Su-27 in 1.5.5

[Bourrinopathe]

Thanks a lot for the feedback and the tests guys.

It's great so many things have been tweaked and fixed.

I'll have to wait until the stable release to check that update.

 

So now the basic autopilot "A" helps you land? Is that a specific behavior of the AP (like the dedicated one in the real Flanker) ? Or just the AP following the assigned flight parameters and the glide slope ?

I'm not sure how the real landing AP works though (some digging would be required).

 

(посад = посадка = landing)

Edited November 6, 2016 by Bourrinopathe

[DarkFire]

Thanks a lot for the feedback and the tests guys.

It's great so many things have been tweaked and fixed.

I'll have to wait until the stable release to check that update.

 

So now the basic autopilot "A" helps you land? Is that a specific behavior of the AP (like the dedicated one in the real Flanker) ? Or just the AP following the assigned flight parameters and the glide slope ?

I'm not sure how the real landing AP works though (some digging would be required).

 

Yes, the standard "A" autopilot will now successfully take you all the way in to a runway. Since the DCS Su-27 doesn't have the dedicated 'land' mode that the button suggests the real one does, I think they incorporated the capability in to the general autopilot function. Probably not entirely unrealistic since the navigation system is programmed with the position & orientation of most local runways anyway.

 

As Ironhand pointed out though, you have to be reasonably well within parameters for an AP landing to be successful, and the pilot still has to control the throttle manually.

 

One thing I'm not yet sure about is whether the AP that our DCS Su-27 has is capable of landing anywhere or whether it needs a Russian ILS for full functionality. I'm tempted to say that it simply works anywhere, so not quite realistic: I vaguely remember reading somewhere that the landing assist in the real Su-27 disengages either at the inner ILS marker or at the runway threshold.

Edited November 6, 2016 by DarkFire

[Ironhand]

A correction to my original post:

 

LALT-6 is actually Route Following Mode with your pitch stabilized to the pitch value at the time you enable the mode. So if you want a steady climb or descent with Route Following mode engaged, this is the mode to use. I've edited my original post.

 

I must have been trimmed to "0" pitch in my original test because I never lost or gained altitude while using LALT-6. Hence my misinterpretation of what I was seeing.

 

Do not use the AP at low speeds, if you're heavy, for landing. The result will not be pretty. Tried it with a gross weight of 28,000 kg and the nose started bobbing up and down severely as soon as I started down the glide path. The initial pitch down initiated an oscillation that the AP couldn't damp. You should be landing at that weight, anyway, but just mentioning it

Edited November 6, 2016 by Ironhand

[Esac_mirmidon]

The maximum landing weight for the Su-27 is 23.000 Kg. 28.000 is well over all maximums.

 

Landings with a max weight between 21.000 and 23.000 Kg are allowed but only if they are only 3% of the total landings of the airframe. This is because the tires maximum resistance.

[Ironhand]

The maximum landing weight for the Su-27 is 23.000 Kg. 28.000 is well over all maximums.

 

Landings with a max weight between 21.000 and 23.000 Kg are allowed but only if they are only 3% of the total landings of the airframe. This is because the tires maximum resistance.

:) Very aware of that. That's why my first test was with the 23,000 kg maximum rather than something higher.

 

That being said, Darkfire, if you want to land heavy (I used 28,000 kg) it turns out you can but the mission waypoints have to be set up very carefully to avoid rapid altitude changes just prior to capturing the ILS. And, even then, you'll likely have to manually dampen (with the AP still engaged) some oscillations from time to time. And you'll still probably break something. :)

 

Anyway, she's now much more enjoyable to fly. I still probably won't be using the AP much myself though.

 

EDIT: Spent a bit more time playing around with the AP. Here's a short (boring) track using "Attitude Hold" mode and "Level to Horizon" or Panic mode. If you decide to watch, I set Attitude Hold for a climbing turn. Disengage after a bit and climb vertically to a stall where "Level to Horizon" is engaged. Notice that "Level to Horizon" starts off with the same lit button as "Attitude Hold". Once it brings me out of the stall and the wings level the "H" button also lights and the combination very slowly brings me to level flight. These are the same two buttons that are lit for the "H" key. Only "H" brings you to level flight much more quickly for some reason.

Edited November 6, 2016 by Ironhand

[DarkFire]

:) Very aware of that. That's why my first test was with the 23,000 kg maximum rather than something higher.

 

That being said, Darkfire, if you want to land heavy (I used 28,000 kg) it turns out you can but the mission waypoints have to be set up very carefully to avoid rapid altitude changes just prior to capturing the ILS. And, even then, you'll likely have to manually dampen (with the AP still engaged) some oscillations from time to time. And you'll still probably break something. :)

 

Anyway, she's now much more enjoyable to fly. I still probably won't be using the AP much myself though.

 

Good points. For heavy landings I usually have the airbrake out and use higher throttle settings to compensate. For very heavy landings I usually come over the runway threshold at around 310 Km/h then chop the throttle as I flare. I certainly wouldn't trust the AP to do any of that but for regular landings at 20,000 - 23,000Kg (tops) the AP isn't a bad option.

 

Despite how user friendly the Su-27 is now compared to the old version of the ACS, I still don't consider it to be a particularly new-pilot-friendly aircraft compared to something like the Eagle or M2000.

[*Rage*]

Very difficult to read all this without being able to fly! I'm back tomorrow but I'm very excited about what I'm reading.

[Ironhand]

...

Despite how user friendly the Su-27 is now compared to the old version of the ACS, I still don't consider it to be a particularly new-pilot-friendly aircraft compared to something like the Eagle or M2000.

:) But much less prickly than it used to be...

 

Just want to point back to my previous post which I edited with an interesting (but visually boring) track using Attitude Hold and Level to Horizon modes: Post # 30

[DarkFire]

Very difficult to read all this without being able to fly! I'm back tomorrow but I'm very excited about what I'm reading.

 

A quick synopsis for you:

 

1. Cross-talk between roll & yaw is gone. Turning at any speed and any weight is now much more crisp and precise with no wallowing.

 

2. The AP is now functional down to much lower speeds, probably around 320 Km/h or even lower depending on weight. This means that landing using AP is now possible. Cruise with a full AA war load & full fuel is also now possible up to 12,000m altitude and beyond.

 

3. The adjusted AOA limiter will now protect you from over-G at any weight & at any speed. Turning off the AOA limiter using the W key gives you the same handling as the old version, i.e. no G limit.

 

Ironhand - Thanks, interesting track.

[*Rage*]

^^ Essentially fixed the Su27. Just beautiful.

[Stuge]

You can still break it with full roll + pull at high speed.. whether this will happen by accident to me or not remains to be seen :)

 

But yes after short testing it is much much better well done great fix!

[ebabil]

why does fixing a canopy visual take so long? other airplanes don't have this problem. is there another problem for fixing this?

[Ironhand]

why does fixing a canopy visual take so long? other airplanes don't have this problem. is there another problem for fixing this?

I imagine that it's simply a matter of resources and priorities. The most critical "bugs" or issues will get the resources first. It's sort of like a hospital emergency room. My son had severed the tip of his finger with a knife. I rushed him to the ER which was very busy. They told me the'd get to him within 20 minutes. Just as they were about to take him an ambulance rolled in with someone in much worse shape. To make a long story short, this happened time and again and it was several hours before they were actually able to deal with his finger. Something analogous is probably going on with the canopy.

Edited November 7, 2016 by Ironhand

[DarkFire]

You can still break it with full roll + pull at high speed.. whether this will happen by accident to me or not remains to be seen :)

 

But yes after short testing it is much much better well done great fix!

 

Multi-axis control inputs seem to generate a... suspiciously large amount of G compared to single-axis inputs. I'm not sure if this simulates additional airframe stress caused by differential bending moments applied to respective wings, or whether the cumulative G is slightly too high. In any case, ever since we got airframe damage modelling the old high-speed maximum barrel roll tactic for missile avoidance has become mostly fatal.

[DarkFire]

One other thing I've noticed with the new ACS is that the slight cockpit shaking that would start at around 18-20 degrees AOA can now start slightly earlier. Depending on speed etc. it can start at 15-16 degrees AOA. No more severe in amplitude than it used to be, so I guess it's even more useful now as a warning that you're approaching relatively high AOA and should consider easing off.

[Pocket Sized]

Multi-axis control inputs seem to generate a... suspiciously large amount of G compared to single-axis inputs.

 

This is most likely accurate. Pitch/roll coupling is a mysterious thing.

[Pocket Sized]

Also, a point about the new G limit behavior:

 

The over G warning buzzer/light are triggered at a consistent G level, always. They are tuned to be most useful in a typical dogfight configuration/GW.

 

But somehow it really feels like the G limiter varies with GW. This seems counterintuitive. Why integrate the fuel/stores weight into the FBW but not the G warning, even though the latter would be much easier to do?

[GGTharos]

WAG:

 

The FBW is there to shield you from something you cannot do in your flight sim: Sense g's. Likewise, most of us don't use an FFB stick so you don't get the stick shaker kick. Even with an FFB stick, the travel is so short and the forces so small that you could easily pull through, IMHO.

 

So, it's a compromise of realism of the warning system of that aircraft (AFAIK) and the FBW function. I'm not even certain that you should have a g-limiter at all, IIRC it was an AoA limiter only. Again, just off the top of my head here - I might be wrong about what the real limiter does.

[GGTharos]

It is most likely not accurate at all, IMHO. The reason here is that you're involving the same lift surfaces as you would in a straight pull-up.

 

I could be wrong, but I personally consider this to be an FM oddity.

 

This is most likely accurate. Pitch/roll coupling is a mysterious thing.

[Yo-Yo]

Also, a point about the new G limit behavior:

 

The over G warning buzzer/light are triggered at a consistent G level, always. They are tuned to be most useful in a typical dogfight configuration/GW.

 

But somehow it really feels like the G limiter varies with GW. This seems counterintuitive. Why integrate the fuel/stores weight into the FBW but not the G warning, even though the latter would be much easier to do?

 

The g-limiter preserves not the certain g-limit but the certain airframe stress forces. So it must be and it is set for it.

By the way - the limiter works on both AoA and g values.

[JunMcKill]

WAG:

 

The FBW is there to shield you from something you cannot do in your flight sim: Sense g's. Likewise, most of us don't use an FFB stick so you don't get the stick shaker kick. Even with an FFB stick, the travel is so short and the forces so small that you could easily pull through, IMHO.

 

So, it's a compromise of realism of the warning system of that aircraft (AFAIK) and the FBW function. I'm not even certain that you should have a g-limiter at all, IIRC it was an AoA limiter only. Again, just off the top of my head here - I might be wrong about what the real limiter does.

 

By the way, was repaired the problem with the FFB joys and the SU-27 trimming? I had to disable mine on Windows registry to fly the SU-27, two updates ago!

[*Rage*]

The g-limiter preserves not the certain g-limit but the certain airframe stress forces. So it must be and it is set for it.

By the way - the limiter works on both AoA and g values.

 

Thanks for the clarification Yo-Yo.

[DarkFire]

The g-limiter preserves not the certain g-limit but the certain airframe stress forces. So it must be and it is set for it.

By the way - the limiter works on both AoA and g values.

 

Thanks for the clarification about this. :thumbup:

[SinusoidDelta]

This is most likely accurate. Pitch/roll coupling is a mysterious thing.

 

With regards to flight testing I've seen this called a rolling pull out. Here's an ancient WWII document which mentions it.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930092856.pdf

 

A lot of the results on google are paywalled. There may be some documents available on DTIC. I haven't checked.

[JazonXD]

Not sure if this has been discussed already, but from what I've gathered, doesn't the real life ACS in the Su-27 is only calibrated for one weight configuration? So it doesn't care if you're max weight and 1.2M, it'll still let you pull over G and break your wings?