TSIO360MB & McCauley 2 bladed prop ground-run static RPM numbers

[shawnd]

Hey folks, wondering if anyone has actual numbers for static RPM from ground run on a M20K 252 with TSIO360MB engine and McCauley 2 bladed prop. We installed an IRAN'ed engine with new cylinders pistons (edit, what I get for late night typing) and rings and its warm compression numbers are 1: 66 2: 76 3: 75 4: 72 5: 65 6: 72. The turbo is able to produce MAP up to 37" with most runs ranging between 35.5 to 36.3". We used calibrated digital gauges to get the unmetered fuel pressure to be at 6.34-6.6 PSI at 700 RPM and metered fuel pressure at 16.01 PSI at WOT. Unfortunately, our RPMs are showing 2480-2500 at the WOT with 35.5-36.3" MAP and ~2580-2600 when near 37". Pressure altitude was 920' and OAT 19 degrees C. Airplane has brand new McCauley props and the paperwork from the factory shows blade angles at spec. We did find issues with the OHed prop governor initially but it has been repaired and then also been checked by a reputable third party for proper functioning at 2700 RPM.

Few folks have recommended a high speed taxi test to see if the RPMs go up due to the unloading of the wings, which is next on our list now that the fuel setup has been confirmed. But this is still bothering me. I haven't been able to get an actual number of what someone saw for static RPMs at WOT during a ground run. @Will.iam I believe you went through this recently - any notes on what you experienced? Maybe @M20Doc has some ideas?

Appreciate any help!

[Pinecone]

Have you checked that the tach is accurate?

[shawnd]

We tried to measure with a handheld tach but ran into issues. The RPMs being reported by two different mags and two independent gauges (JPI & stock) were identical.

 

[A64Pilot]

I’d fly it as I don’t think you have a problem, but even if you did she will fly a pattern at 100 or so RPM low, and if there is a real problem, you’ll know prior to rotation.

High speed taxi tests aren’t performed at full throttle, and you need to be at takeoff power to really tell.

[Guest]

#1 verify the tachometer/ engine RPM at max power with a known accurate source.  Being off up to 50 RPM wouldn’t be a big issue as long as it picks up to the correct RPM for your engine model on the take off run.

The older versions of SID97-3 had a chart used to calculate fuel set up numbers when full RPM couldn’t be obtained on the ground.

Clarence

 

[shawnd]

Thanks @A64Pilot - that's what my A&P is of the opinion as well. The high speed taxi test is planned as full throttle with stop at takeoff airspeed or earlier if RPM is achieved, or a pre-determined point on the runway at the home airport's longest airport. Since the a/c is out of annual, need a ferry permit for the test flight but need to know the a/c is safe for the permit - has become a chicken and egg problem.

 

@M20Doc Thanks - we did follow the guide (M0 now instead of SID97-3G) to tune in the fuel settings in the first run which was at 2580 (instead of 2700). Further runs were at 2480 which is not covered in the table. Hence this post. 

 

Random thought - since TSIO360 -LB engines achieve 2700 RPM at 40" and my test runs on the -MB indicate I get ~2600 at 37" and ~2500 at 35.5-36.3, could my engine be accidentally misconfigured? What could I check if this is remotely possible? During the IRAN, a new cam was installed but the part number matches. Other than it was seals, bushings, gaskets, piston and rings. Pulling at straws at this point. 

 

 

 

[Will.iam]

I can only give you data points for me. When we had to overhaul a perfectly fine working governor because it had the AD for the wrong bearings, we did static run and got it up to 2680 rpm. A&P said that was good because it would rise on takeoff roll. He was right and it went to 2720. He said a little over is fine but my digital tach flashes at me when over 2700 and i do not want to get used to ignoring an alarm for fear of an overspeed not being caught so we turned the governor down to 2650 and that works. BL you should be able to get 2650 static. My engine is at TBO. 

[Will.iam]

17 hours ago, shawnd said:

Thanks @A64Pilot - that's what my A&P is of the opinion as well. The high speed taxi test is planned as full throttle with stop at takeoff airspeed or earlier if RPM is achieved, or a pre-determined point on the runway at the home airport's longest airport. Since the a/c is out of annual, need a ferry permit for the test flight but need to know the a/c is safe for the permit - has become a chicken and egg problem.

 

@M20Doc Thanks - we did follow the guide (M0 now instead of SID97-3G) to tune in the fuel settings in the first run which was at 2580 (instead of 2700). Further runs were at 2480 which is not covered in the table. Hence this post. 

 

Random thought - since TSIO360 -LB engines achieve 2700 RPM at 40" and my test runs on the -MB indicate I get ~2600 at 37" and ~2500 at 35.5-36.3, could my engine be accidentally misconfigured? What could I check if this is remotely possible? During the IRAN, a new cam was installed but the part number matches. Other than it was seals, bushings, gaskets, piston and rings. Pulling at straws at this point. 

 

 

 

Your random thought I don’t think you need more power as in flight i have pushed the prop forward and achieved 2700 with a manifold pressure of 25” before.  

[A64Pilot]

A prop in flight due to induced flow “unloads”, The induced airflow from forward air speed decreases the effective pitch.

A helicopter for instance requires a lot more collective pitch to hover out of ground effect due to induced airflow

That’s why a fixed pitch prop airplane may only get 2200 static, but may pick up a lot of RPM in level flight. My little C-140 is 2200 static, but 2550 or so in level flight.

 

[shawnd]

Thanks @Will.iam and @A64Pilot.

Instead of doing high speed taxi run and getting the cylinders up to temp again without flight - we have decided to go do the break-in flight and collect data while we are at it. I am hoping mine jumps up from 2500 (worst case) to 2700 shortly after lift off. 

@Will.iam mine has too many variables at this point, new piston & rings, new bushings, bearings, cam, fuel pump was repaired and prop governor case was replaced as part of AD but then the shop initially screwed up the internals as well.

[Will.iam]

On 7/6/2022 at 9:36 PM, shawnd said:

Thanks @Will.iam and @A64Pilot.

Instead of doing high speed taxi run and getting the cylinders up to temp again without flight - we have decided to go do the break-in flight and collect data while we are at it. I am hoping mine jumps up from 2500 (worst case) to 2700 shortly after lift off. 

@Will.iam mine has too many variables at this point, new piston & rings, new bushings, bearings, cam, fuel pump was repaired and prop governor case was replaced as part of AD but then the shop initially screwed up the internals as well.

Good points but i will say i have not seen a plane on initial power up for takeoff not achieve max RPM +- 50 at start of takeoff roll. This has been the case in all my neighbors airplanes from baron 55 twins cessna 182 172, lake amphibians, star-duster and mooney c, e, f, j, bravo, ovations. In fact it is one of my parameters for aborting the takeoff as i only have 2600ft runway and if I’m not making rated power at the beginning there’s too much risk i will not clear the trees at the end of the field.  

[shawnd]

Lets see how this goes. I have a 5330 feet runway without obstacles at the end.

[shawnd]

Wanted to post an update as I am jumping with joy over here. Despite the lower numbers for the static ground runs, the airplane performed beautifully and the prop easily climbed up to and maintained 2700+ RPM during takeoff. Wanted to share in case others run into this conundrum in the future. It was a suspenseful run-up and takeoff run as I was quite sure that it would be hard to get the 200 extra RPM, but voila! My mood improved drastically as the rest of the 2 hours ticked by at 4500 feet. Good to know that every engine is a bit different and sometimes you just have to let them free to see what they can really do.

Always appreciate the support and feedback on MooneySpace, but wanted to give a special shout-out to @A64Pilot @kortopates - thank you