Trim Tab

GMAS mentioned at TC something about an allowable amount of play in the trim tab. I was doing a pre-flight and noticed it wiggled (vertically) about 1/8" -1/4" Is this in the reasonable range?

Keven
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Wendie 99

[Bob Cook]

Kevin

Been thru this one. It should be as tight as possible with very LITTLE play. I don't know where you are measing the play. The problem is the joints inside the elevator panel. One the mechanic tightened things up there was a decrease in what I would call "flutter". You could feel it in the yoke and espcially when cruising along in stable air.
GMAS could probably tell you the limits from the manual but I would say there was perhaps 1/16" of play at the trailing edge of the tab.

I didn't think about it until the clinic in TC when we talked about the flutter, but I can't seem to get the plane trimmed well enough in stable air not to porpoise, i.e., I'll be trimmed in stable air, but my alititude will vascillate up and down 100' or so. I don't really feel anything in the yoke, but the plane has always done it since I bought it last August, so maybe I don't know what a proper 337 yoke feels like. I'll look forward to any more comments from the Board, and I'll have my mechanic look at it next week.

Thanks,

Keven
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Chevrolet Corvette C5 Specifications

[rick bell]

had alot of horz. stab. flutter at curise, yoke really started to shake up and down (estimate 1/2 inch up and down). replaced
the attachment bolts (they showed small amounts of wear where they penterated the sleve). i was amaized that flutte took place with about 1/8 looseness. replaced the bolts and all is stable.

[Bob Cook]

Kevin

I doubt this would cause your problem. I find mine quite stable once trimmed. GMAS refered to this problem mentioned by Rick and myself to be "boom bounce". It is noticeable. I would say this is an area that should be monitored closely as a flutter will develop in the boom (flexing). The solution was mentioned by Rick.

Bob

[GMAs]

Kevin... any play is too much play... but, we have to have some to make the parts go past each other... smile...

We have found that you should not have much more.... than about 1/16 to 1/8 inch movement at the rear of the trim tab... that means that all the bolt to plate fittings are pretty tight...

They are common parts.. and not to expensive... make sure you use new nuts and bolts... and kotter pins... when you take them appart and put them back togeather again... Just tightening (torquing the bolts and nuts tighter)... won't do... it will take the play out for a while but it will make the system work harder and will loosen up more later... but, it will make the plane slow in reaction and major cause for the ... I trimed it and it changed after a while ... syndrome.. when it got some vibration to move it around and relive the pressure...

Make sure you use kotter pins and or new nuts that are the positive locking type... no nylocks or fiberlocks here... we don't want this thing coming loose in flight...

If you look in the illistrated parts manual you will see the trim tab and its attaching hardware... it show a good picture...but, the discription of the parts are not too good...

Most of the time you will find the two flat plates that attach the push pull rod to the bell crank is the problem... here these just egg the holes out... the bell crank has needle bearings in it... so it hardly wears out .... it only will do it.... IF ITS IS NOT LUBED... Hmmmmmmm.... and the U channel is again not the problem most of the time... so that leaves the little plates on each side... which are really cheep... but, the bear directly on the bolt... and as such have a high wear rate... again if ITS NOT LUBED REGULARY.....


to get the in and out... use small fingers... smile... check the whole system for wear and play by grabbing the rear of the elevator.. and holding firm... keep it level like its in flight and then try and move the trim tab up and down...noting the amount of play from one position to the other... if its close to 1/4 inch... time to see your mechanic... and show him this posting... Hope this helps... GMAs...