forward slips - eeeeeeeeeeeee!

[EdFred]

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. 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.

There's an Ypsilanti, Maine too?

 

[rottydaddy]

Training for tailwheel in the Aeronca. Slips are my flaps, basically. Fortunately, I have always enjoyed slips.

Jim G

I hear you... I found it easy enough to just trim for 65 and let the Champ do its thing, but forward slips are a lot of fun in those things. Even tried it both ways- slipping out of the turn to final, then back across, just for the hell of it- on the landing in my first clip here:

http://www.pilotsofamerica.com/forum/showthread.php?t=17277


I wish I had video of some of my slipping approaches at Brown, though- they worked out better.


Enjoy that Champ time, Jim... you made the right choice!


I'm glad to see that others are a little more reluctant to sideslip- I'm still a bit of a "crabber" when it comes to crosswinds, just because I don't like to get low, slow and crossed-up that much farther from the threshold.
Straightening out of a crab over the runway scares some people, but that's just the method I prefer.

But there's nothing like a really sweet sideslipping approach when you have it set up just right and the air's not too bumpy!

Either method is as safe as the pilot's judgement is sound... no right or wrong way, really.

But for a steep, slow approach without flaps, a good forward slip helps tremendously.

 

[gprellwitz]

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".

Thanks for that quote!

And, FWIK, I checked the 172S POH and it's the same as the 172R POH. In the Normal Operating Procedures -- Landing section, it has the warning about avoiding steep slips with full flaps because of a slight tendency for elevator oscillations. It really seems, though, that the stars have to be in alignment for it to happen, and it's pretty much a non-event when it does.

 

[Lawreston]

There's an Ypsilanti, Maine too?

EdFred: I, momentarily, scratched my head when I saw that, too.

Most PoA don't know that you've landed the same route as the three photos just preceding this series. (Well, we'll forget that you approached LP whereas the NOTAM called for RP for #25).

Y'all come back now, y'heah?

HR

 

[vancamjr]

Nice to have slips in the toolbox when asked to make short approach. Gear down, full flaps, idle power, and a healthy slip...thats the stuff short approaches are made of.

 

[sierra]

we did forward slips Monday night. what a freaky feeling. no flaps at all - just slipped all the way down.

whee! fun!

it's not a big deal until you get close and have to straighten it out. then since we had no flaps...

i can't imagine having flaps that mattered (-; must be pretty different!

 

[Bill]

whee! fun!



i can't imagine having flaps that mattered (-; must be pretty different!

Wow, where you been?

 

[KennyFlys]

You use flaps when you land?

 

[c170bm]

Grant read your post with interest Thanks for your views

Unless your flying a B-52 ( or something with X-Wind landing gear that you can land in a crab} you should use the side slip landing in a X-wind, which I have done many times in A/C like B-17 and DC-7s this is the best way for the a/c, instead of tearing the rubber off LOL

There are some models of 170/172 that can become UNCONTROLABLE with full slips and FULL FLAPS I have been there and very nearly killed my self

The Western ACO removed that prohibiation from my 170BM during STC flight test , which envolved over two hundred flight test hours in the experimental Catagory quailifying the 170B with a 175 empeonage ( I appoligize for my typeing and spelling ) Please visit my Avtek Home Page


this all is regardless of what your "Test Pilot" may say

 

[jesse]

There are some models of 170/172 that can become UNCONTROLABLE with full slips and FULL FLAPS I have been there and very nearly killed my self

Which model 172 becomes uncontrollable with full slips and full flaps?

this all is regardless of what your "Test Pilot" may say

I know you don't much like me. I know you like to play the game of throwing your non-stop attacks towards me. As I've said in the past--I'm not going to play this game.

He said "test pilot" as a joke. I know I've typed numerous times on this forum that I am not a test pilot. I wouldn't make a claim that stupid. I am in no way qualified nor do I fly airplanes that need to be "tested".

Well. Too far aft is not a good thing. It tends to flatten the spin. I'm no aeronautical engineer, nor am I a test pilot with a team of engineers advising me.

The 'research' that Grant is referring to is a video I made trying to excite a Cessna 172. The video is mostly a non-stop full flap / full slip / full stall turn. I made it to show that a Cessna 172 P will not do anything exciting with full flaps while doing a full slip. I have tested this in: Cessna 172M, Cessna 172N, Cessna 172P, Cessna 172 SP. I am not saying that it's impossible--I'm saying I've never been able to make anything happen. I encourage people to safely familiarize themselves with the handling properties of their airplane first hand. From there they can make intelligent decisions on how they want to fly.

The turn you see to the left is with the following control inputs: Power off, full flaps, full right rudder, elevator full aft, almost full left aileron. After flying this configuration for awhile I flew in and out of the stall. Still nothing exciting.

http://youtube.com/watch?v=5xDxj_CRfqY

Ignore the comments. There are lots of flight sim wanna be pilot *******s out there on Youtube.

 

[poadeleted20]

There are some models of 170/172 that can become UNCONTROLABLE with full slips and FULL FLAPS

First I've heard of that. I know there is an oscillation which can occur in a 172 if slipped with flaps extended, but it is entirely controllable and can be stopped immediately by centering the ball with rudder. Perhaps this is a problem only in...

[your] 170BM ... with a 175 empeonage (sic)

...which isn't exactly what Cessna sent out the door of their factory and thus is not representative of the unmodified 170/172 fleet.

 

[SkyHog]

Don't forget, you can NEVER! EVER! Slip a 172 with full flaps.

Oh, and slipping stalls = instant death via spin.

edit: Nevermind, I guess someone beat me to it. Gotta love airplane "phobias"

 

[flyersfan31]

There are lots of flight sim wanna be pilot *******s out there on Youtube.

I don't think all those modifiers are necessary before the word "a-hole."

Slips are fun. Feels like an elevator -- down, down, down. I love 'em.

 

[flyingron]

I've slipped a 172 (N) hard with flaps lots of times. It's part of our old standard "yes, I can maintain 120 knots to the numbers" approach at Dulles. Once you get to the threshold, you go into a full rudder deflection slip and when the speed hits 110 and then 85 you move the flaps in as allowed.

I got the oscillation once, but my wife didn't even notice it happening. You don't really have to do much but take your feet of the pedals for a second.

It's not the presence of flaps that makes a difference in the efficacy of slips but the amount of vertical surface. I can slip the Navion, but it really doesn't steepen up the descent much as there just isn't that much drag added. Of course, if you're approach requires a steeper descent than full flaps and gear down in the Navion, you'd probably ought to go around.

 

[tonycondon]

It's not the presence of flaps that makes a difference in the efficacy of slips but the amount of vertical surface. I can slip the Navion, but it really doesn't steepen up the descent much as there just isn't that much drag added. Of course, if you're approach requires a steeper descent than full flaps and gear down in the Navion, you'd probably ought to go around.

excellent point. modern gliders, with their pod and boom designs, have fairly ineffective slips, however they are equipped with powerfu airbrakes. Old gliders, like mine, with large side areas in the empennage have highly effective slips, and relatively weak airbrakes.

 

[Upandout]

I'm glad I read all of this. I saw the placard on the 172N I rent and never pressed for more information about it, and none of the instructors I flew with made a point of demonstrating it to me. Now I have something to try out next time I go up.

 

[poadeleted20]

I'm glad I read all of this. I saw the placard on the 172N I rent and never pressed for more information about it, and none of the instructors I flew with made a point of demonstrating it to me. Now I have something to try out next time I go up.

Just remember -- if something weird happens while you're slipping that 172 with flaps extended, take your feet off the rudder pedals and it should stop.

 

[c170bm]

The reason is , and this is a quote from thre ACO is ther shielded and unshield rudder

My C170B had that placard I changed the Tail and during certification flights the FAA removed the need for that placard

 

[sierra]

I think slips are a hoot in the grummie. Didn't like 'em much in the cessna, but I'm not really sure, in retrospect, if that was because i had like NO time in the cessna and a lot of time in the grumman and by then was more comfortable with flying in general.

my son didn't like it much when i realized once, on a x-country with really hot tailwind (ever see a traveler do 160kts?) that i had to lose some altitude or i'd be landing in the next state. I said, say, has your instructor done slips with you? and proceeded to demonstrate (great way to lose altitude LOL). He said it was the worst feeling he'd ever had in an airplane.

 

[rottydaddy]

Just remember -- if something weird happens while you're slipping that 172 with flaps extended, take your feet off the rudder pedals and it should stop.

I'd also recommend trying it at altitude, just as you should have been taught to glide with the plane "dirtied- up" in the first place... short final is no place for experiments.
Me, I've never investigated full slips with full flaps in 172s, but I've done plenty with 2 notches out, and never noticed anything odd except the "why am I slipping when I have flaps out?" feeling...

 

[poadeleted20]

I'd also recommend trying it at altitude, just as you should have been taught to glide with the plane "dirtied- up" in the first place... short final is no place for experiments.

Perhaps, but I've been flying (and slipping) 172's with full flaps for nearly 40 years, and I've never experienced the oscillation, so you could spend a lot of time playing around at altitude without ever experiencing it yourself. Of course, if you've never slipped a 172 with flaps (especially full flaps), it would be wisest to try it the first time with an instructor who's done it riding shotgun.

 

[ScottM]

The reason is , and this is a quote from thre ACO is ther shielded and unshield rudder

My C170B had that placard I changed the Tail and during certification flights the FAA removed the need for that placard

I don't understand what you wrote. what is "thre ACO" and what is a "shielded and unshield rudder"?

 

[Bill Watson]

The reason has been with flaps interfering with flow over the horizontal stap. And as stated elsewhere I don't thing the 172 was ever placarded against it. Rather it was warning in the POH. Something like "avoid slips with more than 20 degrees"

** 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?

 

[Pilawt]

The reason has been with flaps interfering with flow over the horizontal stap.

Click here for a description of this phenomenon (actually two different phenomena) as described by a Cessna test pilot and aerodynamicist.

And as stated elsewhere I don't thing the 172 was ever placarded against it. Rather it was warning in the POH. Something like "avoid slips with more than 20 degrees"

Some older (at least through 1966) Cessna owners manuals actually did say "prohibited", but that was apparently not reflected in the TCDS.

Perhaps, but I've been flying (and slipping) 172's with full flaps for nearly 40 years, and I've never experienced the oscillation, so you could spend a lot of time playing around at altitude without ever experiencing it yourself.

I've felt the mild oscillation a couple of times, no biggie; but never the sudden pitch-down. Cessna engineers said that phenomenon was "elusive and hard to duplicate," but they thought they should mention it in the handbooks anyway. Sparky Imeson (in his book, Taildragger Tactics) says he's demonstrated hundreds of full-flap slips to students and only had the sudden pitch-down happen a couple of times.

 

[Upandout]

I'd also recommend trying it at altitude, just as you should have been taught to glide with the plane "dirtied- up" in the first place... short final is no place for experiments.
Me, I've never investigated full slips with full flaps in 172s, but I've done plenty with 2 notches out, and never noticed anything odd except the "why am I slipping when I have flaps out?" feeling...

Yeah, I meant at altitude. Since that plane has 40 deg of flaps I haven't had much need to steepen up the approach anymore than that, and with just me in there it stalls somewhere south of 50 anyway.

Thanks for trying to keep me out of the weeds