RPM Adjustment

[Txbyker]

Ever since I have had my M20R it has always topped off at 2490 RPM.  I asked my MSC to adjust it and he said something about having to reset the governor and did not do it at my last annual.  I feel like if I could just twist the RPM knob past the current stop maybe 1/8 turn it would go up to 2500 RPM which is where it should be set based upon my base configuration.  My question is, do you think if I have an A&P adjust my cockpit MP knob stop nuts a little bit so that it will turn just a bit more would that work or is it indeed something to do with the governor?

 

Russ

[slowflyin]

I fly a Hartzell and the adjustment is at the prop.  Try checking your prop owners manual and it should describe the procedure.

[tascher]

Russ,

The adjustment is either the high RPM (low pitch) stop on your prop governor or (less likely) the low pitch stop on the prop itself (page 6-34 in the Hartzell manual). With a 2500 RPM limited Ovation, I'd go for a stop adjustment just over your book high limit of 2500 - I don't recall the precise rule, but I think 1% or 2% over is legal.

Tom

[carusoam]

1) test the tach for accuracy...

2) Get the correct paperwork, swap out the tach and a few parts...

3) Go all in for 2700rpm!

Thinking out loud,

-a-

[triple8s]

I didn't think you were legal to spin any of them over 2500 except the PHC-J3YF? I mean a few rpm over probably wouldn't hurt but I'd be afraid to raise the rpm that much on the McCauley legal or not. Wheres our resident prop man?

[Cody Stallings]

I would verify the Tach with a hand held optical Tach.

Try an make all of your rpm adjustments with the prop Gov if possible, the low pitch stop in the propeller is only affective before the prop gov comes online. However, you can turn it out a 1/4 turn an get your rated RPM for a couple seconds, but the gov will pull it back.

The low pitch setting on the propeller, if possible should not be manipulated. If to much pitch is added, it takes forever to make rpm on the takeoff roll. If you flatten the blade angle to much, the gov will see the quickly approaching overspeed coming, an try a pull it down very fast. When this happens the propellers blade angle will fluctuate till the prop gov finds it happy spot, while all of that takes place you don't have Maximum takeoff performance.

[Cody Stallings]

Overspeed chart

[tascher]

I didn't think you were legal to spin any of them over 2500 except the PHC-J3YF? I mean a few rpm over probably wouldn't hurt but I'd be afraid to raise the rpm that much on the McCauley legal or not. Wheres our resident prop man?

Cody is the go-to here and his Hartzell over speed chart answers it - 103%, but you're right, I should have made it clear that my suggestion to allow for a percent or two over 2,500 only applied to the props rated to 2700. I'd believe that there are currently 4 that meet that standard with approved STCs for Ovations (sorry not to have looked up the specific numbers):

Hartzell "Top Prop" 3 blade

Hartzell certified for the Acclaim S

Hartzell composite 3 blade

MT composite over wood core 4 blade

Tom

[Andy95W]

Thank God my analog tach isn't readable to 10 rpm increments!

[Guest]

I doubt that 10 RPM will make any difference in take off performance. Leaving non essential gear and excess fuel out of the plane will make a greater difference.

Clarence

[N601RX]

I've found the engine rpm app on my iPhone to be very accurate. It matches the jpi exactly.

[WAFI]

What crazy bent flat head screwdriver or miniature hanger elf do you use to adjust the stop screw on the governor? The lock not doesn't seam hard but the clearance for the screw is tight. 

My RPM currently will go to 2750+ if I let it. Part of my per-departure check is to pull the prop back a touch before taking off. I was going to wait to adjust this to when I get a three blade but who knows when that will happen. So...

Procedure seams pretty easy:

Fly WOT everything forward, reduce RPM until 2699 , land without touching prop, adjust stop screw to close the gap, and go fly again.

 

[A64Pilot]

On 8/23/2014 at 5:44 PM, Andy95W said:

Thank God my analog tach isn't readable to 10 rpm increments!

That’s exactly it, all the limits were written back in the day when instrumentation was an ish thing.

Plus many devices that read to a single decimal only display it, they aren’t necessarily that accurate, some sensors are extraordinarily accurate often the hall effect ones, some aren’t.

I can assure you 10 RPM is within the noise level, you won’t be able to measure the difference. I’d be surprised if the governor will hold RPM that closely, with modern electronics we expect digital accuracy from analog devices, we are often disappointed. My tach will show something between 2660 and 2690 depending on conditions. Extrapolating numbers from factory analog tach.

[PT20J]

According to Lycoming SB369 https://www.lycoming.com/sites/default/files/SB369S Engine Inspection after Overspeed.pdf you are allowed an overspeed of up to 270 rpm, so 50 rpm is not really a concern. If you do decide to adjust it, be careful as the older McCauley governors had plastic backs and the part where the adjusting screw fits has a tendency to crack.

Skip

[WAFI]

4 minutes ago, PT20J said:

According to Lycoming SB369 https://www.lycoming.com/sites/default/files/SB369S Engine Inspection after Overspeed.pdf you are allowed an overspeed of up to 270 rpm, so 50 rpm is not really a concern. If you do decide to adjust it, be careful as the older McCauley governors had plastic backs and the part where the adjusting screw fits has a tendency to crack.

Skip

Noted, thanks for sharing the Service Bulletin. I was aware of some leeway but not that much, good to know. Me being me will want to go through the torture of getting it exact because what else would I do with my time. 

[PT20J]

51 minutes ago, WAFI said:

Noted, thanks for sharing the Service Bulletin. I was aware of some leeway but not that much, good to know. Me being me will want to go through the torture of getting it exact because what else would I do with my time. 

Yeah, me, too. Ask my wife 

[A64Pilot]

If it’s 50 high I’d leave it, that’s standard practice for float planes, a little extra oomph to get on step is helpful, then pull it back right after T/O.  I think a half turn back on my Maule kept it at 2400(it’s max) but I had the extra 50 if things were tight.

Mine is about 50 low, I got a good look at the adjustment and decided it wasn’t worth it, but once did a short flight with everything forward, and darned if in level flight it’s close to redline. I was looking at T/O RPM and never thought it might bump up a little in high speed, but it does a little, or maybe it’s oil temp or hot Wx who knows?

[Guest]

9 hours ago, WAFI said:

What crazy bent flat head screwdriver or miniature hanger elf do you use to adjust the stop screw on the governor? The lock not doesn't seam hard but the clearance for the screw is tight. 

My RPM currently will go to 2750+ if I let it. Part of my per-departure check is to pull the prop back a touch before taking off. I was going to wait to adjust this to when I get a three blade but who knows when that will happen. So...

Procedure seams pretty easy:

Fly WOT everything forward, reduce RPM until 2699 , land without touching prop, adjust stop screw to close the gap, and go fly again.

 

First, verify the accuracy of the tachometer data before adjusting anything.  Generally governor screws are 20-25 RPM per revolution.

[MMsuper21]

After upgrading to digital tach I was about 50 to a 100 high at times. Spoke with Prop shop at my airport and they suggested to cycle the prop 6 times and let it drop 500 rpm’s to reset. Which fixed it for me it only sometimes goes over 20-50 depending on DA. 

[Pinecone]

It seems that up to 10% high is OK.Hmm, I can get back to 2700 RPM instead of 2600 on my -SB.

[Will.iam]

And you will be making more than 220hp for sure. I wonder how much more per 10 tpm increase that does? Maybe 1hp per 10 rpm’s so 100rpm would gave u 230hp? Sounds reasonable at least. 

[takair]

On 10/3/2022 at 12:02 PM, PT20J said:

According to Lycoming SB369 https://www.lycoming.com/sites/default/files/SB369S Engine Inspection after Overspeed.pdf you are allowed an overspeed of up to 270 rpm, so 50 rpm is not really a concern. If you do decide to adjust it, be careful as the older McCauley governors had plastic backs and the part where the adjusting screw fits has a tendency to crack.

Skip

But, isn’t the 10% only allowable for 3 seconds?  They even call for logging < 5% and correcting it.  I know this is in the noise of many tachs, but I don’t see this SB as giving much flexibility in setting the red line.

[PT20J]

19 minutes ago, takair said:

But, isn’t the 10% only allowable for 3 seconds?  They even call for logging < 5% and correcting it.  I know this is in the noise of many tachs, but I don’t see this SB as giving much flexibility in setting the red line.

The pub (as many Lycoming pubs) is not very clearly written. Perhaps 5% is a better number. 

[A64Pilot]

18 hours ago, Will.iam said:

And you will be making more than 220hp for sure. I wonder how much more per 10 tpm increase that does? Maybe 1hp per 10 rpm’s so 100rpm would gave u 230hp? Sounds reasonable at least. 

Somewhere there exists a HP/RPM chart for aircraft engines, similar to the tip speed calculators for props, I’ve not even looked for years, but it’s out there, can’t find it now.

RPM is really significant in HP production, more than I expected. Lycoming in particular derated engines via RPM by application. The 235 HP fuel injected 540 only turned 2400, where the carbureted low compression 235 540 turned I think 2600.

There are very significant differences between the 300 HP 540’s and the lower power ones, it’s not just a 300 HP motor with the RPM turned down, don’t mean to say that, just saying a 50 RPM increase in RPM makes a bigger difference in power output than I expected

[PT20J]

horsepower = torque/5252 x rpm  (5252 is a conversion factor for English units of measurement in hp, lb-ft, rpm)

If the BMEP (torque) is constant, then horsepower varies linearly as rpm.