Cruise RPM setting

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.


Found it . It's a Nigel thing.


Bertie

Hmm most airliners are set up to operate most efficiently at L/D Max
+5%. In the case you cannot achieve this in a piston powered aircraft,
please read the POH section on performance. 2300 rpm was always good
in a 172 IIRC, the fact that you can rent dry is a plus.

Have a great one!

Bush

On Sun, 14 Oct 2007 03:16:39 -0000, 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

Vg = Best Glide Speed (I'm sorry, I should have specified) = L/D max.

Sorry, I should have made that clear.