In doing a lot of hand flying, I am surprised at how small the FD Roll Bar deflection is in certain cases, where I would have intuitively expected a larger deflection. For example, in the included screen shot, I am within 0.2nm of the LNAV course and need to make a heading change of over 30 deg, yet the FD roll bar has barely moved to just outside the central white square. When I begin the turn to intercept the LNAV course, the roll bar centers at around 10 deg bank angle and remains there all the way to a 30 deg bank angle. I had shown this to a RW pilot (who has flown NGs in the past) over the weekend and he did not seem to think that this was representative of the real aircraft.A more broader question I was wondering about is what is the roll bar deflection proportional to? Is it the desired bank angle to attain the commanded lateral course? So would the deflection be the same for a 40 deg heading change versus a 60 deg heading change because both would be accomplished by a 30 deg bank angle? Or would there be more deflection for the 60 deg change as it is larger than the 40 deg heeading change, but the bar would center at a 30 deg bank angle? (I use 30 deg bank angle because that is what the AP uses and I'm assuming that the APis in sync with the FD). Curious to know and am hoping some RW pilots or PMDG can chime in here.Rushad Ed.

A more broader question I was wondering about is what is the roll bar deflection proportional to? Is it the desired bank angle to attain the commanded lateral course? So would the deflection be the same for a 40 deg heading change versus a 60 deg heading change because both would be accomplished by a 30 deg bank angle? Or would there be more deflection for the 60 deg change as it is larger than the 40 deg heeading change, but the bar would center at a 30 deg bank angle? (I use 30 deg bank angle because that is what the AP uses and I'm assuming that the APis in sync with the FD). Curious to know and am hoping some RW pilots or PMDG can chime in here.

Can't tell you much here, but the desired bank angle depends at least on the required ΔHDG. That's just how the control law works methinks. I think I've seen part of it recently somewhere. Can't recall any exact number, but IIRC say the desired bank angle increases in a linear manner up to a ΔHDG of 30° or so (give or take some), then stays at its maximum value (assuming max bank of 30°, otherwise it'll be less obviously).But control laws for other modes are probably way more complex, e. g. a localizer capture will not only depend on your offset to final course, but also closure rate and other things. VNAV etc might be the worst as they'll have to incorporate a ton of performance data as well I'd suppose. So it's everything but trivial to give a simple answer as to what drives the FD deflection. Grab a book or two dealing with control engineering and be prepared for the headache...

Thanks Etienne and Jason, for your replies. My practical concern re. following the FD bar was the fact that the deflection of the FD roll bar seemed small, even for a relatively significant change in HDG or even LNAV path. I also tried it out (several times) on the ILS, and there too the deflection seems small even at less than 1,000 ft AGL and with the LOC diamond at approx 25% deflection. Also, as I mentioned above, the FD bar remains centered over a large range of bank angles - I would have guessed that it would provide more 'precise' guidance.Hope folks with some RW experience can provide more insight.Rushad Ed.

I have also noticed this behaviour on ILS approaches. Following the roll bar doesn't really seem to be enough to keep the aircraft on the localizer -- as you say, you can develop quite a significant deviation on the localizer but the roll bar stays pretty much centered. As a result, I always end up flying the localizer on raw data. The pitch bar, on the other hand, does provide useful guidance and following it will keep the aircraft nicely on the glideslope.I would also welcome comments on this from RW 737 drivers.Martin Boehme

I found the fd and also the hugs to be quite lazy and slow...seems they often seem to be behind what is needed, which is to how thy are designed to be, they should preempt turns etc. in fact the hugs is worse than the fd, hugs seems to follow your lead rather than other way round sometimes!I find it far harder to follow either the hugs or fd to keep me on track...have no issue in following them as such from a skill point of view, it more hat following them leads to, you only have to notice ho different an angle or pitch that occurs as soon as autopilot is switched on to realise how far out they are, because they don't seem to be very responsive you often become off path, compared to other aircraft I fly.I don't think they deflect enough and are sluggish...so don't think you are alone with this...perhaps worth a ticket.

I have also noticed that the roll FD bar appears sluggish.On an ILS approach I tend to turn them off and use the FPA instead. When hand flying I use them as a guide but will use slightly more bank if required. Maybe the real bars are like this. It would be nice to know. I guess one way to find out is to fly the same SID without weather with and without the autopilot connected and see how much the bars move in each case.