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(Narrator) In Australia today
30,000 route miles of airlines are in continuous operation
and air travel is accepted as part of our everyday life.
The safety factor is still however a much-discussed topic of travellers.
Probably because first they are not aware that on a mileage basis
air travel is safer than road travel
and secondly they have not been fully informed of the efficient organisation
technical skill and scientific endeavour which has and is being applied
to ensure freedom from mishaps.
Operational value is the paramount consideration in the design of the
aircraft for the Royal Australian Air Force
but the safety of the air crew
is provided for to the maximum possible extent.
Enormous loads are imposed on the wings by violent manoeuvres
an adequate strength is insured by careful design
and the most searching tests so that accidents such as this shall not happen.
To investigate problems associated with aircraft and to prevent such accidents
the Council for Scientific and Industrial Research
has established the Division of Aeronautics
at Fishermans Bend, Melbourne.
In order to give a clear idea of the methods used in the laboratory
for applying test loads to aircraft wings
let us first use this model
to demonstrate the method of investigating the strength of wings.
The loads in normal flight act upwards on the wing surfaces
but with a large wing it's often more convenient in the laboratory to turn the wing
upside down.
To support it centrally from the test frame at two points
and to apply the loads downwards.
Loading frames bearing on specified positions
are placed around the wing.
To produce the desired loading distribution
the frames are connected by a lever system and then by cables
to hydraulic loading units bolted to the floor,
which is designed to resist the maximum test load.
The loading units are worked by oil pressure.
The oil being supplied through a common pipeline
from a single pumping unit.
The pressure and therefore the load can easily be controlled by one operator.
Now that we have the idea,
let us follow in some detail the procedure required for testing
an actual wing in the laboratory.
At the end of World War Two,
Australia was producing large numbers of the renowned Mosquito aircraft
and it's fitting that we tell of the testing of the wings
of these famous fighter bombers.
The wings are tested in a test bay
having a reinforced concrete floor 120 feet in length
and capable of withstanding a uniformly distributed load
of 300 tons.
However, before the wings are placed in test
to determine their strength and confirmation to airworthiness requirements
much preliminary planning must be carried out,
a considerable portion of it in the drafting room.
The first thing is to consider the design of the wing.
Then to determine the test loads
and finally to plan the loading system.
The laboratory workshops
are fully equipped to manufacture the wide range
of specialised testing equipment required.
A good example of the precision work necessary
is the manufacturer of the hydraulic loading jacks,
the rams of which must be ground to very close tolerances.
The jacks are of the packless ram type
and the sliding parts must have a very high surface finish
to eliminate friction
because the actual test loads applied to the wing
are determined by measuring the oil pressure in the hydraulic system.
Meanwhile the wing has been prepared for testing.
It is turned upside down.
This position being a convenient one
in that the simulated air loads may be applied downwards
by the loading units attached to the test floor.
In interpreting the following sequence,
the inverted position must be borne in mind.
As part of the plan method to obtain
correct load distribution between the fuselage and wing,
a dummy fuselage is attached.
The tank bay covers are part of the stress structure
and a carefully screwed into position.
While still on trestles, the loading stations are marked out
in accordance with the loading plan.
After as much work as convenient has been carried out with the wing at ground level
it is hoisted up and moved into the test position.
This wing is one of a series of Mosquito wings being tested
and therefore the lower sections of the loading frames,
by means of which the loads will be applied
are already in approximate position above the hydraulic jacks.
Great care is taken to ensure that no damage is done to the wing.
This is particularly important because the Mosquito wing derives much of its strength
from the outer skin of plywood.
There is a double skin on the compression surface
and a single skin on the tension surface.
To the center section at the wing
steel structures are attached representing the front
and rear fuselage section.
As mentioned earlier
these dummies structures are necessary to ensure the correct loading conditions
at the wing fuselage joints.
The front and rear sections are connected by steel cross members
and the whole structure suspended from a rigid test frame
by two stud links.
One at the front and one at the rear.
The wing and its dummy fuselage are therefore
free to roll about the central cord wise axis.
In order to represent the engine loads
it is necessary to apply loads to the engine mounts.
These loads are approximately opposite in direction to the air loads
therefore in the inverted test position
the engine loads must be applied upwards.
The engine mounting
is connected by a ball and socket joint with a stout steel column.
The column transmits the upward load from a bank of five hydraulic jacks.
On the previously marked positions
pivoted loading blocks covered with thick felt are placed along the wing.
One set on a front spar and one set on the rear spar.
On these blocks the loading frames will rest.
The frames for applying the air loads are now placed
in the approximately correct positions
along the span of both port and starboard sides.
The frames may be put on singularly
or if the wing under test is one of a series of the same type of wing,
in a group which is more convenient and saves considerable time.
The lower part of each loading frame is then raised
and attached to the opposite member.
These lower sections are not in direct contact with the wing
but transmit the load to the upper frames by front and rear connections.
The testing equipment applies loads to these lower beams by a lever system.
The position of the lever connecting links is carefully adjusted
to obtain a correct test load distribution from frame to frame.
The load is applied to the lever system by flexible steel cables
connected to hydraulic jacks
some of which we saw being manufactured in the workshops
The jacks are actuated by oil supplied by pumps
capable of delivering at pressures as high as 3,000 pounds per square inch.
The loading units are bolted to the specially constructed test floor.
As the wing supports over its span the weight of the test rig
as well as the superimposed load,
the rig is weighed and the required allowances made.
It is usually necessary then to add weights to parts of the rig
so that the rig weight everywhere will be a uniformed percentage
of the design ultimate test load.
Deflection of the wing during the test are measured by fine steel wires
attached at desired positions along both front and rear spars.
The wires pass around pulleys clamped to the floor
and then over a defection measuring scale
attached to an indicator board.
One board being at each wing tip.
In this way deflection of the wing during the test
can be measured quickly and accurately.
As the wing is suspended at only two points
it will, if the loading is slightly asymmetrical,
tend to roll to the most highly loaded side.
It is therefore necessary to take measurements
at the center of the wing of the amount of roll
in order to make corrections to the deflection readings.
A final checkup is now made of the equipment.
The loading frames and their positions are examined.
As are the hydraulic jacks and associated cables and levers,
the pumping units and all the other many parts of the equipment.
Slings are attached to the overhead electric hoists
in order to catch the fractured wing section when ultimate failure occurs.
The wing is now ready for test.
The first phase of the test is to apply a proof test load.
The oil pumps are started
and the load maintainer valve opened.
The load maintainer controls the supply of oil at constant pressure
to the two outer jacks
which apply a balancing load to each engine mount
Sufficient balancing pressure is now applied to all the loading jacks
to take out the slack in the rig.
The jacks are so weighted that all float at the same pressure.
Unlike the outer engine jacks, which exert a constant force throughout the test
the inner engine jacks apply the varying test load on the engine mounts.
The pump operator calls for all the recording equipment to be set at zero.
And he sets his oil pressure gauge at fifty pounds per square inch
which is the calibrated pressure at which the jacks float.
The zero readings of the dial indicators at the wing's centre are recorded.
The wing deflection indicators
are also set at zero.
The first loading is to be 25 percent of the design ultimate load.
The load is gradually applied in planned increments.
At the previously directed levels in the loading
the pump operator holds the hydraulic pressure constant
calls the loading, in this case 25 percent,
and directs that all deflection readings be recorded.
The deflection markers give a direct reading of the deflection at the wing
at specified positions along its whole length.
The dial indicators at the wing's centre
record any slight roll of the wing to either side.
To check that the hydraulic system and levers are
transmitting the calculated load, proving loops
and also strain gauge links have been incorporated.
After all readings have been noted
the load is increased in set stages
until the load has been built up to the test proof load.
The test proof load which is arbitrarily selected and specified by
the Air Worthiness Authority
must be applied for at least one minute
during and after which the wing must remain in an airworthy condition.
All the Mosquito wings used in these particular investigation
were proof loaded to 90 percent of the ultimate design load.
Having withstood the first proof loading
the wing is now subjected to repeated loadings to 90 percent.
All pumps are switched on.
Failure might occur from fatigue
or if the wing does not fail under a specified number of loadings
its ultimate static strength may have been influenced.
Repeated load testing is in its infancy.
The staff at the Division of Aeronautics
being the first to carry out such work on large aircraft structures.
In this particular case the peak load of each cycle is over 50 tons.
No small load to be applied and released up to six times per minute.
The repeated load control permits the load to cycle between any desired limits.
A counter records the number of cycles.
The wing has now withstood 5,000 repeated loadings
without any apparent damage
The final test,
the determination of the ultimate strength of the wing,
necessitates testing to destruction.
The load is to be applied in scale increments
up to 90 percent of the design ultimate load
and then gradually increased until ultimate failure occurs.
This crucial test of the wing's strength
is witnessed by representatives of the organisation for whom the test is being
carried out,
in this case the Royal Australian Air Force
and by the senior officers of the Division of Aeronautics.
At 90 percent, to which point the wing has previously been proof loaded
the pump operator directs the recorders to make readings.
Then to remove the dial gauges from the centre of the wing
and finally to stand clear.
The load will now be gradually increased until failure occurs.
The loading has increased to 100 percent of design ultimate load.
From previous experience it's considered the failure will be in this area.
[Sounds of pumps]
[Sound of splintering wing]
The failure is typical of this type of wing.
The ultimate strength of the wing was in excess of the designed ultimate load.
It represented a force of approximately nine times gravity
acting on a fully loaded Mosquito aircraft weighing over eight tons.
Upon removal of the loading frames the collapsed wing is more clearly revealed.
As part of the complete record of the test the various failures are photographed
and some of these photographs used to illustrate reports.
To investigate the cause of failure
it's necessary to cut the wing up for thorough examination.
Material test coupons are also removed
and from these the laboratory workshops prepare test specimens.
In the Materials Strength Testing Laboratory
these test specimen are examined
to determine the basic strength properties of the material built into the wing.
Routine specification tests are made of impact strength or toughness.
Tensile strength is also an important characteristic.
As is strength in compression.
With wooden constructions
the moisture content of the specimens is an important factor.
Besides all these routine tests
the laboratory is well equipped for the numerous non-standard tests
often required in research work.
Finally, having obtained all the test results,
it is necessary to analyse them and prepare a report.
This report covers the wing tested
but similar reports are issued covering the numerous applied and fundamental problems
associated with the aircraft industry
and carried out by the Division.
The design of faster and more efficient aircraft
and the safety and comfort of all who travel by air
are dependent to a considerable extent upon aeronautical research
and the wide field of general scientific research
being carried out in Australian and other laboratories
throughout the world.
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