Napier Sabre: Why 24 cylinders?

[VSN_Razor]

As someone who doesn't understand much about mechanics, what are the benefits of the 24 cylinders over the "usual" V12 engines?

 

I see only a tiny bit more of horsepower, so the advantage must be somewhere else. Can someone explain it for me, please?

[Jaws2002]

The Napier Sabre was coming from a line of "H" air racing engines. There were a lot of routes engine development tried during the 20s and thirties, to increase performance.

The engine is arranged in "H" shape. It's basically two flat engines connected together in a single block. You see, before that there was only one safe way to increase the number of Cylinders and still be able to cool the engine. That was the Radial engine. However, very few radials could get more then two rows of cylinders and still have effective cooling.

The V engine got different problems. Once V shape engines got more then 12 cylinders, the crankshaft became too long and the vibrations were too great. 

The designers at Napier wanted to increase the number of cylinders, without the large cross section that comes from a Radial engine. This guys made engines for racing, so the cross section of the engine was directly related to drag and speed.

 An engine arranged in H, can have a lot of cylinders, (high displacement),while still having lower cross section and drag than a radial, with the same number of cylinders.

 

 

 Another thing. Most engines are not designed from the ground up, from a clean piece of paper.  The designer start from somewhere. Maybe they built this H engines based on flat six or flat 12 engines they already had access to. It's easier to increase performance that way, than designing everything new, from scratch.

 

Anyway, once the Germans taught them how to make aerodynamic cowling for large radials, with the FW-190, the Brits abandoned the H engine and went with a large Radial.

Edited September 1, 2019 by Jaws2002

[ZachariasX]

1 hour ago, VSN_Razor said:

As someone who doesn't understand much about mechanics, what are the benefits of the 24 cylinders over the "usual" V12 engines?

 

I see only a tiny bit more of horsepower, so the advantage must be somewhere else. Can someone explain it for me, please?

More cylinders also make it possible to have less individual (per cylinder) displacement while maintaining (or increasing) total displacement, producing in some way a „smaller“ engine that can be run at higher rpm.

 

Think of an engine as an air pump. If you have a 30 L engine that can run at 4000 rpm, it will make the same power as a 40 L engine run at 3‘000 rpm. The higher revving engine will be smaller, have less frontal cross section and be lighter than the 40 L engine, giving the plane a better performance. The Sabre runs up to 4000 rpm, 3700 rpm cruise. That’s racing, baby! The Merlin likes about 2000 rpm for cruise. Same as Griffon or the DB-60X.

 

The Sabre was just that. A true racing engine. Downside is, if a bunch of common troglodytes have to keep that complicated thing running out there in the cold and dirt, problems. If you don‘t really need the last 10% performance, then you go with those low rev, high displacement monsters like a Griffon or a DB-603. Or an R-2800. Things that you can actually procure to the masses.

[Pierre64]

Animation created by Sergio Pasquali found on the great Hawker Tempest page : www.hawkertempest.se

(my apologies if already mentioned)

[SCG_OpticFlow]

On 9/1/2019 at 10:49 PM, Jaws2002 said:

The Napier Sabre was coming from a line of "H" air racing engines. There were a lot of routes engine development tried during the 20s and thirties, to increase performance.

The engine is arranged in "H" shape. It's basically two flat engines connected together in a single block. You see, before that there was only one safe way to increase the number of Cylinders and still be able to cool the engine. That was the Radial engine. However, very few radials could get more then two rows of cylinders and still have effective cooling.

The V engine got different problems. Once V shape engines got more then 12 cylinders, the crankshaft became too long and the vibrations were too great. 

The designers at Napier wanted to increase the number of cylinders, without the large cross section that comes from a Radial engine. This guys made engines for racing, so the cross section of the engine was directly related to drag and speed.

 An engine arranged in H, can have a lot of cylinders, (high displacement),while still having lower cross section and drag than a radial, with the same number of cylinders.

 

 

 Another thing. Most engines are not designed from the ground up, from a clean piece of paper.  The designer start from somewhere. Maybe they built this H engines based on flat six or flat 12 engines they already had access to. It's easier to increase performance that way, than designing everything new, from scratch.

 

Anyway, once the Germans taught them how to make aerodynamic cowling for large radials, with the FW-190, the Brits abandoned the H engine and went with a large Radial.

 

The Junkers Jumo 222 engine tried to combine those two approaches, inline and radial into a "hexagon" of 6 inline banks of 4 cylinders each https://en.wikipedia.org/wiki/Junkers_Jumo_222

 

After the war, the soviets continued work on multi-bank engines, first with the idea to use them in heavy bombers and later in ships, see the M-501 engine: https://oldmachinepress.com/2016/09/05/yakovlev-m-501-and-zvezda-m503-and-m504-diesel-engines/

 

 

[Finkeren]

On 9/1/2019 at 11:08 PM, ZachariasX said:

More cylinders also make it possible to have less individual (per cylinder) displacement while maintaining (or increasing) total displacement, producing in some way a „smaller“ engine that can be run at higher rpm.

 

Think of an engine as an air pump. If you have a 30 L engine that can run at 4000 rpm, it will make the same power as a 40 L engine run at 3‘000 rpm. The higher revving engine will be smaller, have less frontal cross section and be lighter than the 40 L engine, giving the plane a better performance. The Sabre runs up to 4000 rpm, 3700 rpm cruise. That’s racing, baby! The Merlin likes about 2000 rpm for cruise. Same as Griffon or the DB-60X.

 

The Sabre was just that. A true racing engine. Downside is, if a bunch of common troglodytes have to keep that complicated thing running out there in the cold and dirt, problems. If you don‘t really need the last 10% performance, then you go with those low rev, high displacement monsters like a Griffon or a DB-603. Or an R-2800. Things that you can actually procure to the masses.

 

Yeah, it's important to keep in mind, that more displacement doesn't necessarily add up to greater power output. The prime example is the AM-35A on the MiG-3, which has an absolutely insane displacement of 46.6 L, compared to the 36,6 L of the Sabre, yet produces only 1350hp at 2000rpm.

[Brano]

at 2050rpm ?

[JtD]

My answer to questions like "why did you do it like this" typically is "because I can". So why use 12 cylinders if you can use 24 and get away with it? Twice the power output of a contemporary V12 justifies a lot.

[JimTM]

19 hours ago, Pierre64 said:

Animation created by Sergio Pasquali found on the great Hawker Tempest page : www.hawkertempest.se

(my apologies if already mentioned) ...

 

Great animation! It's interesting how they use the cylinder sleeves in place of valves.

[ZachariasX]

What is probably the best thing, few will notice. Look at the rotation speed of the crankshafts and the pinions on them. How Napier coupled those two crankshafts was absolutely great, something the Germans never came up with when they welded together two engines to get one big engine.

[MiloMorai]

Lycoming XR7755

 

General characteristics

• Type: 36-cylinder turbosupercharged liquid-cooled "star" (9 banks at 40° angles, 4 cylinders in each bank) aircraft piston engine
• Bore: 6.375 in (161.9 mm)
• Stroke: 6.75 in (171 mm)
• Displacement: 7,756.3 cu in (127.103 l)
• Length: 121.35 in (3,082 mm)
• Diameter: 61 in (1,500 mm)
• Width: 60.5 in (1,540 mm)
• Height: 61 in (1,500 mm)
• Dry weight: 6,050 lb (2,740 kg)

Components

• Valvetrain: Single overhead camshaft per bank with separate cams for takeoff and economical cruise (Variable valve timing)
• Supercharger: Impeller diameter 14.4 in (370 mm), at 6:1 drive ratio
• Fuel system: Carburettor (-1 and -3); Fuel injection (-5)
• Oil system: pressure system - 100 psi (690 kPa) at 500 lb/min (230 kg/min) flow rate
• Cooling system: Liquid-cooled

Performance

• Power output:
• 5,000 hp (3,700 kW) at 2,600 rpm takeoff
• 4,000 hp (3,000 kW) at 2,300 rpm cruise
• Specific power: 0.64 hp/cu in (29 kW/l)
• Fuel consumption: ~580 gal/h (480 imp gal/h; 2,200 l/h)
• Specific fuel consumption:
• 0.70 lb/hp/h (0.43 kg/kW/h) at takeoff power
• 0.485 lb/hp/h (0.295 kg/kW/h) at 70% power
• 0.37 lb/hp/h (0.23 kg/kW/h) at minimum cruise power
• Power-to-weight ratio: 0.82 hp/lb (1.35 kW/kg)

[Bremspropeller]

Because 23 wasn't enough.

[ZachariasX]

6 hours ago, MiloMorai said:

Lycoming XR7755

Poor schmocks. Before doing what basically sank the pivot of Nazi aircraft projects, they just could have called up Hamilton and asked them what size a prop would be that is driven by 5‘000 hp. Then they could have looked for aircraft where you could mount such a prop without having it to stick in the lawn tail first.

 

~25% less specific power than the Jumo222. Half as much of that as the Sabre. The Wasp Major is one ton lighter, yet only 20% less power. But lots of cylinders indeed.

 

That engine alone weights as much as a whole Bf-109 ready to... to follow orders.

[Lusekofte]

I have not the fainest idea about aeronautical machinery. But I operate hauling equipment together with Mammoet at the moment on equipment up to 2000 hp.

One thing about volume in engines is the sheer power it guves behind each horsepower.

HP is created by turbos , superchargers and intercoolers. I am too bad in english to be too technical. True power come from volume, that is the power one can rely on. At least in hauling business.   

[wombatBritishBulldogs]

I'm sure the design team "Torqued" about it quite a lot before manufacturing one !

[DD_Crash]

There used to be a saying, "there is no substitute for cubic inches"

[ZachariasX]

3 minutes ago, DD_Crash said:

There used to be a saying, "there is no substitute for cubic inches"

Of course there is. Liters.

 

[DD_Crash]

Well it was an American saying

[Tyberan]

Oh man I didn't realise the sabre had sleeve valves too. Just think of the complexity of 24 rotating and linear movement of all those sleeves and timed. I bet the fitters loved that

 

 

[SCG_OpticFlow]

https://en.wikipedia.org/wiki/Wright_R-2160_Tornado

Wright R-2160 Tornado

General characteristics

• Type: 7-bank, 42 cylinder inline radial engine. (7-banks with 6 cylinders in each bank)
• Bore: 4.25 in (107.9 mm)
• Stroke: 3.625 in (92 mm)
• Displacement: 2,160 in³ (35.39 l)
• Length: 96 in (2438 mm)
• Diameter: 35.5 in (901.6 mm)
• Dry weight: 2,400 lb (1088.6 kg)

Components

• Valvetrain: Single overhead camshaft, Two valves per cylinder
• Supercharger: 2 x turbosuperchargers
• Fuel system: Direct injection
• Fuel type: 100/130
• Oil system: Dry sump
• Cooling system: Liquid cooled

Performance

• Power output: 2,350 hp (1,752 kW) at 4,150 rpm for takeoff
• Specific power: 1.08 hp/in³
• Specific fuel consumption: 0.67 lbs/(hp*h) (0.407 kg/(kW*h)) at takeoff
• Power-to-weight ratio: 1.59 kW/kg (0.97 hp/lb)

[GP*]

On 9/11/2019 at 9:08 AM, DD_Crash said:

Well it was an American saying

“There is no replacement for displacement.”

 

Except forced induction, or course. Better yet, both! 

[6./ZG26_Klaus_Mann]

It has 24 Cylinders for the same Reason Moto Guzzi built a 500cc V8!!! when others were still running twins of singles. More Cylinders at the same Displacement means more Power because you can Rev higher because you have less Stroke and smaller, lighter Pistons.

 

For the same Reason this Monstrosity had a 1.5l V16 to overpower the 8s, 10s and 12s.

 

Edited September 17, 2019 by 6./ZG26_Klaus_Mann

[Brano]

On 9/11/2019 at 4:03 PM, DD_Crash said:

There used to be a saying, "there is no substitute for cubic inches"