S-turns on final

[Molesworth 1]

Given that one needs at least 30 degrees of bank to accomplish this, is there not a danger of a spin-in?

My own reasoning is that if they are done at 20-25 knots above stall speed and in a steep descent (which is the reason for the S-turns) the angle of attack will not be high.

[mad_jock]

If the angle of attack according to your theory is not high you won't stall therefore you can't spin in.

It has been known for instructors on there tod to be doing 60deg banked S turns at approach speed. Wouldn't do it myself as I prefer to do a side slip if to much height. I would only use S turns to lengthen the approach if we required an extra few seconds to get a clear runway.

If your that far off profile you need to resort to S turn's or side slip go around and get it right the next time.

[Rod1]

S turns are discouraged in Gliding in favour of a 360. Less risk of spinning in.

Rod1

[bingofuel]

As long as the speed is appropriate for the angle of bank I see nothing wrong with a steep S turn, although I prefer sideslips myself if the aircraft allows it.
It can make all the diffference in a PFL, but if I was flying a normal approach and finding I needed an S turn, I might just be asking myself 'why?' and consider going around and flying a better approach,

Bottom line is fly the aeroplane, but try to set a good example as well. I would hate to see a student or inexperienced pilot try to emulate such a manoeuvre unless they were well aware of the pitfalls.

[englishal]

but if I was flying a normal approach and finding I needed an S turn, I might just be asking myself 'why?'

ATC spacing for example? I've been asked to make an S turn by the tower before.

The fact of the matter is that as long as the wings are unloaded, they cannot stall and without a stall a spin cannot happen. Try a decent wingover and you can have the ASI reading near enough zero at 60 degrees of bank and not even the chirp of a stall warner.

Something to remember if you need to do an S turn / get slow / have an EFATO...If you PULL on the other hand you might find yourself in trouble.

[Mark1234]

As others have opined, i'd be looking to sideslip, or quite likely go around unless there's a specific good reason for the S turn.

To the original question, in my opinion there is little danger - provided you don't fly the plane like a hamfisted moron - i.e. don't heave back on the stick, and do use the footrests for their intended purpose

1) A stall in a turn does not mean a spin. It means a stall. Recovered by unloading the wing. Spins require a stall and a rate of yaw.
2) the aircraft will not stall unless you heave back on the controls.

Stall speed doesn't actually increase with angle of bank, it increases with wing loading. If you hold level, at 60deg you'll be pulling 2G, that's why the stall speed goes up. If you don't try to hold the nose up, banking the aircraft makes no difference, as in englishal's example. Anyone here heard of stall stick position? Seems to be a rarely taught concept..

Originally Posted by Rod 1

S turns are discouraged in Gliding in favour of a 360. Less risk of spinning in.

I find that quite interesting - I was taught (gliding) to always keep the field in sight, and never ever turn away. It takes more height than you think to do a 360, especially in any breeze, you loose height *AND* distance to the field. Would also question that there's less risk of a spin.

[Rod1]

Mark1234

Several pages in “Gliding” by DP on this. He makes the point that S- turns need as much turning as a 360 with more potential to get it wrong, and states that S-turns are discouraged. This message was also very firmly pushed by my instructors, but I may be out of date…

Rod1

[mad_jock]

Mind you how many instructors teach side sliping these days.

Or is it another tool in the box that has been forgotten.

[cats_five]

Originally Posted by mad_jock

Mind you how many instructors teach side sliping these days.

Or is it another tool in the box that has been forgotten.

It's on the Bronze training card at my gliding club. Unfortunately a lot of glass single-seaters nose dive if you try combining airbrakes and a side-slip.

[mad_jock]

I wasn't on about gliding instruction.

The more I see of gliding instruction, the method of instructor training and upgrading the more I see how !!!!e the alleged professional powered instruction is.

[IO540]

I don't see a problem with S-turns - they are just normal left/right turns. Even the Space Shuttle does them to lose energy

But if somebody is flying the final approach at Vs + 0.01% then maybe not such a good idea...

A sideslip is also not a good idea in some types, I gather, due to disturbance of elevator airflow. So they would be type-specific, whereas any plane can do S-turns.

I would also not do S-turns on short final - too much risk of not ending up lined up with the runway (fairly obviously).

[robin]

S turns are perfectly acceptable depending on the layout of the site

At my gliding site between certain heights you would never make a 360, but a downwind then into-wind turn to land on the wide bit of the field is fine.

In gliding we are taught to be flexible and to plan ahead and use whatever safe landing areas are available.

Each site is different and you'll be briefed accordingly

[gpn01]

Originally Posted by Mark1234

I find that quite interesting - I was taught (gliding) to always keep the field in sight, and never ever turn away. It takes more height than you think to do a 360, especially in any breeze, you loose height *AND* distance to the field. Would also question that there's less risk of a spin.

You've obviously benefited from quality instruction :-)

Going back to the original post, if you've been taught properly and your skills are considered by the instructor who signs you off as suitable for solo then there's no reason why an S-turn should increase the risk of spinning compared to a 360-turn. Admittedly it does require up to three manouvres (e.g. roll left, roll right, roll straight) that may need good co-ordination but that's not much different than, say roll left, maintain turn, roll straight. If you can't fly co-ordinated then I'm not sure if you should be solo.....

In gliding, as Mark1234 mentions, s-turns are preferred because you're able to keep the landing area in sight. As we don't have an engine this can be quite important when judging the circuit. Additionally 360-turns in the circuit significantly increase the risk of collision (do you really want to turn back to face opposite direction traffic?).

[dudduddud]

Well a 360 on approach is against the law where I'm from (and probably where you're from too!)

The safest option obviously is to do a go-around and try again but if you are in a pinch and you want to get back to the apron before that clock ticks over, s-turns are the safest bet.

The reason for this is that, in my New Zealand cpl flight test pass, I was marked down for slipping on final. The problem is that if you were to get into an out-of-balance stall (just say) at the low altitudes of final approach, you will not recover. If you are flying in-balance s-turns and for some reason you stall, you may be able to recover.

If you find yourself with passengers in that situation and you have to use s-turns to get down...

Tell the passengers beforehand!!!!!

I can't imagine anything more terrifying as a non-pilot passenger than having the plane roll over to 60 degrees angle of bank left and right so close to the ground during a manouvre which is widely touted as the most dangerous of the whole flight!

[Genghis the Engineer]

The reason for this is that, in my New Zealand cpl flight test pass, I was marked down for slipping on final. The problem is that if you were to get into an out-of-balance stall (just say) at the low altitudes of final approach, you will not recover. If you are flying in-balance s-turns and for some reason you stall, you may be able to recover.

I've been similarly criticised for this flying with UK instructors when sideslipping a PFL.

Personally, I think it's cobblers. A low level stall will almost certainly kill you whatever sideslip you have on in all likelihood, but so long as airspeed as maintained at or above 1.3Vs and below Va the risk of stalling is no greater than in a normal approach. At the same time, a sideslipped approach is much better for maintaining runway centreline and touchdown point visibility than an S-turn. That and the bank angle of the S-turn increases stall speed, so you either have to increase speed or reduce safety margins. Additionally, a slowly approached stall with full sideslip is unlikely to actually turn into a spin, that usually comes with more rapid deceleration.

However, we will fly the way that makes our examiners happy of-course

Better still, if too high, take flaps early. Won't work on all aeroplanes, but on many it will.

G

[Piper.Classique]

However, we will fly the way that makes our examiners happy of-course

Sideslipping-I asked my examiner about this, relative to the PFL, before flying my commercial GFT The reply was to the effect that if the flight manual didn't prohibit it then it was OK. So I did, and I passed.

At the same time, a sideslipped approach is much better for maintaining runway centreline and touchdown point visibility than an S-turn.

Yes, and it's fun. Mind you, so are the S turns....
I would argue for both in a forced landing, as being easy to vary, rather than flaps which tend to be a rather coarse and essentially one-way adjustment.

[Mark1234]

I've also been criticised for sideslipping. Personal theory is that it's so uncommon it scares people who might not be familiar and current. People fear what is out of the ordinary. Try landing a pitts without sideslipping

Now, caveat emptor: this is most likely entirely type, and possibly aeroplane specific, but I went out and deliberately stalled a decathlon in a full blooded, rudder on the stop sideslip. Guess what it did?

Stalled. That's it. No wing drop, cleanly and straight ahead. No drama. Who'd have thought it?

No guarantees that all a/c will behave in such a benign manner (and I am in very regular spin practice), but my take is that a rate of yaw is required for a spin. In a steady sideslip in a straight line both wingtips are travelling at exactly the same speed.

[It flies]

Mind you how many instructors teach side sliping these days.
Or is it another tool in the box that has been forgotten.

I'm halfway through my PPL course and I just learned to sideslip. So it is still being taught.

Anyone here heard of stall stick position?

Mark1234, can you please explain what you mean by this?

[BackPacker]

Stalled. That's it. No wing drop, cleanly and straight ahead. No drama. Who'd have thought it?

I've never flown a Decathlon but my gut feeling tells me that this is not entirely unexpected. Being a high-wing, the center of lift is above the center of gravity. Because of that, it doesn't need dihedral to remain stable. And from memory, it also doesn't have any sweep. It's basically a straight plank wing. That means that the lift and AoA, even in a severe sideslip, is more or less identical left/right. (There might be a little blanking from the fuselage though.)

With a low-wing aircraft you need dihedral to remain stable. In a sideslip, this causes a difference in AoA left/right, and this would induce, I think, a wing drop when stalling.

At least, that's what my gut feeling is telling me. Next time I'm up in the (low wing) R2160 I'll try a full-rudder stall and see what happens. (And yes, I'm current in spinning an R2160.)

Mark1234, can you please explain what you mean by this?

What Mark means is that a stall is not so much associated with speed, but with the AoA of the wings. And these have an almost 100% direct relationship with stick position. In other words: when you pull back at the stick, the aircraft will stall at the same stick position, regardless of speed, actual weight/balance, altitude and a number of other factors. As long as you keep the stick/yoke forward of this position, you will not stall or spin.

(Note that the stall stick position may vary slightly with the engine power setting though, since the propwash over the tailplane makes the tailplane more effective. In addition to this, the propwash also has an effect on the AoA of the wing portion that's in the propwash.)

[Gertrude the Wombat]

if I was flying a normal approach and finding I needed an S turn, I might just be asking myself 'why?' and consider going around and flying a better approach

There's another method which works with at least some Cessnas.

Full flap, just point the nose down. You lose height as fast as you like, and it doesn't speed up enough to bust the flap limiting speed. OK so you might end up a bit fast over the hedge, but it works if you've got 2km of tarmac runway.