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Announcing NEW Boeing 777 'Seattle' - Pre-Release

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Re: Announcing NEW Boeing 777 'Seattle' - Pre-Release

Postby Octal450 » Fri Apr 19, 2019 4:03 am

Pitch C*U law is now done INCLUDING trim ref airspeed. There may be a few bugs, but from what I can tell it is solid so far.

No High Speed or High Alpha protections yet. We'll see about those later.

You want to test it? https://github.com/it0uchpods/777
If all is ok, will continue. I am looking forward to hear testing reports!

Kind Regards,
Josh
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Re: Announcing NEW Boeing 777 'Seattle' - Pre-Release

Postby Isaak » Fri Apr 19, 2019 9:56 am

Hi Josh, thanks already! I'm testing your changes at the moment and found one small bug in the trim: the reading of the trim setting (between the trim lever and the parking brake lever) is stuck at 4° nose down and doesn't move with trim.

The roll protection and AP disengagement seem to work fine. Thanks!
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Re: Announcing NEW Boeing 777 'Seattle' - Pre-Release

Postby Octal450 » Fri Apr 19, 2019 2:05 pm

Hi Isaak,
That is not a bug, this is due to YAsim requiring an absurd amount of downward trim in the 200s. I have not yet added the bias. As soon as I do, it will indicate correctly.

How did you find the C*U law for pitch?

Kind Regards,
Josh
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Re: Announcing NEW Boeing 777 'Seattle' - Pre-Release

Postby Isaak » Fri Apr 19, 2019 2:44 pm

Ok, thanks! I still have to get used to the C*U law, I do feel it is working, but I 've never experienced it before so it's hard to say if it behaves as an experienced pilot would expect. I think I didn't feel pitch compensation in turns as described here (under 11.8 ). I've only made one landing with it and now (after reading up on it) I'm wondering if my rather hard landing was the result of the flare compensation not being implemented yet? Anyway, as usual I really like your work. Well done!
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Re: Announcing NEW Boeing 777 'Seattle' - Pre-Release

Postby Octal450 » Fri Apr 19, 2019 4:33 pm

Hi Isaak,
Good to hear.
The turn and flare compensations aren't done yet. I wanted to make sure the basic law is ok first. But yes, the hard landing is because when the power drops, C*U will add a significant downward thetadot to try and return to trim airspeed. I believe the flare compensation removes this effect and introduces a lower but still somewhat there effect. In a conventional plane like 737, nose will get a bit heavy in flare, but not nearly as much a airspeed change in flight due to ground effect (if I understand it right)

I just added pitch trim bias. Now the indications should make sense. Keep in mind, I updated the F/CTL page to show the infos properly (including the DIRECT and NORMAL stuff, try flicking off the PFC switch on the overhead :mrgreen:)

Kind Regards,
Josh
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Re: Announcing NEW Boeing 777 'Seattle' - Pre-Release

Postby Octal450 » Fri Apr 19, 2019 4:52 pm

Isaak, why is the 777-300ER and 777-300 YAsim so different? It should be changed to match the -300 in my opinion, the ER is a bit wronger.

https://www.diffchecker.com/IeOYBiJd

Kind Regards,
Josh
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Re: Announcing NEW Boeing 777 'Seattle' - Pre-Release

Postby Isaak » Fri Apr 19, 2019 5:19 pm

Well, I didn't code the FDM, but I can imagine the 300ER is quite different compared to the 300: longer wings, larger and stronger engines, higher MTOW and MLW... This all has an impact on the manoevring characteristics I guess. What do you think is wrong?
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Re: Announcing NEW Boeing 777 'Seattle' - Pre-Release

Postby Octal450 » Fri Apr 19, 2019 5:32 pm

Ahh, OK, I didn't know that. I was confused since the behavior is vastly different to every other 777 variant.

I added flare compensation. It looks like the YAsim has no ground effect for drag, as speed lose very fast during flare. But the pitch behavior now is better.Maybe I can slow the retard rate of the throttles to compensate, I think the real one does it somewhat slowly as well.

Keep in mind the YAsim weirdly pitches up when around less than 100ft, hence you barely had to flare it. Now that the FBW will remove this behavior, you can flare the 777 like other aircraft.

Kind Regards,
Josh
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Re: Announcing NEW Boeing 777 'Seattle' - Pre-Release

Postby Isaak » Sat Apr 20, 2019 8:31 pm

Hi Josh,

I tested your flare fix in the 300ER. I feel that it works, but still I have a very hard time to keep the nose position under control after main gear touchdown. If I don't interfere the nose wheel seems to be pushed into the tarmac, and because of the natural pitch sensitivity of YASIM this results in me overcompensating so the front and rear passengers would go through a rough up-and-down-roller-coaster-ride after touchdown :p I didn't test other versions, maybe the experience is different on them? I prefer to test on the 300ER because I fly it mostly and am most familiar with its behaviour.

At this moment, the C*U Law still costs me a lot of effort to control the plane, as I am not familiar with the 'counter-intuitive' behaviour of the trim wanting to maintain a target speed instead of modifying the stabiliser position directly. If I 'm correct, if I push the trim down (in flight) it should increase the target speed? Or am I interpreting the C*U law wrong? At this moment I have a lot of difficulty when approaching manually to reduce the speed, because the trim is pushing me down as I reduce the throttles and/or increase the flaps to get into final landing config. It's no fun being pushed below the glideslope to maintain the 160 knots I was in with flaps 20. Maybe I 'm doing something wrong, so please see this as constructive feedback that you can react to if I'm doing something wrong :)

On a sidenote: I made a small commit to FGaddon to disable the 3D HUD, as discussed last month, because it's partly out of view in the standard cockpit view.
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Re: Announcing NEW Boeing 777 'Seattle' - Pre-Release

Postby Octal450 » Sat Apr 20, 2019 8:43 pm

Dear Isaak,
I have rebased my GIT with your SVN. Thanks.

Due to bad FDM behavior, at touchdown, the nose tends to slam down due to the low speeds. I did not notice this behavior when I touched down about 132kts. (140kts approach). But maybe I can do something.

The C*U is designed that you should pretend it is not there. Essentially, it does what regular airplanes do. The 777 YAsim does not behave how it should. Generally, if you are level flight and trimmed, put some downward trim in a conventional aircraft, the aircraft will tend to speed up, then pitch up a bit and slow down, a few times until it settles at an airspeed in a descent. The C*U law essentially sharpens up the trim behavior and makes it more predictable. All you need to do is use the trim keys to adjust the trim ref speed until the pitch stays stable, just like how on a conventional aircraft you use the trim keys to adjust the hstab until the pitch stays stable. The other big advantage of C*U is that the aircraft only needs to be trimmed when changing speed. If changing configuration, like adding flaps, the system compensates automatically. Please see this video here for more info: https://www.youtube.com/watch?

Timestamp 12:50.
I have attempted to emulate this behavior.

So if the plane is pushing you down, you need to "trim up". So use the trim up keys to do that, which decreases the trim ref speed.

Essentially, pretend the law isn't there and you are flying conventionally a realistic FDM and for the most part, it will behave as you expect.

Kind Regards,
Josh
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Re: Announcing NEW Boeing 777 'Seattle' - Pre-Release

Postby Isaak » Sat Apr 20, 2019 9:50 pm

Thanks for the extensive explanation and the very good video. I completely understand the philosophy now :)
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Re: Announcing NEW Boeing 777 'Seattle' - Pre-Release

Postby Octal450 » Sat Apr 20, 2019 10:54 pm

Awesome! :)

Josh
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Re: Announcing NEW Boeing 777 'Seattle' - Pre-Release

Postby Isaak » Mon Apr 22, 2019 10:24 am

Hi Josh,

I did a flight from LEBL to EHAM just now with a copy I downloaded three hours ago. All went well and I 'm getting used to the C*U-law. I guess this will confuse some users who don't visit the forums, but it soon starts to feel quite natural and certainly adds to the realism. For me, roll control, flare override and the general normal logic all work as expected and can be pushed to FGaddon, unless you want to add more features before porting over.

Kind regards,

Isaak
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Re: Announcing NEW Boeing 777 'Seattle' - Pre-Release

Postby Octal450 » Mon Apr 22, 2019 1:15 pm

Hi Isaak,
Great too hear! I am going to try and add some overspeed and stall protections, then I'll bring it over

Kind Regards,
Josh
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Re: Announcing NEW Boeing 777 'Seattle' - Pre-Release

Postby biloute974 » Mon Apr 22, 2019 2:09 pm

Hello.
For me it works perfectly, the plane to a healthier, more realistic behavior.
I just have a big problem for several days, but it does not come from the 777, the multiplyer is disconnected regularly and it is uncomfortable when there is a controller.
One thing, I find that the flaps give too much stress to the speed during the takeoff phases, I do not know if what I say is quite explicit. For example, flap at 15, limit speeding too much.
Another thing, is it normal for the auto-throttle to activate itself during the takeoff phases?
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