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Good Museum Practice

Way back in our infancy we looked to the museum world for advice and thank goodness we knocked on the right door first time. We would soon discover that museologists (yes, that's a thing) were an interesting breed to say the least. They live by very few hard and fast rules so while one will tell you to wipe carefully with cotton buds and de-ionised water then leave alone thereafter, another will say pull the object apart, whatever it may be, to consolidate and conserve. But a few common threads do run through their work and one of them is to make sure everything can be reversed. Well we really blew that one because no way could K7 ever be put back to that rotten wreck but there's lots of photos to tell the story and who would want that anyway?

Another is to make sure that old material can be differentiated from new and we did that by painting the new bits green. That said, we did cheat a bit because if we could incorporate a piece of old material we'd claim that part as old when in many cases it mostly wasn't but in the grand scheme of things does it really make any difference?

But there was another rule that we have also lived by and we only came across it because the first museum person from whom we sought advice was Chris Knapp, head of conservation at IWM Duxford and Chris's most important rule was, 'reality dictates'.

Chris didn't mess about.

He came to assist us when we were stripping the innards out of the hull but we couldn't release the lead ballast because the bulkhead it was attached to had collapsed trapping it. Chris suggested we chiselled the heads of a few awkward rivets to release the bulkhead. Chisel! Really? but he was insistent so that's what we did. We'd not done anything like that until then.

Then, when we asked what should be done about the mud under the corrugated floors that had gone in as a fine slurry then dried out and set like concrete in there, Chris simply said we had to get it out by whatever means.

"It's trapped," We pointed out.

"Then take the floor off"!

"It's riveted on from the outside with about a million rivets and it' sitting on it. How are we supposed to do that?"

"Put it on a rollover jig" Chris said, as though it was the most obvious solution in the world, that we were clearly being a bit stupid and where was our jig?

We realised at this point that the bar would have to be raised so we built a jig and took the floors off.

The mud inside was everywhere but the exercise taught us that sometimes we had to get bold with the situation.

This would would come to define our way of doing things, it gave us the confidence to take on the bigger tasks and when time came to start reassembling parts onto a rebuilt frame a new rollover jig was a must and no question.

We learned a lot from Chris about how to get big and bold but he also schooled us on the finer points and the need to keep things reversible where possible so when we sat down to plan our new on board air delivery setup there were a few ground rules.

We would not create any new holes anywhere, we could only use what was there to begin with and it must be possible to reinstate the old arrangement at any time either for display purposes or in case we develop a way to get it working safely again and want to put it back.

Then the new kit had to be safe and reliable too.

Storing the air was a no-brainer. The original spherical bottles hold 15 litres of air each and 15 litre diving bottles are inexpensive and would be easy to package in the space available. We also bought 300 bar bottles, though we only fill them to 232 bar, so we have extra safety and extra capacity if needed.

They had to be mounted to the boat in some way without drilling holes but that was easy too. The old frame came off and we built a new one to utilise the same four bolt holes. We snaffled the steel from the roof rack company next door. Waste not, etc.

The botles clamp at the necks and also have a steel band around them when fully installed so they're not going anywhere.

But diving bottles as they arrive are no use for starting an engine because the problem is the pillar valve, the tap that lets the air out when you want to go for a dive. Dive kit is designed to not let you drown as much as possible so the valve will flow enough air to keep a frightened diver oxygenated until he/she panics and blows themselves to the surface but it won't flow enough air to start an Orpheus. We had to have new fittings made up.

These are machined from stainless and stressed to a minimum of 500 bar and they will let the air out of the bottles at an alarming rate. Next we had to take all this air to one place so we had a manifold block made up. This had to accept the air from both bottles then send it off to a pair of valves that we'll get to presently. It also needed various other ports for filling, draining and to attach a pressure gauge plus a couple of extras for things we don't know we need yet.

In its original form we decided it was too heavy to mount to the frame so it went back to the machine shop to have the bits marked in blue taken off.

This, in combination with some bespoke hoses made for us by Armtec Engineering down the road in exchange for a few welding jobs, let us store and deliver air using only the four original bolt holes onto the deck of the boat but next we had another problem to solve. How to mount our start valves without drilling holes.

On the old setup the valves are smaller and dangle from the necks of the bottles but we couldn't do that because the valves we use are much bigger.

After the small Hunting plane was retired and the second set of starting equipment was sunk (see previous diary entry) you could be excused for thinking that that was the end for Lucas Rotax's start kit but it wasn't. It evolved and grew until it became the rapid start system for the V Bombers. If you dig around inside a Vulcan you will find the great-grandchild of Bill Vanryn's valves waiting to get your weapon of mass destruction off the ground before the other side's weapons of mass destruction arrive and obliterate your airfield. Better still, it's all mechanical apart from one simple solenoid and is astonishingly reliable. We started a Vulcan engine after it lay dormant for 36 years and the valves worked perfectly first time. But we wanted to do better than old second-hand parts so we asked nicely and were given some brand new still in the bag examples by the Vulcan To The Sky project as they had no need of rapid start capability. All we had to do was work out where to mount them and this time we had to be a little cuter.

Back in the Beryl days there was a filter and LP fuel cock mounted up on the bulkhead at the back of the air intakes.

This was long gone by the time we arrived but the corroded remains of its bracket was there and so was the plate to which it was originally mounted complete with a fine set of fixing holes we could use.

All we had to do was unbolt it, wrap it up and put it away in case it's needed again and we had six bolt holes to which to mount our valves.

Now you would think it was in the bag but it just doesn't work like that with K7. The problem now was that we had to mount the valves to a new plate and this would have to be done from behind, which meant if ever we wanted to remove the valves to service or replace them we'd have to remove the plate along with them but the plate, you will notice, has the nuts on the outside and that's because the bolts that fasten it to the bulkhead are countersunk because they sit pretty much against the fuel tank, which lives immediately behind that bulkhead with no access for spanners or anything else. What you do is bolt the plate into position then fit the bulkhead. To make matters worse, the bulkhead is a horror story to load because you have to loosen off the entire intake structure to get it in or out.

We had to be able to mount that plate from the front.

We got lucky for a change because it turned out that at some time there had been captive nuts riveted where the bolt holes are so we had a handy set of rivet holes we could use to affix another plate 3/8" thick into which we put 1/4BSF helicoils.

People ofen think Helicoils, or thread inserts, are some kind of a bodge but they were designed to put strong threads into soft alloys and are anything but. The threads are infinitely stronger than if you just cut them into the native metal so we Helicoiled the holes and riveted on our mounting plate for our mounting plate.

Notice the yellow etch prime and you can just make out the bead of choccie there too. Now we could bolt a second plate onto that one without having to get behind it so the bulkhead was loaded and we set about mounting our valves.

Mich and Gordon created the hardware to mount the valves whilst Clever Barry made up a special fitting to mount the valves as one rather than have a hose or rigid pipe between them and that way we could keep them within the bounds of the mounting plate.

Now the valves can be attached to the plate from the back using countersunk screws, which are all UNF threads because for some reason that's what's used on Bristol Siddeley engines and anything that ever attaches to or near them, then that plate can be similarly screwed to the bulkhead, from the front, using BSF threads, which are typically what K7 is held together with. There'll be a test later so be sure to keep up.

There are two valves and, if anyone wants to go full-nerd, I can write a separate post on those or even a separate post for each one later but the quick version is that the top one has a total of three moving parts and lets the air out of the tank into the second one and the second one takes in air at tank pressure then lets it out again at 250psi to drive the starter. Apart from a small solenoid on the upper one they are purely mechanical.

So that gave us the two main elements of the new arrangement, air storage and the valves to send it where we want it how we want it. Next we had to mate it all together and first on the list was where to mount the manifold block so routing the hoses would be easiest. We finally settled on bolting it to the bottle frame near the bottom facing the valves. This kept the hose runs to a minimum and the weight low down. We drilled through and welded sleeves into the frame tubes so we could put some weight on the bolts without crushing the frame tubes then bolted it all together so Chris, our local hydraulic hose manufacturer, could come over to measure up and make some hoses.

The maximum pressure we could ever use is 300 bar, that's what the bottles and valves are rated to and it's also the most our compressors can deliver but our self-imposed max working pressure is 3200 psi like in the old days, or a smoot over 200 bar so all the hoses are rated to handle this with some margin.

With the major elements settled upon it was time to look at the finer points and despite all the equipment being up to the job, compressed gas is still dangerous and a major risk is that the pressure regulating valve (the lower one) might stick or fail in some way and deliver tank pressure downstream to the start turbine, which is only good for a few hundred psi and which would scream to a billion revs then explode if it didn't just explode to begin with.

This risk is dealt with by a bursting disc that does exactly what it says on the tin. It's an all or nothing protection for the downstream part of the valve. We could put a relief valve in but what if that sticks?

The bursting disc is either perfectly intact or blown to smithereens, nothing in between and if it goes, tank pressure is vented safely to atmosphere and nothing explodes. It is quite a frightening happening, mind you but other than a risk to one's underwear it's safe enough. The problem is that the discs are a consumable and sometimes they explode and you can't nip to your friendly Avro dealership for new ones so to be future proof, and we like to be future proof, we had a word with Clever Barry who immediately built a rig, took some parts into his workshop and calibrated everything then made up a supply of discs for various pressures.

That made us safe. Things like the final arrangement for charging the bottles, instrumentation and non-return valves, etc. could be fine tuned at the end but first we had to see whether the contraption worked.

Our first test was to see whether it would deliver air when commanded then stop again as required. We also wanted to measure how much air it consumed and to that end, Bill Vanryn had designed a test nozzle years earlier that we'd used on the original start system rebuild. It perfectly mimics the amount of air the starter needs and creates the right amount of back pressure. We fastened the test nozzle to K7's trailer and fired some air through it using the onboard electrics from the cockpit to see if all of that still worked too.

The nozzle is a simple enough device but has proved invaluable in understanding the performance of the air systems.

With a calibrated nozzle we blew a load of compressed air into the street along with quantities of dust and debris from beneath the boat and, better still, the figures we were seeing from our new setup were very encouraging.

Next we had to see if the nozzle values were matched when spooling an engine with our modified starter but we weren't going to build it all into the hull then lug everything outside to give it a go. It was much easier to secure the start equipment to a trolley, charge it up then see if it would start an engine on the rig. We always enjoy running up an engine so no one needed asking twice.

The complete start rig was bolted and clamped to a trolley then carefully wheeled over to our engine that waited fuelled and powered up. All we had to do was attach the air pipe and electrical connector to fire the air valves and we'd see if our new creation was up to the job.

Safe to say that was the fastest we had ever started an Orpheus. It was ridiculous! We knew the starter was very efficient by now and we knew we were sending the correct amount of air to it but on pressing the button the thing shrieked into life and was lit and up to speed so fast that I forgot to take my finger back off the button for an extra second or so beyond what was needed. Better still, we had enough left in the bottles for a second start and that was with mostly empty bottles that hadn't been completely blown when we began.

We have some extra neighbours since we last ran up our engines too so we'd been over the road and told them what we had planned for Saturday and invited them for a look-see. Everyone likes a good jet engine adventure so there were more than a few extra visitors once we'd shut everything down. All in all it was an unqualified success.

The next big test is to put all the bits together in the boat and see if we can perform the first live start using on board air only since 4th January 1967 and if we can do that it will be a major milestone.

Our brief was always to get K7 to as close as possible to how she was on the morning of the 4th January 1967 and that includes on board air start capability. But the old equipment just isn't safe to use as it stands and like for like parts aren't available so he compromise is that we've had to design, build and commission something new to do the job but we've done it in such a way that the old configuration can be put back at any time just as it was.

Good museum practice and, as Chris Knapp would undoubtedly remind us, 'reality dictates'.

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Stop Press

The RM have issued a letter but their link doesn't work so here it is.

1 Comment

Rhys Nolan
Rhys Nolan
Jan 22, 2023

As ever, a brilliant write up which we can understand, and shows the devotion continues. True to the motto, . My admiration knows no bounds.

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