An Olympic Javelin

//An Olympic Javelin

An Olympic Javelin

Having just finished a Stearman restoration, and having pretty much kept to the original drawings, there was one thing that I found a bit too crude – unworthy of an aircraft with this quality of manufacture.  The javelins.  After all that work to cut a broom handle in half lengthways, chip out a few slots then clamp the two halves back together with a couple of screws.  Somehow it didn’t seem right.  Here’s how we made a better javelin, adjustable for perfect alignment and length.

The design consist of five sections, to allow for adjustment in both length and rotation, in order that the result fits a rigged aircraft precisely without any tendency to deflect the wires, however small.   For this you will need about 6ft of hard maple, machined to 1-1/8” x 5/8”, and 4ft of dural tube, 1” diameter, with a wall thickness of 1/16”.

First,  precisely measure the centres of the two front flying wires, and the three rear wires where they cross.  I’m assuming we’re dealing with a fully rigged aeroplane with wires tensioned and set.  Whilst the rear landing wire is probably intended to pass equidistant between the two flying wires, this is not always quite the case, and here we have the opportunity to get the centres as they actually are, not how they were meant to be.

The components consist of a nosepiece in two parts, a centrepiece in two parts, a tailpiece in two parts and two spacer tubes.

Each of the wooden components is made up from pieces of hard maple (to match the Sensenich wood prop if you have one) and glued and screwed together as shown.

First, cut the hard maple to lengths A,B,C,D,E and F as shown in Fig 1.  Square the ends accurately.  Clamp the work appropriately, and using a router, cut shallow slots across the flat maple sections exactly 3/32” deep and 3/4” wide, with centres to match your earlier centre measurements  (see fig 3) The two pieces are glued and screwed together to made pieces 1/1/8” square, with two slots 3/16” deep and 3/4” wide. The removable centre section is attached to the main body of the section with two screws, which will be replaced later. 

Assuming you have access to a lathe, make a couple of suitable shoes (see fig two, that can run between centres, and simply machine the glued and screwed sections to a 1” diameter dowel (hard maple turns beautifully) Turn a rounded nosing on one end of the front piece, and a tapered cone on the tail piece.

At the other end, turn a 1” long step down to 7/8” or just a hair over for a snug push fit in the dural tube.

The centrepiece with its single slot is made in the same way differing only with the step down being turned on each end.

Once the three parts are machined, the screws can be removed, and the three removable cap sections should drop out.  The screws are then replaced with a countersunk machine screw of 1” length retained by a recessed stopnut in the underside.  Once the nuts have been pushed home into a slightly undersized recess, they are held permanently with epoxy resin.

The enlargement of the centre slot of the tailpiece to take the crossing landing wire is best done from a precise measurement on the aircraft and is the only tricky part of the operation.  You may also take this opportunity to subtly alter all the slots to precisely the angle that the respective wire passes through. 

With a little trimming, it should be your aim to get the three sections sitting easily on the wires, with sufficient clearance for whatever padding you choose to use round the wires themselves.

Once the three parts are clamped in position on the bracing wires, the precise length of the dural spacers can be measured.  Once these are cut, drill four small holes at each end to locate the four screws that will finally lock the components together. I used round-headed woodscrews of 3/8” length, but I would now take the trouble to countersink any replacement.  Now the five parts can be assembled off the aircraft, offered back up and the cap strips clamped in place. 

On my aircraft the wooden parts are varnished and the metal tubes painted the dark blue of the fuselage.  Not only to they look very good, but by clamping the wooden pieces to the wires prior to locking the tubes in place, allows them to centre exactly in position, and the take up any slight idiosyncrasy in the rigging of a particular aircraft. 

The broomhandle brigade may think all this is too much of a fiddle – but despite everything it was probably only a day’s work – and they really do work well and look very good.

By |2016-11-13T09:33:44+00:00August 5th, 2002|Flying-Wire|Comments Off on An Olympic Javelin

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