AH-94 Has a tendency to roll?

[Fuzzysmore]

Both watching drewski's video on the helicopter, and personal experience with playing with friends the heli has some weird flight characteristics where you turn a lil too much or dont tickle the rudder the aircraft just flips itself uncontrollably, anyone else notice something similar to this? also!! we need better transfer of control from front to back seat.

[醉仙望月]

This is how helicopter physics works.
The rotors rotate counterclockwise, so the helicopter has torque to yaw.
The tail rotor counteracts the torque, resulting in a tendency to roll.
You need to use the thumbstick to trim.

[Nerro]

Also, the rotor blades produce lift (like a plane's wings) but because of the rotation, the lift is stronger on the right side.
The faster you go, the more unbalanced the lift get. If you go too fast, the lift will make you spin and you'll lose control.

[PaX]

All helicopters do

[PaX]

Originally posted by Nerro:

Also, the rotor blades produce lift (like a plane's wings) but because of the rotation, the lift is stronger on the right side.
The faster you go, the more unbalanced the lift get. If you go too fast, the lift will make you spin and you'll lose control.

This is called disymmetry of lift Normally helicopter blades flap to correct it.

It will not make you spin out of control, It will actually make you pitch nose up and roll slightly.

[rmooney01]

Normally what happens is someone is going too fast and they think adding collective will help get them out of it. When reducing collective and slowing down is what needs to be done. Retreating blade stall and vortex ring are the 2 greatest causes of heli sim crashes outside of getting shot down. In my experience anyway.

[Tajin]

I don't think vortex effect is a thing in vtolvr but retreating blade stall sure is.

[rmooney01]

I was just saying, wasn't speaking of VTol VR just heli sims in general. Certainly failed a few times in DCS from it.....

[Fele]

skill issue

[AdmiralTigerclaw]

Originally posted by Tajin:

I don't think vortex effect is a thing in vtolvr but retreating blade stall sure is.

Test it.

Fly to a few thousand feet AGL. Put your nose at 7 degrees up to level to zero-ish speed, and drop the collective and begin a descent. Maintain that collective for several seconds and see if you begin to descend faster, then slowly add power and see if you can arrest your fall.

[Roger Longkoch]

Originally posted by 醉仙望月:

This is how helicopter physics works.
The rotors rotate counterclockwise, so the helicopter has torque to yaw.
The tail rotor counteracts the torque, resulting in a tendency to roll.
You need to use the thumbstick to trim.

It's not how they work. You seem to be confusing yaw with roll. The OP is right, there's massive uncommanded roll.

[醉仙望月]

Originally posted by Roger Longkoch:

It's not how they work. You seem to be confusing yaw with roll. The OP is right, there's massive uncommand roll.

As you know, the tail rotor counters the torque applied to the fuselage by the rotation of the main rotor. Since the tail rotor generates lift in the horizontal axis, it also produces a force which will move the helicopter across the ground (tail rotor drift ).
To offset this, the rotor disc is rigged such that it tilts in the direction of this movement to introduce a horizontal component of lift which opposes the tail rotor drift and keeps the helicopter steady in the hover.
So we now have two horizontal thrust components, one from the main rotor and one from the tail rotor. Now all forces act around the CoG (Center of Gravity), and it is from there that all accelerations to the aircraft to move it are measured. Therefore, if the centers of these two forces are not inline with respect to the CoG, i.e. the same vertical distance from the CoG, then a rolling "couple" is created between them and the fuselage will roll until the opposing forces are equal and opposite. This is why many helicopters hover with one skid low.
As the helicopter moves into cruise flight, the vertical stabilizer increasingly offsets the main rotor torque so the power required by the tail rotor and the angle of attack needed to offset torque reduces, therefore the roll couple force reduces and the deck of the fuselage will roll back towards level. The horizontal stabilizer also generates lift which further counters the roll such that in cruise, you are using little, if any pedal.

[Roger Longkoch]

Originally posted by 醉仙望月:

As the helicopter moves into cruise flight, the vertical stabilizer increasingly offsets the main rotor torque so the power required by the tail rotor and the angle of attack needed to offset torque reduces, therefore the roll couple force reduces and the deck of the fuselage will roll back towards level. The horizontal stabilizer also generates lift which further counters the roll such that in cruise, you are using little, if any pedal.

You are all confused. You don't counter roll with pedal.

[醉仙望月]

Originally posted by Roger Longkoch:

You are all confused. You don't counter roll with pedal.

You still don't understand what I'm saying.
The tail rotor prevents yaw about the main rotor shaft, but it creates a tendency to drift because the tail rotor generates thrust to one side. To counter this tendency the main rotor thrust is displaced toward the retreating side and the helicopter in effect flies sideways in the opposite direction, at the same speed it would be translated by the tail rotor. This results in the helicopter holding its ground position, but rolling due to the main rotor thrust now pointing towards the retreating side.
https://mediawiki.ivao.aero/images/e/e3/Ekran_Resmi_2020-02-09_19.00.50.png
You can search for "Tail Rotor Roll".
Tail rotor roll is a tendency for the helicopter to rotate about its vertical Center of Gravity (CoG). The amount of roll is dependent upon the vertical offset of the tail rotor from the vertical CoG, and the magnitude of the tail rotor thrust applied. The direction of the roll is dependent upon whether or the not the tail rotor lies above or below the vertical CoG, above will result in a roll towards the advancing side, and below will result in a roll towards the retreating side.
This is not the way this phenomenon is described in several books, it is however the correct one.

[AdmiralTigerclaw]

Let me also chime in with things:

Helicopters are terrifyingly fickle things and subject to an innumerable number of aerodynamic forces. It is by the power of 70 years of engineering that we have reached the point where most problems are solved by design, not pilot skill.

The first one is counter-torque.

If the rotor assembly rotates counter-clockwise from a top down perspective, the helicopter main body is going to want to spin clockwise.

This is countered with the tail rotor, obviously, which will push thrust out the left side to stop that spin.

As a primary consequence of that thrust, the helicopter will want to drift to the right.
As a secondary consequence of how high up the tail rotor is placed, the helicopter may desire to roll right.

To counter the primary consequence, the main rotor's overall tilt as seen from the back will be to the left, just enough to correct for the drift and settle it.

However, the consequence of offsetting the thrust to the right is that the thrust now passes right of center mass, causing a desire for the left side of the vehicle to fall or roll left.

Back at the tail rotor's secondary effect, a desire to roll right, you can adjust the tail rotor height in the design stage to try and nullify the left roll induced by the tilted main rotor.

However, all these things are connected, and every tweak changes one of the other consequential effects. Tilting the rotors changes the lift profile of the blades in flight, forcing you to bake in some adjustments to the swash plate, which in turn changes some of the drag as the rotors circle the vehicle. Moving the tail rotor changes the CoM even as you work to adjust for it. A whole lot of computers and simulation goes in to smoothing the changes out until the desired flight profile is in reach. And that's before you stop and think about the combat parameters you have to design around.

After that, you have to account for stores and load. People, fuel, and ordinance move the CoM and change the weight of the vehicle. Flight regimes such as hovering in ground effect and flying at a hundred knots change out some characteristics, such as introducing weathervaning or reducing the lift of the helicopter along the retreating blade while enhancing it on the advancing blade, which makes the vehicle desire to roll left more as you pick up speed.

For all these changes, there is your direct control, and there is Trim. Helicopter flight instructions mention that you should 'slowly' and 'smoothly' make changes to the collective and cyclic, and that while the blades are in motion, 'Your Hand Never Leaves The Cyclic'. And for good reason. Hard, fast changes do bad things and don't give you time to react to how the vehicle wants to fly. So the best thing you can do, especially at takeoff, is slowly add power, correct for undesired drifts, and trim in your new neutral.

Full computer FBW flight assist helps greatly, and I'm honestly confused why the AH-94 doesn't have an assist system, as futuristic as it is. There are coastguard helicopters that can hover themselves without a pilot so much as in the seat.

[Roger Longkoch]

Originally posted by AdmiralTigerclaw:

Let me also chime in with things:

Helicopters are terrifyingly fickle things and subject to an innumerable number of aerodynamic forces. It is by the power of 70 years of engineering that we have reached the point where most problems are solved by design, not pilot skill.

The first one is counter-torque.

If the rotor assembly rotates counter-clockwise from a top down perspective, the helicopter main body is going to want to spin clockwise.

This is countered with the tail rotor, obviously, which will push thrust out the left side to stop that spin.

As a primary consequence of that thrust, the helicopter will want to drift to the right.
As a secondary consequence of how high up the tail rotor is placed, the helicopter may desire to roll right.

To counter the primary consequence, the main rotor's overall tilt as seen from the back will be to the left, just enough to correct for the drift and settle it.

However, the consequence of offsetting the thrust to the right is that the thrust now passes right of center mass, causing a desire for the left side of the vehicle to fall or roll left.

Back at the tail rotor's secondary effect, a desire to roll right, you can adjust the tail rotor height in the design stage to try and nullify the left roll induced by the tilted main rotor.

However, all these things are connected, and every tweak changes one of the other consequential effects. Tilting the rotors changes the lift profile of the blades in flight, forcing you to bake in some adjustments to the swash plate, which in turn changes some of the drag as the rotors circle the vehicle. Moving the tail rotor changes the CoM even as you work to adjust for it. A whole lot of computers and simulation goes in to smoothing the changes out until the desired flight profile is in reach. And that's before you stop and think about the combat parameters you have to design around.

After that, you have to account for stores and load. People, fuel, and ordinance move the CoM and change the weight of the vehicle. Flight regimes such as hovering in ground effect and flying at a hundred knots change out some characteristics, such as introducing weathervaning or reducing the lift of the helicopter along the retreating blade while enhancing it on the advancing blade, which makes the vehicle desire to roll left more as you pick up speed.

For all these changes, there is your direct control, and there is Trim. Helicopter flight instructions mention that you should 'slowly' and 'smoothly' make changes to the collective and cyclic, and that while the blades are in motion, 'Your Hand Never Leaves The Cyclic'. And for good reason. Hard, fast changes do bad things and don't give you time to react to how the vehicle wants to fly. So the best thing you can do, especially at takeoff, is slowly add power, correct for undesired drifts, and trim in your new neutral.

Full computer FBW flight assist helps greatly, and I'm honestly confused why the AH-94 doesn't have an assist system, as futuristic as it is. There are coastguard helicopters that can hover themselves without a pilot so much as in the seat.

Another glaring issue with the AH-94 happens when you switch off the AP and your cyclic is off because your hand isn't in the right position. You then get a wild moment when anything can happen. This is the problem with VR controls.