Tail Rotor is the Wrong Way Around

[Northstar98]

Hi Everyone,

While trying to learn the Hip, I noticed something a bit peculiar with the tail rotor - it's mounted back to front.

Looking top-down, the Hip's rotor spins clockwise; this would mean that the torque from the rotor would act to spin the fuselage of the helicopter counter-clockwise - the tail of the helicopter would move to the right, and the front would move to the left, when viewed from behind the helicopter.

This means that the tail rotor would have to act to move the tail to the left, so the thrust needs to act from right to left ('pushing' the air to the right).

However, if you look at the direction the tail rotor spins (which is accurate for the blade orientation), and the angle of the blades; it would 'push' the air to the left, which would mean the thrust it would generate would act from left-to-right, pushing the tail to the right, reinforcing the torque, instead of opposing it.

It's like the tail-rotor was modelled to be on the right side of the boom, but they put it on the left; if you were to rotate the tail rotor assembly so that it's on the other side (around the z axis/yaw axis) it would be correct.

In all 3 images below, the anti-torque pedals were centred.

This issue was also reported in this thread, 4 years ago, but this was before the Hip received further animations to the rotor systems.

Edited November 11, 2021 by Northstar98
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[Art-J]

Well, it's not like the rotor is the wrong way around for this particular Hip version (kudos for catchy drama-headline though :D), but the initial pitch is modelled incorrectly, and they didn't fix it when they added animation years ago.

 

Unfortunately, I get an impression that all ex-Belsimtek-developed modules are on the bottom of the fixing priority list nowadays, unless they can serve as a test-bed for new ED-modules (ie. multicrew added to the Huey recently).

[Northstar98]

On 1/26/2021 at 6:32 AM, Art-J said:

Well, it's not like the rotor is the wrong way around for this particular Hip version (kudos for catchy drama-headline though :D), but the initial pitch is modelled incorrectly, and they didn't fix it when they added animation years ago.

Well, I gave it the headline because if you rotated the tail rotor assembly around so that it was on the other side, it would work the way it's supposed to.

I realise that Hips have the tail rotor on the left (or at least the overwhelming majority do), and some have it on the right; but our tail rotor looks like it was built to be on the right-hand side but it was put on the left, if that makes any sense.

If you were to keep it on the left, you'd have to invert the aerofoil; it's not symmetrical AFAIK EDIT: it actually looks like it is pretty symmetrical, so you're right; all they would need to do is change the pitch and invert the swashplate animation (right now right pedal causes the swashplate to move inwards, which would act to increase blades the AoA of the blades, which would cause it to produce more lift, moving the nose faster to the left).

On 1/26/2021 at 6:32 AM, Art-J said:

Unfortunately, I get an impression that all ex-Belsimtek-developed modules are on the bottom of the fixing priority list nowadays, unless they can serve as a test-bed for new ED-modules (ie. multicrew added to the Huey recently).

Yeah I get that impression too unfortunately, kinda a shame.

Edited November 11, 2021 by Northstar98
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[Crash *]

vor 6 Stunden schrieb Art-J:

Unfortunately, I get an impression that all ex-Belsimtek-developed modules are on the bottom of the fixing priority list nowadays, unless they can serve as a test-bed for new ED-modules (ie. multicrew added to the Huey recently).

That is exactly my opinion. It all takes forever. The modules are really worth being treated better.

[Isegrim]

Iam curious now ......   will we see this BUG modeled to the Mi 24 again? 

 

 

ISE

[TomChaai]

The direction of rotation makes sense, the tail rotor control animation makes sense. When you push the right pedal, the negative AoA of the tail rotor blades reduces, so it is in the direction of creating more force pulling to the left.

However I'm not so sure about the default blade AoA is such huge a negative, it looks like it would be creating forces pushing to the right most of the time.

Could it be due to the airfoil, the blades create too much pulling force, so they actually have to set it in negative AoA in neutral?

Anyway a photo of the mechanism in real life would help.

[Northstar98]

On 2/2/2021 at 10:50 AM, TomChaai said:

The direction of rotation makes sense, the tail rotor control animation makes sense. When you push the right pedal, the negative AoA of the tail rotor blades reduces, so it is in the direction of creating more force pulling to the left.

The animation sorta makes sense-ish. When you go left pedal the swashplate retracts (i.e moves to the right), this increases the current AoA which would create a force that would move the helicopter's nose to the left (though combined with the torque from the main rotor already would make the helicopter wildly yaw to the left).

Similarly for right-pedal; the swash plate extends, which reduces the current AoA, which would reduce the thrust of the current configuration, this wouldn't necessarily push the nose to right because it still needs to overcome the torque from the main rotor (which should push the nose to the left) but the tail rotor is still reinforcing the torque (i.e it's still providing a force in the same direction, just less of one).

It seems to me that while the directions are correct for the desired effect, though I'd expect right pedal to increase the AoA (obviously on the correct side), because the tail rotor now has to overcome torque + provide extra thrust to yaw the helicopter in an opposite direction to torque, whereas for left pedal I'd expect it to provide less thrust, therefore decrease AoA, allowing the torque to yaw the helicopter to the left (the tail rotor still opposes torque as it should, but to a less extent).

Quote

However I'm not so sure about the default blade AoA is such huge a negative, it looks like it would be creating forces pushing to the right most of the time.

Replace most with all and yeah, across its whole AoA range, the thrust it would provide reinforces the torque from the main rotor.

Quote

Could it be due to the airfoil, the blades create too much pulling force, so they actually have to set it in negative AoA in neutral?

Strongly doubt it, the current set-up is like a pusher, when it should be pulling, that's the entire problem. It's like they took a rotor that was supposed to be mounted on the right side of the helicopter, but mounted it on the left, such that the AoA is the wrong way around. (Of course inverting the rotation and inverted the leading/trailing edge, so it spins the right way i.e clockwise)

The animations kinda make sense, but are still borked because they're applied to a basically borked tail rotor, the increase/decrease in AoA are reversed compared to the real one, though the change in forces do sorta make sense.

Quote

Anyway a photo of the mechanism in real life would help.

Here's one, it's a little difficult to tell, but the rotation of the rotor is correct (i.e clockwise from this position). But the AoA is in the other direction (if you look at the blade at the 6'oclock position, you can see it would direct air towards the boom (pull configuration), which would produce thrust that would yaw the helicopter to the right (i.e opposing torque, as it should)).

If the pilot were to give it some right pedal, the AoA of the blades should increase; producing more thrust to counterbalance the torque (tail-rotor thrust > torque) - yawing the helicopter to the right.

If the pilot were to give it some left pedal, the AoA of the blades should reduce; producing less thrust, allowing torque to yaw the helicopter to the left (the rotor still produces thrust that opposes torque, but in this configuration thrust from the tail rotor < torque from the main rotor).

At the moment, the animation makes sense in so far as the model produces less thrust to yaw right and more to yaw to the left, even though in both cases, the model is set up so that the thrust from the tail rotor reinforces torque, instead of opposing it.

Edited November 11, 2021 by Northstar98
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[TomChaai]

On 2/4/2021 at 7:22 AM, Northstar98 said:

 

The animation sorta makes sense-ish. When you go left pedal the swashplate retracts (i.e moves to the right), this increases the current AoA which would create a force that would move the helicopter's nose to the left (though combined with the torque from the main rotor already would make the helicopter wildly yaw to the left).

 

Similarly for right-pedal; the swash plate extends, which reduces the current AoA, which would reduce the thrust of the current configuration, this wouldn't necessarily push the nose to right because it still needs to overcome the torque from the main rotor (which should push the nose to the left) but the tail rotor is still reinforcing the torque (i.e it's still providing a force in the same direction, just less of one).

 

It seems to me that while the directions are correct for the desired effect, though I'd expect right pedal to increase the AoA (obviously on the correct side), because the tail rotor now has to overcome torque + provide extra thrust to yaw the helicopter in an opposite direction to torque, whereas for left pedal I'd expect it to provide less thrust, therefore decrease AoA, allowing the torque to yaw the helicopter to the left (the tail rotor still opposes torque as it should, but to a less extent).

 

 

Replace most with all and yeah, across its whole AoA range, the thrust it would provide reinforces the torque from the main rotor. 

 

 

Strongly doubt it, the current set-up is like a pusher, when it should be pulling, that's the entire problem. It's like they took a rotor that was supposed to be mounted on the right side of the helicopter, but mounted it on the left, such that the AoA is the wrong way around. (Of course inverting the rotation and inverted the leading/trailing edge, so it spins the right way i.e clockwise)

 

The animations kinda make sense, but are still borked because they're applied to a basically borked tail rotor, the increase/decrease in AoA are reversed compared to the real one, though the change in forces do sorta make sense.

 

 

 

Here's one, it's a little difficult to tell, but the rotation of the rotor is correct (i.e clockwise from this position). But the AoA is in the other direction (if you look at the blade at the 6'oclock position, you can see it would direct air towards the boom (pull configuration), which would produce thrust that would yaw the helicopter to the right (i.e opposing torque, as it should)).

 

If the pilot were to give it some right pedal, the AoA of the blades should increase; producing more thrust to counterbalance the torque (tail-rotor thrust > torque) - yawing the helicopter to the right.

 

If the pilot were to give it some left pedal, the AoA of the blades should reduce; producing less thrust, allowing torque to yaw the helicopter to the left (the rotor still produces thrust that opposes torque, but in this configuration thrust from the tail rotor < torque from the main rotor).

 

At the moment, the animation makes sense in so far as the model produces less thrust to yaw right and more to yaw to the left, even though in both cases, the model is set up so that the thrust from the tail rotor reinforces torque, instead of opposing it.

 

 

 

 

 

I've checked in the game again. If you apply full left pedal, it is huge negative, if full right pedal, it is flat.

(There is a bug/trick to inspect flight controls even after the rotors stopped, just fully disconnect electricity before the rotor stops, the hydraulics will keep working)

Compare to screenshots where it is already slightly positive in rest position, I'd say you are right, the modelling geometry or part animation is off. Couldn't tell which though.

This is another angle of the real thing, thanks to credited author.

[TomChaai]

Just saw this.

Ми-8 серый 96742 запуск и взлёт Кубинка 2020 - YouTube

Pretty much confirmed the in-game model is distorted, the default AoA is too much negative.

Hope they get around to fix it, seems they got too much on their hands at the moment.

[AlphaOneSix]

You guys have already figured this out, but just to add the raw numbers, the tail rotor pitch minimum (full left pedal) is -6°20' and the maximum (full right pedal) is 23°20'.

[Northstar98]

On 3/20/2021 at 1:58 PM, AlphaOneSix said:

You guys have already figured this out, but just to add the raw numbers, the tail rotor pitch minimum (full left pedal) is -6°20' and the maximum (full right pedal) is 23°20'.

Awesome, thanks!

Edited November 11, 2021 by Northstar98
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[Flappie]

Here's a video showing the wrong tail rotor blades orientation in DCS:

 

 

One needs to compare it with this one posted by TomChaai:

 

 

Mi8_startup.trk

[Hueyman]

Yup, many little things to improve on older BST models, hope they’ll do it.

BTW, one of the rotor blade is .. smaller for some reason  

3D artist sometime should do like mechanics : check a wrench ( funky animation here ) hasn’t been left here before shipping final product 

[fapador]

Big mistake in my opinion, Big discrepancy from the real rotor. It must be corrected asap. I have noticed it myself in the past years but didn't make the effort to create a post as I have shelved the Mi-8 and don't play it anymore.

Personally, such mistakes are what make  me question more complex things like fm, and if they are modelled accurately . Which some people here will swear upon...

Anyway, the repair will require graphics animation model correction, so don't expect for it to be resolved quickly. 

 I would also like to mention that there are  ton of other critical model inaccuracies also on the other belsimtek product , (as  @Hueyman for example has reported in some excellent topics). They have been higlighted in repetition over the years but nothing has changed because the teams are always  busy with the newest module.

I think the community shouldn't be relaxed in such matters and we should always highlight our demand for such issues to not only be resolved, but be fixed fast. Otherwise we will be stucked in this neverending loop which is  to maintain a holding pattern always waiting for the developers. Old modules need love and attention from the devs too and not being treated as completed work .

Edited November 11, 2021 by fapador