Altitude hold in autohover - can't make it work

Aircraft always drifts away from set altitude.

I push the altitude button on the autopilot control panel, set autohover, set altitude with collective while holding the collective brake button, release and... it just keeps climbing. I move the collective down just a tiny bit and it starts sinking, sinks past the target altitude and keeps sinking. It should have enough control authority, the collective is more or less in the right place to start with.

What am I doing wrong?

I believe you still have to return the collective to neutral position after climb/sink.

What I found is that altitude hold is more or less for fine tuning. I can still climb/sink with it on.

Yeah, I know it only has a little bit of control authority and you can over-ride it if you move the collective too far. But I'm making tiny movements of the collective and it alternates between rising and sinking very slowly.

There is a switch next to the altitude channel button which determines if the held altitude value is barometric or radar height. This switch is three position with the center position a bit of a mystery. Make sure the switch is in either of the two non-centered positions. In the center position I think it doesn't do anything.

The collective brake lever acts as the trigger for what altitude value should be held. This value is recorded at the moment the lever is released. The collective brake lever should always be held whenever the collective is being moved and if you want to temporarily suspend the altitude hold input.

The altitude channel works by adjusting the collective blade angle and it has a lot more authority to reduce it to lose lift than to increase lift. You want to be sure that you have at least enough collective in by the hand lever to hover. You can see how much authority it has be moving the collective without holding the brake lever and seeing how much you can add and subtract before the hold channel is unable to compensate.

Yeah, I know it only has a little bit of control authority and you can over-ride it if you move the collective too far. But I'm making tiny movements of the collective and it alternates between rising and sinking very slowly.

I don't know how sensitive your collective is or how much is tiny but I just tried it and works as expected for me.

If I'm sinking by -2, -3, then applying altitude hold will bring me back up. But if I'm descending more than that, then I'm still descending.

Does it do the same thing if you use the altitude hold button instead of collective brake?

There is a switch next to the altitude channel button which determines if the held altitude value is barometric or radar height. This switch is three position with the center position a bit of a mystery. Make sure the switch is in either of the two non-centered positions. In the center position I think it doesn't do anything.

 

The collective brake lever acts as the trigger for what altitude value should be held. This value is recorded at the moment the lever is released. The collective brake lever should always be held whenever the collective is being moved and if you want to temporarily suspend the altitude hold input.

 

The altitude channel works by adjusting the collective blade angle and it has a lot more authority to reduce it to lose lift than to increase lift. You want to be sure that you have at least enough collective in by the hand lever to hover. You can see how much authority it has be moving the collective without holding the brake lever and seeing how much you can add and subtract before the hold channel is unable to compensate.

I think the switch was the issue, tried it with it in radar alt and it worked... mostly. It's still incredibly sensitive, have to check on it and adjust collective because I still get drift but its manageable, about 5-10m in per minute.

I think the switch was the issue, tried it with it in radar alt and it worked... mostly. It's still incredibly sensitive, have to check on it and adjust collective because I still get drift but its manageable, about 5-10m in per minute.

How can you have so huge altitude changing? I can fly like forever and radar as well barometric will keep me well on the set value, what now the radar one will have delay with altering terrain height and its limitation for authority.

But for me it really feels about that 16% authority range that I can lave the collective to have it automated.

I move the collective down just a tiny bit and it starts sinking, sinks past the target altitude and keeps sinking.

Can't see it mentioned, but pretty sure it's modeled that the moment you move the collective you clear the assigned altitude, so you have to get level first, then set it, and if you've got too much (or little) collective in for the system to compensate & adjust the collective, you have to re-set the altitude hold.

Moving the collective doesn't change the captured value. It's the collective brake lever (moment of release). If you turn on "flight director" mode you can see this behavior visually on the HUD.

The collective brake does set the altitude hold (when you let it go, not when you release the brake), but unless you're using a model collective, the collective and the collective brake are decoupled in the SIM - so you can move the collective without releasing the brake.

In the real aircraft, you have to release the brake to move the collective, & at the point where you'd finished moving the collective and released the brake, the altitude hold would reset the value.

In the sim you don't have to release the brake to move the collective, & if you just move the collective without gripping (releasing) then letting go (also releasing :-)) the brake, you appear to just clear the altitude hold setting.

Move the collective, reset the brake.

OK, I did not realise it cleared the setting. I was moving the collective hoping to return it into the range that the auto-altitude had control authority but now it makes sense that if I was clearing it, then it would sink past set value.

Is it enough in this case to just tap the collective brake off/on and then it sets your new altitude?

yes

I've discovered there is a difference in behavior between height-hold-channel off and height-hold-channel on plus collective brake lever held. This is distinctly different than the other attitude channels where the trimmer button being held down disables the value hold function of that channel entirely. Of course there is still some dampening and rate limiting for safety but otherwise you have direct control.

This is not the case for the altitude hold channel which being on still is in between the collective handle and blade angle even when the brake handle is held. With height channel on and brake lever held moving the collective handle doesn't give the same authority as height channel off.

Flying in this method with height channel + brake lever hold you will find that blade angle is very "sticky" around 0m/s VS. I don't think that's supposed to be there. I think the brake lever is supposed to suspend any altitude holding function as long as it is held depressed.

So when you engage ALT Hold, how do you keep the Blackshark from slowly drifting up or down while your heads down in the Shkval?I have been troubled by this for years.

So when you engage ALT Hold, how do you keep the Blackshark from slowly drifting up or down while your heads down in the Shkval?I have been troubled by this for years.

The Ka-50 auto-pilot appears to have a limited range of collective control (trim authority).

For example if the auto-pilot's hover is "sinking", you'll need to add a *little* collective and watch the VVI - if the auto-pilot is now able to hold the hover (0 m/s), your input was sufficient, OTOH if you add too much, the auto-pilot can't adjust for the excess input and the helicopter will start to rise.

In general, if you are already in a stable (0 m/s) hover, engaging auto-hover should maintain it but it's always best to check the VVI before going heads down.

Note: Crosswinds and sloping terrain can cause issues due to drift, downwash, etc., so it's important to consider wind direction and obstacles when planning an attack/hover and allow enough clearance before engaging hover hold.

I agree and understood everything you just stated,in fact, my experience has been as you described. Often I get it stable at 0 VVI,watch it for a few seconds, then go heads down. Even on flat terrain, after a minute or so, I find it has slightly increased or decreased, and I then make very minut adj to the collective. Always chasing it though! I just thought I was missing something to correct that, thanks.

I agree and understood everything you just stated,in fact, my experience has been as you described. Often I get it stable at 0 VVI,watch it for a few seconds, then go heads down. Even on flat terrain, after a minute or so, I find it has slightly increased or decreased, and I then make very minut adj to the collective. Always chasing it though! I just thought I was missing something to correct that, thanks.

It's not just you and I think it's bugged.

Altitude hold works perfectly in low or no wind condition. Even with some collective deviation, altitude hold keeps the altitude steady.

But once you add some wind, it behaves... strange. Just with 10m/s at 1000, it's near impossible to keep it constant altitude with altitude hold. You can get it close enough but will still climb or descend. What's stranger is that if I keep fairly steady altitude "without" altitude hold, and then activate altitude hold, I start climbing faster.

I'm no Blackshark pilot but something doesn't seem right.

By the way, with 10 m/s wind, it rotates like mad too. Even with headings hold. That normal too? Ka-50 autopilot can't compensate for wind?

No, the AP can't compensate for wind on its own.

You either properly trim the aircraft so it's within the AP authority limit or it starts drifting/turning. I tried with 15ms crosswind and the helicopter didn't turn a bit.

I tried ALT HOLD in a hover (same 15ms crosswind) and after about 4 minutes I noticed the helicopter rising slightly and stabilizing at the wrong altitude. Could have been the result of time acceleration, but I was impatient. Happened in both BARO and RDR.

AP can't compensate for wind, sloping ground etc IRL either.

It's not a bug, chaps, it's the delights of driving something that naturally wants to turn upside down an thrash itself (and you) to pieces.

Something over 7300 hours in real ones and holding a stable hover is still something that takes a lot of concentration. Add some funky wind and it gets proper challenging...

Well,,, if its a natural characteristic of the BlackShark,,, then all is well then, thanks

It's not how challenging it is that bothers me. It is that autopilot doesn't help.

It's just as challenging to hold hover with or without autopilot.

As someone pointed out, it's all about the collective brake. This helo can melt your brain when you first take it out, then you get the aha moment, and finally understand how the autopilot/trimmer works and life is good.

The collective brake should be held for even the slightest movement of the collective, in the real helo, you would be forced to. The Mi-8 actually has an option under special for "hydro lock" which forces this.. the Ka-50 has no such option but that doesn't take away from the fact that this is how the helo needs to be operated.

For you TM warthog owners, I've put the collective break of the springy side of the speed brake switch. My thumb is always resting there and I ensure I engage it each time I move the collective, settle the helo best I can around 0 FPM vertical, then release the brake when I'm happy. The autopilot will have 15% authority from that position, and will set the altitude on release. Becomes second nature using that switch, I use it for all helos.

AP hover hold can compensate for wind. The Doppler system scans the ground and detects movement. In fact if it's moved off the saved point it will attempt to get back to it. 10m/s might be a little much depending on the relative heading of the wind.

Radar alt hold should hold you within a meter for minutes on end if everything is set right.