Note: Descriptions are shown in the official language in which they were submitted.
1053477
This invention relates to apparatus for indicating rate
of ice accretion and is particularly intended for use in aircraft.
Apparatus according to the invention includes test
surface upon which ice forms in use, first and second gas conduits
each communicating at one end with the outlet of a gas pressure
regulator the inlet of which communicates with a qas supply, and
the regulator having a control port whereby the regulator is
supplied with a reference pressure, the regulator operating to
maintain its outlet pressure at a predetermined amount in excess
of the reference pressure, first and second restrictors in said
first and second conduits respectively, said first and second
conduits terminating at their ends remote from the regulator, in
first and second orifices respectively, said first orifice being
adjacent, and presented to, the test surface, means sensing
difference in the pressure in the first and second conduits
intermediate their orifice and their restrictor respectively and
supplying a signal dependent upon such pressure difference to an
indicator to operate the indicator , a control conduit connecting
the control port of the regulator to the second conduit at a
point intermediate the second orifice and the second restrictor
whereby the reference pressure for the regulator is the pressure
existing in the second conduit intermediate the second restrictor
and the second orifice and, mea.ns for moving the test surface
relative to the first orifice at a predetermined speed, the
arrangement being such that when no ice is present on the test
surface then the first orifice is unrestricted, and there is no
pressure difference between the first and second conduits but
when ice forms on the test surface the ice obstructs the first
orifice to an extent dependent upon the thickness of the ice
layer on the test surface thus resulting in an increase in
pressure in the first condult downstream of the first restrictor
related to the thickness of the ice layer on the test surfàce,
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the difference in pressure between the first and second conduits
being sensed by the sensor, and since the pressure difference is
directly related to the thickness of the ice layer on the moving
test surface, the indicator thus indicating the rate of ice
accretion.
Preferably the test surface is a cylinder which is
rotated at a known speed, said first orifice bein~ adjacent to
and presented to the cylindrical surface of the cylinder and the
cylinder having associated therewith means for continuously
removing ice from the test surface as the test surface has moved
past the first orifice.
The accompanying drawing is a diagrammatic represen-
tation of apparatus in accordance with one example of the
invention.
Referring to the drawing, the apparatus for indicating
rate of ice accretion includes a small wing-like nacelle of
airfoil cross-section (not shown) which protrudes from the
fuselage of the aircraft and is positioned sueh that conditions
at the leading edge of the nacelle will be related to conditions
at the regions of the surface of the aircraft where it is
important to know the rate of ice accretion. The surfaces may
for example be the leading edges of wings, or the air inta'~es
for the engines of the aircraft. The leading edge of the
nacelle is formed with an aperture within which is exposed part
oftAesurface ofacylinderll, thecylin~er llbeinq ofcircular cross-
section andbeingrotatableabout itslon~itudinal axisat apre-
determined constantspeed bya drivearran~ement tnot.shown).mhe surface
ofthe'cylinder llconstitutes ane'ndless testsurface androtation of
the cylindercauses thecylin'drical surfacecontinually tobe e~posed
to theairflowover~he'leadingedge ofthe'nacelle.Thusthe surface
of the cylind~r 11 will, in flight, be subject to atmospheric
conditions related to the atmospheric conditions found on the
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regions of the aircraft surfaces which it is important to ~now
the rate of ice accretion. If the atmospheric conditions are
such that ice would form on the regions in question, ice will
form similarly, and at a related rate, on the surface of the
cylincler 11 passing through the zone of ice accretion defined by
the aperture in the nacelle.
Within the nacelle is positioned a metal block having
a part cylindrical surface coaxial with, and spaced from the
- cylindrical surface of the cylinder 11. The block 12 is formed
with a through bore 13 defining an extension of a first
conduit 14 which terminates at the part cylindrical surface of
the block 12 in an orifice 15. The orifice 15 is thus adjacent,
and presented to the test surface, and is spaced therefrom by a
predetermined distance. Spaced along the conduit 14 from the
orifice 15 is a restrictor 16 and on the side of the restrictor
16 remote from the orifice 15 the conduit 14 communicates with
the outlet 18 of a pressure regulator 17. The pressure regulator
17 is of known form, and may for example be a FAIRCHILD DIFFEREN-
TIAL PRESSURE REGULATOR manufactured and sold by Fairchild
Industrial Products Division and known as their Model 59. The
pressure regulator includes an inlet 19 which is connected to a
supply of clean, filtered air under pressure, conveniently from
the conventional air pressure system of the aircraft. In
addition the regulator includes a control port 21 whereby a
reference pressure is applied to the regulator. The operation
o~ the regulator basically is to ensure that the pressure at the
outlet 18 is always a predetermined amount in excess of the
- pressure at th~ control port 21. It is of course essential that
the pressure at the main inlet 19 is in excess of the maximum
required pressure at the outlet 18. The Fairchild Regulator
mentioned above is adjustable and in this case is so set as to
ensure that the pressure at the outlet 18 is always three pounds
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per sq~lare inch in excess of the control pressure applied at the
control port 21.
The regulator outlet 18 also communicates with a
second conduit 22, the conduit 22 terminating at its end remote
from the regulator 17 in an orifice 23 of dimensions such that
it establishes a pressure drop similar to that across the
orifice 15 when the orifice 15 is unrestricted by ice, that is
to say the inherent pressure drop across the orifice 15. ~ore-
over, intermediate the orifice 23 and the regulator outlet 18
the conduit 22 includes a restrictor 24 of dimensions similar to
the dimensions of the restrictor 16 of the conduit 14.
A pressure sensor 25 communicates with the conduits 14,
22 intermediate their orifices 15, 23 and their restrictors 16,
24 and thus will sense any difference between the pressure in
the conduit 14 intermediate the restrictor 16 and orifice 15 and
the pressure in the conduit 22 between the restrictor 24 and the
orifice 23. The sensor 25 produces an output signal which is
dependent upon the pressure difference sensed by the sensor and
the signal is applied to an indicator 26 to operate the indicator
26. The nature of the output signal of the sensor 2~ will be
dependent upon the nature of the indicator 26. However, it is
preferred to use a simple electrical meter as the indicator 26,
and thus the sensor 25 is arranged to produce an electrical out-
put signal suitable to operate the meter. The meter constituting
the indicator 26 will be ~ositioned remote from the sensor 25,
for example on the control panel of the aircraft, and if the
sensor 25 produces only small electrical signals then it may be
desirable to include means for amplifying the output signal
before it is supplied to the indicator 26. It will be understood
that the restrictors 16, 24 and the orifices 15, 23 need not be
identical. However it is desirable that the restrictors and
orifices are so related that ratio of the pressure drops across
1053477
.he restrictor 16 and the orifice 15 in the ice free, that is to
say unrestricted, condition of the orifice 15, is equal to the
ratio of the pressure drops across the restrictor ~4 and orifice
23. The equilization of the ratios of pressure drops simplifies
the setting-up of the sensor and indicator of the system in that
it facilitates the achievement of a reliably repeatable zero
position and furthermore ensures an operating response approach-
ing linearity so that a su~stantially linear scale can be
provided on the indicator 26.
A further conduit 27 is connected at one end to the
control port 21 of the regulator, and is connected at its other
end to a point in the conduit 22 intermediate the orifice 23 and
the restrictor 24. Thus the control pressure for the regulator
17 is derived from theconduit 22, so that a constant pressure
difference is maintained across the restrictor 24.
Adjacent the block 12 there is provided a scra~er blade
28 which is positioned closely adjacent, or actually bears
lightly on, the test surface of the cylinder 11. The function
of the blade 28 is to remove any ice which has formed on the
test surface when the test surface has moved passed the orifice
15. Thus assuming a layer of ice has formed on the test
surface then the layer of ice will pass in front of the orifice
15 and then will be removed by the blade 28 so that the test
surface is cleaned in readiness to pass again through the
aperture of the nacelle where, provided icing conditions remain,
a ~urther ice layer will form and will be car~ied back on the
t~st surface to pass the orifice 15.
The operation of the system is as follows. Clean, dry,
filtered air under pressure is supplied to the regulator 17 from
a convenient source such as the conventional air pressure
system of the aircraft. The pressure supplied to the inlet 19
of the regulator is in excess-o~ the:maximum pressure required at
the outlet 18 of the regulator, and the regulator operates to
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ensure that the pressure at the outlet 18 is constantly at a
convenient value for example, three pounds per square inch in
excess of the pressure in the conduit 22 intermediate the orifice
23 and the restrictor 24, regardless of the pressure in the
conduit 22. In the event that no ice forms on the test surface
then the gap between the orifice 15 and the test surface of the
cylinder 11 is such that the orifice 15 is unrestrictea that is
to say exhibits only its own inherent restriction. As the
orifice 15 and the orifice 23 produce equal pressure drops in
this condition provided that the restrictors 16, 24 are correctly
sized then the pressure in the conduit 14 will be equal to the
pressure in the conduit 2~ and there will be no pressure differ-
ence to be sensed by the sensor 25. Under these conditions the
indicator 26 is arranged to read zero.
The other extreme condition is when the ice thickness
on the test surface cylinder 11 fully closes the gap and reduces
the flow in conduit 14 to zero. Under this condition there is
no pressure drop across restrictor 16, thus the sensor 25
experiences the full pressure drop across restrictor 24 which is
maintained constant regardless of ambient atmospheric pressure
by the regulator 17, and the sensor provides a signal correspond-
ing to f~ll scale deflection on indicator 26.
As will be explained more fully hereinafter the meter
constituting the indicator 26 is calibrated with a scale
representing rate of ice accretion on the cylindrical, test
surface of the cylinder 11. When the aircraft flies into
atmospheric conditions which will give rise to icing then ice
will form on the test surface of the cylinder 11 and the thickness
o~ ~he layer of ice which forms will be dependent upon the
severity of the icing conditions. Since the cylinder 11 is
rotating at a known speed then the thickness of the layer of ice
which forms in a given period of time on the test surface ïs
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`~presentative of the rate of ice accretion on the test surface.
As stated above, the rate of ice accretion on the test surface
will bear a known relation to the rate of ice accretion on the
regions of the aircraft where it is important to know the rate
of ice accretion.
Any ice which forms on the test surface will be moved
across the orifice 15 by the rotation of the cylinder 11, and
thus will restrict the orifice lS to an amount dependent upon
the thickness of the ice layer. A restriction of the orifice 15
will give rise to an increase in the pressure in the conduit 14
intermediate the orifice 15 and the restrictor 16. However,
there will not of course be a similar restriction of the orifice
23 and so the pressure in the conduit 22 will not alter. Thus
the sensor 25 will sense a pressure difference between the
conduits 14, 22 the pressure difference being directly related to
the degree of restriction of the orifice 15, and thus being
directly related to the thickness of the ice layer on the test
surface. It follows therefore that the indicator ~6 will give a
readins ;nich is directly related to the ra.e of ice accretion,
and provided the relationship is first established then the scale
of the indicator 26 can be calibrated in terms of rate of ice
accretion.
Since the test conduit 14, and the reference conduit 22
are supplied with air from a common source, namely the outlet of
the regulator 18, then fluctuations in supply pressure will not
alter the pressure difference between the two conduits, and so
will not affect the reading of the indicator 26. Moreover, by
utilizing the pressure in the conduit 22 intermediate the orifice
23 and the restrictor 24 as the reference pressure for controlling
the regulator 17, the apparatus i5 insulated from the effects
of variations in external atmospheric pressure. It will be
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1053477
. . .
understood that variations in external atmospheric pressure can
arise either from barometric changes, or from altitude changes.
Thus ~he reading of rate of ice accretion given by the indicator
26 is totally independent of both supply, and atmospheric pressure
I variations.
It will be understood that alternative forms of
regulator can be utilized if desired, and that other forms of ice
removal, other than the blade 28, could be utilized if desired.
For exam~le, the blade 28 could be replaced by a rotating cutter,
or some form of localized heating means. ~oreover, the cylin-
drical endless test surface could if desired be replaced by the
plane surface of a rotating disc, or could be replaced by the
surface of an elongate wire, or ribbon moved at a known speed
passed the orifice 15. In the case of a wire or ribbon, it is
probable that no ice removal means would be required since
sufficient length of wire or ribbon could be provided for the
apparatus to function for the duration of a flight without the
same region of the wire or ribbon being required to pass the
orifice 15 for a second time.
20~ Whatever the nature of the test surface chosen it will
be appreciated that if desired the drive mechanism for the test
surface can be arranged to be selectively operable at two or
more predetermined speeds, the indicator 26 having an appropriate
equivalent number of scales thereon. Thus in very light icing .
conditions the pilot would select the slow movement of the test
surface thus giving time for a substantial thickness of ice to be
built up on the test surface before passing the orifice 15. On
the other hand in heavy icing conditions where the ice layer
would for example be thicker than the gap between the block 12
and the test surface then the pilot, or an automatic signal
device sensitive to a full scale reading of the indicator 26,
would select a faster speed of movement of the test surfacè, and
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in each case the observer would read the rate of ice accretion~
from tlle appropriate scale o~ the indicator.
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