I wouldn't recommend this technique as a standard procedure. One need only ask themself how many times have they been doing a practice engine out scenario where they discovered that they were no longer at their best glide speed which they had been targeting. All this because they were busy doing a cause check or busy doing a shutdown procedure or busy assessing how their positioning with their chosen landing area was working out, etc. There are plety of distractions during this procedure and speed is inevitable going to end up off target sometimes. Best to have a fair bit of margin above the stall to account for this.

Posters on this thread seem to me to be about 50/50 split between knowledgeable, helpful folk and Walts/trolls. Folk with a bit of experience can tell the difference, but I do worry about any body else reading it.
ATB

We lost several photo flying KZ 7s in the 60s for that reason.
You are low and slow, kick the rudder to get a strut out of the photo, the fin stalls and the rudder locks out. On the 7 the only way out of this was a full stall.

I have no experience, and therefore no comment about the KZ 7. Over the years, and with different flight test programs, I have found that a very few airplanes can be flown to this extreme condition. Certain Cessna 180/185's can get there, particularly as floatplanes. I've done it in a King Air B200, for which it is a know characteristic, and a certification special condition. In the case of these types, recovery can be accomplished with appropriate use of the rudder - it just was not a positively state as other types. But, the rudder did not "lock", or it would not be certified. In both cases, this was powered flight, idle power flight was more benign. The turbine DC-3 will exhibit unfavourable rudder forces with very large rudder deflections, which is alarming. The DC-3 was certified before today's more modern standards - I consider it an exception, for which competent training is pretty important. I have slipped 172's with flaps extended, and experienced the burble in pitch which is warned as an "avoid". Again, manageable within normal pilot skills, as long as you just keep flying it. I have never made any version of a 150 loose positive directional stability, and I have the most experience on them.

During testing of a modified Cessna Grand Caravan last winter, the authority required that I demonstrate a stall to the break from a 75% power climbing 30 degree bank turn in each direction, with full rudder applied in each case. (Yes, this is about a spin entry). The airplane handled it just fine, no rudder lock, benign recovery attitudes.

I find a sideslip to be a very useful tool for descent control, and have done it in many types with no difficulty nor alarm, though no, I would avoid it in a DC-3!

Can you elaborate ?

The position out the wing (the wing station) of the outboard end of the flap corresponds poorly with the outboard end of the horizontal stabilizer. In a slip, the wake off the outboard end of the flap can impinge on the H stab, and blanket part of it, and perhaps induce some elevator motion, which will create unexpected momentary pitch control forces, and some pitching. It's more surprising than a real problem, but it is a thing. It varies with models of the 172, some are worse than others, but it was the cause of the "avoid slips" placard common to most 172's. It's also a thing with C 170B's. It's worthy of understanding, and an imperfection with the design, but it did pass certification, and is manageable. C 150/152 don't suffer, as their flaps don't reach as far out the wing. 18x don't seem bothered by it (I've tried all of them!).

Why don’t you assist the people you worry about by telling them who the trolls are.



Well back in this thread, I mentioned the potential importance of using a slip(yes it is a forward slip) when appropriate..

I was well aware that there are occasional rare cases of aircraft types that one wants to avoid using this procedure(such as the C170B with ‘barn door’ flaps), a type I used to fly. That is why I stated in that post “if safe to do so in aircraft type”, which in my opinion would be most of the light single engine propeller types(and the 767-200 for those who know the story).

You may have to dig around to find out how a particular type behaves. A type club can be very useful as that is where I learned about C170B handling characteristics in a slip, which can be deadly due to stalling the horizontal stab.

Ah. Thanks. It's good to finally have an explanation for that placard and a warning of what to expect if it's ignored.

I seem to remember that a C152 would go down like a lift with full flap, IAS about 5 KT above full flap stall speed, idle power, and side-slipped as hard as possible. Total control was retained throughout. I have no idea what the rate or angle of descent was, but it seemed very steep indeed, especially with a good headwind.

I’m thinking the instructor showed you a forward slip.


https://cimg0.ibsrv.net/gimg/pprune....cbc98325ba.png

From the handling, I see side and forward slip as just names. I got my PPL on an aircraft without flaps or airbrakes. Most of my flying has been on an aircraft with airbrakes, not flaps. I can stop a slip without taking my hand off the throttle, so I seldom used the airbrakes. Only recently did I encounter the term "forward slip".
The distinction is like that between "Stop:sign-braking" and "Red-light-braking" which I don't think driving instructor has ever taught. :)

is there a difference ? All the aircraft and its fin knows is the relative airflow, which in both diagrams would be 180 degrees to the flight path, and have the same effect on the aircraft, except one is from the left and one from the right. The path over the ground is irrelevant to aerodynamics.

Yes, there is a difference! Can you not see the picture?

Hint- look at the ground path and the angle between said ground path and the leading edge of the wing.

Sitting at 10 knots above the stall on the approach? Your operating outside the normal envelope of the aircrafts operation, it’s called Loss of Control
( I)

Slipping is only one option. S Turns and diving the height off are two other ways of varying the glide path and should be easily accomplished by any FI.

Rather than stalling the fin I'd suggest you got too slow and stalled, where upon the aircraft snap rolled., An instructor with student in similar circumstances in a 152 said recovery took 500'.

One author has said in a typical Cessna 152/172/182, depending on the amount of slip, the airspeed can easily be off by 20%, which means the energy is off by 40%. This is enough to cause real trouble. Location of the static source induces errors.

Yes they are names, but there is a difference. I think most people, even pilots, intuitively think of the slip as a side slip because the side of the airplane is headed towards the runway, not the spinner/longitudinal axis. Just my guess as to why so many get it backwards.

A lot in aviation is taught incorrectly. Like two molecules leaving the leading edge, then because of a rendezvous they have set up at the trailing edge, the one on the top of the wing goes faster. I have heard lift described thusly from more pilots than I care to admit.

A miss is as good as a mile.

Any landing you can walk away from is a good landing.

Any landing that you can fly away from is a great landing.

Nobody panicked even if they didn’t nail the landing.

Once you become a glider, your options are limited, and although all private pilots train for engine out emergencies, it’s hard to get over the instinct that altitude is good.

Once upon a time, a man spun in and landed his single engine plane inverted in a field, with his family onboard, near where I lived because he thought that it was better to press on regardless at the edge of an approaching hurricane rather than sit it out and await better weather the following day.

The plane looked pretty good, aside from being upside down and somewhat crunched. No survivors.

Forward slip vs side slip versus crab landing…

If you land with your landing gear at an angle to the runway, you risk the sideways force collapsing them under the plane.

Always best to land with the plane aligned with the runway.

I have landed with strong steady crosswinds in a forward slip on approach according to the above diagram, which I was told was a crab landing, then switched to a side slip in order to keep the landing wheels aligned directly with the runway, albeit with plenty of rudder which meant that the upwind wheel touched down first, and the other main touching down second when speed/lift dropped sufficiently.

I have also done S turns on approach if I wanted to burn off speed/time/landing distance, but only when there was another plane ahead of me on the runway/approach.

Yes, this pair could have done S turns/weave back and forth to burn off speed/distance, but they may not have had the time/leisure to think it through and it may not have reduced their altitude fast enough.

Also, in terms of “slips” when you are not trying to land…

If you want to go from point A to point B in a crosswind, you will be pointing into the wind in order to maintain heading to your destination, so you will be flying “sideways” relative” to the ground.

It reduces your net speed over the ground, which increases your fuel consumption for a given flight, but otherwise crosswinds are only a major problem when you try to land.

Hat, coat, door…

Wind correction angle is not a slip.

Good advice from DAR. Cessna 172H POH - Slips are prohibited in full flap approaches because of a downward pitch encountered under certain combinations of airspeed and sideslip angle. (Presumably 30° is OK as full flap is 40°)

172S on the other hand says - Steep slips should be avoided with flap settings greater than 20° due to a slight tendency for the elevator to oscillate under certain combinations of airspeed, sideslip angle, and center of gravity loadings.

Why? Quote from a DAR post elsewhere, source "Cessna, Wings for the World" by Cessna test pilot William Thompson.So if you fly an A to K model 172 you could be in for a surprise.

Difference in dorsal fin.

172K
https://cimg1.ibsrv.net/gimg/pprune....7782aedcd1.jpg

172L
https://cimg3.ibsrv.net/gimg/pprune....9fed0eccfe.jpg

Does it follow that it's more conservative to side-slip to the right if your static port is on the left of the aircraft? ie presenting the static port to the airstream will result in the IAS being lowered rather than raised ?

Doesn't the Cessna single engine fleet have a static port each side?
Also there are reasons to slip one way or another, wind direction, direction of engine rotation for example. The trick is to "ahem" use the correct attitude for the airspeed you want.

The ones I'm aware of have only a single port on the left side.

db, with the Cessna and its left side static port I'd expect that a slip to the left would have the port seeing increased pressure, slip to the right reduced pressure. The question then becomes what does the pitot see? An academic paper says,The summation of all the effects you need to become a test pilot.

Cessna 150/152's have the static port on the left fuselage side only. All other Cessna's I'm aware of have at least two static ports, left and right, interconnected. Newer Cessnas with G1000 have four static ports. Any flying you do which causes an angle off approaching 20 degrees for the pitot tube or static port introduce noticeable errors. Interconnected static ports greatly reduce the effect on the static side of the instruments. Very specialized or swiveling pitot tubes reduce this effect for airspeed readings, but are generally not worth the trouble and expense.


https://cimg4.ibsrv.net/gimg/pprune....41770fe3fa.jpg

Quite apart from discussing what the pitot 'sees' when side slipping and what forward speed pressure sensing it feeds to the ASI.compared to actual speed (during a sideway slip).
{I have my own pet theoriy !]

Sorry, but differentiating between forward slip & side slip is meaningless; even when forward slipping I'll aim to track towards a particular ground feature. Your diagram above is deliberately deceptive, the forward slip omits any wind effect & is clearly right rudder, left wing down, the side slip is left rudder, right wing down. What does the diagram mean by "flight path"? The forward slip part suggests that "flight path" = "heading before applying the rudder" but if we apply that definition to the side slip part then the heading before applying the rudder would be directly into wind, in which case the ground track/path would also be directly into wind. Adding some left rudder and right wing down won't change that. That is a very, very poor diagram.

Lets imagine I'm flying towards an airfield, there's a crosswind from the left so I have adjusted my heading so that my ground track is straight torwards my destination. When I start my descent I realise that I have left it too late & will be too high so I decide to add some extra drag by feeding in some right rudder, using left wing down to maintain my track towards the airfield. This is what you would call a forward slip. Fortunately the runway in use is aligned with my direction of travel, my descending forward slip is taking me down the extended centreline of the runway. It's a quiet airfield, I make the usual radio calls announcing I'll be joining straight in on to final approach & continue my right rudder, left wing down flight all the way down final, through the roundout & hold off until touchdown.

At what point did the forward slip magically transform into a side slip?

That is not my diagram. Prove your point with documentation.

I am not arguing that in both you don’t cross control the same way. They do serve two different purposes and are semantically different, otherwise there wouldn’t be two different names. If you can’t understand this I don’t know what to say.

Deliberately deceptive? Seriously?

Maybe the FAA’s diagram is better:

https://cimg8.ibsrv.net/gimg/pprune....f692ddaea3.png
https://cimg2.ibsrv.net/gimg/pprune....e7619a1fb9.png

https://cimg3.ibsrv.net/gimg/pprune....395d73b46.jpeg

Old Bridge landings
 

I have landed at Old Bridge a few times and like a lot of airports in NJ there are tall trees around. The trees get taller every year and the neighbors can object to getting them cut down so the impact can creep up on you. The tree line can also create some interesting wind patterns. Where I was based at Somerset it could be tricky when landing on 12. That end of the runway was in a box canyon of trees and the wind made a vortex. As you came over the trees the wind was often very different than the wind sock at mid field.
The result was keeping a bit high and fast on a long final was a good idea. I did my PPL in a 172 based in the area and was always shown to use S turns to bleed off speed and I did so frequently. It worked very well. Keep the nose pushed down and watch the runway picture. We did practice some slipping as well but I can't remember any limits on flaps. I do remember it was a very effective way to dump altitude in a hurry. It felt uncomfortable the first few times. A good skill to practice.
I can't find if it says how far from the airport and what height they were at when the engine quit. Does anyone know?
Was the plane based there?

From the FAA airplane flying handbook:From the FAA airplane flying handbook:Technically, there is no difference between a forward slip and a sideslip, in that they both require crossed controls. However, the purpose of each is different, in that the intention of the forward slip is to lose altitude without increasing airspeed while maintaining ground track and flightpath, even though the nose of the aircraft will no longer point in the direction of the flightpath, while the intention of the sideslip is to maintain aircraft heading and flight path, relying on a countering crosswind to maintain ground track - essential in landing to ensure that the nose is pointing straight down the runway, i.e. aircraft heading is aligned with flightpath to avoid drift and lateral loading on the undercarriage.

This is the "wing down" method of crosswind landing, as opposed to the "crab" method, where there is no crossed control, and the nose is pointed into wind so that the ground track is aligned with the runway - with the nose yawed to align with the runway just before touchdown. I've always been a crab man myself, but I'm a Cancerian, so it was written in the stars. ;)

so what do you call it if you are high on final and are crabbing to maintain centreline and then decide to enter a sideslip to drop some excess height and in doing so align the aircraft's nose parallel to the centreline? a side forward slip maybe? :)

It is probably just me but I struggle to see the need to give a sideslip 2 different names when it is the same manoeuvre with identical control inputs. You can use it to lose height without speed or lose speed without gaining height or to assist an observer look out the window or whatever.

It's not just you, me too! I want to go there, but will cross control it and point it over there for a time, to best achieve that. The arrows and terms are of less consequence, if it was safe, and worked as intended!

A check of the manuals I have 150, 152, 172 have single port, 182, 206, 210, 207 have dual. With the plethora of versions of a particular model Cessna built it would pay to check the particular aircraft you're about to hire.

Too easy. Quite sure the Cutlass (172RG) has two ports ;)

The 172M I fly has one, on the left. Which is why I was speculating that pointing the nose right of track might lead to reduced IAS due to increased static pressure, while perhaps the pitot would be less sensitive to direction. Although of course I'm sure it's not as simple as that and I would be foolish to do anything other than be aware the IAS will have increased error in a slip.

(just musing, just a thought experiment. Please don't haul me over the coals for inventing my own POH)

True, but still wise of you DB. I stand corrected that some 172's have only one port, and your observation, and reason for awareness are wise. That being said, when I slip, which is often, I'll fly with a reserve of speed anyway, so a possible position error will be less significant.

How much "extra speed" then ?
And surely being a test pilot you'd have already checked at safe height various non straght ahead slow flight ASI readings to determine if your guess is near the mark or even valid ?
And what about the sideways air across the forward facing pitot effects ??

No, it isn't. It is just as hilariously deliberately deceptive as your previous diagram. In order to induce an artificial difference between the two supposedly different slips the FAA diagram omits the crosswind in the second picture and therefore has the aircraft flying an entirely different heading before slipping.

The FAA's fig 9-13 must have a crosswind from the left. That is the only way that the aircraft can be flying into the relative wind, ie direction of flight through the air, and still be tracking down the runway. In co-ordinated flight the aircraft heading would be directly into the relative wind, the pilot then feeds in some right rudder and left wing down and the heading is now aligned with the track over the ground. Fig 9-14 deliberately omits any crosswind, in order to track down the runway the aircraft is flying down the runway. If the crosswind implicit in fig 9-13 was added to fig 9-14 then to track down the runway the aircraft would have to fly slightly into wind to compensate for the crosswind, in other words the airflow/relative wind would come from the left of the runway, as in fig 9-13. When the pilot adds some right rudder and left wing down to 'forward' slip fig 9-14 would look identical to fig 9-13.

To put it bluntly, the difference between the two images in the FAA handbook is not that the aircraft is flying two distinct, different manoeuvres but that one image includes the effect of a crosswind, the other image does not. That's it. They are only semantically different because someone chooses to make them so, it reminds me of the asinine distinction between gliders and sailplanes that some US glider pilots like to make. If you want to carry on making the distinction, help yourself, but don't come on to an international forum and start lecturing people "that's not a sideslip, that's a forward slip" and expect not to be laughed at.

Qualitative, rather than quantitative. I'm certainly not slipping to fly slowly, so if the slip is achieving what I want it to, that's good enough for me.

The safe height for this is desk height, before flight, as it's a review of the flight manual position error correction table, for the intended speeds - but knowing that if the airplane has any aerodynamic modifications, the position error correction table in the original flight manual is probably no longer correct. Once you're airborne, there is no way to know the difference IAS to CAS unless the aircraft is instrumented for it.

Yes, I have tested a number of aircraft with the swiveling pitot static head (photo posted earlier in this thread). That is one of the few ways to gather position error data for an aircraft. On my 150, I was able to measure IAS to CAS errors as much as 19 MPH in high AoA and slips. I've used it on a number of modified aircraft. It's particularly useful on helicopters during autorotation, where there is no other means to determine position error. There's also a GPS method, usable in precise level flight, but hardly useful in high AoA, or power idle flight.

Thank you DAR,

But what is your experience/opinion on slow slipping finals ASI when the PITOT has the airstream skiddig partially sideways acrtoss it. And as a corollary what that means for wing lift at that configuaration & velocity ?