S-turns on final

[Say again s l o w l y]

Gertrude, I'm going to slap your legs for that one!

If you are in a normal powered aircraft such as a Cessna Spamcan and you find you need to s-turn or slip it in, then go around and do it again properly.

If you have had an engine failure and have no choice, then do whatever you need to get in. Read the flight manual as to whether sideslips are prohibited (For those who assume that Cessna 172's are prohibited, then RTFM. Not all 172's are.) and then go and practise the damn things at altitude until you can do it without screwing up.

It isn't hard and might just get you out of trouble one day.

S-turns are fine, but side slips at least keep you pointing in the right direction.

Am I right in thinking that people haven't been taught how to side slip whilst training for their PPL? If so, I'm going to shake my head in disbelief.

[Pace]

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.

It is worth noting the control movements at differeing speeds. At slow speed ie in the flair you may pull the column back almost to the stops or some 9 inches.

The rudder is the same! At slow speeds almost full rudder is required for a given effect with a large movement on the rudder peddles.

Now at cruise speed measure the column movement to displace the aircraft to a given angle. You will be shocked that the 9 inch or so movement at slow speeds now reduces to maybe half an inch for a given displacement.

The control forces are high and there is no way in a high speed stall you could move the control column to the slow speed position to achieve a high speed stall.

There is nothing more wrong with an S turn on finals than a sideslip. All you are doing is increasing your track distance to touchdown and hence increasing your spacing to the aircraft in front.

Both require a certain amount of minimal skill the S turn with less danger as your glideslope remains the same as does the rate of descent as equally does your speed.

Pace

[Mark1234]

Oh good, I was hoping someone would bite! I might have guessed backpacker would get it, It is as he describes (let me know how the slipped stall in the robin goes - I have theories, but very interested in the outcome).

We're all familiar with the concept that you trim for a speed, and if you vary the power the a/c will climb/descend, but remain at the trim speed; the elevator is just a larger, more authoritative trim tab.

To be honest I'm not sure that weight and balance do not change the position, however, empirically they don't change it a noticable amount on anything I've flown. The simple fact remains that if the stick is forward of a certain point you're fat and happy, if it's back around that point you should be paying close attention.

Originally Posted by Pace

Now at cruise speed measure the column movement to displace the aircraft to a given angle. You will be shocked that the 9 inch or so movement at slow speeds now reduces to maybe half an inch for a given displacement.

The control forces are high and there is no way in a high speed stall you could move the control column to the slow speed position to achieve a high speed stall.

Pace, I suspect you may be mixing deck/aircraft angle with AOA the angle of the wing to the relative airflow. At higher speed, wing DOES stall at the same stick position (as close as I can measure it), but at significantly more G loading (provided the wings don't drop off..) throw in a bit of rudder and its called a flick or a snap depending on where you're from. Not something to do in a PA28, but they fly by the same aerodynamics as the pitts, decathlon etc.

[It flies]

O.k., Mark1234 & BP.

let me know how the slipped stall in the robin goes

Mark1234, I suggest you have a go in the Pitts and report back?

[Flyingmac]

S-turns are handy when you've been cut up on final. Sideslips are handy when you've cut somebody else up on (long) final. Both should be taught a lot more than they are.

[Pace]

Pace, I suspect you may be mixing deck/aircraft angle with AOA the angle of the wing to the relative airflow. At higher speed, wing DOES stall at the same stick position (as close as I can measure it), but at significantly more G loading (provided the wings don't drop off..) throw in a bit of rudder and its called a flick or a snap depending on where you're from. Not something to do in a PA28, but they fly by the same aerodynamics as the pitts, decathlon etc.

Mark

If it was as simple as that it would be an easy task to make stall free aircraft right from 747s to 152 by limiting the stick movement to just before the stall.
Sadly it isnt that simple.

Aircraft manufacturers would not need to bother with all the expensive gizmos to prevent a stall in heavies but would have a simple stop before that AOA is reached .

Pace

[BackPacker]

If it was as simple as that it would be an easy task to make stall free aircraft right from 747s to 152 by limiting the stick movement to just before the stall.
Sadly it isnt that simple.

Aircraft manufacturers would not need to bother with all the expensive gizmos to prevent a stall in heavies but would have a simple stop before that AOA is reached .

Actually I recall from reading Langewiesches Stick and Rudder that it is that simple, and aircraft that were impossible to stall (and thus, spin) have been done in the past. Precisely by limiting elevator travel.

However, these aircraft were also a bitch to land, needed especially strengthened and long landing gear and such since they could not flare properly.

[Pace]

http://en.wikipedia.org/wiki/Stall_(flight)

Backpacker

This makes a good read see the list of anti stall devices you could make a fortune

pace

[Mark1234]

Pace, I refer you to my previous comment:

Originally Posted by Mark1234

To be honest I'm not sure that weight and balance do not change the position, however, empirically they don't change it a noticable amount on anything I've flown. The simple fact remains that if the stick is forward of a certain point you're fat and happy, if it's back around that point you should be paying close attention.

I'm sure there are reasons why it might not so simple - config changes (flaps will definitely change the position), weight and balance, perhaps regulatory requirements, in all of which the big tin has to accomodate much more variance. In any case, I believe you're still incorrect in as much as I quoted you.

However, it is but a useful tool in your armoury. I (for whatever my opinion may be worth) would recommend it is used two ways:
1) For pretty much 1G flight at slow speeds (i.e. approach), with respect to the configuration of the day - i.e. having previously stalled in that configuration at altitude to establish a datum.
2) As a gross error check. IF the stick is back in your guts you should be considering very carefully what you do next. If it is well forward you can be fairly comfortable.

I make no claims to know it all, I've just sought out interesting people to fly with, and done a lot of dual time, particularly aerobatic where you get to explore things a little more than those who get their PPL then avoid dual like the plauge.

@it flies - sure, I'll try to remember next time I'm up.

[Crankshaft]

There is nothing more wrong with an S turn on finals than a sideslip. All you are doing is increasing your track distance to touchdown and hence increasing your spacing to the aircraft in front.

Both require a certain amount of minimal skill the S turn with less danger as your glideslope remains the same as does the rate of descent as equally does your speed.

Generally I agree with you Pace. However I would consider a S turn to be somewhat more than just an increase in track distance. The bank itself increases the induced drag (especially at greater bank angles) and therefore also increases the rate of descent - steepens the glidepath.


It seems to be forgotten here that some aircrafts are not well suited for either of sideslip or S-turn. For example some modern aircraft with slim rounded composite fuselages do not increase its rate of descent as significantly as for example Piper Cubs or Decathlons in a sideslip. In many of those composite aircrafts it is much more efficient to use an S-turn. Similarly there are also some aircrafts that aer no good for S-turns depending on sluggish roll rate for example.

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

I think you missed the point in doing sideslips/S-turns. We practice this for being able to land following an enginge failure when a go-around obviously is not an option.

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.

The idea of making sideslips or S-turns is to be able to land even when you don't have that 2km tarmac, i.e to touch down at your aiming point rather than 500m after.

[generalspecific]

S turns on finals.... every time I do an ILS approach

[robin]

Side slips are also best when landing some of the 'long-nosed' types or bi-planes even when the wind is down the runway.......

Always good to keep in practice when flying tail-draggers

[UV]

S-turns are handy when you've been cut up on final. Sideslips are handy when you've cut somebody else up on (long) final. Both should be taught a lot more than they are.

....and how does that, and any of this S turn business, comply with the requirement for all turns in the circuit to be in the same direction as that set by other aircraft*? And surely good airmanship dictates that that if you cannot continue the approach safely you go around.

*Sorry, I do not sit here with volumes of the ANO in front of me ready to quote articles and sub articles, and sub sub articles!

UV

[Pace]

S turns on finals.... every time I do an ILS approach

Full deflection to the right then full to the left sounds good! General Specific is that intentional ?

Actually know someone who did a barrel roll on the ILS and came out on the button

Seriously though I am not suggesting you do 45 degree banked S turns but in VMC there is nothing wrong with gentle turns to adjust the spacing a bit.

You actually have increased vision good speed rather than dragging the speed back to just above the stall to get that spacing and done correctly a safer manouvre than a go around...... but what do I know

Frankly what is good airmanship???

Pace

[Gertrude the Wombat]

Gertrude, I'm going to slap your legs for that one!

I thought that would wind someone up!!

It works though. I did it once on a glide approach when I'd misjudged the wind, and the instructor was perfectly happy - I got onto the runway, if it had been a real forced landing in a field we'd have walked away which is all that matters.

No, I wasn't taught sideslipping near the ground on my PPL. It's on my list of things to ask for on my next hour-with-an-instructor.

[flybymike]

S-turns are handy when you've been cut up on final.

But sure confuse the hell out of the guy behind you who is rapidly catching up....

[Pace]

FlyByMike

Thats his problem! He can go round or even better he can do S turns too

Pace

[SNS3Guppy]

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

Why does one need 30 degrees to do S-turns on final approach? Is this a British regulatory or standards requirement? There's no such practical need. Practically speaking, one can do a steep turn on final without stalling or harm, or one can do very mild banking to do S-turns.

There's no reason to expect a spin simply from doing S-turns. The airplane won't spin unless you allow it to spin.

Actually I recall from reading Langewiesches Stick and Rudder that it is that simple, and aircraft that were impossible to stall (and thus, spin) have been done in the past. Precisely by limiting elevator travel.

Wolfgang's book is somewhat outdated, and while making for good reading, is not technically correct, and is not accurate. As a general picture, perhaps, but don't take it to heart.

Efforts have been made to create unspinnable aircraft. The Ercoupe was one such effort, albeit unsuccessful. Limiting elevator travel will NOT prevent a spin.

At higher speed, wing DOES stall at the same stick position (as close as I can measure it), but at significantly more G loading (provided the wings don't drop off..)

A stall has no bearing on stick position. Stall is a function of angle of attack, not stick position, not pitch angle, not power setting, not weight, not center of gravity...but of angle of attack for a given aircraft configuration.

I can demonstrate for you quite easily a stall in a variety of stick positions in the same aircraft; forward, aft, neutral, along with a variety of ways to stall the aircraft. I can also do the same thing in order to enter a spin. Divorce in your mind the concept of stick position and angle of attack; they are not related, and marrying the two concepts can simply confuse you...or get you killed. Relating stick position to a stall is a fallacy, and a dangerous misunderstanding of basic aerodynamics, and basic airmanship.

Furthermore, pilots have been killed stalling and or spinning an airplane with the control lock in. No aft travel at all, and pitch taking place as a consequence of power setting.

Given the extensive variety of aircraft available, one shouldn't attempt to make such broad, sweeping statements as the notion that an aircraft can't stall or spin if stick motion is limited. I've been able to fix the stick in position and move the airplane about simply by standing and leaning this way or that...I could just as easily stall the airplane, and subsequently spin it without any stick motion at all, if I desired.

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.

This is 100% untrue. The aircraft will stall at the same angle of attack for a given configuration, but not the same stick position. Given more experience in aircraft, or a variety of aircraft, you'll realize this. An aircraft can be stalled with the stick forward or aft, and CG will have a significant bearing on the position of the stick, as will power setting, etc. The aircraft can be stalled slow or fast, pointing skyward or at the ground, light or heavy...and the stick position will vary throughout those regimes.

Now...as far as sideslips and forward slips go...

When I was younger and inexperienced, I was a big user, and a big proponent of the slip. Much easier than reconfiguring the aircraft, it's really just "free" drag...and unlike lowering flaps or doing something else to alter the aircraft configuration, the slip can be instantly disposed, with an instant performance recovery.

This comes at a price, however, and one that's seldom advertised. I've seen it on big aircraft and small, and I've personally handled the broken parts and seen the trends. One seldom hears it mentioned, but a slip puts an enormous air load, even at low airspeeds, on the vertical stabilizer. In many aircraft, including most light airplanes, one might be shocked to find out just how little is holding that vertical stab in place...usually two brackets or bolts.

I maintained a fleet of 30 single engine Cessna's years ago, that were used for mountain flying, tours, sightseeing, and a lot of canyon work. Slips were used a lot to get into some of the strips we used, and regularly used for landings, and other types of flying that we did. I found a trend among many of the airplanes; cracked vertical stab attach brackets...meaning complete failure of the part. As a result of the findings, the parts were changed from an aluminum alloy, to steel. Never the less, we found more cracks.

I've found them on large four engine airplanes (which we also aggressively slipped into canyons in exactly the same way we do it in light airplanes) during inspections. We've learned in recent years, with fortunately more publicity, that airplanes can be broken at speeds considerably less than Va...something that many didn't believe would happen, just a few years ago. Slips are hard on the airframe.

Now, I've done a lot of flying in airplanes without flaps, and slips are often used in such airplanes. I don't do slips as a rule, any more, regardless of what I'm flying, because I know the cost and the stress on the airframe.

[Flyingmac]

Since when was an S-turn against circuit direction? That would be a U-turn according to my recollection of the alphabet, and since when was a side-slip a component of an unsafe approach? I've flown into many a tight strip where the safest option was slipping in for obstacle clearance.

There appears to be two types of flyer on this forum. Pilots and aeroplane drivers. Eventually some of the latter will become the former. Some never will.

[Mark1234]

Originally Posted by SNS3Guppy

I can demonstrate for you quite easily a stall in a variety of stick positions in the same aircraft; forward, aft, neutral, along with a variety of ways to stall the aircraft. I can also do the same thing in order to enter a spin. Divorce in your mind the concept of stick position and angle of attack; they are not related, and marrying the two concepts can simply confuse you...or get you killed. Relating stick position to a stall is a fallacy, and a dangerous misunderstanding of basic aerodynamics, and basic airmanship.

Ok, I'm sceptical I admit - I think I understand pretty well, so please, explain - I'm always happy to learn. Taking away pod mounted engines with big power/pitch couples, and also disallowing establishing an unsustainable climb angle then centering the stick, which is, even to the meanest intelligence obviously going to lead to a stall, just how DO you demonstrate a stall with a forward stick position?

As far as I understand it's just basic aerodynamics: (most) aircraft are speed stable - you increase power you climb at the same speed, decrease to descend at that speed. Trim (or more coarsely stick position) sets speed.