MCP VS Thumbwheel direction

[scandinavian13 5,192]

14 hours ago, Chock said:

Well, there you said it youself, keep it straighforward; a rotating knob, with clockwise to increase and anti-clockwise to decrease is about as simple as you can get. It's intuitive too, since pretty much everything else in the world - from a gas cooker hob switch, a volume knob, a car ignition switch, watch winder, light switch dimmer etc, etc - moves in that way, which is presumably why Airbus did it that way.

Correct. Keep it simple. The Boeing logic, and my own explanation of it, is the simplest and purest in relation to the discussion at hand. Everything related to the pitch axis - pitch on yoke, trim wheel, trim rocker, and, of course, the V/S knob - uses the same method and logic. I can see your logical flow, but it's not as intuitive as you'd suggest. Rotate about the lateral axis by rotating a button perpendicular to that axis? Logical by comparing it to a volume knob, sure, but again there's a logical leap.

V/S knob in Boeing: you rotate the wheel about its lateral axis, in the same direction the plane will rotate about its lateral axis. You can then fine tune this by looking at the MCP to see the value of the direct instruction. In other words, your intention of "I want to pitch over/down" is logically core to the action you're commanding by rotating the V/S wheel in that same direction, about the same axis. The rate is secondary to that action.

V/S knob as you're describing: you rotate the wheel in the direction of the "standard" increase/decrease command (as compared to a volume knob), about an axis perpendicular to the intended direction of rotation, on a logical jump from the core issue of affecting pitch itself to having to work backwards from the rate. In other words, your intention of "I want to pitch over/down" is logically secondary to the action you're commanding by rotating the V/S wheel in an abstracted direction, about a different axis. The rate is primary to that action. Pitch itself is secondary (i.e. you have to work backwards from the rate to determine direction). Again, I see how this is not a tough concept to understand, but it is not as 'primal' as you might suggest.

[vololiberista 205]

An Interesting point on cockpit design. The datum adjust knob on the VC10 autopilot designed in the mid sixties follows the logic clockwise positive anticlockwise negative. The Datum Adjust knob works with whichever manometric lock is engaged i.e. IAS hold, Mach hold or Altitude hold. So it's not a new concept!

https://vads.ac.uk/diad/bres/pub/COID/218/34.jpg

[Ralgh 43]

I have flown the 737 and then the A320 family of planes for the last 17 years and at least for the way my brain works it makes no real difference what the input method is or its relation to the axis of the plane. I'm am shooting for a specific vertical speed and I know how to make that input to get the desired result. It seems like this thread is making something that is pretty simple sound overly complicated. 

[Bert Pieke 7,585]

1 hour ago, Ralgh said:

I have flown the 737 and then the A320 family of planes for the last 17 years and at least for the way my brain works it makes no real difference what the input method is or its relation to the axis of the plane. I'm am shooting for a specific vertical speed and I know how to make that input to get the desired result. It seems like this thread is making something that is pretty simple sound overly complicated. 

That is fine, but for the pitch wheel on Boeing airplanes, or Bendix King autopilots, the thumbwheel operates like the trim wheel.  It is not adjusting the VSI value, but the aircraft attitude = pitch.

[Ralgh 43]

7 minutes ago, Bert Pieke said:

That is fine, but for the pitch wheel on Boeing airplanes, or Bendix King autopilots, the thumbwheel operates like the trim wheel.  It is not ajusting the VSI value, but the aircraft attitude = pitch.

I may be misunderstanding what your saying but both planes are adjusting pitch to attain the vertical speed you have selected because, as we know, that's how planes work. When changing altitude whether it's the thumb wheel in the 737 or a knob in the Airbus when you dial -1500 both planes are going to give a flight director command to descent at 1500 FPM and if the autopilot is engaged the plane will descend at 1500 FPM.

[Bert Pieke 7,585]

Agree.. it is a pilot interface issue, as stated above.

[Fabo 213]

On 4/13/2017 at 7:34 PM, Ralgh said:

I may be misunderstanding what your saying but both planes are adjusting pitch to attain the vertical speed you have selected because, as we know, that's how planes work. When changing altitude whether it's the thumb wheel in the 737 or a knob in the Airbus when you dial -1500 both planes are going to give a flight director command to descent at 1500 FPM and if the autopilot is engaged the plane will descend at 1500 FPM.

NGs will, as will other modern Boeings. Originals and back would have a pitch wheel a la DC-6, which would not aim for a set value, I believe. I suppose the commoniality was one of the points of making the VS wheel in this way, not as a rotary knob as in Airbus