Empennage Group – Civil Aircraft
H – and V-tails also are lifting surfaces and use semi-empirical equations similar to those used for the wing. The empennage does not have an engine or undercarriage installation. It may carry fuel, but in this book, fuel is not stored in the empennage. The drivers are the same as those in the wing group mass.
Equation 8.20 is modified to suit the empennage mass estimation. Both the H – tail and V-tail plane mass estimations have a similar form but they differ in the values of constants used.
MEMPcivil = 0-0213 x (MTOM x nult)0-48 x Sw0-78 x AR x (1 + k)0-4/(CosA x t/c0-4)
If nonmetals are used, then mass changes by the factor of usage. For example, x% mass is nonmetal that is y% lighter, the component mass would be as follows:
MEMPcivil nonmetal — MEMPcivil – x/y x MEMPcivil + x x MEMPcivil (8.24)
In a simpler form, if there is reduction in mass due to lighter material, then the mass is reduced by that factor. If there is a 10% mass saving, then:
MEMcivil_nonmetal — 0-9 MEMcivil „all metal
Writing the modified equations in terms of this book’s nomenclature, Equation 8.23 is changed to the empennage for an H-tail and a V-tail as follows. For all H-tail movement, use kconf = 1.05; otherwise, 1.0.
Mht = 0-02 x kconf x (MTOM x nult)0 48 x Sw0-78 x AR
x (1 + k)0-4/(CosA x t/c0-4) (8.26)
For V-tail configurations, use kconf = 1.1 for a T-tail, 1.05 for a midtail, and 1.0 for a low tail.
MVT = 0.0215 x kconf x (MTOM x nult)0-48 x Sw0-78 x AR x (1 + k)0-4/(CosA x t/c0-4)
8.10.1 Nacelle Group – Civil Aircraft
The nacelle group can be classified distinctly as a pod that is mounted and interfaced with pylons on the wing or fuselage, or it can be combined. The nacelle size depends on the engine size and type. The nacelle mass semi-empirical relations are as follow.
Jet Type (Includes Pylon Mass)
For a BPR greater than 4.0, MNAC_jet = 6.7 x thrust (kN) per nacelle. (8.28)
For a BPR less than 4.0, MNAC_jet = 6.2 x thrust (kN) per nacelle. (8.29)
Pods are slung under the wing or placed above the wing with little pylon, unless it is an aft-fuselage-mounted pusher type (e. g., Piaggio Avanti). For the same power, turboprop engines are nearly 20% heavier, requiring stronger nacelles; however, they have a small or no pylon.
For a wing-mounted turboprop nacelle:
MNAC_pr0p = 6.5 x SHP per nacelle (8.30)
For a turboprop nacelle housing an undercarriage:
MNAC^prop-U. c = 8 x SHP per nacelle (8.31)
For a fuselage-mounted turboprop nacelle with a pylon:
MNAC_prop = 7 x 4 x SHP per nacelle (8.32)
For tractor types, the nacelle is forward of the engine bulkhead; for pusher types, it is aft of the engine bulkhead – both have an engine mount. This mass is not considered a fuselage mass, even when it is an extension of the fuselage mould line.
For a fuselage-mounted, piston-engine nacelle:
Mnacpiston = 0.4 x HP per nacelle (8.33)
For a wing-mounted, piston-engine nacelle:
Mnacpiston = 0.5 x HP per nacelle (8.34)
If a nonmetal is used, then mass changes by the factor of usage. For example, x% mass is nonmetal that is y% lighter, the component mass would be as follows: