Coordinated Flight/Ball

[fapador]

It has other issues though,  at level flight it tends to roll. It also has a fuselage that sits too horizontal like a UH-1C and is not angled properly in relation to the skids. I also think it feels too stable and heavy, this might be  caused by a bunch of other limitations of the x-plane engine like lack of pre-cone and undersling rotor representation or over-efficient props producing large amounts of thrust that X-plane tends to calculate.    

 

Edited September 9, 2021 by fapador

[fapador]

@BIGNEWY Any update on this issue? Is this being investigated at all as there has been a month since I reported it. Can we expect something?

[BIGNEWY]

On 9/8/2021 at 1:42 AM, pbishop said:

So this conversation got me curious so I did some work.....  I'll go through the process very briefly because I think the details are probably going to take a while to explain.

 

The following data was exported from DCS using the export.lua into a log file:

 

	arg Value
IAS	117
Rudder	184
Longitudinal Stick	186
Lateral Stick	187
Collective	200

 

The searchlight (arg value 410 on/off) was used to mark data when stable on a test point to find the data afterwards.  Stable on point was trimmed at the desired airspeed in level flight for at least 1 min.  After the minute in stable flight, the marker was turned on between 5 and 10 seconds long.

 

The average position over the data with marker on was used to plot control position.  The position values were converted from full range (+max/-min) to a percentage of the full travel.  The flight test data from the UH-1H report was then also converted to percentage to allow it to be plotted on the same graph.

 

Some notes:

The following table provides the setup between the two tests.  A difference between the two is there is no calibrated airspeed in DCS (not sure how you could correct for a simulated installation anyways) so indicated airspeed was used assuming no installation error.  A different CG chart then the one posted before is used (see end of post), as theoretically it may be closer to the CG we can simulate in DCS, slightly more forward.  No idea if long/lat CG data can be extracted, so it is N/A.

 

	UH-1H Flight Test Data	UH-1H DCS Data
Gross Weight (lb)	8740	8840
CG Long (in)	132.4	N/A
CG Lat (in)	0	N/A
OAT (C)	24	24
Density Alt (ft)	5220	5100

 

Now for the interesting bit:

 

 

 

 

 

 

@pbishop Do you have track replays from your testing?

 

 

17 hours ago, fapador said:

@BIGNEWY Any update on this issue? Is this being investigated at all as there has been a month since I reported it. Can we expect something?

 

I have no news to share the helicopter devs are very busy currently. 

If you have track replay examples please add them. 

[pbishop]

On 10/4/2021 at 9:36 AM, BIGNEWY said:

 

@pbishop Do you have track replays from your testing?

 

 

@BIGNEWY Sorry I don't have a track.  However, I can repeat it when I get some time in the next couple of weeks and post it.

[fapador]

 

[Tim_Fragmagnet]

Having flown this module for hundreds of hours.

 

It's not that you don't need to give it right pedal, it's that the slip indicator is just wrong.

It has been broken like this since at least 2016, which is the earliest I can remember noticing the crabbing with the ball centered.

I figured an issue as major as a basic flight instrument not functioning properly would be big enough to get fixed relatively quickly, but at this point I doubt it will ever get fixed.

This is what level flight looks like at high speeds with the ball centered.

Edited December 19, 2021 by Tim_Fragmagnet

[fapador]

On 12/19/2021 at 8:38 PM, Tim_Fragmagnet said:

Having flown this module for hundreds of hours.

 

It's not that you don't need to give it right pedal, it's that the slip indicator is just wrong.

It has been broken like this since at least 2016, which is the earliest I can remember noticing the crabbing with the ball centered.

I figured an issue as major as a basic flight instrument not functioning properly would be big enough to get fixed relatively quickly, but at this point I doubt it will ever get fixed.

This is what level flight looks like at high speeds with the ball centered.

@BIGNEWY @NineLine

[Fakum]

OMG,, LOL,,, now wait a sec,,, so I have tried many times to fly the Huey with the ball centered, especially at high speeds, just so I could make it as efficient and fast as possible. I always found myself flying kind of sideways when I get the ball centered,, felt awful! I eventually gave up that practice and ignored the ball. So ignoring it as I have is the best thing to do under current conditions?

[Tim_Fragmagnet]

3 hours ago, Fakum said:

I eventually gave up that practice and ignored the ball. So ignoring it as I have is the best thing to do under current conditions?

Correct
Here is the difference between instrument coordinated and actual coordinated flight in the huey as shown by real-time telemetry on tacview
Flying by the indicator

Actual coordinated flight

Notice anything? Yeah, you have your right pedal requirement, the slip indicator is just wrong so no one thinks the right pedal requirement is there, then it gets reported as a flight model error when it's literally a bug with a flight instrument.

Just ignore the slip indicator entirely tbh. I'm not sure if it's even correct in turns.

Edited December 22, 2021 by Tim_Fragmagnet

[fapador]

Everyone massively report this pls .Your observations  @Tim_Fragmagnet are very valid thank you very much!

Edited December 23, 2021 by fapador

[Fakum]

@Tim_Fragmagnet Thank you for that!

[Grievo]

I'm not saying that the ball is modelled correctly. I think it feels a bit off as well.

However, it is perfectly normal to crab along a track with the ball centred in a crosswind. The ball just shows the aircraft is flying in balance aerodynamically. It has nothing to do with the track over the ground. In fact, in a crosswind, you would expect the nose of the aircraft (the heading) to be somewhere between where the wind is coming from, and the path over the ground (the track). Don't forget that at 90 knots cruising speed, or thereabouts, a crosswind will have a greater crabbing effect on the aircraft, as there is a smaller forward velocity component.

I realise this is a "suck eggs" comment for many of you, but there seemed to be some confusion in some of the posts above. 

[Tim_Fragmagnet]

I will personally confirm that this issue is completely unrelated to wind, as it remains prevalent in missions with no wind at all.

[admiki]

I think this is not correct. Even though tacview is showing it otherwise, it's bounded to ground track.

Consider this. You are flying with your disk level (disregard aerodynamics to keep this simple). Even though you are moving forward, your rotor is still trying to torque your fuselage to the right. You still need either tail or tailrotor to keep you in trim. Either one of those will push your tail to the right and as a consequence, you will crab to the right in straight&level no wind flight.

[Grievo]

8 hours ago, admiki said:

I think this is not correct. Even though tacview is showing it otherwise, it's bounded to ground track.

Consider this. You are flying with your disk level (disregard aerodynamics to keep this simple). Even though you are moving forward, your rotor is still trying to torque your fuselage to the right. You still need either tail or tailrotor to keep you in trim. Either one of those will push your tail to the right and as a consequence, you will crab to the right in straight&level no wind flight.

Your instinct is correct, regarding the sum of forces and the push of the tail rotor thrust vector, however helicopters are usually designed with a slight tilt to the main rotor mast to offset this phenomenon. It is called "tail rotor drift". 

[Tim_Fragmagnet]

That phenomenon is actually called translating tendency, and it is also a far more subtle effect than what the incorrect slip indicator makes happen.

[Grievo]

Dammit Tim, now I have to hit the theory books again to pick up my game!

From what remember also, it’s more of a consideration in the hover rather than in forward flight. 

[admiki]

Yes, it's translating tendency, but it's effect is the same for same power level regardless whether you are in hover or in forward flight. 

[Tim_Fragmagnet]

2 hours ago, admiki said:

Yes, it's translating tendency, but it's effect is the same for same power level regardless whether you are in hover or in forward flight. 

It's funny you say that, because translating tendency is a small enough effect that you can negate it by applying cyclic. Which doesn't work here because this issue isn't translating tendency.

It's also funny you say that, since the issue at hand is based on speed and not torque.

 

The issue isn't translating tendency, the issue is the slip indicator for whatever reason not reading properly while in motion at cruise speeds or higher.

The flight model realistically depicts the requirement of right pedal input to properly trim out the aircraft in cruise, yet the slip indicator does not follow this requirement and in fact directly opposes it.

As the need for right pedal increases, so does the leftward motion of the ball. Almost as if the slip indicator were not a dynamic flight instrument but were scripted to act in specific ways in specific situations, but was accidentally scripted to act backward for this one.

Edited December 24, 2021 by Tim_Fragmagnet

[fapador]

20 hours ago, Grievo said:

Your instinct is correct, regarding the sum of forces and the push of the tail rotor thrust vector, however helicopters are usually designed with a slight tilt to the main rotor mast to offset this phenomenon. It is called "tail rotor drift". 

This does not apply on the huey. the mast is 90 degree perpendicular to the tail rotor. The kiowa on the other hand has the rotor mast 5 degrees down left angled 

 

On 12/23/2021 at 2:30 PM, Grievo said:

However, it is perfectly normal to crab along a track with the ball centred in a crosswind. The ball just shows the aircraft is flying in balance aerodynamically. It has nothing to do with the track over the ground. In fact, in a crosswind, you would expect the nose of the aircraft (the heading) to be somewhere between where the wind is coming from, and the path over the ground (the track). Don't forget that at 90 knots cruising speed, or thereabouts, a crosswind will have a greater crabbing effect on the aircraft, as there is a smaller forward velocity component.

The slip indicator works according to gravity and centripetal acceleration. That means it will be affected by direct position in relation to ground... but since dcs doesnt even model earth curvature I am pretty sure the slip indicator is a  simple wrongly implemented script.

Edited December 24, 2021 by fapador

[Grievo]

On 12/25/2021 at 5:04 AM, fapador said:

The slip indicator works according to gravity and centripetal acceleration. That means it will be affected by direct position in relation to ground...

 

Then why would pilots or navigators need to work out headings to achieve a certain track over the ground when there's a crosswind? If they could just fly the track bearing with the ball centred? The balance ball has no idea where it is geographically. It just indicates the aircraft is in coordinated flight.

 

[fapador]

7 hours ago, Grievo said:

Then why would pilots or navigators need to work out headings to achieve a certain track over the ground when there's a crosswind? If they could just fly the track bearing with the ball centred? The balance ball has no idea where it is geographically. It just indicates the aircraft is in coordinated flight.

 

Nope not correct,  Geographical location affects the ball, gravity in earth is not exactly same in all locations . The ball doesn't care about heading or track it just shows that all the forces are neutralized thus nothing is hindering efficiency. Think of sailing for example you loose the sails or take them in according to where the wind is coming from to maximise efficiency and gain speed but you dont necessarily have to change boat course. The ball is affected by centripetal acceleration that means a twisting action as seen from above top down view. It is possible to have a centered ball and still drift sideways but the heading will be maintained at least on theory (or in a flat earth). Nevertheless, the pictures tim has posted are no wind condition 

Edited December 26, 2021 by fapador

[admiki]

While I know that gravity force does fluctuate, I don't think it fluctuates even close enough to affect the ball

[fapador]

9 minutes ago, admiki said:

While I know that gravity force does fluctuate, I don't think it fluctuates even close enough to affect the ball

There is no exact answer in this, It simply depends... consider not only gravity location but for example if you pull stick and raise g's. That for example will pin the ball down and will allow a small untrimmed condition while still being shown as fully centered 

Edited December 26, 2021 by fapador

[admiki]

Now you are going off tangent. Topic of this thread is straight and level flight over ground, not force vectors in turns