The De Havilland DH 60 Moth
A brief Chronology of the Moth thru the summer of 1928.
Too many
words have been written by too many really knowledgeable people for me to
attempt even a brief history of the type.
Therefore I shall confine myself to the simplest of sketches, noting
only the major milestones which led to the development of the two versions
included in this package.
Captain
Geoffrey de Havilland flew the first DH 60 (not yet named the Moth) for the
first time on Sunday, 1925. The plane
was a small biplane with a 29 foot wingspan and a maximum takeoff weight of
1298 pounds, although some sources quote 1240 or 1260 pounds. The engine was an ADC
(Aircraft Disposal Company) Cirrus I, a 60 horsepower air cooled four cylinder
inline which gave the plane a nominal top speed of 90 mph and a cruising speed
of 75 mph. A 15 Imperial gallon fuel
tank in the top wing center section allowed for a range of about 320 miles, and
the wings were designed to be folded back (a feature which I did NOT include in
this model) so that the airplane could be stored indoors without requiring a
full sized hanger. The airplane was
intended to serve both the private owner and the government sponsored flying
clubs then being proposed, and the projected price was 885 pounds (which I
shall now begin noting as L885, even though I don’t have the appropriate sign
on my American keyboard).
The airplane
was an immediate success and sales were brisk (for the day). An attempt to count serial numbers indicates
that at least 62 were produced by the De Havilland factory at
In 1926
attempts were made to find a better and more powerful engine. In part this search was inspired by the fact
that the Cirrus I used surplus cylinders from the World War I Royal Aircraft
Factory (RAF) air cooled V-8 engine, and the supply of those cylinders was
becoming exhausted. To fill the void,
ADC developed its own cylinders and created the Cirrus II, an engine of greater
displacement which produced 84 horsepower.
De Havilland began offering this engine as a Moth option late in 1926.
The other
engine adopted was the Armstrong Siddeley Genet I, a
five cylinder radial engine that produced a nominal 75 horse power. This engine was installed on a small number
of Moths, perhaps less than a dozen, most of which ended up serving the Royal
Air Force.
January,
1927, saw the introduction of the 1927 Moth, also known as the Cirrus II Moth
and occasionally as the Moth II. This
model not only had the 84 horsepower Cirrus II engine but featured a slightly
larger airframe with the wing span extended to 30 feet. Other less visible improvements were also
made, but the “improvement” most prominently advertised by the folks at De
Havilland was that the already low price of L795 was further reduced to L730. Between 31 and 40 Cirrus II Moths were
delivered. More might have been built,
but just three months later, De Havilland introduced the DH60X.
DH60X featured
two readily apparent changes. The first
was the installation of a larger 19 Imperial gallon fuel tank in place of the
smaller unit on previous versions. The
second was the lowering of the engine by several inches, a change which significantly
improved the pilot’s forward visibility.
There were other less obvious changes, the biggest probably being an
increase in the stagger between the lower and upper wings. This became the standard Moth configuration
for the next year.
By serial
number count, at least 302 DH60X aircraft were built by De Havilland at
Things
remained fairly static for the next year, until April, 1928. That month saw the
first installation of the split axle landing gear which quickly replaced the
“spreader bar” landing gear previously used.
At the same time, the first set of Handley Page “autoslots”
was installed on a civilian Moth, although the Royal Air Force had been
operating them for some time. Apparently
they had not been offered previously because in addition to the cost of the autoslots themselves, Handley Page received a license fee
for each set, a fee which was paid by the customer and which frequently
exceeded the cost of the autoslots themselves. It was rumored that Captain de Havilland was
so irritated by the arrangement that he insisted that only one set of autoslots be owned by the company for testing
purposes.
The small
change introduced in May was the first three-piece windscreen which replaced
the “blown” Plexiglas units previously used.
However June brought the biggest change when the first Gipsy engine was
mated to the airframe. Initially
developed as a 135 hp racing engine, this four cylinder inline engine was
de-rated to 85 horsepower for use in the Moth.
With this engine installed the airplane became the DH60G Gipsy Moth, and
this version of the Moth outsold all Cirrus powered Moths combined. When the last Gipsy Moth was delivered in the
late summer of 1933, the factory at
Late in 1928
one more version emerged. In response to
requests by operators who used their airplanes in more primitive areas where
seemingly minor damage could keep the airplane on the ground for extensive
repairs, the company introduced a metal tube framed fuselage. Produced in tandem with the wooden framed
DH60G and X airplanes, this airplane was designated the DH60 M “Metal Moth”,
and it became the most popular version of all, with nearly 900 being built
worldwide.
The
Planes
This package
includes two planes. The first is DH60X G-EBUZ,
c/n 478, as it might have looked if delivered in the
late summer of 1927. I found one picture
of this airplane taken in December, 1927.
The picture is in black and white, so the choice of colors is a guess on
my part. The aircraft was stricken from
the record in December, 1934.
The Gipsy
Moth is G-AAHI, c/n 1082, as it might have looked when
delivered in 1929. This aircraft is
still active today and photographs are available showing it with green fuselage
and silver wings and red fuselage and white wings. I chose the green livery.
I based the
instrument panel on vintage rather than modern photographs and for that reason
they are basic to the point of being stark.
There were no electrical systems, starters, lights, radios, or
gyros. Most of these conveniences were
available at the time as options, but the vast majority of Moths appear to have
been used in daylight visual flying conditions, so that is how I set them
up. For those who insist on talking to
people when they fly, I did put the default ATC popup in the 2D panel.
Performance
and Specifications
As is common
when studying really old airplanes, I found that the published specifications
varied from one source to another. Where
I could find them, I quote figures given in contemporary reports. Where I could not find such reports, I used
an “average” figure based on the sources I do have at hand.
Perhaps the
biggest disconnects are in the area of weights.
In his excellent book The De
Havilland DH. 60 Moth, Stuart McKay notes that the early DH60X weighed 853
pounds empty and 1370 pounds fully loaded, but most published sources quote the
much higher figures of
955# and 1750# respectively.
Since I intended my Moths to be as they were originally configured, I
elected to use the lighter weights quoted my Mr. McKay.
I had a
stroke of good luck when it came time to figure the weights for the Gipsy Moth. As noted, G-AAHI is still active, and as
such, it’s C of A is available on line listing the
approved gross weight. I wish everything
I did was that easy!
I
encountered one other puzzle as I created the flight dynamics of these airplane. Most
sources agree that the Cirrus II delivered 84 or 85 horsepower at 2000 rpm, but
output for the Gipsy I is not so well defined.
Some
notes about flying the Moth
Flying does
not get much more basic than it is in the Moth.
I included a very rudimentary even though it appears that the checklist as
we know it did not actually come into common use until sometime in the mid
1930s. Prior to then, a “real pilot” was
expected to know what to do and when to do it without outside aid. I often wonder if that attitude didn’t
contribute to the rather high accident rates experienced in those bygone days
….
There are a
couple of items that may catch the unwary by surprise. The fuel tap is the lever mounted on the left
rear cabane strut.
Vertical is ON, 45 degrees counter-clockwise is OFF. The switches are on the forward decking on the
left side of the fuselage. You cannot
reach through the glass with the tool tip to flip them ON any more than you can
reach through the Plexiglas on a real plane.
Slide yourself to the left until you have a clear shot at the switches
to turn them ON.
When you
check the oil pressure after engine start you will see absurdly low
values. Normal oil pressure for the
Cirrus is 5 to 15 psi with a maximum limit of between 25 - 30 psi where a
pressure relief valve opens. (The normal
operating pressure for the earlier Cirrus I was lower at 5 to 10 psi!) When I first encountered these numbers in an
article about the airplane I thought it was a misprint, but I later found a
Cirrus II engine manual and confirmed them.
The
pressures for the Gipsy engine are only about 10 psi higher.
The takeoff
run is short. I recommend lifting the
tail just enough to get the skid out of the sod and letting the plane fly off
in a tail low attitude. Best rate of
climb speed appears to be about 55 mph, but for better visibility and engine
cooling 65 mph works just fine. At this
point you will discover one of the two major differences between the two
versions of the Moth. The Cirrus is a
right hand engine and the Gipsy is a left hand engine. While neither is going to pull the nose
around like the Merlin pulls a Spitfire, you need to remember that the Cirrus
requires right rudder on takeoff and climb whereas the Gipsy requires left
rudder.
The best
word to describe cruise flight in the Moth is “leisurely.” In March, 1928, De Havilland
ran fuel consumption tests which indicated that the most efficient cruise speed
for the DH60X was 79 mph where the engine burned 4.3 Imperial gallons per
hour. Similar tests run on the Gipsy
Moth later that year indicated that the Gipsy was most efficient at 76 mph
where it burned 4.35 gph. However it appears that the
average pilot not engaged on a world spanning record flight simply set 1800 rpm
and let it go at that. This usually
yields a true airspeed in the low 80s and a fuel burn around 4.5 Imp. gallons an hour. Note
that the fuel is read in
Landing is pretty
much a non-event. I fly downwind at
cruise power and as I pass abeam the touchdown point, I close the throttle and
begin slowing. About the time the speed hits 65 I turn base and I hold
that speed till turning final. Once established
on final the other major difference between the two versions becomes
obvious. The DH60X has a “plain” wing,
but the later Gipsy Moth is equipped with the Handley Page Autoslots. I fly the X down final no slower than 55 mph,
but with the autoslots, I can comfortably fly the
final at 50 mph indicated (the slots extend at about 53 mph) and still have the
energy and elevator authority to make proper three point landings.
As is
typical of the era, the long nose effectively blocks your forward vision on
final. At the same time, with all that
drag, the airplane comes down at a pretty good rate. Both conditions argue for what later became
known as the “Spitfire Curved Approach,” which basically means a fairly tight
pattern with a continuous shallow turn from down wind to short final. As always, the best way to find out what
works best for you is to experiment and then practice.
There are no
brakes on these Moths, but even so the plane rolls to a stop in short
order. It takes a certain amount of
power to keep the plane rolling when taxiing and the best way to change
direction is to give a quick blast of power while applying full rudder into the
turn. Do not leave the power in for any
length of time because the plane accelerates quickly, especially when light.
Once more,
this is flying at its most basic. No radios, no clock. Navigation
is done by following a pencil line on a chart.
With no lights you must you land with the sun and spend the evenings at
the local pub. It doesn’t get any better
than this. Enjoy!
jcdouglass
31-12-08
SPECIFICATIONS
1927 De
Havilland DH60X
Span:
30’ Chord 52.4” Wing Area
243 square’ Airfoil RAF 15 Modified
Length 23’
8.5” Height 8’ 9.5”
Empty
Weight 859# Useful Load 511# Gross Weight 1370#
Vne (no one called it that in those days) 160 mph
indicated airspeed
Vh * 98
mph true airspeed at sea level
Cruise
speed
85 mph true airspeed
Stall
speed
40 mph indicated
Service
Ceiling
14,500 feet
Fuel
Capacity
19 Imp/ 22.8
Oil
Capacity 2.4
Imperial gallons
1929 De
Havilland DH60 G Gipsy Moth
Span:
30’ Chord 52.4” Wing Area
243 square’ Airfoil RAF 15 Modified
Length 23’
11” Height 8’ 9.5”
Empty
Weight 920# Useful Load 730# Gross Weight 1650#
Vne (no one called it that in those days) 160 mph
indicated airspeed
Vh
* 102
mph true airspeed at sea level
Cruise
speed
85 mph true airspeed
Stall
speed
40 mph indicated
Rate of
Climb 550 fpm
Service
Ceiling
14,500 feet
Fuel
Capacity
19 Imp/ 22.8
Oil
Capacity 2.4
Imperial gallons
*Vh is the airplane’s maximum speed at maximum gross weight
at the altitude at which the engine produces maximum power – sea level in this
instance.
All these
performance figures were achieved or calculated on a standard day at maximum
gross weight.