Is it a problem if my engine runs at, say, 2,750 RPM?

[RobertE]

After an engine and prop overhaul It looks like the prop governor setting is about 50 RPM too low.  I’ll fix that soon, but here is the problem.  My tach indicates about 100 RPM too low but, let’s face it, any device that far off can’t be trusted with precision measurements.

So what’s the consequence if when resting the prop governor i wrongly set it a bit high?  If in pursuit of 2,700 I mistakenly achieve 2,750 will that produce some adverse outcome?   Thanks.

[kortopates]

Both are fixable, your max rpm setting and your tach. That's what you want to do.
Of course I knew you were joking about exceeding redline


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[takair]

There is another very recent thread on overspeeds, including the Service bulletin reference with what you need to do depending on how much and how long you run over speed.  Some outcomes are not so pleasant, at least to your wallet.

[kaba]

What if ....when Full forward RPM is set and RPM shows 2700 on t/o roll then exceeds 2800 RPM when gear is retracted.
Any significant issues with engine if quickly reduced to 2700 RPM.
I may have read than the helo of IO-360 application has 5min max limit for 2800RPM.
Any educated opinions?


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[Yetti]

Look up your engine in Lycoming and see what the real redline is.  

You don't want your prop tips to go supersonic.  There are some calculators to find what supersonic is for say a 72" prop.

The 2700 RPM comes from the Mooney Type data Sheet.

https://www.lycoming.com/sites/default/files/SB369N Engine Inspection after Overspeed .pdf

Edited November 22, 2017 by Yetti

[N201MKTurbo]

I think there is a tach app for your phone that is very accurate. I think there are ones that use the camera and some that use the mic.

check it out and let us know.

[StinkBug]

My governor was set too low when I bought the plane, and getting to the adjustment screw is a major pain. When I had it in the shop we managed to raise the rpm, but now it will go about 20-40rpm over just after take off. It's such a pain to adjust that I called that good enough. I simply learned exactly how many turns out from full in on the prop knob it takes to hit 2700 and made that setting the last step of my run-up. 

[markejackson02]

Most important thing to remember is to move the throttle slowly so that governors and such can keep up.  I used an iPhone app that measured sound pulses to check my tach and it indicated within 25 RPM.

 

[RLCarter]

Had to turn mine down (25 rpm), IA threatened to take my b-day away......

[Aerodon]

A Seneca II has a 200hp TSIO360EB engine, redline at 2575.  The Seneca III has a 220 hp TSIO360KB, redline at 2800 for 5 minutes.  My understanding is that there are differences in the engines, including different valve springs.  This allowed Piper to increase the gross weight and performance charts.

There are planes that use a lower redline than the actual engine TC.  Aerostar 600A comes to mind, its redline is 2500rpm/290hp, but the engine can do 2700rpm.

Aerodon

 

 

[MB65E]

That's what test flights are for. No harm at 2750. It should be adjusted. However, Most might adjust it with the propeller knob. I would not be worried . Just operate the throttle smoothly to allow the GOV to catch up.

-Matt

[Guest]

Why worry?  All of those caution arcs and red lines are for other people to worry about.  If it hasn’t blown up yet it’ll be fine.

Clarence

[takair]

Since many of us are running Lycoming 360s, here is what Lycoming says in SB 369P: 

-Max RPM is 2700.....no 5 minute limit.

-momentary over speed is defined as 10% for 3 seconds....2970 for 3 seconds max.- no inspection required.

-more than 3 second shift requires at 2970or greater requires a significant inspection...expensive.

-up to 5% for more than 3 seconds.....so between 2700 and 2835for more than 3 seconds requires:

“Corrective Action After Engine Overspeed NOTICE: All incidents of overspeed must be recorded in the engine logbook, including corrective action. 1. When the overspeed occurrence is less than 5% of the rated engine speed, the recommended corrective action for all engines is as follows: a. Identify and correct the cause of the overspeed. b. In the engine logbook, record the overspeed incident, any inspections, and corrective action. “

So, it seems even 50 rpm for more than 3 seconds counts...  Keep in mind that some of this is also prop harmonics.  The IO-360 A1A in the early Mooney’s did not have harmonic balancers and is considered hard on the prop.  The types of failures that these harmonics cause can be difficult to detect and can occur rapidly.  This is one reason the prop manufacturers are so conservative on their maintenance and have so many ADs.  They will always blame the plane, pilot or tachometer first, maybe they are not wrong?

[RobertE]

Thanks, everyone.  Let's be honest, though.  Who among us has a tach that is so accurate and displays so precisely that we could be confident we weren't running 25 or 50 RPM too high or too low?

 

[Skates97]

29 minutes ago, RobertE said:

Thanks, everyone.  Let's be honest, though.  Who among us has a tach that is so accurate and displays so precisely that we could be confident we weren't running 25 or 50 RPM too high or too low?

 

I recently learned that at 2,700 on my tach it is actually only at about 2,610-2,615 based on the strobe the shop put on it.

[thinwing]

The 0360 in my Pitts was set for 3100 rpm as an experimental...hp calculated out to 235 hp of so...of course this was an experimental application and I had a Shute..never any issues though

[takair]

Perhaps an extreme example of an over speed or perhaps they don’t make magnetos like they used to.....http://www.kathrynsreport.com/2015/11/accident-occurred-november-15-2015-in.html.  Either way, there is a limit...

[Hank]

1 hour ago, takair said:

Perhaps an extreme example of an over speed or perhaps they don’t make magnetos like they used to.....http://www.kathrynsreport.com/2015/11/accident-occurred-november-15-2015-in.html.  Either way, there is a limit...

Per the NTSB report, the manufacturing process for the nylon magneto gears has not changed in the last 20 years. At work, we mold gears every day using molds that are more than 20 years old, and some brand new ones still being approved. No, they are not aerospace gears . . . .

[MB65E]

1 hour ago, takair said:

Perhaps an extreme example of an over speed or perhaps they don’t make magnetos like they used to.....http://www.kathrynsreport.com/2015/11/accident-occurred-november-15-2015-in.html.  Either way, there is a limit...

Great article!! I've lost controlibility in a tsio550e with a hartzell counterweighted propeller before. High speed decent in an experimental. It didn't overspeed but went from 2600rpm to 2700rpm and the prop control was pulled all the way out. I'm glad it had a counterweighted propeller. Leveled off and it came back. 

MT has some strange govoner requirements. Their propellers use oil pressure differently than a hartzell. I wonder what GOV was on their "test aircraft" 

-Matt

[takair]

7 hours ago, Hank said:

Per the NTSB report, the manufacturing process for the nylon magneto gears has not changed in the last 20 years. At work, we mold gears every day using molds that are more than 20 years old, and some brand new ones still being approved. No, they are not aerospace gears . . . .

I had forgotten you work in that industry.  It seems like the new, “disposable” magnetos started appearing about 20 years ago.  When I look at some of the magneto gears I almost wonder if they are aerospace gears!?  They are certainly approved, but they do not instill confidence.  I often wonder why they don’t use some sort of composite gear.  It seems like I recall some of the older magnetos having “phenolic” gears.  The “nylon” seems to get embriddled with the temperature cycles.  They seem to come apart way too often (once is way too often) and are one of the other weak links when we overspeed. (Google “magneto gear” and you will see image after image of missing teeth).  

[Hank]

I've never seen anything molded out of phenolic, it must have gone by the wayside before I started in '89. Nylon 6,6 is heavily used in automotive for "under the hood" parts, it's tough and holds up well. That said, we don't mold our gears from nylon. They are also very small, lightly loaded and in a much nicer environment (sealed up and not much above outside ambient temps).

I have machined some pieces of phenolic, it's messy, powdery, inlaid with fabric, and i kept a vacuum running the whole time

[whiskytango]

13 hours ago, Skates97 said:

I recently learned that at 2,700 on my tach it is actually only at about 2,610-2,615 based on the strobe the shop put on it.

This raises an interesting issue.  How often do we get our instruments calibrated (other than pitot - static / transponder)?  What if the MAP gage was reading 1 or 2 inches too low?  That could result in engine overload problems, especially for intercooled turbo aircraft.  I have two fuel flow instruments in my K model and they never show the same fuel flow rate.  Which one, if either, is correct?  How about CHT / EGT and TIT thermocouples? I am curious how often other MS folks get these instruments calibrated.

[Hank]

I had the dynamic balance on my prop checked at annual this year, it hadn't been done since the prop was installed in '03? Not only was the balance still 0.01, but the prop was within 10 RPM from 1500-2700. Good to know!

There's no need to calibrate EGT since the actual number is immaterial, it's jist the relationship between them and distance to peak that matters. Some planes, including some Mooneys, do not even have numbers on the EGT dial, only 25° hashmarks. Personally, I  find the numbers to be useful as I'm leaning, i don't have to count hashmarks; it's even more so during descent when I'm enrichening to maintain cruise EGT. 

Thermocouples don't generally drift in my experience at work. They are either functional or broken. Some default to 0° when broken, some go to 999° (in our planes, that would be 9999°, we rarely reach 700° at work).

I don't have fuel flow on my plane. Is your measurement coming from a turbine in the line? Surely both readouts aren't attached to the same instrument? While my first reaction is to thi k that gasoline is a great solvent, surely it wouldn't be gunked up, I've read too much about spiders and injectors having "blue goo" inside them. Talk to your mechanic about cleaning your fuel flow instrument(s) sometime, it can't hurt.

Edited November 23, 2017 by Hank

[Guest]

20 hours ago, RobertE said:

Thanks, everyone.  Let's be honest, though.  Who among us has a tach that is so accurate and displays so precisely that we could be confident we weren't running 25 or 50 RPM too high or too low?

 

Most people with a modern engine monitor, and those with a Horizon digital tachometer should be getting very accurate readings.  Old cable drives are less accurate.  I believe I read in the FARs there is a requirement for accuracy, its in the CAR's in Canada as well.

Clarence