345. Job Half Done

Looking at yesterday’s list, there are relatively few we can actually tick off, and we are going to have to come back again in a couple of weeks. to finish the job off.

But we’ve done the best we can, and we’ve each brought home a selection of jobs that can be progressed better at home.


Here, at least, is the repair to the rear fuselage fabric which has gone very well indeed.

2018-02-07 Rear Fuselage.jpg

The tailskid, though it’s invisible, is just awaiting some more bolts of the right length to be ticked off.

I’ve repositioned the pulsometer a little lower to see if it will stay full all the time, and I’ve brought back the inlet piping for modification when I’ve got access to a proper torch to undo the silver solder, and Theo’s got the tacho drive gearbox to make a slightly more secure mounting for it.

And the two big jobs are going okay. last night I cleaned the petrol tank, and swilled it out half a dozen times then left it full of water overnight, and today Jean-Michel Munn resoldered as many of the the leaking rivet heads as he could find. He air tested it and found a couple more, but it’s looking under control, and when he’s got it airtight they are all set up to etch and paint with two-pack epoxy which should look a lot smarter than the previous paint which was applied in something of a hurry.

But the job which kept me awake last night – the broken piston rings – seems to have come to a satisfactory conclusion. It was generally agreed by Phil and the manufacturers of the rings that the most likely cause was too small a gap between the ends of the ring. Getting it just right is a complex dance; different manufacturers (the le Rhone was built by at least four different factories) recommended different amounts, and it’s complicated by the fact that it’s a ‘choked’ bore; the diameter is 4 thou (thousandths of an inch) smaller at the top than the bottom, to allow for the fact that in flight the top is hotter than the bottom and will expand more. You measure the gap by inserting the ring on its own into the bore and measuring the gap between the two ends – and it’s anyone’s guess whether this should be at the bottom or top or somewhere in between!

But the consensus – based on the fact that it was the topmost rings that failed in every case – was that the gap had been a bit too small, and the gap was closing right up at the top of the bore, causing the ring to bind and overheat. thankfully no other damage had occurred, so a replacement set has been ordered and will be fitted in a week or so.

We were only there for three days, but our sense of gratitude to the guys in Engineering at Shuttleworth can’t be overstated. They have a completely unique facility and breadth of experience in this very specialist field, and would be quite within their rights to guard it jealously and not let anyone in. Instead of which, they move other precious artefacts around to give us space in the wonderful warm hangar, welcome us in with cups of tea, lend us their tools, and freely give their time to advise us about the problems we face.

To all of you, but particularly Jean-Michel, Phil, Andy, Rory and Gareth, a huge, huge thank you.

One other excitement – Theo brought up the half propeller which we’re going to shoot holes in. He’s wrapped the fabric round and applied the first coats of dope, and my job now is to apply more dope to the fabric band and varnish to the rest before we see how much damage a 0.303 bullet actually does!

No photo yet – I want to preserve the surprise…

And finally, you may remember the YouTube channel called the Great War Team, who have been assembling one of the most consistently entertaining and knowledgeable accounts of WWI week by week. They came to Stow Maries and did a special episode on 1264, and i suggested that they might like to do another special on the Coastal Motor Boats that were developed from an idea originating from three junior officers including Grandad’s younger brother, Bill. Bill helped to develop them and served on them throughout the war with very great distinction – it is generally believed that he deserved a VC for his part in the Kronstadt raid, but they’d already awarded two and so he must missed out.

Anyway, their researchers took the material I provided and expanded it enormously, resulting in an excellent brief summary of their use in WWI.




6 thoughts on “345. Job Half Done

  1. John 'Simba' Evans

    I believe the Pratt & Whitney radials that powered the PBY Catalina and B-24 Liberator also had choked bores for the same reason. All the best, and thanks for the link to the piece on the CMBs. Friends with me when I last visited Duxford wondered why I was photographing an ‘old motor boat’ as well as the aircraft – when I told them about the Kronstadt action and Augustus Agar VC, they understood and thoroughly approved. All the best with the work and I hope to get to Old Warden some time in the summer to see Grandad’s Aeroplane fly.

    1. Thanks John. People have suggested that having built Grandad’s aircraft, we should now build his brother’s CMB. But it seems a bit ambitious for us!

  2. Ted Timberlake

    This is possibly a dumb query, but why did they have choked bores and not parallel. What was the advantage.

  3. Nothing dumb about it! The idea is that because the cylinder head is much hotter than the rest, you end up with a parallel bore once it’s warmed up. In our case, we run the engine up to full chat more or less immediately, and that’s likely to have been when the damage occurred. I don’t quite know why we aren’t advised to let the engine warm through first before opening up fully, but we aren’t – mainly because everyone is so scared of overheating on the ground.

  4. Ted Timberlake

    Thanks for this. I guess that because the cylinders in a radial or rotary are in effect separate entities the heating up element has to be allowed for by having a choke to the bore. While in a motor that is an inline or Vee, essentially there is a block the cylinders that heat up more evenly and a parallel bore works in that case. Good luck sorting the ring gaps.

  5. Thanks. We’ll open her up again during the summer and see. I might also try leaving it a little longer before checking full power, though I imagine a binding ring will bind as well at half power as full!

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