Please turn word wrap on. ********************************************************* REPORT ON UNKNOWN VARIABLES IN FS98/CFS .AIR FILES (9/99) S. M. Baugh, Ph.D. smbaugh@adnc.com (home) smbaugh@wtscal.edu (work) ************ INTRODUCTION I have been playing with some of the unknown variables in section 1101 of the FS98/CFS .air file for a bit. I had these variables set as 2 byte integers, and noticed that: (a) these values are only used on prop airplanes (not jets or the glider) by MS; (b) the first 3 values in the series of 4 made no perceivable difference on flight characteristics, while the last did somewhat. While evaluating something else, I noticed a pattern and changed the unknown values in FDE to read as 8 byte floating point values. Immediately, the values made more sense and had noticeable effect on the flight characteristics in FS98 (I haven't tested these with CFS yet). Here is my provisional report. I will be glad to hear your opinions on the function of these variables. Only two are pretty easy to nail down. I will describe what I have observed, but welcome other suggestions at the email addresses above. (This report replaces my earlier notes on 1101,E2 which was evaluated as a 2 byte variable.) ***************** THE NEW VARIABLES Var1 = 1101, offset: 154-160 [$9A-A0] Elevator Airspeed Effect Var2 = 1101, offset: 162-168 [$A2-A8] Elevator Response Var3 = 1101, offset: 212-218 [$D4-DA] Prop Effect on Rudder Var4 = 1101, offset: 220-226 [$DC-E2] Rudder Damper? I will refer below to these variables by the numbers above. E.g., Var1 is sec. 1101, offset 154-160. To see these variables in FDE, add the following lines to fdectrl.txt in the appropriate places in section 1101 "Flight Dynamics": 1101,154, Elevator Airspeed Effect (props only),Float8,1 1101,162, Elevator Response (props only),Float8,1 1101,212, Prop Effect on Rudder,Float8,1 1101,220, Rudder Damper? (props only),Float8,1 (Comparable changes can be made to AirEd's AirEd.ini file, but you will have to renumber the entries in section 1101. Use the "double" data type.) ************ OBSERVATIONS (Please note the default FS98/CFS values for all MS generated planes below. From these we can gather that FS98/CFS expects; e.g., a negative number in three of the variables.) VAR1 ("Elevator Airspeed Effect"): A negative number is expected. A positive number here has the interesting effect of reversing the rudder; i.e., pull back and you dive, pull up and you climb! A high number makes the airplane stall very quickly. There is already a variable identified as the maximum angle for the elevator, but this functions similarly (and very dramatically). The CFS Bf 109 has the highest values here; giving this plane an tendency for elevator induced stall. Also note the relatively high value on the Sopwith Camel. This stall effect is especially seen in a sharp turn while holding back pressure on the elevator. Default range: -0.04096 to -0.8. VAR2 ("Elevator Response"): A negative number is expected. A high negative number here reduces the effectiveness of the elevator. It is interesting to note that planes as different as the Extra, Camel, and P-51 have the same number. The Cessna 182 has a zero, and the German fighters vary a little. A positive number likewise prevents elevator effectiveness. Although found only on prop planes, this variable does not seem to be connected to the effects of the prop slipstream as far as I can tell. Any help here would be appreciated! Default range: 0 to -12.0. VAR3 ("Prop Effect on Rudder"): A (small) positive number is expected. This is the most interesting of the lot and simulates prop effect on the airplane's tail. A high number here gives the airplane dramatic increase in yaw authority, but only with the throttle on. If you pull back on the throttle, the effect is removed, even though the airspeed is the same. Evidently, this simulates the prop slipstream hitting the rudder surface. Note that the Sopwith Camel has the highest number of all here, which would be consistent with a WWI design. Default range: 0.002048 to 0.1024. VAR4 (Rudder Damper?): A negative number is expected. A positive number sent a CFS plane into a severe Dutch roll, while an increased negative number gave it yaw oscillations. I am least sure of what to name this variable. In FS98, it damps out all rudder effect when set to a high negative number (e.g., -50.0) (though not as evident in CFS). You can hardly yaw the airplane regardless of throttle position. It also damps out most of the prop torque effect on takeoff (this is what I was actually looking for, but I'm not sure that this is the value's real purpose). Note that only the CFS P47 and Bf 109 have values higher than the standard -5. These planes have noticeably reduced rudder response over other CFS planes for this reason. Note below that the FSFS/FS98 Converter assigns a value much too high here (-30.0). This means that we have to compensate elsewhere. Now we can set this value to -5 and change other yaw values back to normal (?) values. Why VAR4 exists in light of the other yaw variables in the .air file is a mystery. Any ideas?! Default range: -5.0 to -16.0 (-30 for FSFS/FS98 Converter). That's my report. What follows is a listing of the FS98/CFS values MS uses for your reference. Again, any suggestions on improving this evalutaion welcome. Steve Baugh *********************** FS98/CFS DEFAULT VALUES {Note: the 737, Lear, and Glider have zeros in these values which leads to conclusion that these are prop influenced characteristics, or at least smaller craft that these.) The following lists Var1-4 for each MS default airplane: Cessna 182 and 182RG (82" prop) 1. -0.0512 2. 0 (Note: the only prop plane with a zero here.) 3. 0.002048 4. -5.0 Extra 300S (74" prop) 1. -0.04096 2. -10.0 3. 0.06168 4. -5.0 Sopwith Camel (84" prop) 1. -0.06144 2. -10.0 3. 0.1024 4. -5.0 CFS P-47 Thunderbolt (156" prop) 1. -0.05 2. -10.0 3. 0.07168 4. -5.0 CFS P-51 Mustang (134" prop) 1. -0.04096 2. -10.0 3. 0.07168 4. -5.0 CFS Hawker Hurricane Mk I (129" prop) 1. -0.04096 2. -10.0 3. 0.07168 4. -5.0 CFS Spitfire Mk I and Mk IX (114" prop) 1. -0.04096 2. -10.0 3. 0.07168 4. -5.0 CFS Fw 190A (130" prop) 1. -0.06 2. -7.0 3. 0.07168 4. -5.0 CFS Bf 109E and 109G (122" prop) 1. -0.8 2. -12.0 3. 0.01 4. -16.0 ******************** Default FS98 Converter (prop size varies) 1. 0 2. 0 3. 0.035 4. -30.0 Note especially the too high value here for rudder damper (VAR4)! and the zero for VAR2 following the Cessna. You will want to adjust for other types of planes! 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