Hi, Andy Ross wrote:
Maik Justus wrote:Therefore for an wing without flap, spoiler and slat [...] no surface element is generated.Ah, OK. Yes, this was indeed a bug; I'm kinda shocked that we never noticed this before, it's been there since the code was written. And unfortunately it affects *all* wings with segments that like between a control position and an edge. Which means that we're going to need to retest the solution results for basically every YASim aircraft once this goes in. Ick. :( As always, it's nicer to hear about bugs as bug reports, and not as anonymous changes in a 120k patch file. :) Can you (1) split this out into a separate patch as above, (2) add a comment explaining the two new entries in the table, and (3) write "10" instead of "8+2" (or BOUND_COUNT or sizeof(bounds)/sizeof(bounds[0]), etc...).
Here it (the patch) is.But before testing it with any YASim aircraft: I probably found another bug in surface.cpp. For "general lift" and "flap-lift" the effect of stall is calculated in stallFunc() resp. FlapLift(). These functions are similar. In stall they return 1, without stall the "pre stall value" and in between a cubic interpolation. But the results are used quite different. While the result of stallFunc() is reduced by one and than used as factor for an additional lift, the result of FlapLift() is directly added to the lift. In stall, stallFunc() returns 1, which gives (after the mentioned calculation) a summand of zero, but FlapLift() returns a non neutral summand 1. Therefor in stall we get an additional lift from nowhere. If I interpreted the code correct, YASim-fuselages are (nearly *) ) always in stall and produce lift. If the fuselage is large in comparison to the wing, this amount can be rather high. (Maybe this causes the YF-23 to climb without thrust?). In the bo the additonal lift at cruise speed is larger than the drag of the fuselage.
I suggest to change the FlapLift() function to return zero in stall:
diff -u -p -B -r1.6 Surface.cpp
--- Surface.cpp 10 Mar 2006 19:46:16 -0000 1.6
+++ Surface.cpp 6 Aug 2006 15:24:43 -0000
@@ -300,11 +300,11 @@ float Surface::flapLift(float alpha)
if(alpha < _stalls[0])
return flapLift;
else if(alpha > _stalls[0] + _widths[0])
- return 1;
+ return 0;
float frac = (alpha - _stalls[0]) / _widths[0];
frac = frac*frac*(3-2*frac);
- return flapLift * (1-frac) + frac;
+ return flapLift * (1-frac);
}
float Surface::controlDrag(float lift, float drag)
*) If I interpreted the code correctly, fuselages are nearly always in
stall. I think this is another bug. Either they should be always in
stall, or they should have more realistic stall parameters. Now they are
only not in stall at a very small region (+- a half degree) around an
incidence angle of 0 (for flap-lift calculation). The lift of the
fuselage of the bo is producing rather high torque. Due to the bug in
FlapLift, the no-stall in exactly horizontal flight results in a
suddenly appearing pitching of the bo.
For fuselages the stall values of the surfaces are not set and therefor
they are defined in the surface-constructor :
for(i=0; i<4; i++) {
_stalls[i] = 0;
_widths[i] = 0.01; // half a degree
}
We could add
if(_stalls[0] == 0)
return 0;
to FlapLift() (like in stallFunc()) and maybe add adjustable stall
parameters to fuselages as in wings.
Maik
YASim.diff.gz
Description: application/gzip
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