What's your M20J RPM on Take off Roll?

[corn_flake]

I have a M20E with J engine, and I have been spending the past few months trying to troubleshoot a problem of not getting full RPM during take off roll.  My AP/IA seem to think I should get 2700 RPM on a static run.  However, I have since found a Lycoming advisory that suggests that static run on the ground should only yield max RPM minus 100.  I think @jetdriven on here also mentioned in another post that most J doesn't get any where near full rpm on take off roll.   However, since I'm only getting 2450 on static run, that still leave me with 150 below the the spec.  But then again, I also start wondering if I'm chasing a problem that exist only in my head.    After all, who doesn't want more HP!!

I know most pilot doesn't run their engine to full power on the ground due to safety concerns.  So here I'm wondering if you have a M20J power plant,  could you share your take off roll RPM.  Basically, the rpm you get when the throttle is push all the way forward at the beginning of the take off roll.  I'm getting around 2515  as picture shown below.   You can also view my Savvy chart using the link here.  https://apps.savvyaviation.com/flights/3937822/8a8a1f82-c4a6-4678-b5cd-f59c5541fa44. Per my AP/IA's advise.  here is troubleshooting roadmap.    

1. Clean Injectors - Done and have no effect

2. Send Fuel Servo / Fuel Spider for flow testing - in progress

3. Overhaul Mag

4. Flush governor and check prop low pitch

 

[PT20J]

At static run up, the prop blades should be sitting on the low pitch stops and at rated power it should turn slightly less  than 2700 RPM (the service manual calls for up to 50 RPM less). As you accelerate, the prop will speed up to 2700 RPM at which point the governor should begin increasing pitch as necessary to keep it there.

If it doesn’t turn nearly 2700RPM static, 

1. The tach is not reading correctly, or

2.  The governor is adjusted incorrectly, or

3. The engine isn’t putting out rated power, or

4. The low pitch stop is not set to spec.

Skip

[carusoam]

The laws of physics keep the prop from reaching full rpm in a static condition...

So many things affect the prop in the static condition....

• ground proximity....
• wind blowing...
• wind direction...
• changes in wind...

And it draws a lot of dirt through the blades....

Once moving for a few seconds... full power, full rpm, full FF should all be working as expected...

A good gov, can hide a low power engine for a while.... 2700 rpm is important for T/O distance... as is MP... as is FF....

Flake, what is the max rpm you are supposed to be seeing?  2700, yet during that flight of data, the prop is spinning closer to 2600 rpm...

In order to get book performance numbers... you have to have all the other book numbers to begin with...

• Prop (make model)
• Engine (make model)
• MP
• RPM
• FF (Since you have this device... compare to what the docs say you should be using for max power)

 

use a smart phone app to verify your tach’s accuracy...

Looks like it might be time to get the gov adjusted properly... grab a few flights of data to see if the tach is always showing the same low rpm...

 

PP thoughts only, not a mechanic...

Best regards,

-a-

[Skates97]

A simple thing to check is if your prop cable has slipped, not allowing full travel to the stop on the governor. I had that happen a little after getting the plane. I thought it was related to changing plugs, but it was the cable that had slipped. 

 

[David Lloyd]

Read and reread what Skip wrote.  Being that the Savvy chart shows no more than 2550 rpm or there about, I doubt the problem is with either the low pitch stop, tach inaccuracy or engine power.  The prop governor needs to be adjusted so the engine can achieve 2700 rpm about half way thru your takeoff roll.  Oh, and you may need a different mechanic, one that understands the function of the low pitch stops in the prop and what the prop governor does.

[Guest]

If you have a McCauley propeller the fine pitch stop can not be adjusted in the field, a Hartzell propeller can be adjusted.  In my experience many J models will not make even the 2650 RPM static that Skip mentions above, most will reach 2700 on take off when the governor is adjusted correctly.

Aside from an indication problem or mis adjustment of the governor, it could be an engine that just can’t make the torque to turn the prop to rated RPM.

Clarence

[corn_flake]

@Skates97  Thanks!!  I'll check the prop control linkage today.  

Few things I should have mentioned 

• Engine model is IO 360 A3B6D
• RPM has already been verified using hand held optical tach. 
• Prop design is Mccauley 90DHB-16E
• Fuel flow is about 16 gph as indicated in the Savvy chart.  
• MP is as indicated in the Savvy chart
• Compressions are 76/80, 76/80, 74/80, 76/80
• Both cylinders and valves were checked using a borescope and no issue found

In a dive, I can get the RPM to reach 2700 if I'm not careful.  Does this mean, low pitch stop is adjusted properly?

@M20Doc  Besides @jetdriven, you are the second person that mention M20J will not make 2650 rpm on static run.  I start to think if I'm fighting a imaginary problem that only exist in my head.  

[Guest]

If the only way to get 2700 RPM is in a dive, you’re not imagining a problem, there is a problem.  I’d disconnect the propeller control cable, and back the high speed stop screw on the governor out several turns, safety the arm against the stop and run it up to full power and see what the RPM does.

Clarence

[Ragsf15e]

Are you getting 2700 during your takeoff roll?  Maybe just before rotation, or only in a dive?  If it’s only in a dive, needs adjustment!

[FloridaMan]

I see 2700 RPM on my takeoff roll in my m20f

[takair]

If he gets 2700 in a dive, doesn’t that indicate that the governor is governing to 2700 and might it not indicate the low pitch stop on the prop or an engine not making power?  Wouldn’t changing the governor setting simply cause an overspeed in a dive? 

[carusoam]

So...

We grab another screen shot of Flake’s data...

we show two important lines to go with the EGTs and CHTs...

The rpm and FF... rpm is labeled tach...

When Flake firewalls the throttle... the engine immediately responds with 15+gph and 2645 rpm...

Flake reports everything working well mechanically... by physical inspection, and all available data...

The only thing not working as expected is rpm, which is about 50 rpm low...

 

Isn’t the first response to go see the mechanic familiar with the CS prop and have him adjust the max rpm to 2700 rpm?

Or is there something that indicates there is a broken part somewhere, or something else not set up properly?

Find the prop rpm set-up procedure... it may cause a bunch of other things to change like max FF and mixture...

It is really cool when your engine is working 100% as expected...

 

PP thoughts only, not a mechanic...

[carusoam]

As far as chasing something that is real vs. something in your head....

There are many low cost things that could be checked above that didn’t get an answer...

And some expensive things that are getting done that aren’t really expected to be the challenge...

There is one thing that is real... Max rpm not being reached...

But, the usual things associated with the RPM challenges that other MSers have experienced don’t seem to be getting addressed...

So let’s write this down....

• Gov seems to be working properly... in some parts of the graphs...
• gov may be working properly everywhere.... but why does the pilot keep touching the blue knob....? 
• Gov max setting isn’t set properly...
• If the pilot isn’t touching the blue knob... and the rpm is setting itself... this is a do not fly something is very wrong...
• The tach looks like it is controlling pretty flat-lined, while the MP drifts lower with altitude.... ordinary signs of proper gov operation...
• How old is the blue knob, is the cable falling apart, are there any wear issues with the control cable?
• If the blue knob is as old as the plane... don’t be afraid to knobs out.... they have a tendency to fail after thousands of hours get put on them...

 

If you keep changing the blue knob... the tach data moves around.... we can’t tell if the engine is doing this or the pilot is doing this... 

Was this rpm shift commanded by the pilot or did it happen on its own?  See the data and the line in the graph below... looks like the pilot turned the knob back until reaching 2466 rpm...

If you want to solve a problem... it is really helpful to solve that one problem at a time...  it will get more complex on its own...

Best regards,

-a-

[FloridaMan]

Also, I know he’s got an engine monitor and all, but I’d want to confirm that the tach is reading accurately. 

[corn_flake]

The change at 17:42 into the flight is pilot induced.  Transitioning from climb to a level flight.  This is evidenced by the fact that MAP remain relatively flat until 23:56.  I'm one of those pilot that flight with red knob all the in from until I'm ready to land.   

[corn_flake]

1 minute ago, FloridaMan said:

Also, I know he’s got an engine monitor and all, but I’d want to confirm that the tach is reading accurately. 

RPM was verified by multiple hand held tach.  

[carusoam]

Get a good look at every inch of the cable attached to the blue knob...

Expect that the cable may show signs of being frayed...

Observe the gov going from full out to full in...

Expect that the knob May be moving correctly, but the other end may not be traveling the whole distance...

 

This is something that has been reported on MS a few times over the years... 

Best regards,

-a-

[corn_flake]

My AP already tried to adjust the governor high RPM setting and it did has made no effect on the static RPM.   Assuming if the issue is caused by the prop/governor, the next step is to flush and governor and check the low pitch stop.   Of course, I'll check the cable first.  

[corn_flake]

Or I may try what @M20Doc suggested to isolate the governor from the cable.  

[carusoam]

For the gov to control the rpm setting...

parts inside the gov have to move....

Sounds like the set point in the gov isn't getting moved with the cable....

How confident in your mechanic are you?

New governors are better and lower cost than old governors...

You might be bumping into a situation where it makes less sense to chase down issues with the old gov....

Compare prices of OH and brand new... 

Lots of MSers have gone with the PCU 5000 governor(?)

Still check on the old cable... low cost to have swapped out and be good for another decade and 2k hours....

+1 on Doc’s recommendations... 10X more valuable than ordinary PP ideas... he has the knowledge and decades of experience.... and supplies a great MS pizza party too... 

PP thoughts as usual...

Best regards,

-a-

[corn_flake]

15 minutes ago, carusoam said:

+1 on Doc’s recommendations... 10X more valuable than ordinary PP ideas... he has the knowledge and decades of experience.... and supplies a great MS pizza party too... 

Was there a pizza party I missed?!  

I'm heading the the airport to check the cable first.  I'll need to wait for my AP to try Doc's suggestion.  

I'll look into the PCU 5000 as well.  I assume it has STC for Mooney.  

[PT20J]

You’ve eliminated the tach as a source or error.

Next I’d check the governor as Clarence suggested.

If that’s not it, I’d make sure that the prop is the correct model and check the blade angle. This can be done on the airplane.

If the prop checks out then all that’s left is the engine.

Skip

 

[carusoam]

Real important...   Doc supplied pizza for the MS party at KOSH last year...  @yvesg Yves did the ground work getting the Pizza to show up in the right place on time....

KOSH and the Mooney Caravan is a giant concert of moving parts.... everyone takes on different roles to make it happen... it is impressive to see up close.

Probably the largest gathering of MSers in the world...

Sitting face to face, talking Mooney... much better than typing on a keyboard.... 

The PCU is a Hartzell product...  STC is required... Your plane/engine should be on their list... check asap... as soon as practical.

Best regards,

-a-

[bradp]

I use the engine rpm app to verify my tach/ it’s pretty spot on with the mechanical gauge in my case.  Useful app. 

[Guest]

From the McCauley manual:

https://mccauley.txtav.com/-/media/mccauley/files/manuals/mpc26ow.ashx?la=en&hash=7F613FABB08554A85D2AB8E61549614D09B0F362