Drift Angle Indicator

[Avio]

I was trying to fly to a waypoint using the Doppler system, flying at about 170 km/h. All looked good on the way there, but the Drift Angle Indicator kept showing the needle pointing to the left about 10 degrees, even though I looked to be flying straight, with the slip ball in the center with no rudder input. Even then, there seemed to be a gradual left drift. I had to intentionally put in some left rudder in order to center the Drift Angle Indicator so that the Hip could fly straight. But that caused the slip ball to go to the right of center.

 

Anyone knows what is the correct way to track straight on course? Keep the Drift Angle Indicator needle centered, or keep the slip ball centered?

 

[Caster]

I found this vid by vsTerminus to be really helpful, there's a specific section for fixing drift once you're coordinated, but I reccomend the whole vid 

 

[Avio]

I had watched that, but not sure if the video showed the Doppler being turned on, or not.

 

The manual stated that at 170 km/hr or so there should be no rudder input needed, and indeed the ball is centered around that speed, meaning the Hip is flying coordinated. If the Drift needle is to be centered, a strong left rudder needs to be applied, resulting in the ball swinging to the right, and that is not coordinated.

 

Can someone helps to clarify -- the Drift Angle top center index refers to the aircraft's nose direction, while the needle shows the ground track, is that right? Or is it the other way round?

 

I believe the needle shows the ground track, thus the left drift over time. If so, to fly with the ball always centered, one would need to intentionally crab the aircraft's nose to the right, so as to maintain straight up ground track? This is getting a bit confusing.

 

[ftmch]

Flying co-ordinated in a helicopter is not the same as flying in a straight line. He explains in the video that you need to have a slight right-down attitude to fly the Hip in a straight line, which will cause the ball to be slightly right of centre. That drift indicator works regardless of whether you've turned on doppler nav, because it is showing the ground track relative to your nose.

 

Basically, don't correct with rudder input, correct with a gentle right bank.

[Art-J]

2 hours ago, Avio said:

I had watched that, but not sure if the video showed the Doppler being turned on, or not.

 

The manual stated that at 170 km/hr or so there should be no rudder input needed, and indeed the ball is centered around that speed, meaning the Hip is flying coordinated. If the Drift needle is to be centered, a strong left rudder needs to be applied, resulting in the ball swinging to the right, and that is not coordinated.

 

Can someone helps to clarify -- the Drift Angle top center index refers to the aircraft's nose direction, while the needle shows the ground track, is that right? Or is it the other way round?

 

I believe the needle shows the ground track, thus the left drift over time. If so, to fly with the ball always centered, one would need to intentionally crab the aircraft's nose to the right, so as to maintain straight up ground track? This is getting a bit confusing.

 

 

Check the episode 17 from the same tutorial playlist, it covers the Doppler operation quite nicely.

[Raven (Elysian Angel)]

Or add/subtract the amount of degrees offset to/from your intended heading. That seems to work pretty well for me...

Edited April 7, 2021 by Raven (Elysian Angel)
typo

[Kuna]

Use autopilot heading and roll trimm manually

Wysłane z mojego Redmi 6 przy użyciu Tapatalka

[Avio]

Thanks for the helpful advice, folks. Was thinking of the option of offsetting the heading by the drift amount to compensate as one method. Will try it out, as well as the method of using autopilot and trimming roll to zero the drift.

 

[Hiob]

Keep in mind, that the cruising speed for the hip is >200 kph (220-240). It is probably build to be level and coordinated at that speed.

Edited April 7, 2021 by Hiob

[Avio]

Okay so I've tried using both methods and here's the finding -- right after take-off and still climbing to cruise altitude and getting settled on the required heading, I manually put in the needed crabbing angle to compensate for the drift, by intentionally offsetting the Hip's nose by the amount indicated by the drift angle indicator. And once settled in a stable cruise altitude, I kick in all autopilot modes and fine-tune the heading using the autopilot Roll knob to get the drift angle needle centered.

 

From there the Hip flies rock solid precise. Best of both worlds !

 

On 4/7/2021 at 6:51 PM, Hiob said:

Keep in mind, that the cruising speed for the hip is >200 kph (220-240). It is probably build to be level and coordinated at that speed.

 

I think the manual says above 150 - 170 kph, progressively more right rudder would be needed to keep the ball centered. So far I tried indeed that seems the case.

[vsTerminus]

You guys have it figured out, but more or less to summarize,

 

- The slip ball will tell you when you are coordinated, but it does not account for the drift caused by your tail rotor. It cannot detect it.

- If you want to fly coordinated and straight you need to fly a few degrees right of your intended heading to counteract the drift.

- If you want to fly straight and don't need to be coordinated your slip ball will rest on the line right of center.

 

 

Now if you flip over to the pilot navigator's side,

 

- The doppler drift gauge will show you the difference in your heading (the direction you are pointed) and your track (the direction you are moving).

- "Kick the needle" with your pedals until it is centered and cancel any bank it induces with cyclic roll.

- Centering that needle will put you out of coordinated flight, but you'll be flying a true heading.

- If you stay coordinated and leave the needle left of center, the number it reads is how many degrees to the right you should adjust your heading to compensate.

 

 

Which is better? Which do real world pilots do typically? I don't honestly know.

I assume they probably fly coordinated for comfort / economy reasons and just adjust their headings, but I'm not a real world pilot so I can only guess.

[admiki]

You want to fly coordinated at all times for best performance. 

If you need to fly a heading, get stabilised on that magnetic heading, read drift, move oposite for same ammount.

[Avio]

Thank you fellows, for the very helpful advice.

 

This drift indicator is indeed an awesome piece of technology, considering its usage back in those days before GPS.

 

[ftmch]

If it all becomes too annoying remember that the Mi-8 is one of the modules where the NS430 actually integrates into the cockpit. I've not had to go there yet though, even on flights from Al Minhad to Fujairah.