Cruise RPM setting

Tina,

and he's
paying $100 an hour dry Hobbs time,

As I said, my remarks hold only if cost is independent of power setting.
Dry rentals are very uncommon, AFAIK. And I overread his remark that he
is indeed renting dry blush. Sorry!


Sure, but in
terms of learning good flying techniques, don't you think slower is
better than faster?

Not at all. Both is important, IMHO.

--
Thomas Borchert (EDDH)

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.

What power settings are in the airplane's operation manual? Any setting
listed by Cessna in the manual should be fine. Just don't forget to
lean properly.

Matt

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 -

Mortimer Schnerd, RN wrote:


One thought about continued flight at 1800 rpm: if you were running with the
carb heat on to avoid icing, then you're ingesting unfiltered air. Best to keep
that at a minimum if you can.



In a cruise flight you should be running the amount of carb heat that
gives you a carb temp of 40F.

Don't they teach Flight for Range in the U.S.?

Start at cruise RPM. Record the airspeed when things have
stabilized. Reduce the RPM by 100, wait for everything to stabilize,
including adjusting the throttle for the RPM target, trim the airplane
for level flight, and record the airspeed again. Do this in 100 RPM
increments until the airspeed suffers a much bigger drop than with the
previous settings, and go back to the last setting. Now you have the
lowest fuel flow for the best airspeed. Be sure to lean as necessary
and keep that RPM where it should be. Remember the power setting for
that airplane for the next time.
Best endurance involves finding the lowest RPM where the
airplane will maintain altitude. It'll be a pretty slow airplane. Slow
flight involves a lower airspeed but more power to maintain the
altitude.

Dan

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

By Aerodynamic Definition, your most efficient cruise speed for time
aloft is the the drag curve minima (point between the induced drag
curve and the profile drag curve), which also conveniently happens to
be defined as Vg. This is the speed at which the aircraft requires
the least amount of energy to stay aloft.

Power back to maintain Vg, lean the hell out of it (At such a low
power setting detonation is a non-issue), and cruise to your hearts
content.

Do not fly "as slow as possible", keep in mind if your airspeed drops
below Vg, your power requirements will actually go back up.

-Scott

Bob Moore wrote in
46.128:

EridanMan wrote
By Aerodynamic Definition, your most efficient cruise speed for time
aloft is the the drag curve minima (point between the induced drag
curve and the profile drag curve), which also conveniently happens to
be defined as Vg. This is the speed at which the aircraft requires
the least amount of energy to stay aloft.

By who's definition? In 50 years of flying, 39 years of instructing,
10 years military and 25 years of airline flying, I've never heard
of Vg, L/D Max maybe, even Best Glide Speed, but Vg? Not here in the
USofA.


Neither have I. And I can add glider to that list.


Bertie