Problems 'stepping on the ball'

[Frogfoot1606687865]

Hi, when flying the KA50 I have noticed that the ball in the yaw indicator below the ADI (and backup ADI for that matter) always seems to be ofset to the right. If I add rudder, and adjust cyclic so that the ball is centered the Aircraft is obviously sideslipping. I have found the a much more accurate indication of sideslip is the Rocket aiming reticule. If I select rockets, and keep the aiming reticule centered the A/C will be perfectly aligned with the direction of flight.

Has anyone noticed this, or am I doing something daft here.

 

Tom

[Bucic]

Forget about stepping on the ball in Ka-50. The subject has been discussed extensively in the rookie thread. Please use the search function to search through it. Basically the vain sensors up front your HUD are far better indicators of side slipping. All of that has been explained so well, IIRC, that you probably won't have a single additional question :)

 

Edit:

My style is - conclusions first, then the BS ;) (if I'm wrong here, correct it ASAP)

 

• AC flies in a straight line, there is no lateral acceleration and yet the ball is off center - gravity and AC bank is to blame
  
• the "ball in the center" is not your goal. Coordinated flight is. The ball is just a flawed instrument which might help you achieving coordinated flight.
  
• coordinated flight prevents excessive drag and all of the bad things which follows higher drag
  

 

 

 

Now the BS:

 

Gravity is the only thing I can think of :) The ball channel is U-shaped so if it's tilted to a side (AC flying with slight bank angle) even by a little it will be off center even when there's no lateral acceleration.

 

Also recently I asked myself "WHAT'S THE WHOLE THING WITH KEEPING THE BALL CENTERED?!" - in any AC. Certainly not to have all the instruments looking symmetrical and nicely. Let's do this on a fixed wing AC. Let's also ignore the details of what's happening when you just started moving the control stick to side. Let's say you are already in a turn. Now when you don't fly by the book you are either in skidding turn or slipping turn. In both cases you are simply facing the airflow with much greater fuselage cross section than in coordinated flight thus suffering from increased drag compared to the drag value in coordinated flight.

 

You've observed yourself that the praised ball has its flaws. What I would recommend is to, after you explain to yourself all the aspects of using turn coordinator, do some reading on this little fella on the windshield (Wikipedia calls it "yaw string" ...:smartass:)

 

 

... and compare it to this slightly bigger fella (the vertical one *) ...

 

 

And now here

 

IMO these fellas show what's important in coordinated flight better than the ball.

 

Finally you don't realize how much you missed if you haven't read this book:

 

 

 

* which do its job for horizontal plane obviously :D

Edited May 25, 2010 by Bucic

[Frogfoot1606687865]

Thanks for pointing me to that thread, it seems that because a certain amount of cyclic input is required (due to asymmetrical lift from rotors) the A/C is banked during forward flight the ball wil be affected by gravity, and therefore be offset. However this brings up the point that when in fast forward flight, left cyclic is required to eliminate side slip leading to a slight left bank, I would expect that if the ball was only being affected by gravity I would expect it to be offset to the left not the right.

 

Cheers

Tom

[Bucic]

And it isn't? :D

[average_pilot]

I prefer the "you are doing a very big turn that looks like straight flight" explanation. But it can be that both effects are in play, although not necessarily adding up to the final effect.

 

Also, I have noticed that with time you get an intuitive feeling of the amount of rudder needed to avoid side-slip.

[Meehau]

Let's say you are already in a turn. Now when you don't fly by the book you are either in skidding turn or slipping turn. In both cases you are simply facing the airflow with much greater fuselage cross section than in coordinated flight thus suffering from increased drag compared to the drag value in coordinated flight.

 

It`s not just the sake of side airflow, but in fixed ac in skid turn (when ball is outside of the turn) there emerges additional force of up and lateral direction which may lead to decreasing of speed and following stall.

 

You've observed yourself that the praised ball has its flaws. What I would recommend is to, after you explain to yourself all the aspects of using turn coordinator, do some reading on this little fella on the windshield (Wikipedia calls it "yaw string" ...:smartass:)

 

Well...The yaw string versus ball unconformity is not a flaw, but it`s a normal occurence, because they show two different things based on two different principles. The ball shows the actual direction of resultant force of weight and centrifugal forces and if this direction is parallel to the direction of lift force we are in coordinated and therfore - correct turn. Consequently the yaw string shows slightly offset as it has nothing to do with balance of forces, because the airflow in a turn will never be head-on.

[Bucic]

It`s not just the sake of side airflow, but in fixed ac in skid turn (when ball is outside of the turn) there emerges additional force of up and lateral direction which may lead to decreasing of speed and following stall.

You surely mean the decreased airspeed on 'inner wing' and increased airspeed on 'outer wing'. If no then I'm not aware of any other unwanted forces in such situation :) Besides in my whole 'article' I mentioned only those aspects that are common for fixed wing and rotorcraft on purpose. Spin is not helicopter pilots' concern.

 

Well...The yaw string versus ball unconformity is not a flaw, but it`s a normal occurence, because they show two different things based on two different principles. The ball shows the actual direction of resultant force of weight and centrifugal forces and if this direction is parallel to the direction of lift force we are in coordinated and therfore - correct turn. Consequently the yaw string shows slightly offset as it has nothing to do with balance of forces, because the airflow in a turn will never be head-on.

That was a joke actually :) And I didn't say that yaw string has something to do with balance of forces. What I wanted to say (and I said, IIRC) is that in both cases (fixed and rotorcraft) a string or vane sensor give better indication in terms of achieving no side slip.

 

Also, I have noticed that with time you get an intuitive feeling of the amount of rudder needed to avoid side-slip.

:thumbup:

This is where the "vain sensor exercise" is very useful - where you set your cockpit camera so that you can see the vane sensors to use them as reference.

[26-J39]

Besides in my whole 'article' I mentioned only those aspects that are common for fixed wing and rotorcraft on purpose. Spin is not helicopter pilots' concern.

 

Bucic... Do you have a link to "Your" article?

Would like to check it out..:)

[Bucic]

Bucic... Do you have a link to "Your" article?

Would like to check it out..:)

If you want articles go to New York Times, if you want essentials, ask Bucic 8) The quoted post is 'the article'. What you can't find in the quoted text is obsolete to you as a helicopter pilot :) If you, however, still feel you need to learn more, refer to the mentioned FAA's Pilot's Handbook (free for download!) and, later, a rotorcraft handbook. I don't have a link to the latter one handy, sorry

 

 

 

Also it is a good routine to search through forums entering a keyword of your interest and in the 'User name' field (poster) enter e.g. one of these nick names:

AlphaOneSix

AirTito

I mention this because I recall one of these gurus posted on the subject few times providing some details. IIRC it was in a dedicated topic. Too bad there is no 'topic linking' feature on the forums.

Edited May 26, 2010 by Bucic

[Obiwan]

[...] refer to the mentioned FAA's Pilot's Handbook (free for download!) and, later, a rotorcraft handbook. I don't have a link to the latter one handy, sorry

 

 

You can find the FAA handbooks at http://www.faa.gov/library/manuals/aircraft/

[Speed]

Different subject, but while we are mentioning it, why does the standby ADI always get so @$#$#ed up saying I'm in a nose dive or a steep turn when I am in a level hover?

[Avilator]

Different subject, but while we are mentioning it, why does the standby ADI always get so @$#$#ed up saying I'm in a nose dive or a steep turn when I am in a level hover?

In real life, this would be caused by the gyro having less-than-prefect bearings. Over time, the gyroscopic effect is no longer able to return it to the fully upright position, and it "leans over." In BS, I don't know if ED modeled a really bad ADI or what.

[Bucic]

Different subject, but while we are mentioning it, why does the standby ADI always get so @$#$#ed up saying I'm in a nose dive or a steep turn when I am in a level hover?

Read the DCS BS official FAQ.

[Logan9773]

I'll write this partly for myself ( future reference in case I forget ). But, yeah, from my experience flying the sim, the ball really does not show slip. And if you think about it, why should it? The only thing it shows is Yaw and Bank. It was really meant to show just Yaw, but if you bank slightly or more, gravity will cause the ball to roll in the direction of the bank. Yaw is the opposite, inertia will cause the ball to roll in the opposite direction. I think thats right. :smartass: I agree that the wind vane sensors up front are very useful and should be combined with the ball for proper flight. In a steady hover they also show the wind that is blowing against you ( it bends the vanes while your still ).

Edited May 28, 2010 by Logan9773

[Frederf]

Read the DCS BS official FAQ.

 

The FAQ doesn't contain the answer to his question. The FAQ only mentions that the S-ADI will drift over time slowly. Large accelerations drifting more than small accelerations. This is not the cause of the question.

 

The problem with large pitch or bank attitudes and the S-ADI is that the motion of the gyro has angular limits with physical stops. Hitting these stops applies acute precession forces that drastically alter the original reference attitude. After reference is skewed, recaging is required. This is the the effect central to the stated question.

[Bucic]

Oh, sorry. I thought he just didn't uncage his ADI. But hey, it didn't hurt, if he read the FAQ :P