later Landing Autothrottle?

[dresoccer4]

Quick q: has the landing autothrottle (ATC) been implemented yet?

[SUBS17]

Auto throttle is modeled but it does not operate safely or properly. 

[kengou]

No it is not properly implemented. I believe it kind of works with half flaps, but you don't land at half flaps anyway so it's not really relevant.

[dresoccer4]

16 minutes ago, SUBS17 said:

Auto throttle is modeled but it does not operate safely or properly. 

 

14 minutes ago, kengou said:

No it is not properly implemented. I believe it kind of works with half flaps, but you don't land at half flaps anyway so it's not really relevant.

 

ok good that means I haven't been doing something wrong.

Do you know if landing ATC is planned to be implemented? I read it was in the works but that was 2 years ago. Wasn't sure if they just decided it wasn't worth the effort

[fagulha]

15 hours ago, dresoccer4 said:

Quick q: has the landing autothrottle (ATC) been implemented yet?

ATC it´s implemented but what you refering to, ACLS, it´s not yet implemented. And it´s planned to be implemented although it´s due. Probably in next big update or forward because the Hornet will be finished this year (although future updates and fixes will continue).

[Dragon1-1]

In theory, ATC is implemented. In practice, it doesn't work too well (read: will screw up your approach and more likely than not dunk you in the sea). On top of that, the engine spool-up time appears to be too long, which complicates things. I hope that these things will be looked at soon.

[BarTzi]

27 minutes ago, Dragon1-1 said:

In theory, ATC is implemented. In practice, it doesn't work too well (read: will screw up your approach and more likely than not dunk you in the sea). On top of that, the engine spool-up time appears to be too long, which complicates things. I hope that these things will be looked at soon.

 

ATC has two modes afaik. Cruise is implemented , while PA (the one you use to land) is not implemented properly.

[Dragon1-1]

Last time I tried it out, it seemed like it attempts to hold on-speed AoA. Of course, it fails miserably at that, but I don't know if it's because of bad code, poorly chosen PIDs (or whatever parameters the controller is based on), or using real PIDs with unrealistic engine response.

[kengou]

17 hours ago, dresoccer4 said:

 

 

ok good that means I haven't been doing something wrong.

Do you know if landing ATC is planned to be implemented? I read it was in the works but that was 2 years ago. Wasn't sure if they just decided it wasn't worth the effort

Yes it's definitely planned to be implemented. Who knows when, but the Hornet is nearing completion so I can predict with confidence we'll see it before the end of the year.

[SUBS17]

8 hours ago, Dragon1-1 said:

Last time I tried it out, it seemed like it attempts to hold on-speed AoA. Of course, it fails miserably at that, but I don't know if it's because of bad code, poorly chosen PIDs (or whatever parameters the controller is based on), or using real PIDs with unrealistic engine response.

IRL it does not behave like that.

8 hours ago, BarTzi said:

 

ATC has two modes afaik. Cruise is implemented , while PA (the one you use to land) is not implemented properly.

 

ATC has only 1 mode actually, it is for one purpose only.

[dresoccer4]

1 hour ago, SUBS17 said:

IRL it does not behave like that.

 

ATC has only 1 mode actually, it is for one purpose only.

 

I've read it has two modes, for two purposes. 

 

1) normal flight (speed)

2) landing (AoA)

 

And they behave differently.

 

 

[Curly]

The auto throttle system on the hornet has two separate operating modes. When the flaps are up, the system operates as Velocity Control System (VCS). This is what the good book, NFM-000  pages 1-2-8 to 10, call the ATC cruse mode.  In cruse mode, Air data (air speed) is feedback and causes the throttle to move. Thus controling the air speed.

 

If the flaps are in half, and few other criteria are meet, pressing the auto throttle button engages the Approach Power Compensator. Which the good book, NFM-000, calls The ATC Approach Mode.  When the auto throttle is in APC mode, it's designed to maintain an angle of attack of 8.1 degrees and modulates the throttles to do so. Seems easy on paper, but the dynamics are orders of magnitude more complicated than the Cruse Mode. In APC mode, system Feedbacks include angle of attack, G, pitch rate, stabilizer command, and bank angle. Each input has unique impact on the change in angle of attack and thus command of the throttle. So each input needs a unique set of gains.

 

 

 This is a block diagram of the system from an old AGARD report. This diagram tells us, a negative amount of G, positive pitch rate, a stabilizer command trailing edge up (stick aft), or an angle of attack of more than 8.1 will cause the throttles to advance.  Each input is gained  depending on they individually effect the angle of attack. The gains are based on the unique characteristics of the Hornet and the engine performance.

 

In short the system is complicated, dynamic and dependent on the basic flight and engine models. If those models we’re in flux, every time you changed a  flight / engine model parameter you would have to go back and figure out your APC gains again. That’s probably why the APC and the Automatic Carrier Landing system will be one of the last systems implemented. Who knows, maybe it’s all ready built with the AGARD gains, but increased thrust of the EPE engines make behave poorly.  

Link to the AGRAD: https://www.sto.nato.int/publications/AGARD/Forms/AllItems.aspx?RootFolder=%2Fpublications%2FAGARD%2FAGARD%2DCP%2D509&FolderCTID=0x0120D5200078F9E87043356C409A0D30823AFA16F60B00B8BCE98BB37EB24A8258823D6B11F157&View=%7B7E9C814C-056A-4D31-8392-7C6752B2AF2B%7D

 

That AGARD report is a pretty interesting read too. There's a lot of details about the Hornet buried in there. How the hud computes the flight path marker and even the old (pre 10.5.1) Trim to AOA command schedule.

There’s some cool experiments described too. Ski ramp takeoff with a Hornet anyone?

Here’s a low fi version of the same doc.

https://apps.dtic.mil/dtic/tr/fulltext/u2/a244869.pdf

[BarTzi]

On 3/11/2021 at 9:39 PM, SUBS17 said:

IRL it does not behave like that.

 

ATC has only 1 mode actually, it is for one purpose only.

See Curly's comment above. Two modes.

Edited March 12, 2021 by BarTzi

[SUBS17]

It has only 1 mode only, it is for landings and that is all. UA/PA does not change it, what it does is holds AoA not speed. Cruise is an odd place to use Auto-throttle.(it was not designed for that, but it is an interesting use for it) Flaps should always be full for landings, you set your AoA with gear down, hook down and full flaps, then engage Auto throttle and it should hold the AoA for the approach. Its performance should be identical to the F-14 in DCS Auto throttle where on approach it holds AoA and the pilot can make small stick inputs for the landing. It works extremely well in DCS F-14.

Edited March 13, 2021 by SUBS17

[Rescue]

1 hour ago, SUBS17 said:

It has only 1 mode only (...)

 

 

Hey there,

Maybe you are a hornet pilot or an engineer and know way better than we all BUT according to NATOPS Flight Manual F/A-18 A/B/C/D (...)

I-2-8 

2.1.2. (Automatic throttle Control) (and 2.1.2.1. (ATC Approach Mode)):

 

It has 2 modes

 

"The automatic throttle control is a two mode system that

automatically maintains angle of attack (approach mode) or airspeed (cruise mode) by modulating

engine thrust in the range of flight idle through military."(...)

 

While ED postet the link to it some time ago, i won't state any further that this one is public etc.

 

Also Curly stated it pretty well https://forums.eagle.ru/topic/264735-landing-autothrottle/?do=findComment&comment=4595973

 

 

Grettings

Edited March 13, 2021 by Rescue

[SUBS17]

That is 1 mode that you describe there. 

[BarTzi]

6 hours ago, SUBS17 said:

That is 1 mode that you describe there. 

 

There are two modes, as described in NATOPS.

 

2.1.2 Automatic Throttle Control (ATC). The automatic throttle control is a two mode system that
automatically maintains angle of attack (approach mode) or airspeed (cruise mode) by modulating
engine thrust in the range of flight idle through military.

 

2.1.2.1 ATC Approach Mode. The ATC approach mode is engaged by pressing and releasing the
ATC button on the left throttle with the FLAP switch in HALF or FULL and the trailing edge flaps
extended at least 27°. When ATC is engaged in the approach mode, the flight control computer
modulates engine thrust to maintain on-speed AOA. The computer uses inputs of AOA, normal load
factor, stabilator position, pitch rate, and angle of bank to generate command signals. These signals
drive the engine mounted throttle control units which in turn command the engine fuel controls. The
computer uses AOA as the primary input to generate command signals. However, normal load factor
provides increased stability, stabilator position provides increased or decreased thrust for pilot induced
pitch changes, pitch rate provides lead during pitch maneuvers, and bank angle provides additional
thrust during banking maneuvers. Normal disengagement is accomplished by pressing the ATC button
or applying and holding force to either throttle.

 

2.1.2.2 ATC Cruise Mode. The ATC cruise mode is engaged by pressing and releasing the ATC
button on the left throttle with the FLAP switch in AUTO. When ATC is engaged in the cruise mode,
the existing airspeed is used by the flight control computer to modulate engine thrust to maintain this
existing airspeed. The existing airspeed is the airspeed being sent from the ADC to the flight control
computers via the mission computers. An ADC failure inhibits the ATC cruise mode of operation. The
FCC uses true airspeed from ADC via the mission computers at the time of engagement to generate a
command signal. This signal is then used as a reference to generate an error signal that drives the
engine mounted throttle control units. Normal disengagement is accomplished by pressing the ATC
button or applying and holding force to either throttle.

Edited March 14, 2021 by BarTzi

[Stearmandriver]

What an odd argument... and what an odd claim, that a cruise autothrottle mode that holds speed and not AoA is unusual. 

 

Basically, every aircraft that has an autothrottle system works to hold cruise airspeed.  This includes all airliners and most corporate jets, as well as military aircraft. 

 

The approach mode that holds angle of attack is what's unusual.  Other naval aircraft have this system too, but it is FAR less common than a speed hold mode. 

 

And yes, AoA and speed are two entirely different things.  They're related to some extent but very fluidly... there are ways to change each that doesn't affect the other, or that causes them to diverge in opposite directions than you'd expect.  The term "on-speed AoA" is used often here and I think gives some folks a misunderstanding that a given airspeed will always correspond to a given AoA.  That's only true for a given weight and most importantly, under a 1g condition.  As soon as you change loading on the wing, speed and AoA diverge. 

[Blaze1]

On 3/12/2021 at 3:54 AM, Curly said:

The auto throttle system on the hornet has two separate operating modes. When the flaps are up, the system operates as Velocity Control System (VCS). This is what the good book, NFM-000  pages 1-2-8 to 10, call the ATC cruse mode.  In cruse mode, Air data (air speed) is feedback and causes the throttle to move. Thus controling the air speed.

 

If the flaps are in half, and few other criteria are meet, pressing the auto throttle button engages the Approach Power Compensator. Which the good book, NFM-000, calls The ATC Approach Mode.  When the auto throttle is in APC mode, it's designed to maintain an angle of attack of 8.1 degrees and modulates the throttles to do so. Seems easy on paper, but the dynamics are orders of magnitude more complicated than the Cruse Mode. In APC mode, system Feedbacks include angle of attack, G, pitch rate, stabilizer command, and bank angle. Each input has unique impact on the change in angle of attack and thus command of the throttle. So each input needs a unique set of gains.

 

 

 This is a block diagram of the system from an old AGARD report. This diagram tells us, a negative amount of G, positive pitch rate, a stabilizer command trailing edge up (stick aft), or an angle of attack of more than 8.1 will cause the throttles to advance.  Each input is gained  depending on they individually effect the angle of attack. The gains are based on the unique characteristics of the Hornet and the engine performance.

 

In short the system is complicated, dynamic and dependent on the basic flight and engine models. If those models we’re in flux, every time you changed a  flight / engine model parameter you would have to go back and figure out your APC gains again. That’s probably why the APC and the Automatic Carrier Landing system will be one of the last systems implemented. Who knows, maybe it’s all ready built with the AGARD gains, but increased thrust of the EPE engines make behave poorly.  

Link to the AGRAD: https://www.sto.nato.int/publications/AGARD/Forms/AllItems.aspx?RootFolder=%2Fpublications%2FAGARD%2FAGARD-CP-509&FolderCTID=0x0120D5200078F9E87043356C409A0D30823AFA16F60B00B8BCE98BB37EB24A8258823D6B11F157&View={7E9C814C-056A-4D31-8392-7C6752B2AF2B}

 

That AGARD report is a pretty interesting read too. There's a lot of details about the Hornet buried in there. How the hud computes the flight path marker and even the old (pre 10.5.1) Trim to AOA command schedule.

There’s some cool experiments described too. Ski ramp takeoff with a Hornet anyone?

Here’s a low fi version of the same doc.

https://apps.dtic.mil/dtic/tr/fulltext/u2/a244869.pdf

Great info Curly!