Low power settings on Rocket?

[wombat]

I'm only 4 flights into my Rocket ownership and am finding that I sometimes want to fly at much lower power settings than even the lowest cruise setting in the manual.

The manual does say not to go below 25" & 2,200 RPM on the descent so I've been using that as my minimum power for everything other than final approach. This results in being way too fast in the pattern of course.

The "IFR By The Numbers" configuration sheet includes a 15" and a 20" power setting so I assume those are relatively safe.

My specific questions are:

• What is the purpose of the 'minimum descent power' and if I go below that (as long as I reduce power by no more than 1" per minute), will that cause any damage?
• What do other pilots use for power settings in the traffic pattern and on final?

 

[Fly Boomer]

1 hour ago, wombat said:

I'm only 4 flights into my Rocket ownership and am finding that I sometimes want to fly at much lower power settings than even the lowest cruise setting in the manual.

The manual does say not to go below 25" & 2,200 RPM on the descent so I've been using that as my minimum power for everything other than final approach. This results in being way too fast in the pattern of course.

The "IFR By The Numbers" configuration sheet includes a 15" and a 20" power setting so I assume those are relatively safe.

My specific questions are:

• What is the purpose of the 'minimum descent power' and if I go below that (as long as I reduce power by no more than 1" per minute), will that cause any damage?
• What do other pilots use for power settings in the traffic pattern and on final?

 

The Rocket documentation goes down to 2200, but Continental now says nothing below 2300.  That said, those numbers are for enroute, not landing.  The issue was with counterweights under high power settings.  For descent, I think it's probably important to make sure the engine is driving the prop, and not the other way around.  During approach and landing, having the prop all the way in also provides a little braking action.  Aside from those issues, I suspect (hope) it doesn't make too much difference at very low power settings.

[Hank]

Paging Dr. Erik again! @aviatoreb

[wombat]

32 minutes ago, Fly Boomer said:

The Rocket documentation goes down to 2200, but Continental now says nothing below 2300.  That said, those numbers are for enroute, not landing.  The issue was with counterweights under high power settings.  For descent, I think it's probably important to make sure the engine is driving the prop, and not the other way around.  During approach and landing, having the prop all the way in also provides a little braking action.  Aside from those issues, I suspect (hope) it doesn't make too much difference at very low power settings.

That makes a bunch of sense.... Occasionally having the prop creating drag instead of thrust, and having the torque be backwards as the air is driving the engine speed faster than the engine power would actually make it go is probably OK but it wears the bearings (and maybe other parts) quickly.       So if you regularly do this on a descent from FL230 it'll cause the engine to need maintenance early but if you only do it on final the bearings will outlast the normal expected life of the engine before overhaul.

[aviatoreb]

11 hours ago, wombat said:

I'm only 4 flights into my Rocket ownership and am finding that I sometimes want to fly at much lower power settings than even the lowest cruise setting in the manual.

The manual does say not to go below 25" & 2,200 RPM on the descent so I've been using that as my minimum power for everything other than final approach. This results in being way too fast in the pattern of course.

The "IFR By The Numbers" configuration sheet includes a 15" and a 20" power setting so I assume those are relatively safe.

My specific questions are:

• What is the purpose of the 'minimum descent power' and if I go below that (as long as I reduce power by no more than 1" per minute), will that cause any damage?
• What do other pilots use for power settings in the traffic pattern and on final?

 

25-2200 is too fast for the pattern.  But those book numbers the lowest being 26-2200 is a cruise setting of 55%.

But Continental much more recently than put out an AD not to cruise at cruise settings with prop slower than 2300 for counter weight issues and some incidents I believe that happened in the Cape Air fleet - so I dont either.  I generally substitute for example 25-2300 for book 26-2200 (its a little higher) and 29-2300 for 30-2200 (again its a little higher).  But in pattern and even in approach, its fun to use much lower settings - e.g. 23-2400 is a common setting I use while working an approach plate and 21-23 -2400 is a fine setting for in the pattern vfr. And of course lower when you turn base then final - dial it down to 17- or 18 and full forward prop as appropriate.

If you are cruising at settings lower than 55% you do need to pay attention to oil temps and cylinder temp to keep an eye if they are too cold.

Edited May 5, 2023 by aviatoreb