Napier Deltic

One problem with the Sea Lion and similar engines fitted in the high speed vessels during WW2 was the fact that most were fuelled with petrol.  As fuel tanks emptied the remaining air combined with fuel to produce a highly inflammable mixture. This issue was graphically proven to the Allies in Oostende on 14th April 1945 when petrol in the dock ignited and destroyed 12 MTBs, damaged 5 more, killed and injured 73 and 84 people respectively.  Unlike the Allies, German fast boats (Schnellboote) were powered by diesel engines.  A team of experts was convened under the chairmanship of Sir Roy Fedden to research put forward a proposal for a lightweight diesel engine for marine use.  Members included Herbert Sammons who was Chief Engineer and later MD of DNS whose influence certainly was to have helped the Company.  They produced ‘The Final Report of the M.T.B. Power Unit Committee from October 1943 to March 1944’ which recommended a 75 – 80 litre sleeve valved 2-stroke supercharged engine of 2,500 HP.  The valve gear was to be of the open-ended sleeve type and the geometric layout to be of the H type using two crankshafts geared to a common drive shaft.  This engine uncannily resembled a diesel version of the Napier Sabre engine and D Napier & Son were recommended to develop this new engine for the next design of MTB for the Royal Navy.  However, the English Electric Company had technical arguments against the Fedden proposition and offered an alternative inverted delta opposed-piston engine.  The E.E.Co. offer  stated precisely that D. Napier & Son would undertake the design, development and manufacture of the proposed engine.

Napier’s unique solution was based on three Napier Culverin aero-engine arranged in a triangular fashion and connected at each corner by a crankshaft.  The engine was a two-stroke opposed piston compression ignition (diesel) engine having three or six banks of three cylinders in a triangular arrangement.  At each corner of this equilateral triangle is situated a crankshaft, each crank having an exhaust (fork) and inlet (blade) connecting rod from the two adjacent cylinders.

Design of the E130 Deltic commenced in 1946 after D. Napier  Son received a contract from the Admiralty to design, develop and manufacture :-

(a)     Single Cylinder Unit (One leg of the Deltic)

(b)     3 Cylinder Unit (One slice of the Deltic)

(c)      6 x full size 18-Cylinder prototype / development engines

George Murray designed a Single Cylinder Unit between October and December 1946 followed by the 3-Cylinder Unit between January and May 1947.  The Single Cylinder unit ran successfully from January 1947 onwards.

The 3-Cylinder test unit ran from October 1947 onwards, with a great deal of trouble caused by unbalanced forces and couplings causing excessive vibration.  The firing in the Crankshaft degrees was as follows:

”  * 40 degree     * 40 degrees     * 270 degrees     * 40 degrees     * 40 degrees     * 270 degrees,  etc  ”

This unit was abandoned but it did prove the design of the fork and blade connecting rod assembly.  In the meantime, the Scavenger Blower was designed, manufactured and rig tested from November 1947 onwards.  The main engine design also proceeded and was completed by the end of 1948.  Around this time a compounded 18-cylinder version was considered and Single Unit Tests were run.

The first engine, designated D18/1 was designed to produce 2,500 BHP at 2,000 RPM and was the prototype Deltic 18-11B intended for installation in new Royal Navy Dark Class motor torpedo boats for which the engines were designed. It first ran on the test bed in April 1950.

The Minesweeper version of the engine was designed and also the 9-Cylinder Pulse Generator Set.  Two of the six development engines built at Napier’s Acton Works were installed in an ex-German E-boat (RN Pennant P5212) at HMS Hornet and ran extensive sea trials from late 1951 onwards, proving the Deltic as a successful design.

The Deltic engine design was fit for purpose and is still in use today fitted in the Royal Navy’s Hunt Class Mine Counter Measures Vessels.  Whilst these boats are currently going through a modification process which includes the fitting of Caterpillar engines, it is incredible to think that 2016 will see 70 years since design of the engine commenced.

The sound (and feel) of Deltic engines can still be experienced today as six British Railways Type V ‘Deltic’ locomotives are preserves.  Furthermore a 9-cylinder Baby Detlic is being recreated.  In the USA there is a long term project to restore a US Navy Nasty Class MTB – PT3.

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