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Boeing 787-8 for FlightGear 2.0.0, working, with Autopilot

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Re: Boeing 787-8 for FlightGear 2.0.0, working, with Autopilot

Postby redneck » Sat Oct 30, 2010 10:59 pm

Nice job. The only issue I had was that the plane struggles to climb beyond FL350. I had default payload, and only 10 percent fuel in the tanks.
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Re: Boeing 787-8 for FlightGear 2.0.0, working, with Autopilot

Postby nickyivyca » Sun Oct 31, 2010 1:21 am

Are you sure that you weren't just used to the old 787s? If you keep going and it's at 230 IAS, .9 throttle, and 100 FPM climb at 43000 feet then that seems like an accurate cruise elevation. I'll test it out myself still.

dany93 wrote:
nickyivyca wrote:....to retune the glideslope, which seems to be unsteady with the new elevator authority. The main problem is transition now instead of the main action-it will go all the way up, then all the way down when it first is enabled. I have to fix that obviously.

(I don't remember that we have changed elevator authority, which seems correct)
I observed this, and, if we speak about the same issue, I think that's neither due to elevator authority nor autopilot.
(I make these tests at KSFO, runway 28R, approach leveled flight 2000, 3000 or 4000 ft. GS beam is catched just before San Mateo Bridge.)
For the autopilot, gs-rate-of climb is the target (reference) given by NAV1 Glideslope for vertical-speed-fps.
If we activate NAV1 glideslope before the GS beam is catched, gs-rate-of climb (Int. Properties/Instrumentation/nav/) is static (steady) and I've seen it at any value (can be 96, or -64).This drives the autopilot to climb or steeply dive. When the GS beam is catched, the gs-rate-of climb can go to 200 then -181, before stabilizing around -20 fps. The autopilot tries to make the vertical speed to follow, but it works well: the problem is gs-rate-of climb, NAV1 glideslope must not be activated before the GS beam is catched.

Are your observations due to this?

Dany

I think that the problem for me was that I was intercepting the glideslope too far off of the correct altitude, which confused it. It performed quite well when I watched the little arrow before I clicked it in.
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Re: Boeing 787-8 for FlightGear 2.0.0, working, with Autopilot

Postby redneck » Sun Oct 31, 2010 1:39 am

Well, I may be used to the old 787s. I'm not used to having to climb at less than 1000 FPM above FL350. It's good that you fixed the flight ceiling though.
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Re: Boeing 787-8 for FlightGear 2.0.0, working, with Autopilot

Postby nickyivyca » Sun Oct 31, 2010 9:05 am

I just did some tests-it did seem quite undercruised. I couldn't use 4000 fpm climb at all, so I'll take a look into it. Service ceiling appeared to be around 38000 feet when I tested.
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Re: Boeing 787-8 for FlightGear 2.0.0, working, with Autopilot

Postby redneck » Sun Oct 31, 2010 4:38 pm

That's funny, b/c after takeoff I think I may have exceeded 4000 fpm, but I'd have to take a look again since the scale is nonlinear, and I'm used to the older 787 that could climb at about 6500 fpm.
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Re: Boeing 787-8 for FlightGear 2.0.0, working, with Autopilot

Postby dany93 » Sun Oct 31, 2010 6:59 pm

I tried. Nickyivyca is right, it can't climb continuously faster than about 3000 fpm with 80 % fuel (is it so bad?). 4000 fpm possible with 20 % fuel (which is not typical of of climbing after takeoff).
redneck wrote: but I'd have to take a look again since the scale is nonlinear

graduations are correct from 0 to 6 by step of 1 (x1000) fpm, but the intermediate digits (1 and 2) are wrong. They should be 2 and 4.

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Re: Boeing 787-8 for FlightGear 2.0.0, working, with Autopilot

Postby nickyivyca » Mon Nov 01, 2010 1:09 am

Moving the cruise alt up to 37000 feet in the FDM seemed to make things good. With my tests you're climbing at at least 1000 FPM until 36000 feet, when it starts to trail off. I'll make another release.

For 2.0/git users, anything that I need to know about? I've fixed what I've seen when I use it, but I only did a few tests with 2.0. I've fixed the Nasal problem, FYI.
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Re: Boeing 787-8 for FlightGear 2.0.0, working, with Autopilot

Postby Rick Ace » Mon Nov 01, 2010 1:51 am

I can't find the latest downloads :(
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Re: Boeing 787-8 for FlightGear 2.0.0, working, with Autopilot

Postby nickyivyca » Mon Nov 01, 2010 3:01 am

This is the version with the fixed cruise.

http://www.mediafire.com/?82944ju6z386szk

Hopefully it'll be the final release. BTW, I just uploaded the United livery to the livery site. How do you upload a paintkit?
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Re: Boeing 787-8 for FlightGear 2.0.0, working, with Autopilot

Postby dany93 » Mon Nov 01, 2010 5:22 pm

You've succeeded to get rid of this nasal error message. Thumbs up!

But I find again some bad behaviours that were overcome in the previous versions:
- some pitch unstabilites or roughness with autopilot driving, when changing altitude setting or during approach (catching glideslope). That's even led to roll unstablities (1 or 2 times).
- Also, in manual control, when moving from climbing to descent, this "hole" in elevator efficiency , followed by a pitch angle "jump"(like the old 787-8).
- At landing (150 kts, 20 % fuel), it's almost impossible to make a soft landing, even by waiting to be low above the runway to cut throttle, because the aircraft falls despite full rudder. The question is that I ignore the procedure for the real aircraft, but I don't like this and I can't believe it needs 89 % of full power to maintain 150 kts during final approach leg at 5 % glideslope.

From these points of view, I greatly prefer the last version (787V2-03, Oct 26, 2010). If this version is uploaded for the main site, I'm not sure to have brought anything.

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Re: Boeing 787-8 for FlightGear 2.0.0, working, with Autopilot

Postby nickyivyca » Tue Nov 02, 2010 5:01 am

I don't know why those things are happening, because it seems to be working fine for me. The FG versions can't be that different...I'll try replicating the problems when I have time.

In my tests, on the 3 degree glideslope at KSFO it needed 55% power for an approximately 15% fuel approach (pax/cargo standard). At 250 KIAS and fuel with wing tanks full, the autopilot seemed pretty stable, I'll do some more tests.

Elevator stall could be happening, I'll try to pinpoint the speed and lessen the problem. I also might be working with the approach if it seems needed, I have had some problems with light landings myself. The transition onto glideslope also could be happening oddly. I'll also do some comparisons with your latest version.

Test results:

-No elevator stall in climb to descent transition at 250 KIAS and 46% fuel. The only time I get it is with almost full flaps and over 220 KIAS.
-With about 55% power and 20% weight I have a standard approach.
-The only problems I have with the pitch autopilot is when you enter the glideslope with the AP far off the slope. The rest is fine, it is slightly rough, I do admit.
-I could touch down pretty lightly on landing.

I'll take the extra release change to slightly modify the speedbrakes code to include either gear instead of just the left one.

Post your solver results with yasim.exe to make sure our yasim.exe's are working on the same page.
Image
The first is the FDM modified by me, the second is your FDM without the tail ballast. This is not to compare the individual FDMs, but to make sure the results from each FDM match up.
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Re: Boeing 787-8 for FlightGear 2.0.0, working, with Autopilot

Postby dany93 » Tue Nov 02, 2010 6:34 pm

nickyivyca wrote:In my tests, on the 3 degree glideslope at KSFO it needed 55% power for an approximately 15% fuel approach (pax/cargo standard).

Sorry. My 89% was in leveled flight, and it came not from throttle but from from N1 = 87 (about 87 %, my calculation 87/98= 89%).
Throttle is better : 72% (leveled flight!) for you to compare. Elevator trim was -0.37 (elevator = 0). Conditions : 20% Fuel, Full flaps, Gear down, 150 kts.
In approach (3 degree glideslope at KSFO, same conditions than above), I agree with you, throttle was 55 - 56 %. Elevator trim was -0.37 (elevator = 0).
It seems that we do have the same aircraft. I hope not to have made you lose too much time with this...

I couldn't obtain solver results like yours. It gives an error message: [EDIT: see my next post, thanks to AndersG]
_____________________________________________________________________________________________
C:\Program Files\FlightGear\bin\Win32>yasim.exe
Usage: yasim <ac.xml> [-g [-a alt] [-s kts]]

C:\Program Files\FlightGear\bin\Win32>yasim.exe C:\Program Files\FlightGear\data\Aircraft\787\787.xml

XML parse error: Failed to open file
at C:\Program (SimGear XML Parser)
Solution results: Iterations: 0
Drag Coefficient: 1.000000
Lift Ratio: 1.000000
Cruise AoA: 0.000000
Tail Incidence: -0.000000
Approach Elevator: 0.000000
CG: x:-1.#IO, y:-1.#IO, z:-1.#IO

Inertia tensor : 0.000, 0.000, 0.000
[kg*m^2] 0.000, 0.000, 0.000
Origo at CG 0.000, 0.000, 0.000
_______________________________________________________________________________
I don't know where the problem is, and I'm not familiar with DOS writing. I've given above some data (throttle at leveled flight, elevator trim in approach) for comparison. I can give you more if you wish. At least, we agree for the 55% power in approach. I'll try again if you see where it comes from, if you need.

At 250 KIAS and fuel with wing tanks full, the autopilot seemed pretty stable

I agree.
But it's rough at 450 kts (Flaps 0, Gear up), up to red / black view at transitions.
And yes, flaps bring unstabilities (but we have to respect max speeds with flaps)

In manual control and climbing at 450kts, the aircraft seems to like going on climbing, it resists when pushing the yoke to go down. If we insist, it is rough, with the red view.

Elevator stall:
250 kts, 50% Fuel, Flaps 0, Gear up: no problem
Flaps 0.5 (15 deg), 20 or 50% fuel, gear down, 250 kts (too fast?), manual control: hole in elevator authority between climbing and descent. Refuses to go down, then goes roughly.
The elevator sometimes seems to lack efficiency. (for me, roughness is due to the autopilot)

I feel that the negative ballast gives pitch unstabilities and I don't understand its positive role. Why did you add it?

Landing (150 kts, 20% fuel, full flaps): I have to keep some thrust until the aircraft touches the ground to make a light landing. Is it the usual procedure?

Dany
Last edited by dany93 on Tue Nov 02, 2010 11:58 pm, edited 1 time in total.
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Re: Boeing 787-8 for FlightGear 2.0.0, working, with Autopilot

Postby redneck » Tue Nov 02, 2010 7:44 pm

dany93 wrote:But it's rough at 450 kts (Flaps 0, Gear up), up to red / black view at transitions.

I would hope it's rough at a speed that high. The plane isn't meant to fly faster than 360 KIAS.
dany93 wrote:In manual control and climbing at 450kts, the aircraft seems to like going on climbing, it resists when pushing the yoke to go down. If we insist, it is rough, with the red view.

Again, why are you testing it at speeds it should NEVER reach, at least with the wings still attached? It cruises at 484 KTAS. That's about 250 KIAS at FL400.
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Re: Boeing 787-8 for FlightGear 2.0.0, working, with Autopilot

Postby AndersG » Tue Nov 02, 2010 7:51 pm

dany93 wrote:I couldn't obtain solver results like yours. It gives an error message:

C:\Program Files\FlightGear\bin\Win32>yasim.exe C:\Program Files\FlightGear\data\Aircraft\787\787.xml

XML parse error: Failed to open file
at C:\Program (SimGear XML Parser)


The explanation is in the message "Failed to open file at C:\Program" - the space in the path is interpreted as the end of the first argument (the file name).
Put quotation marks around the path instead: "C:\Program Files\FlightGear\data\Aircraft\787\787.xml" .

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Re: Boeing 787-8 for FlightGear 2.0.0, working, with Autopilot

Postby dany93 » Tue Nov 02, 2010 11:55 pm

Many Thanks, AndersG!

For Nickyivyca: We have the same results from yasim.exe
______________________________________________________________________

787103110 (last Nicky)

C:\Program Files\FlightGear\bin\Win32>yasim.exe "C:\Program Files\FlightGear\data\Aircraft\787\787.xml"
Solution results: Iterations: 878
Drag Coefficient: 14.791077
Lift Ratio: 126.553314
Cruise AoA: 4.008032
Tail Incidence: -7.370983
Approach Elevator: -0.053839
CG: x:1.521, y:-0.000, z:1.240

Inertia tensor : 10835794.000, -0.016, 1777705.750
[kg*m^2] -0.016, 9426102.000, 0.000
Origo at CG 1777705.750, 0.000, 19604682.000
_________________________________________________________________________________

787V2-03

C:\Program Files\FlightGear\bin\Win32>yasim.exe "C:\Program Files\FlightGear\data\Aircraft\787\787.xml"
Solution results: Iterations: 590
Drag Coefficient: 14.929738
Lift Ratio: 172.599060
Cruise AoA: 2.160232
Tail Incidence: -3.259629
Approach Elevator: 0.039713
CG: x:-0.846, y:0.000, z:0.969

Inertia tensor : 9905441.000, 0.000, 1230656.750
[kg*m^2] 0.000, 16232541.000, 0.008
Origo at CG 1230656.750, 0.008, 25470368.000
______________________________________________________________________________________________
Dany
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