JohnBurke

Actually, the concept is the same, but apparently it's still not well understood.

For donkey's years, ignorant instructors told students that maneuvering speed was a safety speed; any maneuvering under that speed would cause a "stall" before it would hurt the airplane. This, of course, was wrong (still is), but it was passed on in ignorance, and many plots were actually surprised when AA587 shed a tail.

The control input at or below maneuvering speed is a one-time maneuver, and only to a given acceleration loading. It's not a blank check, and it does not account for reversal.

What the rudder does on the ground is irrelevant. The problem isn't the rudder. It's the structure to which it is attached.

I grew up in cubs, slipping airplanes with abandon. It was second nature. I flew large, four engine bombers down canyons, in full slips, regularly. It was part keeping speed under control in a steep descent to a fire. Then I began doing heavy maintenance on them; C checks, and D checks, and began finding fractured attach fittings and hardware for the vertical stab...on multiple aircraft. I quit slipping big airplanes. Mostly small ones, too, as I found numerous cracked vertical stab attach brackets on small aircraft too. None of these airplanes were being operated at high speeds when the sideloads on the vertical stab occurred, but if one considers the load on that stab, given the size, repeatedly, it shouldn't be too hard to understand where those stresses are concentrated, and to imagine the cumulative effect over time.

Reversing direction with the rudder on the ground is irrelevant, as it's not causing bending and torsion on the vertical stab. In flight with an air load, it is. That's where the problem occurs.

With a control jam, pressing on the control to free the jam and a subsequent rapid movement, isn't really the concern. Reversing that input is the structural one-two punch that can lead to damage.

Rolling out? No issue at all, especially given the availability of a tiller and nosewheel steering.

2StgTurbine

Yaw dampers reduce oscillations, but they don't anticipate them. If you apply aileron in an aircraft with a yaw damper, you will get induced yaw (unless you apply it very slowly). Shortly after you apply it, the yaw damper will counter, but it isn't immediate.

Elevation

I think the issue is yaw oscillations on the ground and keeping the plane out of the mud more than structural failure due to aerodynamic loads. If you're breaking a sheer pin, say with frozen controls, you're pushing until you get proper control movement and response not full deflection.

Tangent about light planes: I slip light planes and fly aerobatics as do a lot of folks here. I think the stresses that break planes are occasionally aerodynamic but more often from poor ground handling. Pushing on vertical stabs to steer taildraggers around, for example.

Not saying you are wrong. Snap maneuvers for example are hard on tails. Slips to landing, even fast ones, I'm not so concerned about. By all means watch your planes for wear and tear. I'm always asking dumb questions so I know what to look at and what to replace/monitor. I'm just saying I wouldn't worry about slipping to land in your Cessna 120. The Drop Zone that used to fly 185s and 182s in Omro, WI used to do full slips from altitude to land, and they did it at high speed for thousands of hours. Tail bulkheads held up.

Swept empennage would make me think twice. T tail too.

I guess, after all this typing, I've actually said nothing at all.

​

JohnBurke

Ground operations and flight operations are two different things; there's no load on the vertical stab on the ground. Discussion was had about control reversals or multiple rudder inputs, which become irrelevant on the ground.

On the runway, it's largely irrelevant, too. if the rudder pedal can't be broken free, there's tiller nosewheel steering. If the rudder is pushed and goes full-scale, there's a reason that pedal input to the nosewheel is limited with regard to steering and in comparison to tiller authority. Move the rudder pedals the opposite direction and stop motion if necessary with the tiller.

So far as not discovering a stuck rudder pedal in flight; there's no surprise here. In large, transport-category turbojet airplanes, we don't touch the rudders much, if at all in flight. In many aircraft, not even at steep bank angles, such as a steep turn. Adverse yaw, turn coordination and in some aircraft asymmetric conditions are handled by the autopilot and yaw damper computers. This is both for smoothness and convenience, as well as safety of flight; the computer is far less likely to break an airplane than a pilot .

Regarding the strength of the vertical stab...I've been an instructor and mechanic for a lot of years, flying a lot of conventional gear airplanes in utility flying (aerobatics thrugh ag and fire). A lot of full-envelope, and full-control flying. I've worked on a lot of airplanes, big and small, and yes, I've done the slip from drop altitude to traffic pattern descents, beat jumpers to the ground, had the fuel flow from the low wing in steep banked, full-slip descending turns, for many, many hours...but I've also found that same kind of damage to vertical stab attach brackets and hardware on light airplanes. I flew for an operator with a large fleet of 206/207i's, and found a couple dozen cracked brackets on those airplanes, eventually replacing them with a fabricated steel bracket due to the same, repetative cracking, from slips. As before, I'm not nearly as avid a slipper as I once was, but then a lot of what I do in the cockpit has evolved since the teen years, too. Airplanes can and do break well below Va, all mythology to the contrary be damned.

As for teaching groundloops, I prefer a different approach. I teach to avoid them, and how to manage that. With the exception of parking, groundloops tend to break airplanes.

Elevation

Original Subject:
Frozen servo. Step hard. Maybe get surprise? Be careful of surprise.

Deep into light airplane tangents:
Really what we're getting at is abuse v. fatigue from normal use. I'm not prepared to sit at an EAA chapter or FBO telling starry-eyed youths that Elroy is a fool for foward-slipping his Champ. I'm also not prepared to call you a pansy for choosing not to slip a Beaver, PV-2 or whatnot.

Groundloop teaching:
Letting people get into a low speed ground loop early takes some of the fear out of them. It also introduces them to the limits of their control authority. By taking the fear out of them and giving them idea of controlability limits they're usually able to think and react a little better to swerves at higher speeds. I teach these at taxi speeds, and you talk about groundlooping to park. We actually may be doing something similar here. As with anything precautions have to be taken and awareness needs to exist to preclude breaking stuff (not in a Luscombe, watch the stress you put into the gear etc.).

JohnBurke

Not really a matter of manood or pansyhood, with regard to sideloads on big airplanes, but germane to the discussion, it doesn't take a whole lot to break off the tail, and as we all now know, a pilot can manage it at lower speeds. Having grown up in Pawnees and Ag Trucks and Air Tractors and Thrush aircraft, flying under powerlines, and all manner of Cubs, 180's, Aeronicas, 185's, 120's and 140's and so on, much as stick and rudder and seat of the pants is near and dear to the core of how I think and what I do, I don't spin airplanes any more and I don't slip...and I'm a guy that for a long time was very comfortable feeling the airplane through gear-down, full-flap slips, with full control input. Those small airplanes, 206's and 207's, we were quite sure of the cause, and the fix, and we were able to document it at the time, to the FAA's satisfaction. Ancient history, now.

Perhaps. The argument might be made that swinging the tail into a parking spot is a controlled, or incipient groundloop, though to my thinking it's little more than unlocking or swinging the tail. The groundloop represents more of a departure from control, a ground lomcovak, if one will. At taxi speed, it's quite different than at landing speeds, where it begins to drift and then snaps, and for a moment feels like a flat spin gone wrong. I don't want someone to be fearful of a groundloop, any more than they should be preoccupied with crashing when they should be flying the airplane, but I find a focus on keeping the long axis headed the same direction as travel to be most productive. To each his own. Perhaps different shades of the same can of paint.

rickair7777

In larger-ish 121 jets it seems that nobody wants you to use rudder, just let the YD take care of it. Ideally we shouldn't be banking rapidly anyway.

I keep my feet on the pedals when hand-flying but don't actually use them normally.

And my current shop places the highest emphasis on stick and rudders skills that I've since maybe turboprop days.

2StgTurbine

Well next time you depart on the Whitestone climb out of LGA, take a look at your slip indicator. If you roll slow enough to let the YD do all the work, Tower will be giving you a phone number

JohnBurke

What on earth are you flying?