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jspan_com

Angle of Attack Indicator

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Hi all,According to the "good book" Angle of Attack is defined as: "Angle of Attack is the angle between the relative wind and the chord line of the airfoil. This is not to be confused with the angle of incidence, which is the fixed angle between the wing chord line and the reference line of the fuselage."Now, I want to program an AoA Indicator using an XML string. When looking in the MSFS 2002 SDK (Token Var), the ANGLE_OF_ATTACK_INDICATOR is described this way: "Measures airspeed, (signed fraction of max indication)." The XML A:var ANGLE OF ATTACK INDICATOR is presumeably using the same definition?Anyone who can help me with this one?

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In difference to the "good book" (whatever that is) in FS you find the angle of atack under the INCIDENCE_ALPHA. The variable ANGLE_OF_ATTACK_INDICATOR is useless, that is at least for C. The Concorde angle of attack indicator shows INCIDENCE_ALPHA and not ANGLE_OF_ATTACK_INDICATOR. How to check? Use the Extra 300 and fly upside down. The INCIDENCE_ALPHA is negative, ANGLE_OF_ATTACK_INDICATOR not. In XML (A:Angle of attack indicator,degrees) might be OK, I haven't checked, alternatively check "incidence alpha" also.Arne Bartels

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Hi Arne,Thank you :-)The "good book" is just a general "Principles of Flight" book. I have earlier tried the (A:Angle of attack indicator,degrees), but could not get it to work. The (A:INCIDENCE ALPHA, degrees) however does seem to work OK. I have not reversed the value with the "/-/" expression, maybe I should? For the Attitude Pitch readout I have reversed the value: (A:Attitude indicator pitch degrees, degrees) /-/), see attached image.

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I'm not usre about the exact definition of AOA (whether up or down counted). But from my general aerodynamic knowledge a positive AOA should be coupled to positive lift, so no /-/. The reason for the reversing of attitude indicator pitch degrees is: if the nose shows up, the horizon points down so for "nose up" the indicated pitch is negative.Arne Bartels

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Hi Arne, I just tried AOA with /-/, and that seemed to be an erroneous approach to it. Thanks for the explanation of the Attitude Indicator Pitch, degrees.

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Hi JanAs Arne mentioned, the INCIDENCE_ALPHA variable reports the aircraft BODY angle of attack (which is the angle between the longitudinal fuselage axis and relative wind, ie TAS vector). Although it is of course a major factor for lift, we know wing lift depends on WING angle of attack which is simply: AOAw = AOAb + wing incidence + 0.5*wing twist (at least in FS8) ; FS9 discards any wing incidence and twist data in the aircraft.cfg so AOAw always equals AOAb..not true in FS8.Wing lift is thereafter calculated from AOAw and relevant data of air file table #404 (CL vs AOAw) or Table #1545 if it existsAccording the way this table is build, positive lift can be generated even for small negative AOA angles..It solely depends on the table valuesHope this will clarifyHerv

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Oops, yes forgot that. But I wanted to find an explanation for the sign of AOA that sounded logical.Arne Bartels

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>Hi Jan>>As Arne mentioned, the INCIDENCE_ALPHA variable reports the>aircraft BODY angle of attack (which is the angle between the>longitudinal fuselage axis and relative wind, ie TAS vector).>Although it is of course a major factor for lift, we know wing>lift depends on WING angle of attack which is simply: AOAw =>AOAb + wing incidence + 0.5*wing twist (at least in FS8) ; FS9>discards any wing incidence and twist data in the aircraft.cfg>so AOAw always equals AOAb..not true in FS8.>Wing lift is thereafter calculated from AOAw and relevant data>of air file table #404 (CL vs AOAw) or Table #1545 if it>exists>According the way this table is build, positive lift can be>generated even for small negative AOA angles..It solely>depends on the table values>>Hope this will clarify>>Herv

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>>Hi Jan>>>>As Arne mentioned, the INCIDENCE_ALPHA variable reports the>>aircraft BODY angle of attack (which is the angle between>the>>longitudinal fuselage axis and relative wind, ie TAS>vector). .............>>>>Hope this will clarify>>>>Herv?>Hi Herv?>>Thanks for a very good explanation of the lift aspect. This is>not my special area, but we (the jsPANELS.com ATR42 Team) are>aware of the table 404 (Cl vs AOAw), and are working on it to>improve the ATR flight dynamics for FS9. Therefore I have>tried to put together the ATR Flight Test gauge, which also>might be usable for the calibration of the primary flight>instruments for this aircraft (attached image).> Just set 'wing_incidence' + 'wing_twist'/2 = 0.0. That is, make them cancel (both could be set to 0.0). Then, adjust TBL 404 to get the appropriate CL at zero AoA (~ 0.2) by 'shifting it sideways'. Also, set 1101 "Fuselage AoA at min Induced Drag' to the angle (in degrees) where TBL 404 crosses zero. Typically -2.5 deg (~-0.045 rad). Then, the AC will be compatable with FS9 and FS8. And, 'incidence_alpha' will indicate both body and wing AoA. Ron

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Hi Ron and all,Thank you all a lot :-).These parameters will be most useful, and we will try them out ASAP on our FS9/FS8 ATR42 project.

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