How do you properly crab an airplane?

[drumcat9800]

Hello, I've got a question for the experts. This has been driving me nuts now for a couple of weeks. I'm a student pilot with about 27 hrs. I've searched and read a bunch of stuff to find the answer but have came up pretty much short for an answer. On crabbing the airplane, what is the proper way to do it? Say your lined up on final and have a crosswind... I've read that you turn coordinated into the wind a small amount, 5 or 10 degrees maybe, and then level the wings, return the rudder to neutral and check for any drift. Then repeat, if necessary to adjust for wind. Is this right? In my case, I've been keeping the wings more or less level, not really turning into the wind with coordination. I've been using just the rudder to point the nose to keep it aligned or aimed for the runway centerline. Riding the rudder, so to speak. I realize this makes for an uncoordinated approach. I know you generally want to keep things coordinated. Is this the wrong way? I guess the quicker question is-Is a crab a coordinated or uncoordinated thing? On a side note, I understand the difference between the sideslip and crab methods for landing in crosswinds, so I'm not asking about that. Just wondering how to properly crab... hope this makes sense. Thanks in advance.

[USMCmech]

You're overthinking things a bit.

Crabbing a plane refers to your ground track, if your ground track dosen't line up, then turn the airplane more to make it behave. Don't be looking at the instruments very much at this stage in your training. Turn the plane enough to get back to centerline then turn back enough to stay there.

Useing rudder alone is a poor way to turn the plane. If you had any passengers in the back they would be sliding back and forth as you wag the tail. Since in most trainers you sit right on top of the CG you don't feel this much, but it's still there.

[moxiepilot]

I think the question you're getting at is the proper procedure for aligning the airplane on final when correcting for wind drift, right?

If this is the focus of your question then I suggest getting a copy of the 1999 Airplane Flying Handbook from your instructor so that you can look at the diagram on page 7-8 showing the difference between a sideslip and a forward slip. (I'll get to the reason for using this version over the 2004 version in a minute.)

To get back to your question, though, you have been describing more of a side slip on alignment to final, where you are utilizing your rudder to maintain alignment (and you probably do have one wing lowered). There is nothing wrong with this approach to landing. There also is nothing wrong with a forward slip to landing.

The proper method (which is what your question is asking) for the side slip is to lower the wing into the wind. It should be lowered so that you maintain a groundtrack along the extended centerline of the runway. In effect you are crabbing into the wind at this point. The second part to the side slip is the rudder...

In this case you are to utilize your rudder to maintain the longitudinal axis parallel to the extended centerline as well. This will point your nose on the heading of the extended centerline and will put you in a cross controlled condition.

You are cross controlled because your wing is lowered in one direction and you are using opposite rudder to keep your nose from following in that direction (so to speak).

Now the reason that I refer you to the 1999 version is because there is a pretty clear diagram of the differences between the two types of slips. In comparason, the current version (2004) uses the same picture for both types of slips. The only difference is that they rotated the picture 45 degrees, which is technically incorrect. If the black arrow in the sideslip picture (which shows the direction of movement) was pointed in the same direction of the nose, then the picture would be accurate.

Good luck

[jrh]

I think the previous posts explained it all pretty well.

The only thing I have to add is...isn't this something your instructor should cover with you in person? I don't want to make you feel unwelcome...by all means, if you have a question, ask it here! It just seems like this is a fairly basic concept that your instructor should be covering with you.

Don't be afraid to ask your instructor to clarify ideas. That's what they're there for and what they get paid for.

Sometimes, if you appear to be getting things ok, the instructor assumes all is well, so they stop teaching that particular aspect of flying. If you're fuzzy about something, make sure to speak up.

[drumcat9800]

Thanks for the responses. I will be asking my instructor about it next lesson. I've discussed it before, but at that stage, I think everything was pretty new to me and the details of crabbing weren't as clear as they should be. Actually my question could apply anytime a crab is used, not just necessarily when on final with a crosswind. Say when flying the pattern, or when just trying to keep a certain groundtrack..... In response to moxiepilot, luckily I have the '99 version of the AFH, so I see the diagram you were talking about. Its not so much that part I was asking though.. more of HOW to do the crab right, in other words, do I just use rudder or do I keep things coordinated using aileron and rudder.... but I think USMCmech summed it up pretty well when he said that using rudder alone is a poor way to turn the plane and the back seat folks would be sliding all over the place... Thanks so much for the help.

[MidlifeFlyer]

Originally Posted by drumcat9800

Actually my question could apply anytime a crab is used, not just necessarily when on final with a crosswind. Say when flying the pattern, or when just trying to keep a certain groundtrack.....

I know it's been covered during the prior posts, but let's limit it to crab and leave sideslips out of it altogether.

Simply, crabbing is a =coordinated= maneuver in which you fly straight into the wind enough to compensate for drift and keep your track across the ground where you want it to be.

It's usually easier to visualize in the boat situation. Let's say you are driving a motorboat up a river. You want to keep the boat exactly in the middle of the river, but there is a current running from left to right. So you turn the boat enough into the river that you remain in the middle. The bow is pointing a bit to one side, but the boat stays in the middle of the river as it moves alone.

Change the river into the air and the boat into an airplane.

When you're doing ground reference maneuvers and flying in the pattern (leave final out of it), the amount you crab is guesswork. Let's say you are tracking a road - you turn into the wind and level the wings enough that you stay over the road, even though the nose of the airplane may not be pointed into it.

As your training moves a long, you will get into cross country planning where you will calculate the headings that will compensate for drift based on predicted wind conditions.

[Grabo172]

First of all... welcome to JC Drumcat!

Second.

A crab is a coordinated maneuver, and its nothing more than the heading of the airplane being different than the ground track.

For instance, let's say you are on downwind for RW 36. Your ground track should be a heading of 180 to fly parallel to the RW. With no wind, you fly a heading 180 on your Heading Indicator and you'll be following a good downwind.

But, if there is a wind, let's say from the right, you turn the airplane to a heading to the right of your desired ground track, let's say 170, to hold the ground track of 180. At this point you have 10 degrees of crab.

To sum up, a crab is just a heading change, just like if your instructor told you to fly a heading of 170 when you were at 180, to make your ground track what you need it to be.

Hope this answers your question.

[SteveC]

Originally Posted by Grabo172

But, if there is a wind, let's say from the right, you turn the airplane to a heading to the right of your desired ground track, let's say 170, to hold the ground track of 180. At this point you have 10 degrees of crab.

[picky detail mode]
That's a big right turn from 180 to 170!!!
[/p.d.m.]

[Grabo172]

Originally Posted by SteveC

[picky detail mode]
That's a big right turn from 180 to 170!!!
[/p.d.m.]

Brain not working too early in the morning... I mean 190. (the sad thing is I had 190 originally, then changed it... Need coffee!)

[drumcat9800]

Thanks for all the help ! I appreciate it. I will be trying to do this properly in the future, instead of just riding the rudder to do the crab.