correct as-is F-16C auto trim

[Funflite]

Just to have a question or wish...there not have an auto trim on F-16C,it's a fly by wire aircraft and as i read on it ,all the series on this aircraft have a auto trim function.The cockpit is the workload in mind for the pilots.I never read that a pilot have to trim this aircraft unless the autotrim is damaged.It's a fourth generation of fighter...

[Frederf]

The only time the airplane moves the trim wheels automatically is the pitch wheel to zero during the takeoff roll. Every other time the trim is only moved by pilot input manually.

Other behavior would be fictional. Such features could be added as convenience options but I don't anticipate they are all likely.

[Funflite]

Ok...I heard that from a pilot...but ok...it's a simulator...I will edit default.lua for F16.thank's.

Edited December 8, 2021 by Funflite

[Bunny Clark]

While the aircraft does not move the manual trim wheels, the FCS will automatically keep the aircraft "trimmed" in pitch without any pilot input. You should only need to manually trim roll for asymmetric stores loading.  

[SCPanda]

3 hours ago, Bunny Clark said:

While the aircraft does not move the manual trim wheels, the FCS will automatically keep the aircraft "trimmed" in pitch without any pilot input. You should only need to manually trim roll for asymmetric stores loading.  

Yep. I heard FCS always trims the jet to 1G. 

[Snappy]

16 hours ago, Funflite said:

Just to have a question or wish...there not have an auto trim on F-16C,it's a fly by wire aircraft and as i read on it ,all the series on this aircraft have a auto trim function.The cockpit is the workload in mind for the pilots.I never read that a pilot have to trim this aircraft unless the autotrim is damaged.It's a fourth generation of fighter...

Regardless of the F-16 itself. Having FBW does not automatically mean the aircraft has autotrim. It is frequently a feature or capability of FBW aircraft, but there are also FBW aircraft  which are trimmed primarily by the pilots.

[Aquorys]

On 12/8/2021 at 5:46 PM, Funflite said:

I never read that a pilot have to trim this aircraft unless the autotrim is damaged.It's a fourth generation of fighter...

It's a 70s aircraft though, not an Airbus 350. The FLCS does some things, like keep pitch roughly at 1G, but it doesn't compensate for sudden weight imbalances in roll or for wind that's pushing you somewhere. If you want to take the hands off the controls a bit more, e.g. because you're busy planning, configuring, etc., my suggestion would be, you do a coarse manual trim, adjust thrust and then put the autopilot on attitude hold.

[mobua]

On 12/8/2021 at 5:51 PM, Frederf said:

The only time the airplane moves the trim wheels automatically is the pitch wheel to zero during the takeoff roll. Every other time the trim is only moved by pilot input manually.

Other behavior would be fictional. Such features could be added as convenience options but I don't anticipate they are all likely.

Hi Frederf,

 

I've observed that after takeoff and wheels up, while accelerating in the jet has a pitch up tendency with increasing velocity.

 

Is this correct? Would you care to explain why this is happening as I was under the belief that the FLCS would counteract this?

 

Sincerely

mobua

[Smoked]

2 hours ago, mobua said:

 

 

I've observed that after takeoff and wheels up, while accelerating in the jet has a pitch up tendency with increasing velocity.

 

If you are imputing elevator response when you retract your gear the FLCS will go from reduced gains/input due to gear being down, to normal deflection so you will see a rate increase if you're giving a constant rate of "pull". during the gear cycle.  best thing to do would be include a track file so we can see all of it.   If you are elevator neutral (no imputes) and its doing it, something is wrong.  

[mobua]

3 hours ago, Smoked said:

If you are imputing elevator response when you retract your gear the FLCS will go from reduced gains/input due to gear being down, to normal deflection so you will see a rate increase if you're giving a constant rate of "pull". during the gear cycle.  best thing to do would be include a track file so we can see all of it.   If you are elevator neutral (no imputes) and its doing it, something is wrong.  

Unfortunately I am not able to (and will not for a while) to produce a track.

However the observed condition is easy to reproduce.

A2A loadout,  CAT I

1. Full AB departure,

2. Maintain Full AB.

3. 5 degree climbout.

4. Hands off stick.

You should notice the jet pitch up with increasing speed.

Sorry but this is the best I can do for now.

 

 

Edited December 19, 2021 by mobua
spelling

[razo+r]

1 hour ago, mobua said:

Unfortunately I am not able to (and will not for a while) to produce a track.

However the observed condition is easy to reproduce.

A2A loadout,  CAT I

1. Full AB departure,

2. Maintain Full AB.

3. 5 degree climbout.

4. Hands off stick.

You should notice the jet pitch up with increasing speed.

Sorry but this is the best I can do for now.

 

 

 

Maybe related to this: 

 

[Deano87]

Without a track its difficult to see exactly what you mean but I think this is normal and is because the FLCS is trying to maintain 1G of load on the aircraft along its lift vector. As soon as you pitch up from horizontal you're decreasing how much of earth's gravity is being felt by the accelerometer in the jet and so the jet will pitch up a bit to regain 1G of lift load.

Easiest way of understanding this is to get it going fast at low level and then point the aircraft vertically upwards, now 0% of earths G is contributing to the lift load on the aircraft, and if you let go of the stick the FLCS will pull to 1G of lift load and the jet will pull its way over onto its back and if left to its own devices will keep pulling 1G trying to complete the worlds biggest loop.

In cruise gains the FLCS is not a pitch-rate system like an airbus or something, its G based.

Edited December 19, 2021 by Deano87

[mobua]

22 minutes ago, razo+r said:

Maybe related to this: 

 

Thank you for raazo+r. That's exactly the issue I'm trying to highlight. From the thread you linked it seems it's already a known bug acknowledged by ED.

Thus the jet should not be pitching up due to longitudinal acceleration. Just a shame that it still remains unresolved.

[Deano87]

6 minutes ago, mobua said:

Thank you for raazo+r. That's exactly the issue I'm trying to highlight. From the thread you linked it seems it's already a known bug acknowledged by ED.

Thus the jet should not be pitching up due to longitudinal acceleration. Just a shame that it still remains unresolved.

Does it pitch much if you're just accelerating level and not already climbing?

[TobiasA]

vor 7 Stunden schrieb mobua:

Hi Frederf,

 

I've observed that after takeoff and wheels up, while accelerating in the jet has a pitch up tendency with increasing velocity.

 

Is this correct? Would you care to explain why this is happening as I was under the belief that the FLCS would counteract this?

 

Sincerely

mobua

The jet trims for 1G, any pitch up motion will lead to a slow pitch up motion since 1G on a 45° slope means that there is a sin(45) component in one plane and cos(45) in the other one.

[mobua]

35 minutes ago, Deano87 said:

Does it pitch much if you're just accelerating level and not already climbing?

Yes, it's a compounding effect (a factor of acceleration) where you might start level with the horizon and end up 5-10 pitch up as acceleration decreased.

It is not the behavior I would expect of a sophisticated FBW and oftentimes result in having to manually pitch forward in order to maintain level flight during acceleration.

33 minutes ago, TobiasA said:

The jet trims for 1G, any pitch up motion will lead to a slow pitch up motion since 1G on a 45° slope means that there is a sin(45) component in one plane and cos(45) in the other one.

Thank you Tobias, however, with the question I was looking for an answer in why the FBW was not counteracting the forces to maintain a neutral pitch attitude.

[Deano87]

16 minutes ago, mobua said:

Thank you Tobias, however, with the question I was looking for an answer in why the FBW was not counteracting the forces to maintain a neutral pitch attitude.

Yes but why should it? It's not a pitch rate system, It is not an Airbus, letting go of the stick is not telling the aircraft "Hold this nose angle", its saying "Maintain 1G of lift load on the aircraft". If you're accelerating and the AoA of the aircraft is decreasing I would expect the FPM to rise, and once the FPM is above the horizon because of the way the FLCS will maintain 1G the nose will continue to climb, slowly first and then more rapidly.

[mobua]

54 minutes ago, Deano87 said:

Yes but why should it? It's not a pitch rate system, It is not an Airbus, letting go of the stick is not telling the aircraft "Hold this nose angle", its saying "Maintain 1G of lift load on the aircraft". If you're accelerating and the AoA of the aircraft is decreasing I would expect the FPM to rise, and once the FPM is above the horizon because of the way the FLCS will maintain 1G the nose will continue to climb, slowly first and then more rapidly.

Bare with me not being well versed in the subject.

However, if travelling in a straight line wings level while accelerating at 1G (vertical G), all things equal, shouldn't the FLCS strive to maintain this? As things stand the pitch up tendency would equate to an increase of G above 1.

As such I would expect the FBW to counteract this resulting in a maintained level flight irrespective of AOA or velocity (assuming enough lift is generated to maintain altitude).

Again, bare in mind I'm in deep water in regards to the subject.

Edited December 19, 2021 by mobua
spelling

[Tholozor]

The thing to remember is that your thrust vector (not total velocity, only thrust), is coincident with the aircraft's waterline. As the thrust velocity increases, it increases along that axis.

[b0bl00i]

On 12/8/2021 at 5:51 PM, Frederf said:

The only time the airplane moves the trim wheels automatically is the pitch wheel to zero during the takeoff roll. Every other time the trim is only moved by pilot input manually.

Other behavior would be fictional. Such features could be added as convenience options but I don't anticipate they are all likely.

JAS39 Gripen does autotrim

[TobiasA]

Am 19.12.2021 um 18:20 schrieb mobua:

Thank you Tobias, however, with the question I was looking for an answer in why the FBW was not counteracting the forces to maintain a neutral pitch attitude.

That's how that particular system works.