Napier Nomad / Naiad (????)
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Napier Nomad / Naiad (????)
Talking about Rover gas turbines on another thread reminded me of a half scale cutaway model we had in the Thermodynamics lab at uni.
It was a 12 cylinder horizontally opposed 2 stroke diesel engine coupled via a gearbox to a gas turbine. The gearbox then drove a propellor. The idea behind it all was that for short low altitude hops the diesel part was used and for longer high altitude flight the gas turbine, thus exploiting the best power/fuel consumption characteristics of each kind of propulsion. As I recall (dodgy ground here) the actual result was a beautifully designed engine that was too big and heavy to be practical. As you can see from the heading, I know it was a Napier design, indeed it was probably the most complex engine designed which was an achievement from the company that created the Sabre with its' 24 cylinders in an H formation. I am unsure of the name of the engine, if it wasn't Nomad does Naiad sound familiar to anyone?
Finally, did this monster motor ever get as far as flight trials? If it did what did they fit it to (probably a Lanc or a Lincoln I would imagine)?
It was a 12 cylinder horizontally opposed 2 stroke diesel engine coupled via a gearbox to a gas turbine. The gearbox then drove a propellor. The idea behind it all was that for short low altitude hops the diesel part was used and for longer high altitude flight the gas turbine, thus exploiting the best power/fuel consumption characteristics of each kind of propulsion. As I recall (dodgy ground here) the actual result was a beautifully designed engine that was too big and heavy to be practical. As you can see from the heading, I know it was a Napier design, indeed it was probably the most complex engine designed which was an achievement from the company that created the Sabre with its' 24 cylinders in an H formation. I am unsure of the name of the engine, if it wasn't Nomad does Naiad sound familiar to anyone?
Finally, did this monster motor ever get as far as flight trials? If it did what did they fit it to (probably a Lanc or a Lincoln I would imagine)?
It was indeed the Napier Nomad. Supposed to have very good TSFC, but overtaken by the advent of much simpler turboprops. It was a very complex and heavy device indeed. We had a real one at London Queen Mary College when I was studying (?) applied ULAS Chipmunking plus the occasional Aero Eng lecture in 1969-73!
The Napier Nomad was a beast of an engine indeed. There were two major versions, one of which was flight tested in the nose of a Lincoln if I remember correctly. For more details I will have to go through some books.
The Naiad does ring a bell, anyone know what it was/is?
The Naiad does ring a bell, anyone know what it was/is?
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The Naiad was Napiers first gas turbine engine and the worlds first axial flow turboprop engine.
Like the Nomad it was only tested in a Lincoln.
Rolls Royce also tried wanted to build a diesel with the Crecy, a 26 litre 90 degree sleeve valve two stroke but the air ministry decreed it should be petrol.
Like the Nomad it was only tested in a Lincoln.
Rolls Royce also tried wanted to build a diesel with the Crecy, a 26 litre 90 degree sleeve valve two stroke but the air ministry decreed it should be petrol.
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Didn't Napier design some beautiful engines. I'd love to hear a Sabre roaring along in the snout of a Tempest. I think the Tempest being restored at the moment is a Centaurus powered beastie (Mk II?)
A bit off topic but can somebody verify if the following is true:
The Sabre had a bad reputation with the RAF who imposed a 25 hours TBO on it. Napiers reckoned it was because the engine fitters couldn't break the habits learned on Merlins and weren't setting the engines up correctly. To prove their point Napiers put a Sabre on a test bed and ran it for 3,000 hours. Continuously. Needless to say this was as water off a duck's back to the RAF who continued to overhaul their Sabres after 25 hours. I know that the demands put on an engine in combat don't bear much resemblance to a continuous bench run but 25 hours????
A bit off topic but can somebody verify if the following is true:
The Sabre had a bad reputation with the RAF who imposed a 25 hours TBO on it. Napiers reckoned it was because the engine fitters couldn't break the habits learned on Merlins and weren't setting the engines up correctly. To prove their point Napiers put a Sabre on a test bed and ran it for 3,000 hours. Continuously. Needless to say this was as water off a duck's back to the RAF who continued to overhaul their Sabres after 25 hours. I know that the demands put on an engine in combat don't bear much resemblance to a continuous bench run but 25 hours????
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I think that the most amazing aero-engine I have ever seen is a German hrizontally-opposed Diesel. It has one block and two crankshafts, one at each end of the block.
Each pair of pistons coming towards each other provides the compression, the injectors & valve train being mounted in the centre of the block.
The twin crankshafts are geared together to one output shaft.
This monster (I can't remember its designation - DB-XYZ) is on show at RAF Cosford.
Was the problem with Napier Sabres differential expansion of the sleeve liners? I seem to remember reading that the engines had to be run up every few hours in the winter of 44-45 to keep them warm. If the engines where constantly going though a hot-cold cycle, then this would increase their wear rate - but it they were constantly hot, the rate should reduce and the engines should last. If they did last for 3000 hours, perhaps we should be fitting them into Cessnas!!
Each pair of pistons coming towards each other provides the compression, the injectors & valve train being mounted in the centre of the block.
The twin crankshafts are geared together to one output shaft.
This monster (I can't remember its designation - DB-XYZ) is on show at RAF Cosford.
Was the problem with Napier Sabres differential expansion of the sleeve liners? I seem to remember reading that the engines had to be run up every few hours in the winter of 44-45 to keep them warm. If the engines where constantly going though a hot-cold cycle, then this would increase their wear rate - but it they were constantly hot, the rate should reduce and the engines should last. If they did last for 3000 hours, perhaps we should be fitting them into Cessnas!!
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Junkers made the Jumo 204, opposed piston diesel aero engine (the best way to keep compression ratios up and weight down).Interestingly, Napiers also made the same engine under licence - until the war intervened - as the Culverin. They used their expertise in opposed pistons to good effect with the Deltic marine and railway engines
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Interestingly enough, Commer used supercharged 2 stroke diesels in some of their buses a good few years ago. They had contra-opposed pistons with a central combustion chamber. The main advantage of the time was that there was no cylinder head or gasket to blow!
2 stroke diesels have a lot of other advantages (good power, good economy and low emissions) and i'll wager a few quid that they are about to re-emerge as car engines before too long. They just need a bit more development.
2 stroke diesels have a lot of other advantages (good power, good economy and low emissions) and i'll wager a few quid that they are about to re-emerge as car engines before too long. They just need a bit more development.
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Didn't Napier Sabres have sleeve valves? I remember from my father's technical books that they did. These engines had no valves, but ports in the cylinder and a rotating sleeve outside the main liners that rotated and opened and shut the ports (similar to sliding doors).
The technical problems involved in lubrication of this system were difficult to overcome, so it was a good thing that gas turbines took over!
The technical problems involved in lubrication of this system were difficult to overcome, so it was a good thing that gas turbines took over!
