Figure 9.20. Corrections for laminarization

The compressibility drag of the Vigilante aircraft at zero lift is summarized in Table 9.23.

The compressibility drag at Mach 0.9 is computed as for the civil aircraft example and is given in Table 9.24 along with the drag at both Mach 0.6 and Mach 2.0.

9.19.8 Total Aircraft Drag

The total Vigilante drag at the three Mach numbers is tabulated in Table 9.24. Figure 9.18 shows the Vigilante drag polar at the three aircraft speeds. Figures 9.20 through 9.26 are replotted at the end of this chapter from [3].

9.20 Concluding Remarks

Unlike other chapters, this important chapter warrants some concluding remarks. Drag estimation is state of the art and encompasses a large territory, as described herein. The tendency to underestimate drag is primarily due to failing to note some of the myriad items that must be considered in the process of estimation. The objectives of this chapter are to make readers aware of the sources of drag and to provide a methodology in line with typical industrial practices (without CFD results).

Some of the empirical relations are estimates based on industrial data available to the author that are not available in the public domain. The formulation could not possibly cover all aspects of drag estimation methodologies and therefore must be simplified for coursework. For example, the drag for high-lift devices is only approximate to give some idea.

Readers are advised to rely on industrial data or to generate their own databank through CFD and tests. The author would gratefully receive data and/or substantiated formulations that would improve the accuracy of future editions of this book (with acknowledgment).

Figures 9.19 through 9.26 are replotted from the NASA report in [3].