US2221547A - Heat protected pitot-static tube - Google Patents

Description

Nov. 12, 1940. P. KOLLSMAN HEAT PROTECTED PITOT STA'I IC TUBE Filed March 12, 1938 3 Sheets-Sheet l W mm m TL N W R vK am N T A U H B 7 1 1 6 1 1 9 0 1 8 0 1 Nov. 12, 1940. P. KOLLSMAN HEAT PROTECTED PITOT STATIC TUBE Filed March 12, 1938 3 Sheets-Sheet 2 INVENTOR PHUL KULLSMHN BY Z2 ATTORNEY A IIIIIII ll NOV. 12, 1940. P KOLLSMAN 2,221,547

HEAT PROTECTED PI'IOT STATIC TUBE 'Filed March 12, 1938 3 Sheets-Sheet 3 111 Y RELFIY BHTTERY u W w INVENTOR PHUL KULLSMFIN B ATTORN EY Patented Nov. 12, 1940 UNITED STATES- PATENT OFFICE 2,221,547 HEAT PROTECTED error-swarm TUBE Application March 12, i938, Serial No. 1%,i65

8 Claims. ((71. 73-212) This invention relates to Pitot-static tubes of the type adapted for use with airplanes for the determination of the air speed, oi the craft and relates particularly to heating systems for keeping the Pitot-static tubes free from ice, snow and sleet.

The prevention of the accumulation oi ice upon and in the ports of such a tube is vital for its proper functioning. In an electrical heating system for Pitot-static tubes injuries may occur to the heating element, thus requiring frequent replacement of the heater. Accordingly provision for opening and closing the tube is neces sary ior replacing the heating element which may lead to weaknesses in. the tube structiu'e. Under my invention I prefer m integral, streamlined metallic tube or shell :lor the Pitct static tube proper, within which i provide part of a heating system having automatic provisions capable of supplying heat, conductively transferred throughout the Pitot-static tube to me vent the formation of ice and, in addition so controlled as to prevent over-heating and the burning out of the heater even the air ex posure temperature to which the tube is subjected be relatively high.

In aerial navigation, particularly under conditions of fog, ice and snow, an air speed indicator is an essential instrument from which to com pute distance traveled by a dead. reckoning procedure. But under conditions of fog, snow and ice, particularly at temperatures close to the freezing point, the Pitot-static tube portion of the indicator tends to fill with ice and snow and to fall of functioning. In order to avoid this failure, it is customary to provide an electric heater adjacent the entrance end of the dynamic pressure duct, which serves to raise the temperature of the Pitot-static tube above the melting point of ice, thereby preventing adherence of congealed water to the exterior tube surfaces and melting out any congealed moisture which may enter the dynamic pressure duct. Difiiculty is, however, experienced with such heaters in maintaining them in operative condition because of the low amount of heat which can be dissipated from the tube structure during non-flying periods and the relatively much larger amount of energy required to function for adequate heating during flight intervals. That is, with a plane on the ground in summer weather, a heat energy conversion in the heater of more than a very few watts will overheat the heater and burn it out, whereasin flight under icing conditions, a minimum of about watts is required to keep the tube free of ice. This requires that the heater he switched on when icing conditions occur and switched ofi before landing, else the heater will 4 be burned out and inoperative for the next ascent and the air speed meter may fail for this 5 reason. Furthermore, a heater control ice the tube under the pilots hands is highly objection able item, since it is another thing to burden the memory of a pilot already overloaded and the necessity of protecting the tube heater may re suit in neglect of some other more important iu= strurnent or control, with consequent accident or in atta ning object of safeguarding heater, I propose provisions, either one 01 N which is local temperature controlled switch in the circuit or" the heater may be einploy-ed to out ch current supply when the temperature of the tube and of the heater ap- A preaches an unsafe maximum and to turn it on wh n the temperature of the tube approaches an undesirable minimum. (I prefer to turn on current at a drop oi temperature below it C. and to cut ofi the current at 20 C.)

The present invention provides means ior the automatic protection of the Pitot tube an er by the supply to the tube of suflicieut h at energy during intervals of flying at low temperatures and cuts oh the energy supplied to the heater during nonuiylng intervals and during dying at safe temperatures through "the operation, individually or simultaneously of a pressure actuated switch responsive to dynamic air pressures and of a temperature responsive mechanism which is actuated by the ambient air temperature surrounding the Pitot-static tube, the dynamic duct therein or the airplane itself.

Objectively my invention eflects a saving in expended heater energy, lower maximum temperature at a standstill of a plane when the heater circuit is left on and the elimination of replaceable heater units.

The invention further provides a special type of relay operating in conjunction with a temperature responsive or pressure-responsive member, simultaneously or one at a time, in conjunction with a heater member adjacent the dynamic duct of a Pitot-static tube.

An object of the invention thus is to turn on a Pitot-static tube heater automatically during intervals of flying at low temperatures and to turn it oil during intervals of flying at safe temperatures.

Another object of the invention is to turn on a Pitot-static tube heater during flying intervals and to turn it off during non-flying intervals.

Still another object of the invention is to turn on a Pitot-static tube during flying intervals at low temperatures and to turn it of! during non-flying intervals and during flying intervals at safe temperatures.

Still another object of the invention is to relay-control the heater current to a Pitot-static tube heater.

Yet another object oi the invention is to relay-control the heater current to a Pitot-static tube heater by the combined action of a pressuresensitive and temperature-responsive mechanism.

Still a further object of the invention is to shut off automatically the heater current during nonfiying intervals, to shut off the heater current automatically during flying at safe temperatures and to permit a shutting off of the heater current manually during intervals when the heater is not needed, particularly when the plane is laid up out of service.

Other objects and structural details of the invention will be apparent from the following description when read in connection with the accompanying drawings, wherein:

Fig. 1 is a view in side elevation, partly in section, of an airplane fuselage equipped with the Pitot-static tube and protecting members of the device'of the invention;

Fig. 2 is a View in vertical section of the Pitotstatic tube and heater member of Fig, '3

Fig. 3 is a diagrammatic View of the heater, heater circuits and protecting mechanism of the embodiment of Figs. 1 and 2;

Fig, 4 is a side view, partly in section, of an airplane fuselage equipped with an alternative form of the Pitot tube protecting mechanism;

Fig. 5 is a diagrammatic view of the tube and protecting mechanism of the embodiment of Fig. 11;

Fig. 6 is a diagrammatic view of circuits and apparatus of still another embodiment of the invention;

Fig. 'l is a diagrammatic view of circuits and apparatus of another embodiment of the invention.

In the embodiment of the invention shown in Figs. 1, 2 and 3 the heat sensitive member is placed within the Pitot-static shell to control a relay having heavy, rugged contacts mounted in a position where the contacts are readily reached for maintenance. As shown in Fig. l, the airplane fuselage ifll has mounted thereon a strut member I02 carrying the shell Ill, with- 'in which there is mounted the dynamic duct I III of the Pitot tube structure. The shell I03 serves as the static pressure means, from which the static pressure at any given elevation is conveyed through a tube member I" to instruments which require an accurate static pressure, such as the sensitive altimeter and the air speed indicator. Simultaneously, the dynamic pressure from the duct I is conveyed through a tube I08 to the air speed indicator I01 and such other instruments as utilize the dynamic pressure, mounted upon the instrument board. A heater member I" is mounted within the streamlined Pitot-static shell I adjacent the dynamic duct I for the purpose of supplyin heat thereto in sumcient quantities to prevent the formation and attachment of ice to the inner and outer surfaces of the tube and shell. Also within the shell I there is provided a temperature-responsive member Hi9, which may conveniently be a strip of the brass-invar steel material, well known as bi-metal." A source of heating energy ill such as a battery or a power driven generator is provided and connected, as shown in Fig. 3, to the heater I08 by appropriate leads H2 and Hi, the circuit passing through the contacts ill of a relay Iii. The bi-metal I" has an attached con- 'tact H6 which cooperates with a second contact I I1. These contacts are connected in circuit with the winding of the relay I it.

As long as the temperature of the ambient air through which the plane is flying is above freezing or above a temperature of about 40 degrees Fahrenheit, the bl-metal member I09 holds the contacts H6 and H1 separated, open-circuiting the relay H5 and leaving the relay contacts Ill open, thereby preventing the flow of current through the heater I08. When, however, the temperature of the ambient atmosphere falls much below about 40 degrees, thereby approaching icing temperatures, the bi-metal I" closes the contacts 6 and H1, energizes the relay Hi from the current source Ill, thereby closing the contacts Ill and energizing the heater Thus, it will be observed that while the temperature-responsive member is positioned within the shell of the Pitot tube, the duty required of the control contacts is so much reduced and so light that failures practically never occur and the heavier duty imposed upon the heater circuit contacts is readily carried since the relay contacts are convenient of access. Thus, the device of the invention provides a highly rugged automatic control for the heater member in a Pitot tube structure.

This type of automatic heater thus removes from the pilot's memory and consciousness all necessity for paying attention to any controls for the maintenance of his air speed indicator in operating condition. contacts are readily accessible for servicing by the ground crew, and the heater current is turned on automatically as soon as possible icing temperatures are reached and remains turned on until the temperature rises above the icing point. In addition, the pilot may land without the necessity of attention to the air speed indicator, and may land fully assured that the heater will not be inlured by excess power or overheating and with the assurance that the heater will be ready for immediate service at the next flight.

It is not necessary that the temperatureresponsive elements be in the immediate neighborhood of the Pitot tube since it is the temperature of the atmospheric air which determines whether the heater current shall be on or ofl and not the actual temperature of the Pitot tube. Accordingly the structure of Fig. 'I may be utilized as an alternative embodiment which will be described later.

The presenceof an air stream above some threshold velocity-past the surface of the Pitot tube will insure the safety of the heater member against bum-out and accordingly, the heater member may be turned on as soon as flying speed is reached and may remain turned on until a landing is made.

For this purpose the embodiment shown in Figs. 4 and 5 may be utilized. In this embodiment the same strut member ll! attached to the fuselage I" may be utilized with the Pitot shell I03 and dynamic duct I therein. Branch pipes I24 and I! may be led from thedynamic duct The power circuit control access? I06 and the static duct I05 to the pressure responsive member I26.

The pressure-responsive member tilt may contain a pressure actuated capsule l2"! connected to the dynamic duct I06 and the casing oi the member I26 may be connected to the static duct I05 and shell I03. Adjacent the capsule 1320 there are provided contacts l28 which are connected. in the coil circuit of the relay H5, as shown in Fig. 5. An auxiliary hand switch ltilmay be connected in series with the contacts I28, to com plete the relay coil circuit. The heater member I08 is connected to the power source It 5 through l elaids, asshown, and through the relay contacts Inthe operation of this embodiment, the hand switch I20 may be closed at any convenient time, but the contacts I28 remain open until speed is obtained and the dynamic pressure built up in the duct I04 to such a value as to expand the capsule H1 and thereby close the contacts I28, thus closing the coil circuit of the relay lit, and attracting its armature to close the contacts IM. This permits current to flow in the heater I08, which will continue as long as flying speed is maintained, or until the switch 22s is opened by hand. If the switch I29 is not opened by hand but the plane lands, the loss of flying speed reduces the pressure in the capsule 521 and there by opens the contacts 528 to de-energize the relay H5, open its-contacts H4 and ole-energize the heater I08, thereby preventing a burn-out.

Thus, since flying speed provides an air stream over the Pitot-static tube shell structure suili ciently great to removefrom it any excess amount of heat which might injure the heater, the heater may be energized during all flying periods, under the control of the dynamic pressure in the cap=- sule I21, thus likewise freeing the pilot from the necessity of remembering his Pitot tube heater to make sure that it functions when needed and; does not burn out. That is, a fully satisfactory protection of the tube and of the heater is obtainable by the simple feature of dynamic pres sure control of the heater power supply circuit.

In some instances it may be desired to conserve the electrical energy supply to the utmost, such as during flying in Arctic regions where the nor= mal ground temperatures may on occasion be below freezing. The embodiment oi Fig. 6 provides this function by a combination of tempera ture-sensitive control and pressure control.

As shown in Fig. 6, a similar Pitot-static tube structure is provided consisting of a similar shell I03 housing a dynamic duct I04, adjacent to which is a similar heater I08, the whole structure being mounted in any desired way, such as upon a strut of the same kind as the strut E02 shown in Fig. 1. .A pressure responsive capsule I2! is provided and connected to respond to the dynamic pressure in a manner similar to the cap sule shown in Fig. 4. In addition the capsule may also be acted upon by the static pressure, as hereinbefore described. The capsule I27 oper= ates the contacts I28 for the control of current in the relay coil H5. A temperature-responsive member, which may be a bi-metal strip I09, actuates the contacts H6 and Ill. These con= tacts are connected in series wi h the contacts I28 and the relay coil H5, the entire circuit being energized by the power supply Ill. relay contacts I are closed by the relay when both contacts II6-I I! and contacts I28 are closed, thereby supplying heater power from the power supply III to the heater I08.

The

in the operation of this embodiment of the invention, the heat-sensitive member Hi9 will close the contacts lid-H2 when the termperature approaches the freezing point, or goes below. But the relay circuit is not closed until flying speed is obtained which provides suflicient dynamic pressure to actuate the capsule iii and close the contacts we. Thus, if in flight a ternperature safely above the icing point is reached, the contacts l lG--i i? open, which opens the relay circuit and thereby opens therelay contacts to disconnect the power supply to the heater @033, without regard to the presence or absence of flying speed. Similarly, if the plane lands, the

- lack of dynamic pressure opens the contacts i233,

similarly disconnecting he heater power from the heater without regard to the ambient temperature.

Thus, this embodiment oi. the invention pro vides a automatic control of the Pitot tube heater which not only protects the heater and the air speed indicator readings, but conserves the utmost possible heating power.

It is of course not n cessary that the ternperature-responsive member be positioned in the Pitot tube shell structure. It may be instead positioned at any convenient point which par-= takes of the temperature of the air through which the plane is flying, as is shown in Fig. I.

The embodiment of Fig. 7 utilizes a similar static shell member E03 supported upon a com venient strut, of the type shown in Fig. l. The shell 903 contains the dynamic duct 504 and heater @08. The capsule til is responsive to the dynamic pressure, as previously described, for the operation of the contacts 528 which are con nected as previously described in connection with Figs. 4 to 8. The temperature-sensitive member 625 is placed in any convenient position where it will partake of the normal ambient air tempera ture, and the contacts 622 controlled by the temperature-responsive member l2i are connect ed in series with the contacts H28 in a manner analogous to that of the embodiment of Fig. 6., for the control of the relay H5 and its contacts lit, which turns the current on and ad to the heater Hit.

The operation oi this embodiment is closely similar to the operation of the embodiment of Fig. 6.

Thus, the device of the invention provides a simple system for the continued protection or an air speed indicator system, in which a heater is provided for preventing the accumulation of ice, snow and sleet in and upon a Pitot-static tube structure and in which the heater member is fully protected against the danger of burn-out without burdening the pilots memory or hands with controls and the necessity of operating them to turn the heater current on during icing conditions and to turn it off upon landing.

While there are above disclosed but a limited number of embodiments of the device of the invention, it is possible to provide still other com bodiments without departing from the inventive concept herein disclosed and it is therefore desired that only such limitations be imposed upon. the appended claims as are stated therein.

What I claim and desire to secure by United States Letters Patent is:

l. The combination with a Pitot-static tube for aircraft having metallic static and dynamic pressure ports; of an electric heating element arranged to heat said ports; and means responsive to the speed of the craft for controlling a flow oi electrical energy to said heating element.

2. The combination with a Pitot-static tube having metallic static and dynamic pressure ports; oi an electric heating element arranged to heat said ports; and means responsive to a diii'erence in pressure between said static and said dynamic pressure ports for controlling a flow of electrical energy to said heating element.

3. The combination with a Pitot-static tube having metallic static and dynamic pressure ports; of an electric heating element arranged to heat said ports; and pressure responsive means connected to said dynamic pressure port for controlling a flow of electrical energy to said heating element.

4. The combination with a Pitot-static tube having metallic static and dynamic pressure conduits; of an electric heating element arranged to heat said conduits; a. switch connected to control a flow of electrical energy to said heating element; and a pressure responsive means responsive to the pressure in said dynamic pressure conduit, said pressure responsive means being connected to actuate said switch.

5. The combination with a Pitot-statlc tube having metallic static and dynamic pressure ports; of an electric heating element arranged to heat said ports; a switch connected to control a flow 01' electrical energy to said heating element; and a diaphragm responsive to a difference in pressure between said static and said dynamic pressure ports, said diaphragm being connected to operate said switch.

. 6. The combination with a Pitot-static tube including a metallic shell member having static and dynamic pressure conduits therein; 01 an electric heating element arranged to heat said shell a relay including a winding and an armature, the armature being connected to control a flow of electrical energy to said heating element a switch connected to control a flow oi electrical energy to said winding; and a diaphragm responsive to a diflerence in pressure between said static and I said dynamic pressure conduits, said diaphragm being connected to opearte said switch.

7. The combination with a Pitot-static tube including a metallic shell member having static and dynamic pressure conduits therein; oi an electric 10 heating element arranged to heat said shell; a relay including a winding and an armature, the armature being connected to control a flow oi electrical energy to said heating element; a tem-.

perature responsive first switch within said shell; 15

said static and said dynamic pressure conduits, I.

said diaphragm being connected to operate said second switch.

8. The combination with a Pitot-static tube having metallic static and dynamic pressure conduits; of an electric heating element arranged to 5 heat said conduits; a relay including a winding and an armature, said armature being connected to control a flow of electrical energy to said heating element; a temperature responsive first switch responsive to changes in temperature of the atv mospheric air;v a second switch, said first and said second switch being connected jointly to control a flow of electrical energy to said winding; and a diaphragm responsive to a difference in pressure between said static and said dynamic pressure conduits, said diaphragm being con nected to operate said second switch.

* PAUL KOLLSMAN.

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