Help me with the "Altitude Hold" - button

I do not completely understanding what this button (altitude hold "B") does. It kinda holds the altitude, but not really. Can someone explain?

1. When it is not active my altitude varies (becomes unstable). And when I activate the altitude stabilises. But if I move my collective a bit more, the altitude changes, even though the button is ON. How does it hold the altitude? I don't understand.

2. What's the reason for it activating when I press hover hold, but not de-activating, when I deactivate the hover? The altitude hold is still on? Why? Why doesnt the de-activation of hover give me back my altitude control?

1. Altitude hold does not take over your control of the collective, it "dampens" it, trying to maintain altitude. Moving the collective up or down beyond what the altitude hold can dampen, your altitude will change.

2. Because.

I also find it annoying that the Alt Hold doesnt come off if you remove hover.

But I would think by design. You dont want your altitude to drastically change as you come out of hover. You may climb out of the cover you moved to, or descend into vortex ring.

Is there any "official" explanation on how the "altitude hold" dampener actually holds altitude? When does it decide to hold, and when does it decide to change?

The manual says something about the "Collective brake" and altitude hold. Can anyone explain? I dont really understand it:

"Once the brake has been released and a signal is sent to the navigation system, the lever can be used to assign a new altitude when using the altitude hold mode."

What does this mean?

The collective brake works exactly like the trimmer on the cyclic, but where the trimmer on the cyclic is for the PITCH, ROLL, and HEADING channels of the autopilot, the collective brake is for the ALTITUDE channel. And just like the other channels, the autopilot only has 20% authority over the controls.

An example of using altitude hold in normal flight would go like this:

1. Flying along straight and level, you decide you want to change your altitude.

2. Press the collective brake button (F) and hold it.

3. Adjust your collective to begin a climb or a descent (still holding the collective brake button).

4. Arrive at your desired altitude and adjust the collective to halt your climb or descent (STILL holding that button!)

5. Let go of the button for the collective brake (after you've stabilized at the new desired altitude).

At this point, the altitude channel will do its best to keep you at that altitude (either barometric or radar altitude). Remember that your autopilot can only do so much (20%), so drastic changes in the cyclic (or drastic changes in altitude if using radar altitude hold) will cause the altitude hold channel to work improperly.

Alpha:

Ok, I understand. But what happens if I don't press the F key, and just increase the collective and stabilize at a higher altitude? Will the autopilot descend back to the first altitude?

Or am I just "working harder against" the autopilot when NOT pressing F and increasing collective?

Alpha:

 

Ok, I understand. But what happens if I don't press the F key, and just increase the collective and stabilize at a higher altitude? Will the autopilot descend back to the first altitude?

 

Or am I just "working harder against" the autopilot when NOT pressing F and increasing collective?

You are just working against the autopilot. I will explain:

You are zipping along at a nice stable airspeed and altitude, let's just say 200kph and 500 meters (no special meaning here, just some numbers). You have all autopilot channels on, including altitude. Suddenly, you decide that you are too hot, and your ventilator fan just isn't helping, so you think to yourself "Self, we must get up higher where it is nice and cool!" (I think your self has a great idea, by the way!). So you pull in some collective (let's say for argument's sake, you just pull in a teeny tiny bit of collective), and lo and behold, nothing happens! You VSI stays pegged at zero! So you pull in some more collective, still nothing...then a bit more...until FINALLY your VSI starts to move. "Great!" says self. So your climb is initiated and you have the rate of climb you want (never fast enough when you're sweating and you want some cool air, eh?). Eventually, you start feeling that nice cool air up at 2,000 meters flowing into the cockpit, and you decide that you're high enough, so you reduce the collective until your altitude stabilizes (VSI back at zero).

(but it never "quite" stabilizes...oh it gets close, but something seems amiss...but along you go, oblivious, etc.)

Hey! It's time to turn! (or slow down or speed up or whatever) So you start your bank (or whatever) and the aircraft starts to turn (or whatever)...but then starts to lose altitude (or even gain, depending on what the "whatever" is). "What?!?" says self, very upset that his altitude channel is not working.

Well, your altitude channel IS working. It is trying to hold you at 500 meters. Well, you're way up at 2,000 meters! What is going on?!

Remember back when you were at 500 meters, and you wanted to climb, so you pulled in some collective (a teeny tiny bit, if my memory is correct)? Well your collective input to the collective servo moved (oh yes indeed it did, since it is physically connected, it has no choice!) But your collective control rods are not the only thing that tell the collective servo what to do. The autopilot also has a say. And you autopilot says it wants to stay at 500 meters, so as you're adding collective, the autopilot is taking it right back out. Not out of your control input, but out of the servo. Eventually, your collective movement will exceed 20 percent of its travel. (Note: I have an X-52 throttle, it moved about 10-15%.) When your collective input exceeds 20% of its travel, the autopilot runs out of authority, and your input starts to work. So your started climbing...up and up...until you got to 2000 meters, then you lowered the collective to zero your VSI. The catch here is that your autopilot still wants to lower the collective, but it can't, as it's already "lowering" it by 20% (which you have happily overriden by moving the collective more and more).

Now if you do any maneuver that would cause a change in altitude (just about anything in a helicopter will do that, they sure are touchy), then your altitude would start changing, because your autopilot has done all that it can do.

About this time, you realize the error of your ways, and you hit your collective brake button (just a tap here will do). You have just told your autopilot that you want to hold THIS altitude (2,000 meters). Here it helps to know that your autopilot's input to the servo is not really a direct mechanical linkage like your collective is (it's all computery, using little things called feedback sensors that tell the autopilot exactly where your collective is set and how much pitch is in the blades, etc....very complicated and all that). So when you hit that button, not only does it tell your autopilot to hold this new altitude, it ALSO zeroes your autopilots collective input! Now your autopilot once again has the authority to make minor changes to the collective servo to hold your altitude, and you're back to making turns, etc, without losing or gaining any altitude!

Yay! Everyone wins!

Great post, lots of people overlook the collective brake...I know I did. +1

Of course, if the altitude channel is off, then the collective brake doesn't do anything. :)

Except make it easier for the pilot to move the collective? From what I understand (correct me if I'm wrong AOS), but in real life, the pilot needs to press the collective break any time he wants to move the collective to remove the stick force holding it in place. Obviously, flight simmers have no such restriction and for them, the collective brake only functions as the "altitude trimmer".

Except make it easier for the pilot to move the collective? From what I understand (correct me if I'm wrong AOS), but in real life, the pilot needs to press the collective break any time he wants to move the collective to remove the stick force holding it in place. Obviously, flight simmers have no such restriction and for them, the collective brake only functions as the "altitude trimmer".

What's funny here is that I had written "(at least in the game)" to my post in reference to the brake not doing anything, but I deleted it before submitting, thinking nobody would bring up the real thing. Silly me! :P

:smartass:

Wow, I have never used the collective brake....but now I know why I am always "chasing" the VSI with the collective! Guess it helps to RTFM doesn't it? (Actually I am reading but its a big manual and a lot to absorb.....)!

You are just working against the autopilot. I will explain:

 

You are zipping along at a nice stable airspeed and altitude, let's just say 200kph and 500 meters...

 

...without losing or gaining any altitude!

 

Yay! Everyone wins!

Excellent post - thank you! :thumbsup:

Great! Thanx Alpha!:thumbup:

yeah, very very good explaination thanks A16...it makes a lot more sense understanding that it also resets the autupilots authority , which explains why it feels a little hit and miss some times with the AP/assist channels

So If I understand it right, in your example, the Altitude hold channel will be trying to re-achieve 500 mtrs (by lowering the collective servo), but since you've pushed past its authority, all it can really do is limit your collective input by 20% of it's total (or is that 10% either side of the last set position?), meaning your 0 VSI point will have "risen" by 20% (10%?) of the collective play...and if you sat on that +20% and turned off the altitude assist channel, you'd suddenly gain blade angle and start going up again?

(possibly the worst formulated question in history , sorry)

...really must bind that collective brake button ...I do use it a lot in trying to achieve a stable hover, and in flicking between Radar and Barometric alt hold , but had not understood the interaction well untill now (I think), thanks! .. got to get it on my collective ASAP

AlphaOneSix you are the "MASTER OF THE KAMOV UNIVERSE "

From now to the future all my post will end saying " Yes my master "

PD I always want to be a dark said sith. AlphaOneSix , you could be my Darth Vader Master.

So we have the Cyclic trim (T) and the Collective Hold (F)

I really need to start getting all these buttons on my cougar.

AlphaOneSix you are the "MASTER OF THE KAMOV UNIVERSE "

 

From now to the future all my post will end saying " Yes my master "

 

PD I always want to be a dark said sith. AlphaOneSix , you could be my Darth Vader Master.

Well if it makes you feel even better, I know *much* more about the AH-64A than I know about Kamov aircraft. :)

Then you could be my EMPEROR ¡¡¡ ( only when the Apache goes gold )

Well, my goal is to just make myself a useful part of the team, and I enjoy helping people. Thanks for the kind words.

You are just working against the autopilot. I will explain:

You said it so much better than my meager attempt :thumbup:

So If I understand it right, in your example, the Altitude hold channel will be trying to re-achieve 500 mtrs (by lowering the collective servo), but since you've pushed past its authority, all it can really do is limit your collective input by 20% of it's total (or is that 10% either side of the last set position?), meaning your 0 VSI point will have "risen" by 20% (10%?) of the collective play...and if you sat on that +20% and turned off the altitude assist channel, you'd suddenly gain blade angle and start going up again?

 

(possibly the worst formulated question in history , sorry)

If I'm understanding your understanding (understand?) then you are understanding correctly. At least as far as my knowledge takes me. :D

It have Saitek X52, and it is interesting that game still sees axis even if I disable it (make it into bands or directional axis) via Saitek SST programming software.

That fact is very useful for making automated collective brake:

1)Assign throttle axis to collective via game;

2)Create SST profile and make throttle axis into directional one;

3)Assign "F" key to both axis directions ("+" and "-");

4)Adjust sensitivity of directional axis (I recommend "middle");

It works very simple: after every move of throttle "F" key press is generated; and if "Altitude Hold" is on, it will send new desired altitude for autopilot automatically.

Caveats:

1)Watch out for key combination, which uses "F"; if you hold "Ctrl" key while moving throttle, you may get "Ctrl+F" and etc. I use keyboard only for chat and door control, so this is irrelevant to me;

2)High directional axis sensitivity will make control more fine grained, however Saitek throttles isn't very high quality and exhibit unsteadiness, which by it self may generate key presses while throttle isn't moved physically. This, combined with caveat #1, may give very unexpected results.

It have Saitek X52, and it is interesting that game still sees axis even if I disable it (make it into bands or directional axis) via Saitek SST programming software.

 

That fact is very useful for making automated collective brake:

 

1)Assign throttle axis to collective via game;

2)Create SST profile and make throttle axis into directional one;

3)Assign "F" key to both axis directions ("+" and "-");

4)Adjust sensitivity of directional axis (I recommend "middle");

 

It works very simple: after every move of throttle "F" key press is generated; and if "Altitude Hold" is on, it will send new desired altitude for autopilot automatically.

 

Caveats:

1)Watch out for key combination, which uses "F"; if you hold "Ctrl" key while moving throttle, you may get "Ctrl+F" and etc. I use keyboard only for chat and door control, so this is irrelevant to me;

2)High directional axis sensitivity will make control more fine grained, however Saitek throttles isn't very high quality and exhibit unsteadiness, which by it self may generate key presses while throttle isn't moved physically. This, combined with caveat #1, may give very unexpected results.

How do you assign throttle as collective? I tried in game and it will not recognise axis. Thanks.