T-37A Tweet -- Linear Model

Graduate Research done by Jeff Scott
Advisor: Prof. Michael Selig
Applied Aerodynamics Group
Department of Aeronautical and Astronautical Engineering
University of Illinois at Urbana-Champaign, Urbana, Illinois 61801

Last updated June 7, 2000

The linear aerodynamics model uses stability derivatives to approximate actual aircraft behavior. The T-37A Tweet linear model is based on the following flight conditions (cruise):

Flight Conditions
Variable Variable
in Code 		Description Units Value(s) Source Notes
h Altitude altitude above sea level ft 30000 Roskam pg 501
Alpha angle of attack deg 2 Roskam pg 501
V V_true_kts velocity (true air speed) kts 270 Roskam pg 501 Mach 0.459
q Dynamic_pressure dynamic pressure lb/ft2 92.7 Roskam pg 501
C.G. - center of gravity location % 27 Roskam pg 501
CL CL lift coefficient - ? not available
CD CD drag coefficient - ? not available
Cm Cm pitching moment coefficient - ? not available

The data input into the simulator is listed in the following tables:

Geometry
Variable Variable
in Code 		Description Units Value(s) Source Notes
b bw wingspan ft 33.8 Roskam pg 501
cbar wing mean aerodynamic chord ft 5.47 Roskam pg 501
S Sw wing surface area ft2 182 Roskam pg 501

Control Surface Geometry
Variable Variable
in Code 		Description Units Value(s) Source Notes
emax demax maximum elevator deflection deg +20 - guess
emin demin minimum elevator deflection deg -20 - guess
amax damax maximum aileron deflection deg +20 - guess
amin damin minimum aileron deflection deg -20 - guess
rmax drmax maximum rudder deflection deg +20 - guess
rmin drmin minimum rudder deflection deg -20 - guess

Mass Data
Variable Variable
in Code 		Description Units Value(s) Source Notes
W Weight weight at flight condition lb 6360 Roskam pg 501 converted to Mass
[slug/ft3] in code
Ixx I_xx roll inertia slug ft2 7985 Roskam pg 501
Iyy I_yy pitch inertia slug ft2 3326 Roskam pg 501
Izz I_zz yaw inertia slug ft2 11183 Roskam pg 501
Ixz I_xz lateral cross inertia slug ft2 0 Roskam pg 501

Propulsion Data
Variable Variable
in Code 		Description Units Value(s) Source Notes
Tmax simpleSingleMaxThrust maximum thrust lb 850 Roskam pg 502 estimated from CTx
at sea level
Tmax simpleSingleMaxThrust maximum thrust lb 5700 David pg 251 engine rating
(A-37B Dragonfly)

Aerodynamic Data
Variable Variable
in Code 		Description Units Value(s) Source Notes
CD0 CDo drag coefficient at =0 - 0.020 Roskam pg 502
CD CD_a drag curve slope 1/rad 0.25 Roskam pg 502
CDe CD_de drag due to elevator 1/rad 0 Roskam pg 502 e positive down
CL0 CLo lift coefficient at =0 - 0.20 Roskam pg 502
CL CL_a lift curve slope 1/rad 5.15 Roskam pg 502
CL CL_adot lift due to angle of attack rate 1/rad 2.0 Roskam pg 502
CLq CL_q lift due to pitch rate 1/rad 4.1 Roskam pg 502
CLe CL_de lift due to elevator 1/rad 0.5 Roskam pg 502 e positive down
Cm0 Cmo pitch moment coefficient at =0 - 0.025 Roskam pg 502
Cm Cm_a pitch moment due to angle of attack 1/rad -0.70 Roskam pg 502
Cm Cm_adot pitch moment due to angle of attack rate 1/rad -6.95 Roskam pg 502
Cmq Cm_q pitch moment due to pitch rate 1/rad -14.9 Roskam pg 502
Cme Cm_de pitching moment due to elevator 1/rad -1.12 Roskam pg 502 e positive down
CY CY_beta side force fue to sideslip angle 1/rad -0.346 Roskam pg 503
CYp CY_p side force due to roll rate 1/rad -0.0827 Roskam pg 503
CYr CY_r side force due to yaw rate 1/rad 0.30 Roskam pg 503
CYa CY_da side force due to aileron 1/rad 0 Roskam pg 503 a positive
right aileron up
CYr CY_dr side force due to rudder 1/rad 0.2 Roskam pg 503 r positive left
Cl Cl_beta dihedral effect 1/rad -0.0944 Roskam pg 503
Clp Cl_p roll damping 1/rad -0.442 Roskam pg 503
Clr Cl_r roll moment due to yaw rate 1/rad 0.0926 Roskam pg 503
Cla Cl_da roll moment due to aileron 1/rad -0.181 Roskam pg 503 a positive
right aileron up
Clr Cl_dr roll moment due to rudder 1/rad 0.015 Roskam pg 503 r positive left
Cn Cn_beta weathercock stability 1/rad 0.1106 Roskam pg 503
Cnp Cn_p adverse yaw 1/rad -0.0243 Roskam pg 503
Cnr Cn_r yaw damping 1/rad -0.139 Roskam pg 503
Cna Cn_da yaw moment due to aileron 1/rad 0.0254 Roskam pg 503 a positive
right aileron up
Cnr Cn_dr yaw moment due to rudder 1/rad -0.0365 Roskam pg 503 r positive left

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