Airship Improvements Between Wars
[Illustration: Docked airship]
The wartime airship was a cigar-shaped gas bag with an airplane cockpit,
open to the weather, slung below. The contrast between it and the sleek,
fast, streamlined Navy airship of today is almost as striking as that
between wartime planes and automobiles and modern ones.
Many improvements have been made, even though the airship has not had
the experience of building thousands of units, as the automobile and
airplane have had, or ample funds for research and experiment. Less than
150 non-rigid airships have been built all told since 1914.
The “B” type blimp, chiefly used in the World War, contained 80,000
cubic feet of hydrogen, though some British and French non-rigids were
built in larger sizes, and the United States Navy “C” ships, toward the
end of the war, had 200,000 cubic feet of lifting gas. These compare
with the 416,000 cubic feet of helium in the new Navy “K” ships. Speed,
under the pressure of war needs moved up from 47 miles in the “B” to
close to 60 in the “C,” but is around 80 in today’s “K” ships.
Wartime ships carried three to five men and a day’s fuel. Today’s carry
eight or ten, enough pilots, radio men, navigators, riggers and
mechanics for two full watches, though normally everyone is on duty
during patrols. The “B” was good for perhaps 900 miles, the “K” for well
over twice that distance.
Wartime ships had to keep the control car well away from the bag to
prevent sparks from igniting the hydrogen gas. A windshield was the
pilot’s only protection from the elements. Modern ships, using
non-inflammable helium, have closed cars, streamlined into the bag,
ample room for navigation and radio, sleeping and eating quarters, even
a photographic dark room, can be heated and noise-proofed.
Early airships were pulled down and held by a large ground crew, a
pneumatic bumper bag on the car cushioning its landing. Today’s ships
land on a swiveled wheel, roll up to a mast—or taxi off across the
airport like an airplane and take off.
These, however, are merely flight factors. More important is it that the
wartime blimp was to a large extent hangar-bound. It could go no further
from its base than it could safely return before its fuel was exhausted.
Today’s ships are expeditionary craft, can go almost anywhere, stay as
long as they want. They are no longer land-bound, can be refueled and
reserviced at sea. They are much safer, rank high in this respect among
all carriers whether on land, sea or in the air.
Three independent lines of study contributed to these results, those of
the Army, Navy and Goodyear, each free to follow its own ideas, to
observe results found by the others, adopt them, use them as starting
points for further developments, or discard them.
The improvements were achieved in a relatively short period. The army
started in after the war and carried on a continuing program till 1932.
The Navy, absorbed in its rigid airships, did not get into non-rigids
till the early 1930’s. Goodyear built the Pilgrim in 1925 but its
development program really began with the blimp fleet in 1929.
Noteworthy improvement was found during this period in materials,
structure, design, engines and radio communication, with outstanding
advances along three major lines.
First was increased safety, permitted by helium gas. Wartime airships
used hydrogen because it was all they had, had to develop what
protection they could against fire through construction devices and
operating technique. Hydrogen was not only inflammable, but under
certain conditions explosive. World War pilots had to fly their hydrogen
ships through thunder and lightning storms, dodge inflammatory bullets
if they could. Zeppelin sailors wore felt shoes, with no nails to create
a spark, used frogs for buttons, had to guard against static.
It was a fortunate thing for the airship world when a gas was found in
1907 in Dexter, Kansas, which would not burn. Curious scientists, asking
why, found it was helium, a gas previously identified (in 1869) only in
the rays of the sun. Helium gas is inert, refusing to combine with any
other element, does not deteriorate metal or fabric. It was not much
heavier than hydrogen, the lightest of all gases, so proved a welcome
gift to lighter-than-air.
For some reason, not explained except on the theory that Providence
takes special interest in America, helium has been found in quantity
only in this country. It is a component, present to the extent of two or
three percent in certain natural gas, though ranging as high as eight or
ten percent in favored areas. It can be separated by compression and
liquefaction from the natural gas,—which is that much improved by the
removal of the non-inflammable content.
The world’s chief known supply of helium lies in certain sections of
Texas, Kansas, Colorado and Utah. More important, United States is the
only country having great pipe lines, can distribute natural gas from
Texas to cities as far away as Kansas City, St. Louis and Chicago.
Without such a market operators would have to separate and release the
95% of natural gas to get the 5% of helium, and costs would be still
higher.
Helium is perhaps the most useful of the few natural monopolies given to
this country.
It was only toward the end of the World War, however, that Army
engineers worked out a process of separating helium from natural gas. A
plant was built at Fort Worth and the first cylinders of helium had
reached New Orleans ready for shipment to France to inflate observation
balloons when the Armistice was signed.
Army, Navy and Bureau of Mine engineers worked thereafter to increase
production and cut costs, but as late as 1925 Will Rogers called
attention to the fact that the Navy had not been able to get enough
helium to supply both the Shenandoah and the Los Angeles at the same
time. If one was using the helium the other had to stay home. Two ships,
and only one set of helium, he commented.
The use of helium cut the casualty list on the Shenandoah, would have
saved the Hindenburg. Non-rigid airships have had no fire or explosive
accidents since helium came into use as the lifting gas.
It was the loss by a hydrogen fire of the Italian-built Roma, after it
struck a high tension line at Langley Field in February, 1922, which
fixed the policy of “helium only” for U. S. Army and Navy airships. The
Army’s C-7 was the first airship to use helium. In building the Pilgrim
in 1925, Goodyear followed the same policy—even though it had to pay
$125 a thousand cubic feet for helium while it could have obtained
hydrogen for $5 per thousand.
Further improvements and increasing volume of production brought the
cost down in time from $125 to less than $20, and helium expense became
relatively unimportant in providing safety for Goodyear’s airship
operations.
Important too during this period was the Army’s development of tank cars
for transporting helium. A large item of helium expense was freight, the
cost of hauling 130 pound metal containers which held 170 to 200 cu. ft.
of the gas. It took 250 such containers to inflate Goodyear’s smallest
ship, the Pilgrim. The tank cars hold 200,000 cu. ft. of gas, almost
enough to inflate two Goodyear airships.
Experiments with specially woven fabric and the use of synthetic rubber
cut down the losses resulting from diffusion, and where formerly it was
necessary to remove the helium and purify it every six months, diffusion
losses were cut to one or two per cent a month, with purification needed
only every other year.
In addition to increasing safety, helium permitted improvements in
airship design. The wartime craft had its control cars suspended by
cables from finger patches cemented to the outside of the bag. But with
helium ships the car could be built into the bag, attached by an
internal catenary suspension system to the top of the gas section. Each
exposed suspension cable, no matter how small, creates parasitic
resistance from the air, so that the removal of yards of steel and rope
had the result of increasing the speed of the ship with the same
horsepower.
The second set of major improvements centers around the mooring mast.
The mooring mast idea was not new. The British had built the first ones
during the World War for its large rigid ships, found that a ship
attached to it would swing easily, like a weather vane, continuing to
point into the wind, and that a well streamlined ship would hold
securely even in winds of great velocity.
When Alfred E. Smith ordered a mooring mast built on top the Empire
State building, it was with the assurance from his engineers that even
with the tugging of the 150-ton Graf Zeppelin, the strain would be
little more than the normal push of the wind against the building
itself, that the added stresses would be negligible.
The Germans had had little occasion to use mooring masts.
Friedrichshafen, where most of the Zeppelins were built, lay in a
natural bowl, well protected from the winds, and ships could take off
and land, be walked in or out of the hangar with little risk from the
weather.
Lakehurst, on the other hand, lay in an exposed position, in the path of
coast-wise storms, a frequent battle-ground between onshore winds from
the ocean and storms breaking over the mountains from the west. A study
made later to determine bases for projected American passenger
operations showed that of weather conditions prevailing between Boston
and the Virginia Cape, those at Lakehurst were almost the most
unfavorable.
[Illustration: Four stages in the evolution of the mooring mast. At
the outset large ground crews held the ship on the ground.]
[Illustration: Then a stub mast was placed atop a truck, to hold the
ship on the ground, maneuver it in or out of the dock.]
[Illustration: A high mast, made in sections, can be erected
anywhere, anchored by guy wires, holds the airship securely against
winds of gale force.]
[Illustration: The little brother of the “Iron Horse”, which will
receive the largest of the new Navy blimps, maneuver them on the
field.]
People knew little about airship operating when the Navy base was moved
from Pensacola to Lakehurst on a waste site in the Jersey pine lands
which the Army no longer needed after the war as a proving ground for
its artillery.
This defect proved an advantage. The Navy was forced by the very nature
of things to concentrate on a problem which had been no problem to
Doctor Eckener and his associates. At the urging of Admiral Moffett,
Commander Garland Fulton, Lieutenant Commander C. E. Rosendahl and
others, Navy engineers built a high mast, 180 feet tall, following
British practice, with a service elevator inside, then tackled the
problem of keeping the ship on even keel against up and down gusts.
Since the wind does not come out of the ground, a low mast was
suggested, half the height of the ship, so that when anchored the ship
would all but rest on the ground. The Navy was working on this when an
incident happened to strengthen the argument.
The co-incidence of a wind shift, and rising temperatures one afternoon
as the Los Angeles was resting comfortably at anchorage, started the
tail rising, and it continued to rise till it reached almost 90 degrees.
Then the ship turned gently on its swivel, and descended easily on the
other side, with no more damage than some broken china in the galley.
Still a 700-foot airship has no business doing head-stands, so the low
mast development was rushed through. It proved successful.
The next step was to make the low mast mobile, so that it could not only
hold the ship on the ground but take it in and out of the hangar. First
of these was Lakehurst’s famous “iron horse,” a giant motor-driven
tripod, which rolled out on the airport, hauling incoming ships into the
hangar, took advantage of daylight calms to take ships out into the
field ahead of time so as to be ready to leave on schedule.
On the Graf Zeppelin’s trip around the world in 1929, hangars were
available for fueling stops at Lakehurst, Friedrichshafen, and curiously
enough in Japan, a German shed turned over to the Nipponese after the
1918 Armistice, having been re-erected at Tokio. There was none however
on the American West Coast to house the ship after its long trip across
the Pacific. So the Navy, under direction of Lieutenant Commander T. G.
W. Settle, hauled a mast up to Los Angeles from San Diego (it had been
erected there for the Shenandoah’s flight around the rim of the country
in 1923) anchored it with guy wires. It served the purpose perfectly.
The Germans, skeptical at first, became convinced of the value of the
mast, themselves erected masts at Frankfort, and Seville, at Pernambuco
and Rio de Janiero, used them as terminals.
Once the masting technique had been worked out, the Graf Zeppelin and
the Hindenburg, in the years 1930-6, made a record of regularity which
no other vehicle of transportation has approached. They took off at
times over the ocean for Europe when all other aircraft in the area was
grounded, when the fog hid the entire top half of the ship, and the ship
disappeared into the fog within a few seconds after the “Up Ship” signal
was given. What few delays appear on the record were due to waiting for
connecting airplanes to arrive with the latest European mail for the
Americas.
So far the use of masts had been entirely a matter for the large rigid
airships. The Army did the first development work on high and low masts
for its smaller ships at Scott Field, as well as a landing wheel for
them to ride on. A situation at Akron started experimentation along a
different line. At Goodyear’s Wingfoot Lake Field, Mr. Litchfield
frowned over the expense of having a considerable crew on hand to land
and launch the blimps, with little to do after the ship was in the air.
To an Army or Navy post, with plenty of men in training, this surplus of
men was no difficulty, but any private corporation operating passenger
airship lines would find the expense burdensome.
[Illustration: The Navy L-2, one of the first ships under the
expanded program, lands at Wingfoot Lake, Akron, is walked to the
mooring mast.]
[Illustration: Close-up view of engine and cowling, and swiveled
landing wheel.]
[Illustration: With a drogue or sea anchor to hold the airship
steady, supplies or personnel may be taken aboard at sea. (U. S.
Navy photo)]
[Illustration: A newly-hatched airship breaks its shell at Akron,
will try its wings then join the Navy.]
He put the question to his men in 1930, offering cash prizes for the
best solution. Out of many ideas, one clear-cut line of progress
appeared. This was to make the ground crew truck a maneuvering base,
with a mast on top, which could be folded down when not in use. The
truck then could not only hold the ship on the ground, but guide it in
and out of the hangar with more security than by using a large number of
men. Extra wheels mounted on outriggers kept the truck from being turned
over by side gusts. In succeeding years the ground crew truck became a
traveling mooring point which could follow the ship across country, give
it anchorage when night fell, and at the same time act as a traveling
supply depot, machine shop, radio cabin, and crew quarters.
A portable mast, built in sections, high enough for ships to mast at the
nose, was the next step. It could be set up on an hour’s notice,
anchored by guy wires and screw stakes for more extended operations.
Gradually the airship became independent of the hangar, came to use it
only for overhaul and the purification of its helium gas. The blimp
could be fueled and serviced completely in the open.
Lacking a dock in San Francisco, at the time of the Exposition in 1939,
the Goodyear blimp Volunteer moved up from Los Angeles, based on a mast
for five months. The only time it sought shelter was when a splinter
from the propeller pierced the bag, causing a leak. The ship flew 60
miles down the bay to the Navy base at Sunnyvale, like a boy coming in
from play to have a splinter removed from his finger, went back again,
didn’t even stay over night.
In the winter of 1940-41 the “Reliance” which had been spending its
winters in Miami, using a wartime Navy hangar which the city had moved
up from Key West, found that building commandeered for defense work. So
a mast was set up on the Causeway, and the ship operated with no other
home than that for six months, saw no shelter from the time it left
Wingfoot Lake in early December till it returned at the end of May.
The Navy had a different problem as it moved into the non-rigid picture
in the early 1930’s. Its problem was only incidentally to operate away
from its base at Lakehurst. Ships were getting larger in size, and masts
were needed where they could be moored outdoors, or taken in and out of
the hangar. The solution was a smaller replica of the rigid airship’s
“Iron Horse” except that it moved on large rubber tires, and was towed
in and out by tractor, rather than carrying its own power plant.
A portable mast was also developed for the Navy blimps, with a special
car to haul it around. This mast could be sent to Parris Island or some
point in New England, ahead of time, set up and used as a temporary base
for radio calibrating or other missions.
Navy ships basing at Lakehurst have operated for weeks at a time along
the coast as far north as Bath, Maine, and as far south as the
Carolinas, with a portable mast as headquarters.
Utilization of the mast principle by non-rigid airships not only greatly
increased their radius of operation, and cut down landing crews, but
increased the number of operating days per month.
Pilots of early airplanes used to go out on the airport, hold up a
handkerchief, and if it fluttered, conclude it was too windy to fly. So
early airship pilots, with anemometers on the roof of the hangar and at
points over the field, judged it too risky to take the ships out if the
wind was higher than four or five miles an hour, and then only if it was
down-hangar in direction.
Modern airships lose few flying days because it is too windy to go out.
Under war conditions, when risks must be taken, which need not be taken
for passenger or training flights, very few days would be wasted if
there is military necessity for it.
Navy non-rigids miss few rendezvous with the fleet in exercises out of
Lakehurst, regardless of the weather outside.
If the portable mast revolutionized airship operations over land,
experiments started by the Navy in 1938-39, largely under the direction
of Lt. C. S. Rounds, promise to be just as important in over-water
operations. These showed that the airship could pick up ballast from the
ocean, could get fuel from a passing ship, could change crews at sea.
Ballast is important to a vehicle which growing continuously lighter as
it uses up fuel, must still be kept in equilibrium. Transoceanic
Zeppelins, using hydrogen, had to fly high enough to “blow off” the
surplus gas once or twice during a trip to compensate for the ship
growing lighter. But hydrogen was cheap, and could be manufactured as
needed. American ships could not afford to waste helium, which was a
natural resource. Army and Navy engineers had worked on this, and
equipment developed for the Akron and Macon to condense the gases from
the burned fuel was able to recover more than 100 pounds of water
ballast for every 100 pounds of fuel used.
The blimps didn’t use these since they ordinarily would not be out for
more than a day at a time, still a ready source of ballast would make it
unnecessary to valve helium on long flights.
Ironically enough a whole ocean full of ballast lay below seagoing
airships, but no practical method had been devised to take the sea water
aboard until the Navy tackled the problem in 1938.
That problem may be visualized in the obvious difficulty of maintaining
physical contact between an airship and a surface ship. The two move in
different media, one influenced mostly by the waves, the other mostly by
the wind. The surface ship is moving up and down, the airship subject to
gusts which might break the contact or thrust it violently against the
masts or superstructure of the surface ship. Servicing has been done
under favorable circumstances, but could not be relied on as standard
procedure.
The solution reached was this. The pilot swings his ship down to within
100 or 150 feet of the water, lowers a hose with a small bronze scoop,
not much wider than the hose, so as to lessen the drag.
Twenty-five feet up from the scoop is a streamlined cylinder, blimp
shaped, carrying a small electric pump. This cylinder, nicknamed the
“fish”, has tail fins to keep it from spinning, and skims along the
surface or jumps out like a porpoise, but the scoop is far enough behind
and heavy enough to trail easily beneath the surface, stays directly in
the ship’s wake, continues without interruption to pick up ballast for
the airship above.
The whole gear weighs slightly more than 100 pounds, can pick up water
at cruising speed, can function in rough water or smooth. The Navy J-4,
chiefly used in these experiments, normally consumes 500 pounds of fuel
in five hours of flying at cruising speed. It was able to pick up that
much water ballast in seven minutes.
The next step was to enable an airship to obtain fuel from a tanker or
other ship without physical contact or advance arrangements—even from a
passing merchantman. The pilot asks by radio or voice whether the
surface ship can spare some gasoline, and on an affirmative answer,
lowers or drops on his deck two rubberized fabric spheres connected to
each other by 14 feet of rope—also a note of instructions. The smaller
sphere is an ordinary air-filled buoy, the larger, about three feet in
diameter when filled, is the fuel bag. The surface ship fills the fuel
bag, then drops both bags overboard, being careful only that they do not
get tangled up. Then the airship flies over the two bags, drops a hook
between them, hauls away, pumps the gasoline into its tanks.
The third device permits an airship to anchor in the open sea near a
surface ship to transfer crews or take on fuel and supplies. The anchor
is a cone-shaped rubberized fabric bag, ten feet long, with a diameter
of 2½ feet at the top. It is lowered 50 feet below the airship by two
cables connected with each other by rungs to form a ladder. Half of the
cables’ length is made up of heavy exerciser cord to dampen the effect
of wave movements. On top the cone is a wire mesh cover which allows the
water to pass through, and is strong enough to act as a platform,
supporting a man.
As the cone fills up the airship drops ballast till its “mooring mast”
is half submerged. The principle of the drag rope comes into play—if the
airship starts to rise it finds itself lifting an increasingly heavier
load, counteracting the rising tendency. If it starts to settle down
toward the water, the load is correspondingly lessened and the ship
grows lighter. The result is that the airship is held highly stable,
even in a rough sea. The surface ship then sends a small boat alongside
and dispatches the relief crew members or supplies, them up and down the
ladder, or uses a winch, the platform atop the anchor serving as the
operating base. This system also permits the moving of a sick passenger
ashore, or the rescue of a man overboard.
When the airship is ready to leave its anchorage, the cone is tipped by
a line attached to the bottom, spilling the water, and hauled aboard.
The servicing ship need carry no special equipment. The weight of cone
and ladder is negligible.
By being able to pick up ballast and borrow fuel from a passing ship,
(neither airship nor surface ship need slow down for the fuel exchange
if going in the same direction) the airship greatly increases its radius
of operations.
The advantage of being able to change crews at sea may not be quite as
clear. This, however, grows out of the fact that today’s non-rigid
airship has greater endurance than the crew which flies it. An
anti-submarine, anti-mine patrol calls for constant alertness. Reduction
of vibration and noise, the use of closed cars instead of open cockpits
has lessened fatigue, enabling men to remain on duty over longer periods
than before. But obviously there are limits.
The Navy is conservative in estimating how long its new “K” ships may
stay out without refueling. Weather and the nature of the mission will
have some bearing on that, but if we assume a cruise of 48, 60 or even
72 hours which might be done under favorable conditions and idling the
motors, we still cannot expect a crew of men to remain vigilant and
alert for that length of time.
Extra men for relief watches can be carried only at the expense of the
fuel load. However, if a fresh crew could be sent aboard every 12 hours
from a nearby surface ship, along with fuel, ballast and supplies, the
blimps might operate for extended periods.
No blimps have done this. The fleet might see no need for them to go out
for long periods. However, the possibility has been established, and
might be useful in the emergencies of war, or accident. While the
primary usefulness of the blimp lies in the coastal waters, it can go to
sea if needed—and stay out—can be used in convoy work or as a listening
post.
Other improvements were uncovered during the experiments. A sea anchor
or drogue was devised to enable the airship to “lay to” for extended
periods, without consuming fuel, in case it wishes to use its listening
devices against submarines, make repairs or for other purposes. Plans
have been worked out for landing on the water in quiet bays in calm
weather, utilizing flotation gear, or a three-point mooring to ordinary
mud anchors—facilitating servicing from nearby Coast Guard stations.
Perhaps a significant thing about these experiments is that the
principles seem applicable as well to rigid airships. The ability to
pick up ballast in flight may well eliminate the necessity for
ballast-recovery devices, with a substantial saving in cost, and an
impressive saving in weight.
By eliminating the heavy condensers, and translating that weight-saving
into fuel, it is estimated that the range of a ship of the Los Angeles
size could be increased by 20 percent and ships of the Akron-Macon size
by 15 percent, in the last case amounting to 1,250 miles of additional
cruising radius.
A trans-oceanic passenger airship could start out with virtually no
water ballast at all except a minimum amount for maneuvering, use its
fuel supply as ballast and pick up sea water as needed. This could be
done at 500 feet elevation, at the rate of 80 gallons a minute, using a
30 horsepower motor, could be done in half an hour a day. The ship need
not slow down materially while doing this.
Application of this principle to military airships of the rigid type
might be still more significant. The chief use for the rigid airship in
war would seem to be as a high speed airplane carrier, whose planes
would increase many fold its own reconnaissance range, and would be
expected also to do the major part of what fighting became necessary in
case of enemy contact. The airship itself in that situation would put
more dependence on its speed of retreat and its ability to seek cover in
clouds as the submarine does beneath the surface, than on its own
machine guns and cannons.
One thing brought urgently home to us in the first weeks of the present
war is that oceans are wide, and that the movements of even a huge enemy
fleet are difficult to discover in those endless expanses of water.
Large military airships of five or ten million cubic feet helium
capacity might prove exceedingly useful, if they were able to operate
away from their base for weeks or even months at a time, and they might
be able to do this by utilizing devices similar to those developed for
smaller non-rigids, resting on the sea in calm waters, mooring to
anchored masts they could lower into the water, picking up fuel from
tankers, getting supplies from neighboring ships—in addition to what was
carried to them from the fleet by their own planes.