2100 to 2350 RPM?

[MBDiagMan]

So how sacred is the no continuous operation zone with the IO360?  I find myself sometimes in that range on an approach and it really feels like I need to leave it there.  I guess the key is to change the governor speed to get the right power from a different RPM range.

Any words of experience and wisdom to share?

Also, WHY is this range to be avoided?  That is, what is the engineers explanation?

[RLCarter]

I heard it was due to harmonic vibrations that is bad for everything involved..... But never seen anything other than that

[Andy95W]

In the past few years, there have been 2 schools of thought here at MooneySpace:

1.) avoid at all costs except for transitioning through that range.

2.) never set a cruise rpm in that range, and avoid it if possible.  In the traffic pattern, with the propeller set full forward and the engine producing minimal power, just fly the airplane (not that it matters, but that's what I do).

A few weeks ago, either Rich @N201MKTurbo or maybe @Yetti posted that it was to prevent bad harmonics caused by the power pulses of the ignition stroke at those rpms.  So I'm sticking to what I've been doing for 20 years of Mooney flying.

 

[David Lloyd]

Don't cruise in that RPM range, that would be considered continuous.  On an approach, use what you need and don't worry about it.

[MBDiagMan]

Thanks guys!

[carusoam]

late summary...

1) +1 on harmonics... you will never feel it...

2) +1 on transition... take your time moving through it... don’t leave it there.

3) Make sure it still applies...  if it is the same engine and prop that came with the plane, it still applies...

4) If you got a different prop... it may have a different range or it got eliminated....

5) Some ranges changed over the years... my 65C got a new range to avoid somewhere along the way....

 

In the end... my engine mount broke a pair of welds on the bottom of one of the legs... possibly a result of that range...?

PP thoughts only, not a mechanic...

Best regards,

-a-

[Ross Taylor]

I'm not at the plane...but doesn't that range also have a MP limit?  Like, "don't operate in this range above 24 inches" or something?  If I remember that correctly, it wouldn't be a factor on approach.

EDIT: I looked at photos and confirmed that my RPM limit placard specifically says it applies above 24 inches MP

[ShuRugal]

My manual can't even decide what the red-arc range actually IS.  page 20 of the 1965 M20C manual states "it is recommended that the engine not be operated for cruise purposes within the range of 2150 to 2300 RPM", while while Page 39 declares "Red Arc - Narrow (No continuous operations in this range)" to be 2000 to 2250 RPM.

Considering that the cruise data table gives values for 2300 RPM, i'm going to guess that page 20 is a publication error.

[carusoam]

Things changed between the print date of the Owners Manual and the final range setting....

Where to look up the details...

We could ask, our prop guy...

my 65C tach had a red line added to the exterior of the instrument...

PP thoughts only, not an instrument guy...

Best regards,

-a-

[RLCarter]

You can find the correct range in the TCDS on the FAA's website, also the performance charts will not have the RPM range in them

[R-Banger]

+1 the above comments as it varies with prop and engine combo. Mine is red from 2000-2349 rpm. 

[RLCarter]

Just now, R-Banger said:

Mine is red from 2000-2349 rpm. 

2349, really? My 65 E is 2000~2350

[R-Banger]

Just now, RLCarter said:

2349, really? My 65 E is 2000~2350

Yep it is specifically placarded that way on mine. It's a digital tach versus a arc on a dial.

[RLCarter]

21 minutes ago, R-Banger said:

Yep it is specifically placarded that way on mine. It's a digital tach versus a arc on a dial.

Odd

[cliffy]

The RPM range to be avoided is dependent on the engine and prop combination. 

There is usually and RPM range AND MP combination to avoid. And Yes it has to do with engine internal harmonics. 

If your prop has been changed from the one that it came with from the factory (model, type, manufacturer) then the prohibited ranges for the RPM will be different than what is in the hand book. 

Find the engine model (from the data plate on the engine as what is in the log book may or may not coincide with what is installed on the airplane) find the make a model of the propeller and then go dig out the correct RPM ranges. 

Not that its certain but it wouldn't be the first time someone has and engine or propeller that didn't match what was in the book. 

This is one if the first things I check on a prebuy and something many times missed on most prebuys, No one seems to check the data plates to the log book.

[RLCarter]

35 minutes ago, cliffy said:

There is usually and RPM range AND MP combination to avoid. And Yes it has to do with engine internal harmonics. 

RPM is on the TCDS But didn’t see a reference to MP.....

[Tcraft938]

7 hours ago, cliffy said:

The RPM range to be avoided is dependent on the engine and prop combination. 

There is usually and RPM range AND MP combination to avoid. And Yes it has to do with engine internal harmonics. 

If your prop has been changed from the one that it came with from the factory (model, type, manufacturer) then the prohibited ranges for the RPM will be different than what is in the hand book. 

Find the engine model (from the data plate on the engine as what is in the log book may or may not coincide with what is installed on the airplane) find the make a model of the propeller and then go dig out the correct RPM ranges. 

Not that its certain but it wouldn't be the first time someone has and engine or propeller that didn't match what was in the book. 

This is one if the first things I check on a prebuy and something many times missed on most prebuys, No one seems to check the data plates to the log book.

Excellent advise, and potentially save one $ on a pre-buy.  My AP/IA allowed me to be there and assist in certain things on the two prebuys I did.  The first plane came in the shop and he had me take pictures of data plates on engine, governor, mags, etc.  "One of the best ways to find out up front if we are dealing with someone reputable and cares, or cut corners, or is playing silly games, is to check this stuff out.  Why rip this thing open to find out 4 hours later parts are not legal?  It's a 50+ year old airplane, there may be some checkered past, but hopefully the last 5-10 years someone has sorted that out and kept it good, otherwise YOU'RE going to have to spending $ fixing the sins of others".  We found undocumented parts, signs that maybe not even AP/IA installed and some pencil whipping in the logs and strong indication of corrosion.  Rather than opening more stuff up to confirm the extent of corrosion, I weighed all the factors and very early in prebuy process cam to a No Thank you.   The AP/IA said, "wise choice you saved me time and that saves you $ the $600 pre-buy became $75 and you now know much better what to look for when you look at your next one before a prebuy".  The second Mooney prospect was the opposite experience, him smiling and saying, "I have a feeling you're going to buy this one, if not, you don't really want a vintage Mooney, go find something else".  

This post got me thinking.  My M20 has a two blade Hartzell Scimitar on it and the manual says no restrictions "except for E and F no continuous above 24" between 2350-2550 rpm".  I have a digital tach and on short final or approaches the red light will come on around 2000 rpm, always getting my attention, so I don't fully trust I'm not doing something wrong.  It appears I should either learn to ignore it, and/or get the tach reprogrammed to not give me that red indication.  

[bradp]

My J fwiw is avoid continuous ops 1500-1950 with MP below 15” Hg.   

[Marauder]

So how sacred is the no continuous operation zone with the IO360?  I find myself sometimes in that range on an approach and it really feels like I need to leave it there.  I guess the key is to change the governor speed to get the right power from a different RPM range.
Any words of experience and wisdom to share?
Also, WHY is this range to be avoided?  That is, what is the engineers explanation?

My F has this restriction and I will always end up in that range on leg after the FAF on an approach. I fly approaches at 100 KIAS, even if I slow down to 90 KIAS, I’m still at the bottom end of that arc. I think the word “continuous” means not to set cruise power.


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[mooniac15u]

15 hours ago, MBDiagMan said:

So how sacred is the no continuous operation zone with the IO360?  I find myself sometimes in that range on an approach and it really feels like I need to leave it there.  I guess the key is to change the governor speed to get the right power from a different RPM range.

Any words of experience and wisdom to share?

Also, WHY is this range to be avoided?  That is, what is the engineers explanation?

You should probably think of that range as an electron orbital node.  You should transition instantaneously from one side of it to the other without passing through the space in between.

[BRBENNETT]

Hey guys, I had questions on this topic today and read this thread.  The answer for me lies in the propeller AFMS.  I have attached a copy of what mine looks like.  Hope this helps!!

[EricJ]

It took me a while to figure this out as well, that the scimitar "top prop" doesn't have the limitation if the engine has a crankshaft with the counterweights, at least that's my current understanding.   My tach and engine monitor still show the yellow arc, since that's what was in the POH, and I still avoid it most of the time, and it does have a different vibration in that range, but it is apparently no longer a limitation with my current prop.

Non-counterweight engines still have the limitation, and my understanding of the limitation is that "continuous operation" means anything other than passing through on the way to another RPM.

The limitation is to avoid torsional vibration, which is like repeatedly winding up and releasing a rubber band.   When the crank does that it can eventually fatigue and fail.

On a J the scimitar props are heavier than the ones listed in the TCDS, so maybe that's enough to make the difference.

[Mooneymite]

On 7/9/2020 at 11:04 AM, mooniac15u said:

You should probably think of that range as an electron orbital node.  You should transition instantaneously from one side of it to the other without passing through the space in between.

Yes.  This is definitely true!  I read it on the Internet though I'm not sure what the type certificate says.

Further more, once my RPM went through the red arc and both wings instantly flew off the aircraft from excessive counterweight vibration.  Everyone on board died an awful death....except for me.  

[JimB]

I was curious about this a while back when I first got my Mooney, so I emailed Lycoming Technical Support. They answered very quickly with the response below:

"Operation in this range during cruise flight for any longer than necessary should be avoided due to the restriction. Typically short periods of operation in a restricted range such as during landing or transition to a different power setting would be acceptable but should be avoided whenever possible."

[carusoam]

4 hours ago, JimB said:

I was curious about this a while back when I first got my Mooney, so I emailed Lycoming Technical Support. They answered very quickly with the response below:

"Operation in this range during cruise flight for any longer than necessary should be avoided due to the restriction. Typically short periods of operation in a restricted range such as during landing or transition to a different power setting would be acceptable but should be avoided whenever possible."

That is the category of as good as it’s going to get coming from the engine manufacturer...

Following that advice Loosely for a decade on a 50year old plane... I broke to welds on my M20C’s engine mount... could of been vibration related, but who knows after so long... the vibration could have been an imbalance on an old moderately maintained prop...

+1 on 15U’s explanation for electrons moving from one orbital to another... they seem to skip the energy level in between...

If we used this method light would be emitted each time the prop went from high rpm to low rpm... while making the jump... 

 

This came from the page next to the one Gus was reading... 

Best regards,

-a-

When an electron absorbs energy, it jumps to a higher orbital. This is called an excited state. An electron in an excited state can release energy and 'fall' to a lower state. ... The energy contained in that photon corresponds to the difference between the two states the electron moves between.