Crabs in my Slip

[Mcstealth]

Ok. I'm looking for my maneuvers book. Have not found it yet.

what is the difference In technique between a crab and a slip?

during a recent flight, the instructor said why are you crabbing it? I thought I was using a slip technique to slow down.

david

 

[carusoam]

Crab involves pointing the nose towards the wind and keeping the wings level.  This Maintains the ground track.  This also leaves the plane not aligned down the runway at the time of landing. Without much use of rudder, it doesn't slow you down very much.

Slipping to dump energy involves putting in a lot of rudder, and lowering a wing to offset the turning tendency of the rudder.  Lowering the nose will be required to maintain airspeed.

Definitely check with you CFI to make sure you select which wing goes down properly for the slip.  It should be based on the way the wind is blowing.  

This usually leads to the crab and kick vs slip discussion.

Did that help?

Still not a CFI,

-a-

[Shadrach]

I don't think they are the same.  

A crab maintains desired track by offsetting the nose toward the direction of the wind just enough to maintain a track commensurate with desired (runway) heading.

A slip maintains desired track using bank angle into the wind and rudder to keep the nose aligned with desired (runway) heading as well as a track comensurate with desired (runway) heading. This necessarily a cross controlled maneuver.

 

I transition to #2 at about 1/2mile final for Xwinds.

Employing a slip to slow down requires aileron and rudder in opposition.  I enjoy max control input left wing forward slips on a regular basis. It's fun to do the approach looking out of the side window...

[MyNameIsNobody]

I ALWAYS Crab.  I think it is dead simple in my Mooney.  Never an issue with applying rudder in round-out.  I don't do Texas X-winds...I think Mooney's are VERY stable in a cross-wind crab.  I am NOT cross-controlled in any way in the crab.  Nose is just deflected/tracking the wind.  

[DXB]

Difference in crab vs. slip is as Ross describes above.  I crab until over the fence, then try to side slip just before starting the round out, with varying degrees of success.  The rudder input for this transition is fairly easy.  Judging the opposite aileron input needed to offset drift is less so.  Having an instructor tell me to "think about planting the upwind wheel on the runway" while adjusting the aileron input in the flare seemed to help.  The real art is in dynamic adjustment of both rudder and aileron as you slow down in the flare and ground effect comes into play.   I am not good at any of this.   

[Hank]

"Crab" is when your passengers look out the side window to see where you're going. I've had up to 40° crab in cruise before, making a burger run. Just point the nose wherever it needs to go (into the wind some) so that you move in the direction you want to go. I generally try to fly a 1/2 mile pattern, and about halfway from wings level on final to the runway I transition into a slip.

There are two kinds of slip:  losing excess altitude or speed, and crosswind landings.

To lose excess altitude or speed, just bank one way and push the other rudder. You'll steer out the side window like when crabbing, but your descent rate will increase and your airspeed will get slower. This is a "side slip." When landing in a crosswind, you don't want to land in a crab, it will side load the gear. So use the rudder to point the nose down the runway. Now the wind is blowing you off the side, so use aileron and bank into the wind and steer yourself into alignment with the runway. Ailerons will hold you over the pavement, rudder will keep you pointed straight down it. This is a "forward slip."

Unless, of course, I have the two slip names backwards. I never could get the names straight, although functionally they have never been a problem. Too high, slip or go around; too fast, reduce power and slip, land long if possible or go around; good crosswind blowing, slip to land. The big point of contention about crab and slip in a crosswind landing is when to change over. Some of us do it soon enough to be in good control early, some like to wait and "kick in" the slip at the last minutes,hoping to get it right, not side load the gear or dart towards the edge if the runway.

Its fun practicing side slips at altitude. I used to do it for 1000' to each side, just to get comfortable with it. Climb high, aim towards something distinct and distant, kick full rudder one way and steer towards it with aileron. Watch the VSI & ASI, vary the I outs and see what changes. After dropping 1000' switch directions. Oh, don't have anything laying around loose when you do this . . .

[C-GHIJ]

Go see M20Doc, he can give you a shot that should cure your crabs.   Next time wear protection to avoided the crabs.

[Yetti]

Slips are also good to work to a 1 main wheel landing.  very stable. keeps the upwind wing out of the wind. Requires side friction on the wheel to work, don't try on icy runways. have not tried one in the mooney

[Shadrach]

5 minutes ago, MyNameIsNobody said:

I ALWAYS Crab.  I think it is dead simple in my Mooney.  Never an issue with applying rudder in round-out.  I don't do Texas X-winds...I think Mooney's are VERY stable in a cross-wind crab.  I am NOT cross-controlled in any way in the crab.  Nose is just deflected/tracking the wind.  

It works fine in a Mooney under most conditions. That being said, I don't think that it's best practice from an airmanship standpoint. Not an ideal method in a conventional gear aircraft.

[1964-M20E]

We were discussing this the other night.  The preferred method for small planes is the slip method.  i.e. wing low into the wind and cross controlled with opposite rudder.  This lets you line up on final and stabilize your approach and if you are at full rudder and keep drifting then you know it is more crosswind than the plane can handle.

Of course it goes back to what you were taught when you got your PPL I was taught the slip method.

 

Big iron tends to use the crab method due to low engines and long wing spans make the slip method not desirable.

Edited February 8, 2016 by 1964-M20E

[Hank]

Big iron's landing gear can often swivel 20-30° so they can land in a crab. It's more comfortable for the people in back than a slip, especially when they can't see out front and tell how non-aligned the plane is with the runway.

[Shadrach]

2 hours ago, 1964-M20E said:

Of course it goes back to what you were taught when you got your PPL I was taught the slip method.

I was taught to slips to landing in a crosswind and my instructor made it clear that he thought the "crab and kick" was a less than optimal. He had an Aeronca Chief and a Champ; I was fortunate enough to fly both before I took my check ride. 

[carusoam]

That topic is harder to write about than it is to actually fly.  Flying a well executed slip is a cognitive challenge.  Writing about it is cognitive overload...

I think I basically confused the two types of slips with a slip vs. a crab.

David mentioned using it to slow down.

As Hank pointed out there is a forward slip and a side slip.  One is used to dissipate huge gobs of energy.  The other is used to handle X-winds during landing.

Important for Mooney pilots....  When entering and exiting slips. apply the controls smoothly in both directions.  In other words, it is easy to dump the rudder input. The tale will wag quickly. Something to avoid while low and slow.

Guessing...

(Forward?) slip is used to dump energy...? Example: Full left rudder and lowering the right wing with ailerons.  Your passenger has a great view forward, by looking out their side window. Same thing can be achieved with full right rudder.... Turning the plane sideways (sort of) to the relative wind will slow you down.

(Side?) slip is used to align with the runway while landing in X-wind.  Lower the upwind wing using ailerons, maintain alignment with the runway using rudder. Know how much drag the rudder is generating.  You will be slowing significantly more than usual by doing this.

Did I get any Closer?

This is for conversation purposes only. I am only a PP,  I am not a CFI.

Best regards,

-a-

 

 

[Yetti]

Slip is not just for speed it is good for altitude loss also.  On my checkride, on sim engine out I was high.  Since I was talking everything out loud.   "Looks like I am high"  Examiner "what are"  I was already throwing the plane to a forward slip.  I was taught to use the rudder inputs to move left and right to line up the runway or cows in the field.  They always seemed very stable in the C172.  there is a lot of nose down angle you need to put in a Mooney.  My mooney transition instructor tried to save my very high first engine out at the field attempt with a forward slip.   Depending on which side you do it to you are shadowing the pitot tube.  So airspeed may not be as indicated, so better to feel the plane.  Holding it all the way to the runway and transitioning takes some pretty good piloting. It does look very cool when done properly. defiantly need to feel the airspeed.

[Bob - S50]

13 hours ago, Shadrach said:

It works fine in a Mooney under most conditions. That being said, I don't think that it's best practice from an airmanship standpoint. Not an ideal method in a conventional gear aircraft.

Darn it!  I've been doing both things wrong!  I crab on final then use rudder in the flare to align with the runway and aileron to stop the drift.  The other thing I do wrong is use throttle for speed control.

Whatever works.

[Shadrach]

7 minutes ago, Bob - S50 said:

Darn it!  I've been doing both things wrong!  I crab on final then use rudder in the flare to align with the runway and aileron to stop the drift.  The other thing I do wrong is use throttle for speed control.

Whatever works.

 I just think it's better practice to have the aircraft as close to aligned with the runway as possible before crossing the numbers using fine corrections to hold desired track.  I also fly a tail dragger 25--30hrs a year, but I don't fly it very well.  I have a hard enough time keeping with the thing going where I want it without setting up a yawing movement going into the flare...

BTW, I'm with you in terms of whatever works in terms of pitch and throttle.

Deakin rants a bit about it here.

[bradp]

Anthony after I was used to your bullet point writing, the new writing style I'm not used to again :).  

 

The only appreciable difference I can tell between the control inputs of a fwd slip and a side slip is in the former you drop the nose and use full rudder input to lose altitude or airspeed.   For those of us without air brakes, this, gear and flaps are our air brakes.   The slip to land is done using primarily aileron, just enough rudder to correct and a flared angle of attack.  Gentle like.  

[jlunseth]

Hmm, I think from the OP's original post, that what was going on and what the instructor was commenting on, was a forward slip to slow the aircraft, rather than a sideslip for landing.  "Crabbing" can just mean turning the nose off the axis of the planes travel, which is what you do with a forward slip, you turn the aircraft off the axis, which creates drag.  That's different from a sideslip, only in that in the sideslip you would align the nose with the axis of the plane's travel, but in the forward slip, to achieve maximum drag, you would normally use rudder to turn the nose even further to create maximum drag.

[midlifeflyer]

3 hours ago, jlunseth said:

Hmm, I think from the OP's original post, that what was going on and what the instructor was commenting on, was a forward slip to slow the aircraft, rather than a sideslip for landing.  "Crabbing" can just mean turning the nose off the axis of the planes travel, which is what you do with a forward slip, you turn the aircraft off the axis, which creates drag.  That's different from a sideslip, only in that in the sideslip you would align the nose with the axis of the plane's travel, but in the forward slip, to achieve maximum drag, you would normally use rudder to turn the nose even further to create maximum drag.

Except that "crabbing" is used throughout FAA and other training publications to refer to a coordinated turn into the wind to maintain ground track, which a slip is not. For example, in discussing the various methods for crosswind landings, the Airplane Flying Handbook talks about transitioning from the crab into the slip at a certain point. Deciding to use words in a different way doesn't really help understanding; if anything it confuses things.

To answer the original question, @carusoam said it in the first few responses. A "crab" is coordinated flight into the wind to maintain a ground track. A slip is uncoordinated flight designed to either add drag to lose altitude or maintain a ground track and runway alignment for landing.

To the point of forward slip vs side slip, I agree with those who described them in terms of the purpose of the maneuver. They are aerodynamically identical. We refer to a forward slip when we refer to a slip used to lose altitude without adding airspeed; we refer to sideslip when we talk about crosswind landings.

I guess some folks are also getting into the old "crab and kick" vs "slip all the way" argument. I've always thought it's silly since the only thing that is different between them is the timing of the transition to a slip. If we assume the last 500' of an approach to landing takes a minute, and we count a minute in seconds, that's 60 different seconds along the way in which the transition from crab to slip can occur. Personally, I'm not wedded to any of those 60 seconds.

 

 

 

[bradp]

So what Dave is saying is that if you slip up on your crosswind landing you should be ready to crab into the wind during your go around.  

Clear as mud, see ;-)

[midlifeflyer]

1 minute ago, bradp said:

So what Dave is saying is that if you slip up on your crosswind landing you should be ready to crab into the wind during your go around.  

Clear as mud, see ;-)

Don't know about the mud but it is pretty clear. On the go around, you are not going to climb too well in an anti-aerodynamic slip. As I explain to my students, airplanes don't fly that well sideways.

[bradp]

1 minute ago, midlifeflyer said:

Don't know about the mud but it is pretty clear. On the go around, you are not going to climb too well in an anti-aerodynamic slip. As I explain to my students, airplanes don't fly that well sideways.

I was just tying to be cheeky with that comment, thus the ;-)

[1964-M20E]

Dave

I'm just a PPL but my comment was looking at a long wing it would not take too much bank angle for the wing tip adn engine to be really close to the ground but I might just be imagining things.

 

The first time in a 152 with the instructor demonstrating cross wind technique it looked like the wingtip was going to ht the ground.

[Shadrach]

1 hour ago, 1964-M20E said:

Dave

I'm just a PPL but my comment was looking at a long wing it would not take too much bank angle for the wing tip adn engine to be really close to the ground but I might just be imagining things.

 

The first time in a 152 with the instructor demonstrating cross wind technique it looked like the wingtip was going to ht the ground.

I assure you, you are imagining it. Given the dihedral and the position of the mains, the bank angle required to drag a wing tip with the gear down would be severe. Next time you jack up your plane, jack up one side only and see how much raise is needed just make the unjacked side level. I think you'll be surprised.

[Hank]

Even easier--walk up to your wing tip and put a finger where it touches your leg. Then walk over to the fuselage and see how far it is to the top of the wing. Then compare how thin the wingtip is, and how thick it is by the fuselage. To get the bottom of the wing parallel to the runway, you would need enough aileron to lower the wingtip by the height difference measured on your leg plus the thickness difference. To touch the wingtip, you'd need to go the additional distance of the landing gear leg. I'm pretty sure we'd all run out of rudder before we got that much bank going while trying to land.