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209. Tinkering

11/12/2015

Theo and I spent Wednesday and Thursday looking at a couple of aspects of the engine. We fitted a felt seal to the modified cowling to tray and seal the gap between the cowling and firewall, and reduce the oil contamination of the fuselage sides.

2015-12-10 Cowling modifications

You can see the cutaway in the bottom of the cowling to try and persuade more of the oil to be flung clear of the aircraft by the exhaust valve opening. We’ve had to add a wire across the opening to stiffen the cowling so that the front edge doesn’t contact the rocker bearings on the cylinder heads.

You can also see the quite substantial felt strip (three layers of 6mm felt glued on top of each other) around the back edge. This is positioned so that is is slightly compressed against the firewall when the cowling is in place.

2015-12-10 Cowling seal

The cowling in place, with the seal squashed against the firewall

It replaces the earlier lip seal ( a strip of 3mm thick nitrile rubber screwed to the firewall that pressed on the cowling) which should have worked and didn’t.

This should work but we won’t know if it does or not until we get another opportunity to fly – which may be in January, weather permitting.

We then took the fuselage outside to see if we could use Ian Harris’ expertise to increase the power output at all. It wasn’t as useful an exercise as we’d hoped, because the engine was persistently misfiring. we tried changing plugs, but this didn’t seem to have much effect. It was disappointing – the last time we’d had this problem, we’d changed to the four-electrode plugs, since when it’s run absolutely smoothly, so we thought we’d got to grips with it – but I wonder if the very damp air may have been causing some arcing of the HT across the commutator ring – or possibly oil contamination, though we’d certainly cleaned it well immediately beforehand.

We decided that as we’re going to be at Shuttleworth for their Engineering Days on 2/3 January, we could take advantage of their expertise – again – to see if we can get things running more evenly.

One other major improvement was merely serendipitous. Ian Harris had come to the airfield to help us run the engine and suggest improvements, and offered the use of his bucket of wipes which he uses in his workshop. We found to that they were the best thing yet for cleaning castor oil off the airframe. The advice we had was that the best thing was a dry clean rag while the oil was moist, and that the only thing that would shift it once it had dried was meths. This, however, softened the surface of the dope, and this made it impossible to use it on contrasting colours. well, we haven’t tried the wipes on dried castor oil, but on the fresh stuff it’s an order of magnitude better, and there’s absolutely no reaction with the dope. I went straight home and ordered our own bucketful. result!

The other thing Ian did yesterday was to bring along the completed bomb rack with the bombs mounted on it. It’s now mounted onto the fuselage so that you’ll be able to see how Granddad was able to bomb the Turks and Bulgarians. But I haven’t got a photo – you’ll just have to come to Shuttleworth on 2/3 January if you want to see what it looks like!

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From → Technical

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