unable to reproduce and missing track file question about FBW ''feature'' or ''bug''

[hotrod525]

Hello folks,

During a flight sunday, i experienced a weird take off, as soon as i my wheels were no longer touching ground, FCS pitch violently, tail strike, i barely manage to kept it under control, had to push the stick max forward to have some sort of autority. Tried to trim, FCS page was showing no error, even tought i was fighting the wasp, we ended up at 90 degress ascension, jettison everything, engage the FCS Gain Overide and SPIN RCVRY switch (it was the second time i ever engage it since F18 release lol) in order to finaly stabilise my craft.

 

So what went wrong ? TO Trim was GTG, FCS was Reset and GTG, flaps too... Im no ''expert'' but i do have several hundreds of hour on that baby, was the worst it ever get, only other time i could recall such an issue was when i was catapulted with improper flap and trim.

 

Track too large for forum and dosent load on my own dcs, sorry.

[Hiob]

Have you by any chance be able to have a look at the controls overlay? Just to rule out that it was the aircraft that freaked out and not your flight stick?

Other than that, my best guess would have been T/O trim not set, but you ruled that out already.

[Viral-51st-Vfw]

Iirc this behavior occurs when you hit to trim and you don't have flaps in half(nor full)

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[rob10]

Yep, what @Viral-51st-Vfw said, almost for sure you had flaps in AUTO (rather than 1/2 or full) on takeoff.  You become a rocketship if that's the case and you won't be able to use trim or stick to level it UNTIL you flip it to 1/2 (or full) then back to auto.  Once you do that it will start to behave itself again.  But just make sure you follow a checklist and set them properly (and pay attention to the CK FLAPS caution you'll get when you push throttle ahead with weight on wheels and flaps in auto).

Edited September 23, 2024 by rob10

[hotrod525]

oh i see, im quite sure that you guys are right, i most likely kept it in auto and f. myself up.

 

thanks !

[Viral-51st-Vfw]

I would guess it's a bug, as I can't imagine the real aircraft designers would want it to behave that way, but I also don't have any real life experience nor public documentation to back up that claim.

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[rob10]

5 hours ago, Viral-51st-Vfw said:

I would guess it's a bug, as I can't imagine the real aircraft designers would want it to behave that way, but I also don't have any real life experience nor public documentation to back up that claim.

Discussed at length here:

Personally, since it triggers a MASTER CAUTION if you try to take off with flaps in AUTO I tend to believe it's correct behaviour.  There are lots of reasons why the behaviour might seem illogical, but there could well be other consequences of a fix for this that means it's easier to have a Caution and checklist item to set them to 1/2.
I also have no idea of IRL on this, so this is strictly my feeling.

[Sabadin]

You can successfully take off in Flaps AUTO, just need to ensure you trim down from the default 12NU to 4NU. This is the configuration the CF-188 demo team uses for their Dirty Roll Take-off routine and works just fine in the DCS jet.

[hotrod525]

Planes are all about "procedures" and "setting".
Military are all about "procedures" and "setting".

So that being said, it aint a far stretch for me to consider this a real behavior of the system, since it's all about.... you guest it, "procedures" and "settings" lol. If you dont respect them, the plane will be angry and do thing like that. I kinda feel the same way as Viral and Rob, as it dosent make sens instantly, but military are also about "not making sens all the time" hahaha!

 

Thank you all for your input'

[DummyCatz]

You can check your actual trim position by the tiny '-' symbol in the control indicators (ctrl + enter). If you take-off with the symbol not at neutral position in FLAPS AUTO mode, you may end up with a continuous pull because this trim bias is persistent in the FCS, until you switch the FLAPS down and up again.

 

The following are my in-game observations and might not related to RL values:

There seems to be two independent trim values in DCS F18. One is the actual trim position indicated by the tiny '-' symbol and corresponds to your reference/trim AOA. The other is the pitch integrator or elevator position when WOW which is displayed at the FCS page. Both are affected by the trim button and can be accumulated independently, with different value ranges.

With FLAPS at HALF or FULL, the actual trim position is limited to positive values and act like a bias added to the pitch integrator. The full range of this trim function is like 0-12 deg, which initially corresponds to 6-18 deg NU elevator position. I said initially because once you trim past 18 deg NU, the actual trim reaches its maximum position, but the elevator will still go all the way to 24 deg NU. Now if you trim forward, the elevator position reduces but the '-' symbol moves upwards at the same time, like the trim doesn't wait for the elevator to be reduced below 18 deg NU. So there's no 1 to 1 relationship between the elevator position and the actual trim position, at least in-game. (I'm not sure if its a correct behavior.)

When pressing the T/O Trim button, this trim position is initiated to half way of the full trim range (around 6 deg), and corresponds to 8 deg reference/trim AOA. If you have not trimmed past 18 deg NU or 0 deg ND elevator, the trim position also corresponds to 12 deg NU elevator.

Edited September 30, 2024 by DummyCatz