An Elevator Trim Tab Horror Story

Rob58

Rob58

Moderator
Recently I was talking to a 260C owner who told me an interesting story. While making a minor trim adjustment on climbout, the trim tab suddenly jumped the equivalent of several turns of the knob. The theory is that the long rod inside the tube got stuck somehow, was twisted like a big torsional spring and then after enough load it final snapped lose making a large change in the trim tab position, pitching the nose up suddenly. Since I have never had my trim assembly fully dis-assembled I cannot make the judgment call if this is even remotely possible or just wild speculation. Anybody seen or heard of such a situation? Do you think this is possible? --Rob
 
Mine got real rough and uneven to turn, although it never jumped more than a 1/4 turn at a time. It was the speedometer cable connection at the rear (Cruisair) that had frayed and was ready to break. Changing it was miserable because the forward part of the cable that goes into the long aluminum rod was siezed into the rod. I could not get it loose. It finally involved cutting fabric for access and still was not easy. When you put a new cable in, make sure to use some Never Seize compound on the end. Now sitting here thinking, I am not sure if the -3 has the speedometer cable as part of the trim system. Maybe this will help, maybe not. _____Grant.
 
I'm going out on a limb a little bit here, but I had a 300 Viking back in the 60's. One day on climb out the elevator trim tab cable broke; the tab was trimmed for hands-off climb. The completion of the flight required constant forward pressure on the yoke. There is a lot more to the story but upon landing and inspecting the tab mechanism, which as I recall is similar to a rack and pinion, I rotated the rod by hand to set the tab at neutral with the elevator held in neutral, and continued the flight home safely. Several years later I was involved in a court case where the pilot was killed on take-off in a 300 Viking after his mechanic performed a similar temporary fix to a broken trim tab cable. As memory serves I believe it would be possible under extreme circumstances for the tab end of the cable to not rotate while the pilot adjusted the trim, and then 'break loose' and suddenly change the tab position. As I said, I'm going out on a limb a little bit here because that was nearly 50 years ago and my memory could use some refreshing - but I point this out less someone with trim tab problems is tempted to defer maintenance. Get it evaluated and fixed now.
 
I flew my Cruisair a couple of times while I was waiting for a cable to be made. I also set the trim for neutral which worked, but I had to adjust my cruise speed for the pressure to be reasonable. I imagine that at the much higher speed (and power) of a Viking it would be a real challenge. It worked, but was not fun. _____Grant.
 
I landed at Cottage Grove,OR once for fuel, 'cause we didn't have any at Creswell (~5 mi North of CG). Adjusted trim for take off as part of runup. After take off, I was adjusting the trim for level flight, and it didn't change. Same thing as other posters, cable broke but handle moved. Fortunately, Creswell almost always uses RW 33 so was able to make straight in to Creswell, holding against trim and hardly had to changed heading thru the whole flight. Also not fun! :( Would not want to fly that way for long.
 
All I can say is that based on all the feedback on this thread, along with everything I have read about the danger of trim tab problems: I don't want to take any chances! So in a 14-19 series Cruisemaster what does the trim mechanism design look like? How many moving parts are there that could possibly freeze up or break? --Rob
 
Rob58 - I think you should get a drawing or schematic and evaluate the system for yourself. While it is fun and interesting to share personal stories, anyone answering your question as a statement of fact could be subject to liability. You might want to check the archives for ADs or Service Bulletins, or rephrase your questions. I'm not trying to be a PIA or a scare monger, however caution is suggested - at least from my perspective having "been there and done that".
 
Hi Art... I appreciate your caution and concern. Certainly not my intention to place anyone in a position of liability, nor would I ever take anything offered on the forum as a substitute for the decision of an experienced Bellanca A&P / IA. Nonetheless the forum is one of the few places to share information about our birds and some of the contributors are very knowledgeable. If you might notice from some of my previous posts I have been trying diligently to obtain engineering drawings and specifications - thus far I have not been able to acquire this information and AAC is not too helpful. I do have all of the ADs and service letters. Actually I was hoping that someone reading my post might have drawings on the trim mechanism that they would be willing to share. My theory is that the more information available the better and besides, being a mechanical engineer myself I always like to know how things are put together. Thanks for the good feedback and the words of wisdom... Rob
 
Rob, I think Cy Galley has a lot of drawings, at least for the Cruisair. I have one poor quality drawing of the Cruisair trim if you want it.
 
davism - nothing specific (archives), just suggesting to search through old posts on this forum and in other FAA and NTSB resources to see if there is anything pertaining to elevator trim. I was only making a suggestion in case someone overlooked those 'archives'. I know that when I had my 'incident' referenced earlier, I reported the findings to the Bellanca factory - but I don't know if there was any followup activity such as a re-design or a service letter, etc.

Rob58 - A Google search of "bellanca elevator trim" turned up this gem:

Tail Vibration / Trim Tab Failure Models 14-19, 14-19-2, & 14-19-3

Bellanca/AALLC has recently received a report of severe in-flight tail vibration on a Model 14-19-3 airplane.
The vibration occurred suddenly at high speed and continued until the vibration stopped at low speed.
There was significant structural damage to the airplane.
A review of Service Difficulty records has found a few additional reports of a similar problem.
We are waiting to receive parts from the Model 14-19-3 owner, but investigation of this problem has determined that the most likely cause for the vibration is excessive elevator trim-tab actuating mechanism free-play resulting from one or more of the following: loose or worn parts, an improperly installed taper pin, and/or damage from cumulative/excessive taper-pin tightening.
We are working with the FAA to resolve this issue.
In the meantime, check your airplane’s trim tab during your next preflight: the taper pin should fit tight without deformation to the tube it engages, there should be no motion between the trim tab and the actuator arm and the trailing edge of the trim tab should not have more than 0.020 inches peak-to-peak free-play.

In addition, the Illustrated Parts Catalog for the Viking is also available on the internet and it has detailed diagrams of the parts making up both ends of the elevator trim tab system (http://www.bellanca.us/Bellanca_Parts_Manual.pdf) I don't think the basic design philosophy has changed, so it is likely a good starting point to see how it works. - artL
 
Just for a little general information. The Cruisair trim system is a little different than the later Bellancas. Cruisairs use a threaded rod with standard threads on one end and left hand threads on the other. The rod runs through bronze nuts that are fitted into welded ears on the elevator and trim tab. The turning of the rod brings the two nuts together or apart which makes the trim tab raise or lower. The speedometer cable connection is for flexibility when the elevator moves. The 14-19-3 (not sure about 14-19, or 14-19-2) has a small square tube with a worm gear inside that extends or retracts when you turn the trim cable for the same purpose of raising or lowering the trim tab. Play in the bronze nuts , or worn attatchment points in the ears , or even cracked welds holding the ears can have serious results. I suspect (but dont know for sure) that the worm gear system of the later Bellancas is subject to less wear (less slop) and is a good improvement. ______Grant.
 
Art, the info you found is a gem indeed! You have put my Google search ability to shame as I never saw this one. My sincere thanks!

The article, which appears to be published by AALLC, makes mention that might be several reports of this problem with the 14-19-3 model alone. An FAA advisory bulletin indicates that there were five reports of tail vibration related to the same issue. Considering the size of the fleet, this is significant. Bellanca says that the peak-to-peak play at the trailing edge of the trim tab should not exceed .020. This seems almost unrealistic given the tolerance stack ups with all of the components in the trim mechanism. Just another reason why I would like to have a set of engineering drawings. I have every confidence that annuals coming out of Dan Torrey's shop will have this problem area inspected and fixed if needed, however there are still a number of Bellancas that are maintained by mechanics without the depth of Bellanca experience needed to catch an issue like this. I'm going to continue my research. Thanks again for all of the valuable feedback. --Rob
 
Larry, I was not using the forum when Cy Galley was an active contributor. I have read many of his articles in past newsletters and understand he has been a tremendous resource of knowledge over the years. How would I best make contact with him to ask about his collection of drawings? --Rob
 
That's Robert S!

Cy has retired from his role here as Editor-in-Chief, but has the Club's inventory of drawings. Contact him at: cgalley@mchsi.com. Give him some time to respond, as he is quite busy with family tasks.

The trip tab issue is well known. Those using mechanics other than Dave Pasquale, Dan Torrey, AALLC or Rocket should consider taking your Bellanca to one of them at least once to discover this and many other areas unique to our airplanes. This would have prevented at least one accident that I was witness to - One Man's Opinion.
 
Rob58 - you might check out http://kitepilot.com/N74375/trim/Trim_tab_controls_Bellanca_drawing.jpg

- artL
 
The trim system cable is the same as a tach cable so treat it as such. Years ago I treated the cable with a tach cable lube and it moves too easy all these years. I suggest TriFlow. Start at the crank and keep lubing day after day it works wonders. Lynn the crate
 
Another bit of Bellanca trivia (or maybe a help). For the Cruisair, the front of the speedo/tach/trim tab cable has a piece of square tube swaged on to it that slips into the long aluminum tube that runs the whole length of the fuselage. I discovered that there are two different size swaged endings and opening in the long tube. They are enough different that they will not interchange. I dont know if this was some production run change or just what Bellanca had available at the time, or just what the heck the reason was. I would suspect that the larger one would be an improvement. Another 70 year old plane mystery. ____Grant.
 
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