reported CROSS OVER ALPHA (rudder) FM

[Terzi]

Regarding the rudder limitations of the FLCS, when you bank the jet 90 degrees and apply the full rudder, the nose will always drop. No matter what your speed is, no matter how light your jet is.

But the real F-16 can keep the altitude. Please see this video from 3:55 to 4:05 or 12:15 to 12:30. Before entering 12:15 he says 400kts.

I am not saying something is definitely wrong, but it is worth to check once more.

 

[BIGNEWY]

If you think something is wrong please supply a track replay example and any evidence it is wrong. 

Video is not going to help in this case. 

thank you

[LowGlow]

Hu, I was about to report the same thing.

I agree that Terzi's video does not demonstrate the issue well, but I hope the following does:

https://www.youtube.com/watch?v=JLDjxzQw2o0

As you can see, the Viper pilot in this video performs a perfect Knife Edge maneuver, which is 90° bank, rudder in counter direction to keep nose high, and this video shows quite well that the pilot is able to maintain the jet in stable attitude.

In DCS this is currently not possible. At most you can keep the nose above the horizon for about 2 seconds, but the nose actually starts to fall immediately, no matter what you do.

And like Terzi I also tried different loads, and the surprising thing is that the load does not seem to have any impact on this at all. My expectation would be that with a higher load that it was harder to keep nose high, while with empty load (no weapons, no fuel tanks, low fuel) that it was easier to keep nose high. But that's not happening in DCS, which suggests some simplification of the flight model here?

And as I was already at it, I also played with the Yaw trim knob at the left hand side of the cockpit. The surprising thing here is that it adds angle on the rudder also when rudder pedal is fully pushed. I am not sure if that is correct behaviour either. So yes, you can get some extra degrees rudder angle with Yaw trim, but still no Knife Edge with stable attitude possible in DCS. And as far as I know, real Viper pilots do not use the yaw trim for this maneuver.

[LowGlow]

@BIGNEWYAny feedback on the additional info provided?

[LowGlow]

BTW, how do you make these videos appear embedded on the forum? I only see options for inserting a link or embedding a picture, but not an option to embed a video.

[BIGNEWY]

On 11/5/2022 at 1:57 PM, LowGlow said:

@BIGNEWYAny feedback on the additional info provided?

I have nothing to share, we need to see track replays and any evidence to support the claim. 

thank you

[skywalker22]

1 hour ago, BIGNEWY said:

I have nothing to share, we need to see track replays and any evidence to support the claim. 

thank you

I think there is no need, you can simply try by your self.

[bukizzzz]

Ok just tried it out again. Can't do a sustained knife edge at 90 degrees. Best possible is 45 degree bank otherwise I fall out of the sky. Can provide a track later

[LowGlow]

Am 18.10.2022 um 15:45 schrieb BIGNEWY:

If you think something is wrong please supply a track replay example and any evidence it is wrong. 

Video is not going to help in this case. 

thank you

I got that, but I did provide real footage of a Viper clearly showing that the Viper is capable to perform a knife edge, which means it can sustain attitude with 90° bank without the nose falling down. Do you agree that this claim is backed by provided evidence?

Then the 2nd part would be providing you a track replay of how we tried to perform a knife edge in DCS. But that would still require you to acknowledge the initial claim was correct, that it is possible to fly a knife edge with a real Viper.

[777coletrain]

Well, while this is another video, here is one on the knife edge pass. Seems like it's able to do it

 

[LowGlow]

Looking at 6:40 it does not seem though as if they had more maximum angle on the rudder than in DCS, and looking at the actual Knife Edge, he was not even using full rudder either.  Which makes me think, if the rudder have such a large impact on the real Viper, what could you do with this in a Dogfight if this was correctly modelled in DCS.

[Michal]

knife_edge.trk

On 11/18/2022 at 6:07 PM, BIGNEWY said:

I have nothing to share, we need to see track replays and any evidence to support the claim. 

thank you

 

[Moonshine]

On 11/20/2022 at 9:21 PM, 777coletrain said:

Well, while this is another video, here is one on the knife edge pass. Seems like it's able to do it

 

any news on this?

currently impossible to hold knife edge with a clean jet without the nose dipping down towards -5deg even with full rudder input.

the video posted by 777coletrain suggests a different behaviour in the real jet than what we currently have in DCS. if you listen to that conversation its quite obvious. 

plus tracks have also been posted...

[BIGNEWY]

We can not use video as evidence in this case, we do not know the config of the aircraft, its weight, the weather conditions. 

We are not seeing a problem here, we would need more evidence to make a change. 

thanks

[Terzi]

Yes we don't know the AC config in videos but in DCS the lightest config cannot do it.

[Moonshine]

Yes we dont know the config however, i highly doubt that they fly anything else than clean config with a passenger on board…

[LowGlow]

vor 6 Stunden schrieb BIGNEWY:

We can not use video as evidence in this case, we do not know the config of the aircraft, its weight, the weather conditions. 

We are not seeing a problem here, we would need more evidence to make a change. 

thanks

That more reads like "we don't want to see a problem here".

Current behaviour with DCS is significantly different than those in the demonstrated videos, which even show a knife edge at high altitude and not even going to maximum rudder.

In DCS you can't even hold a knife edge at low altitude, empty load out, yaw trim at maximum, rudder pedal fully pressed.

[darkman222]

Just my 2 cents. As long as we know that the jet we are seeing in the videos is our block 50 Viper, no matter what configuration the real jet has, and wether we know the configuration or not: There should be a configuration we should be able to find in game to recreate the edge pass.

If we cant, the DCS F16 simply cant perform how the real jet performs shown in the videos under no conditions. Do we need to be able to do a knife edge pass in game? Is it a problem? I dont know.

But logic tells me, if it was hard to achieve in real life, or only possible under certain conditions, it would not have been included for an air show  performance.

Edited December 7, 2022 by darkman222

[BIGNEWY]

I have asked the team to take a look

[LowGlow]

Awesome, thanks @BIGNEWY!

[janitha2]

Why is there no corss over alpha in the 16? also note the viper still cant climb with rudder. 
cross_over_aoa.trkTacview-20230101-231630-DCS-F-16C - Caucasus - Free Flight.zip.acmi

 

Edited January 1, 2023 by janitha2

[Tholozor]

That F-16 (88-0445) is a Block 42, not a 50.

[janitha2]

5 hours ago, Tholozor said:

That F-16 (88-0445) is a Block 42, not a 50.

so block 50s some how have a very weak rudder?

my question is that the viper in dcs has a very weak rudder and at 24 aoa the rudder stops working entirely, if you watch the tacview you can see that.
shouldn't the rudder be more effective at high aoa hence corss over aoa?

Edited January 2, 2023 by janitha2

[Tholozor]

The main point I was trying to convey is that the video doesn't provide enough hard data in regards to the handling performance of a Block 50 to achieve that maneuver without knowing the parameters in which it was executed. Different blocks/variants could have differing FLCS tolerances/limits depending on the computer or software installed.

Same video, different thread, it's a good read: 

 

Rudder limits have also been discussed before, which is also under investigation: 

 

Edited January 2, 2023 by Tholozor

[DummyCatz]

2 hours ago, janitha2 said:

my question is that the viper in dcs has a very weak rudder and at 24 aoa the rudder stops working entirely, if you watch the tacview you can see that.
shouldn't the rudder be more effective at high aoa hence corss over aoa?

 

The directional static stability derivative (Cn-beta) of the F-16 reduces significantly at 25 to 30 deg AOA, from positive static stability to neutral and even negative static stability. Hence rudder inputs are strictly prohibited and restricted by the FLCS at high AOA in order to prevent yaw departure, which the F-16 is very susceptible to.

Please refer to 'Rudder Authority Limiter' in the FLCS section of dash one.