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**Mark Goldberg** · 12-06-2021, 06:32 PM

Nev, there is a screw on the governor that adjusts the max allowed RPM. You can set the rpm higher. Although if you fly it at 2575 rpm you will think you have a TON of power. The 250 HP engine on my former BH (now Jared's) is set to 2575. I never heard anyone say it was lacking power. With the 3 blade Trailblazer it will have surprising take off thrust.

Yes, you should see max rpm on the ground with a full power run up. At least that is my understanding although I could be wrong. Mark

**N3UW** · 12-06-2021, 08:17 PM

Nev, as mark says should should be able to adjust the prop governor to give you full 2575 RPM. That is relatively independent of engine HP. I have an o540 on my cherokee with a Hartzell 3 blade prop. At 3/4 to full power you should be easily able to make 2575 rpm. The prop gov has a flywheel inside that adjusts oil pressure to prop to adjust coarseness of blade to lock in the rpm.

**Bissetg** · 12-06-2021, 08:39 PM

Nev, what Mark said is correct. You may wish to check your RPM with an optical tach. Anyone who does helicopter maintenance will have one if your local chap doesn’t. It would pay to confirm your RPM indication is accurate before altering too much given its an initial setup of your instrumentation too.

**zkelley2** · 12-06-2021, 10:26 PM

You can change it to 2700 rpm on the prop governor. It'll be a little trial and error to get it just right. That is unless hartzel set the fine pitch stop limits too coarse, which is possible. Luckily on the hartzel, iirc from reading, as I've never ran one, it's rather trivial to re-set this hard stop.
The extra 125rpm is worth 10 more HP.

**Chris Werner** · 12-06-2021, 11:56 PM

Nev, from my experience with the Lycoming 540 in the Piper Comanche the o-540 was limited to 2575 rpm and the io-540
was 2700 rpm. The only difference in the rotating assembly is a counterweight on the crankshaft. Hartzell required the o-540 to be fit with the io-540 counterweight to run the compact hub propeller. In the certified world Johnstons Aircraft owns the stc to make this change on the Comanche. If the engine you have was built to io-540 specifications (the crankshaft counterweight) I would feel safe turning up the governor.
Chris

**svyolo** · 12-07-2021, 12:27 AM

I have little experience with any of this, but trying to learn it the last 4 years or so, I learned a lot but still don't know squat. There are engine/prop keep-out zones for vibration. There are rpm limits for noise constraints, depending on geographic location. Some 540's are rpm limited for some reason to keep the hp down to 230. Why? I don't know. Maybe airframe limitations/control authority/who knows.

I bought a 540 for weight and balance, and cheap high altitude performance. I would guess I will rarely use 260 hp or 2700 rpm.

**whee** · 12-07-2021, 10:22 AM

I think you’ve likely received all the information you were looking for. I’d like to add a bit of “how it’s supposed to work” type info in relation to the prop governor and the fine pitch stops in the prop.

With a constant speed prop your engine should reach maximum rpm during static run up. During the static run the max rpm should be limited by the fine pitch stops set in the prop. Sometimes these stops are not set right so the engine over revs and to correct it mechanics will adjust the prop governor. This works but the correct solution is to have the fine pitch stops adjusted in the prop. On a Mac this requires a prop shop to partially disassemble the prop, thus mechanics/owners just adjust the governor. On all the hartzalls I’ve look at there is an adjustment bolt on the hub.

As soon as the plane starts rolling the prop governor takes over and controls engine rpm.

What I would do if I were you, Nev. 1. Confirm the counter weight and prop configuration is safe to run at 2700rpm.

2. Adjust the prop governor for more RPM. If your prop is properly setup for 2575 then adjusting the governor will not result in gaining any rpm at this point.

3. Adjust fine pitch stops in prop to achieve 2700rpm. This may require you to adjust the prop governor at the same to to make sure it is not limiting rpm.

4. Adjust prop governor till it starts reducing the rpm down from 2700rpm then back it up till 2700 is achieved so the prop is just kissing the fine pitch stops. This will eliminate the short over rev that can occur at the beginning of a takeoff roll. If you listen to other planes you can hear it, it’s a pretty common thing.

Of course I’d do all this rigmarole after breaking in the engine.

I’m calling the kettle black but if your setup is approved for 2700rpm I would certainly make the adjustments necessary to achieve that rpm. There no reason to leave performance on the table even if you don’t think you will use it. There’s no issue with dialing the prop back a few turns before taking off to reduce rpm and noise. I do it all the time.

**Battson** · 12-07-2021, 04:06 PM

I seem to recall Bob asking me when I ordered my engine, whether I wanted the Lycoming 72801counterweights installed so I could run a wider range of propellers. I have them installed.
72801.jpg

Hartzell provided me with the attached "Revised Statement of Limitation" letter, stating I can run the 83" blades at 2700 (+/-50). I recall that Bearhawk Aircraft had to specifically request this letter from Hartzell, at the time I fitted the new propeller - which was purchased through Bearhawk Aircraft. NZ's CAA required a copy of this, because of the book value 150 hour inspection on the prop.

I asked Hartzell's rep about the counterweights, as I had the engine open at the time.
Their reply was: "The stock engine configuration with counterweights is recommended for your propeller."

Nev I suspect you can also get approval to run this prop at 2700 RPM. You won't get 260 hp unless you turn it that fast....

Attached Files

**Pbruce** · 12-07-2021, 04:09 PM

The technical expertise and sheer goodwill on this forum never ceases to amaze me. Thanks Whee!

**Battson** · 12-07-2021, 05:22 PM

According to the Lycoming operators manual, page 3-31 "Figure 3-19. Sea Level and Altitude Performance Curve – IO-540-D":

- At 2700 RPM and 28.5 "Hg it develops 260 hp at sea level.
- At 2575 RPM and 28.75 "Hg it develops 252 hp at sea level.

So you are losing out on a 'colossal' 8 horsepower until you fix the issue. Not worth worrying about before the engine is bedded in Nev

P.S.
At 30 "Hg with ram air and 2750 RPM, the engine should be developing ~275 hp. These are the number we see as the ship breaks ground at seal level with ISA conditions.
Air pressure is especially important for horsepower, having a considerably greater effect on power output than RPM.

**svyolo** · 12-08-2021, 01:35 AM

Nev,
Thinking about it a bit more, if it were me (and I might be in the same boat) I might not really care. I will use 100% power so seldom it won't hurt the prop. I only want the extra power at high altitude, and the most efficient prop rpm at the speeds we fly is slower than for an aircraft that cruises faster. We can take off shorter than we can land.

As a technical exercise, I might want to know. I also have a Bob 540 with the same designation. I also don't know the counter weight configuration so I guess I will have to ask. I wasn't knowledgeable enough then (or now) to have asked to have counterweights installed.

**rv8bldr** · 12-08-2021, 08:47 AM

Nev (et al) please forgive me if it appears I am hijacking this thread as it is not my intention. My lack of technical aircraft engine knowledge is astounding but I have a couple of questions regarding RPM limitations and CS props. I bought a runout O-540-A1D5 and had it completely overhauled , counterweights installed, and lower compression pistons installed (essentially turned it into a B1D5 so I can burn MoGas if I have to). In addition, I bought a HARTZELL HC-C2YR-1BF/F8475D-4 that came off of a Glasair III with an IO-540 and had it overhauled as well.

Questions:

1. Is the RPM limitation always related to the specific engine/prop combination for harmonics? The engine as it came out of the Comanche is RPM limited to 2500, but is that based on the fitted propeller or is because of some difference in the design/manufacture/metallurgy of the crank on that particular model of engine?

2. Given that the overhauled prop came off of an IO-540 that turned 2750, is there any reason to believe that upping the RPM limit to 2700 on my engine/prop combo would have disastrous results?

Thanks in advance

**Bcone1381** · 12-08-2021, 09:37 AM

Below is a link to an FAA document that pertains to some Hartzell Props. It is accessible on the FAA's website.

https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/d7115816308185568625843f00661353/$FILE/P-920_Rev39.pdf

The 13 page document is the Type Certificate Data Sheet (TCDS) for a series of Hartzell Props. This particular TCDS is for number hubs and includes the Hartzell HC-C2YR-1, -2, -4 propeller hubs that Mark asked about in post #13.

The big picture as I see it is.....
There are three variables. A hub, a blade, and an engine. Each Prop Hub receives a number of blade designs and is approved for several engines. On Page 8 of 13 begins a list of Hub, engine and blade combinations that are approved, along with associated limitations...like Blade Length, and required Placards. The Placards show mandatory RPM and Manifold Pressure limitation Hartzell placed on the approved combinations.

If your combination is not listed, then I believe either it's not been tested, or it's been tested and is was not approved. I believe a call to Hartzell will reveal which is true.

Searching TCDS on the FAA website is quite fun. There is a lot of great information in them. Below is a link that will search the TCDS by Type Certificate Holder (manufacturer) like Lycoming, Hartzell or McCauley. Have fun.

https://rgl.faa.gov/Regulatory_and_G...e?OpenFrameset

**Battson** · 12-08-2021, 04:18 PM

Prop to engine matching is a non-issue for composite props like the Hartzell Trailblazer, I was reliably informed speaking to the representative at Hartzell.

Their rationale for the layperson was, think of a metal prop like a big tuning fork. The engine is 'exciting' that tuning fork with it's vibrations. If the engine excites the prop at the right (wrong?) frequency, or a higher mode of the same frequency, then you have an accident waiting to happen. I am assured there's no physical symptoms which a human body will detect to warn that a problem is occurring, normally the first thing you know is part of the prop departs the engine, which is normally followed quickly by the rest of the prop or even the whole engine. Welcome to experimental aviation...

The composite prop apparently has a natural frequency so far above the frequencies generated by a 4-stroke engine, that there's almost no chance of a problem occurring. So I was assured.

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