Aircraft technical Basics: TM 1-412, Aircraft Propellers, 1941: VII. Hamilton Standard Hydramatic Propeller

SECTION VII. HAMILTON STANDARD HYDROMATIC PROPELLER

39. Principle of operation. - a. The centrifugal twisting moment which is always present in a rotating propeller is a very powerful force tending to turn the blades toward low pitch position. In the hydromatic propeller, this blade twisting moment is utilized as the operating force to change pitch toward lower blade angles; while oil pressure acting on a piston in a cylinder opposes the blade twisting moment and provides the operating force to change pitch toward higher blade angles. This direct use of the natural forces eliminates the need for counterweights and simplifies the mechanism. The internal mechanism of this propeller is shown in figure 23.

b. The piston is connected to the blades through cylindrical cams and gears so that the blades change pitch as the piston moves from one end of the cylinder to the other. The oil pressure which provides the operating force toward high pitch is fed into the inboard end of the cylinder where it forces the piston outward and increases the pitch in proportion to the amount of oil admitted. When the piston is in close to the hub, the pitch is low, and when it is out from the hub, the pitch is high. In the extreme outward position of the piston the blades are full feathered.

c. The piston cylinder assembly is so arranged that the piston can be moved inward by oil pressure as well as outward. This is necessary for unfeathering because there is no blade twisting moment available when the propeller is feathered and the engine stopped. It is also desirable to assist the blade twisting moment when the r. p. m. is low during warm-up and taxying.

d. For normal operation, oil from the engine lubricating system is fed through the crankshaft directly into the outboard end of the cylinder, thereby maintaining constant engine pressure on the piston in the direction of low pitch. Oil from the constant speed control governor under sufficient pressure to overcome both the blade twisting moment and the engine oil pressure is fed into the inboard end of the cylinder. The constant speed control admits oil to the cylinder or drains oil from it, automatically increasing or decreasing the pitch as necessary to allow the engine to run at constant r. p. m. regardless of the altitude of the airplane.

e. For feathering and unfeathering, an auxiliary oil pressure supply is retained which must be independent of the engine, due to the fact that feathering causes the engine to stop running. This oil is fed into the propeller through a transfer valve in the base of the constant speed control governor. When the auxiliary oil pressure is applied, the transfer valve automatically cuts out the constant speed control and directs the oil into the propeller.

f. To feather, the auxiliary oil is allowed to flow into the inboard end of the cylinder until the piston has moved to its extreme outward position where the blades are turned to full feathering. Thereupon the engine stops rotating and the propeller remains in the full feathering position of its own accord without need for further oil pressure. During the feathering operation, the oil in the outboard end of the cylinder flows back through the engine lubricating system and leaks past the engine bearing into the sump where it is scavenged in the normal manner.

g. To unfeather, that is, to return the propeller to normal operation, it is necessary to again apply the auxiliary oil pressure, but this time allow it to build up sufficiently to actuate the distributor valve which is in the propeller mechanism. This valve, which is designed to operate only under pressure appreciably greater than that required for feathering, cannot open except when the propeller is in full feathering position and then only when the operator purposely allows the auxiliary oil pressure to increase to the predetermined amount.

h. When this pressure is reached, the distributor valve shuts off the oil passage leading to the inboard end of the cylinder and directs the oil through another passage to the outboard end of the cylinder. At the same time, the distributor valve changes the connection of the engine lubricating system from the outboard end of the cylinder to the inboard end. The auxiliary oil pressure in the outboard end of the cylinder moves the piston back toward the hub, changing the position of the blades from full feathering to a lower pitch. As the piston moves inward, the oil in the inboard end of the cylinder flows back through the engine lubricating system and into the sump.

i. As soon as the propeller shifts from full feathering, it commences to windmill due to the forward velocity of the airplane, and the oil in the sump is immediately scavenged before any great quantity can accumulate. When the windmilling reaches the desired speed for starting the engine, about 800 r. p. m., the auxiliary oil pressure is discontinued and the distributor valve assumes its normal position. The engine is then started and its r. p. m. is governed by the constant speed control which automatically cuts in as the auxiliary oil pressure is discontinued.

j. To summarize, the principle of operation of the hydromatic propeller is as follows : first, three fundamental forces are used to control the propeller; the twisting moment on the blades due to centrifugal force, engine oil under normal operating pressure, and engine oil under boosted pressure from the governor. The necessary balance between these control forces is maintained by the propeller governor, which in addition to boosting the engine oil pressure, meters to or drains from the propeller the quantity of oil required to maintain the proper blade angle for constant speed operation. Second, to feather the blades, an auxiliary pressure supply system is necessary. This consists essentially of an independent oil supply with provision for manual control by the pilot to provide 400 pounds pressure for feathering and 600 pounds for unfeathering. Figure 24 shows the control forces of a Hamilton standard hydromatic propeller.

40. Description.-a. The hub and blade assembly consists of three major parts; the spider, barrel, and blades. The spider may be considered as the foundation for the entire propeller. Its central bore is splined to fit the engine shaft and it is through these splines that the engine torque is transmitted to the propeller. It is equipped at either end with an accurately ground cone seat, and at its outer end, provision is made for the propeller retaining nut and front cone, by means of which the spider it attached rigidly to the engine shaft. Integral spider arms with two bearings on each arm support the blades, taking the great part of the thrust and torque loads from the blades.

b. The barrel is made from a steel forging, heat-treated. The shoulders of the barrel carry the centrifugal loads and provisions are made for the blade packings for oil tightness. It is supported on the spider by means of phenolic blocks located between the spider arms.

c. The blades used with the hydromatic propeller are identical in basic design with those in the Hamilton standard controllable propeller. They differ in slight detail at the inner end and are not inter-changeable between the two propeller types. The blades are manufactured from aluminum alloy forgings and are of semihollow construction. The shank incorporates an internal aluminum bronze bushing which supports the blade on the spider arm. Machined on the outer periphery of the shank is a large radius which takes up the centrifugal force.

d. The dome is machined from an aluminum alloy forging. It acts as a case for the cam operating mechanism and as a cylinder for the piston. The outer surface also serves as a spinner. The assembly comprises the pitch changing mechanism by means of which oil forces on a double acting piston are translated into blade twisting moments. It consists of four major parts; two cylindrical coaxial forged steel cams, a double walled piston, and a dome cylinder which serves also as a housing for the entire unit. The piston and cylinder are machined from aluminum alloy forgings. When the dome unit is installed in the hub assembly, the outer or stationary cam becomes rigidly fixed in the barrel and provides support for the remaining parts of the dome unit. The inner or rotating cam, with which the main drive gear is integral, is supported within the stationary cam by means of ball bearings which take the gear reactions and piston oil forces. The piston motion is transmitted to the rotating cam by means of four sets of cam rollers carried on shafts supported by inner and outer walls of the piston.

e. The distributor valve housing is an aluminum alloy casting provided with cored passages for the operating pressure. A steel sleeve, shrunk into the central bore of the housing, contains ports which aline with oil passages in the housing. During constant speed operation of the propeller, it provides a passage through which engine oil boosted in pressure and metered by the governor is led to or from the inboard side of the propeller piston, and a passage through which oil under engine pressure is conducted to or from the outboard end of the cylinder. During feathering, the same two passages provide means for delivering high pressure oil to the inboard side of the piston and a means of conducting oil from the outboard end of the cylinder to the engine lubricating system. Thus, during constant speed operation or feathering, there is no movement of the distributor valve and the assembly merely provides passages through which oil may flow to and from the cylinder. In unfeathering, the function of the distributor valve is to reverse the above-mentioned passages. The high pressure oil from the auxiliary system is then led in the, outboard side of the piston and the inboard end is connected to the engine lubricating system, thus reversing the pressure differential and moving the piston toward the inboard end of the cylinder in order to unfeather the blades.

41. Installation and removal.-a. The provisions as outlined in section IX are followed in preparing the crankshaft for installation. The manner of installing the propeller is as follows:

(1) Install propeller on crankshaft, sliding it back only far enough at first to engage the threads of propeller retaining nut with those of the shaft. The retaining nut and attaching parts are shown in figure 25.

(2) With the aid of blade beams, turn blades to the feathered position, making sure that each blade is against the 90° or 88° stop pin.

(3) Tighten propeller retaining nut on crankshaft using wrenches provided and a bar approximately 3 feet long. Apply a force of approximately 180 pounds at the end of the bar, and while the force is being maintained, rap the bar once close to the wrench with a hammer weighing not more than 2½ pounds. Determine if one of the locking slots in the nut is in alinement with one of the holes in the engine shaft. If not, repeat tightening procedure until one slot and hole are in alinement. Spacing of the slots in the nut is such that alinement of a slot and hole will occur each 5° of rotation.

(4) Determine that the 1/32-inch copper gasket is in place against adapter flange, inside propeller shaft.

(5) Check valve housing oil transfer plate on base of distributor valve assembly to be sure that it is properly in place with the 1/32-inch copper gasket between it and the valve housing. The oil transfer plate for use with engines which breathe through the propeller shaft has a 1 1/4-inch hole through its center to allow engine breathing. On the plate for use with engines which do not breathe through the propeller shaft, the hole in the center does not go through the plate but connects with the dome oil pressure line in the side of the valve housing.

(6) Lubricate threads of valve assembly, screw into shaft, and tighten with a 12-inch bar, applying a force of about 100 pounds at end of bar and striking bar one medium blow with a hammer weighing not more than 2 1/2 pounds. If locking slots in valve housing are not alined with holes in crankshaft, repeat tightening operation until slots and holes are in alinement. Under no conditions will the valve housing be backed off even slightly in, order to obtain slot and hole alinement. If alinement cannot be obtained, a new gasket will be used or the original gasket lapped.

(7) Install locking ring with pin through retaining nut slot, crankshaft hole, and into valve housing slot. Snap locking ring into position in groove provided for it in retaining nut.

(8) Before installing dome assembly on propeller, check low and high pitch adjustments to see if they are set at the correct angle.

(9) On propellers for engines which breathe through the propeller shaft, remove breather cup, breather tube nut, lock wire, nut, and seal from front end of dome assembly.

(10) Make certain that dome and barrel oil seal is properly installed in groove at the rear end of dome assembly. When installing dome assembly, it is absolutely essential that cam gear in dome be meshed with blade gear segments in proper angular relationship.

(11) Move piston in dome assembly into extreme forward 90° position. This position will be reached when the cam gear stop lugs are against the high pitch stop lugs.

(12) With blades still against the 90° stop pins, slide dome assembly over the end of valve assembly, making sure that the four piston rings on valve assembly enter properly into sleeve inside piston. Turn dome in a counterclockwise direction, until dowel pins in barrel shelf engage with alining holes in base of dome assembly. The dome assembly is installed so that arrows stamped on dome and hub shelf are alined. The blade gears and cam gears, and also dome assembly locating screws and holes, are now in proper alinement, and the dome assembly is shoved, without turning, into the barrel. On engines which breathe through the crankshaft, make sure breather tube on front end of valve assembly is properly started into hole in front end of dome. The dome may now be rapped with a rawhide mallet in order to insure proper seating in the barrel. Turning dome assembly in a clockwise direction in order to aline dowel screws and holes is to be avoided, as this will tend to move stop lugs on rotating cam away from the 90° position, thus allowing gears to mesh incorrectly.

(13) Tighten dome retaining nut in a manner similar to that described for tightening propeller retaining nut, applying a force of approximately 180 pounds at a 4-foot radius. With dome assembly properly seated in the barrel, the front face of dome retaining nut is approximately flush with edge of barrel.

(14) Install dome retaining nut lock screw and safety the screw with a cotter pin.

(15) Install breather tube nut, tighten and safety with a lock wire on propellers installed on engines that breathe through the propeller shaft. Make sure that plug in front of dome is tight and that lock wire is in place on propellers installed on engines that do not breathe through the propeller shaft.

(16) Make certain that barrel oil drain plug is tight and safetied.

(17) With the aid of blade beams, shift propeller into full low pitch position and check all blade angles. These angles are equal and agree with the low pitch stop setting.

(18) Check all external safety wire and cotter pins.

b. To remove propeller from shaft

(1) Put propeller in full feathering position.

(2)  Remove safety screw, unscrew dome retaining nut, and lift off dome

(3) Remove safety screw, unscrew dome retaining nut, and lift off dome.

(4) Remove retaining nut lock wire, back off retaining nut two or three turns, and then remove the distributor valve assembly, using adapter provided.

(5) Remove retaining nut from shaft.

(6) Remove propeller from shaft.

42. Lubrication.-This propeller requires no internal lubrication as all parts operate in oil supplied by the engine. The blades and hub are coated with clean engine oil as outlined in section IX.

43. Propeller controls.-a. The propeller control (fig. 26) is a self-contained governor suitable for mounting on the special built-in pad on the nose of the engine. The unit consists of the same gear type booster pump which boosts the engine oil from engine pressure to higher pressures required to operate the propeller pitch changing mechanism. A pilot valve controls the flow of oil to and from the propeller. It is actuated by the same spring balanced flyballs used in the control for the counterweight type propeller. The minimum limit of the governing range of the unit is set by the low r. p. m. adjusting screw in the speed adjusting rack. A relief valve plunger permits the force of the relief valve to be supplemented by the force of engine oil pressure; thus the relief valve will operate at a pressure equal to engine oil pressure plus the spring pressure. A transfer valve in the base of the unit provides a passage through which the high pressure oil passes for feathering and unfeathering operations of the propeller. The size, weight, and general shape of the control are the same as that of the constant speed control. The method by which the oil enters and passes through the gear pump and is delivered into the hollow portion of the drive gear, is the same as the constant speed control.

b. Figure 27 shows the positions and functions of the various parts of the control during the "on speed," "underspeed," "overspeed," and "in and out" of feather conditions. The "on speed" condition (fig. 27 (3)) exists when the flyball and spring forces are in balance, causing the pilot valve to close the line to the propeller and maintain a given blade angle. Both pressure and drain ports are closed during this condition. All oil from the gear pump is by-passed through the relief valve back to the inlet side of the pump. The "underspeed" condition (fig. 27 (1)), exists when the speed of the flyballs has been reduced and the spring force overcomes the force of the flyballs. In this condition, the spring forces the pilot valve down. The upper land of the valve moves below the metering port in the drive gear and cuts off the high pressure oil, and the lower land moves into the recess in the gear and opens the propeller line to drain. When oil drains from the rear of the hydromatic piston, the blades assume a lower angle and permit the engine speed to return to its original value, and the flyballs and speeder spring in the control unit return to a balanced state, as shown in the "on speed" condition. In the "overspeed" condition (fig. 27(2)), the flyball speed has increased, their forces have exceeded the force of the speeder spring, and the pilot valve is raised. The upper land of the valve then opens the ports through which then high pressure oil flows and the lower land closes the drain. Since oil pressure to the rear of the piston increases the blade angle, the engine speed is reduced and the flyball spring forces return again to a balanced state as shown in the "on speed" condition. During the feathering and unfeathering operations of the propeller, high pressure oil from an auxiliary source is supplied to the propeller through a transfer valve in the base of the constant speed unit. The function of this valve is to cut off oil from the unit to the propeller and open the passages through the engine nose to the high pressure feathering oil. The valve assembly consists of a plunger, a return spring, and a ball check. The auxiliary high pressure oil forces the plunger against the spring, as shown in figure 27 (4). When either operation is completed and pressure at the source of the auxiliary oil supply is reduced, the spring returns the ball to its seat and reopens the propeller line to governor oil. The propeller then operates as a constant speed propeller.

c. Installation of the governor and cockpit controls (fig. 28) should be in accordance with installation drawings covering the particular airplane, except that the following precautions should be taken:

(1) The controls should be checked to insure their proper functioning before installing on the engine.

(2) To install the governor, remove cover from surface on which governor is to be mounted. Set governor in position, checking fit of governor circular lining boss.

(3) The governor securing nuts should then be placed  on the mounting studs and run down finger tight. Remove governor head and check backlash and freedom of movement while tightening governor securing nuts. It is essential that these nuts be tightened evenly. The securing nuts should not be drawn down excessively tight, as this may cause displacement of the gasket material in the vicinity of the mounting studs and result in warping the governor base. In some cases it has been noted that the governors are susceptible to binding after having the nuts tightened. This condition can be relieved by slacking off slightly one or more nuts. The nut or nuts causing the difficulty can be determined by trial.

(4) It is advisable, during tightening of the securing nuts, that the propeller shaft be rotated to at least three positions, checking the governor for backlash and freedom of movement at each point. The primary precaution is to make sure the governor turns freely when assembled to its drive on the engine.

(5) Connect auxiliary line and cut-out switch wires if used.

d. The governor and cockpit controls are removed as follows:

(1) Disconnect cockpit control from unit.

(2) Disconnect high pressure pipe from base of control unit. On some governors the cut-out switch is also disconnected.

(3) Remove mounting stud nuts.

(4) Remove governor. If it is necessary to temporarily remove a unit between propeller overhauls, the cockpit control should be moved to the high pitch (low r. p. m.) position and the pulley or lever shaft and should be marked in relation to cover before removal from the control shaft. This will permit reinstallation in exactly the same position and facilitate readjustment of the control system.

44. Operation.-a. (1) The engine is started with the propeller control in low pitch (high r. p. m.) position. This position reduces the load or drag of the propeller and the result is easier starting and warm-up of the engine, also is normally the position of the propeller prior to stopping the engine.

(2) For take-off, climb, and flight, the operation instructions governing the engine airplane combination should be consulted for best r. p. m. position.

(3) When gliding in to land the airplane, the propeller control should be in a position to allow a lower r. p. m. than take-off r. p. m. This is a safety precaution to prevent speeding the engine beyond a safe r. p. m. in case of an emergency.

(4) Prior to stopping the engine, the propeller control should he moved to low pitch high (r. p. m.) position.

b. Feathering is accomplished by supplying oil from an independent source, not controlled by the governor, to the inboard end of the cylinder at pressures sufficient. to move the cam rollers over the feathering or low mechanical portion of the cam slots under any conditions of r. p. m. and power that may be expected in flight. In some airplanes, the feathering oil pump receives its supply from the hopper tank connection in which cold or atmospheric temperature oil may be delivered, resulting in excessive pressure in the feathering oil line which will operate the pressure cut-out switch. This in turn will stop the feathering pump motor. With the motor stopped, the propeller feathering cycles is not completed. However, this can be overcome by again depressing the control switch and holding it in by hand until the feathering cycle is completed. This will require that the operator watch the propeller carefully and release the switch as soon as the propeller ceases to windmill. At any time, the automatic feathering action can be interrupted by manually pulling out the control switch to break the motor circuit. The windmilling propeller will then resume constant speed operation without further attention.

c. Unfeathering the propeller consists essentially of reversing the passages in the distributor valve in order to permit the high pressure oil from the auxiliary system to act on the outboard end of the piston while the inboard end is connected to the engine lubricating system. To unfeather, it is necessary only to depress the propeller control switch and hold it closed until the propeller is unfeathered to the desired r. p. m. (800) then promptly released.

d. In case of emergency, when it is necessary to feather the propeller in the shortest possible time (if the engine has stopped for minor cause and has been permitted to rotate due to windmilling of the propeller) the instructions given for emergency feathering should be followed. In case of practice feathering while flying, the period of time the propeller is left in the feathered condition will not exceed I5 minutes. This requirement is necessary because during the feathering operation the quantity of oil forced into the engine nose may be great enough to seep down past the piston rings of the lower cylinders into the combustion chamber, and if not removed before rotating the propeller, may result in damage to the engine. The following instructions apply when feathering the propeller in flight.

(1) Emergency feathering.

(a) Close propeller feathering switch.

(b) Close throttle.

(c) Move mixture control to idle cut-off position (depending on type of engine and carburetor).

(d) Turn off fuel supply.

(e) Leave ignition switch on until propeller stops and then turn off.

(2) Practice feathering.

(a) Close throttle,.

(b) Move mixture control into idle cut-off position.

(c) Turn off gasoline supply to engine.

(d) Close propeller feathering switch.

(e) Leave ignition switch "on" until propeller stops, then turn switch off.

(3) Unfeathering (return from, feathering).

(a) Turn ignition switch "on" with throttle closed.

(b) Set propeller cockpit control to the minimum r. p. m. (high pitch) position.

(c) Turn on fuel supply.

(d) Close propeller control switch and keep closed until tachometer reading reaches 800 r. p. m. Then pull out switch.

(e) Allow engine to operate at this r. p. m. until required temperature is obtained. Then open throttle gradually, causing engine to speed up to the minimum. r. p. m. or the speed for which governor is set.

(f) Adjust mixture.

(g) Adjust throttle and governor setting to desired power and engine r. p. m., and synchronize.

e. In connection with the feathering and unfeathering operation of the propeller, the following points will be carefully noted:

(1) In flight, the propeller begins to windmill and crank the engine as soon as it starts to unfeather. The engine speed increases rapidly as power is applied and automatic unfeathering proceeds.

(2) It is important when unfeathering a propeller after the engine has cooled, to idle at slow speed until the engine is thoroughly warmed up before bringing it up to speed, otherwise serious damage may result due to poor lubrication. The windmilling action of unfeathering is a very powerful cranking force and will easily over-speed the engine beyond safe idling speed unless care is taken to stop unfeathering while the propeller is still at very high angle.

(3) After unfeathering to about 800 r. p. m. at an air speed of approximately 125 m. p. h., the engine may be permitted to warm up as long as desired without tendency to speed up. It is only necessary to open the throttle to cause the propeller to shift to a lower angle when the governor takes charge.

(4) If the engine idling speed becomes excessive for warm-up purposes, the speed is reduced by closing the propeller control switch to partially feather again. The switch is released when the desired r. p. m. is reached.

(5) The operation of the propeller distributor valve is such that the blades cannot be unfeathered by means of the auxiliary high pressure oil until they have first reached the fulI-feathered position. Thus, after an interruption in the flow of high pressure oil, a reapplication of the pressure will cause the propeller to move toward the feathered position regardless of whether its direction of motion, prior to the pressure interruption, was toward feathering or toward unfeathering.

(6) From the above it is evident that should the feathering switch be closed (or the high pressure oil applied) inadvertently, the feathering action can be stopped and the propeller returned to constant-speed control by manually reopening the control switch (or discontinuing the high pressure supply). If accidental operation of the feathering control has resulted in complete (or nearly complete) feathering the propeller is unfeathered in the normal manner.

(7) Oil pressure is not required to hold the blades in the full-feathered position. Once the blades have been feathered and rotation stopped, torque producing aerodynamic forces are in equilibrium and there is no tendency for the propeller to rotate.

45. Inspection and inspection maintenance.-a. When per-forming a preflight inspection, the range of operation of the Hamilton standard hydromatic propeller is checked as follows:

(1) After completing the engine warm-up, open throttle to some intermediate engine speed, for example 1,800 r. p. m.

(2) Move propeller control to high pitch (low r. p. m.) position and note decrease in engine r. p. m.

(3) Without. disturbing throttle setting, move propeller control to low pitch (high r. p. m.) position and note increase engine r. p. m. If both increase and decrease in engine r. p. m. is indicated on the tachometer, the propeller is functioning correctly.

h. An inspection is made after initial installation and before each flight for oil leaks. Between the blades and hub, around the base of dome, and between the two halves of the hub oil leaks are most likely to occur. If a check on the tightness of bolts and nuts fails to correct the condition, the services of a trained propeller mechanic. should be obtained. Any leak should be corrected before flight.

c. The markings on both blade and hub are inspected for deterioration. In event the markings or protective coating are not in good condition, the propeller is removed from the crankshaft and markings or protective coating renewed with the propeller on the balancing stand. This is accomplished by a qualified propeller propeller mechanic.

d. At the specified periodic inspection. the retaining nut of the hydromatic propeller is checked as follows:

(1) Remove lock ring and breather cup from front of dome. (This applies to installations on engines which breathe through the propeller shaft.)

(2) Remove lock screw from dome retaining nut and unscrew nut. This nut is attached to the dome and acts as a puller when the nut is unscrewed.

(3) Remove dome assembly.

(4) Remove lock ring from propeller retaining nut.

(5) Check retaining nut for looseness by using tubular wrench together with composite wrench and a bar approximately 3 feet long. Apply a force of approximately 180 pounds at end of bar, and while this force is being maintained, rap bar close to the wrench with a hammer weighing about 2 1/2 pounds. (It is not necessary to remove the valve assembly but care should be taken to prevent damage to it by the wrench.)

(6) Install lock ring with pin through retaining nut slot, propeller shaft hole, and into valve housing slot. Snap wire into position in groove provided for it in retaining nut.

(7) Install dome assembly.

(8) Install dome retaining nut lock screw and safety the screw with a cotter pin.

(9) Install breather cap and safety it with locking ring provided.

e. All controls, switches, pumps, etc. are inspected for security of , mounting. All external braces and fittings are inspected for cracks, elongated holes, and for other defects. Any defect noted is corrected before flight.

FIGURE 23. - Cut-away of the Hamilton standard hydromatic propeller.

FIGURE 24.-Propeller control force.

FIGURE 25.-Retaining nut and attaching parts.

FIGURE  26.-Governor assembly

FIGURE 27. - Operation of the governor (shematic view)

FIGURE 28, - Auxiliary control system