forward slips - eeeeeeeeeeeee!

woodstock

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we did forward slips Monday night. what a freaky feeling. no flaps at all - just slipped all the way down. it's not a big deal until you get close and have to straighten it out. then since we had no flaps I ended up floating fairly far down the runway - compared to my short fields that is! in other words - I bet I wouldn't have thought twice about how far I went, before. now that all we have done is short fields lately, going that far down the runway seems like a waste - very inefficient!
 
woodstock said:
we did forward slips Monday night. what a freaky feeling. no flaps at all - just slipped all the way down. it's not a big deal until you get close and have to straighten it out. then since we had no flaps I ended up floating fairly far down the runway - compared to my short fields that is! in other words - I bet I wouldn't have thought twice about how far I went, before. now that all we have done is short fields lately, going that far down the runway seems like a waste - very inefficient!

So great to see you learning to fly forward slips full tilt.

Don't forget their main secondary use is scaring the .......
out of unknowing PAX on LDGs when neccessary.
 
Dave Krall CFII said:
So great to see you learning to fly forward slips full tilt.

Don't forget their main secondary use is scaring the .......
out of unknowing PAX on LDGs when neccessary.

You can add unsuspecting CFIs...I had a guy nearly jump out of his skin with a loud shout when I started a slip to a landing. Ever since then I always try to announce the manuever before engaging, especially if it's a CFI pumped and primed to take control.
 
woodstock said:
we did forward slips Monday night. what a freaky feeling. no flaps at all - just slipped all the way down. it's not a big deal until you get close and have to straighten it out. then since we had no flaps I ended up floating fairly far down the runway - compared to my short fields that is! in other words - I bet I wouldn't have thought twice about how far I went, before. now that all we have done is short fields lately, going that far down the runway seems like a waste - very inefficient!

My first flight in the flapless Citabria I used a lot of rwy, even in a slip. After that I realized how critical it was to manage the energy. Another long landing and I then realized I needed to better plan the landing from much further out. After that, it was a fairly typical approach and landing.
 
how off is your ASI?

I went around the first time b/c I thought we were doing 80 on short final.
 
woodstock said:
we did forward slips Monday night. what a freaky feeling. no flaps at all - just slipped all the way down. it's not a big deal until you get close and have to straighten it out. then since we had no flaps I ended up floating fairly far down the runway - compared to my short fields that is! in other words - I bet I wouldn't have thought twice about how far I went, before. now that all we have done is short fields lately, going that far down the runway seems like a waste - very inefficient!
Slips are kind of fun! Usually, if you're trying to land, you would be in landing configuration -- at least partial flaps on some aircraft, full on others such as my Cherokee -- then your airspeed would be right where you want it. Therefore no float...
 
Coincidence--I spent Friday morning with a C172 student who had scared himself recently in crosswinds and wanted experience with slips and cross-controlled stalls. We did the latter first and then practiced no-flap landings with slips.

Your experience with floating down the runway is very common. It often occurs because the pilot doesn't properly adjust the pitch attitude when transitioning from a forward slip, which, as you know, involves a more pronounced nose-down attitude than a normal approach. If the pitch attitude stays where it was as the wings come level and the nose swings around, speed increases, especially if the flaps are retracted. And so, as you round out, you have a lot of extra energy to dissipate, and especially with no flaps, no extra drag to help. Down the runway you fly.

You can find much useful information about slips (both forward and sideslips) in Chapter 8 of the Airplane Flying Handbook.
 
I love the graphics!

I continue to be confused as to why we have 'forward' slips and 'side' slips, based on flight path in relation to the runway. When someone starts a slip on downwind, slips all the way around base and onto final down to the numbers... is that a side slip or a forward slip? The control movements don't change. Seems to me a slip is a slip - as the graphics show.
 
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The distinction between forward slips and side slips is a continuing source of confusion, and to some extent it is unnecessary. But here's how I explain the concepts to students.

Side slip: The object of this type of slip is to keep the nose aligned with the runway while making the airplane slide into the wind at a rate that matches the drift that the wind is causing. In other words, the goal is to move the airplane "sideways" into the wind while keeping the nose aimed at the runway. The technique is basically lower a wing to stop the drift and use rudder as necessary to keep the pointy end aligned with the runway.

We use side slips whenever we land in a crosswind, at least during the final stages of the roundout and touchdown.

Forward slip: The goal of a forward slip is to create a steep descent angle without building airspeed. You accomplish this by turning the airplane's fuselage away from the flight path to create drag while using bank to maintain the desired track over the ground.

These days, a forward slip is primarliy useful if you're trying to make an emergency landing. But back in the day, when many airplanes did not have flaps (and often had poor visibility over the nose) and many airports were short strips with a final approach path obstructed by trees, forward slips were standard operating procedure for getting down to the runway. Knowing how to perform forward slips is still very useful, however; for example, the technique comes in handy if you have to land without flaps, and it also can be used to help correct a high approach.
 
At the risk of (as my sister used to say) "beating a dead horse to death", I still have a question. As I understand it, the control inputs for a "side" slip and a "forward" slip are essentially the same, it's the objective that distinguishes one from another?

(Not trying to be a smart ass, just trying to understand the difference)
 
gibbons said:
At the risk of (as my sister used to say) "beating a dead horse to death", I still have a question. As I understand it, the control inputs for a "side" slip and a "forward" slip are essentially the same, it's the objective that distinguishes one from another?

(Not trying to be a smart ass, just trying to understand the difference)

That's how I think of the difference between them.
 
The inputs are essentially the same, although some would argue that you lead with the aileron for a sideslip and start with the rudder for forward slip. In practice, of course, the actions are essentially simultaneous.

The main difference in control inputs is the amount of deflection.

A side slip usually doesn't require (and in some airplanes with low-slung engines should not involve) a significant bank or a large amount of opposite rudder.

A forward slip, to be most effective, usually calls for much larger control deflections.
 
Slips should be a mandatory part of competency. Pedal to the metal, opposite rudder, nose below the horizon. You need to slip to get in at ASE, EGE, but you never know when in an engine fail situation your bacon may depend on it.
 
Funny, I recently stated my opinion on another board that a slip is a slip is a slip (in response to this very thread from Elizabeth!).

My distinction between the two would be that in a side slip, there is greater latteral movement through the air mass (when compared to the flight path), and in a forward slip, the same movement occurrs, but the airplane is yawed and pitch decreased so that the effect is applied more towards the forward track through the air mass. Still in effect, same same.
 
Forward vs side slip? Just take the pictures Bruce posted and rotate them 15 degrees either way to show either one. Fact is that aerodynamically, there's no difference. The only practical difference is whether your primary consideration is alignment of the fuselage with an object on the ground or not.
 
BruceAir said:
You can find much useful information about slips (both forward and sideslips) in Chapter 8 of the Airplane Flying Handbook.

Hey, Bruce, those pictures are IDENTICAL. They're just rotated 45 degrees.

No wonder students have a hard time learning the concept.

In my case, forward slips are one of those areas like cardinal directions where I have to think about it way more than I should. I have no problem at all with handling crosswinds, but if I try to slip in for a landing I have to think "Ok, full OPPOSITE rudder, so like if I push the left pedal I need to turn the yoke, ummmmm.... right. RIGHT?"

I know that getting it wrong gets you a snap roll and that would be sorta bad. This reminds me that I need to practice it some to get back some semblance of muscle memory for it. I should see how fast the snap would be to see if I have time to wise up.
 
mikea said:
I know that getting it wrong gets you a snap roll and that would be sorta bad.

Only if you also haul back on the yoke enough to stall the airplane. A snap roll is basically a horizontal spin. Otherwise, hard aileron and rudder together would put you into an aileron roll variant.
 
If you're still confused about slips, do read the section in Chapter 8 of the Airplane Flying Handbook, which I referenced earlier in this thread. You can download the whole book in PDF format for free.

It does a good job of laying out the theory. And as I pointed out in my original post, the difference between the maneuvers is the objective. In that sense, the distinction is somewhat similar to that between a normal and short-field landing. The inputs and aerodynamics are essentially the same; the difference is a matter of degree.

It's puzzling to me why slips remain so mysterious, however. As I noted in a post in another thread here at PoA, slips are one of the maneuvers specifically required during pre-solo training, and they're a Task on the private pilot PTS.
 
BruceAir said:
It's puzzling to me why slips remain so mysterious, however. As I noted in a post in another thread here at PoA, slips are one of the maneuvers specifically required during pre-solo training, and they're a Task on the private pilot PTS.

Since when, Bruce? Seriously, I do not recall having to perform this maneuver when I trained, in 1979. I feel it should have been a required maneuver, though, if it wasn't.

Having said that, I recall the examiner asked me to land on the numbers without flaps. I did it, but without slipping.

Jim
 
Well, as far back as I can remember (and I did my student flying in the early 1970s), FAR 61.87 has said:

Sec. 61.87 - Solo requirements for student pilots.

(a) General. A student pilot may not operate an aircraft in solo flight unless that student has met the requirements of this section....


(c) Pre-solo flight training. Prior to conducting a solo flight, a student pilot must have:

(1) Received and logged flight training for the maneuvers and procedures of this section that are appropriate to the make and model of aircraft to be flown; and

(2) Demonstrated satisfactory proficiency and safety, as judged by an authorized instructor, on the maneuvers and procedures required by this section in the make and model of aircraft or similar make and model of aircraft to be flown.

(d) Maneuvers and procedures for pre-solo flight training in a single-engine airplane. A student pilot who is receiving training for a single-engine airplane rating must receive and log flight training for the following maneuvers and procedures:

(1) Proper flight preparation procedures, including preflight planning and preparation, powerplant operation, and aircraft systems;

(2) Taxiing or surface operations, including runups;

(3) Takeoffs and landings, including normal and crosswind;

(4) Straight and level flight, and turns in both directions;

(5) Climbs and climbing turns;

(6) Airport traffic patterns, including entry and departure procedures;

(7) Collision avoidance, windshear avoidance, and wake turbulence avoidance;

(8) Descents, with and without turns, using high and low drag configurations;

(9) Flight at various airspeeds from cruise to slow flight;

(10) Stall entries from various flight attitudes and power combinations with recovery initiated at the first indication of a stall, and recovery from a full stall;

(11) Emergency procedures and equipment malfunctions;

(12) Ground reference maneuvers;

(13) Approaches to a landing area with simulated engine malfunctions;

(14) Slips to a landing; and

(15) Go-arounds.

And, as I noted in another post, slips are included among the Tasks in the Private Pilot PTS (Task K in Section IV) (that doesn't mean the examiner will require you demonstrate them, only that slips are among the items your instructor should have trained you to accomplish to the PTS standard and that they're fair game on the flight test).
 
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mikea said:
Hey, Bruce, those pictures are IDENTICAL. They're just rotated 45 degrees.

No wonder students have a hard time learning the concept.

In my case, forward slips are one of those areas like cardinal directions where I have to think about it way more than I should. I have no problem at all with handling crosswinds, but if I try to slip in for a landing I have to think "Ok, full OPPOSITE rudder, so like if I push the left pedal I need to turn the yoke, ummmmm.... right. RIGHT?"

If there's no wind, then it doesn't really matter which way you slip to lose altitude. If there is a crosswind, bank into the wind with aileron and in either case just stop/prevent a turn with the rudder. If the crosswind doesn't require as big a slip as you need, the nose will actually point away from the crosswind.

I know that getting it wrong gets you a snap roll and that would be sorta bad. This reminds me that I need to practice it some to get back some semblance of muscle memory for it. I should see how fast the snap would be to see if I have time to wise up.

AFaIK this is a myth, at least in many of the singles we fly. Many trainers (and perhaps others I haven't tried) don't have enough elevator authority to stall in a full slip, and without a stall you cannot spin or snap. And IME in a Skyhawk or Skylane all you get if you do approach a stall in a full slip is some buffetting and a tendency for the wings to level themselves. I would be surprised if a Cherokee behaved any differrently. Stalling out of a skid OTOH can lead to a significant departure from "normal" flight.
 
I like doing slips, i learned them early in my training and don't hesitate to do it if i have to. I like to do them for practice in case i would have to slip to get down in a field with an engine out, or i think it would blow the smoke to the side if there ever was a fire of some sort.
 
Training for tailwheel in the Aeronca. Slips are my flaps, basically. Fortunately, I have always enjoyed slips.

Jim G
 
I hate slips.. i am uneasy with them.... But you need to learn them for those crosswinds
 
Teerawood said:
I hate slips.. i am uneasy with them.... But you need to learn them for those crosswinds

And getting in over trees to short fields. And dumping altitude without going supersonic or floating to the edge of the earth. And for that whole engine out landing one shot deal you may get one of these days.

Figure out why you hate them and do something about it until they're your friend.

Same goes for stalls.

Just IMO.
 
I love FORWARD slips, really dislike side slips. I usually foward slip, kick out the crab and land. The only time I've had trouble was one real windy day doing an ILS after "breaking out" (from under the hood) my usual technique of crabbing and adding rudder didn't work. I just plain ran out of rudder to hold the center line.

After that experience, I've started to use the side slip more to gain proficiency.
 
** bump October 2007 **

Some aircraft are placarded against forward slips with full flaps (I have been told a C-172 would be an example, which is an aircraft I have never flown) and some are not (Arrow for example). What is the reasoning behind this?

I have been told that it is due to the flaps interfering with air-flow over the rudder when in a slip in the C-172. Would this hold true for all over/high wings?
 
** bump October 2007 **

Some aircraft are placarded against forward slips with full flaps (I have been told a C-172 would be an example, which is an aircraft I have never flown) and some are not (Arrow for example). What is the reasoning behind this?

I can categorically state that there is not a general prohibition against forward slips in the C-172. IIRC, there were a few models (maybe only one?) that had a placard instructing one to avoid slips with full flaps because in some instances oscillations could result. Not a prohibition. They were relatively benign, IIRC. Our very own test pilot Jesse had done some research on this. Perhaps he would care to comment?
 
** bump October 2007 **

Some aircraft are placarded against forward slips with full flaps (I have been told a C-172 would be an example, which is an aircraft I have never flown) and some are not (Arrow for example). What is the reasoning behind this?

I have been told that it is due to the flaps interfering with air-flow over the rudder when in a slip in the C-172. Would this hold true for all over/high wings?

I'm amazed--- it took 28 posts before the 'C172 "no slips with flaps" canard' dropped out of the blue.
In the past this would have been in one of the first five posts!!!
 
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I can categorically state that there is not a general prohibition against forward slips in the C-172. IIRC, there were a few models (maybe only one?) that had a placard instructing one to avoid slips with full flaps because in some instances oscillations could result. Not a prohibition. They were relatively benign, IIRC. Our very own test pilot Jesse had done some research on this. Perhaps he would care to comment?

Here is what the POH says for the 172L (1971):
"Slips should be avoided with flap settings greater than 30° due to a downward pitch encountered under certain combinations of airspeed, side slip angle, and center of gravity loadings."

What those combinations are, I haven't fully figured out yet.

Here is what the POH for a 172R (1990's-2000's) says:
"If flap settings greater than 20° 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 airplane."

I don't have the POH's for other models handy at the moment.

In all my hours of flying 172s, I've only experienced a pitch oscillation during a slip with flaps once, and that was in a 172R. It was a mild buffeting that I felt in the yoke more than anything, and was no big deal. IIRC I was in a pretty steep slip.

I read somewhere that the earlier models prior to the L had this pitch-down problem, but the L didn't because it had a larger dorsal fin-- even though the L-model retained this note in the POH. (This is just what I have read on the web... it may or may not be correct.) Later models have even larger dorsal fins.

Seems like the reasoning behind the notes/placards changed over the years from a pitch-down to an oscillation.
 
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Why would you even need to do a forward slip if you have 40 degrees of flaps in? those tend to get you down pretty quickly.

Bharris - 28 posts and almost two and a half years!
 
Why would you even need to do a forward slip if you have 40 degrees of flaps in? those tend to get you down pretty quickly.
Guess you've never landed at McEnnan Airport in Ypsilanti ME -- the cross-runway is 1700 feet measured from the base of the 50-plus foot tall power transmission line towers at one end to the trees at the other.:hairraise: You need everything you can do to steepen the descent over the power lines so you get down and can stop before you run into the trees.
 
I can categorically state that there is not a general prohibition against forward slips in the C-172. IIRC, there were a few models (maybe only one?) that had a placard instructing one to avoid slips with full flaps because in some instances oscillations could result. Not a prohibition. They were relatively benign, IIRC. Our very own test pilot Jesse had done some research on this. Perhaps he would care to comment?
There were some old Cessna owners handbooks (e.g., 1958 C-172 and 1959 C-175, of which I have copies) which said that slips in full-flap approaches were "prohibited." But as Cap'n Ron has truthfully noted, these old-style handbooks did not have the force of law as do the TCDS or the new-style POH.

Note that there are two different aerodynamic phenomena discussed in the context of of flaps and slips in high-wing Cessnas. During flight test Cessna engineers sometimes encountered a sudden pitch-down, and though it was elusive and hard to duplicate intentionally, they thought it worthy of a note in the handbook. That phenomenon appeared to have been eliminated by the larger dorsal fin on the C-172L. The other is the benign oscillation which sometimes occurs in later models.
 

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Why would you even need to do a forward slip if you have 40 degrees of flaps in? those tend to get you down pretty quickly.

Short fields and emergencies. I can't think of any other situation where a stabilized approach might require full flaps and a full slip.
 
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Cool! So far, we have the appropriate references from '58, '59, L, and R. I don't remember anything from S, but will check when I get home.
 
Cool! So far, we have the appropriate references from '58, '59, L, and R. I don't remember anything from S, but will check when I get home.
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 "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 172L's larger dorsal apparently solved the pitch-down issue, they kept the cautionary note in the POH because of the latter phenomenon.

The 1966 C-172F manual also said "prohibited"; the book for the 1972 C-172L (first year of the big dorsal) said "should be avoided".
 
I've felt the buffet in a full slip with full flaps in a 172R and S, but we were intentionally trying for it at altitude, and were REALLY slow. I'd never be that slow when slipping to a landing until the flare, at which point the slip is relaxed.

It's not even a scary sensation, but I can see where it might alarm a passenger.

Forward slips are a terrific manuever, for correcting a too high / too fast situation on final. In an engine out situation (single or multi), I tend to try to be a little hot on final, and then when the landing is assured, I lose the excess energy with a forward slip. Since you have lots of ways to lose energy, but no way to add it in that situation, it works well.
 
Here is what the POH says for the 172L (1971):
"Slips should be avoided with flap settings greater than 30° due to a downward pitch encountered under certain combinations of airspeed, side slip angle, and center of gravity loadings."

What those combinations are, I haven't fully figured out yet.

Speaking of "L," here's my C-172L 'Hawk landing on #25 Wiscasset, ME. Several years ago the airport, in a survey by AOPA Pilot, was rated the 3rd worst crosswinds airport(the worst was somewhere in the Hawaii chain).

HR
 

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Power lines, trees, and -- well, no crosswind on this final -- but nearly the all-around ideal
training environment. (Wiscasset, Maine)

HR
 

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