Vibration point on sensenich prop

[riobison]

On my O320 in a RV9A with the sensenich (2600 rpm restricted prop) 1 light speed EI, 1 Mag and 9:1 CR.

If I inadvertently exceed the 2600 RPM it stays smooth to 2630+ RPM then by 2650 it's obvious that I need to reduce my RPM.

I was wondering what everyone else has noticed, or not?

Thanks

Tim

 

[Jpm757]

So are you thinking that 2600 rpm is a no no, but operating below and ABOVE that is OK?
Might run that by Sensenich? I think they will say no.

 

[riobison]

So are you thinking that 2600 rpm is a no no, but operating below and ABOVE that is OK?
Might run that by Sensenich? I think they will say no.

No, that's not what i was saying. I was only stating what I was noticing and I was looking for comparisons.

In all honesty I had always wondered if the vibration that the prop is placarded against was something subtle that may not even be noticed by the pilot, or if it's blatantly obvious that you don't want to go there.

Now having an EI and higher compression I'm curious if that has changed anything from a stock motor that Sensenich would have done the testing on.

At least in my configuration I know its the latter, its there and blatantly obvious that you don't want to go there. With a FP prop it doesn't take much to pick up an extra 40 rpm on the tach when cruising at 2600 rpm.

Again, I was just wondering what everyone else has noticed or not with this prop on this engine.

Thanks

Tim

 

[rvbuilder2002]

Dangerous vibrations that can cause failure of a propeller can be undetectable by people in the airplane.
I was involved with the in flight propeller testing many years ago that was done in collaboration between Vans Aircraft and Hartzell propeller engineers.
They were quite surprised when we started testing using alternative ignition systems with variable ignition timing capability.
Some test conditions turned a propeller that would have had no limitations, into one that would.
We never did any actual testing with higher than standard compression (8.5-1 on the parallel valve engine used in the testing) but based on the rest of the test data it was likely that increased compression would have a negative impact as well.
The insidious thing about this is that unless testing has been done on a specific engine configuration / propeller combination, there is no way to know there is an issue until something bad happens.
It has been so long ago, that the typical modern day home builder doesn’t know anything about the big spread the word campaign that EAA 50+ years ago together people to stop cutting down the diameter of fixed pitch metal props taken off of certificated aircraft. There were a lot of accidents caused by catastrophic propeller failures. Changing the length, changes the natural resonant frequency of the propeller. That is one reason metal propellers have dimensional limitations regarding doing repairs.

 

[Radioflyer]

...
They were quite surprised when we started testing using alternative ignition systems with variable ignition timing capability.
Some test conditions turned a propeller that would have had no limitations, into one that would. ...
The insidious thing about this is that unless testing has been done on a specific engine configuration / propeller combination, there is no way to know there is an issue until something bad happens. ...

RVBuilder's comment raises a question. In my case, I have a Sensenich 72fm8s9-1-85 on a TMX O-360 with dual mags. Sensenich says there are no RPM limitations whatsoever (Install List #207). However, I was intending to replace one of the mags with electronic ignition. Hmmmm..., anyone running this prop/engine with electronic ignition?

 

[gasman]

On my O320 in a RV9A with the sensenich (2600 rpm restricted prop) 1 light speed EI, 1 Mag and 9:1 CR.

If I inadvertently exceed the 2600 RPM it stays smooth to 2630+ RPM then by 2650 it's obvious that I need to reduce my RPM.

I was wondering what everyone else has noticed, or not?

Thanks

Tim

I have a 6A O320 LSI and hi comp pistons also. In level flight, I have to push it to exceed 2600 rpm. It won't just happen inadvertently.

You should be running a 79" pitch prop....

 

[riobison]

Dangerous vibrations that can cause failure of a propeller can be undetectable by people in the airplane.
I was involved with the in flight propeller testing many years ago that was done in collaboration between Vans Aircraft and Hartzell propeller engineers.
They were quite surprised when we started testing using alternative ignition systems with variable ignition timing capability.
Some test conditions turned a propeller that would have had no limitations, into one that would.
We never did any actual testing with higher than standard compression (8.5-1 on the parallel valve engine used in the testing) but based on the rest of the test data it was likely that increased compression would have a negative impact as well.
The insidious thing about this is that unless testing has been done on a specific engine configuration / propeller combination, there is no way to know there is an issue until something bad happens.
It has been so long ago, that the typical modern day home builder doesn’t know anything about the big spread the word campaign that EAA 50+ years ago together people to stop cutting down the diameter of fixed pitch metal props taken off of certificated aircraft. There were a lot of accidents caused by catastrophic propeller failures. Changing the length, changes the natural resonant frequency of the propeller. That is one reason metal propellers have dimensional limitations regarding doing repairs.

I don't disagree with you and old enough to remember some of those old articles.

Probably a large % of us flying with alternative ignition and compressions.

In all honesty I was surprised by what I found and how close it is to the 2600 prop limitation. 500 hr plane, no incidents and no accidents. I've checked what I can with prop tracking etc and no one around here to dynamic balance it. But, I will check the prop clocking as its not stopping at where most of the RVs prop stop at. Then again prop clocking appears to vary depending on who's writing the article.

I started this post to see what everyone else is seeing. Not getting much feedback on it so I don't know what to think.

But for me, I don't like RPM restricted props. Yes I run my RPM high on long flights at altitude at the top RPM (15% of my flights). The other 85% Im loitering around at 2000 rpm. With this prop Im already down 100 rpm and I probably want to give myself another 50 rpm safety factor so now I'm leaving more speed and performance on the table.

I don't think this prop is for me. I'm probably better off looking at composites that might be a little more tolerant of deviation from the Normal AC configuration and harmonics.

Thanks
Tim

 

[riobison]

I have a 6A O320 LSI and hi comp pistons also. In level flight, I have to push it to exceed 2600 rpm. It won't just happen inadvertently.

You should be running a 79" pitch prop....

Under 9000 DA mine will easily exceed 2600. A strong running O320 that doesn't burn any oil, I'd hate to change anything. Yes more pitch but then I'll lose out on the climb rate.

I don't think this prop is for me. I'm probably better off looking at composites that might be a little more tolerant of deviation from the Normal AC configuration and harmonics. Probably a GA.

Thanks
Tim

 

[Ralph Inkster]

Tim
I’m sending you a PM
Ralph

 

[riobison]

Got it and thanks Ralph

Tim

 

[rvbuilder2002]

Under 9000 DA mine will easily exceed 2600. A strong running O320 that doesn't burn any oil, I'd hate to change anything. Yes more pitch but then I'll lose out on the climb rate.

I don't think this prop is for me. I'm probably better off looking at composites that might be a little more tolerant of deviation from the Normal AC configuration and harmonics. Probably a GA.

Thanks
Tim

The best prop match on an RV for the best possible "Total Performance" using a fixed pitch prop, is one that requires some amount of throttle reduction below about 12K density altitude to stay at or below 2700 RPM.

My 6A with a 180 fixed Sensenich does a TAS of 168-169 kts starting at about 10.5K with a slight throttle reduction in MP to keep me around 2600 RPM (it would exceed 2700 at that DA and WOT). That is an RPM it is happy and very smooth at. Though I don't personally have a concern about spinning it faster, it just makes more noise and burns more fuel but doesn't seem to go much, if any faster.

If I cruise higher, I can keep pushing the throttle in a bit more with each increment of 1000 ft and have the same or just slight faster TAS.
In my airplane this is actually a benefit since it has a carb.
With the carb., reducing the throttle setting slightly makes the mixture more balance because of the slight angle of the throttle plate.
When I am operating at the sweet spot for altitude/RPM/MP/ Mixture, my CHT spread is about 6 degrees and the EGT's are relatively close as well with the leanest at about -20 lean of peak.

So in reality I have a combination Climb / Cruise prop. It just all depends on how someone chooses to operate.
You having the hard limit of 2600 is a bit more of a compromise, but if I owned your airplane, I wouldn't' change it because of the hit on take-off and climb performance.

Follow-up
I wasn't meaning to imply that everyone running higher compression and or advanced timing is flying a ticking time bomb in regards to their propeller...

What I was meaning to say is that unless it is an engine configuration / prop combination that has been tested using test equipment typically used for that work, there is no way to know for sure because it is not something you can feel.
That is why Hartzell has the warnings and disclaimers on their web site regarding installing their propellers on engine configurations that they have never tested.

 

[rmarshall234]

The best prop match on an RV for the best possible "Total Performance" using a fixed pitch prop, is one that requires some amount of throttle reduction below about 12K density altitude to stay at or below 2700 RPM.

My 6A with a 180 fixed Sensenich does a TAS of 168-169 kts starting at about 10.5K with a slight throttle reduction in MP to keep me around 2600 RPM (it would exceed 2700 at that DA and WOT). That is an RPM it is happy and very smooth at. Though I don't personally have a concern about spinning it faster, it just makes more noise and burns more fuel but doesn't seem to go much, if any faster.

If I cruise higher, I can keep pushing the throttle in a bit more with each increment of 1000 ft and have the same or just slight faster TAS.
In my airplane this is actually a benefit since it has a carb.
With the carb., reducing the throttle setting slightly makes the mixture more balance because of the slight angle of the throttle plate.
When I am operating at the sweet spot for altitude/RPM/MP/ Mixture, my CHT spread is about 6 degrees and the EGT's are relatively close as well with the leanest at about -20 lean of peak.

So in reality I have a combination Climb / Cruise prop. It just all depends on how someone chooses to operate.
You having the hard limit of 2600 is a bit more of a compromise, but if I owned your airplane, I wouldn't' change it because of the hit on take-off and climb performance.

Follow-up
I wasn't meaning to imply that everyone running higher compression and or advanced timing is flying a ticking time bomb in regards to their propeller...

What I was meaning to say is that unless it is an engine configuration / prop combination that has been tested using test equipment typically used for that work, there is no way to know for sure because it is not something you can feel.
That is why Hartzell has the warnings and disclaimers on their web site regarding installing their propellers on engine configurations that they have never tested.

^^^^
This

I think FP props get a bit of a “bad rap” when compared to CS props. Especially when one takes into account the added weight, complexity and cost. I had a FP wooden prop on my -3 and it would out climb an Extra 300 and exceed VNE in straight and level flight. I can’t take credit for having chosen and ordered that prop but the previous owner and the prop maker clearly knew what they were doing.

 

[riobison]

The best prop match on an RV for the best possible "Total Performance" using a fixed pitch prop, is one that requires some amount of throttle reduction below about 12K density altitude to stay at or below 2700 RPM.

My 6A with a 180 fixed Sensenich does a TAS of 168-169 kts starting at about 10.5K with a slight throttle reduction in MP to keep me around 2600 RPM (it would exceed 2700 at that DA and WOT). That is an RPM it is happy and very smooth at. Though I don't personally have a concern about spinning it faster, it just makes more noise and burns more fuel but doesn't seem to go much, if any faster.

If I cruise higher, I can keep pushing the throttle in a bit more with each increment of 1000 ft and have the same or just slight faster TAS.
In my airplane this is actually a benefit since it has a carb.
With the carb., reducing the throttle setting slightly makes the mixture more balance because of the slight angle of the throttle plate.
When I am operating at the sweet spot for altitude/RPM/MP/ Mixture, my CHT spread is about 6 degrees and the EGT's are relatively close as well with the leanest at about -20 lean of peak.

So in reality I have a combination Climb / Cruise prop. It just all depends on how someone chooses to operate.
You having the hard limit of 2600 is a bit more of a compromise, but if I owned your airplane, I wouldn't' change it because of the hit on take-off and climb performance.

Follow-up
I wasn't meaning to imply that everyone running higher compression and or advanced timing is flying a ticking time bomb in regards to their propeller...

What I was meaning to say is that unless it is an engine configuration / prop combination that has been tested using test equipment typically used for that work, there is no way to know for sure because it is not something you can feel.
That is why Hartzell has the warnings and disclaimers on their web site regarding installing their propellers on engine configurations that they have never tested.

I agree and most of my flying where Im concerned about the RPM is above 8500 ft. Not just a hit on the 2600 RPM but probably need to set my limit at 2550 so I have a bit more of a buffer and now a 150 rpm hit.

Of course out west here DA in the summers are generally north of 6000' taking off so I do need the RPM for the TO and the climb.

Ralph is able to do a dynamic balance so before I make any major changes such as buying another prop, we will start with the easy stuff for troubleshooting, prop clocking etc.

I haven't see anyone else mention that they have noticed the vibration on their planes with this prop.

So does that mean no one else has noticed it? Or no one wants to admit that they have been to the dark side and have noticed it but won't talk about it?

Tim

 

[Steve Iacoviello]

I agree and most of my flying where Im concerned about the RPM is above 8500 ft. Not just a hit on the 2600 RPM but probably need to set my limit at 2550 so I have a bit more of a buffer and now a 150 rpm hit.

Of course out west here DA in the summers are generally north of 6000' taking off so I do need the RPM for the TO and the climb.

Ralph is able to do a dynamic balance so before I make any major changes such as buying another prop, we will start with the easy stuff for troubleshooting, prop clocking etc.

I haven't see anyone else mention that they have noticed the vibration on their planes with this prop.

So does that mean no one else has noticed it? Or no one wants to admit that they have been to the dark side and have noticed it but won't talk about it?

Tim

I suspect most of us respect the 2600 rpm limit and do not violate it.

 

[lawrence]

sensenich vibration

Tim: i set my tach to 2600 on my sensenich at 8500da or higher.always.
infrequently,it changed. if it did it was only 10-15 rpm over.
and i would reset to 2600.my engine was very smooth at that rpm.
"temporary and infrequent 10-20 rpm over 2600 is not concerning"
that was my takeaway from a conversation with a sensenich engineer.
the same engineer also said
"vibration above 2600 was real and the 2600rpm limit was important to observe" the 2600 rpm limet has some cushion. never,never run continuous above 2600.
set your tach to 2600 and enjoy.
lawrence

 

[Steve]

I configured my tach on the G3X to show yellow at 2600 rpm and red at 2700. It's tough to hold a steady rpm westbound across Wyoming in the afternoon returning home from Oshkosh and still make a respectable ground speed.

 

[Freemasm]

This topic has breached a few different areas. I was not involved in the design/application of this PP and prop; however:

RPM limits. It is extremely doubtful that 2600 is a hard limit for the prop. Basically, it makes little sense to apply pieces of rotating equipment with different rpm limits in this case. Though nothing prevents such, it does not follow good design practices and we are talking reputable OEMs. Different industries have different standards but in general, any piece of rotating equipment should be capable of a 10% over speed without the need for tear-down/possible visual inspection only. Some are as low as 5% but typically require over speed protection (automated control response); not the case in our world.

Critical frequency. The 2600 limit sounds as though it is intended to avoid a critical frequency/resonance. (2nd critical? Hopefully a rotor dynamicist will reply). This is supported by the fact that vibration levels increase a mere ~30 measured rpms above the stated limit. Stress amplitudes increase dramatically at these operation points. Even if fatigue cracks aren’t initiated, the engine main bearing loads and subsequent wear increase by magnitudes at these operating points.

Torsional vibration. The advanced timing and increased compression ratios make for higher power pulses which can lead to fatigue issues and subsequent catastrophic failure.

Observe the OEM limitations. They are there for a reason. The TV and critical frequency issues are more scary as this isn’t a case of taking advantage of the OEM’s design margins.

Be safe. Off the soapbox.

 

[riobison]

Well made some changes for the good

Well made some changes for the good;

I reclocked the prop from 10-4 to 2-8 as per RVator 10/92 and checked the tracking, it was good.

This certainly felt better SOP but due to weather I wasn't able to wind it out on my trip to Spring Bank.

Ralph did a Dynamic Balance on it and we had to relocate the existing 14 gram wts a few inches and now have it at down to .06 IPS.

On take off it felt similar to the previous flight that morning. The next day I was able to get some good weather, get the RPM up to where I had noticed the vibration at the start of all of this, and it was gone. So smooth................

So not a lot of changes but enough to make a difference and that's what counts.

Tim

 

[Freemasm]

Glad things are running smoother. Please don’t be fooled. The OEM limits still apply. Not adhering to them could have expensive, serious, consequences.

Stay safe, Sir.