The lift curves are very different (blue = Du Y Thesis).
I've made tests with the
PA18 160 hp at default load,
Pitch alpha = Du Y = erik,
Pitch elevator, below:
- Code: Select all
<function name="aero/moment/Pitch_elevator">
<description>Pitch moment due to elevator</description>
<product>
<property>aero/function/qbar-induced-psf</property>
<property>metrics/Sw-sqft</property>
<property>metrics/cbarw-ft</property>
<property>fcs/elevator-pos-rad</property>
<!-- <value> -1.2004 </value> --> <!-- Du Y -->
<!--value> -1.8 </value--> <!-- from dany93 -->
<!-- + -0.10584 (5.88%) = -1.90584 -->
<table>
<independentVar>/sim/model/j3cub/pa-18</independentVar>
<tableData>
0 -1.8
1 -1.9058
</tableData>
</table>
<value>0.67</value> <!-- 0.67 x (-1.8) = -1.206 ~ Erik ini, dany, tests, stiffness issue -->
</product>
</function>
factor 0.67 in order to get again the initial basic value from erik (-1.8 x 0.67
~ -1.21 for J3Cub, or -1.9 x 0.67 ~
-1.27 for PA18).
In the
Lift tables, I've changed aero/alpha-rad for
aero/alpha-wing-rad in order to take the FDM <wing_incidence> 0.0349 rd ( 2deg) into account. (this is the wing angular shift from the fuselage axis).
This gives (both are kept, can be selected by un-commenting)
- Code: Select all
<function name="aero/force/Lift_alpha">
<description>Lift due to alpha</description>
<product>
<property>aero/qbar-psf</property>
<property>metrics/Sw-sqft</property>
<property>aero/function/kCLge</property>
<table>
<!-- USA-35B -->
<!-- <independentVar lookup="row">aero/alpha-wing-rad</independentVar>
<independentVar lookup="column">aero/Re</independentVar>
<tableData>
1668183 3707224
-1.5700 0.0000 0.0000
-0.3491 -0.0085 -0.5085
-0.2443 -0.5085 -0.8136
-0.1745 -0.5085 -0.5085
-0.0873 0.1017 0.1017
0.0000 0.5339 0.5339
0.0873 1.2204 1.2204
0.1309 1.4746 1.4746
0.1745 1.5000 1.6272
0.2182 1.6201 1.7797
0.2618 1.5645 1.8306
0.3054 1.4272 1.6272
0.3491 1.3138 1.4238
1.5700 0.0000 0.0000
</tableData> -->
<!-- Du Y -->
<independentVar lookup="row">aero/alpha-wing-rad</independentVar>
<tableData>
-0.0349 -0.0500
-0.0175 0.0500
0.0000 0.1250
0.0349 0.3000
0.0698 0.5000
0.1047 0.6800
0.1396 0.8800
0.1745 1.1000
0.2094 1.3000
0.2443 1.4750
0.2793 1.6200
0.3142 1.7250
0.3316 1.7750
0.3491 1.8130
0.3665 1.8000
0.3840 1.7500
0.4014 1.6200
0.4189 1.1750
0.4363 0.7500
</tableData>
</table>
<table>
<independentVar>aero/function/total-wing-damage</independentVar>
<tableData>
0.0000 1
1.0000 0
</tableData>
</table>
</product>
</function>
1 - As I had changed for aero/alpha-wing-rad, I have made some tests with the initial aero/alpha-wing-rad lift table.
USA-35BAt stall, stick kept pulled, no flaps, the aircraft pinches down then balloons with
~ 37 kts airspeed,
alpha-deg 15
pitch-deg 7.5
vertical speed -500 to -600 ft/mn.
It is mild, but I could not make a 3-point touchdown (with or without flaps).
2 -
Du Y CL table balloons with:
35 kts,
-480 ft/mn
alpha-deg 14,
pitch-deg 7
jsbsim/aero/alpha-rad 0.249 (~ 14.3 deg)
jsbsim/aero/alpha-wing-rad 0.284
However, the wings are not at their stall angle (which is 20 deg).
Without flaps, the 3-point touch is doable but a bit delicate because the 'stall' is brutal.
airspeed 33 - 34 kts,
11 -14 deg pitch angle.
The stall occurs rather because of the decreasing airspeed (we are not at the CL Max).
With full flaps, a very soft near-3-point touch is possible (9 - 10 deg pitch) because the aircraft looses height very softly at the end, at grazing the ground with the stick full pulled back.
At 105 - 110 kt airspeed, the pitch attitude is close to zero (-1.5 deg) because of the CL curve at low angles.
With such different lift curves, I let you test, maybe choose or match the curves. The Du Y curve seems more pleasant but I do not know if the behavior is realistic, it is not the J3Cub wing profile.
The USA 35B CL is unusually high at low alphas. The Re = 1.668 E6 curve might be more "rounded".
Airfoil Tools for Re = 1 E6.
The Du Y curve is more usual, however its CL-max angle cannot be reached.