What's with the slow stabilizer lately?

[Weta43]

Still seems to me looking at your slow motion video that at 00:31 after you've released the stick the top stabiliser is flat while the bottom one is angled nose down - they start from different angles relative to the airframe.

 

Not saying this is the explanation, but if the deflection rate schedules are written relative to the aircraft's reference axis, but the elevators start at different places, the movements will rates from 'centred' will be different.

[SinusoidDelta]

The su-33’s CG is also much further forward due to several factors. The screenshots show how much further aft the Su-27’s tail boom extends. The su-33 also has an increased wing area. Non-split flaps, larger slats. These are two different airframes. I wouldn't expect the take off trim stabilator position to be the same for both aircraft when they aren't the same aircraft. IIRC in level flight the flankers stabilizer AOA should be ~0.

 

Yoyo would have to describe deflection rates response differences. I could make plenty of reasonable guesses as I'm sure many people reading this thread can.

 

Unless what I’ve read is false, the Su-33 is a fully digital triple or quadruple redundant FBW

 

This is unlike the Su-27’s which is partial analog FBW:

 

Source: (https://www.digitalcombatsimulator.com/en/products/planes/flanker_fc/?PAGEN_1=3

 

Referring to that link again,

 

 

Now, recall the variables I mentioned in the su27fmoptions.lua. Match them to the FCS block diagram and chart above (the others are in the Link)

 

I don't think it is essential Yoyo explain this to us. The dots are already there to connect. The lua is commented out, nothing seems obfuscated, we have the FcS diagrams and charts There's no reason you can't experiment with the values. I don't have any desire to edit the lua because I have no idea what the pitch response should be. No one does. If YoYo does, I don’t think he’s going to share that information. The Su-33 response ≠Su-27

Edited October 27, 2017 by SinusoidDelta

[PeaceSells]

^^ But the question of this thread remains: Is the slow pitch up/down response of the Su-27 realistic?

[Flow]

Kind of a thread jack, but looking for an answer.

What is the ideal IAS for best maneuvrability / close air combat in the Su-27 ?

Depending on aircraft weight, I believe it is in the 600 - 700 kph ?

[Ironhand]

Weta43, SinusoidDelta,

 

I think we're talking past each other. I'm addressing the speed of the stabilizer's upward motion and the fact that the sim Su-33's more closely mimics that of the real-world Su-27.

 

^^ But the question of this thread remains: Is the slow pitch up/down response of the Su-27 realistic?

The problem primarily exits in the upward direction. There's no inhibition in the downward direction. The FBW system is definitely kicking in and inhibiting the speed of movement in the upward direction. The swing upward begins quickly and, then, suddenly slows.

 

The sim Su-27 manual states that, when the longitudinal channel of the FBW system is in landing-takeoff mode, the stabilizer deflects in accordance with control stick inputs and rate of pitch. Sitting stationary on the runway the rate of pitch is zero. That being the case, pressing the "Y" key should have no effect because there should be nothing to "pull through". Yet it does. A final video. I'm not going to bother pointing out when it's engaged in the timeline. It's easy enough to spot.

 

 

 

 

Kind of a thread jack, but looking for an answer.

What is the ideal IAS for best maneuvrability / close air combat in the Su-27 ?

Depending on aircraft weight, I believe it is in the 600 - 700 kph ?

In a word, yes.

Edited October 27, 2017 by Ironhand

[SinusoidDelta]

^^ But the question of this thread remains: Is the slow pitch up/down response of the Su-27 realistic?

 

That's the million dollar question. And that's what I was saying. We don't know. No one knows. You can't validate a model if there is nothing to validate against. Control surface deflections are tied to aircraft behavior programmatically, however, what we are viewing in DCS is an animation of the model so while that may be correlated to a behavior it does not imply causation for a behavior. The stabilizer keeps being single out too when there are multiple control surfaces deflected. The leading edge slats for example play a HUGE role in pitch response.

[SinusoidDelta]

Weta43, SinusoidDelta,

 

I think we're talking past each other. I'm addressing the speed of the stabilizer's upward motion and the fact that the sim Su-33's more closely mimics that of the real-world Su-27.

 

 

The problem primarily exits in the upward direction. There's no inhibition in the downward direction. The FBW system is definitely kicking in and inhibiting the speed of movement in the upward direction. The swing upward begins quickly and, then, suddenly slows.

 

The sim Su-27 manual states that, when the longitudinal channel of the FBW system is in landing-takeoff mode, the stabilizer deflects in accordance with control stick inputs and rate of pitch. Sitting stationary on the runway the rate of pitch is zero. That being the case, pressing the "Y" key should have no effect because there should be nothing to "pull through". Yet it does. A final video. I'm not going to bother pointing out when it's engaged in the timeline. It's easy enough to spot.

 

 

 

 

 

In a word, yes.

 

This is how I interpret the longitudinal FBW. We've been provided a 1st order block diagram and the 3 control states have also been described verbally. The signal flow is unambiguous.

 

In LANDING MODE pitch rate is still fed through the damping transfer function. The assumption that LANDING MODE stabilizer rotation cannot possibly have (leading edge downward) damping is incorrect. The block diagram flow path tells us it absolutely can have damping in LANDING MODE.

 

 

Edited October 29, 2017 by SinusoidDelta

[Ironhand]

...

 

In LANDING MODE pitch rate is still fed through the damping transfer function.

 

 

Thanks for taking the time to produce these. If I understand you correctly, you're arguing that the diagram indicates that, with a pitch rate of "0", pitch rate still has a damping effect on the stabilizer.

 

:)

 

Someone forgot to implement that in these aircraft:

 

 

 

 

IDK. I remain unconvinced. But, then again, the above airframes could have a slightly different system. I just have a hard time understanding how nothing happening in Landing/Takeoff mode except for the control stick being moved (in the videos I created) can suddenly dampen the movement of the stabilizer, when the real deal in flight with their gear extended for landing display less damping than we see in the sim.

 

Or am I misinterpreting the meaning of "pitch rate" and the term simply means is control stick fore/aft movement even when the aircraft is stationary? But, anyway, I'm having a blast in this airframe regardless of how it's depicted.

[SinusoidDelta]

That is not what I’m arguing. That is an inductive assumption. We actually are closer to agreement than anything. The only thing I’m saying is that damping exists in this mode. Let me explain further. A block in a 1st order, control system block diagram is called a transfer function. The transfer function is defined by a curve. The curve and polynomial, along with its variables, are defined in fmoptions lua. The damping transfer function itself is what could be incorrect here.

[Ironhand]

Mmmmm... I don't think anyone so far in this thread has argued that the damping shouldn't exist at all in this mode. I think everyone is in agreement that it should. Rather, as you say, it's how it's displayed in the sim.

[SinusoidDelta]

Mmmmm... I don't think anyone so far in this thread has argued that the damping shouldn't exist at all in this mode. I think everyone is in agreement that it should. Rather, as you say, it's how it's displayed in the sim.

 

That’s the impression I was getting when you say:

 

Someone forgot to implement that (damping) in these aircraft:

 

 

 

 

Or this:

 

The sim Su-27 manual states that, when the longitudinal channel of the FBW system is in landing-takeoff mode, the stabilizer deflects in accordance with control stick inputs and rate of pitch. Sitting stationary on the runway the rate of pitch is zero. That being the case, pressing the "Y" key should have no effect because there should be nothing to "pull through". Yet it does. A final video. I'm not going to bother pointing out when it's engaged in the timeline. It's easy enough to spot.

 

This is all beside the point though. I’m only trying to help illustrate the FBW modes and the specific transfer function responsible for the behavior you are referring to.

[Ironhand]

...I’m only trying to help illustrate the FBW modes and the specific transfer function responsible for the behavior you are referring to.

And well done, too.