Errant slip indicator?

[Nealius]

Just getting into the Su-27 and I'm noticing the slip indicator showing quite a bit of slip. Page 115 in the manual indicates the Su-27 has a roll-yaw crossfeed system, yaw stability system, and yaw damper in its FBW laws. In this case I would expect to not see any slip on the slip indicator. 2+2=3 at the moment. What's missing?

Edited December 2, 2021 by Nealius

[Cmptohocah]

On 12/2/2021 at 3:25 AM, Nealius said:

Just getting into the Su-27 and I'm noticing the slip indicator showing quite a bit of slip. Page 115 in the manual indicates the Su-27 has a roll-yaw crossfeed system, yaw stability system, and yaw damper in its FBW laws. In this case I would expect to not see any slip on the slip indicator. 2+2=3 at the moment. What's missing?

 

I don't think the Flanker's modeled that well. But since I have never flown one IRL, I can't really make comparisons.

One thing that strikes me is that it's completely unstable airplane which is supposed to be FBW. You trim it for a straight and level flight, let go of the controls and it will sooner, rather than latter, either start climbing or descending on its own. Not to mention that a trimmed airplane is supposed to always tend to return to it's trimmed state, which our Flanker definitely does not do.

[Kilo]

3 hours ago, Cmptohocah said:

One thing that strikes me is that it's completely unstable airplane which is supposed to be FBW. You trim it for a straight and level flight, let go of the controls and it will sooner, rather than latter, either start climbing or descending on its own. Not to mention that a trimmed airplane is supposed to always tend to return to it's trimmed state, which our Flanker definitely does not do.

That's Russian flight control philosophy. The ideea was that a Western-style FBW law would confuse a pilot as to what his speed is, so the nose up/down behaviour was artificially modelled to give the pilot a sense of his speed. I would guess this would be less of an issue for us if FFB joysticks were mainstream, so that we could feel what the plane was doing...