After a productive time in February, this month caught me out with a minor puncture wound to my hand, that despite a bucket load of TCP and Savlon failed to heal as it should. Instead it decided to grow into what has provisionally been diagnosed as a pyogenic granuloma, which I for one had never even heard of but hey ho every day is a school day. Currently I am waiting for the specialists to notify me what they are going to do about it but conversations to date suggest it is likely to be a small operation to cut it out, followed by histology to check there is nothing more serious as causation. In the meantime as it will spontaneously profusely bleed, I am under orders to down tools to avoid risk of infection until they sort it, which is somewhat frustrating to say the least.

On a more positive note Luke Carver of Wixroyd very kindly sent us a selection of captive bearing rod and jaw ends to mock up the front mountings for Longbow’s twin jet engines. We will obviously have to machine something in appropriate material for the turnbuckles but this will be a big help in forming a good idea of what will be needed.

Whilst I was stuck playing the wounded soldier I was confined to desk work on Longbow and with the jet engine cradle provisionally set in the hull last month, I could at least finalise the steel plate design that will connect that cradle to the main timber stringers of the boat. With the cradle being in round steel tube and the stringers themselves being curved in shape this was not as straight forward as it might at first appear, so I have been back and forth measuring in the hull and then playing about with drawing on the PC.  

With organising getting these steel plates laser cut to how I finally wanted them meant a trip to our sponsor WEC. Whilst I was there it would have been rude not to have called in to the department there which had received the three Orpheus jet engines on behalf of the Ruskin Museum, or perhaps more correctly I was just nosey and wanted to have a good look at them in person. 

As luck would have it the Ruskin and WEC had their own jet engine specialists there dealing with the unpacking and checking over the engines which had recently arrived in shipping containers from abroad. I didn’t want to get in their way but they very generously allowed me to have a nice look around the engines and chat with their engineers over a brew. As always I will readily grab any chance I get to learn from time served gas turbine engineers so it was great to quiz them about the Viper jet engines for Longbow whilst I was there and watch them boroscope inspecting the three Orpheus engines. Prior to my visit the engineers had fabricated a temporary transport cradle for some of the engines but I did get to see them welding and fitting a blanking cover for the output from am Orpheus gearbox that would normally be connected to the generator. 

The models of Orpheus the Ruskin have been gifted to date are two 803’s and a single 101. The 803’s were made for the Fiat G91 aircraft and the 101’s for the Folland Gnat aircraft. I am somewhat familiar with both of these versions of the engine as we deep stripped and rebuilt a 101 version of the Orpheus whilst running the loose replica of Bluebird, the K777 over a decade ago and I had also swapped out an 803 Orpheus turbine wheel a few years back for my good friend Dave Warby to use within his spare engine for the jet hydroplane Spirit of Australia II.  

From what I could outwardly see at time of my visit to WEC the engines all appeared to be in good order which was confirmed by the gas turbine engineers I was chatting with. The following photo shows the three Orpheus engines with two 803’s on the left and a 101 version on the right:

I must admit to be being a little bit jealous that we didn’t have at least one of them in the same condition to use in the K777 all those years ago, as it would have saved us a lot of work with deep strip and overhaul at the time. Having said that it was a great learning exercise to work with the gas turbine engineers on that project and it has thankfully stood me in good stead ever since. 

Within Bluebird K7 a 701 model of Orpheus was used for her last record attempt in 1966/67 of which that model of Orpheus is now as rare as hen’s teeth pretty much confined to the odd one or two lurking in a museum as a static exhibit. Indeed the other models that remain serviceable are not far behind in rarity these days and hence the value of all versions of the Orpheus engine has shot up tremendously. For the restored Bluebird K7 a 101 version of the Orpheus appears to have been fitted to the craft when it ran at Bute in 2018. 

I am aware that there has been some discussion upon social media about the differences between the Orpheus models, so perhaps given my currently goosed hand, some aptly ham fisted clarification between these versions of the engine may be helpful for those with an anorak related dependency. The following is given in good faith and as always a little sarcastic humour but please note the usual caveat of not to rely upon my wittering as if I have made an error, then I will gladly hold my blood dripping hand up in apology to those more knowledgeable.

In the first instance it is not unreasonable to suggest that the 701 version of the Orpheus is more incestuously related to the 803 model than it is to the 101. This being somewhat reflected by the fact that Bristol Siddeley who manufactured the Orpheus engines at the time helpfully produced a little booklet specifically for their close knit family of 701, 703 and  803 Orpheus engines but the 101 version like some poor ‘outcast’ doesn’t get a mention.   

The following photo of the 701 version of the Orpheus turbine wheel as displayed in the Ruskin Museum’s recovered Bluebird K7 engine, is compared against the 803 version of the Orpheus turbine wheel below and from that comparison one can immediately see they have around the same family sibling number of turbine blades:

Counting the number of blades we get to around 125 blades on the 803 version of the turbine wheel and an outside diameter of around 28 inches. However when we compare this to the ‘outcast’ 101 version of the Orpheus we only get around 79 blades but the outside diameter of the turbine is actually considerably larger at 30 inches which is shown in the following photos, so the 803 turbine is approximately 2″ smaller in diameter than the 101 version:

Blade length of the turbine wheels of the 701 / 803 family are around 11cm but the ‘outcast’ 101 version of the Orpheus is considerably longer at 14cm again as shown in the following photos:

In fairness this difference between Orpheus engines has perhaps been more obvious to me than others for a few years now given I have different versions of the turbine wheels in my workshop staring me in the face every day I walk in there:

If you can read the following only once and remember it you are more on the ball than me so here we go. For the 101 version of the Orpheus at its compressor the stator blades are made of steel to stages 1,2, 5 and 6 whereas stages 3 & 4 are made of aluminium alloy. Have you got that? Because this is not the same as the 701 version of the Orpheus where stator blade stages 1,2,3 & 4 are made of aluminium alloy and 5 & 6 are made in steel. Have you really remembered all those two different sequences because just to top it off the 803 version of the Orpheus is different again as it uses steel stator blades for stages 2,3,4 & 5, then aluminium alloy on stages 1 & 6. Don’t worry there is no test at the end. 

I am not sure when this will come up in a pub quiz but just in case it does you will be pleased to learn that the 701 version of the Orpheus turbine blades are made of Nimonic 90, whilst on the 803 version they are formed of either Nimonic 100 or 105. 

For the visually impaired the 701 and 101 version of the Orpheus have their oil tank mounted on top of the compressor casing, whilst on the 803 version it is bolted on to the port side but putting a top mounted oil tank on an 803 is no drama as it simply bolts on with extended pipe-work. 

With the 701 and 101 version of the Orpheus the fuel filter is bolted to the underside of the compressor casing – good luck with changing that with the engine in a boat; whilst on the 803 version it is, at least in relation to a boat far more accessible being mounted to the port side of the engine. 

The 101, 701 and 803 versions of the Orpheus have jet pipes and respective aluminium alloy shrouds that all mount to the main engine in a similar fashion but they vary in length simply to suit aircraft application.  

The 101 and 701 version of the Orpheus has a front engine steady bracket (with spherical bearing to allow for expansion), which is located on the starboard side of the engine, whereas the front mounting on the 803 is a similar arrangement but mounted from the front bottom centre. The 101, 701 and 803 versions of the Orpheus all have similar main engine mountings, that is to say being via trunnions on each side of the delivery casing. The starboard side trunnion is spherical so as to subject one side of the engine to lateral restraint, whilst the port side trunnion is parallel to allow for expansion. 

The 701 version of the Orpheus has a drive for a 3 or 3.5KW generator whereas, the drive for the 803 is larger being for a more powerful 4KW generator. In Bluebird K7 it appears that no generator was fitted to either the original 701 engine and neither was one fitted to the more recently installed 101 version of the Orpheus engine.

The 701 version of the Orpheus has a ‘B’ sized Lucas fuel pump whilst the 803 version has a larger capacity but not that much physically bigger Lucas ‘D’ fuel pump. Photographs for comparison of Orpheus fuel pump types is given below: 

Because of the larger capacity fuel pump and larger capacity generator, the gearbox casing on the 803 version of the Orpheus is larger than that on the 701 and 101 versions. However I do not wish to overstate this difference in size especially comparing the 803 and 101 gearbox casings having looked at them side by side at WEC. This being especially so since the fuel inlet for the 101 version is at the front as shown in the photo and has to be allowed for, whereas this is not the case with the 803 version as the fuel inlet elsewhere out of the way. Again photos for comparison shown below: 

The air intake duct of the 701 and 101 version of the Orpheus casing is comparatively short to contain the air starter, whereas the 803 version casing is longer to contain the cartridge starter. Again photos of both the Rotax air starter (shown in the foreground) and the Associated Electrical Industries (aircraft group) cartridge starter (shown in the background) are illustrated together as follows for comparison:

For those who have never seen a cartridge start for a jet engine they are compared to air start and indeed electrical start relatively simple and spectacular in essence being an explosive shell like a large shogun cartridge where the expanding gas from igniting that cartridge very rapidly spins up the cartridge start gearbox in the nose of the engine which in turn spins up the jet engine as seen in the following video:

Of note with the 803 Orpheus twin cartridge shell casings are fixed to the side of the upper compressor casing that then feed explosive air to the cartridge starter on the nose of the engine. Of note Bristol Siddeley also make reference to the 701 version of the Orpheus being able to be cartridge started. 

There is a polished steel fireproof bulkhead bolted to the delivery casing of all three versions of the Orpheus under discussion (701, 803 and 101 versions), this being slightly different in shape to fulfil its design function within the specific aircraft each were designed for. That is to say to abut the respective aircraft internal frames. For the absence of doubt the photographs below show the bulkhead frame which forms part of the Orpheus engine and its function:

Photographs we have viewed appear to suggest this steel bulkhead that forms part of the Orpheus engine had to be cut away on both the port and starboard sides of the 701 version of the Orpheus to fit within Bluebird K7 for her last record attempt. Likewise reference to photos appears to show the steel bulkhead on the 101 version of the Orpheus engine similarly had to be cut away on port and starboard sides to fit within the restored Bluebird K7. It is not therefore unreasonable to expect that a similar area of cutting away of the fireproof bulkhead on the 803 version of the Orpheus would be required if that model of  engine were to be fitted within the craft. 

The 803, 701, 703 and the 101 versions of the Orpheus all have mechanical fuel pumps as part of the engine, a combined control unit (barometric pressure control, throttle valve and flow distributor), an air-fuel ration control with associated pressure switch, a jet pipe temperature limiter and a pressure ratio limiter. They all also have 7 burner cans. 

Maximum static thrust of the 803 version of the Orpheus is 5,000 lbs, its sibling the 701 Orpheus has a maximum thrust of 4,700 lbs and the ‘outcast’ 101 version of the Orpheus is the least powerful in the line up comparison at 4,500 lbs maximum thrust. 

Of note the 803 version of the Orpheus, because of its relatively larger fuel pump is rated by Bristol Siddeley to suit low altitude operation, whereas the 701 version of the Orpheus was actually restricted in available take off thrust (but not at high altitude) because of the limitations of the Lucas B sized fuel pump. The reader may find this somewhat interesting given it was the 701 version of the Orpheus that was used in the final record attempt for Bluebird K7, where maximum thrust of the Orpheus was obviously required in the boat to attempt the record operating not far above sea level. 

Anyway that is enough of my waffling to keep the anoraks amongst our readers happy for a while and hopefully I will get my hand sorted soon (though am not holding my breath given the backlog and strain our poor NHS is under), to get back working on Longbow sometime in April. Take care folks and watch out for those splinters! 

Pin It on Pinterest

Share This