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

D_C71

D_C71

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D_C
When I began initial flight training, before I was solo'ed, my instructor taught me forward-slips as another tool during approach to landing.

The training aircraft was a Cessna 152. When I later transitioned to a 1973 Cessna 172 for Instrument instruction, (though not a part of instrument instruction) forward-slips with flaps were still Ok per my instructor in this aircraft.

I didn't fly from mid-April 2006 'til August 2007, but when I did (at another flight school) I was told that Forward-Slips with Partial or particularly Full-Flaps applied, were unsafe in Cessna 172's.

In May of 2008 (during my Tailwheel-Endorsement and Instrument Proficiency Check to re-establish my Instrument currency training - C-170B and C-172) I encountered two more CFI's at another flight school (in Fullerton, CA) that prohibited Forward-Slips with Flaps as well (said it was unsafe.)

I looked this up recently on AOPA's website and found numerous articles, both Pro and Con, regarding Forward-Slips with Flaps and Cessna light, high-wing aircraft.

They acknowledged the earlier placarding advised against the practice, but said it was NOT an outright Prohibition.

The advocates of the practice say the risks of inadvertent stall, spin, etc, are exaggerated.

Forward-Slips are taught and demonstrated during Private and Commercial practical tests (checkrides) upon request of the FAA designated examiner.

In practice, I used to use the FS technique frequently and never experienced any problems, but perhaps I was just lucky?

I would really like to keep this tool available in my repertoire, but not if it is truly unsafe. If it is (basically safe) what "Proof" do I supply to an Instructor I meet to convince him/her that it IS safe in a Cessna?

I printed out the AOPA articles, this being one of the more recent:
http://www.aopa.org/members/ftmag/article.cfm?article=7591

Depending on the model-year, there is often literature in the POH on the subject.

Oh well, what are your thoughts/opinions on the subject?
 
they're fine. there is a chance that with full flaps and the proper loading condition you could blank out some of the flow over the tail, creating an annoying slight buffet. I had this happen to me last week in a 172. the yoke just bobbed in and out slightly. flight control was not compromised.

your latest instructors dont understand the difference between avoid and prohibit. you're right, the forward slip is a great tool and I would recommend staying sharp on them. In a 40deg flap cessna with a forward slip, you can really make a nice, steep, safe approach.
 
Unless someone can show a placard to me that says "prohibited" instead of "avoid" then I say no.

This is actually a big pet peeve of mine regarding instructors, because most people don't really understand the point behind the limitation, and if you're a CFI and you freak on someone for slipping with full flaps in a 172 of ANY year, you don't deserve to have your ticket.
 
D_C71 said:
Oh well, what are your thoughts/opinions on the subject?
Click to expand...

Welcome to the Can of Worms Hotline!

Anyway, welcome to the board -- you'll get lots of responses, but will still have to come to your own conclusions.

It's true that many Cessna POH's specifically warn against slips exceeding 30 seconds duration with flaps extended. The most logical reasons I've heard have been fuel unporting and tail blanketing (airflow disturbance causing loss of effectiveness of the horizontal stabilizer).

Yet, many of us have slipped C152s/172s/205s longer than 30 seconds and have lived to slip again.

I admit there are few manuevers more useful than a well-executed slip. On an older Cessna with 40 degrees of flaps, you can lose some serious altitude in a very short distance.

A valid question for folks who need to slip for longer than 30 seconds is "why?"

If you're that high on final, maybe you need to work on something other than slips.
 
It's not truly unsafe. Without getting overly technical, in certain configurations there is a tendency for the rudder to be blanketed in a full flap slip, causing a momentary oscillation that if watched for, is easily correctable.

I've done full flap slips, including full flap crosswind landings, and have never even detected the oscillation.

btw, there are a few 172 models in which the advisory is arguable a limitation, in which "not recommended" is "prohibited". As I recall, the 172G is one of those.
 
midlifeflyer said:
btw, there are a few 172 models in which the advisory is arguable a limitation, in which "not recommended" is "prohibited". As I recall, the 172G is one of those.
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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...
 
btw, for the usenet refugees, remember the slips with flaps T-shirt? I still have mine.
 
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.
 
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Hello, Can of Worms Hotline? This is JimBob, what do you think about this:

I had a CFI tell me during a checkout ride not to do slips with flaps in a 182RG because the "Extra pressure on the low-wing flap could cause it to break, which would throw the airplane out of control."
 
CJones said:
Hello, Can of Worms Hotline? This is JimBob, what do you think about this:

I had a "Chief CFI" tell me during a checkout ride not to do slips with flaps in a 182RG because the "Extra pressure on the low-wing flap could cause it to break, which would throw the airplane out of control."
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LOL! That's awesome.

BTW, after hearing shirt, I'm totally having an "I slip Cessnas with flaps" shirt made.
 
yep - though I never did get one (I haven't flown a C-172 since the early 90's).
 
Tom-D said:
Cessna says "AVIOD" 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.
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That must be why Piper does not mention it then. Low wing pilots are more skilled the high wingers!!







Well if we are gonna have one open can of worms why not two? ;)
 
CJones said:
I had a CFI tell me during a checkout ride not to do slips with flaps in a 182RG because the "Extra pressure on the low-wing flap could cause it to break, which would throw the airplane out of control."
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same guy told me that too. i dont listen very well, either. :)
 
smigaldi said:
That must be why Piper does not mention it then. Low wing pilots are more skilled the high wingers!!

Well if we are gonna have one open can of worms why not two? ;)
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Yeah, but the passengers can enplane without getting rained on in a high-wing airplane....

canofworms1.jpg
 
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I'll give a slightly different take on it. As I understand it the newer (post early to mid 70's) 172's may have the oscillation or vibration if slipped with full flaps as other folks have noted. The older 172's may have the nose drop if slipped with full flaps. The thought is the nose drop would get you in a bind if it happened at low level. Supposedly the later 172's had larger horizontal stabilizers which eleminated the nose drop problem. I haven't measured horizontal stabilizers to see if there is any truth to the story. Maybe Jessie or Henning know since they are the source of all info.:D

Hey, I know it must be true 'cause I read it on the internet. I haven't gone looking for a nose drop on an old 172 but I might in the near future since my hangar mate flies one. I have slipped N's & P's with full flaps and the only vibration was one CFI's face when I ignored his protests.:smile: I gave him the not prohibited line and he was such a book guy that he shut up.
 
um, these paxs, how do they stay dry before they get to the airplane?
 
bob, the pilot very carefully taxis the airplane up right next to the door. its like the red carpet treatment! :)
 
Whether it says "Prohibited" or "Avoided", except for an emergency, or maybe getting some unexpected lift on short final... or an extreme approach into a strip so short you may get into it but not out of it (LOL), I think if you are slipping with full flaps in a 172 you have already screwed up. :yesnod:

The purpose of flaps for landing is to eliminate the necessity for a forward slip. In the old days, when flaps were not ubiquitous, it was SOP to come in fairly close and high (in case the engine quit), then chop the power and fwd slip like crazy. Flaps made that largely unnecessary, although it takes some of the fun out of a short-field landing, IMHO. :D

With full flaps, yes, even 30 degrees as is the case with some models, a 172 can make a very nice, stable, steep approach, at a low rate of descent... especially if you keep the pitch angle to a minimum and use power to control descent rate. A Helio Courier it isn't, but a 172 is pretty capable in the short-field department.

Too many 172 pilots have flown final with 40 degrees of flaps at the same IAS they would fly the same approach without flaps, so they don't quite appreciate what the flaps can do for them. with 40 degrees hanging out, a 172K will stall wings-level at about 49 mph indicated.Usually less, based on my own experience. So why come in at 60-70 mph? 1.3 Vso is a good starting point, but if you're trying to make a good short-field landing over obstacles close to the threshold, you can go quite a bit slower over the fence, and it makes a big difference.

That being said... I've never seen a "prohibited" placard in a 172, but yes, they might wobble a bit if you do slip aggressively wit full flaps, and I guess that has takn some pilots by surprise.

But again, if you have full flaps out, you shouldn't need to slip to steepen your approach.
 
First, the only airplane to which this applies is the Cessna 172 series. No other Cessnas, no Pipers, no Grummans, etc.

Second, as stated in the current relevent documents, it says "Avoid." The "prohibited" language seen in some old owner's handbooks has been deleted, as has been the companion "Prohibited" placard. All it should say is "Avoid slips with flaps extended," or words very close to that.

Third, aerodynamically speaking, a slip is a slip is a slip. There is no aerodynamic or aircraft response difference between a forward slip and a side slip. The only difference is ground references. Thus, aerodynamically, whatever happens in a side slip will happen the same in a forward slip, and vice versa.

Fourth, the issue is an oscillation (not a flutter) which can develop when slipping with flaps extended. Now, I've been flying C-172's for 40 years, and slip them with flaps all the time (especially during crosswind landings), and have yet to experience this, but I understand it's possible, and have talked to maybe two or three pilots who have experienced it.

Finally, even if it happens, it's no big deal. Don't panic, don't get excited, don't do anything abrupt or crazy. If feel the oscillation, all you have to do to make it stop is center the rudder.
 
Use an umbrella.

besides, cars and airplanes don't get to mix it up at KBED

Also, my paxs can get in while the airplane is in the heated hangar.
 
rottydaddy said:
Whether it says "Prohibited" or "Avoided", except for an emergency, or maybe getting some unexpected lift on short final... or an extreme approach into a strip so short you may get into it but not out of it (LOL), I think if you are slipping with full flaps in a 172 you have already screwed up. :yesnod:
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I guess you make all your landings on runways perfectly aligned with the wind?
The purpose of flaps for landing is to eliminate the necessity for a forward slip.
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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.
In the old days, when flaps were not ubiquitous, it was SOP to come in fairly close and high (in case the engine quit), then chop the power and fwd slip like crazy. Flaps made that largely unnecessary, although it takes some of the fun out of a short-field landing, IMHO. :D
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What made that unnecessary was improved engine reliability.
Too many 172 pilots have flown final with 40 degrees of flaps at the same IAS they would fly the same approach without flaps, so they don't quite appreciate what the flaps can do for them.
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They also get to experience long floats down the runway, and usually overcontrol the flare when doing it.
 
The warning was to avoid forward slips with full flaps when C-172s were equipped with flaps that could be extended to 40 degrees. After Cessna restricted the ability to drop flaps no more than 30 degrees, the warning was discontinued for those aircraft.
 
AuntPeggy said:
The warning was to avoid forward slips with full flaps when C-172s were equipped with flaps that could be extended to 40 degrees. After Cessna restricted the ability to drop flaps no more than 30 degrees, the warning was discontinued for those aircraft.
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You still find the advisory in later 30-flap 172's.
 
I fly an "L" Model with 40° flap. They are great and I slip with them too. At my home field, there's a railroad track and a tree line right at the approach end of a downhill runway with a displaced threshold. I like to come in a bit high to give me a bit of cushion over the tracks/trees and use the 40° to give me a nice slow touchdown so I don't need to really ride too hard on the brakes to make the turnoff to the ramp. If going uphill, I use the 30° and coast to a stop. But I certainly use the slip if I need or want to. I've never felt the buffet, except at altitude as an experiment to see if I could feel it.

Runway 14/32

Dimensions: 3806 x 75 ft. / 1160 x 23 m Surface: asphalt, in good condition Weight bearing capacity: Single wheel: 20.0 Runway edge lights: medium intensity
RUNWAY 14 RUNWAY 32 Latitude: 33-36.970000N
33-36.484500N Longitude: 083-27.863833W
083-27.389000W Elevation: 636.0 ft.
694.0 ft. Gradient: 1.5%
1.5% Traffic pattern: left
right Runway heading: 145 magnetic, 141 true
325 magnetic, 321 true Displaced threshold: no
1131 ft. Markings: nonprecision, in good condition
nonprecision, in good condition Visual slope indicator: 2-light PAPI on left (3.00 degrees glide path)

Touchdown point: yes, no lights
yes, no lights Obstructions: 14 ft. trees, 270 ft. from runway, 280 ft. left of centerline, 5:1 slope to clear
 
FWIW I was told as long as you keep the nose down the FLaps won't blank out the tail.
 
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