US 2494625 A
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Description (OCR text may contain errors)
Jan. 17, 1950 E. MARTIN AIRFOIL HEATING MEANS Filed Nov. 5, 1945 INVENTOR [r/e Mew/"fin ATTORNEY.
Patented Jan. 17, 1950 UNITED STATES PATENT OFFICE AIRFOIL HEATING MEANS Application November 3, 1945, Serial No. 626,491
This invention relates to heating devices for raising the temperature of selected portions of hollow airfoil members and particularly the leading edge of hollow metal aeronautical propeller blades to facilitate removal of ice coatings and to prevent the formation of such coatings.
An object of the invention is a hollow airfoil member in which selected portions may be efficiently heated at will.
Another object is simple effective means for holding the heating element in position.
A further object is the provision of heat insulating means preventing dissipation of heat except where desired.
Other objects and advantages will be apparent from the specification and claims, and from the accompanying drawing which illustrates what is now considered to be a preferred embodiment of the invention.
In the drawings:
Fig. 1 is a top plan view showing the general arrangement of the propeller in which all but one blade has been broken away, the de-icer strips and their source of electricity.
Fig. 2 is a front elevation of the blade with the heater strip applied and a portion of the covering member removed to show the heater strip.
Fig. 3 is an enlarged plan view of the heater strip.
Fig. 4 is a side view of the heater strip, and
Fig. 5 is a section taken on line 5-5 of Fig. 2.
The invention is shown as associated with a controllable pitch propeller having a hub It and any desired number of blades it, only one of which is shown in the drawing. Each blade has a shank l4 rotatably mounted in hub it! for pitch changing movements. Each blade carries a heater strip l6 which may be electrically heated. The electricity may be supplied in any desired manner and is shown as supplied through slip rings ill from any suitable source of electricity such as a storage battery 20, the usual electrical system of the airplane or a separate generator. The hub I0 is mounted on and rotated by an engine 22.
The heater strip IS in its now preferred form is a rubber sheet 24 in which nichrome heating wires 26 are embedded. Various modifications of the heater strips may be utilized so long as the heat is applied adjacent one surface of the heater strip and the strip is capable of conforming to the shape of the inner surface of the airfoil to be heated. For instance, a heater strip of conducting rubber such as described in Park and Rhines U. S. application Serial No. 626,504, filed on even date herewith, may be used in place of the one specifically disclosed herein.
The heater strip is located on the inner surface of the airfoil member 28 to be heated, in this case a hollow metal propeller blade l2. The hollow metal propeller blade has a strength member or core 30 extending substantially the entire length of the blade. The covering member 28 has an airfoil cross section as shown in Fig. 5 and is secured to the core member 30, preferably by soldering, throughout the area of contact between the core and the covering member. The core is considerably smaller in cross section than the in-- side of the covering member so that air spaces are left between the core and leading edge of the .covering member and between the core and the trailing edge of the covering member. For further details of the blade construction reference may be had to my copending U. S. application Serial No. 484,229, filed April 23, 1943, for Propeller.
The heater strip l6 which may be of any desired extent is initially secured to the inner surface of the covering member 28 by an adhesive such as rubber cement. If the heating wires 26 are closer to one side of the heater strip than the other, the heater strip is placed in the blades so that the heater wires are as close as possible to the covering member 28. After the heater strip has been located in position, filling material is inserted in the space between the core member 30 and the leading edge of a covering member 28 and, if desired, also in the space between the core memher and the trailing edge of the covering member. The filling material is preferably a rubber composition which, when heated, gives off gasses which form innumerable pockets in the filling material and greatly expand the filling material to form what is known as expanded rubber. Either sponge rubber or closed-cell rubber, such as described in U. S. Patent No. 2,299,593, may be used. The rubber to be expanded may be cemented onto a supporting backing, such as canvas, and inserted into the blade cavities in strip form. This expanded rubber provides a very light yet strong filling material which has good heat insulating properties. The rubber in expanding presses on the inner face of the heater strip I B and forces the outer surface of the heater strip into intimate contact with the inner surface of the covering member 28. The inner surfaces of the blade and the outer or exposed surface of the heater strips are coated with a suitable cement, such as a rubber cement. Sufficient filling material is then inserted in the blade cavities so that after heat treatment, vulcanization, and expansion, the material remains under compression and thus continuously forces the heater strip into contact with the inner surface of the covering member 28. The heat treatment acts to bond the filling material to the blade and heater strip and holds the heater strip in position against displacement from any of the forces set up during operation of the propeller.
Although the heater strip has been shown as having the heating wires uniformly distributed, the wires may be arranged to give any desired distribution of heat, such as concentrating the heat at the leading edge or grading the heat from the leading edge backward toward the trailing edge or giving any desired proportion of the heat radially of the blade, such as increasing the quan-- tity of the heat outwardly of the blade to com-- pensate for greater heat loss of that portion of the blade. To accomplish the heat distribution, heater strips such as shown in the Park and Rhines U. S. application Serial No. 626,504, or Mazur U. S. application Serial No. 626,490, filed on even date herewith, may be utilized.
It is to be understood that the invention is not limited to the specific embodiment herein illustrated and described, but may be used in other ways without departure from its spirit as defined by the following claims.
1. In combination, a hollow metal propeller blade comprising a metal shell having an airfoil shaped outer surface and an inner surface, a heater strip adhesively secured to, pressed against, and covering a selected portion of, said inner surface, means localizing the application of heat to, and additionally holding said strip against, and positioning said strip on, said inner surface comprising heat insulating multi-cellular filling material substantially filling the hollow blade adjacent the heater strip and bonded to the heater strip and said inner surface and surround ing said strip, said strip being located between said heat insulating filler material and said inner surface and at the portion of the blade to be heated.
2. In a metal propeller blade having a metal core secured to opposite sides of a metal airfoil covering and spaced from the leading edge of the airfoil covering, a heating element adhesively secured to and additionally held against the inner surface of the airfoil leading edge portion in heat transferring relation therewith, means localizing the application of heat to, and holding said element against, and positioning said strip on said surface, comprising, a heat insulating multi-cellular filling material substantially filling the space between the core and the covering at the leading edge side of the core, bonded to said covering and core and to said element and surrounding said element, said element being located between the filling material and the airfoil leading edge portion.
3. The method of forming an airfoil having a heating element incorporated therein which comprises, forming an airfoil shaped hollow member, placing a heating element in said hollow member over a selected portion of the inner surface of said member and causing said element to adhere to said selected portion, then inserting heat insulating material, which may be treated to cause it to give off a gas and expand, into the hollow interior of said member, treating said material to cause it to give off a gas and form a multiplicity of cells in said material and expand said material, while in position in said hollow member, against the inner surface of said member and against the exposed sides of said element to thereby press said element against said surface and embed said element in said material, then curing said expanded material and permanently bonding said material to the exposed surfaces of said member and the exposed sides of said element, to, by means of said material, adhesively secure said element to other portions of said surface and permanently secure both said expanded and cured material and said element in and to said member.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 1,950,411 Larsen Mar. 13, 1934 2,106,761 Roberts et a1 Feb. 1, 1938 2,402,770 Poekel June 25, 1946 FOREIGN PATENTS Number Country Date 231,919 Great Britain Apr. '7, 1925