The Milwaukee Tank engine was a 115 hp (86 kW) air-cooled version of the Curtiss OX-5, and was intended as an aircraft engine. It was tested in a Waco 10.

Designed in 1924 as a military successor to the Curtiss D-12, initially named the Conqueror it was later given the military designation of V-1570 (and GV-1570) based on its displacement of 1,569 cubic inches (26 L). Developed from V-1550 by Arthur Nutt in 1929 V-1570 and GV-1570 Conqueror received ATC 7, developing 575-650hp.

The engine featured open ended cylinder liners (advanced technology for the period) and pressurized liquid cooling. Developments including the use of a supercharger gradually increased power output until reliability problems due to overheating and coolant leaks became apparent.

The Curtiss V-1570 Conqueror was a 12-cylinder vee liquid-cooled aircraft engine. Representing a more powerful version of the Curtiss D-12. The Conqueror featured enbloc type jacket construction, in two banks of 6 each. The cylinders were wet sleeve type of heat treated hydraulically forged carbon steel screwed and shrunk into cylinder heads. Four interchangeable tulip valves seating directly in bronze inserts. Th crankshaft was an eight bearing type.

The gear case assembly was geovable as a unit. Pistons were ribbed head type aluminium alloy. Master and articulated connecting rods.

Avaliable at extra cost was and Eclipse hand inertia starter.

The engine entered production in 1926 and flew in numerous aircraft.

Military funding for further development of the Conqueror was cut in 1932, efforts by Curtiss to market the engine for civil airliners failed and the line was dropped from production.

Applications:
Consolidated A-11
Curtiss A-8
Huff-Daland XB-1
Curtiss B-2 Condor
Tupolev TB-3
Douglas Y1B-7
Atlantic (Fokker U.S.) XB-8
Thomas-Morse YO-23
Douglas O-31
Douglas O-43
Dornier Do X
Curtiss P-1 Hawk
Curtiss P-6 Hawk
Boeing B-9
Boeing XP-9 (Model 96)
Curtiss XP-10
Berliner-Joyce P-16
Curtiss YP-20
Lockheed YP-24
Consolidated Y1P-25
Consolidated P-30
Curtiss XO-30 (not built)
Mormon Meteor III (custom Bonneville salt flat race car)

Specifications:

V-1570-59
Type: 12-cylinder liquid-cooled Vee aircraft engine
Bore: 5 1⁄8 in (130.2mm)
Stroke: 6 11⁄32 in (161.1mm)
Displacement: 1,570.4 in³ (25.73 L)
Cooling system: Liquid-cooled
Power output: 675 hp (504 kW) at 2,450 rpm
Specific power: 0.43 hp/in³ (19.6 kW/l)

V-1570
Type: 12 cylinder 60 deg V, direct drive and geared, water cooled
Rating – direct drive: 600 hp at 2400 rpm
Rating – geared drive: 600 hp at 2450 rpm
Displacement: 1569 cu.in
Compression ratio: 5.8-1
Bore: 5 1/8 in
Stroke: 6 1/4 in
Height: 36 5/8 in
Length – direct drive: 63 1/16 in
Length – geared drive: 68 27/32 in
Width: 26 5/16 in
Weight – direct: 755 lb
Weight – geared: 845 lb
Fuel consumption: not more than .53 lb/hp/hr
Oil consumption: not more than .015 lb/hp/hr
Lubrication: Pressure and scavenging pumps
Ignition: dual Scintilla
Carburation: 2 Stromberg Dual type NA-Y6-O
Spark plugs: 2 per cylinder B.G.

V-1570-A Conqueror
1931
Displacement: 1569ci
Power: 700hp

V-1570 Super Conqueror
1933 Geared and supercharged
Displacement: 1569ci
Power: 800hp

The Army submitted a specification for a new engine on 15 August 1923. The fixed-price contract was won by Curtiss following its bid of 13 November 1923, and was for the construction of three engines, known as the R-1454, with an option for three more. The Curtiss V-2 was a 12-cylinder Vee liquid-cooled aircraft engine. The first engine was delivered in September 1924, and it managed 405hp at 1650 rpm. A modified cylinder (Type M) developed by S.D Heron, an independent contractor, was fitted to the engine, and the Army picked up the option in the contract in February 1926.

The appearance of the lighter Pratt & Whitney Wasp engine effectively killed off the R-1454, and the Army and Curtiss agreed to terminate the contract almost at once, with only three built.

Specifications:

R-1454
Type: 12-cylinder liquid-cooled Vee aircraft engine
Displacement: 1,454 in³ (23.8 L)
Cooling system: Liquid-cooled
Power output: 405 hp (302 kW) at 1,650 rpm

The Curtiss R-600 Challenger was a six-cylinder, double-row, air-cooled, radial engine for aircraft use built in the United States in the late 1920s. It developed 180 hp (134 kW) at 2,000 rpm.

The R-600 featured cast aluminium alloy heat treated cylinder heads screwed and shrunk onto forged steel barrels. The rocker boxes were cast integral with the cylinder heads. The crankcase was cast in two parts, splint on the centre line of the front row of cylinders. There were two Silchrome valves per cylinder, seating on bronze inserts.

The crankshaft was a two-throw counter balance tye, with two master rods each fitted with two short H section link rods. The pistons were ribbed aluminium alloy.

The carburettor is exhaust jacketed around the barrels, using a hot-spot elbow fitted with a valve to control the amount of exhaust heat admitted to the carburettor.

Accessories available at extra cost were a propeller hub, engine driven fuel pump, starter, generator, gun synchroniser, and tool kit.

Applications:
ANBO VI
Curtiss Robin
Rearwin 2000

Specifications:

R-600
Type: 6 cylinder, air cooled, staggered fixed radial
Rating: 170 hp at 1800 rpm / 180 hp (134 kW) at 2,000 rpm
Displacement: 603.4 cu in (9.89 L)
Compression ratio: 4.9-1 or 5.25 to 1
Bore: 5.125 in (130.2 mm)
Stroke: 4.875 in (123.8 mm)
Length: 42 5/32 in
Diameter: 42.625in (1082.7 mm)
Weight: 420lb (190.5 kg)
Fuel consumption: not more than .55 lb/hp/hr
Oil consumption: not more than .020 lb/hp/hr
Lubrication: Pressure and scavenging pumps
Ignition: 2 Scintilla
Carburation: Stromberg 2 barrel NA-U4-J
Spark plugs: 2 per cylinder B.G. 1XA

The Curtiss OXX was an early, dual ignition water-cooled V-8 aero engine derived from the Curtiss OX.

The 1917 OXX-5 produced 75hp from 567.44ci.

The OXX-6 received certification in Group 2, producing 102hp from 567.44ci.

Applications:
Aeromarine 39
Aeromarine 40
Burgess-Dunne
Curtiss Autoplane
Curtiss F
Curtiss FL
Curtiss JN-4
Curtiss MF
Curtiss N-9
Standard J-1

Specifications:

OXX-5
Displacement: 567.44ci
Power output: 75 hp

OXX-6
Type: 8-cylinder water-cooled Vee aircraft piston engine
Bore: 4.25 in (114 mm)
Stroke: 5 in (127 mm)
Displacement: 567 in³ (9.3 L)
Dry weight: 401 lb (182 kg)
Cooling system: Water-cooled
Power output: 100 hp (75 kW) at 1,400 rpm
Compression ratio: 4.92:1

The OX-5 was the last in a series of Glenn Curtiss designed V engines, which had started as a series of air-cooled V-twins for motorcycles in 1902. A modified version of one of these early designs was sold as an aircraft engine in 1906, and from then on the company’s primary market was aircraft. The basic design had slowly expanded by adding additional cylinders until they reached the V-8 in 1906. They also started enlarging the cylinders as well, but this led to cooling problems that required the introduction of water cooling in 1908. These early engines used a flathead valve arrangement, which eventually gave way to a cross-flow cylinder with overhead valves in 1909, leading to improved volumetric efficiency. The US Navy ordered a version of this basic design in 1912 for its A-1 amphibious aircraft, which Curtiss supplied as the OX. These improvements and others were worked into what became the OX-5, which was first built in 1910. The OX-5 was almost identical with OX-2 but Berlin magneto and Zenith carburetor. By this point engine design was a team effort; the team included Charles Manley, whose earlier Manley-Balzer engine had held the power-to-weight ratio record for 16 years.

First run in 1915, the OX-5 was an early V-8 American liquid-cooled aircraft engine built by Curtiss. It was the first US-designed engine to enter mass production, although it was considered obsolete when it did so in 1917. It found widespread use on a number of aircraft, the most famous being the JN-4 “Jenny”. Some 12,600 units were built through early 1919. The wide availability of the engine in the surplus market made it common until the 1930s, although it was considered unreliable for most of its service life. The engine can be found powering many Edwardian automobile racing specials on the historic racing scene.

Like most engines of the era, the OX-5’s high-temperature areas were built mostly of cast iron, using individual cylinders bolted to a single aluminum crankcase, wrapped in a cooling jacket made of a nickel-copper alloy. Later versions used a brazed-on steel jacket instead. Cylinder heads were also attached to the crankcase, using X-shaped tie-downs on the top of the head attached to the block via four long bolts. Fuel was carbureted near the rear of the engine, then piped to the cylinders via two T-shaped pipes, the cylinders being arranged so the intake ports of any two in a bank were near each other. The cylinders had one intake and one exhaust valve, each operated by a pushrod from a camshaft running between the banks. This arrangement caused the outer exhaust valves to have a rather long rocker arm. The pushrods were arranged one inside the other, the exhaust valve rod being on the inside and the intake valve rod a tube around it. The aluminum camshaft bearings were a split type bolted together and held in place by lock screws. The pistons were cast aluminum.

The OX-5 was not considered particularly advanced, nor powerful, for its era. By this point rotary engines such as the Oberursel or Gnome-Rhone were producing about 100 hp (75 kW), and newer inlines were becoming available with 160 hp (120 kW) or more. Nevertheless the OX-5 had fairly good fuel economy as a result of its slow RPM, which made it useful for civilian aircraft. The OX-5 was used on the Laird Swallow, Pitcairn PA-4 Fleetwing II, Travel Air 2000, Waco 9 and 10, the American Eagle, the Buhl-Verville CW-3 Airster, and some models of the Jenny. The primary reason for its popularity was its low cost after the war, with almost-new examples selling as low as $20. It was often used in boats as well as in aircraft.

The engine was considered unreliable, but unreliable is a relative term: aviation engine technology had not fully matured at the end of WWI. Certainly the JN4 with the OX-5 was underpowered, but the OX-5 proved a much better engine than the Hall Scott A7A that was the achilles heel of the Standard J-1, the substitute primary trainer. In particular the valve gear was fragile, and it had no provisions for lubrication other than grease and oil applied by hand, leading to an overhaul interval as short as fifty hours. Additionally the engine featured a single spark plug in each cylinder, and a single ignition system, in an era when ignition equipment was less reliable.

Built by several contractors in large numbers, the OX-5 suffered from uneven quality control. However, while the overwhelming majority of training accidents in the U.S. were in JN-4s, this was because JN-4s were flown by the vast majority of trainee pilots, and the accident rate in the US for primary training was four times less than the advanced training rate in France (virtually all US airmen getting advanced training in France), approximately 2800 flying hours in the US primarily in OX-5 powered JN-4s per fatality to 761 hours per fatality in France in other types. Very few fatal accidents were caused by engine failure, although the lack of power may have been the cause of the many tailspins that took about forty five percent of training lives. The replacement of the A7A in Standard J-1s was contemplated, but the cost of $2,000 per aircraft compared with the need (by the time the J-1s were grounded in June 1918 JN-4s were in sufficient supply) led to the rejection of this idea.

The OX-5 itself would be replaced by the well-proven Wright Aeronautical-built version of the 150 hp Hispano-Suiza HS-8a V8 engine in the nearly 930 examples of the later production Curtiss JN-4H Jenny biplanes.

Gallery

OX-5
Type: 8-cylinder water-cooled 90° Vee piston engine
Bore: 4.0 in (102 mm)
Stroke: 5.0 in (127 mm)
Displacement: 503 in³ (8.2 l)
Length: 56.75 in (1441.45 mm)
Width: 29.75 in (755.65 mm)
Height: 36.75 in (933.45 mm)
Dry weight: 390 lb (177 kg)
Valvetrain: One intake and one exhaust valve per cylinder, pushrod-actuated
Fuel system: Duplex Zenith Carburetor
Oil system: Gear-pump 40 to 60 psi 3-gallon sump
Cooling system: Water-cooled
Power output:
90 hp (67 kW) at 1,400 rpm
105 hp (78 kW) at 1,800 rpm for brief periods
Specific power: 0.21 hp/in³ (9.5 kW/l)
Compression ratio: 4.9:1
Fuel consumption: 8.0 US gal/h (30.8 l/h) at 75% power
Specific fuel consumption: 0.53 lb/(hp·h) (0.32 kg/(kW·h)) at 75% power
Oil consumption: 0.5 US gal/h (1.9 l/h) at 75% power

The H-1640 was an air-cooled, two-row 12-cylinder radial with the cylinders aligned fore and aft in a hexagonal layout. The cylinder banks were placed at 60° intervals. One piece cylinder heads shared a single overhead camshaft, the propeller was directly driven. It was thought that the use of a Townend ring would prove more aerodynamically efficient over an inline engine. The engine first ran in 1927, by aligning the cylinders the diameter of the engine was less than more conventional radial engines.

The H-1640 was the first airworthy ‘inline radial’ and was sponsored for flight testing in a range of aircraft by the U.S. Government. Among the types selected were the Thomas-Morse XP-13 and the Curtiss XO-18. Although the engine was also intended for civil use in the 600 horsepower class continued cooling problems with the rear cylinders caused the project to be canceled with few production engines being built.

Applications:
Curtiss XO-18
Curtiss XP-22 Hawk
Curtiss YP-20
Curtiss P-6 Hawk
Thomas-Morse XP-13 Viper

Specifications:
H-1640
Type: 12-cylinder, two-row, air-cooled radial engine
Bore: 5⅝ in (142.9 mm)
Stroke: 5½ in (139.7 mm)
Displacement: 1,640 cu in (26.9 L)
Diameter: 45 in (1,143 mm)
Dry weight: 900 lb (408 kg)
Valvetrain: Overhead camshaft
Fuel system: Single Stromberg NA-U8J carburetor
Cooling system: Air-cooled
Reduction gear: Direct drive, right-hand tractor
Power output: 615 hp (459 kW)
Specific power: 0.38 hp/cu in (17 kW/L)
Power-to-weight ratio: 0.68 hp/lb (1.13 kW/kg)

The 1922 Curtiss D-12 (ATC 10) was an aero engine of 18.8 litres capacity. A re-designed K-12 by Arthur Nutt. It was a water-cooled V12, producing 443 hp (330 kW) and weighing 693 lb (314 kg). It was designed by Arthur Nutt in 1921 with enbloc type jacket construction in two banks of six each. The cylinders were of heat treated hydraulically forged carbon steel with the head end closed.

Four interchangeable tulip valves seating directly in each cylinder head. The crankshaft was carried in eight bearings. The gear assembly is removable as a unit. The pistons are ribbed head type aluminium alloy. The connecting rods are master and articulating.

An accesssories costing extra was the Eclispe hand inertia starter.

Three Curtiss D-12 was used in the Curtiss CR-3 for the 1923 Schneider Trophy race. In racing trim the V-1400 D-12 gave 619 hp, against the normal 435 hp.

Fairey Aviation of England imported 50 Curtiss built examples in 1926, renaming them the Fairey Felix.

Applications:
D-12
Curtiss CR
Curtiss Falcon
Curtiss R2C
Curtiss PW-8
Fokker D.XII
Macchi M.33
Wittman D-12 Bonzo

Felix
Fairey Firefly I
Fairey Fox

Specifications

Curtiss D-12/Felix
Type: 12 cylinder 60 deg V, direct drive water cooled
Rating: 435 hp (330 kW) at 2300 rpm
Displacement: 1145 cu.in (18.8 liters)
Compression ratio: 5.3-1
Bore: 4 1/2 in (114.3 mm)
Stroke: 6 in (152.4 mm)
Length: 56 3/4 in (1441 mm)
Width: 28 1/4 in (717.5 mm)
Height: 34.75 in (882.6 mm)
Weight: 680 lb
Fuel consumption: not more than .53 lb/hp/hr
Oil consumption: not more than .015 lb/hp/hr
Lubrication: pressure and scavenging pumps
Ignition: 2 Scintilla
Carburation: 2 Stromberg Dual type NA-Y5-F
Spark plugs: 2 per cylinder B.G.

The 1922 Curtiss C-6 is a six-cylinder, water-cooled, inline aircraft engine and is a development of the Curtiss K-6 engine redesigned by Arthur Nutt. The C-6 features an overhead cam and aluminum cylinder jackets.

Applications:
Curtiss Lark
Curtiss Oriole
Curtiss MF Seagull
Laird C-6 Special
Pitcairn PA-1 Fleetwing
Pitcairn PA-2 Sesquiwing
Travel Air 2000
Waco 9

Specifications:

C-6
Type: 6-cylinder water-cooled inline
Dry weight: 420 lb
Valvetrain: Two intake and two exhaust valves per cylinder, pushrod-actuated
Cooling system: Water-cooled
Power output:
160 hp at 1,250 rpm
161 hp at 1,760 rpm
Fuel consumption: .5 lbs per hp per hr
Oil consumption: .016 lbs per hp per hr
Power-to-weight ratio: 0.38 hp/lb