Forward Slips with Flaps, Cessna... Is it Ok?

[brcase]

Depends on the Model of C-172. The B-model owners manual I fly occasionally says "Slips are prohibited in full flap approaches becasue of a downward pitch encountered under certain combinations of airspeed and slideslip angle." (page 3-6 of the manual)

There is no "not recommended" about it.

I know later models removed the prohibition or changed it to a "not recommended"
Brian
CFIIG/ASEL

 

[Dan Thomas]

IIRC, a CAP C172N180HP model I flew had a placard "Slips with full flaps PROHIBITED"

I checked the POH but didn't find the reference to the placard.

Might be a CAP thing...

Might be a 180 hp STC thing.

The Type Certificate Data Sheet is the authoritative document for these things. The 172 has Type Certificate 3A12, and under the Notes section, Note 2, paragraph C, we find this:

D. On flap handle, Models 172 through 172E
(1) "Flaps - Pull to extend
Takeoff Retract 0°
1st notch 10°
Landing 0° - 40°
(2) "Avoid slips with flaps down."
E. Near flap indicator Models 172F (electric flaps) through 17271034, excluding 17270050)
"Avoid slips with flaps extended."

Serial 17271034 is a 1978 172N. There is no futher mention of the "Avoid Slips" placards on any further 172s up through the Q model. I think they just dropped the whole thing as being too paranoid. The term "Prohibited" is not found anywhere in reference to slips with flaps extended.

For the R and S models, required placards are as noted in the POH and parts manuals. We have an S here; I'll have to have a look at it to see if it has that placard. I can't remember seeing it.

The POH's for these new airplanes are "serialized;" specific to a particular airframe serial number. Seem to carry more legal weight.

And I've slipped 172s with full flaps many, many times and never felt anything unusual.

Type Certificate Data sheets are here:
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/MainFrame?OpenFrameSet

Dan

 

[EppyGA]

Attached from 172N POH

 

[ScottM]

Attached from 172N POH

We cannot see onto your hard drive.

 

[BillTIZ]

1974, 172 and Skyhawk Owner's Manual (POH) 172M
Normal Landings
"Normal landings are made power off with any flap setting desired. Steep slips should be avoided with flap settings greater than 20degrees due to a slight tendency for the elevator to oscillate under certain combinations of airspeed, sideslip angle, and center of gravity loadings."

Crosswind Landing
"When landing in a strong cross wind, use the minimum flap setting required for the field length. If flap settings greater than 20degrees are used in sideslips with full rudder deflection, some elevator oscillation may be felt at normal approach speeds. However this does not affect control of the aircraft."

"Maximum allowable crosswind velocity is dependent upon pilot capability rather than airplane limitations. With average pilot technique, direct crosswinds of 15 knots can be handled with safety"

So it says, Avoid, not Prohibited.

 

[gismo]

Depends on the Model of C-172. The B-model owners manual I fly occasionally says "Slips are prohibited in full flap approaches becasue of a downward pitch encountered under certain combinations of airspeed and slideslip angle." (page 3-6 of the manual)

There is no "not recommended" about it.

I know later models removed the prohibition or changed it to a "not recommended"
Brian
CFIIG/ASEL

I think that if you looked at a current "POH" for your model 172 you'd find that the language has changed. It is true that a few models came with pilot handbooks that contained the "Slips are prohibited". In any case
all limitations and required placards are required to be listed in the TCDS for the aircraft and AFaIK there's no such limitation in the TCDS for yours.

 

[EppyGA]

We cannot see onto your hard drive.

Actually not on my hard drive. Just some extra crap that got pasted in.

 

[Areeda]

My story is that I alway believed that avoid means don't do unless necessary. Prohibit means don't $@%#ing do it.

So when I was a new instructor and had student high on final that wouldn't make PTS standards who asked me what can I do, I would say try a forward slip.

When one of my first private pilot candiate did this on her checkride
the examiner asked "What does the POH say about doing that"
she said "avoid it"
examiner asked so why did you do it,
she said "Joe said avoid does not mean prohibit"

She passed.

He asked me "So do you really think it's a good idea to tell student pilots that it's not necessary to follow the recommendations in the POH, that the only things important in there are the absolutes?"

My primary students do not slip on final anymore unless it is really reallyimportant.

Joe

 

[gismo]

He asked me "So do you really think it's a good idea to tell student pilots that it's not necessary to follow the recommendations in the POH, that the only things important in there are the absolutes?"

I'd have replied: "I discussed the specific issue of slips with flaps and had the student experiment with that condition at a safe altitude with me in the right seat. I made it clear that just because some manufacturer's advice is bogus, that doesn't mean that any of it should be ignored without a good understanding of the specifics."

My primary students do not slip on final anymore unless it is really reallyimportant.

So how do you propose that students deal with crosswind landings? Even with crab and kick you are slipping for some time, and to handle a strong one, you sometimes need to combine the two. Finally, slipping is hands down the most effective means of controlling the glide path during a power off emergency landing, allowing the plane to have enough excess energy down final to ensure the touchdown won't be short without carrying that excess beyond the threshold with the inevitable extended float. And coupling the fact that full flaps are almost always a benefit for any emergency landing with the likelihood that the surface wind will not be right on the nose when the field choices are limited makes for a huge advantage in being able to slip with full flaps. Wouldn't you want your students to have some experience with this under your watchful eye before facing a true emergency landing on their own?

 

[Pilawt]

Here's what Bill Thompson, former Manager of Flight Test & Aerodynamics at Cessna, had to say about the issue of slipping with full flaps in the 172 (Cessna -- Wings for The World, by William D. Thompson, Maverick Press, 1991, p. 41):

With the advent of the large slotted flaps in the C-170, C-180, and C-172 we encountered a nose down pitch in forward slips with the wing flaps deflected. In some cases it was severe enough to lift the pilot against his seat belt if he was slow in checking the motion. For this reason a caution note was placed in most of the owner's manuals under "Landings" reading "Slips should be avoided with flap settings greater than 30 deg. due to a downward pitch encountered under certain combinations of airspeed, side-slip angle, and center of gravity loadings". Since wing-low drift correction in crosswind landings is normally performed with a minimum flap setting (for better rudder control) this limitation did not apply to that maneuver. The cause of the pitching motion is the transition of a strong wing downwash over the tail in straight flight to a lessened downwash angle over part of the horizontal tail caused by the influence of a relative "upwash increment" from the upturned aileron in slipping flight. Although not stated in the owner's manuals, we privately encouraged flight instructors to explore these effects at high altitude, and to pass on the information to their students. This phenomenon was elusive and sometimes hard to duplicate, but it was thought that a pilot should be aware of its existence and know how to counteract it if it occurs close to the ground.
​

The larger dorsal fin of the 1972 C-172L apparently eliminated that phenomenon.

The "oscillation" mentioned in this thread is an unrelated phenomenon that Thompson described in newer models in full-flap slips: "a mild pitch 'pumping' motion resulting from flap outboard-end vortex impingement on the horizontal tail at some combinations of side-slip angle, power, and airspeed."

So although the pitch-down issue had been solved in 1972, they kept the cautionary note in the POH because of the latter phenomenon.

Unfortunately Cessna contributed to the "end of the world" fear of slips with flaps, by not explaining the phenomenon in the manuals; and in fact, many earlier C-172 manuals expressly said that slips with full flap were prohibited. I rummaged through my collection of old Cessna owners manuals:

1958 C-172: "prohibited"
1959 C-175: "prohibited"
1966 C-172F: "prohibited"
1972 C-172L (first year of the big dorsal): "should be avoided"
​

The manuals for these older models have been revised since then, but that's what a lot of us old-timers read back then and remember.

 

[D_C71]

Thanks for the Info. I printed it out so now I have some ammo for the next time I see those instructors or others in the future.

 

[rottydaddy]

I guess you make all your landings on runways perfectly aligned with the wind?

Are we confusing "forward" with "side"? There seems to be two camps, but what I'm talking about is a "forward" slip, that is, slipping with the nose wherever it needs to be, as opposed to a "sideslip", which is also cross-controlled, but with rudder used to keep the nose aligned with the runway.
Some people call the first type a "side slip" because the plane's nose is pointed sideways relative to the runway, but I call it "forward" because the plane is slipping more in line with the runway. Or more importantly, more in line with the ground track. Forward.

You can certainly do the first (the "forward") in a crosswind, but assuming you don't need to steepen your approach, in a crosswind, either crabbing or side-slipping would make more sense than forward-slipping.

Here's my reasoning: in a sideslip, you're taking the relative wind more on the nose (assuming wind speed is not very close to airspeed- which it better not be!). In a forward slip, you're presenting the side of the airplane a lot more to the relative wind. A lot more. More drag, plane slows down without having to reduce power and/or pitch up. Doesn't work the same way as flaps, but the purpose, on the landing approach, is the same: to steepen the approach without increasing airspeed or rate of descent (although a forward slip will usually make the airplane "want" to descend at a higher rate, but you can check that with power).

When you do this in a crosswind, the nose points downwind... not the best attitude to be in when you eventually try to get the nose back on the centerline. Not usually a problem, but not ideal. In any sort of wind where you don't want to take this chance, you 're better off crabbing (nose into wind) or side-slipping (nose already on centerline, or at least the long. axis parallel to it). Crabbing means rudder work as you round out, flare, or whatever... but you're moving the nose downwind. Less likely to run out of rudder that way. In fact, crabbing or side-slipping will show you much, much sooner if you have enough rudder authority for a given xwind landing than the fwd. slip, where you may find out later than you like.


I've never had anyone try to convince me otherwise, but I'm ready to learn...

There are several purposes for flaps, including improving visibility over the nose during landing, increasing lift/drag during landing to allow increased descent angle without increasing airspeed, and increasing drag in the flare.

I understand all the benefits of flaps. But you usually get a much better view of the runway, and obstructions, in a fwd slip than straight ahead with flaps. But yes, better a flatter pitch agnle with flaps than mushing a lot to reduce airspeed.

At any rate, in my mind, with a 172 in particular, you're using the flaps to fly a steeper approach, period. On a long runway with no obstructions, they're not needed, although the most common mantra is "use 'em if you got 'em". I usually use 'em, I'm in the habit of normally dropping ten degrees abeam the numbers, mostly to slow down sooner, but I did fly out of a short field with obstructions for a while (Marlboro: 2200 feet with over 400' displacement at one end) where you did not dare use more than 20 degrees with a 172, or you would simply not be able to go around after touching down.
I learned how to make the most of those two notches, and could even land there without flaps pretty well. 3000 or more feet is a piece of cake in a 172 with no flaps, even without slipping, assuming you have nothing tall close to the threshold. It's a relatively slow airplane, so I see no sense in carrying full flaps (even 30) on a shallow-ish approach to a long-ish runway. One or two notches helps with the pattern turns, especially that last one, but it's not absolutely necessary, as it might be with a much faster plane.

What made that unnecessary was improved engine reliability.

Sure, to some extent, but some people still approach in a similar fashion, and with a short runway with obstructions, with no flaps, they may have to. Without flaps, in such a situation you have to either forward-slip or make a "mushing" descent. Or one can be stupid and dive for the runway... So again, flaps do many things, but this is what they do best, IMHO... and the only thing they are needed for, assuming you don't want to slip or try a "helicopter" approach.

They also get to experience long floats down the runway, and usually overcontrol the flare when doing it.

Yup. No argument there. I think I was a typical student in that it took me a while to get comfy letting a 172 glide to the runway with full flaps the way it wants to (pretty slowly). It was revelatory the first time I got over my anxiety and just let it slow down and sink. It doesn't take much extra speed to really mess up what should be an easy 172 landing... even well within flap-operating limits.


Veering back on-topic: do all the Cessna placards always warn against forward slips, or any slips? I can't remember.

 

[AuntPeggy]

Early in my training, my CFI insisted I learn to forward slip to a landing. I wasn't ready and objected, but that is another story. Today in my C-172, I side slip whenever there is a crosswind on landing. Keep the nose pointed straight down the centerline using the rudder, one wing low. If I am high, I forward slip to lose altitude; wings level, nose a little high and right or left, full rudder; then transition to the side slip before flair.

If you don't slip in a crosswind landing, the side-loading on landing causes a skipping that I consider as dangerous as pointing the nose to the side of the runway toward hangars instead of down the centerline.

Are we confusing "forward" with "side"? There seems to be two camps, but what I'm talking about is a "forward" slip, that is, slipping with the nose wherever it needs to be, as opposed to a "sideslip", which is also cross-controlled, but with rudder used to keep the nose aligned with the runway.
Some people call the first type a "side slip" because the plane's nose is pointed sideways relative to the runway, but I call it "forward" because the plane is slipping more in line with the runway. Or more importantly, more in line with the ground track. Forward.

You can certainly do the first (the "forward") in a crosswind, but assuming you don't need to steepen your approach, in a crosswind, either crabbing or side-slipping would make more sense than forward-slipping.

Here's my reasoning: in a sideslip, you're taking the relative wind more on the nose (assuming wind speed is not very close to airspeed- which it better not be!). In a forward slip, you're presenting the side of the airplane a lot more to the relative wind. A lot more. More drag, plane slows down without having to reduce power and/or pitch up. Doesn't work the same way as flaps, but the purpose, on the landing approach, is the same: to steepen the approach without increasing airspeed or rate of descent (although a forward slip will usually make the airplane "want" to descend at a higher rate, but you can check that with power).

When you do this in a crosswind, the nose points downwind... not the best attitude to be in when you eventually try to get the nose back on the centerline. Not usually a problem, but not ideal. In any sort of wind where you don't want to take this chance, you 're better off crabbing (nose into wind) or side-slipping (nose already on centerline, or at least the long. axis parallel to it). Crabbing means rudder work as you round out, flare, or whatever... but you're moving the nose downwind. Less likely to run out of rudder that way. In fact, crabbing or side-slipping will show you much, much sooner if you have enough rudder authority for a given xwind landing than the fwd. slip, where you may find out later than you like.


I've never had anyone try to convince me otherwise, but I'm ready to learn...




I understand all the benefits of flaps. But you usually get a much better view of the runway, and obstructions, in a fwd slip than straight ahead with flaps. But yes, better a flatter pitch agnle with flaps than mushing a lot to reduce airspeed.

At any rate, in my mind, with a 172 in particular, you're using the flaps to fly a steeper approach, period. On a long runway with no obstructions, they're not needed, although the most common mantra is "use 'em if you got 'em". I usually use 'em, I'm in the habit of normally dropping ten degrees abeam the numbers, mostly to slow down sooner, but I did fly out of a short field with obstructions for a while (Marlboro: 2200 feet with over 400' displacement at one end) where you did not dare use more than 20 degrees with a 172, or you would simply not be able to go around after touching down.
I learned how to make the most of those two notches, and could even land there without flaps pretty well. 3000 or more feet is a piece of cake in a 172 with no flaps, even without slipping, assuming you have nothing tall close to the threshold. It's a relatively slow airplane, so I see no sense in carrying full flaps (even 30) on a shallow-ish approach to a long-ish runway. One or two notches helps with the pattern turns, especially that last one, but it's not absolutely necessary, as it might be with a much faster plane.


Sure, to some extent, but some people still approach in a similar fashion, and with a short runway with obstructions, with no flaps, they may have to. Without flaps, in such a situation you have to either forward-slip or make a "mushing" descent. Or one can be stupid and dive for the runway... So again, flaps do many things, but this is what they do best, IMHO... and the only thing they are needed for, assuming you don't want to slip or try a "helicopter" approach.

Yup. No argument there. I think I was a typical student in that it took me a while to get comfy letting a 172 glide to the runway with full flaps the way it wants to (pretty slowly). It was revelatory the first time I got over my anxiety and just let it slow down and sink. It doesn't take much extra speed to really mess up what should be an easy 172 landing... even well within flap-operating limits.


Veering back on-topic: do all the Cessna placards always warn against forward slips, or any slips? I can't remember.

 

[midlifeflyer]

Are we confusing "forward" with "side"? There seems to be two camps, but what I'm talking about is a "forward" slip, that is, slipping with the nose wherever it needs to be, as opposed to a "sideslip", which is also cross-controlled, but with rudder used to keep the nose aligned with the runway.

And the aerodynamic difference between the two is....?

Ron isn't confusing anything. A slip is a slip.

AFAIK, the various aircraft POH that recommend against full flap or extended slips don't differentiate between the two. They just say "slips".

 

[twdeckard]

Cessna says "AVOID" because if you stall it, you are set up for a cross controled spin.

When on final and slipping, stalling and spinning would not be much fun.

It is unlikley to spin from a forward slip with top rudder. Grab a small model airplane and visualize it. The high wing has the high angle of attack and stalls first, the high wing drops and the airplane recovers to a stable condition. This is very different than the situation when using the rudder to cheat a turn to final.

 

[twdeckard]

Rather than cut and paste my diatribe on slipping with flaps, I'll post a link to my blog entry on the subject:

http://ground-effect.com/2007/12/01/high-wing-slips-with-flaps.aspx

The blog was a lame experiment but I did air out my opinion on the slips with flaps controversy. It shows me wearing Gene's t-shirt for a polar bear plunge!

 

[tonycondon]

it *might* be true that a 172 is resistant to spinning from a slip, but that certainly isnt the case in all airplanes. I did a very nice spin entry from a slip in the Extra 300, took me about a full turn to figure out what had happened.

 

[twdeckard]

it *might* be true that a 172 is resistant to spinning from a slip, but that certainly isnt the case in all airplanes. I did a very nice spin entry from a slip in the Extra 300, took me about a full turn to figure out what had happened.

I was being too general and this is probably dangerous. My experience was confined to a 150 aerobat and we could not get it to depart from a slip without being ridiculously aggressive (and likely permitting/inputing enough yaw so the spin was in no way a function of the slip itself).

I also carry the prejudice that a 172 won't spin to the right unless you are very deliberate.

Politically, I am very pro-slip. Its an excellent way to shed airspeed and altitude on an engine out approach and doesn't corner you as easily as extending the flaps.

 

[Dan Thomas]

Are we confusing "forward" with "side"? There seems to be two camps, but what I'm talking about is a "forward" slip, that is, slipping with the nose wherever it needs to be, as opposed to a "sideslip", which is also cross-controlled, but with rudder used to keep the nose aligned with the runway.
Some people call the first type a "side slip" because the plane's nose is pointed sideways relative to the runway, but I call it "forward" because the plane is slipping more in line with the runway. Or more importantly, more in line with the ground track. Forward.


At any rate, in my mind, with a 172 in particular, you're using the flaps to fly a steeper approach, period. On a long runway with no obstructions, they're not needed, although the most common mantra is "use 'em if you got 'em". I usually use 'em, I'm in the habit of normally dropping ten degrees abeam the numbers, mostly to slow down sooner, but I did fly out of a short field with obstructions for a while (Marlboro: 2200 feet with over 400' displacement at one end) where you did not dare use more than 20 degrees with a 172, or you would simply not be able to go around after touching down.

Veering back on-topic: do all the Cessna placards always warn against forward slips, or any slips? I can't remember.

A forward slip is aerodynamically identical to a sideslip. The only difference is whether the nose is pointing at the target or not, and it depends on the crosswind, not the relative wind. The airplane has absolutely no idea which you are doing.

Flaps in a 172 lower the stall about 5 or 6 knots, enabling a slower approach, and add lots of drag, making the approach steeper. That same drag shortens the landing roll. I use all the tools in my toolbox, and all the equipment on my airplanes. I'm one of those guys who does not believe in getting used to using a lot of runway, as someday I'll have another forced landing (I've had two real engine failures) and maybe this time the available field won't be so long and I'd better be proficient. And I don't like abusing the brakes to get rid of speed that I could have lost on final instead of the runway, and flaps let me do that.

I just wish these airplanes still had manual flaps, like the 180 and 185 and my old Auster. Dumping the flaps on touchdown put the airplane farther into the stall and increased the weight on the wheels, making a really short landing possible. The electric flaps are soooo slow, and as they pass through 20° they actually increase the lift and take the weight off those tires.

Dan

 

[RogerT]

IIRC, a CAP C172N180HP model I flew had a placard "Slips with full flaps PROHIBITED"

I checked the POH but didn't find the reference to the placard.

Might be a CAP thing...

Wouldn't that placard be listed in the type certificate if it needs to
be there?

 

[dmccormack]

Wouldn't that placard be listed in the type certificate if it needs to be there?

One would assume so....

 

[gismo]

it *might* be true that a 172 is resistant to spinning from a slip, but that certainly isnt the case in all airplanes. I did a very nice spin entry from a slip in the Extra 300, took me about a full turn to figure out what had happened.

Some airplanes will and some won't and CG is often a factor. But even those that do will provide considerably more time to react when entering a spin from a slip than a skid. Typically spin resistant airplanes like a 172 will just mush if you apply full up elevator in an aggressive slip although I can't say for certain that this would be the case with the CG at the aft limit.

I suspect that the incipient spin you encountered in the Extra would have recovered itself almost immediately had you simply centered the controls when the down wing started to come up.

 

[tonycondon]

I suspect that the incipient spin you encountered in the Extra would have recovered itself almost immediately had you simply centered the controls when the down wing started to come up.

Perhaps, if i could think that fast.

 

[jesse]

I think it is time to pull out my Youtube video from several years ago. It is the 1st result on Google for "slipping stall".

That was a full slip held aggressively in a full stall. I've never been able to get a 172 to do anything exciting in slips. If you're lucky you might get the yoke to shake a bit--but it is still perfectly safe-- and as soon as you let go of the slip inputs it stops. If you ever did get something exciting to happen the airplane has to roll through wings level and into the spin. This isn't going to happen crazy fast in a 172.

 

[SkyHog]

I think it is time to pull out my Youtube video from several years ago. It is the 1st result on Google for "slipping stall".

That was a full slip held aggressively in a full stall. I've never been able to get a 172 to do anything exciting in slips. If you're lucky you might get the yoke to shake a bit--but it is still perfectly safe-- and as soon as you let go of the slip inputs it stops. If you ever did get something exciting to happen the airplane has to roll through wings level and into the spin. This isn't going to happen crazy fast in a 172.

Great memories. I remember the day this argument first came up too well.

 

[poadeleted20]

Depends on the Model of C-172. The B-model owners manual I fly occasionally says "Slips are prohibited in full flap approaches becasue of a downward pitch encountered under certain combinations of airspeed and slideslip angle." (page 3-6 of the manual)

Old book, superseded. See the current TCDS.

 

[ScottM]

I think it is time to pull out my Youtube video from several years ago. It is the 1st result on Google for "slipping stall".

That was a full slip held aggressively in a full stall. I've never been able to get a 172 to do anything exciting in slips. If you're lucky you might get the yoke to shake a bit--but it is still perfectly safe-- and as soon as you let go of the slip inputs it stops. If you ever did get something exciting to happen the airplane has to roll through wings level and into the spin. This isn't going to happen crazy fast in a 172.

Why you are not dead from your reckless act is a miracle!!!

How did you recover from such a near fatal event!!

 

[poadeleted20]

Are we confusing "forward" with "side"?

Nope. Aerodynamically, there's no difference between a forward slip and a side slip. The only difference is ground references. Thus, whether you're doing a forward slip or a side slip, the oscillation issue is the same. Which is why...

Veering back on-topic: do all the Cessna placards always warn against forward slips, or any slips? I can't remember.

... the advice (not warning) just refers to "slips."

 

[gismo]

Perhaps, if i could think that fast.

With a roll rate of 400 degrees per second, it's not hard to get a little behind, especially when you're used to the ponderous roll rates in a "high performance" glider like your Cherokee.

 

[poadeleted20]

It is unlikley to spin from a forward slip with top rudder. Grab a small model airplane and visualize it. The high wing has the high angle of attack and stalls first, the high wing drops and the airplane recovers to a stable condition. This is very different than the situation when using the rudder to cheat a turn to final.

...thus creating a skid, not a slip. And yes, skidded turn stalls at low altitude are often fatal because the nose slices down, not up and over, as in a slipped turn stall.

 

[tonycondon]

With a roll rate of 400 degrees per second, it's not hard to get a little behind, especially when you're used to the ponderous roll rates in a "high performance" glider like your Cherokee.

yea. the good news is that even if you're half a turn or a full turn behind the airplane in the spin, you can still recover from it.

and actually my glider is pretty nimble ailerons are about half of the span on it and it rolls very nicely.

 

[Areeda]

I'd have replied: "I discussed the specific issue of slips with flaps and had the student experiment with that condition at a safe altitude with me in the right seat. I made it clear that just because some manufacturer's advice is bogus, that doesn't mean that any of it should be ignored without a good understanding of the specifics."

Lance, it's not that I don't agree with you on the issue of slips with full flaps in Cessnas. I think we disagree about what to teach to primary students.

IMHO I believe we should stress a thorough understanding of the manufacturers documents, the POH, the engine manual and such.

Yes there are things that I believe bogus in the sense they are overly conservative. These slips, prohibitions on LOP operations are a couple of them.

The problem is what process should a new private pilot use to disregard the published procedures? Again I think that's a topic best left for after the checkride.

So how do you propose that students deal with crosswind landings?

Side slip with partial flaps if it is a significant crosswind or full flaps if not.

Finally, slipping is hands down the most effective means of controlling the glide path during a power off emergency landing

I agree and we practice slips with and without flaps. We discuss the difference between a recommendation and a prohibition. I'd much rather deal with the "oscillations of doom" and get the plane on a par 5 fairway than smoothly run into the trees behind the green.

As a wise man once said "there are no limitations if you don't plan on flying the plane again"

Joe

 

[rottydaddy]

A forward slip is aerodynamically identical to a sideslip. The only difference is whether the nose is pointing at the target or not, and it depends on the crosswind, not the relative wind. The airplane has absolutely no idea which you are doing.

I agree that they both do pretty much the same thing (cause the airplane to move laterally and "want" to descend). And they do it pretty much the same way.


But regardless of wind, in a fwd slip, you are definitely presenting more wing surface, and surface in general, to the relative wind, because most of the relative wind has to do with the plane's actual path thru the air, and the wing is more or less pointed along the flight path. It's not quite the same thing as merely crabbing.

I can't believe the relative wind is going to be square to the wing spar (as if you were flying along with all conrols neutral) when you are flying like that. How could that be?

Even in a pretty extreme wing-low side slip to prevent drift in a high crosswind, the relative wind angle still consists more of the direction of travel and less of the movement "into the wind" (relative to the runway centerline). As in crabbing flight, you're flying along with the wind, regardless of airplane heading, so the airplane doesn't know or care what the wind is doing relative to the ground track. With the nose pointed more along the path of flight, the RW is going to have a different effect than in a fwd slip. Right?

Forgetting wind and runway for a moment, we can see that both kinds of slips result in the airplane traveling at an angle somewhere between the nose and the low wingtip. That's why they call it a slip. But I believe for what is typically thought of as a fwd slip, to increase drag primarily, the angle between the nose and the path of flight is greater. If that were not so, then to descend more steeply in a side-slip approach while still pointing the nose right at the target, you'd merely have to lower the wing more. That won't work. You can try it with no wind- it's possible to keep a wing slightly low and check the resulting yaw with rudder. Check it only so far as the centerline and you will miss the runway if you keep increasing bank but do not let the nose go past the centerline. To stay on target you will eventually have to make it a forward slip. Now, assuming zero crosswind component, is the air flowing at the same angle to the long. axis in both cases? I don't think so. Am I crazy?

At any rate, for me, the fwd slip works better to come down steeper and slower, and the side slip works better to correct for drift, regardless of airspeed or descent rate. If they were aerodynamically the same, I don't see how this could be. I realize that there is an area where they sort of overlap, especially in stronger xwinds where a side slip will require a lot of control input, but I don't think they are quite the same.

 

[rottydaddy]

Early in my training, my CFI insisted I learn to forward slip to a landing. I wasn't ready and objected, but that is another story. Today in my C-172, I side slip whenever there is a crosswind on landing. Keep the nose pointed straight down the centerline using the rudder, one wing low. If I am high, I forward slip to lose altitude; wings level, nose a little high and right or left, full rudder; then transition to the side slip before flair.

If you don't slip in a crosswind landing, the side-loading on landing causes a skipping that I consider as dangerous as pointing the nose to the side of the runway toward hangars instead of down the centerline.

This is sensible. This discussion reminded me of something important about all methods of xwind approaches: in the end, in order to touch down straight, sooner or later you must side slip.

Sometimes I like to start with a crab then start side-slipping, but I don't fwd slip except to sink more. In a side slip, once you are set to negate the drift, you know exactly what you will need at touchdown (barring of course the fact that it's never really constant). Try fwd-slipping to the flare in a crosswind and you won't really know what it will take, despite having already gone past the centerline while pushing the tail upwind with rudder. If you are holding that fwd slip, you probably have enough rudder to land straight, but you will have to set that rudder angle as you level off, etc. With a side slip established earlier, it's already sorted out.

 

[poadeleted20]

The problem is what process should a new private pilot use to disregard the published procedures? Again I think that's a topic best left for after the checkride.

I think the appropriate concern of the examiner was not that the applicant slipped with flaps, but rather that she couldn't articulate a rational reason for doing so in spite of the POH/placard advice. It's not against a "published procedure," since the POH discusses crosswind landings using flaps. The applicant should, however, be able to explain why the advisory is there, what it means, why it's better to go ahead and slip with flaps in some circumstances, and what to do if the oscillation starts.

 

[SkyHog]

Are we confusing "forward" with "side"?

Ron is 100% right on it, you can't really confuse forward with side, since they're the same thing done in different locations.

edit: err....just to reiterate that for like the dozenth time, my bad. Didn't see the other posts after this one for some reason. lol.

 

[jesse]

A slip is a slip. call it side, forward, or whatever. I prefer just to call them slips.

 

[gprellwitz]

A slip is a slip. call it side, forward, or whatever. I prefer just to call them slips.

Actually, they're only slips on the bottom half.



On the top half they're camisoles. (Sorry, couldn't resist!)

 

[Dan Thomas]

I agree that they both do pretty much the same thing (cause the airplane to move laterally and "want" to descend). And they do it pretty much the same way.


But regardless of wind, in a fwd slip, you are definitely presenting more wing surface, and surface in general, to the relative wind, because most of the relative wind has to do with the plane's actual path thru the air, and the wing is more or less pointed along the flight path. It's not quite the same thing as merely crabbing.

I can't believe the relative wind is going to be square to the wing spar (as if you were flying along with all conrols neutral) when you are flying like that. How could that be?

A crab is coordinated flight. It's not a slip, where the relative wind is coming from somewhere other than straight ahead. A forward slip is to add drag and descend more steeply to the runway and the nose is pointed away from the runway's axis. The wind in a left forward slip, let's say, is coming from 15° to the left if there's no crosswind and the airplane's nose is pointed 15° away from the track.

In a sideslip to counter a crosswind from the left, we could have the same relative wind 15° to the left of the airplane's nose. It's the same thing exactly, and generates the same drag as the forward slip. The only difference is that we're doing it to keep the wind from pushing us off the approach track while keeping the airplane lined up with the runway so the wheels will roll in the desired direction when they touch down.

In a stronger crosswind the relative wind will be more than 15° when we sideslip (if the airplane has enough control authority to command more slip, which many don't), and in a weaker crosswind the angle will be less. In any case, the airplane itself has no idea what the difference between a forward slip and a sideslip is. In both cases the wind isn't from straight ahead.

And related to that is the fact that the relative wind angle gets larger and larger as we slow down on the runway. If we have a 20-knot crosswind and we're approaching at 60 knots, the relative wind angle is 18.4° to the wing IF we have the airplane properly lined up. As we slow through 30 knots, the wind is now 56.3° off the nose and if we're not paying attention and have full aileron and a bunch of rudder into the wind, the upwind wing will rise and we'll lose it. The flight isn't over until the airplane is tied down. The accident database has enough accounts of control loss in the rollout because the pilot figured he was done the landing.

Dan

 

[Areeda]

I think the appropriate concern of the examiner was not that the applicant slipped with flaps, but rather that she couldn't articulate a rational reason for doing so in spite of the POH/placard advice. It's not against a "published procedure," since the POH discusses crosswind landings using flaps. The applicant should, however, be able to explain why the advisory is there, what it means, why it's better to go ahead and slip with flaps in some circumstances, and what to do if the oscillation starts.

Ah yes another incompetent CFI well I may not be totally incompetent but I'm not confident. I have made so many mistakes.

I will discuss this with him. He's a mentor and really cares about the candidates. That's why I use him.

I kind of agree that a new private pilot should have a healthy respect for what's in the POH. My role as the Instructor and purveyor of the truth in aviation is very suspect. In general the POH is better than me.

I really want them to have a healthy respect of my opinion compared to the POH and engine manual. With all due respect they need more disdain of opinions on the Internet. Let's just say the same place I learned about forward slips with full flaps also said it's ok to fly in loose formation for cool pictures.

Joe