[Helicopter] Abrupt induced yaw when flying over edge of elevated helipad

User Support Hub Aircraft & Systems
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1

Are you using Developer Mode or made changes in it?

No

Have you disabled/removed all your mods and addons?

Yes

Which aircraft are you reporting an issue about? (Please also add the proper tag for it)

Bell 407 and all helicopters using the MSFS flight model.

Which aircraft version are you experiencing this issue on? (You can find this listed in the Content Manager under the Aircraft Name)

All

Brief description of the issue:

When leaving an elevated helipad in level flight, especially when the course is not perpendicular with the edge of the helipad, a sudden yaw rotation is induced without any pilot input, that can turn the helicopter almost 180 degrees. See the video linked below, from 0:07 to 0:12, note that there was NO PILOT INPUT on the anti torque pedals that would introduce that yaw. No input obviously means no additional input, other than some left pedal needed to maintain the heading while approaching the edge in a straight line.

The strength of this effect seem to depend on the rotation direction of the rotor and on which side the helicopter leaves the pad. CCW rotors like the Bell 407 will cause issues when leaving to the left, CW when leaving to the right, see videos below.

Also please note that I DO EXPECT some effect when crossing the edge of an elevated helipad, I’m not complaining that there is an effect, the problem is the extent and inconsistency of that effect.

Provide Screenshot(s)/video(s) of the issue encountered:

Bell 407 leaving the pad to the left, abrupt, violent yaw: groundeffect.mp4 - Google Drive

Cabri, leaving the pad to the left, notice the effect is very minor: CabriLeft.mkv - Google Drive

Cabri, leaving the pad to the right, abrupt, violent yaw: CabriRight.mkv - Google Drive

Detailed steps to reproduce the issue encountered:

Select the Bell 407 and start a flight at the Rainbow Air Incorporated Heliport in Niagara Falls. Hover and then turn 45 degrees to the left and slowly start moving forward until the center of the aircraft reaches the edge of the helipad.

PC specs and/or peripheral set up if relevant:

Not relevant

Build Version # when you first started experiencing this issue:

Only started flying helicopters with 1.35.21.0, issue could have been there before, as ground effect problems are well known, see Helicopter ground effect transition is abrupt and requires large inputs to recover - Aircraft - MSFS DevSupport and Helicopter ground effect transition is abrupt and requires large inputs to recover. The above problems can also be seen in the second part of the video, where the helicopter is abruptly kicked up when it reaches the edge of the helipad.

This issue pretty much kills all the fun when flying helicopters to elevated platforms like oil rigs, hospital roof platforms, logging helipads like in Heli Logging Revelstoke BC. CA for Microsoft Flight Simulator | MSFS, or even 50 cm high helicopter dollies used at HEMS bases.

:loudspeaker: For anyone who wants to contribute on this issue, Click on the button below to use this template:

1 Like
2

I can’t tell from the video how strong this effect is and how much it would require to counter it. However, it’s important to note that you leave the pad at this moment and so you change and leave the ground effect in an instant. The whole air cushion is gone at this point and the aerodynamics and the air’s effect on the helicopter change a lot. I can’t tell if this is actually correct behaviour but SOMETHING will happen at this point. I’m not a rotary but a fixed wing private pilot and I know all kind of these effects well enough. A sudden terrain drop, trees or buildings etc, everything affects the plane, often quite suddenly and stronly.

3

On MSFS it’s exaggerated and unrealistic… unpredictable ground effects as such would make any heli landing dangerous… when you look at helicopter real life, they don’t go up and down when doing stable hover… you don’t need to counter effect every seconds. The air is pushed by the rotor and don’t go up to make gusts, i mean slightly but not as strong as in msfs.
It’s almost impossible to stable hover in the sim.

2 Likes
4

As long as you’re on an open field, hovering on a runway for example, you’ll be very stable with the pedals, also in ground effect the amount of collective will control the height over ground. More collective and the helicopter will hover higher, less collective, it will sink down. You don’t have to constantly correct the hover height. You do have to control your position all the time with tiny corrections. The direction of the nose is comparably easy to maintain, slightly more pedal input towards the direction of the rotation of the main rotor with increased collective. The higher you get during hover the more pedal input you’ll need though as far as I remember with the most counter steering as soon as you get out of ground effect. Leaving the ground effect (or increasing the height that much in a short time) when leaving the heli pad will certainly require more anti torque since you will need more collective to maintain the altitude and not dropping back down. This is all correct. But knowing the scripted behaviours in MSFS this might very well be quite exaggerated. But you will definitely have to “work the pedals”, not as the OP stated “note that there was NO PILOT INPUT on the anti torque pedals”. I know he meant into the rotation, but he’ll definitely have to counter it.

I want to add:
It is very unwise to hover in ground effect over a ridge or the end of the helipad. That’s already very difficult in RW and all above in the sim it will most likely not be simulated as complex as in reality and therefore will lead to strange behaviour. If you takeoff from a higher helipad you’d climb vertically out of ground effect and then accellerate forward.

1 Like
5

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7

Thanks for the explanation and the helicopter flying lesson, it certainly helped moving this topic out of the bug section :slight_smile:.

Anyway, I edited the post to make it clear that the helicopter was trimmed, anti torque applied already to maintain heading while approaching the edge in a slow forward flight. When it reaches the edge, I make no more changes to the controls.

“when leaving the heli pad will certainly require more anti torque since you will need more collective to maintain the altitude and not dropping back down”

See, that exactly is the problem, that I do not add collective, don’t change any of the controls but there is still this violent yaw movement, in fact, you can even see the heli ballooning up a bit, instead of losing altitude, as one would expect when getting out of ground effect without adding collective.

Just out of curiosity, I retried this with the Cabri, which has a CW rotor. Guess what, when flying over the edge of helipad the yaw is the opposite of the 407, this time to the right.

Interestingly, when crossing to edge to the left, the effect is minor:
CabriLeft.mkv - Google Drive

However, crossing to the right, there is that violent yaw:

Again, stable, slow forward flight, cyclic forward, right anti-torque, and appropriate collective for this setup, with no additional pilot input, helicopter yaws to the right over 90 degrees and lifts a bit when crossing the helipad edge, then yaw stops without pilot input.

1 Like
8

Please see the existing Bug Report:

and the response below


JummivanaSenior Community Manager [Z-8]

Oct 24

Via the linked thread, the SDK team has marked this as acknowledged and will be fixed in a future update. Conversation around this subject should remain on the SDK forums. Thanks!

9

The first mistake is trying to depart or land on an elevated surface within the ground effect area. You would normally enter or use the ground effect area once you are on top of the elevated surface as you can crash with the edge if you suddenly lose that extra lift on any area of the rotor. Second mistake is to approach or depart following a non perpendicular path in case you still want to use the ground effect area inmediatelly. This can result in an abrupt pitch and bank change as the blades will not find a symmetric surface below (one side of the rotor can get extra lift when the other is not getting it). You can still do those things as you may have no other alternatives in some situations but you need to be prepared to compensate the effects, so don´t expect a smooth result. These problems are real and serious accidents can happen.

Cheers

2 Likes
10

I’m aware of that and also linked it in my original post. That report however does not talk about the sudden induced yaw, only the ballooning.

1 Like
11

Guess these aerial application guys have no idea how to fly a helicopter:

Did you look at the three videos I linked?

Please try staying on topic, is that violent yaw is realistic? Does it happen in real life with this extent? Does it happen in real life only when crossing the edge in one direction and not in the other? Please.

12

Sure, you can fly the way you want and you may not have any other option to proceed indeed. What I mean is that it won´t be as smooth as is you were doing the same maneuver on land instead of on an elevated surface so you can expect those effects to happen.

Cheers

13

Yes, I’m fully aware of that, and never expected it. Neither a 90 degree yank to the side.

14

What happens when you decrease collective on an american helicopter like the 407 (blades rotating anticlockwise)? You produce less lift and a left yaw. In case you increase collective you will produce more lift and a right yaw. On european ones like Cabri (clockwise rotation) yaw is the opposite. In both cases you need to use pedals to compensate that.

What you see in the helipad is similar while not being exactly the same thing. Entering helipad on ground effect increases lift while leaving it decreases it. That´s why you see on your videos how 407 and Cabri turn to different directions when performing the same maneuver. Wind conditions will also require more or less pedal, or even no pedal at all if wind alone is able to compensate the induced yaw.

I don´t mean MSFS is perfect but I would say it behaves fine in this case.

Cheers

15

Sure, but increasing lift or decreasing lift due to the environment only without changing collective input won’t change the anti torque needed.

And I did not change the collective setting at all. Also, how would that explain the significant difference of this effect between the directions leaving the pad?

16

Even if you are not changing the blades pitch manually via collective inputs the airflow changes when a part of the rotor exits ground effect while the other still remains on it and viceversa. For the rotor portion in OGE (out of ground effect) the angle of attack decreases and the lift decreases. For the rotor portion in IGE (in ground effect) the angle of attack increases and lift increases.

Cheers

17

I’m not an aerospace engineer, so won’t argue about that. Not sure how what you are saying explains the yaw and the subtle ballooning when leaving the helipad. And the asymmetry of the effect depending on which direction we leave the pad.

So do you think that the behavior in the videos is realistic?

18

Helicopters in game are fine but they are not realistic at all. You can’t do a full roll with a Cabri below 100kts in real life nor with any piston helicopter in general. All helicopters in game, including the existing third party ones from addons, can do that while few in real life can really achieve such aerobatic maneuver (Bo105 for instance can).

However their basic principles are implemented at least, rotors air flow interacts with the scenery and objects, provided that they have bounding boxes (trees for instance don’t have it in game so they are transparent) and existing wind affects both main and tail rotors.

You can activate de air flow visualization in game to see what happens. It’s a game for home entertainment, with some complexity, but a game at the end.

Cheers

19

Ok, so you agree that the behavior I demonstrated in the videos is not realistic. And since this thing is called a simulator, can we please call a non-realistic behavior a bug? Please?

20

I didn´t say that. In my opinion the behaviour at the helipad is still correct but helicopter simulaton in general is not realistic in this game as you can do impossible things with them (in particular aerobatics). However the general behaviour of helicopters is implemented reasonably fine as the main effects you would see on helicopters also exist in game. But this is just my opinion.

What you see in your videos happens for two reasons:

  1. As rotor front section enters helipad area it will have have extra lift due to ground effect. This will result in an initial small roll which affects airflow as well as rotor plane will not be horizontal after that. Without compensation helicopter will tend to yaw because rotor plane will be less horizontal while it will still get that extra lift in frontal section only caused by the helipad.

  2. When rotor front section leaves helipad the extra lift on the front section is reduced. This will result in a roll as well (with yaw tendency too if not compensated) and nose willing to point down. Once nose starts to pitch down you see the ballooning effect because rotor plane has changed and is not horizontal again, resulting in an increase of translation speed and therefore further addional lift.

So even if you don’t touch controls rotor will still behave as it does when you move collective and cyclic on purpose during normal flying, because there’s a helipad generating extra forces on rotor now instead of a pilot moving the controls. But basically the same corrections are still required in any of those cases.

Cheers

21

Honestly, never expected such a pushback in something which seems to be related to a well known bug, IRL pilots also detailing how the ground effect transition is flawed in FS2020, like @WolfActual here: Plenty of room for improving the helicopter physics, flight model and controls - #43 by WolfActual

Last questions for you, before I give up:

  1. how do you explain the asymmetry of this effect (no significant change in yaw when leaving to the right with the Bell, but a violent yaw to the left when leaving to the left side)?
  2. if a sudden, over 90 degree yaw is realistic when leaving an elevated platform at an angle, especially if this is asymmetric and depends on the rotor rotation direction, how come the Pinnacle and Ridgeline Operation part of the FAA does not warn about it?