Slip and Crab
 

Well, I am not sure of the difference between these two maneuvers. I understand that slip is achieved by using opposite rudder and aileron movements and that it is generally useful while landing crosswinds and where you want to lose height quickly. And then, what is crabing? How is it achieved and how is it different from a slip?

Cheers !

RE: Slip and Crab
 

Crabbing is a natural function and really isn't a manuver performed by the airplane, such as stunts. Crabbing describes an offset to the heading course to compensate for crosswind. The crabbing is really only noticed from the ground, or by observing the course flown, as opposed to the course made good.

RE: Slip and Crab
 

When crabbing is done all of the airplane controls will typically be in a neutral (centered) position. If you wanted to fly a ground path that went exactly North but had a wind that was out of the East (from the right) you would need to turn the nose of the plane a few degrees right (into the wind) to maintain the desired ground track. The amount of deviation depends upon the speed of the plane and of the wind and the relative angles.

In full scale, and in severe conditions, this could mean that to see where you are actually going you would have to look out the side windows. That would be a LOT of wind of course and a slow plane.

In full scale "crab angle" is also the difference between "course" and "heading".

RE: Slip and Crab
 

Here is some great video of real airplanes crabbing ...

http://www.metacafe.com/watch/39256/crosswinds/

Neil

RE: Slip and Crab
 

The descriptions of the crab are correct. A slip is accomplished by using opposite aileron and rudder (right aileron, left rudder or vice versa) for wind correction and to hold the aircraft on centerline when landing in a crosswind. For example, if you were landing with a right crosswind, you would apply right aileron, and counter act that with left rudder to stop the turning tendency and hold the aircraft on the centerline of the runway until touchdown. A slip can also be used to lose alot of altitude quickly without increasing airspeed in full scale aircraft.

RE: Slip and Crab
 

Slips must be used with care however. In some models of planes it is possible to disrupt the airflow over the tail and lose control. NOT a good thing at low altitude.

RE: Slip and Crab
 

Here are several interesting sites to read:

http://www.av8n.com/how/htm/snaps.html

http://www.risingup.com/forums/archi...php/t-383.html

http://en.wikipedia.org/wiki/Slip_(aerodynamic)

RE: Slip and Crab
 

That's odd, because when I land in a cross wind, my plane's nose automatically wants to go into the wind--they want to "weathervein." So, for example, let's say the cross wind is coming from my back. On the landing approach, my planes all tend to want to nose toward me (into the wind). I usually let them fly this way until they appear to be heading toward me, then I correct with rudder in the opposite direction. Just a blip of rudder to straighten the plane back into a parallel course with the runway. After a little time, the plane will nose back into the wind again, and a blip of rudder is needed once again. This goes on until just before touchdown, when I give the final blip of rudder that straightens the plane out for touchdown--keeping side-forces on the gear to a minimum. This is what I have always referred to as "crabbing." Maybe I was confused....

RE: Slip and Crab
 

I hate landings like that, although I realize they're not this extreme in every day life. Here's an example of such extreme flying, in every day life: http://www.metacafe.com/watch/30410/...treme_landing/
I sure am glad I didn't go to Hong Kong before they opened the new airport.

RE: Slip and Crab
 

I suppose we could get into the age old discussion on whether a plane feels cross winds and waste a lot of pages of words on the subject, What do you think?

2slow2matter, what you discribe sounds like crabbing to me, where did you get confused?

Rajeev seemed to have slips understood, so I only descussed crabbing. By the way, there are two types of slips: Side and Forward. Now, children, whom can explain each?

RE: Slip and Crab
 

2slow
Your plane shouldn't weathervane. It is merely flying in an airmass and doesn't "know" what direction the wind is coming from. It should tend to remain flying wings level in whatever direction you tell it to if trimmed properly, but you know that.
Yes, it is a typical technique to fly to the flare point in a crab and then kick rudder as you initiate the the landing flare. (Unless a Navy pilot, in which case you just slam into the deck/runway).:D Sorry Navy. Don't forget a LITTLE opposite aileron to keep the wing from dropping when you do this. It will tend to weathervane once on the ground.

RE: Slip and Crab
 

The difference between the two is that a Crab is done to overcome a crosswind (as was already mentioned)

A slip is done regardless of wind conditions, and is used to bleed off excessive speed when landing (Or otherwise rapidly losing altitude).

So for example:

If you are landing in a crosswind, you may need to Crab into the wind to stay lined up with the runway - or - If you are flying from point "A" to point "B" in a crosswind, you'll need to Crab into the wind to stay on course.

Whereas, if you start your final approach too high, you may want to side-slip the plane to keep from gaining too much speed as you decend.

RE: Slip and Crab
 

Sometimes they are done together as in the case of the old lady in the TV commercial who say's "I've fallen and can't get up!".

However....It's good to see a discussion in the beginners forum that centers around the use of rudder. I know several turbine pilots that don't keep a hand on the left stick while flying, just pathetic. Flat turns, slips, flat figure eights upright and inverted, will all make you a much better pilot.

RE: Slip and Crab
 

There are times when you need to do them simutaneously too.

Basinbum - beat me by seconds. :D

RE: Slip and Crab
 

Side: Airplane stays aligned to the runway, plane is banked a bit toward the wind.
Forward: Nose is pointed (crabbed) a bit into the wind.

RE: Slip and Crab
 

In Imac competition the orientation of a plane flying a straight line is not judged, only the direction of travel. In other words it is more important (and harder) to fly a straight wind corrected heading than it is to just let the plane look like it is flying straight while being taken off course by the wind. This applies to up and down lines as well.

RE: Slip and Crab
 

Good Job Chuck! Your reward is the knowledge that you are the winner.

Both use cross control of Ailerons and Rudder. The idea behind the "Sideslip" was to attempt to get the airplane to stay on the centerline of the runway for landing in cross winds. The idea is to get the plane slipping the same amount the cross wind is pushing the plane off the centerline. You'd turn base and crab until it you felt it was time to see how much sideslip was needed to maintain the CL of the runway. Cross wind landings done correctly took skill and was something only practice ever made me comfortable with. Forward slips were in use more with planes before flaps became common. They are still good to know and are used to loose altitude without gaining a whole bunch of speed, or to dump speed.

I think they are more difficult to use in R/C because it's more difficult to determine how much or how little is needed as we're not in the cockpit to see whats going on. Foward slips are a good way to dump altitude when your final approach ends up to high. Most useful when dead stick!!

RE: Slip and Crab
 

In a crab, you are correcting the HEADING to maintain the TRACK down the runway. That is -- to keep the airplane tracking down the runway centerline you have adjusted the direction that the nose is pointing, to maintain that track. The plane is not weathervaning, you are pointing it in that direction, whether you realize it or not. If your HEADING is straight down the runway centerline in a cross wind, the TRACK will fall off downwind, even though the plane is pointed where you think you want it to go.

RE: Slip and Crab
 

How many knew that B-52's have crosswind landing gear? All of the wheels actually turn to align with the runway centerline during landing so the plane does not need to de-crab for touchdown. Wing-tip clearances did not allow for normal crosswind landing techniques. The plane actually lands flying sideways. Naturally there is a limit to this feature.

http://www.geversaircraft.com/ac/landinggear.htm

RE: Slip and Crab
 

I knew that!!

RE: Slip and Crab
 

I flew models for about 14 years before I was able to land in a slip. Actually, it was flying lessons that helped me get the technique down. I highly recommend taking a few lessons, particularly in a tail dragger.

Many of the sims, like G2 will allow you to program a cross wind and practice slipping.

The all time greatest plane to learn slips has got to be a Cub ! You probably can't have any more fun than landing a Cub in a mild crosswind.:D

I consider landing in a slip an advanced manuever. Its easy to get confussed and there is little room for error. I don't recommend it for beginners.

RE: Slip and Crab
 

I've flown a pretty pair variety of full scale tail draggers and they can either teach you how to use the rudder or kill you (or the plane)

RE: Slip and Crab
 

I absolutely agree. In addition to the coordination problems of juggling the rudder & ailerons, the crossed controls can cause either pitch-up, which can stall you, or pitch-down, which can dig a hole. It is not a novice move & it should be well-practiced (with lots of altitude) before actually trying it on a landing..

RE: Slip and Crab
 

Actually it just shows that I can read and understand. ;)

RE: Slip and Crab
 

Crabbing is what my back trailer does when coming off of Donner Pass with a set of doubles, barefoot in the snow & ice. Slippng is what the front trailer is doing while the crabbing back trailer is trying to push it off the mountain, & finally puckering is what my behind is doing while trying to swallow the driver seat during the whole harry process.

The moral to the story boys & girls is don't be lazy, just pull over & sling the chains![8D]