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#1
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Herb;
First let me say I don't think your "Dangerously Modified Aircraft" has anything to do with this, it seems far too common a problem. You will have to wait to find a Herb unique problem to blame on your lovely looking mods. My mechanic believes the root cause of this is both in the elevator trim tab play and in the elevator bell-crank play. Both have a series of hardware (bushings, bolts etc) that are relatively cheap and easy to replace and he claims keep these fresh and you shouldn't have any problems. In my case the trim tab hardware was all replaced by the prior owner and my mechanic replaced all the elevator bell-crank stuff a couple of annuals ago. Again back to his theory, he claims that the elevator is subjected to an inordinate amount of "prop pulse" given how close the rear prop is to the elevator. As I recall it, the hardware in the bell crank was indeed all pretty cheap except for one long bushing. I also recall that the tolerance for play in the bell crank was really tight...their was a series of thin washers that you buy from Cessna as well and then install as few or as many as necessary to get within spec on the bellcrank play. The expensive bushing could have been fabricated I guess but I ended up shelling out to Cessna for it...like $170 as I recall for the one key long bushing. Hope that helps. Bill 
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#2
08-24-11, 09:23 PM
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Hi Herb,
I have made this comment before somewhere in an earlier post. When I first purchased my G model, I had the boom bounce on a fairly regular basis. Getting the cable tensions to spec seems to have solved the problem for me. Have never had it again. (Tomorrow, I'll have it, thanks! ;o) ) Anyway, I would tend to agree with last post as well. I would think that anything that can allow elevator movement beyond what is commanded by the pilot, would cause the issue. I did have my trim tab hardware replaced last annual because it seemed to me it had excessive play. I was not experiencing any problem but my IA agreed the play was too much. I cannot recall at the moment what was all replaced but my records would tell the story. Anyway, I would agree that anything that keeps flight controls in spec would go a long way to getting factory intended flying qualities. It would seem to me that flight controls out of spec in any manner could cause the aerodynamic gremlins such as the boom bounce many of us have experienced. Ed
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#4
08-24-11, 11:56 PM
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Herb,
I apologize but unfortunately I do not have much for you to go on. I checked both the work order and log books and both entries say the same thing. "Trim actuator hardware loose. Secured all trim actuator hardware." Total labor 0.3 hours. The records indicate that nothing was replaced but simply secured. Sorry, I wish I could be more helpful. Ed
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#5
08-26-11, 10:44 PM
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No worries Ed
I looked into some parts and they are expensive. I will try to rebuild without having to buy new if possible.
__________________
Herb R Harney 1968 337C Flying the same Skymaster for 47 years
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#6
09-06-11, 08:32 AM
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The service manual may be helplul, e.g. the 1965 THRU 1973 SERVICE MANUAL Sect. 8-3 ELEVATOR - TROUBLE SHOOTING table pg. 8-3 has two suggestions to address "SLIGHT UNDULATION OF TAIL DURING FLIGHT".
__________________
Paul T337C
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#7
09-06-11, 08:48 PM
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I solved my boom bounce by adding a bit more torque to the elevator hinge bolts. I had to go beyond the recommended value. My IA didn't want the compression on the bearings but in the end the smooth stable flight characteristics were persuasive. Check for even the slightest play and eliminate it. If you can't find anything try a bit more torque on those hinge bolts a bit at a time.
Best of luck _travis
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