avoiding continuous operation - RPM/manifold

[dominikos]

There is a placard in my plane that states ‘avoid cont. operations between 1500 & 1950 RPM w power settings below 15” hg manifold pressure”.  I was told that a brief operation in this range on the final approach are acceptable. In my experience, it is impossible to avoid it as I adjust MP on approach. Do you guys have any hints/tips on how to avoid it or whether it is acceptable for brief period?

As said, I was told not to worry about it but thought I would ask for another opinion(s).

[LANCECASPER]

You don't need to be at low RPM on final, just low MP. If you have to go around it's good to just push one lever forward.

[dominikos]

I should be clear, I never touch RPM lever - propeller is always at max. There are just times when I bring MP down to adjust for higher speed on final. It might be just lack of my experience that results in larger than needed MP adjustments that take MP below 15 and as a result RPM from above 1950 to below 1500.

[carusoam]

Seems like there is no way around it...

Then it depends upon what continuous operation means...

The placard is a warning that harmonic vibrations exist in that range...

1) Don’t use it as a cruise setting...

2) Stay out of it as often as possible...

3) Get your prop dynamically balanced... similar, but completely different...

4) Damage from these unfelt vibrations can be hazardous to the engine’s internal parts...

5) external damage may be found in broken welds on the engine mount...

6) Some tachs are properly marked with a yellow range... others, less properly have a red arc... (hard to avoid that?)

My M20C broke two welds on its engine mount... So I was flying with three bolts holding the engine in place....

Three out of four ain’t bad... - Meat Loaf

To get rid of the placard properly... requires a different engine/prop combination...

If you would like a new / different prop... this may be the reason you have been looking for...

PP thoughts only, not a mechanic...

 

Best regards,

-a-

[N201MKTurbo]

I usually keep the RPMs above the yellow until short final, then bring the throttle back to idle and land. Usually about 300 feet from the threshold.

[David Lloyd]

On approach is not continuous operation.  Although some Cessnas might qualify for that.

[Tim Jodice]

12 hours ago, carusoam said:

Seems like there is no way around it...

Then it depends upon what continuous operation means...

The placard is a warning that harmonic vibrations exist in that range...

1) Don’t use it as a cruise setting...

2) Stay out of it as often as possible...

3) Get your prop dynamically balanced... similar, but completely different...

4) Damage from these unfelt vibrations can be hazardous to the engine’s internal parts...

5) external damage may be found in broken welds on the engine mount...

6) Some tachs are properly marked with a yellow range... others, less properly have a red arc... (hard to avoid that?)

My M20C broke two welds on its engine mount... So I was flying with three bolts holding the engine in place....

Three out of four ain’t bad... - Meat Loaf

To get rid of the placard properly... requires a different engine/prop combination...

If you would like a new / different prop... this may be the reason you have been looking for...

PP thoughts only, not a mechanic...

 

Best regards,

-a-

An MT prop gets rid of all restrictions. 

[Pete M]

On 11/7/2020 at 6:34 PM, dominikos said:

I should be clear, I never touch RPM lever - propeller is always at max. 

I'm confused by this. What model is it? Why never touch the prop? Max Rpm limited to 2500...eagle? There are benefits to reducing rpm. Fuel savings and less wear to name two.

[dominikos]

20 minutes ago, Pete M said:

I'm confused by this. What model is it? Why never touch the prop? Max Rpm limited to 2500...eagle? There are benefits to reducing rpm. Fuel savings and less wear to name two.

M20J, I do adjust RPM in flight but not in approach / landing when I set it to high.