Board index FlightGear Development Aircraft

F-16 upgraded to 'production' status

Questions and discussion about creating aircraft. Flight dynamics, 3d models, cockpits, systems, animation, textures.

Re: F-16 upgraded to 'production' status

Postby redneck » Wed Mar 28, 2012 6:36 pm

Well, Idk about fixing the HUD. And I actually see no reason to change it now that I've managed to come up with a fix for the approach issue. I used the default fuel load, approaching at 166 KIAS (11000 lbs fuel, so 133 + 33 KIAS). Pitch at approach is about 3.25 degrees. The max pitch for flare is about 9 degrees. That's still kinda high though. I could just be flaring poorly due to the fact that I haven't flown this plane in a while. Maybe some of you more experienced virtual F-16 pilots can try this out.

See, I hadn't realized the speedbrakes were supposed to produce lift. In most planes, their only purpose is to produce drag, so I found it really odd that anyone would want to extend them while on approach. The shape of the speedbrakes convinced me further that they would not produce lift, since it was a split surface that deflected in both vertical directions, which I believed would produce equal lift in both directions, thus cancelling any upward lift. Anyway, it turns out that the speedbrakes are supposed to produce lift (at least I don't see any reason why they would be set up in the FDM to produce lift if they weren't supposed to). Furthermore, the amount of lift they can produce doesn't seem to be limited at all, like with the flaps and slats. So, I added a multiplier under the table. I had no idea where to start, so I went ridiculous, using a value of 10. It was quite funny to find that the increase in lift was so enormous that the F-16 was forced into a loop, and it became impossible to force the nose down at all when I extended the speedbrakes. They pretty much rendered the elevons useless. So, using 10 as my upper limit, and 0 as my lower limit, I began a process of bisection, or a binary search, to find a multiplier that produced plausible results. This process was actually VERY fast. So, here's your fix.

Open the FDM file, and search for "Lift_due_to_speedbrake_deflection". Under the table, but within the product tabs, add the following:
Code: Select all
<value>2.8125</value>

Approach with the speedbrakes extended, and enjoy!
Call Signs: redneck, ATCredn (unspecified freq atc)
FGFSCopilot
FGFSCopilotATCEdition
System Specs
Model: Alienware M15x, OS: Windows 7 Professional 64-bit, RAM: 3 GB, CPU: Intel i3 quad core at 2.4 GHz, GPU: Nvidea GeForce GTX 460M 1.5 GB GDDR5
redneck
 
Posts: 3630
Joined: Mon Feb 02, 2009 2:17 am
Location: Pennsylvania, USA
Version: 240

Re: F-16 upgraded to 'production' status

Postby mr_no » Wed Mar 28, 2012 8:41 pm

Sorry, that didn't work that well.
It gives a lot of lift all in wrong situations. It makes the plane not want to land.
My flaps solution still works better, but you do have to flare a bit.
Mosquito-XE JT-5B-autogyro Extra-300s STOL-Ch701
User avatar
mr_no
 
Posts: 362
Joined: Thu Jan 19, 2012 2:20 pm

Re: F-16 upgraded to 'production' status

Postby Ernest1984 » Wed Mar 28, 2012 8:46 pm

redneck wrote in Wed Mar 28, 2012 6:36 pm:Open the FDM file, and search for "Lift_due_to_speedbrake_deflection". Under the table, but within the product tabs, add the following:
Code: Select all
<value>2.8125</value>

Approach with the speedbrakes extended, and enjoy!


Hey!
This parameter works! But now, the speedbrake "power" is a little too big (nose is going quite much down but the lift is too big like mr_no mentioned). If i would like to make it a little less powerful, what i have to write there? 2.0000, or 3.0000 for example, in which "direction" i should go?
EPWA-hub: ERJ-195 clsgn: ERNIE
-----------------------------------
Around The World with B1900D!
callsign: AROUNDw - currently suspended till the FG will have a proper look on different locations
User avatar
Ernest1984
 
Posts: 438
Joined: Wed Dec 01, 2010 3:47 pm
Location: Poland / Canada
Callsign: ERNIE
Version: 2.10
OS: Mac OS X 10.8.2

Re: F-16 upgraded to 'production' status

Postby erik » Thu Mar 29, 2012 10:51 am

Just to add to this thread, the FC is it this time over compensating for the pitch-down moment caused by the speedbrakes. It's this effect that makes the rather small speedbrakes so effective but I expect that this is causing the high alpha that makes it hard to see the runway at the moment.

So to fix this the FC needs to be adjusted, not the lift or pitch tables.

Erik

Update; where I used FDM I actually meant FC (flight computer)
Last edited by erik on Fri Mar 30, 2012 7:37 am, edited 1 time in total.
erik
 
Posts: 1520
Joined: Thu Nov 01, 2007 1:41 pm

Re: F-16 upgraded to 'production' status

Postby redneck » Fri Mar 30, 2012 5:01 am

Ernest1984 wrote in Wed Mar 28, 2012 8:46 pm:
redneck wrote in Wed Mar 28, 2012 6:36 pm:Open the FDM file, and search for "Lift_due_to_speedbrake_deflection". Under the table, but within the product tabs, add the following:
Code: Select all
<value>2.8125</value>

Approach with the speedbrakes extended, and enjoy!


Hey!
This parameter works! But now, the speedbrake "power" is a little too big (nose is going quite much down but the lift is too big like mr_no mentioned). If i would like to make it a little less powerful, what i have to write there? 2.0000, or 3.0000 for example, in which "direction" i should go?

Hmm. I thought it seemed normal. I approached at 166 KIAS on the default load, and had no problems landing. Perhaps you guys are flaring too hard. Anyway, I doubt you'll be satisfied with that answer. To reduce the lift from the speedbrakes, simply decrease that value I posted.
erik wrote:Just to add to this thread, the FDM is it this time over compensating for the pitch-down moment caused by the speedbrakes. It's this effect that makes the rather small speedbrakes so effective but I expect that this is causing the high alpha that makes it hard to see the runway at the moment.

Actually, in my experience the speedbrakes actually force the nose up. If you don't believe me you can try what I did. Just as a little experiment, add a multiplier to the lift due to speedbrakes table of 10. Then, takeoff and get some altitude. When you extend the speedbrakes, the plane will pitch up very forcefully. The elevons will be completely overpowered, and the plane will fly a loop. You will have no vertical control until you retract the speedbrakes. That's the value I started with. I then worked down to the one I posted. Also, it seems you haven't read the complaints very will. The poor runway visibility on final was a result of approaching at speeds that would work fine in RL, but for some reason are too slow for this FDM. From that, I can only guess two possible variables responsible for this: lift or weight. I expect the weight is accurate. It should be much easier to find than the coefficients for the various lift functions for this aircraft. Therefore, I suspected that somewhere the lift was inaccurate.
Call Signs: redneck, ATCredn (unspecified freq atc)
FGFSCopilot
FGFSCopilotATCEdition
System Specs
Model: Alienware M15x, OS: Windows 7 Professional 64-bit, RAM: 3 GB, CPU: Intel i3 quad core at 2.4 GHz, GPU: Nvidea GeForce GTX 460M 1.5 GB GDDR5
redneck
 
Posts: 3630
Joined: Mon Feb 02, 2009 2:17 am
Location: Pennsylvania, USA
Version: 240

Re: F-16 upgraded to 'production' status

Postby erik » Fri Mar 30, 2012 7:40 am

redneck wrote in Fri Mar 30, 2012 5:01 am:
erik wrote:Just to add to this thread, the FDM is it this time over compensating for the pitch-down moment caused by the speedbrakes. It's this effect that makes the rather small speedbrakes so effective but I expect that this is causing the high alpha that makes it hard to see the runway at the moment.

Actually, in my experience the speedbrakes actually force the nose up. If you don't believe me you can try what I did. Just as a little experiment, add a multiplier to the lift due to speedbrakes table of 10. Then, takeoff and get some altitude. When you extend the speedbrakes, the plane will pitch up very forcefully. The elevons will be completely overpowered, and the plane will fly a loop. You will have no vertical control until you retract the speedbrakes. That's the value I started with. I then worked down to the one I posted. Also, it seems you haven't read the complaints very will. The poor runway visibility on final was a result of approaching at speeds that would work fine in RL, but for some reason are too slow for this FDM. From that, I can only guess two possible variables responsible for this: lift or weight. I expect the weight is accurate. It should be much easier to find than the coefficients for the various lift functions for this aircraft. Therefore, I suspected that somewhere the lift was inaccurate.


What you actually are doing with adding a <value/> tag is overriding the table with just one value. It is not a multiplier factor. And what you experiencing is the result of the tables (forces and moments) and the flight computer (over)correcting for it's result. Without disabling the flight-computer you can't say for sure which is the result of the coefficients (tables) and which of the flight computer.

Erik
erik
 
Posts: 1520
Joined: Thu Nov 01, 2007 1:41 pm

Re: F-16 upgraded to 'production' status

Postby erik » Fri Mar 30, 2012 7:44 am

redneck wrote in Fri Mar 30, 2012 5:01 am:
erik wrote:Just to add to this thread, the FDM is it this time over compensating for the pitch-down moment caused by the speedbrakes. It's this effect that makes the rather small speedbrakes so effective but I expect that this is causing the high alpha that makes it hard to see the runway at the moment.

Actually, in my experience the speedbrakes actually force the nose up. If you don't believe me you can try what I did. Just as a little experiment, add a multiplier to the lift due to speedbrakes table of 10. Then, takeoff and get some altitude. When you extend the speedbrakes, the plane will pitch up very forcefully. The elevons will be completely overpowered, and the plane will fly a loop. You will have no vertical control until you retract the speedbrakes. That's the value I started with. I then worked down to the one I posted.


What you actually are doing with adding a <value/> tag is overriding the table with just one value. It is not a multiplier factor. And what you experiencing is the result of the tables (forces and moments) and the flight computer (over)correcting for it's result. Without disabling the flight-computer you can't say for sure which is the result of the coefficients (tables) and which of the flight computer.

redneck wrote in Fri Mar 30, 2012 5:01 am:Also, it seems you haven't read the complaints very will. The poor runway visibility on final was a result of approaching at speeds that would work fine in RL, but for some reason are too slow for this FDM. From that, I can only guess two possible variables responsible for this: lift or weight. I expect the weight is accurate. It should be much easier to find than the coefficients for the various lift functions for this aircraft. Therefore, I suspected that somewhere the lift was inaccurate.

There you would be wrong, I have all data for the F-16 for up to 90 degrees angle of attack and I have more confidence in that data than in some gut feeling.
Erik
erik
 
Posts: 1520
Joined: Thu Nov 01, 2007 1:41 pm

Re: F-16 upgraded to 'production' status

Postby redneck » Fri Mar 30, 2012 1:36 pm

erik wrote in Fri Mar 30, 2012 7:44 am:What you actually are doing with adding a <value/> tag is overriding the table with just one value. It is not a multiplier factor.

Funny that jentron told me otherwise. And what he said made sense to me. If you multiply a bunch of properties, and then a table value, why can't you just multiply that by some value without having to plug in new numbers for the whole table?
erik wrote in Fri Mar 30, 2012 7:44 am:I have all data for the F-16 for up to 90 degrees angle of attack and I have more confidence in that data than in some gut feeling.

Interesting. Well, hey. I'm much more satisfied with real data than anything else too. So, if the data is accurate, than what about the sources these people are using for finding VREF? Is 133 + 3 KIAS for every 1000 lbs of fuel correct? Or should it be higher? Without any modification, I typically can't approach with the runway in sight if my speed is below 250 KIAS. That's WAY more than these guys' sources are saying for a full load!
Call Signs: redneck, ATCredn (unspecified freq atc)
FGFSCopilot
FGFSCopilotATCEdition
System Specs
Model: Alienware M15x, OS: Windows 7 Professional 64-bit, RAM: 3 GB, CPU: Intel i3 quad core at 2.4 GHz, GPU: Nvidea GeForce GTX 460M 1.5 GB GDDR5
redneck
 
Posts: 3630
Joined: Mon Feb 02, 2009 2:17 am
Location: Pennsylvania, USA
Version: 240

Re: F-16 upgraded to 'production' status

Postby erik » Sat Mar 31, 2012 9:03 am

redneck wrote in Fri Mar 30, 2012 1:36 pm:
erik wrote in Fri Mar 30, 2012 7:44 am:What you actually are doing with adding a <value/> tag is overriding the table with just one value. It is not a multiplier factor.

Funny that jentron told me otherwise. And what he said made sense to me. If you multiply a bunch of properties, and then a table value, why can't you just multiply that by some value without having to plug in new numbers for the whole table?

Jentron seems to be right although it seems a bit counter intuitive to me.
Defining a <value/> tag before the table defines an offset, defining a <value/> tag after the table is a multiplication factor..

Erik
erik
 
Posts: 1520
Joined: Thu Nov 01, 2007 1:41 pm

Re: F-16 upgraded to 'production' status

Postby Ernest1984 » Thu Apr 05, 2012 10:50 am

How to add a shadow to the airplane?
EPWA-hub: ERJ-195 clsgn: ERNIE
-----------------------------------
Around The World with B1900D!
callsign: AROUNDw - currently suspended till the FG will have a proper look on different locations
User avatar
Ernest1984
 
Posts: 438
Joined: Wed Dec 01, 2010 3:47 pm
Location: Poland / Canada
Callsign: ERNIE
Version: 2.10
OS: Mac OS X 10.8.2

Re: F-16 upgraded to 'production' status

Postby erik » Fri Apr 06, 2012 7:48 am

I think shadows come automatically with FlightGear 3.0

Erik
erik
 
Posts: 1520
Joined: Thu Nov 01, 2007 1:41 pm

Re: F-16 upgraded to 'production' status

Postby Ernest1984 » Fri Apr 06, 2012 9:18 am

But this will be in... When? ;)
I saw some planes have them now, so i suppose there's some script?
EPWA-hub: ERJ-195 clsgn: ERNIE
-----------------------------------
Around The World with B1900D!
callsign: AROUNDw - currently suspended till the FG will have a proper look on different locations
User avatar
Ernest1984
 
Posts: 438
Joined: Wed Dec 01, 2010 3:47 pm
Location: Poland / Canada
Callsign: ERNIE
Version: 2.10
OS: Mac OS X 10.8.2

Re: F-16 upgraded to 'production' status

Postby erik » Fri Apr 06, 2012 11:47 am

The intentions is to make 3.0 the next release. Some of the code is already in GIT. That's where the shadows come from.

Erik
erik
 
Posts: 1520
Joined: Thu Nov 01, 2007 1:41 pm

Re: F-16 upgraded to 'production' status

Postby Gijs » Fri Apr 06, 2012 11:51 am

Next release will be in August (but it could be that the shadows won't be included in that release yet, in which case they'll likely be in the February 2013 release).
I saw some planes have them now, so i suppose there's some script?

No script. Those aircraft have a semi-translucent 2D plane in their 3D model with the outline of the aircraft. With a bunch of animations, the plane rotates with respect to the aircraft to make it stick to the ground. But these are fake shadows: not changing shape when the sun-angle changes, only looking nice on flat terrain and not casting shadow on aircraft parts.

It does look better than nothing, but that's about it ;)
Airports: EHAM, EHLE, KSFO
Aircraft: 747-400
User avatar
Gijs
Moderator
 
Posts: 9365
Joined: Tue Jul 03, 2007 2:55 pm
Location: Amsterdam/Delft, the Netherlands
Callsign: PH-GYS
Version: Git
OS: Windows 10

Re: F-16 upgraded to 'production' status

Postby Philosopher » Wed Aug 15, 2012 9:34 pm

Hello,

I would like to help develop the F-16 and possibly work on an AFTI variant, but I need you to answer a few questions for me:
• Do I need a account on Git? If not, then how do I give you my changes?
• Do I need to be on the devel/mailing list?
• Is there some things I can start with? I would love to help, and I know how to do Nasal and model XMLs, but please don't have me work on the JSBSim aerodynamics. Bitte?? The FCS is fine, but I am not good at the aerodynamics, they are too non-intuitive for me, especially with the alpha and beta tables thrown in there.

I have already modified the ICP.ac file to have "thicker" buttons as I felt that was closer to the pictures on xflight.de. I also added pick animations (that actually move the buttons) and edited the switches.nas file to manage the buttons. They don't do much right now, but I have it so that the com1 button is always the opposite of com2 and they are both toggled by clicking either button. I did the same thing for the A/A and A/G buttons. The numerical buttons go down when pressed and spring back when released.

I also added a repeatable pick to the brightness slider to adjust the HUD brightness, but I didn't know what any of the other sliders would be on flightgear, such as contrast, symbology brightness, and reticle "DEPR" (depression?). The brightness slider also rotates upon adjusting the value.

All buttons that I animated use the pick animation to write a property (/controls/switches/[name]) that is "pick"-ed up (pun intended) by a listener set in switches.nas. Note: I will move the properties to /controls/switches/icp before I release it, or to wherever you feel is best, I just saw a switches parent node and jumped on it.

Thanks,
Philosopher (Callsign AFTI)
Thanks,
Philosopher
(inactive but lurking occasionally...)
Philosopher
 
Posts: 1590
Joined: Sun Aug 12, 2012 6:29 pm
Location: Stuck in my head...
Callsign: AFTI
Version: Git
OS: Mac OS X 10.7.5

PreviousNext

Return to Aircraft

Who is online

Users browsing this forum: No registered users and 2 guests