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Home arrow Engineering arrow Small Unmanned Fixed-Wing Aircraft Design. A Practical Approach
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Constraint 4: Desired Cruise Airspeed

We next look at the cruise speed requirement. If q denotes the dynamic pressure at cruise conditions, the required thrust to weight ratio T/W as a function of the wing loading W/S can be calculated as:

The Python implementation once again sweeps a sensible range of wing loading values to build the appropriate constraint diagram:

In [60]: WSlistCR_Pa = np.linspace(Start_Pa,8500,Resolution)

TWlistCR = []

i=0

for WS in WSlistCR_Pa:

TW = q_cruise_Pa*CDmin*(1.0/WSlistCR_Pa[i])

+ k*(1/q_cruise_Pa)*WSlistCR_Pa[i]

TWlistCR.append(TW) i=i+1

WSlistCR_kgm2 = [x*0.101971621 for x in WSlistCR_Pa] figCruise = plt.figure()

PlotSetUp(0, WSmax_kgm2, 0, TWmax, '$W/S,[,kg/m*2]$' , '$T/W,[,,]$')

axCruise = figCruise.add_subplot(111) axCruise.add_patch(CruisePoly)

Out[61]:

Constraint 5: Approach Speed

Assuming a given target approach speed (which, at the start of the typical final approach translates into a dynamic pressure gAPP) and a maximum lift coefficient CAPPachievable in the approach configuration (with the high lift system, if present, fully deployed), the wing loading constraint can be formulated as:

The approach speed constraint will thus impose a right hand boundary in the thrust to weight versus wing loading space at:

In [62]: WS_APP_Pa = q_APP_Pa*CLmax_approach WS_APP_kgm2 = WS_APP_Pa*0.101971621 print '{:03.2f} kg/m*2'.format(WS_APP_kgm2)

15.41 kg/m*2

In [63]: WSlistAPP_kgm2 = [WS_APP_kgm2, WSmax_kgm2, WSmax_kgm2

, WS_APP_kgm2, WS_APP_kgm2 ]

TWlistAPP = [0, 0, TWmax, TWmax, 0 ]

AppStallPoly = ConstraintPoly(WSlistAPP_kgm2,TWlistAPP

,'grey',0.1)

figAPP = plt.figure()

PlotSetUp(0, WSmax_kgm2, 0, TWmax, '$W/S,[,kg/m*2]$'

, '$T/W,[,,]$')

axAPP = figAPP.add_subplot(111) axAPP.add_patch(AppStallPoly)

Out[63]:

 
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