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Good Vibrations?

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Thu Sep 25, 2014 6:51 pm

Good Vibrations?

I have only had my Cherokee for a few months and I have about 20 hours in it.

I was taking off this evening for a local fun flight, no problems with start, I ran it up no problem, but when I took off, there was a moderate vibration that I have not felt before. It stopped about 500 ft in the air, I decided to stay in the pattern and as I turned back for downwind, had a lesser vibration again and then smoothed out almost immediately.

After I landed, I did the run up again, no problem, took off again, no vibration no problem, flew for about 40 minutes, no return.

Something to be concerned about? Am I just jittery in my early hours with this plane?
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Thu Sep 25, 2014 6:56 pm

Re: Good Vibrations?

If you felt it, it's worth looking into. I'd suggest having your IA check the mags and the plugs. A misfiring plug (which can be caused by either a plug problem or a mag problem) can cause the sort of vibration you described.

Cary
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Thu Sep 25, 2014 6:57 pm

Re: Good Vibrations?

Seems like some precession and bad engine mounts pads mixed up right. What's your TT engine, prop?
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Thu Sep 25, 2014 7:09 pm

Re: Good Vibrations?

Or something loose rattling around for a few minutes. Inspection plate, wheel pant, flaps rigged a bit off....

Your laptop you forgot on the tailfeathers!

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Thu Sep 25, 2014 7:14 pm

Re: Good Vibrations?

8GCBC wrote:Seems like some precession and bad engine mounts pads mixed up right. What's your TT engine, prop?



1682 hours on engine 150 hours on prop
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Thu Sep 25, 2014 7:18 pm

Re: Good Vibrations?

mnewb1 wrote:
8GCBC wrote:Seems like some precession and bad engine mounts pads mixed up right. What's your TT engine, prop?



1682 hours on engine 150 hours on prop


Were the (4) mounts changed at overhaul?

Did it seem to be a vibration (shaking the airframe) or mis-firing (rough running engine)?
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Thu Sep 25, 2014 7:20 pm

Re: Good Vibrations?

8GCBC wrote:
mnewb1 wrote:
8GCBC wrote:Seems like some precession and bad engine mounts pads mixed up right. What's your TT engine, prop?



1682 hours on engine 150 hours on prop


Were the (4) mounts changed at overhaul?

Did it seem to be a vibration (shaking the airframe) or mis-firing (rough running engine)?



believe they were, and it felt like the plane vibrating not the engine missing
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Thu Sep 25, 2014 8:04 pm

Re: Good Vibrations?



OK I had the go pro running, from the time I lift off until about 1000Ft AGL, the vibration is there then ends.....
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Thu Sep 25, 2014 8:21 pm

Re: Good Vibrations?

Looks violent in the video. Get a reliable A&P mechanic before you fly again.

I believe I have seen similar vibrations associated with engine mounts on Cessna singles. Check the logs during the time of the engine change and see if mounts were replaced? Also, visually inspect for engine sag and mount deterioration.

There could be many other possibles too. Have an A&P upfront ASAP.
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Thu Sep 25, 2014 9:14 pm

Re: Good Vibrations?

Do those Cherokees have cowl flaps? If so, maybe check the security of those as well. Big pieces of sheet metal bouncing around in the prop wash can transmit nicely to the seat as well...just a thought.
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Thu Sep 25, 2014 9:17 pm

Re: Good Vibrations?

Try tapping the brakes right after lift off?
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Fri Sep 26, 2014 4:05 am

Re: Good Vibrations?

Could also be a sticking exhaust valve. Have you done the 400 hour valve stem inspection? ( there's a sb on it).
Pete ( 30 year cherokee owner)
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Fri Sep 26, 2014 7:17 am

Re: Good Vibrations?

The reason c180bill says tap the brakes is wheel wobble after lift off will cause this and it appears to me to be what is happening. My 170 did this and hitting the brakes in the air will stop it instantly. You've got smaller tires and wheel pants so I am not sure.
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Fri Sep 26, 2014 7:47 am

Re: Good Vibrations?

Yep looks like wheel wobble . You say it came back on approach ? My wheels wobble on just about every lift off .Maybe I should stop landing with my brakes on . Square tires suck.
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Fri Sep 26, 2014 9:52 am

Re: Good Vibrations?

it sounds like it could be wheel wobble, except why would it come back after it went away? I've never seen a wheel spin back up in the air.
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Sat Sep 27, 2014 4:58 am

Re: Good Vibrations?

pouellette wrote:Could also be a sticking exhaust valve. Have you done the 400 hour valve stem inspection? ( there's a sb on it).
Pete ( 30 year cherokee owner)


http://www.caa.si/fileadmin/user_upload ... SB388C.pdf
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Sat Sep 27, 2014 10:04 am

Re: Good Vibrations?

The shaking is going on a bit long for wheel wobble (even for a 208).

I'd get that thing checked out before I flew it again.
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Sat Sep 27, 2014 11:13 am

Re: Good Vibrations?

I do not know how heavy your engine is but - I have found some bad engine mounts - on some fully amortized rentals by holding the prop nest to the spinner and moving it up - down - left -right.

Is there any signs of the spinner contacting the cowling?

Having the vibration coming back during approach makes me think that whatever it is seems to occur at some resonant point of RPM and or airspeed.

Best wishes with it

Chris C
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Sun Sep 28, 2014 2:49 pm

Re: Good Vibrations?

My first thought was wheel wobble - but the vibration lasts too long to be wheel wobble. Even bushwheels with huge rotational inertia don't spin for that even half that time.

The vibration stops for a reason... Something changes at the time it stops. Think about what happens at that exact moment, do you reduce power, adjust controls, airspeed passes a certain point, engine temp above a certain point??? That may give you some clue to the cause.
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