Red zone for RPM's?

Moonbat · March 10, 2020

The JPI EDM930 in my plane came with the settings between 2100 and 2350 RPM designated in RED. So I have studiously avoided continuous operation in that range. The plane has a turbo-normalized IO360-A1A engine and an MT-Prop (3 blade). Before I owned this plane, it had two different Hartzell 2-bladed props on it (no - not at the same time!), and, of course, at one time it was not turbo-normalized. I have read all the STC's related to my equipment, and find only that the current MT-PROP has a limit: No continuous operation above 2700 RPM. I see in the older Hartzell prop STC's, there are limits on ranges similar to the 2100-2350 range that is marked in RED on the JPI digital tachometer.

There is also a "Power Plant Limitation" noted in the original POA. On page 45, it says "No Continuous Operation in this Range": 2100-2350. This is the likely reason for the "Red Arc-Wide" limitation on continuous operation between 2100-2350 RPM.

Does anyone know the "why" of that limitation?

(I am aware that most props on planes like this run more efficiently at around 2400. Efficiency is not what I am asking about. I am asking if there is some other reason that the 2100 - 2350 RPM zone might be RED. I've never noticed any vibration in that zone as I transition through it.)

Edited March 10, 2020 by Moonbat
details from the POA

March 10, 2020

There is a vibration issue with the engine / propeller combination in that rpm range. It’s a limitation from the type certificate.

Clarence

**Hank** · March 10, 2020

1 minute ago, M20Doc said:

There is a vibration issue with the engine / propeller combination in that rpm range. It’s a limitation from the type certificate.

And not all dangerous / damaging engine-propeller harmonics can be felt by the person in the front seat . . . .

**EricJ** · March 10, 2020

It is due to torsional vibration on the crankshaft and is propeller dependent. Usually it's a yellow "don't stay here", i.e., no continuous operation, band, though. I don't think I've seen it red before.

March 10, 2020

There is also an AD from way back listed against Mooney.

Clarence

**N201MKTurbo** · March 10, 2020

You should check the STC for the MT prop. It may have changed the red zone.

BTW, the red zone was on 360 engines without counterbalanced cranks and Hartzell propellers.

Moonbat · March 10, 2020

Thanks for those replies. I have read the STC's related to the MT PROP, and find only this limit statement: No continuous operation above 2700 RPM.

Do you think the statement in the STC supercedes the limit stated in the POH?

Super 21 Model M20E Owners Manual - POH1196 M20E - page 45.pdf

Edited March 10, 2020 by Moonbat

**N201MKTurbo** · March 10, 2020

The TC only lists the limitation with the Hartzell installed. There is no limitation with the McCauley installed. With no limitation in the TCDS the prop TCDS would be the controlling limitation.

It looks like you can remove the restriction.

Moonbat · March 10, 2020

That sounds like the answer I was hoping for! I'll do a bit more research first, but, in summary:

1. M20E s/n 670008 with its original Hartzell prop has a limit in the POH for a range of RPM's to avoid.

2. M20E s/n 670008 with a replacement Hartzell prop, a different model than the original in #1, has a limit in its STC for a slightly different range of RPM's to avoid.

3. M20E s/n 670008 with a replacement MT-PROP has a limit in its STC for >2700 RPM operation.

So, the assumption is that with the MT-PROP, one can operate continuously and safely anywhere south of 2700 RPM.

March 10, 2020

When I had the MT prop on my E model I remarked the tachometer to remove the caution arc. When I sold the airplane and reinstalled the Hartzell I had to re-apply the caution arc. The MT should only require a red line per the STC.

Clarence

**carusoam** · March 10, 2020

Summary...

1) There is a yellow caution range added tachs...

2) It is highly recommended to avoid this range for long... more of a transition through zone, then a hang out for a short period of time zone...

3) It can’t be colored red... because that is a no go zone... and it would be impossible to get to the other side...

4) Eric did an awesome job of explaining the torsional vibration and other details...

5) Some pilots can feel it... other pilots in other planes... there is so much other vibration, the detrimental one may be hidden...

6) It is prop and engine combination dependent...

7) My 65C got the AD early in life... the solution was to put a trimmed red label on the surface of the tach’s clear plastic face to depict the range... CB special!

8) Getting a JPI to properly match your updated prop / engine combination... starts with a phone call and providing data...

9) JPI is familiar...

MS rocks!

Best regards,

-a-

Nukemzzz · March 10, 2020

2 hours ago, carusoam said:

Summary...

1) There is a yellow caution range added tachs...

2) It is highly recommended to avoid this range for long... more of a transition through zone, then a hang out for a short period of time zone...

3) It can’t be colored red... because that is a no go zone... and it would be impossible to get to the other side...

4) Eric did an awesome job of explaining the torsional vibration and other details...

5) Some pilots can feel it... other pilots in other planes... there is so much other vibration, the detrimental one may be hidden...

6) It is prop and engine combination dependent...

7) My 65C got the AD early in life... the solution was to put a trimmed red label on the surface of the tach’s clear plastic face to depict the range... CB special!

8) Getting a JPI to properly match your updated prop / engine combination... starts with a phone call and providing data...

9) JPI is familiar...

MS rocks!

Best regards,

-a-

It’s actually a red zone on my 66’ E. Strange because my SN is 1126.

M20F-1968 · March 10, 2020

7 hours ago, Moonbat said:

7 hours ago, Moonbat said:

The plane has a turbo-normalized IO360-A1A engine and an MT-Prop (3 blade).

I have a 1968 F model with a RaJay Turbo Normalizer. Mine is highly modified and I thought of putting MT prop on it when I did the rebuild. I was cautioned against that

since the RaJay STC was designed to be used with the Hartsell prop, and using a different would require vibration testing to be legal. Given that I have so many modifications on the airplane already I chose to forgo a prop change and stay with that already approved. The issue is whether the two STC'd parts (prop and turbonormalized engine) would work together at all altitudes. You may want to check you documentation for what authority was relied upon to use this combination.

John Breda

**takair** · March 10, 2020

I was surprised by the references to the restriction of 2100-2350, mentioned above, because mine is placarded and marked 2000-2350. I did the research years ago, but had to refresh my memory. If I read the AD correctly, if you have am “undampered”, 200hp, IO-360 with Y shank Hartzell blades, the tach must be remarked with the broader restriction and a red (not yellow). arc applied there. Mine is a 1964 with an A1A, which implies undampered, so it may only be applicable to this year....don’t recall when they went away from the A1A.... Anyway, if you have an undampered engine, take a look at this AD and see if you read it the same way I do.

https://hartzellprop.com/wp-content/uploads/2012/12/2002-09-08.pdf

As a side note, regarding the OP question, I agree with others, the restriction applies to the specific prop and engine combination, but I would wonder if they tested or analyzed undampered versions of the engine.

HRM · March 11, 2020

Avoid CONTINUOUS operation.

...and just the other day an old and wise MSC owner made a comment to me about how certain topics cycle around. This has been discussed ad infinitum.

My comment was that it would be nice if there was a way to search answers to these questions, but the search mechanism for MS is weak and for MAPAlist almost non-existent.

Then there are the thread stealers, who muddy the issue with off the wall commentary :lol:

Oh, and welcome 'Junior Member' @Moonbat!

**carusoam** · March 11, 2020

If only there were a website... where you could ask questions... and get relevant answers...

The interesting part...

Something in the rules had clearly changed... as Rob Takair has nicely pointed out... With a pic!

Back in the day... The yellow arc was once a red arc...

today... Red means do not cross... it is even a do not touch...

Then there is that redline... Vne.... (different topic)

Best regards,

-a-

**takair** · March 11, 2020

Just now, carusoam said:

If only there were a website... where you could ask questions... and get relevant answers...

The interesting part...

Something in the rules had clearly changed... as Rob Takair has nicely pointed out... With a pic!

Back in the day... The yellow arc was once a red arc...

today... Red means do not cross... it is even a do not touch...

Then there is that redline... Vne.... (different topic)

Best regards,

-a-

You are correct. With today’s emphasis on human factors, the arc would likely be yellow, but the old AD takes priority. In general terms, red implies that a pilot should take immediate action and yellow implies that there is an action to be taken, but it is not as urgent. With regard to the red arc, It would be nice if they applied a definition to the word “continuous”. One persons definition may not be the same as another’s. Was just having a similar discussion about the yellow airspeed arc. My wife’s definition of discomfort as a result of turbulence is different then mine, and an air show pilot or Red Bull racer would laugh at my definition......and might pull the wings off of even a Mooney if they took it literally.

HRM · March 11, 2020

15 minutes ago, carusoam said:

today... Red means do not cross... it is even a do not touch...

Nonsense, I touch it all the time--it's exhilarating!

If you want to get to green, you have to go through red.

Fun story. Did a FR once with a young CFI who had never flown in a Mooney. On climb out he completely freaked out staring at the tach. I had to teach him about "no CONTINUOUS operation" :rolleyes:

Nukemzzz · March 11, 2020

We should petition the FAA to make the Vne section plaid.

(Obscure Space Balls reference if you didn't get that one)

RobertGary1 · March 11, 2020

Removing the yellow zone is one of the reasons people change props, engines. I run an A3B6 series engine with my Hartzell prop and now my only limitation is 2700 RPM. The STC for my engine change included a list of props and what limitation existed for each combo.

-Robert

Moonbat · March 11, 2020

Just to wrap this up, the applicable STC to my Mooney N3215F s/n 670008, with an IO360 A1A engine (with 6th order counterbalances) and an MTV-12-B-180-59b three-bladed composite prop is FAA STC SA02461NY. The limits noted under the "Tachometer" section of the STC are:

Green Arc: 1500 to 2700 RPM (Normal Operating)

2700 RPM (Maximum limit)

I've already sent the information to JPI and they'll prepare a way to upgrade the digital tachometer face for my EDM930 to reflect this limit and eliminate the 2100-2350 red band. Life is good.

(Interesting side note: While carefully reading this STC and the documentation about this prop, I discovered it was made to be a hot prop. Hmmmm... )

**takair** · March 11, 2020

17 minutes ago, Moonbat said:

Just to wrap this up, the applicable STC to my Mooney N3215F s/n 670008, with an IO360 A1A engine (with 6th order counterbalances) and an MTV-12-B-180-59b three-bladed composite prop is FAA STC SA02461NY. The limits noted under the "Tachometer" section of the STC are:

Green Arc: 1500 to 2700 RPM (Normal Operating)

2700 RPM (Maximum limit)

I've already sent the information to JPI and they'll prepare a way to upgrade the digital tachometer face for my EDM930 to reflect this limit and eliminate the 2100-2350 red band. Life is good.

(Interesting side note: While carefully reading this STC and the documentation about this prop, I discovered it was made to be a hot prop. Hmmmm... )

I’m curious. Where were you able to find the counterbalance type for your A1A?. I had thought they cut in with the A1B6. I’m very possibly looking for the wrong thing.

Ragsf15e · March 11, 2020

Interesting thread. I have a ‘68 F with A1A engine and Mccauley 3 blade. I have the 2100-2350 yellow band on my JPI930. I assumed this was because it’s in the TCDS. You guys think changing the prop out changed the tcds limitation?

**EricJ** · March 11, 2020

15 minutes ago, Ragsf15e said:

Interesting thread. I have a ‘68 F with A1A engine and Mccauley 3 blade. I have the 2100-2350 yellow band on my JPI930. I assumed this was because it’s in the TCDS. You guys think changing the prop out changed the tcds limitation?

The STC for the new prop would be more correct since it is supplementary to the TCDS. I'm in the same boat, as my JPI is marked per the TCDS but the STC for my Hartzell Top Prop carries no yellow arc limitations. I can still feel that the vibration is different in the yellow arc, so I try to minimize time spent there.

Edited March 11, 2020 by EricJ

**carusoam** · March 11, 2020

When looking for the rest of the hot prop parts...

There should be a ring mounted on the front of the engine...

And something connected to the shaft or prop that runs against the ring...

This would be the important system required to transfer electricity to a spinning prop.

Best regards,

-a-

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