Minimizing tach time in controllable-pitch plane

polaris

polaris

Pre-takeoff checklist
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polaris
My flight school charges by tach time. This is great when you are flying fixed-pitch planes in the pattern/instrument approaches because your RPMs are almost always *NOT* at max rpm. (2000rpm on approaches, downwinds, etc.)

However, in a controllable-pitch plane, you are likely at high-rpm on approaches/downwind, which doesn't confer any advantages -- in fact, you are worse off, because you are being charged at 2500rpm when you are only doing 90 kts.

If the plane allows for a 20"/2000rpm cruise, is it advisable that I fly approaches and extended downwinds like that? And then go full-rpm when I am about to approach the missed approach point/short final?

Or is that too risky in case something does go wrong?

ETA: Now that I think of it, 20"/2000rpm would probably not give me the right approach speed on an instrument approach.

I am just thinking out loud, so it's not something I have tried, or will be trying any time soon. Perhaps the difference in $$ is negligible to be worth the hassle.
 
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Also, even if you have the prop control all the way in, the RPMS won't max out unless you are full throttle, too. If you pull back on the throttle sufficiently, the RPMs will drop.

You push the prop control all the way in on your pre-landing check list so that if you need to go full throttle for go around, you have full power, not because you need full RPMs for approach/landing.
 
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PPC1052 said:
Also, even if you have the prop control all the way in, the RPMS won't max out unless you are full throttle, too. If you pull back on the throttle sufficiently, the RPMs will drop.
Click to expand...

True. Although I think I kept noticing that around 20" or 18" or so I was still around 2500 rpm if I had set it that way. Which irked me a bit. But I'll lighten up.
 
You must fly your approaches real fast.

At approach speed in a 172RG, 177, or 182, your prop is at the fine stop and is significantly below max RPM even with the prop fire walled.

For a 182, the 2000 foot cruise performance table using 2400 RPM (as high as it goes) gives you at least 124 KTAS at standard temperature.

You can play this game at cruise, a little. But in the pattern? No difference.
 
MAKG1 said:
You must fly your approaches real fast.

At approach speed in a 172RG, 177, or 182, your prop is at the fine stop and is significantly below max RPM even with the prop fire walled.
Click to expand...

Hmm, then maybe I was thinking about the legs leading up to the approach. If I'm being vectored during practice approaches. I could fly those legs 20"/2000rpm instead of 24"/2400rpm cruise. That might work. But probably negligible.
 
My thinking is the constant speed prop would be better for you in cruise anyway. You can drop down the RPMs while maintaining a fast cruise speed. That's why you have the constant speed prop. Otherwise, we would all just have fixed pitch climb props.
 
I don't bring the props forward until my MP/power is below what would sustain max RPM. There is no need for max RPM when you are descending.
 
PPC1052 said:
Also, even if you have the prop control all the way in, the RPMS won't max out unless you are full throttle, too. If you pull back on the throttle sufficiently, the RPMs will drop.

You push the prop control all the way in on your pre-landing check list so that if you need to go full throttle for go around, you have full power, not because you need full RPMs for approach/landing.
Click to expand...

If there is no one waiting at an intersection, no animals (including humans) near the runways, and I have the runway to myself, I see no need for going full-up on the prop control at all. As Henning says, once you pull the throttle back far enough the prop governor will go to its stops and further movement of the prop control will accomplish exactly nothing.

Bob Gardner
 
Not even considering "tach time $", I like to cruise at lower rpms (bottom of the green arc) for reduced noise, vibration, and fuel consumption anyway.
And you don't need to push the prop control forward until you have made your final throttle reduction on approach to land.
To me, all that is good pilot technique.
 
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