Sig Kobra balsa kit

Michael · December 24, 2017, 03:17:30 PM

I am building one balsa kit this year, and it is a Sig Kobra. It's a smaller version of the King Kobra that Robert Pike started building a couple months ago at one of the TEMAC building classes.

This kit produces a smaller version, about 45" wingspan, of this speed/pattern sport model. It calls for a .19 to .35 glow engine, so I think my high-speed 25-size 4S system from my now demolished EF-1 racer will be a good fit. It's a simple 4 channel model (no retracts; no flaps), and I think it's a good size for TEMAC. I can probably bring it to the field assembled. Converting it to suit an electric motor and battery will be part of the fun. The kit includes many printed parts (not die not laser cut) that will need to be cut out by hand.

octagon · December 24, 2017, 04:13:55 PM

Should be nice. Colour scheme?

Frank v B · December 24, 2017, 04:29:18 PM

Michael,

I have always liked that plane. I have never built or flown it but several people way back had and warned me to reinforce the wing ribs that hold the slots for the main landing gear. They usually supply slotted basswood LG blocks that glue into the rectangular slots in the bottom of the ribs towards the centre. There is a bit of a plywood doubler for each rib but usually not the full length of the rib.

The Kaos series of planes from Great Planes had the same problem (built 3 of them). I sistered 1/16 plywood to the full length of the rib that had the LG blocks and never had a problem. On all scratch-built planes I have built I have made the slotted LG mount one continuous piece of pine (trimmed 1x2) that acts as a joiner for the two wing halves.

For what it is worth.

Frank

Michael · December 24, 2017, 04:32:02 PM

Colour scheme? I don't know. Maybe something Canadian? Probably dependent on what leftover colours of covering I have.

Thanks Frank, I'll reinforce the landing gear blocks.

An internet search found a similar electric conversion that was successful with the same power system.

Michael · December 24, 2017, 04:35:14 PM

I was thinking of using two aileron servos (one in each wing) instead of one mounted in the center of the wing, and I was considering using electric retracts, but I decided to try to keep things as simple as possible. It also means no aileron linkages visible on the outside of the plane.

Andy Hoffer · December 24, 2017, 06:02:38 PM

Quote from: Frank v B on December 24, 2017, 04:29:18 PM
Michael,

I have always liked that plane. I have never built or flown it but several people way back had and warned me to reinforce the wing ribs that hold the slots for the main landing gear. They usually supply slotted basswood LG blocks that glue into the rectangular slots in the bottom of the ribs towards the centre. There is a bit of a plywood doubler for each rib but usually not the full length of the rib.

The Kaos series of planes from Great Planes had the same problem (built 3 of them). I sistered 1/16 plywood to the full length of the rib that had the LG blocks and never had a problem. On all scratch-built planes I have built I have made the slotted LG mount one continuous piece of pine (trimmed 1x2) that acts as a joiner for the two wing halves.

For what it is worth.

Frank

I would definitely offer two cents, but pennies are out of circulation now, so I'll spring for a whole nickel.

Andy

Michael · December 25, 2017, 04:03:58 PM

Having fun !!!

Michael · December 25, 2017, 04:11:00 PM

I've decided to use one servo per aileron, as opposed to one servo for both as per the instructions/plans. That will in fact be simpler.

Michael · December 30, 2017, 06:19:55 PM

Wing is complete; just needs a bit more sanding and then ready for covering.

Carved wingtips, cap-strips, landing gear blocks and servo bays.

octagon · December 31, 2017, 09:26:53 AM

Nice work, looks very good.

the giant · December 31, 2017, 01:23:01 PM

This is a classic. Nice looking work Michael. Can't wait to see it up close.

Michael · January 02, 2018, 11:01:56 AM

Fuselage well underway.
Blind nuts in the firewall for motor and nosegear; formers and triangular balsa glued in.

Note the printing on the inside balsa fuselage sides. The plans are essentially on the wood.

Michael · January 02, 2018, 04:19:23 PM

Wing 'hold-down' dowel; tapped hardwood blocks for the plastic screws; smooth wing-fuselage fit; tail temporarily pinned in place.

Andy Hoffer · January 02, 2018, 04:21:58 PM

Does this come with limbo pole collision avoidance technology?!!

Andy

Michael · January 05, 2018, 09:44:18 PM

Fuselage is taking shape. Battery-hatch built, and nose will have a air-intake scoop at the bottom front of the nose, sort of like a P51D Mustang.