The International Cessna^® 170 Association

Hello!

I’m sorry for disturbing. I am a LSA and PPL pilot and I need some advice from someone with technical knowledge on flight controls systems.

Assuming a conventional flight control system on a light airplane (cable operated, pushrods or other variation) do you figure out an internal failure causing the actuated surface to deflect and jam beyond current position? That is, is there a way to fail (bellcrank, pulley, I don’t know) in which the surface might jam to an extreme position, beyond the position that was when the failure occurred?

I figure out the only possibility is the surface jams in current position or becomes freefloating due to linkage/cable failure and in this case it returns to neutral position because of airflow acting and neutralizing the surface.

Basically, as an example, if the pilot haven’t use more than one third control deflection, can you figure out a control system failure which results in surface being jammed more beyond that position?

What do you think?

Thank you so much! I really appreciate your help.

A birdstrike to a counterbalance area of a flight control (elevator, rudder, or aileron on some aircraft) may damage the surface and cause it to deflect due to deformation.
A "balance" cable breaking in an aileron circuit might also cause it if other fouling of the cable system is involved, tho' highly unlikely, IMO.

It would take a force of some sort. One such force might be control flutter.

By Tony Bingelis wrote:
FLUTTER? WELL, SIR, flutter is what a flag does wildly on the flag pole on those days when it is too windy for you to fly. But to better relate it to our subject, it should be described as a potentially destructive vibration or buffeting of an aircraft due to an out-of-balance condition of one or more of its control surfaces.

Flutter usually results in a component departing the aircraft not getting stuck in a position beyond it's intended travel but I suppose under the right circumstance it could stick. Flutter is caused by improperly balanced control surfaces for the flight regime undertaken. In other words on a certified airplane that has been tested to certain limits to insure flutter does not occur, flying beyond those limits, VNE for example could induce flutter. Or maybe in that certified aircraft the weight of the control surface changed because of a weight shift from a mechanical failure or may be ice stuck to the surface.

But under normal circumstance on a certified aircraft I can think of no reason a control surface would be forced past its intended travel specially with so little control input.

gahorn wrote: A "balance" cable breaking in an aileron circuit might also cause it if other fouling of the cable system is involved, tho' highly unlikely, IMO.

I figure out if the ailerons are rigged to deflect upwards when you pull the stick, in case the balance cable (I guess you mean the cable between the two ailerons, basically the cable which closes the loop), they would both deflect somewhat upwards in respect to the angle of atack, but they will deflect symmetrical or with insignificant difference. That is considering just the cable between the 2 ailerons is failed. What other fouling of the cable system do you mean?

What I'm interested is high asymetrical deflection which can't be counteracted with the other aileron thus resulting in uncomanded and unrecoverable roll. The same for the other surfaces, of course, with their particularities.

Bruce Fenstermacher wrote:It would take a force of some sort. One such force might be control flutter.

By Tony Bingelis wrote:
FLUTTER? WELL, SIR, flutter is what a flag does wildly on the flag pole on those days when it is too windy for you to fly. But to better relate it to our subject, it should be described as a potentially destructive vibration or buffeting of an aircraft due to an out-of-balance condition of one or more of its control surfaces.

Flutter usually results in a component departing the aircraft not getting stuck in a position beyond it's intended travel but I suppose under the right circumstance it could stick. Flutter is caused by improperly balanced control surfaces for the flight regime undertaken. In other words on a certified airplane that has been tested to certain limits to insure flutter does not occur, flying beyond those limits, VNE for example could induce flutter. Or maybe in that certified aircraft the weight of the control surface changed because of a weight shift from a mechanical failure or may be ice stuck to the surface.

But under normal circumstance on a certified aircraft I can think of no reason a control surface would be forced past its intended travel specially with so little control input.

Quite interesting. You mean flutter induced by control malfunction itself? From your post, what I didn't understand is if you meant flutter induced by the control failure itself (linkage failure, cable, pushrod, pulley, bellcrank etc.) or by other factors directly related to flutter (e.g. losing the weights, gaining surface weight due to ice stucked inside etc.)? Basically you meant flutter induced in the absence of initial flight control malfunctions or after as a consequence?

Your question was could a control surface be forced past it's limit.

In a nut shell I said yes by some force. It simply won't do it itself. Then I speculated one such force, flutter.

When we talk about a balance control surface we are not talking about one balanced against another as in an aileron system. Each control surface is balanced about its point or rotation. I suppose sometimes positively balanced and sometimes negatively balanced depending on what is required for the system.

Do not be confused by the tern balance cable, the one between ailerons in some cable systems having anything to to with the actual balance of the control surface.

If your question is could the deflection of one aileron cause the other to deflect past its limit then I would say no. Because the limit of the aileron would be designed to hold any force from the other aileron should that happen. Of course we are talking under normal design criteria.

I'm sorry if it was misunderstood, it created some confusion here. (maybe I did not express myself clearly enough what was the question.)

So, the question was if due to a control system malfunction/failure the surface could deflect/jam in an unfavorable position for the pilot to recover with the remaining controls considering the pilot didn't deflected the surface in that position when the failure occured. Actually I haven't thought about it to jam past or beyond its designed travel limits, it may be two thirds of its travel or towards full travel and it's enough to induce an out of control situation.

That is, the pilot flying straight, smth brokes and the surface suddenly deflects to a position other then current and towards an extreme, of course not towards neutral where it would deflect if there is no input due to a cable failure for example. Or, it's in a turn, a failure happens and the ailerons might deflect and jam beyond current position. Maybe the questions seem really dumb, I explained childish hoping I'll do better understood as, however, even flying those aircrafts, I don't have deep knowledge about different flight control systems schemes used on conventional light airplanes, that's why I'm asking. Maybe you wonder why I'm interested in those things, I'm working on a flight control malfunctions seminar and so doing a research on the ability of the pilot to cope with different kinds of those and different kind of failures. Read some accidents and incidents reports, however, without a deep understanding of those systems failures I can't draw some main ideas and how critical are those situations.

A trim tab could fail/disengage...and perhaps cause the elevator to move strongly, ...but I doubt
the pilot couldn't control it.
John Pugliese recently experienced an elevator hinge bolt fail, and he was barely able to handle
it. He thought he might lose the plane. (probably a poor preflight)

Why are you concerned about this?

In most small aircraft I know of if a control itself ie cable or control fitting broke freeing the control surface to deflect as it wants, the surface will not deflect at all but return to a neutral position. The aircraft would be very controllable assuming the remaining functioning controls had enough authority.

What I mean is most airplanes could lose their rudder with very little effect because the pilot could steer with ailerons and elevator. If the aircraft loses the ailerons, in most cases rudder could be used to control the aircraft but rudder does not have the same authority in roll as ailerons so the pilot could get the plane in an attitude that rudder itself could not recover from.

Loosing the elevator the pilot would vary throttle to effect altitude changes but this is very difficult requiring lots of thought and the pilot can easily and quickly get to far behind the airplane to recover.

I thought about a pulley, bellcrank, pushrod and other parts, I don't know, if there is a way when they break, somehow due to brake reaction (or maybe impact, Gs?, I don't know, just wondering) might move and stuck with the surface somehow and jam it deflected in a position more beyond neutral and so you won't have enough control with the remaining controls and their secondary effect. Personally myself, I can't figure out a way which it might break to happen so, however, I don't know in details how those parts are usually rigged in different systems used on conventional light planes and that's why I'm asking.

The seminar will focus on the ability of the pilot to cope with any kind of control failure and not having deep knowledge on control system malfunction I would not want to induce people in error with some false assumptions. One part will be a brief analysis of flt control accident reports and althought they are quite rare, it is somehow obvious that their outcome is not really succesful. I knew that such a problem is pretty manageable, however, looking into reports I wouldn't say so. Unfortunately there are no many details on reports, so I think it is important to figure out if the ability and preparation to handle this kind of emergency is directly related to the outcome of it or it might occur other factors which prevented those pilots which crashed to recover from such a situation. I'm thinking about vibrations or flapping in the wind which might get stucked the surface in an unfair position to recover, don't know.
(P.S. Yeah, I know, one would say that looking in statistics you'll also find that stall/spin is unpreventable/unrecoverable considering the high number of occurences. )

I think the main idea will be that knowing how to properly use the reamining controls and their secondary effects you have a decent chance to bring you back on ground safely. Of course, all the technicques will be in detail presented including those less known like steering with the doors, changing CG with seat position etc. I found pretty good stuff on the Internet regarding these.

As long as the surface was not deflected in an unfavorable position when the jam occured (usually only at aerobatics it is necessary to deflect the stick more than a half and that is an environment where you have to use a parachute), I can't find on my own a way to jam a control so, but certainly I don't want to make some wrong assumptions, and of course there will be all kinds of questions from folks there.

Noted the flutter aspects (including trim tabs). From your post, what I didn't understand is if you meant flutter induced by the control failure itself (linkage failure, cable, pushrod, pulley, bellcrank etc.) or by other factors directly related to flutter (e.g. losing the weights, gaining surface weight due to ice stucked inside etc.)? Basically you meant flutter induced in the absence of initial flight control malfunctions or after as a consequence? Flutter triggers control failure or control failure triggers flutter?

Of course, I asked for advice from my local flying club mech and tech guys, however, I haven't found about flutter and other aspects in detail related to this topic. So, that's why I asked also here.

Thank you very much guys! I would really appreciate any further ideas and help here.

Radio control aircraft and real aircraft control systems are really apples to oranges. If a radio control servo stops, it also fixes the control surface. If the control surface is in a bad position, bad things happen. If the servo is disconnected and the pilot recognizes this the aircraft is just as controllable, maybe even more, as a real airplane is with a free control.

Even if controls jam in one direction or another, in most cases an experienced pilot who remains calm can control the aircraft with remaining controls. It may not be pretty and the aircraft can easily get away from the pilot but it can be done.

Starman170 wrote:...The seminar will focus on the ability of the pilot to cope with any kind of control failure and not having deep knowledge on control system malfunction I would not want to induce people in error with some false assumptions. One part will be a brief analysis of flt control accident reports... so I think it is important to figure out if the ability and preparation to handle this kind of emergency is directly related to the outcome of it...(I), don't know.
(P.S. Yeah, I know, one would say that looking in statistics you'll also find that stall/spin is unpreventable/unrecoverable considering the high number of occurences. )

I think the main idea will be that knowing how to properly use the reamining controls and their secondary effects you have a decent chance to bring you back on ground safely. Of course, all the technicques will be in detail presented including those less known like steering with the doors, changing CG with seat position etc. I found pretty good stuff on the Internet regarding these.....As long as the surface was not deflected in an unfavorable position when the jam occured (usually only at aerobatics it is necessary to deflect the stick more than a half and that is an environment where you have to use a parachute), I can't find on my own a way to jam a control ....
...Of course, I asked for advice from my local flying club mech and tech guys, however, I haven't found about flutter and other aspects in detail related to this topic. So, that's why I asked also here.

Thank you very much guys! I would really appreciate any further ideas and help here.

Seminar? SEMINAR??? Pardon me but,.... you've never heard about flight control flutter, but you're preparing to GIVE a seminar on flight control malfunctions and how to "handle this kind of emergency"....??? ...using "doors" and "shifting CG"...???

BTW, did you happen to read what I posted above? What leads you to think that flight control failures are predominantly due to broken cables?
What kind of gorilla do you think is pulling/pushing on these things that lead you to imagine a 7X19 strand of steel cable rated at 7,000 lbs of breaking strength, inspected at least annually, is the most probable item subject to break?
The most probable scenario is likely to resemble the event I mentioned above: A fastener or hinge pin fails, and air pressures from relative wind dislodges the surface from it's normal range of motion to something never before experienced, imparting overwhelming feedback forces to the cockpit controls and resulting in wild gyrations of an out-of-control aircraft.
Why anyone might think such a failed hinge-fastener wold not result in the possibility of the flight control completely leaving the primary flight-structure and bang-away at the fuselage or adjacent controls? (I had something similar happen in a Cheyenne-II and it was most distracting.) John's defective outer elevator-hinge-bolt could just as easily have slipped completely out of position, thereby releasing the elevator to pull the Other Elevator out-of-position via the torque-tube, both of which would then have been constrained mostly by the rudder (through which that tube passes) and the push-pull bellcrank (which likely would then jam the yoke out-of-position against his chest) and he could have lost ALL the benefits of having controllable tailfeathers! Such deflected/out-of-position controls might easily end up in a smoking hole.

Why can't such a catastrophic failure occur to a rudder? Of course it can! In fact, I believe it's highly possible, seeing how taildragger rudders are subject to abuse from lack of proper protections during storage and how they are attached to a ground-steering system design closely-related to the common grocery-cart using jack-chains! There are numerous incidents of tailwheels falling off during the high-speed portion of take-off/landing, and the tailwheel, captivated by it's jack-chains, flailing-away at the rudder and beating it into deformation.
And what might limit the controllability issue to primary flight control systems? What if a tailwheel fails or jams in a turn, causing the landing plane to swerve into bystanders or parked aircraft? How about parking brake failures in crosswinds....causing a landing airplane to blow a tire ...(a too-common occurance to those previous non-believers)....and swerve into a crowd?
Excuse my tongue-in-cheek curiosity, but... Where can we attend this seminar that, after a few anecdotal conversations on the internet, is going to be conducted, in which someone will expertly teach others about how to deal with what they've likely never previously experienced or known about? (I don't think John felt very calm, and he's certainly more expert about such matters than previously.)

Even if controls jam in one direction or another, in most cases an experienced pilot who remains calm can control the aircraft with remaining controls. It may not be pretty and the aircraft can easily get away from the pilot but it can be done. I really doubt that, especially thinking about the elevator or ailerons both or the other inoperative, if it's jammed deflected more towards an extreme, I can't figure out how you would control it using the remaining controls.

The seminar will be at a local flying club in Ukraine. As I previously stated, I don't have any experience with this kind of problems or any deep knowledge on flight controls systems. If I had, I wouldn't ask for help. I am convinced that it seems inappropriate for me to prepare a seminar on the issue not having enough experience, I know that and that's why I'm struggling to do my best. Actually, there are very few pilots who have had experience with something like this and fortunately I can say I'm not one of them. The idea is to present it more like an analysis. I do not understand why you're so surprised I mentioned some less-known techniques which might make the difference in an emergency. I found cases when shifting CG helped the pilot a lot to reach a landing attitude in a pitch control malfunction emergency, especially in a glider where you don't have power to use it as a pitch control. I think it worths to know that. Obviously I'm not going to say there that if you run out of rudder you have to use the doors, but as a last resorts it might help a lot, search for it and you'll see it was demonstrated that you can steer a Cessna using the doors, it seems that you misunderstood it, maybe my fault not being clear enough. Actually, I think I'm not going to present myself those techiques, there are very good publications/books that I'll use as a support in my presentation.

What leads you to think that flight control failures are predominantly due to broken cables? Actually nothing. It was just an assumption on how things can get wrong. I never said that flt control malf. are predominantly due to the broken cables. I was talking about them cause I found them in reports, and not necessary cable failure, also bellcrank, pulley, other components in the linkage system. I told you what I imagined on my own that can go wrong. I appreciate your scenarios and even I would be glad to help me establish which are the most common and critical problems. I really appreciate any related advice. Basically, that's what and why I asked for. Thank you!

We (the 170 Association) recently had a member that lost a bolt from the right elevator hinge on his 170. The only thing holding it on was the bolts in the bellcrank and the trim actuator arm. Fortunately, even though it took a lot of physical effort to control, it did not jam in an up or down position and through very careful maneuvering he was able to land safely. I think in these instances, you just do whatever you feel the need to do at the time to survive. Don't panic (easy to say) and don't stall.

I guess it's the same case mentioned above.

John Pugliese recently experienced an elevator hinge bolt fail, and he was barely able to handle
it.

Isn't it?

That is correct..same event. But it's not an isolated case...it has occurred in other aircraft.
Other types of failures have also occurred...for example, ice has bridged across stabilizers and
counter balance weights of controls and locked them....then the pilot has broken the control free,
only to discover the control blocked out of position by the icicles.
Anyway, I doubt a discussion forum such as this wil prove to be much value as an aerodynamics
design course for emergency training.
And I doubt too many closed cockpit gliders have the ability to accomodate much weight shifting
to overcome greatly displaced flight controls in an emergency.
Good luck with your seminar.