# Franklin O-405

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O-405/6AC-403 Type Piston aircraft engine National origin United States Manufacturer Franklin Engine Company First run 1942

The **Franklin O-405** (company designation **6AC-403**) was an American air-cooled aircraft engine of the 1940s. The engine was of [six-cylinder, horizontally-opposed layout](/source/Flat-six_engine) and [displaced](/source/Engine_displacement) 405 cu in (6.64 L). The power output was between 200 hp (149 kW) and 250 hp (186 kW) depending on variant. The **O-405-9 (6ACV-403)** was a vertically mounted, fan cooled version for helicopters.

## Variants

**6AC-403 (XO-405-1)**
- 200 hp (149 kW) at 2,750 rpm

**6ACSA-403 (XO-405-3)**
- Supercharged, 220 hp (164 kW) at 2,750 rpm

**6ACGSA-403 (O-405-5)**
- Supercharged, geared propeller drive at 0.632:1. 250 hp (186 kW) at 3,200 rpm

**6ACV-403 (O-405-9)**
- Vertically mounted, fan-cooled helicopter version, 245 hp (183 kW) at 3,275 rpm

## Applications

- [Culver XPQ-15](/source/Culver_XPQ-15)

- [Doman LZ-1A](/source/Sikorsky_R-6)

- [Doman Pelican](https://en.wikipedia.org/w/index.php?title=Doman_Pelican&action=edit&redlink=1)

- [Fairchild XUC-86B](/source/Fairchild_24)

- [Fleetwings XBQ-1](/source/Fleetwings_XBQ-1)

- [Kellett XR-8](/source/Kellett_XR-8)

- [Sikorsky R-6](/source/Sikorsky_R-6)

## Specifications (6AC-403/XO-405-1)

*Data from* [*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

### General characteristics

- **Type:** 6-cylinder air-cooled [horizontally opposed](/source/Flat-6) aircraft piston engine

- **[Bore](/source/Bore_(engine)):** 4.625 in (117.5 mm)

- **[Stroke](/source/Stroke_(engine)):** 4.0 in (101.6 mm)

- **[Displacement](/source/Engine_displacement):** 403.2 in³ (6.6 L)

- **[Dry weight](/source/Dry_weight):** 405 lb (184 kg)

### Components

- **Cooling system:** Air-cooled

### Performance

- **Power output:** 200 hp (149 kW) at 2,750 rpm

## See also

**Comparable engines**

- [Continental Tiara 6-260](/source/Continental_Tiara_series)

**Related lists**

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

## References

**Notes**

**Bibliography**

- Gunston, Bill. (1986) *World Encyclopedia of Aero Engines*. Patrick Stephens: Wellingborough. p. 57

v t e Franklin aircraft engines By displacement O-110 O-120 O-150 O-170 O-175 O-180 O-200 O-225 O-235 O-265 O-300 O-315 O-335 O-350 O-400 O-405 O-425 O-500 O-540 O-595 O-805 Two-cylinder engines By displacement O-110 O-120 By company designation 2A-110 2A-120 2A4-45 2A4-49 2AL-112 Four-cylinder engines By displacement O-150 O-170 O-175 O-180 O-200 O-225 O-235 By company designation 4A-225 4A-235 4A4-100 4A4-75 4A4-85 4A4-95 4AC-150 4AC-171 4AC-176 4AC-199 4ACG-176 4AL-225 Sport 4 Six-cylinder engines By displacement O-265 O-300 O-315 O-335 O-350 O-405 O-425 O-500 By company designation 6A-335 6A-350 6A3 6A4 6A8-215 6AC-264 6AC-298 6AC-403 6ACV-245 6AG-335 6AG4-185 6AG6-245 6AGS-335 6AGS6-245 6AL-315 6AL-335 6AL-500 6ALV-335 6AS-335 6V-335 6V4 6V6-245-B16F 6V6-245 6V6-300-D16FT 6V6-300 6VS-335 Eight-cylinder engines By displacement O-400 O-540 By company designation 8AC-398 8ACG-398 8ACG-538 8ACGSA-538 8ACSA-538 12-cylinder engines By displacement O-595 O-805 By company designation 12AC-596 12AC-806

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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Adapted from the Wikipedia article [Franklin O-405](https://en.wikipedia.org/wiki/Franklin_O-405) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Franklin_O-405?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.