De HAVILLAND HYDROMATIC AIRSCREW PROPELLER AIRCRAFT BRITISH EDUCATIONAL FILM 75764

the three main Assemblies of the de havilland hydra-matic airscrew of the barrel and blade assembly the distributor valve housing with its file conductor sleeve and the dome assembly which are assembled in that order in many installations the constant speed unit is fitted to the engine crankcase immediately behind the air school and is driven by a quill shaft a special gasket is used between the crankcase and the constant speed unit and no other jointing must be used the nuts securing the constant speed unit are tightened down evenly and firmly before connecting the pilots control with the barrel and blade assembly slung carefully clean off the splines on the air screw shaft and in the bore of the spider see that the rear comb is in position and undamaged insert the oil conductive sleeve using the extractor as a convenient handle note particularly that the oil conductor sleeve is an air screw part likely smear the splines of the air screw shaft with anti seeding compound when offering up the earth group great care should be taken to get both sets of splines in alignment no undue force should be used and when the shaft had entered the air screw should slide smoothly into position next insert the front cone oil seal water then the front car oil seal between the air screw shaft and the Spyder shape to fit the bottom of its groove taking great care that it is kept square with the sharp take great care that no damage is done to the feather edges of the oil teal now turn the blades in the barrel to move the gears aside assemble the split comb around the flange of the air screw nut and screw them into position on the air screw shaft a strong tube spanner is used to tighten this nut and the leverage is applied through a short tunnel with extension Q's the torque or between 750 and 900 pounds feet is required and at it is difficult to obtain this talk without an unwieldy length of lever the nut is jerked up as far as possible and finally with the loads still on the tummy bar one or two smart reps are given to the tummy bar with a lead hammer to ensure that the air screw is full tight in position fit the snap ring into its groove the distributor valve housing joint washer is now smeared with grease and inserted in the air screw shaft where I'll conduct a sleeve marking paint is then smooth over the joint phase of the distributor valve housing the housing is then screwed into position in the a screw shaft to add thing if the housing is bearing evenly on the copper Jascha note that for screwing up the housing is turned in an anti-clockwise direction if on removing the housing the marking is unsatisfactory and it is felt that the housing is not pulling hard down upon the washer a second washer may be added to make the joint effective the distributor valve housing should be put up with a talk not exceeding 100 pounds feet it was seen that whereas the air screw nuts was screwed up in a clockwise direction the distributor valve housing was screwed up in an anti-clockwise direction because it has a left hand thread at it in our end an effective lock is made possible therefore by employing a single lock wire whose Tang engages both components it will be seen that the Tang is thickened up to fits both the calculations in the air screw nut and the locking grooves in the distributor valve housing before mounting the dome it is essential to turn all blades into the full though it is possible to turn the blades by half a better control is had by using a torque bar there is then less risk of damage to the segment teeth the full feathered position is obtained when the end teeth of the gear segments are felt to encounter the stops in the barrel support blocks on non feathering air schools the blades are adjusted to the degree markings on the barrel around the blade aperture the oil seal rings on the distributor valve housing require attention these should be liberally oiled after rotating the rings to ensure that oil reaches the goo see that the ring gaps are not in line before installing the dome it is most important to see that the stop lugs on the rotating cam are in contact with the coarse pitch stops on the stop ring this is evident that the piston is back as far as possible in the dome and that the cams are in that full feathered position the dome barrel oil seal is now stretched into position around the fixed cam base with the feathered edge away from the dough now remove the dome plugs from the dome assembly and insert the special handing bar the handling bar enables the assembly to be lifted about its center of gravity having noted the assembly position from the markings on the dowels and the markings on the dowel holes offer up the dome assembly should the dowel holes in the fixed cam base not engage the dowels in the barrel shelf the whole dome assembly should be turned through a full revolution in the direction of our scooter tations this is most important now engage the dome retaining nuts this nut has not only to secure the dome but it also has to carry the load arising from the preload on the gears and the compression of the dome barrel oil seal the necessary torque is applied with a special spanner the dome securing nut is locked by means of a grub screw this in turn is wired to prevent its unscrewing before operating the a screw under pressure the blades should be turned by hands to the fine pitch position as a check that the dome has been correctly installed for this check the use of torque bars is most essential the movement of the blades can be observed against the degree markings stamped on the barrel at the blade apertures and should it be within a small margin it will be immediately apparent should the pitch operating mechanism have been incorrectly meshed as one tooth displacement on the smaller size air screw will produce an error of about eight degrees and on the larger size one of about ten and a half degrees finally the dome plug is inserted this is tightened down onto its oil seal unlocked by means of a lock while the de havilland hydra-matic air screw owes much of its reliability to the careful manufacture of its individual parts these are produced in one of the most highly specialized branches of the aircraft industry by the skillful use of elaborate tools their craftsmen should maintain the same high standard of our friendship when installing it to use after the installation of the de havilland hydra-matic a screw the aircraft should be wheeled out for engine running and air screw adjustments for engine starting and for air screw testing the use of auxiliary storage batteries is essential by relieving the aircraft batteries of the heavy loads imposed by a screw testing they preserve the proper aircraft voltage which certain of the instruments require before commencing to check the air screw for adjustments and operation under par the air screw control lever is put to the maximum rpm position and the engine started up and RPM to warm up the air screw lever is then drawn back to the minimum rpm position and left until the revolution ceased to fall this indicates that the air screw dome has filled with oil the air screw control lever is then pushed forward and exercised over its entire range to ensure that all the air has been replaced by oil this condition is indicated when the RPM follows the movement of the control lever the ASCO control IVA is then pushed fully forward into the maximum rpm position and the throttle opened up to the takeoff boosts as specified on the engine data plate the RPMs should remain at the maximum permissible in this case 3000 opportunity should be taken at this time to note the amount of over swing and the time taken for recovery normal over swing is about 100 rpm similarly when the throttle is brought back the under swing of the needle should be noted its amplitude should be of the same order and should rapidly subside finally the constant speed leader is brought back to the minimum rpm position during this movement the RPM indicator needle should follow the constant speed lever closely until the minimum rpm governing is reached on this installation this is at about 2,000 rpm and should occur when the constant speed lever is at the end of its quadrant if the air screw is being adjusted to the engine for the first time it will often be found that the maximum obtainable rpm is either more or less than the maximum permissible adjustment then have to be made at the constant speed governor which is fitted with stops to restrict the maximum rpm as required behind the protecting cover on the mechanically operated governor will be found the maximum rpm stock achieved headed screw with a locking nut when the RPM is fun to exceed the maximum permissible the procedure for adjustment is as follows with the constant speed lever fully forward the engine is opened up to take off boost then the constant speed lever is drawn back until the required rpm is shown the position of the control lever in the quadrant is now marked and the engine stopped the maximum rpm stop is now unlocked and screwed in until it is just felt to make contact with the stop arm on the speed control shaft the adjustment is then made to bring the air screw lever to the take-off position in its quadrant when the governed rpm is found to be less than the maximum permissible first unscrew to stop one turn and run up the engine to ascertain what increase of rpm is effected by a single turn of the stop the stop can then be turned the required amount to complete the adjustment the controls are then adjusted so that the control shaft lever just makes contact with the stop with the a screw IVA in the maximum rpm position large multiple engined aircraft are often provided with hydraulic control to their constant speed units adjustment is more easily affected in these installations since it is required merely to screw up the cover one term and to note the corresponding decrease in rpm the necessary adjustment clockwise or in this case anti-clockwise is then made to obtain the correct maximum rpm the cover must have course the locks with the engine opened up to about 1,000 rpm the feathering switch is given a firm deliberate pressure as the blades turn into the feathering position the RPM will drop to about 500 or 600 by the time the operation is complete after approximately 10 seconds the feathering button will throw out indicating that the a screw has feathered the engine should then be stopped by switching off in order to verify that the blades have reached the full feathered position to unfeathered the pilots feathering switch is again depressed and held in the closed position until the blades are seen to have resumed a normal flying angle subsequently the airscrew may be untethered with the engine running to do this hold in the feathering switch until the RPM rises to 800 and let go where the engine is permitted to run it will occasionally be found that the a screw commences to unfetter soon after reaching the feather'd position without the pilot switch being operated this action is not abnormal it occurs by reason that engine oil pressure is still acting within the dome after the feathering pressure has been cut off this cannot occur in flight as a feathered air screw will stop the engine even though the throttle be left open and the switch left arm

Channel: PeriscopeFilm

Views: 220,844

Keywords: Periscope Film, Stock Footage, Propeller (Means Of Propulsion), Hamilton Standard, De Havilland (Aircraft Manufacturer), Aircraft (Type Of Fictional Setting), Royal Air Force (Armed Force)

Id: fvCmQAetyag

Length: 26min 11sec (1571 seconds)

Published: Fri Aug 21 2015