Bristol M1C (oz13637)

About this Plan

Bristol M1C. Radio control scale model for electric power. Wingspan 48 in. Scale is 1/8.

Direct submission to Outerzone.

Note see prototype build thread of this design by Pat Lynch on RCGroups at: https://www.rcgroups.com/forums/showthread.php?724898 for several pages of good build pics.

Photo [main pic] shows completed model by Pat Lynch, grabbed from the above thread.

Update 20/2/2022: Added article, thanks to RFJ.

Quote: "Full-size FREE Plan feature. A 1/8th scale electric-powered model, designed by Peter Rake with prototype model built and described by Pat Lynch. Bristol M1c.

Some months ago, Peter Rake asked, would I be interested in doing a prototype build of a Bristol M.1c in a size that he knew I liked - around 46 to 48 inch. Naturally I said yes please, without having the faintest idea what an M1c Scout was!

A bit of research told me that very few M1cs were built (a hundred or so) because the RFC preferred biplanes, although the type did see limited service in the mid-to-late part of the Great War.

I do not think any originals survive to fly today, but several Collections have authentic replicas - complete with original rotary engines, so reference material is in abundance. The Bristol is quite an elegant machine with a round-section fuselage and curved wing leading edge (LE), both of which make the design just a little more challenging plus, of course, there's that spinner.

A few photos of the real aircraft were gathered (mostly of the Shuttleworth replica) and one of Manzano Laser's excellent wooden propeller kits was ordered to go with Charlie's short kit. This was an inch or so too large, but was of the right shape. A few preliminary calculations showed that, if a scale-sized prop of 12.5 in was used, the motor would need to be a low kV outrunner of about 120-150 watts input. A 'bell' motor of 750 kV was purchased to run from 3S LiPo at around 15 amps.

Fuselage: This design is a new departure for Peter. The fuselage is built in two half-round parts split horizontally, making it easy to build over the plan without jigs. Extra structural rigidity around the firewall/undercarriage/wing mounting areas is created by use of an internal box and ply cross-members.

The crutch elements were glued and pinned over the plan, then the main half-formers fixed and the two 1/8 balsa 'box' sides, slipped into the frame assembly and glued. Finally, the 1/8 ply firewall half was secured with PVA as was the rear undercarriage (U/C) mounting plate. After gluing the tailskid support plate, the 1/8 x 1/16 stringers were added. These had been cut slightly over-width to allow some light sanding later.

Brass tubes anchoring the undercarriage (U/C) wire were bound to the lower firewall and U/C plate with fuse wire and epoxy then four small brass brackets were fixed to the fuselage for the flying wires under the wings. With the lower half still pinned to the board, the hatch, underside sheeting, and U/C wire were fitted. The U/C legs were made in a V-shape for each side, then bound and soldered to two cross-members as per full-size. The axle is suspended in the V with hat elastic.

The upper fuselage half is similar in the method of building, just detail differences - sheeting, mounting tubes for the pylon, wings etc.

The pylon fits into lengths of tube, bound epoxied or both, to ply cross-pieces. The wings will have short lengths of piano-wire inserting into brass tubes running through the fuselage. Minor detail items are some 1/16 sheet inserts to reinforce the areas around fuel tank filler and foot steps.

The tailplane is located in a 1/8 wide slot cut into the sheeted area in the upper half of the rear fuselage. This is done while the upper half is attached to the board, cutting the slot parallel to the centre-line is easier.

The servo mounting and control cables/guides were installed before joining fuselage halves together. A 1/32 ply guide ensured all the cables leave the fuselage in the correct place. The cables were fitted, labelled and coiled up in the rear fuselage. After adding a battery box and painting the visible interior grey, the two fuselage halves were carefully aligned and clamped. When satisfied that all was aligned, CA was run into the join and allowed to set. The remaining sections of the nose were sheeted, and some basic dummy interior framing added to the cockpit area. The M.1c had a rather sparse cockpit and did not warrant a huge effort.

The cowl is fairly straightforward - two lite-ply rings with 1/32 ply wrapped around, and some balsa laminations glued on the front and sanded to shape. The cowl is secured to the firewall with three screws. The front of the cowl is sanded at an angle to match the rear of the spinner which has a small amount of down and right thrust. The motor is fastened to the firewall on a ply disc sanded to give two degrees right and down thrust.

Wings: The wing is fairly straightforward. The two spars are straight-grained and moderately hard balsa. The trailing edge (TE) is 3/32 bass - it is fairly thin and the bass is less fragile than balsa would be. The wings are aligned with the fuselage with piano wire pegs in brass tubes glued into the 1/8 ply root ribs. The rigging should pull the wings into the fuselage. Because of the round section fuselage, a lamination of balsa ribs is shaped to fit the gap between wing root and fuselage.

The leading edge (LE) is laminated from three strips of 3/8 x 1/16 balsa. The ply and bass parts plus the balsa spars were glued together (PVA) and allowed to dry. Then the various ribs were fixed in place, bevelling where required..."

Supplementary file notes

Article.

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