Rolls-Royce motoren

Informatie over de Rolls-Royce Dart motoren in de Fokker F27 Friendship vindt u hieronder.

Tekst in het Engels.

Since early 1957, the beginning of Fokker F27 Friendship operation, the performance has been gradually improved. The aircraft is characterized by a variety of mark numbers and engine combinations. When the F27 first entered service, it was powered by Rolls Royce Dart 6 Mk511-7 engines. In the following years, two more Dart 6 variants were introduced: the Mk511-7E and the Mk-514-7.

In 1959 the more powerful Dart 7 (R Da7 Mk-528-7E) was introduced on the F27. The main differences with the Dart 6 are:

– three-stage i.e. two-stage turbine

– directly coupled reduction gear

– increased LP diffuser throat area

– increased HP impeller diameter

– increase of flame temperature by 30º C

– turbine gas temperature reading i.e. jet pipe temperature reading for higher accuracy in engine control


The Mk-532, Mk-536 and the Mk-535 engines are developed from the Dart 7 Mk-528-7E. They differ in take-off ratings and maximum continuous power. The Mk-536 has an intermediate contingency rating. As the FAA does not accept intermediate contingency ratings, the Mk-536 is not certificated under FAA rules. For high elevation airports (over 9.000 ft) the special Mk-536-7P rating was developed. This rating is not FAA certificated as well.

In October 1984, Fokker introduced the more fuel efficient Dart 7 Mk-551 engines on the F27. The major change, relative to earlier Dart 7 engines, to improve airflow in the compressor section, the number of low- and high pressure diffuser vanes was increased and their aerodynamics improved; a new interstage guide vane casing was also introduced. The three-stage turbine was rematches to the advanced compression system, and modified low pressure turbine blades (NV-controlled Nimonic 115, together with flame tubes in Haines-188, a high quality material), was introduced as well as changing the inlet nozzle guide vanes.

All existing Dart RDa 7 engine ratings could adopt Mod 1850, thus improving engine efficiency and reduction of fuel consumption. Engine rating as such and water-methanol consumption remained unchanged. In this way the MK-551 engine could achieve Mk-536 power ratings with a reduced air mass flow and a reduced fuel flow at lower turbine temperature.

During development of the Mk-551 engine, it was discovered that further improvements to the compressor were possible. This has led to the Mk-552 engine which in fact an improved version of the Mk-551. The Mk-552 engine offers the same power ratings as the Mk-551 at a further reduction in fuel consumption.

All existing RDa 7 engine ratings could adopt Mod 1860, improving engine efficiency and reduced fuel consumption. Especially beneficial to operators flying long distance flights or to Fokker Troopship / Fokker Maritime operators who should be enabled to increase mission range. Engines incorporating the Mod 1860 kit could be up-rated. In general, the RDa 7 Mk 552 engine was recommended to those operators who, for operational reasons, required the higher wet power.

Briefly summarizing the advantages of this latest Dart RDa 7 development in the eighties, can be described as follows: The aforesaid changes indeed resulted in an engine that achieved the power ratings of the RDa 7 versions while reducing air mass flow and cutting down fuel flow at lower turbine temperatures , which resulted in increased dry engine ratings, and consequently reduced water/methanol consumption during take-off and increased power during climb and cruise, even in the higher temperatures of desert environments.

When the same engine rating was retained, and Mod 1860 only were introduced, aircraft performance remained unchanged. Only result was a fuel consumption reduction of some 10% over an average one-hour flight. In many cases no water-methanol or only a small quantity had to be carried, meaning that the payload could be increased by the appropriate weight

By May 1989 some 130 engines had been converted to Mod 1860 or Mk 552 for 16 customers and the continuing committed programme for conversions extended to 1993. It should come as no surprise to learn that the bulk of the Mod 1860 / Mk 552 committed customers were Fokker F27 operators.