Home Engineering Small Unmanned Fixed-Wing Aircraft Design. A Practical Approach
A Bigger Single Engine Design: Decode-2
The next aircraft we consider is an enlarged variant of Decode-1 that has 50% greater payload capability and endurance, a larger margin on installed power (a shorter ground roll is
Figure 11.3 Decode-1 spreadsheet snapshot - inputs page.
Figure 11.4 Decode-1 spreadsheet snapshot - results summary page.
Figure 11.5 Decode-1 spreadsheet snapshot - geometry page.
Figure 11.6 Decode-1 outer geometry as generated with the AirCONICS tool suite.
specified), and usefully lower landing speed, all made possible by the use of an inverted V tail and large flaps. The inverted V tail is allowed in the design process by reducing the tail volume coefficients needed by 30%, which gives a smaller, lighter tail and easier control of the static margin. The flaps allow a greater lift coefficient in the landing configuration and hence lower approach speed. Decode-2 is also a single pusher design with a nose-mounted camera system. The design brief is set out in Table 11.10 and the secondary dimensions in Table 11.11. The wing loading is slightly lower (this is now controlled by the choice of maximum landing Cl land of 1.55) but a slightly less stringent rotation at takeoff of 14° is chosen. The other parameters given in Table 11.2 are held fixed as before.
Table 11.10 Design brief for Decode-2.
Table 11.11 Estimated secondary airframe dimensions for Decode-2.
Table 11.12 Resulting concept design from spreadsheet analysis for Decode-2.
Table 11.12 (Continued)
The first five entries here are manipulated by the solver tool within the spreadsheet to maximize the range.
The resulting design is detailed in Tables 11.12 and 11.13 along with the screenshot in Figure 11.7. The aircraft is shown in flight in Figure 11.8 and the outer shape modeled with AirCONICS in Figure 11.9. Note that our spreadsheet sketch does not distinguish between an H and an inverted V tail (simple horizontal and vertical projections being provided); this level of detail has to be worked up after the initial spreadsheet-based concept has been defined, which is straightforward to create within AirCONICS.
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