What's with the slow stabilizer lately?

So, in the end, do we concur that, while the animation of the control surfaces might be a bit slow, the aircraft's behavior in this regard is as it should be?

Sorry. Had to ask.

So, in the end, do we concur that, while the animation of the control surfaces might be a bit slow, the aircraft's behavior in this regard is as it should be?

 

Sorry. Had to ask.

Yes. I concur at least. :)

So, in the end, do we concur that, while the animation of the control surfaces might be a bit slow, the aircraft's behavior in this regard is as it should be?

 

Sorry. Had to ask.

It seems so, but it is indeed confusing. One of these days I noticed that, after pulling the stick all thee way back with the 'limiter override' (Y) on, trimmimg aft would make the stick move further back. Whether it actually effects maneuvering I don't know.

(stick was trim reset to center before doing that)

So, in the end, do we concur that, while the animation of the control surfaces might be a bit slow, the aircraft's behavior in this regard is as it should be?

 

Sorry. Had to ask.

Instantaneous performance of the Su-27, I never said it is not accurate as I have never tested it. Now that people have tested it, it's great that is really close to the chart.

What I have tried to explain in this thread (and I'm still trying unsuccesfully :D) is that the pitch control is too slow. Like, waaaaaaay too slow, not a little slow. The fact that when Su-27 is at 24deg AOA the turn rate is accurate is great. What I am saying is that when the stick is pulled quickly, it takes too long until aircraft reaches max AOA (or max G, depending on conditions). This post shows visually very well what I mean:

https://forums.eagle.ru/showpost.php?p=3253965&postcount=1

The difference in response in LJQCN101's videos between the two aircraft is absurdly large. Contrary to what some believe, the difference is not because of the canard on Su-33. Look how fast and animated the stabilizer on Su-33 is, on Su-27 it barely moves. Su-33 has a much much faster pitch response, despite the aircraft is heavier.

You're talking about the onset time now, which we don't have data for ... indeed that should be simply a question addressed to Yo-Yo.

Now I think I'm getting the concern.

I think the stick pitch damping parameters are located in FMoptionsSu27.lua

Great source of Su27 info: https://pictures.abebooks.com/isbn/9781857802474-us-300.jpg

Chapter 11.

Great source of Su27 info: https://pictures.abebooks.com/isbn/9781857802474-us-300.jpg

 

Chapter 11.

 

Yes, Yefim Gordon was the source I mentioned for the hydraulic information

Unfortunately there is no data about the flight control system.

I wonder if Yo-Yo is modeling onset based on pilot strength or something ...

I wonder if Yo-Yo is modeling onset based on pilot strength or something ...

I'm really not sure. It looks like the input damping for x and y is determined based on curve derived from load factor and dynamic pressure.

Speaking of x and y.

Does anybody know how the axis are aligned with the FM?

As I understand it: x = roll, y = yaw and z = pitch. At least thats how it is in the F-15 FM.

No idea. How are you certain for the F-15? From the moment of intertia and cg values in the fm options lua?

Thats where i got it from, yes.

I've been fiddling with them in the past and from memory thats how it is.

Roger that. I guess you’re aware then, those parameters aren’t in the su-27 fmoptions lua :(

I’d like to think the coordinate axis conventions are common across all FM but have no way of knowing.

Do you have any ideas on what the FCS variables represent in the su-27 lua?

affirm, they are not.

Don't know what the parameters in the -27.lua means.

And before i fill you up with bulls**t, let me just doublecheck the coordinates in the F-15 FM again, because they doesnt seem to pit with aerospace coordinates.

My previous post was, as i said, from memory.

EDIT: double checked, and the F-15 FM is indeed arranged like i wrote in my previous post.

Instantaneous performance of the Su-27, I never said it is not accurate as I have never tested it. Now that people have tested it, it's great that is really close to the chart.

 

What I have tried to explain in this thread (and I'm still trying unsuccesfully :D) is that the pitch control is too slow. Like, waaaaaaay too slow, not a little slow. The fact that when Su-27 is at 24deg AOA the turn rate is accurate is great. What I am saying is that when the stick is pulled quickly, it takes too long until aircraft reaches max AOA (or max G, depending on conditions). This post shows visually very well what I mean:

https://forums.eagle.ru/showpost.php?p=3253965&postcount=1

 

The difference in response in LJQCN101's videos between the two aircraft is absurdly large. Contrary to what some believe, the difference is not because of the canard on Su-33. Look how fast and animated the stabilizer on Su-33 is, on Su-27 it barely moves. Su-33 has a much much faster pitch response, despite the aircraft is heavier.

I've been away and noticed your post last night. Decided to run a few quick flights to take a closer comparative look. The results were interesting. Just passing them.

First, a quick description of how these videos were created. I made the initial flight in the Su-33 and saved the track. I then opened the track in the ME and changed the Su-33 to the Su-27 and adjusted fuel so that the gross weight matched the original as close as possible (within 50 kg). Saved the altered track. The videos were then generated. This guaranteed that the handling of the flight stick was exactly the same. It also guaranteed (unfortunately) that, once both aircraft were in motion, their trajectories were going to be very different. (Their pitch requirements also differ quite a bit.)

Sitting on the runway. Both horizontal stabilizers begin their motion simultaneously but the Su-27's motion then becomes constrained in discrete steps. (As a side note, I hadn't noticed that the Su-33's flaps and ailerons are also put in motion if the stabilizer movement is more than momentary until just this morning.)

Takeoff rotation and subsequent flight. I'll have to re-video this one. I hadn't been planning to use it but I think it's showing that, even at takeoff speeds, ram air is already being taken into consideration in the Su-27 to damp the pitch channel . It is not in the Su-33:

At flight speeds, ram air is definitely playing a roll in damping the pitch channel. The horizontal stabilizers hardly move in the Su-27. It seems not to be a factor in the Su-33. Don't know if both, one, or neither depiction is correct:

@Ironhand:

Man, those are some ingenious videos!

Regarding the take-off, I think that, besides the damping that you pointed out, one thing that's also playing a big role in making the Su-33 take-off sooner is it's much higher lift and authority at very low speeds (carrier ops aircraft).

After take-off and during the entire flight, we can also see that the Su-27 pitches up due to the infamous "airspeed trimming law" much more than the Su-33.

It's nice to see these videos with the two of them perfectly synchronized side by side!

@Ironhand:

 

Man, those are some ingenious videos!

 

Regarding the take-off, I think that, besides the damping that you pointed out, one thing that's also playing a big role in making the Su-33 take-off sooner is it's much higher lift and authority at very low speeds (carrier ops aircraft).

 

After take-off and during the entire flight, we can also see that the Su-27 pitches up due to the infamous "airspeed trimming law" much more than the Su-33.

 

It's nice to see these videos with the two of them perfectly synchronized side by side!

Thanks. I wanted to control for stick inputs and this seemed to be the best way to do it.

As far as the takeoff video is concerned, lift probably plays a part but I think the damping in the Su-27 has already come into play. I'm going to take another look at it in the morning. Hopefully I'll have a better video comparing the two aircraft then.

The Su-33 does seem to take much less trimming. I was trimming during its flight to keep the trajectory close to level. The Su-27 didn't seem to feel it was enough. :)

It seems to me that after the initial stick movement in the first video the resting point for the elevator is quite different (See snip below - Different amounts of trim ?), and that the Su-33 rotates faster at take off because of this, and responds from a higher AoA in the 'cobra' video also because of this.

the speed of movement looks pretty similar over that central part of the deflection in the first video (& in all return and downwards displacements), but the Su-33 gets to max deflection faster at least in part because it starts from closer to max deflection.

Canards? I don’t see how pitch rate and pitch response of an aircraft with canards can be compared to one without. Would you compare pitch rate / response of the F-15 S/MTD to the F-15C for example? No.

I don’t mean to debase your effort here Ironhand, I just don’t understand the relevancy.

Canards? I don’t see how pitch rate and pitch response of an aircraft with canards can be compared to one without. Would you compare pitch rate / response of the F-15 S/MTD to the F-15C for example? No.

 

I don’t mean to debase your effort here Ironhand, I just don’t understand the relevancy.

You can see in the video in flight that the stabilizers move up and down much slower in the Su-27 than in the Su-33. And coincidentally at the same time the Su-27 pitches up and down much slower than the Su-33. I wouldn't attribute that to the canards alone.

I'm not even sure the SU-33 FM is finished, so who knows how things compare. Only Yo-Yo can tell.

It seems to me that after the initial stick movement in the first video the resting point for the elevator is quite different...

Your observation puzzled me. I hadn't noticed it myself but it's there. I realized that I hadn't removed the curve from my joystick pitch axis for either aircraft. I set it to zero just in case that was a factor and re-ran the "test". Here it is in slow motion:

...the Su-33 gets to max deflection faster at least in part because it starts from closer to max deflection.

Both aircraft's horizontal stabilizers have 15° to travel to reach max deflection in the "up" direction. They only differ in the "down" direction. The Su-27 travels 15°, while the Su-33 only travels 12°, to reach max deflection. But I'm reading that off the ° markings on their respective fuselages. So I suppose that's no guarantee that the observation is correct.

Canards? I don’t see how pitch rate and pitch response of an aircraft with canards can be compared to one without. Would you compare pitch rate / response of the F-15 S/MTD to the F-15C for example? No.

 

I don’t mean to debase your effort here Ironhand, I just don’t understand the relevancy.

No debasement taken. :) For the moment I'm not in the least concerned with the pitch rate of either aircraft. This entire thread started due to an observation that real world Su-27s seemed to have a faster horizontal stabilizer response than we see in our sim's animation. The OP then pointed to the comparison videos Svend_Dellepude posted in his "FCS pitch response comparison between Su27 and Su33" thread as an example of the Su-33's stabilizer response being closer to that of real-world Su-27s. I don't know how SD generated his videos. I simply wanted to create side by side comparisons using a single set of stick inputs for each comparison. I found the results interesting and posted them.

What they show is that there are, at this moment, profound differences in how each aircraft's horizontal stabilizers respond to identical stick inputs. The Su-27's matches the -33's in the downward direction. The same is not true in the upward direction. Here they are very different. The Su-33's response is both faster and smoother in the upward direction.

I'm not even sure the SU-33 FM is finished, so who knows how things compare. Only Yo-Yo can tell.

I have no idea either. At this point, the Su-33 has no restrictions on the longitudinal channel while sitting on the ground. The Su-27 does. Pressing the "Y" key in this situation has no effect on the -33. It does on the -27. And once in the air, there never seems to be any change in the -33's stabilizer response. There's a huge change in the -27's. That might change for the -33 in the future. As you say, we don't know how "finished" they consider the -33's flight model to be. And, in the end, this is about the animation, anyway, not the flight model itself. They could just as easily have no movement displayed and the aircraft react just as they now do to stick inputs.

And, in the end, this is about the animation, anyway, not the flight model itself. They could just as easily have no movement displayed and the aircraft react just as they now do to stick inputs.

Yes, it could, but after seeing the videos I highly suspect ED is simulating aerodynamic forces on the aircraft based on the position of the control surfaces. This would mean that the aircraft is maneuvering as a result of the movement of the control surfaces (stabilizers, in this case).

Yes, it could, but after seeing the videos I highly suspect ED is simulating aerodynamic forces on the aircraft based on the position of the control surfaces. This would mean that the aircraft is maneuvering as a result of the movement of the control surfaces (stabilizers, in this case).

Could be, I suppose.