Slipping with Flaps

[Bruce Fenstermacher]

OMG! Why is the windshield full of mother earth instead of runway? How did all that stuff from the rear get up here under the panel and windshield? S.O.B.! This is a p--s poor place to be!

Had I been twenty feet lower at the start if this maneuver, I would not be telling about it now.

Thanks BL. How fortunate for us you had those twenty feet and that you are here to pass on first hand experience.

[daedaluscan]

Charlie, 20 degrees and a slip should be OK. The warning is against a full flap slip.

Good, that was my feeling , and I usually do this with plenty of altitude to get myself onto the approach I want, often on base.

Flying into my little home base (1700ft runway) after learning to fly at Victoria (7,000ft) I found myself REALLY high yesterday and after the "should I slip?" thought went through my head (I had 40° flaps) I just added power and went around. Most relaxing.

[cessna170bdriver]

This is making sense to me now.

If the horizontal stab was to be completely blanked out it makes sense that the nose would 'flop down'.
It would depend greatly on the AOA and configuration when entering the slip to get it 'just right' to nullify the entier tail at once.
Else, you'd just get the soft feeling described (or the slight bobbing I mentioned) as the tail would only by partially obscured.

But if you did null the tail, it makes complete sense for the plane to pivot around the center of lift as the center of gravity is forward of that. Arguably, the more forward the CG is from the CL, the more dramatic the effect would be.

The pivot point would be at the center of lift which is very different from a traditional stall.
In a wing stall, the wing falls thru the air as the nose drops to re-establishes the right AOA.
In a tail stall, the wing is still flying. There wouldn't be a 'fall' but rather a see-saw pivot.

Would be interesting to do some wind tunnel tests or model it in software.

wow.

Actually, while in flight the pivot point (for roll and yaw as well as pitch) is always the center of gravity. Normally the center of lift lives right at the center of gravity resulting in zero pitch rate. When the horizontal stab and elevator lose effectiveness the center of lift moves aft, providing the torque to pitch the aiplane down. I made exactly the same mistake Dick did early in my ownership of '98C and what surprised me the most was how quickly it happened. Another few feet lower, and I wouldn't be here to tell the tale either. Also like Dick, I took a closer look at the owner's manual and found this:

The flaps on the 170 allow steep, well controlled approaches making slips unnecessary. Slips with full flaps are to be avoided because if the slip is extreme enough at a relatively high airspeed, the airflow is disrupted over the tail surface resulting in a sudden and steep, downward pitch of the nose.

Not exactly a prohibition but MUCH stronger than a "recommendation". Note that the italics are not mine, but appear in the manual for emphasis. I agree with the earlier poster who said that if you have full flaps in a B-model and are still too high on the approach, you've already screwed up enough to justify a go-around.

[ghostflyer]

I have tried slipping with flaps in 170A model and at 5000ft and NO way known will I do that again. It was just me and nearly full tanks of fuel. It was at full flaps and nose up slightly ,the ASI was a shade over 75 kts and I add the ailerons fully to the left and rudder nearly to the full right (crossed controls ) and before I knew it I was in a vertical situation . It took a long time to regain control even when controls were at neutral position. This happened so quickly ,it shocked me . I lost 1800ft . Never again.
Engine was at idle also plus a friend who used to be a test pilot for Husky ,suggested that I had entered a deep stall , I occasionally slip with no flap with no problems ,.But with the small flaps etc etc some thing is upset aerodynamically .

[LBPilot82]

I have tried slipping with flaps in 170A model and at 5000ft and NO way known will I do that again. It was just me and nearly full tanks of fuel. It was at full flaps and nose up slightly ,the ASI was a shade over 75 kts and I add the ailerons fully to the left and rudder nearly to the full right (crossed controls ) and before I knew it I was in a vertical situation . It took a long time to regain control even when controls were at neutral position. This happened so quickly ,it shocked me . I lost 1800ft . Never again.
Engine was at idle also plus a friend who used to be a test pilot for Husky ,suggested that I had entered a deep stall , I occasionally slip with no flap with no problems ,.But with the small flaps etc etc some thing is upset aerodynamically .

Well that is (disturbing) news to me. I have an A model and quite frequently use slips with full flaps. I often fly short approaches in the pattern where at 1000ft agl abeam the numbers I reduce power to idle, apply full opposite rudder and use bank and pitch to slip all the way to the numbers in a constant turn. It teaches you a very different way to control the airplane not to mention being fun. I have tested this full slip many times at altitude and never had a problem, and when done in the pattern I never get below about 75mph. I wonder if your "situation" was simply a stall with cross coordinated control inputs?? Very interesting and making me question my short approaches in this plane!!

[ghostflyer]

When I read what the last person wrote it sent a cold shiver down my back. However I do have a 180 hp up the front and the Cof G is more forward than a O-300 equiped aircraft. As stated by a number of people in the past every aircraft is different. however I will continue to take Mr Cessna advice. The serial no. of my aircraft is 19006.

[LBPilot82]

When I read what the last person wrote it sent a cold shiver down my back. However I do have a 180 hp up the front and the Cof G is more forward than a O-300 equiped aircraft. As stated by a number of people in the past every aircraft is different. however I will continue to take Mr Cessna advice. The serial no. of my aircraft is 19006.

Well don't let me scare you into thinking I am a reckless pilot. Remember, there is nothing against slipping a 170 or 170A. The previous post is the first I have ever heard of having any issue with slipping an A model which is why I chimed in. Was no one ever taught short approaches (slipping) to land before?? It teaches one valuable lessons in aircraft control and energy management IMO.

Hmm... I may have scared away any future students!!

[Bruce Fenstermacher]

Richard, I slip all the time with my A model with full flaps. As you and I have stated there is no warning against doing so in a '48 or A model. The flaps in these airframes are totally different than the B model in size and operation and though even less of difference the elevators are also not the same.

I have also never heard of anyone with an A model having the elevator stall such as the B model is capable. Doesn't mean it can't happen. I also wonder if Ghostflyer didn't stall the wing in his A model. Interesting he has the 180 which the B model I've encountered the stalled elevator phenomena in the most also had. I believe it also has a more forward CG.

[ghostflyer]

When the incident happened when I was testing my aircraft after the engine change , I was super aware what was happening to flight controls ,engine performance . What stunned me how quickly I lost the 1800ft before recovery. Normally in a stall you push the nose over and add power if necessary , but when it happened I had green everywhere and travelling vertical . I had control over the ailerons but nothing on the elevators.For a brief moment I thought I had dropped a wing . Final recovery was done at about 105kts indicated and I retracted the flaps . I have passed this situation over a number of "experts" and received all different answers. Adding a 180hp to a 170a makes a totally different animal. I am very cautious when flying a modified hybrid . Further testing was done at 7500ft . We only had 2issues after the modification which were the flap extension /crossed controls and very high fuel consumption . High fuel consumption has been addressed.

[canav8]

When I read what the last person wrote it sent a cold shiver down my back. However I do have a 180 hp up the front and the Cof G is more forward than a O-300 equiped aircraft. As stated by a number of people in the past every aircraft is different. however I will continue to take Mr Cessna advice. The serial no. of my aircraft is 19006.

Well don't let me scare you into thinking I am a reckless pilot. Remember, there is nothing against slipping a 170 or 170A. The previous post is the first I have ever heard of having any issue with slipping an A model which is why I chimed in. Was no one ever taught short approaches (slipping) to land before?? It teaches one valuable lessons in aircraft control and energy management IMO.

Hmm... I may have scared away any future students!!

Richard, I have flown with you. You are a good pilot. I saw you demonstrate the slip in your A model. I have no qualms with this type approach for a landing with only one big exception. A slip is used to help the pilot get in to position to land. This would only be necessary if poor planning on the approach occurred or if the high approach was intentional. A GO-Around is the safer course of action. This should be considered only as another tool in your tool bag of tricks. It should not be common practice as we discussed. The 170 B model is a different animal then the straight or the A model 170. Folks please pay attention to this. In the B model, a pilot cannot advocate a slip with full flaps as discussed because of tail plane stall not main wing stall. It is insidious and an unknown. The only known is that a tail plane stall has been known to cause loss of control in the B model. Please do not go out to be test pilots. Keep your day job.

[blueldr]

Canav8,
If you do a lot of flying in the back country, I don't believe "Poor planning" is always the only reason to have to slip with flaps extended.

[Bruce Fenstermacher]

Canav8,
If you do a lot of flying in the back country, I don't believe "Poor planning" is always the only reason to have to slip with flaps extended.

BL with the exception of the B model, I agree and I don't think that is what Doug said.

[lowNslow]

Canav8,
If you do a lot of flying in the back country, I don't believe "Poor planning" is always the only reason to have to slip with flaps extended.

Then the question is if you are performing a high drag approach due to runway length and/or obstacles - are you going to be able to takeoff?

[Bruce Fenstermacher]

Canav8,
If you do a lot of flying in the back country, I don't believe "Poor planning" is always the only reason to have to slip with flaps extended.

Then the question is if you are performing a high drag approach due to runway length and/or obstacles - are you going to be able to takeoff?

Karl this is an excellent observation. What I'd say is that one who is purposely employing a slip because the approach demands it has likely already decided they were capable of a departure. And as we already know we can land a 170 in a shorter area than we can depart, I personally, in other than a B model, would use the technique to land as short as possible thus creating more room for error on the roll or perhaps to climb out of a bulked landing. In other words I'd rather sweet the added complication of a slip to a shorter landing than perform a normal angle approach to the same length runway and sweet stopping before hitting the end of the landing area.

When I fly a B model I resign myself to the fact that a slip is not part of the bag of tricks to either correct an approach or plan for their use as part of the approach profile. In my experience with the B model this is not much of a loss because the flaps are so effective a slip with them really adds nothing to the approach.

Here is the bottom line for me and I think the message we all need to spread to every B model owner. In a B model we have been warned against slips with full flaps by the manufacturer. We have at least two first hand accounts here in the last week from members who unknowingly slipped with full flaps and found themselves in a situation they did not want to be in. It is very likely we just lost two fine folks and it is looking more and more like a full flap slip could be the cause. I'll bet there are hundreds of close calls and many more that did not survive we don't know about.

I never, other than at safe altitude for demonstration of this effect, slipped my B with full flaps and I never plan to do to purposely do so. I don't think many would plan inverted flight in their 170B and I put full flap slips in the same category.

[LBPilot82]

I'm with Doug that practicing slipping may not be something that we should practice all the time, but it should be something practiced IF your plane can do so. I have lots of time teaching in 172's, 182's and 206's where slipping with flaps is not recommended just as with our B models. But what happens when you find yourself with a flap malfunction and need to slip without flaps? Of course, this is much more likely in a 172 with electric flaps than with our cable system. Either way, those flying with 170B's or 172 should be proficient at slipping with no flaps. If you have an airplane that CAN slip with flaps, you'd better be comfortable with doing so. What about if your engine fails and you need to get into a tight spot? I would rather use a slipping short approach technique than set up a longer approach and hope I can make the runway if the winds change. When I taught tailwheel in Supercubs, I always made full flap short approaches part of the training. I think that any training you can get, even if you think you will never use it, may be worth the time one day.