Su-25T FM question

[ericinexile]

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... :)

 

I believe this aspect of the flight model is overdone. Short wheel coupling certainly does make ground ops a little tricker. However, on dry pavement a pilot can depend on tire friction to privide very positive directional control. Much of that friction seems to be absent on the Su25. I'm not talking about braking friction here but rather lateral tire friction and the ability to resist skidding.

 

If I am wrong and this really is modeled correctly then I suggest that the Russians switch to a better tire supplier...perhaps Goodyear.

 

Smokin' Hole

[tflash]

I would also suppose that while you accelerate on the runway, the forward force vector will more and more stabilize the aircraft an that it is more difficult to chance course by wheel steering. This is not the case while taking of with the Su-25T: the slightest movement at the end of the run will totally bring your plane off course and get you into the grasslands.

[nscode]

If I am wrong and this really is modeled correctly then I suggest that the Russians switch to a better tire supplier...perhaps Goodyear.

 

if those are from the same manufacturer of the MiG-21 tires, the ones that can hold their spot against full AB (on dry surface), I would say there's not much to better on their part :)

[Yo-Yo]

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.

 

The brakes are not useful at low speed. There's only a one way to use them during landing - to reduce speed to 400 kph. Then landing gear, flaps and high AoA decelerate the plane much more effective. So retract it when you begin a final approach.

[Yo-Yo]

I believe this aspect of the flight model is overdone.

 

Smokin' Hole

 

Unfortunately no... the real Su-25 pilots tried the model and consider the ground handling very close to real.

Frankly, I don't understand the problem to hold the plane straight while running. As for me I apply dead brakes though it's recommended to apply it by impulses and manage to hold centerline.

By the way it's a good idea to release brakes when you begin to lose control, then stabilize the plane.

[Yo-Yo]

if those are from the same manufacturer of the MiG-21 tires, the ones that can hold their spot against full AB (on dry surface), I would say there's not much to better on their part :)

 

Soviet rubber was the strongest rubber in the world... ;)

[Trident]

I suppose the low tire pressure of the Su-25 for better rough field performance also contributes to the problem.

[Force_Feedback]

speaking of rough fields, will we get them in Black Shark? And can we place them by ourselves to base su-25s from them?

[TekaTeka]

All Flight sims make this claim.

 

Sigh. Hawg11, Did you read through this whole thread? Please do not dig up RIP subject.

 

Yeah, I know what you mean and I knew that single fact proof nothing, and Force_Feedback pointed it out right after that post. I just wanted to argue a point to Vati's very rude post. And I said it based on the seriousness of the ED's development team which we all knew very well. I said so right after that post, too. Other flight sims made that type of claim for their advertisement, but ED didn't. You can not find the pilot thing nowhere but one thread in this forum. And we can feel their seriousness even more by Yo-Yo's posts in this thread.

 

Please do not react to this post. It won't produce anything useful. Go back to the nice FM discussion.

[ericinexile]

Unfortunately no... the real Su-25 pilots tried the model and consider the ground handling very close to real.

Frankly, I don't understand the problem to hold the plane straight while running. As for me I apply dead brakes though it's recommended to apply it by impulses and manage to hold centerline.

By the way it's a good idea to release brakes when you begin to lose control, then stabilize the plane.

 

I can't claim to stay on centerline but I do manage to stay within a meter or two. One thing that would help would be differential braking with pressure. Currently (and this seems to be true of all sims) braking is either left/right/off/on with no nuance between those four corners. But enough about ground ops--We're here to FLY!!!!

 

Glad to hear that you ran the model by people who've actually qualified on the plane.

 

Thanks Yo-Yo and give me my Black Shark soon!

 

Smokin' Hole

[Yo-Yo]

Thanks Yo-Yo and give me my Black Shark soon!

 

Smokin' Hole

 

We are working... :)

[TekaTeka]

By the way, this is very convenient tiny tool when you switch between AFM and SFM aircrafts.

LockOn Joystick Profiler

 

I am switching 3 profiles; AFM, Russian SFM and US aircrafts.

[tflash]

Thanks for the link TekaTeka;

 

Yo-yo, there is something I do not fully understand with the small auto-rudder in the tail, above the rudder.

 

It often seems to move in the opposite direction as the rudder I am manually applying. Is it logical for me to apply rudder to the left in a turn while the autorudder moves to the right?

[ericinexile]

Thanks for the link TekaTeka;

 

Yo-yo, there is something I do not fully understand with the small auto-rudder in the tail, above the rudder.

 

It often seems to move in the opposite direction as the rudder I am manually applying. Is it logical for me to apply rudder to the left in a turn while the autorudder moves to the right?

 

Yo Yo will have a better answer. In the meantime, I'll take a stab at it: the smaller surface is a yaw-damper. It's job is to prevent dutch-roll and to coordinate turns. Almost all jets have such a system but usually use the rudder without the need for a separate control--so you don't see it. The reason you rightly notice it act in a manner opposite to your inputs is because you are creating a yaw and it is trying to stop it. Because it is a much smaller surface, it isn't doing any harm to your goal of moving the nose. The way it is supposed to work in more intelligent systems is to recognize your intentional control input and then act to allow the yaw but keep it precise.

 

Smokin' Hole

[Pilotasso]

What strikes me is that very few people know anything about Su-25 handling yet it is said in these lines that LOMAC AFM is unrealistic. I have never had doubts about the ground handling and air brakes efecteviness at low (landing speeds), it corroborates with everything I ever heard of such items.

[tflash]

I think the realism question was settled very early in the thread already. Claims that the AFM is not realistic have been proven wrong.

 

The purpose in this thread is to learn, and understand. I fly MSFS and Lockon as games, of course, but also to enhance my understanding of flight dynamics. The Su-25T FM is extremely helpful in this, since it is not straightforward and sometimes counter-intuitive.

 

I for my part was very surprised the first time I tried to slow down the Su-25T on landing ;)

[Force_Feedback]

I still find it strange that the brakes are not effective even under 150 km/h, and I'll ask again, will we get proper 'unprepared' (flattened grass with metal plates) runways in BS for the su-25(T) to operate from?

[159th_Viper]

I for my part was very surprised the first time I tried to slow down the Su-25T on landing ;)

 

Just like my surprise when I return from a sortie only to find upon touchdown that my Drogue chute has been taken care of by AAA. Touching down at 290km/h or slightly below and standing on the brakes it still takes me the better part of the entire Krymsk runway to stop. Good Times - Gotta love the T-Frog...:)

[Kula66]

What strikes me is that very few people know anything about Su-25 handling yet it is said in these lines that LOMAC AFM is unrealistic.

 

Lets be honest ... not many of us fly F-15s, A-10, Mig-29s and Su-27/33s either! Or any sort of fast jet ... If only. But we all love to speculate!

 

There are many things tough that can be gleaned for good research, discussion and a load of that rare item - common sense!

[Yo-Yo]

Yo Yo will have a better answer. In the meantime, I'll take a stab at it: the smaller surface is a yaw-damper. It's job is to prevent dutch-roll and to coordinate turns. Almost all jets have such a system but usually use the rudder without the need for a separate control--so you don't see it. The reason you rightly notice it act in a manner opposite to your inputs is because you are creating a yaw and it is trying to stop it. Because it is a much smaller surface, it isn't doing any harm to your goal of moving the nose. The way it is supposed to work in more intelligent systems is to recognize your intentional control input and then act to allow the yaw but keep it precise.

 

Smokin' Hole

 

Yes, you are right but the yaw-damper in Su-25 is only yaw-damper without SAS function of coordination turn. The system uses only angular velocity sensor to control the surface. It was done so because the rudder has direct control from the pedal like in WW II planes.

Generally, all controls are direct driven and only ailerons have additional boosters to reduce stick forces. Elevator has aerodynamic servo-compensators (like trimmers).

[tflash]

I found it made a dramatic difference once I removed the rudder control from the z-rotator axis of my Evo Force joystick. To have the rudder on this axis proved to bring very bad habits, I was constantly confounding rudder and aileron in turns, not applying rudder consciously. Waiting for a set of pedals, I now use the default keys to apply rudder, to keep the ball centered in a turn. I get much better flight control this way and the aircraft doesn't loose altitude anymore the way it did.

 

What a joy to fly!