Forward or side slip

[Double Back]

As a non-english speaker I tend to refer to all slips as a side slip.
I hardly use the term forward slip.
How is that for You as born English speaking pilots? You use both terms and in the right context?

[Dream Land]

Let me Google (http://lmgtfy.com/?q=side+slip+or+forward+slip%3F&l=1) that for you. :E

[westhawk]

The only difference between a forward slip and a side slip is what you are try to accomplish by slipping. In terms of aerodynamics, they are identical. A slip angle is a slip angle as far as the airplane is concerned.

The term "forward slip" is most often used to describe an intentional slip for the purpose of adding drag to steepen a descent without a resultant airspeed increase. The aircraft heading is offset from the intended ground track by the approximate slip angle. Pilots of some airplanes with limited forward visibility (such as a Pitts Special) also use this technique during final approach for improved runway visibility. You could think of this kind of slip as being "forward" along your intended ground track.

Side slips are generally intended to slip the airplane "side"ways with respect to the intended ground track for the purpose of countering a crosswind component during landing.

So to summarize, a slip is a slip and the aerodynamic effect is identical. Apparently someone at some time found it necessary to categorize them according to their intended purpose, probably for instructive reasons. You are not the only one ever to be confused by this awkward terminology.

I hope that clarifies more than further confuses your understanding! :confused:

westhawk

[Intruder]

Yes, indeed! It is not confusing at all, even for us American English speakers!

If it looks like you are flying sideways, you are in a forward slip. If it looks like you are flying forward, it is a side slip.

[LME (GOD)]

Aren't you talking about "crab angle"??

[Air Tourer]

No I don't think he is. I would think crab angle is when you are wings level
and due to a crosswind you have to have your nose into wind to track in line with the runway.

[john_tullamarine]

For whatever reason, slip seems to confuse folk.

Slip = the breeze is coming from a direction laterally somewhat off the nose. For zero slip, the wind is head on to the aircraft.

Sidesliip = slip ie terminology only

forward slip = Americanism for slip when the intention is to maintain a desired track generally with respect to a ground feature, eg runway

crab angle = angle betwixt heading and track - need have no slip and generally doesn't.

[cwatters]

Side slip - normally, but not allways, used in the context of turning - for example consequences of incorrect use of rudder in a turn.

Forward slip - As john said.. "slip when the intention is to maintain a desired track generally with respect to a ground feature"... sometimes used to burn excess height.

[westhawk]

Obviously, pilots trained in different places see these definitions in the opposite sense to each other! :{

This should not be too surprising when one considers that many countries don't even agree about which side of the road to drive on!

Perhaps the best way to resolve the issue is to avoid using the "side" or "forward" slip terminology altogether whenever possible. Slip to control drift while maintaining alignment or slip to add drag for a steeper descent. Call it whatever you wish or call it nothing at all!

This is all pretty amusing isn't it?

[chrisN]

Just to add to the (potential) confusion, this is another term used differently in UK gliding from UK power instruction. I don’t know about other countries.

In gliding we use side slip approaches to get rid of surplus height under some circumstances, in addition to airbrakes (or, for our USA cousins, spoilers). It is also used instead of crabbing sometimes, to cope with cross winds.

In either use, I have never heard it called anything but a side slip, but (some of?) the power people call it a forward slip.

We also sometimes use slipping turns, e.g. when much too high on final turn. This is an under-ruddered turn (not likely to cause a spin, which can result from an over-ruddered turn).

In side slips and slipping turns, the ASI is rendered inaccurate to the point of being useless, by the way.

Chris N.

[Capn Bloggs]

Yes, indeed! It is not confusing at all, even for us American English speakers!

If it looks like you are flying sideways, you are in a forward slip. If it looks like you are flying forward, it is a side slip.
"Forward" slip was invented by the experts of the ENGLISH language, the Yanks, to differentiate from the backward slip, which is what they are doing to the language! :}

[Intruder]

Well, if she remains slipless in Seattle, then the upskirt view is much better...

[Brian Abraham]

The first reference to "side slip" I was able to find dates back to 25th June 1910. Sorry, no forward slips, even the Yankee book of aerodynamics par excellence only talks of side slips (Aerodynamics for Naval Aviators). The good book also says about crosswind take off and landing, "Since the airplane must make a true path down the runway, a crosswind during take off or landing will require that the airplane be controlled in a side slip. The rudder must have sufficient control power to create the required sideslip for the expected crosswind".

http://www.flightglobal.com/pdfarchive/view/1910/1910%20-%200495.html (http://www.flightglobal.com/pdfarchive/view/1910/1910%20-%200495.html?search=slip)

[westhawk]

Brian, Aerodynamics for Naval Aviators is a great book and still relevant more than half a century after it's release. :ok:

I agree that AfNA was not the source for the classification of slips into "forward" and "side" varieties taught to generations of American pilots.

While I don't know the origin of this terminology, it has appeared in FAA training publications like the Airplane Flying Handbook and the Pilot's Handbook of Aeronautical Knowledge for many decades. I've also seen the terms used and the techniques for performing them described in numerous commercially produced flight training materials. Demonstration of a forward slip to landing is still a required TASK in the most current private pilot practical test standards (http://www.faa.gov/training_testing/testing/airmen/test_standards/pilot/media/faa-s-8081-14a.pdf). No mention of side slips is made in reference to crosswind landings though!

However I'm still pretty sure most slips are slips only because a sideslip angle exists!

[Brian Abraham]

Thanks westhawk, you saved me some leg work I was about to undertake for my own edification. We certainly don't speak the same language.

side slip = forward slip
accumulator = battery
supercharger = blower
reheat = afterburner
etc, etc

I wonder if there is the corollary to the forward slip, a rearward slip? :p

[italia458]

Forward slip = a slip with the intention of losing altitude. Your ground path may or may not be aligned with your nose, depending on the degree of rudder and applicable aileron you use. If your ground path is aligned with your nose, it could also be said that you're in a side slip. For a forward slip power is to be at idle.

Side slip = a slip with the intention of keeping your nose lined up with your path along the ground. This is typically used on landing to touch down straight while in a crosswind. If there is no crosswind, you won't be able to keep your longitudinal axis lined up with your ground path while in a slip. For a side slip while on approach, power is typically used.

[westhawk]

Certainly Brian. Good examples by the way. Here's more:

Landing gear = undercarriage
Engines = donks (Aussie specific?)
Airport = aerodrome
Ramp = apron (no worries mate, now we have to call it that too!)
Touch and goes = circuits and bumps (I like that one)

Anyway now that we've got this slipping business figured out, (sorted) a little thread creep is excusable I think!

[bubbers44]

westhawk defined it perfectly in #3.

[Capn Bloggs]

Certainly Brian. Good examples by the way. Here's more:
Landing gear = undercarriage
Engines = donks (Aussie specific?)
Airport = aerodrome
Ramp = apron (no worries mate, now we have to call it that too!)
Touch and goes = circuits and bumps (I like that one)

Now that we're "slipping" off thread...

Airplane=Aircraft or Aeroplane! :=

[Double Back]

Tks for the replies, gents! Learned a lot from here.
So it is more a linguistic matter.

IGh.
Nope, not a reincarnation, I never even heard of the story! (You never remember something from Yr previous life isn't it! :) )
Darn, come to speak of it, crosswind landings have always been my favourite, whether in a Cessna or B744... There is no more fun as to teach it to students. I developed a special session for it, using our canal system or a long highway for ground reference to prepare for the actual stuff.

During my period as engineering pilot (B747-2/300 acceptance flights after heavy maintenance) we needed to do a check on "spoiler lay down" which involved a slipping manoeuvre. Always loved that manoeuvre in which You needed to increase very slowly aileron input, without ever releasing it just the tiniest bit as that made the test invalid.
The resulting roll was held by increasing opposite rudder input.
Ahhh, lovely days back then, 17000' over the North Sea, F/D and ATS Off (in case it had one), take a spot on the horizon, mark I eyeball only plus altimeter.... Just a big Piper Cub then.

Looking back I also need to be more consequent in what I call the direction of the (..) slip.
The low wing indicates the direction. Or do some people call it according to the direction the rudder is put in?