NTSB Final Report: Bruce and Kathy Rymes accident

[Bruce Fenstermacher]

Is the Horizontal Stab stalled or is it blanked out by the wing?

The elevator stops making down pressure keeping the nose up, because no, or not enough, air passes over the surface. Technically probably not a stall but the result is the same.

[johneeb]

Is the Horizontal Stab stalled or is it blanked out by the wing?

The elevator stops making down pressure keeping the nose up, because no, or not enough, air passes over the surface. Technically probably not a stall but the result is the same.

Don't these incidents involve a spin? Will an airplane that has only stalled it Horizontal go into a spin?

[bagarre]

It may only be that the impact has the characteristics of a spin. ie: evidence of rotation on impact.
If the plane is placed in a forward slip, it's already sideways to forward travel and uncoordinated. If the tail stops producing sufficient down force (a better description than stalled) and the airplane pitches forward about it's center of lift, it's reasonable that the plane would begin to rotate from the side load of the slip. Also, who knows what input the pilot might make in such an event but if the wing doesn't stall, the plane wont spin but the slip may make it rotate and look like a spin on impact.

Another thought, if the plane pitches down that abruptly, what's going on with the angle of attack on the wing? It's possible that it DID stall if the AOA went over the top of the chord line. Not the stall we think of but there is still forward momentum to deal with. The wing wouldn't be 'flying' straight down the moment after the pitch. It's possible to stall the wing with forward stick and enough forward stick may replicate this event.

I'm speculating.

[GAHorn]

The "stall" is not the wing.... it is the tailplane which stalls.

Consider this: When performing aerobatics, if a pilot wishes to perform a "snap roll".... he is actually inducing a horizontal spin.
First, the airplane must be induced to spin. To do this while in horizontal flight he must first stall the airplane by causing an "accelerated stall". This is done by a rapid pull-up creating additional wing loading, which necessarily also creates increased wake behind the wing.
While the airplane experiences the accelerated-stall, the pilot induces a "yaw" by application of rudder, which speeds up one wing while slowing the other, creating un-even lift between the two wings. The increased lift of one wing causes the airplane to rotate about the longitudinal axis....which occurs very quickly due to the fact the airplane is moving thru the air faster than it might in an ordinary stall. This is what we call a "snap roll".

As for the full-flap/slip phenomena:....
...Since the tailplane (horizontal stabilizer) produces lift in the downward direction (thereby keeping the nose up and the wing at an ordinary angle of attack to produce sufficient lift to support the airplane.... If the airplane is slipped, (banked in one direction while opposite rudder is applied to prevent a turn)... then the fuselage will partially blank out the downwind elevator and horiz. stab. thereby reducing it's effectiveness.

Add to this the downwash of the large B-model flaps (which is immediately in front of the horiz. stab. leading edge) and effectively the stab has suddenly experienced an increase in angle of attack. (Think of it this way: The stab is an upside-down wing. The downwash of the flaps is an upward motion of the relative wind for the stab,... similar to the upward relative wind in front of a wing nearing a stall.)
Now, ... add sufficient forward speed (due to the increased rate of descent imparted by the slip) and the downwash/wake of the flaps stalls the stab.... and the downward-lift of the tail is suddenly lost. NOW the nose will plummet.

On top of all that ...the pilot (in order to prevent a turning-moment during the slip) has applied rudder in the opposite direction of the bank provided by the slip. When the nose plummets...the pilot pulls aft/up on the elevator....while that rudder is still applied. IN other words, the pilot has simultaneously applied bank in one direction while applying rudder in the opposite direction, and when the nose drops he pulls back! (Can you say "snap roll"?) .....while pointed DOWN?

[blueldr]

Very shortly after I had bought my first C-170B, I inadvertantly discovered this tail stalling phenomenon. I had enough experience that there was really no reason to thoroughly read the small owners manual. It was really made for relatively uninformed private pilots and I was, after all, an ATP with vast experience.
The occasion occurred on final approach at Cameron Park Airport near my home here in California. I was a little high coming in with full flaps and saw that a vigorous slip was just what was called for to nail it on the numbers. Very fortunately, I had just enough altitude left to save my ignorant ass, Suddenly the loose stuff in the back was up on the glare shield and I rcovered about an inch and a quarter above old mother earth. Boy, I want to tell you that it will really tighten up the old draw string in a hurry! As a last resort, "read the manual". Especially that little part about slipping with full flaps in a C-170B. There are simply no words capable of explaining how vigorous that pitch down can be.
I think it behooves all C-170B pilots to purposely experience this at a safe altitude.

[hilltop170]

BL-
Was there rotation associated with your event or did it just pitch down going straight? I have never been able to duplicate it.

[SteveF]

My experience and blueldr's are similar but his ability to add color and eloquence to a story is fantastic. Nice job BL !!

In my case the slip was not massive but a light to moderate opposite rudder in the left nose down turn. I was busy but I think that when I stood on the rudder peddles I neutralized the rudder and probably the ailerons also. As I remember it the wings were not in a turn but neutral, neither one down more than the other as it recovered.

[blueldr]

Richard,
In my incident there was NO rotation at all. It was simply a severely vicious pitch down. In view of the difference of the flap systems between the A and B models of the C-170, I do not believe this could be induced in an A model airplane.

[Bruce Fenstermacher]

My personal experience with this phenomena is one of demonstration only. Hence we did not wait for the nose to point down and we did the demonstration at what we considered a safe altitude though the first time it was demonstrated to me, we probably were not high enough.

My friend Dan was the demonstration pilot. One time we were high on approach and I said why don't you slip it in and he said no you don't want to do that. We then climbed to a 1000 ft and he demonstrated how in a full flap forward slip, the elevator would go limp. He said the next step was looking straight down. I'm thinking he experienced this personally.

You see Dan's instructor was of BL's era. The old days. You jumped into an aircraft that was designed in months, built in days with a life expectancy of hours. The flight manual was something you used to swat fly's on the windscreen. And should that fly splat on that warning not to slip with full flaps, and you took notice of it, why by golly you where going to go right on up in the air and explore this. After all it could be something for your bag of tricks should you need it and worse case you might find out you never want to do that again.

What I could tell from Dan was they discovered it was not something you wanted to do on approach. In fact it had very little useful purpose unless you where being shot at and needed to go straight down now. But he and others with "experience" who have experienced this, don't fear the phenomena and feel it gives adequate warning and is controllable, IF you know what to look for AND you detect it. That is one big IF and a bigger AND. I've heard the opinion one can apply full flap and then induce a slip to a point just prior to limp elevator and feather rudder to keep elevator control. I do not subscribe to the opinion this is a smart idea.

I have duplicated this to the point of a limp elevator for my own education. What is a limp elevator you ask. Get in your B model on the ground, engine off. Pull the elevator full aft then push full down. That is a limp elevator and what the elevator will feel like, at least for a second before your looking at the ground. I have demonstrated this to myself to the point that I pulled and pushed the elevator rapidly about 1" or 2" from neutral without the fuselage reacting in pitch. There is no aerodynamic feed back or heaviness on the elevator thus it is limp. Perhaps because I knew what I was looking for and did not push or pull the elevator further is why I did not pitch down. I also immediately released the rudder and the slip.

I have done this in my first 170 which was essentially a stock B model. I did it with wings stock and then again with VGs installed. It is important to note that the VG kit for the 170 includes VGs for the elevator. With the VGs it was much much more difficult to demonstrate a limp elevator. In fact I stopped trying to do it as I did not want to find out that the warning of the elevator going limp just prior to nose down was gone and the plane would simply point straight down. My test pilot button was pegged.

I do not recommend full flap slips with VGs, I only report my experience which is that the VG kit, likely because of the VGs on the elevator, seem to delay the phenomina. I'm not in anyway suggesting the VGs remove it.

IF YOUR ELEVATOR EVER GOES LIMP AT ANY TIME, GET YOUR FEET OFF THE RUDDER.

I personally put slips out of my mind for any amount of flaps. I just didn't do it and I really like to slip. It just was not necessary with the flap authority you have. If you are high in a B model and you have full flaps in I suggest you either go around or maybe push the nose straight over to a higher decent angle. You will not gain that much speed and at no time will you lose the ability to go around should you ultimately decide that is the best course of action.

[hilltop170]

Richard,
In my incident there was NO rotation at all. It was simply a severely vicious pitch down. In view of the difference of the flap systems between the A and B models of the C-170, I do not believe this could be induced in an A model airplane.

I agree Dick, the A Model can be safely stalled and spun with any degree of flaps without fear of loss of control, I have done hundreds of them, flaps up, flaps down, right, left, power on, power off, everything but inverted, I'm not THAT crazy! I flew with and talked with Gene Beggs from Odessa, Texas back in the 1980s. Gene was doing a bunch of spin research in his Pitts S1 at the time and wrote a very informative article on the subject. Based on his work, I got really interested in spins and practiced them frequently in the 170A. I was surprised a few times but never got scared with any of the spin characteristics of the A Model.

What I was referring to in my comment was I have never been able to get the slip-with-full-flap/pitch-down effect in any Cessna with 40degrees flaps. Maybe I have done it wrong but I've tried in 170Bs, 172s, 182s, 180s, and 185s. The later 172s and 182s obviously won't do it because flap travel was limited to 30degrees.

[blueldr]

Bob Dentice, the guy who had a C-170B with a C-175 tail grafted on to it, said that the Modification eliminated the horizontal stadilator stall completely. I have never flown that airplane, buy I sure as hell wouldn't try it down low.

[Kyle Wolfe]

A recent article in case you had not seen...
(broken link follows)
http://www.sportaviationonline.org/spor ... pg=10#pg90

[falco]

This was mostly just a rehash of the NTSB report with not much else added. In his conclusion I didn't think that he gave anywhere near enough emphasis to the tailplane stall and still wonders how the wing could stall at that speed. He also doesn't seem to realize that the best source of knowledge about old aircraft is the type clubs not the FAA or NTSB.

The message from this article seemed to be "we don't really know what happened." The message should have been a loud an clear "DONT SLIP A 170B WITH THE FLAPS ALL THE WAY DOWN", followed by "consult with your type club -- the people who really understand how to operate your airplane"

RIP Bruce and Kathy.

Fly Safe

Pete

[DaveF]

The message from this article seemed to be "we don't really know what happened." The message should have been a loud an clear "DONT SLIP A 170B WITH THE FLAPS ALL THE WAY DOWN", followed by "consult with your type club -- the people who really understand how to operate your airplane"

That's exactly what I told Mac in August when the piece was first posted. I told him he missed a good opportunity to pass along an important message. He replied that he wasn't at liberty to suggest any probable cause beyond what the NTSB said. But that's pretty lame, because he's a columnist; his job is to have opinions. I think the real reason is that he doesn't understand the problem of slipping with full flaps at low altitude. He really thinks this was a stall accident.

[n3833v]

This is one reason it is a plus to belong to a TYPE club for all the information supplied through books, flyers and forums. This is why I believe strongly in belonging to the Cessna 170 Assoc for all the information that is discussed here and at the Convention seminars. In my opinion this also makes us better pilots to be aware of unique situations that arise in flight.
It is always a pleasure to read others experiences.

Thanks all,
John