Not being a real pilot, I don’t know if side slip is allowed on all aircraft or if it is effective for each type. But I recently tested on a couple of planes in the sim and found that some models didn’t seem to descend much when inducing a side slip or front slip. Mostly smaller GA planes could enter a rapid descent in a slip, but that’s more difficult for larger planes. Is this something not well simulated or just how airplanes behave in real life?
In some crosswind landing situations, side slipping a large passenger airplane may be required/advantageous.
However, to do so may be risky due the possibility of scrapping a nacelle if the wings are not level at touchdown. This may be particularly true for outboard nacelles on a four engine airplane.
A more normal large airplane crosswind landing technique is to crab the airplane into the wind until near touchdown and then use rudder to align the airplane with the runway. This requires skill and timing to minimize side drift before the landing gear contacts the runway.
Thanks for the explanation! However I am more concerned about the usage of front or side slip to control descents, especially in steep terrain and when rapid changes in altitude are necessary while not over speeding the aircraft. I did notice some airliners in MSFS behave weirdly in a slip. The amount of aileron input needed to counter the yaw effect is not consistent. Sometimes they slip with full rudder and almost neutral ailerons, whereas GAs needs fully crossed controls to maintain the attitude.
Do a lot of quickˋnˋdirty flights with the PMDG 738 for test purposes. Most times I land the aircraft as well but without any usual approach path. That includes often, I’m too high to land, so I try to loose height with massive sideslips and mostly I can catch the runway. If the aircraft behaves like a real one? Don’t know, I’m not a real pilot, but from the physical part and my understanding, high v/s without gaining speed or even deceleration, it seems correct how the plane behave.
That’s true, with the 736 I can easily maneuver a slip, which I guess to be correct for a study level addon.
Just to confirm, you are referring to forward slip? ie cross controlling the plane in order to increase drag and descent faster or get back on approach path?
Overall, any limitations IRL should be found in the manual. For example on 172 u should find a note that say: “avoid forward slip with full flaps …”
On GA planes, it’s a good practice, working very well on taildragger because of the huge rudder usually and esp usefull on planes without flaps.
On airliners, it’s the same physics, and there are some reports of big tubes that used forward slip, but only in emergency situation, pretty much all were full engines out.
But slipping = unstable approach pretty much, and that’s a go around for any airlines out there, so you will never see an airliner slipping during normal operation IRL but it should work the same.
In the end, from my experiance, it works ok in the sim, i guess it’s a mix of both quality of flight model and airplane geometry. Talking here about my GA flying.
That’s very insightful! Yes, I remembered first hearing about forward slip in bush flying, where slipping down a narrow valley and straightening out just before touchdown is exciting.
Honestly I can’t really tell the difference between a forward slip and a crabbed approach in crosswind. I only noticed that the wing should be level when crabbing, but both require crossing controls and pointing the nose at an angle. They surely are different than side slipping, but what about in between them?
Slipping is not very well simulated, IMHO, but you can do it both for crosswinds and getting down fast. I recall it was much easier IRL with the C152. I don’t think the rudder simulation is very good in the sim. I think crosswind components are too powerful on the rudder, and the fluid dynamics simulation adds to the torque on the rudder.
Also, correct setup of controllers is important. I’m running this setup for the Kodiak now on all my modules. Remember, when you change your controller sensitivities, it takes some time for the brain to adjust (muscle memory). So, if a change feels odd at first, give it some time before trying a new setup.
Most famously the ‘Gimli Glider’!
@Zwen0416 This is a perfect example of slipping an airliner in an emergency situation in order to descend to make the runway:
Yep I was aware of that! Very cool but I found it hard to replicate in the sim (hard to replicate anyway ). As @OldpondGL mentioned, I guess most aircraft in the sim aren’t able to slip properly, with the exception of 737, 146, JF Arrow, Kodiak and a few others (as far as I have tested). To be fair I first noticed the weird behavior when I missed my TOD and didn’t want to waste time. The ATR for example, does slip with YD off, but keeps swinging back and forth and doesn’t want to slow down. For now I guess I would avoid such behaviors in airliners as to be safe
Good to learn. I wouldn’t know that limitation without fully checking the book!
Well a crabbed approach and a forward slip are two different things.
If you have some crosswind component, the plane will naturally crab into the wind, due to the vertical fin being hit by the wind, so even if your plane is pointing 15° right of the runway, your ground path is still straight runway heading, you don’t have to do anything it’s natural, the plane will just flight sideways due to the wind.
Only just before flaring, you want to take that crab out, by applying rudder, and adding some ailerons into the wind. Ailerons because, applying rudder brings induced roll(basically because one wing is " going faster than the other ") and the wind is also adding to that.
A forward slip is another case, you are deliberately putting the plane sideways in the air in order to use the fuselage as a “speedbrake”.
Hope i could make it clear.
About the 172 it is a warning, it’s not prohibited, i know in some clubs it’s prohibited tho. Basically because of the high wing + flaps, the airflow over the elevator can be reduced/turbulent, and that creates some buffeting than can be felt in the yoke. But never heard any incidents due to it.
- The warning was to avoid forward slips with full flaps when C-172s were equipped with flaps that could be extended to 40 degrees**. After Cessna restricted the ability to drop flaps no more than 30 degrees, the warning was discontinued for those aircraft. You still find the advisory in later 30-flap 172’s.
IF YOU ARE REALLY INTERESTED why — (read on)
The basic problem is that sideslip induces a cross flow over the fuselage that can increase the local negative AOA and flow disruptions beyond that already caused by the turbulence and downwash being generated by the flaps. The stabilizer surface on the “lee” side of this cross flow may get enough flow disruption to be felt in the elevator, maybe accompanied by a bit of pitch bobbing at some extreme condition that maximizes the tail loading, like side slipping at forward C of G with large flap angles.
- In spite of its very powerful flaps, the 172’s issue is fairly benign (or there would be a prohibition against using slips with flap as opposed to an advisory).
This can be a significantly worse problem with stabilator or all-flying tails that operate at larger negative AOAs than fixed stabilizer tails, as Cessna Cardinal owners are well familiar with. The Cardinal required slots to be added to the stabilator inboard leading edge to fend off tail root stall during landings, and resulting broken nose gears, during the first year of production, and that was just doing regular landings with maybe a bit of slip due to crosswind (the '68 Cardinal I once owned had the field mod slots added under the “Cardinal Rule” service bulletin - Cessna sent teams out to modify every aircraft pre production cut-in in 1968, somewhere around 500 a/c, and you can slip them with flap all you want).
The stabilator equipped Thorp T-18 homebuilt had to have a flap limitation added due to stabilator stall in sideslip (John Thorp did some testing after an incident in the 60s, discovering that the stabilator could stall with full flap, forward CG and sideslip, causing a nasty pitch over, and advised owners not to use full flap for landing).
If you got here – now you know !!
Be aware that many(all?) large transport category aircraft have a prohibition against putting large sideloads on the vertical stab.
I’ve never heard one that permitted slipping, in modern use anyway. What some old Clipper Skipper did to a 747 in the old days is probably best left to the imagination!
Actually, I recall being advised to be very judicious with rudder in any swept wing jet that I ever flew.
Even tactical jets tended to reserve stomping on the rudders for slow speed maneuvers, lest the back become the front without warning.
In MSFS the modern airliners much of the automation is focused on keeping the aircraft upright and stable despite pilot control inputs. It is possible to disable ALL automation allowing slips, stalls, barrel rolls, loops, and any other desired unusual attitude.
This is for the Kodiak, but the theory parts are applicable to all crosswind landings. For the sake of not making the tutorial even longer I omitted the kind of explanation given above by @N6722C why an airliner would prefer crab to low-wing, but you can also see in the video how the Kodiak will have greater drag when in a slip with more negative VS as a result.
Of course the above post gets a “LIKE” from me – It mentions me in a favorable manner
( I think ? )
This is right. A 5knot crosswind component will have 4 or 5 times the turning effect on the ground than either prop-wash or torque. You can raise these values to excessive amounts in a SEP, but still need to use LEFT rudder in a 5knt right crosswind. Even a 1knot crosswind can overpower the effects of torque & prop-wash.
Also nearly all rudder inputs are massively over-sensitive!with all types of controller (low & high end controllers, twist joysticks) in both aircraft with CFD and without. But moreso with CFD.
My one biggest tip to anyone flying any aircraft in MSFS and not using rudder assist is to reduce the reactivity of your devices rudder/yaw axis to 50% or less and set at least a -30% curve. You will immediately have smoother take off and landings and a much less twitchy experience.
It does! I was just covering myself for the inevitable ‘why do you not use crab’ questions and you explain it well. GA aircraft are not airliners and vice versa . What is good for one is not good for another!