Design Analysis of the
Fairchild C-82 Packet
Part I

By Irving Stone,
Assistant Editor, Aviation

Beginning a comprehensive two-part study of Fairchild's war-born long-range aerial freighter — a fast plane designed around extensive cargo space and affording immediate practical utility for post-war hauling …. The 14th in Aviation's lucid series.

When the rear cargo doors of the Fairchild C-82 Packet swing open, it is impossible to keep one's thoughts on the craft's technical aspects — the almost unbelievable space visible commands all attention. For what is seen is a substantially rectangular 2,870-cu ft room actually larger than some rail boxcars. Also, by providing for end-loading, the design eliminates the 90° turn involved in side loading, and thus accommodates longer cargo with facility.

It is not alone space which makes the plane unique, for its maximum payload is 18,000 lb for 500 mi, 15,500 lb for 1,000 mi, and 13,000 lb for 1,500 mi. Takeoff run at sea level, with gross weight of 42,000 lb, is only 800 ft. Cruising speed is over 200 mph at 10,000 ft, and range is 4,000 mi.

Three considerations underlie the Packet design: (1) Carrying heavy bulky units without dismantling them, (2) transportation of paratroopers, and means for rapid conversion of the craft to hospital use, and (3) towing of gliders.

Units to be transported were considered to fall into three categories: (1) Those which could be loaded under their own power — trucks, tanks, half-tracks, and armored cars; (2) those loaded by power of their own prime movers — cannons, caissons, trailers, field-kitchens, and other miscellaneous units; and (3) those units normally carried in containers of various shapes and sizes — advantageously handled when loaded directly from a truck to the Packet's truck-bed-level cargo floor.

The large rear doors accommodate these types of cargo, and because of the high wing and twin boom and high tail arrangement, can be approached from the rear and sides of the plane, without obstruction.

Since cargo to be transported is predominantly square, sides and top of the cargo compartment are straight for full length to obtain optimum volume usefulness for the airplane.

Use of tricycle landing gear places the cargo floor horizontal for its full length.

Loading is facilitated by two ramps, adjustable to the tread of equipment being loaded, and brought together at the center, they form a single ramp unit suitable for loading litter or seat patients.

As a troop carrier, the Packet affords simultaneous egress for two lines of paratroopers, and coupled with its low controllable speed, permits more than twice the usual concentration of aerial troopers in a given ground area.

In the center of the cargo floor, a door bay permits the dropping of aerial delivery containers carried on rails with electrically operated shackles releasable by pilot or jump-master.

Straight walls of the cargo compartment simplify mounting of supports for litters five tiers high, with sufficient space in the center portion of the fuselage for movement of medical personnel and equipment.

Material of construction in the Packet is generally 24ST Alclad, except for higher strength alloy in various highly stressed members.

Fuselage Main Body Section

The Packet fuselage — 54 ft long and approximately 10 ft wide and 13 ft high — is of semi-monocoque construction and consists, generally, of main and auxiliary frames, stringers, beams, and skin. To facilitate construction, the fuselage has been resolved into six major sections — main body, sides, upper front, upper rear, nose compartment, and rear cargo door compartment.

Main body section —foundation of the fuselage —supports the cargo floor, is composed of frames, stringers, and longitudinal and transverse floor beams, and is approximately 40 ft long from the point of nose attachment to cargo door hinge point. From bottom of floor to bottom contour it varies in thickness from 9 in at its ends to 20 in at the center. Main frames — except for main spar frames — are spaced approximately 35 in apart. Main spar frames are so designated because they fall directly below wing center section spars, and are spaced 72 in apart.

Main frames of the main body section are U-shaped web beams with straight upper chord members and vertical chord stiffeners. Lower chord members are hydropressed contoured C-sections. Web gages vary from .025 to .040 — the latter being at the main spar frames. Upper chord members vary from .032 to .064, and stiffeners are rolled angle sections with gage varying in accordance with thickness of web.

At the end of the main body section the main frame has a double web or box construction. Upper chord is trough-shaped, .072 thick, and is designed to receive upper fittings of loading ramps. Web members are .032 and are reinforced by vertical channel stiffeners. Lower chords are .064 formed angles to which a plate is riveted to complete the box section. At outer ends of the frame, just outboard of the outboard longitudinal beams, cast fittings are provided to receive spring-loaded jack-points to afford support for aft end of the fuselage while it is being loaded.

Auxiliary frames are constant depth C-sections varying from .025 to .032, with the heavier gage between spar frames, and are located between main frames to reduce the length of skin panels to approximately 17 in.

Main body section has 7 longitudinal floor beams, two outboard, two inboard, two intermediate, and one at the center. Outboard beams, 96 in apart, are located above the floor, the beam on the right side running the full length of the cargo compartment, and that on the left extending from the rear cargo door frame to the front entrance door from where it runs forward below the floor. The beams are of web construction of constant height, with rolled angle upper and lower chord members, and tapered channel-section vertical web stiffeners. At typical section, beams are 15 in deep with .020 webs and .051 chord members. The vertical stiffeners are extended beyond the lower chord member to provide anchorage for the outer ends of the transverse floor beams. Lower chord rests on and is riveted to main frame upper chord members, and the web of the outer beam is riveted to the vertical stiffener which forms the inboard edge of the U-shaped main frame. Web of each beam has cutouts for attachment of eight ventilators. At ventilator cutouts, the web is increased to .040, and an additional drop-hammered section is used to stiffen the beam.

Inboard beams, fabricated in lengths to fit between main frames, are located below the floor and spaced approximately 54 in apart. They have web construction with rolled angle upper and lower chord members and vertical web stiffeners. Typical section has .040 web, .060 upper caps, and .040 lower caps. The webs are riveted to the vertical web stiffeners of main frames. Chord members on either side of main frames are made continuous by joining with a splice plate which passes through an opening in the main frame web. Lower chord of the inboard beam follows the contour of the main body section, is spliced for continuity,and passes through notches in the lower chords of main and auxiliary frames.

Intermediate beams — also located below the floor — are made up in sections to fit between main frames and are spaced 30 in apart. They are web beams, with upper and lower chord members spliced for continuity, and have vertical web stiffeners. The beams have a constant depth of 10 in and do not extend to the contour. Typical section has a .032 web and .051 upper and lower caps.

Center beam is similar in construction to the intermediate beam but instead of a single web, has two webs spaced by channel stiffeners. The beam is designed to take loads imposed on it by the spare engine hold-down fittings used for bolting power plants mounted on cradles or to receive eye bolts for lashing other heavy cargo. Hold-down fittings are cast, have a center boss and two flanges, and are designed to sustain a load of 5,000 lb in any direction. The boss is drilled to receive a steel bushing tapered for a ¾-in bolt, and the flanges provide means of attaching the fitting to the center beam web.

Between main spar frames, the center beam is removable and is equipped with fittings at upper and lower cord members to engage mating fittings on the spar frames. The beam is secured by four bolts and when it is removed, the inboard beams and main spar frames form a box-opening approximately 52 in wide by 72 in long for dropping aerial delivery containers.

Transverse floor beams are hat-sections, generally of .032 gage, and are spaced 5.8 in on centers. Used in sections of the cargo floor usually heavily loaded, they extend from the outboard beams to the intermediate beams and are supported in their length by the inboard beams.

Cargo floor — designed for heavy loading and to withstand abrasion and impact — is constructed of 3-ply Douglas fir plywood core to which is bonded a thin sheet of aluminum alloy on the bottom side and a heavier sheet on top having corrugations spaced 10 in on centers. The corrugations are backed with maple strips to prevent crushing of the metal and prolongs the life of the floor by facilitating the sliding of cargo. Between corrugations the floor is coated with non-skid paint.

To facilitate fabrication and maintenance, the floor is constructed in removable sections. Over the aerial delivery opening in the fuselage center, the floor consists of two doors, hinged at outer fore-and-aft edges to the inboard beams, designed to withstand the same degree of loading as the floor proper.

Spaced on 20 in centers in the floor is a pattern of hold-down fittings, each provided with ring and stud for lashing cargo, and designed to sustain an upload of 1.250 lb and side load of 500 lb.

Fuselage Sides

For ease of fabrication, fuselage sides — consisting of main and auxiliary side frames, longitudinal stringers, and skin — are constructed as separate units.

Main side frames have flanged holes and beaded webs, rolled lip angles placed back-to-back to form the inboard chord members, and C-section outboard chord members formed to the contour of the fuselage.

Side spar frames provide the tension tie to the wing center section spars and are tapered from a single frame at the lower portion to a box frame at the upper portion to afford a base for the fuselage-to-wing attachment fittings. One of these fittings is mounted on the inboard flanges of the frame, and the other to the outboard flanges. Cast spacer blocks are provided between the webs to stabilize the upper end and form a rigid base for the attachment of the fuselage-to-wing fittings.

All frames, except spar frames, are notched to permit installation of continuous rolled bulb angle stringers.

Twelve 9-in holes provided in the skin for flush mounting of circular windows are reinforced by an angle on the inside.

Fuselage Upper Front Section

The upper front section is located between the end of the cockpit floor, at station 196½, and the wing center section front spar, at station 319. It consists of a series of arched frames to which horizontal beams are riveted, longitudinal stringers, skin, intercostal fore-and-aft beams, and a covered corrugated floor for accessories.

The arched frames are pressed C-sections with return lip on the inside flange and flanged holes in the webs, and at a typical section, main frames are 4½ in deep, auxiliary frames are 3¼ in deep, and frame gage is .032. The horizontal floor beams are built-up I-members having .020 web and a depth of 5 in at typical section. Fore-and-aft intercostal beams are C-sections with return lip on both upper and lower flanges and flanged holes in the web; gage is .032 and depth is 5 in. at a typical section. Arched frames are notched for installation of continuous bulb angle fore-and-aft stringers.

In the top of the upper front section is a cutout for an air scoop which supplies fresh air to a secondary heat exchanger and ducts mounted just below the fuselage contour. The accessory floor of the upper front section is utilized for mounting radio and avigational equipment. At the end of cockpit floor, where the accessory floor commences, the transverse floor beam is 27 in deep. Upper chord and vertical stiffeners of this member support the accessory floor, and the lower chord members sustain the cockpit floor and its longitudinal beams.

Behind the transverse floor beam are formers with sides tying into the vertical stiffeners and tops secured to the accessory floor longitudinal beams. Formers are rounded at the bottom and notched to permit passing of stringers. A metal cover is riveted to formers and stringers to box the full width of the fuselage. The box beam thus formed serves to stiffen the cross-beam of the frame at the forward end of the accessory floor (station 196½). On the cross-beam are mounted control pulley brackets and engine control bellcranks.

Fuselage Upper Rear Section

Upper rear section extends from the rear center section spar (station 391) to the end of the fuselage at the cargo door hinge point. It is of monocoque construction, embodying main and auxiliary frames, bulb angle longitudinal stringers, and skin.

Because of equipment mounted in this section, main frames are designed as deep web beams, measuring 31 in at a typical section. The .020 webs have flanged lightening holes, lower chord members are double rolled lip angles riveted in both sides of the web, and upper chords are pressed C-sections or angles conforming to the fuselage contour.

Between the wing rear spar (station 391) and the first main frame (station 409) is a box structure housing and supporting three automatic pilot servo units for operating ailerons, elevator, and rudders. Provision is also made for supporting pulley brackets for the servo emergency disconnect mechanism. On both sides of the servo units, fittings are installed on the rear spar and on the first main frame for supporting two tubes, for mounting aileron, elevator and rudder control sectors.

On the centerline, between first main frame (station 409) and second main frame (station 444), a structure is provided for mounting the flap operating mechanism.

Between the second main frame (station 444) and the third main frame (station 479) another box structure houses the self-ejection life raft, and the door of the raft installation also affords an emergency exit for personnel. The box walls and vertical stiffeners also provide support for mounting eight G-1 oxygen bottles and associated tubing.

Space between upper front and upper rear fuselage sections is taken up by the wing center section. On the upper surface of the wing is built the continuation of the fuselage — fuselage cap — similar in construction to the fuselage proper and serving as a tie between wing, upper front section, and upper rear section.

The main body section, left and right sides, and upper front and upper rear sections are riveted together to form the center fuselage structure.

Nose Gear Bulkheads and Beams

At the forward end of the fuselage, at stations 69½ and 87, are bulkhead frames supporting between them a horizontal upper beam and two vertical side beams. On these beams are mounted support brackets for hinging the nose landing gear structural members and retracting mechanism.

Forward bulkhead (station 69½) is an .020 web with vertical and horizontal stiffeners, and flanged contour members around the outer portion. In the center of the bulkhead is an opening to provide clearance for the nose wheel and gear structure, and on each side of this opening is another passage for access to the nose compartment. At the top of the bulkhead, on each side of the center opening, is a cutout covered by a pyramidal housing to provide clearance for the pilot's and co-pilot's control columns in extreme forward position.

Aft bulkhead (station 87), a combination unit at the lower portion and having a former frame attached at the top, is also provided with openings on each side. Clearance for the nose gear retraction mechanism is provided by three smaller openings covered on the aft face by an enclosure consisting of vertical formers, stringers, and skin fitted with an access door to permit inspection (from cargo compartment) of nose gear units.

The horizontal and vertical beams between bulkheads at stations 69½ and 87 are of conventional web, chord, and web stiffener construction. Horizontal beam has an .020 web and is 35 in wide. Web of the vertical beam is .064 above the nose gear torque shaft fittings, and .040 below. Secured between the bulkhead frames, the horizontal beam and vertical beams form a rigid structure to absorb loads imposed by the nose gear and transfer them to the forward end of the fuselage.

On the inboard sides of the vertical beams, fittings are mounted to support eh nose gear lower truss and retraction shaft. Outboard sides of the vertical beams are reinforced in the region of the fittings by two horizontal beams about 10 in deep which run between the bulkhead frames.

The nose gear upper truss supporting fittings are bolted to an auxiliary box beam formed by adding bulkheads and front and bottom sides at the junction of the horizontal beam and the aft bulkhead frame at station 87. The box beam also contains the support fitting for the upper terminal of the nose gear gravity-drop energy-absorber unit.

At the lower portion of the aft bulkhead and bolted to a vertical channel stiffener, is mounted one of the three major airplane jack points.

The nose section extends forward from the bulkhead frame at station 69, and is a conventional semi-monocoque structure having pressed C-section frames, stringers, and skin. It is divided into three compartments by two vertical bulkheads which run full height from the frame at station 69 to that at station 17.5.

The center compartment houses the nose gear in retracted position and at the bottom are three doors operated by the gear. The two rear doors are hinged at the outer edges and the front door is hinged at the forward edge, and all are constructed of double skin, with inner skin formed with depressions.

Left compartment is the lavatory equipped with chemical closet, tissue holder, relief tube, water tank, basin, towel container, and waste paper rack. A circular window affords lighting and visibility.

Right compartment houses hydraulic equipment, and a quick-removable panel in the vertical bulkhead provides ready access for inspection and servicing of nose gear. Entrance to left and right compartments is via openings in the bulkhead at station 69.

The nose section is attached to the fuselage proper by tension bolts through fittings riveted to stringers and mating with similar fittings on the center fuselage structure.

Cargo Doors

Rear portion of fuselage is constructed in the form of two large clam-shell type doors which swing on a vertical hinge line at fuselage sides, and when fully opened provide a loading area 8 ft square.

The doors consist of C-shaped frames, stringers, skin, and a vertical frame where the C-frames terminate, and are held in closed position by latches located in the center and rear members of the vertical frame.

Movement of one door with respect to the other is eliminated by use of four shear pins. Two pins are located at the bottom of the first C-frame and engage two sockets in the fuselage rear frame; the other two are located in the rear of the right hand door and engage sockets in the left hand door.

In each cargo door, two floor sections are provided —rear floor for rear observation and forward floor for paratrooper jumping station. In the side of each cargo door is a smaller door for paratrooper egress. It is of double sheet construction with inner skin recessed in sections to stiffen the outer skin, is hinged at the rear edge, opens inward, and has provision for locking in closed position and hooking in open position.

Cockpit Enclosure

Cockpit enclosure, consisting of formers, stringers, and skin, incorporates a windshield, side windows, and top escape hatches.

Because of the length of the enclosure span, the sloping V-shaped windshield is divided into four sections. Outer panels located in front of pilot and co-pilot are non-shatterable double plate glass with space between for passage of heated air for anti-icing. Center windshields are single non-shatterable plate glass. All panels are flush-mounted on the outside.

From the outboard side of each outer windshield panel, a curved Plexiglas transition section extends to the forward side window and contains a clear-vision panel approximately 6 in square, hinged at the rear edge and opening inward to provide unobstructed vision in the event of failure to keep the windshield free of ice.

Forward side windows — non-shatterable plate glass — slide aft and behind each is a fixed Plexiglas section for general convenience of the crew.

Escape hatches, fitted with doors which can be jettisoned from the crew compartment, are located above pilot's and co-pilot's seats. Each hatch door consists of a metal frame, Plexiglas panel, quick-release mechanism, and guide wires for sliding a sun shade.

Above avigator's station is an astrodome mounted on a square metal frame door releasable from inside and outside to provide an escape hatch for avigator and radio operator.

Wing Center Section

The Packet has a full cantilever, inverted gull, tapered, all-metal wing consisting of a center section and two outer panels which include an integral anti-icing system. The airfoil combination is based on NACA sections incorporating washout determined to prevent wingtip stalling.

Center section, extending to just outboard of the nacelles, is divided into three parts — leading edge, interspar section, and trailing edge.

Leading edge is constructed of .025 C-shaped pressed ribs spaced 7 in on centers, .025 truss bracing, spanwise rolled .025 bulb angle stringers, and .020 inner and .032 outer skin covering. The truss bracing is a hat-section with a flat plate at the base for attachment at web of rib.

Forward portion of the ribs are cut off and flanged for attachment of a spanwise baffle. The baffle, together with inner skin, which runs from the leading edge to 15% of chord, forms a D-duct for spanwise flow of heated air for anti-icing. Outer skin covers the leading edge to front spar, is separated from inner skin by .125 magnesium alloy spacers &fra12; in wide and spaced 3½ in on centers so that alternate spacer strips fall on ribs. The space thus formed conducts heated air chordwise in the D-duct.

Interspar section is constructed of front and rear parallel spars, interspar ribs, and top and bottom surfaces. Spars are of conventional web with extruded upper and lower chord members and rolled vertical stiffeners to which ribs are fastened. Front spar is approximately 38 in deep at the centerline and tapers to about 27 in at outer wing attaching point outboard of nacelle. Rear spar is 31 in deep at centerline and tapers to 22 in at the outer wing fitting. Spar spacing is 72 in, continuous to the tip splice. At each end of the interspar section, main wing hinges are bolted to upper and lower chords.

The spar web is continuous at the center of the section, and chord members are joined by bolted extruded splice plates. The web is .040 for 63 in. each side of centerline, and beginning 52 in from centerline, thickness is increased to .064 out to 174 in from centerline by using a lap splice. Thus, between inboard and outboard fuselage fittings, the spar web is .104 thick. Fuselage fittings — 14ST forged channels with ¼in-thick base and 5/32-in-thick outstanding legs — extend from upper to lower spar chords and are riveted to spar webs. These fittings — one at each main attachment point on front and rear spars — each carry four bolts, and afford a total of 16 bolts to take the full load of the fuselage. Bolts are 5/8-in Fairchild Standard, equivalent to NAS bolts dimensionally and in strength characteristics, but having exceptionally high fatigue-life.

Interspar ribs are .025 web beams spaced 21 in on centers, and have rolled angle chord members and hat-section stiffeners. The web ribs are utilized to form side supporting members for bladder type fuel cells carried in the center section, and provision is made in the ribs to accommodate fuel cell interconnecting fittings.

In the nacelle are two compression ribs spaced approximately 44 in to permit housing of landing gear. The ribs are double web box beams with .051 webs spaced by .064 channel members, and .072 channel chord members on the webs are decked by .064 plate. Forged and cast fittings are internally mounted on the compression ribs to accommodate anchor points for the nacelle steel structure and landing gear structure.

Top surface of interspar section is constructed of spanwise trapezoidal hat-section stiffeners and heavy gage outer skin. Stiffeners are 75ST varying from .125 to .040 from front to rear spar, and at centerline are spliced with bathtub fittings and tension bolts. Skin between spars is lap-spliced 24SRT (heat-aged to afford high strength), with gage varying from .102 at front spar to .064 at rear spar. Brazier head rivets are used between spars, and from front spar forward, riveting is flush.

Lower surface of interspar section is made up of standard corrugation and outer skin. The surface is divided into two parts —front and rear —with the corrugation extending aft from front spar about 24 in and forward from rear spar about 28 in. Between the corrugations, a stressed skin access door provides means for riveting the assembly and installing fuel cells. The corrugated sections and stressed skin access door extend from the centerline to the nacelle inboard compression rib —147 in.

Front spar, rear spar, interspar ribs, compression ribs, and top and lower surfaces are riveted together to form the interspar section.

Trailing edge has conventional pressed ribs and stiffened skin. Special ribs for supporting the flap hinges are constructed as box beams having pressed webs, rolled section chord members, and stiffeners between webs. At the ends of these ribs and between the webs, cast flap hinge fittings are bolted.

Nacelle Frame Assembly

When installed, the nacelle frame assembly becomes an integral unit with the center section, and extends, essentially, from aft of the firewall to just beyond the trailing edge of the wing where the forward boom connection is made. It houses the landing gear in retracted position, provides the necessary load-carrying members to transfer the tail load to the wing, and consists primarily of stressed skin, skin formers or frames, longitudinal hat sections, and six longerons.

Two of these longerons tie into the upper wing surface and form the upper caps of the nacelle torque box, which consists of vertical side webs, extending from directly behind the nacelle compression ribs in the wing proper, and a horizontal web extending aft 60 in from the lower chord of the rear spar; top of the torque box is the nacelle skin.

The two intermediate longerons are arranged to make connection to the lower surface of the center section. Remaining two lognerons stiffen the structure at the bottom and form the mounting points for the landing gear doors — double skin structures with recessed inner skin, reinforced by extruded frames at hinge points. Upper and intermediate longerons are .102 and .072 high strength R301T alloy, respectively; lower longerons are .125 24ST, with .072 doubler added.

Leading and trailing edges and nacelles are riveted to the interspar section to form the center section structural assembly.

Within the leading edge are provisions for mounting oil coolers, cooler inlet ducts, engine controls, fuel, oil hydraulic, instrument and fire extinguisher lines, and electrical wiring. The trailing edge encloses the flight controls.

Outer Wing Panel

Construction of outer wing panel is generally similar to that of center section. Leading edge has double skin construction for anti-icing, and interspar section has similar ribs in the region of outer fuel cells. Outboard of this area, the interspar ribs are .025 hydropressed webs with flanged holes and stiffening beads and .064 rolled angle chord members.

Upper surface consists of standard corrugation and outer skin. The corrugation varies from .102 at inboard end of front spar to .032 near the tip, and extends between spars for approximately 2/3 of the span, and then tapers to a width about 8 in at the front spar near the tip. Where the skin is not stiffened by corrugation, .032 and .040 Z-section stringers are used.

Lower surface is also formed with two-section corrugation externally covered with skin, and a center access stressed skin door is located in the region of the fuel cells. The corrugations varies from .051 at inboard end to .025 at end of corrugation about halfway along outer panel, and is tapered from the end of the access door to the halfway point. Between the end of the corrugation and the wing tip, the lower surface is stiffened by intermediate chordwise .025 hydropressed formers and spanwise .032 hat-section stringers.

The wing tip is constructed as a separate unit, is bolted to the outer panel, and is formed with .020 pressed ribs and channel stringers.

Flaps and Ailerons

Wing flaps extend for approximately 25% of chord, are NACA slotted type, and are constructed of pressed ribs and spars, the latter together with the leading edge skin forming the main structural element. Inboard flaps are approximately 5 ft 10 in long and outboard flaps about 7 ft 8 in. Each flap is attached to the wing by two hinge points on the leading edge. Connection is made with ball bearing links arranged so that flap motion is, first, almost horizontal, then continuing aft with little angular deflection. As flap motion continues, angular travel increases rapidly to a maximum deflection of 40°. Operation is by an electric motor, located in the fuselage, aft of the rear spar, through the medium of a screw-and-nut type actuator connected to the flaps by a system of bellcranks and rods. In emergency, flaps can be lowered by a handcrank.

The aileron installation consists of an inboard and outboard unit, the former measuring approximately 13 ft 7 in and the latter 11 ft 4 in. They have pressed ribs, and metal skin to form the main structure, and pressed tail ribs. The entire assembly is fabric covered. Inboard and outboard ailerons operate as a single unit, and the inboard aileron is also fitted with a droop actuator to lower it with the flaps when the latter are in landing position. This provides additional flap area, and still permits full operation of the ailerons as such.

Booms and Empennage

Constructed in two sections — forward and aft — the boom assembly is approximately 440 in long, supports the tail structure, and houses surface controls and tail anti-icing ducts.

Forward boom extends 334 in from aft of the nacelle and is of semi-monocoque construction utilizing skin, light hydropressed channel sections frames fabricated in halves, and longitudinal bending members. For first 100 in from forward end, the channel frames (four — exclusive of mating frames) are doubled to form composite units back-to-back. Longitudinal bending members are 75ST hat sections varying from .025 to .064, with heavy gages on top and bottom because of gust and tow loads. There are twice as many longitudinal members starting at forward end as those ending at aft end (20 forward and 10 aft, with 10 terminating between).

Splice between nacelle frame and forward boom, and between forward and aft booms is of the bolted tension type employing forgings riveted to the stringers; a riveted skin splice makes the joint semi-permanent.

Aft boom picks up vertical and horizontal tail loads, provides shelves to mount control pulleys, and affords sufficient side bending and torsional stiffness for glider tow fittings at extreme end. These features are accomplished by employing heavy bulkheads, longitudinal members, and stressed skin.

Forward two fitting-supporting bulkheads each consists of back-to-back members having .040 webs and .064 flanges. Between webs is a ½-in plate for supporting the main stabilizer and stabilizer tips. Bathtub type tension fittings mounted in channels take upper and lower fin loads.

Remainder of the frames in the tail cone support the rudder torque tube and glider tow release mechanism.

Between first two bulkheads are an upper and a lower shelf, each consisting of a web and angle caps, forming two horizontal beams to provide strength for side bending. The shelves are spaced sufficiently to provide ample service accessibility for control quadrants supported between them.

On inboard side of boom, between it and the elevator, is a fixed elevator-shaped structure of width equal to rudder throw, serving as a clearance piece.

Provision for the towing two 7,000-lb gliders or one 18,000-lb glider is accomplished by the inclusion of a tow rope attachment at the end of each boom, together with a release mechanism selectively and electrically operated by a switch at pilot's station.

Main stabilizer is standard two-spar construction with ribs and skin. Front spar is approximately 15 in deep with web thickness varying from .025 to .040 from center to either end. Angle caps are .128 in the center and .064 at ends. Distance from front to rear spar is approximately 41 in. Rear spar is approximately 12 in deep with web gage varying from .025 to .040. Lipped angle caps are .064 nested triple in the center and tapering off to one angle at the end. Hydropressed interspar ribs and nose ribs, .025, are spaced approximately 10 in on center. Over interspar ribs are three longitudinal angle skin stiffeners.

The five elevator hinges are mounted externally, are bolted to fittings at the hinge ribs which in turn are riveted to doublers inside. All hinges are designed for down loads but only the end hinges are designed to take side load, and are braced accordingly.

Stabilizer — approximately 304 in long and 64 in wide, fabricated as one unit — is attached to the boom by a single bolt at front and rear spars, making it a pin-ended structure. Elevator is of single spar construction having .032 web and single .040 angle cap top and bottom, with nose and trailing edge ribs of minimum thickness. Nose of elevator has metal skin, and the entire surface is fabric covered — similar to the aileron. Two tabs, one on each side of the centerline, are also of the same construction, one being the trim tab, and the other a spring tab with special operating mechanism. Each tab is 6¾ in wide and 93¾ in long.

Upper and lower fins are also of two-spar construction with hydropressed ribs and all-metal skin. Spars are of standard web and angle type.

Upper-and-power rudder has same construction as elevator, with fabric cover doped in place over the metal structure.

All fixed tail surfaces have anti-icing provisions, with duct in the leading edge, from which hot air flows into an .064 gap between inner and outer skin, thence being exhausted to the outside near the front spar.

Design Analysis of the

By Irving Stone,
Assistant Editor, Aviation

Concluding the comprehensive study of this unique cargo craft, details are presented of the flight control system, landing gear, power plants, equipment, and anti-icing and heating provisions.

The Packet's flight control system is a duplicate and dual installation consisting of cable sectors, pulleys, bellcranks. and push-pull rods. It is duplicate because there are two complete and independent systems —one on each side of the plane —and dual because, through a series of interconnections, either system may be operated from pilot's or co-pilot's station in event of failure of any part of either system.

The two control wheels in the cockpit operate a set of differential ailerons. Each wheel is splined to one end of a torque shaft and the two shafts are interconnected by a chain and cable hookup. A chain, at the end of which two cables are attached, engages a sprocket mounted in bearings housed in the forward torque tube support and connected to the torque tube by a universal joint. The two cables run down and aft over a series of guide pulleys to a triple-grooved sector located just aft of the center section rear spar. Another cable engages this sector and is led behind the rear spar over guide pulleys to a horizontally mounted differential bellcrank located halfway along the inboard aileron. A push-pull rod bolted to the forward arm of the bellcrank, extends to an idler lever from which another push-pull rod operates the outboard aileron differential bellcrank. Between the outboard aileron horn and the differential bellcrank, the aileron operating rod is installed.

Aileron Droop Mechanism

Inboard ailerons, in addition to their normal functions, are also used to assist flaps in landing. This is accomplished by inserting an electrically operated screw actuator unit between the differential bellcrank and the inboard aileron horn. The actuator motor is operated by a switch mounted on the flap operating mechanism which actuates the switch upon reaching a point corresponding to just beyond flap takeoff position. The two aileron actuators are electrically synchronized so that both ailerons will drop simultaneously.

The linkage is so arranged that the control wheel moves 150° either side of neutral to move the aileron from 12° down to 24° up.

Elevator Control

Elevator control is obtained by fore-and-aft movement of the control column, pivotally mounted on an inverted V-truss in the front end and an A-truss in the rear. The column is fastened to the forward truss through the housing which holds the aileron sprocket, and is fastened to the rear truss by a gimbal engaging a ball bearing trunnion mounted on the column. The two control columns are interconnected by a K-truss bolted to two trunnions on each column.

To the cross bar of the A-truss is bolted a push-pull rod operating a vertically mounted sector. To the sector is fixed one cable of a continuous cable system which runs aft over a series of guide pulleys to a triple-grooved sector located aft of the center section rear spar. Two other cables are fixed to this latter sector — an interconnecting cable running crosswise to a similar symmetrically located sector in the duplicate elevator system, and another cable which runs along the rear spar over a series of guide pulleys to the nacelle and through the boom to a horizontally mounted sector in the aft boom. On the aft boom sector is an integral arm which operates the elevator push-pull operating rod. An interconnecting cable anchored to the sector passes through the stabilizer to engage a similar sector of the duplicate system installed in the opposite aft boom.

The control column moves a total of 18 in to move the elevator from 25° down to 35° up.

Rudder Control

Rudders are controlled by movement of a pair of top-hung type pedals adjusted for long and short leg positions by a pawl connecting the pedal to a ratchet on the actuating arm. Through a push-pull rod, the actuating arm imparts movement to an arm bolted to a horizontally mounted torque shaft carrying the rudder sectors and pedal interconnecting arm. A push-pull rod connects the other pedal to this arm to cause each pedal to move in the opposite direction.

The cable system — similar to that of the elevator — transmits pedal movement to an interconnecting sector at the aft boom where the two systems are again interconnected. From the latter sector, cables pick up a set of rudder horns mounted on a torque tube by which both the upper and lower rudders are actuated.

With pedal movement of 22° rudders correspondingly move 35° right or left.

Surface locks are located close to control surfaces to protect against damage by ground gust. Each lock is, basically, a rotating cam which mates in the locked position with a machined surface on the bellcrank or sectors. Lock cams are actuated by cables attached to interconnecting sector wheels, and pulling a handle located to the left of pilot actuates all lock cams simultaneously. In the locked position, the operating handle lies across pilot's seat and prevents him from taking off with surfaces locked. In the event of cable failure in flight, the lock control is designed to keep the cams in unlocked position.

To avoid subjecting control systems to overload by pilot or by gusts on the surfaces, two sets of surface control stops are installed — one in the cockpit at the steel structural mount and the other at the operating bellcranks closest to the surface — with the provision for adjustment to assure the proper travel of the movable surfaces.

Trim tabs are used on inboard aileron and rudders, and a spring tab and trim tab on the elevator. Trim tab controls are conventional in design, consisting of control units mounted accessible to pilots, cable drums, pulleys, cable, and irreversible screwjacks at the tabs. Tab control units incorporate dials and stops and allow for a small amount of overtravel.

Elevator tab to the left of the centerline is a trim tab, and the one on the right is a spring tab. Spring tab action is accomplished by holding the elevator horn in neutral, balanced against a 142-lb compression spring (mounted within the elevator) to permit 7½° of horn motion either side of neutral in relation to the elevator. Horn motion is transferred by push-pull rods and levers to produce 30° up or down movement of the tab in the direction desired to aid the movement of the elevator.

A rigid push-pull rod and bellcrank system operates the four flaps. A motor-operated screwjack and nut actuator is located in the fuselage center rear upper section. Rotation of the screw causes the double-lugged nut to move fore-and-aft on the screw, and to each lug is bolted a horizontally mounted bellcrank pivoted between two V-braces, one on top and one on the bottom. Free ends of the V-braces are bolted to the housing mounting the screw and motor, while the apexes of the braces support the bellcrank.

To the other arm of the bellcrank is bolted a push-pull rod which runs outboard to the inboard flap operating bellcrank. Another push-pull rod connects a similar operating bellcrank at the outer end of the inboard flap —there being two operating points on each flap. Other push-pull rods extend outboard to pick up the two outer flap operating bellcranks. Each bellcrank operates a push-pull rod connected to a vertically mounted beam. Upper end of the beam is hinged to the wing structure and lower end is hinged to the operating point on the flap leading edge. A three-position switch located on the control pedestal is operated to lower the flaps.

An A-10 electrically powered automatic pilot is used in the Packet and consists of a Gyro Flux Gate transmitter. Flux Gate amplifier, master direction-indicator, servo amplifier, three servo motors, Gyro-Horizon indicator, bank-and-turn indicator, controller unit, clutch switch, and an emergency manual servo disconnect control.

The Gyro-Flux Gate compass system — from which the directional signal is derived — includes a transmitter, amplifier, and master direction-indicator and two repeater indicators. The Flux Gate transmitter is located on the tip of the left sing outer panel, and the amplifier on the left side vertical bulkhead in the front section of the fuselage. The master direction-indicator is mounted on the instrument board in front of the pilot and with the bank-and-turn and Gyro-Horizon control, forms part of the pilot's flight control instruments.

The controller, mounted on the fixed portion of the instrument board directly in front of pilot, enables him to climb, dive, or make correctly co-ordinated turns by means of the automatic pilot.

The Gyro Flux Gate transmitter and amplifier and the three flight indicators are directly connected to the electrical power bus and to the inverter. These instruments are used by the pilot during manual and automatic flight. Electrical power is supplied to the servo amplifier through a control switch located on the forward overhead control panel. A push button solenoid switch located adjacent to the control switch engages or disengages the servo motors. The servo motors may also be disengaged electrically by push-button switches, one located on each control wheel.

The servos are rigidly mounted aft of the center section rear spar. They are staggered in the fore-and-aft direction to place the three servo pulleys in line with the interconnecting cables of aileron, elevator, and rudder control systems. The interconnecting cable which wraps around the servo pulley links the automatic pilot into each system when the clutch switch is placed in engaged position. With the automatic pilot clutch disconnected, the servo units rotate freely, permitting manual control of the surface.

In event of failure of the servo units, the drums may be disconnected manually and simultaneously by pulling up on the servo emergency disconnect lever mounted on the control pedestal. A cable system connects the lever to the clutch disconnects on the servo.

Anti-Icing, Heating, and Ventilating

The anti-icing system protects all flight surfaces and air intake scoops (carburetor, oil cooler, heating and ventilating, and anti-icing.)

Heat for the system is obtained by passing ram air, from a scoop on the lower portion of each primary cowl, through four crossflow type heat exchangers located in the exhaust systems between collector rings and exhaust stacks.

Exchangers are connected by a trunk duct extending across the wing center section and fuselage, thus permitting functioning of the entire system even though one engine is inoperative. From this duct, another leads to the outer wing leading edge duct extending the entire length of the outer panel and tip. After passing through the leading edge duct, the air dumps into the inner portion of the wing and exits on leading edge of ailerons. Center wing section anti-icing is accomplished similarly.

From a main trunk within each boom, a duct leads to the empennage, and smaller ducts lead to stabilizer tip, and upper and lower fins. Heating of these surfaces is accomplished similarly to the outer wing panel except that the air exits onto upper and lower outside surfaces through a series of small holes.

Windshield anti-icing is by hot air from main trunk cross-duct, and after dispersal between the double glass panels, the air is dumped outside of fuselage below the windshield.

The system for crew and cargo compartments secure heated air from the main trunk duct across fuselage, supplied from the two inboard heat exchangers. The heated air, passed through a secondary heat exchanger, then being distributed through ducts to anemostat units on each side of cockpit. Other ducts bring in air for defogging windows and avigaiton dome.

Ventilation is accomplished by introducing to the heating system, variable amounts of cold outside air, with proportion controlled by crew.

Anti-icing and heating and ventilating systems are electrically controlled from the switch panel above and between pilot and co-pilot. Two switches permit selection of heat from all four heat exchangers for anti-icing; from all four exchangers for anti-icing and fuselage heating; from two inboard heat exchangers for fuselage heating; and from the heat exchangers at either engine for any of these purposes.

Two manual push-pull controls to valves in the cockpit ducts control temperature of crew and cargo compartment, and temperature can also be adjusted from crew chief's station in cargo area. Electrically operated valves at each heat exchanger permit dumping of hot air overboard, and similar valves are located in each duct leading to anti-icing areas and fuselage heating duct.

For prevention of fire, asphyxiation, and damage to structures because of excessive heat, thermostats controlling each dump valve are located at each heat exchanger and in wing internal area. A carbon monoxide indicator is located in the fuselage. Warning light on the control switch panel indicate the position of the dump valves and the presence of carbon monoxide.

Nose Gear

The Packet is equipped with fully retractable landing gear consisting of non-steerable nose gear, main landing gear, emergency gravity extension mechanism, and warning and indicating system.

No appreciable movement of the center of gravity of the airplane is encountered (less than one percent) as the landing gear units move from fully extended to fully retracted positions.

Nose gear consists of an Aerol shock strut, single side strut and axle unit, hydraulic shimmy damper, 44-in smooth contour tire mounted on magnesium wheel, upper truss, lower truss, retracting unit, and two retracting links.

The nose wheel shock strut has a self centering device which forces the wheel in a fore-and-aft direction as load is removed. At upper end of the strut a fitting is provided for attachment to the upper truss. At lower end are two cantilever arms for attachment of lower structure. Provisions are made at lower end of the piston for bolting the side strut and axle unit, and to the cylinder is bolted the shimmy damper.

Upper truss is V-shaped, and tubular units are equipped with double-lug forged fitting at the apex and two single-lug forged fittings at the free ends. Double-lug fittings are welded at midpoint of tubes for bolting a forged steel beam that holds the retracting links.

Lower truss consists of two outer tubes and an X-brace. At both ends of outer tubes, fittings are welded to form the upper and lower joints and also to provide lugs for bolting the X-brace.

Retracting mechanism consists of ball bearing screw-and-nut actuator, side mounting frames, double sprocket and chain train, torque shaft, and two retracting arms. The screw-and-nut actuator converts rotational motion at high speed to linear motion at low speed. A motor drives a planetary reduction gear train which turns the screw to cause linear movement of the nut.

A solenoid clutch is incorporated to instantly engage the motor with the gear train upon application of current, or to disengage it when current is shut off. The clutch has a brake which automatically retards the gear train when clutch is disengaged, to prevent the lending gear from continuing to move when the current is discontinued by pilot or limit switches.

The nut is gimballed to driving arms on two upper sprockets keyed to a spindle with ends supported in ball bearing housings in the center of the side frames. Upper ends of the side frames are bolted to supporting fittings on the forward part of the fuselage, while the lower ends support a torque shaft on which are mounted two sprockets and two retracting arms. Lower sprockets are located in the plane of the upper sprockets and retracting arms are in the plane of the retracting link. The torque shaft is supported at its ends by bearings located in fittings at the vertical fore-and-aft fuselage beams, and in turn supports the lower truss and a brace strut which ties the upper truss upper support fittings and the lower truss upper support.

Kinematic linkage of the nose gear — a parallelogram in form, with sides consisting of shock-strut, upper truss, lower truss, and brace strut — permits the wheel and shock strut to move vertically during retraction. Retraction is accomplished by movement of the nut which causes rotation of the upper sprockets, whose motion is transmitted through chains to the lower sprockets tot urn the torque shaft and retracting arms. The latter push the retracting links, and cause the upper truss to rotate about it supper supports, thus lifting the shock strut and wheel into retracted position. Upward movement of shock strut rotates the lower truss about the torque shaft, which guides the motion of the shock strut.

For gravity extension of nose gear, the actuator is provided with a quick-release mechanism which disengages the screw from the gear train and allows the screw to rotate freely, the nut being forced down under the weight of the gear. To control the speed of drop, and energy-absorber unit is provided —basically a hydraulic actuator which dissipates energy by passing fluid from one side of the piston to the other, via an orifice. Fluting the inside of the lower end of cylinder increases the orifice area, and when the piston reaches these flutes, the increased area accelerates the flow of the fluid to speed the drop sufficiently to permit the down locks to snap in place.

Main Landing Gear

Main landing gear —extending approximately 12½ ft from upper support point to bottom of wheel — consists of two shock struts, upper and lower drag struts, interconnecting transverse beam, and horizontal link bar tying the main upper truss to the upper drag struts. One end of each retracting link is mounted on the bolt which fastens the horizontal link bar to the upper drag trusses, and the other end is bolted to two retracting arms fixed to a torque shaft which supports the retracting mechanism and its supporting side frames. Ends of the shaft are mounted in bearings housed in the nacelle steel structure.

Upper main truss is made of two swaged tubes with forged hinge fittings welded to upper ends and forged knee fittings welded to lower ends.

Upper ends of an X-brace space the swaged tubes 43 in at top, while lower ends of brace and a spreader tube space the swaged tubes 30 in at the bottom. Provision is also made on the swaged tubes for attaching the ends of the link bars.

The lower main truss has two swaged tubes with welded forged knee fittings at the top and opened at the bottom to receive the shock struts. Tubes are held 30 in apart by an X-brace bolted to fittings on the side of the tubes.

Upper drag struts — the king post trusses with apex on the bottom — have fittings welded to the lower ends and the apex, to attach to the lower drag struts at the end, and to the retracting link and horizontal bar at the apex. The main tube is made to extend at the upper end to the transverse beam — an oval-shaped tube with tapered ends on which are welded two sockets for receiving the upper drag trusses, two hinge fittings for mounting the beam to nacelle structure, and two lug-type fittings for supporting the side frames of the retracting mechanism.

Lower drag struts are tubes with forged ends and separated by K-bracing to space them 30 in apart.

On the cylinder of each shock strut are welded two double-lugged fitting — one on top to receive lower drag strut, and one on bottom on which is bolted a jacking link. On the rear side opposite these fittings, is welded a jacking fitting of AAF standard dimensions. A forging at the lower end of the piston straddles the axle, and is provided with two attaching bolts.

A small hook on the front face of the forging is used to engage the jacking link to facilitate servicing and installation of the wheel. When the jacking link (on the cylinder) is swung down over the hook (on the piston), the two attaching bolts are removed, and the plane is jacked at the hacking points on the cylinder. As the plane rises, the piston extends (because of the weight of the wheel) until the jacking link contacts the hook, and the piston then moves up with the cylinder and away from the axle to permit the 56-in wheel to be rolled from under the shock strut fittings.

Retracting links and arms and retracting unit consisting of an actuator, chains, sprockets, and torque shaft, are similar to those used on the nose gear, but larger. Two energy-absorber units are used on each main gear and, except for length, are also similar to nose gear installation. During retraction, the retracting link forces the upper drag strut to rotate about the hinge points of the transverse beam, and the horizontal tie bar forces the upper main truss to rotate to the rear about the upper hinge fittings. Rotation of upper truss breaks the knee joint between upper and lower main truss and carries the upper end of the main lower truss to the rear and upward. At the same time, the rotation of the upper drag strut carries the lower drag strut and the lower end of the main lower truss upward.

Landing Gear Control

Landing gear is controlled from the cockpit by either pilot or co-pilot. Freed of the locating slot, the handle is pulled to a vertical position to retract the gear, thus turning a shaft on which are mounted two pulleys, and cables anchored to the pulleys actuate a series of levers and cams which cause the down locks to open, freeing the retracting arm and permitting the torque shaft to be rotated.

On reaching the vertical position, the handle is pushed to the side into a positioning slot and actuates switches in the landing gear motor circuits to cause retraction of the gear. Retracting arm, on reaching the maximum position, trips a switch to stop the actuator motor.

To extend the gear, the operating handle is moved forward and down to the normal down position. Engagement in the position slot actuates a switch in the circuit and the gear moves to the extended position. As spring-loaded dogs engage the latches on the retracting arm, they actuate a switch which cuts off the current.

In the event of power failure, the gear may be extended by gravity by pushing the control lever forward and down, past the normal down position to emergency down position.

A safety switch, installed on each landing gear unit to prevent accidental retraction of the gear when the airplane is on the ground, closes the motor circuit only when the oleo struts are extended — as in takeoff, with load removed from the strut. As an additional precaution, a ground lock consisting of a steel pin (with a red streamer for visual attraction) is inserted into the locking links to prevent unlatching of the locking dogs. With locking dogs engaged, the gear cannot be retracted.

Two lights in the cockpit indicate the position of the gear. A green light indicates that it is down and locked, whereas a red light indicates that it is neither fully retracted nor fully extended and locked. No lights show when all gear units are fully retracted, but to avoid landing with gear retracted, a warning horn sounds and a red light shows when the throttles are pulled back.

Landing Gear Door Operation

Forward section of the nose wheel doors is operated directly with push-pull rod actuated by the gear retracting link. As the gear extends, the front door opens fully to allow the wheel to pass and is again closed when the gear has reached fully extended position. Rear doors remain open after the gear extends. They are operated by push-pull rods actuated by two arms (on a torque shaft mounted on housings on the vertical beam in the nose section) in turn operated by push-pull rods actuated by movement of lower nose gear truss. Side frames of the truss have welded hinge brackets which provide attachment for the operating rod.

Nacelle doors, because of their great length, are actuated at front and rear by a parallel system of torque shafts and arms interconnected by cables. Main operating arms are hinged on main landing gear torque shaft and are held in the door-open position by torsion springs on the rear torque shaft. Operating arms are combination arm and pulley arrangements. The door-operating push-pull rods are fastened to the ends of the arms, and cables anchored to the pulleys run to the top of the landing gear well over two sets of guide pulleys to similar pulleys of arm and pulley arrangement hinged on a torque shaft at the rear of the well. At the end of these arms, door-operating push-pull rods are hinged.

After main landing gear torque shaft has moved through 2/3 of its full travel, it picks up the actuating arms and carries them with it as it moves to the fully retracted position. Nacelle doors remain opened when the landing gear is fully extended.

Brake Hydraulic System

Pressure for operation of wheel brakes is obtained from 1,000-psi hydraulic system. A motor-driven gear-type pump maintains pressure in two accumulators separated by check valves. One accumulator supplies pressure to the power brake valves connected to the outboard units of the dual duplex brakes, while the other supplies the valves connected to the inboard brake units. This, in effect, provides two independent systems for the operation of the brakes, and failure of one of the systems results in the loss of only half of braking capacity. In event of power failure, the accumulators, when fully charged, are of sufficient capacity to safely bring the plane to a stop.

System pressure is regulated by a starbird type pressure switch with power contacts adjusted to close at 960 psi and open at 1,160 psi. Warning light contacts, adjusted to close at pressures below 800 psi, energize indicator lamps located on instrument panel, to warn pilot of failure of pump to maintain normal system pressure. Pressure gages attached to the air side of accumulators and mounted on the instrument panel indicate preload air pressure when the accumulators are discharged and hydraulic pressure when accumulators are charged.

Power Plant

Two P & W R-2800, type C, twin row radial engines, each rated at 2,100 hp, power the Packet. They have single stage, two speed internal superchargers, two-position spark advance, built-in torquemeters, manifold pressure regulators, and Hamilton Standard three-bladed constant speed propellers, 15 ft 2 in in diameter.

Each engine is suspended on six flexible brackets on a conventional steel tubular mount bolted at four places to the nacelle structure through which the loads are carried to the wing.

Primary cowl is NACA type, fabricated in three radial sections fastened together and to two support rings on the engine by trunk-latch type fasteners.

Support rings consist of circular channel sections and mounting brackets which fasten the rings to the engine rocker boxes. Rear ring also serves to mount cowl flap hinge brackets, operating motor, and actuating screwjacks. The jacks are operated in series by flexible torque shafts, which, when assembled, form a continuous drive.

The secondary cowl consists of a stainless steel baffle ring and five detachable cowl panels. The baffle ring separates the power zone from the accessory compartment. The cowl panels are supported on the baffle ring in front and the firewall in the rear. Portions of the baffle ring and cowl flaps are cut out to provide for the installation of the air induction scoop at the sop and to afford openings on each side for installation of heat exchangers. Between the baffle ring and firewall, a stainless steel well is formed around each heat exchanger to protect the accessory compartment from heat and fire.

The exhaust system consists of an exhaust collector, two heat exchangers, and two tail pipes for each engine. The collector is supported on the engine mount structure and connected to the engine ports by flexible joints. Each collector has two outlets, one on each side, to exhaust the gasses through the heat exchangers and outboard through the tail pipes.

Front end of the heat exchanger is supported on the exhaust collector and rear end on the tail pipe, in turn supported by two levers — one on top and the other on the bottom — designed to allow for expansion of the collector and expansion of the heat exchangers.

On the centrally located pedestal are two engine control quadrants interconnected by torque tubes. Push-pull rods connect the control levers to arms on the horizontal torque tubes. Arms from the center of these tubes are connected by push-pull rods to irreversible bellcranks which prevent creeping of the control levers.

A series of parallel push-pull rods extend aft to the wing front spar, branch off to either side, and follow the spar to the nacelle. At this point a group of bellcranks turn the rods forward to other bellcranks on the front face of the firewall. The propeller and carburetor air controls follow the firewall to a point opposite the controls on the engine to another set of bell cranks. Flexible push-pull controls pick up and go to the propeller governor an the carburetor air valves. Throttle and mixture controls run to the outer part of the firewall to a set of bellcranks, where quick disconnect push-pull rods go forward to the engine levers.

Fuel and Oil Systems

Fuel is carried in four tanks located in the wing between the front and rear spars —two consisting of 4 interconnected cells each, and two consisting of 6 interconnected cells each. Each cell has a 10 x 16 in opening at the bottom reinforced with a molded rubber fitting with metal ring insert to which is bolted an access door.

At each corner of the side walls are 7/8-in fittings —the upper to vent the cell and the lower to permit the flow of fuel from one cell to the other. Between the two lower fittings is located a 2-in fitting to allow a greater flow when the tanks are being filled. Flapper valves cover these lower fitting to retain fuel over the fuel outlet when the airplane is in a bank. Adjacent cells are bolted at each fitting to the wing rib which separates them.

On the upper wall of each cell are 10 snap-type hanger fittings to prevent the cell top from collapsing.

In the access doors of four cells are provisions for mounting a submerged type electrically operated booster pump to insure adequate fuel pressure at takeoff and at high altitudes, and also to prevent vapor lock at high altitude. In event of failure of the engine-driven pump, the booster pump may be used to afford adequate fuel supply.

The four tanks are piped so that left tanks supply fuel to the left engine, and the right tanks supply fuel to the right engine. A transfer system connects these two independent systems so that in the event of failure of one engine, the fuel can be transferred for use in the other. Both engines can be operated from fuel in any one tank.

Fuel is brought together at a selector cock operated from the cockpit, to enable pilot to select the desired tank, then flows to a strainer and finally to the engine-driven pump. Between the selector cock and the strainer is installed an emergency shut-off cock located on the aft side of the firewall, to permit pilot to close the fuel supply at the firewall in the event of engine fire. This cock is electrically operated and the same actuator is used to simultaneously close the oil emergency shut-off cock.

The bladder type cells may be replaced with self-sealing fuel cells without necessitating structural changes.

Two elliptical 55-gal oil tanks —magnesium alloy or self-sealing units —are strapped in cradles provided on the nacelle structure, and incorporate a hopper to segregate the diluted oil and aerate the oils returning to the tanks.

From the outlet at the bottom of each tank, the oil flows through an electrically operated emergency shut-off cock to the engine. Two bosses on the inlet fitting at this shut-off cock accommodate both the oil dilution line and the drain line.

Oil from the engine is passed through elliptical aluminum alloy oil coolers equipped with type D-9 oil temperature regulator valve which allows oil to pass through the cooler or bypass around it. Surge protection is also provided to protect the core of the cooler from damage because of excessive oil pressure. From the coolers, oil is led back to the tanks for re-circulation to the plane's power plants.

In event of damage to one of the tanks, both engines can be supplied with oil from the other tank. This is accomplished through a transfer system consisting a four-way two-position selector cock and a hand wobble pump.

Electrical and Communication Systems

With the exception of the hydraulically operated wheel brake, the Packet uses electrical power. A 24VDC single wire bus system supplied by a 34-amp-hr battery, 200 amp high speed generator driven by each engine, and a 200 amp auxiliary power plant, furnishes power to the 52 separate circuits, which make up the wiring system. All wiring, with the exception of the ignition system, is of the open type and is supported by quick-opening cushioned clamps. Wires are protected, where necessary, by Vinylite insulating tubing.

The bus system extends from the main junction box (located in the cargo compartment) from which three branches lead — one to each junction box in each nacelle and a third to a nose junction box.

Two inverters are used to supply 440-cycle AC to operate the automatic pilot and radio equipment.

Radio equipment consists of 10 receivers and 6 transmitters, to which are led 14 externally mounted antennas. The twin beams and large fuselage permit the use of long antennas, widely separated from the structure, for the command and liaison sets.

Two command sets are used —one of high and one of very high frequency —for short range plane-to-plane communication. A liaison set is used for long distance plane-to-base operations. Two radio compasses permit simultaneous bearings to be taken from two ground stations, while two radar sets —one of short and one of long range —are used for avigational purposes.

An absolute altimeter indicates the altitude of the plane above the terrain. To facilitate landing in bad weather or at night, blind landing equipment is also provided.

In identification set and six interphone stations complete the radio system.

Equipment and Furnishings

On a centrally located cockpit pedestal are mounted controls for engines, propellers, tabs, and landing gear, and switch and circuit breaker panels. Radio controls are installed on overhead panels in the center of the cockpit, within reach of pilot and co-pilot. Interphones, oxygen equipment, heated-suit rheostats, map case, emergency axe, and first aid kits are mounted on cockpit side walls.

Flight and engine instruments are installed on a large shock-mount panel hinged at the bottom for tilting 45 deg. aft to provide accessibility to rear of panel. The entire panel may be removed as an assembly by pulling two electrical plugs and disconnecting flexible tube assemblies at bulkhead fittings mounted on a bracket at panel center.

Because of the considerable distance between pilot's and co-pilot's seats, duplicate flight instruments are provided.

For storage of pilot's and co-pilot's personal effects, a glove compartment is provided at each end of the instrument panel.

Radio equipment is installed on the auxiliary floor to the rear of the cockpit.

Removable soundproofing-and-insulating Fiberglas panels and interior trim cloth are used throughout the entire fuselage.

Forty-two removable canvas seats, provided on the sides of the cargo compartment for accommodation of paratrooper or other personnel, are retractable and built in two, three, or four-man sections equipped with safety belts. Each section is mounted on a rear rube rigidly fastened to clamp fittings on the fuselage outboard longitudinal beam, and seat legs are hinged to a front tube. When folded back against the sides of the fuselage, the seats are clear of the cargo space, and when extended the legs are held to studs in the floor tie-down fittings. Seat backs, made of interwoven canvas straps, are hung by hooks from handrails fastened to side beam inner chord members.

As an ambulance plane, the Packet accommodates arrangements of 34 litter patients and 5 attendants, or 22 litter patients, 22 seat patients, and 3 attendants, or 13 litter patients, 40 seat patients, and 2 attendants.

Litters are supported between fixed wall brackets fastened to the side of the cargo compartment, and suspension straps are hung from ceiling fittings. Loops (over which are lock fittings) are spaced 17 in apart to form tiers of 4 or 5 litters. When not in use, suspension straps are folded from bottom to top and stowed in bags located on the ceiling.

The life raft compartment, located in the fuselage upper rear section, is equipped with a canvas cinch with shock cords to support the six-man raft. A pull on the release handle in the cockpit releases the raft compartment door and then opens the carbon dioxide bottle to inflate the raft which forces itself out of the compartment. To prevent the raft from drifting too far before boarding, a mooring rope secures it to the plane. The raft compartment can be used as an escape hatch after raft ejection.

Oxygen System

Pilot's and co-pilot's oxygen installations consist of type A-12 demand regulator, pressure gage, flow indicator, mask, and duration graph. Each of the other crew members have regulator, indicator, and mask.

For safety, co-pilot's and avigator's demand type oxygen regulators are manifolded to 3 G-1 oxygen cylinders; and pilot's, radio operator's, and crew chief's regulators are manifolded to 5 cylinders.

Two portable demand type units are located in the cockpit, convenient to crew members. An additional portable unit is located at crew chief's station in cargo compartment. Five portable rechargers are placed at various points in the plane.

For troops or litter patients there is a continuous flow system supplied by four J-1 oxygen cylinders lashed to the floor in the forward part of cargo compartment and connected to the piping system by flexible hose. Since these cylinders are installed only when required, no permanent mounting cradles are provided. Five continuous flow regulators, located under the floor in the fuselage rear section, supply oxygen to 43 automatic coupling outlets strung along the side walls, for attachment of mask hoses.

The oxygen filler valve is on the left side of the fuselage, accessible from the outside. Crew system and troop system are filled from the same valve. A line valve, accessible from the inside, separates troop system filler line from that of crew system, and when the valve is open both systems are filled simultaneously. Since no check valve is used on the cylinders, the line valve is closed after the troop system has been filled to prevent oxygen from feeding back through the filler line from the J-1 cylinders. If it is desired to extend the range of the crew system by using the J-1 cylinder, the line valve is left open. The G-1 cylinders are equipped with check valves on the filler line side, and hence oxygen from these cylinders cannot feed back into the troop system.

Fire Extinguisher System

Carbon dioxide for the power plant fire extinguishing system is carried in 6 shatter-proof 5-lb capacity cylinders. Selector valves direct discharge to either engine, as desired.

Discharge of CO2, and selector valve setting, is accomplished with solenoids controlled by selector switches mounted on cockpit control pedestal.

In the engine power zone, nozzles located at the rear of the base of each cylinder discharge the gas in fan-shaped pattern. In the accessory compartment, a perforated ring is used. Individual leads run to nozzles in the carburetor air induction system blast tubes and the heat exchangers.

Acknowledgment: This analysis of the Fairchild C-82 Packet was made possible by the generous aid and cooperation of the management and engineering departments of Fairchild Aircraft Div of Fairchild Engine & Airplane Corp, Hagerstown, MD. Particularly credited are M Cozzoli, project engineer; W O Hammer, assistant project engineer; group leaders H L Stroud, wing; W P Maloney, fuselage; C W Jones, empennage; M A Cawl, control surfaces; C E Hammer, electrical; F L Boucher, landing gear; N C Bryan, power plant; T Hoffacker, fixed equipment; and G N Fryer, engineering illustrations. Appreciation is specially extended to J H Wales, Jr, assistant to general manager, for his valuable assistance.

This article was originally published in two parts in the August and September, 1945, issues of Aviation magazine, vol 44, nos 8 and 9, pp 115-139 in August, pp 115-127 in September.
A PDF of this article, recovered from microfilm, is available on the site.
The original article includes 8 photos, a 3-view and 27 detail drawings, and 2 data tables in Part I, 4 photos and 14 detail drawings in Part II.