RW Pilot input on prop rpm please

[Ryan B]

I've never flown a plane with a constant speed prop in real life. There's obviously cruise settings with lower prop rpm - that I understand. What always confuses me is descent. In some PoH's it recommends prop fine to increase resistance ...ie the prop acts like wall to slow you down. My question is when do I set it to fully fine? I wouldn't want to tear up my engine hehe.

[Keith Smith]

Check the POH regarding extended operations at peak RPM. Most training aircraft can be operated at redline all day long. For noise abatement and cabin comfort, I back mine off to about 100rpm below redline if the goal is a high RPM setting. Otherwise, I'll keep the rpm towards the bottom of the green to minimize noise.

[Ryan B]

... I back mine off to about 100rpm below redline if the goal is a high RPM setting. Otherwise, I'll keep the rpm towards the bottom of the green to minimize noise.

This what I'll shoot for in the legacy during descent then... I think the setting would be 2600rpm.

[Orest Skrypuch]

Because the prop is unloaded you can overspeed the prop a bit in descent if you push it full forward, the governor often lets it get away a bit, but seldom anything significant.

Whatever the POH says, is the first advice, unless there has been new data since the POH was written. (a good example is Lycoming leaning & runup procedures)

I own a Dakota, which is an O540 with a constant speed prop. For me it is full forward for takeoff, bring it back to climb power and RPM at acceleration height (800 to 1000 ft AGL). There are a variety of ways of leaning during climb, the easiest is just to maintain the takeoff run EGTs, but the RPM does not change. Once level choose an RPM that makes the engine sound nice, and then pull the throttle if required, to set to cruise power. Lean it out to peak, or slightly lean of peak if your engine can do it.

On the descent, nose it down, but don't touch the RPM or throttle controls. Once you reach 21", pull the throttle to maintain it, gradually increase the mixture, that will typically keep you below yellow line and on a 2.5* to 3* descent path. At 40nm, you should be no higher than 12,000ft.

As part of the approach check list, advance the RPM to climb setting.

Land.

Done.

* Orest

[Ryan B]

Thanks for the insight! 21in MP in the realair lancair is too much in a descent hehe... that thing is so slippery. I usually have to do 15inMP with 2600rpm and rich mixture to keep it in the green arc.

[Keith Smith]

Yep, they're very different airplanes. Most constant speed prop airplanes will let you descend at a reasonable rate with wide open throttle from cruise altitudes. Not so much in the Lancair. If I do much more than 500fpm, I'm into yellow arc world with the power wide open.

However, to pull power is to fail, so I limit it to 500fpm and just start my descents further out

[Ryan B]

However, to pull power is to fail, so I limit it to 500fpm and just start my descents further out

Is this shock cooling you're talking about?

[Keith Smith]

No, it's a penchant for going as fast as possible for as long as possible.

[Orest Skrypuch]

Well, the OP did not specify a plane type, and the numbers will be different for different planes, of course, but the general principles are similar.

Yep, pulling power to descend (from cruise) is indeed failing to properly manage your planes energy.

* Orest