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Old 07-09-2018, 09:02 AM   #1
draconus
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Default Difficult landing training

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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Old 07-09-2018, 01:55 PM   #2
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On that crosswind I don't think you can safely use the parachute.
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Old 07-09-2018, 06:52 PM   #3
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Quote:
Originally Posted by draconus View Post
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.
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Old 07-10-2018, 08:36 AM   #4
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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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Old 07-10-2018, 06:28 PM   #5
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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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Old 07-12-2018, 08:26 AM   #6
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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.

Last edited by draconus; 07-12-2018 at 08:31 AM.
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Old 07-18-2018, 09:05 PM   #7
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Quote:
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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
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Old 07-12-2018, 01:53 PM   #8
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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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Old 07-12-2018, 02:14 PM   #9
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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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Old 07-12-2018, 11:11 PM   #10
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Quote:
Originally Posted by draconus View Post
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
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