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Difficult landing training


draconus

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Su-25T: I'm trying to master "Landing - difficult" training mission but most of the time I end up with blown front tire and on the grass. After touchdown (airspeed 240-260kph) I try to hold the nose up a little (down to 200kph), the aircraft drifts right so I counter with rudder to stay centered on the runway but after releasing parachute (about 150-190kph) it veers off to the right so much I cannot counter and end up in the grass. The only way I can stay on the runway is when I wait long enough before releasing the chute, slow down and steer left beforehand. I did not check when exactly the tire is blown yet.

Is it the strong crosswind causing all the problems? I have no problems with smooth landings VFR, good conditions.

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Su-25T: I'm trying to master "Landing - difficult" training mission but most of the time I end up with blown front tire and on the grass. After touchdown (airspeed 240-260kph) I try to hold the nose up a little (down to 200kph), the aircraft drifts right so I counter with rudder to stay centered on the runway but after releasing parachute (about 150-190kph) it veers off to the right so much I cannot counter and end up in the grass. The only way I can stay on the runway is when I wait long enough before releasing the chute, slow down and steer left beforehand. I did not check when exactly the tire is blown yet.

Is it the strong crosswind causing all the problems? I have no problems with smooth landings VFR, good conditions.

The mission has a 5 m/s crosswind coming in from the right which is enough to grab your chute and yank you around, if you deploy it too soon. Best to just use the brakes and stop without it, if you have the runway length.

 

EDIT: Just flew it. Not the prettiest thing once down on the runway but no chute and, I think, no blown tire. So It's possible to stop short of the end of the runway without a chute. In fact, had to taxi further down to the turnaround to get to Beslan's parking.


Edited by Ironhand

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OK, thanks, no chute then.

Now about tires: What are the common blowing up conditions besides high speed and hard touchdown? Can I start to brake safely from 200kph? Do I have to ease it/pulsate? Is brake temp even modeled here? Even if not, I want to do things the right way as to not overheat it. Do you use differential braking or just rudder to center?

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OK, thanks, no chute then.

Now about tires: What are the common blowing up conditions besides high speed and hard touchdown? Can I start to brake safely from 200kph? Do I have to ease it/pulsate? Is brake temp even modeled here? Even if not, I want to do things the right way as to not overheat it. Do you use differential braking or just rudder to center?

As a general rule, I "pulse" brake unless I'm coming up on the end of the runway and it's "lock" the brakes or break the aircraft even more by running into something off the runway. Can't comment on the "safe" braking airspeed as I usually judge it by how quickly the ground is going by. I'm sure I don't start until under 200, though. AFAIK, overheating isn't modeled here.

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Thanks, did another try - smooth touchdown, throttle idle, airbrake, waited until 190kph then pulse braking until closing to the end of the runway (then brakes locked), no chute. It was OK but nose tire blown again. Looked at the replay and it was blown the moment it touched the ground. Either speed too high or I suspect the lateral movement caused by rudder use.

btw: Flew your mission Su-25T Butami-Kutaisi.miz and, as always in good wheather, landed smoothly, no tires blown.


Edited by draconus

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Just to reinforce the point, and this applies to any of the Russian aircraft with braking chutes - the chute will produce a strong weather vane effect in strong cross wind conditions. If you have the runway length then it's much better to land as slowly as possible (keeping aircraft weight and it's effect on glide slope in mind) and aerobrake as much as possible before gently application of the wheel brakes.

 

There are a few runways in the Caucasus where this is unlikely to be possible due to the short runway length. IIRC the shortest is only about 1.7Km from threshold to threshold, with the longest being something like 3.6 Km.

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the chute will produce a strong weather vane effect in strong cross wind conditions

Yeah, about that, I noticed in the same mission, when already on the ground, turned upwind with chute out, I can stand still without braking, but if I increase the throttle (not max) I start to roll backwards... Seems like blowing your own sails works here :)

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Yeah, about that, I noticed in the same mission, when already on the ground, turned upwind with chute out, I can stand still without braking, but if I increase the throttle (not max) I start to roll backwards... Seems like blowing your own sails works here :)

 

That's quite cool actually, I had no idea it was modelled to that level. Thrust reverser drag chute :lol:

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Personal wish list: DCS: Su-27SM & DCS: Avro Vulcan.

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That's quite cool actually, I had no idea it was modelled to that level. Thrust reverser drag chute :lol:

Could be this case:

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Could be this case:

 

Yes, that's exactly what I imagined was happening. It would be an interesting but difficult experiment (very difficult to be consistent) to see whether the best throttle setting for a roll-out with chute deployed is zero or actually slightly above zero, i.e. whether there is a point where the back draught from the chute is greater than the forward thrust.

 

By nothing more than intuition I think this may be true for the Su-25 but is unlikely to be true for the larger aircraft like the Su-27 / -33. May also be true for the MiG-21.

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Personal wish list: DCS: Su-27SM & DCS: Avro Vulcan.

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Thanks, did another try - smooth touchdown, throttle idle, airbrake, waited until 190kph then pulse braking until closing to the end of the runway (then brakes locked), no chute. It was OK but nose tire blown again. Looked at the replay and it was blown the moment it touched the ground. Either speed too high or I suspect the lateral movement caused by rudder use.

btw: Flew your mission Su-25T Butami-Kutaisi.miz and, as always in good wheather, landed smoothly, no tires blown.

 

Maybe you are too heavy! did you drop the fuel tanks ? i did it today :thumbup:

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Maybe you are too heavy! did you drop the fuel tanks ?

Definitely not a case. Total fuel 300Kg, ext. tanks empty, no weapons.

My only problem left is the front tire blown after touchdown.

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The nosewheel tire on the Su-25 is way too sensitive. Even the slightest amount of skid and it blows. Not realistic and makes crosswind landings rather difficult.

You have to apply rudder rather slowly so that the nosewheel doesn't start to skid.

 

Any too fast input and the nosewheel blows really quick.

 

Talking about skidding nosewheels IRL:

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The nosewheel tire on the Su-25 is way too sensitive. Even the slightest amount of skid and it blows. Not realistic and makes crosswind landings rather difficult.

You have to apply rudder rather slowly so that the nosewheel doesn't start to skid.

Any too fast input and the nosewheel blows really quick.

Thx, that's the trick. I landed safely while keeping tires in good condition, very carefuly using the rudder. Had to be hard on the brakes OTOH.

 

I would think that after abusing the Eagle's mains, russian technology will cut me some slack ;)


Edited by draconus

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  • 2 weeks later...

In a crosswind situation like that where you can't use the chute, surge the brakes. You cannot just stand on them they'll overheat (same thing in big trucks, too heavy, too fast). If you have to come in without chute like that, land as slow as you can manage as far on the end as you can manage, and surge the brakes just a couple seconds at a time using as much of the runway to stop as you can.

 

The 25 has relatively high tricycle gear, not as bad as some but bad enough. If you lock the gear up it will lurch to one side, which also increases weight on that side, which increases heat, which increases likelihood of blowout. It also makes it hard to control.

Де вороги, знайдуться козаки їх перемогти.

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If you come in too hot, you can pop the chute for a second or two to quickly scrub off some speed. then ditch it before it drags you too off line as you slow.

 

It's not necessary with that mission though - don't come in too hot ;), and as mentioned above, brake, release, brake, release.

 

I'd modify that to brake straight, release, correct track, brake straight, release, correct tack, etc

 

You can leave the brakes on full, as long as you're not trying to turn at the same time.

Cheers.

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You cannot just stand on them they'll overheat (same thing in big trucks, too heavy, too fast).

Sounds like general aviation advice cause I don't see it modeled here.

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When you press the W key, it takes about 2.5 seconds for the brakes to be fully applied.

(watch the hydraulic gauges)

If you let the brakes go to full pressure and try to turn the wheel (add rudder) you'll scrub the tyres off.

If you pump the brakes they never get to full pressure and don't scrub off.

 

Or conversely, if you apply the brakes in a straight line letting them go to full pressure, then release and reapply adjusting track while the pressure is lower - again you won't scrub the tyres off...

 

I've seen this, Zhukov has seen this.

Cheers.

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Sounds like general aviation advice cause I don't see it modeled here.

 

Can't help you. Tire overheating through excessive speed, weight, or braking exists ingame with the Su-25.

Де вороги, знайдуться козаки їх перемогти.

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Things, you guys, say are indisputable but does stepping on the brakes and holding them on a straight line for prolonged time have any bad effect in game? (I didn't test it)

 

I was already trying to get the answer at #4:

https://forums.eagle.ru/showpost.php?p=3560832&postcount=4

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Depends on speed, weight, ambient temperature, and duration. In general no, but if you come in hot and heavy and lock the brakes down, especially if it's hot, you've got a good chance of blowing one or more tires. It'll usually be the smaller nose gear first, but if there's a crosswind or you lurch to one side for some reason it would likely be whatever tire takes the brunt of it.

 

Set the temp about 40C, load near max and stand on the brakes asap you'll have a pretty good chance of seeing it, especially if you hit a bit hard. Unless it is broken. I blew many tires in my early days slamming down at 5ms and locking the brakes down before I realised 5ms is MAXIMUM and you're supposed to use the chute whenever possible.

 

-edit use Groomlake they have a really long runway. Run down it at a decent speed 300+, especially with a bit of weight. You should blow the tires way before you make it to the end, even with no braking.

 

-edit

In your linked post, yeah you can shut down from 200ish without problem usually. It's mostly when you start right after touchdown and are still going pretty fast.


Edited by zhukov032186

Де вороги, знайдуться козаки їх перемогти.

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use Groomlake they have a really long runway. Run down it at a decent speed 300+, especially with a bit of weight. You should blow the tires way before you make it to the end, even with no braking.

I don't have NTTR yet and somehow I couldn't create my own mission with 25T so I was just abusing the brakes in training and instant missions. I tried my best but failed to break anything on a straight line.

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Although most simmers do not care about things like landing weight, for the real Su-25 it is specified as follows:

 

It is absolutely forbidden to land the aircraft with total weight exceeding 13 300 kg, such landing is allowable only in emergency and all weapons that are jettison-able have to be jettisoned. The manual moreover states that landings with total weight more than 12 200 kg are allowable only in rare cases and can form only 3% of all landings, if this number is exceeded the aircraft has to undergo a major technical overhaul.

 

Of course it is possible to land Su-25 even at 19500 kg, but you are putting the gear assembly tires and airframe over their projected stress levels.

 

When landing with weight below 12200 kg, you can touch the runway safely at 230 - 240 km/h without problems and land on real wheels, aerobrake and than release chute without ever touching brakes, just like RL. DCS has a very good FM for Su-25 very close to published numbers.

 

People often moan about flight models, minor cockpit details or small systems errors, but operate their aircraft in a way, which would be unimaginable in RL.

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I don't have NTTR yet and somehow I couldn't create my own mission with 25T so I was just abusing the brakes in training and instant missions. I tried my best but failed to break anything on a straight line.

 

Interesting. Maybe something changed. Ok, I'll give it a go, too. Brb

 

-edit can confirm

It is there. Ambient temperature 42' and full fuel and four drop tanks, I started down the runway, no wind, no brakes. By the time I got to the end I was doing 500kmh, lifted off, popped into external view, and all I had left were little nubs with shreds of tire. All three wheels were gone.

 

This from cold start immediately running down the runway.

Reviewing the track. Right tire blew at 440kmh. Left tire at 445. Nose tire lasted to 462, but it was slightly off the ground half the time.

Reflew this part a bit more carefully, with tiny down trim to keep the nose on the ground. Left and right tires blew simulatenously (almost) at 440ish, nose tire again blew at almost exactly the same point, around 462.


Edited by zhukov032186

Де вороги, знайдуться козаки їх перемогти.

5800x3d * 3090 * 64gb * Reverb G2

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