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Nov 01, 2018, 04:37 PM
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Build Log

36" Sopwith Triplane by Mike Roach


This summer I finally got a chance to get back to building, and I decided to give Mike Roachs 36 Sopwith Triplane a try. Mike very generously posted the plans for this model here, and has allowed me to cut short kits for it. Ive always been fascinated by the Triplane and the exploits of its pilots, and figured that I could kill two birds with one stone by building a model Id always admired while doing a prototype build of the short kit at the same time. The short kit contains 15 different-sized sheets of balsa and plywood, containing over 150 CNC-cut parts, as well as full-sized laser-printed plans. The plans are for Mikes original Speed 400-powered prototype as published in Flying Scale Magazine in 2000, but Ive made a few mods to the short kit parts and these changes are noted as they arise in this build log.

Steve
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Nov 01, 2018, 04:43 PM
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If you don’t like building wings, you should stay away from triplanes...Building the wing panels for Mike’s design is straightforward if a little repetitious, with a few points to note. The first is that the wing struts are laminated from two plys of 1/32” plywood, resulting in 1/16” thick struts that are quite rigid. I laminated mine with carpenter’s glue, and then clamped them between some straight pieces of scrap plywood while they dried to prevent any warps or bends.

The second point of interest is that for each wing panel, the root rib and the special outboard strut rib sandwich made up of two 1/32” ply ribs with a 1/16” balsa filling need to be installed last, once the wing tip has been blocked up with 3/4” dihedral to ensure these ribs are vertical since they will hold the cabane and outboard wing struts in the correct vertical orientation.

Finally, the spar notches in my ribs needed a couple of strokes from a flat file to open them up to just fit on the spars snugly. Since balsa thickness varies a bit from sheet to sheet and from the nominal sheet thickness, I prefer to cut notches a tick under their nominal width to ensure a snug fit. Builders should note that the short kit contains two variants of the rib identified as R3 on the plans – one has a wider spar notch to accommodate the spar and dihedral braces for the top and bottom wings, and the other a narrow slot to fit the spar alone.

Top and bottom wings are identical except for the short centre section that holds the two top wing panels together. Plywood dihedral braces work well to join the panels together and set the 3/4” dihedral required under each wing tip. I chose not to join the two bottom wings together immediately, preferring to set up the plywood dihedral braces once the fuselage was built.

Building the wings, I realized that my short kit was a few ply ribs short of the full requirement, and added them to the cutfile.
Last edited by Steve85; Nov 01, 2018 at 04:49 PM. Reason: early onset Alzheimer's...
Nov 01, 2018, 05:54 PM
Gorilla glue rocks
Spit100's Avatar
Well doesn’t this look like fun!

Jon
Nov 01, 2018, 06:01 PM
Registered User
Not much beats a triplane and the Sopwith Triplane is just so pretty.
Nov 01, 2018, 06:54 PM
I eat glue
Sorry I never got to meet up with you when you were here, maybe next summer!
Nov 02, 2018, 10:26 AM
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Welcome aboard, gents! Baldguy, the weather just wasn't cooperative, so I never actually made it out the the club field while I was "down home". Next year I'm going to have to reserve some space in the car for a completed model I could fly (if the weather permits!)

Steve
Nov 02, 2018, 11:21 AM
I eat glue
That was probably the only bad stretch of weather we had were when you were here.
Last edited by baldguy; Nov 02, 2018 at 11:22 AM. Reason: Too stupid to spell properly
Nov 02, 2018, 02:32 PM
Slip the surly bonds...
Sopwith Mike's Avatar
I do remember all those wings! It was a lovely looking model but I would try fitting ailerons were I to do it again. Good luck Steve.
Nov 02, 2018, 05:14 PM
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Thanks Mike. The parts come together really well. Ailerons would be a relatively straightforward modification, but I'm going to build mine as per the plans and see how it turns out.

Steve
Nov 02, 2018, 05:24 PM
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On to the fuselage!


Fuselage construction consists of sheet balsa and ply parts for the fuselage forward of the cockpit, and conventional longeron, stringer and vertical and horizontal braces aft of the cockpit. The forward fuselage is a very sturdy design, and could easily benefit from some judicious lightening, although I built mine as per the plans. Given the very short nose moment of the Triplane, any lightening efforts should focus on the fuselage aft of the centre of gravity. Mikes original model was powered with a Speed 400 brushed motor in a reduction gearbox, with the firewall and motor mount shown in the plans tailored for this motor combination. The short kit has been modified to use a brushless outrunner, and a new firewall and firewall brace have been included. Battery location is unchanged for the short kit, but the battery could be mounted directly to the rear of the ply firewall to counter any tail-heaviness.

Laminated ply cabane struts fit into the slots in the upper fuselage sides (they should be flush with the outside surface of the sides), and then 1/16 balsa sheet is used to fill the slot on the inside of the fuselage. 1/32 ply scab braces are then glued over the whole strut mounting area on the inside surface of the fuselage. Once both sides were assembled ( a left and a right hand side...), I marked the positions of the firewall, firewall brace and servo tray on the inside of the sheet sides, and glued scrap 1/8 square balsa to the sides to serve as supports for the internal ply parts. While this wasn't a complicated challenge, I decided to modify the cutfile for future kits to add tabs and slots to facilitate alignment of these parts.
Nov 03, 2018, 09:17 AM
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Looking good. Nice to see another Tripehund fancier bringing one to life. Looking forward to watching your build.
sp
Nov 03, 2018, 09:26 AM
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Thanks sperry. I was just looking over your Triplane build thread and picked up a few ideas for finishing mine. I'm further into the build than this log depicts, and have been considering options for setting up the wing incidences as part of final assembly. Your experience using a magnetic building board to make adjustable jigs is one I need to try.

I like your colour scheme; it's one I hadn't seen before. I'm going to be doing a very conventional "Black Maria" scheme, since Raymond Collishaw was Canadian .

Steve
Nov 04, 2018, 09:28 AM
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Once the locations of the internal fuselage parts were marked and bracing was installed, I used Titebond glue to glue them into place, taking care to ensure all the parts were installed square to the fuselage side. The left hand fuselage side was then glued and clamped to the right hand fuselage assembly and allowed to dry overnight. Once dry, the rear fuselage posts were glued together, using the light ply tail skid mount to ensure the correct rear fuselage shape. Upper and lower cross braces were added next, and turtle deck formers a to e were glued to the uppers. Finally, 1/16 x 1/8 turtle deck stringers were added to complete the rear fuselage.
Nov 04, 2018, 06:12 PM
Slip the surly bonds...
Sopwith Mike's Avatar
It all looks very familiar!
Nov 04, 2018, 06:50 PM
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Quote:
Originally Posted by Sopwith Mike
It all looks very familiar!
Well I should hope so!


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