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Side-slip without stalling

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Side-slip without stalling

Old 21st Apr 2015, 09:56
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thing

Quote:
In other words if you are turning left use right rudder to slip, if right, use left rudder.
They wouldn't be slipping turns if you didn't...
Isn't over ruddering called skidding?
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Old 21st Apr 2015, 10:39
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My 2p is that you won't actually have much time to think about that, and look for a spot if it actually happens, and I'd argue: You already know where the survivable 'put it on the deck' spot is; you either spotted it as soon as you got airborne, or you spotted it (or had a general picture of the nearby terrain) when you landed there earlier.

If you didn't, you should have.

If it all goes abruptly quiet at 450', by the time you've got the nose down, and approximating glide speed, you're already at or below 350ft. And if you already know that the paddock to go for is a few degrees left (or right) and immediately ahead, don't dick around checking for things like "below vfe"; you're within a few knots of glide speed. Of course you can get the flaps down. It's not a jet airliner.

I'd be stuffing the nose down fast and dropping the boards as I did so, and not formalising a side-slip (unless the landing zone was offset, when a slip could well be beneficial). This is no time for finesse. You only need enough finesse to retain control of the aircraft. Unless you're dangerously slow, if you know you're going to be a bit high from the get-go (and you would) stamp on each pedal in turn and keep the wings more or less level. The resultant double-skid will increase your descent angle quite a bit for a few seconds, and a few seconds is all you have. (Try this at safe altitude. Repeat at reduced speed. Repeat etc until it stalls. You will then know the speed and feeling when you loose control as a result of full rudder deflections near the stall.) During those few seconds, turn the gas off, bleat mayday, kill the electrics (only after the flaps are down in a Cessna), and tell any pax to brace.

Land slightly too fast. Even way too fast. (You have to; you were too high.) Keep "flying" the aeroplane after touchdown, with the brakes on, to try and avoid breaking the nosewheel from the inevitable undulations. Aim for the softest looking spot at the end of the paddock. If it's a deep ditch, consider a handbrake turn prior to reaching it (also known as a ground loop, which is a bit tricky in a trike.) If it's a fence, or trees, try and put the nose between the solid areas. Once it's stopped, double check the master and fuel are actually off, and get the hell out.
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Old 21st Apr 2015, 10:41
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"Check Vfe"! Screw that. Put down as much flap as you can at whatever speed you care to (but don't get slow) and sideslip it all the way to the flare and then make it more of a 'check' and get it on the ground to allow friction to do its job. Who cares about a few pulled rivets if you walk away from a catastrophic engine failure with such limited options? Don't try and grease it on because all that lovely field of yours is getting used up as you mince along trying not to upset the champagne glasses. As for EFATO 'checks'; turn off the fuel and anything else is a bonus.

Sounds agricultural, I know, but there is a difference between the real thing and training, where flap overspeeds etc are looked upon badly
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Old 21st Apr 2015, 11:58
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Problem with flap over-speed is not just a few pulled rivets, but total failure of one flap and not the other...
In that case you will be talked about in the past tense..


I think for the high wing aircraft, Flaps Out Slips are not so effective, as the fuselage obstructs the far side flap airflow.
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Old 21st Apr 2015, 12:03
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You're not going to be overspeeding flaps down in an efato situation though, are you?
Unless you lower the nose too much - way too much, and delay putting them down.
It's pretty much not possible.
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Old 21st Apr 2015, 12:31
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b) GO full flap ASAP, and slow down to just above stall speed streight ahead, DO NOT BANK or you WILL STALL/SPIN in, and let the airplane sink. The lower speed will cover less ground while sinking fast. At 50ft a gentle forward nudge to get some speed to flare properly.)
Now that is a very good technique and was taught to me by a very experienced examiner at my CPL skills test (I think the exact words were "Short field, you call that SHORT field, let me show you a proper short field!)...

Anyway during his demo, he whacked in full flap and brought the speed back to about 50 kts in a 172SP. We had quite a high AOA but were coming down nicely. He stuck it on the end of the runway, slammed on the brakes and had stopped sub 100m (I know this as there was an intersecting runway and we stopped before the intersection)......He then made me try it.

Advantages are that you have low forward speed so will stop quickly (and have less fwd energy if you end up hitting something). You have a steep descent so with headwind you can land in a field close in. Disadvantages are that you are close to stall speed so have to be a bit careful and should only use this when on a final approach, so no turning.
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Old 22nd Apr 2015, 01:15
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On a PFL I personally like a side slip for shedding excess height. In the scenario given I would wish to land with full flap but I would be more happy doing the slip with intermediate flap to shed the height and selecting full flap before landing.

However, if I judged that I could get the job done by simply dropping full flap and not bothering with a side slip, all well and good. Equally, if I still needed a steeper approach I would be prepared to slip with full flap. To my mind, there is no single correct answer. It depends being familiar with the performance of your aircraft and responding to what you see out the window with some of that 'pilot '
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Old 22nd Apr 2015, 02:43
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I'd be very wary of making an approach at ~50kt following an engine failure. You might find - too late - that it takes a fair bit more than 50' of height to build up enough speed to make a flare viable. Particularly if the a/c is near or at MAUW.

I know a guy who got behind the drag curve in a 207 following an engine failure. The impact marks showed the wingtips hit the ground almost at the same point as the fuselage impact point. (They all died on impact.)
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Old 22nd Apr 2015, 03:26
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Just a technical terminology note:

To lose altitude as rapidly as possible, without changing direction, one uses a forward slip. Useful even with normal engine power, if one must make a no-flaps landing.

A side slip is used to counter drift from a crosswind in a normal landing.

http://avstop.com/ac/flighttrainghandbook/imagetck.jpg

They are more or less the same thing, using the same technique - crossed rudder and aileron controls. The difference is that in a sideslip, the nose remains pointed in the direction of travel (runway centerline), whereas with the forward slip, the nose is pointed off to the side of the direction of travel, presenting the side of the aircraft to the slipstream, thus adding drag to allow a steeper descent.

Or put another way, in a forward slip, the slip is in the direction of travel, while in a side slip, the slip is in the direction of the wind.

Of course, if one is trying to make a no-flaps landing or come down fast, and ALSO counter a x-wind, one can make a slip "in between" a pure forward or side slip.

I've made several forward slips to an actual landing in primary and recurrent training, in response to the instructor/check-pilot putting his hand over the flap lever and saying "You have no flaps - how are you going to land this thing?"
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Old 22nd Apr 2015, 03:26
  #30 (permalink)  
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Some aircraft, particularly gliders, have unreliable airspeed indicators when slipping

.. interesting comment .. can you cite any aircraft for which the ASI is much good in a slip situation ? PECs are pretty sensitive to such abuses ..

They are more or less the same thing

I suspect that most of us would have the view that they are exactly the same thing .. albeit used with different intent. It might be useful to revisit your definitions in any case ...
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Old 22nd Apr 2015, 04:54
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It might be useful to revisit your definitions in any case ...
John T:

I think I understand the problem here. In the US, slips are defined exactly as described by pattern_is_full. (FAA Flight Training Handbook) Sometimes people aren't aware that not all countries of the world use exactly the same terminology to describe things though. In any case you correctly point out that a slip is a slip aerodynamically speaking...

With respect to an engine failure after takeoff and still at low altitude, I agree with previous posters who suggest that getting the nose down without delay is first priority. Fail to do that and the rest is just academic. From 450' AGL, you'll be on the ground in less than 30 seconds so there's little time for niceties. Use as much flaps and slip as necessary to get to the landing spot with as little maneuvering as possible. With no power available, getting slow may leave too little energy to check the (steep) descent. I wouldn't recommend a speed any slower than book short field landing speed. At around 60 kts at 50', there won't be much energy left by the time you get the nose up to a landing attitude. And not much margin for error either. On the day, you'll just have to be up to the task. Best to practice this at a safe altitude beforehand so you'll at least have an idea what to expect...

westhawk
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Old 22nd Apr 2015, 07:02
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Some aircraft, particularly gliders, have unreliable airspeed indicators when slipping

.. interesting comment .. can you cite any aircraft for which the ASI is much good in a slip situation ? PECs are pretty sensitive to such abuses ..
Good point, John. Sloppy writing on my part. I should have said "some aircraft have MORE unreliable airspeed indicators when slipping". I have flown some gliders with "pot pitots" in the nose, where the needle goes almost to the stop during a slip.
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Old 22nd Apr 2015, 08:51
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Going back to the original post, why is the question even being asked? If you have a licence and are worrying about this, I suggest you go and find an instructor and get some practice. If training, you will be shown what to do.

As for the checklist, it is an example of "paralysis by analysis." Bin it and stick to the EFATO vital actions you have been/will be taught.
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Old 22nd Apr 2015, 09:10
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I'm with Shortstripper. Interestingly, I've also had the opportunity to explore assymetric stalling in an extra.

I would tend to slip before extending flap - it's the irreversible nature of flap extension that puts it to the bottom of the toolbox for me.

The argument for speeding up - that is - making the wing as inefficient as possible (without irreversibly changing its shape), also makes sense to me. I would advise against thinking in terms of "rate of descent", rather it's the angle. The further away from best glide speed one is, the shorter (not necessarily sooner) the distance covered until touchdown.

On slipping - I agree with Shortstripper's description of behaviour approaching the stall in a slip. Yes, there is roll, but it's the right way, and gives an opportunity for correction, as long as the ball is low, not high.

I will ask one question though - 1g stalling speed in a slip versus balanced flight for a given config etc... Which is higher?
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Old 22nd Apr 2015, 11:33
  #35 (permalink)  
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Some very helpful information here. Thanks for sharing your expertise. Forgive me if I don’t reference specific responses.

So, Why did I ask the question?
I have a couple of hundred hours (albeit over a couple of decades) and have just re-validated my IMC / IRR after an extended lapse. I am going through the self-imposed process of re-establishing my skills and confidence. This involves setting specific objectives for each sortie and writing a careful account of actual lessons learnt / areas for improvement next time. My limited gliding experience has added some useful ideas to my powered flying. For example, as I line up for departure, I mentally rehearse … ‘wind is from the left / right and if the cable breaks (engine stops) I will … ‘
Looking at my local airfield, 3 of the 4 departure directions offer good options, but the fourth is a bit restricted, hence the scenario; I will probably need to dump altitude pretty quick. Anything that works here will also be useful anywhere else.

Going back to first principles and reviewing my PPL training material, I found there was stuff on side slip and stuff on flaps, but nothing on side slip WITH flaps. Searching PPRuNe brought up the link in the original post – an interesting discussion, but no clear steer for ‘if the engine stops I will …’

SO, here is my simplified, safest course of action, condensed from the above, based on my usual mount, PA28-161 …
Nose down (attitude for initial approach speed). No flap. Max side slip, in one direction only. Nose right down to shed more energy. Aim a bit short because of the resultant higher speed. Short final Straighten up. Full flap. Steer, touch down, brakes, steer.

What do you reckon? Does this need fine tuning still? Coarse tuning?

The low speed, high descent rate option is interesting, but, in my case, perhaps more likely to end badly given other variables (gusting, workload, stress).

I will work on the following suggestion as well over the next few weeks. … “if you know you're going to be a bit high stamp on each pedal in turn and keep the wings more or less level. The resultant double-skid will increase your descent angle quite a bit for a few seconds, and a few seconds is all you have. (Try this at safe altitude. Repeat at reduced speed until it stalls. You will then know the speed and feeling when you lose control as a result of full rudder deflections near the stall.)”

Smokey L - Just saw your post - I will give that a bit of thought.

BTW Spilt fuel + hot exhaust or electrical short circuits = bang. Therefore I WILL want to shut off fuel and electrics. And in a PA 28 I would also like to unlatch the door. No check list required, it’s all in my head.

Thanks again

SD
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Old 22nd Apr 2015, 11:43
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I think an engine failure at 450' in a PA28 won't give you time to think much to be honest. It almost has to be instinctive at that height in that type of aeroplane. Nose down, pick a point and aim for it, end of! ... You'll have no time to worry about shutting down, cracking doors as all your brain capacity would (should) be channelled towards just flying.

Also, in my experience, engine failures are rarely so obvious or immediate which can also confuddle the brain! A slower loss of power leaves you wondering what's happening which is actually far more dangerous than a "bang, splutter, stop" situation.

SS
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Old 22nd Apr 2015, 12:37
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it's the irreversible nature of flap extension that puts it to the bottom of the toolbox for me.
Why would flap deployment be irreversible? Sure, you've got to adjust pitch if you remove flaps, opposite from the pitch you need to apply when deploying flaps, but other than that flaps are just a flight control. To be used, or not, as and when required.

If you deploy flaps thinking you're too high and need more drag, and then subsequently find yourself too low, why not simply remove flaps, partially or fully?

I'm also a glider pilot so quite used to the use of air brakes. In a glide approach, I tend to use flaps the same way. The only complication compared to gliders is that the pitch required to compensate for flap deployment is more, compared to airbrake deployment.

The only way you'd end up in trouble when you remove flaps, is if your actual glide speed is below the green arc. But as Vbg is normally very close to Vy, you should be well into the green arc in this situation.
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Old 22nd Apr 2015, 15:11
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One step at a time.

One never "knows" if or when an engine will fail.

Take off, accelerate to best climb, and clinb out.

Somewhere , somewhere, nobody knows "when", the engine fails.

Step ONE : You are too late.
By the time you realise what's happened, 2 seconds are already gone, and you are 5 kts below best climb speed.

THIS is your starting point when the brain comes alive. Flame out altitude minus 50 ft and minus 5 Kts of best climb speed. (best case scenario)
-------------------------------------------------------------

Step ONE : AGAIN, first reaction from the trained brain. LOWER the nose, do NOT stall. => Altitude = minus 100 ft.

Step TWO : Now that you have limited forward visibility => Where to go? => Altitude = minus 200ft.

Step THREE : The airplane is broken anyway, who cares, but "we" have to survive. => Decision time => Land it in, or controlled crash it in, depending on "what is in front of me?" => Altitude by now = minus 300 ft.

Step FOUR : How do I get there? => Prime at this altitude in MAINTAIN controlled flight and NO BANKING => If Flaps, go full flaps ASAP to increase low speed controllability and increase the marging to stall speed..

But if we started out at 450 ft? Sorry guys too late, its time to flare.

I seriously wonder if you have time to start a slip, get out of the slip, and flare. And you have to do it automatically, as you can not drift your eyes away from the airspeed indicator.

Flap handle, fuel cut-off, magneto's, battery. All switches done with eyes on the airpseed indicator.

MOST IMPORTANT is a controlled contact with the ground, at the lowest forward speed and under POSITIVE control.
If required, and within a few degrees, aim the fuselage between obstacles.

REMARK : Trees. Avoid trees with your wingtips, as cartwheeling around usually ends in disaster.

If you see a forest in front? STALL the airplane above the densest tree collection.

Long time ago, we did ALL spin training above a forest, never over open ground or water.
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Old 22nd Apr 2015, 15:31
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Vilters,

I agree with what you say (see post above). However, forget about looking at the ASI! If you are unable to fly by attitude and feel, you are unlikely to be able to walk away from this scenario whatever your cockpit emergency routine is.

Also, EFATO at 450 feet in a PA28 is a lot different to the same height in say a Piper Cub. Whilst decisions are similar, one offers more time and better prospects than the other. Point is, no two EFATO are ever going to be the same for all sorts of reasons. I guess that's kind of what you were saying though wasn't it?

SS
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Old 22nd Apr 2015, 17:24
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Every engine failure at low altitude will be different.

Different in altitude, attitude, speed, there are no standard engine failures.

I stressed on the airpeed indicator, and would continue to stress on the airspeed indicator for a simple fact ; Every airplane behaves differently.

When loosing the engine in a climb, some airplanes will pich forward, some will pich upwards. God only knows at what speed or altitude you will be in when the engine quits.

Flying "by feel" requires a well trimmed airplane, with the ventilator running.

You add the extra task to retrim the airplane to be able to fly by "feeling".

At below 500 ft, there simply is very little time, and lots of things to do.

Also do not eliminate the "panic" factor.
The sudden and unexpected loss of engine, the time it takes to realise what's just happened. NO sound any more. SOUND is very important, and it's gone. The airplane is not talking to you any more as you expect it to do. Lots of "uneasy" things,. And do not forget the passengers either. They will start to panic as well.

Retrimming to fly by feel, will require the extra seconds and altitude you simply do not have.

Speed, flaps, speed, magneto's, speed, fuel cut-off, speed, and that's about it.

Speed is your life.

Sure you'll have more time in a J-3, and less in a Cessna or an Archer.


To add:

"Flying by feel."

Every flap adjustment, you would have to retrim.
Gear => Youd' have to retrim.

An unexpected engine out, is no time to fly by feeling.

Also, the engine is out.
No pressure blowing over the tail- or flap surfaces any more.

The yoke (or stick) will give you a completely different feeling as what you are used to, even in training, in simulated engine outs.
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