In the Winter 2005 Issue of
Pobjoy
British light aviation in the years between the World Wars is very nearly the story of one family of engines. The one dissenting voice was David Pobjoy. He was happy to accept that an inline air cooled four on Halford/de Havilland lines would always be cheaper than his high revving seven-cylinder geared radial. However, he believed that this very real advantage would be outweighed by the lighter weight and lower lifetime cost of his preferred design.
His first engine, the P, was originally intended to power the Cranwell CLA4 designed by Nick Comper for the 1926 Lympne trials. It is appropriate that the popular Comper Swift was later a significant Pobjoy user. The P passed its civil type test in late 1928 and entered production in 1930. The neat little 2.5 litre (152 cu in) 67 hp P grew up into the R and later the Cataract and Niagara series, finally producing 130 hp from 3.13 litres (191 cu in). The earlier engines are particularly identified with the delightful Comper Swift, but powered a variety of other light sporting aircraft and experimental autogiros as well as the twin-engined General Aircraft Monospar.
My Wife Calls it an OBSESSION !!!!
Part 1: BP 75 and Bristol Aquila
Anyone who has run a small business will be aware of the frustrations involved. So to stop myself losing my mind I started to build radio control model aircraft which over the years became bigger and bigger. Eventually, I fell for the Popular Flying Association’s advertisement, “Now you have built a model why not build a full size aircraft?” The aircraft chosen was Max Brugger’s Colibri powered by a 1600 cc VW.
I really enjoyed the building but, due to a number of things (mainly the building of a new bungalow) I no longer had time or money for flying. The aircraft was sold on. The next few years passed in a blur of painting, gardening, gardening and gardening until suddenly I realised that I should be thinking of what to do when I retired. I still had copies of the Colibri drawings and it occurred to me that it would be rather nice to build a model of the aircraft exactly as the full size but of course to do this I needed a flat four, four-stroke engine. The start of the OBSESSION!!!!!
Images of Brian Perkins' BP 75 and Bristol Aquila model engines.
Aero Engine Drawings by Frank Munger
An Aero-Engine that “Never Was”
The Fabulous Packard “A-833”
It
hardly needs saying that for every aero-engine design that actually makes it
into production, there are always scores of others, which for one reason or
another, fall by the wayside. Some designs never get further than human
imagination; others get sketched out onto paper and binned; some are drawn up as
meaningful written proposals only to be rejected by Boards or Committees. Only a
tiny percentage are lucky enough to find the right combination of suitability,
acceptance, funding and manufacturing capability that allows even a prototype to
be constructed.
The Packard “A-833” was designed by Lionel Woolson in 1923, probably his first attempt at a complete engine. This project certainly got further than the dream or paper sketch stage but it was never built and in all probability it wasn’t even blueprinted. However, Woolson was sufficiently proud of his creation to file a patent application in 1923 which was subsequently granted in 1929. Today, the patent document is the only remaining evidence of this interesting engine. The patent documents describe and illustrate only the structural features of the motor - no performance or dimensional figures are given. However, if the spark plugs in the drawings are standard 18mm types, then the cylinder bore works out at about 5 5/16” (135 mm) and the stroke, 6 1/4” (159 mm) to give a capacity of 833 cu in (13.66 l). In line with the standard reference system used by Packard to identify their engines, it would therefore have been denoted as A (for aircraft) 833. The first production model would have been 1A-833; the second 2A-833 and so on.
Early Axial Flow Turbojet Engines
The early concepts and application of the centrifugal and axial-flow turbojet
engines were discussed in the Torque Meter Vol. 2, No. 3. Here, we look at the
further development and application of the single-shaft axial-flow turbojet
engines, with a glance at the first of the twin-shaft turbojet developments. To
allow the turbojet engine to meet various flight demands, it was found that a
twin-shaft design, with concentric drive shafts, would allow the low-pressure
(LP) turbine, driving the front fan and low-pressure (LP) compressor, to reach
its optimum operating speed, while the high-pressure (HP) turbine, driving the
high-pressure (HP) compressor, could then find its own optimum operating speed.
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