Design and development Heinkel He 177

1 design , development

1.1 engines
1.2 surface evaporation cooling
1.3 defensive armament
1.4 wing
1.5 dive bombing
1.6 undercarriage

design , development

in 1936, company of heinkel flugzeugwerke received details of new bomber specification reichsluftfahrtministerium (rlm). specification, first proposed rlm on 3 june 1936 – ironically, same day main advocate luftwaffe having strategic bomber force, general walther wever, lost life – called aircraft more advanced dornier 19 or junkers ju 89 ural bomber prototypes general wever had championed. bomber aircraft specification required plane carry bomb-load of @ least 1,000 kg (2,200 lb) on range of 5,000 km (3,100 mi), maximum speed of not less 500 km/h (311 mph) @ altitude.

this formidable specification, calling did aircraft able outrun modern fighter – expected top speeds of main force schnellbomber concept – , outperform, considerable margin, bomber in service. on 2 june 1937, heinkel flugzeugwerke received instructions proceed construction of full-scale mock-up of projekt 1041 bomber a. completed in november 1937, , on 5 november 1937 allocated official rlm airframe type number 8-177 , same day luftwaffe high command (okl) stipulated new design should possess sufficient structural strength enable undertake medium-degree diving attacks. heinkel flugzeugwerke s estimated performance figures projekt 1041 included top speed of 550 km/h (342 mph) @ 5,500 m (18,050 ft) , loaded weight of 27,000 kg (59,500 lb). in order achieve these estimates, heinkel s chief designer, siegfried günter, employed several revolutionary features.

engines

a later db 610 power system a-5 version-the db 606a/b powerplants similar in configuration, outermost pair of engine mount forgings not shown

the 177 required @ least pair of 2,000 ps (1,973 hp, 1,471 kw) engines meet performance requirements. no engine in german aviation power-plant industry @ time developed such power. four-engine version have been possible engines daimler-benz db 601 four-engine layout involve higher propeller drag dive bombing. use of 2 counter-rotating propellers on heavy bomber offered many advantages, such substantial reduction in drag, reduction of dive instability , marked improvement in maneuverability. 8 initial v-series prototypes, , larger number of a-0 pre-production models of 177, displayed airspeed , maneuverability comparable many heavy fighters of time.

portside view of db 605 engine in bf 109g s nose - visible engine mount forging similar each side of db 606/610 used, along power system s special centreline mounting unit.

for 177, günter decided employ 2 of complex daimler-benz db 606 power system setups propulsion. had employed these engines on record-breaking heinkel 119 reconnaissance aircraft prototypes. consisted of pair of db 601 liquid-cooled 12-cylinder inverted-vee inline engines mounted side side in nacelle – 119, centrally within fuselage, behind heavily glazed cockpit enclosure – driving 1 propeller. 2 engines inclined inwards 30° when mounted onto either side of common, vertical-plane space-frame primary engine mount, inner cylinder banks disposed vertically. common gear-housing connected front ends of 2 crankcases, 2 crankshaft pinions driving single airscrew shaft gear. outer sides of each of component engines crankcases connected nacelle firewall through forged mountings similar used either single db 601 or db 605 engine-powered aircraft installation. when combined central space-frame mount designed power system format, resulted in daimler-benz coupled twin-crankcase power system having trio of engine mount structures within nacelle accommodation. starboard db 601 component engine had fitted mirror-image version of mechanically driven centrifugal supercharger, drawing air starboard side of engine. 2 of db 606s, each of developed 2,600 ps (2,564 hp, 1,912 kw) take-off , weighing 1,515 kg (3,340 lb) apiece, power 177. db 606 — , eventual replacement, daimler-benz db 605-based db 610 — 2 production german aviation powerplants designed surpass 1,500 kw of power, germans had considerable challenges in developing during war production-ready, combat-reliable aviation engines.

surface evaporation cooling

for aerodynamic cleanliness, günter intended dispense usual system of drag-producing engine radiators , planned on using surface evaporative cooling system instead. such surface cooling – in form of simpler surface radiators instead – had been used on british high speed racing seaplanes 1929. sort of system pioneered on 8 examples built of heinkel 119 high speed reconnaissance aircraft prototype series, flying twin-crankcase db 606 power system engine success beginning, , intended use on 100 high-speed fighter prototypes. coolant water pressurized, raising boiling point, in case 110 °c (230 °f). superheated water leaves engine enters expansion area pressure drops , water flashes steam. steam cooled running in pipes along outer skin of fuselage , wings. before design of 177 finalized, clear such system incapable of dealing vast amount of heat generated each of twinned db 601-based powerplants, forcing abandonment of idea of using evaporative cooling systems, in favour of conventional annular radiators fitted directly behind each propeller. these resembled, larger in capacity than, fitted junkers ju 88a bomber, , added 177 s weight , drag.

defensive armament

he 177 a-5 tail gun position, mg 151 cannon , bulged upper glazing upright gunner s seating

günter s original intention had been equip 177 3 cockpit-controlled remote gun turrets, 2 of them come junkers ju 288 program, leaving 1 manned emplacement in tail. compared manned position, remotely controlled, turreted defensive armament emplacement system traded technical complexity reduction of size, weight , drag; had advantage gunner placed in protected position, best possible view , less risk of being blinded flash own guns. although work on remotely controlled aircraft defensive systems had reached relatively advanced stage in germany in late 1930s, progress in field within germany s aviation , armaments systems engineers , manufacturers prove insufficient keep pace 177. result, 177 had modified accommodate larger , heavier manned positions, such manned rear dorsal turret fitted examples of greif, armed 13 mm mg 131 machine gun. installation meant fuselage had receive structural strengthening in several locations. of later production aircraft received remote forward dorsal turret, fernbedienbare drehlafette (translated remotely operated rotating gun-mount , abbreviated fdl ) 131z, armed 2 mg 131 machine guns, located @ point on fuselage directly above wing root s leading edge, rotating hemispherical sighting station dome located short distance forward of turret , offset starboard, behind forward cabin area.

a 7.92 mm mg 81 defend against head on attacks; 2 lower rows of nose glazing panels painted on protect crew searchlight glare.

a compact tail gun position fitted rearward defense, armed 1 mg 131 machine gun streamlined glazing meant gunner lay prone, severely restricting comfort on long missions. revised tail gun position bulged upper glazing fitted 177 a-3 , later models, permitted gunner sit upright. revised design required reduction of lower end of rudder surface clearance. mg 131 gun replaced 20 mm mg 151 cannon or in few instances, semi-experimental twin mg 131z mount, twinned 13 mm calibre guns mounted 1 above other, @ rear of standard bulged upper glazing emplacement. usually, 7.92 mm mg 81 machine gun in flexible mount positioned in upper starboard side of cockpit nose glazing defense against frontal attacks. undernose, inverted-casemate bola gondola (a common ventral armament fitment on many german bombers), full width of fuselage emerged under nose , centered under forward cabin, had flexibly mounted, drum-fed 20 mm mg ff cannon @ front end added forward defense , flexibly mounted mg 81 machine gun in rear, initial a-1 version. mg 151 cannon replaced forward mg ff cannon in later production models, mg 131 replacing mg 81, rearwards ventral defense.

wing

he 177a-3 suzy of 2./kg 100, 1944. note flaps cover entire trailing edge.

the 177 had fowler-type extensible trailing edge flaps, covered trailing edge of wing, including portions covered ailerons. each aileron comprised upper , lower portions, latter arranged slide rearwards flap extension, while upper part retained function of providing lateral control take-off , landing. original wing design did not take account stresses resulting operation of fowler flaps. rechlin report dated 9 october 1942 stated:

examination has shown strength of 177 s wings one-third below estimated heinkel. reason uneven rigidity of individual members consequent deformation under load. condition not recognized heinkel @ proper time, failure tests having been undertaken late in view of size of structure.

tests on 40th production a-1 aircraft in september 1942, revealed serious outer wing panel component damage after 20 flights, due aerodynamic stress diving attack exercises. costly , extensive strengthening needed solve problem, increased aircraft s weight. starting later versions of 177 a-3, fowler flaps along outboard wing sections removed , strengthened wing design introduced on 177 a-5.

dive bombing

he 177a in shallow dive. 177 meant have dive-bombing capabilities

the inaccuracy of horizontal bombing during ural bomber program demonstrated weaknesses in german bombsights , created doubts effectiveness of method. in luftwaffe believed dive-bombing more effective way destroy targets. technical data supported accuracy of stuka bombing achieving greater target destruction on dornier 17s or heinkel 111s. experience of condor legion in spain tended support idea dive bombing superior , led believe pinpoint accuracy possible, diverted attention improving horizontal bombing. during final inspection of projekt 1041 mock-up on 5 november 1937, ernst udet mentioned okl s new dive-bombing requirement ernst heinkel, replied aircraft never capable of it. 177 had strengthened support stresses imposed pull-out dive; later, required angle dive-bombing attacks increased 60°, necessitated further structural strengthening , big increase in weight.

problems arising requirement dive-bomb @ 60° never satisfactorily solved, due constant increases in loaded weight. despite strengthened airframes, possible overstress airframe during dive-bombing. although german bomb-sights of 1930s inadequate, later versions of lotfernrohr 7 proved comparable american norden bombsight. introduction of lotfe 7, offered error of 20–30 metres (66–98 ft) release altitude of 3,000–4,000 metres (9,800–13,100 ft) , hermann göring s rescinding of dive-attack requirement on 15 september 1942, barred-gate type dive brakes on wing s lower surfaces, placed forward of each of outboard ends of fowler flap panels, omitted 177as built after initial a-0 pre-production batch. photo of 1 of 12 destroyer 177a-1/u2, heavy-cannon-armed test airframes, showed retracted dive brake panel still fitted on undersurface of outer starboard wing.

undercarriage

closeup of 177a s portside twin-strut main landing gear, showing details of welded-together engines tight engine installation ventral side of cowling.

during development, anticipated weight of 177 increased main undercarriage design sufficient handle 32 metric tons (35 short tons) loaded weight, difficult achieve. engine nacelles , wings had little room main undercarriage members, needed longer usual, ground clearance large diameter four-blade propellers. after several extremely complex arrangements had been considered during initial design, novel system adopted. instead of wheel leg under each engine nacelle, 2 wheel legs attached main spar @ each nacelle, outboard legs retracting upward , outward shallow wing wells , inboard legs swinging upward , inward similar wells in wing roots, units enclosed flush fitting wheel , strut doors, met under each engine nacelle when extended. during retraction cycle, forward-oriented lever-action lower gear strut sections, on wheels mounted onto axles, pivoted 90° angle 120° when extended main gear leg, able fit wheel wells. conventional rearwards-retracting single-leg twin wheel arrangement each main gear used on 2 prototypes built (one during war, 1 post-war) of 274 in france. drawings made tricycle gear arrangement amerika bomber entry version of proposed 277 february 1943, depicted single main gear struts twin wheels. 177a s own landing gear maintenance needs, 2 hours required change main gear tire, using special heinkel-designed 12 metric tons (13 short tons) capacity main gear jacks , blocks.