Utilizing advanced composite materials
and manufacturing techniques
Rockwell Aviation Services, Inc. can
design, test, and manufacture
electrically heated ice protection
systems for commercial and military
fixed and rotary wing aircraft.
APPLICATIONS
Engine Air Intakes              Control Surface    
                                          Horn Balances

Leading Edges                   Helicopter Rotor
                                          Blades

Propeller Spinners             Horizontal and
                                         Vertical Stabilizers
DESCRIPTION OF METAL SPRAYED HEATERS

INTRODUCTION

The Metal Sprayed heater is an electric heater mat, most commonly used to warm
aircraft surfaces, and thus prevent or melt ice formations. The heater consists
basically of a pattern of sprayed on metal heating elements embedded between two
layers of insulating material. Metal Sprayed heaters can be applied directly on the
surface to be heated, or produced in a prefabricated form and secondarily bonded to
the component. Insulating gaps between the heating elements are kept narrow so that
the elements usually comprise more than 93% of the total area. Metal Sprayed
heaters are strong, light (0.3 to 0.85 lb/sq.ft.) and thin (0.03 to 0.07 inch) They can be
designed for a wide range of power loadings (from 0.1 to 30.0 watt/sq.in.), with the
heating intensity either uniform or graded according to special needs. Metal Sprayed
heaters are fabricated to operate at nearly any voltage, AC or DC (depending upon
the particular customer installation requirement), with full temperature control assured
through the selected external control system (optional). Maximum surface temperature
is usually about 120 degrees Celsius (250 degrees Fahrenheit), but higher values
may be obtained for short periods under certain conditions. Thermal response is
rapid, making Metal Sprayed Heaters ideal for intermittent or cyclic heating.


METAL SPRAYED HEATER CONSTRUCTION

HEATER ELEMENTS


Metal Sprayed heater elements consist of granular metallic electrical resistance paths,
sandwiched between layers of insulation. The heater element is flame sprayed under
controlled conditions on the surface of the base insulation in the form of strips with
varying widths and thicknesses to give the required heating intensity. The base
insulation of the component on which the heating element path is to be sprayed is first
masked off in accordance with a carefully designed and engineered drawing prepared
for each Metal Sprayed installation, much like an electronic printed circuit. The
granular metallic material is then sprayed on the base insulation, the circuit resistance
checked locally, touched up as necessary by adding or removing element resistance,
masking removed, and the outer insulation applied over the heating elements.

TERMINALS

The standard terminals for connection of the aircraft electrical supply and control
system to the Metal Sprayed heater are usually bonded to the inside of the
component structure to permit power connections from the rear side. Special terminals
may be installed anywhere else desired or as dictated by special installations. The
terminals are installed such that the post projects through the base insulation, and the
heater element is then sprayed directly to that post. The external connections from the
electrical source are connected to the terminals after the component is installed on
the related aircraft or end item.


INSULATION

There are normally two insulation layers used in Metal Sprayed heater construction.
The first, the base insulation, is that layer over the component structure which
separates the heater element and electrical components from the component
structure. The component structure, if metal, is grit blasted prior to application of the
base insulation. The second layer, the outer insulation, is the protective insulation
applied over the heating elements. A very tough, heat resistant, thermosetting plastic,
with a glass cloth reinforcement is used for the insulation material.

EROSION PROTECTION

Metal Sprayed is usually protected with an EROCOAT application over the outer
insulation. EROCOAT is a special rain erosion resistant coating, designed to give
maximum protection to the heater under severe erosion conditions which are
encountered by modern aircraft. EROCOAT is also electrically conductive, and
provides a discharge path to aircraft ground, thus preventing high static voltages from
discharging to the heater elements, and possibly damaging the outer insulation. It also
provides protection from stones, hail, and other foreign objects. In special cases, a
metallic sheath may be installed over the Metal Sprayed heater when the heater is
installed on components subjected to extreme erosion conditions, or where impact with
hail, sand, dust, and even small stones may be expected. One typical installation is on
the leading edge of helicopter rotor blades, protecting it from both rain and sand
erosion. In some cases, such sheaths will take the place of EROCOAT protective
coatings since they provide erosion and impact protection, and also provide an
electrical path for static electricity discharge.

METAL SPRAYED HEATER INSTALLATIONS

The normal Metal Sprayed installation is able to withstand severe impact and normal
abrasion without physical or electrical failure. Its toughness allows it to be exposed to
any weather condition or aircraft environment without suffering either thermal or
mechanical fatigue. Final color finish is usually applied by the aircraft manufacturer
over the complete heater. However, Metal Sprayed will have an erosion protective
coating and in many cases this acts as a final finish, since it can be applied as a
smooth glossy coating. Metal Sprayed heaters are approved by the cognizant
government agencies in the United States of America and Great Britain, and are
installed and in use on wide range of military and civil aircraft to heat engine intakes,
airfoil sections, tail units, auxiliary air scoops, propeller spinners, helicopter rotor
blades, and many other vital components needing protection against ice or very low
temperatures in flight.



Copyright © Rockwell Aviation Services, Inc. All rights reserved.
NH24468, NH24468-152, NH24468-154, NH24468-156, NH24468-66, NH24468-70,
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