What's the difference between "autohover" and coming to a hover and trimming?

[Bearfoot]

So can someone tell me the difference between the following:

 

(1) come to a hover (or close enough) and engaging the autohover

(2) come to a hover, making sure all four autopilot/stablization channels are on (pitch, yaw, heading, and altitude), and then pressing and releasing the trimmer

 

 

Also, when I engage autohover, the "altitude hold" channel comes on. When I click the autohover switch again to disengage it, the altitude hold channel stays on. Is it normal practice then to reach down and switch it off for normal flight?

[Retu81]

The main difference is basically the wind effect. If you stop to a hover and trim the helicopter there, you'll eventually start to drift again when the wind changes.

 

Autohover is a 4-channel autopilot, which tries to actively hold your position in space (lateral + altitude), that's why the altitude hold comes on as well.

[Rogue Trooper]

Auto hover will bring you to a hover when in low speed (4 or 5KM)

Auto Hover will also adjust the Helicopter to hold your position over the ground in which you activated Auto Hover, This can be seen on the HSI indicator which has longitudinal & lateral deviation bars (a centered cross in normal flight). If the chopper drifts whilst in Auto Hover, the bars on the HSI will drift from the center and the Auto Hover will adjust the flight controls to bring the chopper back into this central position.

A re-trim whilst in Auto hover will re-center these longitudinal & lateral bars and the current ground position will now be the new hold position.

 

It is also possible to come into Auto hover with higher speeds by chasing the HSI bars and constantly trimming (click trim) until stability is achieved.

 

It is normal for altitude hold to come on

 

Without Auto hover the chopper will drift but still hold its heading, altitude Pitch and roll.

[Frederf]

Auto-hover, or as it should be called hover hold, utilizes the Doppler radar system to record and maintain a point over terrain. It does trigger the altitude hold channel on but that can be done manually.

 

The big deal is that when you engage the mode (or trim after) it captures the location directly below you. Not only will it keep this position but it will fly back to it if moved away. The drift from this point can be seen by the needles forming a cross in the middle of the navigation instrument (HSI or Russian equivalent).

 

This is also a good critic of your hovering skills. Unless you put the helicopter in a good trimmed condition when engaging auto hover (or trimmer button release after) the AP won't have the authority to fly to and maintain it. If you engage auto hover and the needles center without any touches to the controls then it was a good entry. If not, practice more.

 

Flying with the altitude hold depends on your technique. You should always press and hold the collective handle brake (default F) every time you move the collective handle. The brake is like the trimmer button for the collective and will disable the altitude hold while it's being held. Squeeze, move, release every time. You'll find the altitude hold is no longer a problem if you do this habit.

[Bearfoot]

Thanks, everyone for the great answers. Really helpful.

 

So, basically, the biggest difference is while both 4-channel trimming and autohover maintain aircraft altitude, pitch, heading, etc., only autohover (tries to) maintain the aircraft horizontal position relative to the ground.

 

 

 

@Frederf: Thanks for the discussion of the collective brake. That was going to be my next question! And thanks for pointing out the effectivess of the autohover is contingent on the state/stability of the aircraft when initially engaging autohover. That explains some puzzling behavior.

 

 

Now I just have to figure out how to come to a hover less like a rodeo bull on a combination of high-grade PCP with a too-tight belt has just been stung by a very angry wasp

[Frederf]

Yes, it's the Doppler navigation system, the same thing that gives you ground speed in the HUD and the slow speed vector line. I don't know the words in Russian but I like to remind anyone I can to think of it as a hold because it absolutely won't adopt a hover from not in one but it can keep you in one you make.

 

I find slowing to a stop best if one treats the collective as slowly lowering and it is the job of the cyclic to prevent altitude loss. By the time the 50kmph speed vector line shows on the HUD (assuming NAV HUD) freeze both controls and start adding back in collective as lift drops and pitch back down to hover attitude as the line shrinks to zero size.