Each engine on the B-29 has two turbo-superchargers which boost the manifold pressure for takeoff and provide increased air pressure at high altitudes.
Engine exhaust gas passes through the collector ring and tailstack to the nozzle box of each supercharger, expands to atmosphere through the turbine nozzle, and drives the bucket wheel at high speed.
A ramming air inlet duct supplies air to the impeller which increases its pressure and temperature. However, in order to avoid detonation at the carburetor, the air supplied to the carburetor passes through the intercooler, where the temperature is reduced. The internal engine impeller, driven by the engine crankshaft, again increases air pressures as it enters the intake manifold. High intake manifold pressure results in greater power output.
Supercharger Regulator Operation
The amount of turbo boost is determined by the speed of the turbo bucket wheel, and the speed of the bucket wheel is determined by the pressure difference between the atmosphere and the exhaust in the tailstack, and by the amount of gas passing through the turbine nozzles. If the waste gate is opened, more exhaust gas passes to the atmosphere via the waste pipe and decreases the tailstack pressure.
Electronic Turbo-supercharger Control
The electronic turbo-supercharger control system on B-29s consists of separate regulator systems, all simultaneously adjusted by a single turbo selector dial located on the pilot's aisle stand. Each system controls the induction pressure of the particular engine through a Pressuretrol unit connected directly to the carburetor air intake.
Electrical power for the entire system comes from the airplane's 115-volt, 400-cycle inverter.
Each regulator includes a turbo governor which prevents turbo overspeeding both at high altitude and during rapid throttle changes.
Both exhaust waste gates on each engine are operated by a small reversible electric motor which automatically receives power from the regulator system when a change in waste gate setting becomes necessary to maintain the desired manifold pressure.
In case of a complete failure of the airplane electrical system, or failure of the inverter, the waste gates on all engines remain in the same position as when failure occurred, and approximately the same manifold pressure that was in use at time of failure, is available.
If a failure occurs in any one the electronic regulator systems, provision is made for the waste gate motor to drive the waste gate to the open position, and no supercharger boost is available on that particular engine.
Upon installation of the equipment, the system is adjusted so that a selector dial setting of 8 furnishes maximum desired takeoff power. A dial setting of 10 furnishes maximum emergency power.
All engines should deliver the same power at a dial setting of 8. If it is necessary to adjust power on individual engines, use a screwdriver to turn the calibration screws located on the turbo selector dial unit.
HIGH ALTITUDE OPERATION
When flying at high altitude, you may reach a point where further turning of the selector dial fails to produce an increase in manifold pressure. This means that the overspeed portion of the turbo governor is limiting the turbo speed to safe rpm. When you encounter this condition, turn the manifold pressure selector dial counter-clockwise until it controls manifold pressure again. This prevents undue wear of the overspeed governor mechanism.
You can obtain full emergency power (war power) at maximum engine rpm and full throttles by releasing the dial stop and turning the selector to setting 10. However, this setting places heavy strain on the engines and must be used only in emergencies and then only for periods not exceeding 2 minutes.
HIGH ALTITUDE OPERATION OF THE B-29
Compressed air for supercharging the fuselage compartments is supplied by the inboard turbos of the inboard engines. After compressed air passes from the impeller into the carburetor air duct, some of the compressed air is directed through the cabin air duct, through the aftercooler, and into the cabin through the cabin air valve. This happens only when the cabin air valve is open.
When the cabin air conditioning system is used, the aftercooler flap is closed to provide heat, opened to provide cooling. With the aftercooler flap closed, hot air from around the exhaust collector ring is directed through the aftercooler to heat the cabin air. With the aftercooler flap open, cool air is directed through the aftercooler, overcoming heat of compression and reducing the temperature of the cabin air.
Air is released from the cabin by two automatic regulators in the rear pressurized compartment, which maintain the following cabin pressures:
0 to 8000 feet-Pressure differential of 1".
8000 to 30,000 feet-Cabin altitude 8000 feet.
30,000 to 40,000 feet-Cabin altitude increases from 8000 feet to 12,000 feet.
Cabin-pressurizing controls and indicators are located at the flight engineer's station ...
The job of pressurized and depressurizing (except in emergencies) belongs to the flight engineer. He mast watch outside and cabin altimeters outside and cabin rate-of-climb indicators, cabin differential pressure gage, and cabin air rate-of-flow gages.
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