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Prop Vibrations ?

H

HotDoc

I'm New Here
Hello everyone,

we have an RV-7 w Aerosports IO 375 w dual Pmags and a Hartz C2YR-1BPFP/F7497-2. Seems to run fine (14 hrs logged) so far, but a friend has raised the issue of vibration problems. Can anyone comment on that topic? Is it safe to continue operation?:confused:
Thanks,

HotDoc
 
Short of having a dynamic balance done, I'd find someone who has a bunch of experience flying behind Lycoming 4 bangers. They all seem to be a little different. The combination on the -8 is smooth as silk, while a similar combination on my Hiperbipe is much rougher in comparison.
 
I think the only way to settle it is to have it dynamically balanced. Everything else is purely subjective.
 
I agree a dynamic balance and make sure there is nothing rubbing/touching from the engine to the cowl other than baffling material.
 
vibration or resonance?

It is likely that your friend is raising the issue of resonance/harmonics rather than vibration (as in balance). Hartzell tests and approves certain prop/engine combinations for acceptable resonance characteristics and does not recommend unapproved combinations.
There is lots of discussion on this site about the issue.
Also, see for example
http://www.vansaircraft.com/pdf/Hartzell_c2yr.pdf

This relates to the older blended airfoil prop that Van's supplied. For the current prop, Van's site refers builders to the Hartzell site for information. Electronic ignition, fuel injection, high compression can apparently affect resonance characteristics. Whether it is a problem is a separate question.
Bill Brooks
Ottawa, Canada
RV-6A
 
C-GRVT said:
It is likely that your friend is raising the issue of resonance/harmonics rather than vibration (as in balance). Hartzell tests and approves certain prop/engine combinations for acceptable resonance characteristics and does not recommend unapproved combinations.
Click to expand...

Right on.

Prop blades vibrate in many interesting ways. Speaking for myself, I have no interest in flying a metal prop which has not been subject to a vibration survey on the engine configuration of interest.

I have an older friend who once worked in an experimental area of a very large aerospace concern. He told me the scariest thing he had ever seen was propeller blade vibration in the lab, using a variable rate strobe, and if I bought a strobe and played with it enough I might not fly anymore. Well, naturally I bought one.....
 
Recommended CS-Prop for IO 375

Well guys,

I start to understand the issue. What kind of prop would you recommend for the IO 375? We couldn't find any real recommendations other than "it should work".

Thanks,

HotDoc
 
Hi, probably I am the one who raised the concerns.
And yes I am referring to harmonic vibrations, according to Hartzell they are not detectable by the pilot.

There is a restriction given by Hartzell - tested was this prop with the ECI-370. Max 24" MAP below 2450 RPM. What makes me thinking is that it was not tested with electronic ignition which we have. All I know is that it has to be tested to be sure. One can look up on the IO-360 (200hp) without dampeners and with this prop and see very similar restrictions. Also without electronic ignition and as I said it has to be tested to be sure.

I am thinking that the composite WW200RV prop is save although not tested. Quite some guys flying this combo and composite is much less prone to vibes.
 
SuperCubDriver said:
Hi, probably I am the one who raised the concerns.
And yes I am referring to harmonic vibrations, according to Hartzell they are not detectable by the pilot.

There is a restriction given by Hartzell - tested was this prop with the ECI-370. Max 24" MAP below 2450 RPM. What makes me thinking is that it was not tested with electronic ignition which we have. All I know is that it has to be tested to be sure. One can look up on the IO-360 (200hp) without dampeners and with this prop and see very similar restrictions. Also without electronic ignition and as I said it has to be tested to be sure.

I am thinking that the composite WW200RV prop is save although not tested. Quite some guys flying this combo and composite is much less prone to vibes.
Click to expand...
WW 200 RV or maybe an MT ?natural composite? since you?re in Germany Mt must be in your back yard.

Even though there are no RPM/power restrictions for my I0-360-A1A and MTV 15B 183 33 I was told by MT USA I would get better service life from my prop if I followed the restrictions for the Hartzell, I believe the RPM needs to be 2550 or greater at or above 24?, I cruse at 2400 and 22?.
 
A good prop balance with a vibration spectrum analysis would be a good place to start. I can do both of these with my equipment, however, I'm not saying this is the same as Hartzell doing a full blown stress test but it would rule out the subjective "feels bad to me" type measurement.

Here is a vib plot and spectrum analysis plot, find a good prop balancer to do this for you and go from there.

RV8%2520Dalham2.png.jpg


The above Hartzell prop was more than double the upper limit at 0.414 IPS (the red circle is the 0.2 IPS upper limit). When I got done (3 runs) it was down to 0.016 IPS and the reduction in vibration was quite noticable.

RV8%2520Dalham1.jpg


The spectrum analysis above shows frequency (CPM) from 150 to 15,000. This allows me to look at all the major harmonics of the engine/prop. An abnormal vibration is easily spotted with this equipment.
 
For those of you flying the Whirlwind Propeller, please note in the manual in big bold letters "Must be dynamically balanced prior to flight" (or something very similar). I did this one today and the owner was absolutely amazed at the difference it made. From what my customers have told me, I think the lighter the prop the more noticable the difference is on balance issues.

This one started at 0.482 IPS (way out of limits) and we ended up in 3 runs at an amazingly low 0.006 IPS (one of the very few I've ever seen this low and is pure luck to get one this low!).

Whirlwind%2520prop%2520bal.jpg


So if have a light weight prop (whirlwind, MT, FP) do yourself a favor and get it balanced :D

For those of you interested the 3 runs are:
Run 1 = Initial balance run.
Run 2 = Balance run with test weight.
Run 3 = Balance verification run with final weights installed.
 
Last edited:
Radial balance and propeller blade modes are not the same thing.

Blade modes:

 
Again, VAF is great

Seen those vibration modes (especially the "C" ones) many years ago while in the ultralight industry. Disconcerting to be sure.

But the reason for this post is to say this thread got me alarmed about my stock M1B and the B/A 7497 because I have been operating well into the "bad zones" that are placarded for some other B/A-engine combinations. (2500 RPM WOT, Low RPM High MP)

I had it in my head that I "knew" there were no limited ranges but when searching through my documentation I could find no PROOF.

I looked at the Hartzell sight for an evening. No joy.
After multiple searches on VAF with differing terms, I finally found a post here from Hartzell that put my concerns to rest.

Post from Les Doud (Hartzell)

I went to the document he mentioned and it still does not show the M1B specifically but it does show the M1A.

Sigh of relief.

I may be looking at an RPM restriction if I go electronic ignition later.
 
I was instrumental a few years back in getting MT engineers to come to the US to do a vibration analysis of the MT7 and the Egg Subby H6 engine. It is quite an involved flight test process. Andy Parish provided the airplane and piloting while all the data was collected and later evaluated by the guy from Germany. The data came in good for Subby drivers with that prop and engine.

The same needs be done with some of the combinations we see with Lycoming. It might cost some bucks but it would place to rest and end speculation on the subject.

Other than that, if in doubt, go Catto :)
 
I've looked into harmonic resonance issues quite a bit, and while I'm far from educated, I DO know it is a complicated issue based on many variables - and can be catastrophic.

That said, how many reported cases are there of a Hartzell prop coming apart due to HR?
 
Walt,
unfortunately I don´t have the range all the way to Texas. Dynamic balance is on my list for sure.
Did you ever do vibration tests with and without electronic ignition? How do they usually compare?
From where does the limit 0.2 IPS come from?
 
I've done "tons" of RV's with electronic ignition and have not noticed any difference in balance results or harmonics. Admittedly I have not done an analysis between the two as each engine has its own characteristics so to get accurate results you would have to do a spectrum analysis on the same engine with and without electronic ignition. Most engines are very similiar, but each is distinctly different. Internal engine balance, gas pressures etc. will never be identical on any 2 engines.

The "industry" standard as well as the Hartzell manual recommends balancing to less than 0.2 IPS, however, here is a note from the McCauley manual:

"Most dynamic balance equipment manufacturers specify 0.15 - 0.2 ips as being an acceptable level. McCauley Propeller Systems agrees that 0.15 - 0.2 ips is an acceptable level, but our experience has shown that 0.07 ips or lower is noticeably smoother."

We now have equipment that is capable of balancing to much lower levels than previously possible, the 0.2 IPS industrly "standard" was somewhat based on equipment limitations.
 
MTV-9 with no RPM restrictions with IO-375 dual PMAG

We are flying an RV-7 with Aerosports Power IO-375 with dual PMAGs since more than one year (140 hours) with an Hartzell C2YR-1BPFP/F7497-2.
We followed the discussions in this forum concerning harmonic resonance vibrations with this propeller - engine combination and therefore asked Aerosports Power + Hartzell + emagair do run vibration tests to identify any RPM/MAP restrictions for this combination. However after several attempts to get the test done we gave up end of 2013 and decided to replace the Hartzell propeller with a 3 Blade MTV-9 Propeller. MT recently conducted the vibration analysis tests with our plane. We now received the official E-241 document stating no operational RPM/MAP restrictions with the MTV-9 propeller with the IO-375 + dual PMAGs.

A performance comparison between the Hartzell C2YR-1BPFP/F7497-2 and the MTV-9 is also available. I will post the results in a new thread
 
I know Hartzell did do Vibe testing on the O-360/IO-360 with EI, which is what resulted in the 7497 replacing the 7496.

There are hundreds of planes flying behind the 360/7497-2 setup, that is the known/tested quantity. The reality is, if you go with an experimental, low volume engine, you can't expect a value-minded manufacturer to test every single engine/ignition/prop combination.

I'm with the "It should be fine" crowd, I'm sure there are plenty of them flying, and I haven't heard of a single 7497 coming apart yet. MTV-9's on the other hand?
 
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