FG best developed airliner

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it0uchpods
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Re: FG best developed airliner

Postby it0uchpods » Wed Oct 04, 2017 3:34 am

Hi
I agree with what you say about the FDM, however, the post was mainly talking in the systems department, I do agree the 707 FDM is very strange, especially in the flight controls. (and that silly ground effect, feels like I lost half the weight of the plane at 20ft AGL)

I personally rate my airplanes using feedback from others, not every developer picks it himself.

I think there are a few major parts of FDM rating:
* lift/drag/inertia etc
* flight controls
* engine simulation
* balence

These all contribute to having a nice FDM.

I had to stiffen the flight controls in my A320 FDM to get the FBW response correct, so what I have planned is to use the stiffened controls for when FBW is active, and to use the realistic feeling controls when the law has degraded. Your thoughts on this idea @KL-666? That is one thing where the customization of JSBsim helps for it.

But flight controls isn't everything. Shotty performance in other areas (which the 738 definitely has) bring the total score back down.

I'd personally rate the 707 about a 2.5 star.
I'd rate the 738 FDM a 3 star. (maybe 3.5)

But because FG doesn't allow half stars, developers like to *round up* and show it off further.

As for my comment, I also meant it in a general way.

Regarding the YV738, I wanted to continue restoring the feel to it, but I never got around to it due to being busy with other things. Maybe I'll get to it one day.

Kind Regards,
Josh
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Re: FG best developed airliner

Postby KL-666 » Wed Oct 04, 2017 1:26 pm

Hi It0chpods,

I may understand this stiffening wrong. But to me it sounds like there is still direct control, but stiffened in way that it feels like FBW. I do not think you can catch all FBW characteristics this way. In the real plane there is software between the stick and the control surfaces which does more than only protect. Since we are in a software environment it should be possible to write such a separate software unit, which is then used less or not at all in a degraded law.

About the FBW doing more than only protect, will these things work with only stiffening the controls?

1) If a pilot yanks the stick e.g. left or right to the max, the software should think: Ah, the pilot wants me to make a roll to the max, so let's make a nice controlled roll to the max for him. As i understand the stiffening, it will not make the nice controlled roll.

2) If a pilot puts the plane in a turn with say 10 degrees pitch, and lets go of the stick, the plane should dead accurate maintain the turn and pitch. I suppose that only stiffening the controls maintains the characteristics of direct flight, and the plane will sink from it's pitch, though only a lot slower.

Trying to write a true FBW software unit may be extremely difficult. But if you still do it that way, and get only the main behaviours right for now, it is worth the effort, because then you or anyone else can perfect it more at some time in the future.

Kind regards, Vincent

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Re: FG best developed airliner

Postby it0uchpods » Wed Oct 04, 2017 2:09 pm

Hi Vincent
No, that's not what I meant (language barriar?)

I'll explain it further (exluding yaw):
UNDER NORMAL LAW:
* Roll is a rate demand
* Pitch is a G demand
* If stick is released, roll and pitch are maintained automatically by the system
* Autotrim is active

UNDER ALTERNATE LAW:
* Roll is direct to hydraulics
* Pitch is a G demand
* If stick is released, only pitch is maintained automatically by the system
* Autotrim is active

UNDER DIRECT LAW:
* Roll is direct to hydraulics
* Pitch is direct to hydraulics
* If stick is released, nothing is maintained by the system
* Pilot must manually trim

What I will add is:
The stiffened flight controls are in effect ONLY when the FBW is maintaining something. In normal, pitch and roll are stiffened, in alternate, only pitch is stiffened, and in direct, nothing is stiffened. When not-stiffened, the plane will feel much accurate, to the way the real plane does.

The stiffening is only active when my FBW PIDs are flying the flight controls, and this was done to get a more tight and responsive response from the system.

Writing the FBW init itself depends on the aircraft, The Airbus FBW maintains roll and pitch when released, so I just use rate based PID controllers, and a roll rate, pitch rate, and g-load commander which applies roll rate, pitch rate, and g-load commands from the sidestick input. In total, I have been working on my FBW system for over a year now, and it's become fairly accurate recently.

Once I have the system in to restore the "proper" feeling flight controls when the FBW PIDs are not active, I would like you to try it and let me know how the flight controls feel. (Should feel like a conventional aircraft without FBW) (The FBW can be downgraded at any time by going into the FBW settings, selecting the override for FBW mode, and selecting DIRECT)

Kind Regards,
Josh
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Re: FG best developed airliner

Postby KL-666 » Wed Oct 04, 2017 2:31 pm

Hi It0uchpods,

I clearly did not understand that you already made a very sophisticated FBW unit. I suppose the stiffening will contribute positively to the feel. I'll have to try when it is released. But i am not sure if i can say anything sane about it, because i never felt real airbus controls.

What i miss in your FBW description is the role of auto throttle. If remember correct from a far past reading, then with pitch, you go where you point the plane, and the the auto throttle makes sure the same speed is maintained.


Kind regards, Vincent

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Re: FG best developed airliner

Postby it0uchpods » Wed Oct 04, 2017 2:36 pm

Hi Vincent
OK, yes. This unrealistic stiffening is just to help the PIDs perform better under certain situations.

The autothrottle is not part of the FBW at all, it is part of the FMGS. If the A/THR is on, the autothrottle works exactly like in Boeings. The only difference is that the levers don't move, the levers define the Max-thrust the autothrottle is allowed to use. Hence, why the the lever is left in climb when the autothrottle is on, so that the autothrottle is allowed to use up to climb limit.

Kind Regards,
Josh
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Wecsje
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Re: FG best developed airliner

Postby Wecsje » Wed Oct 04, 2017 2:37 pm

@KL-666

Why don't you fly the plane now? There are no bugs, and everything that is implemented works. I fly it on VATSIM each day (atm still using route man, but soon the fplan page should be ready).

Regards,

Charlie (Wecsje)
IDG
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Contact methods: Discord (Wecsje#6351), FG Community Discord (https://discord.gg/DW23dnf), Steam (Wecsje)
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Re: FG best developed airliner

Postby it0uchpods » Wed Oct 04, 2017 2:41 pm

Because he dislikes scarebus' for reasons I still don't understand.

J
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Re: FG best developed airliner

Postby Wecsje » Wed Oct 04, 2017 2:43 pm

So what would be the point to wait until V1.0? It will only be more "scarybus", and now it is still simple to use, but later on you might want to read through the tutorial, or participate in the IDG sponsored A3XX training.

C.
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Re: FG best developed airliner

Postby KL-666 » Wed Oct 04, 2017 9:24 pm

Having fun guys? Well i do not mind giving a Scarebus a spin in a simulator. It is not really life threatening from my office chair. The reason i lately got very little time for things like trying out aircraft is this:

http://www.thejabberwocky.net/viewtopic.php?f=17&t=140&p=21902#p21902

After half a year intensively flying to all those airports, i will now take a sabbatical half year to recover.... Just kidding. But there will be dip in flying activity now. I will try that plane some time in the near future.

@It0uchpods
You are right about that auto throttle. It of course plays it's part fine from outside FBW. How could i forget! I must be a bit tired from all the flying.

Kind regards, Vincent

KL-666
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Re: FG best developed airliner

Postby KL-666 » Sun Oct 08, 2017 3:46 am

Alright, had a short time to give the a318 a spin. The die by wire seemed to be quite adeqate. A monky can fly the plane as airbus advertises.

There is just no way to activate the autothrottle. When pushing the speed selector button, it complains about setting something in the flight computer. This order of things is dead wrong. A flight computer may direct the autopilot, but it can never be limiting to the autopilot. If this limiting is in real scarbusses, then they are even more scary than i thought.

So, either please give me info on how to enable autothrottle without programming the flight computers, or i'm done with the excessive dangers of scarebus.

Kind regards, Vincent


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