Digital vs Manual Flight controls

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zero-one

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Unread post04 Jan 2020, 10:08

This is not supposed to answer the question "Which is better" because we all now Digital is the way to go. The question I would like us to ponder on is if Manual flight controls can do things that are impossible with Digital FCS.

A good video by the Grim Reapers rose my curiosity on this subject.


Since DFCS simply interprets what it thinks you want to do, wouldnt it be impossible to do maneuvers that the computer cannot interpret. '

I remember watching a video of a Raptor demo pilot where in he explains that while doing the tail slide, the Raptor will notice that the aircraft is falling backwards, so the FCS will try to drop the nose down because its better to go down nose first than tail first, the pilot has to yank the stick back to tell the computer to keep the nose pointed up.

This gives me the impression that doing some of the things in manually controlled aircraft will be impossible or very hard to do in a digital controlled aircraft.

The Russians had a saying when developing their own FBW.
"FBW makes a bad pilot good but also makes a great pilot mediocre as well"
I don't agree with it, but I realize why they thought that way
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basher54321

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Unread post04 Jan 2020, 12:43

How to define this?

There have been both Analogue and Digital FBW control systems over the years - and technically you could program them to act the same way as an old fashioned manual system I guess. So for example you could put a FBW system in the F-4 and have it act in the same way as with manual controls with no limits. This would be mostly pointless however.

I think what you are getting at is control systems with no limits because AFAIK even some of the old fashioned direct control systems had limiters that prevented the pilot from doing certain things.

The Su-27 has had what is termed as an analogue FBW system sitting alongside a partial manual control system since it came into service so best forget any off shoot comments about what the Russians think of it - they are well aware of the advantages.


Regarding the Mugs F-4 depart in Dogfights.
1. "Dogfights" does not necessarily portray what happened entirely accurately.
2. It almost looks like another version of put on the brakes he will fly right by - and yes the MiG pilot might have been confused by the departing F-4 (maybe?) - also the F-4 crew would need to have a good idea of the MiGs position and closing rate before attempting such a thing.
3. You could question the Flight Moddeling in that game anyway but quite why that person thinks they can recreate the F-4 using other aircraft is beyond me. The F-4 has some pretty unique characteristics.


So although it looks wow the notion that pilots should be able to easily depart an aircraft during actual combat has been proven flawed. The majority of F-4 (especially USAF) pilots in Nam had little to no BFM training and were not super pilots like Mugs - if they departed it for whatever reason (SAM avoidance etc etc) the outcome was often the loss of an F-4 and often the crew. Outlaw mentioned one losing control against an A-7 in an exercise with again the loss of an F-4.

So instead of the one pilot can do the "OMG super somersault" the people that actually know what they are doing put in FBW to help the pilot be a superior combat pilot.
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quicksilver

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Unread post04 Jan 2020, 15:43

If he truly ‘departed’ the jet at high speed and 1500’ AGL, the fact that he 1) came out of it without crashing and, 2) found himself in a position to immediately engage again was pure luck. The description sounds more like a ‘high G roll over the top’ (with a whole lotta rudder) as the MiG was approaching a ‘guns‘ position. If not at the time, later, a common and practiced maneuver for guns defense. Also easy to eff-up and ‘depart’ from.
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quicksilver

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Unread post04 Jan 2020, 16:15

“This gives me the impression that doing some of the things in manually controlled aircraft will be impossible or very hard to do in a digital controlled aircraft.”

Yeah, like overstress or break the jet (structurally), or depart controlled flight and lose the jet and mort one’s self, or cripple yourself for life...

Generally speaking, digital fbw flight control systems enable pilots to do things that were once not safely repeatable by every pilot in a given squadron. Occasionally, the system ‘protects the pilot too much‘ and we see those things resolved in flight test (witness F-35). But for the vast majority of circumstances, digital fbw is a great and awesome thing that has made carefree aircraft handling a common and assumed condition of flying fighters.
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zero-one

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Unread post05 Jan 2020, 10:53

quicksilver wrote:Yeah, like overstress or break the jet (structurally), or depart controlled flight and lose the jet and mort one’s self, or cripple yourself for life...


No doubt, I'm not proposing that we go back to Hydraulically controlled fighters for the possibility of making that 1 in a million backflip that was supposed to be impossible. What I'm really wondering is, will it still be possible to do, supposedly impossible maneuvers on FBW limited aircraft, thats it, forget tactical implications, thats a discussion for another thread

And yes I know there are so many other maneuvers that are routine for FBW aircraft but very difficult for manually controlled aircraft, like maintaining the perfect AoA on an F-16 to atain the highest possible G for that speed and altitude.
Correct me if I'm wrong, but in a manual jet, you need to keep 1 eye on your AoA and another on your KCAS gauge and another on your G and balance them out. in an F-16 you pretty much just pull back and brace your core and legs for the upcoming Gs.

But There have been more than one instance where pilots reported that they were able to maneuver a particular type of aircraft that was supposed to be impossible, or at least impossible for that aircraft.

Here we see a Belgian F-104 do the Touch-roll-touch, something that was deemed impossible by Lockheed test pilots. will


Will that still be possible in FBW? Personally I think it depends on the limits programmed on the CLAWS, but thats just me
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quicksilver

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Unread post05 Jan 2020, 13:39

Why would anyone care about that F-104 “maneuver” and how exactly is it relevant to anything anyone bought the aircraft to do? What does it have to do with one kind of flight control mechanization versus another? Ever see a Blue Angel solo do a dirty roll on takeoff?

Digital fbw doesn’t prevent pilots from doing STOOPID stuff in a jet, including things that get them killed.

“...you need to keep 1 eye on your AoA and another on your KCAS gauge and another on your G and balance them out.“

Yes, but that doesn’t have anything to do w flight control mechanization. It was more or less difficult depending on the cockpit instrumentation layout of whatever aircraft type you were flying, and the aerodynamic characteristics of the jet. And, it got a whole lot easier when the HUD was invented.
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zero-one

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Unread post05 Jan 2020, 14:47

quicksilver wrote:Why would anyone care about that F-104 “maneuver”

Like I said, I'm not really concerned with "how is it relevant" if at all, the only question I have is, is it possible.

See with FBW, whats impossible is pretty much set in stone, specially with modern CLAWS, if the limiter says you can't do it, then you can't do it no matter how hard you try. But Basher has a really good point in that, some CLAWS are programmed to behave like manual controls, they're just there to keep the thing flying.

And some, like the F-16's is optimized to pull Gs. If I'm not mistaken if you pull back on the stick, you're essentially asking for Gs not AoA. So the CLAWS will give you the right amount of AoA to pull the most Gs at that speed. I'm pretty sure its far more complicated that that. It might seem like you're limited in what you can do as a pilot, but at the same time you're also extremely effective in a dogfight.
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quicksilver

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Unread post05 Jan 2020, 15:35

“I'm not really concerned with "how is it relevant"“

Then you shouldn’t be concerned, period.

“See with FBW, whats impossible is pretty much set in stone, specially with modern CLAWS, if the limiter says you can't do it, then you can't do it no matter how hard you try.“

Sometimes. But, there’s this neat feature on most jets called “the paddle switch” whereby one can turn those limiting features off — of course, with accountability now squarely on one’s shoulders for what happens after that (not to mention the ‘how did you get the point where you need to do so’ in the first place).

In the best programs there is a constructive dynamic that occurs between pilots and engineers in aircraft design/development and flight test whereby limits to what a jet can or can’t do are adjusted based on technical requirements versus ‘desirements’ risk and cost. We see and/or read about the outcomes of those kind of processes every day. F-35 would be but one example. One of the videos from Edwards from the period where hi-alpha testing was happening is representative; it features one of the test pilots — Dave Nelson — talking about doing things to maneuver the jet, including ‘going beyond the limits‘. Later, one of the engineers describes the goal as ‘not allowing a pilot to exceed the limits.’ (or something close to that). If spaz can’t find it, I’ll dig it up later.

Here ya go — https://m.youtube.com/watch?v=aWji8AcOYGA

Limits are typically in place because there are bad things that happen when one goes beyond them. Where catastrophically bad things exist that will very rapidly cause harm to the jet, one’s person, or both — margin is built in.
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zero-one

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Unread post05 Jan 2020, 17:25

quicksilver wrote:“I'm not really concerned with "how is it relevant"“
Then you shouldn’t be concerned, period.


Well see, I didn't know about the paddle switch and I wouldn't of had these great responses from you and Basher if my only concern was "is it tactically relevant"
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quicksilver

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Unread post05 Jan 2020, 17:48

zero-one wrote:
quicksilver wrote:“I'm not really concerned with "how is it relevant"“
Then you shouldn’t be concerned, period.


Well see, I didn't know about the paddle switch and I wouldn't of had these great responses from you and Basher if my only concern was "is it tactically relevant"


‘Relevance‘ is not just about ‘tactical employment.’ It’s about safety and long term preservation of assets.
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wrightwing

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Unread post05 Jan 2020, 21:12

zero-one wrote:
quicksilver wrote:Why would anyone care about that F-104 “maneuver”

Like I said, I'm not really concerned with "how is it relevant" if at all, the only question I have is, is it possible.

See with FBW, whats impossible is pretty much set in stone, specially with modern CLAWS, if the limiter says you can't do it, then you can't do it no matter how hard you try. But Basher has a really good point in that, some CLAWS are programmed to behave like manual controls, they're just there to keep the thing flying.

And some, like the F-16's is optimized to pull Gs. If I'm not mistaken if you pull back on the stick, you're essentially asking for Gs not AoA. So the CLAWS will give you the right amount of AoA to pull the most Gs at that speed. I'm pretty sure its far more complicated that that. It might seem like you're limited in what you can do as a pilot, but at the same time you're also extremely effective in a dogfight.


CLAWS are more about what you can't do, than what you can do. They allow you to fly more aggressively than you otherwise would, as it takes the guesswork out of the equation, for a pilot.
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vilters

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Unread post05 Jan 2020, 23:00

The F-16 was designed as an all round dogfighter.
At the time (1970 to early 1980) optimized for WVR. => Hence the nice look around canopy.

But with your eyes on the bandit, you can not see your instruments.

And with such a yank and bank easy to fly but UNSTABLE airframe, any pilot could pull it above and beyond its limits.
FBW is there to PROTECT pilots going out of the envelope during "hard use".
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zero-one

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Unread post06 Jan 2020, 07:45

vilters wrote:The F-16 was designed as an all round dogfighter.
At the time (1970 to early 1980) optimized for WVR. => Hence the nice look around canopy.


This gives me the impression that the current F-16 blocks are no longer optimized for WVR.
Correct me if I'm wrong but today's block 50/52 are still every bit as formidable in WVR as the OG F-16 if not more.

I'm aware that it has so many other capabilities and roles now and that it is a tad bit heavier but nowhere near the extent where it's traditional dogfighting prowess will be compromised.

If I may quote Lt. Col. Fred "Spanky" Clifton
The Pratt-powered Blocks 25, 32 and 42 are good performers, but not great. The GE-powered Blocks 30, 40 and 50, plus the Pratt-powered Block 52 are absolute beasts.


So if he puts the 52 in the same category as the 30 which many say is the ultimate F-16 ACM machine, then I think they're in pretty good hands.

I'm curious about the block 60 and 70/72. Any idea how they would stack up in the BFM scale? They're more capable all around no doubt.
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Unread post07 Jan 2020, 01:38

1. "Dogfights" does not necessarily portray what happened entirely accurately.


I'm sure McKeon was an exceptional F-4 driver, but my first impression having seen that on the original show was....

....if the Phantom could actually do that, they still be building them. (It can't)

I tend to agree with QS that it was probably a high G rudder reversal that got a little squirrelly and somewhat disorienting with maybe some manual flap manipulation to recover....there's a whole bunch of side loads in that type of maneuver which can create the impression of something else occurring....other than what actually is. (Many, many intentional A-7 departures and countless T-37 spins)

(Sidebar:

Ever see a Blue Angel solo do a dirty roll on takeoff?


I flew Phantoms with the Blue's A-4 solo who actually had one of the mains touch the runway unintentionally at NAS New Orleans out of the dirty roll. Probably at a somewhat lower speed than the F-104 maneuver and certainly not planned.)

There's a lot of comfort in having the Flight Controls take care of you....at the completely acceptable cost of a reduced amount of ego and squadron Darwinism.
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Unread post07 Jan 2020, 02:26

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