Lift Turbo-fans

Summary:

In the past decade many powerplant systems have been proposed for VTOL aircraft. Of these, flight tests have shown the lift jet and vectored thrust engine to be practical and suitable for forming the basis of operational VTOL military strike aircraft. High on the list of proposed VTOL powerplant systems is the lift turbo-fan which has the inherent advantages of better hover fuel consumption, lower efflux velocity and lower jet noise. So far there has been no practical demonstration of this type of powerplant in Europe, and it is useful to look at some of the studies that have been made to compare the characteristics of the lift fan and the lift jet.

The paper compares the Rolls-Royce RB 162 16:1 thrust/weight ratio lift jet and its installation with a range of Rolls-Royce lift fans derived from the RB 162 using the latter as the gas generator.

The comparisons between the basic engines reveal the fan to have worse thrust/volume, thrust/weight and response rates. The installation of these engines in a lift pod is fully described showing the equipment required for complete VTOL powerplant. A comparison of the Installed weight breakdown for the two types of pod is made. Some of the advantage of the fans’ inherently lower fuel consumption is lost in the longer take-off transition time which accrues from the higher momentum drag of the lift fans and higher pod drag.

Looking to the future, the authors suggest fan engines based on more advanced gas generators and having a greater degree of ingenuity to minimise the weight and volume penalties.