500 grams just fine.

I started building floats for the Twinstar in late winter

Flying for last times on frozen sea on March 2013

I tested using the GoPro directly under the fuselage. Temporary landing gear on the picture above was made from a metal hanger

Picture taken by GoPro mounted under the fuselage. Note the tip of port side landing gear

I went to the Suomenlinna sea fortress on 5 April 2013 to get some good aerial footage. Flying there was pretty easy, but problems started to appear when I tried to land the plane because of small hills of the island.
I crashed into a decomissioned cannon because Twinstar disappeared behind one of those hills just before landing, It took some damage from the collision: starboard motor gondola ripped off and mounting plates of the wing cracked. Motor gondola was fixed in one day, but I thought that the plane needed some kind of scheduled maintenance because it had flew over hundred flights and 24 hours. I installed Twinstars floats at the same time as I made the maintenance.

Duralumin landing gear for the floats

Plywood mounting plates for the landing gear glued on the fuselage with slow cure epoxy.

Floats attached to the airplane.

I had to rebuild part of the floats to get the Twinstar float at level.

Moving on water with own power for the first time! Differential thrust is used to turn the aircraft on water.

First flight with floats. You can see that this isn't going to end well...

Twinstar made a hard landing on water. I tried to drive it nearer to the coast, but motors didn't work. Then the starboard ESC began to smoke and I realised that it was in short circuit caused by the salt water. I waded to the plane and disconnected the battery. I took the Twinstar to home, and then ripped away the broken ESC.

Twinstar is now waiting for replacement ESC and I have learned something about the importance of water sealing...

Technical specs:

Battery: Turnigy 3600mAh 3S 20C LiPo
Motors: 2*HobbyKing 2824 1300KV (850 g @ 16,8 A; 192 W per motor)
Servos: 4*HexTronik HXT900
ESCs: 2*Turnigy Plush 25 A
Props: APC Thin E 8 X 4
Transmitter: Hitec Aurora 9 (2,4 Ghz)
Receiver: Hitec Optima 7
Telemetry: Hitec HTS Blue Complete set

Payload: ~ 500 g
Max flight time: 30 min (3600 mAh 3s Li-Po)
Empty weight: 1088 g
Loaded weight: 1572 g
Thrust to weight-ratio: 1,13:1

Power: 192 W (combined power 384 W)


Arunabha42 on June 29, 2013
I only have a month of my college break left and now you tempt me with this. Cracker of a build! I shall buid my twinstar. Someday :)
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Finncopter on June 29, 2013
I would defintely recommend Twinstar as a second or third rc airplane. It is very relaxing to fly but on the same hand has abilty to fly basic aerobatics and carry some payload.
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Corsair2014 on June 29, 2013
very cool man(:

any plans for fpv?
i may look at one of these for fpv someday
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Finncopter on June 30, 2013
I have been thinking getting FPV equipment, but it is mostly my small budget that stops me doing that. I would need 1,3 GHz transmitter, -receiver, goggles, a new plane just for FPV flying and also a licence to use the 1,3 band. It would be fun to fly Twinstar with FPV, but I can't mount anything in forward part of fuselage because plane is allready a bit noseheavy and batterypack cannot be moved any further back because of elevator and rudder servos.
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imperialcapital_AI on July 4, 2013
Thanks for sharing. Very curious about how the Optical RPM sensor works? It's just for displaying the RPM on your OSD, or it sends signal to the receiver then ESC to keep the motor speed?
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Finncopter on July 4, 2013
The Optical RPM sensor is from Hitecs HTS-Blue telemetry kit. I don't have OSD or FPV equipment yet, so i have to read the data from my aurora transmitter or from ipad which can be connected to aurora via cable. I think that the optical RPM sensor is only some kind of light sensor, that counts passes of props shadow.
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zev on June 29, 2013
awesome! what a saga!
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Finncopter on June 29, 2013
Thanks from positive feedback :-)
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Flying Fox on November 19, 2014
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Tale of Twinstar