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.
DESCRIPTION OF METAL SPRAYED HEATERS
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
Metal Sprayed heater elements consist of granular metallic electrical resistance paths, sandwiched between layers of insulation. The heater element is 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.
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.
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.
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,
NH24468-158, NH24468-52, NH24468-162, NH24468-77, NH24468-68, NB24468-080
FAA Repair Station ZWXR058J
Electro-Thermal Ice Protection Systems
Copyright 2014 © Rockwell Aviation Services, Inc. All rights reserved.
2465 Railroad Street, Corona, California 92880, USA
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