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8

R-80 Tiger Moth – Wing Spars

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         Rob Brooke

 

The picture shows the interplane strut attach hardware on one of the main spars. The angled plate will accept the load of the flying wires; the vertical plate will take the compression load of the strut. The plates are fastened with ¼” AN bolts. The holes in the wooden spar are 3/8”, but provided with aluminum bushings which reduce the bolt hole diameter to ¼”. The bushings serve to reduce the point load of the smaller bolt.

 After all the spars were built, the last remaining step was to position the hardware which attaches to each and to drill the bolt holes necessary for its attachment. The hardware consists of attachments for the interplane struts (this is a biplane, remember) and, in the lower wings, hinges for the ailerons and the brackets for the bellcrank which will operate the ailerons. There will also be hardware for attaching the wings to the fuselage, but that is not positioned until the wings are being rigged to the fuselage.

As mentioned, after the spar caps and web are joined to form the spar, the web must be provided with stiffeners and reinforcements must be provided wherever hardware is to be attached. The  picture shows the outboard half of a main spar. The web stiffeners can be seen and the large area of plywood reinforcement provides a strongpoint where the interplane strut hardware will be bolted.

 There will also be hardware for attaching the wings to the fuselage, but that is not positioned until the wings are being rigged to the fuselage.

The spars are now finished. They took about a month and a half to build. The ribs took about a month. Next discussion – a wing.