Very basic Hornet questions
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Agree this seems very important… but I still don’t understand how it works in conjunction with/without AT though.
And do we know how the trim callbacks work in BMS? Eg. if I hit the AFResetTrim keybd command … does it return the target-AOA to what it was the moment the gear deployed?
That is a good question. If I have auto-trimmed and attempt landing but then “Bolter” does the aircraft remain trimmed when I fly off the carrier and retract gear? And if so, how to reset that when going around for a new attempt?
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That is a good question. If I have auto-trimmed and attempt landing but then “Bolter” does the aircraft remain trimmed when I fly off the carrier and retract gear? And if so, how to reset that when going around for a new attempt?
In my very limited testing, the AFResetTrim callback does apply. I’m not totally sure I understand it though … it didn’t seem to reset to the original target-aoa-at-gear-down… it almost seemed to be trying to drive aoa to zero? Hard to tell, the jet was behaving very strangely… I ended up raising gear, for the go-around, to regain some controllability.
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According to the doc it is
What do you consider should be different ?
With plane at equilibrium, airspeed and aoa are geared together … control one, you control the other. So in a way you’re both saying the same thing.
But one key difference would emerge, when changing flaps from ‘half’ to ‘full’. Hugely increased drag, but also increased lift.
If atc is controlling for airspeed, it would presumably need to raise throttle to near/full mil power.
If atc is controlling for aoa, it will presumably need to cut throttle, to get aoa back on target.
I don’t know what the RL jet does, but the docs I’ve found indicate that in approach-mode, we should expect it would control for aoa.
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What the f18 flcs does when gear down is adjusting the pitch to get the trimmed AOA (for instance if you trim 8 deg AOa and push throttle it will pitch up trying to catch 8deg Aoa)
Then the AT is also adjusting speed to get the trimmed AOA
This is a combination of both
This must have been some interesting code to write … seems like an under-specified equation. Two inputs (elevators and throttle) but just one output (AOA)
Is it something like 2 separate PD control-loops, each tuned to 50% effect, and they always work in coordination?
Or is it more like … the elevators’ neutral position is simply fixed to the desired/trimmed angle (eg. 8.1) and then throttle control takes over from there?
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- b. I don’t really understand the E-bracket HUD indicator … what is it showing? It seems to be very sensitive to throttle position.
Answering my own Q here … it seems the easy way to think about the E bracket, is as a digital HUD display of the analog “AOA tape” instrument we have on the Viper.
The centerline of the “E” corresponds to 8.1° AOA. I think the top/bottom of the E are +/-1° respectively. (Or maybe +/-0.5°? It seems very sensitive.)
It’s somewhat redundant with the 5-level indexer lights, and the “alpha” display on the Hornet HUD, and it’s a little distracting… I wish there was a way to turn it off. But hey at least I understand what it’s trying to tell me now.
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(I have a lot of very basic questions about operation of the ATC so starting a new thread to focus on that)
https://www.benchmarksims.org/forum/showthread.php?42522-Hornet-auto-throttle-bugs-quirks -
Trying to learn the fly the Hornet. I can take off and land ok (well the LSO is not impressed with my efforts). I feel like maybe I’m getting some basics wrong.
After re-reading the Naval Ops doc, I still have a lot of basic questions…
1. Take-off Trim:
- Does this automatically revert once airborn, or do you have to remember to manually invoke a trim-reset?
2. Auto-throttle:
- Does it ever automatically disengage? (Does manually adjusting throttle override it, temporarily? Or when holding the ap-paddle switch?)
With gear down and flaps full, it doesn’t seem to hold AOA for me… I begin to sink, my aoa rises and the stall warning beeps.
3. Trim for Landing:
- There’s a note in the docs about using pitch-trim to adjust the AOA setpoint… how does this work (does it require/assume auto-throttle is engaged)?
4. Landing attitude / E-bracket:
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a. What’s the optimal attitude and AOA for landing … the indexer seems to want me at about 8° AOA … So, 5° nose up and 3° glideslope?
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b. I don’t really understand the E-bracket HUD indicator … what is it showing? It seems to be very sensitive to throttle position.
With flaps full I’m having a hard time controlling pitch… I find myself pushing forward on the stick to keep nose at 5° which feels awkward and weird… like I’m fighting against AP trim or something… am I doing it wrong?
5. Gain switch:
- What is the GAIN switch (SimF18FCSGainToggle) about … under what circumstances do we use that?
Hi, Airtex, We’ve been doing a good bit of Rhino flight model testing lately, so perhaps I can add something from the BMS perspective…
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Yes in the Hornet, and now yes in the Rhino, with the acdata files from the Mafia Files.
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Yes, as Lorik described. Keep in mind that the auto throttle has a cruise and and an approach mode. In AM it’s to command AOA, and is commanded with flap as half or full. In BMS it does work as described on p. 7-61 of the Naval manual. Btw, the attached is a good reference for the Case 1 approach
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just set full flaps for carrier landing, and drop the gear, no trimming needed
4)Yes, 8 AOA is optimal. The E bracket you describe is an AOA display set for 6-10 deq, so of course the sweet spot in the center is your desired 8 deg. Think of it as a “fine tuning display” for the Indexer on the HUD frame. If you’re on speed, you shouldn’t have to push down on the stick as you describe -
The Gain Switch can be confusing, as it’s not a G-limiter override like the MPO on the Viper. What the Gain switch on the -18 does is override the FLCS and lock the TEF’s and LEF’s to 3 degree down. It’s there in case of system failure such as (if memory deserves) AOA probe failure. Don’t use it in normal ops.
The Hornet/Rhino does have a G-limit override, which is supposed to engage with stick hard aft and paddle switch pulled. I say supposed to as that’s not how it’s current modeled. It’s like the paddle is always engaged. In testing I’ve pulled 9+ G at Mach 0.9 without the paddle, and it’s not supposed to do that. This is something we’re working on.
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Thanks @drtbkj … trying out the Rhino mods is next on my list, but I figure I should try to nail down some of the basics first.
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Thanks @drtbkj … trying out the Rhino mods is next on my list, but I figure I should try to nail down some of the basics first.
You very welcome.
All, I’ve been a little hesitant to mention it, as the Rhino files have been changing a lot in the last few days, but it looks like the major F18E fixes are done. The files currently in the Mafia Files, in both “1958” and “4.35 acdatas” , fix all the major issues. I now feel comfortable recommending downloading them The one acdata thing to do is to remove “FlcsBitRpmVar 0.00” from f18e.dat. That seems to solve the constant FLCS BIT FAIL I was getting. That’s not currently in the Files, as I’ve only tested it once, in one theater.
We’re continuing to work on the flight model, and the visual modeling of the formation lights, launch bar, AAR probe, and Nav Mode SmS page. However, beyond those, we are happy to present a fully functional Rhino to you… -
This must have been some interesting code to write … seems like an under-specified equation. Two inputs (elevators and throttle) but just one output (AOA)
Is it something like 2 separate PD control-loops, each tuned to 50% effect, and they always work in coordination?
Looking at external view, focusing on the elevators … with gear down, flaps full, approach-mode ATC does appear to manipulate both throttle and elevators to achieve target AOA.
I got some pretty wild oscillations, when disrupting the equilibrium (eg. hitting speedbrake briefly). So, like Stevie said, the important technique here is to get the plane stable and very close to on-speed AOA, before engaging ATC.
It’s pretty nice, once you get stable and trimmed right.
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One of the most important aspect is that when you engage landing gear, the autotrim will set your trim for the angle that you are at then. So make sure you have an alpha of 8 degrees when you drop gear.
More notes from my flight testing …
The Pitch-Trim-controlling-AOA mode – appears to be activated when flaps are deployed to Half or Full (regardless of gear up or down).
This is contrary to what the BMS-Naval-Ops doc says, but it doesn’t seem to control for AOA with gear-down flaps-up (auto). It seems to take its initial setpoint for AOA from the moment I change flaps from ‘auto’ to ‘half’.
In typical pattern one drops gear and flaps at near the same time, so not a big problem. Just added to my confusion trying to learn how this jet works…
[Edit/Update: also just changing flaps from ‘half’ to ‘full’ or vice-versa, seems to re-set current AOA as the new target AOA … so plenty of chances to get this right, without messing with trim up/down much]
This has had me ripping my hair out, but now that I know how it works I kinda like it … eg. on a bolter/go-around you can gently push stick fwd to lower aoa and toggle flaps to ‘half’, locking in ~4° for the go-around … then gently pull back to 8° and toggle flaps back down to ‘full’ to get back on-speed for approach
It’s actually easier-done-than-said … just cut throttle and pull back on stick … as FPM passes through the center of the E-bracket, hit your SimTEFCMDDec key ([shift+F11] by default I think).
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More notes from my flight testing …
The Pitch-Trim-controlling-AOA mode – appears to be activated when flaps are deployed to Half or Full (regardless of gear up or down).
This is contrary to what the BMS-Naval-Ops doc says, but it doesn’t seem to control for AOA with gear-down flaps-up (auto). It seems to take its initial setpoint for AOA from the moment I change flaps from ‘auto’ to ‘half’.
In typical pattern one drops gear and flaps at near the same time, so not a big problem. Just added to my confusion trying to learn how this jet works…
[Edit/Update: also just changing flaps from ‘half’ to ‘full’ or vice-versa, seems to re-set current AOA as the new target AOA … so plenty of chances to get this right, without messing with trim up/down much]
This has had me ripping my hair out, but now that I know how it works I kinda like it … eg. on a bolter/go-around you can gently push stick fwd to lower aoa and toggle flaps to ‘half’, locking in ~4° for the go-around … then gently pull back to 8° and toggle flaps back down to ‘full’ to get back on-speed for approach
It’s actually easier-done-than-said … just cut throttle and pull back on stick … as FPM passes through the center of the E-bracket, hit your SimTEFCMDDec key ([shift+F11] by default I think).
Hi, airtex,
Firstly, your testing has been quite helpful. Specifically, you gotten us thinking in terms of procedures.
As for this post, things changing with flap makes total sense to me That is what activates ATC. Not the gear.
Once again, it comes back to procedures. The main thing that’s becoming clear is configure the jet, then engage/disengage ATC. This also relates to your earlier point about the throttle “jumping” after you land. As Brother Stevie just pointed out to me , it’s seems logical that BMS will go to whatever setting the throttle is at when ATC is disengaged. So, the procedure after you’ve trapped is to go to flight idle then disengage auto throttle.
Here’s a couple of exact tips-1) full flaps for carrier takeoff/landing
2) Although the RL Hornet does not have auto-flap( the Rhino does) , the BMS Hornet seems to have some form of autoflap. They will go up at around 250 knots. The point is, if you bolter, keep your speed below that.
3) Just to save your hair (;) ) think of ATC this way- configure the jet to what you want, including speed, then just use ATC to hold it. -
what activates ATC. Not the gear.
To clarify, on this branch of the thread, I’m just talking about the pitch-trim-controlling-AOA mode of the Hornet FLCS, which is irrespective of ATC on/off.
The docs had me very confused on this… I don’t claim to know what the RL jet does, but in BMS this mode is activated, and initialized, by setting flaps=half/full… not gear=down.
earlier point about the throttle “jumping” after you land
I just have to retract everything I said about that… I’m using a TM 16000M which has a crappy little slider for a throttle, and it’s hard to tell just by looking, what its position is.
I was sure it was at idle… but now when I sincerely try to repro this, I can’t. So, I must have had the throttle slider up around midpoint and forgotten.
There’s no obvious easy solution for this … in RL jet the physical throttle moves with electric motors. We can’t do that for our HOTAS so we’re left in an inconsistent state that never really happens in RL jet… (viz. ATC may switch off at 70% idle, but physical throttle axis is up around 90% … what should BMS do?)
I can imagine some complex code to not snap to the throttle axis until it’s moved > a certain threshold (like the 0.2 to disengage atc) but that doesn’t seem warranted … as pilot, we should have full command of the throttle when touching down (either on carrier deck or runway).
(The crash investigation team has determined the cause of these incidents is pilot error… caused by lack of sleep, and/or alcohol impairment.
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To clarify, on this branch of the thread, I’m just talking about the pitch-trim-controlling-AOA mode of the Hornet FLCS, which is irrespective of ATC on/off.
The docs had me very confused on this… I don’t claim to know what the RL jet does, but in BMS this mode is activated, and initialized, by setting flaps=half/full… not gear=down.
I just have to retract everything I said about that… I’m using a TM 16000M which has a crappy little slider for a throttle, and it’s hard to tell just by looking, what its position is.
I was sure it was at idle… but now when I sincerely try to repro this, I can’t. So, I must have had the throttle slider up around midpoint and forgotten.
There’s no obvious easy solution for this … in RL jet the physical throttle moves with electric motors. We can’t do that for our HOTAS so we’re left in an inconsistent state that never really happens in RL jet… (viz. ATC may switch off at 70% idle, but physical throttle axis is up around 90% … what should BMS do?)
I can imagine some complex code to not snap to the throttle axis until it’s moved > a certain threshold (like the 0.2 to disengage atc) but that doesn’t seem warranted … as pilot, we should have full command of the throttle when touching down (either on carrier deck or runway).
(The crash investigation team has determined the cause of these incidents is pilot error… caused by lack of sleep, and/or alcohol impairment.
Compadre, IMHO, you’re driving yourself nuts over this. Maybe you need more alcohol Seriously, if you think about it, in real life ( electric motors or not),or BMS, if you’re at “around 90%” throttle when you come off ATC, what’s the jet going to do? Frankly, I want the jet to do “what I tell it to do” via the throttle. So, it’s on me if I don’t go to idle.
Once again, procedures. When you feel the decel. of the hook grab, go to idle. -
One last question … what does it mean when LSO says “well done” right before you grab the wire… I hadn’t heard that before – is it a brevity code? I only know “wave off” and “burner burner”. (kidding)
Thanks everyone for bearing with my questions. I no longer feel like a fish out of water, in the Hornet.
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More advise - start landing the Viper on-speed, instead of fast - if you use the Bracket in the Viper you are actually landing fast, which also has you at a lower AOA.
What makes you say the bracket is fast? On the bracket is on speed, on AoA. Should be 13 degrees at touchdown, 11 to 13 on approach - middle of the bracket is 13 degrees, on AoA, on speed.
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Airtex, Congrats! If you hear that you just got an “ok 3 wire” landing grade.
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Hi, airtex,
2) Although the RL Hornet does not have auto-flap( the Rhino does) , the BMS Hornet seems to have some form of autoflap. They will go up at around 250 knots. The point is, if you bolter, keep your speed below that.BMS is actually right about the 250-kt flap up limit.
Cf. I-2-44 in the real Hornet NATOPS manual. Regarding HALF et FULL modes, it reads : “Above 250 knots, the flaps operate in the auto flap up mode and the amber FLAPS light comes on.” -
Just in case you missed it, we worked quite hard on the f18 and as I said , f18 flcs is unique and has been coded as per information available
It’s not like the f16 that’s is a 100% accurate but still it’s not that bad
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Just in case you missed it, we worked quite hard on the f18 and as I said , f18 flcs is unique and has been coded as per information available
It’s not like the f16 that’s is a 100% accurate but still it’s not that bad
For the record, I am now loving the Hornet and finding it hard to go back to Viper… so much fuel! so many stores! double the engines! flight model feels so nimble, for such a heavy jet! and it has cruise-control!
I hated it at first … flight model felt extremely wompy and awkward to me … but now I realize I was just fighting against the aoa-pitch-trim – and struggling with things like ATC disengaging without warning when I didn’t expect (eg. when flaps=Half and you’re slightly too fast).
My only remaining wish is for improved docs:
– a) describing the aoa-pitch-trim mechanics (and figure out if RL it’s activated by gear-down or flaps),
– b) describing the E-bracket symbology for AOA, and optimal landing configurations, and
– c) outlining the cases where ATC auto-disengages
(and code some sort of HUD symbol or indicator lamp for it