Can a B Model be slipped at a less than 40 degree?

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Bruce Fenstermacher
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Re: Can a B Model be slipped at a less than 40 degree?

Post by Bruce Fenstermacher »

The final determination by the NTSB was that the main wing was stalled and a spin entered which caused the impact. The NTSB could not determine why the wing was stalled.

In personal off record conversations I had with the lead investigator about the phenomena we know about with full flap slips, along with the investigators own personal experience he under took to understand it, he said a slip with full flaps and resulting elevator stall is a plausible reason a pilot would pull back on the yoke into a secondary stall of the main wing with the ensuing spin entry. In other words the glove fits. The NTST just couldn't prove it and therefor could not report it.
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n2582d
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Re: Can a B Model be slipped at a less than 40 degree?

Post by n2582d »

gahorn wrote:The pilot was not inexperienced. He was a rated SEL airplane and certificated sailplane pilot. In fact, the fatal flight was a return-flight from a day of soaring. Sailplanes are often slipped on final approach to quickly lose altitude for landing. No one has any recollection of ever discussing the B-model restriction with him, and that's what makes this so disturbing to those of us who knew him and his wife. We often wonder "why.. WHY didn't we discuss this flight-characteristic with new Members so that everyone would KNOW?"
George, He was well aware of the restriction of slipping with flaps. You can PM for more details if you're interested. I think you've hit the nail on the head with regards to this accident. First -- fatigue: "... the fatal flight was a return-flight from a day of soaring." and "The toxicological study detected the only drug in the pilot's system was Tylenol." I've never been in a sailplane (always wanted to get the rating) but I'm beat after a full day of flying. The Tylenol in his system indicates to me that he was too. Second -- flying multiple aircraft types. In this case on the same day. Being tired and high on the approach he absentmindedly reverted to what he had been doing all day. A friend of mine on the island of Papua landed a C-185 on a river. Trouble is the wheels rather than the floats were on this day. Fatigue was also a player here. Another example of this occurred in my then recently restored 1941 BF12-65 Taylorcraft. I invited a very senior 747 captain to take the left seat which was the only seat with the heel brakes. Being a former crop duster he had tailwheel experience although he was not current in tailwheel aircraft. Taxiing out to the runway we kept going straight where the taxiway curved right. His left hand couldn't find the steering tiller.
ghostflyer wrote:Maybe a half page article in our news letter warning people of the issues with slipping and flap deployment. Showing photo and report .
The Association is to be commended for adding a no slipping with flaps warning in the 170 News magazine. But I still hear of highly experienced pilots who are unaware of this admonition. In the early '80s I checked out in a 170 and an L-19. I don't recall being told not to slip with flaps. Could be I've just forgotten the warning over the years. So in addition to an article in the newsletter I think a permanent "sticky" entry at the top of this forum would be helpful. Provide links to the various threads on this subject. A link to cracks found on the vertical stab attach fittings might also be warranted.
Gary
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Re: Can a B Model be slipped at a less than 40 degree?

Post by GAHorn »

Watkinsnv wrote:Now on cross wind landings wing low opposite rudder up to 30 degrees of rudder. Technically a slip. How many people use this technique. On a calm day or light winds I always use 40 degrees of flaps. I never crab into the wind and try to kick it out like a tricycle gear aircraft. I think its normal to us flaps on landing. I haven't heard a response to cross winds and use of flaps. except some say they like to make wheel landings others full stall landings and get the tail wheel down. I think a crab approach leaves you to greater chance of large loads put on the main gear and ground looping. But the approach is what I'd like to hear more of please.
Cessna test pilot and author WD Thompson addressed that issue when he wrote "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."
It is also well to note that during landing flare the airplane is operating in ground-effect with considerably different reaction to relative wind. The downwash caused by deployed flaps "flattens-out" above the runway approximately at 1/2 the height of the wing span (almost 20' AGL/HAT), so the downwash has less effect for the tail to see at that height.

hilltop170 wrote:Later Cessnas had the max flap position reduced to 30 degrees and there is no restriction to slipping with flaps in the POH. So it is probably safe to assume that "real test pilots" have made that determination.
Yes, of course. But it's important to recognize that many additional changes to the aircraft had been made before they dropped the warning. The 172 is not the 170.
The 172 has larger effective tail surfaces (than a 170) and still reacted badly to slips with flaps deployed. The worst behavior was always related to 40-degrees of flaps, but lesser amounts also had the potential to introduce a rapid, pitch-down oscillation.

The warning against slips with flaps deployed continued until the 1972 model 172-L which, by that time had much modified tail surfaces as well as a much longer dorsal fin to prevent the associated tendency to spin. The leading edges of the horiz stab were re-shaped also, and eventually the flaps were reduced to max deflection of 30-degrees (172-Q model) to get rid of the warning. I think it's important to recognize that just because the 172-Q did not carry such a warning with 30-degree flaps should NOT be interpreted as to apply to the 170 airplane (with it's shorter dorsal and smaller tail surfaces.) The 170 and 172-Q are very different airplanes and the Q-model's handling characteristics are not transferrable to the 170.

(As Bruce mentioned earlier, the 30-degree reduced flap setting had other benefits as well that are not applicable to the 170 series of course... The reduction meant that flaps which failed to retract in a go-around gave less penalty in rejected-landing climb requirements so the gross weight of the 172 was enabled to be raised. Another obstacle to the gross wt increase was the rear doorpost strength that had been lessened with the Omni-vision models became less of a concern with less stress applied by the flap extension limit reduction which also helped facilitate the wt increase.)
Surely no one will suggest that operating a 170B with less than 40 degrees flaps allows a gross wt increase. Neither should other characteristics of later airplanes be imparted to the 170.
'53 B-model N146YS SN:25713
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Re: Can a B Model be slipped at a less than 40 degree?

Post by lowNslow »

c170b53 wrote:I rarely use more than 20, am I a bad pilot? I'm of the mind that at that setting a go-around might be easier so I've become accustomed to using that.
I still see this couple in my mind as if they were still with us. and I find the picture of their crumpled plane disturbing.
Ghost flyer, the belief (I believe) is that the plane came straight down through the trees
There is only a 2mph difference in stall speed between 20 and 40 degrees flap so really very little change in approach speed. The last two notches of flap are mainly for drag management, so if your flying good stable approaches at 20 flap your doing great. There are only a few times I use 40 flaps, too high on approach (i.e. piss poor planning) or an approach over an obstacle at the end of the runway.
Karl
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Re: Can a B Model be slipped at a less than 40 degree?

Post by ghostflyer »

A big thank you to ALL members who had their input into this conversation and high lighted a issue that the FAA should have made known to all aviators with Cessna 100 series. While we "sometimes" didn't agree on little issues at least the subject was instilled into our minds of the dangers of slipping with flaps. I will be having a number of signs/stickers warning of this situation made up and placed in cockpits of my clients aircraft that are applicable .
Now we can all go away and have a beer . Well a cup of tea for me anyway.

I have learnt a lot now on this problem.
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Re: Can a B Model be slipped at a less than 40 degree?

Post by gfeher »

The day before yesterday, I was walking back to my hangar and looked up to see an early C-150 on short final with full 40 deg flaps down. Then he throws it into a pretty good slip at the end to lose some altitude. He straightened it out just before the flare, so he was way too low the entire time to recover from any problem. I don't know if the C-150 has the same problem or to the same degree, but given that I'd been following this thread, it sure made me uncomfortable to watch the whole thing.
Gene Feher
Argyle (1C3), NY
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n2582d
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Re: Can a B Model be slipped at a less than 40 degree?

Post by n2582d »

Harry Clements, a test pilot and engineer with Cessna in the '50s, writes about flight testing the 170C:
As usual, I don't remember if the 170C prototype was flown through certification, but I don't think that was completed. If it was, I wasn't the pilot. But I did get to fly certain configuration proving tests on the 170C some time during its existence. One of those was that of the infamous landing approach “tuck under” experienced on 170's with flaps down, full rudder applied and then diving the airplane, which resulted in a substantial pitch down – which would be dangerous if close to the ground. I had never experienced it, and we didn't understand what caused it, so it was decided to see if the 170C's squared tail prevented it. I entered the situation as described and dived the airplane to flaps down maximum speed. Nothing happened and I thought we might have escaped it with the 170C tail configuration. My boss, who was the observer and had experienced the tuck, said I had to dive even faster, and when I got about 20 mph higher than flaps down max speed the tuck occurred – so the 170C was no different than other 170 models in this respect. I thought the conditions at which it occurred were extreme and could and should be avoided, but in a separate later conversation I learned that one of our test pilots, flying a 170, had flown past the end of a field he wanted to land at, so did an abrupt turn and steep slip approach and encountered the tuck. He escaped harm, but I was shown that the event could happen with even an experienced professional pilot.
In personal correspondence he said, "I'll admit that exceeding the flaps down red line speed to encounter that tuck made me nervous, and we were probably at 5000 feet! I was surprised that one of my test pilot friends had encountered it during a real approach."
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Re: Can a B Model be slipped at a less than 40 degree?

Post by GAHorn »

The high speed tuck is a different matter than the slip with flaps applied.
In high speed tuck, the relative wind/downwash is exacerbated and stalls the entire horizontal, while the slip blanks half.
The high speed tuck requires violation of flaps extended speed of100mph, so it should not normally be encountered.
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Re: Can a B Model be slipped at a less than 40 degree?

Post by n2582d »

George, I respectfully disagree. You've been flying jets too long -- he's not talking about mach tuck. :lol: I think when he is talking about "tuck under" he is referring to slipping with the flaps deployed. He said, "One of those was that of the infamous landing approach “tuck under” experienced on 170's with flaps down, full rudder applied and then diving the airplane, which resulted in a substantial pitch down – which would be dangerous if close to the ground." From his quote I get the impression they were surprised this "tuck under" could happen even at lower approach speeds when slipping with full flaps.

It is interesting that the Owners Manual, when cautioning against slipping with full flaps, talks about "a relatively high airspeed":
The flaps on the 170B 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.
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Re: Can a B Model be slipped at a less than 40 degree?

Post by Bruce Fenstermacher »

Gary, I never noticed that reference to "relatively high speed" before. Or maybe I forgot. :(
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Re: Can a B Model be slipped at a less than 40 degree?

Post by n2582d »

Yeah, that sure seems vague and unnecessary to me. What is "relatively high speed"? 80 mph? 100 mph? Why, when one of the test pilots had experienced this "tuck" during approach, would they add "relatively high speed" to the warning? A pilot might (incorrectly) think that if he slips with full flaps at "a relatively slow speed" he won't experience this "tuck".
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Re: Can a B Model be slipped at a less than 40 degree?

Post by GAHorn »

No problem at all with that comment of yours, Gary. I just read it different and had a conversation with Mort Brown about this very matter in Branson.

Is it possible that Clements was relying upon personal memory rather than documentation or notes?
When I brought the landing-flaps/slip manuever up in conversation with Mort Brown he surprised me by immediately cautioning me about exceeding the flap-speed, and went on to tell of a damaged flap experience he knew of that involved a sudden dive. I replied to him that I wasn't talking about diving faster than 100 mph... I was asking about the landing-flaps/slipping manuever, and he reflected, "Oh... well that's different.." .... hence, the comment I posted above.

It was my imagination that led me to speculate about the flap-downwash/AOA at very high speed on the horiz. stab. after reading Mr. Clements remark, as I've had that discussion with a flight test type on a different airplane which demonstrated that.

(Funny tho', that you'd be aware of the mach-tuck experience common to RED 170's...) :lol: :lol:

(Anyone curious about mach-tuck should read "Handling the Big Jets" by Davies, where he discusses swept-wing aerodynamics. Of course, straight-wing 170s/170As never suffer the problem, only the Red B-models.) :twisted:
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Re: Can a B Model be slipped at a less than 40 degree?

Post by Bruce Fenstermacher »

n2582d wrote:Yeah, that sure seems vague and unnecessary to me. What is "relatively high speed"? 80 mph? 100 mph? Why, when one of the test pilots had experienced this "tuck" during approach, would they add "relatively high speed" to the warning? A pilot might (incorrectly) think that if he slips with full flaps at "a relatively slow speed" he won't experience this "tuck".
Yes if your going to be vague, why mention it except that's the why they talked before everyone was a lawyer and law suits where common practice. Mind set of pilots was different as well. The guy who owned and trained many a pilot in my 170 over 40 years was of that mind set. He would have read that statement immediately gone to altitude and found out exactly what high speed meant. Then he'd teach his student not to exceed it OR if he felt the maneuver useful for something like say, descending through a cloud deck, he'd teach that. Different mind set. They didn't want anyone telling them what they couldn't do, they appreciated a warning for those things not obvious, that might not be smart.
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