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Skidding


Russ
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I'm reticent posting this, as some here leap at a chance to " flame " folks.......but to hell, here goes.

 

Skidding, slipping, was never taught to me, but I know of its advantages...uses....so.....

 

My aircraft has a ? Min airspeed to stall, so if I'm sideways skidding ......what next

 

Pitot tube is not aligned to incoming air, but I'm tracking straight.

 

Can I " over skid "

 

Observations to expect, react to, how,

 

Skidding in on a reasonable Xwind ?

 

In a nut shell.....info

 

And......I intend getting quality training before I utilise the technique, just now chasing background info

 

 

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Sensible question; I'm not familiar with the RAA training syllabus, but if it's the same as the old restricted PPL syllabus, you should, I suspect, have been taught how to use this. Essentially, it consists of using the ailerons and the rudder against one another - so-called "cross controls" - so the aircraft is tracking along the projected runway centreline, but with one wing down and the nose pointing off to the opposite side. This is sometimes called a "forward slip" (if people want to be pedantic). Used this way, it's a means of increasing the drag - by presenting the fuselage side area somewhat - which does much what dive brakes do for a glider.

 

In a cross-wind, you use it differently; line the fuselage up with the runway centreline and keep it there with rudder, and lower the windward wing tip sufficiently to counter the lateral drift due to the crosswind component; you can hold this all the way to a touchdown on the upwind undercarriage leg - in a high-wing aircraft. Some caution is needed in a low-wing aircraft, or you may scrape a wingtip.

 

That's the plus side. The negative side of the equation is that if you stall the aircraft with crossed controls, it will do its best to enter a spin. So you need to watch the speed like a hawk whilst doing this. Most pitot heads start to under-read at yaw angles exceeding about 10 or 12 degrees - so if you maintain the same indicated airspeed, the real airspeed will be higher than what you see - which means not much risk of stalling, but you may exceed the flap speed without being aware of it. I used to use slipping a lot when flying a Super Cub for glider towing - but after a while, the flap hinge brackets started to show cracks; the pitot error was the reason for that. So be careful about slipping with the flaps extended, unless the flap extension speed is at least (say) 15 knots higher than the approach speed.

 

Also, if you hold the slip all the way to touch-down, it's important to arrive very, very gently - because a typical spring-leg undercarriage (or the pivoted undercarriage legs on Cubs or Austers etc) become dead rigid if the line of the resultant force at the wheel happens to pass through the point of attachment of the leg to the lower longeron.

 

So there are some points to watch to use this technique safely; and there are some aircraft in which slipping is prohibited with the flaps extended - the DHC-1 for one. So read the fine print in the Flight manual.

 

 

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The slip, and the skid are two very very different animals. Its almost crazy to mention them together.

 

The airspeed indicator will read erroneously in BOTH. Dont for a second think it will always UNDER read. Ive flown several acft where it actually OVER reads.

 

The slip ( Top rudder) is a very safe manoeuvre. If entered and exited gently with smooth control inputs its quite a benign manourvre.

 

It is ANTI SPIN. Which means, although being in a crossed control state, the aeroplane is LESS likely to enter a spin should the angle of attack increase too much (ie, you are too heavy with the back stick)

 

The SKID, however, is PRO spin. Bottom rudder (in a bank) will cause the nose to yaw in the direction of the turn which is very PRO spin, and spiral dive.

 

So the moral of the story is Top rudder GOOD.. Bottom rudder BAD!!

 

 

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I'd say slipping is an important skill to have mastered if you do ever have to deal with an engine failure. It's hard enough to hit the perfect spot in practice without slipping, let alone dealing with all the added elements in a real one. Best to aim high and use the slip to control your height I reckon. Good enough for that air Canada pilot who ran out of fuel in Gymlie, so good enough for me.

 

 

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The slip, and the skid are two very very different animals. Its almost crazy to mention them together.The airspeed indicator will read erroneously in BOTH. Dont for a second think it will always UNDER read. Ive flown several acft where it actually OVER reads.

The slip ( Top rudder) is a very safe manoeuvre. If entered and exited gently with smooth control inputs its quite a benign manourvre.

 

It is ANTI SPIN. Which means, although being in a crossed control state, the aeroplane is LESS likely to enter a spin should the angle of attack increase too much (ie, you are too heavy with the back stick)

 

The SKID, however, is PRO spin. Bottom rudder (in a bank) will cause the nose to yaw in the direction of the turn which is very PRO spin, and spiral dive.

 

So the moral of the story is Top rudder GOOD.. Bottom rudder BAD!!

Merv

 

Can you explain what you mean by "top" and "bottom" rudder?

 

Cheers

 

Puddles

 

 

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:roflmao:Perhaps referring to types like the Halifax with twin fins so when banked one rudder was on top and the other on the bottom? It was also the classic example of rudder lock per that other thread.

 

 

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You'll find in aircraft like mine that have no drag producing bits side slipping is very much the only trick in the bag, I regularly practice seeing how close I can get to the end of the runway at around 6-700 agl and still land it fairly short.

 

I once tried a sideslip in a Tigermoth to lose a bit of height ,it worked spectacularly , so much I had to use gobs of power to just make the strip,,,,slipping a very draggy aircraft will result in an enormous rate of descent .

 

I wasn't taught to much on slipping ,so pretty much went high and played around with it, that and getting some spin training would be my recommendation all with an instructor ,

 

Matty

 

 

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Regarding this topic - and its correlates - I think it's well worth another look at the long thread from earlier this year

 

started by pmccarthy: "Steering on final with rudder."

 

 

http://www.recreationalflying.com/threads/steering-on-final-with-rudder.112345/

 

Along with the detailed discussion - including about the forward slip - there's this useful video posted by Ultralights:

 

 

 

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To be issued a certificate IAW the ops manual,

 

Section 3.04. 6.4 "Sideslip aeroplane.

 

* Slip is induced to achieve increased rate of decent while maintaining track and airspeed without over stressing flap limitation

 

* Turn through minimum track change of 90Deg's at a constant airspeed using a sideslip.

 

You not only need to be able to sideslip, but also turn the aeroplane through 90 deg's while in a sideslip to be issued a certificate.

 

 

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It's the side slipping I'm keen to master......in me jab

I've always been a bit . . .er,. . ."Uncomfortable" with the top and bottom rudder description, and I appreciate Merv's description, and if it works for most students then fine,. . . but I've seen it misunderstood big style here with our students, Especially when someone with WW2 experience explained it recently at a club chat night. . .the speaker was an ex Lancaster pilot, who got through the war without getting blown to bits or shot down, but he seemed to have seriously missed something in training regarding the mechanics of turning an aeroplane.

 

His explanation of "Top rudder" was that "How else would you keep the nose up in a steep turn. . .? ". . . . oops, W R O N G. . . . . .THE RUDDER IS THERE TO BALANCE A TURN . . . not replace the bloody elevator.

 

If you used rudder the way he described it, all you would do would be to cause th aircraft to sideslip, and the result would be precisely opposite to his intention of holding the nose UP in the turn.

 

Still,. . . .I found that Slip ans Skid, are often mixed up, and this is where these discussions are created. The Americans ( Gawd bless 'em. . .) use the term "Forward Slip" for what most of us term a SIDESLIP. Daffyd confused it a bit a little earlier, with the addition of that dreadful term "CROSSWIND" . . . . sideslips are great in a crosswind, and equally useful, if, like me ( now and again. . .! ) you can't be bothered carrying out an accurate circuit, and find yourself a bit too far above where you ought to be when you turn base or final. . . . whether because of the wind on the ground, ( I call this a GROUNDWIND" ) which could well NOT be straight along the runway of your ( or ATCs choice) . . . aircraft DO NOT understand crosswinds, . . . .they fly STRAIGHT through a thickish fluid generally called air.

 

Now when that air is itself moving in a direction which is not generally perfectly appropriate for your landing purposes, then you will have to ask the aeroplane to "Skew- Wiff" itself a bit by doing some horrible things with the controls, as has already been discussed by other posters. As long as you remember that only RUNWAYS have crosswinds, and not flying machines, then the newer pilot or student may more easily grasp the techniques required to coax the beast onto the ground in a suitable manner, speed and direction which will placate the instructor, the aircraft owner and of course the airfield owner as well.

 

The "Horrible things" you need to do to the controls of your flying machine will vary from type to type, and situation to situation, but most of this will be addressed in the POH, and of course in your training as a pilot.

 

PS, I don't remember "SKIDDING" being one of the landing techniques that I was ever shown. . . . only how to get out of one, after landing at very high speeds on an icy runway in a very heavy aircraft,. . . . . .where the RUNWAY had one of those. . . .CROSSWINDS. . . .

 

Love you all,. . . .no offence intended ( as always )

 

Phil

 

 

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His explanation of "Top rudder" was that "How else would you keep the nose up in a steep turn. . .? ". . . . oops, W R O N G. . . . . .THE RUDDER IS THERE TO BALANCE A TURN . . . not replace the bloody elevator.

Thanx Phil. Yes, if this was a turning thread, I would agree with you (and the lanc pilot). However a slip is an unbalanced turn by definition, and the use of the term top rudder has little or nothing to do with standard turning patter etc.

The Term Top rudder gets rid of 3 horrible words : Left/ Right/ Opposite.

 

I would estimate 40% of the population have to process the information LEFT or RIGHT, its not cognitive. On the same token, Opposite rudder is not always helpfull either. Using the term TOP rudder gets rid of ambiguity once its taught. There are situations where a student applying the wrong rudder input quickly and strongly could be disastrous, so having a VISUAL cue to use rather then ones ability to distinguish left from right (when a wings dropping or suddenly dropped for instance) IHMO works much better then asking for left or right or opposite rudder.

 

 

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The savannah is just a wonderful aircraft to do slips in. This is oldish video I posted just after I got my aircraft flying. Note the rate of decent and you can see the nose swing out and you can steer the plane easily. The top and bottom rudder terms I understand of course but it can be confusing. I am not sure how to explain it best just I fly by the ball and keep it in the middle unless you want it out to the side. Easily kept in the middle so when you want it out to the side it really only should be out to the slip side....not sure why you would want it out of the centre in the skid side...in a RAA aircraft thats for sure.

 

 

 

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We need to standardise the terminology used or it must be self explanatory. We must reduce confusion .

 

Rudder to YAW to the higher wing is what the LANC. pilot was advocating and is a BAD technique. Planes like a LANCASTER will enter a spiral easily. All you have to do is put a small amount of bottom rudder in and it will go into a spiral, so bottom rudder we don't want. If I'm teaching spirals that is how I place the plane into one.

 

( NOTE RAAus planes are not stressed for teaching spirals and unless the manual has changed, it is not done.)

 

So if you are doing a nicely coordinated medium to steep turn and a small rudder input is made in the not wanted direction, the nose will drop and the speed goes up and the height goes down. You are starting to pull "G" and recovery is NOT by applying top rudder. You are nowhere near stalled so the ailerons are used to ROLL THE WINGS LEVEL and you pull out of the dive gently, Power coming OFF if you are steep enough in the dive for it to be not wanted.

 

You would be surprised how quickly a spiral develops.. Stalling Spinning and Spirals are things ALL pilots should understand, and if you do, you won't fear them......... IF you don't , you just are not safe. Nev

 

 

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