Su-27 Flight Model Discussion

[wasserfall]

Hardly conclusive proof. Look at his stick action. He makes literally hundreds of little corrections per minute!

 

Yes he does, but he didn't use the trim button, i don't call it proof just noticed it

[tagge]

Take a look at this video from the Su27 owned by Pride Aircraft.

 

Notice that the pilot never used the trim button!

 

 

Did you also notice he didn't enter the "upside-down shuttlecock of death"-phase and crashed...

 

:D

[GGTharos]

.. because he's a pilot who knows how to fly the aircraft.

 

Burn :D

[Nedum]

Hardly conclusive proof. Look at his stick action. He makes literally hundreds of little corrections per minute!

 

As I do + hundreds of little trim inputs.

The Stick moves in this vid are far less that big as in the DCS Su27.

Have you seen the start and the landing.

Do this in DCS and you will see that the stick moves need much more way.

The loop with this less stick moves were amazing in "our" Su27.

Our stick moves are more or less more at the limit/ we need much more stick way to do so.

A fine short loop with this less stick move would be great. It seems so that we need much more stick way for the same maneuvers as the real Su27.

Edited February 5, 2015 by Nedum

[Esac_mirmidon]

Compare the size of your home joysticks with the Su-27 real stick size.

 

Then you can start to understand the different movements and displacements.

[wasserfall]

The question remains why do we have to trim constantly, beginning after takeoff, gear up, flaps in, speed up, slowing down, and this pilot doesn't all of this, strange.

Any ideas?

[Ironhand]

As I do + hundreds of little trim inputs.

The Stick moves in this vid are far less that big as in the DCS Su27.

Have you seen the start and the landing.

Do this in DCS and you will see that the stick moves need much more way.

The loop with this less stick moves were amazing in "our" Su27.

Our stick moves are more or less more at the limit/ we need much more stick way to do so.

A fine short loop with this less stick move would be great. It seems so that we need much more stick way for the same maneuvers as the real Su27.

Not sure what you're referring to in regards to landing but, as far as taking off is concerned, he does the same initial "jerk" that I do (with the right airspeed) that lifts your nose wheel. Then the stick goes to neutral as you wait for the aircraft to start flying.

 

The loop starts at 800 k/hr (ends at 350k/hr) and the stick pull seems similar to what we do at that airspeed. Unfortunately I'm not at my home computer to double check. But, FWIW, the stick movement didn't seem strange to me.

 

The question remains why do we have to trim constantly, beginning after takeoff, gear up, flaps in, speed up, slowing down, and this pilot doesn't all of this, strange.

Any ideas?

I have the same question. A part of the problem is that we have no idea what iteration of the Su-27's FBW system is being modeled in our version of the sim. I imagine but do not know for a fact, that it has been refined over the years.
Edited February 5, 2015 by Ironhand
clarify a statement

[Svend_Dellepude]

At least two times in the climb at 5:20 and 5:58 the pilot has his thump on the trim button.

[Demongornot]

About the trim, the thing is, i think we need to trim because our joystick have springs to come back to the center, but i think that in the real Su-27 there is no center like this, or maybe it is really light and comfortable and don't require the pilot to fight against it, which is probably why they do flight without trimming !

 

Not sure about it, but it look like it, so rather than trimming the aircraft to flight straight while having the stick center, they center their stick where its needed to flight the aircraft straight...

 

And also unlike a lot of aircrafts that use a small trim tab, on this kind of aircraft (a lot of jet fighters) trimming change the default center of the joystick apparently, even if i'm not sure about how it work on the Su-27, but i'm sure it is in fact different from what we have with our PC joystick that only have a non mobile center point, we need more info on how the trims system work on this but it don't surprise me that real Su-27 pilots don't need to trim.

 

This aircraft is really unstable by nature and unlike F-15 and F-16 he don't have auto trim ! So yeah it also don't surprise me that we need a lot of trimming in DCS, personally i only barely trim it and then do the correction by hand !

 

And i won't be surprised if you told me that this aircraft totally loose control if you happen to release your joystick...

Someone know how behave the real Su-27 Stick here ?

[PLP]

Don't forget that the trim is mostly needed for spring-loaded joysticks. I haven't trimmed a plane since I started using my DIY pure-friction-no-spring stick, and I've almost forgotten all about the Su-27 negative g of death too.

 

I guess that the problem with some DCS modules is that it is hard to handle situations where a huge force would be needed to move the joystick without using ffb technology. Also not sensing g's removes some natural apprehensions I guess.

[tagge]

.. because he's a pilot who knows how to fly the aircraft.

 

Burn :D

 

Touche!

[OnlyforDCS]

The question remains why do we have to trim constantly, beginning after takeoff, gear up, flaps in, speed up, slowing down, and this pilot doesn't all of this, strange.

Any ideas?

 

Im sorry but from watching that video the only objective impression I got from it is that the pilot DOESN'T like to use trim. He could have used it but instead likes to fly hands-on-stick and from the way the aircraft jitters and jerks he doesnt seem to care about keeping it as stable as possible.

 

This video only further reinforces the fact that we have a great PFM in the Flanker.

[wasserfall]

Im sorry but from watching that video the only objective impression I got from it is that the pilot DOESN'T like to use trim. He could have used it but instead likes to fly hands-on-stick and from the way the aircraft jitters and jerks he doesnt seem to care about keeping it as stable as possible.

 

This video only further reinforces the fact that we have a great PFM in the Flanker.

 

How do you know he doesn't LIKE it??, i just observed the fact that he didn't use it, and i like to know why

No conclusions from my side, only curious why.

[Bimbac]

It's not about liking or not liking the trim. The original idea about the trim was to neutralize the forces, which act on control surfaces during the flight. So technically, you don't have to use the trim at all, if you're willing to fight those forces all along, but it can be really uncomfortable during long flights. In modern FBW planes, the FCS trims the airplane for you, so you don't have to touch it, but the airplane still requires the trimming, only difference is that it's not the pilot, who does it.

 

My English is little rusty, so I hope you got the picture, even by my clumsy explanation.

[OnlyforDCS]

How do you know he doesn't LIKE it??, i just observed the fact that he didn't use it, and i like to know why

No conclusions from my side, only curious why.

 

It's an assumption. I don't know why he's not using trim but he's not using it, which is the main point.

[tagge]

It's an assumption. I don't know why he's not using trim but he's not using it, which is the main point.

 

“When you assume correctly, the ass is not u, but me.” - Gerard Caulfield on Assumption

[Demongornot]

I've just perform a test flight on the virtual aerobatic server with the Su-27 without using trims and in direct control only, well it flight very well, at first is seam hard but we accustom really fast and it become easy, in fact i haven't got any issue with negative G to crash !!!

 

I have crash three times, one cause i was playing performing Cobra too low at a wrong diving angle, so 100% my fault.

Second because i have misjudge my visual approach and i was too low, i touch the ground before the runway (not wanted to abort my landing), which have conduct to landing tires explosion and the left engine have not appreciate the impact and was not responding anymore, not a real crash, more a crash landing (i was able to walk away from :D)

And the third was another fail way too low cobra !

 

But it look like in direct controls we need way less trims, i was only slightly compensating, with FBW we need to trim way more apparently, so it look at the flight model is good, in fact this is way more fun for me to flight without FBW, i'll try this in combat, without trims i never get risk to this negative G of death !

I had once this minus 90° stuck position, and i've simply put one engine at idle and the other at 90% or something like this without AB and i was able to recover without problems, even if it had happen to me lower than 5000m, but it was my fault cause i was playing doing high AOA flight experiments !

 

So if there is any problem with the need to trim, it come from the FBW, the flight model itself is fine !

[Frostie]

A few of observations, the fact 99% of users of this flight model have self centering sticks makes flying this sim a pain in the ass.

 

The Trim to Stick button is currently useless, if it worked a'la Ka-50 then this would go some way to improving the previous issue.

[Gaanalma]

I do not know 'if it happens to other, but it is really strange ... if I remove the power trottle, the plane, instead of slowing down and point down, starts to pitch up ... not a bit' strange?

[combatace]

I do not know 'if it happens to other, but it is really strange ... if I remove the power trottle, the plane, instead of slowing down and point down, starts to pitch up ... not a bit' strange?

 

If you throttle down any plane it will try to pitch up. It will do so to increase lift at slow speeds.

[Gaanalma]

At 900 km/h?

[Andrei]

Important thing to keep in mind with the new Su-27 is that:

a) The plane is designed to have neutral stability in the pitch

b) The "FBW" is not your classical FBW that you find in Falcon and Hornet. It's analogue and set to mimic the behavior of the plane that is stable in the pitch axis.

 

Thus, you can imagine that you're flying in the old good Cessna 172. You are trimmed in the horizontal flight, you add throttle, airspeed is rising -> you get a pitch up. Same in Su-27 with the exception that the pitch up moment comes with greater magnitude.

 

The key to a normal flight in Su-27 is quite simple: trim, trim, trim and very gentle stick movements. On my X-52 pro I set the curves for pitch and roll to 15. And my trim buttons are where I can easily get to them with minimal effort. Results in very smooth flight.

[DarkFire]

Sorry to bump this, but can anyone comment on whether this behaviour is realistic? Anyone else see this?

 

Something that I've noticed since the last patch is that below 900 kmh IAS applying bank and returning the control column to neutral results in the aircraft returning to level flight, i.e. the bank angle gradually reduces back to zero, however above 900 kmh IAS this behaviour is not exhibited.

 

I mention IAS specifically as it does not appear to be dependant on TAS or SOG, only on the indicated airspeed.

 

It feels as though if the pilot applies bank the FCS applies an opposite control input, requiring the pilot to maintain a steady stick input for a given bank angle. Is this correct behaviour or an artefact? I feel that this increases my pilot workload at the worst possible times, i.e. low speed close combat, flying accurate landing patterns etc.

[Andrei]

Sorry to bump this, but can anyone comment on whether this behaviour is realistic? Anyone else see this?

 

I thinkit might be due to the fact that at supersonic speeds the aerodynamic focus shifts, thus changing the plane behavior. I'll try asking at the Russian side of the forums - they have flight dynamics guys answering pretty often there. They'd know better.

[DarkFire]

I thinkit might be due to the fact that at supersonic speeds the aerodynamic focus shifts, thus changing the plane behavior. I'll try asking at the Russian side of the forums - they have flight dynamics guys answering pretty often there. They'd know better.

 

Thanks, much appreciated.