Note: Descriptions are shown in the official language in which they were submitted.
106141~
The present invention relates to means enabling the escape of personnel from
vehioles and craft, particularly aircraft, and especially through canopies and
windscreens.
The problem of escape from modern high speed aircraft is generally solved by the
use of an ejection seat which projects the airman out of the aircraft at
high speed, thus avoiding impact with other parts of the fuselage or flying
debris. In many cases there is no time for the canopy above the head of
the airman to be opened in order to facilitate such escape and although, in
some cases~ the canopy may be opened or removed bodily by mechanisms similar
to that used for the ejection seat, even this may not be sufficiently rapid.
Appreciable time can be saved if, instead of removing the canopy as a whole,
an opening is cut in it through which the airman can pass. This in itself
presents a further problem, particularly since the tendency is for canopies
to be strengthened so as to add to the overall safety of flight and to over-
come hazards such as bird strike and so forth~ Such attempts as have been
made so far in this direction have involved the use of explosive cord but
this has been bulky and has consequently restricted visibility,has entailed
in operation spattering of the person with undesirable substances, and is
difficult of testing, over a long term~ that a particular system is still
viable.
According to the present irvention a panel breaking system comprises a fusible
electrical conductor arranged in intimate contact with the material of the
panel in a geometric pattern related to the area of the required opening and
connected to a source of electric power capable of producing a high energy
pulse sufficient to produce fuzing of the conductor.
It will be apprPciated that the panel in this specification is frangible by
106~4~7
the means described and will normally therefore be made of a plastics materic~
of low electrical conductivity. The term "panel" includes cockpit c~n~pies c~nd
windscreens inter alia. The invention is particularly suitable for use with
polymethyl methacrylate and polycarbonate canopies.
The effect of such a pulse of current in an emergency, eg under the control
of the same mechanism as used to operate the ejection seat, is to produce
rupture of the conductor with consequent dissipation of energy and productior
of an explosive shock sufficient to crack the material of the panel to form
the required opening. In addition to the explosive shock, a degree of thermal
shock is simultaneously experienced and the crack is propagated by mechanical
shock/flexure waves through the material This can be carried out under much
more closely controlled conditions than by the use of explosive cord and,
moreover, an improvement in visibility results owing to the small cross-
section of conductor required and the fact that the conductor can be placed
at points on or in a canopy or windscreen where it does not obstruct the view.
The conductor is preferably embedded within the thickness of the panel during
manufacture since this enables the most efficient tran~mission of the released
energy into the material of the panel. This may be achieved either by placing
the conductor between the layers of the laminated structure or by moulding
the conductor directly into the panel. The conductor may also be embedded
subsequent to manufacture by locating it in a groove or channel in the sur-
face of the panel and subsequently filling this groove or channel.
~he fus;ble conductor may be in the form of a wire or tape and the effect
may be enhanced by the inclusion of localised stress raisers~ that is to
say regions which rupture before the remainder of the conductor under high
power conditions, eg sharp bends in the conductor or short lengths of
reduced cros6-section or a combination of both or the use of discrete
1~6~41~
conductor elements in contact at the stress raiser points. Small constric-
tions along the length of the conductor have the effect of producing highly
localised dissipation of energy at the location of such constrictions.
Cracks can be propagated over greater distances in the panel material~ parti-
cularly when using a high energy pulse for shattering the material of the
panel, by using a V ff haped bend in the conductor. This is because the plasma
energy in the arc formed upon disruption of the conductor is directed along
the median line of the angle of the bend in the conductor. The effect can
be further enhanced by placing a constriction at the apex of the V.
Since the use of stress raisers, particularly those of V form can be used
to direct cracks, it follows that a system of fusable elements~ each having
one or more stress raisers can be disposed to create a desired mode of
shattering. In a typical aircraft canopy context there is indeed a desired
mode of cracking, this is that above the head and shoulders of the ejecting
escaper the broken pieces and hence their momentum should be small enough
not significantly to damage the person or vital equipment, while to the
sides larger pieces can be tolerated. A system of fusable elements in
accordance with the invention can readily be arranged to effect this with-
out being visibly obstructive.
While the panel breaking means may merely so cra~e the canopy that the
person may be safely ejected through it, it is usually preferable for it
to be arranged completely to shatter the panel in the mode described in
the previous paragraph. This is best accomplished by a combination of
strategic siting of elements as described above with a source of adequate
energy.
Two types of escape often need to be catered for in a canopy breaking system.
One is the ejection described above; the other is emergency egress which
1~61417
occurs when an aircraft has crash landed and the normal canopy opening meanc
is inoperable or too slow of operation. This latter mode can be catered fo
by canopy removal means, that is by means in accordance with the invention
which separate at least most of the canopy from its frame, without necessa-
rily shattering it.
A canopy breaking system may thus comprise both canopy shattering means and
canopy removal means in accordance with the invention. These two sub-
systems may be ganged for either purpose, ie upon ejection or upon emergency
egress, both will operate,
Operation of the canopy shattering means will normally be one event in a
sequence initiated when the escaper selects to eject, thcugh there may be
an additional fail safe microswitch operated by the passage of an ejector
seat. The circuit for a canopy removal system may include two manual
switches in parallel, one for operation by the escaper and the other~
perhaps beneath a removable or frangible ezterior panel, for operation from
outside.
Of course either sub-system may be connected to act as an emergency or
fail safe back-up for the other. Alternatively it may be preferred to use
an explosive cord system for the canopy removal means, arranged to be opera-
ted by manual switches internally and externally and by~afail safe switoh
associated with the canopy shattering system.
The energy required is predetermined in accordance with the type of opera-
tion required and also the thickness and material of the panel. The other
variables which affect the required energy are the dimensions of the
10614~7
conductor (length and cross-seotional area) and also any variations in the
geometry of the pattern. As a typical experimental example, a 6 inch square
sample of either stretched aorylic or oast aorylic canopy material of thick-
ness between 10 and 20 mm was shàttered by the use of a conductor consist-
ing of 28 swg tin wire of ~- inches length in the form of an equilateral
triangle embedded in the centre of the material using a stored energy of
500 Joules delivered in a time below 1 millisecond. Using nichrome wire
in the same configuration and under the same conditions requires 1 kJ but
delivered at half the rate to produce the same shattering effect.
These differences are the result of differences in the physical constants
of the conductor materials, which may include metals and alloys and even
carbon fibres. The particular physical constant of import in this case is
the Joule integral ( J i dt) for melting. This is illustrated in the
accompan~ing Figure 1 for a variety of materials as a function of the cross-
sectional area of the conductor used to initiate the disoharge. The data
represented in this graph are important in deciding the appropriate dimen-
sion of the cross section of the element at the point where it is desired
to disintegrate it. It can be readily seen from the graph that a reduction
in cross section requires a much lower value of Joule integral, because
the Joule integral is seen to be proportional to the square of the cross-
sectional area, as is well known when applied in the field of electric
fuses. It is for this reason that the small constrictions referred to above
have the effect of producing highly localised dissipation of energy.
A variety of types of electrical power source are available capable of
delivering the necessary amount of energy in the necessary short time
interval. For example, sources using capaoitively stored energy or induc-
tively stored energy are suitable as are also short time rated generators
1061417
and thermal batteries. A very economical form of power souroe con~ists of
capacitively stored energy matched to an inductance which i9 excited by the
flow of ener~y from the capacitor during the melting time of the element
chosen~ this form of course being particularly useful in creating the
plasma projection in a Y formed element. Such melting time is determined
by the data from the graph forming the drawing and a function of the capaci-
tance~ inductance and resistance employed. Electrolytic or ceramic capacito:s-
may be used, thus minimising the weight and bulk of the circuitry and reducing
the required supply voltage.
The capacitors are preferably connected in series across supply~ as this
will minimise the effect of a faulty capacitor. The fusable elements~
switches and inductances if used are then connected in sub-circuits across
the capacitors, the switches being ganged for simultaneous operation. In
a system having canopy shattering and canopy removal subffystems, each
capacitor is advantageously shared between the sub-circuits of the two sub-
systems. The supply may be derived from external points by which the
capacitors may be charged prior to flight~ and possibly discharged after
flight. In this case a trickle charger may be employed to maintain the
charge during flight. Alternatively the supply may be derived indigenously,
preferably in a system ~hereby the capacitors remain uncharged until required.
This may be realised using a set of supply switches in parallel, one for
each sub-~ystem and contingency, connecting the capacitors to a source of
the necessary high voltage supply when operated by the appropriate contin-
gency. A delay system connected between each of the supply switches and
the appropriate sub-system switches can be arranged to close these switches
a few milliseconds after the operation of the supply switches, when the
capacitors will have been adequately charged.
Successful shattering has been achieved with capacitors between 4 p~ and
10614~7
60 ~ at voltages up to ~.5 kV in combination with inductan¢e up to 110
and also with capacitors of an electrolytic type up to 30~000 ~UF capacity
at voltages up to 450 V in conjunction with inductances up to 34 ~ ~ but
the invention is by no means limited to this particular range of values.
A canopy breaking system will now be described by way of example with
reference to the accompanying Figures 2 and 3, where:-
Figure 2 is a view in perspective of an aircraft cockpit canopy fitted with
fusable elements~ and
Figure 3 is a circuit diagram.
As shown in Figure 2 an aircraft cockpit canopy comprises a transparent
panel 11 in a frame 12. Embedded in the panel are five fusable elements 13
in a canopy shattering sub-system and eight fusable elements 14 in a
canopy removal sub-system.
The elements 13 are strategically sited around the area of the canopy
through which an aircrewman will go upon ejection, in positions where
their effect upon visibility is minimised. The elements comprise tin tape
1 mm x 0.0~ mm x 300 mm long formed with a plurality of V bends pointing
around and across the said area in such a manner that upon operation enough
cracks will be generated in the area to break it into pieces which wqll
have insufficient momentum significantly to damage the person or vital
equipment. Leads 15 which connect the elements 13 into the sub-system
circuit hzve ~ull-apart connectors 16 in the region of the frame 12.
The elements 14 are sited around the edge of the panel 11. Each comprises
tin tape 1 mm x o.o8 mm x 100 mm formed with two V bends each pointing in
an opposite direction along the perimeter of the panel. The circuit shown
in Figure 3 comprises five electrolytic 30,00 ~ capacitors 20 connected
1061417
in series between an external point 21 and earth Each capacitor 20 consti-
tutes a power source for fusing elements within the canopy removal and
canopy shattering sub-systems. Thus~ connected across each capaoitor 2
is a switch 22 a 30 ~H inductance 23 and, via conneotors 16 and leads 15
an element 13, in the shattering sub-system, and switches 2 4 and 25 in
parallel, a 30 pH inductanoe 26 and at least one element 14 in the canopy
removal sub-system. The switches 22 are ganged for simultaneous operation
automatically as part of an ejection sequence. The switches-24 are ganged
for simultaneous operation manually by the aircrewman and the switches 25
are ganged for oper2tion externally of the cockpit.
Within the canopy removal sub-system the three forward elements 14A are
connected in series in one sub ff ystem circuit, the centre side and centre
rear elements 14B~ C, E, are each connected in separate sub ff ystem circuits,
and the two rear corner elements 14D are connected in series in another sub-
system circuit, the five sub-system circuits thus made each being serviced
by one of the capacitors 20.
A trickle charger 27 supplied from an aircraft busbar 28 is arranged to main-
tain the charge on the capacitor 20.
The system is prepared for use before an aircraft sortie by charging the
capacitors 20 using a 2.5 kV supply between the points 21 and earth.
During the sortie the charge is maintained using the trickle charger 27.
In the event of an aircrewman initiating ejection, the switches 22 will be
closed automatically within the ejection sequence~ discharging the capacitors
20 through the inductances 23 and blowing the fuzes 13. Due to the current
surge self-excited by the inductances 23 an arc will be set up across the
1061417
disrupting fuse portions at the apex of the V arrangement or arrangements,
and plasma will be directed along the median line of the V9 to augment
the shock caused by the fuse itself. The crack system resulting from the
careful location and arrangement of the elements 13 will ensure that at
least the portion of the canopy in the path of the ejecting crewman and his
seat will be broken into small pieces. The preæsure differential between
the cockpit interior and atmosphere, augmented if necessary by location of
the elements near to the inner and outer canopy surface~ will ensure that
the pieces are projected outwards.
If the aircraft crash Iands the crewman will usually operate the rapid
canopy removal sub-system rather than the normal opening means, and he will
do so by closing the ganged switches 24. The capacitors 20 will then dis-
charge through the inductances 26 and the elements 14, breaking the canopy
away from the same in a mode of operation similar to that of the shattering
sub-system. If the crewman is unconscious the switch 25 may be operated
by an external rescuer, with the same effect. The panel is then pushed,
pulled or lifted away from its frame, pulling apart the connectors 16 in
the shattering sub-system.
In an alternative circuit~ the supply 21 is connected via a parallel switch
system to a 2.5 kV sourc~e within`the aircraft. The parallel switch system
comprises an automatic switch in the ejection sequence and associated with
the shattering sub-system and two manual switches associated with the removal
sub-system. Each of these switches is connected via a delay system with the
appropriate switch, 23, 24, which latter switches are not, in this instance,
operable other than by the delay system. The switch 25 and the trickle
charge circuit 27 are not required.
In operation of this alternative circuit the capacitors 20 are not charged
1061 417
prior to flight and in fact remain uncharged until required. M aking
of any of the switches in the said parallel switch ~ystem allows the ~upply
to charge the capacitors and initiates operation of the delay ~ystem. After
an appropriate number of milliseconds, when the capacitor 20 will be ade-
quately charged~ the delay system will close the appropriate switch 23~ 24
and operate the associated sub-system.
~hat ha6 been described above i6 of course by way of exa ple. Clearly other
ways of carrying out the inrention will occur to those skilled in the art~
and such other ways ay indeed be more suitable in certain circumstances. F~r
exa~ple a continuous electrical conductor aay be used, arranged to break the panel
along the path therof, a system more likely to be used in a c~nopy removal than a
canopy shattering ~ystem. ~owe~er such a syste~ i8 less econo~ical or fail-
-safe than those described.
The systeos described can readily be teated for continuity, which can give a
easure o~ certainty of viability unavailable in explosive cord systeas.
~oreover the use of a plurality of elements as particularly described aean
that the system need not be seriously i-pared by the failure of one.
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