radial vs inline vs naiper h-pattern

[gumbyk]

Modern (for WWII) liquid cooled engines, like a Merlin, used aluminum crankcases and cylinder blocks (with steel sleeves). Something like an R-2800, will have steel cylinders (with aluminum bands) to better handle the increased cylinder head temperature of the air cooled engine. My understanding is that the crankcase will also be steel, but perhaps I am mistaken

Radials have an aluminium crankcase, steel cylinder barrels, and aluminium heads.
As well as being lighter, aluminium transfers heat more efficiently than steel, which is why its used in the head.

 

[Howard Gibson]

Cast Iron isnt cast aluminium. Heat treated cast iron isnt cast iron it is iron normalised, stress relieved or whatever.

Eh?

Cast aluminium is cast aluminium. According to my metallurgy textbook, cast iron is anywhere between 2 and 6.67% carbon. 6.67% carbon makes it a mineral called cementite Fe3C, not a metal at all. Apparently, 2.5 to 4% is normal. They don't heat treat it for higher strength. They might anneal it to relieve stresses.

 

[pbehn]

Eh?

Cast aluminium is cast aluminium. According to my metallurgy textbook, cast iron is anywhere between 2 and 6.67% carbon. 6.67% carbon makes it a mineral called cementite Fe3C, not a metal at all. Apparently, 2.5 to 4% is normal. They don't heat treat it for higher strength. They might anneal it to relieve stresses.

I responded to your post discussing cast Iron and now you are discussing cast aluminium. How can you call cementite "not metal" Steel is also an alloy of Iron and Carbon. Martensite is a super saturated solution of carbon in steel, it has very little carbon but that small amount makes it very hard.

 

[Howard Gibson]

I responded to your post discussing cast Iron and now you are discussing cast aluminium. How can you call cementite "not metal" Steel is also an alloy of Iron and Carbon. Martensite is a super saturated solution of carbon in steel, it has very little carbon but that small amount makes it very hard.

We were discussing cast iron versus aluminium engine blocks. For the record, my metallurgy text is Introduction to Physical Metallurgy, Second Edition, by Sydney H. Avner, professor at New York City Community College. I took this stuff in college.

Martensite is defined as a supersaturated solid solution of carbon trapped in a body centred tetragonal structure. It is the product of extreme heat treating. Carbon makes it harder. Steel alloys normally are below 1% cargon. At high temperature, iron's molecular structure is body centred cubic (austenite). At room temperature, it normally is face centred cubic (ferrite). These phase changes are what makes it heat treatable.

Cementite is not metal. It is a mineral. The molecule is three iron atoms and one carbon atom. Look up the densities and do the arithmetic.

 

[pbehn]

We were discussing cast iron versus aluminium engine blocks. For the record, my metallurgy text is Introduction to Physical Metallurgy, Second Edition, by Sydney H. Avner, professor at New York City Community College. I took this stuff in college.

Martensite is defined as a supersaturated solid solution of carbon trapped in a body centred tetragonal structure. It is the product of extreme heat treating. Carbon makes it harder. Steel alloys normally are below 1% cargon. At high temperature, iron's molecular structure is body centred cubic (austenite). At room temperature, it normally is face centred cubic (ferrite). These phase changes are what makes it heat treatable.

Cementite is not metal. It is a mineral. The molecule is three iron atoms and one carbon atom. Look up the densities and do the arithmetic.

The post I referred to you were discussing converting cast iron to aluminium based on yield strength, cast Irons dont have a yield strength. All Irons and steels have carbon in them as part of the production process and because carbon as an alloying element allows a massive range of properties. If you are arguing that cementite is not metal, you are arguing that steel is not metal either. In fact that has some scientific truth because they are all alloys. The problem comes from the names of all these things being given before the science. You need to already be very good at making things out of steel before you can make a tensile testing machine, tensile testing didnt become common until about 60 years after the first steam locomotive ran. The rest of your post is what I did in my first weeks at Longlands college Middlesbrough, training as a metallurgist. BTW arcraft are generally not made of Aluminium they are made of duralumin, an alloy of aluinium and copper (plus others). The USA and Germany used almost identical dural alloys, the British slightly different.

In the iron–carbon system (i.e. plain-carbon steels and cast irons) it is a common constituent because ferrite can contain at most 0.02wt% of uncombined carbon.[4]​ Therefore, in carbon steels and cast irons that are slowly cooled, a portion of the carbon is in the form of cementite.[5]​ Cementite forms directly from the melt in the case of white cast iron. In carbon steel, cementite precipitates from austenite as austenite transforms to ferrite on slow cooling, or from martensite during tempering. An intimate mixture with ferrite, the other product of austenite, forms a lamellar structure called pearlite.

While cementite is thermodynamically unstable, eventually being converted to austenite (low carbon level) and graphite (high carbon level) at higher temperatures, it does not decompose on heating at temperatures below the eutectoid temperature (723 °C) on the metastable iron-carbon phase diagram.

Mechanical properties are difficult to obtain. Recent review by Bhadeshia provided the following: Room temperature microhardness of 760-1350HV; Bending strength of 4.6−8 GPa; Young's modulus of 160-180 GPa; Indentation fracture toughness of 1.5-2.7 MPa√m [6]​

 

[swampyankee]

The R-2800, at least "The crankcase is composed of three forged aluminum alloy sections held together by through bolts. The nose section houses the reduction gears and torquemeter and has provisions for a full-feathering;, reversible propeller governor" (P&W R-2800).
(emphasis theirs)

Depending on alloy and processing, the strength of cast iron is 295 to 580 MPa. Aluminum, depending on alloy, can be up to 640 MPa. Engine blocks are probably more stiffness-dominated than strength-dominated structures, and stiffness in a complex structure is at least as much a function of geometry as elastic modulus.

 

[gumbyk]

I understand that Magnesium alloy was investigated for crankcase components as well. Not sure if it made it into production though. I do know some modern turbo-prop engines use it in cases.

 

[pbehn]

The R-2800, at least "The crankcase is composed of three forged aluminum alloy sections held together by through bolts. The nose section houses the reduction gears and torquemeter and has provisions for a full-feathering;, reversible propeller governor" (P&W R-2800).
(emphasis theirs)

Depending on alloy and processing, the strength of cast iron is 295 to 580 MPa. Aluminum, depending on alloy, can be up to 640 MPa. Engine blocks are probably more stiffness-dominated than strength-dominated structures, and stiffness in a complex structure is at least as much a function of geometry as elastic modulus.

When discussing strength are you discussing yield strength or ultimate tensile strength, most cast irons dont have a yield strength unless produced to have one like ductile cast iron and malleable cast iron. The cast irons used typically dont have a yield or elongation value, table below from wiki.

Comparative qualities of cast irons[9]​

Name	Nominal composition [% by weight]	Form and condition	Yield strength [ksi (0.2% offset)]	Tensile strength [ksi]	Elongation [%]	Hardness [Brinell scale]	Uses
Grey cast iron (ASTM A48)	C 3.4, Si 1.8, Mn 0.5	Cast	—	50	0.5	260	Engine cylinder blocks, flywheels, gearbox cases, machine-tool bases
White cast iron	C 3.4, Si 0.7, Mn 0.6	Cast (as cast)	—	25	0	450	Bearing surfaces
Malleable iron (ASTM A47)	C 2.5, Si 1.0, Mn 0.55	Cast (annealed)	33	52	12	130	Axle bearings, track wheels, automotive crankshafts
Ductile or nodular iron	C 3.4, P 0.1, Mn 0.4, Ni 1.0, Mg 0.06	Cast	53	70	18	170	Gears, camshafts, crankshafts
Ductile or nodular iron (ASTM A339)	—	Cast (quench tempered)	108	135	5	310	—
Ni-hard type 2	C 2.7, Si 0.6, Mn 0.5, Ni 4.5, Cr 2.0	Sand-cast	—	55	—	550	High strength applications
Ni-resist type 2	C 3.0, Si 2.0, Mn 1.0, Ni 20.0, Cr 2.5	Cast	—	27	2	140	Resistance to heat and corrosion

 

[swampyankee]

When discussing strength are you discussing yield strength or ultimate tensile strength, most cast irons dont have a yield strength unless produced to have one like ductile cast iron and malleable cast iron. The cast irons used typically dont have a yield or elongation value, table below from wiki.

Comparative qualities of cast irons[9]​

Name	Nominal composition [% by weight]	Form and condition	Yield strength [ksi (0.2% offset)]	Tensile strength [ksi]	Elongation [%]	Hardness [Brinell scale]	Uses
Grey cast iron (ASTM A48)	C 3.4, Si 1.8, Mn 0.5	Cast	—	50	0.5	260	Engine cylinder blocks, flywheels, gearbox cases, machine-tool bases
White cast iron	C 3.4, Si 0.7, Mn 0.6	Cast (as cast)	—	25	0	450	Bearing surfaces
Malleable iron (ASTM A47)	C 2.5, Si 1.0, Mn 0.55	Cast (annealed)	33	52	12	130	Axle bearings, track wheels, automotive crankshafts
Ductile or nodular iron	C 3.4, P 0.1, Mn 0.4, Ni 1.0, Mg 0.06	Cast	53	70	18	170	Gears, camshafts, crankshafts
Ductile or nodular iron (ASTM A339)	—	Cast (quench tempered)	108	135	5	310	—
Ni-hard type 2	C 2.7, Si 0.6, Mn 0.5, Ni 4.5, Cr 2.0	Sand-cast	—	55	—	550	High strength applications
Ni-resist type 2	C 3.0, Si 2.0, Mn 1.0, Ni 20.0, Cr 2.5	Cast	—	27	2	140	Resistance to heat and corrosion

UTS. Of course, yield is going to be used for design against operational loads if the structure's design is strength limited. I suspect that crankcase design is more constrained by the need to limit deflections, for example of the main bearings, and production technology than tensile strength. Either cast iron or aluminum blocks are likely operating far below yield strength.

As t vulnerability of radials vs V engine, I think it's more complicated than cooling medium, per se, but the sizes and locations of vulnerable parts of the engine and cooling system. From behind, there's a lot of structure plus a pilot between an enemy fighter and the engine. From below, the block is fairly small compared to the cooling and fuel system. On balance, I think the difference between radial and V-12 damage tolerance has little to do with cylinder arrangement and much more to do with the cooling system. Put a hole in a liquid cooled engine and there's a good chance the coolant runs out.

 

[swampyankee]

I understand that Magnesium alloy was investigated for crankcase components as well. Not sure if it made it into production though. I do know some modern turbo-prop engines use it in cases.

Last I knew, it was pretty universal in helicopter transmissions and gearbox housings. It was also used in the compressor housing of the T-55, T-53, and ALF502 engines and the fan case for the 502, at least until the USAF got pissy about magnesium-based alloys.

 

[MikeMeech]

I understand that Magnesium alloy was investigated for crankcase components as well. Not sure if it made it into production though. I do know some modern turbo-prop engines use it in cases.

Hi
Yes, Magnesium alloy was used in engines, as mentioned in text of 'Internal Combustion Engines Illustrated', Odhams Press Ltd, 1947 reprint:

And an earlier book 'Aeronautical Engineering', Odhams Press, states that Magnesium Alloys were used in the Gipsy-Twelve (of 1938):

As an aside, Magnesium Alloy was used for Helicopter gear-boxes on the Westland Wessex when I worked on them during 1978-81. AGS also had magnesium alloy rivets (green coloured) for use with magnesium alloy materials.

Mike

 

[Deleted member 68059]

No idea why you`re all talking about cast iron, nobody notable made anything major out of cast iron in WW2 aero engines. Why would you,
it has appauling tensile strength as its full of microcracks (which is why its very good for cheap car engine blocks as the cylinder bores hold
an oil film in the microscopic fissures.

The R2800 is aluminium, in terms of mass produced engine only the BMW801 had ferrous crankcases, and they were
most certainly NOT cast iron, but forged steel.

It makes not a lot of difference to durability, as the specific stiffness of virtually every metal is within a tiny band of difference, so small its nearly
irrelevant. To change that you need to go to non-homogenious materials like composites or cermets. Bullet proof engines do not take off
the ground.

 

[Clayton Magnet]

The R2800 is aluminium, in terms of mass produced engine only the BMW801 had ferrous crankcases, and they were
most certainly NOT cast iron, but forged steel.

Any idea why BMW would build the case out of steel, rather than aluminum? Maybe Aluminum was considered more of a strategic resource?

 

[Deleted member 68059]

Any idea why BMW would build the case out of steel, rather than aluminum? Maybe Aluminum was considered more of a strategic resource?

Sadly I dont have enough BMW records to have the conference meeting minuites where you might actually find that out.

P&W had been interested in it. (my book pg 258).

The 801 crankcase weighs almost the same as the Cyclone 14BB crankcase (185 Lbs)

I "suspect" that either it was a strategic descision based on availability of high quality aluminum
castings, or might also have been a hardness question on the "fretting" between the little
"posts" that bolt together in a radial crankcase. It would have been a pretty tricky
manufacturing effort, as natually to weigh about the same as an Aluminium crankcase
it needs to be 3x thinner, so you`re probably looking at typical wall thicknesses of... 4mm ?

Wright Aeronautical had this to say about the Steel 801 crankcase.

 

[MiTasol]

Modern (for WWII) liquid cooled engines, like a Merlin, used aluminum crankcases and cylinder blocks (with steel sleeves). Something like an R-2800, will have steel cylinders (with aluminum bands) to better handle the increased cylinder head temperature of the air cooled engine. My understanding is that the crankcase will also be steel, but perhaps I am mistaken

In the US SOME of the Wright R-1820's and R-2600's (and maybe R-3350's?? - I never worked on one of those) had FORGED steel crankcases - everything else was alloy.
All the Brit engines I have worked on used Al alloy for the main castings though some apparently used magnesium.
AFAIK the same for the Japanese engines - certainly for all the ones I have seen have Al alloy cases.
The BMW 801 had a steel case if I remember rightly but I would not bet on it. I was once told that came from their prewar Wright licences and technology but do not know if that is true.
One of the French engines had a steel case but I cannot remember which. Again there was a connection to Wright engines built under licence

And the aluminium bands on cylinders are cooling fines. Wright often used steel cooling fins on the cylinder barrel but always an alloy head like everyone else

 

[MiTasol]

As Calum says - no-one reputable used cast iron for structure

R-3350's had a lot of engine fires from magnesium but that may have been in the rear (accessory) cases rather than the crank case.

 

[wuzak]

In the US SOME of the Wright R-1820's and R-2600's (and maybe R-3350's?? - I never worked on one of those) had FORGED steel crankcases - everything else was alloy.

Weren't the cylinder barrels steel?

 

[gumbyk]

All the Brit engines I have worked on used Al alloy for the main castings though some apparently used magnesium.

DeHavilland used magnesium in the Gipsy Major series of engines, and I understand in the Gipsy Queen and six series as well. The top cover and rear case was Mg.

 

[msxyz]

Depending on the element/alloy, heat treating can be used either to relieve the internal stresses following cold working (like in a press) or to harden a material (sort of accelerated ageing). In any case, heat treating between two different elements/alloys don't yield the same result and, sometimes, different types of heat treating (temperature, time, quenching in-between heating sessions) can vastly change the outcome.

 

[rednev]

From a battle damage point of view did any style of engine have a more/less protected ignition system ?