News The Space Shuttle for Flightgear 3.6

[JMW]

Are you sure Donamy?

Right ones are far better for me.........

 

[DaveS]

Are you sure Donamy?

Right ones are far better for me.........

I agree, although the colors of the left MDU is more vibrant. The flat colors of the right MDU is more consistent with how they actually should look.

 

[Donamy]

Maybe a happy medium.

 

[Thorsten]

You gentlemen are missing the main idea behind this - it's a perception effect being modeled, which means they will not always look either this or that, they'll change appearance dependent on light level on the flightdeck and MDU brightness setting (and also the user-selected brightness and gamma filters for the renderer).

The colors on the left are intentionally over-exposed, because I'm trying to simulate high brightness setting with close to zero ambient light in the rest of the cockpit - so any screen set to full bright appears pretty radiant under these condition (technically, the contrast between the Airy discs and the unlit background is high and eyes are partially darkness-adapted). You can't see them like this during daytime, or with cockpit lights on (and I have also never seen any real Shuttle pics taken under these lighting conditions - because the rest of the Flightdeck is pretty dark...).

In contrast, colors will appear very muted and difficult to read if there's direct light on the display and it's not set to fully bright.

Which is to say, the displays will (intentionally) look poor and difficult to read if the brightness setting is not good, and you're not supposed to decide what you like better, you're supposed to use the brightness knob

 

[Gingin]

I am reading your topic since the beginning, impressive work and development :thumbup:

I am reading things on page 3 about FC Purge and how heating can affect the purge effectiveness, nice to see all the data form SCOM/Workbook in applications

 

[Thorsten]

Another big moment (for a fan of aerodynamics details like me at least) - I've managed to do the first full roll reversals using the NO Y JET mode in which the Shuttle is controlled only via elevons during entry.

Since this is one of the most fascinating bits of aerodynamics of the Shuttle, some context:

An airplane is usually yawed via the rudder and rolled via the ailerons, and the rudder is used to zero sideslip angle beta.

During entry and down to Mach 5 or so, the Shuttle has no rudder authority and is in fact yaw unstable, thus normally the yaw jets instead of the rudder are used to zero beta, and the rudder is only used for control below Mach 2.5.

Nominally the elevons can roll the Shuttle, this introduces some sideslip as well - which the jets have to null.

The NO Y JET mode controls yaw and roll without having jets available (it's the fallback mode for damaged jets or no propellant left) and lives purely off control cross-couplings.

The control sequence goes as follows:

* Initiating a roll using the elevons causes both a rolling and a yawing moment. The rolling moment is ignored and the yawing moment is used to move the Shuttle to a given sideslip angle and keep it there. This maneuver causes a small roll opposite to the desired direction.

* There is in addition a rolling moment due to sideslip, i.e. the larger beta, the larger the rolling moment - thus using elevons to maintain a finite beta value causes the Shuttle to reverse the rolling direction within a few seconds and to roll into the desired direction

* There is also a rolling moment due to roll rate, so one has to be extremely careful to not feed this mode too much by rolling at a high rate, otherwise the mode can't be damped, leading to an ever-growing roll rate and loss of control.

* There is also a yawing moment due to roll rate which needs to be constantly canceled out by the elevons (which are supposed to control beta to some value), causing some oscillations around the desired roll rate.

* There's also a yawing moment due to sideslip which also needs to be canceled, otherwise beta grows too large for the elevons to control

The resulting control is extremely ungainly and slow - but it actually works! It's like balancing on a needle - there's all these different unstable modes into which this could cascade down, but somehow the DAP keeps it under reasonable control... I still need to implement some filters to make it nice enough to had it to the entry autopilot, but it's fascinating to see 3-axis control over an unstable vehicle by elevons only.

 

[Gingin]

Amazing work once again ! :thumbup:

Nice to see that it works, it must mean that your aerodynamic model is really well tuned to observe some reactions like that.
As you said, it has to be slow with a lot of inertia, better anticipate when the next roll reversal will be needed

But still, controlling a whole entry from mach 25 until mach 5 with adverse yaw/induced roll using just elevons is indeed fascinating aerodynamically wise :thumbup:

 

[Thorsten]

Which is to say, the displays will (intentionally) look poor and difficult to read if the brightness setting is not good

Illustrating this, here's the opposite situation to the above - strong direct light into a screen that's not fully bright tends to make the display difficult to read (sun falling in through the rear windows):

But still, controlling a whole entry from mach 25 until mach 5 with adverse yaw/induced roll using just elevons is indeed fascinating aerodynamically wise

Not sure whether you can do a complete entry - the mode is certified from qbar = 10 psf and higher. If you have no yaw jets before that point, I'm not sure you can keep control (I can eventually test, so far I've only used it between 10 and 50 psf).

 

[Donamy]

I assume the light moves, if the shuttle rolls.

 

[Gingin]

Your screen looks very nice, nice lighting.

I am struggling so far with Flight Gear configuration, gonna have to read basics about the sim.
I am getting no MFD, all blacks


Yeah, it makes sense that with no dynamic pressure, elevons effect will be null in an almost non existing atmosphere, good point

Q bar of 10 happens around something like what, 200 kfeet?

 

[Thorsten]

I assume the light moves, if the shuttle rolls.

Sure - and changes color when in the atmosphere and the sun is low - it'd look silly otherwise

I am getting no MFD, all blacks

Version mismatch? Access permission problem? Reminds me of this one. If it's something different, your support thread is here, we're going to need the relevant error messages from the log file.

 

[Gingin]

Perfect, thanks for the link.
Should I downlozd it from in game add on menu or viz your repository?

Awsome screen, looks almost like in true cockpit with sunset/rise coming in.

 

[Thorsten]

Should I downlozd it from in game add on menu or viz your repository?

Generally the in-sim download gives you the latest milestone which is tested before release and in-sync with the manual.

The repository (development branch specifically) gives you the latest version with all features, but they'll be not documented and there may easily be breakage disabling a mission phase till someone notices. Also, you likely need to run the latest FG core development version to use it. Generally the devel version is more useful if you follow commit messages and are at least peripherally involved in development to have an idea whether what you see is temporary breakage or a longer-standing bug.

(If you do decide to clone the repository, consider a shallow clone, the full history is HUGE).

 

[Gingin]

Perfect, thanks.

I installed last version of FG, gonna try the download via FGadd on thing.
Finger crossed

 

[Thorsten]

But still, controlling a whole entry from mach 25 until mach 5 with adverse yaw/induced roll using just elevons is indeed fascinating aerodynamically wise

I've now tested that this actually works over the range. I've engaged NO Y JET at qbar = 10 psf, Mach number at this point was 25.4 I think, and I flew down using CSS in the roll channel as far as I could - at Mach 4.5 I started to see control issues with the roll becoming unstable and re-engaged LO GAIN which immediately stabilized attitude.

Leaving LO GAIN engaged, I could re-engage the AP in the roll channel and after some S-turn phase was flown into a nominal approach.

Being slightly long on the range helps - I suspect the rapid sequence of S-turns needed if you come in short is a nightmare.

The AP didn't utilize the NO Y JET mode properly yet, I guess it needs to be told that achievable roll rates are a lot lower...

 

[Gingin]

Very nice.

I suspect the rapid sequence of S-turns needed if you come in short is a nightmare.

Ahah, it has to be a lot of inertia and anticipation involved in that

I've engaged NO Y JET.....Leaving LO GAIN engaged,

And if you let Entry Mode switch on Auto, logic will switch automatically on No Y JET if AFT YAW RCS Failure is detected or you have to go manually to no y jet ?

Great Experience !

 

[Thorsten]

I suspect the rapid sequence of S-turns needed if you come in short is a nightmare.

I actually meant roll reversals... sorry, I slept badly last night, but everyone seems to have understood it anyway...

They're going to rather oscillating around the nominal trajectory. With a high sink rate, any roll reversal gives a sudden boost in lift - if you can carry it out fast, it can be caught by alpha modulation, but if you have a slow roll rate, you will rise a lot above the nominal trajectory, which you then have to compensate,....

If you come in long, you can essentially just hold attitude and gradually decrease roll... much better.

And if you let Entry Mode switch on Auto, logic will switch automatically on No Y JET if AFT YAW RCS Failure is detected or you have to go manually to no y jet ?

It's a feature in development - as they say, I can do my magic, but miracles take a bit...

It's the plan, but I don't know whether, say, one yaw jet is still enough to do the job or whether after loosing three it'd be a good idea to switch. CWS software is running fault detection anyway, so the information is there, I just need to decide how to make use of it.

Right now I'm glad I could demonstrate a viable entry, so give it some time to smooth out the hard edges

 

[Gingin]

Nice démonstration, don't worry I am not pushing, just curious

I just saw again the movie Space CoWboys,They do it also all manual for approach ahah

I forgot, what LO Gain stands for?

 

[Thorsten]

And if you let Entry Mode switch on Auto, logic will switch automatically on No Y JET if AFT YAW RCS Failure is detected or you have to go manually to no y jet ?

Okay, I did that one today, the logic should detect the failure of 3 yaw jets on one side and if the switch is in AUTO position automatically switch over.

 

[Gingin]

Nice fine tunning Thorsten :thumbup: