US2482701A - Pitot head - Google Patents

Description

Sept. 20, 1949. RQ L.. ANDERSON PITOT HEAD Filed Nov. l5, 1946 @.@ww RM l y ATToRNES INVENTOR ROLLAND L. AN DERON Patented Sept. 20, 1949 UNITED STATES PATENT OFFICE PrroT HEAD Rolland L. Anderson, Memphis, Tenn.

1 Application November 15, 194e, serial No. 709,899

(c1. 7er-212) 7 Claims.

The present invention relates to air speed measuring devices `for aircraft and more particularly to a dynamic pressure, or Pitot head adapted for use with a separate or fuselage static Ipressure system, the head incorporating means for inhibiting freezing and water locking in the dynamic pressure system.

It is well known that air speed indicators become inaccurate and often fail when operating under certain -adverse conditions. The principal of these are met in heavy precipitation, in dense cloud formations or spray, when water entering the Pitot tube, collects and results in waterlocks in the indicating instrument, upsetting the establishment of correct pressure differentials for accurate operation of the instrument. Another adverse condition is met in flying in sub-freezing temperatures which results in freezing up or clogging up theientrance to the Pitot tube with ice which likewise renders theindicating instrument inaccurate or inoperative.

Attempts, which have not proven entirely satisfactory, have been made in the past to overcome water locking of the Pitot system, such as by the provision of valving and air pumps in the plumbing between the Pitot head and the instrument, by means of which the operator could periodically blow out the system. This, however, is an expensive and cumbersome system, creates the possi-bility of leaks in the dynamic pressure lines, requires the attention and manipulation of Aan operator, and is, at best, only a temporary rectication of the trouble. Prior attempts have also been made to automatically separate, trap and drain water entering'the system before it reached the lines vconifi-ecting the Pitot tube with th-e instrument. These attempts have not proven entirely satisfactory because of the water separatingV principles employed andthe complexity of the required struct-ure. i

Electric heatingl elements have heretofore been employed adjacent the tips of Pitot stati@ tubes to prevent icing. Much of the efl'lciency of these heaters has been lost by lconduction through other parts of the unit to the atmosphere, and by the necessity of a heavy current supply for the heater because of these losses.

It is therefore one `of the objects of this invention to'provide a Pitot head for a Pitot static air speed indicating system which provides for water f Another object Vol the invention is to provide a 551 Y Pitot head of the above character, in which the separated water is drained from the lowest'point in the system regardless of the normal attitude of the plane,and in which there is a large ratio betw-een the drain orifice and the nose Opening of the Pitot tube, Ithus providing substantially full dynamic pressure to the indicating instrument.

Still another object of the invention is to provide a Pitot head of the above character, which incorporates an electric heater arranged symmetricallyrabout the nose of thePitot tube and along the length thereof to give even distribution lof heat to all required critical areas, and in which dead air space is provided about the tube in non-critical regions to prevent heat loss and thereby increase the efliciency of the heating system.

A further object of the invention is to provide a Pitot head of the -above character having a Pitot tube of relatively large diameter, extending in a straight line from the nose or entrance thereof to the rear Vdynamic pressure chamber of the head. l

A still further object of the invention is to provide an electrically heated Pitot hea-d constructed so that the heating element may be removed and replaced without the breaking and reseal-ing any of the Pitot system, and without special tools.

With the above and other important objects and advantages in view, the invention comprises the parts and combinations hereinafter set forth with the understanding that various changes may be made therein, -by those skilled in the art, Without departing from the spirit of the invention.

In order to make the invention more clearly understood, a .preferred embodiment thereof is made the subject of illustration in the accompanying drawings, in which:

Figure 1 is a vertical transverse sectional view of a Pitot head constructed in accordance with this invention.

Figure 2 is a horizontal transverse sectional view taken along the line 2-2 of Figure 1 looking inthe direction of the arrows.

Figure 3 is a cross sectional view taken along the line 3--3 of Figure 1 looking in the direction of the arrows.

Figure 4 is a cross section view taken along the line ll-llof Figure 1 looking in the direction yof the arrows.

Fig-ure 5 is a diagrammatical representation of the nose portion 'of an Iairplane showing the installation of the Pitot tube.

Referring more particularly to the drawings,

there is shown a Pitot head, designated generally as I, preferably of the type supplying only the dynamic pressure to an airspeed indicating instrument, the head functioning in conjunction with a separate, static pressure system. Preferably also, the head I is of the type adapted for mounting in the fuselage of an airplane, usually projecting forwardly from the nose of the fuselage into the airstream, as indicated diagrammatioally in Figure 5, though obviously -it may be externally mounted in accordancewvith usual practice.

The head I comprises a casing 2 forming a rear; laterally attened and vertically elongated., d-ynamic pressure chamber 3 to the extreme upper end of which is secured an internally fr screw threaded nipple 4, by meansgof'which'a dynamic.,

pressure line leading to the airspeed indicating instrument may be connected. point of the wall of the chamber 3 is drilled a singleismall drain orifice 5; Y

SecuredV tothe iorward'wall of thefvchamber, substantially intermediate the nipple -4and; the orie 5; is a circular disc ,fto whichis secured one end oiga cylindrical, sleeve 'I which extends -forwardly from the chamberS but is partitioned therefronrby the'disc I. Secured into the. forward end of the sleeve 'I is a plug 8 which projects forwardly from the sleeve-man externally screw threadedextension 9- onto which is; screwthreadedanose` piece Iof the same diameter-as the sleevel'l. The nose piece ID- is internally bored axiallyto form, with .the plug-:8, an enclosed heating chamber: II'. The` forward end ofthe nose piece is preferablyrounded.

Thel-nose-piece. I', the-plug'fand the discIl are respectively l provided with axially aligned1 apertures I2, I3 and I4 through which pass a Pitot tube-.|51 This tube isstraightafrom endeteA end, extending from substantiallyV flush withithe front ofthe: nose piece l l toY the inner facev of the rear wall'iofthe chamber 3.'. The tube-I 5i preferably is made of aV high heat: conducting metal,v such as heavy wall copper tubing, and is of relatively large inside diameterA to presi-int` al substantially large opening to the airstream. Therear p0rtion ofthe-tube I;I lying withinthe chamber 3; sry laterally flattened vsomewhat and provided with a plurality of upwardly opening airA discharge ports I 6, formedsuch as byV drilling. and/or beveling the end'of-the tube from the ten; While the lower wallr` ofthe tube is provided with a downwardly opening'water discharge porte I'I formed; such as, by beveling the end-,of the4 tube -from-the bottom wall;-

Theftu-be I5 'may be a close-fit in the apertures I2, I3" and Mibut preferably, itis silver soldered or snnilarly securedv in` the apertures I3 and I4 in order to make a chamber IB', formedfby the tube 1; diseS-and-plug 8, airtight. In this connection-it might'f-be mentioned that all permanent joints between the several parts may bey made by silver soldering.

Coiled'about the tube i5, in thenose chamber II, is an elongated, electrical resistance heating element;y designatedgeneralfly, as I9), and'which maybe of any-suitable, conventional design. The coiled heating element is spaced radially, both rremthe tube-'fand the chamber Wall, such asv by coilingfit within a sleeve Zgpreferably of heat insulating material which may be spaced radially from-the tube conveniently,y such asl'by suitable spring washer meansa2lrinterposedfbetween the end of the chamber, the tube andsleeve2ll;v

The ends of the heating element I9'rare1passed In the lowest.`

from the ends of the coil rearwardly through a pair of small, metal tubes 22 extending parallel with and engaging the Pitot tube I5, with their opposite ends passing through and making a tight nt with, or fused in aligned apertures in the plug 8 and disc 6. In order to increase the heat conductivity between the tubes 22 and the tube I5, the tubes 22 may be silver soldered to the tube I5, as indicated at 23 in Figures 2 and 3.

The rear ends; of the tubes 2'2'gtermginate just beyond the rear face ofthewdisc' 6,adjacent opposite side walls of the chamber 3, and have fitted thereon exible insulating conduits 24, through which short conductors 25 connect the opposite ends of the heating element respectively with a pairofte'rminal posts 26 and 21. One of these posts,.,25, is insulatedfrom the head, such as by an insulating strip 2S and insulating washer 29, whilethe post 2'I may consist of one of a pair of bolts passing through the chamber 3 and attaching'` the-insulating@ strip 28 thereto,k as-showrr in ledig-well,`

In; use, `the-Pitot head fmay -beinstalled inthe airplane asindicated, for examplaunFigzuref, bei-ng suitably Y secured. toV the fuselage. structure with at least the nose piecec v I Ileextendingthrough an aperture in the nose ,ofthe-fuselage, Anupwardly extending-lline-301 connectsfthevnipple 4 with the dynamic pressure fitting ,organen-speed indicatingfinstrument; indicated at 3l, whleethe static. pressure ttingofgthe: instrument .may be eonnectedfbya downwardlyeXtending-.line 32 toa sta-tie vent 33 opening-througnthe.;skinof the fuselage at anoptimumflocation.thereon. Thev heaterterminals 2 Galand-f2 'I arefsutiablyonnected to` a: source-oielectric current througl'ra switch 34 .1 ley-conductors:- indicatedl diagrammaticallyfm 35.

Iffthe; airplane.;.is` travel-ingqthrough @regionof heavy precipitation, Iforexample,4 ,a-f considerable amount of water willenterf--the Pitottubeand travel rearwardlywith the;airstream. Because of lfthe relatively largegdiameter-ofsthegtube; I5; a portion of this waterfwi-ll separate from-tthefair strearnfinithe` tube I 5, flowing alngethebottomzof the tube, and; discharge dcxWsIlviardiy; directlyl through theport- I'I in-to theqbottom of lthe charm. ber 3 where it drains through theforicefifunden pressure ofv the=airinthechamber-. Smaller; drops which may -bey carried; as asuch,` bythe. air into thef chamber 3;,willreadilyi settle to thebottom or; the chamber and likewise drainY out. It hasfbeen foundin practice,I that the vertically., elongated dynamic chamber and introducing a straight, large diameter Pitot tube intermediate its f length, provides forcompletely; satisfactory separationzof water ffrom-r, the dynamic airv with-- out baiingftheairstream'in any-way, This is. an importa-nt .feature of theinventiom not only resulting in economy and simplicitywof` manufacture; but: also resulting y inv more eicient' operation by eliminatingfthefpossibility,ofwater brida. ing the spaces between f baillesand f adj acont: surfacesfof-thefhead.

It is tolte-notedl that; the crosssectional area; ofi the orificeY 571s small Withrespectgtothataof the tube I5 (the area ratiot-:the-criticato-the entrance: openingv of theV tube being' approximately 1481),. which thereby assuresV substanln'ally ruil' dynamic: pressure in the chaniber 3f andfaccurateair. speedfindcation byztheinstrumerrt cunneetert therewith.

The heating unitY IIS-Pis onlyzused subrreezingi temperatures where danger of the Pitot tube-icing'A upgmay'exist; Underfsuchconditunsf, the heating element serves as an efficient ice preventing or de-icing unit. In the first place, the major heat is localized, concentrated and symmetrically distributed about the most critical portion of the Pitot tube-its nose-fand'. heats thisuportion by radiation through the confined chamber li. In the second place, the heavy wall of high heat conducting material of the tube, and the insulation provided bythe dead air spacein the chamber I8 between the tube and the outer'sleeve l, efficiently conducts the heat to other, but less critical parts of the head. In this latter connection, it may be pointed out that the chamber l 8, since it is sealed off from the remainder of the head, may, if desired, be evacuated and still further increase its efficiency as an insulator. In either case, the chamber I8 effectually inhibits heat loss through radiation to the atmosphere and thereby reduces otherwise high wattage for the heater and its current consumption. Additional heating efficiency is also obtained by fusing the tubes 2| to the wall of the tube I5, as described above.

It is t0 be noted also, that the heating element may be easily removed and replaced simply by disconnecting its ends from the terminal posts 26 and 21, unscrewing the nose piece I0 from the plug 8, and withdrawing the element from the head.

From the foregoing, it will be seen that the Pitot head according to this invention, will provide for accurate operation of the air speed indicating instrument under all weather conditions. It provides a simple, tight dynamic pressure sysvtem which does not have to be broken and resealed in maintenance, and is simple and economical to install.

I claim:

1. A Pitot head of the character described comprising a straight Pitot tube having a forward entrance opening, a casing forming a vertically elongated chamber enclosing the rear portion of the tube, said tube being positioned intermediate the height of the chamber and substantially perpendicular to the vertical axis thereof, the rear portion of the tube being provided with upwardly and downwardly directed ports, and means for connecting the upper region of the chamber with an instrument, there being a drain orice in the casing adjacent the lowest point of the chamber.

2. A Pitot head of the character described comprising a straight Pitot tube having a forward entrance opening, a casing forming a vertically elongated chamber enclosing the rear portion of the tube, said tube being positioned intermediate the height of the chamber and substantially perpendicular to the vertical axis thereof, the rear portion of the tube being provided with upwardly and downwardly directed ports, and means for connecting the upper region of the chamber with an instrument, there being a drain orice in the casing adjacent the lowest point of the chamber, the cross sectional area of said ori'lce means being substantially smaller than that of the tube.

3, A Pitot head of the character described comprising a straight Pitot tube having a forward entrance opening of substantially large diameter, a casing forming a vertically elongated chamber enclosing the rear portion of the tube, said tube being positioned intermediate the height of the chamber and substantially perpendicular to the vertical axis thereof, the rear portion of the tube being provided with upwardly and downwardly directed ports, and means for connecting the upper region of the chamber with an instrument, there being a drain orifice in the casing 6 adjacent the lowest point of said chamber, the area ratio of -said orice with respect to said entrance opening being approximately one to eighteen. l

4. A Pitot head of the character described comprising a straightl Pitot tube having a forward entrance opening, a casing forming a vertically elongated chamber enclosing the rear portion of the tube, said tube being positioned intermediate the height of the chamber and substantially perpendicular to the vertical axis thereof, the rear portion of the tube being provided with upwardly and downwardly directed ports, and means-for connecting the upper region of the chamber with anY instrument, there being a drain orifice in the casing adjacent the lowest point of the chamber and means for heating the tube at least adjacent said entrance opening.

5. A Pitot head of the character described comprising a straight Pitot tube of high heat conductivity and having a forward entrance opening, a casing'forming a vertically elongated chamber enclosing the rear portion of the tube, said tube projecting forwardly from the casing intermediate the height thereof and substantially perpendicular to the vertical axis thereof, the rear portion of the tube being provided with upwardly and downwardly directed ports, and means for connecting the upper region of the chamber with an instrument, there being a drain orice in the casing adjacent the lowest point of the chamber, shell means surrounding the projecting portion of the tube and forming a circumferential chamber thereabout, an electrical heating element within said circumferential chamber and spaced from said shell means, the intermediate portion of said element being coiled about the tube adjacent the entrance opening thereof, and the end portions of said element extending substantially parallel with the axis thereof and adjacent opposite sides of the tube, and heat conducting means conductively connecting said end portions with said tube.

6. A Pitot head of the character described comprising a straight Pitot tube of high heat conductivity and having a forward entrance opening, a casing forming a vertically elongated chamber enclosing the rear portion of the tube, said tube projecting forwardly from the casing intermediate the height thereof and substantially perpendicular to the vertical axis thereof, the rear portion of the tube being provided with upwardly and downwardly directed ports, and means for connecting the upper region of the chamber with an instrument, there being a drain orifice in the casing adjacent the lowest point of the chamber, shell means surrounding the projecting portion of the tube and forming a circumferential chamber thereabout, an electrical heating element within said circumferential chamber, the intermediate portion of said element being coiled about the tube adjacent the entrance opening thereof, and the end portions of said element extending substantially parallel with the axis thereof and adjacent opposite sides of the tube, and heat conducting sleeve means having an intimate contact with said tube surrounding said end portions of the element. v

7. A Pitot head of the character described comprising a T-shaped casing constituting a vertically elongated rear chamber and a horizontal tubular chamber extending forwardly therefrom intermediate the length thereof, partition means separating said chambers, a tubular nose piece detachably secured to the forward end of the tubular chamber axially thereof and forming a heating;charinlofr1-2v a straight PilQtLtubeLextendingi from Within the rear chamber through said-tubuc` lar chamber andl heatingY chamber and i spaced radially inwardly from the Walls thereof,1he real? portionY ,of the tube being,` provided'. withdlpwardy and'downwardly directed ports;r and means for connecting theupper region of thevchainber with an instrument, there loerlg-av drain oricerL-the REFERNCEs-CITED flhefovllowingj'ireferences 'areA` of J record the le: oi this patent;

UNITED-STATES PA'I'ENTS

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