MEDWAY AIRCRAFT PRESERVATION SOCIETY Ltd

Pobjoy Niagara Engine

​

Unfortunately we do not have an entire engine but what we have has been cleaned and restored to a very high standard.  Should anyone know of another Pobjoy Niagara lurking anywhere, please contact MAPSL.  

​While working at the RAF college at Cranwell, Douglas R Pobjoy was asked to design a small and efficient engine for the college's light aircraft project; this later was developed into the Comper CLA7 Swift.  Building a prototype engine in his workshop at Minster-on-Sea on the Isle of Sheppey, he allowed it to run for 120 hours before submitting it to the Air Ministry for a further 50 hour test.  Passing all its tests, he established a small factory at Hooton Park, Cheshire in 1930 and production of the Pobjoy ‘R’ began.  Short Brothers bought Pobjoy's in 1935.  Later, factories were also established at Northfleet and Rochester Airport, close to the Short Brothers' factory.

​

In 1932, Short Brothers had plans to build a twin engine high wing monoplane to carry five people.  Known as the Short Scion, it was to be powered by two Pobjoy engines of a later mark and known as the Pobjoy Niagara, which gave an increased power to 90HP.  Today, the workshop of MAPSL has one of the last remaining examples of this engine, which has been refurbished and motorised for display purposes.  This particular engine had been sent to the Netherlands for use in a single seat aircraft.  It was at the University of Delft at the outbreak of the war and the only manner in which it could be saved from destruction when the Germans annexed the Benelux countries was to section it as an exhibit and training aid.  Subsequently, it was owned by the family of a former professor from the university until it was purchased by MAPSL in 2015.   Some additional parts are 3-D printed.   

 

For the technical-minded, the engine is a seven-cylinder, four-stroke radial producing 93 HP from a swept volume of about 2900 cc at 3200 rpm, using 'standard grade' petrol of the 1930's, with a weight of about 70 kg (155 lb).  The cylinders are in the same plane, ideal for direct air cooling.  One piston drives a master connecting rod to which the other six are articulated, forming a very compact crankshaft.  The reduction gearbox at the front allows both the engine and the propeller to run at their optimum speeds.  The inlet and exhaust valves are driven by a pair of the cam rings located behind the cylinders.  Dual magnetos, distributors and spark plugs are fitted and there is provision for one or two fuel pumps.   Starting is manual or an electric starter can be fitted.  Novel features include a centrifugal oil filter mounted within the flywheel.  ​

The first batch of images show the rebuild from its arrival when it was just a collection of parts, with some assembled.  The second batch of images show the final assembly, mainly after motorisation - operation of most parts can clearly be seen.  ​​