LUBRICATION SYSTEM B-17 Technical Session for Flight Engineers 10/14/2017

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1 LUBRICATION SYSTEM B-17 Technical Session for Flight Engineers 10/14/2017 The Lubrication System, and most everything else, is described in B-17 MANUALS published by the Army. Note that these Manuals were published in 1943 and TR was built in 1945 with modifications since, so there are differences. Also we have added to the system to improve engine longevity. Significant among those additions are a pre-oil pump and an in-line spin-on oil filter. Different also is the lube oil cooler regulates the oil temperature with partial oil bypass rather than with variable louvers on the cooling air flow. And, the oil dilution system (diluting the engine oil with gasoline to lower the viscosity for cold weather starting) is no longer functional. B17s were built with FOUR independent lubrication systems one for each engine. The significance is that failure in one system has no effect upon the other three systems. All of the four systems are virtually identical. A flow diagram of the lubrication system follows: 1

2 The Lubrication System is a circuit where lubrication oil is pumped into the engine, then pumped out to filtering, cooling, loss make up and then back to the engine again. In addition to lubricating the engine it also helps with cooling. Each lubrication system has the following components: Oil Pump. This is an engine driven gear pump which has an internal pressure relief valve set at 85 PSI. The pump is engine driven; therefore, the oil pressure is zero at engine start and builds up with RPM. Cuno Filter. The oil pump feeds into the Cuno Filter. The Cuno filter is a series of small mesh screens and is checked / cleaned at routine maintenance intervals. The Cuno Filter output feeds directly into the engine. Oil Pressure Transmitter The oil pressure tap is between the Cuno Filter and the inlet to the engine. (This is the point of highest pressure throughout the lubrication oil circuit). The transmitter converts oil pressure (PSI) to an electrical signal which is then read on the Oil Pressure Gauge (gauge located on the co-pilot instrument panel). The oil pressure measured is the feed pressure into the engine. [On the instrument panel there are actually two gages, each with two indication needles thus showing the oil pressure for four engines] Scavenger Pump Oil passes through the engine then accumulates in the engine sump (this is a dry sump engine meaning spent oil is removed from the engine to an oil tank). All of the oil pressure generated by the Oil Pump is consumed in passing through the engine meaning the oil pressure in the sump is zero. The Scavenger Pump then takes the oil and pushes it on to the Oil Tank. The Pump is engine driven (i.e. only operates when the engine is running) Note: The Oil Pump and the Scavenger Pump are both housed in the same case and that bolted to the back of the engine. One shaft drives both pumps. Spin-On Oil Filter This is a cartridge type which filters to a finer degree than the Cuno Filter. This is checked / replaced during at routine maintenance intervals. The Scavenger Pump pushes the oil through this filter. A magnet is strapped to this filter to further extract particles from the oil. Oil Cooler The oil is hot when it leaves the engine. This cooler regulates the oil temperature down to maintain an appropriate viscosity of the oil. The Scavenger Pump pushes the oil through this cooler. The cooler is mounted in the leading edge of the wing. Oil Tank The engine uses oil as it runs so a reservoir of stand-by oil is necessary. Also surge capacity is needed due to varying flow rates between the oil pump and the scavenger pump. The Tank has a temperature acceleration well. This is a pipe that goes from the top oil inlet to the bottom oil outlet there are small holes in the pipe near 2

3 the top and the bottom. What this does is allow the operating part of the oil to reach operating temperature quickly thus, not necessary to heat up the entirety of the oil to minimum operating temperature prior to departure. (a time and fuel saver). Oil Temperature Transmitter The oil temperature tap is between the Oil Tank outlet and the inlet to the Oil Pump. (This is the point of coolest temperature throughout the lubrication oil circuit). The transmitter converts oil temperature to an electrical signal which is then read on the Oil Temperature Gauge (gauge located on the co-pilot instrument panel). [On the instrument panel there are actually two gages, each with two indication needles thus showing the oil temperature for four engines. Prop Feather Pump The propeller is fathered by a side system off the Lubrication System. Oil is tapped off the lubrication circuit to feed the electric motor driven Feather Pump. The Pilot operates this action it is not automatic. The prop can be feathered regardless of what is happening with the engine just so long as there is oil in the Tank. Pre Oil Pump This gives the engine a shot of lubrication prior to engine start. The pump is electric motor driven operated by the Pilot. Lubrication System Operation; The Oil Pump and the Scavenger Oil pumps move the oil through the lubrication circuit and only when the engine is running. The Pilot has no control over the flow of oil through the lubrication system. Some Operation Notes: The Pre-Oil Pump lubricates prior to turning the engine. This is particularly important when the engine has been sitting for while and has the opportunity to become dry most notably this would be done before rolling-the-props and the first engine start of the day. Use of the pre-oil pump after that is per Pilot direction. Note that the Pre-oil Pump pushes oil into the engine. Oil coming out of the engine doesn t happen because the scavenger pump, which pulls the oil out of the engine, is engine driven and therefore not running. Extended use of the pre-oil pump can over-fill the engine with oil. need to be careful. The Oil Pressure Gauge reads the highest pressure in the oil circuit. The oil pressure is affected by oil temperature (cold oil is thick oil thus taking higher pressure to push it through the engine and vice versa). The gauge reads in PSI and has a GREEN arc for the OK operating range. The oil pressure operating range (at operating oil temperature) is 55 to 85 PSI. (Red lines at 55 PSI minimum and 85 PSI maximum). 3

4 There is an optimum operating oil temperature range - which is why the pilots hold the engines at idle after start for a period of time just to warm up the oil. The Oil Temperature Gauge reads in degrees Centigrade and has a GREEN arc for the OK Operating range. The operating oil temperature range is 60 deg C to 87 deg C (Red lines at 40 deg C minimum and 95 deg C maximum). Oil pressure is to be in the GREEN within 30 seconds of engine start. If not, the engine is to be shut down! All four engine oil pressures and temperatures are to be in the GREEN before TAXI commences. Watch those gauges. High oil pressure usually indicates oil passages within the engine are plugged. a no fly situation. Low oil pressure usually indicates a plugged Cuno filter, oil temperature to high, oil pump relief valve not right, a big leak somewhere, or wear in the engine. Oil temperatures not within the limits usually indicates a problem with the oil cooler. If the spin-oil oil filter becomes plugged, that will not be noted on the oil pressure gauge. This filter has an internal bypass which, when plugged, will continue to pass oil to the oil tank and the circuit continues. The oil tank is vented back to the engine, meaning any vapors that accumulate in the oil system, excessive or otherwise, will manifest at the crankcase vent port (the port right on top of each engine nacelle). Note a troubled engine will first show signs here, plus falling oil pressure and rising oil temperatures. Exhaust smoke is also another indicator. Maintenance / Repair of Lubrication System components: (Note: A & P). All FE maintenance / repair is done subject to the overview and approval of an There are components in the lubrication systems that are black boxes. A black box is a component that requires a certified shop to disassemble for repair. From an FE s vantage point, these components either work or they don t. If they don t work, the fix is to replace them with another that does. Maintenance on the interconnecting hoses, electrical connections and adjustments for these components however can be done by an FE supervised by an A & P. Black boxes in the lubrication system are: Oil Pump, Scavenger Pump, Oil Cooler, Pre- Oil Pump, Feather Pump and Transmitters / Gauges. 4

5 Oil Consumption: The engines consume oil. hour. Normally this is about ONE gallon of oil per Hobbs time Oil that is burnt inside the cylinders is exhausted as grey (or white) smoke. By comparison, un-burnt fuel exhausts as black smoke. Smoke is normal at start up. Virtually no smoke is normal in flight. Leaks also happen. The measure of small leaks is the mess it makes on the fuselage of the airplane. Big leaks will likely cause the oil pressure to drop and make a big mess. FE s fix leaks. Oiling TR FEs oil TR. There are FOUR independent oil systems. Each time the airplane is fueled, the four oil tank levels are checked (with a calibrated dip stick). All four tanks should have the same amount of oil at pre-depart (checked during preflight inspection) Maximum oil to be in a tank is 37 gallons (there is room for more but that is reserved for the expansion of the oil when it becomes hot). Minimum amount of oil in a tank before permissible take-off is 20 gallons. FEs add oil only when directed by the Pilot. (Make up oil is usually carried onboard the airplane). The oil is 120 AD (Ashless Dispersant) aviation oil. Mineral oil is used temporally for a fresh engine break-in period. Oiling of TR is managed, and reported to the pilot, by use of the FUEL / Engine OIL / LOAD WORKSHEET. This form is used for every pre-flight inspection AND every time oil is added. The WORKSHEETS are to be sequentially numbered and retained in a binder in the airplane. Side Note: All four tanks depart with the same amount of oil. All four engines are identical. Therefore, in a perfect word, all four tanks always would have the same amount of oil remaining at any time. This rarely happens for multiple reasons, but the post flight tanks should all have about the same amount of oil A big difference in post flight oil is a Red Flag the FE needs to understand why that difference occurred before proceeding. A big difference is about 10 gallons.. 5

6 FE Operational Awareness summary regarding the Lubrication System The Lubrication System in flight is mostly automatic other than engine shut-down, the Pilot has no controls over the lubrication System However, observe the following and all should be OK: 1. Watch the oil pressure and temp at engine start. If there is NO pressure or slow to rise, an engine shut down should follow 2. Watch the oil temperature after engine start. It needs to rise to operating temp (into the GREEN) on all four engines before TAXI begins. 3. Watch the oil pressures and temps in flight they should stay within the operating ranges. Note the readings from one flight day to the next and advise the Pilot of any significant differences even if the readings are still in the OK operating ranges (i.e. within the GREEN on the gauges) 4. Watch the exhaust and oil dribbles in flight for anything unusual. 5. Watch the crankcase vents in flight for anything unusual. FE: Lee Brown Approved: Pilot A & P 6