Model airplane muffler constructions

Claim 2

An airfoil muffler for a single cylinder model airplane engine having a lateral exhaust port, the muffler being of elongated design, having a leading and a trailing edge and being adapted for edgewise movement forwardly through the slipstream of the airplane when the latter is in flight, said muffler comprising a single hollow tubular shell defining an internal expansion chamber for exhaust gases and having a top wall which is arched upwardly in airfoil fashion, a bottom wall, and inner and outer end walls substantially closing the opposite ends of the tubular shell, there being at least one outlet opening in said top wall for the expanded gases in said chamber, said outlet opening being disposed rearwardly and entirely below the crest of the airfoil arch in said top wall to the end that it will communicate directly with the vacuum pocket which is created by such airfoil arch incident to passage of the muffler edgewise through said slipstream.

Claim 3

An airfoil muffler as set forth in claim 1, wherein said bottom wall is arched downwardly in airfoil fashion and is provided with at least one outlet opening which is disposed rearwardly and entirely above the crest of the latter airfoil arch.

Claim 4

A muffler as set forth in claim 2, wherein said shell is of three-piece sheet metal construction in that said top and bottom walls are formed from a single sheet metal blank, folded upon itself in the longitudinal direction of the muffler and heat sealed along the trailing edge of the muffler, and the inner and outer end walls are separately formed and heat sealed around their peripheral edges to the top and bottom walls.

Claim 5

An airfoil muffler as set forth in claim 3, wherein said top, bottom and outer walls are formed of stainless steel sheet metal on the order of 0.015 inches in thickness and the inner end wall is formed of sheet metal on the order of 0.035 inches in thickness.

Claim 6

An airfoil muffler as set forth in claim 4, wherein the trailing edges of the top and bottom walls are heat sealed together so as to subtend a small included angle which defines a sharp knifelike trailing muffler edge.

Claim 7

An airfoil muffler as set forth in claim 2, wherein said top and bottom walls are each provided with plural outlet openings which are arranged in linearly straight rows that extend generally in the longitudinal direction of the muffler.

Claim 8

An airfoil muffler as set forth in claim 2, wherein said muffler is tapered on a small slant angle so that said top and bottom walls define a frustum the large base of which is substantially closed by said said inner end wall.

Claim 9

An airfoil muffler as set forth in claim 7, wherein said inner end wall is planar and the outer end wall is generally arcuate in vertical cross section.

Claim 10

An airfoil muffler as set forth in claim 8, wherein the crest line of said arcuate end wall is substantially parallel to the plane of said inner end wall.

Claim 11

The combination with a model airplane having an engine provided with a cylinder from which there projects radially a tubular extension defining an exhaust port of elongated design and which produces a high sound level by pressure pulses of shock wave severity, of an airfoil muffler for reducing the severity of said shock waves and consequently the sound level, said muffler being of elongated design, having a leading and a trailing edge, and being adapted for edgewise movement forwardly through the slipstream of the airplane when the latter is in flight, said muffler comprising a single hollow longitudinally tapered tubular metal shell of symmetrical airfoil configuration, defining an internal expansion chamber for exhaust gases and having a top wall which is arched upwardly in airfoil fashion, a bottom wall which is arched downwardly in airfoil fashion, and inner and outer end walls of tear drop outline substantially closing the opposite ends of the tubular shell, there being an inlet opening in said inner end wall and a series of outlet openings in each of said top and bottom walls, an adapter plate having a slot extending transversely therethrough, means releasably securing said muffler and adapter plate to the cylinder with the tubular muffler shell projecting radially from the cylinder and the adapter plate interposed between said inner end wall and the cylinder so that said slot establishes sealed communication between said exhaust port and the inlet openings said outlet openings being disposed in the trailing airfoil regions of their respective arched walls and entirely inwardly of the arch crests to the end that they will communicate directly with the vacuum pockets which are created by the airfoil arches incident to forward movement of the airplane and consequent passage of the muffler edgewise through the slipstream of air generated by such forward movement.

Claim 12

The combination with a model airplane having an engine provided with a cylinder from which there projects radially a tubular extension defining an exhaust port of elongated design and which produces a high sound level by pressure pulses of shock wave severity, of an airfoil muffler for reducing the severity of said shock waves and consequently the sound level, said muffler being of elongated design, having a leading and a trailing edge, and being adapted for edgewise movement forwardly through the slipstream of the airplane when the latter is in flight, said muffler comprising a single hollow longitudinally tapered tubular metal shell of symmetrical airfoil configuration, defining an internal expansion chamber for exhaust gases and having a top wall which is arched upwardly in airfoil fashion, a bottom wall which is arched downwardly in airfoil fashion, and inner and outer end walls of tear drop outline substantially closing the opposite ends of the tubular shell, there being an inlet opening in said inner end wall and a series of outlet openings in each of said top and bottom walls, an adapter plate having a slot extending transversely therethrough, means releasably securing said muffler and adapter plate to the cylinder with the tubular muffler shell projecting radially from the cylinder and the adapter plate interposed between said inner end wall and the cylinder so that said slot establishes sealed communication between said exhaust port and the inlet openings said outlet openings being disposed in the trailing airfoil regions of their respective arched walls and entirely inwardly of the arch crests to the end that they will communicate directly with the vacuum pockets which are created by the airfoil arches incident to forward movement of the airplane and consequent passage of the muffler edgewise through the slipstream of air generated by such forward movement.

Claim 13

The combination set forth in claim 10, wherein the rim region of said elongated slot in the adapter plate is recessed to provide a pilot socket into which the outer end of said tubular extension of the cylinder projects and within which it seats, and the side of the adapter plate which opposes the muffler is planar and fits flush against said end wall in face-to-face sealing relationship.

Claim 14

The combination with a model airplane having an engine provided with a horizontally disposed cylinder form which there projects downwardly and radially a tubular extension defining an exhaust port of elongated design and which produces a high sound level by pressure pulses of shock wave severity, of an airfoil muffler for reducing the severity of said shock waves and consequently the sound level, said muffler comprising a single, hollow, longitudinally tapered tubular metal shell of symmetrical airfoil configuration, defining an internal expansion chamber for exhaust gases and having a top wall which is arched upwardly in airfoil fashion, a bottom wall which is arched downwardly in airfoil fashion, and inner and outer end walls of tear drop outline substantially closing the opposite ends of the tubular shell, there being at least one outlet opening in each of said top and bottom walls, the inner end region of said muffler closely underlying said cylinder with the longitudinal axes of the muffler and cylinder extending in parallelism and the outer end region of the muffler projecting longitudinally beyond the cylinder, and an L-shaped manifold having a vertical leg secured to the cylinder and a horizontal leg secured to the end wall of the muffler and provided with an internal passage which establishes communication between said exhaust port and the inlet opening in said inner end wall of the muffler.

Claim 15

The combination with a model airplane having an engine provided with a horizontally disposed cylinder form which there projects downwardly and radially a tubular extension defining an exhaust port of elongated design and which produces a high sound level by pressure pulses of shock wave severity, of an airfoil muffler for reducing the severity of said shock waves and consequently the sound level, said muffler comprising a single, hollow, longitudinally tapered tubular metal shell of symmetrical airfoil configuration, defining an internal expansion chamber for exhaust gases and having a top wall which is arched upwardly in airfoil fashion, a bottom wall which is arched downwardly in airfoil fashion, and inner and outer end walls of tear drop outline substantially closing the opposite ends of the tubular shell, there being at least one outlet opening in each of said top and bottom walls, the inner end region of said muffler closely underlying said cylinder with the longitudinal axes of the muffler and cylinder extending in parallelism and the outer end region of the muffler projecting longitudinally beyond the cylinder, and an L-shaped manifold having a vertical leg secured to the cylinder and a horizontal leg secured to the end wall of the muffler and provided with an internal passage which establishes communication between said exhaust port and the inlet opening in said inner end wall of the muffler.

Claim 16

The combination set forth in claim 12, including additionally an adapter plate interposed between the vertical leg of said manifold and said tubular extension on the cylinder, said adapter plate being provided with an elongated slot which extends transversely therethrough, the upper side of said adapter plate being provided with a shallow recess which extends around the rim region of said slot and into which the outer end of the tubular extension projects in seated relationship.

Claim 17

The combination set forth in claim 13 wherein the internal passage in the adapter plate is of L-shape configuration.