Sloping Off - March 2005
The Walrus Revisited
by Mike Roach
I have long admired Trevor's Supermarine Walrus as it makes its slow and stately way round the various indoor halls we fly in. It has a perfect "sit" in the air and seems to fly, turn and land as if on rails, but I'm assured that this is all down to pilot skill Anyway, I got tired of waiting for him to draw up a plan and get it published, so we agreed that I would do the drawing and put the article together while he sat back and got on with another indoor gem (actually, his grandaughter Annabel filled this spot nicely!), giving me the perfect opportunity to make a second version: perhaps we could fly in formation round the Calshot Velodrome?
The model flies beautifully and is surprisingly robust ... don't ask!
... that perfect 'sit' in the air
You may remember that Trevor based his design on his well-proven SE5: just enough Depron to make an airworthy structure, a fair amount of caron fibre rod, working rigging and the usual GWS hardware. One of the major problems he overcame was the elevator linkage:
I
f the wing was easy, the tail surfaces were anything but! Admittedly, part of the difficulty was self-inflicted as a result of accepting the challenge from a fellow modeller to do an internal linkage to the elevator. After much thinking and tinkering, the fin was fabricated from two thicknesses of Depron, held apart in the centre by two strips of 1/16in balsa. The gap between these strips formed a channel for a thin wire pushrod, which would connect to a 120degree crank mounted in the fuselage. All that remained now was the problem of coupling the wire pushrod to the elevator. Some time ago, I read about a way of connecting pushrods to torque rods using heat shrink sleeving. I remember being somewhat sceptical of the idea at the time, but now it seemed the only way of making a hinged connection within the 1/16in gap between the fin sides. Even so, it took a lot of experimentation and head scratching to get the geometry right and work out an assembly order for it all, but eventually everything seemed to work reasonably smoothly. After this, it was something of a relief to rig up a conventional thin wire snake connection to the rudder!
I'm afraid I took the easy way out and bought a Sullivan Gold-N-Cable from Channel 4 Models near Bournemouth, cut a smooth curved channel into the 3 mm Depron fin and faced it with some very thin Depron sheet I got from Flitehook. The outer cable was then glued into the channel and taken forward to F3. All the other linkages are as Trevor's.
One limiting factor we both addressed was the 7" diameter maximum propellor size. Fortunately GWS make the S2 geared motor for a 7 x 6" prop and this provides more than enough thrust to fly indoors or out. I found out that the real Walrus had a 4-bladed prop made, as was often the way pre-War, from 2 props on a shaft, rather than being lapped together. I discovered that two GWS 6 x 5 props would fit nicely onto the shaft, as long as there was a prop-nut in between them. This reduced the overall diameter even more and still provided more than enough thrust from the S2 gearbox.
Trevor's model keeps his thumbs well occupied in flight, due to the proximity of the prop to the tail surfaces, but the full-sized engine pod was rigged with right and up thrust. This works well on my model, taking away the need for lots of right rudder when the power is on and the throttle/elevator mixing that Trevor uses. And unlike Trevor, I do enjoy painting and decorating! I did most of the work while at the component stage and then fudged in the edges afterwards. I don't suppose that the paint adds more than 15 grams to the total weight so quite intricate work is possible. My markings are done using my PC and Lazertran transfer paper, wetted out with MicroSet according to the instructions on the bottle. I rigged the model with button thread, which is far too strong, but around the right diameter. I like using black thread for rigging (that's what you see when a real biplane is flying past) but most people use silver or grey because that's the actual colour of the wires.
After some trimming flights at Calshot when the model came home in one piece and I was a very relieved pilot, Trevor and I got together at "his" field for a really great photo-call. The sky was blue, the wind slight and the conditions perfect for some really good pictures. Trevor rose to the challenge and took a dozen or so really first class images, which I hope you enjoy. They appeared in the March Aircraft Modeller International, at a much larger size.
I'm still thinking about a waterproof version for flying off Christchurch harbour. The Depron is cut, but I don't know, a second model is never as interesting as the first. It would be fun though! MR
Postscript. While the Walrus building programme was going on, I was invited to the RAF Club in Picadilly for a Christmas Lunch. While wandering google-eyed round the hundreds of paintings on display I came across this one of a Walrus and an air-sea-rescue launch attending to a downed pilot in the Channel. I tried hard to get permission to reproduce the picture in my article for AMI, but ran out of time. Since it was to be auctioned last month, I fear I will never see it again as I certainly can't afford to buy it! But its discovery rounded off a very enjoyable project which has produced a singularly flyable and instantly recognisable model.
