Intermittent vibration in the climb..... Only

[Cody Stallings]

The company I work for has a "bent wing" 67F that I fly, it's great machine.

Yesterday I made a trip from Wynne Ark(M65) to Broken Bow Ok(90F).

The T/O went fine, but in the climb after all the drag creating devices were stowed, as I was trimming, I noticed when I would stop, there would be a slight vibration. Then moving the wheel in any direction would make it go away........ But, it will come back agin maybe a little worse or not as bad as when it first started.

Now it may go 90 sec to five min. Before it starts agin. It's not predictable.

I wanna say that this vibration is very very slight, the only reason I noticed it, is cause I now have the smoothest 3 blade prop ever. Which makes it to where I can feel other things going haywire now.

After departing Broken Bow headed back to the shop(7m2) I started to experiment....... My findings are this.

If you want to climb at 2570 or less, the vibration never shows its face..... My findings don't make me breath any better about this.

Any ideas?

[gregwatts]

Have you had the prop dynamically balanced?

[gregwatts]

Tach error?

[Cody Stallings]

Prop has been balanced, before an after being greesed

Tach is a P-1000, copy's what my Chadwick blade counting tach reads when I lay it on the dash.

I now this may sound strange, but its a low freq vibe. Feels like airframe.

I'm gonna hook a velocimeter to the seatrail, then into the Chadwick 8350 an see where the vibration is coming from. Forward or aft of the seat....... The hunt is on now...

[Cody Stallings]

Hey Jim, you guessed right.... Balanced to .003 IPS. Pretty smooth for a rough running BigBore 4 banger.

[Marauder]

Prop has been balanced, before an after being greesed Tach is a P-1000, copy's what my Chadwick blade counting tach reads when I lay it on the dash. I now this may sound strange, but its a low freq vibe. Feels like airframe. I'm gonna hook a velocimeter to the seatrail, then into the Chadwick 8350 an see where the vibration is coming from. Forward or aft of the seat....... The hunt is on now...

When I read your first post, flight control imbalance came to my mind first. Have you checked over the Heim joints carefully on all the control surfaces?

[PilotDerek]

I now this may sound strange, but its a low freq vibe. Feels like airframe.

Like harmonics? I've heard people say that there can be a harmonics issue with a three blade prop on the M20F's. All except the MT props.

[Cody Stallings]

No I have not.

Is that the kind of project a mooney service center should take on?

I will be honest, I'm not much of a wrench when it comes to airframe. I'm a prop guy.

Are you saying it might be control flutter?

[N601RX]

It may be a gear door not closing up completely, or cowl flap bumping exhaust.

[Cody Stallings]

I understand what you are sayin Derek

This is not prop harmonic, I have felt the shake of a 3 blade that you mentioned on a mooney.

The vibe feels like when you put your hand on a real rough running cloths dryer, then turn thr trim just a tad, an it's gone.

When you are level in cruise it never happens. Just in the climb.

[treebobboy]

Cody,       Have you checked to make sure your step is retracting?      Mikey

[Marauder]

No I have not. Is that the kind of project a mooney service center should take on? I will be honest, I'm not much of a wrench when it comes to airframe. I'm a prop guy. Are you saying it might be control flutter?

It could be anything in the breeze. The fact that you could get it to stop by moving the relative position of the airplane through the controls, suggests it could be something aerodynamic related. Control surfaces, gear doors, loose sheetmetal (I would not think a loose inspection panel could do this) should all be looked over. If you told me you changed power settings, blade pitch, I would expect it to be power plant related. I think just going over the plane completely looking for anything that looks loose is a good starting point. I mentioned the Heim joints because of the fact they are attached to the flight controls and I believe there is an inspection AD on them.

[gregwatts]

I was beginning to think you closed the door with the passenger side seat belt partially out............

[Cody Stallings]

Yes the step is going up all the way. However I think Marauder has a good idea.

I think I will put it on jacks an make sure everything is closed up properly, an check the belly skin to see if they might be flapping.

Do you have the AD# on those hinges by chance?

[Marauder]

Yes the step is going up all the way. However I think Marauder has a good idea.

I think I will put it on jacks an make sure everything is closed up properly, an check the belly skin to see if they might be flapping.

Do you have the AD# on those hinges by chance?

 

Looks like 98-24-11. I will confirm for you.

[Marauder]

Link to Mooney's AD site: http://www.mooney.com/index.php?keywordsearch=&option=com_servicepdf&modelid=3&Itemid=46&sort=modelid&direction=ASC&model=all&categoryid=1

 

AD 98-24-11: looks like it pertains to cracks on the ailerons links. Doesn't specifically call out in flight issues. http://www.mooney.com/images/pdfs/sb-pdf/sbm20-264.pdf

 

I would still look over all of the flight controls and inspect for anything that could vibrate.

[Cody Stallings]

Will do, Thanks for the info

[Hector]

Agree it sounds like an aerodynamic issue, however, the fact that it does not occur when climbing below 2570 RPM does not add up unless climb speed was different. Am I missing something?

[xftrplt]

Then moving the wheel in any direction would make it go away........ But, it will come back agin maybe a little worse or not as bad as when it first started.

Is that the trim wheel you're moving?

If so, could it be that there is a little play in the movable tail trim that allows the vibration, which stops temporarily with slight retrimming, since trimming would take up the slop and then it would resume as the play works itself loose?

[Cody Stallings]

Yes the trim wheel, an it does have a little bit of play in it.

And yes the climb speed was different at the reduced RPM

[Wildhorsesracing]

Check the Magneto timing as well - if it is off it might not show up until higher RPMs. 

[Cody Stallings]

Well, she is up on jacks. The large belly skin was really loose, an installed wrong. It was lapped over the 1 in front if it. While it was off, I lubbed all the Little Ujoints on the trim shaft. I noticed the chain that comes from the wheel below the floor board has some slop in it.

Is that normal,

An the left gear door on the front has some wobble to it. Everything closes nicely though.

Will post hack as I find more sqwaks

[butchgilbert]

I recently had to have my alternator tightened due to the wrong bolts being used to secure the housing. When I squeezed the belt, the alternator would move slightly.

[Alan Fox]

Is that the trim wheel you're moving?

If so, could it be that there is a little play in the movable tail trim that allows the vibration, which stops temporarily with slight retrimming, since trimming would take up the slop and then it would resume as the play works itself loose?

Jack screw play is not possible in flight as the wind pushing on the vertical with almost a 5 foot arm wont allow the tail to (float) I would lean towards nose gear doors , maybe main gear doors...  aerodynamic  flutter is out , as catastrophic damage would be obvious...Maybe a harmonic getting picked up by the fuselage skins .... They are not stressed forward of the rear rollcage bulkhead and are succeptable to vibration........ 

[garytex]

I concur with n74795 that it is a harmonic or sympathetic vibration possibly in the control pushrods.