Su-25T FM question

[GGTharos]

Not only that but if you idle the engine while on the glideslope, you don't lose much airspeed.

[Yo-Yo]

Yo-Yo, out of curiosity - why does Su-25 not slow down much during landing? Gear, flaps, and airbrakes out - it does not want to slow down!

 

There's only one way to avoid it: start your final approach from the speed directed in manual (corrected to square root of actual mass to standard mass ratio of course). The total drag at directed AoA consists mainly of inductive drag so the brakes and even gear drag is much less than aerodynamic drag.

 

 

About 1.2 km to stop. Force_Feedback, you are perfectly determined this distance specified for the real plane. :)

[GGTharos]

Okay - I'm just surprised ... an F-16 with its gear out slows down a lot, you need to put in thrust! :)

[Yo-Yo]

Su-25 as well. Try to start a final approach from 400m alt, 280 kph, follow ILS and try to do it at idle...

[Yo-Yo]

The airbrakes are just there for show, they don't do anything. The designers just added them because they had some *free* time.

 

Negative. They are rather DIVE BRAKES and do their job very well.

Try to dive 25T at the same pitch (30-50) deg from the same altitude (5000 m for example) and check your speed at 2000 m.

[GGTharos]

But it got a pretty useful reply! :)

[Blakk]

the only two complains I have on SU-25T in game-terrible effect of Vikhr pods, I'm highly doubtfull, that this effects is the same in real life, othervise pods should be redesigned. And also low effect of air brakes, allmost no speed loss at all and huge shaking, howewer I have heard from real Su-25T pilots that these brakes are very effective and with minimum of shaking...

[ericinexile]

Yo-Yo,

 

Not to be a kiss-ass but Thanks! You guys really got the flying experience right with the Su25. And I agree that the drag quality "feels" correct to me as well. The Su25 cannot really be compared to an F16 in terms of slow speed deceleration. The F16 has two things working for it (or against depending on perspective): Higher wing loading (I'm guessing) and a huge, draggy intake at idle. Take away the high wing loading of a fighter and most jets have excellent glide ratios.

 

Smokin' Hole

[Yo-Yo]

the only two complains I have on SU-25T in game-terrible effect of Vikhr pods, I'm highly doubtfull, that this effects is the same in real life, othervise pods should be redesigned. And also low effect of air brakes, allmost no speed loss at all and huge shaking, howewer I have heard from real Su-25T pilots that these brakes are very effective and with minimum of shaking...

 

The only thing I can agree - the airbarkes shake only within speed range around 350-400 kph. At 600-700 kph no shaking reported. But we had no information about it before FC release. So the shaking was implemented using common consideration how airbrakes of this form could interact with airflow.

 

The effectiveness of the airbrakes was validated using real data.

[Yo-Yo]

Yo-Yo,

 

Not to be a kiss-ass but Thanks! You guys really got the flying experience right with the Su25. And I agree that the drag quality "feels" correct to me as well. The Su25 cannot really be compared to an F16 in terms of slow speed deceleration. The F16 has two things working for it (or against depending on perspective): Higher wing loading (I'm guessing) and a huge, draggy intake at idle. Take away the high wing loading of a fighter and most jets have excellent glide ratios.

 

Smokin' Hole

 

Thank you!

As for the drag I'd like to mention that F-16 and Su-25 have different wing aspect ratio so F-16 must pay more drag for the same lift at high AoA and this must be the main reason of their difference in deceleration.

[Groove]

Thx for clearing this up Yo-Yo. Being a Su-25 driver i have to tell you something:

 

I HATE this shaking when i deploy the airbrakes on speeds above 500 kmh !

[MBot]

Very interesting Yo-Yo.

 

One thing I noticed is the very high drag of various external pods and that they create a very violent shaking effect above a certain speed. The SPS-141 ECM pod for example seems to cut your topspeed for about 150 kph ( don't know exactly out of my head ). I think that is strange considering that the SPS-141 is also carried by the much faster Su-17. How comes it that such high drag stores create that "limiting airspeed trough shaking"-effect on the Su-25 ? Is that some sort of aerodynamic uniqueness of the Frog ? And why is the SPS-141 so draggy compared to a similar sized RPK-500 ? The bombs and rocket pods seem to have a very limited drag compared to the various pods.

[Pilotasso]

Personaly, while not knowing the Su-25 that well, I can say that the model feels very convincing. At least I can observe some of the aerodynamic quircs Ive been hearing about general aircraft fight charestics.

 

But my heart is broken that the AFM is precisely aplied to a plane that slow and heavy and doesnt offer the best joy of flight like the other fighters would.

[AndyHill]

I've thought about this shaking stuff for a while and I think there might be sort of an issue. Just today I had to sit in a car that had horribly unbalanced tires due to hard packed snow and dirt. The shaking was pretty bad, I could feel it in my body and all the loose objects in the car rattled horribly. I could clearly see the car structure vibrate and if I tried to speak my voice was stuttering. Unlike Lock on (and Sturmovik), the rattling did pretty much nothing to my view outside.

 

I've never been in an aircraft going past its highest recommended aerodynamic speed or deploying airbrakes, but I tend to think that in reality the human body and vision system would act as pretty efficient shock absorbers and keep the view apparently steady. Every time I get the shaking effect I really think the plane should fall apart any moment. Even my G-meter (not the one in-game but the one in my home pit) shows pretty wild readings during the shake and stir stuff. It doesn't have much built-in inertia so it shows any changes really quickly unlike real gauges, I suppose.

 

I'm not even a real pilot so I don't really know anything, but I'd like it if you reconsidered these two issues:

 

1) Is the turbulence / aerodynamic shaking effect overdone in the first place?

 

2) Is the visual representation of the effects too severe compared to how a pilot sitting in a real plane would see it and if it would be more appropriate to have the plane do most of the shaking while the player's view remains mostly steady (this is how for example strike fighters does it).

 

I'm all for realism, but the shaking is a very annoying feature and if there's any doubt at all as far as its present implementation goes I think you should consider softening it as much as you can.

 

________________________________________________________________

Lock on MUST have a dynamic campaign system with multiplayer capability AND dirrefential toe-brakes on an axis

[Kuky]

AndyHill... I asked about this some while ago myself and agree with you fully. The shaking in LockOn is not done well because the shake is applied to the whole screen view instead of just cockpit. The ground should not shake but in LockOn it does. And yes, human brain compensates for this shaking online a camera... but even new cameras technology has built in shake compensators done by software.

[Yo-Yo]

Very interesting Yo-Yo.

 

One thing I noticed is the very high drag of various external pods and that they create a very violent shaking effect above a certain speed. The SPS-141 ECM pod for example seems to cut your topspeed for about 150 kph ( don't know exactly out of my head ). I think that is strange considering that the SPS-141 is also carried by the much faster Su-17. How comes it that such high drag stores create that "limiting airspeed trough shaking"-effect on the Su-25 ? Is that some sort of aerodynamic uniqueness of the Frog ? And why is the SPS-141 so draggy compared to a similar sized RPK-500 ? The bombs and rocket pods seem to have a very limited drag compared to the various pods.

 

We specially checked SPS-141 drag and it is actually the same as for RBK-500, KMGU, S-25. The main difference is that shaking starts at lower speed.

The "limiting IAS (Mach humber) through shaking" is an attempt to force virtual pilots to fly within restricions set for certain payload. For example, in RL MBDs with 100 kg bombs have limit 0.55M.

The shaking presumed because of Mach overspeed for each payload, and the Mach number when shaking begins set individual for each payload.

 

As for Su-17 the pilot must fly it accordingly of the payload limitations so the speed can be limited.

[Blakk]

Howewer, Su-25T with low fuel load and no payload is still a good airplane, I never forget the moment, when I was a teenager and was flying from commercial airport, that was adjusted to the miliary base (Novo-Alexeevka), and suddenly all the people were starring in one direction, less than a mile away it was SU-25 performing set of high class aerobatics, within box of 2x2 miles, rolls, spins, loops...everything was well performed... Later, I found out that a pilot died in a test flight earlier on the same day, and this demonstration was an act of respect from his comrades.

[tflash]

First of all - thank you Yo-Yo for joining this discussion and providing us with detailed info: it shows how much ED cares for these aspects of simulation and is working to produce the best.

 

The question was: "how wrong am I about my criticism of the Su-25T". The answer is clear: I was very wrong!

 

Excellent professionals attract demanding customers, and one of the paradoxes is that we want two things that are somewhat contradictory: realistic simulation on the one hand, and realistic representation on the other.

 

The first you get when the performance numbers and bounderies are right, as you have clearly documented. The second is hampered by the fact that the experience has to go through a small 1600x1200 window whatever, with very limited visual and auditive SA.

 

I find it still very difficult to "sense" the speed difference between 500 km/h and 700 km/h, yet such difference has a big impact on how the aircraft flies.

 

This is one of the reasons the "shaking" issue appears like a scripted behaviour in the simulation. You lack a gradual sense that you are approaching boundaries. Sound effects are rather good in Lockon, but I think developping them further will be essential to allow the users more "feel" with the AFM. The shaking boundary enforces flight within limits, but doesn't translate that into a correct experience.

 

One similar example is the lack of auditive clues when you pitch the nose down. This causes such a dramatic change in airflow that you should hear very loud airflow noise. These noises are necessary for the human brain to learn: they are invaluable memory sources that most humans will use to fine-tune their behaviour.

 

Anyway, I'm enjoying the Su-25T even more now I've learned some new lessons, thanks!

[Kula66]

Is the 25T so unstable on the ground? Seems like applying the wheel brakes causes it to veer off course and touch those air brakes on the ground - and then it starts cartwheeling down the runway! Are the air brakes supposed to be used in landing at all?

 

The 25 seems to have less of a problem ...

 

Now ED have done some work with official data on the A-10, will we see any changes to the FM on that - seems like a dream in comparision to the 25 and 25T!

[SuperKungFu]

i don't think we will see an upgrade in the A-10 for BS, that was for a military contract. But i guess that data will probably carry on to ED's next project?

[Kula66]

i don't think we will see an upgrade in the A-10 for BS, that was for a military contract. But i guess that data will probably carry on to ED's next project?

 

Not an upgrade ... just a few tweaks - perhaps a bit more speed?

 

Ahh the 'Next Project' ...

[MBot]

Reading my cristall glass I am pretty sure that the next ED project will be around the A-10A. Considering the work ED does for the ANG A-10C sim it would be a logical choice. As Olgerd has mentioned, the A-10C avionics will still be classified for quite some time, but by removing most avionics you pretty much end up with a A-10A anyway :) Flightmodel and airframe systems should be the same.

I am not sure if ED would be allowed to use code of such a governmental job in a comercial product, but what would stop them to take the aquired knowledge and simply write down the FM and system modeling "again" ?

[GGTharos]

I think it's because of the CG and narrow wheel base.

The A-10 has a wide wheel base, so less of a problem and ... I think that according to some mutterings on the Russian forums, the A-10A might well be the next to be AFM-ed, 3D click-pitted, etc :)

 

Is the 25T so unstable on the ground? Seems like applying the wheel brakes causes it to veer off course and touch those air brakes on the ground - and then it starts cartwheeling down the runway! Are the air brakes supposed to be used in landing at all?

 

The 25 seems to have less of a problem ...

 

Now ED have done some work with official data on the A-10, will we see any changes to the FM on that - seems like a dream in comparision to the 25 and 25T!

[Yo-Yo]

Is the 25T so unstable on the ground? Seems like applying the wheel brakes causes it to veer off course and touch those air brakes on the ground - and then it starts cartwheeling down the runway! Are the air brakes supposed to be used in landing at all?

 

The 25 seems to have less of a problem ...

 

 

Yes, both Su-25 and Su-25T is very hard to handle on the ground because of their small distance between main weels. It's very usual for cadets to get away from the airstrip.

 

Su-25T has nose wheel more decentered so the initial yaw moment is larger.

 

Virtual Su-25 driving is a good school to drive your car on ice covered road... :)

[Kula66]

Cheers Yo-Yo,

Perhaps its easier with rudder pedals (I use a rocker switch on the HOTAS), but the clearence between the ground and air-brake seems very small, any wobble and they touch ... must need loads of spares.