Chengdu J-20 5th Generation Aircraft News & Discussions

[clarkgap]

Not necessarily true. We have gone thru this before on this forum...

There are three main rules in designing a radar low observable body:

- Control of quantity of radiators
- Control of array of radiators
- Control of modes of radiation

They are not necessarily rules that can be violated. Rather, they are more like guidelines that indicate the degree of obedience to them.

The F-22 has six major flight controls structures. The J-20 has eight. That make the J-20 less obedient to Rule 1. But that does not automatically make the J-20 more visible EM-wise. It forces the engineers to focus on Rule 2.

Rule 2 is what make observers, many of them experts in the field, suspicious of the J-20's canards regarding trying to be as low radar observable as the American fighters.

The canard is a finite body, meaning at some time and somewhere, the radar signal has to leave this structure. How the exiting signals make contact with the other structures is what make the canard detrimental to 'stealth' or not a factor at all. But based upon the current understanding of signal behavior, the J-20's canards with their dihedral is at least suspect to be detrimental to the J-20's attempt to be as 'stealthy' as the American fighters as in Rule 3.

All three rules must work together and this is evident with the UPPER surface of the F-117...

Each 'ridge' is an exit point for an impinging radar signal. So under the three rules, the F-117 has many more structures than the J-20. Lockheed engineers paid close attention to how the three rules interact with each other and the result is that the F-117's RCS is still a secret. Everyone, including China, would love to know that figure. In some ways, the US have been more open with the F-117's RCS than China has with the J-20's RCS. Ben Rich's book at least hinted at that figure.

http://www.f117sfa.org/f117_history.htm

This is why the criticism about the F-35's underside with all the bumps as detrimental to 'stealth' is nonsense. The critics cannot reconcile the F-117's topside and the F-35's underside. As if somehow the laws of physics behaves differently for each jet.

For now, conventional wisdom has it that being parallel in the root plane and no dihedral is ideal. The J-20's canards is one half of that conventional wisdom. Their roots are on the same plane as the main wings, but their dihedral affects how exiting radar signals contact the main wings in terms of direction, angle of approach, and distance.

if the canards parallel to the main wings, it will cause huge RCS.

Did I talk anything about RCS of dihedral canards structure? J-20's canards must stay on different plane in order to improve lift. Just take the less evil.

 

[gambit]

If the jet is taxiing the ramp for takeoff, isn't the FCS on manual anyway? Up until it reaches the end of the runway and ready for takeoff, the pilot switches the controls to the automated system prior to putting it in full throttle?

There is no 'Manual' or 'Auto' mode for the flight controls system. Am not sure what you are asking here. The pre-F-16 aircrafts have fully manual FLCS and some have a form of hydraulic assist or 'boost' capability so we are not going to discuss them.

With a full fly-by-wire flight control system (FBW-FLCS), the system is constantly active. Closed loop and variable gains.

The major components are:

- Pilot commands (stick and rudder pedals)
- Gyros (pitch/roll/yaw attitude)
- Accelerometers (changes in speed 3 axes)
- Air data (pitot/static)
- Surface positions feedback (hydraulics shaft transducers)
- Flight Controls Computer (FCC)
- Central Air Data Computer (CADC)

Everything must be available for the FCC to calculate how much to displace the surfaces.

At timestamps 0:26, 0:35, and 0:46 you can see the F-16's horizontal stabs fluctuating up/down as the jets taxis by. The pilots are not doing anything to the stick.

The paved ramps and runways are not perfectly smooth. They are level, maybe less than one degree of incline, but never completely smooth. So as the jet runs over the many bumps, no matter how small, any changes would be in the pitch (x) axis. This is up/down motion as if you are driving over a dirt road and you feel it thru the car. So just running on the ramp, there is already constant pitch gyro input. If the jet has constant speed, there will be zero accelerometer inputs. There will be air data inputs, pitot (speed) and static (altitude). Pitot would be very low since the jet is at ramp speed. Static would be zero since the jet is physically on the ground.

So as the jet runs over the bumps and has a persistent but unpredictable up/down gyro inputs, the FCC constantly calculate the horizontal stabs movements as if the jet is actually flying. The hydraulics position transducers tells the FCC their actual physical displacements. The FCC readjust the horizontal stabs commands if needed. In other words, the entire FLCS behaves as if the jet is actually flying even though there is full WOW. The FCC constantly tries to make the 'flying' jet as stable as possible.

Off the ramp and on the runway.

As the jet speeds down the runway, higher and higher pitot air input. Accelerometer tells the FCC the rate of forward change. At this time there is still full WOW. As the nose lift and there is no nose WOW, the FCC changes the gains because now it knows the jet is becoming airborne. Once there is no WOW on the main gears, the FCC changes the gains again because now it knows the jet is fully airborne. When the pilot raised the landing gear handle and once all gears are locked up and doors closed, the FCC now has the lowest gains possible because the jet is fully configured for maximum performance flight. The higher the gains, the more the surfaces displace and at higher speed, this would be an out-of-control condition. Therefore, the higher the speed as calculated by the CADC, the less the surfaces will move because there is sufficient aerodynamic pressures on them to maneuver the jet. On the other hand, the higher the altitude, the thinner the air so there is less aerodynamic pressure available, so the jet will need more surface displacement for the same speed as at the lower altitude to perform the same maneuver.

This closed loop is constantly going. There is no pause. Of all the inputs cited above, zero volt is not the same as no voltage exist. A zero volt is actually a valid value for the FCC. So if any inputs above does not exist, the FCC will trigger a failure in pitch, roll, or yaw axis as appropriate. An air data input fail will have the FCC uses its own default air data values and this will trigger an FLCS failure. Any missing hydraulics position feedback signal will trigger the appropriate axis failure. Basically, EVERYTHING must exist.

There are interlock switches that will tell the FCC what the pilot want the jet to do. Switches like the landing gear handle and the landing gear positions. The landing gear handle switch tells the FCC what the pilot want. The landing gear position switch tells the FCC what the landing gear themselves are doing. The two sets of signals are not the same. These signals changes the positions of the wings leading edge and trailing edge for maximum lift. However, if the pilot lower the landing gear handle at 400 kts/hr, a disaster will result because these signals tells the FCC to reconfigure the jet for landing. At 400 kts/hr? The inevitable outcome is an out-of-control F-16 and a crash. So the pilot must know exactly what he is doing at what point in flight. The system is smart but cannot override what the pilot do, intentionally or unintentionally.

So to answer your question, the FBW-FLCS is constantly active and automatic. Like The Force in the Star Wars universe, the FCC obeys your command but also controls the jet for you.

Not sure in the case of these latest and greatest aircraft with FBWSs if the front landing gear is on casters or does it actually have independent turning ability, separate from the pilot using the brakes on the rear landing gears to turn the aircraft one way or the other? It looks like the front gear is tied in to the rudders (V-stabs in the case of the J-20) when the aircraft is grounded but I'm not sure if the front gear turns independently or casts with the rear brakes in these new, computerized jets.

Once there is full nose WOW, the nose gear actually turns the jet on the ground via the rudder pedals while the rudder pedals are still (electronically) linked to the vertical stabs. So as the jet turns on the ground, the rudder(s), or the full stab(s) as appropriate to the jet, moves with the nose gear. Main gear brakes are activated by pressing on the top parts of the rudder pedals.

There's also the standard operating procedure that you, as a former USAF vet are familiar with the way US jets operate but that begs the question, are the systems operating the same way with let's say, French aircraft? British or Swedish? What about Russian? I'm guessing there's probably a standard, where computerized elements are the same across the board but there has to be some differences here and there that create these unusual operations, or ones that we're not familiar with.

The F-16 pretty much set the foundation for the modern FBW-FLCS flight controls laws for all designs, no matter the national origins. The quad signals redundancy is proven reliable over the decades. Change the system at your peril. No one is going to be that foolish.

Another thing to consider is that the US doesn't operate any canard-style platforms, so the process has to be different I would think. That said, the canards are essentially the horizontal stabilizers moved forward of the wings and fuselage and as a result there has to be certain differences in the way those surface controls react, just by default of being placed forward.

You are correct (highlighted). However, the closed loop with variable gains architecture is still the same, just going to a different set of control surfaces and with different displacement degree.

 

[Gomig-21]

There is no 'Manual' or 'Auto' mode for the flight controls system.

But didn't you say this a few pages back?

The reason I went thru all this explanation is because manual pilot actuation of the canards is the best -- not the only -- way to explain the J-20's canards with their full vertical deflection at ramp speed. But that allowance even when full computer control when needed is still an additional pilot workload and possibly dangerous at critical times in flight, such as combat. And the J-20 is a single-seater.

So by stating that a manual actuation of the canards means there is a manual option?
Don't these aircraft have mode switches when the aircraft is on the ground so they can actually operate them strictly by their commands and inputs instead of having the computer dictate the inputs?

Or does the FCS automatically switch once the aircraft is grounded, or no such thing?

I thought you also said that during the flight control checklist done with the crew chief, the pilot cycles through the controls in a manual mode and then through the FLCS, or did I misunderstand?

If a pilot 'cycle' the flight controls surfaces, either before or after a flight, it is to do his own personal checks of the flight controls outside of the standard automatic FLCS checks done in the chocks. Normally, the FLCS are not cycled thru the automatic checks after a flight, only before. Once the pilot returned the control stick to normal, all surfaces returns to default positions.

Pilot (manual) control of a close-coupled canard system? That is dangerous.

 

[Figaro]

 

[gambit]

But didn't you say this a few pages back?

So by stating that a manual actuation of the canards means there is a manual option?
Don't these aircraft have mode switches when the aircraft is on the ground so they can actually operate them strictly by their commands and inputs instead of having the computer dictate the inputs?

Or does the FCS automatically switch once the aircraft is grounded, or no such thing?

I thought you also said that during the flight control checklist done with the crew chief, the pilot cycles through the controls in a manual mode and then through the FLCS, or did I misunderstand?

You misunderstood -- but it was my fault. I will elaborate.

The loop I explained in post 10292 is called the 'stability augmentation' loop. Or 'stabaug' for short.

Pre F-16 aircrafts can turn off stabaug, making flying the jet very difficult and tiring.

From left to right: F-111 => F-4 => F-16.

For the F-111 FLCS panel, the three significant switches are the 'damper' switches, pitch, roll, and yaw. From engine start to landing, they are in the 'NORMAL' position.

For the F-4, I was not on that jet, but I can make an educated guess about its FLCS panel. It is not as sophisticated as the F-111, but it has the ability to turn off the stabaug process.

For the F-16, stabaug is constant.

When you disable stabaug, the burden of compensating for every jolt of turbulence, whether in level flight or in a maneuver, falls on YOU -- the pilot. Ask any non-F-16 pilot on what is it like to fly his jet without stabaug, and he will tell you that it is physically and mentally draining.

In Star Wars, Obi-wan Kenobi said that The Force controls your actions BUT also obeys your command. It is actually the wrong way to put it. The correct way to explain The Force regarding actions is: AS The Force controls your actions, it ALSO obeys your commands.

Flight Controls System Stability Augmentation works exactly like that: You command, the stabaug loop takes over the jet, and compensate for any other commands from you.

That was how I explained to my avionics trainees a long time ago after I got out of the USAF.

On the F-111, flying with the dampers off made for a physically demanding flight, especially at low altitude where there are weather phenomenons. Dampers on -- stabaug engaged -- was like night vs day.

So how does this applies to the J-20 and its canards?

The J-20 -- according to public information -- is an FBW-FLCS jet. That means it has the same FLCS basic architecture as the F-16. The flight controls laws would have some differences to account for the canards. But to give the pilot the option to control them fully manually, like the damper off position in the F-111 and F-4, that is dubious to say the least.

- The fully manual controls of the canards must be on the stick.

- Since the canards are active flight controls elements, the stick controls would have to be something like a wheel, perhaps a thumbwheel, to fully take advantage of its range of displacement.

- This increase the training requirement for the J-20. Like how the V-22 training requires the pilot to know how to fly the V-22 like a fixed wing and a rotary wing aircraft. Or like how the Su jets have full pilot authority over the 3D engine thrust.

- This increase the odds of pilot error. What if in under stress of combat, he turns the canard controls the opposite direction of where he actually want them?

- When is it appropriate to remove the canards from the stabaug loop? Under what flight conditions? Can it be done under maneuvers? Should it be done under maneuvers?

- If the canards under normal stabaug operation assist in roll, how complex must the manual control wheel be to give the pilot the same degree of control as under the FLCC? This also increase the odds of pilot error.

These questions are just the quickest I can come up with based upon my experience. You can be sure there are much more when you delve into the flight controls laws themselves, of which we do not have access to. That means you will have to settle for what I presented.

While it IS technically feasible to give the J-20 pilot full manual authority over the jet's canards, I find it difficult to justify it. The reason why we increasingly make the jet with greater autonomy regarding flight is because we want the pilot to be a killer, not a flyer.

Curious -- I do not see any of the resident Chinese 'experts' on the J-20 engaging in this discussion.

 

[Beast]

Curious -- I do not see any of the resident Chinese 'experts' on the J-20 engaging in this discussion.

As if you are an expert on J-20? May I know which J-20 you have fly on? Zero...

 

[Deino]

As if you are an expert on J-20? May I know which J-20 you have fly on? Zero...

To be fain, I'm sure no-one here in this forum ever flew in a J-20. So by that logic no-one is an expert... or am I wrong.

 

[Beast]

To be fain, I'm sure no-one here in this forum ever flew in a J-20. So by that logic no-one is an expert... or am I wrong.

I never claim I am an expert unlike some who BS about some canard control of J-20 as if he ever flow or sit inside a real J-20 cockpit? Got it?

 

[Gomig-21]

When you disable stabaug, the burden of compensating for every jolt of turbulence, whether in level flight or in a maneuver, falls on YOU -- the pilot. Ask any non-F-16 pilot on what is it like to fly his jet without stabaug, and he will tell you that it is physically and mentally draining.

I've read several accounts from pilots who flew platforms such as the Mirage and even the MiG-21, then were assigned to the F-16 back when it was first introduced to the export market. One of the comments I found very interesting was from a former Mirage pilot who flew the Mirage IIIC and then the V, then was assigned to the F-16 and he actually didn't like the easiness of flying a FBW aircraft. Probably because he was used to the hardship of the older system and was actually comfortable with it, which makes sense. One of his comments was "in the Mirage, you sat in it and had to work it which made you more part of it which was much more appealing. But in the F-16, you were just like a voting member." I thought that was pretty cool and actually very understandable.

I'm sure if he went about it the other way around, he probably would've greatly resented having to work so hard to fly an aircraft after being used to one with a FBWS.

Reminds me of my mother in-law who sat on this old, beat-up recliner for many years and the seat was sunken in and formed in the shape of her butt looool and it was all squeaky and raggedy and didn't look comfortable at all, anymore. My brother in-law goes out and buys her this super duper expensive leather recliner with push buttons and all sorts of easy, comfort settings and she says to him "get that thing outta here!"

In Star Wars, Obi-wan Kenobi said that The Force controls your actions BUT also obeys your command. It is actually the wrong way to put it. The correct way to explain The Force regarding actions is: AS The Force controls your actions, it ALSO obeys your commands.

A very subtle difference.

When you disable stabaug, the burden of compensating for every jolt of turbulence, whether in level flight or in a maneuver, falls on YOU -- the pilot.

It's understandable that those burdensome adjustments are alleviated as a result of the FCS and essentially the computer, but this is the way it was for decades up to and even including fabulous aircraft like the F-15.

So based on 'stabaug,' it's constantly active in these new aircraft which is basically why you're saying that there really isn't an auto or manual mode. I got it now.

So is it reasonable to assume that there are levels of this automated mode or constant stabaug? For example when you separate the flight conditions ("take-off to landing" from "grounded or taxiing,") the levels of that automation is where it's different? It seems like that in the latter, there still is a lot of manual input from the pilot as he's moving and turning the aircraft on the ground, or even checking the flight controls and the computer doesn't play into the operations as much, except for maybe in this specific instance of the canards deflecting, or even the V-stabs turning because there really isn't any substantial outside elements to dictate the need for it. Once the aircraft is throttled up and is taking off, the computer takes a lot more control of the pilot's inputs because now the aircraft is operating and functioning in a much more complex dynamic where there are a lot more outside forces (such as the turbulence you mentioned) that the need for that level of automation increases substantially. That would make sense to me and so there really isn't a turning on or off of that auto mode, but maybe rather a degree of function to that mode based being on the ground or in flight.

While it IS technically feasible to give the J-20 pilot full manual authority over the jet's canards, I find it difficult to justify it. The reason why we increasingly make the jet with greater autonomy regarding flight is because we want the pilot to be a killer, not a flyer.

Now I'm guessing that the canards deflecting like that (or even any of the other control surfaces) while the aircraft is grounded is not a function of the pilot's command but rather an FCS generated command because we don't see it all the time as the J-20 is taxiing or at the ramp, only occasionally. Maybe the flight sensors pick up a headwind or a gust coming from the back of the aircraft (as an example) and the FLCS automatically adjusts to that by fully deflecting the canards to create an air brake enough to slow the aircraft from that gust of wind until the engine automatically decreases throttle to compensate? Seems like a very realistic scenario, no?

But that's only a possibility for the taxiing process. It still doesn't explain that photo where they look like they're being deployed as speed brakes upon landing.

 

[sinait]

To be fain, I'm sure no-one here in this forum ever flew in a J-20. So by that logic no-one is an expert... or am I wrong.

You are absolutely correct.
I believe no one here is an expert on the J-20 or the F-22 and F-35 for that matter.
It would be swell to have a F-22 or F-35 pilot comment here.
I guess we have to make do with retired old pilots with their ancient experience masquerade as experts on 5th gen planes.
.

 

[gambit]

I never claim I am an expert unlike some who BS about some canard control of J-20 as if he ever flow or sit inside a real J-20 cockpit? Got it?

If what I have been saying is BS, then you guys should have no problems countering it, after all, you guys consistently criticizes my technical explanations as coming from only wiki.

But everybody sees thru all of you. No one with some degree of technical interest on how aircraft works takes your criticisms of me seriously. You think I made up the phrase 'stability augmentation'?

http://ieeexplore.ieee.org/document/7322579/

An insight into the knowledge of Automatic Flight Control Systems (AFCSs) gives an understanding of the basic problem of controlling the aircraft's flight, and enhance its ability to assess the solutions to the problems which are generally proposed. Before understanding automatic controlling of an aircraft, it is essential to know how an aircraft will respond dynamically to a deliberate movement of its control surfaces, or to an encounter with unexpected and random disturbances of the air through which it is flying. With these thoughts this paper presents a reasonable self-contained account of the most significant method of designing linear control systems which find universal use in AFCSs.

Note the highlighted 'universal'.

As I have always said in the past and to today, if I post a paywalled source, I will make sure the appropriate keywords are available for ANYONE to use as reference for his own research. That means you guys have ALWAYS been free to prove me wrong, either using your research to pose as someone else, or using your research to prove I misled the readers. The fact that since '09, none of you critics have ever even dinged my technical explanations means the laugh is on YOU, not me.

So from my own experience in aviation, in and out of the military, I understand the J-20 better than ALL of you. I may have been driving Chevrolets all my life, but that does not mean I cannot understand how Fords operates, while ALL of you been on bicycles.

Can any of you disprove that the J-20 canards are coupled to the stabaug loop? Or prove that the canards can be de-coupled from the same at command discretion? Yes, only the J-20 pilot can answer the questions, but that does not mean all my posts about flight controls in general and about the canards in specifics have been fraudulent. My technical speculations forms the foundation upon which the interested readers can do their own research and forms their own speculations. Far better than they can speculate from the real BS that came from you guys that often defies the laws of physics.

 

[siegecrossbow]

I never claim I am an expert unlike some who BS about some canard control of J-20 as if he ever flow or sit inside a real J-20 cockpit? Got it?

The pilot didn't say anything about canard control in that video.

 

[Beast]

The pilot didn't say anything about canard control in that video.

Are you trying to defend gambit claiming his BS claim about control of J-20?

The only person qualify to talk about J-20 and authentic about their talk in J-20 for the control are these few pilots who flow the real J-20.

Flip back my post and see where did I mention about these video related to what? You shall stick back at SDF and stop coming to here if you do not even know who the real culprit you shall challenge.

You misunderstood -- but it was my fault. I will elaborate.

The loop I explained in post 10292 is called the 'stability augmentation' loop. Or 'stabaug' for short.

Pre F-16 aircrafts can turn off stabaug, making flying the jet very difficult and tiring.

From left to right: F-111 => F-4 => F-16.

For the F-111 FLCS panel, the three significant switches are the 'damper' switches, pitch, roll, and yaw. From engine start to landing, they are in the 'NORMAL' position.

For the F-4, I was not on that jet, but I can make an educated guess about its FLCS panel. It is not as sophisticated as the F-111, but it has the ability to turn off the stabaug process.

For the F-16, stabaug is constant.

When you disable stabaug, the burden of compensating for every jolt of turbulence, whether in level flight or in a maneuver, falls on YOU -- the pilot. Ask any non-F-16 pilot on what is it like to fly his jet without stabaug, and he will tell you that it is physically and mentally draining.

In Star Wars, Obi-wan Kenobi said that The Force controls your actions BUT also obeys your command. It is actually the wrong way to put it. The correct way to explain The Force regarding actions is: AS The Force controls your actions, it ALSO obeys your commands.

Flight Controls System Stability Augmentation works exactly like that: You command, the stabaug loop takes over the jet, and compensate for any other commands from you.

That was how I explained to my avionics trainees a long time ago after I got out of the USAF.

On the F-111, flying with the dampers off made for a physically demanding flight, especially at low altitude where there are weather phenomenons. Dampers on -- stabaug engaged -- was like night vs day.

So how does this applies to the J-20 and its canards?

The J-20 -- according to public information -- is an FBW-FLCS jet. That means it has the same FLCS basic architecture as the F-16. The flight controls laws would have some differences to account for the canards. But to give the pilot the option to control them fully manually, like the damper off position in the F-111 and F-4, that is dubious to say the least.

- The fully manual controls of the canards must be on the stick.

- Since the canards are active flight controls elements, the stick controls would have to be something like a wheel, perhaps a thumbwheel, to fully take advantage of its range of displacement.

- This increase the training requirement for the J-20. Like how the V-22 training requires the pilot to know how to fly the V-22 like a fixed wing and a rotary wing aircraft. Or like how the Su jets have full pilot authority over the 3D engine thrust.

- This increase the odds of pilot error. What if in under stress of combat, he turns the canard controls the opposite direction of where he actually want them?

- When is it appropriate to remove the canards from the stabaug loop? Under what flight conditions? Can it be done under maneuvers? Should it be done under maneuvers?

- If the canards under normal stabaug operation assist in roll, how complex must the manual control wheel be to give the pilot the same degree of control as under the FLCC? This also increase the odds of pilot error.

These questions are just the quickest I can come up with based upon my experience. You can be sure there are much more when you delve into the flight controls laws themselves, of which we do not have access to. That means you will have to settle for what I presented.

While it IS technically feasible to give the J-20 pilot full manual authority over the jet's canards, I find it difficult to justify it. The reason why we increasingly make the jet with greater autonomy regarding flight is because we want the pilot to be a killer, not a flyer.

Curious -- I do not see any of the resident Chinese 'experts' on the J-20 engaging in this discussion.

I think you shall refrain from BS about J-20 until you can fully absorbed what the J-20 pilot interview I posted.

 

[Gomig-21]

View attachment 455335

What a beauty. This angle you can see the cupping of the wingtips.
That metallic RAM is awesome, almost identical to the F-22.

Even though the J-20 is a delta/canard design, it has a few similarities to the Raptor, mainly the cockpit and front end of the fuselage. I even noticed a similarity on the inside of the cockpit and that's the PVC or white piping at the front that is probably some sort of conduit for sensitive wiring. I first noticed it on the F-22 many years ago and then it appeared on the J-20 as well.

Has this video been posted before? Either way it's awesome and worth watching again.

https://www.facebook.com/

 

[gambit]

...a former Mirage pilot who flew the Mirage IIIC and then the V, then was assigned to the F-16 and he actually didn't like the easiness of flying a FBW aircraft. Probably because he was used to the hardship of the older system and was actually comfortable with it, which makes sense. One of his comments was "in the Mirage, you sat in it and had to work it which made you more part of it which was much more appealing. But in the F-16, you were just like a voting member." I thought that was pretty cool and actually very understandable.

There are many reasons why the Joe Jetjocks of today's air forces reveres the WW II era fighter pilots and physicality in flying was one of the major reasons.

If Hollywood really wanted to be accurate, the hero's face would not be clear as he flies his Mustang or Spit or Focke-Wulf. The aircraft would be jinking up/down and sideways. Modern day racing prop jobbers are better designed and BUILT than the fighters of WW II. The WW II era fighters are pretty much the ideal man-machine combination. The analogy would be the WW I era fighters are like bicycles, the WW II fighters are motorcycles, and today's jets are automobiles. In the middle is where you will find that balance of what is required of the man to handle the machine. When the last of the WW II fighter pilot die, military aviation will finally lose the link to a time when it took a different form of physical fitness to fly.

It's understandable that those burdensome adjustments are alleviated as a result of the FCS and essentially the computer, but this is the way it was for decades up to and even including fabulous aircraft like the F-15.

So based on 'stabaug,' it's constantly active in these new aircraft which is basically why you're saying that there really isn't an auto or manual mode. I got it now.

On the backbone of the F-111, there are three hydraulic components call 'dampers', one for each flight axis.

In the cockpit, the control stick has direct mechanical linkage all the way to the hydraulic actuators at the wings, horizontal rear stabs, and the vertical stab. Each damper is mechanically linked in parallel to the appropriate axis of those mechanical linkages of the three axes. Each damper is controlled by the FLCC, not by the pilot.

As I pulled back on the stick to execute a pitch up maneuver, the direct linkages moves the surfaces' hydraulic actuators. Let us keep it simple and say 10 mm of movement. As the pitch rate gyro, accelerometer, air data, and hydraulic shaft position transducers send their signals to the FLCC, the FLCC may decides to extend an additional 2 mm of travel. Since the pitch damper is connect in parallel of the pitch axis mechanical linkages, there will be a sum of 12 mm of movement. If the FLCC decides 10 mm of travel is too much to maintain a smooth and stable pitch up maneuver, the FLCC will command the damper to 'subtract' 2 mm for a final 8 mm of movement. This is constant stabaug.

If I turn the pitch damper switch to 'OFF', then I will have whatever displacement I command from the stick.

On the F-16, the three dampers are virtual. They are represented by a section of the FLCC circuit board and assorted math algorithm. Precisely because the F-16 is relaxed stability, there can be no 'OFF' switch. Stability augmentation is a necessity. The F-111 was not designed with relaxed stability. Same for the F-14, F-15, the Mirage series, and just about everything in that era.

If the design is relaxed stability, stabaug is mandatory throughout flight.

So is it reasonable to assume that there are levels of this automated mode or constant stabaug? For example when you separate the flight conditions ("take-off to landing" from "grounded or taxiing,") the levels of that automation is where it's different?

No. Based upon known architecture, stabaug is in play even when there is full WOW. That is where you see the F-16's horizontal stabs go up/down as the jet taxis over uneven ground. It is actually the better and safe state for the jet to be in. When I am on the runway -- not the ramp -- and heading towards take-off speed, I am STILLl on the ground. The FLCS needs to know at the exact moment when the jet is airborne, even if only the nose wheel is off the ground. Better to have that stabaug loop in constant operation.

It seems like that in the latter, there still is a lot of manual input from the pilot as he's moving and turning the aircraft on the ground, or even checking the flight controls and the computer doesn't play into the operations as much, except for maybe in this specific instance of the canards deflecting, or even the V-stabs turning because there really isn't any substantial outside elements to dictate the need for it.

The extreme displacement of the surfaces on the ground are because the FLCC thinks they need to be that way in order to move the jet. Never mind that it is the landing gear that is moving the jet. The FLCS and the stabaug loop is designed to assume the jet is flying -- all the time. WOW or not.

Maybe the flight sensors pick up a headwind or a gust coming from the back of the aircraft (as an example) and the FLCS automatically adjusts to that by fully deflecting the canards to create an air brake enough to slow the aircraft from that gust of wind until the engine automatically decreases throttle to compensate? Seems like a very realistic scenario, no?

No.

The 'flight sensors' you talked about are in the air data system, which is composed of the pitot/static probes and all of them faces forward, and the central air data computer (CADC). Running a few kts/hr at the ramp is not enough to trigger any input voltage to the FLCC. You would need tornado force wind to push the jet fast enough for ram air thru the pitot/static probes to tell the CADC that there is sufficient forward speed.

Wheel brakes are enough for running on the ramp no matter the local wind condition.

It still doesn't explain that photo where they look like they're being deployed as speed brakes upon landing.

That is why it is curious as to why we see so many J-20 with engines running on the ramp with their flight control surfaces fully deflected to maximum. With the canards nearly vertical, they look odd. They could be that way during FLCS self tests but those self tests should have been done in the chocks.

Here is what I speculate...

There is a speedbrake subroutine inside the stabaug loop for the J-20, assuming the jet is designed to use the flight control surfaces as speedbrake function. Never mind the drag chute for now.

Try to imagine and follow me...

- As the jet have main WOW upon touchdown, the FLCC immediately engages the speedbrake utility in its algorithm.

- The flight control surfaces staged to go to their default displacement position for speedbrake function. They are not fully displaced. They displace just enough to create some drag. The canards deflects LE down -- say 5 deg -- to kill lift.

- As nose WOW finally engaged, the flight control surfaces deflects some more to create more drag. The canards deflect an additional 5 deg LE down.

- As airspeed (ground speed) approaches a certain value that the FLCC thinks the tires will be enough to take over maneuvers controls, all flight control surfaces fully deflects to create maximum drag. The canards are fully LE down.

So for all these pictures that we see the J-20 running on the ramp with the canards fully LE down, the pilot just simply left the speedbrake function switch to the 'ON' position.

That is my hypothesis.