slips vs skidding turns

[RobertE]

I think the AOA discussion concerning the safety benefits of adding an AOA instrument has now gone to 9 or 10 pages.  Which got me thinking about the conditions that produce a stall/spin accident during an approach.

 

We all know a spin requires the combo of a stall and uncoordinated flight.  But isn't the type of uncoordinated flight that leads to spins really limited to skids?  Can an aggressive slip (that which many of us were taught to employ to fight a cross wind) ever produce a spin?  I believe the answer is no but, maybe this is something I ought to be certain of!!

 

And on a related note, other than via really aggressive manuevering, is it true that we can all be confident of hearing a stall horn go off at least a moment or two before the stall/spin occurs?  I realize that the indicator may be located on a wing other than the one that stalled first but am guessing the difference in angle of attack between wings isn't so large as to not trigger a warning on the unstalled wing.

 

Thanks.

[Shadrach]

An uncoordinated stall can produce a spin, but I do not believe it is the only way that a spin an happen. Aileron application in a stall can increase AOA on one wing  while decreasing AOA on the other. 

[kmyfm20s]

If by aggressive you mean high airspeed or highly uncoordinated? The slip you should on a constant heading with and proper attitude and maintain appropriate airspeed. This keeps the lift on both wings mostly equal by adjusting aileron input. The classic skidding turn which are the same inputs with rudder and aileron but differ in attitude as the slip and your changing heading. This is accelerating the high wing creating greater lift, decelerating the low wing giving less lift and with the rudder input tightening the radius of the turn creating the stall/spin. In a Mooney with the rudder design I feel like all my slips are very aggressive compared to other aircraft just not as effective. Hope this helps.

[RJBrown]

Best way to learn the answer to your question is to go find out what YOUR plane does. Get up high enough to be safe and find the edge of the envelope. I speculate that the need to use the slip to lose altitude will be over before you get any where near the edge you are worried about.  The slip is to come down without going too fast. As soon as you are on glide slope and landing speed you get out of the slip. In this manuver you are above your final approach speed the whole time.

[WardHolbrook]

Understanding how your airplane behaves out near the edges of the flight envelope is critical. That being said, I believe that the best foundation is one of those extreme unusual attitude recovery / basic aerobatics courses that are becoming more and more available around the country.  Basic aerobatic and extreme upset recovery training takes most of us outside of our comfort zone. (I know that it did for me.) But, I honestly believe that it's something that you really need to do if you want to be the master of your craft. Can you safely fly without it? Of course you can, but it does not take much imagination to come up with the "perfect storm" scenarios where having the training would make all of the difference in the world to you and your family. I'm not talking improbable events either, all it would take would be ATC vectoring you in just a little too close behind that Boeing 757 when you're on approach.

[jlunseth]

There is some evidence that slips can produce spins, even inverted spins, in the long bodies.  Here is one of the stories: http://www.mooneyevents.com/spins2.html

 

I have read a fair amount of material on this, can't tell you where it all is it would take some digging.  We had a couple of threads on the issue a few years ago.  I can tell you that I needed to learn to slip my 231 for my commercial ticket, in order to control excess altitude during the power off 180, and I approached the whole process with some trepidation, but my 231 did just fine with the forward slip as long as I kept the airspeed up at 85.  It is the longer body models after the 231 that had the slip issue.

 

During my training and practice for my commercial ticket I had lots of opportunity to get the stall horn working, actually in my aircraft it is a voice annunciation but same thing.  The annunciation was always well in advance of any actual stall, including a few times when I didn't mean to stall, but your results may vary.  If you read the above piece, I think you will be convinced as I am that you do not want to put a Mooney in an actual, full stall and spin.

 

I realize that you are talking about slipping turns and not forward slips, but they produce the same issue, the angle of attack is higher on one wing than the other, causing one wing to stall first and the other wing to lift over. 

[kmyfm20s]

An uncoordinated stall can produce a spin, but I do not believe it is the only way that a spin an happen. Aileron application in a stall can increase AOA on one wing  while decreasing AOA on the other.

So which wing would someone locate there AOA indicator on?

[Marauder]

So which wing would someone locate there AOA indicator on?

Right wing... The left one is covered already with stall warning devices. Peter made me say that! Sent from my overpriced iPad using Tapatalk

[Marauder]

I may have dreamt this but I I thought I read somewhere that it was not permissible to slip a long body with the flaps deployed.

On my F, I have done what Ward and RJ recommended above. I actually have a fair degree of confidence doing a forward slip in my plane. Mike (201er -- by the way, where has that guy been?) and I discussed this a while back. What was funny was that I love doing left wing down forward slips much more than right wing down. Why is that? Better visibility? Or that I know I will get to the ground faster than the co-pilot (aka my wife)?

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[PTK]

Both skid and slip are uncoordinated maneuvers that can produce a stall. Neither is good when turning base to final!
But the safer of the two is the slipping stall.

In a slip the turn is slowed by rudder but in a skid the turn is sped-up by rudder.

In an uncoordinated stall it is the slower wing that stalls. In a slipping stall the higher wing is the slower one and stalls first. When the higher wing stalls it must fall a longer distance through level before it drops into a spin. This gives you more time to correct and recover.

In a skidding stall the slower wing is the low one. A lot more dangerous.

A mistake, (among a sequence of mistakes), pilots make is introduce rudder to speed-up the turn instead of aileron and skid into a stall/spin.

[RJBrown]

I understood that a forward slip IS what we were talking about. A forward slip is used to dissapate too much energy in the form of altitude and speed. I dont believe that will cause the issue that concerned you.  Yes long bodies have issues slipping that I have heard of, never flown one. A skidding (uncoordinated) turn flown too slow IS what spins are made of.

 Yes to whatPTK wrote above

[FloridaMan]

My understanding is, as PTK said, that a stall where the top wing stalls first will give you more time to recover and you will pass through level. In a skid (bottom rudder), the bottom wing isn't just moving slower, but airflow is also partially blocked by the fuselage allowing it to stall first. In our airplanes, the front falls first (making it recoverable from a stall in the first place). With the top wing still flying, it speeds up, giving even more lift and rolling you into a spin as the nose continues to drop. 

 

I have not done uncoordinated stalls in my Mooney. I have, under the supervision of an aerobatics pilot who has over 2000 hours in Mooneys, stalled my Mooney at 4000ft with full power, yoke held in my lap until told to recover and free reign of rudder. The stall can be a bit violent, but it has never rolled more than what felt like 90 degrees. I am still as nervous as a whore in church doing stalls and will not do them without supervision. 

 

The instructor mentioned that people panic in a spin and, while they think that they are putting in the correct input, that they are fighting a locked opposite leg; he advised me to make sure that I am loose. Regardless, I am still terrified of such risk. Another piece, when doing stalls, is to look outside. Focus on a distant cloud, especially under power and high angles of attack, my Mooney requires significant amounts of rudder before the stall. I think that people may not be used to making the corrections and that helps them find themselves in a spin. The reason that I mention this is that I make a conscious effort on approach to ensure that my feet are loose on the rudders. 

 

Marauder, I have a feeling that right rudder may be more effective on a well-rigged Mooney for a slip. 

[Danb]

I have a long body as well as having 2 J models in the past.last year I took the Mapa safety course and we practiced slips mainly forward slips is order to lose altitude by utilizing the energy, I do not see any or very little difference is slipping in the short bodies vs the long body's. Basically if there is a difference I believe the long body dissipates energy easier than the than my J did, also the Long body seems much easier to land

[carqwik]

Great video to understand the impact of skidded turns on a plane's wing and lift aerodynamics:

 

 

From APS Training...watch and learn why skidded turns are really bad when low and slow....

[John Pleisse]

Not to muddy the waters, but this came up yesterday with a CFI..... Full flap forward slips in Mooneys are bad news, creating elevator stalls? or not so much?

[Marauder]

I think the discussion point is whether you are in a stall configuration when you do a slip. I think the key is whether you are truly stalled or executing a nose down slip. Antares -- BTW you may be correct but I also think that left forward slip is more comfortable for the pilot since they are facing forward with greater visibility. Where's Orville Wright when you need to have him waive in on this? Heck, I would settle for Jimmy Doolittle at this point.

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[Marauder]

BTW -- I am enjoying this thread... Much better than discussing AOA, CamGuard, whether you land with flaps or not, what is the best speed to land at, blah, blah, blah...

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[tomn]

I may have dreamt this but I I thought I read somewhere that it was not permissible to slip a long body with the flaps deployed. On my F, I have done what Ward and RJ recommended above. I actually have a fair degree of confidence doing a forward slip in my plane. Mike (201er -- by the way, where has that guy been?) and I discussed this a while back. What was funny was that I love doing left wing down forward slips much more than right wing down. Why is that? Better visibility? Or that I know I will get to the ground faster than the co-pilot (aka my wife)? :)Sent from my overpriced iPad using Tapatalk

I like left wing down slips better too - don't know why - probably better sight picture. Slipping and cross controlling in general is a very important skill to learn in my opinion. Flying aerobatics can teach you this - did me. I have landed in a very strong crosswind slipping with my foot to the floor and still had to land drifting across the runway. I do not think it would have worked out very well w/out the aerobatic training. Its worth it.

[carusoam]

As for the nonprofessional pilot in a long body....

There is one well known long body accident by somebody important to Mooney. (at least that's how I remember it)

Slips with flaps fully extended can be dangerous. Maybe yes, maybe no...

Transition training demonstrates losing altitude in an emergency descent using gear down, flaps extended, throttle out and prop forwards maintaining speed below Vfe with speed brakes extended...

So all the long bodies got speed brakes... They are effective.

I guess, if the plane's cabin were on fire I might add a full slip for as long as I am conscious....But, I would be keeping the nose down to avoid a stall while getting closer to the ground ASAP!

I use the ball to avoid both slips and skids. PTK and I use the ASI to avoid stalls.

Go speed brakes!,

-a-

[DonMuncy]

The EAA had a webinar tonight on maneuvering flight, including spins, in which this point was discussed. They put these webinars on their site for re-viewing later, but this one will not be posted until tomorrow or so.

[Lood]

"Maintain thy airspeed, lest the earth shall arise and smite thee."

 

And thy attitude...

And thy bank angle...

And the ball centered...

And thy common sense...

 

And thy will never come close to a stall/spin situation, in the circuit.

[fantom]

I use the ball to avoid both slips and skids. PTK and I use the ASI to avoid stalls.

 

 

That's fine, but you're using the ASI only because you don't have an AoA.   BTW, your ASI is another reminder to put down your gear before touchdown.

 

I too, have had one foot to the floor many times in a strong crosswind landing. OK, but never totally comfortable. 

[carusoam]

What is the factory going to put in the new instrument panel for AOA???

Best regards,

-a-

[M016576]

Both skid and slip are uncoordinated maneuvers that can produce a stall. Neither is good when turning base to final!

But the safer of the two is the slipping stall.

In a slip the turn is slowed by rudder but in a skid the turn is sped-up by rudder.

In an uncoordinated stall it is the slower wing that stalls. In a slipping stall the higher wing is the slower one and stalls first. When the higher wing stalls it must fall a longer distance through level before it drops into a spin. This gives you more time to correct and recover.

In a skidding stall the slower wing is the low one. A lot more dangerous.

A mistake, (among a sequence of mistakes), pilots make is introduce rudder to speed-up the turn instead of aileron and skid into a stall/spin.

Just to be clear, it's not the skid that's dangerous on its own, it's stalling the wing in an uncoordinated condition that can be dangerous. This typically occurs unintentionally in the traffic pattern when "wrapping up" a turn at higher angles of attack. A slipping turn actually drives the retreating wing into the airstream... A slipping turn can be more stable than a "coordinated turn", and is definitely more stable than a skidding turn. and assuming you enter and exit the slipping turn precisely, is actually somewhat spin resistant. I use a slipping turn to increasing rates of descent from the perch / 180 when required- executed properly, they are a useful tool.

Skidded turns occur intentionally in aerobatic flight... Rudder triplet departures, etc.

[RobertE]

I think I should clarify my question.  I wasn't talking about turns but, rather, the sort of forward slips that I think most of us were taught to use in order to land in a crosswind. 

 

So, on final, if I've got a right crosswind and, in response, lower the right wing while stepping on the left rudder (in order to remain pointed down the runway) do I risk a spin should my airspeed decay to a stall?  Because getting to stall speed, of course, is roughly what I'm trying to do.  Sure, I want to stall while 6 inches above the runway, but engaging in a behavior that will produce a spin if my airspeed decays while, say, 10 feet off the runway isn't a pleasant thought.