How smooth can an IO360-M1A be?

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Roxi5m9
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How smooth can an IO360-M1A be?

Postby Roxi5m9 » Sat Oct 06, 2018 12:04 am

I have a 2004 DA40 that has a continuous vibration consistent with engine RPM that I am trying to smooth out. It’s not a terrible vibration, but i fly in other planes (not DA40s) that are glass smooth and my engine and prop are recently overhauled. I had the prop dynamically balanced, starting at .16 IPS. After 4 hours and about 12 grueling engine starts and run ups, the best we could get it was .10 IPS, and it doesn’t feel any better. Anytime the mechanic would try to improve upon .1 ips, the vibration angle would drift and increase. This is the only diamond I’ve ever flown and the only airplane I’ve ever owned (meaning:the only plane I’ve cared enough about to pay attention to vibration). But I’ve flown about 30 different types of planes.

So my questions are: have any of you had trouble balancing your prop? And more importantly, are DA 40s just an aircraft that has some vibration? How smooth are your DA40s? Should I be able to get my DA40 to run as smooth as a bonanza?
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Re: How smooth can an IO360-M1A be?

Postby blsewardjr » Sat Oct 06, 2018 1:12 am

I have the aluminum prop on a 2003 DA40. I had it balanced to .02 IPS, but the aircraft still vibrates more than, e.g., a 172. My theory is that the rigid composite airframe is the culprit. I've tried all different cruise RPMs -- the vibrations differs somewhat by feel but not by intensity -- so I fly it at 2450 rpm, which was recommended for the Powerflow exhaust. I've flown both the MT (my aircraft) and the Hartzell composite props (rental). Definitely smoother but the MT prop (original type) was prone to damage and the Hartzell is too expensive to justify swapping out.
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Re: How smooth can an IO360-M1A be?

Postby pietromarx » Sat Oct 06, 2018 4:43 am

I just had my DA40 dynamically balanced (engine running at 2200 RPM) from an IPS of 0.4 to essentially zero (unmeasurable).

This said, the Hartzell composite propeller has always felt smoother than the aluminum one I had on my previous DA40. This one is brand new (undisclosed lightning strike from previous seller) and it had been statically balanced, of course. The metal one on my old DA-40 simply rattled around a lot during startup and shutdown.

There are a lot of moving parts (literally) and I haven't found the DA40 to be much different than the other airplanes I've flown with a -360 motor (including wood Decathlons, metal C172s, and composite DA40s).

You might want to check the engine mounts and see if they've gotten stiff in the last fourteen years (assuming they weren't replaced during your overhauls). The vibration issue was certainly one that made the whole exhaust system crack on early DA40s (I had one that broke multiple times on a 2004).
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Re: How smooth can an IO360-M1A be?

Postby Rich » Sat Oct 06, 2018 2:25 pm

Also check the bolts that attach the motor mount frame to the firewall.

Do not expect the 4-cylinder 360 to be as smooth as the six-bangers you'll find in other aircraft. The MT and Hartzell composite are much lighter than the aluminum props and can make a difference.
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Re: How smooth can an IO360-M1A be?

Postby CFIDave » Sun Oct 07, 2018 4:29 pm

I've been able to fly many different Lycoming DA40s during ferry flights and transition training for new owners, etc. I learned that smoothness of the IO-360 across different aircraft varies tremendously. A few Lycoming DA40s I've flown ran almost as smoothly as a DA40 NG with Austro diesel. :D

Unfortunately one of the worst was the nearly-new DA40 that I owned for 4 years; in cruise the entire instrument panel vibrated. I tried everything I could think of to decrease vibration including prop balancing (of a 3-bladed MT prop), GAMIjectors, finewire plugs, new mags, new wiring harness, etc. I finally gave up, attributing the vibration to that particular engine. The plane otherwise performed well; I was able to achieve 150+ knot cruise speeds.
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Re: How smooth can an IO360-M1A be?

Postby Erik » Sun Oct 07, 2018 4:50 pm

CFIDave wrote:I've been able to fly many different Lycoming DA40s during ferry flights and transition training for new owners, etc. I learned that smoothness of the IO-360 across different aircraft varies tremendously. A few Lycoming DA40s I've flown ran almost as smoothly as a DA40 NG with Austro diesel. :D

Unfortunately one of the worst was the nearly-new DA40 that I owned for 4 years; in cruise the entire instrument panel vibrated. I tried everything I could think of to decrease vibration including prop balancing (of a 3-bladed MT prop), GAMIjectors, finewire plugs, new mags, new wiring harness, etc. I finally gave up, attributing the vibration to that particular engine. The plane otherwise performed well; I was able to achieve 150+ knot cruise speeds.


Could it be a matter of how well the pistons themselves are balanced?

I recently had to replace the cylinders-pistons on my TSIO520NB on my Mooney (argh - there was nothing wrong with them other than they got rounded up on an AD against Titan cylinders). SO it was smooth before as the 6 cylinder Conty's usually are, but I got the new ones from Victor aviation that does a bunch of extra things like gram balancing (many places do) plus flow balancing which is special - and I also had them tune the valves for really tight closing - anyway this engine is amazingly smooth now.
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Re: How smooth can an IO360-M1A be?

Postby Rich » Sun Oct 07, 2018 6:23 pm

For various analyses it's worth thinking of these engines as 4 separate engines, linked together by the camshaft. In addition to differences in the mass of the pistons, etc., each cylinder is prone to deliver a different amount of power than its mates. At 2400 RPM, you get 80 power pulses, If they're all exactly equal, you've got an 80 Hz driving vibration. But if one of the cylinders is a bit lower or higher than the others, you have an unbalanced driving vibration.

Dynamically balancing the prop has a limitation in that it's not done at cruise power settings. So it addresses the mass imbalance of the prop/engine rotating mass, but can't measure the variations that may be introduced at realistic inflight power settings.
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Re: How smooth can an IO360-M1A be?

Postby Steve » Thu Oct 11, 2018 2:24 am

Was a nice day to fly around the Texas Hill Country today, and while up there, I remembered this thread. So I captured a snapshot using the Vibration App on my iPad. My iPad is mounted on the instrument panel using an Angerole mount, which is fairly rigid.

TimeSeriesImage.jpg
FrequencyImage.jpg


The acceleration traces are pretty low (averaging less than 0.25 g. The FFT shows the major components are at approximately 13, 18, and 23 Hz. I was cruising at 2200 RPM. I'm not really sure how to interpret this data yet, other than having it as a baseline for when the engine seems to be running smoothly. I've never done a dynamic balance on the prop, just the static balance they did when overhauling it.

Steve
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Re: How smooth can an IO360-M1A be?

Postby Pilot55 » Thu Oct 11, 2018 4:28 pm

If your engine is running @ 2200 rpm you are turning 36.7 rps. on a 4 cylinder 4 stroke engine it has a power stroke every 180 degrees so the engines power frequency is 18 hz @ 2200 rpm. If a aircraft engine had a heavy fly wheel the pulses of the engine would be dampened and have much less vibration. As long as the prop is close in balance it is mainly our 4 cylinder engines that cause the vibration.
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Re: How smooth can an IO360-M1A be?

Postby Steve » Thu Oct 11, 2018 4:36 pm

Pilot55 wrote:If your engine is running @ 2200 rpm you are turning 36.7 rps. on a 4 cylinder 4 stroke engine it has a power stroke every 180 degrees so the engines power frequency is 18 hz @ 2200 rpm. If a aircraft engine had a heavy fly wheel the pulses of the engine would be dampened and have much less vibration. As long as the prop is close in balance it is mainly our 4 cylinder engines that cause the vibration.


That makes sense, since the X - axis pulses @ 18 Hz are the biggest component. Thanks,

Steve

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