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What is your static full throttle RPM?


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The only way for my M20E to get 2700 RPM during the take-off roll is without any flap.  With flap setting as recommended by POH, it's only producing 2615 RPM.  Since I want to get every bit of performance, I had my A&P out today we did a static full throttle test with engine at full rich and prop full forward.  The best the M20E can do is at static is only 2460 RPM.  Is this normal?   What is your static full throttle RPM?  

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I didn't think it would make a difference with the flap down or up, but apparently I was able to get 2700 RPM with no flap during the take off roll.  

Also, I'm using Horizon P-1000 tach.  I think a tach reading off the p-lead from the mag is much more accurate than the mechanical tach.  

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2 hours ago, corn_flake said:

The only way for my M20E to get 2700 RPM during the take-off roll is without any flap.  With flap setting as recommended by POH, it's only producing 2615 RPM.  Since I want to get every bit of performance, I had my A&P out today we did a static full throttle test with engine at full rich and prop full forward.  The best the M20E can do is at static is only 2460 RPM.  Is this normal?   What is your static full throttle RPM?  

Anything less than 2650 RPM static suggests either an adjustment to the prop fine pitch setting or the governor or both is required.  Flight control position should have no effect on RPM.

Clarence

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1963 M20C new engine and scimitar prop. First flight 2634 was highest I saw on takeoff roll and a little better in flight. AP adjusted governor and linkage. Now the red light on P1000 flirts a little on takeoff roll settles around 2694. Surprised the performance difference with just 60 more rpm. Did dynamic prop balance last week and tach is right on. Static was 2655. 

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Good point on the DA as well.  While the location of the test has 400' MSL and the temperature was around 13 C, I will lean the motor perform the test again.  

Since the fine pitch adjustment on the prop itself is been called into question, I check my prop log book and it shows the pitch is 13.9 degree to 33 degree.  Does any one know how to measure the prop pitch?  Specifically, how far from the center point to measure the pitch for Mccauley prop?  (signaling @Cody Stallings ...)   Also, why was the 13.9 degree selected as the low pitch stop?  Is this specified by the mfg for the motor/aircraft combination or is this set by the prop shop based on actual test run of my specific motor?

 

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Specifications often come from the engine / prop combination... add the gov in for the total package...

The prop/engine combination often gets selected by the plane manufacturer...

The stops for the prop are not often where the prop actually operates... the gov typically controls the blade angle dynamically between the limits... if the prop rests on the stops... the gov has been removed from controlling rpm... over-speed is a high risk when this happens....

Full static runs are typically a maintenance procedure...

Few owners will run the engine hard on the ground... too many rocks/sand get drawn up into the prop at high rpm...

In a few seconds of the T/O roll... MP, RPM, and FF will tell you twice, that the engine is developing full power... now!

Realistically Full mixture is probably not the right mixture for full power... it comes with a heavy dose of excess cooling fuel... which impacts the power being produced...

 

An example of all things being equal... then adding a few hundred rpm... what is the difference in HP, and performance...

When an O1 goes from 2500 rpm to 2700 rpm... the HP is increased from 280 to 310, about +10%...

10% doesn’t sound like very much... but it is really much larger since we are increasing the ‘excess’ HP by quite a bit...

So... this 10% increase in HP leads to much shorter T/O distances, and much higher climb rates.... 800’ vs. 1200’...

 

Back to the topic...

1) There is a procedure for doing static rpm run-ups.... including safety precautions...

2) Follow the procedure...

3) Expect that there is a set of specs to be read... and tested against...

4) What made you think this is a good idea for testing engine output?

5) Pilots have so many other ways to test the output of the engine... once the mechanic has finished with the static rpm part...

 

My home drome experienced a pilot doing a static run-up at the tie down area... in his new 2him C152...

One aged tie down rope failed, unexpectedly (to only one person)... the plane rotated around the other tie down... and crashed nose to nose with the next plane...


focus on this for a minute....

How does the engine know where the flaps are...

7 hours ago, corn_flake said:

The only way for my M20E to get 2700 RPM during the take-off roll is without any flap.  

A well respected MS mechanic gave guidance regarding rpm, and it being independent of flight controls...

You are mixing data from T/O runs, and static runs... and blending in extraneous detail...


On the topic of tach accuracy... you either have it or you don’t... there is no reason to use an inaccurate gauge since the beginning of the smart phone era...

 

Some pilots don’t have accurate gauges... but they don’t post questions about getting 100% power on T/O either... :)

 

Looks like you spent some dough to get educated by your mechanic... (better than not spending money, and not getting educated)

Did you find the result that you were looking for?  (Max rpm is good, right up to red line. Less rpm, is sub-optimal. More rpm is bad, for engine health and wallets)

Aside from static run-ups...   Does your engine now produce full power at full rpm, during the T/O roll?

 

It might help if you ask the question, before spending the money on the mechanic, to report that you could have got more out of the exercise...

 

PP thoughts only, not a mechanic...

Best regards,

-a-

 

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With engine putting out rated power, static rpm should be a little (maybe 20-50 rpm) less than redline. In this condition, the prop is against the low pitch stops and the governor is out of the picture. As you accelerate the prop drag decreases and it speeds up until the governor holds it at redline. The only effect of the flaps is that the takeoff speed will be higher without flaps. Always check the tachometer accuracy first before messing with the governor. 

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9 hours ago, M20Doc said:

Anything less than 2650 RPM static suggests either an adjustment to the prop fine pitch setting or the governor or both is required.  Flight control position should have no effect on RPM.

Clarence

Or alternately the engine is weak (i.e. spalled cam etc)?

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34 minutes ago, DXB said:

Or alternately the engine is weak (i.e. spalled cam etc)?

Yes, I was going to add that, but thought the first thing would be to check the prop and governor, if those have no effect then engine health, magneto timing fuel injector setting come into question.

Clarence

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That’s why I said “with the engine putting out rated power.” If everything is set up right, the rpm at the beginning of the takeoff run is a check on the health of the engine. On the radials that all have superchargers and have takeoff power settings with MAP greater than 30”, field barometric power checks are part of the runup procedure. The drill is to run the power up to a MAP that is the same as the altimeter setting and note that the rpm is within a specified range. In this condition, the prop is on the low pitch stops so the governor is out of the picture.

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The 13.9 degrees is a Engine/Airframe thing put in motion by the manufacturer.

At 13.5 you may have a surging issue as the RPM comes up to fast then the Gov kicks in.

At 14.4 it will never make it to RPM on the roll, however will make RPM in the air.

Any Chance you maybe running a little rich on the grd?

McCauley propellers usually don’t suffer from this issue the way Hartzell does.

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Thanks for all the great input.  

@carusoam   The full power static run was requested and supervised by an IA.  In turn, it was prompted by my concern of the aircraft not developing closing to 2700 RPM on take-off roll.  IA wants to see the symptom for him self before we start making adjustment to the governor.  

@PT20J  I didn't think flap setting would make a difference on the engine RPM during take-off roll.  When I forgot to set take-off flap, I too was surprised the engine log shows it was able to hit 2700 RPM for about 2 seconds during take-off roll.  In some way, I think it does make sense since flap produce additional drag.    

@Cody Stallings  Is 13.9 unique to my motor/prop/airframe combination by actual test run that resulted in 2700 - 50 RPM?   I may have ran a bit rich when I did the full power static test.  I left the mixture at full rich.  Therefore, as someone else has already pointed out, my test may not have been valid without leaning for best power.   With that said, I doubt I can get 200 RPM by leaning mixture.   

Assuming a properly set up motor/prop should develop 2650 on full power static run as suggested Mccauley manual page 102, there are only two possible causes for not get that RPM. 

  1. Prop's lowest pitch is set too hight or prop not returning to lowest pitch setting 
  2. Engine is not producing the rated power due to other factors (overly rich mixture, mechanical problem, etc...)

The next step is to measure prop pitch to make sure it is truly 13.9 degree.  If yes, we will need to determine if 13.9 degree is simply a boiler plate number and field adjustment to lower pitch is proper.  If I move down this path, I believe I need to get a prop shop involved.  

On the other hand, if 13.9 degree pitch is confirmed and adjustment is not allow, IA and I will move on to troubleshooting the motor instead.  

 

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Flake,

The prop comes off the stops when the gov takes over...

The Fine pitch stop, you never see, unless the gov stops working... and the rpm overshoots to the high side...

You really want the stop to be in place... if the gov fails, the rpm will be in a bad place, even with reduced power...

producing enough power to stay aloft, with a broken gov, is the important part of the stops...

So... under max power, the rpm should get to 2700rpm (max rpm for your bird) on the T/O roll...

It may exceed briefly in real life, enough to oscillate and set off rpm alarms on a JPI...
 

The gov is far from digital.. it is a mechanical process controller that is capable of holding steady in flight.. it easily gets confused during acceleration down the runway...

 

Essentially you are getting your prop set-up as if you got it new... because you can... because you want to.. it doesn’t get any better than that...

See if you can find the install procedures for your prop, and gov...

The short cut. is find the setting that gives max rpm... that is a simple gov adjustment... 

Leaning properly for T/O should be part of the procedure.  somewhere around 2-300°F ROP...

 

Keep in mind the stops allow for the prop to have control under various atmospheric conditions...  today’s blade angle that produces 2700 rpm will change with the density of air.. which is a function of T&P...  setting the stops in too narrow of a range can be problematic under different conditions...

 

PP thoughts only, glad MS has a prop guy...

Best regards,

-a-

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If the propeller has to much Low-Pitch that will have to be adjusted in a Repairstation.

Figuring out there pitch setting on the plane will be a real pain in the Butt.

That number comes from your engine/plane/blade design, engineers much smarter than me come up with those angles.

 

Has it been making RPM in the past? Or has it been lacking?

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On 11/24/2019 at 2:04 AM, corn_flake said:

The only way for my M20E to get 2700 RPM during the take-off roll is without any flap.  With flap setting as recommended by POH, it's only producing 2615 RPM.  Since I want to get every bit of performance, I had my A&P out today we did a static full throttle test with engine at full rich and prop full forward.  The best the M20E can do is at static is only 2460 RPM.  Is this normal?   What is your static full throttle RPM?  

As Cody said, it is important to know if this is something new or if it's always been that way. The prop pitch stop settings are specified in the TCDS for the airplane and should have been set the last time the prop was in the shop. What prop do you have? Here is the TCDS page for M20E props.

TCDS_20191125_0001.thumb.jpg.123792eae1c477ad9d45c5fac601c3d9.jpg

If you are unsure of the low pitch setting, you can measure it on the airplane. I did this for the museum DC-3 which is a real PITA requiring a tall ladder:). There is a special prop protractor tool made for this whereby you measure the angle at the hub and the angle at the specified blade station and it subtracts the two to give the blade angle, but you could do the same thing with a digital protractor. The easiest way to find the 30" propeller station is to put the prop horizontal and drop a plumb bob from the center of the hub to the ground and then use a steel tape to measure out from that point. Drop a plumb bob along the blade until it hits the 30" point on the tape and mark the blade station.

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@Cody Stallings  As far as the engine log that is available to me, the engine has never made 2700 RPM on take off since 2013.  Even on a cool day.  

@PT20J  Is the prop pitch always measured at 30" station?  I have read some are measured at 75% from the hub center.  

I'm not planning to change the low pitch limit unless the measurement shows anything other than 13.9 degree.  If I get to that point, I will need to send it to a repair station.  

@M20Doc  Also, this is a Mccauley two bladed prop. 

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1 hour ago, corn_flake said:

@Cody Stallings  As far as the engine log that is available to me, the engine has never made 2700 RPM on take off since 2013.  Even on a cool day.  

@PT20J  Is the prop pitch always measured at 30" station?  I have read some are measured at 75% from the hub center.  

I'm not planning to change the low pitch limit unless the measurement shows anything other than 13.9 degree.  If I get to that point, I will need to send it to a repair station.  

@M20Doc  Also, this is a Mccauley two bladed prop. 

Your E model must be modified for there to be a McCauley propeller on it.  The type certificate shows a Hartzell.

Clarence

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