Q400 pitch reading reference on ADI
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Q400 pitch reading reference on ADI
Hello fellow aviators,
Question for the Q400 drivers on here:
My operator teaches us to read-off the pitch value with reference to the upper edge of the ac symbol on the ADI as opposed to the middle of it, as one was once taught in flight-school. I may be picky on this but it just seems so counter-intuitive.
Any idea as to why the avionics are designed in that way or are we simply doing it wrong?
How do other operators handle this?
Cheers
Question for the Q400 drivers on here:
My operator teaches us to read-off the pitch value with reference to the upper edge of the ac symbol on the ADI as opposed to the middle of it, as one was once taught in flight-school. I may be picky on this but it just seems so counter-intuitive.
Any idea as to why the avionics are designed in that way or are we simply doing it wrong?
How do other operators handle this?
Cheers
Join Date: Jun 2014
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It doesn't matter really where you read it off - as long you always use the same reference.
I guess reading of the top of the bird is a bit more conservative w.r.t. to tailstrike. I'd suspect it's a personal technique, rather than some fancy avionics design.
I guess reading of the top of the bird is a bit more conservative w.r.t. to tailstrike. I'd suspect it's a personal technique, rather than some fancy avionics design.
In Oz we are told to reference it by the top of the box.
I guess by using the top of the box, you have a definitive reference line as opposed to a point in the middle which could become subjective.
I guess by using the top of the box, you have a definitive reference line as opposed to a point in the middle which could become subjective.
Last edited by Going Nowhere; 12th Jul 2017 at 12:13.
What does the autopilot fly? I've only flown the smaller Dash 8s with the double cue and the autopilot flew with the flight director in the centre of the box, in which case I'd suggest the centre of the box is the pitch reference. On the BAe146 on the other hand, the autopilot flies with the flight director pitch bar at the top of the box (when it can find the flight director at all.)
Aero, Your comments stir some thoughts: initially, yes the FD should be the same as the autopilot.
However, reconsidering, certainly for the 146, the FD does not use the same control law nor the same mechanism of control, - autopilot servomotor vs muscle; thus there could be a difference - static / dynamic.
The FD is optimised for the manual task, whereas the autopilot has to consider the control system lags without all of the feedback cues available to the pilot - visual, seat of the pants.
Sidestick, the hazards of guessing #2, i.e. you don’t know, is that misleading speculation and personal technique can lead others astray. Always reference personal techniques to the manufacturers advice or the design principles - if in doubt ask them. The choice of FD reference may make a significant difference to either to the accuracy or ease of flying the system - reduces the tendency to hunt around a datum.
Also, unless you have an approved system for takeoff, or a very sophisticated computation for ‘head down’ landing, tail strike should not be a consideration. Tail clearance during takeoff is a true geometric attitude, opposed to a computed - desired value from an approved FD.
However, reconsidering, certainly for the 146, the FD does not use the same control law nor the same mechanism of control, - autopilot servomotor vs muscle; thus there could be a difference - static / dynamic.
The FD is optimised for the manual task, whereas the autopilot has to consider the control system lags without all of the feedback cues available to the pilot - visual, seat of the pants.
Sidestick, the hazards of guessing #2, i.e. you don’t know, is that misleading speculation and personal technique can lead others astray. Always reference personal techniques to the manufacturers advice or the design principles - if in doubt ask them. The choice of FD reference may make a significant difference to either to the accuracy or ease of flying the system - reduces the tendency to hunt around a datum.
Also, unless you have an approved system for takeoff, or a very sophisticated computation for ‘head down’ landing, tail strike should not be a consideration. Tail clearance during takeoff is a true geometric attitude, opposed to a computed - desired value from an approved FD.
Safetypee, good points. Noted that the 146 a/p and f/d are completely separate systems and often don't agree.
The reason I mentioned it is because it was something I had particularly noticed as a difference between the two aircraft. The Dash 8 classic autopilot will put the cross hairs squarely in the middle of the box, "in the cats bum" as we'd say. In fact, it's been a while, but I seem to recall the Dash 8 flight director will "snap" to the centre of the box when you engage the autopilot, they will then move as a single unit. I don't know if the -400 is like this or not as I haven't flown it, but surely the op has observed these things.
The 146, when flying a steady attitude (i.e., not trying to manoeuvre), will always have the cross hairs aligned with the top of the box. I only suggest that looking at where the autopilot puts the box reference the flight director in steady flight on the Dash 8 400 would give a clue as to the intended pitch reference. This is all if it doesn't explicitly state the reference in the FCOM.
Personally I think the difference between flying the centre of the box vs the top is so small that it doesn't matter, but it obviously matters to someone.
The reason I mentioned it is because it was something I had particularly noticed as a difference between the two aircraft. The Dash 8 classic autopilot will put the cross hairs squarely in the middle of the box, "in the cats bum" as we'd say. In fact, it's been a while, but I seem to recall the Dash 8 flight director will "snap" to the centre of the box when you engage the autopilot, they will then move as a single unit. I don't know if the -400 is like this or not as I haven't flown it, but surely the op has observed these things.
The 146, when flying a steady attitude (i.e., not trying to manoeuvre), will always have the cross hairs aligned with the top of the box. I only suggest that looking at where the autopilot puts the box reference the flight director in steady flight on the Dash 8 400 would give a clue as to the intended pitch reference. This is all if it doesn't explicitly state the reference in the FCOM.
Personally I think the difference between flying the centre of the box vs the top is so small that it doesn't matter, but it obviously matters to someone.
