How to deal with severe yaw coming out of ETL?

[fargo007]

Hiya guys,

 

Mi-8 driver new to the Huey. I really love this machine. It's awesome.

 

I'm wondering what techniques there are to anticipate/prevent/mitigate what seems to be a severe right yaw coming out of ETL, for which it seems there's just not enough pedal.

 

Thanks for any tips or advice.

[Holton181]

You mentioned it yourself: anticipate

It's not an on/off action of the pedals at exit of ETL, you need to anticipate it and start counteract before it actually happens.

And practice. Practice is good ;-)

[Quadg]

i think its a bug in the scripted nature of the event.

sometimes it happens sometimes it does not. and it seems to ignore pedal input.

it can feel even stranger on really windy days when it does it.

 

try hover taxing about at speeds near translational lift and you will notice it in the pedals. sometimes.

 

anyway it feels totally scripted. almost like you have dragged a skid on the ground and its dragging you round. (to high for that)

or its ignoring your right pedal as you increase collective to stop, then loads it on all at once and you yaw right. as you cross ETL. it seems to be in the swap from left to right pedal as you slow the helicopter and then increase collective. i think its yawing left so we press right pedal, get no response and put in more right pedal and then it loads on all at once.

 

anyway luckily it does not happen all that often and its easy to fix when it does it but its hard to diagnose.

 

you need to use the pedals a lot less in the huey than the mi-8

because you have to work the collective less. because the single engine is more responsive so finding the balance is easier.

 

but you have to work the cyclic more (no autopilot)

 

why the huey pilots going the other way find the mi-8 easier and harder to fly :)

so try working the collective and pedals less. don't let your mi-8 muscle memory take over :)

this is another way to avoid it happening so often.

[Holton181]

Never noticed that "scripted" behavior myself. Will look for it in the future.

[fargo007]

Thanks, I will be practicing today. One of the reasons I point it out - I never see a real Huey doing this when coming in for a landing.

[fargo007]

Experimenting - turning off rudder trimmer helped a lot with this.

 

I have to keep tabs on the rudders all the time now, but in and out of ETL and other performance curves are much smoother and controllable.

[FragBum]

Thanks, I will be practicing today. One of the reasons I point it out - I never see a real Huey doing this when coming in for a landing.

 

In real life you feel it as you transition so it's easier to control but look at the aircraft and watch for signs of skewing and anticipate, it will work after some practice. :thumbup:

 

BTW try the Gazelle for yaw. :D

Edited January 2, 2018 by FragBum
<typo> & BTW

[Robert31178]

Thanks, I will be practicing today. One of the reasons I point it out - I never see a real Huey doing this when coming in for a landing.

 

I would also say that this is because you don't see new pilots flying it. Read enough books about Vietnam and you will regularly see that the Huey would "wobble" on landing in the hands of a newer guy.

[fargo007]

Definitely getting the hang of it now. Yes, I'm one of those knoobs. ;-)

 

Good points guys, thank you.

 

Man, Belsimtek knows how to do a kickass helicopter. I love the Huey, and I was already in love with the Mi-8.

 

Setting it up with miniguns keeps it light and stone cold deadly.

 

Shutting off that rudder trim has kept my feet a little more 'alive' on the pedals, and knowing that I'm going to add collective coming out of ETL, I'm a lot more ready to add some left pedal to counteract it AS it's happening, rather than when it's too late.

[Robert31178]

Oh yes, no one ever mentions that you should uncheck that box. If you have the rudder trim set with your pilot trimmer it jacks up your fine maneuvering on approaches and hovering.

[Weta43]

i think its a bug in the scripted nature of the event.

It's not a scripted event.

 

sometimes it happens sometimes it does not.

because it's not scripted.

 

it can feel even stranger on really windy days when it does it.

You mean when you slow down enough that the aircraft starts to weathervane and the wind starts to add to the tendency of the plane to yaw as you apply power ?

 

Try displaying the control display to check that you have turned off rudder trim and haven't just run out of rudder because the sim has trimmed it all away for you.

[fargo007]

Oh yes, no one ever mentions that you should uncheck that box. If you have the rudder trim set with your pilot trimmer it jacks up your fine maneuvering on approaches and hovering.

 

This is EXACTLY the issue and the fix.

[Flamin_Squirrel]

The best way to avoid rapid yaw when passing through ETL is to not pass through ETL rapidly! If you slow down more gradually then you won't need to add power so abruptly which is a major cause of the yaw.

 

 

You mean when you slow down enough that the aircraft starts to weathervane and the wind starts to add to the tendency of the plane to yaw as you apply power ?

 

 

 

The wind will not cause any yawing. An aircraft will not weathervane unless it is in contact with the ground.

 

 

If you intend to come to a hover over a point on the ground with the wind coming from a direction other than straight ahead, it may make things more difficult however.

[Weta43]

An aircraft will not weathervane unless it is in contact with the ground.

 

Any aircraft with a tail intended to add to directional stability will turn into the apparent wind - whether it's on the ground, in a hover or at VNE.

Turning into the wind is weathervane-ing - that's what they're made to do :-)

 

That's one of the reasons why aircraft ( including helicopters - makes no difference from a lift point of view for them ) land and takeoff into the wind not with it.

 

If the wind is coming from behind, the wind will try to turn the aircraft around to face into the wind.

 

If the direction it wants to turn the aircraft coincides with the direction the increased torque reaction is yawing the plane in as you compensate for decreased lift as you leave ETL, you'll have more to fight with the rudders. If it wants to spin the aircraft in the other direction, it will help with controlling the yaw.

 

The effect will be more pronounced the slower you're moving relative to the ground (so the larger the component of apparent wind-speed is generated by the surface wind).

[Flamin_Squirrel]

Any aircraft with a tail intended to add to directional stability will turn into the apparent wind - whether it's on the ground, in a hover or at VNE.

Turning into the wind is weathervane-ing - that's what they're made to do :-)

 

Weathervaning or weathercocking [1] is a phenomenon experienced by fixed wing aircraft on the ground and rotorcraft on the ground and when hovering.

 

Question: if you're in forward flight with a crosswind from your left, do you A) drift right, or B) yaw left? The answer is A. In forward flight the apparent wind is always straight ahead; the actual wind has NO effect.

 

The only time the actual wind has any influence is when you're trying to fly with respect to a point on the ground, i.e. landing a fixed wing plane on a runway or hovering over a fixed point on the ground. Question: if you're (trying) to hover with a crosswind from your left, do you A) drift right, or B) yaw left? The answer is STILL A.

 

The act of adding left cyclic to maintain your position over the ground in this case will result in the apparent wind to come from the left which may well cause a left yaw; but this left yaw is NOT caused by the wind itself, it's caused by the pilot effectively flying the helicopter sideways in an equal and opposite direction to the wind in order to maintain position over the ground.

 

Hopefully this explanation makes sense.

Edited January 5, 2018 by Flamin_Squirrel

[Weta43]

Oh it makes perfect sense, but by your own words:

 

The only time the actual wind has any influence is when you're trying to fly with respect to a point on the ground

 

Which, apart from A2A refuelling, is pretty much all controlled flight isn't it ?

 

Every time you fly you're going from A to B, both of which will be defined with reference to points on the ground, and which will require you to take the movement of the air you're moving in relative to the ground into account.

 

Any time there's a wind that's direction relative to the ground isn't exactly aligned with your intended path, you'll end up flying at an angle relative to your intended course.

 

That's particularly true as you slow for a landing.

 

If you were in a helicopter flying from a point to another point due north of the origin @ 100 km/h, and there was a wind from the west at 100 km/h, to fly the desired course you'd have to point the nose 45 degrees left relative to your actual direction of travel (NW) - weathervaned to fly into the apparent wind - and you'd travel due North.

 

When you got to the point you wanted to land at and slowed, the apparent wind would rotate westerly as you did so, and unless you did something to stop it, the tail of the helicopter would rotate the aircraft into the wind, so that at the point you reached zero ground speed you would be facing west.

 

You have just weathervaned into the wind. If you took 10 seconds to go from 100 km/h due north GS to zero GS, you'd have yawed left at 4.5 degrees a second.

 

If you added right rudder to maintain the original aircraft alignment, or more to line up North for landing as you dropped from ETL, and the rotor rotation was such that you normally needed to add right rudder as you lost ETL to stop the helicopter rotating you would need to add more right rudder than normal because of the wind. If the rotor rotation was such that you would normally add left rudder to maintain the aircraft's alignment as you left ETL, you wouldn't need to add as much rudder as normal.

 

Question: if you're (trying) to hover with a crosswind from your left, do you A) drift right, or B) yaw left? The answer is STILL A.

 

Actually, as I said earlier, & you also posted, if you're hovering with reference to a point on the ground (& if you're not, you're not hovering) you'll tend to yaw left as you drift right unless you specifically counter the torque effect of the wind on the tail.

 

If you're doing that, you may as well counter the drift, which would make the answer neither.

 

 

Edit:

To illustrate the point I've attached an image showing the controls indicator flying the Mi-8 in a 10 m/s wind.

See the rudder input to hold a steady hover in the left section where the wind comes from the left, with that in the middle where the wind comes from the front, and the right, where it comes from the right.

 

In the section on the right, the wind acting on the tail is doing a significant job countering the rotor torque, in the middle there's a 'normal' amount of rudder to hold a steady hover, and at the left more than would be normally necessary as the wind on the tail is added to the normal torque from the rotors.

 

If you were exiting ETL travelling in one of these directions relative to the ground and wanted to maintain that physical heading, you'd need to add different amounts of rudder as you slowed depending on which direction you were flying in relative to the wind.

Edited January 5, 2018 by Weta43

[Gunnars Driver]

Never noticed any yaw more than normal on the huey.

 

Did a flight just to check, and I didnt see it this time either.

____________\\\

For the real UH-1:

Right yaw comes from torque on main rotor.

The UH-1H has 30knots as maximum cross wind at hover which means the tail rotor can handle 30 knots plus a margin.

ETL speed is around 20 kt.

_____________________

 

In the module, the by me estimated speed( no wind) when the tail rotor not longer can hold the helo square to the wind if taking of sideways seems quite right.

 

I use DCS World open beta, latest version. Have only installed it and adjusted controls, axis and buttons. Not changed any yaw trim settings.

[FragBum]

Ah yes there is also seems to be an apparent ETL effect increasing the rotor lift. I did some tests and the heli is most certainly pushed by the wind in the direction the wind is travelling.

 

The other interesting thing is the amount of slip and slide you get when you try to track a circle path as well as more variation of ETL as you track the circle. It would be fantastic to have grass with wind effect to give you a feel for the wind across a field although the bushes seem to move in response to the wind at lest that's what it appears to be doing . :D

 

 

The attached missions are basic ver 2.2.0 NTTR map with all 4 current helicopters for the "All" and "Huey" only for the Huey version.

 

Wind is 25KPH (ish) from the north with fuel levels for a realistic test flight.

NTTR_25KWindtestAll_01.miz

NTTR_25KWindtestHuey_01.miz

[Holton181]

Just like to add my two cents regarding weathervaneing.

If you have ever been flying a small helicopter IRL in gusty conditions, where the wind is coming from all sides, you know by heart it is weathervaneing in all flight regimes!

[Flamin_Squirrel]

If you were in a helicopter flying from a point to another point due north of the origin @ 100 km/h, and there was a wind from the west at 100 km/h, to fly the desired course you'd have to point the nose 45 degrees left relative to your actual direction of travel (NW) - weathervaned to fly into the apparent wind - and you'd travel due North.

 

What you've described is compensating for drift across the ground to achieve the desired track across the ground, but there are NO aerodynamic effects from doing this at all. The airflow with respect the helicopter is still coming from straight ahead; there is no yawing, no weathervaning.

 

When you got to the point you wanted to land at and slowed, the apparent wind would rotate westerly as you did so, and unless you did something to stop it, the tail of the helicopter would rotate the aircraft into the wind, so that at the point you reached zero ground speed you would be facing west.

 

No. As the helicopter slows it is still moving straight ahead with respect to the surrounding air in which it is flying. The fact that the air is moving across the ground is totally irrelevant. If the helicopter needs to come to a hover on a windy day (lets assume 10kts from the left) then the helicopter will then need to be flown sideways to the left at 10kts to achieve 0kts GS. The act of flying sideways may cause a yaw that needs to be counteracted, but this isn't caused by the wind - you could be flying left at 10kts in a 10kt wind blowing in any direction, it makes no difference.

 

Think of a hot air balloon for example. The basket hangs directly under the canopy; it doesn't matter which direction the wind blows, it has no aerodynamic effects what so ever. Only if you were to tether the balloon, bringing it into contact with the ground, will the wind be able to affect it.

[Weta43]

there is no yawing, no weathervaning. (...) What you've described is compensating for drift across the ground to achieve the desired track across the ground,

 

The definition of yaw given in Wikipedia is below. This conforms with my understanding of yaw prior to visiting their page. If you think it's wrong and misinforming the general population you can - and perhaps for all our benefits should - edit it and explain why the original was wrong.

 

Yaw:

A yaw rotation is a movement around the yaw axis of a rigid body that changes the direction it is pointing, to the left or right of its direction of motion. The yaw rate or yaw velocity of a car, aircraft, projectile or other rigid body is the angular velocity of this rotation, or rate of change of the heading angle when the aircraft is horizontal. It is commonly measured in degrees per second or radians per second.

(...)

Yaw velocity can be measured by measuring the ground velocity at two geometrically separated points on the body, or by a gyroscope, or it can be synthesized from accelerometers and the like.

 

In the case of the slowing helicopter with a real motion North, but a heading that changes from 315 degrees @ 100km/h GS to 270 degrees @ 0 km/h GS.

This is precisely a movement around the yaw axis of a rigid body that changes the direction it is pointing, to the left (...) of its direction of motion

 

When maintaining a course relative to the ground, as a helicopter exposed to a crosswind slows, it will tend to yaw into the wind unless the pilot applies rudder to compensate.

 

Edit:

or you can look at this intro page from NASA:

https://www.grc.nasa.gov/WWW/k-12/airplane/yaw.html

 

In flight, any aircraft will rotate about its center of gravity, a point which is the average location of the mass of the aircraft. We can define a three dimensional coordinate system through the center of gravity with each axis of this coordinate system perpendicular to the other two axes. We can then define the orientation of the aircraft by the amount of rotation of the parts of the aircraft along these principal axes. The yaw axis is perpendicular to the wings and lies in the plane of the aircraft centerline. A yaw motion is a side to side movement of the nose of the aircraft as shown in the animation.

 

NASA defines yaw relative to a 3 dimensional coordinate system, not relative to the apparent wind.

 

Edit 2 ! :)

Just for good measure please re-read Holton181's post above (below):

Just like to add my two cents regarding weathervaneing.

If you have ever been flying a small helicopter IRL in gusty conditions, where the wind is coming from all sides, you know by heart it is weathervaneing in all flight regimes!

Edited January 5, 2018 by Weta43

[Flamin_Squirrel]

I'm going to say this again. Once airborne A STEADY WIND HAS NO AERODYNAMIC EFFECTS.

 

I'm a degree qualified chartered engineer with a fixed wing pilots license and well on my way to getting my rotary licence. I'm not making this up.

 

I get the feeling you're simply not gong to listen though.

[Weta43]

You may be an Engineer, but I assume you're not speaking ex cathedra here ?

 

Looking back, I think there are two things happening here:

 

1/You've drifted off topic. Please re-read the thread title: "How to deal with severe yaw coming out of ETL?".

 

The question of whether "A STEADY WIND HAS NO AERODYNAMIC EFFECTS." is true or not isn't the question being discussed. It's a truism.

 

The question is whether you will experience yaw forces that you have to counter with rudder as you exit ETL while trying to maintain a specific ground heading and experiencing a crosswind.

 

We're only concerned with motion relative to the ground (which is consistent with how NASA define yaw).

 

As you slow in a crosswind while maintaining a ground track the apparent wind will change direction, the aircraft will try to hold its nose into the apparent wind, therefore the aircraft will try to turn relative to the ground, which according to NASA's definition of yaw, is exactly the same as saying that the aircraft will try to yaw into the wind (as the term 'wind' only has meaning relative to the ground).

 

Yaw is not angular movement or offset relative to the air-mass the aircraft is moving through, it is an angular movement or offset relative to the bodies direction of movement which is measured against a set of fixed 3 dimensional coordinates

 

You're a pilot. Try this thought experiment.

You're in the Navy's new hypersonic upgrade of the Storch.

Top speed 2000 m/s, stall speed < 5 m/s.

there's a 5 m/s crosswind at 90 degrees to the runway you intend to land at.

 

Put yourself in that plane at an altitude of 10 m and at top speed lined up with the runway but some distance out. Your nose will essentially be pointed at the far end of the runway (less angular difference than your regular instruments can measure), and be closely aligned with your direction of travel (your TVV). Now set a gyroscope so that it is aligned with the axis of the aircraft.

 

Now hold that altitude, maintain alignment with the runway, and slow for approach to reach 5 m/s IAS half way down the runway.

As you slow, to maintain your movement's alignment with the runway your nose will gradually turn the nose into the wind as the direction of the apparent wind changes (unless you stop flying in a coordinated fashion).

 

At the point in time where you reach 5 m/s IAS you will still be flying but have zero ground speed. your nose will be at 90 degrees to the runway.

 

Though you're still heading into the apparent wind, your nose will be 90 degrees offset from where it was pointed when you started your approach (, or from your initial TVV) ,or from your initial gyroscope setting.

 

Your gyroscope shows you have yawed 90 degrees during your approach :-),it seems to me common sense says you have yawed 90 degrees, so in what sense have you not yawed as a result of a change in ground speed while flying a constant ground track in a constant wind ?

 

2/ When you loudly say "A STEADY WIND HAS NO AERODYNAMIC EFFECTS"

 

I think you're confusing apparently steady wind with actually steady wind (the differential with the integral if you like :-).

In forward flight the apparent wind is always straight ahead

In the experiment above the earth experiences a constant direction of wind, the plane experiences a slowly changing direction for the apparent wind.

In the thought experiment above, the aircraft's alignment to the ground obviously changes by 90 degrees, but your point seems to be that it maintains a constant relationship relative to the air-mass it is moving in - ie that it always points into the apparent wind.

 

Except it doesn't.

 

for the aircraft to physically rotate relative to the ground a torque has to be exerted on it to overcome its rotational inertia.

 

Where does the torque come from if there is a steady wind ?

 

From the fact that the aircraft not experiencing a constant wind - it is continually misaligned with the rotating apparent wind and so is constantly being pushed around by the force of the air striking the upwind side of its tail plane.

 

The aircraft is constantly experiencing tiny yawing moments relative to the air-mass, only these are too small at any given moment for the pilot to differentiate between actual constant state wind and the small changes that are constantly occurring, but the integrated effect is to rotate the aircraft 90 degrees relative to the ground.

 

And, while not writing this in blood, I think that's about me on the subject....

[Rogue Trooper]

A chopper, by its very design, with its lift system above its centre of gravity and its out stretched light weight anti torque boom is the epitome of a weather vane.

Once in forward flight and due to the choppers design this may be far less soo, but at low speed it is very relevant.

Edited January 6, 2018 by Rogue Trooper

[FragBum]

Some more observations,..

 

Just did another test and with 60Kph wind Huey can't easily turn to +/-90deg of the wind and shows signs of wind milling into the wind. Which I thought was the reason for putting a vertical tail on a helicopter and why I would normally reduce pedal input as relative airspeed increases. Doubly so for the Gazelle. :D)

 

The other 3 can turn which gets interesting but also show signs of wanting to turn into the wind, I'ts kinda hard to to determine at lower wind speeds because I'm already on the pedals to maintain direction so I am likely masking the effect at lower wind speeds. I think?

 

At 100Kph that gets real interesting as soon as the sim starts and reckless from there on,... :music_whistling:

 

The other interesting thing I see is that the airspeed indicator or the wind speed in the mission builder has an issue.

 

The indicated airspeed reads high and seems like the wind speed value gets has some error I have used the following approximations.

 

7M/sec == 25Kph indicated nadda but slight ETL onset

 

17M/sec == 60Kph indicated 100Kph and lots of lift (16.667)

 

27M/sec == 100Kph indicated 150kph (26.667)

 

Huey

 

25Kph indicated nadda

 

60Kph occasional flicks of the needle

 

100Kph indicates 80Kts ish (aka 150Kph)

 

This would have issues for the indicated air speed. I'm thinking assuming no wind straight and level flying for instance when cruising at 100Kph indicated airspeed what is my actual airspeed 100Kph, 150Kph. What does that mean for the calculated lift and other flight dynamics of DCS?? Or is it just the "wind speed"that is incorrect?

 

 

Could some please check the miz's I may have stuffed it up. :cry:

NTTR_60KWindtestAll_01.miz

NTTR_100KWindtestAll_01.miz