Altittude knobs A320

[wiedehopf]

.1 Mach per click would also be a bit on the coarse side.
.01 seems more reasonable

it has nothing to do with 32bit though.
everything to do with the fact 32 is a power of 2.

[Uplinker]

A right bunch of comedians you lot are; you should be doing stand-up......

....Although, wiedehopf is right, ha ha !, it must be 0.01 Mach !!

[compressor stall]

Uplinker, Why don't you just read it in the FCOM?

[vilas]

FE Hoppy

Are the knobs single rate or dual rate?
If dual I hope you know the rate required to change from fine to course adjustment!

Sure!

V/S or FPA knob Range (V/S) : –6 000 to +6 000 ft/min 2 clicks = 100 ft/min If the flight crew turns the knob slowly, each click equals 100 ft/min.

[FE Hoppy]

Define slowly please. That is the "rate" i'm looking for.

[vilas]

Stopping at each click i.e.click by click.

[Chu Chu]

32 points on a compass?

[FE Hoppy]

Originally Posted by vilas

Stopping at each click i.e.click by click.

are you sure?

try 3 clicks at a time and see if that gives you fine or course adjustment ;-)

[Uplinker]

Uplinker, Why don't you just read it in the FCOM?

'cos that's far too easy !

[EEngr]

Most probably a binary (power of two) thing. Unless the knob has a physical scale and pointer, who would notice that 360 degrees isn't exactly one turn (at one degree per click).

On the A330 it has 33 clicks a turn

Spinal Tap reference?

[MurphyWasRight]

Originally Posted by EEngr

Most probably a binary (power of two) thing. Unless the knob has a physical scale and pointer, who would notice that 360 degrees isn't exactly one turn (at one degree per click).

On the A330 it has 33 clicks a turn

Spinal Tap reference?

Or mechanical fix for a SW fence post counting error?

While back I did some work for a company where it was faster to change the HW (fpga) than the SW when a simple offset error was found.

Does the 33rd click get you back to starting point, if so so might call it 32 clicks.

Wonder if the 'testing' of click counts has produce any noticeable track deviations yet

[wiedehopf]

no spinal tap reference (had to look that one up)

i have no freaking idea how many clicks the knob on the A330 has.
but using the same logic the A380 knobs should have 38 clicks murphy

[EEngr]

who would notice that 360 degrees isn't exactly one turn (at one degree per click).

Now that I've had coffee and shaken the cobwebs out of my skull: At one click per degree, it would take 11.25 knob rotations of a 32 click knob to go through 360 degrees of heading. So there's no direct correlation between knob position and heading.

One click per degree makes sense because that's a logical increment for changing a heading. Need to change by three degrees? Three clicks. But the reference for the absolute heading would be a readout. Not the knob position. One could get one click per degree and one knob turn for 360 degrees of heading. But then the angular size of a click would be pretty small and difficult to set precisely by hand.

Back in the analog days, it was common practice to have a dial indicator concentric with a knob. But to gear the knob so that one degree of indicated change would take 10 degrees or so of knob rotation, making precise settings easier to accomplish. But the gear ratio between knob and dial wasn't exact (in some cases a friction drive).

When we went to digital controls, separating the display and knob functions, it made sense to add detents to the knob for touch feedback. So, one degree per click and let the software keep track of the absolute setting. The click size can then be anything that gives precise and easy control.

There are two ways of implementing a digital knob: A position encoder, that actually reads the knob position, multiplies it by some ratio and keeps track of the number of turns in software. Or, more simply, a knob that produces a single pulse plus a direction of rotation signal, letting the software increment/decrement the absolute value. This is much like a computer mouse, which has no idea where it is but sends the system up/down, left/right pulses and lets the software calculate from that. The latter is much easier to implement. A dual rate knob would simply check the rotation speed (clicks per second) and increment/decrement at a faster rate. All done in software.

[MurphyWasRight]

Originally Posted by EEngr

This is much like a computer mouse, which has no idea where it is but sends the system up/down, left/right pulses and lets the software calculate from that. The latter is much easier to implement. A dual rate knob would simply check the rotation speed (clicks per second) and increment/decrement at a faster rate. All done in software.

A lot of mouse drivers have a dual rate function, above a certain speed the cursor move much farther for each pulse. Just checked mine and it is fairly obvious when fast mode kicks in.

[Uplinker]

Wonder if the 'testing' of click counts has produce any noticeable track deviations yet

On the FBW Airbus, rotating any of the four knobs in question will cause the numerical display above it to unblank and indicate the value selected*. The knobs can be rotated round and round to change their respective values on these FCU displays. However, unless the knobs are actually pulled as well as turned, the aircraft will ignore them**, so the number of clicks per turn or the increment per click can be ascertained without the aircraft deviating at all




*Apart from the altitude display which is always active and does not blank.

** Apart from the altitude knob which will change the altitude pre-selected, but the aircraft will not react until the knob is pushed or pulled.

[SeldomFixit]

It was a dark and stormy night. Nothing on the instruments but the maker's name. Given that Aviators are a most curious bird, by their very nature, I'd have thought everyone secretly harboured a "need to know", just so you did.

[Dan Winterland]