FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1949
1949 - 0589.PDF
April jth, 1949 403 opened up, the rotor drive take-up remains smooth by virtue of clutch slip, and snatch loads are thus obviated. A triggering mechanism is incorporated in the bobweight linkage, so that the weights may be held down in order to allow the engine independently to be run up to maxi- mum r.p.m. The primary drive shaft is supported at the centre in large roller and ball bearings carried in an annulus bolted into the gearbox casing, and the nose of the shaft runs in a slightly smaller roller bearing supported in the gearbox front cover. Immediately forward of the centre bearings, the main driving bevel is splined to the shaft, whilst at the forward end of the shaft, in front of the nose roller, is splined a ring to which is bolted the driving half of the universal joint at the foot of the front rotor transmission shaft. The drum of the rotor brake is bolted to the splined ring: this brake, which is of normal Girling expanding, At left is a detail of a rotor shaft coupling, showing the enclosed ball-type steady bearing and flexible- plate joint, whilst at right is a plan view of the epicydic sub-stage reduction in a hub gearbox. twin-shoe pattern, by reacting on the primary drive shaft thus serves all three rotors. On top of the main driving bevel is a wheel which gives drive through a torsion quill shaft to the Lockheed hydraulic pump mounted on the head of the gear box, and to the rotor tachometer. By the use of this second hydraulic pump, which is driven from the rotor side of the clutch, provision is made for maintenance of full flying con- trol (which utilizes the Lockheed hydraulic Servodyne system) of the autorotating rotors in the event of engine failure. Bolted on the front of the clutch bell housing is a toothed ring through which power is transmitted to two lay shafts, the port member for cooling-fan drive, and the starboard member available as an auxiliary drive if required. On each layshaft is a bevel drive to vertical shafts, the port assembly driving the vacuum pump and engine tachometer generator, whilst the starboard shaft drives the transmission oil pumps. • resulting in substantially constant - velocity drive. All three rotor gearboxes and hubs are identical and interchangeable, but are individually set relative to the fuselage at varying inclinations, in order both to give dihedial effect and a measure of torque reaction compensa- tion. Each hub gearbox, a D.T.D. 289 magnesium casting, is bolted to a light alloy adaptor casting carried in the end of the outrigger boom, the output half of the upper universal of each transmission shaft being bolted to a splined driving cup in the bore of the driving bevel; in fact, this is a reverse similitude of the coupling at the input end of each shaft. We have already stated that the reduction between engine and rotors is made in two stages, but the second stage, at each hub gearbox, is in fact divided into sub- stages, the first of which, with a ratio of 0.65:1, occurs between the driving bevel and the crown wheel. The actual drive path in each hub gearbox is somewhat circuitous. The crown- wheel is carried at the head of a truncated cone, the base mouth of which is splined to a vertical shaft running coaxially within the cone, up to the sun-wheel of the epicyclic train, in which the second sub-stage reduction ratio, of 0.266:-1, is vested. The -- • , sun-wheel is a plain spur N. \ % v gear, giving drive to three O V VJ planet pinions reacting against a fixed annulus dowelled to the gearbox casing. The planet carrier is splined direct to the base of the rotor hub spider and thus forms the actual hub driving member. It is carried in twin-row, Timken taper-roller bearings at the head, which take the static and flight loads of the rotor, and a large roller bearing at the base, which caters for journal loads. Drive Distribution Drive to the front rotor is given virtually direct off the nose of the primary drive shaft, but for the port and star- board rotors, transmission is by means of bevel pinions meshing with the main driving bevel. These are each in turn hub-splined to a cup transfer-member, to the rim of which is bolted the driving half of the lower universal joints of the transmission shafts. Each of these latter is a light alloy tube of 4$in diameter and 9 gauge wall thickness. Speed reduction between engine and rotors is in two stages, i.e., the normal engine reduction of 0.42:1, and a further reduction of 0.174:1 at each hub. By this means, the torque carried by the transmission shafts is kept reason- ably low. Each rotor shaft is carried in enclosed ball-type steady bearings, housed in transverse diaphragms across the interior of the boom, and on the engine side of each bearing the shaft is divided and joined by flexible steel plates to compensate any whip in the drive. The shafts terminate at the head in universal joints, the angles through which are identical with those of the universals at the feet, this measure Blade Articulation The rotor hub spider is a high-tensile steel forging in the form of a stem splined to the planet carrier and embody- ing three spokes which form the pivot members, with needle roller bearings, for the massive flapping links. These latter are light alloy forgings and are each formed at the outer end with twin forks in which the blade root fitting pivots, also in needle roller bearings, to form the drag hinge. Off the root of the outer half of the drag hinge is an arm picking up the piston rod of a Lockheed oleo-pneumatic snubber unit anehored to the flapping link to restrict azi- muthal accelerations, i.e., velocity variations in the angular dispositions of the blades. Each blade is individually snubbed. On the drag hinge axis is a universal joint at the outer end of a torque shaft through which blade pitch change is effected. The blade itself is carried in twin-row Timken taper-roller bearings in the outer half of the drag hinge link. At the inner end of each torque shaft is a swing-link carrying a twin-row taper roller bearing at its outer end, in which is pivoted a spindle to which the pitch-change drop-arm from the swashplate is pin-jointed at its foot. The swashplate assembly is carried at the crown of the rotor hub mechanism and is employed to translate control input motion into blade pitch-change. Thus far is properly the limit of the rotor drive trans- mission system, although in carrying the description to its logical conclusion we have necessarily had to deal with the blade articulation linkage. The mechanical action of blade pitch-change will, however, be included in the follow- ing issue, together with an examination of the hydraulic powered-control system and the inter-rotor control distri- bution for flight manoeuvre. C. B. B-W. • (To be concluded next week)
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
