# Nacelle Group Mass

Engine thrust = 17,230 N (3,800 lb) per engine with a BPR < 4.

Mnac+pylon = 6.2 x thrust (kN) per nacelle = 6.2 x 17.23 = 106 kg per nacelle Two nacelles = 212 kg.

8.11.2 Undercarriage Group Mass

MTOM = 9,500 kg low-wing mount; MU/C_wing = 0.04 x 9,500 = 380 kg

8.11.3 Miscellaneous Group Mass

Fortunately, there are no miscellaneous structures in the examples considered herein.

8.11.4 Power Plant Group Mass

This is determined from statistics until it is sized in Chapter 10. A typical engine is of the class Allison TFE731-20 turbofan with thrust per engine = 15,570 N to 17,230 N (3,500 to 3,800 lbs).

If a manufacturer’s dry weight is available, it is better to use it rather than semi-empirical relations. In this case, the manufacturer’s dry weight is in the public domain. MdrYeng = 379 kg per engine. This gives:

(T/ Wdry_e„gine) = 17,230/(379 x 9.81) = 4.63

The total power plant group mass can be expressed semi-empirically as

Meng per engine = 1.5 x MdrYeng per engine = 1.5 x 379 = 568.5 kg.

For two engines, Meng = 1,137 kg.