How a Round Engine works

[old man emu]

This has been posted before, but it is well worth viewing in you are interested in aircraft engines.

 

 

 

[facthunter]

You can see that wooden work. Nev

 

 

[Pominaus]

Thanks for sharing; great to see inside!

 

Just thought I'd add that pre about 1920, it was actually the cylinders that rotated (with the propeller attached to the cylinders essentially), and the crankshaft stayed stationary, basically just bolted to the front of the plane. The main advantage was that as nearly all the mass of the engine was rotating, it basically became it's own fly wheel. This saved weight (having a separate flywheel) and because the engine had a very large mass, improved reliability just by having a lot more energy stored in the flywheel. To get fuel, air and oil to the engine, it was fed through the crank case and centrifugally pulled to the cylinders.

 

Ultimately though reliability of engines improved and the downsides ended their reign - they're a total loss system, as the centrifugal force wont allow the oil to go in any other direction than away from the crank case; the spinning cylinders create drag as they spin & add a gyroscopic effect that interferes with handling; planes were getting faster (as were engines) compounding the problems. Plus as they were fading out, designers were starting to realise you could get a little thrust boost by shaping the cowling on a radial engine - essentially the beginnings of a journey that lead to the jet engine - and that worked better on stationary cyllinders that interfered less with the airflow across them.

 

Hope it's interesting/new info to some :)

 

 

[onetrack]

By far the most incredible piece of round engine engineering, has to be the Bristol-Centaurus sleeve-valve radial. Not only an incredibly complex piece of engineering, but also exceptionally quiet.

 

 

 

[geoffreywh]

also, according to a book I have, the longest "Time Before Overhaul" of any aero engine. Namely 5000 hours

 

 

[Neil_S]

Thanks for sharing; great to see inside!Just thought I'd add that pre about 1920, it was actually the cylinders that rotated (with the propeller attached to the cylinders essentially), and the crankshaft stayed stationary, basically just bolted to the front of the plane. The main advantage was that as nearly all the mass of the engine was rotating, it basically became it's own fly wheel. This saved weight (having a separate flywheel) and because the engine had a very large mass, improved reliability just by having a lot more energy stored in the flywheel. To get fuel, air and oil to the engine, it was fed through the crank case and centrifugally pulled to the cylinders.

 

Ultimately though reliability of engines improved and the downsides ended their reign - they're a total loss system, as the centrifugal force wont allow the oil to go in any other direction than away from the crank case; the spinning cylinders create drag as they spin & add a gyroscopic effect that interferes with handling; planes were getting faster (as were engines) compounding the problems. Plus as they were fading out, designers were starting to realise you could get a little thrust boost by shaping the cowling on a radial engine - essentially the beginnings of a journey that lead to the jet engine - and that worked better on stationary cyllinders that interfered less with the airflow across them.

 

Hope it's interesting/new info to some :)

They were also air-cooled, and the faster they rotated the more cooling the cylinders received - quite neat really....

 

 

[facthunter]

The rotating engine was cooled better, (and were refered to as "Rotaries' at the time), than a "normal" (for today)type . There was a significant power loss associated, called "windage". Later complex German ones had the engine rotating at 1/2 prop speed ( Siemens Halske), later in the war. A very complex twin row radial. Bentley also made the BR2 Twin row fitted to the later Sopwith's. The high displacement rotating engines were slow revving but had large torque capability so gave a good rate of climb suited to defending with fighters with a quick response capability. Very low overhaul times. The early ones about 4 (four) Hours between tear downs, being common. They were all four stroke despite some having little spring loaded valves in the pistons. (The main reason for the short overhaul times) They used castor oil (which ended up over everything) at a high rate.. For the period a fine example of engineering and machining, mainly by the French who were the world leaders in that type of thing. The steel cylinder walls were only about 1 MM thick. The engines were quite light weight for their displacement. Truly a work of art and with a distinct sound if you hear one of the real ones working. Once WW1 was "finalised", they disappeared having little place in "civilian " flying being somewhat "thirsty". Nev

 

 

[Pominaus]

The rotating engine was cooled better, (and were refered to as "Rotaries' at the time), than a "normal" (for today)type . There was a significant power loss associated, called "windage". Later complex German ones had the engine rotating at 1/2 prop speed ( Siemens Halske), later in the war. A very complex twin row radial. Bentley also made the BR2 Twin row fitted to the later Sopwith's. The high displacement rotating engines were slow revving but had large torque capability so gave a good rate of climb suited to defending with fighters with a quick response capability. Very low overhaul times. The early ones about 4 (four) Hours between tear downs, being common. They were all four stroke despite some having little spring loaded valves in the pistons. (The main reason for the short overhaul times) They used castor oil (which ended up over everything) at a high rate.. For the period a fine example of engineering and machining, mainly by the French who were the world leaders in that type of thing. The steel cylinder walls were only about 1 MM thick. The engines were quite light weight for their displacement. Truly a work of art and with a distinct sound if you hear one of the real ones working. Once WW1 was "finalised", they disappeared having little place in "civilian " flying being somewhat "thirsty". Nev

Thanks for expanding :)

 

I've always wondered, with a rotary engine, obviously all those parts rotating around a hub... there needs to be a high level of accuracy in the manufacture so it doesn't shake itself clean off the plane. Do you know if they had the technology at the time to achieve that, or were there any fun little "hacks" like cutting/adding weight to balance the mass?

 

 

[derekliston]

One of the things I've always found strange about radial engines is that, although they all have a 'Master cylinder' it is not cylinder number 1, but may be number three for example. I have never known why this is.

 

 

[facthunter]

Pominaus, they had a high degree of accuracy as to the balance of individual parts like cylinders which are fully machined from a solid alloy steel billett. The out of balance in some rotaries comes from the way the articulating rods vary the stroke. By and large the balance is good especially with some of the early ones which had a rather trick way of locating the conrods so they stayed in line with the centre of the crankpin. All the conrods and pistons rotate around the crankpin which is stationary often using two largish ball races as a bearing. The motor itself rotates around the mainshafts which are also stationary. The propeller is attached to the engine and turns with it and the carburettor breathes through a hollow mainshaft. Nev

 

 

[onetrack]

I'm currently carrying out extensive repairs to a 1920 Brockway truck engine, which is reputedly crude by todays standards - but I'm regularly surprised by the level of sophistication of WW1-era engineering in this engine.

 

The engineers and manufacturers of this era knew all about, and how to manufacture, exotic and high strength metals - and they produced some superb examples of highly sophisticated engineering design.

 

The quality and range of their cast iron was excellent, and they knew how to produce high-strength cast iron by adding strengthening metals. They regularly produced high grade alloy-steel fasteners.

 

The only difference to today is, they did WW1 engineering with flat-belt-drive lathes, and milling machines, and grinders, and they hand-finished a lot of items with great skill.

 

Where the old engines fell down was poor-quality fuels and oils, and low-grade sealing materials. Leather was the major component of oil seals, and copper-asbestos was commonly used for gaskets.

 

Electrical insulation was poor quality, reliant on woven cotton, and the electrical components themselves were pretty crude. WW2 saw huge advances in synthetic materials that we still use today - nylon, butyl rubber, rayon, and even teflon.

 

If you check out the NZ Vintage Aviation website and examine some of the engineering, in say, the likes of the Scottish Beardmore engine, you will see some excellent early 20th century engineering handiwork.

 

Also, the Powerhouse Museum has a good range of aero engines dating from pre-WW1.

 

You can nearly always get a full description of the designs in the Powerhouse collection, by scrolling down the page and clicking on the "Full Description" red button.

 

=Aero-engines"]MAAS Museum Collection