Su-25T landing gear and brakes realism!

[Maverick Su-35S]

Hi,

         Just a tip:

 

From around 15km/h (what I'd estimate) it stopped in 2.2 seconds (probably at grip limit). That means it had ~0.8Gs of deceleration. Can the braking force on the wheels of the Su-25s in DCS, please be increased to more realistic levels? The braking system should have enough authority to lock the wheels. Those are not bicycle brakes. At the same time, the nose gear steering is so extremely fragile that even small bumps can break it. The real airplane's landing gear was built to be tough!

[virgo47]

I don't know how it is modelled in the game, but compared to the picture the braking effect really looks much weaker. For Su-25(T) there is also no wheel brake axis, so we can't squeeze it fast, it takes more than 1s to even get to the full pressure. (At least from the cockpit instruments, which - strangely - are not even consistent in Su-25T and Su-25. It looks like Su-25T has the hydro and brake pressure swapped, but I'm only guessing that the red area is for the hydraulic pressure gauge and not for the brake gauge.)

Is there any public info about the brake deceleration of Su-25/T available? With just a rough measurement, it takes over 9s to stop Su-25 from 50 km/h, which is terrible, but how real it is I have no idea.

[Maverick Su-35S]

On 10/1/2023 at 1:03 PM, virgo47 said:

I don't know how it is modelled in the game, but compared to the picture the braking effect really looks much weaker. For Su-25(T) there is also no wheel brake axis, so we can't squeeze it fast, it takes more than 1s to even get to the full pressure. (At least from the cockpit instruments, which - strangely - are not even consistent in Su-25T and Su-25. It looks like Su-25T has the hydro and brake pressure swapped, but I'm only guessing that the red area is for the hydraulic pressure gauge and not for the brake gauge.)

Is there any public info about the brake deceleration of Su-25/T available? With just a rough measurement, it takes over 9s to stop Su-25 from 50 km/h, which is terrible, but how real it is I have no idea.

It's not real. Simple as that. Indeed in our sim we can't have a brake axis so to apply full braking in 0.1 seconds if needed as it probably is possible in reality, but I've just done a test for this purpose only and compared the constant maximum achieved braking deceleration of the DCS Su-25T with that from the real footage and in DCS it decelerates at a noticeable lower rate. But braking is not the only problem and I've addressed the second problem regarding the extremely fragile nose steering (and all sorts of apparently zero knowledge grinning tried to ridicule me about it) which easily breaks if you go over the grass or at the smallest bumb possible and also the main gear is a bit too sensitive and it can bend from forces as low as just from exiting a turn on the tarmac and the gear that starts getting compressed after finishing the turn gets bend...! This is absolutely ridiculous and I'll bring a track here to prove both once again. Hopefully, they'll try making it a bit more resistant as it should. Su-25s are made to takeoff and also land on rough grass terrains and not break. Also, if you look at the design of the Su-25s main landing gear you'll see it's similarity to that of an F-18 (and we know how tough that is as it can land with 4 fuel tanks and other weapons on the wings on the runway like on the carrier and have no damage to the gear). It's a very "shock absorbing" gear and it's also meant to have the Su-25 land on a carrier. Yes, there was once an incident with a gear collapsing on an Su-25 on a carrier. Design is one thing..., maintenance is something totally different!

[AJaromir]

According to flight manual you should turn only at speeds lower than 10 km/h. Also mind the propper rudder pedals technique. Rule number one: Heels on floor. Not on pedals. Only for wheel braking. I've landed with overweighted SU-25T without issue. 

 

[Maverick Su-35S]

On 11/26/2023 at 6:59 PM, AJaromir said:

According to flight manual you should turn only at speeds lower than 10 km/h. Also mind the propper rudder pedals technique. Rule number one: Heels on floor. Not on pedals. Only for wheel braking. I've landed with overweighted SU-25T without issue. 

 

With all due respect, can you please reply in the topic's subject and not 100% off-topic? Seriously..., who talked about steering at various speeds? Who talked about how you should keep your feet on the brakes? Please reply only after a bit of thinking. Regarding the "steering", cause that's the only word you used regarding something from what I've said, it was about the steering mechanism that breaks, not at what speed you should steer for reasons all other than breaking the mechanism. The manual tells about the speed limit so that at max steering you won't have the plane land on a wing! You didn't understand anything from what I was talking about. I was talking about how fragile the nose wheel steering mechanism is and breaks/fails at any small bump that it encounters, a good example being when rolling on the grass at ANY speed, even at 0.5km/h if you want to talk about speed or when coming from the grass back on the tarmac, again regardless with what speed you do it, it no longer works. Do you understand now?

[AJaromir]

Lets do some tests. Wheels and steering system will not break when you don't smash the rudder pedal. Because it is possible to skid the front tyre if you turn it too fast. For that reason is important to avoid nose wheel turning specially at take off and landing, that's why you should have heels on floor. Generally avoid grass. This happens with almost every aircraft in DCS. Grass is simply no go. The grass is full of water and mud into which the plane will sink.

Edited August 5, 2024 by AJaromir

[AJaromir]

To measure speed the status bar is used and is set to show true airspeed. Weather is set to 0 wind at all. Used airfield is Batumi, start from runway hot. I will use 100% fuel, full flaps, just like in video.  First I reach desired speed + 1km/h, then reduce power to idle. Once the speed drops to nominal, I press and hold wheel brake and at the same time I start the stopwatch.(because I don't have 3 hands).  Once the status bar shows 0, I stop the stopwatch. I will always measure 3 attemps. For every attemp I restart mission. G constant will be 9.81

SU-25A, 100% fuel, no payload gross weight 13179 kg, full flaps:

From 15 km/h (= 4,17 m/s) ground speed to 0 km/h :

1) 3,49s

2) 3,32s

3) 3,46s

Average = 3,42 seconds. Means decelleration speed 1,22 m/(s^2) => 0,12G

Edited August 4, 2024 by AJaromir

[AJaromir]

SU-25A, 100% fuel, no payload gross weight 13179 kg, full flaps:

From 100 km/h (= 27,78 m/s) ground speed to 0 km/h :

1) 17,36s

2) 17,52s

3) 17,35s

Average = 17,41 seconds. Means decelleration speed 1,6 m/(s^2) => 0,16G

Edited August 4, 2024 by AJaromir

[virgo47]

Just a side note: 1 m/s = 3.6 km/h, not the other way around. 100 km/h is 27.777... m/s

[AJaromir]

1 hour ago, virgo47 said:

Just a side note: 1 m/s = 3.6 km/h, not the other way around. 100 km/h is 27.777... m/s

Fixed. Thank You.

On 9/30/2023 at 1:18 AM, Maverick Su-35S said:

. That means it had ~0.8Gs

0,19G. Not 0,8G

15 km/h = 4,17 m/s

a=(v-v_0)/(t-t_0) = 4,17/2,2 = 1,9 m/(s^2)

G = a/g = 1,9/9,81 = 0,19G So you missed your math only by 0,61 G and my measurement is very close to your observation.

Edited August 4, 2024 by AJaromir

[AJaromir]

SU-25T, 100% fuel, no payload gross weight 15331 kg (2152 kg heavier than SU-25A), full flaps:

From 15 km/h (= 4,17 m/s) ground speed to 0 km/h :

1) 3,75s

2) 3,91s

3) 3,78s

Average = 3,81 seconds. Means decelleration speed 1,09 m/(s^2) => 0,11G

[AJaromir]

SU-25T, 100% fuel, no payload gross weight 15331 kg (2152 kg heavier than SU-25A), full flaps:

From 100 km/h (= 27,78 m/s) ground speed to 0 km/h :

1) 20,51s

2) 20,41s

3) 20,35s

Average = 20,42 seconds. Means decelleration speed 1,36 m/(s^2) => 0,14G

[AJaromir]

Summary:

OP's observation results - 0,19 G (not 0,8 G)

SU-25A:

From 15 km/h - 0,12 G; deviation = 0,07 G

From 100 km/h - 0,16 G; deviation = 0,03 G

SU-25T:

From 15 km/h - 0,11 G; deviation = 0,08 G

From 100 km/h - 0,14 G; deviation = 0,05 G

Edited August 4, 2024 by AJaromir

[AJaromir]

Turning test. Tried to start every turn at 25 km/h

 

[AJaromir]

One thing is the braking power increases gradually because It is not axis, but button. It is intentionally. Just like when you try to control aircraft by mouse and keyboard and press the left arrow, the stick also don't move from neutral to max deflection in no time. It is intentionally slow to be able to set some specific value. For the same reason the brake button does not apply the full brakes instantly because it could result into too strong braking power.

Edited August 4, 2024 by AJaromir

[draconus]

On 9/30/2023 at 1:18 AM, Maverick Su-35S said:

From around 15km/h (what I'd estimate) it stopped in 2.2 seconds (probably at grip limit).

Clearly an air show. Aircraft has empty pylons and loaded with minimum fuel to stay light and keep safety.

[AJaromir]

I think issue is not in SU-25T. Issue is in grass. There is difference between default grass and grassy airfield. If you land on grass, you will always ditch in with whatever aircraft. If you land on grassy airfield, you will not dich in. Simple solution is to keep yourself where you should be. Not where you should not be.

Edited August 5, 2024 by AJaromir

[draconus]

Yes, and there's also different terrain. There are places where you will crash trying to land on the grass and other where you'll be safe. Also you can freely taxi through grass but you have to keep the speed. You'll stuck if you let it stop.

[AJaromir]

This is what I am talking about. Please let me show you my video:

 

Edited August 5, 2024 by AJaromir

[Ironhand]

On 8/5/2024 at 2:24 PM, AJaromir said:

This is what I am talking about. Please let me show you my video:

 

 

Unfortunately, what your video demonstrates is not universally true. Even around airfields, there are places you can do that and places that you can’t. It varies from map to map and airfield to airfield. Some are far more forgiving than others.

[AJaromir]

Yes, on grassy airfield you can enter the grass. On the concrete airfield you can not (and you should not) enter the grass. Caucasus and NTTR is based on the oldest SDK for DCS 2.0. Marianas is the representative demo of the newest SDK.

Edited August 8, 2024 by AJaromir

[sunwolf]

by the way, Nobody need a lock for nose wheel on SU-25T in DCS??Take off and land with cross wind is hard difficult in Su-25T in DCS.I would crash when I use rudder at high air speed.

Edited August 24, 2024 by sunwolf

[draconus]

1 hour ago, sunwolf said:

by the way, Nobody need a lock for nose wheel on SU-25T in DCS??Take off and land with cross wind is hard difficult in Su-25T in DCS.I would crash when I use rudder at high air speed.

Practice, practice, practice. You'll get to it. Be gentle with the rudder.

[Maverick Su-35S]

On 8/4/2024 at 7:44 PM, AJaromir said:

Lets do some tests. Wheels and steering system will not break when you don't smash the rudder pedal. Because it is possible to skid the front tyre if you turn it too fast. For that reason is important to avoid nose wheel turning specially at take off and landing, that's why you should have heels on floor. Generally avoid grass. This happens with almost every aircraft in DCS. Grass is simply no go. The grass is full of water and mud into which the plane will sink.

 

I see you are full of imagination for trying to invent incoherent pretexts, but sorry, it won't work that way!

1. The LG of the Su-25 is more robust than you seem to imagine and for a bit of thinking exercise, if not even the tire doesn't blow up from lateral force, how can the steering system fail that easily? And speaking of thinking, is there any other aircraft for which the steering gets stuck like that from a simple tarmac touch or smallest little non-uniformity in the grass? Show me one cause I'm genuinely curious. Only the Su-25s steering system needs a little attention to be logically at least as resistant as the one on the Su-27 and also the main landing gear needs the same attention to be somewhat more resistant to lateral forces only, as every time I steer the Su-25 on tarmac at some 50-80km/h and it's heavily armed and the wheel from the interior of the turn lifts off the ground a bit and then retouches after I reduce the steering, that landing gear fails. Very non-logically, not the one on which the weight of the whole plane is fails, but fails the one which re-touches the ground=).

2. I can use the rudder with the heels on the ceiling and still won't brake the steering systems or gear on ANY other airplanes, not just FC3, so avoiding the grass only has to do with it's coding..., which can be changed if people are kind. Btw, only the FC3 aircraft remain stuck in the grass. DCS level aircraft never do. I'm curious about your new explanation for that?

3. Wet grass? Mud? Sinks? =))). You are brilliant! Now I just wonder how would your proposed tests would look like! Perhaps you never heard of a Boeing 737 that landed on a grass strip, while it's main tires had quite a very good ground tire pressure (if you know what that is) on a fully rained, soaked mud as you like to bring in and not only that the landing gear withstood the forces without breaking apart nor even bending, but days after that mishap, it also took off from that same strip. Yes, it was relatively lighter, but the soil didn't just dry out that fast and still took off. Not to even mention the plentiful of videos showing soviet fighters taking off from exactly that..., wet mud terrains! And you want to come and explain how FC3 airplanes like F-15 or MIG-29 remain stuck on dry grass at full AB. Instead of accepting the truth and reality, you play the same game like many others I've seen doing so, by trying to invent all sorts of nonsense. You've found the wrong guy;).

I simply wish I could help ED correct things in DCS. I wish I could know how to fix the damn thing myself if I'd be allowed to. Me and others who want to correct it, are at the mercy of ED's developers for their time and effort (and I understand them as they are overwhelmed with important bugs) in trying to look into these things as well when they get the chance.

[draconus]

6 hours ago, Maverick Su-35S said:

I simply wish I could help ED correct things in DCS.

I counted 0 (zero) tracks in this thread. Looks like you want to discuss more than help or report.

FF modules also can stuck in grass.

That Su-25 can already taxi through grass was already shown. (https://forum.dcs.world/topic/334474-su-25t-landing-gear-and-brakes-realism/?do=findComment&comment=5496978)

IRL, depending on how much the nose wheel has sunken into the mud, AB can actually make it worse due to the force angle.

Anyway, the ground friction and types is not what is fully simulated in DCS so I suggest not to jump between different problems - one problem per thread is my best advice and also proper bug report rule.