Note: Descriptions are shown in the official language in which they were submitted.
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1 ~ of the Invention
The present in~ention relates to ic~-prevention
sy~tems for aircraft struc~ures, and more pa~ticularly, to an
apparatus for measurement of ice thickness employing ultra
sonic pulse echa techniques.
The problems relating to the formation of ice on
aircrat s~ructures are well known. In certain cli~atic condi-
tions water droplets ~ay exist at subfreezing temperatures in a
liquid state. These supercooled droplet~ nucleate and ~orm ice
upon contact with the aircra~t surface~. Ice the~efore tends
to form on the leading edges of aircraft s~ructures. The ice
can degrade aircraft performance through increasing the effec-
ti~e weight o~ the aircraft and by increasing drag re~istance
and reducing lift provided by~the airfolls.
lS Various ice detection devices are well known. In one
known detection device, a probe is provided which extends
beyond the surface to be monitored. ~owe~er, the manner of ice
accretion on such prabe is different from the manner of ice
accretion on the ~urface to be monitored. Hence, the accretion
rate on the probe will be higher than the accretion rate on the
~ur~ace to be monitored.
In another known device, the ice thickness is
mea~ured by the changing capacitance o~ a surface capacitor due
to the dielectric properties of the ice which has accreted on
the probe. One problem with ~hi3 latter class of devices is
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1 that in o~der to accu~htely interpret the data received from
the probe, the type oE ice (rime, glaze, or mixed) must be
known to the user~
It is there~ore an object of the present invention to
provide an apparatus ~or measurement of ice thic~ness which can
be mounted flush with the surface upon which ice accretion
thic~ness is to be measured~
It is another object of the present invention provide
an apparatu3 for measurement of ice thic~ness which i~
insensitive to types of ice accreted. .
It i~ yet another object of the present in~ention to .
provide an apparatus or meas~rement of ice thic~ne-~ which is .
flush with the surface upon which ice acc~etion thic~ne~ is to
be measured and can also measure the rate of ice accretion.
lS It i~ a further object of the present invention to
pro~ide an apparatus for measurement of-ice thic~ness employing : .
ultra-sonic pulse echo techniques to measure ice accretion .
thickne~s and al90 the rate at which :ice is accre~ed. .
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Summary of the Invention
The present invention relates to an apparatus for .
: measurement o~ the thickness of accreted ice and rate of .
accretion employing an ultra-so~ic pulse e~ho ~echnique,
comprising an ice-accreting surface and means mounted at said
surface for transducing an ultra-sonic signal into said ice.
25 The invention also relates to a method for detection of the
presence o~ ice on a surface, comprising the step~ of
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1 transmission of ~n ultra-sonic pulse into ~aid ice via trans-
ducing means; propagation o~ said pulsq througil said ice to its
periphery and reflecti~n of said pulse bac~ to said transducing
means; and evaluating the time between transmission of said
pulse and reception by said transducing means of said reflected
pulse to obtain ic~ thic~ne~s, and/or ice accre~ion rate.
Description of the Drawings
The preferred embodiment is illustrated in the
accompanying drawings~ in which:
Fig. 1 is a partial schematic, partial blcck diagram
o~ a preferred embodiment of the present invention;
Fig~ 2 is a schematic diagram illustrating the
pulse echo technique of ice thickness measurement; and
Fig. 3 is a graphic represen~ation of experimen~al
- 15 data representing ice growth under heavy icing conditions for
detection of ice thic~nes~ and gro~th rate.
~escri~tion of the Preferred Embodiment
Fig 1 is a partial schematic, partial block diagram
o~ the present invention~ showing ice 14 accreted on the
leading edge 16 of an airfoil 18. Also provided on the leading
edge 16 of airfoil 18 is an ultra-sonic transducer 20.
In a preferred embo~iment, the ultra-sonic sens~r
comprise~ a broad-band, highly damped contac~ ~ransducer. This
type of ~ransducer allows maximum signal penetration in attenu-
ating and scattering mate~ial~ which have accreted thereon.
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1 Pre~erably, such transducer has a cent~r frequency o~ 5 MHz andan element diameter o 0.25 inches. 'rhe transducer 3hould at
least ha~e a cen~er frequency o~ 1 to 20 MH~
Reerring again to FigO 1, the transducer is driven
hy a pulse transmitter o~ a pulser/receiver and 3ignal proces-
sor unlt 22. The pulse transmitter transmits a sig~al to the
transducer 20 via conduc~or 24. This signal cau~es the tran~-
ducer to emi~ a brie~ ultrasonic compression wave. The emitted
~ignal is reflec~ed at the air~ice interface o~ the ice accre-
ted on the transducer and the signal thus reflected back iadetected by the transducer. Thi~ detectad reflected wave is
transmitted from the transducer bacX to the pulser/receiver and
~ignal processor unit 22 by means of conductor 24~ The
received signal is then processed by the signal processor with-
15 in unit 22 and a signal i~ thereafter conducted to a display -~
device 26 by means of a cable 28.
As will be appreciated by those of ordinary skill in
the art; the principle upon which the pulse echo feature of the
invention operate~, is shown in the schematic diagram of Fig.
20 Z~ In Fig. 2, a transducer 20 i~ shown mounted flush with the
su~ace o f air~oil 18. As will be seen in ~he ~igure, a pulse
31 is emi~ted by the transducer and is propagated ~hrough the
ice 14 until it is reflected by the air-ice interface 30. The
echo 32 is detected by the tran~ducer 20, whereupon an ele~tri-
cal pulse, repre entative of the ~trength of the echo~ istransmitted to the receiver of unit 22. The ~ime delay between
the emi~sion oE the pulse by the transducer and its receipt of
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1 the reflected pulse 32 is related to the thic~ness oE the ice.
This relationship is shown in Fig. 2 in the bloc~ enclosing the
formula D (ice thickness) =l/2 of the quantity Cic~ (repr2sent-
ing the speed of sound in ice) x Tp E (which represents the
time b~tween the emission o~ the pulse and the receipt of the
echo~. It will therefore be appreciated that ice thickness D
can ~e detected if the time of propagation can be detected and
the speed of sound in the ice is known.
Furthermore, the inventors have determined that the
speed of sound Cice in ice is insensltive to the type of ice
under examination. This speed has been determined
experimentally to be approximately 3.8 mm~microseconds.
Re~erring to Fig. 3, there is shown a graphic rep-
resentation of e~perimen~al da~a representing ice growth under
heavy icing conditions ~mploying a 4-inch diameter cylinder
with the present apparatus flush mounted at the leading edge
- there~f. The detectors were subjected to an icing cloud at 200
knot~ . The eloud had a med;an valume diameter of 20 microns
and a li~uid water con~ent of l.2 grams per meter cubed . Three
temperatures (-10F., flOF., +27~F., respectively) represent-
ing three types of ice formation (rime, glaze and a second
glaze, respectively) are shown. The graph of Fig. 3 compares
ice thic~ness in millimeters along the ordinate axis to icing
time in minutes al~ng the abscissa axis. The icing rate ~or
each respective formation is represented by the slope of the
respective point-plotted curve shown in the figure.
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1 It will be appreciated that the present apparatu3 ~or
measuremerl~ of ice thic!cness can be advantageou31y used in con-
junctioQ with ice de-icing and anti-icing-devices to protect ~
vehicle from unwanted icing. This is particularly critical in
operation of pneumatic boots, which are only effecti~e within
an cer~ain limited ice thic~ness range. Therefore, knowledge
of ice thickness and ice growth rate i8 critical for ef~icient
operation of such de~ice.
While r~ther specific embodiments have been de~cribed
herein, it will be appreciated that other and further embodi-
ments within the spirit and scope of the present invention are
contemplated. .~
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