Author Topic: New FSXBA Hornet  (Read 1148903 times)

jimi08

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Re: New FSXBA Hornet
« Reply #525 on: November 25, 2014, 09:31:01 pm »
Peter,

To be honest, a few different techniques were used for different parts of the FCS.

PITCH AUTO TRIM:  Uses more of a simple "bang/bang" method.  It's simple and dynamic at the same time, but kinda of a rough way to do business in reference to preciseness.  Basically, the gauge trims the aircraft in two steps, all of this happens once the stick position is sensed to be within about 3% of center on the longitudinal axis.  Once this happens, they gauge looks at the amount of G currently on the aircraft.  If it is anything higher than 1.000 G, then nose down trim is commanded until it is below 1.000 G.  If it is anything lower than 1.000 G, then nose up trim is commanded until it is above 1.000 G.  Once the aircraft is about 1.000 G, the gauge then looks for pitch movement and corrects for it.  If at 1.000 G and the nose is still moving up, command down trim.  If at 1.000 G and the nose is still moving down, command nose up trim.  It does this about 18 times a second.  Because of this logic, the gauges is dynamic and will adjust itself to different weight/balance configurations.  Big difference is the time it takes to trim the jet.  With a nose heavy jet, it takes longer to trim the aircraft out in a nose high attitude and the nose sinks a bit more, due to the time it takes for the extra amount of trim that it needs to dial in to get to the correct setting.  Opposite happens with a tail heavy jet.  The nose tends to continue to travel upward a bit after releasing the stick due to the time it takes to dial in the needed about of downward trim.

ATC: Powered Approach (PA) Automatic Throttle Control (ATC) uses a PID Controller to calculate a precise value to the throttle using integrals and derivatives.  Although the output is very precise and results are quick, it takes a lot of time to tune and is not very dynamic.

G-LIMITER:  I have a few other basic formulas that I use for things such as G Limiters.

AUTORUDDER: The autorudder logic uses a combination.  While the aircraft is rolling, static values are calculated for and auto rudder based on aircraft speed and lateral stick input.  Once rolling has stopped and the angle of bank has been more or less been set, the autorudder shifts to a "bang/bang" method of rudder trim based on whether the aircraft is slipping or skidding.

I only have a basic knowledge of contact points.  I'll have to dig into that when I get some time.
« Last Edit: November 28, 2014, 03:02:11 pm by jimi08 »

Justin "Jimi" Hendrix
FSX Blue Angels
FSXBA F/A-18C Hornet Latest Download Link: http://www.fsdreamteam.com/forum/index.php/topic,6944.msg117011.html#msg1

hd764jvgd843

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Re: New FSXBA Hornet
« Reply #526 on: November 26, 2014, 10:32:21 pm »
Thanks for the explanations Jimi,

I have added the latest sheet with visual overlays to the contact points
- I do not really understand why the reference_datum_position is so much out of place - although it seems to work.
- I have corrected contact point values under the yellow highlighted 'New Hornet (mod)' which were most out of place, so probably impact on FCS should not be that much.

What do you all think of the new suggested contact points? Could they be used as a basis for further refinement of FCS and flight dynamics? I hope this sheet is of some help.

Peter

P.S.
- Found a typo, and did some late adjustments to tanks, engine and weapon cp's to be inside/nearer fuselage.
- I am not sure about the empty_weight_CG_position. I understand that it was changed to facilitate FCSs Pitch Auto Trim, but in my opinion it is placed too much forward. Instead of -27.00 it should be something like -32.00, the default -34.20 seems too much backward (does someone have more info about it?). Is there any way to compensate for a possible movement of its position? As you have explained, when moved backwards, auto trim is always working (aircraft is nose heavy) and the aircraft does not behave as expected.
- the empty_weight_cg_position being too much forward could be likely the reason why aircraft tips over easily during heavy breaking, too.
- I have included some larger top, side and front views with legend for better comparison.

(FA-18 contact points - 2014-11-27d, spreadsheet attached below)
« Last Edit: November 28, 2014, 12:57:19 am by hd764jvgd843 »

jimi08

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Re: New FSXBA Hornet
« Reply #527 on: November 28, 2014, 02:06:20 am »
Was doing a little digging and found this one pilot's inputs.  From http://www.airliners.net/aviation-forums/military/read.main/3592/

Quote
I flew the F-18 in the Navy for a liitle over 4 years. As far as G loading is concerned, the Hornet can pull very high G's. I pulled 9+ on a couple occasions. If it weren't for G-suits, there would be little chance of effectively flying the plane, simply because the centrifugal force would cause the pilot to "black out" and/or "red out".

The Hornet's handling characteristics are outstanding. The center of gravity (CG) is deliberately designed too far aft so as to make the aircraft inherently unstable. The plane is kept in check with a system of computer-based trim surfaces that constantly monitor and correct the airplane's attitude. The end result of such a design is sensational agility.


Not sure of the validity of the author, but seems legit.
« Last Edit: November 28, 2014, 02:19:59 am by jimi08 »

Justin "Jimi" Hendrix
FSX Blue Angels
FSXBA F/A-18C Hornet Latest Download Link: http://www.fsdreamteam.com/forum/index.php/topic,6944.msg117011.html#msg1

hd764jvgd843

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Re: New FSXBA Hornet
« Reply #528 on: November 28, 2014, 11:08:20 am »
Then I guess the original empty_weight_CG_position of -34.20 sounds about right, corroborating what he said, as it its behind the 1/4 chord which is the usual cg position for a normal plane or glider.

How did you come up with the -27.00 value, so the Pitch Auto Trim levels out exactly here? It seems to be 1/2 of the fuselage length, just coincidence?
« Last Edit: November 28, 2014, 11:19:20 am by hd764jvgd843 »

hd764jvgd843

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Re: New FSXBA Hornet
« Reply #529 on: November 28, 2014, 11:16:44 pm »
Hello Jimi,

just noticed an odd behavior. Aircraft (v14.15) is wiggling its tail, caused by rudders, moving slightly left and right trying to autocorrect. Oscillations are about 2-3 times per second. It is quite noticeable at higher speeds, at various flight conditions, with no stick input - see screenshot.

Peter

jimi08

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Re: New FSXBA Hornet
« Reply #530 on: November 29, 2014, 02:10:08 am »
Just flew it are a few various speeds (i.e. 600, 300, 150) and didn't really notice anything.  Have you modded yours at all?

Justin "Jimi" Hendrix
FSX Blue Angels
FSXBA F/A-18C Hornet Latest Download Link: http://www.fsdreamteam.com/forum/index.php/topic,6944.msg117011.html#msg1

hd764jvgd843

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Re: New FSXBA Hornet
« Reply #531 on: November 29, 2014, 03:10:09 am »
I've noticed the wiggling effect with my modded version first. Removed my mod and confirmed it is there with the out of the box 14.15 version, too. You can amplify it by reducing yaw_stability to e.g. 1.5 and setting rudder_trim_effectiveness to 1.0, but it is also noticeable with default settings.
When you toggle through the views stop at 'tail', zoom in to 0.8 and you can see the rudders moving like being caught in a kind of stable resonance. Get speed above 550, at low altitude, keep the plane level, take hand off the stick, and the rudders will wiggle a little bit.
I traced it back to the FCS Auto_Rudder.xml. It stopped when I replaced it with an old .xml of FSXBA version 12.3.2. Version 14.14 has the error too. But version 14.14 'Auto_Rudder last good.xml' does NOT have the wiggling, but autorudder behavior with that .xml is odd at high speeds, meaning too much rudder effect, one cannot do any clean barrel rolls.

For now I use xml out of version 12.3.2, which works fine, but does not show the visual rudder animations.

Peter
« Last Edit: November 29, 2014, 03:11:54 am by hd764jvgd843 »

jimi08

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Re: New FSXBA Hornet
« Reply #532 on: November 29, 2014, 05:11:41 am »
Well, in that case... yes you will notice wiggling if you mess with the yaw stability and/or rudder trim effectiveness.  As mentioned in a few posts above, the current auto rudder uses a few different logics to get the desired effect.  Part of that logic is the Bang-Bang method that I was talking about.  If the gauge senses a slide occurring, it will induce opposite rudder.  If it senses a skid, it will induce more rudder in the direction of the turn.  Because the gauge is always seeking coordinated flight, it will "wiggle" a bit while finding it.  I will tend to happen once you set the aircraft on a set bank angle.  The stability and effectiveness were adjusted to minimize the wiggling that occurs due to the gauge.  The default settings were 5.2 for yaw stability and  0.3 for rudder trim effectiveness.

The older system wasn't a dynamic system as this one is.  That's why you will not get the wiggling.  It was set on a basic algorithm that got the job done, but wasn't very flexible.  The one now is a dynamic one, constantly changing based on current situation.  It does a better job correcting based on a variety of bank and/or speed combinations.

Either way, I'll look into it.

Jimi

Justin "Jimi" Hendrix
FSX Blue Angels
FSXBA F/A-18C Hornet Latest Download Link: http://www.fsdreamteam.com/forum/index.php/topic,6944.msg117011.html#msg1

hd764jvgd843

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Re: New FSXBA Hornet
« Reply #533 on: December 02, 2014, 08:26:34 pm »
Here is the latest update of the modified contact points. Flight dynamics seems ok. To compensate for new fuel and station_load's cp's I have moved the empty_weight_cg slightly backwards.

If you like to give it a try, I have included .cfg and .air files for fsx, CS, and New Hornet versions. I have also reworked some of the weapons textures - add/replace into textures folder. Zuni's are yellow now.

I have also repositioned the tail hook, but have not yet have time to test it. Furthermore I am not yet fully satisfied with how the plane looks standing on the ground, although fsx and cs versions are ok, without changing the new cp's for the gear section.

Peter

(attachments below)

Jax

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Re: New FSXBA Hornet
« Reply #534 on: December 02, 2014, 11:56:30 pm »
Roger! Thanks. Heavily testing this bird!!! ::)
vRCAF
No.416/433 TFS

jimi08

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Re: New FSXBA Hornet
« Reply #535 on: December 13, 2014, 07:58:04 pm »
Gents,

Please find below the latest update for the FLEET BIRD, FA-18C_FSXBA2014 FLT14.16. 

Link: https://drive.google.com/file/d/0B3So3WwTLPRZRW1DRVFYOVB1MkE/view?usp=sharing

Changes include:

-Replace basic two-step algorithm with Proportional/Integral Device (PID) for turn coordination.  Allows for faster and more accurate response for autorudder  and fixes the "tail wagging" experience by some of you.

-Updated Thrust scalars...again...  Seems to be a never ending battle with this.  Tried a different profile than before.  The results are a much easier handling jet IRT throttle control.  Exact speeds are easier to maintain, and throttle control during formation station keeping is improved.  Still have work to do with re-adjusting afterburner thrust and thrust at altitude (35,000).  Will continue to work at it.

-G-Limiter adjusted to match closer to the 7.5 - 10.00 G range.  Previously the limiter would engage at approx. 6.5 G.

-Re-enabled the default autoflap programming for the leading edge flaps only.  Although the angles are slightly off, the overall logic of the scheduling is closer than what I currently can program (having problems programming leading and trailing edge flaps to schedule separate from each other).


That does it for now.  As usual any and all feedback is greatly appreciated.


-Jimi

Justin "Jimi" Hendrix
FSX Blue Angels
FSXBA F/A-18C Hornet Latest Download Link: http://www.fsdreamteam.com/forum/index.php/topic,6944.msg117011.html#msg1

hd764jvgd843

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Re: New FSXBA Hornet
« Reply #536 on: December 14, 2014, 12:34:34 pm »
Hello Jimi,

thanks for the update!

In the panel.cfg under the FCS section there is a G_Limiter gauge listed, but no xml file seems to be present in the FCS folder? Am I missing something here?

Some feedback concerning dry and wet thrust:

- I noticed that in .air file at No. 1523 "Turbine variable Inlet" is set to True. As far as I understand it it should be set to False in case of the FA-18. This setting had a huge impact when I accidently changed it within AirEd, doing my own mods and could not figure out why the aircaft suddenly had so litte power at high altitude above Mach 1+ speeds. When I noticed and reset it, things went back to what I expected.

- How did you come up with a fuel_flow_gain of 0.903 value? As I found no information on that so I left it unchanged in my mod.

- Doing some calculations on the F404-GE-402 for the inlet_area I came to a value of 4.1848 ft2 confirming to be very close to the original 4.2895 ft2. But it all depends on how fsx/the sim defines engine nacelle inlet area: a) nacelle inlet of the engine stand alone/blank, or b) nacelle inlet of the fuselage provided to the engine, for in RL they work in conjuction with each other? Lacking further detailed information, I decided to leave it as it is, to the original value here.

Length/Diameter (overall): 158.8/34.8 IN
Dry Weight:     2,282 LBS
Thrust (DRY): 11,950 LBS
Thrust (A/B):  17,700 LBS
SFC (DRY):       0.676    

- What do you think of the following setup? It perfecly matches performance at high altitude... but I am not sure how realistic it is for subsonic speed and acceleration at sea level.

Performance (At Maximum Takeoff Weight) F/A-18C/D:
- Max level speed: More than Mach 1.8
- Max speed, intermediate power: More than Mach 1.0
- Acceleration from 460knots to 920knots at 35,000ft: under 2 min (35,000ft: 460knots = Mach 0.79  ;  920knots = Mach 1.59)
See references posted here:
http://what-when-how.com/military-weapons/fighters-military-weapons/
http://www.fsdreamteam.com/forum/index.php?PHPSESSID=5igml7o8t6atmkmepmte2oadm4&topic=6944.435

Peter

(.cfg and .air provided below)

P.S. As I have not yet come up with a satisfying conclusion concerning the cp business, here is the latest update I have done so far, in case you are interested.
« Last Edit: December 14, 2014, 02:19:26 pm by hd764jvgd843 »

jimi08

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Re: New FSXBA Hornet
« Reply #537 on: December 15, 2014, 03:00:05 am »
Gents,

Two updates in one day for the Fleet Bird, FA-18C_FSXBA2014 FLT14.18!

Link:  https://drive.google.com/file/d/0B3So3WwTLPRZdUkzV2hxeHp6LUk/view?usp=sharing

Additional changes include:
-Another update to autorudder logic to include Rolling Surface to Rudder Interconnects (RSRI)
-M61 Cannon now available and functional in TACPAC enabled servers.

Justin "Jimi" Hendrix
FSX Blue Angels
FSXBA F/A-18C Hornet Latest Download Link: http://www.fsdreamteam.com/forum/index.php/topic,6944.msg117011.html#msg1

dreaminsight

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Re: R: New FSXBA Hornet
« Reply #538 on: December 19, 2014, 05:05:30 pm »
An appereciated update would be full TacPack compatibility ;D and  solving this stupid problem of the blue interiors. Otherswise the aircraft is perfect!

jimi08

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Re: R: New FSXBA Hornet
« Reply #539 on: December 19, 2014, 08:54:39 pm »
An appereciated update would be full TacPack compatibility ;D and  solving this stupid problem of the blue interiors. Otherswise the aircraft is perfect!

Well if you know how to incorporate full TacPack and want to show me how.... I'm all ears.

As for the blue interiors, are you running Direct X 10?

Justin "Jimi" Hendrix
FSX Blue Angels
FSXBA F/A-18C Hornet Latest Download Link: http://www.fsdreamteam.com/forum/index.php/topic,6944.msg117011.html#msg1