Sideslip
 

I find it interesting that instructors, from different countries, use different names/definition on basic aviation concepts.

USA: Slip/skid - slip=yawing nose outside the turn, skid= yawing the nose inside the turn. The slip can be a tool, the skid not so (stall/spin). Sideslip= used for crosswind("side"wind) landings, using only enough rudder to parallel centerline, while bank correct drift. Forward slip= used to lose excess hight, usually with full rudder, bank contol track, normally in to wind to make transition to sideslip safe and easy. Sliping turn=forward slip in turn.

In some other countries the word skid is not used...
Every slip is called sideslip....:rolleyes:
How do you then explain the transition from forward slip to sideslip. What do you call a skid?

Question:

Which countries use the term skid? Forward slip?

I've read somewhere that the Brits used the term sideslip for landing in sidewind. Do you know the history of these terms and why there is so much confusion out there?

Not quite- there's there is indeed the sideslip or "wing low" technique...some Brits also use "crab" for the wings level "kicking off drift" method.

Be interesting to see the answers you get, might be a case of " you say tomatoes and we say tomatoes "...,,.:E :}

I can't speak for all Australians and not saying this is a 'textbook' answer but I generally think of slip/skid as out of balance flight that occurs when the aircraft is turning and sideslip as out of balance flight when tracking straight.

Slip when the tail of the aircraft is slipping inwards on a turn, skid when it is skidding outwards in the turn. Usually (but not always) slipping or skidding is unintended.

I think of sideslip as out of balance flight when the aircraft is not yawing (ie when travelling in a straight lateral path), and is something often done deliberately.

eg sideslip is used (particularly on aircraft with no flap) to increase the rate of descent on approach or to get better visibility on approach (eg in an aircraft like a Pitts where over the nose visibility is not great) or to allow the aircraft to stop drifting when there is a cross wind on a landing etc.

I have heard people use terms like 'forward slip' and recall someone arguing there are multiple types of sideslip (and who had different names/uses for all of them - high nose/low nose/forward etc) but for me I just think in terms of skid/slip occurring when the aircraft is out of balance in a turn (due to over or under ruddering) and sideslip when the aircraft is out of balance when travelling straight.

Like I said, that may not be technically correct but is how I personally use (and think about) those terms in practical flying and how I used the those terms when I was instructing.

Probably I'm just a slow coach sort of chap.

Sideslip, to me, just means that the wind is coming other than from dead ahead. Can apply in straight or turning flight. One can be really fancy and talk about slip and skid, if that's useful.

Push your luck too much with slip angles and it can get interesting ...

Beyond that, I get a bit weary.

I am with JT.
The only term I ever use, irrespective of aircraft attitude, flight phase or configuration, is sideslip, either left or right, sometimes knowledge of the magnitude is useful.
Never use the term "balanced" as I can never be sure what people mean by this term. That is, do they mean zero sideslip, or ball in the centre?

That is, do they mean zero sideslip, or ball in the centre?

Now, that just has to cause some head scratching and bring out a question or two, I would warrant .....

for practical purposes I think that elegantly sums it up.


I used to teach it as when your bum was not being pushed left or right in the seat (and sometimes got students to close their eyes while I flew out of balance and got them to tell me me which way). Not saying it was the best way but thought it might help develop an instinctive feel for it rather than only know by staring at the ball.

Jongster, as I said is "out of balance" flying with sideslip, ball not centred, flying with zero sideslip ball not centred, or flying with sideslip with the ball centred?
That is why I never use the term.

Feeling humbled, I just learnt something :O

I'd never really thought about situations where the aircraft could have the ball (or your bum) centred but be sideslipping before but yes... wings level, aircraft tracking straight but the longitudinal axis not dead on to the airflow

eg with propellor P factor trying to yaw nose one way, compensating for that with rudder and keeping wings level so tracking straight - straight and wings level would mean ball in the middle.

In that situation - is it in balance? Buggered if I know!

Thanks a lot zzuf :mad: I can no longer say "keep it balanced". Bugger. :uhoh:

Thinking something like a glider's yaw string would indicate difference from a balance ball in that situation...

Hi Jonkster, have a look at the theory of asymmetric flight as well - small bank angle changes can change sideslip angle markedly, even change the direction of sideslip.
Yaw strings were good enough for Air NZ DC8's......

As I suspected, there is a confusion out there on very basic concepts.

The US Private Pilot PTS/ACS states clearly what is required knowledge and skill for the checkride. The same for the glider pilot certificate. A correct forward slip shall be demonstrated, and if no wind, the sideslip shall be explained. If unable, you may fail the checkride.

In a glider, a skid in the circuit to land could fail the checkride. To demonstrate the difference between skid and slip I have this done in a turn at altitude. A skid + stall (as in base to final turn) will start a spin, a slip, on the other hand, will first level the wings.

This is how I teach the forward slip:

https://youtu.be/yxy2MnUnfUM

Thanks Wingman - pretty clear I would fail those tests as I have no idea of what is required! The terms are meaningless to me. I would suggest that sideslip in either direction, at the stall, upright, inverted, turning or straight, is a recommended spin entry technique.
The video was a full rudder sideslip to the left in the landing configuration. I couldn't see the forward part. Perhaps a video of a backwards sideslip would be enlightening.

zzuf, yes I'm aware of the resistance to these concepts out there, as I fly internationally. That's why I started this thread.

As long as you can explain these ideas, the words you use don't matter much to me, except in preparation for a FAA checkride. I do favor these definitions, though, as they make explanations better. I suppose you don't use the word "skid" either, eh..?

Zuff - Well this was the point with this thread, to illustrate the different opinions about about a basic concept.

As long as you can make a meaningful explanation for your student, then I don't care what words you use, except in the preparation for a FAA checkride.

I favor these definitions. They makes it easier for students to understand and differentiate them, i.e. sideslip for crosswind (sidewind) landing, forward slip to lose hight.

I suppose you don't use the word "skid" either?

Zuff - Well this was the point with this thread, to illustrate the different opinions about about a basic concept.

As long as you can make a meaningful explanation for your student, then I don't care what words you use, except in the preparation for a FAA checkride.

I favor these definitions. They makes it easier for students to understand and differentiate them, i.e. sideslip for crosswind (sidewind) landing, forward slip to lose hight.

I suppose you don't use the word "skid" either?

Zzuf, I would have to disagree a little bit there - I know of at least one reasonably common, spinnable aircraft, that (from practical experience) you can stall while sideslipping and so long as you are not yawing (ie doing the kind of sideslip you might do on an approach to lose height), it will stall in a reasonably stable and docile way without entering a spin.

The first time I tried this I was very green and had been arguing with another much more experienced instructor, that doing this would cause it to spin. He said OK let's do it and see. We went up to altitude and did it - I was quite surprised (and firmly put in my place) when it stubbornly refused to enter a spin that way.

However the very same aircraft enters a spin sharply if you stall it while yawing in a 'skid' (by that I mean applying enough rudder to cause the aircraft to yaw but while holding off bank) eg what might happen low to the ground if a pilot is scared of banking but wants to change the aircraft direction to line up with a strip and so subconciously boots it around with their feet.

At that point I agree - pretty generally I think that form of sideslip in a stall will spin most spinnable aircraft (and similar to what you say, for some aircraft 'out spin aileron' is the recommended spin entry technique).

For me I think yaw and its direction is the issue that results in different behaviour when sideslipping in the stall. ie - when excessive rudder is causing yaw, when stalling, it gets interesting.

NB for the earlier case where it won't spin - I most certainly cannot say it applies to all aircraft and am curious to hear about ones that behave differently.

JT, responding to earlier comments that you edited, I would say yep, fair enough.

I think you are right - my terminology and description (and my recollection of what inputs I am actually using) is fuzzy. It would not be helpful for a student at all if I was to explain this like I have here.

What is concerning is I know I have explained it much like that in the past :eek:

This has opened a can of worms for me!

I am now sitting here in a swivel chair pushing myself left and right visualising exactly what control inputs I put in and how the aircraft responds and am now thinking that maybe what I am thinking I do is not what actually I do! :)


I am looking at my hand and feet position in the swivel chair for the two imagined configurations and... they seem to be pretty similar - yet one I know from experience will result in a spin and the other a floppy stall :hmm:

The difference seems to be one involves continuing yaw, the other is tracking straight (but with the nose yawed to the side).

I am wondering what causes the the sharp spin entry I described when I imagine I am 'over ruddering a turn, holding off bank' sideslip compared to the more docile stall behaviour when I imagine myself in a 'cross controlled' tracking straight, one wing down nose sideways approach type sideslip.

Could it relate to perhaps the stall in the former is an accelerated stall due to the aircraft turning? Almost a subtle flick manouvre?

I need to go and try it and see what actually I am doing with the controls and what happens rather than relying on what I think I have been doing.

JT, responding to earlier comments that you edited, I would say yep, fair enough.

I deleted those comments because, on re-reading your post, it was clear that I had misread it first time around .. mea culpa.

You would do well to heed zzuf's comments .. his background is more than eminently suited to this sort of discussion. Hopefully, he will continue in the discussion.

Likewise, I shall endeavour to get djpil interested in joining the discussion.

Between the two of them, you have a wealth of relevant knowledge and experience.

As to your comments, above, it probably involves not so much the mere fact of slip .. but what happens to rolling moments, drag asymmetry, etc when the aircraft lets go for whatever reason ...