Crabbing Slip / Sideslip

4 Answers

1. 
   

   
   

   Brian on Nov 20, 2010

   James,
    
   Slip – A cross controlled, uncoordinated, flight condition where by the tail falls in the direction of the bank. Commonly used for crosswind landings, as a method of losing altitude, or whenever rudder is not used for turn entry. Note: There is NO aerodynamic difference between a slip for landing, a slip in a turn, or a slip to lose altitude. In other words, a slip is a slip is a slip. All that changes is the purpose for it.
    
   Crab – A technique used to keep the ground track straight with a crosswind current. I use the word current because I believe it is easier to understand if you picture a boat crossing a river. The crab technique is identical to this. The aircrafts nose is angled into the current using trial and error or experience to determine how much crab is needed to successfully fly a straight ground track to the runway.
    
   There really is no technique that is better than another, in my opinion of course. I find the slip is an outdated technique whose primary purpose was ensuring no side load on touchdown in tailwheel craft. However, learning to fly an aircraft more precisely is never a bad or dangerous thing.
    
   The crab I find is easier to learn I think because the visual picture isn’t so obscured as is with the more awkward slip condition. It is the technique I prefer to use, but certainly not the only one worth learning.
    
   One final tip, when entering a slip it is easier to learn to add ailerons first and then rudder — i.e. bank and then rudder into the slip. The reason being, aerodynamically, when we apply rudder in one direction the aircraft will attempt to bank in that direction (some people call this aerodynamic condition pro verse roll). Since we will need to bank in the opposite direction, if we apply rudder first we are now forced to overcome this aerodynamic bank caused by the rudder application.
    
   Try it both ways at altitude with your CFI and you’ll see how much harder it is to bank if rudder is applied first. Do this by applying full rudder and a second or two later attempt to bank the opposite direction to approximately 20-30 degrees. Next, bank 20-30 degrees and then apply rudder. In reality, both rudder and bank are added together. Until you can do that, however, consciously apply aileron first. 

   +1 Votes 3 Votes  2 Votes

2. 
   

   
   

   Micah on Nov 22, 2010

   When I fly these maneuvers I try to keep all of them very simple. The answer below will probably be too simplistic, but see if these ideas help.

   Crab: the crab is a method to control for crosswind during any stage of flight. You are flying forward and the wind is coming from one side and pushing you to the other. You turn the nose of the airplane slightly into the wind and neutralize the effect of the crosswind. You’ll have to determine how much by judging the track that results (or just turn to the heading your GPS suggests).

   Forward slip: the forward slip is a method for losing altitude quickly at a controlled airspeed. You must practice this in the “oh, no, my engine’s on fire maneuver.” The forward slip takes full opposite rudder and as much aileron input as is required to keep your airplane in control and on the appropriate track. (Always slip into the wind.)

   Side slip: the side slip is a method for controlling track, much like the crab. Use the ailerons to “turn into the wind” and use the rudder to “keep your feet straight.” If your airplane is too far right or left, make slight changes with the ailerons to move the airplane back to centerline. If your airplane is pointing too far right or left, straighten the nose with the rudder.

   Whether the sideslip or crab is a better method for landing depends on many factors, but remember this: your objective is to land on centerline and remain on centerline. If you land in a crab then your wheels are not pointing down the centerline. A crabbed approach will almost always require the sideslip method to safely finish the landing.

   +10 Votes 11 Votes  1 Votes

3. 
   

   
   

   NavyWings on Apr 29, 2012

   I’m a retired Navy pilot who flew large 4 engine aircraft. Training preference has always been (still is) slip vice crab but (and there’s always one) the best procedure is the one you’re best at. That being said, objectively the best procedure, all else being equal, is a slip. And it’s not based on landing gear stress, though that is a tertiary benefit.
   Landing touchdown is probably once of the most critical times of flight. Decrabbing at touchdown requires input in all three axis. You need to input rudder for the crab, aileron to prevent drift and pitch for the flare. A lot of inputs during a critical phase. A slip however only requires inputs in one axis, the pitch axis if it’s executed correctly. Far less inputs needed to be executed simultaneously. If your approach is set up properly with respect to airspeed, descent rate andzero drift with a slip input, you’ll track right down centerline and be aligned as well all the way to touchdown. You only need pitch input to flare and touchdown on upwind wheel. If you’ve watched them both from the ground, the slip to flare is always more smooth than the crab.
    

   +14 Votes 14 Votes  0 Votes

4. 
   

   
   

   Walter on Dec 20, 2012

   Thank God for Navy Wings.

   I recently got very sensitive to this issue because I was on a (unnamed airline) flight where the pilot attempted “kick”ing the rudder on landing. As a commercial pilot in the back of the airplane, it irked me. It was an extremely uncomfortable feeling for the passengers and certainly resulted in a lot of burnt rubber.

   Fly like you are flying IFR. Remember, there is a ‘key’ position where your altitude, airspeed and configuration should all be on parameters for landing. Next is a decision height where you should make the choice of whether you are actually going to bring the aircraft in contact with the ground. If you get to DH and you have decided that you are going to land, you should line up your aircraft with the runway.

   Until DH, crab. After DH, transition to a slip. That means, make the transition from crab to slip between DH and flare. That means going from coordinated flight to cross controlled flight. Wing low, into the wind as necessary to counteract the wind drift, opposite rudder to maintain the center line, nose down, to maintain approach airspeed and power, to maintain glide slope. Make this transition smoothly before flare.

   There are very few times you should want to “kick”, “yank” or “jerk” any of your controls, especially, just before touchdown. I hate that great instructors would use these words to describe the transition procedure from crabbing to slipping.

   I also want to mention that the 7 degree angle mentioned in one of the blogs about the engines hitting the ground in a slip is applicable only with the gear up.

   +11 Votes 11 Votes  0 Votes