AF447 Thread No. 3

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FBW versus "conventional" one mo' time

I am going with Smilin', Retired and Wolf for several things.

Meanwhile, and for many here that have not flown A FBW system, regardless of the model.....

We must remember that except for the Viper manual pitch override feature, that 99.9% of all pilot commands to the jet are filtered and interpreted and adjusted and the beat goes on.

Between you and the control surfaces are filters and gains and such that use control surface deflection capabilities and limitations and rates. The term "direct" control law just ain't so. Maybe A33Z can chime in here, but I'll bet a bottle of scotch that even in "direct" law that the confusers are tailoring your control stick inpouts to allow for aero and mechanical properties of the control surfaces and some of the aircraft's aero and structural considerations.

Secondly, I have not seen an AoA-based FBW system. I HAVE flown a sim with a rate law ( AFTI F-16). It had an additional bias for attitude. In short, it sucked!! That being said, most folks relate trim to pitch. So if you have to hold back stick for an AoA, you trim a bit so you have a "neutral" stick. The Airbus doesn't work that way.

I prolly should ask one of my shuttle friends to tell us how its FBW system works, but I would bet another bottle of scotch that is resembles the 'bus and the Viper.

Lastly, I am against this term "autotrim". We early Viper instructors did our best to expunge the term. In the case of the 'bus, all it means is that a) if you increase or decrease speed, the THS will change to provide the one gee command, b) if you roll into a bank the confusers will add enuf gee command to stay in level flight , and c) at a pitch attitude above zero the confusers will subtract a bit of the gee command to climb at an attitude, but that attitude is not the major player. It's still gee! How many times do we have to say this? Unlike the 'bus, our litle jet assumed the "trimmed" gee if you let go of the stick. And unlike the 'bus, we could manually trim the jet for a gee. Let go and the sucker went to whatever gee you had trimmed for. Didn't care about speed or attitude or roll angle. It went for "normal" gee. The Airbus does not do this.

later, and I await A33's inputs.