US2427673A

US2427673A - Air-heating system

Info

Publication number: US2427673A
Application number: US443126A
Authority: US
Inventors: Harry B Holthouse
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 1942-05-15
Filing date: 1942-05-15
Publication date: 1947-09-23
Anticipated expiration: 1964-09-23

Description

m 1947. H. B. HOLTHOUSE 2,427,673

AIR HEATING SYSTEM Filed May 15, 1942 4 Sheets-Sheet 1 I J x i 4 6 I 47 five/2%]? Sept 1947. H. a. HOLTHOUSE 2,427,673

AIR HEATING SYSTEM Filed May 15, 1942 4 Sheets-Sheet 2 Sept. 23, 1947. H. B. HoL'n-lousE 2,427,673

AIR HEATING SYSTEM Filed May 15, 1942 4 Sheets-Sheet 3 f f /r flaiify p 1947- H. B. HOLTHOUSE 2,427,673

AIR HEATING SYSTEM Filed May 15, 1942 4 Sheets-Sheet 4 Patented Sept. 23, 1947 UNITED STATES AIR-HEATING SYSTEM Harry B. Holthouse, Chicago, 11]., assignor to Motorola, Inc., a corporation of Illinois Application May 15, 1942, Serial No. 443,126

Claims. (Cl. 237-2) This invention relates generally to air heating systems and in particular to a system for heatin and distributing air in an aircraft. I In large aircrafts and particularly in large bombing planes having a plurality of operators located in different parts of the fuselage, such as the nose, tail and body portions, many difliculties have been encountered in comfortably heating the portions occupied by the operators. It is recognized of course that planes of bomber type operate at extreme high altitudes and corresponding extreme cold temperatures and have cruising speeds normally of several hundred miles per hour. In a heating system having a single heated air outlet the distribution of heat to all portions or spaces to be heated is prevented by any drafts or air currents passing through the plane. Because of the speeds at which these bomber planes travel it is readily understandable that any small openings in the fuselage to the atmosphere result in high velocity and turbulent air drafts within the plane. Heated air, when discharged from a single source may, therefore, be carried entirely outside of the plane without ever passing through some portions thereof. In attempts to overcome these disadvantages in the air systems having but a single heat outlet, air from such outlet has been piped to the plurality of spaces or compartments to be heated. This procedure, however, is generally unsatisfactory because of the bulk of the hot air conduits, the inconvenience in their assembly, and further because of the heat lost in the transmission of the heated air.

In further efforts to provide a suitable heating system for an aircraft having a plurality of spaces therein, a heating unit of internal combustion type corresponding to each space is provided, with the air and fuel mixture for burning in the heating units being supplied from a common mixing unit such as a carburetor. This system is not entirely successful, however, because in the transmission of the air and fuel mixture the fuel condenses from the mixture so that the operation of the heating units is relatively ineflicient and unreliable.

It is an object of this invention, therefore, to provide an improved air heating and distributing system.

.Another object is to provide an improved air heating and distributing system for an aircraft having spaces or stations to be heated located remotely from each other.

A further object of this invention is to provide a heating system for an aircraft comprised of a plurality of heating units of internal combustion type each of which is adapted to be operated over a wide range of altitudes of varying pressures and oxygen densities.

Yet a further object of this invention is to pro- 2 vide an air heating system which utilizes a plurality of combustion portions having air and fuel separately fed thereto for burning from common air and fuel supply means.

Yet another object of this invention is to Provide an air heating system having a plurality of heat distributing portions located remotely from each other and operatively associated so as to completely eliminat any heat transmission losses therebetween.

Still another object is to provide a, heating system having a heating unit of internal combustion type in each one of a plurality of stations in which a proper air and fuel mixture is pre pared at each station and retained until ready for burning.

A feature of this invention is found in the provision of an air heating system comprised of a plurality of combustion portions for heating air adapted to be operated at a low pressure, with air and fuel being separately conducted to a corresponding portion at a pressure above such low pressure. Each combustion portion is operatively associated with means adapted to reduce the air and fuel supply pressures to substantially said low pressure and to mix the same for burning at such low pressure. The conduits for carrying the air and fuel to the combustion portions can thus be relatively small while a combustion portion can be located wherever heat is desired.

Another feature of this invention is found in the provision of an air heating system for an aircraft comprised of a plurality of spaced combustion portions operated at substantially atmosheric pressure and fed from common air and fuel supply means, in which the air and fuel are separately supplied to each combustion portion in relative quantities providing for a substantial- 1y uniform mixture over a wide range of altitudes of varying oxygen contents and pressures.

The air and fuel are supplied at atmospheric temperature so that the problem of heat losses in the air and fuel supply systems is entirely eliminated.

Further objects, features, and advantages of this invention will become apparent from the following description when taken in connection with the accompanying drawings in which:

Fig. 1 is a diagrammatic illustration of the fuselage of a bombing plane showing the arrangement therein of the operators compartments which are to be heated Fig. 2 illustrates diagrammatically the operating' arrangement of a plurality of heating units comprising the heating system of this invention;

Fig. 3 is a sectional detail view of a heating unit;

Fig. 4 is a transverse sectional view through the combustion portion of a heating unit taken along the line 4-4 in Fig. 3;

Fig. 5 is a detail sectional view of an air and fuel mixing means operatively associated with each heating unit;

Fig. 6 is a diagrammatic control circuit for opcrating the heating system shown in Fig. 2;

Fig. 7 is a sectional view of a modified form of heating unit with parts thereof broken away to more clearly show the construction thereof;

Fig. 8 is a transverse sectional view taken along the line 8--8 in Fig, '7;

Fig, 9 shows the application of a heating unit in conjunction with an inflatable garment adapted to be worn by an operator of an aircraft;

Fig 10 is a detail transverse sectional view of a fuel metering mean diagrammatically illustrated in Fig. 2 for each heating unit;

Fig. 11 is an enlarged fragmentary elevational view as seen along the line illl in Fig. 2; and

Fig. 12 is a detail plan view of a combination fuel valve and switch unit utilized for each heating unit and diagrammatically illustrated in Figs. 2 and 6. t In the practice of this invention there is provided an air heating and distributing system for an aircraft having a plurality of operator compartments therein, which comprises a heating unit of internal combustion type located in each of such compartments. Each heating unit includes a combustion portion having a corresponding fuel conditioning means for preparing an air and fuel mixture for burning therein. Air and fuel are supplied separately to each fuel conditioning means from a common supply means, with such air and fuel being heated together to at least a fuel vaporizing temperature by electric heating means corresponding to each conditioning means. The separate feeding of air and fuel to each heating unit and the preparation of the air and fuel mixture for burning immediately at a corresponding combustion portion assures a proper mixture for burning and resultant efficient operation of each heating unit. Electric air moving means corresponding to each combustion portion projects air to be heated in a heat exchange relation with a combustion portion and into a corresponding compartment. The electric air moving means and heating means corresponding to a-combustion portion are connected together in a common circuit having a plug element adapted for connection with a source of electrical power such as a power circuit in the aircraft. By virtue of this constructionand assembly of the combustion portions the air in each compartment is positively heated while the bulk and complexity of the 1 means common to such portions and extended between the same are of a' small size to provide for their installation in a minimum of space.

At high altitudes the operation of internal combustion devices is greatly affected by the variations in barometric pressures and oxygen supply. Thusat high-altitudes and a corresponding reduced ox ygen content of the air at suchaltitude, more air must be supplied at the high altitudes as compared to a lower altitude or ground level to provide for an efficient operation of the heating'unit at all altitudes. The'=invention, therefore, contemplates the provision of pressure responsive nose and intermediate portions thereof. As shown diagrammatically in Fig, 2 the heating system is comprised of a plurality of heating units [2 of internal combustion type, only one of which is indicated, corresponding in number to the compartments ll. Air for combustion is supplied by a fan l3 from a transmission duct I4 common to all of the heating units and having a connection It corresponding to each thereof. Fuel for each unii is supplied by a pump i1 through a common line [8 having a branch line l9 connected to a corresponding heating unit. The pump is operatively associated through suitable mechanism 22 with a motor 2| of series wound type, which also operates the fan l3. Since each heating unit i2 is similar in construction and operation only one thereof will be referred to in the following detailed description.

A heating unit I2 (Figs. 3 and 4) includes a housing 23 of cylindrical shape open at the opposite ends thereof. Axially extended within the housing is a combustion portion or chamber 24 having an air supply chamber 26 at the inner end thereof which is separated from the combustion chamber by a partition or dividing wall 21 which closes such inner end of the combustion chamber. The outer end of the combustion chamber extends to the end 45 of the housing 23 and is closed by a cover plate 28.

The combustion chamber 24 is divided longitudinally thereof into four axially extending but connected passages 290-2 9d by a partition member 3i of substantially X-shape. The combustion chamber inlet 32 and outlet 33 are formed in the wall portion 21 in communication with the

passages

29a and 29d, respectively. Located within the inlet 32 is an air and fuel mixing unit. indicated generally as 34, which extends within the air supply chamber 26. The outlet 33 is provided with a tail pipe 36 projected within the air supply chamber 26. Also extended within the air supply chamber 26 is a second tail pipe 31 larger in diameter than the tail pipe 36 but in coaxial alignment therewith so as to form a space between such two ail pipes within the air supply chamber 26 for a purpose to be later noted. The tail pipe 31 projects outwardly from the housing 23 and is adapted for connection with a suitable exhaust pipe (not shown) to carry the exhaust gases away from the heating unit l2 and outside of theaircraft.

The outer wall or body portion of the combustion chamber 24 is provided with angularly spaced axially extending heat radiating fins 38.

Oninsertion of the combustion chamber 24 within the housing 23 the outer ends of the fins 38 engage the inner periphery of the housin 23 so that an annular passage 39 for air to be heated is formed about the combustion chamber and within the housing. Theair to be heated 5 housing-end 4.6.. The heated air is discharged from the housing 23"at the end .45 thereof.

The air supply chamber 26 is connected directly with a correspondingconnection IE to the commonair duct I4. In one embodiment of the invention the chamber 26 has a volume of about fifty-four cubic inches with the air therein having a pressure of less than 3 inches of water.

small volume of the chamber 26 the air duct i4 is correspondingly small-so that it can be in- 2 the duct l4 may be progressively decreased in.

its cross sectional area between the first and last heating units I! connected thereto to provide for a suflicient volume of air being supplied to all of such units. The proper distribution of supply air to the heating units I! may be further facilitated by the operation of a valve member 58 arranged within a corresponding air duct |6 to control the flow of air therethrough.

A corresponding fuel line I!) for the heating unit I! is connected at one end to the common fuel line I8 and at its opposite end to a fuel injection nozzle 41 formed as a part of the air and fuel mixing means 34. The rate of feed or supply of fuel to the mixing means 34 is determined by a fuel feed unit 63 connected inthe fuel line connection l9. This unit 63 is diagrammatically illustrated in Fig. 2 and shown in detail in Fig lil and includes a body member 64 of sleeve form threadablyconnected at its inlet end 61 directly with the fuel line 19, and at its outlet end to a bored plug 66 which in turn is connected to the line I911. The body member 64 is of a length to provide for the formation therein between its end 61 and the plug 66 of a cavity or fuel reservoir 68 which is filled with a fuel filter of felt or other suitable like material. The reservoir 68 is in fluid connection with a bellows unit 69 comprised of a pair of flexible mating diaphragms having an air space or pocket therebetween. The expansion and contraction of the bellows unit 69 is responsive to the fluid pressures within the reservoir 68 and serves to cushion or absorb any fuel surges in the cavity in a well known manner, so as to provide for a substantially uniform pressure and flow of the fuel at the reservoir outlet. Referring to Fig. it is seen that the bellows or expansible means 68 is expanded against the pressure of the air to the outside thereof. It is apparent of course that in high altitude flying the air pressure is reduced so as to correspond-, ingly decrease the air pressure tending to compress the bellows means. This condition impairs the function of the bellows means to level the pulsations in the fuel resulting from the action of the pump I 1. Also at reduced air pressures the diaphragms may be entirely pulled apart by the fuel pressures pushing outwardly thereon. To assure a proper operation of the bellows means 69 at all altitudes there is provided a casing or enclosure 10 which is air sealed about the bellows means 69. The space within the casing 10 is at an atmospheric pressure corresponding to ground level. A substantially constant air pressure is thus maintained on the bellows means 69 regardless of the flight condition of the aircraft. It is apparent of course that any desired air pressure may be used within the casing 18 depending upon the operating characteristics of the bellows means 69.

The fuel line l9a, between the unit 63 and the fuel nozzle 41 is of a length of about 9 inches. Extended over approximately two thirds of this length and within the line I9 is a core member 1| which may be provided in wool, yarn, glass, wire or the like. The member 1| functions to retard and meter the fuel admitted to the fuel injection nozzle 41 by virtue of its increasing the resistance to the flow of the fuel in the line I9; The flow at the core member occurs as a result of a capillary or surface tension action between the surfaces of the core member and the fuel line. This action provides for a definite creeping of the fuel about the core member irrespective of the fuel pressure producing the fuel flow, an increase in pressure serving merely to accelerate this creeping action. Since the bellows means 68 operates to level the fuel pulsations leaving the reservoir 68 a substantially uniform fuel pressure occurs at the outlet therefor so that the fuel passes about the core member at a substantially constant rate. Increasing the diameter of the core member decreases the flow through the line, but also increases the capillary flow of the fuel by virtue of the increase in the surface of the core member. It is thus readily apparent that a variation in both the diameter and the length of the core member 1| relative to the fuel line |9a effects a corresponding variation in the metering of the fuel to the fuel injection nozzle of the conditioning means 34. As illustrated in Fig. 2 fuel is supplied to the common fuel line It by a pump l1. However it is to be understood that the fuel line I8 may be connected directly into the fuel system of the motive power for the aircraft regardless of the operating pressure of such fuel system, since the proper rate of fuel feed to the conditioning means 34 can be readily accomplished by a proper relative selection of a'core member 1| and fuel line IS.

The air and fuel mixing means 34 (Figs. 3 and 5) includes a casing member 48 which is closed at one end and open at the end 49 thereof with the passage 29a. A mixing chamber 5| at the closedend of the casing 48 is separated from an equalizing chamber 52 by a perforated plate member 53. The equalizing chamber 52 in turn is both defined and separated from the combustion chamber passage No by a perforated heat insulating plate 54 spaced inwardly from the open end 49 of the casing 48. Extended substantially axially through the casing 48 and supported in the

partition plates

53 and 54 and projected outwardly from the closed end of the casing 46 is a combination electric heating and igniting unit 56 which includes a resistance coil 51 supported in a spaced relation within a metal tube 58.

In the operation of the air and fuel mixing means 34 the fuel delivered to the nozzle 41 is directed into the mixing chamber 5|, the fuel nozzle being located within the air supply chamber 26 and mounted directly on the casing 48 at the mixing chamber 5|. A portion of the air for mixing with the fuel enters the nozzle 41 from the air chamber 26 through ports 59 in the fuel nozzle and travels with this fuel into the mixing chamber 5|. Additional air from the air chamber 26 is admitted directly into the mixing chamber 5| through apertures 6| formed in the casing 48 about the fuel injection nozzle 41. The fuel within the mixing chamber 5| is heated to at least a fuel vaporizing temperature by the combination unit 56 to provide a thorough mixing thereof with the air in the mixing chamber 5|. The casing 48,'partition plate 53 and tube 58 are constructed of a heat conducting material so as to readily receive and conduct the heat radiated by the resistance coil 51 to substantially all portions of the conditioning unit 34. The vaporous air and fuel mixture passes through the perforated plate 53 into the equalizing chamber 52 which in cooperation with the perforated insulating plate 54 acts to reduce the turbulence in the mixture and to disperse the mixture substantially uniformly over the entire cross section of the casing 48. This combustible mixture passes through the apertured plate 54 and across the open end 62 of the tube 58 into the effective igniting zone of the combination unit 53 which functions as a heat gun. In other words the heat developed by the coil 51 is projected outwardly from the open end 62 of the tube 58, the heat generated being dependent upon the watt input to the resistance coil 51. The combustible mixture is thus ignited by virtue of the temperature at the end 62 of the tube 58 being of a degree capable of igniting such fuel without the mixture itself directly contacting the coil 51.

As predously mentioned the air within the chamber 26 is at a pressure of less than about 3 inches 01 water. Since the air is admitted into the combustion chamber 24 at this pressure it is apparent that combustion takes place within the combusti n chamber at substantially atmospheric pressure. The arrangement of the tail pipes 36 and 31 within the air chamber 26 provides for a flow of air from the chamber into the tailpipe 31. This flow of air creates a Venturi action across the tail pipe 36 and hence at the combustion chamber outlet 33 to facilitate the passage of the exhaust gases therefrom. The air within the chamber 26 thus acts at both the inlet 32 and outlet 33 to move the combustible mixture and exhaust gases through the combustion chamber. As is best illustrated in Fig. 3 it is seen that the air supply chamber 26 also func tions as an expansion chamber relative to the air admitted thereto from the pipe l6. As a result air may be carried in the transmission duct M at a pressure above the pressure within the air supply chamber 26, with the pressure of the air in the duct I4 being reduced in the chamber 28 to a pressure of less than 3 inches of water because of such expansion. The duct line H may thus be further reduced in size to provide for its installation with a minimum of interference with the other installations in the aircraft. It is to be understood that because of the expansion function of chamber 26 any type fan or even an air compressor could be used in place of 'the sirocco type fan illustrated.

From the above description, therefore, it is seen that air and fuel are supplied separately and in controlled quantities to each heating unit I2 and are mixed together for burning by an air and fuel mixing means 34 corresponding to each of the units. Further the air and fuel can be conducted to the heatin units under wide variations in pressure, since the air chamber 26 and fuel metering device 63, operatively associated with each of the heating units, function to reduce the air and fuel pressures to a value providing for their burning in the combustion chamber at a normal operating pressure. In connection with the air duct l4 it is obvious that such a line may be of a rigid or a flexible construction since it carries only atmospheric air. In other words there is noproblem of lost heat in the transmission of the supply air since the air is supplied at atmospheric temperature and is not mixed with the fuel until it reaches a fuel conditioning unit 34. As a result both the air and the fuel supply lines may be made relatively small and without any special heat insulating provisions.

In the control circuit for the heating system shown in Fig. 6 the motor 42 and resistance coil 51 corresponding to a heating unit I 2 are connected together in a series circuit. Each series circuit is provided with a plug portion '|2 for connection with a corresponding electric receptacle I3 which are connected together in series and included in a power circuit C having a battery 14. The motor 2| for the air supply fan l3 and pump I1 is connected to the power circuit through a suitable plug and socket connection 16, and in series with a voltage regulator 96 to be later fully xplained. The operation of the motor 2| is controlled by a switch 11. Since an entire heating unit weighs about 13 pounds it is capable of bein readily installed and removed as a complete package unit.

Each heating unit I2 is selectively operated by a combination fuel valve and control switch unit 18 shown diagrammatically in Figs. 2 and 6 and in detail in Fig-12. The unit 18 is connected in a corresponding fuel line l9 and includes a valve member I9 having a stem portion 8| and an operating lever or handle 82. The stem 8| has a pin 83 projecting radially therefrom, which acts as an actuator for a switch 84. When the handle 82 is in an on position, as shown in Fig. 12, the valve member 19 is in an open position and the pin 83 in a position to close the switch 84. The on position thus provides for the operation of a heating unit. To stop heater operation the handle is moved to its off position. This manipulation closes the supply of fuel to the heater and moves the pin 83 out of engagement with the switch 84 to open the same.

As was previously mentioned the motor 2| is of series Wound type so that it inherently seeks a speed at which it will operate at full load. In other words the motor operates to retain a constant load thereon regardless of the speed of its operation. When the heater is operated at altitudes approaching 20,000 feet the speeding up of the motor 2|, resulting from the reduced air load on the fan by the decreased density of the air at such altitudes, is sufiicient to compensate for the reduced air density so that a substantially constant supply of oxygen is fed through the fan inlet 86 into the duct l4 and hence to the conditioning units 34 (Figs. 2 and 11). Combustion conditions in each heater are thus retained substantially the same as the combustion conditions at ground level. This increase in speed, however, is not great enough to maintain ground level combustion conditions at altitudes in excess of about 20,000 feet. In order, therefore, to maintain ground level heater operation at altitudes above 20,000 feet and up to about 50,000 feet further compensation for the increased rarification in the air and reduction in oxygen content is provided by means now to be described.

The inlet 86 to the air duct I4 is operatively associated with damper means 81 for controlling the passage of air therethrough to the heater units l2 (Figs. 2 and 11). The damper means is illustrated as bein of a usual type including louvers 88 connected to a common actuating member 89 for simultaneous movement to open and closed positions relative to the inlet 86. The actuating member 89 is operated by a bellows unit 9| which is responsive to variations in atmospheric pressures to operate the louvers.

The bellows unit 9| is comprised of mating diaphragms 92 composed of a flexible metal or like material to form a closed space having a spring 93 therein acting to push the diaphragms apart. The space within the diaphragms 92 is evacuated to a pressure of substantially zero pounds per square inch while the pressure of the spring 93 is such that at ground level the atmospheric pressure is sufficient to press or squeeze the diaphragms to a closed or fully compressed position. It is readily apparent, of course, that a closed position of the bellows does not indicate a closed position of the damper means since the louvers 8B are retained partially open at ground level to admit suficient air into the duct l4 to maintain proper combustion in the heater units i2. Further the spring 93 may be calibrated so that the bellows unit 9| remains closed up to an altitude at which a control of the damper means is desired. This is accomplished by setting the spring pressure to correspond to the pressure at the desired altitude. The bellows unit 9| is carried on a bracket 95 in a manner such that the movement of the diaphragms 92 is additive relative to the actuating bar 89. In other words the movement of the bar is double the movement of each diaphragm 92.

To efiiciently operate the heater at all altitudes the power available for the operation of the motor 2|, the capacity or size of the fan l3, and the size of the inlet 86 when the louvers 88 are in full open position are relatively determined to provide for a supply of air having enough oxygen therein for proper combustion at the highest altitude at which the heaters are to operate. When this relation is determined the opening 86 and the power supplied to the motor 2| are relatively and progressively decreased to provide for the eiiicient operation of the heaters at ground level. Since the louvers are intended to be wide open only at the extreme altitude of 50,000 feet and corresponding rarified atmosphere, a partially closed position of the louvers at ground level and corresponding heavier atmosphere permits the delivery of an oxygen supply to the heaters which is substantially equal to the supply of oxygen at the high altitude. In the operation of the heaters, therefore, as the atmospheric pressure is reduced with an increase in altitude the bellows unit 9| is expanded by the action of the spring 93 to progressively move the louvers 88 to a wide open position. This progressive change in the size of the inlet opening 86 as varied by the louvers 88 continues until the louvers are in their wide open position corresponding to the highest altitude at which the heater is adapted to operate with ground level eificiency. As a result of the air becoming less dense with an increase in altitude the load on the motor produced by the fan decreases so that the motor increases in speed concurrently with the movement of the louvers to their open position. The increase in the speed of operation of the motor 2| and hence of the fan l3 over the entire range of altitudes at which the heater is to operate is accomplished by means now to be described.

As previously mentioned the size of the fan l3, the power applied on the motor 2| and the size of the opening 86 are relatively determined to compensate for the reduced oxygen content of the rarified atmospheres at high altitudes. The size of the fan l3 relative to the motor 2| is such that at ground level the motor is substantially incapable of operating the fan when the louvers 88 are in a wide open position. In other words the fan is oversize relative to the motor for operation at ground level with the louvers 88 entirely open. The louvers 88, therefore, are only partially open at ground level to permit an operation of the fan l3 by the motor 2| which provides sumcient air for combustion. However, with an increase in altitude and a resultant decrease in the air load on the fan l3 the louvers 88 may be progressively opened without stalling the motor 2|.

In the operation of a series wound motor, the increase in speed thereof is directly proportional to the reduction in the load thereon up to a limit which might be termed a fiat point or "point of constant speed.- In other words the ratio of speed to load follows a straight line curve up to a flattening out point thereon at which the speed remains substantially constant. This increase in the speed of a series motor with a reduction in load is often referred to as the unwinding of the motor, The unwinding characteristic of a series type motor is utilized in the present invention to provide for a substantially continuous increase in the speed of operation of the motor 2| over the entire range of altitudes at which the heaters are to operate.

Thus referring to Fig. 11 the voltage regulator 96, previously referred to, is carried on the duct l4 and includes a regulating arm 91 operatively connected to the actuating member 89 for operation by the bellows unit 9|. The voltage regulator or rheostat 96 functions to increase the power applied to the series wound motor 2| with an increase in altitude to augment the speeding up of the motor resulting from its being of series wound type. Thus for example assume the volt age regulator at ground level to be adjusted such that the voltage applied on the motor 2| is only about 60% of its rated voltage. With an increase in the altitude and corresponding decrease of the air load on the fan |3,' the motor 2| while operating at 60% of itsrated voltage will un rated voltage so that a third unwinding there-- of occurs. It is seen, therefore, that the series motor 2| operates to continuously increase in speed with a reduction in load thereon for each voltage at which it is operated. Thus by varying the applied voltage from some value below its rated voltage to a value above its rated voltage a continuous increase in speed thereof over a wide speed range can be obtained. This operation of themotor 2| in conjunction with the use of an oversized fan and adjustable louvers 88 provides for a wide compensation for the reduction in oxygen content in the rarified atmospheres at high altitudes so that the supply of oxygen at all altitudes is maintained substantially constant. Combustion conditions over the entire range of altitudes at which the heaters are operated are thus retained substantially uniform. It is to be understood of course that in those instances where a series wound motor is not utilized that the rheostat control of this invention may be used to progressively increase the speed of operation of some other type motor.

Since the speed of the motor 2| as controlled by the voltage regulator 96 might not be required until after some predetermined altitude, the operation of the voltage regulator may be delayed until such predetermined altitude is reached. Thus the regulating arm 91 (Fig. 11) is mounted for pivotal movement on a shaft 98 which also carries an arm 99 having a slot |0| therein for receiving a pin I02 mounted on a link I03 carried on the actuating bar 89. It is seen, therefore, that the arm 91 remainsstationary until the lost motion in the pin and slot connection is taken up after a predetermined movement of the actuating arm 89 by the bellows unit 9 I.

In conjunction with the oxygen control it may be found necessary under some conditions of operation to change the rate of fuel feed supplied to the heaters I 2. To maintain a substantially uniform fuel mixture at all altitudes the rate of fuel supply may be varied concurrently with the variation in the oxygen supply over a portion of the range of altitudes at which the heater is to operate. Thus referring to Fig. 2 the actuator bar 49 is formed with a slot I04 adapted to receive a. pin III carried at one end of a pivoted link member II". The opposite end of the link member ID! is pivotally connected with a valve member I08 formed as a part of a valve unit I 09 connected in the fuel supply line I8 ahead of the pipe connections I 9. The pin and slot connection I04- I06 provides for a lost motion between the bar 89 and the link I01 so that movement of the link I! is not immediately responsive to the expansion of the bellows unit 9|. In other words, the supply of fuel to the heaters I2 is not varied in response to atmospheric conditions until an altitude is reached at which the pin I06 is in driven engagement with the bar 89. After this engagement takes place the air and fuel supplied to the combustion chamber is concurrently varied in response to the barometric pressures acting on the bellows unit 9|. It is to be understood, of course, that under some conditions of operation the fuel may be varied over the complete range of altitudes at which the heater is to operate.

A modified form of heating unit I2 is shown in Figs. '7 and 8 which is similar in all respects to the heating unit I2 in Fig. 3 except that the heat radiating fins 38' thereof are positioned transversely about the combustion chamber 24'. Similar numerals of reference, therefore, will be used to designate like parts. The combustion chamber 24' is positioned transversely across the housing 23' with the air chamber 26 projected from one side thereof. The housing 23' at the end III, thereof, is formed to extend partially about the periphery of the fins 38 to direct the air moved by the fan 42 in a heat exchange'relation therewith. The fan 42 and driving motor 4I therefor are mounted at the opposite end H2 of the housing, and project the heated air rom the housing end III. The operation of the heating unit I2 is similar in all respects to the heating unit I2 of Fig. 3 so that a further description thereof is believed to be unnecessary.

The heating unit I2 is illustrated in Fig. 9 for heating an inflatable garment I I3 adapted to be worn by the operator of an aircraft. As shown in Fig. 9 the air circulating fan 42 is of a sirocco type, as compared to the propeller type fan 42 shown in Fig. 3. The sirocco fan operates with less volume but at a higher pressure than the propeller type fan, which pressure is utilized to inflate the garment H3. The discharge end 45 of the heating unit I2 is provided with an extension 4 having a flexible conduit H6 adapted for fluid connection with the garment H3 as by a slot and bayonet connection I I1. On operation of the heating unit I2 the pressure of the heated air as produced by the fan 42' is suflicient to inflate the garment H3 and to circulate heated air therein and about the body of the operator.

Fluid connected at one end with the extension H4 and at its opposite end with the fan 42 is a by-pass conduit H8 for feeding unheated air into the garment H3. The extension H4 has a vent or opening H9 for exhausting heated air.

12 The exhaust of the heated air and the flow of cool or unheated air into the connection H6 are concurrently controlled by a common valve member I2I so that any proportion of heated and cool air can :be supplied within the garment I I3.

As shown in Fig. 9 the operator is in a sitting posture. In order to circulate air entirely about the operator, the garment at the seat portion is provided with a porous cushion I22 which permits heated air to be circulated therethrough. It is to be understood of course that if the operator is normally in some position other than a seating position, such as in a prone position which might be assumed by the operator carried in the blister or bulge I23 at the bottom of the fuselage I0 (Fig. l) the porous material I22 would then be across the front of the garment. The end of the sleeves, and the neck portion of the garment II 3 may be suitably formed with openings to permit heated air to be circulated within the gloves I24 and about the head of the operator. Since the garment I I3 is generally worn over the shoes of theoperator heated air is admitted about the feet through the tops of the shoes. By virtue of this arrangement heated air is positively directed immediately adjacent the body of the operator regardless of the air current conditions present in the compartmentin which he happens to be located. Instead of the garment I I3 being vented at the sleeves or at the throat it may be made out of a suitable porous material or fabric which gradually permits the heated air to escape therefrom. It is apparent of course that the flexible conduit I I6 can be connected any where about the garment H3 depending upon the normal movements of the operator so as to offer a minimum of interference to such movements.

From a consideration of the above description and drawings, therefore, it is seen that the invention provides a'heating system for furnishing heated air to a plurality of remotely located spaces in which a heating unit in each of such spaces are operatively connected with common power, air and fuel supply means adapted to be installed in a, minimum of space. The air and fuel are supplied separately to each heating unit and are mixed at the unit for burning. The combustible mixture supplied to each combustion portion for burning is thus retained substantially uniform so that each heating unit operates with maximum efficiency. Although air and fuel are separately supplied to all of the heating units from common supply sources such air and fuel are in an unheated condition so that the problem of heat transmission losses between the various heating units is completely eliminated. It is understood of course that the air and fuel connections of a heating unit with a corresponding common transmission line may be of a flexible construction so that a. heating unit can be readily moved about within a corresponding space or compartment which is to be heated. Further the operation of the heating system is not dependent upon any air velocities resulting from the plane being in flight, and can be operated at all times and at all altitudes.

Although the heating system has been illustrated and described in conjunction with an aircraft it is to be understood that the heating units may be arranged in any large open space to distribute heated air therein, or applied to any condition requiring a plurality of heated air outlets. It is to be understood also that although the invention has been described with respect to several preferred embodiments thereof it is not to be so limited since modifications and alterations can be made therein which are within the full intended scope of this invention as defined by the appended claims.

Iclaim:

i. In an air heating system for an aircraft having a plurality of spaces therein, a heating unit in each of said spaces, means separately supplying combustion air to said units from a common source, means separately supplying fuel to said heating units from a common source, means included in each heating unit for mixing the air and fuel supplied thereto for burning, and altitude responsive means common to said heating units and operatively associated with said air supply and fuel supply means to maintain substantially uniform the air and fuel mixture supplied to each heating unit over a wide range of altitudes of varying oxygen contents and pressures.

2. In an -air heating system for an aircraft adapted for operation over a wide range of altitudes of varying barometric pressures and corresponding oxygen contents, a plurality of heating units, means separately supplying combustion air to said heating units including common air moving means, means separately supplying fuel to said heating units from a common source, means including means common to said heating units and responsive to barometric pressures for controlling the rate of flow of air to said heating units by said air moving means, and means for maintaining the rate of fuel feed to each heating unit substantially uniform over said range of altitudes.

3. In an air heating system for an aircraft adapted to be operated over a wide range of altitudes having varying atmospheric pressures and corresponding variations in oxygen content, a plurality of heating units, means separately feeding air to said heating units, means common to said units and responsive to "atmospheric pressures for controlling the rate of feed of said air to each heating unit, means separately feeding fuel to said heating units from a common source, and pressure responsive means for maintaining the rate of fuel feed to each heating unit substantially uniform over said range of altitudes.

4. In heating apparatus utilizing a liquid fuel, the means for supplying liquid fuel to said apparatus including in combination a supply line, fuel feed means connected in said supply line and having a liquid reservoir therein, expansible means fluid connected with said reservoir and having an air pocket therein, said expansible means being acted upon by the liquid pressures in said reservoir, a sealed enclosure about said expansible means having an air pressure therein of fixed value, and means in said supply line retarding the flow of fuel from said reservoir td control the rate of liquid fuel flow to said apparatus.

5. In heater apparatus having means defining a combustion chamber, the combination of a fuel supply for said combustion chamber including a fuel line, fuel feed means connected in said fuel line including a fuel reservoir having an outlet, expansible means fluid connected with said reservoir and having an air pocket therein, said expansible means being acted upon by the pressure of the fuel in said reservoir, a sealed enclosure about said expansible means ,having an air pressure therein of fixed value, and a longitudinally extending core member arranged within said fuel line at said outlet to retard and control the flow of fuel from said reservoir to said combustion portion.

6. In heater apparatus having means defining a combustion chamber, the combination of a, fuel supply including a supply line fluid connected with fuel moving means which produces a pulmeans being expanded by the fluid within acting against the air pressure on the outside thereof, and a sealed enclosure about said diaphragm means having an air pressure therein of fixed value. said diaphragm means being responsive in operation to the fuel pulsations in said reservoir to maintain a substantially uniform fuel pressure at said outlet.

7. In heater apparatus for an aircraft including means defining a combustion chamber, the combination of a fuel supply providing for a, substantially uniform fuel feed to said combustion chamber over a range of altitudes of varying atmospheric pressures including a fuel line, fuel feed means connected in said fuel line having a fuel reservoir with an outlet, diaphragm means fluid connected with said reservoir having an air pocket therein, said diaphragm means being expanded by the pressure of the fluid therein acting against the air pressure on the outside thereof, a sealed enclosure about said diaphragm means having an air pressure therein of fixed value, and a longitudinally extending core member in said fuel line at said outlet retarding the flow of fuel therethrough to control the supply of fuel to said combustion portion.

8. Aircraft heating apparatus including in combination a plurality of heating units spaced apart in said aircraft and each having a heat exchanger part, fuel supply means common to all said units, air supply means common to said units and means for conducting air therefrom for mixing with the fuel for burning, means responsive to altitude changes acting on said air supply means to provide a relative increase in the volume of air delivered to said heating units as an increase is required for the desired burning of the fuel at increased altitudes, and means for conducting heated air away from each heat exchanger part.

9. Apparatus for heating an aircraft, comprising a plurality of fuel burning devices located at different points about said aircraft, a fuel feed system for supplying fuel to said devices and including parts common to said devices, an air supply system for supplying combustion air to said devices and also including parts common to said devices, and means common to said devices for controlling certain of the common parts of said systems in order automatically to vary the amount of fuel and the volume of air supplied to each of said devices in accordance with variations in the altitude at which said apparatus is operated.

'10. In an air heating system for an aircraft, a plurality of fuel burning devices located at different points about said aircraft, a conduit system for supplying combustion air to said devices and including a conduit common to said devices and having an air inlet opening, damper means for variably opening and closing said opening, a liquid fuel feed system for delivering liquid fuel to said devices and including a fuel feed control valve common to said devices, and an altitude responsive device for operating said damper means and said valve to maintain substantially {miform the air and fuel mixture supplied to each of said devices over a wide range of altitudes.

HARRY B. HOLTHOUSE.

REFERENCES CITED The following,v references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Goerg Oct. 17, 1939 Cracker Apr. 18, 1899 Batter Feb. 16, 1909 Ofeldt Nov, 2.4, 1908 15 McCollum Apr. 28, 1942 Number