vibration

Hey folks. N914C continues to be a blast. I have never flown a plane that likes to fly so much! We have, however, developed a vibration. at 13 hours on this new/old engine, we have an uneven feeling to the engine. Now we have never developed over 2300 rpm for climb and 2500 for cruise. I know the prop pitch is steep. I show 74/80, 75/80, 76/80 and 64/80. could I still be waiting to seat 1 cylinder? I do have much air from pvc tube with test. could the prop be out of balance. any similar situations?
http://webpages.charter.net/db.kelley/my_foster_rv1.htm
thanks
Dan

Vibration

Getting the prop balanced is always a good idea, but it's not normally the kind of thing that just starts causing increasing vibration, unless something has fallen off. Do you have CHT and EGT probes on all 4 cylinders? This will tell you a lot. I'd also check the plugs - both physically and the color - and make sure they all look good. Does the vibration change if you move from the left to the right mag? Are you running a carb or EFI?

stepdaddy said:

Hey folks. N914C continues to be a blast. I have never flown a plane that likes to fly so much! We have, however, developed a vibration. at 13 hours on this new/old engine, we have an uneven feeling to the engine. Now we have never developed over 2300 rpm for climb and 2500 for cruise. I know the prop pitch is steep. I show 74/80, 75/80, 76/80 and 64/80. could I still be waiting to seat 1 cylinder? I do have much air from pvc tube with test. could the prop be out of balance. any similar situations?
http://webpages.charter.net/db.kelley/my_foster_rv1.htm
thanks
Dan

Click to expand...

What engine and mount do you have? If is an O-320 on a Conical Mount, be sure and get the better islolation mounts from Vans.

Are the exhaust pipes properly held in place? Are they hitting the botom of the fuselage?

Can you feel the vibes at any and all RPMs? Can you feel it on the ground? And is it the same feeling running on either "mag" alone?

Are the plugs on the 64/80 in as good shape as the others and not full of oil/lead and in need of replacing?

Are there no wires rubbing and allowing the spark to a plug to jump to the engine case?

Just a few questions from someone who spend a lot of time chasing "vibrations".

James

Your web site has photos that may help

I looked at your website and saw several detail photos of your engine installation that may help some knowledgable individual help you. It is certainly nothing to be ignored. I see that it is fuel injected; 4 into 1 exhaust system; remote oil filter; wood prop. I give no recommendations because you could be facing a failure in the near future and I don't want to be a part of a bad decision on your part. I have had vibrations and I have had failures at your stage of the project and I can feel your concern. I just kept checking and flying as cautiously as I could and worked through the problems with some risk and expense. At one point I installed a "rich" mod to my carburetor and I find that I get vibrations if I don't start leaning the mixture soon enough. Good luck.

Bob Axsom

Common vibration sources

Does this describe your vibration?
A "new" vibration. Seems to have started as some time recently. Oddly harmonic with the engine but doesn't seem to be completly isolated within one particular vibration range. Vibration seems to pulsate (waaa waaa waaa...). Seems more common in cruise and decent. Once it starts it seems to keep going, but doesn't start immediately after takeoff - seems to start ranomly several minutes after takeoff. Onset of vibration is slightly gradual (not on like a light switch) - takes a few seconds to reach maximum amplitude and then is steady.

While the spark plugs are out for visual inspection, might as well re-check the propeller track. Are you running a wood prop? Might check torque on bolts.

Vibes

Does brake application stop the vibes? As the wheel bearings and new grease get freeer they can spin up with airspeed and vibrate the gear legs. I often apply brakes in flight when I get a vibe, and it is often the cause.

Hope the fix is this simple!
RV-4 VH-PIO

I'd look at your prop first, it could be the low cylinder is causing a harmoic with the prop. Might want to have someone borescope out the valves in that low cylinder just in case. When you do a compression test you can listen to where the air is leaking out of, if it's coming out of the breather tube, then your not broken in yet, if it's coming out of intake or exhaust you have a valve problem.

I chased a vibration for a LONG time before I happened on a service bulletin for the Husky with an O360/conical mount. It just so happens I have a 360/conical mount from an R22. I had torqued the eng. mnt. bolts WAY to much and had the engine basically bolted to the firewall. I complied with the service bulletin from Husky (dynafocal mounts w/metal spacers) on my conical mount...oh happy day!
One thing you might try, see if the vibration is rpm relate or speed related. This will really narrow down the possiblities. Speed related could be aerodymics, rpm related is more engine/prop type stuff. My vibes amplitude didn't increase in a dive with the rpm low, but did increase with increased rpm.

Previous to that, I had...
braced the unsupported section of lower cowl between the pipes,
balanced the prop - twice.
re-timed the mags (you really want to try that!)
tore all my hair out
chewed off my fingernails
fiddled with wheel pants
fiddled with gearleg fairings
fiddled with baffles
screamed "why are you doing this to me????!!!" at my airplane
(this didn't help at all, by the way)
Actually, the list goes on and on....

Jeff

Tires...

Ok, looks like Grant guessed at what I was alluding to. Spinning wheels in flight can be some of the most troubleing sources of vibration - no one ever believes it could possibly be that. It's usually the nose wheel. With the nose wheel off the ground you should not be able to get more than one revolution when spinning by hand.