Robison, Morris M.

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 The Knowledge Bank at The Ohio State University Ohio State Engineer Title:  "Electrical Bomber" Creators:  Robison, Morris M.  Issue Date:  1945-06  Publisher:  Ohio State University, College of Engineering  Citation:  Ohio State Engineer, vol. 28, no. 7 (June, 1945), 12-13, 32, 36.  URI:  http://hdl.handle.net/1811/36181        "Electrical Bomber"By MORRIS ROBISON, AERO. E. IllPrior to the advent of the B-29 Superfortress,America's greatest air weapon lay in her heavybombers, notably the B-17 and the B-24. Much hasbeen said about the effectiveness of these planes,of their great bomb loads and extreme accuracyin destroying the enemy's productive areas, butlittle has been told of the planes intricate work-ings, the means by which the planes become effi-cient forces of destruction.Taking the leading role after the engines andfuselage, is the part that electricity and electricalequipment plays in sustaining flight. A descrip-tion of the major parts will convince the readerof the importance of this equipment.The entire aircraft embodies a complete elec-trical entity, a system for generating current,storing it and converting it to power, heat, andlight. This entity provides a convenient means bywhich we can subdivide and describe the system.The generating system consists of four 200amp., 30 volts d.-c. generators, one attached to anddriven by, each engine. Voltage regulators lo-cated in the bomb bay keep the voltage at 28.5.These generators naturally do not supply anypower while the engines are not running, so thatsome current source must be available for start-ing the engines. This current is supplied by three24-volt storage batteries which are kept chargedby the generating system. They are not for con-stant use as their capacity is rather small. Al-ternative to using the ships batteries, a smallgas driven power supply is located in the rearof the ship. The one-cylinder engine drives a75 amp. generator, the output of which is suffi-cient to energize the engine starter. By startingthis small unit by hand, the aircraft engine canbe started without depleting the storage batteryreserves. After the first engine is running, the out-put of its generators is more than sufficient tosupply the other starting current needs, enginestwo, three, and four.Little more can be said about the current stor-age system. It is in effect the three storage bat-teries mentioned. They are not much good forcontinuous service, but indeed there is little usefor a current supply if none of the engines is run-ning in flight.Of the three current consuming categories inan aircraft, heat and light are probably the twoless important. Not that we could consider abomber without heat and light, but the currentdemand is far less than that asked for by thepower units of the ship. Of these two, the heatdemands the least amount of current—currentto heat the flying suits of the flyers and crew.The lighting system is chiefly that of the ex-ternal lights, landing and passing lights, recog-nition lights, running lights, and bombing lights.Important internal lighting is that supplied forthe instrument panel, the navigator's desk andthe radioman.Mention has been made of the "power units" inan aircraft without explanation of what theyare or what distinguishes them from the otherR.EIAYMOTORFLYWHEELPIG. ISTARTING CIRCUIT ^current consumers. I feel it would be justifiableto put into this category all units which in some-way consumq current to do work. I think it wouldinterest the reader to know how these unitswork as well as what they are for. In nearlyall of these units an electric motor of some typesupplies the energy but it would be well to seethe various methods of using the energy.The engine starter previously mentioned isinitially a high current consumer. It consists ofa small electric motor directly attached to aheavy five-inch flywheel. Prior to starting, thismotor and flywheel are energized until they re-volve at about 12,000 RPM. When they reach thisspeed, they are coupled to the engine through acompound planetary gear system which deliversthe high torque, slow RPM required for startingthe engine. It is the kinetic energy of the revolv-P a g e 1 2 T h e O h i o S t a t e E n g i n e e rBATTERY"START*HOT SPARKBOOSTER"MESH"SOLENOIDREVERSING MOTORWHEEL DOWNFIG. ZRETRACTION SYSTEMing flywheel and motor which supply the startingtorque. A rather simple circuit (Fig. 1.) showshow the motor is energized and the engine started.In starting the engine the pilot holds thetoggle switch in the "Start" or up position forabout 10 to 20 seconds until the flywheel is up tospeed. Then he throws the toggle down to the"mesh" position. This closes the solenoid meshcircuit which engages the gear system to the stillengine. At low starting speeds the magneto is in-operative so that an extra hot delayed spark issupplied by the booster circuit in parallel withthe mesh circuit. When the engine begins to fire,the magnetos supply the spark and the pilot re-leases the toggle disengaging the mesh systemand opening the booster circuit.The retractable landing gear is quite frequentlyoperated by electrically driven screw jacks. Thereare usually other alternatives, hand operated orhydraulic lift devices. In this type of device,use is made of remotely placed relays whicheliminate the necessity of running high currentleads to the cabin. The pilot's wheel switch closesthe relay energizing the motor jack, and whenthe wheel retracts into the fully locked position,a micro limit switch automatically breaks thecircuit preventing damage which would resultfrom overtravelling screw jack. A typical circuitis shown in Fig. 2.Very similar circuits and methods are used tooperate the wing flaps used in takeoff and land-ings, and to open and close bomb bay doors.On a B-17, control of the propellor pitch isachieved by a hydraulic servo unit deriving itspressure from gear type oil pumps in each engine.During flight the change in pitch is automaticallyJ u n e , 1 9 4 5controlled by the engine itself but in combat thiscontrol is lost if an engine is shot out by anti-aircraft batteries. It is vital that the pilot is ableto bring the propellor into "full feathered" posi-tion—edges turned directly into the wind—sothat the "windmill" effect does not cause the planeto lose altitude or in severe cases shake tReengine from its mount. To accomplish this fea-thering an auxiliary oil pump mounted in thenacelle and driven by an electric motor suppliesoil at 400 p.s.i. to the servo unit bringing the propblades into the wind. Similar to this oil pressurepumps are many pumps throughout the ship, muchlighter in construction. They consist chiefly ofgasoline booster pumps, transfer pumps to redis-tribute fuel when unbalancing occurs, anti-icerand de-icer pumps.It might be interesting to distinguish for thereader the difference between the anti-icer andthe de-icer system. Anti-icer is the device whichprevents the formation of ice on the leading edgesof the propellor. It is rather simple but unique.Briefly a small electric pump controlled by a rheo-stat pumps a mixture of alcohol and glycerine toa slinger ring located at the center of each propel-lor. Small outlets at the root of each blade per-mits the liquid to flow down the length of theblade while it is rotating and effectively producea typical anti-freezing mixture. On the otherhand, a de-icer system is one which removes ice,after formation, from the leading edges of the(Please turn to page 32)6LYC0L SYSTEM RHEOSTAT300T WINGVACUUMPRESSURE.ELECTRIC DISTRIBUTOR VALVE ]FJG3ANTI-ICER AND DE-ICER SYSTEMM*P a g e 1 3SCREWJACK"DOWN"UP"ELECTRICAL BOMBER"(Continued from page 13)airfoils, wings horizontal and vertical stabilizer.Wing icing, strangely enough, does not neces-sarily occur only when the air tempertaure isbelow freezing. It is known that icing canform at temperatures near 50 degrees F. due toa phenomenon known as supercooling. Thistakes place when the moisture particle strikesthe surface of the fast moving ship. To combatthis condition, which gives the ship poor flyingcharacteristics and overloads it, an intricate airpressure and vacuum system of de-icer boots hasbeen developed. It is in the control and operationof these boots that electrical distributor valvesplay their role. (Fig. 3.)To defend the ship, gunners must be able torely upon the smooth, certain operation of theirturrets. There are many types of turrets inoperation today. One of them is the type whichreceives electrical power from the craft and uses(Please turn to page 36)p a g e 3 2 T h e O h i o S t a t e E n g i n e e rWhere do you want to GO ?If you're like some twenty millions of your fellow Americans, you're gettingset to fly as soon as you can after the war. How soon will this be? Wherewill you be able to go? What about comfort? And cost? Here's whatan American airman who has flown all over the world can tell you:I "No place worth seeing will be out ofreach . . . The main routes are beingflown daily — more than 110,000 milesof them. Key airfields are fully developed— hundreds more are in the making. Thefinest flying equipment ever designed willbe ready for use soon after the war ends.2 "The peacetime versions of the big twin-% engine Curtiss Commando, for instance,will carry 36 to 45 people with all thecomforts of a drawing room . . . soft,roomy seats — plenty of space — an at-tractive powder room — complete diningservice—they'll be tops in luxury travel. . .34."And as for speed . . . well, when multi-engine transports can cross the country insix hours, you get some idea of theconcentration of power in their WrightCyclone engines — the same dependableengines that power the B-29 Superfortsand the giant Martin Mars."Vacations in Mexico, in Rio, on theMediterranean, by air, may seem fantasticright now. Yet 27 airlines, are alreadyplanning to take you to the markets andthe playgrounds of the world at a costwell within your reach . . . "F I R S T I N F L I G H TCURTISSWRIGHTA I AIRPLANES • ENGINES • PROPELLERS[ Aviation offers a bright future for College Engineers: Write Engineering Personnel Bureau, Curtiss-Wrizht Corporation, Passaic, N. J. ]June , 1 945 Page 33"ELECTRICAL BOMBER"(Continued from page 32)it to crate hydraulic pressure to drive the turrets.This consumes a great amount of current and isprobably one of the most important uses.The importance of the electrical instrumentsand the radio cannot be overlooked. In a ship likethe B-17, with four engines, it would be a seriousproblem to have to run tubes and pipes and link-ages from each engine to the cabin for instrumentuse. The electrical system instruments reduceeach intrumsnt line to a few wires which, are moreeasily run to the cabin. This requires a smallmotor generator unit; the motor end is a d.-c.30-volt motor, and the generator is a 40-volt a. c.required for the selsyns.In distinction to the B-17, the B-24 accomplishesmany of these aforementioned functions by useof hydraulic units. There has been a great con-troversy over the relative merits of each system.It is true that each have their advantages, but thegreatest, I believe, lies in the beating electricalequipment will take in combat as compared tothe sensitiveness of hydraulic to enemy fire. Per-haps the ever more widespread use of electricalequipment in the B-29 is an indication that it istaking precedence over its competitor, hydraulic.I do not mean to infer that hydraulic is on its wayout but its use will be restricted to those placeswhere it can do a job more efficiently and neaterthan can electricity.P a 9 e 3 6 T h e O h i o S t a t e E n g i n e e r

"Electrical Bomber"

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"Electrical Bomber"

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