Hartzell RPM restrictions question

The Hartzell props have various RPM restrictions, depending on the engine used. For example (this list is combined from various prop models):

1) Continuous operation is prohibited above 22" manifold pressure between 2050 and 2200 RPM

2) Do not operate above 22" manifold pressure below 2350 RPM.

3) Operation above 2600 RPM is limited to takeoff. As soon as practical after takeoff the RPM should be reduced to 2600 RPM or less.

4) Maximum engine RPM must be limited to 2650 RPM.

5) Avoid continuous operations between 2000 and 2250 rpm.

6) Stabilized operation is prohibited above 25" manifold pressure between 2300 and 2550 RPM and below 15" manifold pressure above 2600 RPM.

Being a low-time pilot and having never flown a constant speed prop, I don't know the severity of these restrictions. Are they just annoying? Do they seriously hamper cruise or take-off or aerobatics?

Thanks in advance,
Dave

To my knowledge, none of the restrictions you mention apply to the O-320. The O-360 has a lot of restrictions because it's an over-square engine -- its stroke is larger than its bore. This apparently changes the harmonics of the engine vibration into a range that effects the prop.

It's something to think about if economy is important to you. You'll hear people say that you might as well get an O-360 because you can always pull back the throttle if you want to save gas. But that's not exactly true if you've got an "avoid continuous operation" restriction in your 50% power range.

My O-320 / Hartzell combination lets me pull the power back and sip gas like a C-150, while still indicating 150 MPH. And yet I still get better than 2000 ft/min climb off the deck (solo). At the top end, it's true that I'm about 10 mph slower than an O-360. But I can still cruise at 200 mph TAS when I need to. It's plenty for me.

Constant Speed Prop restrictions

Davepar said:

The Hartzell props have various RPM restrictions, depending on the engine used. For example (this list is combined from various prop models): Dave

Click to expand...

As you state you have superimposed restrictions from several prop, engines and electronic ignitions and FADEC systems. The typical restriction for a Hartzell HC-C2YK-1BF/F7666A-(2,4) on a Lycoming (I)O-360-A, B 180 HP series engine:

"Avoid continuous operations between 2000 and 2250 rpm."

That is it. That is the only restriction. This restriction has been around a long time. What is new is electronic ignitions, new aftermarket Lycoming clone engines and new Hartzell blade models. Using the above example with lightspeed electronic ignition you have the additional restriction:

" Reduce RPM after T/O to 2600rpm as soon as practical"
" Blades are life limited to 20,000 hours"

How serious is it to operate in the restricted RPM range. The answer is it is a CAUTION to avoid CONTINUOUS operation at these RPM. This is a conservative effort not to adversely affect blade fatigue life. Most pilots reduce RPM after takeoff, so that is not an issue. As far as 20,000 hours life limit, most blades die from wear (filing chips and dings) and corrosion well before then.

To operate for a short time in the restricted range will cause no problem. The engineers have conservatively assumed you will operate at those RPMs for some percentage of the time with a extra ?margin of safety?, but if you operated there all the time, you will reduce the calculated theoretical fatigue life. That reduced life is still likely more than you'll ever fly. These props are very well tested. So think about any experimental prop with an unknown vibration survey on your engine/prop combo.

jonbakerok said:

You'll hear people say that you might as well get an O-360 because you can always pull back the throttle if you want to save gas. But that's not exactly true if you've got an "avoid continuous operation" restriction in your 50% power range.

Click to expand...

I don't understand the comment about not being able to pull the power back with an O-360 and a constant speed prop. You can easily achieve any power setting you want and still remain outside the continuous operation rpm range limits. Example: O-360 and HC-C2YK-1BF/F7666A-(2,4) (magneto or electronic ignition) at Sea level

2000rpm @ 20" = 50%
2250rpm @ 22" = 56%
2350rpm @ 22" = 67% etc......................

Obviously you can achieve any power you want. Constant-speed propellers offer higher efficiency over a wider speed range compared to fixed-pitch propellers. This enables the you to optimize, takeoff, cruise and climb for maximum efficiency and performance.

Note: the upper 2600 rpm limit is not a factor for normal cruise. Most of the time you set rpm at 2350-2500rpm. Anything over 2500rpm just makes more noise for very little gain in speed.

Cheers, G