Stalls in slips on landing

[Tony2]

What is the best way to get a stol aircraft down with slips?

 

The question comes about due to the Pitot being on one side.

 

Say a zenith 701 stol 30knot stall

 

So one can expect slipping left and right would give differrent results for air speed + no cross wind / and cross wind 90 degrees plus and minus say 20 degrees + delay of the asi

 

And practice slip stalls at altitude what can go wrong

 

Thank you in advance

 

Tony

 

 

[motzartmerv]

G'day.. I wouldn't be stalling while slipping if i were you...The result wold almost certainly be a spin, and RAA acft are not permitted to do these dangerous manouvers.. Because the acft would be out of co-ordinatin when the stall is induced , one wing would stall before the other and the resultant roll yaw and dive would be quite pronounced..When near the stall you need to stay off the rudder and only use it to pick uop a dropped wing..remember your stall speed will increase in a slip due to the higher wing loading..

 

As for the different stall speeds aither way due to the pitot tube, im not sure that it would cause a significant differance, but don't quote me on it..ask ur instructor.. The jab has a large pitot as apposed to the smaller ones ive seen and ive not noted any differance..

 

cheers

 

 

[Ultralights]

the stall is a function of AOA more than speed. when slipping, its usually to loose height rapidly, by allowing steep decent without an increase in speed., and so the aircraft is usually in a nose down attitude. lessening the chance of a stall. when going into a slip, you should be well above the stall speed anyway.

 

 

[Tony2]

G'day.. I wouldn't be stalling while slipping if i were you...cheers

Thank you for the replies

 

That was the point of the question," Avoiding"

 

Short field landing being closer to the stall, and the angle of attack keeping, the nose low what would you say would be the slowest air speed ( loaded question )

 

This all so comes about no matter how many stalls you pratice it will never be the same close to the ground, in ground effect, engine out, windmilling, etc.

 

I found this a cross wind simulator get like a million hours practice in an hour

 

think about it really 1000 landings gives you how many seconds of flare to touch down

 

http://www.xwindsim.com/xwind200.php

 

watch the video http://www.xwindsim.com/media/xwind200.wmv if windows won`t play it (no codec) just download free video player better than microsoft

 

http:http://www.videolan.org/vlc/

 

thanks again:hug:

 

Oshkosh audio interview really good

 

http://www.airventure.org/radio/clips/2007/INT-DD-Brad%20Whitsitt-Xwind%20Landing%20Sim.MP3

 

same if the above won`t work in mp3 format

 

http://tinyurl.com/2w9ypm

 

 

[motzartmerv]

Well...in a situation like that you would be at best glide speed..which obviously is different for evry acft.. with a stall at around 30 kts, id estimate that the best glide speed would be somwhere around 45-55 kts..but thats just a guess, ur acft would have a published best glide speed..The speed would give you a reasonable safety margain over the stall so a slip would still be quite safe.., however, you wouldn't be slipping much while in the ground effect which only works at an altitude of 3/4 of the length of the wing..And an engine at idle produces more drag then a fully stopped one, so ur performance in a aglide wuld be slightly better with the dead engine as apposed to a practise glide with the engine idleing..

 

hope this answers your questions

 

cheers

 

 

[bilby54]

Hi Tony2,

 

Be a good fella and don't get anywhere near stalling speed in this configuration as you will contact the ground in a rapidly gyrating manner!!! If you are concerned then please go and have ride with either an instructor or a competent pilot.

 

Stall speed changes for each aircraft configuration and as Ultralights stated, it is a function of A of A. The problem with having the pitot on one side of the aircraft is that the inlet becomes shaded when it is on the uphill side during a side slip and reduces the pressure applied to the ASI. If your ASI is indicating a slow speed during a side slip, the normal reaction is to lower the nose and increase speed - all safe and no problem......

 

If the ASI is indicating faster than normal in a side slip it is due to the pitot being on the downhill side where the pressure is greater. What does the good pilot do??? pull the nose up to reduce speed back to where they are taught to approach and there lies the problem that is likely to kill you.....

 

The aircraft in a side slip is set up to enter a spin and has a higher stalling speed than when clean. The only reason that it doesn't stall is due to the angle of attack being lower than critical and this is indicated by the speed. ASI's have all sorts of errors but this one is position error due to the fuselage either blanketing or over pressuring the tube. Learn to fly by attitude in a side slip and practice at a higher than safe height as wing drop is almost intantaneous and completely disorientating.

 

Side slips are fun but not close to the ground without experience.

 

 

[Guest pelorus32]

I'm concerned about this thread. I think that some of the information in the thread is of doubtful accuracy at best.

 

Please go and see your friendly local instructor and talk to them about safe conduct of sideslips in your aircraft and in the kinds of configurations that you anticipate. Do not place your life in the hands of the information in this thread. I am not saying that there is not good information here, but there is certainly a lot of doubtful info as well and I don't think it serves any good purpose to go sifting through what is here and pronouncing on that info. Off to the local instructor is the safest way.

 

Sideslips are useful things when conducted safely and with good knowledge of what is going on.

 

Kind regards

 

Mike

 

 

[motzartmerv]

Mike..please feel free to correct anything i have posted that is inacurate.. I can take a hit:cool:

 

 

[Guest pelorus32]

G'day Merv,

 

that's not really the issue. The issue for me is that this is quite a complex subject and the thread so far has not even begun to touch on the key issues. In addition some aircraft are not cleared for sideslip in some or all configurations.

 

I am concerned that "advice" in these situations can be dead dangerous and that isn't intended as a pun but as a possible statement of outcome.

 

I don't want to deal with any of the technicalities here because of that concern - that the original poster needs to discuss this particular issue with a qualified instructor with respect to the particular aircraft and configuration and then - if safe - practice it with an instructor.

 

Regards

 

Mike

 

 

[bilby54]

So one can expect slipping left and right would give differrent results for air speed + no cross wind / and cross wind 90 degrees plus and minus say 20 degrees + delay of the asi

 

Sorry I didn't pick up on this furphy in my earlier post about delays in the Air Speed Indicator. The ASI is a very sensitive pressure gauge that responds quite rapidly to changes in air pressure - any delays are measured with scientific instruments!

 

This 'delay theory' has come about by people not understanding the instrument and confusing it with aircraft inertia which has delay on both acceleration and deceleration. The only effect that a common garden variety ASI cannot detect is air density and that is why there are those little windows on the flight computer for altitude and temperature (showing my age!). If an ASI has delay, why does it pick up immediate changes of speed in turbulence because that is exactly what is happening to the airframe.

 

Side slips cause a large amount of drag on the airframe as it is designed to safely loose height but in doing so, the aircraft has lost a lot of its forward inertia. An imminent stall in this situation is hard to recover :yuk: and is not for the faint hearted so take Mikes advice and go with an instructor.;)

 

 

[Ben Longden]

I would have a good yarn with your instructor first.

 

Ben

 

 

[motzartmerv]

Perhaps a dissclaimer then..

 

Your title of the thread was, Stalls in slips on landing..

 

In short..don't.. And practising a stall at height while in a slip is a big no no aswell...

 

Talk to your instructor.. If your acft is checked out on slips then get him to teach you how to do it safely..Other then that, if your high, go around..

 

cheers

 

 

[Bigglesworth]

Even I have to agree there, instructor, or at least practise at altitude ONCE you are confident of recovery from unusual attitudes.

 

Interesting thing I found with a sideslip on final for short runways is: A sideslip needs more speed, not due to ASI/pitot, but because of the angle of the wing. Roll out from a slip, and you will be well above your final speed, and speed is just as bad as height.

 

They are a powerful tool, and should be treated with respect due to their ability to catch the unwary.

 

Also a slip needs a certain amount of height to roll out from, so a plane can't be slipped right to the ground to make a steep approach.

 

 

[bushpilot]

Hmmmmm - All this talk of the dangers of side slipping makes we wonder how I survived my early GA days when I had a quarter share of a Piper Colt; no flaps so we were taught slide slip approaches as a matter of course.. Did heaps of them and never thought about the 'consequences' aired here... Maybe ignorance is bliss - sometimes.. :;)2:

 

 

[Guest pelorus32]

G'day Chris,

 

I don't think that side slipping is dangerous but I do think that the train of "advice" in this thread could contribute to dangerous outcomes.

 

As an example a well known RAA registered aircraft - currently available - has as a secondary effect of yaw a vicious pitch down behaviour. You don't want to slip that one on approach.

 

There are very well known GA aircraft that are not approved for slipping in certain configurations.

 

Talk of stalls in this thread stopped short of the real issues in slipping an aircraft, nobody was talking about the aerofoil which is most critical in a slip and it's not the wing.

 

I just felt quite strongly that slipping is a good and valuable tool in flying but that our "advice" was falling well short of what the OP needed in order to use it safely.

 

Regards

 

Mike

 

 

[bushpilot]

Thanks Mike - and I do take your point.. Mine was meant to suggest that there is a lot that I did not know when I was trained many years ago.. I actually do think that more knowledge is better... my 'ignorance is bliss' was tongue in cheek..

 

Cheers

 

Chris

 

 

[Tony]

In the Thruster/Gemini one can slip OK in order to lose the height, in order to make the runway 'forward' (which means steeper descent) or side ways to slip in 'that parallel runway', but not in order to lose the speed for the god sake !!!!

 

If one loses the speed it WILL STALL both wings or (WORSE !) one wing for the slip. If one pulls up or unfortunatelly idle the engine in endeavor to 'experiment' with the slips below 200 feet one should have his/her coffin pre-paid.

 

Thruster/Gemini can drop one wing at low height without reasons 'normally' apparent to pilot.

 

Hope this thread of mine will save lives.

 

 

[Guest TOSGcentral]

Hmmm! I am very much in accord with Mike’s views on this one – the subject is very type specific and it is difficult to generalise without the danger of misleading people.

 

I have over 150 types in my books and have side slipped most of them. I have never experienced anything approaching a loss of control situation. On the other hand I will not side slip anything if I have flap hanging out in the breeze.

 

I can generalise (I think reasonably fairly) in one area though. The higher you hold the nose in the slip then the greater will be the rate of descent. This could be critical in low inertia ultralights that do not accelerate well at all.

 

When you kick off the slip you could find yourself in the pre-stall regime area of high drag and maintaining a high descent rate that you are then not able to abate quickly enough even with the application of full power!

 

I am however a little dubious of the advice “consult your instructorâ€Â. You really need to be sure you are going to get the right drum in reply, and the instructor needs to be very familiar with the type that is the subject of the enquiry. I will tell you a little story.

 

Very many moons ago, at the UK national gliding centre, we had just packed up for the day and had dinner. Then, as was our wont, the four staff instructors (that I had the misfortune to be responsible for) gathered in the bar for the normal evening ritual of fraternising with the course members socially – who insisted on plying us liberally with free beer (those were the days of cheap living for us and the biggest challenge was not getting that smashed that you were unfit for work the next day).

 

With the first round of pints lined up and yet untasted, a couple of the staff got into an increasingly heated debate about stalling in side slips. Now we were all quite experienced instructors, flying every day, normally doing spin training every day, and knew our aircraft backwards. Yet pretty much the same points were raised as have been brought up in this thread.

 

I got fed up with it. I had done about 30 flights that day and did not really want any ‘bar flying’. Besides, for once we had a couple of female students on course and I am fond of female company and did not want to waste any!

 

So I pointed out that there was a Pawnee and ASK13 tandem seated trainer sitting right outside the bar, waiting for the evening course, and we were all tug pilots, and for a changed we had 8/8 blue outside – so instead of quacking about it, go to a few thousand and find out! Meantime I promised to look after their fresh beers and do the bit with the course members!

 

So they did! The results were as follows: The ASK13 is a reasonable stall trainer if a bit benign, and will very convincingly spin if provoked. They were unable to stall the aircraft in a full slip because they simply ran out of elevator authority – and they tried everything. They could not make the aircraft stall in a side-slip! If it does not stall then it cannot spin!

 

But as Mike has belaboured the point – that may not apply to all types, so just take this as a bit of insight to the subject but not perhaps particular to what you fly.

 

My own experience though is much in accord with the findings of my staff that summer evening. You can sit there with full opposite rudder and full back stick, be going down like an express lift, but I never got even close to the actual stall.

 

To conclude – I would like to take up one point Motz made and that is using the rudder to pick up a down-going wing at the stall – DON’T! You have no need to! Simply relax the back pressure, lateral damping reinstates itself and you have full control back – instantly! Start stuffing around with the rudder in an out of control situation and you can buy into more trouble than you were wanting.

 

One day on a routine spin training exercise, in a very spin orientated glider, my student lost presence of mind and applied the full opposite rudder after going around a few times but held the stick back. That aircraft span with an extreme nose down attitude. It simply stopped spinning right and commenced spinning left , very smoothly and with no change in attitude. That was nearly as disorientating as an inverted spin and we came around the bottom at 800’ having departed 3000’. I had just enough height to get the thing over the airfield boundary fence so we did not have to de-rig it!

 

Y’all be careful out there and get the right advice and know your aircraft!

 

Aye

 

Tony

 

 

[Yenn]

The object of a slip on approach is to get rid of excess height. Do you agree?

 

I have slipped Thrusters and the Corby that I now fly and all I do is get a good slip going and push the nose down. The slip gives loads of drag and pushing the nose down makes you descend and also keeps the speed up. There is no fear of stalling as long as the nose is down and your intention is to lose height. If you are so near the ground when you slip, there is no need to lose height and if you are going too fast, you should have acted earlier and the best thing is to go around.

 

The great thing about slipping is, that as opposed to flaps, when you finish the slip you are in a clean condition, whereas with flaps you are dirty and they need a lot of care if going around.

 

 

[Guest Juliette Lima]

Thanks Tony and Mike,

 

Getting a little worried about some of the responses to the initial question.

 

More importantly, what was the outcome of your extra curriculum activities ?

 

Cheers and thanks for the benefit of your years of experience presented in story form.

 

JL

 

 

[Guest pelorus32]

There is no fear of stalling as long as the nose is down and your intention is to lose height.

Tony,

 

as ever you put the whole thing so well.

 

I would like to make one comment - not about Tony's post but about the comment from Yenn above and another post in this thread on the same theme.

 

First, I am not talking about stalls in slips (as Yenn and others were) - I note Tony's comments. Rather I am commenting on stalls in general.

 

Nose position - that is pitch attitude has NOTHING to do with whether an aircraft will or can stall. This is very important. You can stall an aircraft with the nose vertically down. You can also have the speed below "stall speed" with the nose vertically up and not necessarily stall the aircraft.

 

The ONLY thing that leads to a stall is exceeding the critical angle of attack. That can be achieved at any pitch angle.

 

Regards

 

Mike

 

 

[motzartmerv]

Why have i been taught to pick up a dropped wing with rudder?? By more then 1 instructor in more then 1 school??...

 

Tosgcentral, as usual your post is exellent and backed up by experiances.. So your saying that we shouldn't pick the wing up with rudder?..in a high alpha stall with flap out and under lots of power wing drop (in the jab) is a common accurance.. I understand that relaxing back pressure will unstall the wing, but if that wing drops too far what will happen?

 

I must say i can see how ppl could easily be confused reading these posts..some say talk to your instructor, others say thats not such a good idea..and others just plain talk in riddles and expect us to desipher a code to get the relevant info...

 

just my 2 cents

 

cheers

 

 

[Tony]

Well, agreed here, sort of...

 

The idea of picking up the stalled wing by ailrons is questionable because a stalled wing will stall even more with 'intuitive' ailron input. So the only input left OUGHT to be is the stick forward for the better speed and the ruder for better prospect of the already grim situation.

 

See, the true pilots will not get in to this strife, because they are totally opportunistic.

 

SPEED IS THE GOD, the Rudder is important and good Ailrons input just helps the flying along for the better what was already decided.

 

One can slip side ways with the flaps down if one knows how.

 

However, the combination of slip and stall is a grave one for sure to me.

 

What is the purpose of stall ?

 

Good Lord, a stall is not a normal flying situation, it is a NO NO....is it not ?

 

I know four ways how to lose height on final:

 

1) Power back and maintain the glide speed by stick forward

 

2) S turns

 

3) Slipping forward - cross control

 

4) Stall at once - only for those real experts who know how to drop from 300 - 200 FT in 5 seconds (!) still going straight - and more importantly only good for those ones who knows where exactly is the bottom for this.

 

 

[Guest TOSGcentral]

Motz – I will respond to two of your points – at the expense of drifting somewhat off from the topic of this thread.

 

Firstly, I quite agree with you that it is a lousy situation to be in when you are either trapped between experienced people expressing opposite opinions, or, you eventually become experienced enough to understand the import of the difference in standards of the training system and its inhabitants.

 

Unfortunately it is the students who require the comfort and security and they do not have the experience to pick and choose who is or is not right. The training system therefore has a duty of care to be predictable, but above all it must be right in what it does!

 

So I am quacking that you do not pick up a down-going wing at the stall with rudder. That will appear to be blatant heresy to probably the majority of readers and will deeply contradict how and what they have been taught to do. So let us examine the situation.

 

I am not saying you cannot pick up the wing with rudder! What I am saying is why bother as you are just stuffing around wasting time in an out of control situation. You are also adding drag to an already high drag circumstance and so adding to sink rate when you probably do not want to be sinking at all. Furthermore, sooner or later you are going to have to get the back pressure off the stick to move out of the stall regime – so why not do that first? It is what is causing the problem!

 

Let us examine exactly what is happening. The wing is dropping because it has been moved (possibly by a gust or unwise use of ailerons very near the stall) to beyond the stall angle of attack. It ‘stops flying’ so it goes down – that is the wing drop at the stall.

 

The downwards vertical motion of the wing increases the angle of attack to beyond the stall A of A so the wing continues going down and this is the essential ingredient for the establishment of auto rotation (or the spin as it is usually termed).

 

Another method of expressing this (and this is what is actually happening) is that you have lost the natural stability of the wing in roll and shed it’s lateral damping!

 

Now, chances are that you have never heard of lateral damping because stability is not (usually) actively taught as an air exercise and at best you are told to read about it as part of BAK. That is a great shame because it has killed hundreds of people!

 

Lateral damping is very simple. If, in normal flight, the wing is disturbed in roll by say a gust, one wing goes down and so meets the air at an increased relative A of A, develops more lift, and so rises again, and will continue doing so until both wings have re-established equilibrium of lift.

 

If this happens when the aircraft is near the stall and the stall A of A is exceeded on the downgoing wing, then the downgoing wing cannot lift itself because it is stalled – so it carries on going down and the grim march towards auto rotation has now begun.

 

As Mike very correctly states – the stall is primarily a product of relative A of A, but it can also be influenced by airspeed. This is where ‘pick it up with rudder’ comes in. If you yaw the aircraft away from the down-going wing then you increase its airspeed and shallow out the A of A and so develop the lift you require. Try and use the ailerons and you just increase the mean angle of incidence of the wing and make the situation worse as the A of A deepens.

 

On the other hand just relax the back pressure on the bloody stick and rotate the entire aircraft out of the stall and the downgoing wing stops going down as if you had stuck a rock under it, lateral damping is reinstated and the ailerons will work normally again. That takes about half a second! So why stuff around with the rudder? There is a reason and it is a very strange one! It is called ‘tradition’!

 

The structure and methodology of flying instruction began being formalised during the First World War and consolidated itself in the inter war years. During the Second World War pilots were mass produced and the training hardened around high wing loading trainers and fighters with massively powerful, high torque engines.

 

Dropping a wing at the stall in one of these was a very serious business because the chances were very high that the aircraft would progress into autorotation very rapidly indeed. So the wing drop in the stall recovery became actually spin prevention.

 

If you think about it applying opposite rudder to a down-going wing is actually all the major components of the side slip – which is used to lose height faster – but is essential to prevent progression into auto rotation.

 

As commercial and GA flying began becoming an industry, training was dominated by ex military pilots who introduced their tried and tested methods that had trained hundreds of thousands of pilots.

 

As civilian flying matured to the point that it was training its own pilots from scratch, that methodology continued to be used in both practical application and greatly influenced personal and structural attitudes. It did not really matter if it was right or wrong – it worked and professionals do what they are paid to do!

 

Where the wheel really came off the wagon was when Recreational Flying came to the fore – firstly from the Gliding movement and then the veritable explosion of the ultralight world in the late 1970s.

 

Gliding was sufficiently and obviously different from mainstream aviation that its training system was able to develop its own methodology peculiar to the aircraft styles being flown. But I can assure you that in the mid 1960s the influence of GA was still very evident in glider flying training.

 

Ultralights however were very similar to GA (or at least the tri-axis control versions) and I believe there was a much stronger influence of ‘we have to be seen to be doing it the GA way to be taken seriously’ than there was development of training orientated to the broad spectrum of people who wanted to fly these machines – or indeed the piloting needs and techniques the aircraft style actually demanded, for they were certainly not complex, high wing loading fighters, and will not abruptly enter spins!

 

So traditional training methodology has persisted whether it is relevant or not to what we actually fly. Along with that comes difference of opinion that is generated via control movements attempting to maintain a status quo and high experience professional instructors such as Piggot, Scull and Valentine who did indeed make massive inroads to recreational flying instruction methodology.

 

I suppose I should add myself to that list – they were all personal friends that I worked with over the years, for years, and I guess I did my share of training system analysis and development.

 

To round this off – I repeatedly see on these forums, and hear around the airfields, what amounts to a fear of spinning and stalling. This is probably because they are no longer taught to the depth that they once were. They are simply conditions of flight that need to be understood and barricaded against by techinques, not be apprehensive of.

 

I have done thousands of spins and I do not particularly like them other than as an aerobatic manoeuvre – it is just something that I did and had to do a rather lot of. But I did far more work in the pre spin preventative area and made damn sure that what I taught was very relevant to what I was flying.

 

In the light recreational aircraft area most will be in the incipient spin stage for at least one rotation before they settle into auto rotation. This equates to four stages – the stall, wing drop at the stall, incipient spin, and established autorotation.

 

For the first three it is only necessary to de-stall the aircraft by relaxing the back pressure on the stick, getting flying speed and sorting out the attitude. If you have been asleep (and you just about would have to be to get into a full spin) it is only then that you need the full bit of full opposite rudder to rotation and be prepared to hold the stick against the front stop and wait if that is found necessary. Even then recovery is not assured unless you are in correct weight and balance and the type has been adequately test flown.

 

The big danger in any loss of control situation is not actually what is happening (it matters little in practical terms if you are stalled, spinning or spiral diving) it is the rapid height loss and where that takes you!

 

Picking up a wing with rudder in a light recreational aviation aircraft will escalate that height loss when an instinctive relaxation of back pressure will resolve the situation entirely in half a second!

 

Does that answer your questions Motz?

 

Aye

 

Tony

 

 

[motzartmerv]

Thanx Tony, it sure does.. I can understand your point.. The only acft i have spun in was a skyfox, is wing drop and subsequent nose down and rotation was very rapid and what i would call violent.. And also the stick needed more then relaxing of the backpressure it needed a pretty posative pole foward to unstall the wing..

 

I will practise some stalling tommorow when i go flying and use your techniques and see how it works for me in the jab...i must say it will be hard to fight the urge to keep the wing up with rudder but having said that, you are deffinatly right about the wing unstalling quite quickly after relaxing the backpressure...

 

I guess my only concern would be in a real world situation...Let me explain

 

Say an engine has failed and we are on short final and gliding to our chosen paddock..Now ive ballsed up the angle distance with my turns and have come up slightly short, so in trying to stretch the glide i have come back to far on the stick or even better i havnt stuffed up but i have encounterd some gusting turbulance and the acft enters astall at say 20 feet with a significant wing drop..Now, if i dont pick up that wing at the same time as poleing forward to unstall what ends up is a flying acft again wth a a very low wing and subsequently pointing not where i needed it to be..that fraction of a second where i have had to reallign with the paddock is lost and i hit the trees on side of the paddock..

 

Most of the stalling we do is at altitude in a training situation (technically) where a wing dropping and subsequent change of heading is not a problem, but at 20 feet when im trying to squeeze into a paddock im sure it would be a problem...

 

Now i can already hear the responses.."DONT STALL AT 20 FEET".hehe..

 

Tony please dont get me wrong, i completly agree with your experiances regarding stalling..how could i not, your years of flying and training oithers speak for themselv's..How would your techniques relate to the above situation..

 

As usual i look forward to your reply..

 

cheers