The A321 seems to have an issue when cruising at a high altitude. Just today, I took off from Sacramento, en route to Burbank, when my aircraft entered a Dutch Roll at 38,000 ft MSL. My cruise speed was at Mach 0.8 with around a 60% load.
For those of you who are unfamiliar, a Dutch Roll is an out-of-phase oscillatory motion in which an aircraft sways from side to side, due to disturbances in the lateral and directional motion.
This isn’t the first time that the A321 has behaved out of the norm, but if anyone can provide tips on preventing this, that would be great!
Sometimes the in-game physics like to troll a bit 😂 In all seriousness, do you cruise with a set trim? I always recommend 10-18% trim when cruising in the A321.
The 321 can be tricky, but I’d suspect the aircraft might’ve been a bit heavy for FL380. As far as trim is concerned, I trim until the magenta line disappears, that ensures you’re trimmed appropriately for said configuration. Try descending to a lower initial cruise altitude, the 321 often requires step-climbs. I’ve flown this bird many times in game and never encountered the Dutch roll.
The A321 has never seemed to fare well up high around those sorts of altitudes, even without a heavy load (at least in my experience). I don’t really see how this could have happened. It’s possible you were too heavy for that altitude but given the route and the load, I really doubt that. Hopefully someone else can shed some light on this
Just too heavy. The easiest fix is flying lower, trim may help slightly but not sure. IF’s A321 is most efficient at FL280 so it has a pretty low max as well.
As someone who flies the A321 a lot, and who has had his fair share of experiences like yours - IMO the dutch roll is an autopilot issue, specifically with autopilot trying (and failing) to hold a heading - in other words this is an issue for the devs to solve.
Other aircraft have this issue as well, in other flight regimes - ive for example noticed that the MD11 cant capture an ILS in APPR unless you are at or below cca. 190kts, if above that it just keeps overcorrecting weirdly - and that weird overcorrection is the same issue that causes the A321 dutch roll. If you turn off LNAV/HDG autopilot the roll stops by itself, but you cant fly like this obviously.
So, back to the issue at hand, id advise two things:
As others said, you were too heavy, descend lower. The flight/load envelopes in which you can fly the A321 at or above FL380 are very very limited. Stick to FL360/370 as an altitude limit in most cases on regular A321 routes.
Other factors contribute to the roll. In my experience trim does nothing to contribute. Angle of attack management helps, but is very limited. Accelerating to .81 mach helps a little. Besides that:
2.A Watch out for wind, a crosswind in cruise is very bad and often induces a roll, as well as a tailwind component, if im not mistaken - ive forgotten some of my tricks of the trade ;)
2.B Experiment with Center of gravity balancing. I vaguely remember loading more cargo in the front of the plane helps stabilise it, as the “regular” IF loading, balancing front and back cargo, contributes to the A321 getting tail heavy, which obviously exacerbates the dutch roll by making the plane basically a giant pendulum which autopilot will keep swinging until an unlucky swing kicks off autopilot, sending you straight into the ground :)
Wow, thanks so much for the information! The reason why I was at FL380, was because SimBrief planned my route and gave me that altitude. I also think that the A321 needs a physics rework as well because it behaves in almost the opposite manner as its shorter family aircraft. The A321 acts stiff when controlling, when it should be the most controllable A320 family aircraft, due to the longer moment arm between the CG and tail.
Step climbing: use stepclimbs planned by simbreif
(if you dont use simbrief, try climbing to fl300, and if its stable, climb 1000ft more and repeat) (if you dont use any flight planner youre a criminal)
Fly a bit slower: a normal cruise speed in an a321 is M.74-M.78
There is no fbw or hydraulic system in the game so basically all the planes have the same auto pilot and you can go to mach one in the 787 and do -3.000~ m/m for Europeans and -10,000fpm for Americans in the a 380 and go super close the the edge of space in the fighters so ya. It could also be a stall idk or the plane turned a bit too aggressively and is actively trying to stabilize like for example accidentally turning of the ap i do that alot when trying to step climb manually or increase/ decrease speed, hdg or climb rate.
Hi, others have mentioned trim, but I don’t see how trim has anything to do with the A321’s oscillating roll dependence on flight conditions.
Trim is merely a hold assist for the elevator position.
Such assist is a separate concept from flight stability as a function of weight, speed and density altitude (effective pressure altitude experienced by the aircraft).
At standard temp, 60% load, and FL380 near the vicinity of cruise speed, I tested something like 4 degrees angle of attack.
If you spike the rudder in one direction, under the above conditions, you get a sense of the tendency for yaw oscillations.
FL380 is rather up there in altitude, and the A321 modelling I think, is just challenged under the load, speed, and density altitude that result in the measured 4 degree angle of attack at such altitude.
Descending somewhat until more fuel is burned off, for example, seems to give more stability related to the decrease in angle of attack (again due to a lower density altitude for the given load and achievable IAS).
But any moment arm increase in yaw torque would also be affected by any differences in tail and rudder scaling as well as rudder input and damping rule compensation?
OP’s flight was only a hour or so long so it’s very unlikely step climbing was necessary. The problem is that the A321 physics are broken so using something from Simbrief isn’t gonna work.
This is really unnecessary and also against RSVM rules. Doing this could result in cruising at an old flight level going west or an even flight level going east. You really just have to be reasonable based on past experiences and know to stay closer to maybe FL340 at that weight, etc.
I don’t. I copy real world flight plans when possible and get performance data and altitudes from community topics and never have issues with unstable cruising.
Really depends on cost index, though “standard” is M.78. But yes, M.80 is a bit fast. But given OP’s high altitude and therefore low IAS for his weight I doubt going M.02 faster was a significant contributor.
Today I have experienced the same problem by flying the 737-700 flying from FNLU to FACT. After 2 hours of flight the plane started doing that but a few minutes later it stopped doing it. I thought it was the wind since it had crosswind at about 50knts.
Multiple people in this thread have suggested slowing down, which you should absolutely not do! This is a clear mixup on the relation (inverse correlation, to be more precise) between IAS and AoA
The dutch roll is induced by autopilot overcorrections, but is provoked exclusively by an increased Angle of Attack, which will increase if you slow down. Cruising at a slightly faster .8 - .81 mach is the only way to avoid the roll, besides cruising at a lower altitude obviously. Very strong crosswinds in cruise are also to be avoided
Hi, crosswinds only have an effect if they are variable and change rapidly enough.
If you had a steady 250kt crosswind, it would have no aerodynamic effect on the aircraft, as the aircraft is drifting with the wind mass, as it proceeds through that wind mass as if it were in still air.
Of course, the ground track and time to destination would be affected by the drift. But again, no aerodynamic effect.
Of course, we are in full agreement there. I specifically said very strong crosswinds in cruise, since a >80kts crosswind at higher flight levels is most often accompanied by some variation in the wind, gusts and turbulence ;)