Prototype De Havilland DH66 Hercules G-EBMW
The prototype De Havilland DH66 Hercules G-EBMW in its original configuration with ailerons only on lower wings.


The De Havilland Aircraft Company DH66 Hercules was designed to meet the needs of Imperial Airways for their Cairo to Karachi route. They had a requirement to have sufficient power in reserve to maintain height, following any kind of engine failure. Aircraft also needed to be able to cope with the elevated terrain and high temperatures found on this challenging route. 


The DH66 Hercules placed the De Havilland DH10, which had been designed as a bomber towards the end of World War 1 and thus featured little in the way of refinement.  Conversely, the DH66 Hercules led the way for future airline travel.


It was a large, two-bay biplane with a fuselage of steel tubular construction, powered by three Bristol Jupiter VI engines. The tail surfaces included three fins and rudders, a low-set tailplane and elevators, with a smaller fixed tailplane mounted level with the top of the fins.


The prototype (G-EBMW) was flown for the first time at Stag Lane on 30th September 1926. Initial testing however, had revealed poor lateral control and so ailerons were fitted to all four wings.


Within 3 months, the air route to Karachi had been inaugurated with a flight by the second aircraft (G-EBMX) which after leaving Croydon on 27th December 1926, arrived in Karachi on 8th January 1927. Imperial Airways ordered five aircraft, the last entering service in March 1927 and the type proved immensely reliable and successful in service.


De Havilland DH66 Hercules G-EBMW one engine out
The prototype De Havilland DH66 Hercules G-EBMW demonstrating its ability to fly with one engine shut down.


Four additional aircraft, featuring enclosed cockpits and a tail wheel (rather than a skid), were ordered by West Australian Airways to replace their fleet of DH50s. These were completed in 1929 although their enclosed cockpit design was later retrofitted to the earlier production machines. Passenger accommodation in these machines was provided for up to 14 passengers, as well a a quantity of mail bags and they operated between Perth and Adelaide.


Two additional machines, built to the same 1929 configuration, were ordered by Imperial Airways giving a total production of eleven aircraft, seven of which were UK registered with four in Australia.


De Havilland DH66 Hercules closed cockpit
De Havilland DH66 Hercules in post-1929 configuration with cockpit enclosure.


Other than their commercial use on the route to India, a notable survey flight was made in December 1931 using a DH66 Hercules (G-AARY), which flew to Cape Town to investigate the extension of the Empire Air Route into South Africa. This route began regular operations in 1932.


Alan Cobham also used a DH66 Hercules (G-ABMT leased from Imperial Airways) as part of an Air Pageant Tour to South Africa in 1932 to 1933.


Three other machines (G-EBMX, G-AUJQ and G-AAJH) also served with the South African Air Force (SAAF serials 260-262) the last two of these remaining in service until they were finally retired and scrapped in 1943.


DH66 Hercules Specification

Powerplant Three 420 hp Bristol Jupiter VI radial engines
Span 79 ft 6 in
Maximum Weight  15,660 lb 
Capacity 2 pilots, wireless operator and 7 passengers plus 465 cu ft mail compartment and 155 cu ft baggage compartment.
Maximum Speed 128 mph
Cruising Speed 110 mph


Number Built

A total of 11, four of which were registered in Australia.



There are no surviving DH66 aircraft.


More information

12 Default Profile Image
BAE Systems
The information shown is based on that available at the time of the content creation. If you have any additions or corrections then please contact us via email - All images BAE Systems / Ron Smith copyright unless otherwise shown.