US3504860A

US3504860A - Adjustable spike nozzle for thrust motors

Info

Publication number: US3504860A
Application number: US380962A
Authority: US
Inventors: Kenneth C Wilson
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1964-07-07
Filing date: 1964-07-07
Publication date: 1970-04-07
Anticipated expiration: 1987-04-07

Description

April 7, 1970 K. c. WILSON 3,504,860

ADJUSTABLE SPIKE NOZZLE FOR THRUST MOTORS MOVABLE COWL (BALANCED FORCES Filed- July 7, 1964 l6 FIXED COWL.

FIG. IB. (PRIOR ART) 23 s2 4 64 70 Ml FlG. 3.

66 I I y 44 1, M INVENTOR. 28 4 38a, V KENNETH 0. WILSON FIG. 4 BY (4. ATTORNEY.

United States Patent 3 504 86 ADJUSTABLE SPIK E N OZZLE FOR THRUST MOTORS Kenneth C. Wilson, Cumberland, Md., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed July 7, 1964, Ser. No. 380,962 Int. Cl. B63h 11/10 US. Cl. 239-26519 3 Claims This invention relates to jet propulsion motors and more particularly to improvements in adjustable area exhaust nozzles for use with such motors.

In the art of jet propulsion, it is well known practice to vary the area of an exhaust thrust nozzle, with change of altitude of the vehicle being propelled by a thrust motor, to thereby compensate for the change in atmospheric back pressure and control the motor thrust in such manner that the motor operates at optimum efiiciency under all conditions of back pressure. Motors of this type have been constructed to operate close to the ideal isentropic process in which entropy remains constant with a change in enthalpy. Such type of process is described in Gas Turbines for Aircraft, by Driggs and Lancaster, published by the Ronald Press Company, New York, 1955, pages 32 and 33.

FIGS. 1A and 1B of the accompanying drawing illustrate isentropic spike nozzles of the type referred to. In FIG. 1A the rear end of the thrust motor is provided with a fixed spike and the area of the exhaust annulus is varied by positioning the movable cowl. In FIG. 1B the cowl is fixed and the area of the exhaust annulus is varied by positioning the movable spike. In the FIG. 1A system the axial gas forces on the cowl are balanced (F =F which is an advantage, since the movement of the cowl can be effected with a small actuating force. One of its disadvantages, however, is that the cowl occupies space outside of the motor thus increasing weight and bulk to the overall system. In the FIG. 1B system the foregoing disadvantage is obviated but the motor gas pressure is applied to substantially the entire cross section of the spike thus creating a high unbalanced force tending to move the spike toward closed position. The spike support must thus be of adequate strength to withstand such unbalanced force. As will also be apparent, high actuating force is necessary to move the spike to a desired position. Both systems also have the disadvantage of moving parts which are subjected to high temperature gases and deposits which may hinder their movement.

Among the general objects of the invention are the provision of a movable spike nozzle which obviates the disadvantages of the prior art, above referred to.

Other, and more specific objects, are the provision of a movable spike nozzle which, as compared to the prior art devices, reduces stresses, reduces weight, reduces spatial requirements to thereby permit increased volume for the motor propellant and increases reliability.

A further object is the provision of a movable spike nozzle which is substantially balanced by the gas forces, thus requiring a relatively small actuating force for positioning it.

A further object is the provision of a movable spike nozzle which permits increased expansion ratios within equivalent or less spatial requirements of the prior art.

A further object is the provision of spike actuating apparatus which is disposed within the spike, thus utilizing a heretofore unused space.

A further object is to decrease the mass of movable nozzle parts, to thus reduce their inertia effects, and permit more rapid movement with minimized actuating force.

"ice

Still further objects, advantages, and salient features wlll become more apparent from the description to follow, the appended claims and the accompanying drawing, in which:

FIGS. 1A and 1B are cross sections of prior art;

FIG. 1 is a broken away side elevation of an exemplary form of the invention;

FIG. 2 is a section taken on line 22, FIG. 1;

FIG. 3 is an enlarged section taken on line 33, FIG. 2; and

FIG. 4 is a cross section of an alternative form of a component of the invention.

Referring now to the drawing, an exemplary environment of the invention is illustrated in FIGS. 1 and 2 in which any conventional thrust motor 10 is provided with a combustion chamber 12, containing a solid propellant (not shown), the rear end of the motor terminating in an inwardly curved cowl 14 within which a movable spike 16 is disposed, thus providing a variable area annular discharge orifice 18.

Referring now to FIG. 3, spike 16 comprises an outer shell 20 of graphite, having threads 22 which engage corresponding threads on a spike shell insulator 23 composed of Spauldite. The outer shell and insulator are otherwise secured together by a member 24 which threadedly engages the insulator, provided with a shoulder or flange 216 which engages the rear end of the outer shell. This member is preferably an asbestos phenolic material. Angularly spaced vents 27 are provided to bleed off gases produced by the charring of phenolic insulator 23.

An aluminum support tube 28 is secured at its forward end to the front bulkhead 29 of the combustion chamber, the tube being covered with an insulating material 30, also preferably of Spauldite. A frusto-conical aluminum pressure plate 33 is disposed on the rear end of the tube, its exposed surface being covered by an insulator plate 34-, the pressure plate and insulator plate being secured in position by a nut 3-6, disposed on an actuator 38, the nut threadedly engaging the rear end of tube 28. O-

rings

40, 42, prevent leakage of gas from the combustion chamber.

The outer edge of insulator 34 is provided with a cylindrical flange 44 which telescopes within an asbestos phenolic ring 46 of U-shaped cross section, the outer surface of the ring threadedly engaging a graphite spike spacer 48 having a plurality of webs 50, the outer ends of the webs terminating in a two part ring 52 which is secured to cowl 14in any desired manner. As shown, this comprises an asbestos phenolic ring 54 and a covering aluminum ring 56, secured to the cowl by a snap ring 58.

The forward end of ring 46 is provided with a plurality of angularly spaced apertures 60 which permit gas pressure to be applied to the forward face 62 of shell 20 and the forward face 64 of insulator 23. As will be apparent, the total area of these two faces is a small proportion of the total cross section of the spike. The spike is thus urged rearwardly with a force equal to the combustion chamber pressure times the area of these two faces as illustrated by rearwardly directed arrows. The spike is urged in the opposite direction by pressure of the gas downstream of nozzle 18, acting on the entire cross section of the spike, as illustrated by forwardly directed arrows. While this area is considerably in excess of the area of

faces

62, 64 the pressure is considerably less than combustion chamber pressure. As will now be apparent, the force tending to move the spike in a desired direction may be controlled by suitably proportioning the area of

faces

62, 64 to the spike cross section if the combustion chamber pressure and pressure on the rear side of shell 20 are known. In the preferred embodiment, the area of

faces

62, 64 is so chosen to provide a force tending to move the spike in a rearward direction.

Actuator 38 may be of any suitable type such as an electric motor or a piston which is actuated by fluid pressure, either gas or hydraulic. If electric, control wires may extend through tube 28 to suitable control apparatus in the motor and if actuated by fluid pressure, the pressure may be applied through the tube. In either construction, a reciprocable actuator rod 66, affixed at one end to member 24, is provided which may control the position of the spike. In one embodiment, the actuator may be considered as a single action piston in which the control force is additive to the force of the exhausting gases. Thus, the rearward force on faces 62, 64 would be slightly in excess of the forward forces on the entire spike cross section, tending to move the spike toward a smaller throat aperture, and the force applied to the actuator, when movement is desired, would be slightly in excess of the difference between the rearward and forward gas forces.

FIG. 4 illustrates another form of actuator wherein a double acting piston 68 may be moved in opposite directions by selective application of fluid pressure through tube 28 and a separate conduit 70. This construction may be preferable in motors which require very rapid movement of the spike, such as in motors in which it is desirable to terminate burning of the propellant by rapidly moving the spike to a maximum nozzle opening position thereby interrupting propellant combustion.

What is claimed is:

1. In a variable throat area convergent-diveregnt nozzle of the isentropic spike type for use with a gaseous thrust motor having a cowl member fixed to the rear end of the motor and having an annular surface forming the outer wall of the convergent portion of the nozzle and terminating in a circular opening at the throat of the nozzle, a circular spike member movable axially relative to said opening having a first portion forming the inner wall of the convergent portion of the nozzle and a second downstream portion forming the inner wall of the divergent portion of the nozzle, said inner wall of the convergent and divergent portions being subjected to pressure of the gas, producing a first force tending to move the spike member forwardly to increase the area of the throat, the improvements, in combination, comprising:

(a) said spike member having a cylindrical tubular portion slideably disposed within a stationary tubular cylinder and having an annular end surface of considerably less area than the projected area of said convergent-divergent portions, said cylinder communicating with said chamber, to produce a second force tending to move the spike member rearwardly to thereby decrease the area of the throat,

(b) and an actuator disposed within said spike member and operatively connected thereto, so constructed to produce a force in excess of the difference between said first and second forces, to thereby move the spike member to a desired axial position.

2. In a variable throat area convergent-divergent nozzle of the isentropic spike type for use with a gaseous thrust motor having a cowl member fixed to the rear end of the motor and having an annular surface forming the outer wall of the convergent portion of the nozzle and terminating in a circular opening at the throat of the nozzle, a circular spike member movable axially relative to said opening having a first portion forming the inner wall of the convergent portion of the nozzle and a second downstream portion forming the inner wall of the divergent portion of the nozzle, said inner wall of the convergent and divergent portions being subjected to pressure of the gas, producing a first force tending to move the spike member forwardly to increase the area of the throat, the improvements, in combination, comprising:

(a) said spike member having an annular surface, subjected to chamber pressure, of considerably less area than the projected area of said convergent-divergent portions, producing a second force tending to move the spike member rearwardly to thereby decrease the aera of the throat,

(b) an actuator disposed within said spike member and operatively connected thereto, so constructed to produce a force in excess of the difference between said first and second forces, to thereby move the spike member to a desired axial position,

(c) a fixed tube having its forward end secured to a forward bulkhead of the motor and its rear end secured to a fixed circular plate.

(d) said spike member having an annular portion surrounding the periphery of said plate and slideable relative thereto,

(e) said annular portion forming the area upon which said second force is applied, and

(f) means extending through said tube for controlling the movement of said actuator.

3. A nozzle in accordance with claim 2 wherein,

(g) said first portion of said spike member is cylindrical and slideably disposed within an annular ring member supported by said cowl member by a plurality of angularly spaced webs.

References Cited UNITED STATES PATENTS 2,570,629 10/1951 Anxionnaz et al. 2,811,827 11/1957 Kress. 3,192,712 7/1965 Nash et al.

SAMUEL FEINBERG, Primary Examiner

Claims

1. IN A VARIABLE THROAT AREA CONVERGENT-DIVERGENT NOZZLE OF THE ISENTROPIC SPIKE TYPE FOR USE WITH A GASEOUS THRUST MOTOR HAVING A COWL MEMBER FIXED TO THE REAR END OF THE MOTOR AND HAVING AN ANNULAR SURFACE FORMING THE OUTER WALL OF THE CONVERGENT PORTION OF THE NOZZLE AND TERMINATING IN A CIRCULAR OPENING AT THE THROAT OF THE NOZZLE, A CIRCULAR SPIKE MEMBER MOVABLE AXIALLY RELATIVE TO SAID OPENING HAVING A FIRST PORTION FORMING THE INNER WALL OF THE CONVERGENT PORTION OF THE NOZZLE AND A SECOND DOWNSTREAM PORTION FORMING THE INNER WALL OF THE DIVERGENT PORTION OF THE NOZZLE, SAID INNER WALL OF THE CONVERGENT AND DIVERGENT PORTIONS BEING SUBJECTED TO PRESSURE OF THE GAS, PRODUCING A FIRST FORCE TENDING TO MOVE THE SPIKE MEMBER FORWARDLY TO INCREASE THE ARE OF THE THROAT, THE IMPROVEMENTS, IN COMBINATION, COMPRISING