An attachable electro-impulse de-icer for de-icing an aircraft structural member includes an inductor coil disposed in proximity with the outer surface of the structural member. The coil is supported by a flexible, ice-accumulating support member (surface ply) that permits the coil to move relative to the structural member. Preferably the coil and support member are formed in an integral construction that can be attached to the leading edge of the structural member. The coil and support member are rapidly, and forcefully, displaced away from the structural member upon passing a short-duration, high-current pulse through the coil. The current flow creates an electromagnetic field that induces eddy currents in the support member (if made of metal), and the structural member (if made of metal). Upon collapse of the electromagnetic field in the coil, the support member is pulled rapidly to its rest position adjacent the structural member. Alternative arrangements are provided wherein (1) a metal target is disposed in proximity with the outer surface of the coil, (2) a metal target is disposed in proximity with the outer surface of the structural member, and (3) an additional target (doubler) is attached to the inner surface of the structural member.

BACKGROUND OF THE INVENTION 
1. Cross-Reference to Related Patent 
U.S. Pat. No. 4,875,644, issued Oct. 24, 1989, entitled "Electro-Repulsive 
Separation System for De-Icing," by Lowell J. Adams, et al., the 
disclosure of which is incorporated herein by reference (hereinafter 
referred to as the "Electro-Repulsive Separation System Patent"). 
2. Field of the Invention 
The invention relates to de-icers for aircraft and, more particularly, to 
de-icers that operate by deforming ice-accumulating surfaces. 
3. Description of the Prior Art 
The accumulation of ice on aircraft wings and other structural members in 
flight is a danger that is well known. As used herein, the term 
"structural members" is intended to refer to any aircraft surface 
susceptible to icing during flight, including wings, stabilizers, engine 
inlets, rotors, and so forth. Attempts have been made since the earliest 
days of flight to overcome the problem of ice accumulation. While a 
variety of techniques have been proposed for removing ice from aircraft 
during flight, these techniques have had various drawbacks that have 
stimulated continued research activities. 
One approach that has been used extensively is so-called mechanical 
de-icing. In mechanical de-icing, the leading edges of structural members 
are distorted in some manner so as to crack ice that has accumulated 
thereon for dispersal into the airstream. A popular mechanical de-icing 
technique is the use of expandable tube-like structures that are 
periodically inflatable. Inflation of the structures results in their 
expansion or stretching by 40% or more. Such expansion typically occurs 
over approximately 2-6 seconds and results in a substantial change in the 
profile of the de-icer, thereby cracking accumulated ice. Unfortunately, 
expansion of the devices can negatively influence the airflow passing over 
the aircraft structure. Also, they are most effective when ice has 
accumulated to a substantial extent, approximately 0.25 inch or more, 
thereby limiting their effectiveness. Desirably, ice removal would be 
accomplished long before accumulations approximating 0.25 inch have been 
attained. 
A more recent mechanical de-icing technique utilizes internal "hammers" to 
distort the leading edges of structural members. Such an approach is 
exemplified by U.S. Pat. No. 3,549,964 to Levin et al., wherein electrical 
pulses from a pulse generator are routed to a coil of a spark-gap pressure 
transducer disposed adjacent the inner wall of the structural member. The 
primary current in the coil induces a current in the wall of the 
structural member and the magnetic fields produced by the currents 
interact so as to deform the member. 
U.S. Pat. Nos. 3,672,610 and 3,779,488 to Levin et al. and U.S. Pat. No. 
4,399,967 to Sandorff disclose aircraft de-icers that utilize energized 
induction coils to vibrate or torque the surface on which ice forms. Each 
of these devices employs electromagnetic coils or magneto-restrictive 
vibrators located on the side of the surface opposite to that on which ice 
accumulates. In U.S. Pat. No. 3,809,341 to Levin et al., flat buses are 
arranged opposite one another, with one side of each bus being disposed 
adjacent an inner surface of an ice-collecting wall. An electric current 
is passed through each bus and the resulting interacting magnetic fields 
force the buses apart and deform the ice-collecting walls. 
A more recent approach is shown by U.S. Pat. No. 4,690,353 to Haslim et al. 
In the '353 patent, one or more overlapped flexible ribbon conductors are 
imbedded in an elastomeric material that is affixed to the outer surface 
of a structural member. The conductors are fed large current pulses from a 
power storage unit. The resulting interacting magnetic fields produce an 
electroexpulsive force that distends the elastomeric member. The 
distension is almost instantaneous when a current pulse reaches the 
conductors, and is believed to be effective in removing thin layers of 
ice. Although the device disclosed in the '353 patent is believed to be an 
improvement over previous mechanical de-icing techniques, certain 
drawbacks remain. One of the drawbacks relates to the direction of current 
flow in adjacent electrically conductive members. It is believed that the 
current flow disclosed in the '353 patent produces inefficiencies that 
significantly restrict the effectiveness of the device. 
The Electro-Repulsive Separation System Patent discloses a device that is 
an improvement over that disclosed in the '353 patent. In the 
Electro-Repulsive Separation System Patent, the electrically conductive 
members are arranged such that a greater electro-expulsive force can be 
generated than with the serpentine configuration disclosed in the '353 
patent. Also, the Electro-Repulsive Separation System Patent teaches the 
delivery of a current pulse of predetermined magnitude, shape and duration 
that provides more effective de-icing action. 
Despite the advances taught by the prior art, particularly the 
Electro-Repulsive Separation System Patent, there remains a need for a 
de-icer that provides effective de-icing action. In particular, it is 
desired to have a de-icer that has the force-generating capabilities of 
various prior mechanical de-icers without the drawbacks associated 
therewith, such as large size, difficulty in retrofitting existing 
structural members, and other problems. 
SUMMARY OF THE INVENTION 
The present invention overcomes the foregoing drawbacks of the prior art 
and provides a new and improved de-icer especially adapted for attachment 
to external surfaces of structural members. In one embodiment of the 
present invention, an inductor coil is positioned in proximity with the 
outer surface of a structural member. The coil has a first side that is 
disposed in contact with the surface and a second side that is spaced from 
the surface. The coil is movable away from and toward the surface. A 
support member is provided for the coil, the support member being flexible 
in order to permit the coil to move relative to the surface. A portion of 
the support member defines an ice-accumulating surface that moves in 
response to movement of the coil. Preferably, the coil and support member 
are provided in an integral construction that can be bonded or otherwise 
attached to the leading edge of the structural member without modifying 
the structural member. 
An alternative embodiment of the invention calls for providing a metal 
target that is disposed intermediate the coil and the support member. 
Another alternative embodiment calls for disposing the target intermediate 
the coil and the structural member. Yet an additional alternative 
embodiment calls for providing a target (doubler) that is attached to the 
inner surface of the structural member. 
With each embodiment of the invention, the support member is rapidly, and 
forcefully, displaced away from the structural member upon passing a 
short-duration, high-current pulse through the coil. If the structural 
member is metal, the structural member functions as a target and the coil 
is displaced away from the surface; if the structural member is non-metal 
(such as a composite material), and if a surface-contacting target is not 
used, the coil remains positioned against the surface. The current flow 
creates an electromagnetic field that induces eddy currents in the target, 
structural member (if metal), and support member (if metal). Upon collapse 
of the electromagnetic field in the coil, the support member is pulled 
rapidly to its rest position. 
In contrast with prior mechanical de-icers, the de-icer according to the 
invention is exceedingly effective, while avoiding many of the drawbacks 
of the prior art. Most of the forces that are applied to the structural 
member are compressive forces that are more easily accommodated than 
tensile forces that are produced by various other mechanical de-icers. 
Further, the device can be fitted readily to structural members, either as 
part of new construction or as a retrofit. 
Because the device operates on an eddy current principle, it completely 
avoids problems arising from directional current flow, and it provides a 
more effective ice-shedding action than has been possible with previous 
devices. In part, the effectiveness of the device is enhanced because the 
ice-accumulating surface is displaced a relatively great distance at a 
high rate of acceleration. Although the displacement is not enough to 
negatively affect the airflow passing over the structural member, the 
displacement is more than 20 times greater than the displacement that 
occurs with such devices as are disclosed in prior eddy current-type 
de-icers. The device also produces about 20% greater eddy current 
induction than prior internally disposed eddy current de-icers because the 
coil and the target are in surface-to-surface contact with each other, or 
nearly so. The referenced internally disposed de-icers require a 
substantial gap between the coil and the structural member in order to 
prevent possible damage to the coil upon rebounding of the structural 
member. The efficiency of the present invention also is great because the 
ice-accumulating surface that is displaced is relatively thin and is 
resiliently mounted to the structural member. In those de-icers that 
distort the structural member itself, the ice-accumulating surface is 
relatively thick and may be relatively difficult to distort. 
The foregoing and other features and advantages of the present invention 
will become more apparent when viewed in light of the description of the 
best embodiment of the invention and the drawings that follow, which 
together form a part of the specification.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention provides a technique especially adapted for de-icing 
the leading edges of structural members. De-icing is the removal of ice 
subsequent to its formation upon a leading edge. A leading edge is that 
portion of a structural member that functions to meet and break an 
airstream impinging upon the surface of the structural member. Examples of 
leading edges are the forward portions of wings, stabilizers, struts, 
nacelles, rotors, and other housings and protrusions first impacted by an 
airstream. 
FIGS. 1-3 illustrate a known mechanical de-icer 10 and electrical circuitry 
therefor. The de-icer 10 includes first and second coils 12 that are 
disposed within a structural member (such as a wing) 14 near the backside 
of the leading edge thereof. The surface of the structural member 14 is 
made of metal such as aluminium which will be referred to as the "skin." 
The coils 12 are mounted to a spar 16 by means of a mounting bracket 18. 
The coils 12 are circular in plan view. A circular, unalloyed aluminium 
disk 20 is bonded to the inner surface of the leading edge directly 
opposite each of the coils 12. 
Referring to FIG. 2, each coil 12 is connected in series with an energy 
storage capacitor 22 and a thyristor 24. A diode 26 is connected in 
parallel with the capacitor 22. An electrical impulse is initiated by 
supplying a trigger pulse to the thyristor 24, allowing the capacitor 22 
to discharge through the coil 12. Because the thyristor 24 has diode 
properties, the current follows the first positive loop of the RLC 
response, after which the thyristor 24 reopens the circuit. This leaves 
the capacitor 22 reverse-charged. Such reverse-charging reduces capacitor 
life substantially. For that reason, the diode 26 is placed across the 
capacitor 22. 
Referring to FIG. 3, a typical spanwise installation of the coils 12 within 
a wing is shown. Each of the coils 12 is separated laterally from other 
coils 12 by about 16 inches. The coils 12 are supplied a single power unit 
28 that includes a transformer 30. The capacitor 22 is connected across 
the secondary side of the transformer 30. A switching device 32 is 
connected to each of the thyristors 24 in order to provide a trigger pulse 
to the thyristors 24. 
When the capacitor 22 is discharged through each coil 12, a rapidly forming 
and collapsing electromagnetic field is created that induces eddy currents 
in the disk 20 and the metal skin 14. The electromagnetic fields resulting 
from current flow in the coil 12, the disk 20, and the skin 14 create a 
repulsive force of several hundred pounds magnitude, but with a duration 
of only a fraction of a millisecond. A small amplitude, high acceleration 
movement of the skin 14 acts to shatter, debond, and expel the ice. Two or 
three such "hits" are performed in short order, separated by the time 
required to recharge the capacitor 22, and then ice is permitted to 
accumulate again until it approaches an undesirable thickness. By 
appropriate control of the switching device 32 the coils 12 can be 
activated sequentially in order to create a "ripple" effect that is 
believed to be more effective in shedding ice due to the propogation of 
skin movement in both chordwise and spanwise directions. 
As will be appreciated from the foregoing description, the referenced 
de-icer 10 depends for its effectiveness upon deformation of the skin. The 
displacement of the metal surface subject to icing is very limited; 
typically it requires three impact pulses to remove accumulated ice under 
all icing conditions. Further, although the skin is displaced only to a 
limited extent, it is necessary to produce high forces in order to 
accomplish even that limited displacement. An additional problem is that 
the forces are "negative" forces in that they apply a tensile load to the 
leading edge. Aircraft structural members are designed to better withstand 
compressive loads, rather than tensile loads. 
Referring now to FIG. 4, a de-icer according to the invention is indicated 
by the reference numeral 40. The de-icer 40 is similar to the de-icer 10 
in that it employs a coil 42. However, as will be discussed below, the 
de-icer 40 differs significantly from the de-icer 10. The differences will 
be apparent from the description that follows. 
The de-icer 40 as shown in FIG. 4 is formed in an integral unit that is 
bonded or otherwise securely attached to the leading edge of a structural 
member. The leading edge, or skin, of the structural member is indicated 
by the reference numeral 44. Typically the skin 44 will be made of metal 
such as an aluminium alloy. The coil 42 normally will be a multi-layer 
coil comprised of individual planar coil elements (see the discussion that 
follows with respect to FIGS. 9-11). In all of the embodiments described 
herein, the coil 42 is a unitary structure that has no portions that move 
relative to each other. For purposes of the present discussion, the coil 
42 will be indicated schematically as a single element. The coil 42 
includes a first surface that at rest is in contact with the exterior 
surface of the skin 44, and a second surface that is spaced from the skin 
44. The coil 42 is not bonded to the skin 44, so that it can move away 
from and toward the skin 44. 
The second surface of the coil 42 is covered by a surface ply 46. The 
surface ply 46 preferably is not bonded to the second surface of the coil 
42. The lateral edges of the coil 42 are abutted by a flexible, 
non-metallic filler layer 48 in order to provide a smooth transition with 
the contour of the skin 44. The de-icer 40 is bonded or otherwise securely 
attached to the skin 44 by means of the layer 48. The surface ply 46 is 
bonded to the layer 48. At the ends of the surface ply 46, the surface ply 
46 is bonded or attached by a fastener (not shown) to the skin 44. 
Accordingly, the coil 42 and the surface ply 46 are able to move away 
from, and toward, the skin 44 intermediate the portions of the layer 48 
that are bonded to the skin 44. It will be apparent from an examination of 
FIG. 4 that the surface ply 46 not only forms a major portion of the 
exterior surface of the de-icer 40, but it also functions as a support 
member for the coil 42 (together with the layer 48) so as to keep the coil 
42 properly positioned relative to the skin 44. 
The coil 42 preferably is made of unalloyed copper. Reference is made to 
U.S. application Ser. No. 07/437,489, filed Nov. 15, 1989, by Lowell J. 
Adams et al., entitled "Planar Coil Construction," the disclosure of which 
is incorporated herein by reference, for a more complete description of 
the coil 42 and how it is manufactured. The surface ply 46 can be 
manufactured from any suitable metal commonly used for the exterior 
surfaces of structural members, such as aluminum, titanium or stainless 
steel foil. The surface ply 46 also could be made from a thin layer of 
thermoplastic film such as polyetherether ketone ("PEEK"). Such a material 
has excellent rain erosion characteristics, while being readily formed to 
any desired shape. The ply 46 can be made from other suitable non-metal 
materials, if desired. The adhesive used to bond the surface ply 46 to the 
layer 48 can be any adhesive commonly used to join surface plys to other 
parts of de-icers, although a modified epoxy film adhesive such as EA951 
(manufactured by Hysol Corporation) is preferred. The filler layer 48 can 
be made of any known flexible, non-metallic material used with de-icers 
such as rubber, fiberglass, and the like. 
Referring now to FIG. 16, a schematic electrical circuit for the de-icer 40 
is indicated by the reference numeral 60. The circuit 60, with minor 
modifications, is described in detail in the Electro-Repulsive Separation 
System Patent. The circuit 60 charges a bank of capacitors 62 (only one is 
illustrated for simplicity) which serve as high-voltage energy storage 
devices. The metal surface ply 46 and any target or doublers, if used, 
should be connected to the aircraft ground in order to minimize 
electromagnetic interference. When de-icing action is desired, a control 
pulse 64 is fed to a trigger circuit 66 which enables discharge of the 
capacitor 62 through one or more silicon controlled rectifiers (SCR's) 68 
to provide a high-current pulse output 70 to the coil 42. Whenever an 
output current pulse 70 is desired, a dump load 72, which maintains the 
capacitors 62 in a discharged condition, is removed by opening a switch 
74, thereby allowing charging current from a charging circuit 76 to charge 
the capacitors 62 to the desired voltage. When the SCR 68 is triggered 
"on," the capacitor bank 62 is discharged into the coil 42. A high-current 
pulse is produced, the magnitude of which is monitored by means of a 
current transformer 78. 
Referring to FIG. 17, the current pulse may be a clean overdamped 
exponentially decaying sinusoidal waveform that is achieved by the RLC 
electrical circuit values. In the event that the component values of the 
RLC circuit are selected in a known manner such that the circuit may be or 
become underdamped or oscillatory in nature, the circuit should be 
configured such that a rectifier 80 dumps the stored energy of the circuit 
inductance into the de-icer load, producing a single, non-oscillatory 
pulse having an extended trailing edge. 
If the capacitor 62 has a capacitance of about 500 microfarads, and if the 
circuit 60 is operated as described previously, a current flow having a 
peak value of about 3000 amps at 1250 volts will be discharged through the 
coil 42. The coil rise time will be about 100 microseconds and the decay 
time will be about 200-300 microseconds. A strong electromagnetic field 
will be generated that will induce eddy currents in the skin 44 and the 
surface ply 46 (if metal). In turn, electromagnetic fields will be 
generated by the skin 44 and the surface ply 46. The electromagnetic 
fields thus generated will create a large repulsive force having a 
duration of only a fraction of a millisecond. The impact force will be 
transferred by the coil 42 to the surface ply 46, creating a 
small-amplitude, high-acceleration movement of the surface ply 46 that 
will be sufficient to break up and shed any ice that has accumulated. 
Referring now to FIG. 18, a plot of displacement, velocity and acceleration 
for the surface ply 46 is shown. As shown in FIG. 18, the surface ply 46 
is displaced about 0.065 inch, with a peak acceleration of about 18,750 
times the acceleration due to gravity (G's) and with a peak velocity of 
about 380 inches per second. The compressive and expansive forces that are 
generated are reversed during collapse of the electromagnetic fields, 
thereby producing a pressure wave across the surface ply 46. The coil 42 
and the surface ply 46 are rapidly pulled to the rest position shown in 
FIG. 4. As can be seen from an examination of FIG. 18, the peak retraction 
velocity is about 270 inches per second, and the peak acceleration is 
about 13,750 G's. In effect, the coil 42 and the surface ply 46 not only 
are repulsed from the skin 44, but they also are powered back toward the 
skin 44. As can be seen from an examination of FIG. 18, there is minimal 
"bouncing" of the coil 42 and the surface ply 46 upon retraction against 
the skin 44. It also will be appreciated that the initial displacement of 
the coil 42 and the surface ply 46 away from the skin 44 apply primarily 
compressive loads to the skin 44, rather than tensile loads. 
Referring now to FIG. 19, a plot of force versus coil current is shown for 
a laboratory force vice test. Four test results are shown. The lines 
bearing the reference numerals 90, 92, 94 are plots of force versus 
current for coils operating on the so-called electro-repulsive principle 
disclosed in the Electro-Repulsive Separation System Patent. The line 
labeled 96 is a plot of force versus current for a coil 42 operating 
according to the invention. Line 90 was generated using a four-layer 
serpentine coil. The line labeled 92 is a plot of the results utilizing a 
four-layer flat coil etched from rectangular sheets of copper. The line 
bearing the reference numeral 94 is a plot of the results utilizing a 
four-layer planar coil etched from square sheets of copper. The line 
bearing the reference numeral 96 is a plot of the results using a 
four-layer, planar, rectangular coil 42 operated according to the 
invention. As can be seen from reviewing FIG. 19, the invention produced 
markedly superior results compared with any prior coils tested. The 
results were particularly dramatic compared with flat serpentine coils 
(line 90). At a coil current of 1700 amps, the planar coil 42 generated 
well over 1000 pounds of repulsive force, whereas the serpentine coil 
generated less than 200 pounds of repulsive force. 
Alternative embodiments of the invention are illustrated in FIGS. 5-8. 
These alternative embodiments will be described in order. Where 
appropriate, reference numerals that designate elements common to the 
various embodiments will be carried over from Figure-to-Figure. 
Referring to FIG. 5, an alternative embodiment of the invention is 
indicated by the reference numeral 100. The de-icer 100 employs an 
attachment layer 102 that is bonded or otherwise securely attached to a 
metal skin 44 in substantial surface-to-surface contact. An additional 
target 104 (a so-called "doubler") can be disposed on the inner surface of 
the skin 44, if desired. It is advantageous to use the target 104 if the 
metal skin 44 is not thick enough to induce adequate eddy currents. The 
coil 42 is disposed on the outer side of the layer 102. The coil 42 is not 
bonded to the layer 102 so that the coil 42 can move away from, and 
toward, the layer 102. The surface ply 46 covers both the coil 42 and the 
layer 102. The filler layer 48 (only a portion of which is shown) provides 
a smooth contour with the skin 44 as in the embodiment described in FIG. 
4. It is expected that the layer 102 will be made of a non-metal material 
such as adhesive film, fiberglass, and the like. 
An advantage of the de-icer 100 is that the de-icer 100 can be manufactured 
as a prefabricated, integral unit for subsequent attachment to the skin 
44. It is believed that the de-icer 100 will be easier to attach to the 
skin 44 than the de-icer 40. Further, because the layer 102 is attached to 
the skin 44 in substantial surface-to-surface contact, the attachment 
between the de-icer 100 and the skin 44 is exceedingly strong. 
Referring to FIG. 6, another alternative embodiment of the invention is 
indicated by the reference numeral 110. The de-icer 110 is similar to the 
de-icer 40, both in structure and operation, except that a metal target 
112 is disposed on the second side of the coil 42, intermediate the coil 
42 and the surface ply 46. The filler layer 48 is bonded to the skin 44 in 
substantial surface-to-surface contact, but the coil 42 is not bonded to 
the skin 44 so that it can move away from, and toward, the skin 44. It is 
expected that the skin 44 in the embodiment shown in FIG. 6 will be made 
of a metal or composite material. The target 112 preferably is bonded to 
the ply 46 by an adhesive such as EA951. The coil 42 and the target 112 
are separated by a thin separation ply, or release layer 116. The layer 
116 enables the target 112 to move away from, and toward, the coil 42. It 
is expected that the target 112 will be made of a paramagnetic material 
such as aluminum. The release layer 116 can be made of a non-stick, 
thermoplastic material. A suitable material for the layer 116 is 
commercially available from the Richmond Division of Dixico Incorporated 
under the trademark A5000. If desired, the position of the coil 42 and the 
target 112 could be reversed such that the target 112 is in contact with 
the outer surface of the skin 44 and the coil 42 is bonded to the inner 
surface of the surface ply 46. 
Referring to FIG. 7, another alternative embodiment of the invention is 
indicated by the reference numeral 120. In this embodiment, the skin 44 is 
made of a composite material. The de-icer 120 includes a metal target 122 
that is disposed on the second side of the coil 42. The coil 42 and the 
target 122 are separated by a separation ply, or release layer, indicated 
by the reference numeral 124. The filler layer 48 includes a backing 
portion 126 that extends across the front portion of the de-icer 120. The 
portion 126 is spaced from the outer surface of the target 122 by a void 
128 and a release layer 130. The release layer 130 is in contact with the 
outer surface of the target 122. The surface ply 46 is bonded to the 
backing portion 126. 
The de-icer 120 enhances the force that otherwise can be applied to the 
surface ply 46. During coil activation, the coil 42 remains in contact 
with the skin 44. The release layer 124 remains attached to the target 122 
and separates from the coil 42. The target 122 is displaced away from, and 
thereafter toward, the coil 42. By incorporating the void 128 in the 
de-icer construction, the target 122 moves a considerable distance before 
the layer 130 impacts the backing portion 126. The momentum thus generated 
provides an enhanced impact force. In turn, it is expected that a 
shorter-duration current pulse can be used to produce equivalent de-icing 
action compared with the de-icer 40. 
If desired, the skin 44 could be made of metal, in which case the target 
122 would be eliminated. Further, the positions of the coil 42 and the 
target 122 could be reversed, as described with respect to the embodiment 
of FIG. 6. 
Referring to FIG. 8, an additional alternative embodiment of the invention 
is indicated by the reference numeral 130. The de-icer 130 is similar 
conceptionally to the de-icer 120. As illustrated, the skin 44 is made of 
metal. Instead of the void 128 being placed adjacent the backing portion 
126, however, the void 128 is disposed intermediate the skin 44 and a 
release layer 132 that is in contact with the coil 42. In the de-icer 130, 
the target 122 has been eliminated, and the coil 42 is in contact with the 
inner surface of the backing portion 126. If the skin 44 is made of a 
composite material, then a metal target (not shown) could be used in 
conjunction with the coil 42. By using the de-icer 130, the retraction 
force that occurs during the fall of the shaped high-current pulse can 
enhance movement of the surface ply 46, thereby creating a very effective 
ice removal action. 
Referring to FIGS. 9-11, certain components of the coil 42 are shown. In 
FIG. 9, a first sheet-like member 140 is defined by a first, continuous 
electrical conductor having a plurality of turns 142, a first end 144 and 
a second end 146. The first end 144 defines an electrical input to the 
member 140, while the second end 146 defines an electrical output from the 
member 140. The member 140 is formed from a single sheet of unalloyed 
copper or aluminum having a thickness of about 0.016 inch. The turns 142 
have a width within the range 0.070-0.125 inch. 
In FIG. 10, a second, sheet-like member 150 is defined by a second, 
continuous electrical conductor having a plurality of turns 152, a first 
end 154, and a second end 156. The first end 154 defines an electrical 
input to the member 150, while the second end 156 defines an electrical 
output from the member 150. The member 150 is formed from a single sheet 
of unalloyed copper or aluminum having a thickness of about 0.016 inch. 
The turns 152 have a width within the range of 0.070-0.125 inch. 
In FIG. 11, the members 140, 150 are illustrated in a "completely 
superimposed" coil arrangement indicated by the reference numeral 160. In 
this arrangement, the turns 142 are disposed immediately adjacent 
comparable turns 152. The ends 146, 154 are joined as by soldering to form 
an electrical connection. As will be appreciated from an examination of 
FIG. 11, electrical current directed into the first end 144 will follow a 
path through the turns 142 that is in the same direction as the current 
flow through the superimposed, adjacent turns 152. The first member 140 
typically has 121/4 turns (81/4 turns are shown for clarity of 
illustration), as does the second member 150. Accordingly, the 
superimposed members 140, 150 define a coil 160 having 241/4 turns. 
Although the members 140, 150 are illustrated as being rectangular, they 
could be square, circular, or any other desired shape. 
Referring to FIG. 12, a coil 170 is defined by a spiral-wound, continuous 
conductor that is formed from a flat ribbon having a width of 
approximately 0.19 inch and a thickness of approximately 0.025 inch. The 
coil 170 includes approximately 40 turns that are tightly wound to form an 
inner diameter of about 0.25 inch and an outer diameter of about 2.25 
inches. The ends of the conductor are provided with connectors 172, 174 
for connection to a source of electrical current. The coil 170 is less 
desirable than the coil 160, in part because of its greater thickness. 
The coils 160, 170, in conjunction with other components such as suitable 
dielectric materials and encapsulation materials, are used to manufacture 
the coil 42. Additional details concerning the coil 42, including the 
materials and techniques that can be used to manufacture it, can be found 
a concurrently filed application entitled "Planar Coil Construction," 
application Ser. No. 07,437,489, filed Nov. 15, 1989, by Lowell J. Adams 
et al., and assigned to the assignee of the present invention. 
Referring now to FIGS. 13-15, various spanwise arrangements of the coils 42 
are illustrated. In FIG. 13, the coils 42 are spaced approximately 16 
inches, equidistantly on either side of ribs 180. The de-icers 40 are 
aligned with each other at the centerline of the leading edge of the skin 
44. The centerline is indicated by the dashed line 182 in FIGS. 13-15. 
In FIG. 14, upper and lower coils 42 are provided in a manner similar to 
that described for FIG. 13. As in FIG. 13, the coils 42 are spaced about 
16 inches spanwise from each other, equidistantly on either side of the 
ribs 124 and equidistantly above and below the centerline 182. 
In FIG. 15, the coils 42 are staggered spanwise relative to the centerline 
182. That is, one coil 42 is disposed above the centerline 182, while 
adjacent coils 42 are disposed an equal distance below the centerline 182. 
As with the embodiments illustrated in FIGS. 13 and 14, the coils 42 in 
FIG. 15 are disposed about 16 inches apart, equidistantly on either side 
of the ribs 180. 
By arranging the coils 42 as shown in FIGS. 13-15, expansive forces 
generated by the coils 42 create a small amplitude, high acceleration 
movement and stress-producing wave across the leading edge of the skin 44, 
causing ice to be broken up and shed. The impulse force of each coil 42 is 
dependent upon the size and construction of the coil 42 and the overall 
de-icer construction (as illustrated in FIGS. 4-8). 
When the coils 42 are placed on the centerline 182 as shown in FIG. 13, the 
coils 42 may be energized sequentially or simultaneously (as elements 1, 
2, 3, etc.), or as odd or even groups (1, 3, 5 . . . , or 2, 4, 6 . . . ). 
In the configuration shown in FIG. 14, the coils 42 may be energized 
sequentially or simultaneously as groups on the upper surface (1, 3, 5 . . 
. ) followed by groups on the lower surface (2, 4, 6 . . . ) or vice 
versa. The coils 42 also may be energized as staggered groups such as 1, 
4, 5 . . . , followed by 2, 3, 6 . . . , or vice versa. In some cases, the 
number of coils 42 may be minimized as shown in FIG. 15, and energized in 
groups such as 1, 3, 5 . . . , followed by 2, 4, 6 . . . , or 
simultaneously as a staggered group 1, 2, 3 . . . . From the foregoing, it 
will be appreciated that the coils 42 can be attached to the skin 44 in a 
variety of placements and the coils 42 can be energized in a variety of 
sequences for effective de-icing action. 
Mechanical de-icers operating on the eddy current principle, such as that 
illustrated in FIG. 1, have used an inductor coil to induce eddy currents 
in a metal surface many times larger than the inductor coil itself. As 
shown in FIG. 20, for a one-inch radius coil, the eddy current is induced 
only into a limited radius around the coil. FIG. 21 indicates that the 
eddy current density decays rapidly, particularly at distances away from 
the center of the coil. Most force is generated within a 1.25.times.radius 
distance of the inductor coil radius. For existing applications where the 
skin of the structural member is thin, a metal doubler or target with a 
radius of about 25% larger than the inductor coil radius is adequate to 
enhance the impulse force produced. 
The de-icer according to the invention shown in FIGS. 6 and 7 uses a target 
included as part of the de-icer itself without the requirement of using 
the skin of the structural member as a target. Although certain of the 
embodiments described herein (particularly that shown in FIG. 4) use a 
metal skin to contribute to the resulting impact force produced by eddy 
currents, such usage of the skin is not necessary to proper functioning of 
the invention (except for the embodiment of FIG. 4). The invention will 
function adequately with skins made of non-metal materials such as 
graphite/epoxy. 
Referring to FIG. 22, a plot of pressure on a metal target (expressed as 
eddy current density) versus time at various radii is illustrated. Almost 
all of the pressure is generated within a distance of 1.25 times the 
radius of the inductor coil. Thus, targets utilized with the present 
invention need only approximate the size and shape of the inductor coil 
for effective force generation. At most, the target should have a radius 
25% larger than that of the coil. 
Forces on the metal target consist of a normal force acting outwardly, away 
from the inductor coil, which force varies with radius. This variable 
force is represented in FIG. 23 which is a plot of pressure versus time at 
various radii from the center of the target. The lines on the right side 
of FIG. 23 pass below the abscissa, indicating that the force on the 
target reverses in direction with the collapsing magnetic field. As 
indicated previously, this feature of the invention means that the target 
not only is powered outwardly, but it is powered inwardly as well. 
There also is a radially acting force that initially tends to compress, or 
shrink, the target and which then tends to expand the target. The radially 
acting forces can be used to advantage when conducting de-icer operations 
because the radially acting forces create a pressure distribution wave 
(ripple effect) that acts across the surface of the de-icer when the 
target flexes. Typical radially acting forces on the targets are shown in 
FIGS. 24 and 25. FIG. 24 is a plot of radial in-plane force per unit area 
of target surface, while FIG. 25 is a plot of radial distribution of 
in-plane force per unit target area. In FIG. 24, pressure is plotted 
versus time for various radii. In FIG. 25, pressure is plotted versus 
radius for various times. As with FIGS. 20-23, FIGS. 24 and 25 show that 
the eddy current-created force peaks rapidly and decays rapidly. FIGS. 24 
and 25 also show that radial forces at a distance greater than 25% of coil 
radius are not significant. 
The impulse force produced by the inductor coil is dependent on the 
diameter of the target, the thickness of the target, and the material from 
which the target is made. The conductivity of the material as well as its 
thickness determine the eddy current that will be produced for a 
particular spacing between the inductor coil and the target. The shape of 
the inductor coil and the shape of the target also may be varied to obtain 
a maximum impulse force for a particular construction such as a curved 
airfoil. FIG. 26 is a plot of impulse force versus target thickness for 
various target materials. Although copper is seen to produce the best 
impulse curve, other materials such as 1145 aluminium provide acceptable 
performance. 
Other design considerations in addition to target size and thickness 
include whether the target should be laminated (two or more layers) and 
whether the layers should be made of the same material. As to thickness, 
it is believed desirable to provide a target having a thickness of about 
one electrical skin depth for best impulse production. If desired, the 
target can be made of two layers--one for strength and a second layer of 
different material having improved electrical conductivity. It has been 
found that increasing the target thickness increases the impulse produced. 
Nevertheless, the target generally should be kept as thin as possible in 
order to minimize weight and disruptions to the contour of the structural 
member. In work with the design of doublers (targets on inner surface of 
structural member), it has been found suitable to choose a doubler 
thickness that equals one-half the electrical skin depth at the circuit 
frequency. 
It also has been found that matching the electrical period and the 
mechanical period gives the best results. Specifically, the electrical 
period should be chosen to be one-eighth that of the natural period. If 
the coil current has a long rise time, a thicker target is required. Test 
results with prior mechanical de-icers that employ doublers indicate that 
that the optimum electrical period is twice the mechanical period. It is 
believed that a similar relationship between the mechanical and electrical 
period apply to the present invention. 
Previous test results have utilized a uniform thickness of airfoil skin 
and/or doubler. It is possible that the thickness and shape of the target, 
and the spacing of the target from the coil, can be varied to tailor the 
force produced in the target and to enhance transfer of the force to 
ice-shedding surfaces. 
Although the invention has been described in its preferred form with a 
certain degree of particularity, it will be understood that the present 
disclosure of the preferred embodiment has been made only by way of 
example, and that various changes may be resorted to without departing 
from the true spirit and scope of the invention as hereinafter claimed. It 
is intended that the patent shall cover, by suitable expression in the 
appended claims, whatever features of patentable novelty exist in the 
invention disclosed.