Problems with the Turn Coordinator bubble?

[Frederf]

Being a fixed wing pilot I'm rather familiar with the turn coordinator. Most of the time having the little black marble centered in the curved fluid-filled tube is exactly what you want (some say all of the time).

 

However with the Ka-50 while I can contort the pedals to align the ball it seems to really upset the aircraft. In straight-n-level cruise flight I trim and notice that the ball is off to one side so I input pedal and straighten up again and trim that. So I have the instruments showing happiness but the whirlybird just doesn't look right, we're skidding all over the terrain in this weird cross control situation. It also takes a lot of pedal input to make the ball line up which doesn't make sense at 200 kmph with a windvane body.

 

Is the instrument nuts or am I? :joystick:

[Slayer]

I'm sure someone will correct me if I'm wrong....My guess would be that the ball is representing the "body" of the Ka-50. Your rotor is not always in a fixed parallel plane in relation to the body of the helicopter, it changes when you move the cyclic. So what your doing is trying to level the body of the helicopter while your rotor is in a different angle, thus you side slip etc. I think in this situation it doesn't represent what you do in a fixed wing aircraft.

 

Get it flying straight ahead then look at your external view, you will see what I mean.

[slug88]

No, as indicated in the manual, the bubble is a sideslip indicator with the same function that it would have in any fixed wing aircraft. I'm not sure what exactly your problem might be, Frederf, perhaps you could post a track illustrating this?

[Bobcat]

Frederf

 

Someone (Ivank) who knows a lot more about flying than I do posted this not so long ago

 

When you trim two things happen, Cyclic stick position is held and rudder position is also held ... (i.e. a new zero point for the cyclic and rudder pedals is set).. no problem there but what also happens is at the instant you release the Trimmer button a new reference heading is sent to the Heading Hold part of the AP/Damping system. If the HDG HOLD blue switch is on then the autopilot will try and keep the last commanded reference heading by Rudder input. So lets say you are roaring along on a heading of 090, You set the desired Pitch attitude, and trim. Good all is well, then you start manoeuvring in heading, Lets say you start a turn to the left ... initially you bank to the left but immediately you notice a resistance to turn ... thats because the Heading Hold function is applying opposite rudder in an attempt to keep your nose pointed 090. The solution is simple deselect Heading hold when manoeuvring in fact I am now deselecting it most of the time. The only time I ever turn it on is when I want to maintain a specific heading like in the hover or on a long straight leg. Doing this means you don't need to hold the trim button in when manoeuvring.

 

I have the trimmer and HDG hold switch on the Flight stick coolie hat switch. With a little practise you can trim and HDG hold rapidly even whilst manoeuvring. A typical sequence might go like this. Flying along on a straight heading so HDG hold is on, you decide to make a heading change you de select HDG hold , fly to the new heading, get the ball centred, re select HDG hold then a quick trim to set the new reference heading. Another scenario is when you need to centre the skid ball... des select HDG Hold before you do it. Centre the ball , hit the trim, re engage HDG Hold then another quick trim to send the new ref heading to the Heading hold computer. The Helo will now pretty much hold the desired heading and the ball will be centred This method also assists in the blade collision problem at high speed. Since you no longer have cross controls trying to fight the HDG hold yaw input versus balanced flight.

Also if you have the DH/DT switch (just behind the FD push button) in the middle or neutral position then the diamond on the hUD heading scale will always indicate the current HDG HOLD reference heading. This should be your default selection imo for 99% of your flying.

 

Make sense?

 

Bobcat

[Slayer]

This was the only thing I find in the book:

 

Yaw indicator. Indicating the yaw of the aircraft, this indicator displays a ball in a liquid filled tube. If there is no yaw in the flight path, the ball will be centered. If there is yaw, the ball will be displayed in the opposite direction of yaw. The sideslip indication ball moves by local acceleration so it will not always display the actual sideslip. This depends much on the type of maneuver you are flying.

[EvilBivol-1]

There is one known issue with the slip indicator, which is that it should not be jittery like it is. Not sure if anything else you're seeing is a problem or not.

[Valcor]

The yaw forces seem a bit off in cruise IMO. It seems overly sensitive to turn and changes in roll without changing power. Most helicopters can be flown with zero input on the pedals while at cruise, including turns, and have the ball centered just fine as long as you are not changing the power settings.

Edited January 7, 2009 by Valcor

[Buznee]

I also had a bit of an issue understanding this but under closer inspection and analysis I think it makes sense.

 

First of all the jitteriness I think is actually indicating the vibration the helicopter is going through. There should be more vibration in forward flight due to the lead lag motion / force caused by flapping and inputted from the rotor into the fuselage increases as you go faster and as you increase load factor.

 

As for the issue with the turn coordinator causing the aircraft to be in a funky sideslip or condition when trimming to center it I think is mostly due to winds. The winds tend to naturally weathervane the aircraft nose-in, tail-out. Therefore naturally with wind the aircraft wants to point into the wind. This is similar to a fixed wing. Therefore when flying with cross wind the turn coordinator will show that the aircraft is slipping with respect to its flight track. If you correct using trimmer you will input a diff. collective

(yaw) trim. If you have all the autopilot dampers on, the aircraft is going to try to keep the ball in the center all while keeping the same heading and constrained to a certain bank and pitch. This is while it is fighting the wind. Try flying with and without crosswind to see if there are changes in the way the aircraft looks when flying with the ball centered. I'm thinking more and more that with cross wind its okay to have the ball not centered because your purposely slipping the aircraft to minimize side fuselage drag. If you have the heading autopilot damper off, it should weathervane into the crosswind and the ball should not be centered... i think.

 

I believe in route mode its difficult to get the funky uncoordinated look because the aircraft is trying to follow a ground course using mostly bank. If there so happens to be some cross wind and you trim the aircraft to keep the ball in the center the autopilot is going to try to keep the aircraft flying along the course by keeping the aircraft banked. In a fixed wing its like slipping the aircraft in using aileron and opposite rudder to keep the nose pointed towards the course, which requires the aircraft to be banked to keep it from slipping. Some-one chime and clean this mess up :megalol:

[Frederf]

Yeah the ball is jittery but I accept that it's not "damped" like a real ball in a fluid filled tube, it's just a software representation of (deep breath) the lateral component of local apparent gravity in the coordinate system of the helicopter body with all the little numerical jitterings that comes with it. I fly with jitter camera on (Shift+J) so I don't really notice since everything is jittering (it's a great camera mode by the way, give it a shot).

 

I considered that it was the autopilot fighting me in some way. I'll try it with the yaw AP channel completely off and see if I can get it to do it again. If it's the AP I'm going to have to figure out a way to prevent it.

 

EDIT: I'm guessing that it was just strong winds. I'm still getting it but never on the training missions with 0 / 000 wind. The heading hold of the autopilot fights me when I'm in the neutral position of the DT - Trim - DH switch but never when I'm in DT or DH with RTE mode off.

Edited January 7, 2009 by Frederf