DESIGN ANALYSIS OF
Messerschmitt Me-262 Jet Fighter

PART I — THE AIRFRAME
By John Foster, Jr,

Managing Editor, Aviation

The first detailed engineering study of Germany's top jet propelled fighter — the 15th in our series — reveals may unorthodox design and construction features and shows the importance of the production engineer in its development.

Germany's most successful jet propelled plane, the Me-262, is an unusual combination of radical and orthodox design, materials combinations, and workmanship, some of the latter being surprisingly sloppy. It shows, too, that the production engineer had as important a place in its development as anyone connected with the project.

A low-wing monoplane of 40 ft 11½-in span, 34 ft 9-in length, and 11 ft 4-in over-all height, it was used as a fighter, fighter-bomber, and ground attack craft, and was apparently also designed for photo reconnaissance use.

The very tip of the fuselage looks exactly like a propeller spinner — and may well be just that — with a hole cut in front so that a gun camera mounted inside, reached by a small, quickly removable access plate set in the left side. A solid web bulkhead backs this section up, serving as a jacking point. Then follows a 14½-in section enclosing a flush-riveted channel-shaped former, the whole being screwed to the next section which contains the nose wheel and the four 30-mm MK-108 cannon grouped high in the nose section.

Since the length of these guns is but 3 ft 6 in, a very compact installation has been achieved with no external projections. A large spherical support around the barrel near the aft end facilitates adjustments during sighting in operations.

The guns are usually set to converge at 450 meters. The MK-108 fires 575 - 600 rounds per min with a muzzle velocity of 1,570 fps, and weighs but 134 lb. Compressed air for charging is carried in eight bottles set inside the fuselage on the left ahead of the cockpit.

The two top guns carry 100 rounds each, the bottom pair 80 each, and all are fired simultaneously by a switch on the contact stick.

Although the 262 was designed as an interceptor, Hitler ordered it made into a bomber. The result was installation of two jettisonable bomb racks, each carrying one 550-lb bomb. Additional armament on later models consisted of 24 R4M 5-cm rockets, 12 under each wing, and it is reported that the Germans planned to install up to 48 under each wing.

Skin of the 6 ft 5½-in long section aft of the spinner is .080 sheet steel. Since the cannon are mounted high, the use of steel in that section is understandable because of the blast effect, but even the belly skin is of the same material. It is possible the employment of steel was dictated by transportation difficulties rather than design considerations or lack of aluminum, for reports emanating from Germany indicate that the Nazis were not pressed at any time for this material. However, since the nose section carried both the heavy armament and the nose wheel, the added strength of the steel may have been a deciding factor.

The cannon are most accessible, for two 35¼-in long access doors, piano hinged 1½ in off the top centerline, can be quickly opened simply by loosening two flush toggle latches like those used on cowling of the FW-190 exposing all the gun mechanism as well as the ammunition drums.

This whole nose section attaches to the mid-fuselage in a simple but effective manner. At each lower corner is a 1-in (approx.) high-tension steel bolt fastening it to the solid web bulkhead of the mid-section. At the top, some 6 in from the centerline, are two 1½-in steel tubes, also bolted to forged fittings on the mid-section bulkhead and extending forward to the bulkhead at the front end of the gun access doors. Both these tubes are built as turnbuckles so that alignment adjustments can be easily made. Thus it would be possible for a trained crew to change a damaged nose section in the field in short order, or it would be a simple matter to install a nose equipped with different armament or photo recon units.

At the end of the nose section, the Me-262's fuselage cross section is practically an equilateral triangle, only slightly rounded out.

First bulkhead in the mid-fuselage section is solid web aluminum alloy with six vertical and two horizontal hat shaped stiffeners.

At a point 16¾ in back is a channel shaped former, flush riveted to the skin, and 16 in farther aft is another solid web bulkhead, with vertical and horizontal hat shaped stiffeners. Practically all the space between the two solid bulkheads is taken up by the fore fuel cell (which will be discussed in detail in the section devoted to the fuel system). The bottom panel of this section consists of a waffle grid, double stressed skin, 34¾ in long and 55 in wide. The panel is attached to the fuselage by flush screws and captured nuts, the same system employed on the FW-190 panel beneath the fuel cells. Interchangeability of these panels evidently was not much of consideration in Me-262 production, for the screws were set approximately 1¾ in. apart but with variations of as much as ¼ in. and considerable misalignment.

Every Nazi pilot apparently was his own Führer, for the Germans call the next section the Führerraum, or pilot space. And they must have been little Führers, for the rudder pedals are quite close to the seat and there is no fore-and-aft adjustment either on the pedals or the seat. An average sized American sitting in the cockpit finds his knees sticking well up in the air right in front of some of the instruments.

Only one channel-shaped former extends form the cockpit rail to the bottom of the fuselage at the cockpit which is, in effect, a horizontally-disposed cylindrical section with part of the wall sliced off. This "cockpit liner" section was designed for pressurization, but the craft examined had no means of developing pressure and there are no reports of any of the 262s actually operating in combat with pressurization.

Further evidence that cockpit pressure was an unused design feature is found in the windshield, a conventional three-piece flat-plate unit in which the front piece is 3½-in bullet proof glass, set in a steel frame, but merely screwed in without the usual synthetic rubber mounting found in other German craft. The seal — which certainly does not appear to be designed for pressure — appears to be plastic designed only to prevent normal air leakage.

The cockpit canopy consists of two rounded plastic glass sections mounted in a frame with flat fore-and-aft pieces and tubular base. It pivots on the right side for entrance and exit, and it can be locked closed only from the inside by a lever which drives pins into holes set in the base of the windshield frame and the turtleback section. A 16-mm-thick head and shoulder silhouette armor section, which extends up and over the back of the pilot's head, is bolted to the canopy frame just ahead of the turtleback section.

Either the Germans changed their own minds about instrumentation or had them changed by Allied bombing, because original designs called for more instruments than are actually installed — at least that's the case on some late planes. The main instrument panel is divided in two sections, with flight instruments on the left, engine instruments on the right.

Flight instruments include: Artificial horizon, combined with bank and turn indicator, airspeed indicator (some of which have been red-lined at 658 mph), altimeter, rate of climb indicator, repeater compass, and blind approach indicator.

Engine instruments include: Two tachometers of two-speed variety to give readings from 0-3,000 rpm and from 2,000-15,000 rpm. (generally red-lined at 8,900 rpm); two gas pressure gages indicating up to 1 kg/cm2; two gas temperature gages indicating up to 1,000°C (with marks on the gages at 680°); two oil pressure gages; and fuel gages for front and rear tanks. Called for in design plans, but not installed in craft studied, were two fuel injection pump pressure gages, marked at 65 kg/cm2.

Just below the center of the main panel is the bomb switch panel, marked for dive or level bombing and for instantaneous or delayed action fusing.

Above the main panel is the gunsight, in most cases the old-fashioned REVI 16B reflector type, which can be swung to the right out of the way for takeoff and landing.

On a slanting panel just to the left of the main board are valves for emergency operation of flaps and landing gear; oxygen flow indicator; oxygen pressure gages (not on all planes); and oxygen valve.

On a horizontal panel just below this unit are: Position indicators for flap and landing gear, and buttons, immediately aft for operating both these systems; stabilizer pitch indicator; stabilizer adjusting switch; fuel selector valves; rudder trim tab crank; and release cable to jettison rocket units for assisted takeoff.

A corresponding panel on the pilot's right contains pitot heater switch; Very signal switches; radio frequency selector and on/off switches; starter switches for starting motors; and switches to select low speed indicator on the tachometers.

The electric junction box is installed below these panels outside the fuselage cockpit liner, and it is easily accessible from the ground because it is located just above the wheel well.

At the base of the main panel on the left is pull handle for the nose wheel brake, a unit evidently installed to facilitate stopping on the small turfed fields which the Germans were forced to use during the later stages of the war.

Just under the windshield base frame, also on the left, is a pull lever to operate a small square air scoop set in the fuselage side. This apparently was a late factory modification — and the workmanship would certainly never have passed German inspection in the early days.

The pilot's seat is adjustable only up and down on a parallelogram frame, and it is locked in position by a lever under the front of the seat which engages a pin in ratchet teeth. Unlike earlier German craft, the Me-262 has no bungee cord to facilitate moving the seat. The upholstered back of the seat is held in place by two clip springs to facilitate removal for access to the battery, which sits just behind the seat frame.

The seat itself does not incorporate armor plating; this is, instead, attached to channel-shaped vertical and horizontal stiffeners riveted to the solid aluminum alloy bulkhead which begins the aft fuselage section and forms the front panel of the rear fuel cell space. The bottom skin panel for this section measures 35½ x 60 in and is similar in construction to that under the front cells. In the middle of this fuel cell, some 17¼ in back, is a former which is built-up double channel section up the sides to the second-from-centerline stringer, from which it is single channel. This former, like most others, has cutouts for the stringers.

In this connection it is interesting to note that the Me-262 has no longerons, employing only hat-section stringers — one along the top centerline aft of the cockpit; five along the sides (with one ending at former 14); and five along the bottom (the two outermost ending at former 15).

The bulkhead forming the aft end of the rear fuel cell is a solid web but is sheet steel of approximately .080 gage.

An unusual construction feature is found throughout much of the aft fuselage section, where the formers are made of the aluminum skin sheets themselves. In fabrication, the skin sheets are formed to the fuselage contour, then the aft ½ in is joggled to the thickness of the metal itself — about .050 — then bent inward to form a channel or J-section. The next skin is lap jointed and flush riveted in place.

Whether this method of construction should be blamed or merely the type of labor available is not precisely known, but many of the joints were not at all clean, requiring the use of considerable filler to smooth them out. Careful study, however, seems to indicate it was probably more the quality of labor than the design, for many of the rivets were somewhat out of line and had required considerable filler themselves to give anything like a smooth finish.

Immediately aft of the cockpit the fuselage shape starts its change to a very narrow elliptical section only 2 ft wide at a point just ahead of the stabilizer.

Construction of the tail cone is, in some respects, quite like that on the FW-190. It bolts to the aft fuselage section with the joint larded (at least on some planes) with liberal quantities of filler and covered by a doped fabric strip in a vain attempt to get a smooth surface.

The former aft of the joint is a built-up ring riveted to a steel I-beam section which slants aft 47° from the vertical and extends up some 2 ft above the fuselage top to form the lower part of the front fin spar.

The end of the tail cone, 4 ft 8¼ in aft of the former just mentioned, is a stamped flanged aluminum channel section member which also serves as the bottom of the rear fin spar and rudder post.

Connecting the tops of these two spars is a horizontal stamped flanged channel member upon which the stabilizer is mounted. In production, the stabilizer must be installed before the fin and rudder are put in place.

Then the fin, the spars of which have steel plates riveted to their lower ends, is attached to the tail cone by seven bolts along each side of the front spar and four on each side of the rear spar. In construction, the fin is built up in two halves, divided on the vertical plane of the fuselage axis. The halves are then bolted together along the spar line through access holes in the skin. These holes — of approximately 1 in dia — are then covered with small doped-fabric patches. The joint along the leading edge is covered by plywood fairing which is screwed on. Rounded tip of the fin is built in two halves, welded together and attached to the main body by flush screws. A single-sheet, deep-drawn aluminum fairing is fastened by 41 flush screws to the base of the fin and top of the fuselage.

Chord of the rudder is narrow, being but 20½ in at the widest point, but there is plenty of depth, for the rudder has an overall height of 6 ft 11 in, extending from the top of the fin to the bottom of the tail cone. A small tip is screwed to the top just above the large mass balance, and the main section of the unit follows conventional construction practice.

The spar is D-section, with the curved part fitting closely inside the fin trailing edge. Conventional stamped flanged aluminum ribs with lightening holes extend back to the trailing edge, where the skin surfaces are crimped together and riveted with 3/8-in ordinary round-head rivets.

Fore part of the bottom portion of the rudder, beneath the lower hinge, is comprised of two formed sheets flush riveted to the spar and lowest rib. The aft portion containing the formation light is made up of two small formed sheets attached by flat screws.

Although the rudder is quite deep, it has but two hinges, both typical self-aligning ball bearing units. The top bearing is set just beneath the mass balance, the lower at the bottom rib, where push-pull controls also attach.

Oddly enough, the combination servo and trim tab has four hinges and, comparing its construction with other parts of the plane, it showed every evidence of having come from a different shop. It too, has a mass balance, set right under the top self-aligning ball bearing hinge. The two middle hinges are small metal blocks with vertical pins holding them to the tab and yokes attaching to the rudder false spar, giving a universal joint effect. The lower hinge is a vertical pin extending up from a rudder rib. Trailing edge of the tab is formed by crimping together the skins, around which a strip is folded and flush riveted. It is 36¾ in deep, with 4-7/16 in chord at the top and 6 in at the bottom.

As is the case with several other German planes, the 262s all metal stabilizer is adjustable, the incidence being changed by a small electric motor operating a screw jack mounted inside the fin fairing on the front face of the frame to which the vertical fin is bolted. This unit is very similar to that on the FW-190.

With a span of 12 ft 4 in, the stabilizer is built in top and bottom halves, which are bolted together through access holes that are later fabric covered. On the craft studied, no attempt has been made to mask the joint along the leading edge, and reports on other planes indicate this was general practice. In view of the workmanship, which left some rather ragged gaps in the skin joint along that edge, it is strange that the manufacturer had not at least applied some filler and fabric.

The stabilizer has a built-up I-beam spar located 24 in from the leading edge and 18¾ in ahead of the trailing edge. It is attached to the fuselage by through bolts to two forged fittings set in ball bearings at the axis of the angle adjustment. The leading edge has a 25° sweepback.

All metal elevators follow conventional design practice, with a stamped flanged spar, rounded metal leading edge shrouded into the stabilizer trailing edge, and stamped flanged ribs. The trailing edges are formed simply by crimping the skins together and riveting — with ordinary rivets as is the case with the rudder.

Outboard hinges are self-aligning ball bearing units, set just outside the large mass balances at the tips, while the center units are of similar type set just beneath the vertical fin.

Both elevators have 27 x 2½ in mass-balanced trim tabs set near the inboard end. These tabs were apparently designed as interchangeable servo units, for a small arm at the outboard end extends up from the right one and down from the left, and captured enemy documents show an anchoring arm designed into the stabilizer trailing edge. However, the operational experience or Allied bombing made completion of this plan impossible, for the tab arms were not connected to the stabilizer and, in fact, the tabs had been riveted into immobility by small gusset plates at each end. Nevertheless, each tab had four hinges, with ball bearing units at each end and pins through yokes for the two in the middle. As is the case with the rudder trim tab, the trailing edges of the tabs are nicely flush riveted.

One-piece pressed-aluminum stabilizer fillets are held in place by a leading edge pin which moves up and down between greased strips riveted to metal brackets just above the adjusting jack, and by screws — one top and bottom — 10 in aft of the stabilizer spar.

There are many interesting variations in both design and workmanship in the 262's wing which, though approximately like our laminar flow foils, has a plan form which is angular, to say the least. The leading edge has a 20° sweepback; the spar sweeps back 12°, starting at the fuselage side; the trailing edge sweeps forward 8½° to the outboard side of the power plant; then sweeps back 5° from there on out. All this and 6° dihedral, too.

The wing is built around a composite I-beam main spar having steel booms and built up dural web, tapering in depth from 14½ in at the centerline to 3 in at the tip attachment fitting. Spar boom caps are ¾ in thick at the centerline, the upper being 4¼ in wide, the lower 4¾.

Built in two sections, the spar is spliced at the centerline where the webs are flanged and bolted. Steel splice plates, ¾ in thick by 8 in long, go over both the top and bottom of the boom caps and are held in place by six through bolts on each side of the web. Incidentally, none of these bolts were safety wired on one plane that had been accepted by the Luftwaffe. Small steel wedges are placed between the splice plates and lower capes, for the taper on that surface starts right at the centerline.

Three heavy steel hat shaped stiffeners are riveted to the front face of the spar between the centerline and fuselage skin, which is 33 in away where the spar sweepback begins, and hat shaped aluminum stiffeners are used from there on out.

Since the spar is at about 35% MAC, nose ribs are longer than they would be in a two-spar wing and consequently vary in construction. Compression ribs have hat shaped vertical stiffeners, others are of conventional stamped flanged construction with riveted stiffeners and holes where necessary for control connections. Two large J-section spanwise stringers are used ahead of the main spar, and one is placed between it and the auxiliary spar.

This latter structure, set 38½ in behind the main spar at the centerline, is 12 in deep at that point and is a channel shaped aluminum structure with hat shaped stiffeners, extending out to the wingtip to carry flaps and ailerons.

The top skin of the wing, varying from .083 at the leading edge to .080 at the trailing edge, is flush riveted except at the base of the leading edge where it is flanged out and riveted to the bottom surface. Here, however a rolled .010 steel sheet section is riveted in place to give a true airfoil behind the slots.

These units, with .040 steel skin, extend from the fuselage line 40½ in to the power plants, and from there to the wingtips, the outer segment being built in two sections of 77½ and 48½ in lengths connected by a ½-in long steel pin.

Each segment is bolted to two curved steel guide tracks which slide over ball bearing rollers bolted to wing ribs. Travel of the slots is a maximum of 6 in at the inboard end and 2-5/8 in at the tip. The slots open automatically at 186 mph in gliding angle and at 279 mph in a climb.

The 5¼-in wingtip, with its integral formation set in a transparent plastic covering, is built in two halves, flush riveted to an inboard rib and spar. The two halves, flush riveted to an inboard rib and spar. The two halves are welded together around the outer edge and, on at least one craft, a thoroughly sloppy weld it was. Its method of attachment, however, is neat and can be accomplished fairly fast with simple tools.

A horizontal pin near the leading edge slips into a holed angle plate on the wingtip rib, then the tip is pushed toward the planes so that an angle bracket slips int a forged fitting riveted to the end of the spar, whereupon a through bolt with self locking nut is pushed down from the top through small access holes. At the time the tip is pushed toward the wing, a vertical plate slips into a yoke attached to the end of the auxiliary spar with the result that a three-way fastening is obtained with only one bolt being necessary.

All metal ailerons are of conventional design, having a channel-section aluminum spar, rolled sheet aluminum leading edge, and stamped flanged ribs. At the trailing edge the two skins surfaces are crimped and riveted to a flat ¾-in strip. Here, as on the rudder and stabilizer, the rivets are not flush.

The ailerons are built in two sections. Each have a 42-in span, and the two sections are connected via the control bracket, which is split so that one half is riveted to the outboard rib of the inner section, the other to the inboard end of the outer section. A self-aligning ball baring hinge also serves as a connecting point for the two sections, and similar bearings re bolted to ribs aft of the auxiliary spar at each end.

Evidently the 38-5/8 x 3 in trim tabs were originally proposed as servo tabs, but in practice they ended up only as ground-adjustable units, for the control arm, riveted to the outboard end of the inner aileron section, is attached by a turnbuckle rod to the aileron-operating bracket rather than being attached to the wing to give the servo action.

Unlike the elevator hinge points provided in the rudder and elevator trim tabs, those on aileron tabs are simply straps bolted to the aileron and hooked around pins in the tab. Like those on the other tabs, however, the trailing edges are neatly flush-riveted.

Flaps are built in two sections: The inboard (which has a 21¾-in chord) extending 38½ in from the wing root to the power plant, and the outer section extending 48¾ in. from the power plant. With rolled aluminum leading edges, stamped channel-section spar, and conventional ribs, they are built in two halves, bolted together except at the trailing edge where the skin surfaces are crimped and riveted (with brazier head rivets) to a ½-in aluminum strip.

Ball bearing rollers at both ends of each section run in 7-in steel guides which re bolted to the auxiliary spar so that, in operation, the flaps move back and down, for the guides slant down 35½° from the top to the bottom wing surface. This action is imparted by hydraulically operated toggles which force the flap bodily aft approximately 5½ in —and down because of the guide — except for the final 5° of flap action, which is a pivot movement. The upper wing surface extends out over the flap so that even when extended to the full 50°, the flap leading edge is shrouded for 10½ in.

The flap actuating cylinder is set at a 45° angle to the front face of the main spar directly ahead of the oleo hinge point and is attached to one corner of a triangle whose apex is its hinge point on the spar. Where the piston attaches there is also attached a push-pull rod which extends across the plane to the left to a bell crank set just over the left power plant, with a push-pull rod going straight back to the aft face of the auxiliary spar. Here it is connected to an arm extending down from a torque tube connected to the toggles which force the flaps back and down.

Right side flaps are actuated by a tube going straight back from the base of the triangular member connected to the actuating piston.

Pilot error in forgetting to lower the landing gear is avoided through the system being so arranged that the flaps cannot be extended until the landing gear has been put down.

The left outboard flap on the craft examined has markings at 0, 10, 20, 30, 40, and 50°, with the 20° mark in red for takeoff.

Three of the lower wing skin panels, extending over three ribs each, are held in place by flush screws placed approximately 1½ in apart. While the primary purpose may have been to facilitate access, the small number of units requiring maintenance give rise to the belief that it may have been employed to facilitate production by eliminating blind riveting.

Quite an unorthodox method is used to attach the wing to the fuselage. Near the base of the root nose rib, 9 in aft of the leading edge, a 1-in bolt goes through a two-sided forged bathtub fitting which is bolted to the aft face of bulkhead backing up the front fuel cell. A similar sized bolt is used on the root rib aft of the auxiliary spar. Then, riveted to the top wing skin at the fuselage line is a 1-3/16 x 1-3/16-in steel angle member through which 17 bolts and self-locking nuts attach it directly to the fuselage skin.

On the first Me-262 brought to this country for study, many of the holes in the fuselage skin had been elongated and some were as much as 1/16 in out of line. When the craft was being prepared for flight tests, the holes were reamed to take 7/8 in bolts and an additional steel strip was used to back up the vertical half of the angle member.

The wing fillet, just over 73 in long, is held in place by a cable anchored to an angle bracket at the trailing edge and going under seven hooks riveted to the attaching angel-member, with a turnbuckle at the front keeping it snug. The fillet around the leading edge is a drawn light aluminum alloy section attached by eight flush screws.

Oleo struts for the main wheels of the hydraulically retractable tricycle landing gear are hinged in a built-up steel box structure on the end of spanwise spars extending 30 in from the root rib midway between the main and auxiliary spars.

The 26-in-long forged oleo strut is 5½ in in dia. and has conventional torque scissors on the aft side designed for a 20-in piston travel. In preparing the craft for flight tests it was found that the main wheels had considerable lateral play, but when the normal 1.200 lb pressure was built up, the wobble disappeared.

The retracting jack is bolt-hinged to a steel fitting bolted to the root rib at the end of the front spar of the landing gear torque box, while the piston is attached to the front of the oleo strut by a ball and socket joint.

Fairing for the main gear is built in two section, both of which are double-skinned grid-type structures with the top section hinged to the torque box end and the lower bolted to a bracket welded to the oleo piston just above the axle.

In operation the main wheels swing up and into the bottom of the fuselage, with the right strut operating an actuating valve at the end of its arc. This valve in turn closes fairing doors which are hinged at the fuselage centerline and which serve as the landing gear up lock.

To accomplish this, a hydraulic cylinder is attached parallel to the aft face of the main spar just to the left of the fuselage centerline. Its piston is connected to a welded steel box type bell crank which, in turn, is attached by a universal joint to another box bell crank set between two stamped flanged vertical plates set along the centerline. At the lower corner of this bell crank are universal joint tie rods connected to the leading edge of the built-up fairing doors, and at the upper rear corner is a flat steel tie rod connected to a triangular shaped built-up bell crank attached to similar tie rods on the trailing edge of the fairing doors.

Thus, when the oleo strut hits the actuating valve, the piston moves to the right, forcing the tie rod-connected bell cranks to snap the doors closed under the wheels, with the 90° change in direction between the units serving as the locking mechanism after the hydraulic pressure on the piston is relieved.

The nose wheel retracts aft and up into a well below the armament compartment, the wheel, near the end of the retracting arc, striking a transverse tube which pulls the double skin fairing door closed. Spring loaded pins moving into the piston serve as up and down locks.

German drawings studied in connection with this article show provision for the conventional torque scissors, but on the later model craft examined, the nose wheel contained a built in shimmy damper. The nose gear retracts and extends after the main wheels have been locked either up or down.

Both the landing gear and flap operating systems have connections with a compressed air bottle which can be cut in for emergency operation of the two systems.

Surface controls present several odd and interesting features. The control stick, for example, is mounted in a ball and socket joint set in the bottom of the cockpit liner, extending down 4 in and ending in a welded angle bracket. Attached by a ball bearing joint to one face of this bracket is a ¾-in tube extending to the right above the main spar. Just inside the fuselage, and bolted to the top boom of the spar, is a bell crank from which 1-in push-pull tubes extend, with one universal joint in each at the fuselage side (to compensate for spar sweepback) out to bell cranks set just ahead of the aileron control arms..

Attached to the aft face of the angle bracket on the stick is a 5/8-in elevator operating tube going aft to a self aligning ball bearing crank set just over and ahead of the auxiliary spar, from which a 1-in tube extends to the left side of the fuselage and another bell crank to connect to a similar sized push-pull tube going aft. A third bell crank is set in the empennage near the stabilizer leading edge. Extending straight aft from this crank is another push-pull rod connected to the elevator horn and, just ahead of the horn, a large mass balance which can be ground adjust on the fulcrum.

This balance is in addition to those already noted as being set in the elevators themselves, and may be a late modification. Reports from abroad have indicated that at speeds over 500 mph. the ailerons and elevators of the 262 become extremely hard to move and that an extendable control stick designed to give increased leverage had been developed. However, no such stick, or provisions for its installation could be found on the craft studied, and it is held possible the mass balance just discussed has been utilized in its stead.

Rudder pedals are very similar to those on the FW-190, incorporating the main wheel brake pedals as integral units. A torque tube extends aft from the right pedal inside the cockpit liner, then through a seal to a bell crank where another tube extends to the left side of the fuselage to a second crank which is connected with the push-pull tube extending to the empennage, where a third crank, with adjustable mass weight, is connected to double tubes connected to the enclosed rudder horn.

The fuel system consists of two 238-gal main tanks plus a 53-gal reserve and, at least in design plans, and auxiliary tank of about 170 gal capacity. Both self-sealing main tanks have plywood coverings and are suspended by two straps on the ends of which are bolts that go up through pressed fittings riveted to the inside of the fuselage skin about two-thirds of the way up the side. Nuts are put on the bolts through access holes in the fuselage skin, with the holes covered by doped fabric patches.

Each of the main fuel cells has two booster pumps and the reserve tank has one, the system being so arranged that fuel can be pumped from any tank to either engine, or fuel from the rear tank can be pumped to the front.

The reserve tank (at least some of these have not been self sealing) goes just in front of the main spar. It is trapped to a single-skin panel, 19¾ in deep by 66¼ in wide, that is reinforced by six hat shaped stiffeners and is attached to the fuselage by flat screws placed approximately 1¾ in apart.

Evidence of the Nazi's attempts to get more range out of the Me-262 is shown by plans for installation of the 170-gal auxiliary tank aft of the rear main cell. It is not known how extensively, if at all, this plan was carried out, for the craft studied was the latest model produced and it had no such installation. Instead, the radio was installed in the space and, a little farther aft, the master compass and oxygen bottle. Access to these units is via a 17½ x 15¼-in door held in place by four quick fasteners.

Radio installation consists of the usual German equipment — FuG 16Z or FuG 16ZY (VHF R/T, D/F and retransmission facilities for ground control stations) and in some cases IFF had been installed.

Whether Hitler was finally convinced that the Me-262 was not the world's hottest bomber or whether the Luftwaffe went ahead in the face of his orders is not known, but one final modification of the craft — the Me-262 B2 — was in the works when the Germans capitulated.

This was to make the plane a two-man, radar-equipped night fighter. Principal changes necessary were made in the cockpit, where the pilot's seat appears to have been pushed forward slightly to help make room for addition of the radar operator's screens and seat immediately behind. This, of course, meant changing the design of the canopy to give the necessary length, and relocation of the aft fuel tank, normal radio equipment, oxygen bottles and master compass, all of which were pushed further aft in the fuselage.

Study of the plans for this change does not indicate that much, if anything, had been done to compensate for the added weight aft of CG and, since the craft had to be trimmed nose heavy for take-off as originally designed, it is believed that even more trim had to be applied for the night fighter version. Too, since the 262 was not the most maneuverable to begin with, it is believed that the radar-loaded version was not as good a combat craft as the original day fighter version.

The concluding part of this study will cover the Junkers Jumo 004 gas-turbine jet-propulsion power plants, used in the Me-262 but designed for use in other craft as well.

Acknowledgment
For unusual cooperation, Aviation is deeply grateful to Col J M Hayward, Chief, Technical Data Laboratory, ATSC, and to Capt Irving P Brown, Chief, Capts W H Carter and H R White and Lts J E Arnoult, F D Van Wart, and Bernard Ellis of the Foreign Equipment Branch. Special thanks are due Sgt Robert Foster, Hangar Chief; Staff Sgt Harry Kirkpatrick, Crew Chief; Tech Sgt Warren Stoddard; and Sgts George Ledbetter and Wilfred Vigor.

DESIGN ANALYSIS OF
Messerschmitt Me-262 Jet Fighter

Part II — The Power Plant
By John Foster, Jr,

Managing Editor, Aviation

First complete engineering study ever published on jet power plant reveals, in addition to fundamental principles of jet propulsion, the design and production compromises made by limitations of materials.

As is the case with the airframe of the Me-262, the Junkers Jumo 004 axial flow gas turbine jet power plant is a compromise between design desire and available materials and production facilities.

Outstanding evidence of compromises resulting from lack of materials is the fact that more than 7% of the air taken in is bled off for cooling purposes. Despite this, however, most engines were found to have a service life of about only 10 hr, against a "design life" of 25-35 hr. Additional compromises are evident in the design, which shows that the production engineer — undoubtedly hampered by lack of both plant facilities and adequate skilled labor — has been as important a factor in its construction as was the designer.

But the Germans had made real progress in overcoming materials difficulties, for just after they capitulated that development of a new alloy of excellent heat-resistant qualities had made it possible to get up to 150 hr service in actual flight tests, and up to 500 hr on the test stand.

A large unit, the 004 is 152 in long from the intake to the tip of the exhaust; 30 in in dia at the skin around the six combustion chambers, with maximum diameter of the cowling reaching 34 in.

The circular nose cowling is double skinned, the two surfaces being welded together near the leading edge and held in position by riveted channel shaped brackets. Diameter at the intake end is 20 in, the outer skin increasing to 31½ in, the inner to 21½. Inside the cowling is an annular gasoline tank which is divided into two sections, the upper being of ¾-gal capacity feeding fuel to the starting engine, the lower of 3¼-gal capacity, feeding starting fuel to the combustion chambers.

The nose cowling attaches by eight screws in captured nuts to the annular-shaped combination oil tank and cooler. Having 3-gal capacity, this tank has a baffle close to the inner surface so that as warm oil is fed in from the top it is cooled as it flows around to the bottom of annulus and the tank proper.

The oil tank, in turn, is attached by 23 bolts on a flange to the aluminum alloy intake casting. This unit comprises the outer ring, with flanges on both front and rear faces, four hollow streamlined spokes, and the inner ring.

Moving back to the front of the unit, though, we find inside the nose cowling a fairing which looks just like a propeller spinner, increasing in size to 12 in at the intake casting, leaving approximately 220 sq in intake area. This spinner houses the starting engine, a two-cylinder two-cycle horizontally opposed gasoline engine which develops 10 hp at 6,000 rpm. The starting engine has its own electric starting motor; and, for emergency, extending out to the front of the spinner is a cable starter similar to those found on outboard boat engines. The engine is 12½ in long, 10 in wide, 8¼ in high, and weighs 36 lb.

The starter engine is bolted to six studs in the bevel gear casting, which contains bears to drive the accessories. Each of these gears is carried by ball and roller bearings, with the drive shafts fitting into internally splined stub shafts on the bevels. There are two drive shafts extending through two of the hollow fairings of the intake casting, one going up to the accessory case which is mounted atop the intake casting, the other extending down to the main oil pumps, which are set inside the lower part of the intake casting.

The bevel gear casting, also of aluminum alloy, is bolted to twelve studs set in a flange in the front face of the intake casting.

The rear side of the intake casting's inner ring is cup-shaped, housing the front compressor bearing. This unit is comprised of three thrust races — each with 15 bearings — mounted in steel liners set in a light hemispheric-shaped housing which is kept in contact with the female portion of the intake housing by the pressure of ten springs held in place by a plate bolting to the intake casting. The outer bearing races are mounted in separate sleeves which fit on the compressor shaft.

This design not only allows for preloading the bearings during assembly to ensure even distribution of thrust, but the bearing assembly can be left intact during disassembly simply by withdrawing the compressor shaft from the inner sleeve.

Next in the fore-to-aft sequence ins the aluminum alloy stator casting, which is built in top and bottom halves held together longitudinally by eleven 3/8-in bolts through flanges on each side, with attachment to the intake casting by 24 3/8-in bolts through a heavy flange. Running the entire length of the bottom half of the casting are three .7-in dia passages, one serving as part of the oil line leading to the rear compressor and turbine bearings, one connecting oil sumps (which are located in both intake and main castings), and one serving as part of the oil return line from a scavenge pump set in the rear turbine bearing housing.

Just aft of the fourth compression stage in both halves of the stator casting is a slot, inside of which is a ring with a wedge-shaped leading edge pointing upstream and set to leave a .08-in opening to bleed off air for part of the cooling system (which will be discussed later in a separate section.)

Like the stator casting, the stator rings, which consist of inner and outer shroud rings and stator blades, are built as subassemblies, then bolted in place and locked by small tabs.

Considerable variation, both in materials used and methods of construction, was found in this section. In early production units, for example, the inlet guide vanes and first two rows of stator blades were of stamped aluminum with airfoil profiles; and in assembly, ends of the blades had been pushed through slots in the shroud rings and brazed in place. In other early engines, the third stator row varied both in material and method of attachment. In some cases it would be of aluminum, but without airfoil; in others it would be of steel with the ends turned to form flanges which were spot welded to the shroud rings. The remainder were stamped sheet steel, zinc coated.

One late-production engine examined showed a combination of all the variations, with the inlet guide vanes and first two rows of stator blades of stamped aluminum, and the rest steel, indicating the Germans may have been swinging over from aluminum to steel exclusively. Apparently all the steel blades had been enameled, but this protective coating on the last row, where temperatures reached approximately 380°C., appeared to have been burned off.

Methods of attaching blades to shroud rings also varied. On the inlet guide vanes and first two rows, the ends of the blades had been pushed through slots in the shroud rings and brazed in place; the 3rd, 6th, and 7th rows had a weld all around the blade end; the 4th, 5th, and 8th row blade ends had been formed into split clips which were spotwelded to the shroud rings.

The outer shroud rings are channel shaped with an angle bracket riveted to each end, this bracket in turn being bolted to a stud set in the casing just inside the mating flange. Inner shroud rings are flanged along the leading edge, with the exception of the 7th row, which is channel shaped.

Except for the inlet guide vanes and the last row of stator blades, which act as straighteners, stator blades are arranged as impulse blading — they are set at nearly zero stagger and simply serve as guides to direct the airflow into the rotor blades.

The compressor rotor is made up of eight aluminum disks held together by twelve bolts each through shoulders approximately at mid-diameter, with the entire unit being pulled together by a 38-75-in long, .705-in dia tie rod which has been estimated to have a stress of some 40,000 psi, with a force to pull the assembly together figured at about 16,000 psi.

Diameters of the disks increase from the low to high pressure ends as follows: Stage 1, 13.86 in, Stage 2, 14.68 in, Stage 3, 15.61 in, Stage 4, 16.44 in, Stage 5, 17.18 in, Stage 6, 17.85 in, Stage 7, 18.24 in, and Stage 8, 18.34 in.

To carry the compressor bearings there is attached to each end disk a steel shaft with an integral disk carrying a round-faced washer. This shaft goes through the disk and is tightened by a nut so that the face of this washer (rounded to facilitate alignment) bears against the disk face. The flange on the rear shaft has six slots around its outer edge, into which fit projections on the rear disk. Thus torque is transmitted from the turbine to the rear compressor disk, and from there on to the other disks by the bolts previously noted as fastening the disks together, the torque being transmitted to the compressor unit around the faces, rather than through a central shaft.

Compressor rotor blades, of which there are 27 in the first two stages, 38 in the rest, are all stamped aluminum with machined roots fitting into pyramid shaped slots in the rotor disk. Through the aft face of each blade root, directly under the blade trailing edge, is a small screw set longitudinally and extending into the disk.

Tip stagger of the blades is about the same through the first six stages of compression, but increases in the last two. Chord of the blades decreases through the eight stages as follows: 1.95 in, 1,94; 1.34; 1.33; 1.30; 1.30; 1.24; and 1.21.

Blade profiles in the first two stages are very similar (possibly even designed to the same section), while the third stage has a thicker section. Stages 4, 5, and 6 have thinner sections (here, too, possibly the same), with about the same chord as Stage 3, while the last two stages, though set at greater pitch and having slightly narrower chord, have generally similar camber and profiles.

Clearances between the rotor blades and the stator casting are .103 in over the first three stages and .04 over the remaining five. Axial clearances between rotor disks and inner stator shroud rings range from .1 to .15 in, and axial clearances at roots between rotor and stator blades are .5 and .6 in.

Backbone of the 004 is a complex aluminum casting which, in addition to providing the three engine attaching points, supports the compressor casing — through 25 bolts — the entire combustion chamber assembly, the turbine nozzle, the aft compressor bearing, the two turbine bearings and, through the combustion chamber casing, the entire exhaust system. Moreover, in the base of each of the six ribs supporting the combustion chambers, there are cored passages, five of which carry cooling air, one carrying lube oil. And, while the air passage area remains constant between the compressor and combustion chambers, the main casting changes the shape from annular to circular at the entrance to the chambers.

In the front of the casting, at the tip of the last stator row, is an 18-3/8-in die. ring with a serrated inner surface fitting closely to serrations on the aft face of the last compressor disc. Air bleeding through the serrations is carried aft through cored holes in the casting to cool there front face of the turbine disk and, on hollow-bladed turbines, to cool the blades themselves.

Just outside and in back of this ring are the fairings which divide the air and direct it into the individual combustion chambers. These fairings, in turn, are surrounded by a 28-in o.d. ring with 25 bolt holes for attaching the compressor casing. Besides the bolt holes there are 18 openings, six of which carry the air bled off from the compressor on aft for exhaust system cooling, and twelve smaller ones which take cooling air around the combustion chambers.

Around the outside of this ring, extending back to a heavy flange to which the combustion chamber casing bolts, are twelve raised longitudinal ridges arranged in pairs. These have machined faces having four bolt holes and two aligning pins serving s the forward engine pickup points. With six such pickup points, the engine was designed for a wide variety of mountings. In the case of the Me-262 plates with collared nuts were fastened to the two on either side of the topmost unit.

Overall length of the main casting is 37¼ in, with the previously mentioned ribs tapering down from the aft face of the ring structure to the central longitudinal member which has an 8¾-in dia at the aft end.

The aft compressor bearing, having 16 rollers, is set in the front of the main casting inside the serrated ring, the housing being attached to the casting by 14 bolts.

The turbine thrust bearing is set inside the main casting, with the centerline of the balls 24-3/8 in back of the front edge of the serrated ring, and the main turbine roller bearing is bolted into the rear end.

Each of the six combustion chambers is built up of three major components having a combined weight of 19 lb First, there is a mild steel outer casing, of 5¾ in dia at the entering end flaring out to 8-5/8 in, and having a length of 20-5/8 in. The front end has a collar with a rubber sealing ring which is pushed up against the aft face of the main casting to take care of air leakage and to compensate for the difference in casting and combustion chamber expansion.

Fitting inside the front end of this casing is the flame tube, which has two main components — the entry section and stub pipe assembly. The fore part of the entry section flares out somewhat as does the outer casing, and at the front end has a six-blade swirler. This unit is made of 22 gage mild steel with a black enamel coating. The stub pipe assembly is made up of ten flame chutes welded to a ring (which is welded by brackets to the rear end of the flame tubes and to a 4-in dished baffle plate at the rear. To help direct air into the chutes, ½-in circular baffle plates are riveted to the forward ring. Material of this unit is mild steel with an aluminized finish.

Third major component of the combustion chamber is an 11-in long 20-gage aluminized steel liner having a corrugated outer skin which permits cooling air to flow inside the outer casing. This liner fits into the aft end of the casing. The aft ends of the combustion chambers are bolted around flanges to a ring of six rings which fits over there rear end of the main casting.

Ignition interconnectors between chambers are of but 15/32 in dia, and starting plugs are provided in three of the six chambers. These elements, as are the fuel plugs, are enclosed in streamlined fairings.

Surrounding the combustion chambers is a 16-gage mild steel double skinned casing having flanges welded at both ends — that at the front end attaching by studs to the main casting; that at the rear attaching to the turbine inlet duct outer flange, the nozzle ring assembly flange, and the exhaust casing flange. Besides the bolt holes in the front flange, there are 24 of similar size, twelve leading to six ducts of 22-gage steel which carry the air bled from the fourth compressor stage through the combustion chamber casing, and twelve directing air around the combustion chambers. These ducts also help stiffen the skin, as it takes the weight of the entire exhaust system.

Six large hand holes are cut in the casing just behind the flange. These give access for making minor adjustments to burners and the three ignition plugs.

A little more than halfway aft around the combustion chamber casing is a heavy collar comprised of two channel shaped members, and inside the casing at this ring are six tie rods, connecting it to the main casting. Any one of these six units can serve as the aft engine pickup point; in the case of the Me-262 it is the top one.

Ducting from the combustion chambers to the turbine nozzle changes the air passage from the six circles to annular shape. Attached to the combustion chambers by bolts, this 19-gage aluminized mild steel unit is made in two parts, the rear of which is welded to a heavy flange. Studded to this flange from the inner shroud ring of the turbine nozzle assembly are two mild steel diaphragm plates. These, in turn, are studded to the rear end of the main casting, and so support the inlet ducting and turbine nozzle ring. On the rear of the outer turbine inlet ducting a light flange mates with a flange on the rear of the combustion chamber casing. Thus the turbine inlet ducting, to which the combustion chambers are attached, is supported partly the diaphragms, and partly by the skin.

Maintenance crews really take a beating as the result of the final design, for it is a major operation to get at the combustion chambers. First, the variable-area nozzle operating shaft must be removed so that the complete exhaust system assembly can be taken off. Then, unless special equipment is available, the engine must be placed upright on the turbine disk and burner pipes and ignition leads disconnected from the combustion chambers. Then the compressor casing-main casting joint can be broken and the whole front end lifted off. Next the rear compressor bearing assembly, torque tube, and locking ring can be removed and the main casting assembly removed — when the nut on the front end of the turbine shaft is unscrewed. The rear diaphragm plates can then be removed and the turbine inlet ducting and combustion chamber assembly lifted off. Then the front diaphragm plate is removed and the turbine inlet ducting, with the combustion chamber assembly, lifted out of the casing. At this point, as one sweating engineer who did the job declared, "Now, Bub, y'can take out the individual combustion chambers."

An unusual feature of the 004's design is the use of hollow turbine nozzle blades through which cooling air is fed from the compressor via the main casting and supporting diaphragm plates. The two-part outer nozzle shroud ring is made of mild steel and both parts are welded to a ring that is joggled and flanged to mate with flanges through 36 bolts on the inlet ducting and the aft flange of the combustion chamber casing. In addition to the bolt holes the flange has 36 sets of three holes for cooling air passage.

The 35 nozzles are made of austenitic sheet steel, .045 in thick, bent to shape around a 1/16-in radius to form the leading edge. Between the sheets at the trailing edge are spotwelded four wedge shaped spacers, 1 in long and tapering from 1/8 to .020 in, leaving a .020-in gap down the trailing edge through which the cooling air escapes.

In assembly, the blade tips are closed, pushed through slots welded to the outer shroud ring, and the roots are pushed through slots in the inner shroud ring and spotwelded in place on the inner surface of the ring.

To this ring, in turn, is welded a heavy, mild steel flange and second flanged ring, the two flanges picking up with the diaphragm plates which support the assembly from the rear of the main casting.

Two types of 61-blade turbines are used. Originally both blades and disks were solid, later hollow blades and lighter disks were introduced at a saving of approximately 40 lb.

The solid disks were of hardened chrome steel, taking stresses of about 15 tons at maximum rpm. Cooling is effected by spilling air bled back through the main casting against the disk face then up over the blade roots and out between the blades.

The 12¼-oz solid blades are forged from an austenitic steel containing 30% nickel, 14% chrome, 1.75% titanium, and .12% carbon, corresponding closely to "Tinidur", a Krupp alloy known before the war, and are attached by three machined lugs drilled to take two 11-mm rivets each. Maximum centrifugal blade stresses have been estimated at 18,000 psi, and gas bending stresses at 2-4,000 psi. Study of the solid blades indicates that the roots didn't get much above 450°C due to the cooling air flow up from the disk, but near the center it appears the temperatures got up to about 750°C. This applies to service models, not those previously mentioned as having given the longer flight and test-stand life.

Disks for hollow blade turbines are of lighter material than the solid types and have attached, across the front face, a thin sheet flared out near the center. This picks up the cooling air and, via ridges on the disk, whirls it out toward the blade roots where it goes through two small holes drilled in the disk rim up through the blade and out the tip.

Made of the same material as the solid blades, the hollow type are formed by deep drawing a disc through a total of 15 operations. In assembling the turbine, the blade roots are fitted over grooved stubs on the disk rim. Two small holes on each side take locating pins to hold the blades in place during assembly, but they take no stresses.

With a silver-base flux in the grooves, the entire unit is put in an oven at 6-800°C, warmed for 20 min, then heated to about 1,050°C in 40 min, then cooled in still air at room temperature before hardening in a gas or air oven.

Later production units have two rivets in the blade trailing edges near the tips, a modification made necessary by cracking caused by vibration.

The turbine is attached by six studs to a short shaft carried no two bearings housed in the main casting. The front bearing is a single-race ball thrust, the rear a single-race roller type, and both are cooled by oil only Connection of the turbine and compressor is vi a heavy, internally splined coupling.

The exhaust cone is made up of aluminized mild steel, and consists of two major components: outer fairing is double skinned, with cooling air bled from the compressor flowing between the skins to within 15-¾ in of the exit where the inner skin ends. Outside the other skin from there to the end is another skin, flared at the leading edge to scoop in cooling air. It is attached by spot welded corrugations.

Attached to the outer fairing by six faired struts is the inner fairing, tapering from 19½ in at the turbine end to 9-¾. This unit houses a rack gear — driven by a shaft entering through one of the struts — which moves a "bullet" extending from its aft end. Actuating this bullet over its maximum travel of approximately 7-3/8 in varies the exit area between 20% and 25%. It is set in retracted position for starting to give greater area and help prevent over-heating, then moved aft to decrease the area and give greater velocity for takeoff and flying. The movement is accomplished by a gear-type servo motor set near the accessory housing and connected by a long torque tube to gears set on the exhaust housing over one of the struts leading into the previously-mentioned rack gear.

Originally the unit was supposed to operate automatically over small ranges at extremely high speed and altitudes to give maximum efficiency, but on some engines examined the necessary lines had been blanked off. The two-position operation is obtained through a mechanical linkage with the throttle so that the bullet moves aft at between 7,000 and 7,500 rpm.

Since the necessary cooling system played a very important part in both the design and construction of the 004, it is felt best to note it briefly as a separate part of the study. It consists of three major stages, as follows:

  1. Air bled off after the 4th compression stage.
  2. Air taken off just after the last compression stage.
  3. Air bled off between the compressor and combustion chambers.

In Stage 1 the air is picked up by the ring after the 4th compressor row and is directed into six cored passages in the stator casting, then at the combustion chamber casing it is divided so that some of the air goes through six ducts in the combustion chamber casing skin, some goes inside the casing and around the chambers themselves. That which goes into the ducts continues aft and, through small holes in the flanges, between the double skin of the exhaust cone outer fairing. Majority of the air goes straight on aft to the end of the inner skin, but some is taken through the six struts connecting the inner fairing into that unit to cool the rack gear and bullet.

In Stage 2 the air goes through the serrations between the compressor and the main casting, into two of the six cored passages in the casting back to the turbine. Here, on the original engines, it was spilled against the face of the turbine disk and moved out to escape between the turbine blades. On engines with hollow blades, however, the air is ducted across the space between the two diaphragm plates supporting the turbine disc where it is picked up by ridges and forced up through the turbine blade roots out through the blade tips.

Stage 3 cooling air, bled off between the compressor and combustion chambers, is ducted through three passages in the main casting to the space between the turbine nozzle-supporting diaphragms, then up through the turbine nozzle vanes and into the slip-stream through the trailing edges of the vanes.

It is estimated that Stages 1 and 3 take approximately 3% each of the total air movement, and that Stage 2 probably takes at least half as much; thus better than 7% of the available flow is taken off because of a lack of higher heat-resistant alloys. Additional performance penalties are evident in the fact that ducting is necessary, complicating both the weight and production pictures.

Air is not the only cooling medium, for the lubricating system too is employed. In this system, two gear pumps circulate lube oil to the front compressor bearing assembly, the accessory-drive bevel gears, and the accessory gears. Another supplies oil to lubricate and cool the rear compressor and both turbine bearings, the latter two being sprayed and splashed, respectively.

The two main pumps, mounted beneath the engine and driven from the bevel gears through a nose casting strut, deliver 190 gal/hr each. The two-part scavenge unit is built into the turbine bearing housing and is driven by a gear cut into the sleeve which serves to return oil to the cooler. In level flight, one part of the unit, a 300-gal/hr pump, returns oil through one of the cored passages in the main casting, then through a passage in the stator casting to the pump in the bottom of the intake casting. In climbs, the other part, a 90-gal/hr gear pump, picks up the oil and feeds it into a common return line to the air-oil separator. Oil is returned from the main pump to the separator by a 300-gal/hr pump driven by the same shaft as the delivery pumps.

Two types of fuel are used on the 004: gasoline for starting and J-2 brown coal "crud" for running. The gasoline is carried in the lower part of the annular tank set in the nose cowling, and is automatically cut off after ignition at about 3,000 rpm. This is fed by an electrically driven pump delivering 80 gal/hr at 28 psi. Near the end of the war it was found that centrifugal crude oil was also used as operating fuel.

The main single-stage electrically-driven gear type pump has a maximum delivery of 500 gal/hr at 1,000 psi. at 3,000 rpm.

Most interesting of the accessories is the all-speed governor, a 17-lb unit consisting basically of a centrifugal governor, oil pump and spill and throttle valves. In operation, oil goes through a passage to the pilot piston and is distributed to outer faces of either the spill or follow-up piston, depending on movement of the flyweights. Both the pistons move at the same time, adjusting the fuel spill to counteract changes in engine speed. The distance between the spill and follow-up pistons varies according to the flow of oil through the passages so that the spill piston action is a step-by-step operation controlled by the follow-up which returns to normal position after each step. A throttle valve is linked with the governor cam so that when the throttle is advanced the fuel flow increases and response is immediate. The governor then takes over and adjusts the engine speed to a predetermined value set by the position of the cam.

Acknowledgement

In addition to the staff of the Foreign Equipment Branch, Technical Equipment Branch, Technical Data Laboratory, ATSC, Aviation extends heartfelt thanks to Col R L Wassell, Chief Special Research Branch, Power Plant Laboratory, ATSC; Lt Col P F Nay, Assistant Chief; Maj R I Berge, Administrative Officer; Capt W C Gerler, Project Engineer; and Mr A T Miller, Chief Technician.


This article was originally published in two parts in the October and November, 1945, issues of Aviation magazine, vol 44, nos 10 and 11, pp 115-135 (October, Part 1), 115-130 (November, Part 2.)
The PDF of this article includes the extensive illustrations, including a ledger-sized foldout of the Jumo engine.