Typhoon FM: What's With The Pitch-Roll Coupling?

[Guest deleted@258843]

Hey folks, genuinely curious if anybody knows what's going on with this, and why there is a left rolling tendency when pitching up and vice versa when pitching down.

 

Thought this was so strange that it may be a bug. Really interested in if there is some mention of this happening in real life, and if so, what the explanation is for it. 

[AndyJWest]

Gyroscopic forces (pitch causes yaw), interacting with dihedral effect (yaw causes roll)maybe?

 

What sort of IAS & power setting are you seeing this at?

[Guest deleted@258843]

Seems to happen at all speeds, even with the engine turned off.

 

What's more, you can keep the needle centered and you still get the weird roll left when pitching up.

 

I am thinking it may be a bug of some kind.

[US41_Winslow]

Gyroscopic forces act at a 90 degree angle to the direction the force is applied, so when you pitch up in the Typhoon, you should see some yaw to the left.  This yaw causes the left wing to go slower and the right wing to speed up, resulting in the airplane entering a left-hand turn if the pilot does not correct.  However, I can’t think of why this would happen if the airplane stays coordinated or the propeller is stopped.

[Guest deleted@258843]

31 minutes ago, Miners said:

Gyroscopic forces act at a 90 degree angle to the direction the force is applied, so when you pitch up in the Typhoon, you should see some yaw to the left.  This yaw causes the left wing to go slower and the right wing to speed up, resulting in the airplane entering a left-hand turn if the pilot does not correct.  However, I can’t think of why this would happen if the airplane stays coordinated or the propeller is stopped.

 

 

I understand this. But there is no appreciable left yaw when this is happening. You can keep the needle centered and it still does this.

[QB.Gregor-]

It still happens when the engine and prop are completly stopped. The game might still model the engine as spinning however that's not consistent with other planes in the sim. The Fokker Dr1 and Sowith Camel both have a similar roll effect but here it goes away when the engine stops spinning. https://streamable.com/34ksk9

Edited June 2, 2021 by QB.Gregor-

[Yak_Panther]

The elevator trim tabs are moving differentially. One moves trailing edge up the other moves trailing edge down. When the trim is set neutral, 0%, there is no pitch roll coupling. It’s a bug.

[QB.Gregor-]

3 hours ago, Yak_Panther said:

The elevator trim tabs are moving differentially. One moves trailing edge up the other moves trailing edge down. When the trim is set neutral, 0%, there is no pitch roll coupling. It’s a bug.

What do you mean, there is no pitch roll coupling? It's still happening for me: https://streamable.com/zzf3g3 I would assume the trim tabs are just a visual bug, with no effect on the FM. They work like you would normally expect. If they were modeled like they look, you wouldn't be able to trim the pitch axis since they would just cancel each other.

[NIK14]

4 hours ago, QB.Gregor- said:

What do you mean, there is no pitch roll coupling? It's still happening for me: https://streamable.com/zzf3g3 I would assume the trim tabs are just a visual bug, with no effect on the FM. They work like you would normally expect. If they were modeled like they look, you wouldn't be able to trim the pitch axis since they would just cancel each other.

No. You would roll with the current set up...that's why we are rolling. For pitch, i.e stab trim the tabs have the same travel on each side, that means not opposite directions. The main wing trim tabs take care of roll. I am expecting a hotfix.

[QB.Gregor-]

34 minutes ago, NIK14 said:

No. You would roll with the current set up...that's why we are rolling. For pitch, i.e stab trim the tabs have the same travel on each side, that means not opposite directions. The main wing trim tabs take care of roll. I am expecting a hotfix.

But the roll is not affected if you change the pitch trim, even when you reverse them. There isn't any roll effect when going in a straight line. I think we agree on the effect the trim tabs would have if they were modeled like they look visually.

However they just function normally -> that bug is just the visual animation, in the underlying physics modeling they are working correctly. You can see the plane still pitch-rolling in my video (https://streamable.com/zzf3g3) in which both the tabs are neutral and level with the elevator.

I think this thread's original issue is something else.

[RedKestrel]

19 minutes ago, QB.Gregor- said:

But the roll is not affected if you change the pitch trim, even when you reverse them. There isn't any roll effect when going in a straight line. I think we agree on the effect the trim tabs would have if they were modeled like they look visually.

However they just function normally -> that bug is just the visual animation, in the underlying physics modeling they are working correctly. You can see the plane still pitch-rolling in my video (https://streamable.com/zzf3g3) in which both the tabs are neutral and level with the elevator.

I think this thread's original issue is something else.

This might be a stupid question...but when the pitch trimmer is at 0%, is that actually neutral, or is the 0% trim position still offset from neutral trim? 

It seems like a weird coincidence that we have pitch/roll coupling happening and an animation error for the trim tabs.

[NIK14]

23 minutes ago, QB.Gregor- said:

However they just function normally -> that bug is just the visual animation, in the underlying physics modeling they are working correctly. You can see the plane still pitch-rolling in my video (https://streamable.com/zzf3g3) in which both the tabs are neutral and level with the elevator.

I think this thread's original issue is something else.

 

You are right...the issue is something else. Pull back or trim full back and it rolls left...pitch forward or trim forward, the plane rolls right. The balance is off. This should be fixed...I can't see any logic or physical reason for this behaviour. It's like flying around with an uncalibrated stick lol

[busdriver]

3 minutes ago, RedKestrel said:

It seems like a weird coincidence that we have pitch/roll coupling happening and an animation error for the trim tabs.

 

The animation error is not related to any behavior. It has been reported. The right elevator trim animation is backwards.

[RedKestrel]

2 hours ago, busdriver said:

 

The animation error is not related to any behavior. It has been reported. The right elevator trim animation is backwards.

That's good to know. Any insight into the rolling tendency? Is that just a normal thing for the Typhoon? 

My understanding is that adverse yaw from gyroscopic forces can induce some roll, but if you're correcting for the yaw then the roll shouldn't happen, right?

[busdriver]

3 minutes ago, RedKestrel said:

That's good to know. Any insight into the rolling tendency? Is that just a normal thing for the Typhoon? 

 

I can repeat the slight left rolling tendency with the Hurricane when starting from hands off wings level and a straight pull (or nose up trim) then releasing the stick. I do not get any right rolling tendency pushing/trimming the Hurricane nose down.

 

For me the Tempest has no rolling tendency in either direction.

 

For me the Typhoon left rolling tendency is slightly more pronounced than the Hurricane, but still pretty slow. Trimming nose up only rolls left and trimming nose down rolls right at a slower rate. Initially I figured engine torque caused the left roll (but it does this with the engine off as well). I have no reason for the right rolling moment.

 

Having said that, I can and have slowed every US/UK single engine airplane down, configured for landing (gear and full flaps), then with my feet flat on the floor (off the rudder pedals) add full power and climb out straight ahead with only a tiny bit of right/opposite aileron. By that you should infer that IMO torque is not significantly modeled. 

 

 

26 minutes ago, RedKestrel said:

My understanding is that adverse yaw from gyroscopic forces can induce some roll, but if you're correcting for the yaw then the roll shouldn't happen, right?

 

That's how I understand it as well. In the hard-wing RF-4 adverse yaw was a significant consideration at high AOA, so much so that we rolled using rudder at high AOA.

[RedKestrel]

18 minutes ago, busdriver said:

 

That's how I understand it as well. In the hard-wing RF-4 adverse yaw was a significant consideration at high AOA, so much so that we rolled using rudder at high AOA.

Maybe slightly OT, but I hadn't heard this term before. What does it refer to? When I google it I get some rock bands and a couple of PR companies, lol. 
 

[JimTM]

50 minutes ago, RedKestrel said:

Maybe slightly OT, but I hadn't heard this term before. What does it refer to? When I google it I get some rock bands and a couple of PR companies, lol. 
 

 

It's a PR company for a rock band with no leading-edge maneuvering slats to enhance its agility and slow-speed handling. That's my guess.  

[busdriver]

So as not to pollute the thread...PM inbound.

[Guest deleted@258843]

Thanks for the replies, guys.

 

So far I have not read or come up with much that would explain what we're seeing (interesting catch about the elevator trim position, though!)

 

Assuming it is a bug, I can think of two things that might result in the behavior we see:

 

1. An error in modeling Gyroscopic Precession: Pitching up/down should result directly in adverse undesired yaw (and maybe indirectly roll if this is not corrected). But perhaps the force value in the code is being mistakenly sent to the wrong axis -- ie. The Longitudinal Axis (roll) instead of the Normal Axis (yaw)?
2. If there is a "damping" value associated with aerodynamic surfaces in the flight model, perhaps the left wing has been mistakenly given a higher value than the right, or vice versa? This could manifest itself as asymmetric lateral stability about the Longitudinal Axis (roll), and would explain why we get left roll when pitching up and right roll when pitching down -- in effect, the left wing would be harder to disturb, up or down, while the right side would not, resulting in a roll moment when pitching. Edit: This additional damping could be in the form of inertia if a higher weight value has been given to one wing (the left)

 

 

Edited for clarity.

Edited July 24, 2021 by Kablamoman

[Guest deleted@258843]

Update for Hotfix 4.602b

 

 

Problem is still present even though they corrected the reversed elevator trim tab in the external view.

[NIK14]

I assume this will never be looked into unless someone provides "data" or other evidence. Seems to be how things work around here.

I'm pretty sure however Sydney Camm didn't design a plane that rolled moderatly left when pitched up and then right, when pitched down.

[Denum]

I think we need another sniff test.

 

I'd be a little more accepting if more aircraft had little quirks on input but seeing as this is the only one, it seems out of place.

Edited June 23, 2021 by Denum

[gimpy117]

On 6/23/2021 at 5:52 PM, Denum said:

I think we need another sniff test.

 

I'd be a little more accepting if more aircraft had little quirks on input but seeing as this is the only one, it seems out of place.

I think so too, there are just so many aircraft that seem to have little to no vices. I was in  a rolling scissors with a Hurricane in an 110 E model and i was able to just keep that bus from stalling to the point the Hurricane was having difficulties. I am not a great pilot...so, its things like that which make me wonder. 

[Guest deleted@50488]

On 6/2/2021 at 11:44 PM, Kablamoman said:

Thanks for the replies, guys.

 

So far I have not read or come up with much that would explain what we're seeing (interesting catch about the elevator trim position, though!)

 

Assuming it is a bug, I can think of two things that might result in the behavior we see:

 

1. An error in modeling Gyroscopic Precession: Pitching up/down should result directly in adverse yaw (and maybe indirectly roll if this is not corrected). But perhaps the force value in the code is being mistakenly sent to the wrong axis -- ie. The Longitudinal Axis (roll) instead of the Normal Axis (yaw)?
2. If there is a "damping" value associated with aerodynamic surfaces in the flight model, perhaps the left wing has been mistakenly given a higher value than the right, or vice versa? This could manifest itself as asymmetric lateral stability about the Longitudinal Axis (roll), and would explain why we get left roll when pitching up and right roll when pitching down -- in effect, the left wing would be harder to disturb, up or down, while the right side would not, resulting in a roll moment when pitching.

 

Regarding 1), why adverse yaw ? Adverse yaw results from aileron induced drag, which is not the case in the described situation.

Assuming the prop rotates CCW in this model, a pitch up corresponds to a force applied to the prop "from bellow", so, 90º ahead the resulting force will be from starboard, thus causing a yaw to the left, and, maybe, the observed yaw-induced roll (left roll)...

 

To me it looks plausible, maybe with an overdone yaw-roll coupling effect, but I really don't know the details about this aircraft aerodynamic characteristics.

 

Edited July 4, 2021 by jcomm

[Guest deleted@258843]

1 hour ago, jcomm said:

Regarding 1), why adverse yaw ? Adverse yaw results from aileron induced drag, which is not the case in the described situation.

Assuming the prop rotates CCW in this model, a pitch up corresponds to a force applied to the prop "from bellow", so, 90º ahead the resulting force will be from starboard, thus causing a yaw to the left, and, maybe, the observed yaw-induced roll (left roll)...

 

To me it looks plausible, maybe with an overdone yaw-roll coupling effect, but I really don't know the details about this aircraft aerodynamic characteristics.

 

 

 

Apologies for being unclear. I was using the term adverse yaw in the literal sense to describe any undesired yaw, including yaw that results from the gyroscopic effect when pitching. The thing is that this yaw should not result in any roll if it is controlled with rudder (ie. keeping the needle/ball centered). The rolling with pitch behavior exhibited by the typhoon in the game happens regardless of whether the needle is centered or not, and indeed even when the engine is seized entirely.

[Fizzix]

it's like one wing is heavy.  They may have offset the center of gravity laterally, to compensate for what should be massive torque.  Since the Typhoon only has fixed aileron tabs, the goal may be to have the plane in trim for cruising.  Of course, this is not the way to go about it.  Maybe they don't have a way to set fixed aileron tabs and the plane would otherwise be untrimmable in roll.

[Guest deleted@258843]

On 7/20/2021 at 5:47 PM, Wells said:

it's like one wing is heavy.  They may have offset the center of gravity laterally, to compensate for what should be massive torque.  Since the Typhoon only has fixed aileron tabs, the goal may be to have the plane in trim for cruising.  Of course, this is not the way to go about it.  Maybe they don't have a way to set fixed aileron tabs and the plane would otherwise be untrimmable in roll.

 

If that were the case it would roll in the same direction whether pitching up or down, or indeed when not pitching at all. Right now it rolls left if you pitch up, and right when you pitch down.  Edit: This is wrong as explained below. Thanks Fizzix.

 

 

 

After flying it for quite a few more hours online, I still think it's some issue with the FM and roll-wise drag/damping for the left wing. I actually had the behavior reverse itself once when my right wing took damage and incurred a drag penalty -- the torque about the roll axis was then reversed with pitching: It rolled right when pitching up, and rolled left when pitching down.

Edited July 24, 2021 by Kablamoman

[Fizzix]

On 7/21/2021 at 6:50 PM, Kablamoman said:

 

If that were the case it would roll in the same direction whether pitching up or down, or indeed when not pitching at all. Right now it rolls left if you pitch up, and right when you pitch down.

 

After flying it for quite a few more hours online, I still think it's some issue with the FM and roll-wise drag/damping for the left wing. I actually had the behavior reverse itself once when my right wing took damage and incurred a drag penalty -- the torque about the roll axis was then reversed with pitching: It rolled right when pitching up, and rolled left when pitching down.

No, you can test it in any other sim, like X-plane, for example, or fly an R/C airplane that is one wing heavy.  It does exactly that, rolls one way under positive G and the other way with negative G

[Guest deleted@258843]

11 hours ago, Flight_Fizzix said:

No, you can test it in any other sim, like X-plane, for example, or fly an R/C airplane that is one wing heavy.  It does exactly that, rolls one way under positive G and the other way with negative G

 

Hey, I stand corrected!

 

Thanks.

 

You're absolutely right. Forgive me, as I've actually experienced fuel imbalances in real sims and experienced for real what it feels like when you run out of aileron trim and the auto-pilot kicks off, but didn't stop to think of how it would behave if the trim was still sufficient and set to keep wings level with an imbalance.

 

In that case, inertia would would have an effect when pitching and create opposing roll torques depending on pitch direction. Effectively making the heavier wing more damped.

 

Thank you again for helping me with something I overlooked! I'll edit my previous response.

 

I think this is a reasonable explanation for the behavior we see in the game if it were unintentional (one wing unintentionally heavier than the other), but I would somewhat doubt that was part of the actual design of the Typhoon. 

[Guest deleted@258843]

Further to the above, I think @Flight_Fizzix has actually gotten really close in figuring this out.

 

After playing around with fuel loads it's become clear the behavior is tied to the typhoon's fuel quantity. If you load up a quick mission with 100% fuel you will really see the effect, but if you load with the bare minimum of 10% the effect is almost absent entirely.

 

It's as if the fuel weight in the FM is concentrated in the port wing for some reason (perhaps the fuel tanks lateral moment arms have been unintentionally shifted left?) -- you can see similar effects in other planes if you have an asymmetric bomb load (try dropping just one wing bomb in a mustang, use roll trim to keep wings level, then pitch up and down and see how the aircraft responds in roll).

 

@-DED-Rapidus I respectfully request that you please have a second look at this. The fact that the rolling behavior in response to pitch changes with fuel load out suggests some kind of asymmetric fuel weight (between the two wings) is being expressed in the typhoon flight model for some reason.

Edited July 27, 2021 by Kablamoman

[Guest deleted@258843]

After some more testing, the weight distribution of the fuel at 100% load is so port-side heavy, that having a single 500 pound bomb on the starboard side wing seems to balance it out.

 

The aircraft will happily pitch without any coupled roll in that configuration.

[=621=Samikatz]

On 7/27/2021 at 8:13 PM, Kablamoman said:

After some more testing, the weight distribution of the fuel at 100% load is so port-side heavy, that having a single 500 pound bomb on the starboard side wing seems to balance it out.

 

The aircraft will happily pitch without any coupled roll in that configuration.

 

The wing tanks in the Typhoon carry 40 UK gallons of fuel, which would weigh about... Well according to this conversion website I used, that'd be a little bit under 300lbs. If, like you said, both tanks were in the same wing, that wing would be a little less than 600lbs heavier than the other

 

I think your theory is correct

[Guest deleted@258843]

All the tanks are indeed in the wing. The "Nose" tanks are actually located in the leading edge of the wing, forward of the main tanks.

 

I hesitated to say the 500lb bomb perfectly balanced the fuel (because the moment arm of the bomb is slightly further outboard) and I don't know the nature of the bug (are the right side fuel tank weight values completely absent or have all fuel tank moment arms been shifted towards the port side, some amount?)

 

It's hard to say, but I think it at least warrants a look by the devs.

[Hitcher]

I swear this fix better be in the next update, its probably such a small adjustment for a big oversight.

It's clear the aircraft was rushed to release with the obvious errors it had, like wrong gun sound and elevator tab animation being incorrect.

That stuff would have been picked up with 10 minutes of testing.

PS stop bothering the engineers))))

Edited July 31, 2021 by Hitcher

[Bilbo_Baggins]

Hey gents, don't have the computer on me. Wondering if the issue been addressed now?

 

11. Adjusted the maximum wing lift of the Hawker Typhoon Mk.Ib. The flight model of the aircraft was reconfigured in such a way that most of the flight characteristics of the aircraft (speed, rate of climb, control stick balancing positions, roll angular velocities) practically did not change;

Edited August 12, 2021 by Bilbo_Baggins

[354thFG_Drewm3i-VR]

1 hour ago, Bilbo_Baggins said:

Hey gents, don't have the computer on me. Wondering if the issue been addressed now?

 

11. Adjusted the maximum wing lift of the Hawker Typhoon Mk.Ib. The flight model of the aircraft was reconfigured in such a way that most of the flight characteristics of the aircraft (speed, rate of climb, control stick balancing positions, roll angular velocities) practically did not change;

I do not think it has sadly. We have shiny new toys, but many of the things that have been released still do not work properly (typhoon pitch roll coupling, tempest turn performances, .50s, 20mm skin damage, etc.).

[354thFG_Drewm3i-VR]

3 minutes ago, Bilbo_Baggins said:

 

Just had a quick spin with the airframe. Definitely seems to have been changed

 

RGDS

Good to hear, I will have to try it.

[Guest deleted@258843]

This particular issue has not been fixed in the latest update.

[354thFG_Panda_]

It is still present and if you take full fuel it is amplified. With the recent changes to it's turning it can be awkward and a bit of a handful in certain manoeuvres and develops into a very nasty spin.

 

Panda

Edited August 16, 2021 by LR.TheRedPanda

[gimpy117]

still no fix. 

 

buy hey, drop tanks right (for the 109 only)