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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

Decode-1 spreadsheet snapshot - inputs page

Figure 11.3 Decode-1 spreadsheet snapshot - inputs page.

Decode-1 spreadsheet snapshot - results summary page

Figure 11.4 Decode-1 spreadsheet snapshot - results summary page.

Decode-1 spreadsheet snapshot - geometry page

Figure 11.5 Decode-1 spreadsheet snapshot - geometry page.

Decode-1 outer geometry as generated with the AirCONICS tool suite

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.

Item

Value

Units

Payload mass

3

kg

Maximum take-off weight set by design

23.5

kg

Maximum cruise speed

30

m/s

Landing speed

12.5

m/s

Take-off speed

16

m/s

Length of ground roll on take-off

45

m

Runway altitude Cruising height

  • 0
  • 121.92

m

m

Table 11.11 Estimated secondary airframe dimensions for Decode-2.

Item

Value

Units

Fuselage depth

225

mm

Fuselage width

250

mm

Nose length (forward of front bulkhead)

200

mm

Diameter of main undercarriage wheels

125

mm

Longitudinal position of engine bulkhead

-250

mm

Vertical position of base of fuselage

-110

mm

Vertical position of tail-plane

0.0

mm

Vertical position of engine

60

mm

Vertical position of center of main undercarriage wheels

-325

mm

Table 11.12 Resulting concept design from spreadsheet analysis for Decode-2.

Item

Value

Units

Maximum fuel weight (without reserve)

0.40

kg

Total wing area

1.554

2

m2

Long position of front bulkhead

688

mm

Long position of tailplane spar

-1407

mm

Coefficient of lift at cruise speed

0.272

Maximum range at cruise speed (Breguet)

37.3

km

Lift at cruise speed

230.54

N

Drag at cruise speed

46.17

N

Table 11.12 (Continued)

Item

Value

Units

Endurance at cruise speed

20.7

min

Limit load factor

3.80

g

Turn rate

68.7

°/s

Longitudinal position of MTOW CoG fwd of main spar

42.1

mm

Maximum possible rotation at takeoff

14.00

°

Engine selected

Saito FG-57T

Specific fuel consumption at cruise speed

0.5

kg/kWh

Maximum required power

2.31

kW

Maximum installed power

3.04

kW

Coefficient of lift at landing speed

1.55

Cl/Cd at cruise speed

15.99

Lift to drag ratio at cruise speed

4.99

Static margin

0.1000

Thrust to weight ratio

0.431

Wing loading

15.12

kg/m2

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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