Flight Model Comparisons

[MikeB54]

As you may recall, I mentioned in an earlier post that my son was coming home for the Holidays and I was going to get him to see how FSX compares to the real F-18.

We did that the other night and the results were interesting to say the least and not what I expected.

I started out by putting him in a cold and dark VRS Superbug.  One of his first comments was, "Is there any way to raise the seat?"  Simple enough in FSX to raise the eyepoint with Shift-Enter.  The problem then became the HUD.  It's not collimated in the Superbug so when we raised the eyepoint the HUD display stayed in it's original position.  I ended up having to tweak the default eyepoint in the aircraft.cfg to get things the way he liked it.  Thanks to Sludge and others who had a rather lengthy discussion about collimated HUDs in an archived post I found.  It was in that post where I learned that the HUD display position was based on the default eyepoint.  I was looking for how to change the HUD position but after finding that post it save me a lot of time.  His overall impression with the Superbug was kind of blase` but he isn't a big fan of the real F/A-18E/F either.

We moved on to the Sludge Hornet with the modified air file.  No problem with the HUD here.  Adjust the eyepoint and the HUD follows suit. There was one thing in particular that he didn't like.  When rolling out of a turn there is a pronounced pitch up.  I loaded the original Sludge Hornet and it did the same thing.  Just for grins I set up a flight with the default Acceleration F/A-18. 

Here is the part that was not what I expected.  As bad as I feel about saying this considering all of the hard work that Sludge and so many other have put into making the Hornet better, my son liked the default Acceleration flight model the best.  It did not have the pronounced pitch up when rolling out of a turn.  To put things into perspective, he had three wave offs in a row for being too high in the Sludge Hornet.  On his first attempt with the default bird he trapped.

Here is what he told me about how things should go on an approach.

1.  Use trim to set the desired AoA when on speed.
2.  Very little front/back stick should be required
3.  Use power to adjust your rate of descent.
4.  The E bracket shouldn't deviate much from the velocity vector once the proper trim is set.

Let me expand on number 4.  What was driving him crazy was that an increase in power would send the E bracket up with no corresponding increase in pitch and vice versa.


Mike

[Sludge]

Mike...

Actually, I couldn't have asked for a better "test subject" as this whole thread has been the goal of the "Sludge Hornet" from the jump. I've always wanted a real-world Hornet driver to fly her and tell me what worked and what didn't. I've noticed several points you talked about, including the "pitch up" when rolling out of a turn. I'm guessing the reason this happens is the auto-pitch that I have done with the .XML file. Also, was wondering about the approach profile and how that worked for the Legacy. Now when you say he used the default Hornet, you mean the straight up "no mods whatsoever" Hornet? The reason I'm asking is that the default Hornet is all AUTO-Flaps, whereas the Sludge is MANUAL-Flaps and is slower airspeed. Might have to go back to the drawing board but hey, thats what spring is for, right?!

Thanks for having your son fly the Sludge, its the ultimate test that I can ask for... and dont ever feel bad for saying he liked the default better. That just lets me know where I may have taken a WRONG fork in the road and what we can do in the future to make things better.

Later
Sludge

[MikeB54]

The pitch up rolling out of a turn happens both with and without the auto pitch enabled.  One thing that Chris didn't like was that with the auto pitch enabled the stabilator nose up was set to 34. Even though the Sludge Hornet doesn't do it, he says that if the stabilator was really set to 34 NU, which in reality it can't be because the max is 24, you would be doing a vertical 360 off the deck.  As he put it, if we want the Hornet to be as realistic as possible the trim should be set to 16 NU as specified in table 8-1 of the NATOPS.  Takeoff trim for field operation should be 12 NU.  The $100,000 question is, can trim sensitivity be set in the aircraft.cfg?  Tweaking the dynamics isn't in my area of expertise but it is something I would like to learn.  I renamed the base.xml file to disable the auto pitch and allow him more control of the takeoff trim.  From looking at the file that shouldn't have messed up too much.

Anyway, he leaves on Sunday so if there is anything specific you would like him to test, please let me know.

Mike

[Paddles]

Mike,
During your tests did you use vLSO? It would be really useful to have real pilot's opinion on this program. 
Thanks!

[MikeB54]

As a matter of fact, he did.   

He liked it but had a couple of comments.  He thinks it grades a bit tough.  There are times when you get a waveoff when the grade is in the "little" category.  i.e. A little low or a little high.  He said those approaches would be allowed to continue, especially if corrective action was taken. 

From what I can tell, in vLSO the waveoff will happen as soon as you deviate outside the "little" cone.  I don't know how hard it would be but if another cone could be added half way between the little low/little high and the low/high cone it would probably be more accurate. Especially since the cones are so small when you are "at the ramp".  Another comment was that unless you are in danger of a ramp strike you aren't going to get a waveoff at the 600' "at the ramp" marker.  At normal approach speed you only have about 3 seconds to touchdown and you would be hard pressed to arrest your descent in time to avoid an "in flight engagement".  From what he tells me, those are not only bad for the aircraft but are also rough on the pilot.

Mike

[Sludge]

Mike...

Anyway, he leaves on Sunday so if there is anything specific you would like him to test, please let me know.

Great, as I'm all up and running, I'll get some fixes out and see how they compare/contrast with the real world Hornet. Hope we can get a Skype session up at some point, so when he is flying a pattern, I can watch and possibly record for future reference.

As he put it, if we want the Hornet to be as realistic as possible the trim should be set to 16 NU as specified in table 8-1 of the NATOPS.

Yeah, the 34 NU auto-pitch on carrier cat-shot is an FSX workaround... it lets me set up the Hornet for hands-off stick cat shot (realistic?) yet as soon as you make a stick input you have direct control back. Whereas, if I program in AUTO Up-Trim... I have no way to put it back to reset the level flight trim. Will have to talk more about this and find the best balance between FSX-playable and what your son's real-world inputs are... remember, since I have no way to alter the inner workings (ie. the hard-coded stuff of the default Hornet; bad auto-flaps logic, etc.) of the FSX Hornet, I have to make certain consessions and many times do workarounds. So having his inputs will get me closer to realistic but will still have to be balanced within the constraints of FSX and a plane that isn't my own.

The $100,000 question is, can trim sensitivity be set in the aircraft.cfg?

Yes, it can... And no, thats not an Obama ripoff political statement. Its in the [flight tuning] section. Simply change the scalar back to 1.0 and you'll have default settings.

Later
Sludge

[Essex]

I have no way to alter the inner workings (ie. the hard-coded stuff of the default Hornet; bad auto-flaps logic, etc.) of the FSX Hornet

Sorry Sludge I don't understand this.
Surely the MDL is mainly cosmetic. In the past I've transplanted a MDL from one plane and used it with a different cfg & air file. I'm not saying I did a professional job of it, but the worst of it was changing the contact points and the flap parameters. Getting the launch bar to work properly may be difficult but who cares if it doesn't show properly? There's no holdback bar anyway.
In theory couldn't we start with just about any pair of cfg/air files (preferably twin engine etc)? I do realise this would be considerably more work, and don't ask me to recommend a plane to start with.
Or is it the VC that causes the problem? I know some planes have a separate MDL for the interior, but as I prefer 2D it's a bit academic for me.
Apologies if I've missed something critical.
Cheers

[Sludge]

Essex...

The whole default Hornet isn't just cosmetic, its the fa-18.dll that controls many of the internal functions of the default Hornet, whereas I'm simply coding .XMLs to get them to work with or around that base. Beyond the legal parts (that its Microsoft's plane), I don't realistically see how to "transplant" the inner workings of another jet into the MDL (exterior and/or interior) of the default Hornet.

Besides, if I knew that much, I would just get a team and develop my own Charlie Hornet. But thats WAYYY BEYOND my current skill level.

Later
Sludge

[Essex]

I seem to have missed something critical.
Needless to say I'm new to this whole thing.
Please keep up the good work.

[SUBS17]

Mike...

Great, as I'm all up and running, I'll get some fixes out and see how they compare/contrast with the real world Hornet. Hope we can get a Skype session up at some point, so when he is flying a pattern, I can watch and possibly record for future reference.

As he put it, if we want the Hornet to be as realistic as possible the trim should be set to 16 NU as specified in table 8-1 of the NATOPS.

Yeah, the 34 NU auto-pitch on carrier cat-shot is an FSX workaround... it lets me set up the Hornet for hands-off stick cat shot (realistic?)
Sludge

If you're refering to pilots not holding the stick on take off for a cat shot thats correct they do take their hand off the stick for cat shot. I've heard the other hand though is on the throttle throughout launch by someone a while back.

[MikeB54]

"Realistic" is exactly what Sludge is trying to do with his Auto Pitch mod.  What is supposed to happen is that on a cat launch the nose will pitch up, hands off, to 10 degrees.  The velocity vector will trail it, but catch up as the airspeed increases.

One big disadvantage we have is that the Hornet auto trims to 1G flight with weight off the wheels.  The VRS SuperHornet does that but the Acceleration Hornet doesn't.  I don't know if that is something that can be added or not but if it could it would make things a lot easier.

By the way, I have been playing around with the TrimEffectiveness settings in the aircraft.cfg.  A setting of about 0.7 (I have to fine tune that some more) seems to work very well.  On field takeoffs with the trim set to 12 NU the jet will fly off on its own at about 170 kts which Chris says is realistic.  Cat launches with trim set to 15 NU, which is as high as it will go, aren't bad but need some tweaking.  It also helped with the pronounced pitch up I was experiencing when rolling out of turns.  Keep in mind that when I was testing this I had renamed the base.xml file in the Sludge Hornet to temporarily disable the auto pitch.  The downside is that since there is no auto trim you really need trim buttons configured on your stick because you will be using them a lot.

On a slightly different topic, cruise performance is off, too.  Cruise AoA isn't specified in the NATOPS.  It mentions 2 settings; dash AoA of approximately 2.5 or lower and cruise AoA of greater than 2.5.  I set up a test where I was cruising at FL200 with an AoA of 3.2 and was only doing 0.45M.  Chris didn't have a specific number for me but said that was way too slow especially since I only had about 5000 pounds of fuel on board at the time.

Mike

[Sludge]

Mike...

Yeah, the auto trim is something that is being worked on by JIMI. He is definately doing alot of the ground work on that one... it's been testing well and might get adopted into the Sludge at some point. Will keep you updated on the progress there.

The trim stuff is something I'm debating about fixing the auto-elevator or just leaving it all to the pilot. Right now, I re-tweaked the Sludge to get closer to the default so that I can fix the "pitch up on roll out". Am getting a hold on the "why" just have to run a few more tests to make sure thats the cut-n-dry reason its pitching up. Here's a good question to ask Chris: on the auto-trim cat launch, does the trim "disengage" from its auto setting once the pilot takes over? Meaning... REAL WORLD... Hornet set at 12 NU TRIM, you do the cat shot and grab the stick, does the FCS sense this and dial the trim back down? This will help me determine if I can make an XML that would disengage the trim and go to an UA auto-trim flight state.

Also, the problem with cruise performance and speeds is also one of the biggest limitations of FSX. FSX accounts for pressure altitude but doesnt CORRECTLY compensate for density altitude. What you end up getting is decent performance up to 8-10k' AGL but then the power/altitude thrust curve falls off way beyond real-world. One of the things I've tried to do was get more real-world mid/high altitude performance from the Hornet, so that you can dogfight in the 20-30k range but with this FSX limitation it's very difficult to overcome. When I looked at the charts, the Hornet is supposed to be at max cruise efficiency around 36k. But again, because of the FSX pressure vs density altitude miscalculation problem, the default (and Sludge) dont fly well (underpowered) in that airspace regime. So that will be a down-the-line fix, when I can full wrap my head around that specific topic and the fixes given out at FSDEVELOPER.com site.

Later
Sludge

[jimi08]

Hey Mike,

As Sludge mentioned, I have been working on a somewhat elaborate Pitch Auto Trim system. It first trims to 1.0 G and then to 0 pitch rate.  It only does this once the the simulator has sensed that the pilot is not providing any pitch input (i.e. flight stick has been released).  Once pitch input has been sensed from the pilot, the trim zeros out and allows the pilot to control the Hornet as normal, and then goes back to re-trimming the aircraft once controls are released again.  I designed the autotrim system to only work when the landing gear is retracted, allowing the pilot to have full control of the trim for takeoff and landing operations.

Like the SLUDGE, my variant is a work in progress.

If you have the time, it would be great if you can check it out and give me some honest feedback (and anyone else for that matter). 

Here's the link if you are interested.
http://www.fsxblueangels.com/forum/viewtopic.php?f=91&t=4584

[GOONIE]

Regarding the trim, one feature I noticed in the super hornet sim, is when you adjust trim with your thumb on the stick, the trim value appeared on the HUD briefly. This was a helpful feature when in the pattern and getting the proper trim value set.

Mike, can you ask your son if the trim value shows up on the Charlie Hornet's HUD?

To the HUD developers on this forum, I think adding this feature to the HUD would be helpful in the pattern, instead of having to look for the trim setting on the checklist page, and since we don't have "seat of the pants" feel or stick force feedback in FSX or sim flying.

The trim value appeared on the HUD only when you changed it, displayed for about 2 seconds above the tacan distance in the lower right.

-CAPT

[SUBS17]

Hey Mike,

As Sludge mentioned, I have been working on a somewhat elaborate Pitch Auto Trim system. It first trims to 1.0 G and then to 0 pitch rate.  It only does this once the the simulator has sensed that the pilot is not providing any pitch input (i.e. flight stick has been released).  Once pitch input has been sensed from the pilot, the trim zeros out and allows the pilot to control the Hornet as normal, and then goes back to re-trimming the aircraft once controls are released again.  I designed the autotrim system to only work when the landing gear is retracted, allowing the pilot to have full control of the trim for takeoff and landing operations.

Thats how the FCS works in PA mode it requires more trim input but in UA mode the trim requirement is less as the FBW does it for you IRL. Its when you have dropped a store, fuel balance etc. That you actually require small amounts of trim from what I understand. FBW is not 100% auto trim in the case of Hornets/F-16 and Superhornet. We've had quite a few debates on this on other forums as to how much trim input is required and a few actual pilots have mentioned how much they had to input and when.