Hi M14P,

Sorry, it’s just my terminology. The ‘deepest’ stall I have done is one where the forward component of speed is very low and the nose wanders around quite a bit and wallows. The yoke must be held all the way back. In this situation it appears that the wings can be kept level by a small rudder input, but the aircraft continues to yaw. Or so it seems from the DI rotating. I certainly wouldn’t condone the abuse of rudder at low speeds or in the stall.

The baby Cessna is a very well engineered and forgiving aircraft, but as you rightly point out the controls of this aircraft are very effective throughout the speed range and sloppiness of the controls can’t really be demonstrated. There is no buffet.
I wonder if there are any trainers in which these effects can be demonstrated?

Noisy

PS my instructor is a farm strip pilot of advancing years who I trust. Obviously this student needs to do some more study!

No apology needed - just making sure you weren't being led astray. That is about as fully developed as your Cessna might get. It is interesting to fly something that will stall without the stick in your stomach - Bulldog, Chippy, FLS Sprint, anything sufficiently 'British' as to behave classically.

Your DI might be precessing due to low vac pressure - look at a feature on the horizon!

I agree with Shortstripper - why not ask if you can try flying around just a knot or two above the stall. It's a real coordination exercise and needs plenty of power to keep things going. Generally, however, I find it a real confidence booster for students. It's also good for explaining the use of rudder for coordination - turning left, large right rudder input for coordination etc.

Yes, I've done slow flying and it's a pain in the :mad: flying around with the stall warner briefly sounding all of the time. It is part of the syllabus. Very hard work. I think I will try out a few different types after I have got my PPL, all being well.
There is a Chippy at the airfield I fly from. Hmmmm. :D

Not sure about that DI: I will have to go away and have a think about it, although my senses were also telling me that the a/c was gently turning.

May I ask what might be a stupid question: what is the point of flying for ages doing stalls, or flying around at just above the stall?

Aerobatics aside, every PPL should be taught how to recover from a stall, and the reaction (controls forward without additional roll input, full power) should be instinctive upon the stall warner going off. But why do so apparently much of it? During normal operations of a plane, the only place one is likely to stall is on turn base to final and then you are likely to be too low to do anything about it anyway (unless you are doing it 5 miles out :O )

In most cases of an inadvertent stall, the plane has been grossly out of trim and the pilot wasn't paying attention to the IAS. Teaching trimming is far more important.

I may have mis-understood, but it seems to me that some instructors have got their hands on a WW1 Luftwaffe training manual and really enjoy it. A bit like the IMC Rating instructor teaching you NDB holds to near perfection, for hour after hour, having planned the headings on the ground from winds-aloft forecasts of course..........

I believe that the whole point of the slow flight element is a sort of what-not-to-do. Except that you're ...er.. doing it.

IO-540

I feel that you are missing the point a bit: The whole point is to teach delicacy of handling, technique and to instill confidence in the student.

Trimming, on the other hand, is very poorly taught but has never been a big issue when it comes to stalling. An aircraft can stall whether it is in or out of trim; your assertion that 'in most cases the aircraft was grossly out of trim' is pure conjecture and more than a little silly.

Take for example a stall spin accident where a chap was circling a friends house and pulling ever harder as the speed decayed/ AoA increased etc... would the outcome have been any different had the stick force been less?

Similarly a recent report included a stall/wing drop whilst the pilot struggled to close the door...

How often do you fly within 10 kts of the stall? Every flight I'd suggest - at take off and during landing. I'm fairly sure that an absolute terror of stalling is at least partially behind many landing accidents i.e. excess speed on final and/or snapping the nosewheel off.

Why bother being taught how to force land? Engine failures are rare so why not just accept a certain rate of fatalities!?

Why bother being taught a lookout since the aircraft you collide with is likely to be the one you don't see!?

Part of the fun of flying is developing a discipline - stall avoidance and aircraft control are components of that.

M14P

Trimming, on the other hand, is very poorly taught but has never been a big issue when it comes to stalling. An aircraft can stall whether it is in or out of trim; your assertion that 'in most cases the aircraft was grossly out of trim' is pure conjecture and more than a little silly.

I would suggest that (stupid behaviour aside, like the cowboy circling a house with an excessive bank angle) most stalls are the result of

1) the aircraft being trimmed to a low speed, and the pilot becoming distracted, and the IAS decaying, or

2) the pilot flying say 10kt above Vs and then banking hard (e.g. a very hard base to final turn)

In neither case above is low speed flying going to help. One must do an immediate stall recovery.

In your example of a pilot trying to close a door, if the plane was trimmed anywhere near right, it would not have stalled hand-off. Like every plane, it would eventually have gone into a spiral dive, but that takes one back to flying the plane first and fixing open doors (or attending to distressed passengers, etc etc) separately - stall training is of no help if you are trying to close a door and forget to fly the plane.

Flying 10kt above Vs is perfectly safe so long as you are trimmed, are wings level, or bank below say 20 degrees. But one will be doing that in so few places (initial climb, or base/final) that in my view it would be better to teach the procedures (e.g. TRIM TO 80KT ON BASE LEG).

My question was not whether to do stall training, but whether to do so much of it. I must have done 3 hours of it myself. It was great fun but mostly irrelevant to normal aircraft operation.

Your examples of forced landings and lookout are not applicable.

I'm no expert but I have found that talking through what you are doing out loud seems to help because you understand what is happening, you can help yourself through the signs of the approaching stall, the symptoms of the stall itself (including wing drop) and the recovery.

In addition it lets your instructor know your thought processes are sound, and helps your confidence no end.

It works for circuit planning too !!

Some people never like stalling but once you've done a load they become just another part of flying.

Please don't be put off by 1 unpleasant element of flying, - and something else which has occurred to me - maybe another instructor might teach it differently so just for this exercise maybe another instructor might be useful ?

cheers

Arc

540

I simply do not agree with your assertions. Stall and spin awareness will remain central to fully understanding the behaviour of the wing in the low speed regime.

More to the point - stalling is required to pass the skills test

Also - bank angle alone has no direct effect on stall speed - only AoA so if you start all of this keep less than 20 deg here nonsense you are leading yourself into an area of false confidence and understanding.

It's quite clear that you are a 'numbers man' which has its place but it strikes me that the original poster is not 'in that market'.

Back to enjoying the whole experience and being confident; might I suggest some well flown demos by your instructor should help restore some confidence (if that's what is lacking).

Um, no, I don't think so. I think that part of the point of the stall training is so that you can recover easily with that amount of height.

Most people turn final hundreds of feet above the ground. You shouldn't need that much height to recover from a stall.

1040

I'm sorry but I think you really are a bit naive if you think that three hours of stall awarness covers everything to the point of boredom. Forget IAS, it's fairly irrellavent and should be treated as no more than I guide. AoA is the main factor closely followed by flying in balance. Well flown tight turns even on base are safe if you have the skill and finesse to fly them well. Far more dangerous is the fool who believes too much bank is unsafe and tries to rudder it around:ooh:

My point about plenty of slow flight and stall practice is that you learn how to recognise the onset of a stall, feel comfortable with it and even use it to your advantage. Many glider pilots scratching for lift low down will appreciate that to stay within the core of some weak thermal will require a very tight turn at a very low speed. Anything more than the very smallest radius of turn will result in a landing so you soon learn to fly on the very edge of the stall. Indeed this all becomes a personal challenge and deeply rewarding when you succeed in getting back up when others would have simply thrown it away and landed out. How does this relate to power flying? simple, it is one more skill to be mastered and is one that could ultimately save your bacon. I won't offer scenarios because you'll just say "only a fool would have got into that position in the first place" ... this may be true, but it happens. After all, to become experienced, requires experiences ... we just hope our training and our own personal standards are enough to get us through them.

IM

Yes.

I'm not sure when you can start to feel you fully understand the stall. Without going through my logbook with a calculator, I must have done somewhere around 100hrs of stalling and spinning and am not even close yet.

But, probably closer than I was with 3 hours, and certainly closer than I was when I managed an inadvertent spin when I only had probably about 200hrs TT in my logbook some years ago (thankfully at a very safe height).

G

You people are right that I am more of a numbers man that some, perhaps. I do like to fly around here and there and do so quite often, just for currency. But most of the time I like to plan a flight, takeoff, fly it (IFR/VFR as necessary) and land, and do so very safely without ever getting anywhere near doing anything dangerous. Never getting anywhere near the stall, for sure. I fly downwind at 100kt (25kt above stall), base at 85-90kt (15-20kt above stall at that config), final at 75-80kt (15-20kt above stall in that config), flare at 70-75kt and that does me just fine.

I am aware that bank angle itself does not raise the stall speed, but that's true only in a 1g descending turn - perhaps true on base to final. If you do a level turn then Vs does go up because the AoA has to increase to support the extra G.

I used to enjoy deep stalls in a PA38 - beats the best fairbround ride. But then it ought to, at £100/hour. The instructor loved it. At the end of all this you get a PPL with which the average pilot cannot navigate accurately enough around UK's busy airspace!

I don't know where this "deep stall" thing is coming from? A deep stall is one in which the elevator is directly blanketed by disrupted air from the stalled wing. This means it becomes ineffective and you can't fly out of the stall as you effectively have no elevator.

I think you mean fully developed stall or perhaps an abrupt stall with a good break.

Flying as you describe is fine and obviously works for you. I don't knock you for that. It's fine If you are only flying from larger airfields and never expect to either force land or use small airstrips. Apart from not getting into a field if flying too fast for fear of stalling, I just think that one day if your luck runs out ... an inadvertant stall might just sneak up and bite you on the bum!
Of course we all fly to a greater or lesser degree on good luck ... I just prefer to have a bit of extra tucked away to give luck a hand :ok:

On the original theme of this thread I would just recommend that if someone feels uncomfortable about stalling, they shouldn't just go through the motions, move on and only re-discover stalling by accident!

IM

Another point about slow flight is that it provides experience in flying the aircraft at the back of the drag curve, when counter-intuitive effects need demonstration. (you need more power to fly more slowly straight and level). Landing itself is a slow flight activity.

So many PPLs have lost touch with these skills, I find PPLs uneasy at slowing down to 50-55 kts for a performance landing in a 152 for example. The pernicious effect is to develop PPLs who approach far too fast and wonder why their wonderplane floats for ever, or alternatively say 'It needs flying on to the runway'. Where is the lost art of holding off? Cessna 172 drivers flying approaches at 75-80 kts when 60 would be more appropriate.

540

I think the message here is that just because you think you've done enough of a certain aspect of training doesn't mean that you know it all.

Obviously you enjoy flying your Saratoga, Lance, Commander, Viking or Comanche (I assume that's what you own) and using it for the purpose that it is designed for. You've rather lost sight, however, of what training is all about. It is about learning and development - it's also about equipping a student with skills needed to cover a broad range of flying.

It's been said before - a PPL is a license to learn. Are you still learning? Are you still receptive to input from others? What makes you think that in 3 hours you have the answer to stall/slow flight awareness training? You wondered if you were asking a stupid question - well no, you are not. There are no stupid questions apart from those that are never asked! You just didn't seem to want to hear any answers.

RogerF gets where I'm coming from too (I think!)

Next time you need your 'flight with an instructor' drop me a line and I'll be pleased to spend a day with you. I guarantee you'll learn something (even if it's just that you don't like me!) and I am certain that your views will change.

Like Genghis I probably have more than a couple of hundred hours spent stalling and at the back side of the drag curve. I would love to share some of what I've learnt with others.

If you're really worried, for less than $900, you can have one of these:

http://www.angle-of-attack.com/Default.htm

Sharing what I'm learned
 

I'm not a QFI, but I do occasionally help teach groundschool on a course for baby test pilots. I've posted below some notes from that course which might be of interest.

All is (c) Genghis, but by all means any instructor who can make use of this feel free to copy it and make appropriate us. One of these days I'll find the time to put all this together and publish a book, but I'm far too damned busy at the moment.

There are some tables that normally go in this text, but they're only really relevant to test pilots, and anyway I don't know how to post a table in Pprunetext.

G





The Unaccelerated and turning flight stalls

The unaccelerated stall is very important to the airworthiness of a fixed wing aeroplane in a number of ways. It is essential to the definition of many of the critical operating speeds - the approach speed and Va in particular are functions of the stall speed. It also defines the manoeuvre margins for a turning aeroplane, and for most light aircraft codes, decide whether the code may be applied at all, particularly for microlights.

The conduct of stalling tests on a new or significantly changed aeroplane is a potentially hazardous business, and flight testing practices is a whole separate subject; however, the references cover this in good detail. There are however a number of points pertinent to the testing which are not always well understood, and are worth repeating here: -

· The stall is entered at flight idle, at (by convention) a deceleration rate not exceeding 1 kn/s from a trimmed speed of around 1.4 Vs..
· It is impossible in all but some gliders to conduct a stalling test in level flight, the aircraft will be descending.
· No two aircraft types will give identical stall or warning, it is important that the characteristics for the type and variant is identified, repeatable, and documented in the pilots handbook. Many airworthiness standards give overly simplistic definitions of the stall, which may or may not reflect what actually happens - be guided by these, but not bound by them.
· Stall speed data is meaningless from an airworthiness perspective without the ASI having been calibrated .
· Stalling characteristics will vary with CG and power setting. With CG expect to see higher stall speeds at fwd CG, and more dramatic post-stall behaviour at aft CG. With increased power settings, stalling speeds are likely to be lower with more nose-up stalling attitudes. Increased power again, is likely to generate more dramatic post-stall behaviour; some aircraft which are extremely benign when stalled at idle power will tend to enter immediate incipient spin (sometimes with no stall warning) when stalled at high power settings (two examples of the latter characteristic are the UK air cadet variant of the Grob G109b motor-glider, and the Ultraflight Spectrum microlight).
· The stall is not necessarily marked by the classical pitch-break beloved of flying instructors. It may be marked by a loss of nose-up authority (most microlights), an AoA triggered Klaxon (the Aviasud Mistral), an air horn supplied by air pressure from the wing under-surface (Cessna 150), or other cues. The bottom line is that the stall occurs when the pilot ceases to have absolute control over the aircraft - but learn and understand the precise definition used by the standard in use. Equally, ensure that the test pilot, flight test engineer, and airworthiness engineer are all in complete agreement as to the stall definition in use for a test programme, and subsequent documentation.
· Wing-drop at the stall is normal to most aircraft, it is the magnitude of it that is critical to airworthiness. The wing drop limits of all standards assume that correct recovery action is being taken.

The turning flight stall

For the purposes of civil certification, the turning flight stall is universally carried out at 30° of bank in a co-ordinated turn, although requirements for power and flap settings may vary. Since this is an unaccelerated stall, again the entry rate will be no greater than 1 kn/s.

It is almost inevitable that any aircraft will suffer from undemanded rolling at the point of stall, and this is generally more marked in a turning flight stall. There is no universal value which dictates the acceptable limits of this, and it is important to be aware of what the relevant standard says. The terminology universally used for this undemanded rolling motion is “into the turn” and “out of the turn”. If an aircraft is banked to the right, and at the point of stall it banks more to the right, then it is said to have rolled “into the turn” (this incidentally is a characteristic most commonly associated with low wing aircraft), whereas if it tends to roll towards wings level (a characteristic most often found in high wing aircraft) then it is said to have rolled “out of the turn”.

Regardless of the precise wording of any requirement, it is important that stalling from a co-ordinated turn cannot cause a spin. The author has seen several aircraft which did display this tendency (i.e. never assume that it won’t be there!), the best known of which is the North American Harvard which routinely will enter an incipient spin from a stall at PLF or MCP - a characteristic which is believed to have killed a good many student pilots during WW2. Similarly any marked pitch-up or control force lightening at or near to the stall should be regarded as unacceptable.


Recovery from the unaccelerated stall

Most aircraft will pitch down, with varying degrees of severity, at the point of stall. This naturally puts the aircraft into a dive from which the existing trim setting should allow it to recover without pilot input - although for an efficient (and comfortable) recovery correct handling by the pilot - initially to allow the aircraft to recover flying speed, then to pull out of the dive and re-establish straight and level flight (probably with an increase in power) is considered normal.

However, it is important (and some standards, although not all do discuss this) to ensure that the acceleration immediately following the stall cannot lead to an inadvertent exceedence of Vne / Vmo / Mmo. Also the pullout (especially that pull-out naturally caused by the pitch trimmer setting) must not cause the normal acceleration or Angle of Attack limits to be exceeded.



The accelerated or dynamic stall

Whilst for the purposes of determining stalling speeds a 1 kn/s deceleration is universally used, this is not necessarily appropriate to every real-world situation. Indeed, most microlights will have some difficulty in entering a stall at only 1 kn/s. For this reason, most standards also require consideration of a more rapid stall entry, either from a rapid wings-level pitch-up, or from a steep turn. The specific requirements of each standard do however vary considerably; this is unsurprising since in the more coarse manoeuvres, the different weight-classes of aircraft inevitably will be flown in very different ways.

How aircraft behave in response to this is very variable. Most aeroplanes will display a more marked nose-down pitching motion (or a measurable one, if none existed before) at the point of stall. Aeroplanes with laminar flow lifting surfaces are likely to display less wing-drop at the stall (because both wings stall at the same time), whilst aeroplanes with more conventional wing surfaces are likely to display more wing drop. Some high wing aeroplanes, when stalled from a steep turn will tend to roll naturally wings-level before naturally resuming straight and level flight (probably as the wings stall, pendular stability becomes the dominant roll effect).

The following table shows the main requirements of the various standards. The reader should however treat this with caution - all the standards are somewhat vague (and often probably too relaxed) in their requirements, and it is most important to construct tests which reflect the way in which the aircraft will actually be flown. Most organisations dealing routinely with flight testing (particularly those dealing with the lighter end of aircraft certification) will almost certainly have their own type or class specific schedules and guidance which should also be referred to - and may well be much more useful than the main certification standard.

This table doesn’t give much information on test conditions. Unless stated otherwise, test conditions are the same as for 30° turning flight stalls discussed above.

The stall warning margin in a dynamic stall

For all the listed standards, stall warning requirements are the same as for the unaccelerated stall. Whilst at first glance this is entirely sensible, in practice it is not and the sensible airworthiness team will aim to go beyond the minima of the standards.

Consider for an example, JAR-23. JAR -23 has a requirement for a minimum 5 knot stall warning margin, and a test deceleration speed for the dynamic stall of 3-5 knots per second. This potentially would give a pilot as little as 1 seconds warning of the impending stall - only enough for the most alert pilot (in an aircraft high elevator power and a very short SPO) to take appropriate action. For any aircraft that is likely to be routinely flown in violent turning manoeuvres (e.g. aerobatic aircraft, utility aircraft used for short field or agricultural operations, any military aircraft or most training aircraft) it is important that the pilot is given clear and unambiguous warning of the impending dynamic stall. Apart from the obvious artificial stall warning devices, ways in which this might be achieved include high stick forces, very high nose-up pitch attitudes, alarms triggered by AoA sensors.

Going beyond the minima of the airworthiness standard in this way can require some courage, particularly if potentially expensive modifications to the aircraft may be required. However, any recent set of fatal accident reports should furnish one or two cases of aircraft loss due to a pilots failure to recognise the dynamic stall - this and the risk of litigation is generally sufficient to convince the most bloodyminded company accountant.

References
- Flying Qualities and Flight Testing of the Aeroplane, Darrol Stinton
- Flight Testing Homebuilt Aircraft, Vaughan Askew
- Flight Test Guide for Normal, Utility and Acrobatic Category Airplanes, FAA, AC23-8

shortstripper

Yes sorry I meant an abrupt stall; a PA38 usually drops a wing pretty quickly.

Re forced landings or short strips: I actually use the POH figures and config; I am not adding 10kt or whatever for good measure. With a Vs of 59kt, 70-75kt on final when starting the flare is fine. I know some people say that a landing should be a full stall, with the horn going off, nose way up etc but I don't go for that; for a start you don't get much rudder authority.

It is easy to land in a distance which one can never takeoff from later. Isn't that true for any aircraft? It certainly is for mine.

RogerF

I do know about the back of the curve, believe me. All I have to do to get there is fly at 18"/2300 (the normal approach config) and drop the gear while forgetting to put some power back on (20"+) right away. Another way to get a nice suprise (especially nice if in IMC) it is to descend on autopilot in VS hold mode with less than 18" MP (very tempting if gear isn't down) and not put power back on when the AP reaches the preset ALT and levels off :O

Recovery from the above, if needed while maintaining altitude, needs a lot of power applied right away. But I wouldn't choose to fly on the back of the curve deliberately... there isn't any point. Engine cooling is one reason.

M14P

I do learn something on every flight. The 45-hr PPL is indeed a "license to learn". I suppose I got into this thread because someone seemed to be doing a lot of this.

It is a pet subject of mine; the way the PPL includes a lot of this sort of thing while leaving out the stuff which is just as essential if somebody wants to actually fly anywhere afterwards. This situation is understandable given that nearly all PPLs chuck it in shortly afterwards (maybe this is one reason why they do?) so there is no pressure on schools to turn out pilots who can confidently go places. But I won't say any more on this.

Certainly isn't the case for mine :p ;)

FFF
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