Bug in PFM? Canards change pitch when going >900km/h or <800km/h

Hi!

During regular flight, the canards should be more or less level. But as soon as the Su-33 goes faster than ~900 km/h, the canards will pitch up a few degrees and stay at that angle. This causes the plane to suddenly pitch up and it needs a big abrupt trim correction.

The canards only go back to the default angle when the Su-33 slows down to below ~800 km/h. This of course causes the plane to suddenly pitch forwards and it needs a big abrupt trim correction again.

Here is a video showing the behaviour from external view and cockpit. Look at the speed and the canard/aircraft pitching behaviour:

To me this seems to be a bug, or is this behaviour intentional?

Intentional. Normal control of fly by wire system depending on the speed.

But such a rapid shift? Pitch angle of the canards is either zero or instantly positive.

Shouldn't there be a smooth transition depending on speed, not ON/OFF?

Why should they go up at high speed at all? The plane needs even more downtrim then than it already needs at increasing speed.

To mimick positive stability. Would be nice to be smooth but hey these things weren’t even built with rwrs in real life

Why would the 33 suddenly need positive stability at high speed flying when the 27 flies just fine without canards? To me that seems like a waste of energy (higher drag).

To me that rapid change seems very wrong, the adjustment of the canards should be continuous and not ON/OFF. Flying in formation must be scary IRL if the DCS behaviour is correct, with Su-33 suddenly jumping upwards as soon as they reach 900 km/h.

Actually, the speed at which it occurs varies with altitude; it's not tied to a specific IAS, TAS, or Mach number. But at whatever airspeed it occurs, it is abrupt. I don't have a realworld manual for it, unfortunately, to see if there's anything on it. That said, the fact that it's abrupt doesn't make it a bug. There are a lot of things that seem odd that turn out to be correctly modeled with the Russian aircraft.

Thanks for the time Ironhand!

It might be worth politely asking ED, who knows we may get a nice response from Yo-Yo about the canards on the PFM.

There are a lot of things that seem odd that turn out to be correctly modeled with the Russian aircraft.

This needs to be sticky’ed on every sub forum. :D

Actually, the speed at which it occurs varies with altitude; it's not tied to a specific IAS, TAS, or Mach number. But at whatever airspeed it occurs, it is abrupt. I don't have a realworld manual for it, unfortunately, to see if there's anything on it. That said, the fact that it's abrupt doesn't make it a bug. There are a lot of things that seem odd that turn out to be correctly modeled with the Russian aircraft.

There's a lot of stuff in Western aircraft that's bizarre and illogical, too. One guy I saw the other day was saying Apaches have a form of stability augmentation intended to ''protect'' the pilots from errors, but it's prone to wigging out and randomly trying to kill you, ala the recent 737 MAX debacle. He said they warn you about it in training to always be ready for it to do that, but it's never been corrected or really highlighted so as to avoid disrupting supply and maintenance contracts + bad pr from admitting a ''mistake''.

I seriously doubt we are alone in whitewashing design... ummmmmm... ''quirks''.

That sounds very fishy. There's a reason why it isn't corrected, and it isn't going to be some BS reason.

:-)

You have a more generous view of corporate morals than I see evidence of them deserving...

From their point of view it's not a BS reason if it increases return to shareholder - that's what 'defence' companies exist to do...

Supplying equipment with which to defend the country is a means to an end, not the end in itself.

Thanks to some Republican lawmaker I can't remember the name of, company directors have for some years had a legal obligation to maximise returns to shareholders.

Social goods like better defence for the country or a safer flight for a pilot are not reasonable goals for a company to strive for beyond the point where achieving them generates additional revenue :-)

If refusing to acknowledge fault and labelling a software glitch a feature saves some millions in actual remediation costs, and possibly saves some billions in lost future earnings by avoiding reputational damage from publicity, that's the proper course for a board & their managers to take to the very outer limits of what the law will allow - even if it leaves service men and women vulnerable.

The bottom line is not BS to a defence contractor.

the canards control air flow across the wing. by taking that shape at high speed they probably greatly reduce the drag created by the wings. by reducing the airflow across them.

thus more than compensating for the increased drag of the canards.

would be my wild assed guess :)

That sounds very fishy. There's a reason why it isn't corrected, and it isn't going to be some BS reason.

Even a cursory overview of military history, particularly modern military industrial history will reveal literally thousands of examples of this very sort of thing. There are any number of reasons why stuff like that happens, and yes, they very often are indeed "BS reasons" related to money, politics, pride, etc. It's nothing new, and it's not something that no longer happens in "modern times" ;) A particularly well known example is literally the entire military production line of 1940s Nazi Germany, which was consistently hobbled by the ego and ignorance of Hitler and Goering. Nobody disputes that particular example, but it's hardly an outlier. This is all OT though, so I'll shut up ;)

Yeah. but the question is still pertinent and it should be answered with facts.. All these speculations and assumptions will stray us away from the truth.

I wonder what the most polite way to ask Yo-Yo would be? I would assume he knows best

I've PM'd him about it.