S-turns on final
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From: Amsterdam
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?
And no, flying inverted with full forward stick, leading to an inverted stall disqualifies also. As do out-of-limits CofG positions.
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From: USA
An aft center of gravity may result in a stall with a forward stick, and no...one needn't exceed CG limits.
When losing half or more of one's weight quickly, common in certain general aviation aircraft...one can have the stick buried against the forward stops and still climb without any ability to arrest the climb. I've experienced that hundreds of times. A number of pilots have died in such a situation. The stick position is irrelevant; angle of attack is the consideration in the stall.
I said nothing about pod mounted engines, nor establishing unsustainable climbs and then centering the stick.
With a student, I prefer to demonstrate stalls with the airplane level on the horizon, and prefer to demonstrate a stall recovery with nearly imperceptible movement of the stick and a very, very slight decrease in angle of attack...this tends to show the student that a stall isn't something to be feared. Too many students have been shown violent stalls, have been floated in their seats, and scared by inexperienced instructors who felt that a big, dramatic recovery was a necessity.
Stick position during the recovery may be aft, may be neutral. The rapidity with which one causes a stall to occur, and the acceleration of the stall itself, play some part in stick position, but to suggest that stick position remains the same for a high speed stall as with a low speed stall is utterly ridiculous. It doesn't, nor does stick position have any bearing. One doesn't teach stall recovery by instructing a student to put the stick to a "safe" position, but to decrease angle of attack.
Certainly various kinds of stall recoveries are possible, depending on the stall condition. Also depending on the airplane, and on the altitude and circumstance in which the stall occurs. Some aircraft will tolerate nearly any kind of recovery, others won't. Some won't recover well at all. Some take very long distances. A deep stall in a Learjet, despite the substantial power available, can take nine thousand feet of recovery, and will continue or occur with full forward stick...and indeed many business class aircraft are recovered in climbing stalls by rolling to a steep bank, unloading the wings, and letting the nose fall through the horizon while adding power...one doesn't push the nose forward...which is a poor habit that one "gets away with" in light aircraft. Again, different techniques for different circumstances...but to suggest that stick position has any bearing on stall, or the inability to stall, is ridiculous.
Certainly one may need to have the stick buried in one's abdomen to induce a stall in a given airplane under some circumstances, but may find it stalls quite admirably with the stick in the center of it's range of movement, under another circumstance. In my present assignment, I can induce a stall by banking at altitude without any need to move the control column aft...go too steep, no movement will be evident or necessary, but an accelerated stall will occur.
Some airplanes, when flown at a high angle of attack, will require significant forward stick to prevent stalling. The airplane may then be stalled while holding forward stick, proving again that stick position has no bearing on when the aircraft stalls...that is, one can never say that the airplane always stalls at the same stick position, because this is patently untrue.
When losing half or more of one's weight quickly, common in certain general aviation aircraft...one can have the stick buried against the forward stops and still climb without any ability to arrest the climb. I've experienced that hundreds of times. A number of pilots have died in such a situation. The stick position is irrelevant; angle of attack is the consideration in the stall.
I said nothing about pod mounted engines, nor establishing unsustainable climbs and then centering the stick.
With a student, I prefer to demonstrate stalls with the airplane level on the horizon, and prefer to demonstrate a stall recovery with nearly imperceptible movement of the stick and a very, very slight decrease in angle of attack...this tends to show the student that a stall isn't something to be feared. Too many students have been shown violent stalls, have been floated in their seats, and scared by inexperienced instructors who felt that a big, dramatic recovery was a necessity.
Stick position during the recovery may be aft, may be neutral. The rapidity with which one causes a stall to occur, and the acceleration of the stall itself, play some part in stick position, but to suggest that stick position remains the same for a high speed stall as with a low speed stall is utterly ridiculous. It doesn't, nor does stick position have any bearing. One doesn't teach stall recovery by instructing a student to put the stick to a "safe" position, but to decrease angle of attack.
Certainly various kinds of stall recoveries are possible, depending on the stall condition. Also depending on the airplane, and on the altitude and circumstance in which the stall occurs. Some aircraft will tolerate nearly any kind of recovery, others won't. Some won't recover well at all. Some take very long distances. A deep stall in a Learjet, despite the substantial power available, can take nine thousand feet of recovery, and will continue or occur with full forward stick...and indeed many business class aircraft are recovered in climbing stalls by rolling to a steep bank, unloading the wings, and letting the nose fall through the horizon while adding power...one doesn't push the nose forward...which is a poor habit that one "gets away with" in light aircraft. Again, different techniques for different circumstances...but to suggest that stick position has any bearing on stall, or the inability to stall, is ridiculous.
Certainly one may need to have the stick buried in one's abdomen to induce a stall in a given airplane under some circumstances, but may find it stalls quite admirably with the stick in the center of it's range of movement, under another circumstance. In my present assignment, I can induce a stall by banking at altitude without any need to move the control column aft...go too steep, no movement will be evident or necessary, but an accelerated stall will occur.
Some airplanes, when flown at a high angle of attack, will require significant forward stick to prevent stalling. The airplane may then be stalled while holding forward stick, proving again that stick position has no bearing on when the aircraft stalls...that is, one can never say that the airplane always stalls at the same stick position, because this is patently untrue.
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From: Amsterdam
When losing half or more of one's weight quickly, common in certain general aviation aircraft...one can have the stick buried against the forward stops and still climb without any ability to arrest the climb. I've experienced that hundreds of times. A number of pilots have died in such a situation. The stick position is irrelevant; angle of attack is the consideration in the stall.
But more importantly, what I think is the case here is that these types of aircraft have a trim that moves the whole tailplane, and a stick which independently moves the elevators attached to that tailplane. In that case, yes, stick position on its own is not directly related to the AoA/stall. If you have trimmed too far forward you can bury the stick in your abdomen and not stall, and if you have trimmed too far aft you can push the stick all the way forward and still not prevent a stall. What we probably should have said is something along the lines of "pitch position largely determines the AoA (and thus the stall), where pitch position is the result of trim position plus stick position".
And of course losing half the aircrafts weight may lead to a massive CofG shift and a massive out-of-trim situation. Which may not be correctable by stick alone. Which may lead to a stall with full forward stick.
So, good point. Thanks.
but may find it stalls quite admirably with the stick in the center of it's range of movement, under another circumstance. In my present assignment, I can induce a stall by banking at altitude without any need to move the control column aft...go too steep, no movement will be evident or necessary, but an accelerated stall will occur.
Again, good point. But I do wonder what the trim position is in that kind of flight regime, and what the resulting speed of that same trim position would be much lower down.
Certainly various kinds of stall recoveries are possible, depending on the stall condition. Also depending on the airplane, and on the altitude and circumstance in which the stall occurs. Some aircraft will tolerate nearly any kind of recovery, others won't. Some won't recover well at all. Some take very long distances. A deep stall in a Learjet, despite the substantial power available, can take nine thousand feet of recovery, and will continue or occur with full forward stick...and indeed many business class aircraft are recovered in climbing stalls by rolling to a steep bank, unloading the wings, and letting the nose fall through the horizon while adding power...one doesn't push the nose forward...which is a poor habit that one "gets away with" in light aircraft. Again, different techniques for different circumstances...but to suggest that stick position has any bearing on stall, or the inability to stall, is ridiculous.
And I need to smile at the picture of the CEO of BigBucks Inc., cruising along at FL410 in his private jet, fat, dumb and happy sipping his champagne, and all of a sudden there's some turbulence, a buffet and the next moment the aircraft is doing a 90-degree wingover.
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From: Londonish
Have to confess I also hadn't considered swept wings and high altitudes - rather outside my experience, as is throwing most of the payload overboard 
I do ponder this though
If you don't move the stick (or have the trim move? going along with backpacker's thinking), then banking the a/c will result in the nose dropping and entry to a descending turn, still at 1G right? How is an accelerated stall possible under those circumstances?
I do ponder this though
In my present assignment, I can induce a stall by banking at altitude without any need to move the control column aft...go too steep, no movement will be evident or necessary, but an accelerated stall will occur.
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From: USA
But more importantly, what I think is the case here is that these types of aircraft have a trim that moves the whole tailplane, and a stick which independently moves the elevators attached to that tailplane.
That's not too far removed from typical general aviation operations, given that many jump operations involve commonly used airplanes such as Cessna 182's and 206's.
The trim on many ag type light general aviation airplanes doesn't move the stab, but a trim tab on the stab. A common example is the Cessna A188B AgTruck. This airplane is little more than a Cessna 185 with the wing on the bottom, instead of the top...and a slightly longer nose to hold a 300 gallon hopper. It's got the same tail and horizontal stab and elevator, and works the same way.
A difference that many ag type airplanes have in trim is that they trim roughly...rather than giving fine trim such as we see in a Cessna 172, where the trim is moved by small degrees by repeatedly spinning a trim wheel, the ag aircraft use a single lever..push it forward a few inches and you have full forward trim, pull it aft and you have full aft trim. One doesn't really trim ag airplanes out that much. When punching off a load, I find if it's a downhill run I will often put in full forward trim or put my hand on the trim as I get set to push the button, then push it forward as the load goes out. Then throttle. I've seen myself pointing at the sky on a few occasions with the stick fully forward against the stops.
With the heavy tankers, trim systems vary considerably; the P2 has a variable camber horizontal stab rather than a moving stab, whereas the 4Y utilized a trim tab on the elevators with a conventionally fixed horizontal stab. Systems varied with each airplane, but aren't particularly relevant here. Point is that the all-flying tail or trimmable tail isn't really a consideration here. In fact, the full flying tail or stabilator is more common in light airplanes, and fully trimmable stabilizers are also common, especially in older light general aviation airplanes.
What I think you're talking about here is the coffin corner. High altitude meaning that your Mach limiting number (or whatever it's called) creeps down while your stall speed creeps up. Go a little too fast and you get into the transonic regime with all its associated dangers, go a little too slow, or load the wings just a little too much, and you get into a stall.
And I need to smile at the picture of the CEO of BigBucks Inc., cruising along at FL410 in his private jet, fat, dumb and happy sipping his champagne, and all of a sudden there's some turbulence, a buffet and the next moment the aircraft is doing a 90-degree wingover.
The reason, incidentally, that one rolls the wings and lets the nose fall through the horizon during a climbing recovery is to protect the airplane. Simply pushing forward can overstress an airplane, and in a turbojet, with climb rates that can range from two thousand feet a minute to twelve thousand feet a minute (ala LR24), one can wrinkle the wings pushing forward. Rolling and letting the nose fall through the horizon accomplishes two things; it unloads the airplane and lets gravity and aerodynamics protect the airframe as one recovers, and it automatically reduces angle of attack as the nose falls through and the flight path changes. Simple stall recovery in a large jet is a little different, too...typically one powers out of the stall without movement of the control column, or very slight movement.
This, of course, does little to help the private pilot who is considering S turns on final.
S turns will not cause a stall. S turns will not cause a spin. S turns don't need to be steep or shallow, particularly...they're just there to cause the airplane to cover more distance by turning back and forth, while making less progress forward toward the runway. They may be performed for traffic delays, or to allow more time to get down from altitude. I've done S turns at the Aspen airport in the US...where one crosses the VOR at 14,000' and reaches the runway at 7,800'. The S turns are mild, and allow the descent without an excessive rate or rush...and sometimes may be necessary due to aircraft limitations. I've done them in the traffic pattern at local airports at times, and I've been requested to give an S turn at busy commercial airports, too. It's another technique a pilot can do, commercial or private, to put the airplane on the runway and adjust timing and altitude in the process.
Stalls should be thoroughly understood, including the mechanism, and mechanics of the stall. Pilots need to understand what causes a spin, how to prevent a spin, how to recognize a spin, and how to the fly the airplane and not spin...and of course, how to recover from a spin. Pilots should not be taught that a stall occurs at the same stick position, because it most certainly does not. Pilots should not be taught that the stall occurs aft or forward of a certain stick position, either...because this simply is not true.
Operate an airplane in slow flight. Approach the crossover on the power curve where more and more power is required to fly slower and slower. Note the trim note the stick position. The airplane can be trimmed off to fly just above a stall, with power on, and the stick position, or trim position will be decidedly different than where it's trimmed for cruise, or for another circumstance in which the airplane may be stalled. In some cases, the stick may be full aft to cause a stall, and in others it may be in a more neutral, or even forward position (and this doesn't consider tailplane stalls in icing, another subject entirely, but a stall none the less...proponents of limiting aft stick movement would be in a world of hurt in a tailplane stall, where aft stick is used to recover).
When someone suggests that S turns on final will cause a stall or spin, they're really suggesting a lack of understanding of stall and spin dynamics; this is an alert that additional study and training is required. The same can be said for an assertion that stalls always occur at the same stick position.
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From: 75N 16E
There is a very important phrase I once read...
"An aircraft can stall at any airspeed, any altitude and any attitude".....
In some aeroplanes applying full power too early during a stall recovery has the effect of increasing nose up pitch so the aeroplane could remain stalled with the stick fully forward...to answer the one about forwards stick stalls.
"An aircraft can stall at any airspeed, any altitude and any attitude".....
In some aeroplanes applying full power too early during a stall recovery has the effect of increasing nose up pitch so the aeroplane could remain stalled with the stick fully forward...to answer the one about forwards stick stalls.
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From: Londonish
Originally Posted by englishal
There is a very important phrase I once read...
"An aircraft can stall at any airspeed, any altitude and any attitude".....
In some aeroplanes applying full power too early during a stall recovery has the effect of increasing nose up pitch so the aeroplane could remain stalled with the stick fully forward...to answer the one about forwards stick stalls.
"An aircraft can stall at any airspeed, any altitude and any attitude".....
In some aeroplanes applying full power too early during a stall recovery has the effect of increasing nose up pitch so the aeroplane could remain stalled with the stick fully forward...to answer the one about forwards stick stalls.
@it_flies: Did as you suggested. 1 up, S2A - left wing down, right rudder, no noticable break, just settled into a nose high, high descent rate mush. Slight tendency to roll out of the slip, held with aileron (so they weren't stalled). Full back and out stick, full in rudder. Other way around, right wing down it eventually over several seconds rolled into the left wing and began a slow, steep spiraling turn (which I didn't wish to explore). Not drawing any conclusions as to whether it was a spin or spiral, but it initiated very slowly - effectively I ran out of aileron to counteract the rolling tendency.
I suspect that the rolling tendency is due to a combination of the slightly swept upper plane, and fuselage blanking of the lower. No particular conclusions to be drawn, a different CG might result in a more determined behaviour, the aileron application might be sufficient to trip the outer wing into a stall, etc..
@Guppy
"A large airplane operated at altitude may stall in a steep bank, and not simply maintain a 1 G loading and descend. "
I'm still struggling to get my head around this. We all agree (I think) that a wing stalls because of an increased angle of attack. Now, rolling into a turn does not intrinsically increase the angle of attack - that's set by the aerodynamics - speed, tailfeathers, etc.. - it simply re-orients the lift vector, and as gravity doesn't re-orient, the nose should fall. If you want to maintain your vertical trajectory, you must increase the AOA to compensate for the lift vector, which is clasically what causes the turning stall. In order to increase the AOA, you must apply some moment around the wing to 'rotate' it and increase the AOA - typically by use of aft stick/trim/etc. What did I miss?
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From: U.K.
Oh dear Mark. Before you get shredded by the aerodynamicists amongst us, may I suggest a quick reread of a basics aerodynamics book.
I'm just rushing out so haven't got time for an indepth post, but you might want to read about how the angle of attack changes when rolling.
I'm just rushing out so haven't got time for an indepth post, but you might want to read about how the angle of attack changes when rolling.
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From: Londonish
No need to shred (!) I'm thinking you mean that there will be an increase in the AOA of the downgoing wing, and a decrease of the upgoing? I'd expect that to be significant at large rates of roll, but largely insignificant at the sorts of roll rates used by bizjets and airliners - there I may be wrong.
I confess I'd assumed that the stall was in the turn, not due to the roll effects.
I confess I'd assumed that the stall was in the turn, not due to the roll effects.
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From: Netherlands
Thanks Mark1234. I appreciate your effort. But from reading your description it's unclear to me whether you tried a stall from a sideslip or a slipped/skidded level turn?
My last lesson got cancelled thanks to the volcanic fiasco, but next time I will try to ask my instructor about this.
My last lesson got cancelled thanks to the volcanic fiasco, but next time I will try to ask my instructor about this.
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From: Londonish
A sideslip. Originally did this in the decathlon after being admonished on a checkride for sidesliping a PA28. "If you get slow you'll spin and die in a smoking hole" (from an instructor). On the other hand, one of my aeros instructors taught slips all over the place as an approach technique. Being as I wasn't worried about spinning the decathlon, I thought about it a bit, then went nice and high to see what happened.
No effort. The comments from you and BackPacker lead me to more thinking, and more experimenting. Always good to learn.
No effort. The comments from you and BackPacker lead me to more thinking, and more experimenting. Always good to learn.
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From: Netherlands
Always good to learn.
A sideslip.
Then repeat with skidded and slipped turns. I wondered whether the behaviour would be as written here (from the stalling in a turn thread):
If the airplane is slipping toward the inside of the turn at
the time the stall occurs, it tends to roll rapidly toward
the outside of the turn as the nose pitches down
because the outside wing stalls before the inside wing.
If the airplane is skidding toward the outside of the
turn, it will have a tendency to roll to the inside of the
turn because the inside wing stalls first.
the time the stall occurs, it tends to roll rapidly toward
the outside of the turn as the nose pitches down
because the outside wing stalls before the inside wing.
If the airplane is skidding toward the outside of the
turn, it will have a tendency to roll to the inside of the
turn because the inside wing stalls first.
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Originally did this in the decathlon after being admonished on a checkride for sidesliping a PA28. "If you get slow you'll spin and die in a smoking hole"
If you get too slow in a slip at low altitude, you will spin and die.
However, you can choose to keep the speed safe.
I used to be a big fan of slipping as a way of losing altitude quickly, but having read SNS3Guppy's comments about the impact on the vertical fins am having second thoughts.
To return to the original question, I see no problems with using S-turns to increase the track distance to touchdown, so long as airmanship says it is appropriate under the circumstances.
I've done it many times, when joining straight in under ATC control and making room for circuit traffic.
Like most things in flying, you have bear in mind the 'law of the situation' and make the best choice; you may be able to slow down and you can always go around.
Can't say I like the idea of doing a 360 on final and would be likely to decline and go around, but equally that probably is reflective on my ability to fly and others may be perfectly comfortable with that.
