Questions about Auto Throttle
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@airtex2019 - that’s not exactly correct. The jet actually tries to maintain 1G…if you are trimmed to 1G level flight. As I keep saying, design Cruise AOA is 3 or 5 (or whatever you’ve previously trimmed to) - so that’s what you should see, at 1G.
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@airtex2019 - The nose pitches because the “Target Trim” has changed and the power setting hasn’t - this is what I mean by the “state” of the airplane and how the Hornet is more sensitive to this because it’s FCS is based on it.
You need to think more in terms of the energy state of the jet, and not just what you are doing with the controls. As I keep saying, the FCS doe not manage the AOA “set point” - the pilot does. And this is true with ATC or not, but ATC (or simply not adjusting power) is a good way to see the effect. IF ATC works properly…
If you trim and maintain power setting, the nose will pitch up, and/or you will climb. Your AOA is being managed by the combination of your forward and vertical speed components - this is why ATC always snatches the throttles aft out of my hand if I select it on downwind, and I have to input forward stick to kill the climb.
As previously stated, the pilot maintains full authority to trim to any AOA he wishes during all phases of flight - there is no limiting just because you happen to be in PA Config. So you should be able to use the “full range” of callbacks on your stick. Your Target AOA for approach/landing is 8.1 - period. But the pilot has to trim to that himself, on the stick.
My habit pattern is to brake turn and select gear down/flaps full at 250 (Hornet uses full flaps for ALL landings - the only reason you’d go to half flaps UA is to slow down for a dissimilar wingman). If you exceed 250 with flaps down they will blow up, and you will get a CAUTION, have to slow, and cycle the flap switch.
I establish downwind, and then I trim to 8.1…usually immediately after noting three in the green (gear has to be down and locked to retain the setting) and wings level. This is where/why I need to push forward stick to maintain pattern altitude, because at this point I’m still way too fast and high on the power for 8.1 AOA…again - throttles have to come back, ATC or not. Now it’s time to capture on-speed, continuing to slow down. It’s still possible to slow further coming off the 180 IF you have not selected ATC - once you select ATC it is going to lock-in that speed…which is yet another reason I don’t care much for ATC…ATC is the only thing that will kick off at WOW and greater than 80 KCAS.
What on-speed will be is HIGHLY dependent on GWT - the lighter you are, the slower it will be (and this also works with the Viper Indexer). For about 4000 lbs remaining it should be something around 128-135 knots. On-deck fuel for a Hornet is 2000 lbs remaining. But you will still fly 8.1 AOA.
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@airtex2019 - In Cruise - ATC controls for constant airspeed, and AOA will vary with GWT.
In Approach - ATC will still control for constant airspeed (on-speed, as selected by the pilot)…but the kicker here goes back to energy state - in approach, power controls sink rate, nose controls speed.
It’s possible to drag the approach long or short using the nose to displace the Velocity Vector, as long as you don’t over-control and kick ATC off. But ATC is managing power to maintain AOA such that you touch down around 800 FPM - thus managing sink rate, really.
It’s the vector sum of sink rate and forward speed that is being controlled to maintain AOA.
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@Stevie said in Questions about Auto Throttle:
As I keep saying, the FCS doe not manage the AOA “set point” - the pilot does.
Yes, I get that part. I am asking, what is the initial AOA setpoint when the pilot hasn’t touched anything yet (after lowering the gear/flaps to enter approach mode).
The answer may be as simple as “8.1°”. Or it may be “whatever your AOA was at the moment you lower your gear… subject to a minimum of 6°” or it may be something more complicated, based on flaps settings or something.
For now, put aside all the pilot-procedure and theory-of-flight stuff … pretend you’re MavJP and you need to write some code to emulate the FCS … that code has to do … something. What does it do?
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@airtex2019 - the answer is that it is whatever it was before he lowered the gear and flaps. Lowering the gear and flaps changes nothing as far as changing the Trim setting goes.
The code has to do nothing…until the pilot inputs/sets Trim.
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@Stevie Great! I think that probably makes sense. We’re getting close … next question – is it the gear, or the flaps, that switches the FCS into the approach mode. BMS docs say gear… but it seems like the RL docs indicate it’s switching flaps out of ‘auto’ into either ‘half’ or ‘full’ (maybe with nuance of also actually being slow enough for the flaps to extend).
If that (flaps switch) is correct, then BMS implementation is pretty close to reality (within bounds of it being 90% Viper avionics of course) and so my complaint of this “quirk” is mostly just a doc-bug.
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@airtex2019 - It’s actually the combination of both gear and flaps…if either fails, then the whole thing fails down another path. And because you have to be below 250 to get/keep the flaps down, speed factors too.
Most things (if not everything) that happens in a Hornet happens in combination.
And given that FCS is Avionics…without a real Hornet Avionics model, BMS will always fall short.
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@Stevie yes no doubt there is a 1000 page manual full of details that won’t/don’t easily map onto the existing Viper avionics codebase… but BMS team did write some special-case Hornet code for things like autothrottle, and pitch-trimming mechanism is different than Viper.
just trying to make sure what we do have, is as correct as possible, or at least working as intended and documented…
one little note, it seems BMS does implement the airspeed condition, for the FCS pitch-trimming… I’d never tested this case before, but I just did a quick flight and noticed with flaps=‘half’ around 280 kts… it didn’t start to command pitch until my airspeed dropped below ~250 kts. that was a nice nuance.
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@airtex2019 said in Questions about Auto Throttle:
@Stevie Great! I think that probably makes sense. We’re getting close … next question – is it the gear, or the flaps, that switches the FCS into the approach mode. BMS docs say gear… but it seems like the RL docs indicate it’s switching flaps out of ‘auto’ into either ‘half’ or ‘full’ (maybe with nuance of also actually being slow enough for the flaps to extend).
If that (flaps switch) is correct, then BMS implementation is pretty close to reality (within bounds of it being 90% Viper avionics of course) and so my complaint of this “quirk” is mostly just a doc-bug.
BMs f18 flcs has been coded with the real doc on the knees
Which does not prevent that some
Detail might have been misread -
@Mav-jp yep now I’m leaning that it’s mostly just a doc-bug. I’ll find the relevant pages and post them to Micro in the docs subforum…
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@Mav-jp
https://forum.falcon-bms.com/topic/24448/falcon-bms-4-37-1-documentation-bug-reports/26Perhaps you can confirm or deny my quick and dirty testing notes…
1/ verify AOA-trim range, it seems to be approx +/-2° … which happens to be the width of the E-bracket
2/ confirm if approach-mode-autothrottle AOA setpoint is always the same as pitch-trim AOA setpoint … in my limited testing, it seems to be, and mathematically it would seem to almost have to be, else the two control loops would fight, and oscillate or diverge wildly
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@airtex2019 - it shouldn’t “command” pitch. If it’s doing that, it’s wrong, or you aren’t really understanding what should be going on. What you report seeing at 280 knots is totally wrong - your flaps should have blown up at 250, and you should be seeing a FLAPS Caution.
People aren’t understanding (or aren’t even wanting to understand) just what is happening with the dynamics of the airplane - and this gives rise to all sorts of complications between pilots and coders - which is what I do for a living, really - translate real world issues/observations into coder-lingo for resolution, for RL airplanes.
People are doing a great job of reporting…but nothing is getting resolved.
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@Stevie said in Questions about Auto Throttle:
which is what I do for a living, really - translate real world issues/observations into coder-lingo for resolution, for RL airplanes.
People are doing a great job of reporting…but nothing is getting resolved.Why not spend 20 min hop into the TR24 training mission, give it a try, and report what’s wrong?
Yes obvs there’s 1000 pages of stuff that is not implemented. But putting that side and focus on the handful of things like pitch trim in approach mode, which BMS did make effort to at least closely approximate… why not help test and give feedback?
I feel like I’m not using the right plane lingo and you’re reacting to that, and if so I apologize, I’m just trying to communicate as best I can.
With atc off, how does the plane “trim for aoa” without commanding pitch? What’s the right terminology?
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@airtex2019 - the fact that the pitch changes is a result of physics, not of anything the FCS is doing directly. As previously mentioned, with ATC off and not in PA, the FCS is not trying to “trim” to or maintain anything other than design Cruise AOA (which as I keep saying is either 3 or 5, I can’t recall) or the last pilot Trim input, whichever has last occurred. And in PA, maintaining the combination of 8.1 (or the pilot selected) AOA and on speed is more a function of throttle input and not stick. With ATC engaged, the FCS is in “command” of the throttle - the pilot still has command of the stick. With ATC off the pilot has to do both jobs.
What the FCS is actually doing is to seek 1G flight and not any “command” AOA, and power setting factors here - the pilot cannot trim the jet without an accompanying change in power setting…if he desires to maintain level flight at his current altitude. The FCS has little or nothing to do with this - it’s just physics. The jet isn’t actually “trimming” in the sense you are thinking of - it’s more like it’s “seeking equilibrium” with it’s current state.
When the pilot trims the jet, he places the aircraft at a different point on its lift curve wrt his present AOA - and this is the change in the “state” of flight condition Trim induces - again, simple physics. The FCS doesn’t try to do anything with this other than try to maintain 1G - and even then, only unless the pilot overrides that by commanding a control input with the stick - Trim or otherwise.
The physics behind lowering flaps is that you change the mean camber of the airfoil and as such change the wings Pitching Moment (and induced drag) and the nose rises. Again, the Hornet FCS doesn’t “command” anything regarding this - it’s just physics.
Where you are going wrong is in continuing to insist that the Hornet FCS is “commanding” anything in these circumstances. I’m perfectly willing to consider that the Viper FLCS works differently and that most people here are familiar with that system/design, but the Hornet FCS actually IS different because it’s control logic and design approach are different. So you have to consider the whole picture if you are going to understand those differences.
And the biggest thing that I can tell that is wrong with the BMS Hornet FM right now is that it is letting you keep putting the jet into situations that the RL jet will simply not let you get into - starting with the Flaps; which is the most straight-forward thing that could be fixed right now. The jet will simply not let you extend flaps above 250 knots - ATC on, ATC off, gear up, gear down, any combination of those, don’t care - the Flaps will not extend or remain extended above 250. Period. And if the switch and Flap positions disagree you get a Caution. That’s one thing the FCS does actually do.
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@Stevie
For the avoidance of doubt, BMS Hornet doesn’t actually begin extending the flaps until airspeed drops below 250 kts. That is all I meant when I said “setting flaps=half at 280 kts” above – I was referring to the position of the cockpit switch, not the physical extension of the flaps.I don’t fully understand everything you’re saying, but that’s ok I’ve hijacked this thread into oblivion and taken way too much of your time in the process. I appreciate your effort. I can certainly believe real-Hornet FCS is very different than BMS-Viper-modified-to-be-Hornety FCS. Seems like I need to find better docs somewhere… and do some homework.
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@airtex2019 - yes…and you should induce a Caution if you do this. Do not select Flaps half or full above 250. That’s a placard violation. A lot of what we’ve been talking about gets down to basic airmanship like this, really…which is always good discussion. I’m always up for that!
I think one of the biggest issues with a Hornet (or a Viper, for that matter) is that it isn’t “governed” by any one book - there are a whole pile of books…particularly where the Hornet is concerned - and this is where my saying “the book ain’t the end-all” comes from; there’s more than one. And you aren’t going to find a lot of what you’ll be looking for, in this case.
One of the things that makes the Viper such a ripe jet to model is that there is a TON of information available about it, and that’s because so many people operate it.
Anyway, this has been all-good for me because I actually have to teach this stuff to other Engineers that fly the Trainer…which is one of the reasons I won’t fly the BMS Hornet - too much negative Training for me to try and keep sorted out.