Today we’re taking a look at the de Havilland DH.66 Hercules.
This was one of a collection of aircraft that helped to shrink the world in the 1920s and
1930s with the establishment of long-distance mail services.
Air mail had been experimented with as early as 1911, but most of these early services
were brief, lasting only a couple of months, if that.
It wasn’t until after the first world war that long-term air mail services finally became
established, though even then a lot of it was limited to either domestic or short-distance
international routes.
This was partly due to the range limitations of many aircraft at the time, but mostly due
to concerns about cost, and of course the not-so-quiet lobbying from various persons
interested in the established rail and naval mail routes.
However, the rapid development of engine technology, and that of multi-engine aircraft design,
meant that long-distance mail routes across remote regions were rapidly becoming feasible,
and this was where the aeroplane was most sorely needed.
One of the first of these more remote routes was the desert air mail service, which was
opened by the RAF in 1921.
This ran air mail between Cairo and Badhdad, and there were long-term hopes for the route
to be extended all the way to India.
Between 1921 and 1925 this route was faithfully flown by aircraft such as the de Havilland
DH.9A, and the Vickers Vernon, but when Imperial Airways took over the desert air mail service
that year a replacement was needed.
Not only were the DH.9As and Vernons wearing out fast, but Imperial Airways wanted something
larger, more up to date, and more reliable.
They drew up a specification requiring an aircraft to be built with multiple engines,
with ample reserves of power for emergencies, and it was to be built with tropical conditions
and rough landing strips in mind.
Unsurprisingly de Havilland proposed a replacement themselves, not wishing to lose such a valuable
customer, and after a review their proposal was accepted, with an order being placed for
five aircraft.
Powered by a trio of 420hp Bristol Jupiters, The DH.66 was Geoffrey de Havilland’s most
ambitious design since the Amiens and Oxford bombers of the first world war.
It was also a significant upgrade in every respect, as the company had learned valuable
lessons with other aircraft designs over the previous seven years.
Owing to a shortage of high-quality spruce, and various considerations that wooden spars
and ribs tended to deteriorate quickly in tropical conditions, the DH.66 was primarily
constructed from steel tubing.
This was a notable shift for de Havilland, who had not yet jumped on the trend of metal
airframes that was becoming firmly established by the middle of the decade, and indeed it
was a trend he would continue to resis- with this being one of the few exceptions.
Within the large steel framework, two plywood box structures would form the main cabin and
rear baggage compartment; in classic 1920s style, the two pilots sat in an open cockpit,
as enclosed canopys were still considered a hindrance, and in the main cabin there was
room enough for a radio operator, seven passengers, and up to 465 cubic feet of mail.
Its unclear when construction of the prototype began, but it was complete by the beginning
of Autumn in 1926.
The name Hercules had been selected through a competition held by the Meccano Magazine
in June, and it was with this name printed on the side (though some sources do dispute
this), that the aircraft first flew on September the 30th.
The only change required from the flight trials was to have ailerons fitted to all four wings,
to improve lateral control, and following this the aircraft was transferred to Imperial
Airways and it left England for Cairo on December the 20th.
The end of the year marked the transfer of the desert air mail service from military
to civilian control, and this was marked by a historic flight that was completed by the
second de Havilland Hercules.
This aircraft completed a route that took it from Croydon, England, all the way out
to the city if Delhi in India…after which it was then named the City of Delhi as well,
inheriting the title of an older de Havilland DH.34 that had been lost two years earlier.
Commercial operations officially began on January the 7th, 1927, with the first Hercules
completing a route between Basra and Cairo, and all five aircraft were delivered and operational
by the end of March.
Like all Imperial Airways aircraft, they were individually named.
You had the City of Cairo, City of Delhi, City of Baghdad, City of Jerusalem, and the
City of Teheran.
Thanks to their sturdy design, the Hercules aircraft managed remarkably well in the harsh,
unforgiving conditions of the Middle East, and because of this, in 1928, they caught
the attention of West Australian Airways, who operated aircraft over equally harsh,
unforgiving, and slightly more spider-infested conditions on the other side of the world.
After being given permission to open a new air service between Perth and Adelaide, the
company selected the DH.66 as the obvious aircraft to carry their passengers, and an
order was placed for four Hercules later that year.
West Australian Airways also made a request for several modifications to make the aircraft
more suitable for their long-distance service.
The pilot’s cockpit was now covered by an enclosed cabin with sliding windows, seating
capacity was increased to fourteen, and a tailwheel was to replace the old-school tailskid.
In the end this final modification was removed, as the tailwheels failed to survive repeated,
rough landings, and the tailskid, though rudimentary, was actually found to be both more comfortable
and safer.
The Australian service was inaugurated on the 29th of May.
Two aircraft, the City of Perth and the City of Adelaide completed the 1450 mile route
in 14 hours, carrying a combined total of 21 passengers.
The other two airframes were held in reserve, but less than a year later one of them would
be sold to Imperial Airways to replace the loss of the City of Teheran, which had come
to grief in a non-fatal forced landing.
Four more DH.66s were built after the Australian order.
All of these were the modified type with the enclosed cabin, and this modification was
also added to the remaining aircraft from the original order.
The eleventh, and final, DH.66 was delivered in January of 1930.
Though they were not built in large numbers, as was the case with many commercial aircraft
of the time, the de Havilland Hercules tallied quite a few achievements.
The sixth aircraft to join Imperial Airways would open the first official extension of
its air routes to India in 1929.
In 1931 the Hercules would assist in completing the first official air mail service from Australia
back to England, and later on that year the same aircraft would complete survey flights
down into south Africa, foreshadowing the next major expansion of the Empire Air Route.
This particular aircraft, now named the City of Cape Town, would go on to become the starring
attraction of Sir Alan Cobham’s travelling air show when it came to the area.
A couple of the Hercules aircraft would also find themselves as pioneers of aerial pest-control.
The City of Basra, and the City of Jodhpur, both conducted so-called dusting flights to
help combat swarms of locusts in various parts of Africa.
As the City of Jodhpur was wrecked when trying to take-off from a boggy swamp, an exercise
in futility if there ever was one, the City of Basra would do the bulk of this work, dropping
hundreds of pounds of horrifically dangerous arsenic-based powders over the course of 1935.
Remarkably, the last operational use of the DH.66 occurred during the second world war.
Though the majority had either crashed, or had been retired by this time, two Hercules
had been sold to the South African Air force in 1934, and in the early stages of the war
they would fly as military couriers.
A third aircraft was also in South African possession at this time, but it was not actually
flown, instead it was reduced to spares in order to keep the courier aircraft running
for as long as possible, this they did until finally being withdrawn from service and scrapped
in 1943.
Despite being successful, the DH.66 was not immediately followed by a successor.
In fact, de Havilland mostly stuck with light aircraft throughout the 1920s and 1930s.
It would not be until the mid-1930s that a new transport of more than two engines was
developed, the DH.86, though by this point its construction methods put it at an immediate
disadvantage over the competition.
But the story of the DH.86 is one for another day.
As always, thank you all so much for watching, and a big thank you of course to the Patreons.
Once again, this video is going up whilst I’m away so this list cant be updates, but
rest assured as soon as I am back we’ll include all our newest members.
A special thank you of course to our wing commander tier patreons, our highest tier
members…
I’m hopefully going to be expanding my plans for Patreon in the next month or so -time
and plans permitting- which should hopefully see some more stuff for all members.
I just need to finish up some back end stuff and we should be good to go.
But that’s an update for later, as always, thank you all so much for watching, and I’ll
catch you all next time.
Goodbye.