Impossible to fly for anyone else?

[Solway]

pilot mind and good grades are the best limiters :)))

Edited June 9, 2015 by Solway

[GGTharos]

Yes, it's pilot training. Virtual pilots pull -g all over the place. Real fighter pilots don't, it destroys your +g tolerance at minimum.

 

Doesn't the real aircraft have some kind of limiter to stop the pilot from pulling too many - Gs

[Mr Whippy]

Yep. It's up to you to understand how an aircraft behaves and flies. No matter what the FBW does, it can't change physics.

 

I don't expect the FBW to change physics.

 

But I'm still curious why you'd desire such overly sensitive controls in given flight conditions when you could instead have them not overly sensitive.

 

Ie, if the aircraft wobbled about somewhat and the not unsubstantial forces on the arm would move the stick enough to propagate a feedback loop.

 

Unless again this is a limitation of our non-FF sticks operating in 1G downwards conditions while sat at a computer and stationary.

 

 

So to summarise. At 30.000ft and TAS of say 400kts, the Su27 controls input range is about 10% useful, with the other 90% just range that will mean you get too much AoA and lose control?

 

So the pilot has to increasingly finely balance inputs under very high g forces, with a big waggly stick that flaps around, to the point it may feel like it's on a hair trigger, vs at 10,000ft at the same TAS?

 

 

I'm more than happy to accept this is the way it is, if it really is. I just can't see what pilot or engineer would see virtue in that behaviour if they can get rid of it.

 

Dave

[Esac_mirmidon]

Not only training. There is also a mechanical AoA - G limiter. The system is there to help pilot's training.

[IonicRipper]

3. pls share your experience what jet AC aerobatics do you make with such negative overloads (I really do not know any ones) when she goes to inverted stall. I think it was a pilot mistake.

 

It certainly was a pilot mistake. I was trying to dip the nose down to avoid an incoming missile. I didn't realize I was pulling so much negative G by doing so.

[pepin1234]

The Su-27 tend to blackout every time we try to maneuver. Even when is a simple turn. With the F-15 does not happen even when they have more G. No clue here...

[GGTharos]

But I'm still curious why you'd desire such overly sensitive controls in given flight conditions when you could instead have them not overly sensitive.

 

It isn't over-sensitive for me.

 

Ie, if the aircraft wobbled about somewhat and the not unsubstantial forces on the arm would move the stick enough to propagate a feedback loop.

 

There is feedback last I checked, you just have to fly the aircraft such that you don't just spike right past this feedback and straight into a departure.

 

Unless again this is a limitation of our non-FF sticks operating in 1G downwards conditions while sat at a computer and stationary.

 

That is also a factor.

 

So to summarise. At 30.000ft and TAS of say 400kts, the Su27 controls input range is about 10% useful, with the other 90% just range that will mean you get too much AoA and lose control?

 

At 30000 and TAS of 400kts you're barely flying at 250kts IAS or so and you need to finesse the aircraft. Any AoA spikes at such speeds will happily develop into a departure if given half a chance - the aircraft will slow down QUICKLY and yaw can also develop QUICKLY. You're in the realm of 30-60 deg bank turns and slow roll response, not in the realm of turning and burning.

 

So the pilot has to increasingly finely balance inputs under very high g forces, with a big waggly stick that flaps around, to the point it may feel like it's on a hair trigger, vs at 10,000ft at the same TAS?

 

What matters for maneuvers is IAS, not TAS. Get rid of TAS in your thinking of this RIGHT NOW. :)

 

I'm more than happy to accept this is the way it is, if it really is. I just can't see what pilot or engineer would see virtue in that behaviour if they can get rid of it.

 

You'll have to ask the engineer/pilot about that. The Su-27 is an aircraft that was essentially one of the first to implement a robust augmentation system. It was done in consultation with pilots and implements what THEY asked for. They are assumed to know what they're doing, and the FBW is there to help inform them of something things but it isn't there to stop them from doing those things.

[GGTharos]

How much g are you actually pulling, with what onset rate, do you have the g-ex already accomplished or not, how long are you pulling this g for?

 

There are a few things could be happening:

 

1) Your perception of what is actually occurring is flat-out wrong

2) You're pulling high g's for longer than you believe, with high onset rate

3) The intense g-tolerance training for US pilots is simulated. No, it isn't, but some of us wish it was (9g for 30 sec, in game you get 5sec) :)

4) Virtual Eagle pilots may have simply learned to finesse their aircraft and g management better than you ...

 

The Su-27 tend to blackout every time we try to maneuver. Even when is a simple turn. With the F-15 does not happen even when they have more G. No clue here...

[GGTharos]

It is not a limiter. You can pull right through it, though it will certainly inform you that you have reached the operational limit.

 

Not only training. There is also a mechanical AoA - G limiter. The system is there to help pilot's training.

[Esac_mirmidon]

I don't call it just information. XD

 

The pilot must pull or push the stick with such great effort to counter the limitator that he is not piloting anymore, he is fighting the stick. And also if the pilot pull or push to much the stick will try itself to return to the center with a strong counter force.

 

 

Very strong counter force.

 

And the manual talks about AoA-G limitator. So if the systems limits to a certain degree how much you can pull or push the stick under certain AoA or G values is indeed a limitator. IMO.

[Mr Whippy]

It isn't over-sensitive for me.

 

 

 

There is feedback last I checked, you just have to fly the aircraft such that you don't just spike right past this feedback and straight into a departure.

 

 

 

That is also a factor.

 

 

 

At 30000 and TAS of 400kts you're barely flying at 250kts IAS or so and you need to finesse the aircraft. Any AoA spikes at such speeds will happily develop into a departure if given half a chance - the aircraft will slow down QUICKLY and yaw can also develop QUICKLY. You're in the realm of 30-60 deg bank turns and slow roll response, not in the realm of turning and burning.

 

 

 

What matters for maneuvers is IAS, not TAS. Get rid of TAS in your thinking of this RIGHT NOW. :)

 

 

 

You'll have to ask the engineer/pilot about that. The Su-27 is an aircraft that was essentially one of the first to implement a robust augmentation system. It was done in consultation with pilots and implements what THEY asked for. They are assumed to know what they're doing, and the FBW is there to help inform them of something things but it isn't there to stop them from doing those things.

 

Thanks for the detailed reply.

 

I know what you mean wrt IAS vs TAS.

 

It just seemed a logical approach that with IAS there would be some linearity in the control input vs expected aircraft output vs altitude.

 

 

But I suppose the IAS vs TAS curve is different for every aircraft, since all aircraft have different aerodynamics and thus performance varies non-linearly vs air density.

 

I suppose I need to fly with an IAS and TAS readout to get an idea of what is really going on and build up the relationship mentally between the two values in different conditions.

 

 

 

It's ironic really that IAS is used with such an aircraft, where the pilot is deciding to fly so much with knowledge and consideration and fineness, to then rely on an automated value like IAS.

Given the mantra of the flight system design, you'd think TAS would be used entirely, and the pilots just understand what the capabilities are at varying air densities and TAS.

 

 

 

I'm going to have to find a book about the Su27 that has lots of information from the pilots and engineers.

I'm intrigued by some of these choices because they seem illogical, but there must be some logic there which suggests I'm missing a lot about these aircraft!

 

 

Thanks

 

Dave

[pepin1234]

4) Virtual Eagle pilots may have simply learned to finesse their aircraft and g management better than you ...

 

Don't know exactly how long I turn with high G. I don't have the time to do this Test. I just write here what I feel. I use to fly all my DCS modules in Simulation Flight level. All what I can say I feel not good taking combat with the Su-27 with this PFM. Hope ED get a good tune for the next upgrades.

[msalama]

I just write here what I feel.

 

I used to do that a lot too in my time, until I realized most things I felt were wrong actually weren't. I suggest you give this some thought as well.

 

Carry on, fetching me coat ;)

[Ironhand]

...

It's ironic really that IAS is used with such an aircraft, where the pilot is deciding to fly so much with knowledge and consideration and fineness, to then rely on an automated value like IAS.

Given the mantra of the flight system design, you'd think TAS would be used entirely, and the pilots just understand what the capabilities are at varying air densities and TAS...

Dave, it's pretty standard that all aircraft use IAS to fly the aircraft. The reason is that a glance at your airspeed tells you, within reason, how the aircraft is going to behave. But there's more involved than just airspeed--no matter how you reference it. The air densities you keep mentioning also have an effect on engine performance. Thrust goes down as altitude goes up. So the penalties incurred in maneuvering at sea level are magnified at altitude. That's yet another piece of your puzzle.

Edited June 9, 2015 by Ironhand

[Svend_Dellepude]

Don't know exactly how long I turn with high G. I don't have the time to do this Test. I just write here what I feel. I use to fly all my DCS modules in Simulation Flight level. All what I can say I feel not good taking combat with the Su-27 with this PFM. Hope ED get a good tune for the next upgrades.

 

Forget about earlier SFM. You need to unlearn everything you ever learned with SFM and start over with PFM.

It's simply another world that get's a lot easier if you stop blaming the FM for being flawed and try to find out what you can and can't with this FM.

 

I used to do that a lot too in my time, until I realized most things I felt were wrong actually weren't. I suggest you give this some thought as well.

 

Carry on, fetching me coat ;)

 

+1

Can't be said enough times, but it seems most ppl doesn't believe this.

 

I hate fighting in the SU-27, but more because of lack of experience in it and because i can't get used to flying with the metric system, but i love flying it. It react's so gentle and smooth and will do what ever you ask of it as long as you don't bash the stick around like some brute.

[GGTharos]

I know what you mean wrt IAS vs TAS.

 

It just seemed a logical approach that with IAS there would be some linearity in the control input vs expected aircraft output vs altitude.

 

There is a linearity of control input vs speed. Altitude is already built in by the virtue of using some form of IAS.

 

But I suppose the IAS vs TAS curve is different for every aircraft, since all aircraft have different aerodynamics and thus performance varies non-linearly vs air density.

No, the curve isn't different for every aircraft. TAS is corrected EAS (IAS corrected to CAS corrected to EAS). That's what the aircraft's sensors give you, and it's based on altitude density, not on the aircraft.

 

I suppose I need to fly with an IAS and TAS readout to get an idea of what is really going on and build up the relationship mentally between the two values in different conditions.

You fly with IAS and Mach. IAS tells you roll rate and pitch response, Mach tells you sustained g for a given altitude.

 

You can SORT OF subsitute TAS for Mach, but all TAS tells you really is how fast you're going from point A to point B (more accurately though, GS tells you that).

 

It's ironic really that IAS is used with such an aircraft, where the pilot is deciding to fly so much with knowledge and consideration and fineness, to then rely on an automated value like IAS.

IAS is not an automated value. It is what the aircraft 'feels'. Other forms of AS are usually derived from IAS.

 

There's no irony here, IAS is how it's done (or more accurate derived forms of IAS, such as CAS/EAS).

 

Given the mantra of the flight system design, you'd think TAS would be used entirely, and the pilots just understand what the capabilities are at varying air densities and TAS.

Why would you use TAS when IAS/CAS/EAS is what's important when it comes to knowing the effect of control deflection on the aircraft's trajectory?

And why would you burden pilots with making some form conversion of TAS to IAS in their head, or correlating graphs when they really shouldn't need/have to? No one does this. Not in fighters, not in airliners.

 

I'm going to have to find a book about the Su27 that has lots of information from the pilots and engineers.

I'm intrigued by some of these choices because they seem illogical, but there must be some logic there which suggests I'm missing a lot about these aircraft!

The book you should be looking for is something like this: http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/pilot_handbook/

[Robin_Hood]

But I suppose the IAS vs TAS curve is different for every aircraft, since all aircraft have different aerodynamics and thus performance varies non-linearly vs air density.

 

No, it is not. The IAS/TAS conversion is only dependant on atmosperic conditions, as it is caused by the decrease of air density with altitude.

I am not sure you understand what IAS and TAS really are. As has been said, pretty much all aircraft use IAS (or CAS, which is basically the same - just corrected for known errors).

 

Here's a short explanation for anyone not familiar with the different airspeeds.

 

Indicated Airspeed is the speed that the aircraft feels, ie. the rush of air around it, the impact of air molécules. The denser the air, the more the aircraft will feel the air. This is why IAS basically governs the behaviour of the aircraft. Your stall speed, never exceed speed, etc... will be IAS.

True Airspeed is the velocity of your aircraft relative to the air (it is therefore your "true" speed). But note that for the same TAS, the aircraft will "feel" less speed if the air is thinner.

So for a given TAS, IAS decreases the higher you go. And for a constant IAS, TAS will increase.

At sea level, IAS = TAS.

Ground speed of course is the speed of the aircraft relative to the ground, and takes the wind into account, as TAS = speed of the aircraft relative to the air and Wind = speed of the air relative to the ground, therefore Ground speed = TAS + Wind = speed of your aircraft relative to the ground

 

The real question is not why would anyone want to rely on IAS, but more why would anyone want to rely on TAS, which is not very useful for the flying of the aircraft.

Of course, TAS is used also, in relation to all things navigational, since it describes your "real" speed. After correcting for the Wind, TAS gives you ground speed.

 

Hope it helps.

 

PS: For the record, I don't have any particular problems with the Su-27 PFM, I am intrigued as to why so many people have trouble with it. Apart from the sneaky inverted departure and the annoying trim requirements (meaning the extreme variations in required trim at some speeds), it is quite pleasant to me to fly and fight in.

 

EDIT: Aaaaand I was sniped by GGTharos!

[ShuRugal]

It's ironic really that IAS is used with such an aircraft, where the pilot is deciding to fly so much with knowledge and consideration and fineness, to then rely on an automated value like IAS.

 

The reason IAS is a more relevant value for maneuvering info is that it is not just an indicator of speed, but of the mass-airflow rate past the aircraft.

 

As you know, air density decreases as altitude increased. This means that for a constant TAS, there is much more air flowing around and interacting with the bird at sea-level than at 10km altitude. Using TAS to indicate speed and decide how to fly the plane forces the pilot to check his altitude and reference that with his TAS to decide how hard he can maneuver.

 

However, IAS is inversely proportional to altitude: As air density drops, so does IAS, even at a constant TAS, and it does so at a fairly linear rate. Using IAS, the pilot only needs to know one number when deciding how hard to pull through a maneuver, because for any given IAS, the mass-flow around the plane will be roughly constant (or at least have minimal variation), and thus the control surfaces with generate the same force and the lifting surfaces will provide the same lift.

 

TL;DR version: 500 kph IAS at sea level gives approximately the same maneuvering ability as 500 kph IAS at 10km, but if you try to maintain 500 kph TAS at 10km, the plane will fall out of the air, even though it flies perfectly fine at 500 kph TAS at sea-level.

[21stCenturyPilot]

I've got a trick for the Su-27.

 

I never trim it. I use Lalt-3 level mode then when it is levelled use Lalt-9 cancel autopilot. Now it is trimmed.

 

The nose seems to twitch and squirm around too much. I've seen the Su-27 Flanker B do the cobra and it's normal routine of rolls, loops and fly-bys at an airshow, I've also seen a lot of video footage of it and also seen just about every other jet fighter fly at airshows. The real Flanker seems much smoother and less twitchy, it doesn't fly like the PFM in FC3. My 2c.

[DarkFire]

I've got a trick for the Su-27.

 

I never trim it. I use Lalt-3 level mode then when it is levelled use Lalt-9 cancel autopilot. Now it is trimmed.

 

The nose seems to twitch and squirm around too much. I've seen the Su-27 Flanker B do the cobra and it's normal routine of rolls, loops and fly-bys at an airshow, I've also seen a lot of video footage of it and also seen just about every other jet fighter fly at airshows. The real Flanker seems much smoother and less twitchy, it doesn't fly like the PFM in FC3. My 2c.

 

While that's true, it's also accurate to say that the likes of Pugachev, Kvochur and the other display pilots are THE most elite Flanker pilots available with thousands of hours in the type. I don't know how true this is but I remember watching an English dubbed version of a Russian documentary (actually more like an advert for the Sukhoi company. The Russian deputy prime minister jumped in an Su-27 and took it for a test flight!!! :shocking: ) in which somebody working for Sukhoi explained that the electro-mechanical or electro-hydraulic flight system used on the Su-27 and MiG-29 was designed so that elite, highly experienced pilots could potentially get more from it than would be possible with what one might call a traditional digital FBW system.

 

The point being that the pilots who fly those amazing airshow routines are the best pilots in the world in those aircraft and probably aren't representative of a front-line Russian air force pilot. Same with the Red Arrows here in the UK: the RAF takes proficient pilots from line squadrons and then assumes their existing experience as a starting point from which to build.

 

As far as the Flanker being twitchy, I think that part of the problem is that the trim adjusts rather drastically with each input. If the response to trimmer input could be 'slowed down' a bit (not sure how else to explain it) I think trimming would be a lot easier...

[Saeid]

DCS SU27 is impossible to control

 

Hi all, so I added SU27 module to my DCS World as I couldn't resist the offer on steam.

 

The flight model is totally different than f15. I constantly go in loops, spins, stalls...you name it. and all sort of stuff. It seems that it requires constant pitch trim whenever you change your trust...

 

So I want to know is it me that sucks or there is any tips and tricks to keep the damn plane maintained? Any specific X/Y axis settings on my joystick (I got X55)? please give advise...:helpsmilie:

[Wizard_03]

It needs a lot of trim because the center of gravity and aerodynamic center in the 27 is reversed unlike most fighters. (ect F-15) This makes the aircraft naturally unstable, I.E. you let go of the controls or your not always on top of them and it starts to do its own thing instead of trying to return to straight and level.

 

This characteristic is one reason why the aircraft is so maneuverable. However when your not doing ACM it can be frustrating to deal with. I would make sure you trim the aircraft's pitch based on the speed as it will need to be trimmed a lot with speed changes. Also learn about the auto pilot modes, they help a ton if your just flying around. then just practice a lot, you will eventually learn to predict where the fighter wants to go when your not trimmed, and this will help you get good with ACM dog fighting. :thumbup:

[Mowgli]

Not for nothing the Admin moved your post to this thread - start from the first post - you'll find your answers.

 

Treat it Gently - your Flanker

Edited June 22, 2015 by Mowgli

[DarkFire]

Hi all, so I added SU27 module to my DCS World as I couldn't resist the offer on steam.

 

The flight model is totally different than f15. I constantly go in loops, spins, stalls...you name it. and all sort of stuff. It seems that it requires constant pitch trim whenever you change your trust...

 

So I want to know is it me that sucks or there is any tips and tricks to keep the damn plane maintained? Any specific X/Y axis settings on my joystick (I got X55)? please give advise...:helpsmilie:

 

In relation to axis settings, most people use between 15-25 curvature for both roll and pitch. Personally I use 18 for both. This gives smooth control but retains the possibility of drastic inputs in emergency situations.

 

Generally the Su-27 is all about hours and hours of practice. The more you fly it the better you will get but don't expect to master it in a couple of half-hour sessions. Also be very gentle with stick inputs at low speed. Finally, unless you really, REALLY know what you're doing do not ever touch the "S" key. This turns off the flight control system and gives you direct input. Again, unless you know precisely what you're doing turning off the ACS is almost guaranteed to kill you very, very quickly.

[Ironhand]

 

...any tips and tricks to keep the damn plane maintained? Any specific X/Y axis settings on my joystick (I got X55)? please give advise...:helpsmilie:

No tricks. Just put some curve into your axis settings and don't throw the stick around. She will fly as smoothly as you do.

 

And, yes, you have to either trim for speed or fight the stick to some degree. I usually enter several clicks of nose down trim before I start my takeoff roll. And shortly after takeoff, you'll find yourself trimmed about 1/3 or so of the stick's travel nose down. Unless you are trying to get to "hands off" flight, that's usually enough for most purposes.

 

A few videos to watch to see how well she can behave:

 

 

 

 

 

The following thread might also prove helpful. It's long but, during the give and take, a lot of good info was provided: Su-27 Flight Model Discussion. If you take the time to read through it, you'll understand why she behaves the way she does.

 

 

Rich