Cruise RPM setting

I cannot speak about a 172 but if you are actually cruising in slow
flight, as opposed to flying slow, I hope you are considering your
cylinder head temperatures and oil temperature.

John

john wrote:
Shortly after getting my private license I went to a different FBO and
got checked out in their aircrafts - C172 and Piper Cherokee.

I talked with the CFI and asked what RPM settings he would recommend.
I'm renting dry, so one way to reduce cost is to slow down and thus
save fuel. At the present time I'm just building hours towards my
commercial ticket. Rarely am I in a hurry to get anywhere. He
mentioned that if I needed to get somewhere quickly, to keep it around
2400. If I'm just building time then to reduce to 2300. It will save
fuel as well as reduce the sound level.

The CFI no longer flies out of that airport, so I don't have contact
with him. I'm interested in others opinions related to rpm settings.
Is there any harm to the engine with reducing the RPM even lower, say
2200 or even 2100 RPM. I will confess to bringing it back to as low
as 1800 for a short X-C and found it to be good slow flight practice.,
which gave my one leg a work out in order to keep the bubble in the
middle. I wouldn't want to make many flights at 1800 though.

In the 172 I have reduced fuel from over 7.5 gph at 2400rpm to about
5.5 gph at 2200-2300.

Thanks,

John

Thanks for all of your imputs.

I don't have a 1974 POH, but I do have one for the 1978. It list the
green arc as 2200 - 2700, so as long as I keep it in the green I
should be alright. I'll check the 1974 POH next time I use that
plane, but I would be surprised if it is different since they have the
same engine. I do keep an eye on the temp guage. The main plane that
I fly tends to run a little hot anyways so reducing the throttle helps
keep the temps where they need to be.

In response to Kontiki's suggestion on new and interesting place, I
need the X-C time as well, so yes, I try to pick x-c trips when I have
more than an hour or two planned. Last week I took a friend up so
that he could take pictures of some land. When he was finished I
asked if he needed to get back right away. Since he didn't, I
diverted to an airport 30 miles further south where we landed and
grabbed a coke. I only need another 2 hours to complete the X-C
requirement, which I should complete next week when I take another
friend out for dinner. However, my goal is to land at every public
airport in the state. So I will have more than the hours needed in
that catagory.

John


On Oct 14, 8:08 am, The Visitor wrote:
I cannot speak about a 172 but if you are actually cruising in slow
flight, as opposed to flying slow, I hope you are considering your
cylinder head temperatures and oil temperature.

John



john wrote:
Shortly after getting my private license I went to a different FBO and
got checked out in their aircrafts - C172 and Piper Cherokee.

I talked with the CFI and asked what RPM settings he would recommend.
I'm renting dry, so one way to reduce cost is to slow down and thus
save fuel. At the present time I'm just building hours towards my
commercial ticket. Rarely am I in a hurry to get anywhere. He
mentioned that if I needed to get somewhere quickly, to keep it around
2400. If I'm just building time then to reduce to 2300. It will save
fuel as well as reduce the sound level.

The CFI no longer flies out of that airport, so I don't have contact
with him. I'm interested in others opinions related to rpm settings.
Is there any harm to the engine with reducing the RPM even lower, say
2200 or even 2100 RPM. I will confess to bringing it back to as low
as 1800 for a short X-C and found it to be good slow flight practice.,
which gave my one leg a work out in order to keep the bubble in the
middle. I wouldn't want to make many flights at 1800 though.

In the 172 I have reduced fuel from over 7.5 gph at 2400rpm to about
5.5 gph at 2200-2300.

Thanks,

John- Hide quoted text -

- Show quoted text -

john wrote:

I don't have a 1974 POH, but I do have one for the 1978. It list the
green arc as 2200 - 2700, so as long as I keep it in the green I
should be alright. I'll check the 1974 POH next time I use that
plane, but I would be surprised if it is different since they have the
same engine.

That's simply the normal operating range. The POH will also have graphs
or tables that will give you power and fuel burn information for various
altitudes and temperatures. Use them.

I often hear pilots saying things like, "What rpm should I use for cruise?
" and hardly ever hear the correct answer, which is : It depends. What it
depends on is the amount of power you wish to generate, and the density
altitude at which you'll be flying. To make a given percentage of power,
the rpm required will increase as the density altitude increases (in a fixed
pitch plane like the 172). If you want to fly around at an economical 55%
power setting, the rpm you should set will be very different if you're flying
low on a cold day, or high on a hot day.

Quick example : The rpm that I use in my Cherokee to fly 75% cruise at 6,
000 ft. on a hot day is very close to the rpm that I'd use to fly at 100%
power (not a good cruise setting) near sea level on a standard day.

John Galban=====N4BQ (PA28-180)

--
Message posted via AviationKB.com
http://www.aviationkb.com/Uwe/Forums...ation/200710/1

It seems to me that you would set up whatever power required to cruise at
best L/D and that would necessarily give you best range. Brett



"JGalban via AviationKB.com" u32749@uwe wrote in message
news:79bea10122a88@uwe...
john wrote:

I don't have a 1974 POH, but I do have one for the 1978. It list the
green arc as 2200 - 2700, so as long as I keep it in the green I
should be alright. I'll check the 1974 POH next time I use that
plane, but I would be surprised if it is different since they have the
same engine.

That's simply the normal operating range. The POH will also have graphs
or tables that will give you power and fuel burn information for various
altitudes and temperatures. Use them.

I often hear pilots saying things like, "What rpm should I use for
cruise?
" and hardly ever hear the correct answer, which is : It depends. What
it
depends on is the amount of power you wish to generate, and the density
altitude at which you'll be flying. To make a given percentage of
power,
the rpm required will increase as the density altitude increases (in a
fixed
pitch plane like the 172). If you want to fly around at an economical
55%
power setting, the rpm you should set will be very different if you're
flying
low on a cold day, or high on a hot day.

Quick example : The rpm that I use in my Cherokee to fly 75% cruise at 6,
000 ft. on a hot day is very close to the rpm that I'd use to fly at 100%
power (not a good cruise setting) near sea level on a standard day.

John Galban=====N4BQ (PA28-180)

--
Message posted via AviationKB.com
http://www.aviationkb.com/Uwe/Forums...ation/200710/1