Engine Installation for Supersonic Aircraft


Factors affecting supersonic aircraft engine positioning.

The presence of volume-dependent wave drag means that the location of the engines may make a large difference to drag. In particular, interference of the nacelles with the fuselage, wing, and other nacelles is very sensitive to the relative position and orientation of the nacelles. The nacelle placement for supersonic aircraft can take advantage of favorable interference and detailed studies have shown that aft wing placement of engines can reduce the drag of the installation to little more than that associated with the skin friction drag of the nacelles.



Some of the interference effects are listed in the table below:

Effects of Nacelle on Lift and Drag
Interference Drag
Interference Lift

Nacelle Pressure Drag
Nacelle Interference
Increases Wing Lift

Nacelle-On-Wing/Body
Interference
Wing Interference
Decreases Nacelle Lift

Wing-On-Nacelle
Interference
  

Mutual Nacelle Interference
Adjacent Nacelles
Self-Interference
from Wing Reflection
 



In addition to wave drag and lift considerations, nacelle placement is influenced by a variety of practical considerations such as:

Inlets must be placed away from main gear to avoid excessive water ingestion.

Inlets must be located in an area ofd the wing with uniform flow, away from the leading edge shock to assure inlet stability. The inlets are often separated from each other laterally to improve the inlet stability as well.

The longitudinal position is constrained by structure, ground clearance, rotor burst, and flutter considerations. The spanwise position is governed by these same issues as well as engine-out yawing moment.

Nacelle Design

The nacelle size for SST engines follows different rules from those of subsonic engines. Nacelles tend to be much longer because of the length dependence of wave drag and because more substantial speed reduction must occur in the inlet. Typical inlet losses are still much higher than for subsonic inlets. Initial nacelle sizing can be based on many previous detailed studies and experience with the Concorde.

Some data on a Turbine Bypass Engine (from 1992 Langley AIAA Paper), based on: Onat, E.; Klass, G.W.: A Method to Estimate Weight and Dimensions of Large and Small Gas Turbine Engines. NASA CR 159481, 1979.

TBE Sample Engine Summary
Design Mach Number: 1.6 2.0 2.4
       
Weights:      
Bare Engine + Accessories, lb 9,252 9,278 9,567
Inlet / Nacelle, lb 1,343 2,243 3,837
Nozzle, lb 4,O0O 4,000 4,000
Total, lb 14,596 15,521 17,424
       
Nacelle Dimensions:      
Length, ft 31.83 31.74 34.92
Maximum Diameter (at engine), ft 6.20 6.20 6.20
Reference Diameter (at exit), ft 4.47 4.96 5.92
Inlet Capture Diameter, ft 4.53 6.01 5.52
Maximum Area, ft2 30.19 30.19 30.19
Reference Area, ft2 15.69 19.32 23.93
Inlet Capture Area, ft2 16.12 19.71 23.93
       
Performance (installed):      
Takeoff:      
Design Corrected Mass Flow, lb/sec 700 700 700
Installed Net Thrust, lb 70,610 69,035 65,482
Overall Pressure Ratio 29.07 29.18 18.93
Specific Fuel Consumption lb/hr/lb 0.8756 0.8728 0.9293
Cruise:      
Cruise Altitude, ft 45000 55000 65000
Installed Net Thrust, lb 29,628 21,911 18,955
Overall Pressure Ratio 27.50 21.30 12.04
Specific Fuel Consumption, lb/hr/lb 1.1177 1.1991 1.3098
Overall Efficiency, percent 34.51 40.21 44.18