# Curtiss H-1640 Chieftain

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Unusual American 12-cylinder radial aero engine

H-1640 H-1640 engine at the National Air and Space Museum Type Radial aero engine National origin United States Manufacturer Curtiss Aeroplane and Motor Company First run 1926 Number built 8[1]

The **Curtiss H-1640 Chieftain** was an unusual American 12-cylinder [radial](/source/Radial_engine) [aero engine](/source/Aircraft_engine) designed and built by the [Curtiss Aeroplane and Motor Company](/source/Curtiss_Aeroplane_and_Motor_Company) in the mid-1920s.[2] In contrast to most multi-row radials, where the cylinders in the rows are staggered to present better airflow for cooling, the Chieftain used the [inline radial](/source/Inline_radial_engine) arrangement with the cylinders behind each other to allow pairs of cylinders to share a cast [cylinder head](/source/Cylinder_head) and [camshafts](/source/Camshaft). The design saw some use in the 1920s but was quickly passed by newer designs.

## Design and development

The H-1640 was an air-cooled 12 cylinder two-row radial with the cylinder rows aligned rather than staggered as in most multi-row radials. One piece [cylinder heads](/source/Cylinder_head) shared a single [overhead camshaft](/source/Overhead_camshaft) and the propeller was directly driven. By aligning the cylinders the effective diameter and frontal area of the engine was less than more conventional radial engines, and it was thought that the use of a [Townend ring](/source/Townend_ring) could make the engine more aerodynamically efficient than an [inline engine](/source/Inline_engine_(aviation)). The engine first ran in 1927.

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](/source/XP-13_Viper) and the [Curtiss XO-18](/source/Curtiss_Falcon). Cooling problems with the rear cylinders caused the project to be canceled with few production engines being built.

A similar engine is the [Bristol Hydra](/source/Bristol_Hydra) although this engine had 16 aligned cylinders, forming an [octagon](/source/Octagon). Further similar engines are the [Armstrong Siddeley Hyena](/source/Armstrong_Siddeley_Hyena) and the much larger [Armstrong Siddeley Deerhound](/source/Armstrong_Siddeley_Deerhound).

## Applications

A Thomas-Morse [XP-13 Viper](/source/XP-13_Viper) fitted with a Curtiss H-1640 Chieftain during testing

- [Curtiss XP-22 Hawk](/source/Curtiss_XP-22_Hawk)

- [Curtiss YP-20](/source/Curtiss_YP-20)

- [Curtiss P-6 Hawk](/source/Curtiss_P-6_Hawk)

- [Thomas-Morse XP-13 Viper](/source/Thomas-Morse_XP-13_Viper)

## Specifications (H-1640)

Curtis H 1640 Engine - located at the Wings Over The Rockies museum, Denver, CO

*Data from* *enginehistory.org*[3]

### General characteristics

- **Type:** 12-cylinder, two-row, air-cooled radial engine

- **[Bore](/source/Bore_(engine)):** 5⅝ in (142.9 mm)

- **[Stroke](/source/Stroke_(engine)):** 5½ in (139.7 mm)

- **[Displacement](/source/Engine_displacement):** 1,640 cu in (26.9 L)

- **Diameter:** 45 in (1,143 mm)

- **[Dry weight](/source/Dry_weight):** 900 lb (408 kg)

### Components

- **[Valvetrain](/source/Valvetrain):** Overhead camshaft

- **Fuel system:** Single Stromberg NA-U8J carburetor

- **Cooling system:** Air-cooled

- **[Reduction gear](/source/Propeller_speed_reduction_unit):** Direct drive, right-hand tractor

### Performance

- **Power output:** 615 hp (459 kW)

- **[Specific power](/source/Power_density):** 0.38 hp/cu in (17 kW/L)

- **[Power-to-weight ratio](/source/Power-to-weight_ratio):** 0.68 hp/lb (1.13 kW/kg)

## See also

**Related lists**

- [List of aircraft engines](/source/List_of_aircraft_engines)

## References

Wikimedia Commons has media related to [Curtiss H-1640](https://commons.wikimedia.org/wiki/Category:Curtiss_H-1640).

### Notes

1. **[^](#cite_ref-1)** [https://oldmachinepress.com/2012/11/09/curtiss-h-1640-chieftain-aircraft-engine/](https://oldmachinepress.com/2012/11/09/curtiss-h-1640-chieftain-aircraft-engine/)

1. **[^](#cite_ref-2)** Gunston 1989, p. 46

1. **[^](#cite_ref-3)** [Curtiss Chieftain](http://www.enginehistory.org/Curtiss/Chieftain.pdf) www.enginehistory.org Retrieved: 17 September 2009

### Bibliography

- Gunston, Bill. *World Encyclopaedia of Aero Engines*. Cambridge, England. Patrick Stephens Limited, 1989. [ISBN](/source/ISBN_(identifier)) [1-85260-163-9](https://en.wikipedia.org/wiki/Special:BookSources/1-85260-163-9)

v t e Curtiss aircraft engines Inline engines A-2 B-8 C-6 D-12 K-12 K L O OX-5 OXX S V V-1570 V-2 Radial engines H-1640 R-600 R-1454

v t e United States military piston aircraft engine designation system H (four-bank H-configuration inline) H-1640 XH-2240 XH-2470 XH-2600 XH-3130 XH-3730 H-4070 IV (inverted-V inline) IV-1430 IV-2040 IV-2220 L (single-bank inline) L-330 L-365 L-375 L-390 L-410 L-440 L-510 L-825 O (opposed) O-15 O-40 O-45 O-90 O-100 O-145 O-150 O-170 O-175 O-180 O-190 O-200 (C) O-200 (F) O-205 O-235 O-290 O-300 O-335 O-360 (C) O-360 (L) O-405 O-425 O-435 O-470 O-480 O-520 O-540 (F) O-540 (L) O-550 O-580 O-805 O-1230 R (radial) R-250 R-265 R-270 R-370 (LB) R-370 (K) R-420 R-440 R-500 R-540 (W) R-540 (K) R-545 R-550 R-600 R-670 R-680 R-720 R-755 R-760 R-790 R-830 R-915 R-975 DR-980 R-985 R-1044 R-1300 R-1340 R-1454 R-1510 R-1535 R-1640 R-1670 R-1690 R-1740 R-1750 R-1820 R-1830 R-1860 R-2000 R-2060 R-2160 R-2180 R-2600 R-2800 R-3350 R-4090 R-4360 R-7755 V (upright-V inline) V-720 V-1150 V-1237 V-1400 V-1440 V-1460 V-1510 V-1560 V-1570 V-1650 (P) V-1710 V-1950 V-3420 V (inverted-V inline) V-770 V-1650 (L) VG (inverted-V inline) VG-1410 W (three-bank W-configuration inline) W-2779 See also: X-1800 US military gas turbine aeroengines Piston engine configurations

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