Sopwith Dove (oz12234)

About this Plan

Sopwith Dove. Free flight scale model biplane, for Mills 1.3 diesel engine.

Quote: "INTRODUCTION The first time I saw a Sopwith Dove was a photo in an issue of Aeroplane Monthly' magazine. I turned the page and there it was in all its glory. Turned ali cowl, varnished wood and sky blue top surfaces. It looked right straight away. Later I saw the Dove fly at Old Warden and had to build one.

On investigating the documentation, I discovered that the Dove is a civil two-seat conversion of the Pup. It is typically Sopwith, but nothing on it, for this type of model, is the same as the Pup. The wings have sweepback, which helps the flying, and all the other shapes are different to the Pup. As far as I can see, it is an entirely different aeroplane. A very good photo-pack (all you will need apart from a 3-view, is available from David Boddington).

The model is very accurate and competitive, but not overly complicated. It follows traditional building methods and should not be too much of a problem for those who have produced something similar in the past. The scale size may seem odd, but is governed by three factors. Firstly you can just conceal an inverted Mills 1.3 engine. Secondly, this conveniently works out to be an optimum size for a competitive outdoor scale free flight model. Third, my fingers are too clumsy to make it any smaller.

The following text is not intended to be an exhaustive explanation on how to build the Dove, but covers most of the procedures with details of the tricky bits.

FUSELAGE: The fuselage is a basic box with formers and stringers added. Pre-bend the lower longerons to prevent warps. This can be achieved by wetting the area of the wood to be bent and bending the spruce across a tin can with a night light candle inside it. Continue until the wood is formed into the correct shape, not twisted and dry. Be careful, it gets very hot.

Before fitting F1, you need to adapt the engine-mounting method to suit your engine. Beware of the excessive amount of down thrust 8° and side thrust 3° needed. You will need to offset the engine a fair amount so that the prop shaft exits through the centre of the Le Rhone crankcase. Will the prop clear the cowling? Don't mount the prop too close to cowling or it will get dented each time it lands (been there, done that, etc). The plan is for a Mills 1.3 and uses a modified commercial mount fitted to tapered layers of plywood. On the reverse side of F1, epoxy beach bearers to support mounting screws. The cut out in F1 is needed to access intake for rear induction engines, cut to suit. Front induction engines do not need this or the diagonal firewall.

On the underside of the fuselage behind the cowl, an inverted 'V'channel is fitted. For front induction engines, this can be static but for the Mills I fitted a trap door with hinges and a spring clip to access engine intake. When all these considerations are sorted, epoxy E1 to fuselage. Reinforce with fillets of balsa.

When fitting undercarriage wire tubes, ensure the rear one is very well braced, as it takes all the landing shocks. The front one is fitted with ali straps wrapped around Fl and bolted into place.

Bolt U/C to F1 and plug in at the rear. U/C cross bracing is non-functional. Wheels are traditional turned ply/balsa sandwich with foam rubber tyres cyanoed on. Epoxy wheel axle-tube in place, ensure it is square to the wheel, with 15 to 20 mm protruding from the back of the wheel. Cut same length and size piano wire. Put this inside the tube and fit into the chuck of electric drill. Spin wheel and shape as desired. Cut off excess tube. Spokes are reproduced using cotton thread wound around the wheel and glued. Cover with nylon to produce the effect of spokes under linen. Apply four coats of dope. Fit tyres after painting.

Glue in place all formers on top of the fuselage. Ensure that they line up correctly for the slope of rear fuselage and cockpit decking. Fit the spruce stringers. Fill in between stringers at formers with scrap balsa. On this aeroplane there are no areas where the covering is proud of the structure e.g. longerons, stringers, uprights and formers, as on some types of this era.

I recommend that the wing centre section be built first, with the cabane wires installed, so that you can adjust the position of the tubes fitted to the fuselage to ensure the angle of incidence on the top wing is correct ie 2-1/2°. Note, the cabane wires plug in to the bottom tubes to allow easy fitting and removal of this section and are fitted permanently later when the cross bracing is added.

Fit out the interior of the cockpit while it is still easy to access. Stain vanish the wood first then fit controls, dashboard and seats etc. NOTE the pilot sits in the front and is installed before the wing centre section is fitted. The top centre section showing the tube joiners bound to the spars and the wire wing joiners in place, bent to the correct dihedral.

THE COWL: The front cowling is one of the main features of the Dove. Mine is made of an ali kettle reshaped over a solid steel former. You could possibly cheat it and make it of fibreglass and paint with ali, but it will not have the same effect. A friend was kind enough to have the solid steel former turned on a lathe at work. Not for the faint hearted! A hard wood one will suffice just as well. The kettle was cut to as near a shape as I could get, and then annealed to soften it. To anneal it I rubbed it with soap and heated it as evenly as possible over the cooker until the soap turned brown and allowed to cool (lots of grumbles from my wife, Sandra, as this stinks the house out for a while). This is clamped to the former with giant jubilee clips. Now the fun begins.

From the bottom up, slowly form the ali around the former, gently tapping with a smooth headed hammer until you are happy with the shape. Cut and trim as you go. Practice makes perfect and may take some persistence. You may have to anneal the ali several times if the process goes on a bit. When happy, remove from former and trim to desired shape. The joint in the ali can be reinforced with a piece of ali and epoxied into place. Reinforce the front opening of the cowling on the inside with a ring of epoxied 18swg piano wire. Now a lot of time has to be spent burnishing out any marks with wet and dry paper. Surface needs to be smooth but not highly polished..."

Sopwith Dove, R/C Model Flyer, June 2003.

Direct submission to Outerzone.

Note main model pic is from Mike Stuart's Flying Scale Model site at http://www.ffscale.co.uk/page3mm.htm and shows the prototype model by Michael Smith which won the Eddie Riding Trophy at RAF Woodale in 2002.

Supplementary file notes

Article pages, thanks to RFJ.

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