Harley Posted January 29 Posted January 29 (edited) Not sure how to word the title, but I'll explain: When deploying the speedbrake on the F/A-18C, when it starts to deploy, and with full deployment, there is a resulting slight nose-up condition. That is expected, but on a 3 position switch, being stow, hold, and momentary deploy, there is something not correlated properly. The deploy switch is momentary and in some conditions, will hold even at a partial deploy, but as soon as the switch is released, even if the speedbrake is still deployed, the resulting and expected nose-up force input seems to be modeled to decrease, meaning the force should still be there, meaning the nose should still be being forced up until the speedbrake is stowed, not just when the switch is released. It seems that the downforce on the tail causing the nose-up condition seems to be modeled against the switch position, not the actual speedbrake position. It's noticeable in the cockpit. The nose begins to come back down, even with the green SPDBRK annunciator on. Speed should likely have an effect on how much downforce is applied, but the AOA increase should be correlated with speedbrake position, not switch position, and it seems that's how it is now. I hope that reads clearly. Still loving this F/A-18C, though. Flying every night. Edited January 29 by Harley More information/clarification.
Hulkbust44 Posted January 29 Posted January 29 Do you have a video to share? There are multiple flight conditions where the speed brake will retract automatically unless you are continuously holding the switch out. Sent from my moto g stylus 5G (2022) using Tapatalk
Harley Posted January 29 Author Posted January 29 (edited) It's definitely only reacting to the switch position. It's something that would be difficult to video, but I can definitely tell it's not right. As soon as I let go of the switch, the nose slowly returns, as if the speedbrake is retracting, but switching to the external view, the speedbrake can still be extended and it's confirmed by the SPD BRK annunciator. It's not a dealbreaker, it's an accuracy issue I noticed right away, and never really brought it up. It's something you can tell isn't right. For what it's worth, I don't know if everyone is using an associated keybind on the keyboard, or a button on a joystick, but on this winwing taurus, it has a fairly accurate 3-position switch, and the extend is momentary, and it automatically returns to the center "hold" position. If the speedbrake is fully eployed, it can stay deployed, depending on flight condition. It doesn't always auto-stow, excepting maybe if the gear is down, or whatever other condition may cause the auto stow to operate, but it doesn't always auto stow, so it shouldn't always produce the AOA decreasing effect unless the speedbrake stows, not just because I release the switch. Edited January 29 by Harley
niru27 Posted January 29 Posted January 29 Could it be the FCLS compensating for the pitch up caused by the speedbrake, by trimming down? The FCS page should tell you The new flight model is definitely wonky: too much ballooning when dropping flaps and nerfing of pitch control.
Harley Posted January 29 Author Posted January 29 I will check, but I don't think it's that. If it were, then it should try to cancel the downforce upon deployment. The super hornet does that, but the legacy hornet doesn't, best I understand it.
Harley Posted January 30 Author Posted January 30 I tried this on the ground to correlate what I was feeling with something I could see. From outside, the speedbrake deploy causes the pitch trim to nose down, perhaps to cancel the nose up that should result from the speedbrake. Then, as soon as I release the speedbrake button, the pitch trim is what changes the pitch, even while the speedbrake is still deployed. I think it's that causing the issue, not the speedbrake. Pitch trim on the elevons increases as soon as I release the button. Maybe this is proper, maybe not. I can't tell now. There's so much going on.
niru27 Posted February 1 Posted February 1 On 1/30/2025 at 9:33 AM, Harley said: Pitch trim on the elevons increases as soon as I release the button I did some testing and you are right, this is exactly what's happening. The pitch change is tied to the Speed Brake Extend button state instead of the actual "Speed Brakeextended state". After the board is fully extended, the FCLS waits until you let go off the EXTEND button to retrim the jet, instead of waiting for the board to close. So the net effect is you flight characteristic is a bit different depending on whether you're holding the Extend button or not. 1
Harley Posted February 1 Author Posted February 1 8 hours ago, niru27 said: I did some testing and you are right, this is exactly what's happening. The pitch change is tied to the Speed Brake Extend button state instead of the actual "Speed Brakeextended state". After the board is fully extended, the FCLS waits until you let go off the EXTEND button to retrim the jet, instead of waiting for the board to close. So the net effect is you flight characteristic is a bit different depending on whether you're holding the Extend button or not. That is a great way to say that. I concur. I think the way it should work is that the pitch should not try to retrim until the board begins to travel during the stow cycle. The net effect should be as close to zero as possible with this function. It likely would be if the trim were programmed to function against the board position instead of the switch position. 2
Fresh Posted February 6 Posted February 6 Good catch! I'll have to watch out for that next time I fly, thanks!
miguelaco Posted February 11 Posted February 11 It would be nice to have confirmation that this is being looked at by the dev team, as it is a pretty obvious issue.
Mav87th Posted February 13 Posted February 13 +1 For what its worth, I think your right Harley. The FCLS should very much trim as the drag increases and not from a switch position in the throttle. Did you examin what happens when you push the speedbrake switch to its "held" position for closing, and then not ever taking it out of the hold position? And make sure its not like in an F-16, where you can "over open" the speedbrakes by holding the speedbrake switch in the open position - gives a little extra opening angle on the speedbrakes. Then when you release the switch the brakes close a tad automatically.
Harley Posted February 13 Author Posted February 13 (edited) 1 hour ago, Mav87th said: +1 For what its worth, I think your right Harley. The FCLS should very much trim as the drag increases and not from a switch position in the throttle. Did you examin what happens when you push the speedbrake switch to its "held" position for closing, and then not ever taking it out of the hold position? And make sure its not like in an F-16, where you can "over open" the speedbrakes by holding the speedbrake switch in the open position - gives a little extra opening angle on the speedbrakes. Then when you release the switch the brakes close a tad automatically. Yes, if I am understanding what you're asking. Any position of the speedbrake, partial or full, I think should result in a countering FCLS retrim, based on the panel position. Full deploy should full retrim, and a portion should retrim proportionally. The switch position is what does it now, where holding the switch in the deploy keeps the flight controls in the retrimmed position. But that switch position is a momentary function, and will spring back to the center "hold" position, and will improperly retrim the elevator function back to the same position as if the speedbrake were stowed upon release of the switch. The airplanes I work on do this with the flaps as well, and retrim the horizontal stabilizer position based on flap position. I know the super hornet does a net zero function when deploying speedbrakes to keep the nose at the same position, and it works really smooth, although that really is a very different bird. But I still think that the retrim function should be encoded against speedbrake panel position, not the switch position. Just to note, it's not a deal breaker, and I love the legacy hornet enough to be building a dedicated sim pit with it, but that part I think is not correct, and changes the nose angle during a strafing run. Hard to compensate for. Edited February 13 by Harley
Muchocracker Posted February 13 Posted February 13 (edited) we've had this one reported for some time. Probably just gonna be a waiting game till they do the next batch of FCS changes. Edited February 15 by Muchocracker 2
Harley Posted February 14 Author Posted February 14 6 hours ago, Muchocracker said: we've had this one reported for some time. Probably just gonna be a waiting game for when they do the next batch of FCS changes. That's what I would figure, honestly. Seems like that wouldn't be difficult to change.
Mav87th Posted February 15 Posted February 15 @NineLine perhaps you can confirm is this is "known" and worked on?
niru27 Posted February 19 Posted February 19 On 2/14/2025 at 4:44 AM, Muchocracker said: we've had this one reported for some time. Probably just gonna be a waiting game till they do the next batch of FCS changes. Is the high altitude, high speed handling reported as well? When you yank the stick in those conditions, the FCS can't make up its mind on how many G's to allow, so there's a constant oscillation in pitch axis --------- Here's a TRK for the Topic Issue: Part 1 : Level flight with ATC and BALT engaged, and Speed Brake fully extended (WW F18 throttle, so the switch physically returns to the centre HOLD position) When I press the button aft (EXTEND), nothing happens as expected But when I release it, there's some pitch input from the FCS, which is wrong, since the board position hasn't changed at all Part 2 : I go into a left hand, level turn When I press the button aft (EXTEND), nothing happens - once again as expected But when I release it, there's some pitch input from the FCS, so the velocity vector leaves the artificial horizon line This issue is particularly problematic when doing Case 1. If you let go of the Extend button, the jet will want to depart from the level break F18 SPDBRK.trk
Muchocracker Posted February 19 Posted February 19 3 hours ago, niru27 said: Is the high altitude, high speed handling reported as well? When you yank the stick in those conditions, the FCS can't make up its mind on how many G's to allow, so there's a constant oscillation in pitch axis Make a separate post, or bump an existing one.
niru27 Posted February 19 Posted February 19 23 minutes ago, Muchocracker said: Make a separate post, or bump an existing one. Done
Dragon1-1 Posted February 20 Posted February 20 On 2/13/2025 at 9:54 PM, Mav87th said: And make sure its not like in an F-16, where you can "over open" the speedbrakes by holding the speedbrake switch in the open position - gives a little extra opening angle on the speedbrakes. Then when you release the switch the brakes close a tad automatically. Note that the Viper only works like that with gear down, because you could scrape the speedbrakes on the runway a bit too easily otherwise. If you deploy the speedbrakes fully with gear up, they'll stay open.
Recommended Posts