investigating Translating tendency is not modeled in the DCS UH-1H

[Tim_Fragmagnet]

Despite being a major function of the flight model in low speed flight, the effect known as translating tendency is not actually modeled.

This effect causes the huey to require a bit of left roll to hover in place due to the force of the tail rotor pushing the entire aircraft to the right. This can be seen in these photos.

This is extremely easy to test in DCS
Simply put the huey into a hover in a mission with no wind.
If you hover rolled to the left, translating tendency is modeled.

Here is a photo  showing the huey hovering completely level in DCS.

null

 

The huey DOES require a bit of left cyclic to hover in DCS, but that is only enough to counter the torque caused by the tail rotor being above the center of mass applying a twisting force to the tail. It's enough to stop the helicopter from rolling, not to stop the translating tendency that isn't modeled.

Edited September 15, 2022 by Tim_Fragmagnet

[Mr_sukebe]

Err.

You sure about that?

You mention that translation tendency is caused by the push from the rear rotor, which is itself accounting for torque from the main rotors.  You’ve stated that DCS models the push from the rear rotor.

 

Isn’t that one and the same thing?  If not, what would cause translation?

[Tim_Fragmagnet]

21 minutes ago, Mr_sukebe said:

You mention that translation tendency is caused by the push from the rear rotor, which is itself accounting for torque from the main rotors.  You’ve stated that DCS models the push from the rear rotor.

 

Isn’t that one and the same thing?  If not, what would cause translation?

Not quite

DCS models the TORQUE produced by the tail rotor
But it does not model the force that actually produces that torque. In effect it just skips a step.

I do not have access to the ability to look at how the flight model actually works, so I cannot guarantee exactly how it actually works.
However, from what I can gather, the forces from the tail rotor were simply modeled as a rolling torque and a rotational torque, nothing more. It does not model the fact that the tail rotor is actually physically pushing the airframe.

At the end of the day, regardless of how it ACTUALLY is modeled in the game, translating tendency is not present on the module when it should be.

Edited September 15, 2022 by Tim_Fragmagnet

[Hiob]

7 hours ago, Tim_Fragmagnet said:

Despite being a major function of the flight model in low speed flight, the effect known as translating tendency is not actually modeled.

This effect causes the huey to require a bit of left roll to hover in place due to the force of the tail rotor pushing the entire aircraft to the right. This can be seen in these photos.

This is extremely easy to test in DCS
Simply put the huey into a hover in a mission with no wind.
If you hover rolled to the left, translating tendency is modeled.

Here is a photo  showing the huey hovering completely level in DCS.

null

 

The huey DOES require a bit of left cyclic to hover in DCS, but that is only enough to counter the torque caused by the tail rotor being above the center of mass applying a twisting force to the tail. It's enough to stop the helicopter from rolling, not to stop the translating tendency that isn't modeled.

 

To be honest, I doubt that the Hueys in the Photos are actually stationary. They are probably going sideways or are accelerating. Because when you watch Videos of Hueys that are really hovering stationary, they are not tilted like that - by far!

Especially the last photo - that just can't be a stable hover.

For example:

 

Edit: 3:00 minutes in the Video clearly proves you wrong.

btw. your definition of translating tendency is also wrong. TT means drift and not tilt of the fuselage.

Edited September 15, 2022 by Hiob

[Tim_Fragmagnet]

8 minutes ago, Hiob said:

To be honest, I doubt that the Hueys in the Photos are actually stationary. They are probably going sideways or are accelerating. Because when you watch Videos of Hueys that are really hovering stationary, they are not tilted like that - by far!

Especially the last photo - that just can't be a stable hover.

First, that last photo has a larger roll because it is a shortbody huey that is lighter than the 1H, so the tailrotor causes it to drift more.

What you're watching with hueys hovering around airfields I can guarantee you aren't stable hovers. Hovers, yes, but they're wobbling around, and drifting. There's no way you'd see the translating tendency in all of that.
Make no mistake, the huey is supposed to hover rolled slightly to the left, if you know what to look for you can spot it a bit easier.



This timestamp here is a clear example of the left skid low attitude the huey hovers with

And at this timestamp you can see the pilot lift off with a left skid low attitude and STILL start drifting to the right

 

[Hiob]

Ok. Have it your way.

Bye!

[BIGNEWY]

7 hours ago, Tim_Fragmagnet said:

Despite being a major function of the flight model in low speed flight, the effect known as translating tendency is not actually modeled.

This effect causes the huey to require a bit of left roll to hover in place due to the force of the tail rotor pushing the entire aircraft to the right. This can be seen in these photos.

This is extremely easy to test in DCS
Simply put the huey into a hover in a mission with no wind.
If you hover rolled to the left, translating tendency is modeled.

Here is a photo  showing the huey hovering completely level in DCS.

null

 

The huey DOES require a bit of left cyclic to hover in DCS, but that is only enough to counter the torque caused by the tail rotor being above the center of mass applying a twisting force to the tail. It's enough to stop the helicopter from rolling, not to stop the translating tendency that isn't modeled.

 

Hi

do you have any data to support this? If so please PM me. 

thanks

[Koty]

Well, it seems pretty straightforward? To generate the anti-torque you generate a force on the tail boom. Since the helicopter (with no sideways cant on the rotor) sits perfectly straight in hover, it would imply the torque is getting cancelled, but no actual force is being generated. It is basic newtonian mechanics so probably just something overlooked in the FM code. It really is as simple as F = T/r.

1 hour ago, Hiob said:

To be honest, I doubt that the Hueys in the Photos are actually stationary. They are probably going sideways or are accelerating. Because when you watch Videos of Hueys that are really hovering stationary, they are not tilted like that - by far!

Especially the last photo - that just can't be a stable hover.

For example:

 

Edit: 3:00 minutes in the Video clearly proves you wrong.

btw. your definition of translating tendency is also wrong. TT means drift and not tilt of the fuselage.

 

... the perspective might be a bit fucky but the left ski is lower at 3:00.

You also tilt the fuselage to counteract the translating tendency...

[Mr_sukebe]

Are you saying that you believe that the Huey in a hover should be slightly canted to one side to account for the transition effect?

Sorry, haven’t checked if that is the case or not.

Is it possible that the main body of the Huey is flat, but with the main rotors slightly canted by the swash plate?

[Tim_Fragmagnet]

6 hours ago, Mr_sukebe said:

Is it possible that the main body of the Huey is flat, but with the main rotors slightly canted by the swash plate?

The huey's main rotor is tilted 5degrees forward, but not to the side. That's why you have to tilt the whole body to counteract translating tendency, because the rotor isn't tilted to the side to innately counteract the drift caused by the tail rotor like some modern helicopters.

Edited September 15, 2022 by Tim_Fragmagnet

[gnomechild]

10 hours ago, BIGNEWY said:

Hi

do you have any data to support this? If so please PM me. 

thanks

What data do you need that isn't provided in the original post?
The UH-1 main rotor shaft is mounted parallel to the z-axis of the airframe.

He posted a photo of a Huey in a stable hover (0kts TS) with no bank (0 degree in F2 view and skids are level with horizon)

That's all the proof that is needed. It should not be possible for the helicopter to be stable in this position unless the translating force of the tail rotor is incorrectly modelled.

The AI Huey also hovers the exact same way BTW. With 0 degrees of bank. Track file attached.
 

UH1H hover.trk

Edited September 15, 2022 by gnomechild
adding track file of AI huey demonstrating stable hover with no bank

[BIGNEWY]

Thanks for the data in the PM, as mentioned I will mention it to the team, and they will take a look when time allows.