Force-feedback Reprogramming for Airliners
Jon Munson 8/4/98

Background:
The problem is that FS98 Converter installs Microsoft Cessna 182 force feedback values by default, or they may not have been altered if provided by the aircraft-file's author.  The stock C182 values aren't bad for a light plane, but feel very exaggerated in amplitude and frequency when used for heavy aircraft.  FS98 itself uses a different, but common, force profile for both the standard LearJet and 737 aircraft, yet it doesn't seem quite satisfactory for either- it's too weak to provide enough "feel", and if scaled-up, still feels very unrealistic.  So included below are configuration values that feel much more appropriate for airliners, providing more intuitive cues as to proper taxi speed and so on.  Disclaimer: all this is rather subject to personal taste, seeing as how most vibration ought to come through an active chair rather than via the stick anyway!

Instructions:
Paste Airliner optimized ground_bumps_parameters (text between the asterisks below) into an appropriate aircraft.cfg file, in place of the existing Microsoft Cessna 182 values that are probably there.  

The usual paths of these files are
C:\Program Files\Microsoft Games\Flight Simulator\Aircraft\Your Unique Airliner\aircraft.cfg
I usually use WordPad for text editing like this (not buggy like NotePad)- in any case, remember to save as text!

BTW- Just to make sure nothing funny happens if FS98 is running when editing an aircraft.cfg file, I first select a different aircraft in the active sim, then after the editing is done, reselect the type just modified so the sim picks-up the new values cleanly.

********************************************
ground_bumps_magnitude1=2000
ground_bumps_angle1=0000
ground_bumps_intercept1=0.8
ground_bumps_slope1=0.16
ground_bumps_magnitude2=2000
ground_bumps_angle2=9000
ground_bumps_intercept2=1.4
ground_bumps_slope2=0.28
********************************************

For those propeller-heads out there that are inclined to want to understand what's being done [like me ;-) ], here's an explanation:
Two force sinusoids can be generated with independant strengths, directions of action, and initial & incremental frequencies (Hz/MPH ground speed).  The goal was to create a quasi-random feel with a dominant frequency that felt like pavement variation and the "cold-set" tire bump rates familair to airliner occupants.  I decided on a 7:4 Lissajous-pattern model with the higher frequency in the lateral (x) axis, and the lower one in the fore/aft (y) direction.  The logic for this is that the spacing between the main gears is normally much less than that of the mains-to-nose gear, so the dominating relative vibrational-mode freqencies would be inversely related.  The initial and incremental frequencies were selected to provide good low speed feel and an appropriate shimmy rate at rotation speed, all the while maintaining the 7:4 relationship.  The magnitudes were set the same to provide the most random feel and to a level that made perceptability good, but without rattling the stick (at least in the next-to-highest force setting that I normally use with the Microsoft Stick).  For smaller aircraft types (i.e smaller tires and gear spacings), one might be inclined to up the slope values somewhat to compensate (0.20 & 0.35 for example).

Good Simmin',
Jon
jmunson@metricom.com