Su-25T crosswind landing blowing nosewheel tire when wheel steering at chute deploy

[majapahit]

Su-25T crosswind landing blowing nosewheel tire when wheel steering at chute deploy

 

Landing the Su-25T in crosswind

Su-25T loaded with ammo and fuel, omitting target practice run, going RTB

 

Su-25T landing crosswind NNW 7 m/sec (141 = ) 321 deg. / blowing nosewheel @ chute out @ necessary wheel steering

 

Landing crabbing at Kutaisa Rwy 25 ( 321 -248 = 73 deg crosswind 7m/sec ) ,

touchdown 1 m/sec , rudder steer for straight rollout, nose down, deploy chute ~200-240 knt,

 

because of the chute deploy Su-25T veers right upwind 15- 20 deg.,

correct with fair lot of nosewheel to stay straight on runway,

 

bang, nosewheel tire blows, always, end off the runway in the grass

 

To correct this behaviour, before chute deploy I can kick rudder left,

when 5- 10 deg. veering left, I deploy chute, Su-25T veers back somewhat to middle of runway and chute brake slows down plane and can start wheelbraking

 

and if lucky come to a crawl without blowing the tire, somewhat in the middle of the runway

 

7 m/sec doesn't seem that much, this seems a somewhat crazy way of landing a Su-25T?

Would this procedure be somewhere near real life crosswind landing Su-25T?

 

 

EDIT:

 

on second thought, this might be a 'bug' or unrealistic chute brake behaviour

 

chute brake should rather 'pull' tail of the plane straight, towards longitudinal momentum of the plane,

and not 'enhance' wind veering into wind because of the cross wind component, this because of the (much) stronger negative breaking vector.

My guestimate would be that the longitudinal braking component easily mitigates a 7 m/sec crosswind component at ~200-250 knt on the cable of a brake chute.

 

- this would be my guestimate of real life chute behaviour?

 

Or, what am I missing?

Edited March 7, 2016 by majapahit

[mvsgas]

I do not think you are suppose to use the chute with crosswind. Also, how heavy where you on landing?

Track from openbeta

[esb77]

You're missing the section in the manual where it explicitly states that for landings with significant crosswinds the procedure is to NOT use the drogue chute because it causes the plane to weathervane (turn into the wind).

 

The chute in real physics is an aerodynamic control surface not all that much smaller than the wings that will try to point you directly INTO the relative airflow. That means that in a crosswind it's going to exert a very, very powerful pull that can exceed the ability of both the gear and the plane's control surfaces to counter.

 

If you think you're going to go off the end of the runway, say on an 1800m runway that's icy, and for some reason you can't divert to a field with longer runway or one with a smaller crosswind component, you can try waiting until the last 500m or so to deploy the chute. Once you're below 100-125 km/h the chute is a bit less likely to pull hard enough to force you off the runway.

 

It's also worth noting that if you're landing with a heavy load, you have to land faster (which makes the chute more of a problem in crosswinds) and you're placing an additional load factor on the landing gear, which of course increases the risk of failure.

 

Basically your problem was a combination of multiple pilot errors:

 

Failing to read aircraft documentation (Check out the manuals in your Docs folder in DCS).

Failing to follow weight recommendations for landing.

Failing to divert to a field with landing conditions appropriate for pilot skill level.

Failing to follow crosswind landing procedures.

 

Given those failures, if the plane was still in a more or less salvageable state, you actually did fairly well. Aside from making all the easily avoidable pilot errors that is.

 

You also might want to learn how vector math works. Predicting crosswind components and how to correct for them is vector addition. Most calculus texts cover that, some trigonometry texts cover it, and of course you can always look it up on Wikipedia.

 

At any rate the only bug is in the pilot training procedures. There's a reason they don't just hand out a pilot's license to anyone who walks into airfield and asks for one.

 

Practice and education. The Su-25 can be a bit tricky in crosswinds because of its big tail fin and narrow gear stance (and improper chute deployment makes it a lot worse), but if you read the procedure and practice, you'll get it right soon enough. :thumbup:

 

I'll also note that having a HOTAS or Pedal axis bound to the rudder really helps a lot when landing the Su-25. Keyboard can be a bit rough, as it lacks fine control.

 

 

Edit: I did the math, and the wind would have been pushing you across (off) the runway at about 24 km/h, and the relative wind direction would have been 6.5 to 14 degrees off of the runway centerline depending on aircraft speed at chute deployment. Pretty much what you described.

Edited March 7, 2016 by esb77

[majapahit]

You're missing the section in the manual where it explicitly states that for landings with significant crosswinds ..

 

(there seems to be a fair bit of unsolicited and rather condescending blabla in the remainder of your reaction, no thank you)

 

7 m/sec (13.5 knt) would or should be considered 'significant' crosswinds? That's horrible.

Edited March 7, 2016 by majapahit

[SFC Tako]

I'd have to say 7m/s is good for a sailing day with landlubbers aboard. It's "friendly" winds if you like. And about the nosewheel: it has happened to me as well :) Only thing to do when using chute is NOTHING, let it do the braking (for good or worse) and THEN release chute and finally, steer and then brake with wheel brakes. BUT I haven't tried 7m/s crosswinds myself yet...will NOW however :)

 

And esb77: You gotta work on your people-skills, man.

 

 

UPDATE: 7m/s is HEAVY crosswind in DCS. No way I could use the chute without bursting the tires. Or damaging something else.

Edited March 7, 2016 by SFC Tako

[esb77]

(there seems to be a fair bit of unsolicited and rather condescending blabla in the remainder of your reaction, no thank you)

 

7 m/sec (13.5 knt) would or should be considered 'significant' crosswinds? That's horrible.

 

 

Well, apologies for the tone. It was a tone for a pilot who didn't read manuals, not a tone for a gamer asking a simple question about a game.

 

 

In terms of the crosswind significance the force on the chutes is proportional to roughly the third power of the relative airspeed. So IAS^3. That's a LOT of force at landing speeds. The chute is attached to the tail of the plane, so there's several meters of airframe acting as a lever that the chute is pulling on. It all adds up pretty quickly.

 

I am a bit nicer than my posts sometimes indicate so for your benefit I present:

 

Crosswind Take-off One of the peculiar features of the Su-25/25T is the short span and base of the landing gear, which makes crosswind take-offs and landings quite challenging. Nevertheless, the aircraft can be held steady while rolling in a crosswind of up to 11-14 m/s, provided the runway is dry. When rolling in a crosswind, the aircraft will tend to bank with the wind, which can be corrected by counter stick force against the wind. The aircraft will also have a tendency to turn into the wind, which can be corrected with smooth pedal input in the opposite direction.

 

and

 

Crosswind Landing When performing a crosswind landing, estimate a lead angle directly to the runway threshold such that the approach can be flown with no bank or yaw. As you flare the aircraft just before touchdown, eliminate the lead angle to align the aircraft with the runway and push the stick into the wind. This will ensure that touchdown is performed with no sideslip and is corrected for the crosswind bank tendency when rolling on the runway. Once the main gear is in contact with the ground, release the pedals to center the nose wheel and quickly, but carefully lower the nose to touchdown the nose wheel. Once stabilized down the runway centerline, engage the wheel brakes. In a crosswind of greater than 4-5 m/s, the brake chute is not used as it would make it practically impossible to maintain the aircraft on the runway. If the aircraft veers when braking, release the brakes, correct heading and only then reapply the brakes.

 

I told you to look in Docs, but really it's in DCSWorld/Mods/aircraft/Su-25t/Docs, so I figured I owed you the effort of going and finding the full text, since I pointed you at the wrong location the first time.

[majapahit]

.. I'd have to say 7m/s is good for a sailing day with landlubbers aboard ..

exactly my thoughts,

 

and a more informative and appreciated response

 

Crosswind Landing When performing a crosswind landing, estimate a lead angle directly to the runway threshold such that the approach can be flown with no bank or yaw.

" estimate a lead angle directly to the runway " surprisingly I usually 'quick and dirty land'-ed in DCS by this way of cross wind lead angle,

 

but I always thought I was bending real life flight rules, since all approach videos I've ever seen show yaw and runway aligned landings. I was sort of abiding by the emergency non-rules of WW2 of course.

 

Actually for the crosswind exercises here I was trying to approach with yaw aligned with the runway, supposedly as required 'by the book ", silly me, what was I thinking.

 

I just read about cross wind landing " without yaw or rolling the plane " this in an Amsterdam Schiphol research paper about cross-landing procedures, but I think or rather see civilian passenger jets always aligning with the runway. Though the paper said " there will often be a combination of yaw and roll " method of crosswind approach.

 

.. In a crosswind of greater than 4-5 m/s, the brake chute is not used as it would make it practically impossible to maintain the aircraft on the runway. If the aircraft veers when braking, release the brakes, correct heading and only then reapply the brakes ..

 

" the brake chute is not used " that's surprizing or perhaps astounding, for the Su-25T will take forever, and more, to bleed-off speed in the roll, and blowing the front tire by breaking while steering is exactly the subject of this thread.

 

Me thinks the " the brake chute is not used " will easily land me over the end of Kutaisa's looong runway, unless perhaps I can touch down at the very beginning of the runway threshold.

 

I'm going to try, test and practice this of course ( 7 m/sec crosswind ), as supposedly this should or must work.

 

THX.

[SFC Tako]

Nalchik is the worst of all places, go there and ace it! :)

[majapahit]

Track from openbeta

 

Just ran your landing track,

that's a plane with empty pylons and you Barely came to a stop at the end of the runway.

 

With full pylons, like I tried, thats not possible

[Hook47]

Yea, this is simply the way it is. Drogue chutes, like a lot of aircraft systems, has pros and cons. The pro being ease of maitainance, lack of brake wear and cheap to replace. The con of course being the fact that you now have a huge and potentially dangerous aerodynamic force acting on the aircraft while landing.

 

I can tell you from my days in the Airborne that parachutes and dangerous and temperamental things!

 

As far as landing with stuff on the pylons. I will have to look at the manual but many aircraft have restrictions about what you can land with pertaining to ordinance and fuel.

[majapahit]

UPDATE: 7m/s is HEAVY crosswind in DCS. No way I could use the chute without bursting the tires. Or damaging something else.

 

I think you're right.

 

Tried the procedure as per the manual, 7 m/sec crosswind all pylons loaded,

 

I can land but I cannot align without bursting the front tire and I'm racing down the runway.

 

Well, that's the end of that scenario.

 

I saw someone describe the Su-25T as a 'flying brick', which is exactly the appeal of the plane (the A10C is leisurely flying compared),

 

but I cannot but wonder if this is real life behaviour / heavy loaded doing a RTB is akin an emergency return to airport after take-off, how much within design rationale is that (perhaps lose the fuel, but fuelburn in Su-25t is like a rocket, when 1500 is called, you better be near approach),

 

the fuel in my practice landing was already 60% carrying 9950lbs weapons.

 

Russian warplanes are renowned for being designed to flying 'always', and 7 m/sec crosswind a Cessna is able to do.

Edited March 8, 2016 by majapahit

[majapahit]

7m/s crosswind = 24mph and that is a huge crosswind for any airframe.

 

I do: google m/sec miles/hr

shows a conversion calculator,

 

I enter 7 m/sec and answer is 15.6586 miles/hour ( = 13.6 knots)

 

13.6 knots is way below your stated 24mph,

 

13.6 knots is a brisk crosswind (great easy sailing) nothing out of the ordinary

 

So?

[mvsgas]

Just ran your landing track,

that's a plane with empty pylons and you Barely came to a stop at the end of the runway.

 

With full pylons, like I tried, thats not possible

 

Dump you weapons, some aircraft can't land with all that weight. Mig-21 is a easy example;

from the manual

8. It is forbidden to extend landing gear and flaps or to fly

with landing gear and flaps extended when carrying eight FAB-100

bombs, or three drop tanks, or four S-24 rockets or two FAB-500

bombs, or four FAB -250 bombs or two UB-32 and two UB-16-57

pods (two guided missiles), or two UB-16-57 pods (two FAB-100

bombs) and two S-24 rockets (or two FAB-250 bombs) when fuel

remainder is 700 to 1100 L.

In emergency situations, when it becomes necessary to land

immediately with above indicated fuel remaining, jettison external

stores from the outboard stations over a safe place before

extending LG, and then land in the usual way.

just one example.

 

I barely cam to a stop because I landed in Nalchik, which only has around 7545ft of runway compare to Kutaisi's 8200ft. The way I tried to practice landing is either Batumy or Nalchik, if you learn to land on those two, you can land anywhere

[majapahit]

Dump you weapons, some aircraft can't land with all that weight. Mig-21 is a easy example;

from the manual ( .. etc etc jettison fuel and ammo)

 

My comment on this is that I can land the Su-25T with the exact same loadout of this exercise, 60% fuelled up and 9950 lbs of weapons load, because of practice, rather easily so, when no wind is dialled into the simulator environment (or headwind which makes things easier still), with use of the chute.

 

So why is that so easy, thus both the execution and the procedure apparently safe.

Edited March 8, 2016 by majapahit

[mvsgas]

You lost me. I no longer know what we are talking about.

[majapahit]

You lost me. I no longer know what we are talking about.

 

"some aircraft can't land with all that weight"

[mvsgas]

To clarify, your saying that you can land with that loadout if no crosswind, is that correct?

Edited March 8, 2016 by mvsgas

[majapahit]

To clarify, your saying that you can land with that loadout if no crosswind, is that correct?

 

exactly, sure can

[SFC Tako]

At 7m/s crosswind, I could not land with full loadout at Nalchik. Well I DID, but not without skidding off the end of the runway. And the chute? Tried it once - BIG mistake :)

I even tried dumping the whole loadout...just barely got to a halt a few inches from the end of the runway. With a blown nosewheel tire, of course ;)

[mvsgas]

exactly, sure can

 

Ok, so we established that you blow the nose tire on cross wind but no problems without wind with a heavy load. How about without a heavy load and less than 30% fuel?

Edited March 8, 2016 by mvsgas

[SFC Tako]

It's fully doable with a chute. But no chute...no nice landing.

[ame]

[/ame]

[esb77]

I was curious about whether your loadout was too heavy, and couldn't find a definite answer.

 

According to Sukhoi, the normal landing weight for an Su-25K is 11020 kg, and the maximum is 13200 kg.

 

Your fuel and weapons loadout gives a gross aircraft weight of roughly around 18500 kg in DCS.

 

The Su-25T supposed to be rated to take off about 2 - 4 tonnes heavier than the Su-25K, but even so, an 18000 + kg plane is probably over maximum allowable landing weight limits. Unfortunately I couldn't find official numbers for the T variant's maximum landing limit and the landing weight limits are not included in the manual.

 

If you dumped or burned fuel until you were down to something like 500 to 800 kg of fuel, it should be much closer to a good landing weight, maybe even within the proper limits for a T variant.

 

 

Edit: I'm pretty sure that the official landing weights for the 25T are greater than for the 25. I've never seen anything mention of improved gear though, so it's entirely possible that the amount of force needed to cause gear failure are the same in both variants. Without more official information I'd recommend always being extra gentle when landing the 25T.

Edited March 9, 2016 by esb77

[majapahit]

Just tested more options

 

7 m/sec crosswind all pylons loaded, chute deploy, disastrous

7 m/sec crosswind all pylons loaded, no chute deploy, drunken rollout, bad ending

6 m/sec crosswind all pylons loaded, chute deploy, unmanageable, mostly tire blow, irresponsible

6 m/sec crosswind all pylons loaded, no chute deploy, swerving, mostly tire blow, , irresponsible

 

5 m/sec crosswind all pylons loaded, chute deploy, EASY

 

WTH? Easy?

 

all with 60% fuel carrying 9950lbs weapons, simulation of going around immediately after a take-off.

 

How curious is this, behaviour seems to want to adhere to the warnings in the Su-25T manual concerning crosswind landing?

 

But what seems the case is a rather artificial tire blow cut-off point was entered or kept in the simulator 'to make sure' the manual is right?

 

My wild guesstimation would be that the real-life front tire of the Su-25T behaves or should or must behave (a lot) better,

 

where the tire collapse due to lateral forces of steering the nose gear, won't occur until let's guess 13 m/sec or 25 knots crosswind, which is the meteorological onset of storm.

 

Where from 6 to 13 m/sec you could and can at least steer your rollout to the end of the runway (perhaps beyond), and enjoy the safety of a plane not catching on fire because of unmanageable roll and/or swerving with mild crosswinds.

 

It's just seems improbable this present tire blow behaviour would be tolerated in an active real life deployment.

 

Then either the - dynamic - lateral forces on the nose tire seem overestimated or miscalculated, or the tire strength to dynamic lateral forces is underestimated or under calculated? Perhaps the available data on these were simply flawed.

 

DCS? what you think.

Edited March 9, 2016 by majapahit

[mvsgas]

I think you just found the cross wind limit of the SU-25T to be 5m/s, thanks. :thumbup:

[majapahit]

I think you just found the cross wind limit of the SU-25T to be 5m/s, thanks. :thumbup:

 

at a 13 knots little breeze, all deployment simply must seize, sorry landing Su-25T wanting to come back in with a slight change of wind, go burn up in flames, because we let you take of with a shitty frontwheel tire?

 

how improbable is that