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How to Tame Your Orpheus

Updated: Jan 5, 2023

Some months ago we read with interest that the Ruskin Museum had acquired a pair of Orpheus engines then realised with horror that they'd made a massive error. The Orph's are the 803 variant for the Italian G91-R fighter, ironically nicknamed a Gina.

It was a good few years ago when we heard that a large number of Orph's were about to be released for sale only to learn they were 803s and therefore completely useless for K7 purposes. At that time we only had one engine and that made it all the more precious. Now we have three, all fully working and regularly maintained and run, but then we were keen to build a spares package and these seemed an ideal solution. But the 803 has a much wider gearbox and a larger fuel pump. The 101 uses a B-size pump, the 803 a D-size. That's the same as on a Vulcan! so none of it will go anywhere near and nor are any of the ancillaries any use either. It was back to the drawing board. Our other engines came along in due course so we're now future proofed. And then it was announced that the RM had got hold of a 101. That's much better. At least that can be made into a suitable engine so in theory a fourth engine has now joined the pool. Heaven forbid we ever get through that many but it's still a good thing but what exactly does it take to make the 101 fit?


In 1966, Bluebird was re-engined with an Orpheus 701 and we certainly don't envy those who took on that job. Hats off because it's an incredibly tight fit in there. Then they took it, totally untried or tested, on a record attempt into the unknown, ran the new setup a handful of times then dropped it and there it lay, abandoned, for 34 years until we relocated and lifted it.

As most will already know, we installed K7's engine last Thursday but we've actually installed it a total of four times so far but this time we hope it will be in for a while.

Our first go didn't really count as the engine had no fuel system or other ancillaries fitted. It was just an exercise to get a look but even in a bare condition we had fouling of the heat shielding and some engine bits. That was mid 2015. Our second try in mid 2016 was a much more in-depth exercise.

The result of K7's short life with an Orpheus engine is that we inherited a lot of undeveloped machinery but also some good stuff. Things like the engine mounts, the packaging for the air start, controls and wiring were all done well, though the controls were smashed and the wiring scrap but at least we could see what had been done and pick it up from there.

Other things weren't so good. The water brake, first fitted in 66 as part of the Orpheus evolution, had inadequate seals so it leaked like an old Land-Rover, and a manufacturing fault that made sorting that particular problem a much bigger deal than it might otherwise have been.

We built an extra tall engine stand so we could work comfortably under the engine and made a start.

Other than the obvious big jobs we discovered unexpected subtleties too. Like the tacho indicator (rev counter) being hopelessly mismatched to the unit on the engine designed to drive it so it always read low. And this must have been the case in 66/67 because we used all the same parts due to happy chance having recorded a part number in a single hi-res photo by Paul Allonby. Perhaps this was the cause of all the trouble with the engine supposedly not giving its best back then.

But by far the biggest problem we faced was trying to get a 101 Orph' into the hole that a 701 filled to capacity when the 101 is 38mm longer. It doesn't sound like a long way, does it, but imagine if you bought a new front door and it was 38mm too wide. It would seem a long way in that instance.

Not only is the engine just a fraction too long, there's also curved frame tubes running beneath it that the aircraft doesn't have so many things had to be relocated to fall between them rather than onto them. The main fuel line on the standard engine goes nowhere near and fouls everything in its path so the filter bowl was swapped for an earlier version then all the rigid piping for the fuel control unit was remade to suit. And that's just the beginning. Clever Barry was consulted and sketches flew back and forth until agreement was reached.

Then we'd make up the parts. And don't forget that we were (and still are) under the watchful eye of the aerospace giant that shall not be named so everything had to be built to the highest possible standard.

The tacho generator (the thing that drives the rev counter) had to go too. We built a small gearbox to relocate it.

If you look closely at the front of the engine in the 5 o'clock position you can see a shiny, circular opening with three bolts. That's the gearbox to correct the RPM reading and mount a slimmer tacho generator to clear a frame tube that runs straight through there.

Most of the fuel control modules needed shuffling forward or backwards to clear a crossmember towards the back of the engine too so stainless steel brackets and mounting plates were made up.

Then everything ahead of the engine had to be remade to lose 38mm.

Of course we had a massive advantage in doing all this work because we hadn't yet fitted the outer skins down the sides of the hull so we could actually see what were working on beneath the engine and get our hands and rulers in to work on it.

Other tasks included a redesign of the engine drains from which small amounts of waste fuel and oil are ejected because in 66 it was simply dumped over the side and, though it would biodegrade very quickly like the natural oils released by decaying vegetation at the margins of any lake, someone unaware of this would kick and scream that we were trashing the planet so we decided it would be easier to catch it and disappear it some other way.

We even made one or two cosmetic changes along the way. The 701 has a different anti-icing arrangement and we were able to obtain the inlet for it, which is visible on top of the engine. We made up a plate to blank the hole and mount the new inlet and bolted it on purely for looks.

It was a long list and the above is far from exhaustive but we worked through it and our first complete engine installation was done by mid 2016. There were still things that weren't done, however.

The hydraulic system for the water brake was still poorly understood and despite a huge effort to learn about, rebuild and operate the old start system (with the generous assistance of Goodrich Power Systems) it was neither powerful enough nor safe enough to actually start the engine so starting had to be done from additional air storage off-board. Something we still hadn't bottomed satisfactorily by the time we went to Bute in August 18.

No matter. On an extremely soggy November day in 2016 we took the stripped back hull with the engine installed and gave K7 her first taste of heat and drama since the 4th January 67.

That was a landmark moment but there was still a long way to go. The engine came straight back out so we could continue building the hull such that it would keep the water out while development of the water brake and start systems continued. The main issue with the water brake was reliability of the ram and keeping the oil on the inside. Much of the hyd setup is simply stolen from the Gnat but the actual brake part is a crude ram that is pushed down into the water. The piston rod was scrap when we found it.

It had been extended post-accident by stored hydraulic pressure. Hyd pressure is stored for a variety of reasons. On the aircraft it allows fast operation of control surfaces or undercarriage whilst utilising a small pump and small oil volume. On the boat it allows the water brake to be thumped down in a hurry even if the engine has gone out and not providing any hyd pressure. Because of that, soon after K7 hit the bottom the stored pressure forced the ram into the mud and there it merrily rotted for 34 years. We saved it by having the corroded surface machined back, metal-sprayed then reground and that was only for starters.

Notice how the colour of the surface of the piston rod changes halfway down. That was an expensive fix!

All the seals in the ram were then redesigned to stop oil from escaping into the lake/loch and that was nothing compared to having to make the hydraulic pump and pipework fit into the confined space beneath an engine slightly too long but we got it packaged eventually.

Our third engine installation was ahead of the Bute trip and included everything we'd learned so far and in mid 2018, only weeks away from travelling to Bute, we made our first static runs with everything connected. This was as far as we were to get for a good while, unfortunately. We were still using off-board starting and used that system on Bute and we hadn't developed a satisfactory method for setting up the throttle linkages either so our idle was too high and we were unable to achieve 100% power. Not that we needed it!

On our return from Bute we stripped the engine back out to have a good inspection of hoses, pipes, wires and everything else to look for signs of chafing or leaks or any other potential issues after 10 days of running on water. We found damage to wiring insulation from spilt kerosene and the paint on the inside of the hull hadn't taken it too well either so that was redone.

We were in the zone working hard ahead of July 2019 when we'd finally been given dates by the Lake District National Park Authority to run on Coniston Water. We were abuzz with excitement. Bute was epic - this would be epic on steroids but without warning it was cancelled. Then we lost all of 2019 while the museum tried to back out of their long standing deal with us. Two years of Covid-19 troubles followed that so we only really got back to our work in 2022. Slowly at first but we've gathered momentum. The big outstanding item left undone was to provide reliable and safe on-board air starting capability as per 66/67 and we're delighted to say we've now achieved that but how we got there is a story for another day.


But, finally, one interesting snippet that came up recently was a naysayer latching onto something. That's what they do. We drop a teaspoon on the floor and they're on it to tell us we're not competent to make tea and therefore we shouldn't be working on K7. It's often pathetic and invariably reeks of desperation but then again sometimes it's entertaining.

This particular naysayer latched onto the fact that we've developed a new air start system and this constituted modification rather than restoration and obviously modification makes us bad.

So, let us break this down.

The Ruskin Museum has an Orph'101 which could be made to fit the boat and that can only be a good thing but let's take a step back. They assure us they have this engine so K7 can be run so if it's going to run then it must be started and if it's going to be started it needs some means of putting sufficient energy into the rotatives that the engine will light and accelerate without frying its turbine.

Safe to say we can forget about converting it to electric start as that would be a major departure and definitely come into the category of modification so to avoid that they'll have to stick with the authentic air start. Besides, the sounds are all part of the experience. The sudden explosion of compressed air is what people heard in 66/67, not the whine of an electric motor. Likewise, we stuck with the old, coil type igniters rather than fit modern cracker-boxes because that's not what K7 is supposed to sound like.

So we're settled on air start, agreed? Now let's assume that they have the start turbine for the Orph'101. Trouble is it uses LP air and is woefully wasteful on HP air, therefore it's impossible to store sufficient air aboard to start the engine. There is a HP variant but it won't fit the 101 engine so what we did was run a hose from the starter to a dry-break connector on the outside of the hull so we could attach an air hose for starting then break it the instant the boat began to move but that's a modification and, as already mentioned, modifications are bad.

That was OK for a while but we didn't rest there and soon redesigned an LP starter to incorporate the means by which the HP one is so frugal with its air. Brilliant, but the old storage and delivery system was lethal when it was new never mind following 34 years of fizzing away in a lake.

To sort that we next designed and built a new and up to date air storage and delivery setup that bolts on where the old one did and remains visually similar. You could call it a modification but that's only when it's fitted and as it's a straight swap for the old one it can be put back to how it was at any time. We're now as authentic as we can possibly be with only a few, reversible 'modifications' but the question is this, if to modify is bad, how on earth would the museum build a running K7 without taking a similar route?

The point being - whichever naysayer came up with the modification is bad theory doesn't have the faintest clue what they are talking about.

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Albert Dexter
Albert Dexter
Aug 20, 2023

"How to Tame Your Orpheus offers a captivating journey through self-discovery. Its insightful narrative parallels the dedication seen in medical fellowship personal statements, as characters navigate challenges akin to medical pursuits. The book's thematic depth resonates with the resilience and passion necessary for success in the medical field. An intriguing blend of fiction and determination."

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