Slips

[MayorQuimby]

Apologies if this is the wrong forum.

I'm an SPL who's a little confused about slips. Slips are something I'd like to feel I could do on final if I'm a bit high, so I recently got my instructor to teach me.

However, since then, I've noticed that there seem to be completely varying opinions out there on aspects of the manoeuvre.

Specifically, I'd be grateful for opinions on the following:

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Whether to initiate the slip with rudder or aileron (or both simultaneously)
Whether to use an increased IAS or just the normal approach speed (or even slower!)
What dangers to be aware of when slipping (am I more likely to spin if I inadvertently stall?)
If slips should be conducted with flap (although this is probably specific to the type)
If slips should be conducted on final at all!
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Thanks.

[low n' slow]

I'm not an expert at slips but I find them very useful when doing flapless landings and such excercises.

What I take into consideration prior to initiating a slip is
- wind, where from and how strong? If it's from the left for sake of argument, I will kick right rudder and bank into the wind. This will result in a wing down method of crosswind approach, although a bit exaggerated.

- turbulence and gusts? Just as a normal approach, increase speed if it seems gusty.

- how will the stabilizer be affected by slipping in different configurations? Flying the C172 for example with full flaps extended in a slip might result in a stabilizer stall.

My belief is that a slip should be performed in relative high speed. Just think of it, why do you want to slip? To lose altitude quickly and without transforming the potential energy into kinetic energy, excessive speed. And if you enter a slip in high speed, say 100 kt for the cessna, there will be a considerable loss of energy in the form of turbulent boundry layers and turbulent wake.

Why should a slip not be performed on final? I really don't know, some might say that unclean flying in the circuit should be avoided due to the closer marginal to a possible spin. But if you keep your speed up I cant see why you should worry about that.

Another reason for not slipping on final might be that as you exit the slip, the airspeed builds rapidly and this might result in a long flare and long overall landing distance. It's happened to me once or twice .

My rule on landings is that everything should be done and all checks completed prior to reaching 200 feet GND. That's to say, no short final checklists, no more flap setting and no more slipping. If you get rid of your excessive height some time before this, you should not have a problem with excess speed on short final.

If you've got serious height problems (too high...), go around OR try wagging your tail: Slip max to the right, and just as you've reached the max point, slip left and so forth. This swing will really kill height as the momentum will cause slip to reach higher maximum points than if you just had used the controll sfc's to maintain a steady slip to one side.

I know I write alot some times but please don't take it all too seriously, I'm just a CPL student and a long way from being an expert in the area!

good luck and best regards/lns

[MayorQuimby]

Thanks low n' slow. What you say makes sense. My impression is that it's a good idea to keep the speed up, just to be safe.

Just realised I probably should have posted this in 'Private Flying'.

[HugMonster]

If you have to sideslip, for heavens' sake keep the speed up, put both rudder and aileron in gently and simultaneously.

Biggest and most immediate danger is of entering an inadvertent spin. It won't take much - just a little unexpected turbulence or gust of wind. It will be your last.

Next danger is of overstressing the airframe. They're not really designed for it. Make a practice of it and you will, sooner or later, do damage.

By far the wisest course of action is to go around and sort out a rather better approach, and try to work out why you're getting too high.

[IRRenewal]

MayorQuimby,

You do not mention what type of aircraft you fly. On some taildraggers you would slip right down to about 10 feet, otherwise you cannot see where you are going.

On the airspeed issue, remember that when you sideslip the ASI will underrread, as the pitot head is not pointing in the direction of travel. If you sideslip a Cessna with 100 Kts on the clock you might be doing 110-120 knots TAS. I suggest you slip on final the same speed as you would normally fly on final. The error in the ASI will give you the excess speed you require to keep it safe.

Initiate a slip by applying both aileron and rudder at the same time, unless you want to lose height and change direction. Apart from wind you could put visibility in the equation. Flying a taildragger with limited forward visibility you might want to slip in such a way that you can see a taxi way, footpath or road, or whatever might affect your landing.

Sideslipping is a wonderfull manouvre. Use it to make the field on a PFL, get rid of some height on final, etc. You can increase your rate of decent and get it back to normal almost instantly. Just go up to a few thousand feet and give it a try.

Cheers

[MayorQuimby]

I'm flying Aerosptiale Rallyes (sort of STOL trainer). Normal approach speed is 60 knots. My instructor got me to keep the speed up towards 80 with no flap when he was showing me a slip on final.

It's not something I'm likely to need much, but I thought it would be good, say in an engine out scenario, if it was 'in my armoury'.
Definitely don't like the idea of putting myself in danger of a spin!

[Captain Stable]

Never a bad idea to give yourself as many flying skills as possible. However, be very wary of "learning" techniques here. Go and find yourself an instructor who can teach you what you want to learn and get you out of trouble during the learning process if you screw up.

Too many private pilots "learn" only in the clubhouse. After getting whatever rating they want (PPL/IMC in most cases) they never fly again with an instructor. They get into bad habits and there is nobody to get them out of them again.

Not a bad idea to put yourself through a GFT with an examiner every year or two.

And mentally rehearse all your emergency drills such as engine fire in the air, engine failure etc. On the climbout, think where you're going to point it if the engine fails three seconds from now. Make sure you can get out a PAN or a MAYDAY call without having to think about all the information. If you can't remember it when you're calm and unstressed, think how much more difficult it would be under pressure.

But most of all, enjoy it all - after all, that's why you got the PPL in the first place! :)

[spudskier]

I myself fly Cessna 152s and 172s. While I am NOT an expert, I am a student pilot working on all my initial ratings (Not at once) including inst, comm, and eventually multi.

For slips, depending on the wind of course, I was taught to do them this way. Full, if not almost full rudder, and a split second later counter with opposite aileron. (Just enough to counter the rudder action) then drop the nose. Not a lot, just enough to keep up your speed while descending. All of these movements should be smooth, yet authoratative. NOT immediate or harsh. Don't stomp on the rudder or jerk the yoke.

On the way out, slowly release rudder and follow with appropriate movements of the yoke (level wings and nose up a tad)

This came in very handy last tuesday as my flaps became stuck at a little less than 10 degrees on the base leg. Had to do a go-around then land with maybe 7 degrees of flaps or so. Came in a little too high, (instructor always says a little high gives you options) sliped, and touched down very smoothly.

[Volume]

You cannot give general statements to slips, they are very depending on the type of aircraft. I´ve flown nerly 50 different types of gliders, powered gliders and small aircrafts and slipped most of them (at least I tried). Some were really pieces of cake some were more like rodeo bulls.
I always start with aileron and apply rudder slightly after, the lesser the adverse yaw moment the earlyer. (On some planes the rudder airflow separates and the rudder is locked by the airodynamic forces, you kned LOTS of force on the pedal to bring it back) Airspeed should be maintained (by keeping pitch attitude constant because your airspeed indicator reverses on a lot of planes and the needle points to some very high speed at the other end of the scale), because going faster brings problems on recovery and going slower MIGHT be dangerous. On many planes a lot of aft stick is neded to maintain speed, especially with flaps extended. On some old wooden gliders you can reduce airspeed to nearly zero, the plane seems to fall vertical from the sky then but is fully controllable. (recovery needs MUCH altitude in this case, so start it early !!!) On the other hand some can enter reverse spin, a really scary thing if it happens to you first time ! I don´t reduce speed any more since I experienced it once.
Some planes are forbidden to slip, some of these are really unable to do so, on others the manufacturer just doesn´t want to spend money in the tests. Some are forbidden to slip with flaps extended, I experienced a complete (all flying) horizontal tail stall when entering the flaps slipstram resulting in a 90° nose down altitude, lots off grass to be seen in front of the cockpit and a heartbeat frequency above 300 ....

If you have enough altitude and no idea of what to do next, just try to slip ANY plane youre flying (best done with an instructor). Try at different slip angles, with different flap settings and at different speeds (just to know the margins). Try to change slip angles and control your glide path with this. Have a look on the altimeter when recovering to know your minimum recovery altitude on approach. Train to end up with your approach speed after recovery.
You might need this experiene one day if your flap actuator quits, you underestimated the tailwind in a glider, your engine doesn´t fully idle or quits completely outside the airfiled or any other unusual situation you might come to. Then it is good to be prepared, to know what your plane does and to know you can manage it. You can avoid some go-arounds at an early state to relief noise sensible neighbours.
And if you fly a plane that is nice to slip, do it regularly to keep trained.

[Low-Pass]

Just a couple of things to add:

1. As low n' slow mentioned, slipping Cessnas (the smaller ones) with flap down is highly unadvisble due to the flaps on the high-wing masking the horizontal stab.

2. Start small and built up. - Used to slip the Tigermoth on final all the time with complete confidence but never went too far. There was another operator on the field who used to bring his Tiger in SIDEWAYS!! Pretty unsafe for a novice and questionable for someone with a lot of experience.

3. With regard to airspeed, it's your IAS that is relevant with the stall, not your TAS. Your pitot tube under read but it won't be by much so don't factor too much into it.

As always, Captain Stable provides sterling advice. An instructor can show you a lot and when you do practice, start of up high to get the feel of it. Have fun :)

[Captain Stable]

I'm feeling very uncomfortable about this thread, so I will emphasise this again:-

Under no circumstances try out anything you read here. As has been pointed out, different aircraft have very different characteristics. Get an instructor to go up with you and demonstrate it. Practise under his/her guidance. When he/she reckons you've got it, even then treat them with the greatest of respect.