vibration issue on first flight

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ronschneider
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Joined: Thu Jul 03, 2014 9:56 pm

vibration issue on first flight

Post by ronschneider »

My express flew for the first time yesterday after many years of building and living. It was a warm day in Tucson and did not have any overheating issues and engine ran very well. I have one wing which is heavy which I will adjust. Right brake was spongy and the ventilation was not sufficient. So far minor issues. The issue I need help with is a vibration issue that started at 135 knots and got worse up to 150 knots and did not want to beyond that on the first flight. My express has the cruciform tail and a IO540c4d5d engine with a two blade prop. The cowling, baffles and engine mount where purchased from Larry Olson. The vibration was not in the panel or the controls but in the plexiglass on the sides of the front seats. It seemed to be in sync with the engine firing on what seem to be more than one cylinder and got less intense as the engine speed increased. I have some ideas but would like to know if anyone had similar results and how to fixed the issue. Is was very loud as well. Thanks Ron Schneider

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kevin
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Re: vibration issue on first flight

Post by kevin »

Do you have any vibration issues during run up?

Does the frequency change with prop/RPM changes on the ground or in flight?

Has anyone checked the actual pitch of each blade of the prop- if one blade is set at a greater pitch than the other(s) it will taking a bigger bite with each rev, and cause asymetric thrust and a vibration as the uneven pull is acting from each side, top and bottom during each revolution. I did not set up your prop, but the blades should be against the low stops at low (full forward) pitch, and if set right should be the same. I would run it up at high RPM like +2000 on the ground and try to cycle the prop down to around 13 to 1500 and see what it does. If you dont find anything conclusive take off at less than full rpm if you have the room and try different prop positions in the air at increasing RPMs.

NOTE: If the vibration changes with the prop you should get it looked at quickly, asymetric prop loading places a lot of stress on the end bearing and the end of the crank which could be really bad if the prop leaves in flight.

Kevin Alderman
A&P, GROL builder of 2 Express CTs
N45WE
kevin
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Re: vibration issue on first flight

Post by kevin »

Ron,

I am gone a lot and I am working on several planes so sometimes it takes me a few days to get back to the forum- if you need something quickly email me at kevin@aas-inc.us or call me at 239-896-7576

Kevin Alderman
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Re: vibration issue on first flight

Post by kevin »

Can you give me the weight and balance of your aircraft please?
ronschneider
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Joined: Thu Jul 03, 2014 9:56 pm

Re: vibration issue on first flight

Post by ronschneider »

Weight and balance excel sheets attached.

Ron
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N221RJweightand bal-2.xls
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kevin
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Re: vibration issue on first flight

Post by kevin »

It looks like your single pilot CG is right at the forward limit. After you fix the door structurally, if this doesnt fix it you might try a little ballast in the aft part of the plane. My empty CG is 78.4 and empty weight of 1759. I have an IO 360 and you have a 540 so your CG should be farther up, so be careful on landing. Getting slow and especially behind the power curve on final with the nose high can easily blank out the horizontal stabilizer causing an abrupt nose down moment. Read Jerrys CAFE report for more info, I uploaded it here for anyone that needs it or wants it.

Also, a far fwd CG causes you to fly nose high to counter the weight which might induce turbulence at the wing root which could be beating on the door. Just a thought.
kevin
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Re: vibration issue on first flight

Post by kevin »

I flew my CT, IO360 200 HP, C/S prop 2 blade- for about 10 hours last week. I too noticed more than average vibration in the side glass during flight at appx 135 knots. Didnt notice it so much until I pulled the RPM back to around 2350 which is my preferred cruise RPM. At 6500 ft and 2350 RPM my cruise speed was around 135 knots at 8.1 gph. At higher RPM and higher speeds the vibration seemed to diminish.

After landing I tried some different rpm ranges as well as some flight tests to see if I can determine the cause- here is what I know so far:
the 2350 RPM on the engine is not it. No abnormal vibration at any specific engine speed combo.

Also, on climbout at 2350 and airspeed around 110, no abnormal vibration.
I climbed to altitude of about 4000 feet, reduced power and pointed the nose down. Airspeed of 140 knots and no vibration. So, it is an airflow issue. It seems related to the prop cycles, airspeed the resultant airflow over the cowling/sidewindow/windscreen intersections. After the holidays I will be flying more and doing more testing. I will keep the group informed.

Kevin Alderman
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