Slip and Crab

[tom_c172]

What is the difference between a Forward Slip, Side Slip and a Crabbing procedure? Aren't they all Cross-Controlled procedures? Is one considered safer than the other and why?

[Frodo]

The Forward and Sideslip are the same thing. These are cross control maneuvers that cause the airplane to fly sideways. In a cross wind, if you slip at the same rate that the cross wind blows, you can fly down the runway and still be pointed down the runway. This allows you to touchdown without any side load on the landing gear. This is especially important when flying tail wheel aircraft.

In a crab, the airplane is coordinated and flys normally. However, if you have a cross wind you need to point the airplane up wind in order to track down the runway. If you touchdown like this, there will be a side load on the gear that may damage the airplane or cause a groundloop in the case of a taildragger. If you use this technique, you need to learn to kick the rudder just before touchdown to align the airplane with the runway. This takes good timing. If you kick the rudder too early the airplane will begin to drift with the crosswind and if done too late it will hit going sideways.

[summitgolfer]

I was taught that a forward slip is a cross-controlled descent maneuver. You can lose alot of altitude without gaining speed. A side slip is essentially the same, but is balanced with a crosswind to allow you to fly straight down the approach, with the upwind wing low. Crab is weathervaning into a crosswind when flying straight and level. I fly a 180, and sideslipping is a normal procedure. Forward slips are something I haven't done in a long time. It must be time to go flying.

[Chapster]

The definition of a Forward slip has already been posted and I shall reiterate; the terminology Forward Slip refers to the technique of increasing drag to allow an increased descent rate. In the absence of wind, the forward slip is a bit diffucult to coordinate and ensure that drift is zeroed out with rudder being applied in one direction and aileron being used to counter the induced roll.


The definition of a Side Slip has already been posted and I shall reiterate; the terminology Side Slip refers to the technique of crosswind landing whereby the upwind wing is lowered and the rudder is applied to counteract the tendancy to turn the aircraft. If coordinated properly, the aircraft will have no tendency to drift to either side of the runway and will track the centerline.

The definition of a Crab has already bene posted and I shall reiterate; the terminology Crab refers to the technique of zeroing drift in a crosswind by turning into the wind sufficiently with the wings level (same as correcting for drift when cross country flying). This technique of crosswind landing can be considered preferable to passengers who may not like to view the runway at an angle when side slipping. However, as pointed out previously, the crab requires precise timing and if performed improperly can impose large loads to aircraft landing gear not specifically strengthend.

Now a crab can be performed flawlessly with practice. Just prior to touchdown, full rudder is applied to align the longitudinal axis of the plane with the runway before the nosewheel touches down. Because of the precision and skill needed, most instructors do not teach this method and opt for the side slip. Additional training with an instructor is recommended before attempting.

Also, it is difficult to maintain a side slip from entry on final to touchdown and an easier method, combining a crab to within several hundred feet of the runway then side slipping, is more practical

If a 747-400 was landing, what method of crosswind control do you think the Captain will employ?

[sharplab]

A forward slip and side slip are not the same. The forward slip is a cross contolled maneauver where the the longitudal axis is angled away from the flight path. Basically if you flight path was 360 degrees then the wings would be banked to the left and the nose (longitudal axis) would be pointed off to the right say around 030 degrees. This is mainly used to create large amounts of drag for faster descents withour increases in airspeed. Also be aware the in any slip airspeed errors will be present. Most airplanes will show a lower then actual airspeed when in a left slip and the opposite when in a right slip. A side slip in simply a slip wher the nose (longittudal axis) of the airplane is alignes with the flight path. This is used mainly for crossswind corrections. A crab is simply flying the airplane normally and coordinated at such a way that you are simply inputting wind correction to keep your desired flight path. If the wind is blowing 090 a 15kts and your course bearing is 360 then flying 360 will take you way off course. Using your flight computer you would get your wind correction angle (about 5 degrees for 110 knot cruise) and then apply that correction and that is your crab. Your heading of of 355 degrees gives you a crab angle of 5 degrees. The name is given because of the crooked way that a crab walks. See how simple it is!! HOPE THIS HELPS EVERYONE!!

Stephen C. Sharp
Comm. Pilot

[Chapster]

Sharplab, are you trying to inform all those who posted previously that their understanding needs correction? You have not demonstrated any new knowledge or any idea not alreayd posted here for this thread...I HOPE THIS HELPS YOU!!!

[forensic]

sharplab, Thanks for your input. I found your examples far more helpful than Chapster's - Plus he sounds seriously arrogant.

[dz302]

I believe a lot has to do with your primary instruction. I was taught the slip method of crosswind approach and used the technique throughout my private training. Once I had accumilated several hundred hours I was flying with a friend who suggested I tried crabbing. After several hours of practice on some windy days I had the technique down, but never saw an advantage.

The airlines use the crabbing method because the passengers are not aware of the unusual attitude as they would be if the pilot performed a slip.

I continue to use the slip to date.

[lawndart]

Ok... this thread has been dead for a while but I'll post to see what happens.

I finished up my check ride on Friday with a slip to a landing. The DPE asked for a forward slip. I asked of he wanted flaps or no flaps. He said it was my choice. The 152 will allow for slips with 20° of flaps but I elected to skip them to demonstrate that I could land without flaps.

I turned an early final, kicked my nose INTO the wind and applied opposite aileron. I slowed myself donw nicely and had a good steep and controlled decent going. The DPE then stated that I was not doing what he asked and I flip flopped into what I call a side slip.

I kicked the nose AWAY from the wind, dropped the opposite wing and finished the final onto the runway, landing with the plane aligned with the runway, on my upwind gear and rolling out to a full stop.

LET ME MAKE THIS CLEAR... over the fence I would have converted from one to the other on my own. I would not land crabbed to the runway.

Now I am worried becuse I have had the DPE tell me I did something wrong, although I demostrated capability in either case and landed the no flapper just dandy. I asked him if he wanted me to do that over but he declined saying that I demomstrated my ability to perform slips and congratulated me on a fine check ride and welcomed me to the club.

So, can someone PLEASE clarify forward slip with relation to the wind. Or, do we just define forward slip as a cross controlled maneuvre used to control speed in a steep decent without respect to wind direction?

My instructor agreed with my actions as this is the methid that we have used thru the course of my training.

[airfreddy]

Hello:

You should always have your down wing into the wind with opposite rudder. So when you kicked the nose into the wind you were technically doing it backwards. I don't know why the examiner called it a side slip though.

Just like your crosswind corrections when you taxi you want aileron into the wind.

So that is the thing I see you did wrong. Just use a model airplane and look at it. If you point the nose into the wind that wing will have a higher angle of attack so that wing is more likely to stall if the wind decides to stop, or if you get a good gust you will have a tendancy to roll the plane upside down. that is why you always want to hold that upwind wing down.

I always teach my students:

The forward slip is used to loose altitude. so if your wind is coming from the left, your left wing should be down

Forward Slip:
1: Aileron into the wind
2: full Opposite rudder
3: Double Descent attitude

Side slip: Is just enough rudder to keep the nose straight down the runnway, airleron into the wind to keep you lined up one the runway.

So whenever you slip you put the aileron into the wind opposite rudder. Forward Slip or Side Slip

Let me know if you need any more help

Airfreddy

[lawndart]

Thanks Freddy....

I had it in my head that the forward slip was nose into the wind and side (as in landing cross wind) was nose away... Silly me. Somethings just get programmed in and are hard to dislodge. Lucky for me I recovered and demonstrated what the DPE really wanted without any problems. The field I fly out and in to is forever cross wind conditions and I have gotten quite used to side slips and IMHO am fairly proficcient (I don't screech a cross wind landing very often) to land in them.

I'll know next time I want to get fancy with an equipment failure drill (flaps, in this case) that I want to forward slip in the same direction I will side slip in the landing

The issue has never been a misunderstanding of what slips are and what they are used for... I've been lectured on this and it really missed the point of my question... not to mention raised my hackles quite a bit. If someone would have simply said (in other conversations) from the start that a forward slip is without regard to wind, that would have helped.

Perhaps I misunderstood something from my primary training. It's a moot point, that phase is over. Now I just need to go get some hours built up so I can get an instrument rating going.

[airfreddy]

You just have to remember if you are practicing forward slips at high altitude for hand eye coordination, then don't worry about the wind. In that case at 3000 feet above the ground you are practicing a maneuver.

When putting it into a real life situation, it becomes "flying the airplane"

If you are real high you would slip it. but make sure you put that aileron into the wind and keep the nose of the airplane double your nose down attitude.

You may want to practice this quite a bit, it will help you break the habit of driving a car. That habit takes hundreds of hours to break. when you get the plane on the gound, the worst thing you can do is start driving a car. But that is natural for your brain so it takes a while to over come.

Practicing slips will help

airfreddy

[Bill Hardy]

Hi all, I am a student pilot in South Africa. At my aerodrome along the coast we have virtually constant cross wind conditions as well...trouble is I was initially taught the "crab" approach - which I found more "natural"... However I usually managed to land either slightly off centre or with some degree of side load! Regarding the slip approach; many authorities warn about the danger of a crossed control approach at low speed wrt. a resulting stall or spin. I am determined, however to learn the slip approach for the following reason: Yesterday I landed in the crab position; didn't input enough rudder to straighten up and found myself pointing about 15 degrees left of centreline on rollout; input right rudder and inadvertently applied rt brake as well. Departed the runway through the general parking area; missed the windsock and several aircraft by centimeters; finished my rollout on the grass to right of runway! ( a "04R approach"). Please tell me this also happens to others! Be warned!

Amazingly, no damage to anything other than my ego...