10-12-2021, 09:42 PM
It is no accident that the jets are mounted where they are so as to recharge the crankshaft oil way immediately prior to the point of maximum loading. Also that the oil way is of generous proportions to act as a reservoir to provide oil for a complete revolution of the crankshaft before recharging.
Compare the jet lubrication of the Seven with a steam locomotive or the Rolls Royce Merlin engine and you appreciate it's simplicity. If we take one of the most famous locomotives, the world steam speed record holder Mallard, each big end has an oil well which was filled up prior to leaving the shed and the oil was fed to the bearing via a felt pad. This had to last for 408 miles ( May 1948) whilst running at 200-300 RPM and producing in the order of 1500 horsepower on the non stop Flying Scotsman. Few people know that Mallard suffered a big end failure during its record breaking run 3 July 1938 when running at 126 MPH or 523 RPM, which was basically a design flaw corrected by a ex Great Western Railway Engineer in the 1950s.
On the other hand I am interested in aircraft, particularly those with reciprocating engines and their lubrication when flying inverted. So I was interested to read in “Hives and the Merlin” by sir Ian Lloyd and Peter Pugh about the problems of big end failure on the Merlin. This was a real head scratcher and was finally solved by Wing Commander Boyd of Boscombe Down and I quote from the book. “He took an aircraft up to 30,000 feet, rolled it on it's back, thus loosing oil pressure, over-revved to 3600 RPM and, with a slight negative G force all the way down, held this condition. This meant that the engine was exceeding maximum RPM for at least 30 seconds whilst starved of oil.” unquote. If it took that to run a big end on a Merlin then I feel sure the Austin lubrication system is more than adequate, so less of the hope please. Wing Commander Boyd was a brave man.
Compare the jet lubrication of the Seven with a steam locomotive or the Rolls Royce Merlin engine and you appreciate it's simplicity. If we take one of the most famous locomotives, the world steam speed record holder Mallard, each big end has an oil well which was filled up prior to leaving the shed and the oil was fed to the bearing via a felt pad. This had to last for 408 miles ( May 1948) whilst running at 200-300 RPM and producing in the order of 1500 horsepower on the non stop Flying Scotsman. Few people know that Mallard suffered a big end failure during its record breaking run 3 July 1938 when running at 126 MPH or 523 RPM, which was basically a design flaw corrected by a ex Great Western Railway Engineer in the 1950s.
On the other hand I am interested in aircraft, particularly those with reciprocating engines and their lubrication when flying inverted. So I was interested to read in “Hives and the Merlin” by sir Ian Lloyd and Peter Pugh about the problems of big end failure on the Merlin. This was a real head scratcher and was finally solved by Wing Commander Boyd of Boscombe Down and I quote from the book. “He took an aircraft up to 30,000 feet, rolled it on it's back, thus loosing oil pressure, over-revved to 3600 RPM and, with a slight negative G force all the way down, held this condition. This meant that the engine was exceeding maximum RPM for at least 30 seconds whilst starved of oil.” unquote. If it took that to run a big end on a Merlin then I feel sure the Austin lubrication system is more than adequate, so less of the hope please. Wing Commander Boyd was a brave man.