Miscellaneous Considerations in Civil Aircraft
Following are additional considerations that could enhance aircraft performance but are not addressed here. At this design stage, none of the additional surfaces described needs to be considered except the dorsal fin. All add to aircraft weight.
1. Winglets. It took some time to establish the merits of having winglets that can reduce or induce drag – some manufacturers claim a reduction as high as 5% of induced drag (i. e., approximately 1.5% in total drag reduction), which is substantial. Currently, almost all large-aircraft designs incorporate winglets. Lear – jet has been using them for some time and they have become a symbol of its design.
2. Dorsal Fin. A dorsal fin ahead of the V-tail could work like strakes on a wing, and they are incorporated in many aircraft – at least to a small degree. They prevent the loss of directional stability.
3. Ventral Fin. This is sometimes installed at the tail end as an additional surface to the V-tail. The ventral fin also serves as a skidding structure to protect the fuselage from damage at excessive early rotation, which causes tail-dragging.
4. Delta Fins. These fins come in pairs at the aft end of the lower fuselage. Not all designs have delta fins; they are used if an aircraft shows poor stability and/or control problems. Aircraft with a flat, rear-loading, raised fuselage upsweep demonstrate these problems and delta fins are deployed to resolve them. A good design should avoid incorporating delta fins; however, on some designs, drag reduction can be achieved with their installation.
Several external-surface perturbations on aircraft add to parasitic drag, including antennas, inspection-hatch covers, vent pipes, and lightning dischargers. Engine and system intake and exhaust ducts and vents also increase drag.
It is suggested that readers determine whether there are any innovative requirements that should be incorporated in the conceptual design. Trends should be investigated continually for ideas to improve on aircraft design.