Altittude knobs A320
 

Hi guys
Why A320 altitude, V/S , heading and speed knobs are completing a turn with 32 click ?

[guess mode]
Because thats what sensor that could be bought off the shelf that was proven safety critical?
[/guess mode]

Always find it hilarious why people want to know such info , even worse if TRIs are asking such questions to students during training

On the A330 it has 33 clicks a turn as far as i know.

A few years on the bus and i never bothered to find out how many clicks it is. It is virtually useless knowledge in my opinion. But then, if it makes you happy...

"Clicks per turn"
 

More important to understand what the particular "knob" does and how to confirm that movement of it has resulted in the intended setting, I think.

Using the inference in Wiedehopf's post I guess the A380 has 38 clicks. I am joking of course.

I'm afraid to even ask how many clicks the 787 has... :}

Well it may not help much knowing the answer but one rotation of HDG knob in A320 it is 32 degrees, it says nothing about altitude knob but VS/FPA is again 32 degrees, in A330 it is HDG 30 degrees. It says nothing about altitude knob and FPA it is again same as A320, 32 degrees one full rotation.

On checks we get asked the duty cycle of the stick shaker motor! Vilas, you need not reply! ;)

;)

For Altitude and Speed select, Concorde used what look like bog-standard "35mm camera film rewind" knobs with fold-out cranks. In an era before digital-push-button FMC flight plan entries, it was probably nice to be able to whizz-whirr one's target altitude up to or down from 60K feet with a rapid crank.

(Concorde pros can comment)

http://www.concordesst.com/inside/co...tures/ap17.jpg
http://www.destoutz.ch/slides/typ_nm...ob_black_2.jpg

When it comes to the number of clicks per revolution in today's knobs - some "human factors" engineer probably had to figure out the optimum number to allow fast adjustments (more clicks per turn), while retaining discrete spacing of clicks for fingertip precision (fewer clicks per turn).

And came up with "32-ish."

In the RAF, an IR renewal always asked what the rpm of the turn and slip gyro was. I know it had 27 in it; 27/270/2700/27000; who cares? Wholigan asked me...(Mil forum).

32 click control knobs ? Have Airbus run out of the 64 click knobs?

32 is a number that comes up often in computing - 32 bit registers were used often in early computing for example. Perhaps it was an easy way for those early, 1980s vintage computers to register inputs?

http://en.m.wikipedia.org/wiki/32-bit

I'm going to twiddle my non-bus knobs this arvo and see if they're 32bit or 64bit!

Rather than how many clicks per revolution of the knob, a more useful thing to know is how much does the target quantity change per each click?

From memory I think Airbus FBW is as follows, (but will check next time I fly):

SPD 1 knot or 0.1 Mach per click
HDG: 1 degree per click
ALT: 100' per click or 1000' per click depending on the setting of the scale selector
V/S: 100' or 0.1 degree FPA per click

Let us know where and when you are going to do this checking and we'll make sure we are watching on Flightradar....:ok:

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

Reminded of the joke about knobs in cockpits :}

My HDG knob is ten clicks per 360.

Bit of a worry when you don't know what each click selects, Uplinker!

Well it wouldn't be much use if each click was 2 degrees would it....

"Turn right 5 degrees"..... "err sorry can you make that 4 or 6 degrees" :}

.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.

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

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

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

FE Hoppy
Sure!

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

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

32 points on a compass?

are you sure?

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

'cos that's far too easy !

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).

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 :)

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 :)

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.

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.

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.

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.