Charging for tach time in a fixed pitch airplane

On 2007-04-30, Brian wrote:
It makes sense to me to charge by Hobbs on constant speed props
because charging by Tach encourages running High MFP and Low RPM. Low
RPM is ok but need to keep the MFP in line with it as well.

That's an old wives' tale, I'm afraid. The best regime to operate an
engine (most efficient and least maintenance) is the lowest RPM and
highest MP for the desired power setting. There are some caveats (some
aircraft have a range of RPMs which you should not continuously operate
the engine), but generally speaking, using the lowest RPM possible for
the desired power setting results in less noise, less vibration and less
wear on the engine.

The thing about operating engines (specifically normally aspirated flat
engines like most of us use) 'above square' is hogwash, I'm afraid.

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Doesn't this also bring up the question of when is an overhaul due
(according to hours)?
At 2000 hobbs hours or 2000 tach hours?
Lou

In article .com,
Lou wrote:

Doesn't this also bring up the question of when is an overhaul due
(according to hours)?
At 2000 hobbs hours or 2000 tach hours?
Lou

Tach

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Bob Noel
(goodness, please trim replies!!!)

Bob Noel wrote:
In article .com,
Lou wrote:

Doesn't this also bring up the question of when is an overhaul due
(according to hours)?
At 2000 hobbs hours or 2000 tach hours?
Lou

Tach

BZZT Wrong answer. Time in service. Tach is acceptable,
so are elapsed time meters. I don't even have a recording
tach in my plane.

In article , Ron Natalie wrote:

Doesn't this also bring up the question of when is an overhaul due
(according to hours)?
At 2000 hobbs hours or 2000 tach hours?
Lou

Tach

BZZT Wrong answer. Time in service. Tach is acceptable,
so are elapsed time meters. I don't even have a recording
tach in my plane.

argh, I knew better than that too.

:-(

--
Bob Noel
(goodness, please trim replies!!!)

On May 2, 3:29 am, Bob Noel
wrote:
In article , Ron Natalie wrote:
Doesn't this also bring up the question of when is an overhaul due
(according to hours)?
At 2000 hobbs hours or 2000 tach hours?
Lou

Tach

BZZT Wrong answer. Time in service. Tach is acceptable,
so are elapsed time meters. I don't even have a recording
tach in my plane.

argh, I knew better than that too.

In Canada, at least, the time used for such things as engines
is Air Time, described in the regs like this:

"air time" - means, with respect to keeping technical records, the
time from the moment an aircraft leaves the surface until it comes
into contact with the surface at the next point of landing.

Technical records include engine logs. So a tach could be way
off if you spend a lot of time taxying or running up or doing other
non-flying stuff.

Dan

On May 1, 7:18 am, Dylan Smith wrote:
On 2007-04-30, Brian wrote:

It makes sense to me to charge by Hobbs on constant speed props
because charging by Tach encourages running High MFP and Low RPM. Low
RPM is ok but need to keep the MFP in line with it as well.

That's an old wives' tale, I'm afraid. The best regime to operate an
engine (most efficient and least maintenance) is the lowest RPM and
highest MP for the desired power setting. There are some caveats (some
aircraft have a range of RPMs which you should not continuously operate
the engine), but generally speaking, using the lowest RPM possible for
the desired power setting results in less noise, less vibration and less
wear on the engine.

The thing about operating engines (specifically normally aspirated flat
engines like most of us use) 'above square' is hogwash, I'm afraid.


Agreed, But how do you make a simple rule of thumb for this for pilots
with less then 100 hours or like my latest student that is starting
his primary instruction an an airplane with a constant speed prop.

The problem with your statement is that with new, or low time pilots,
as is often typical in clubs, that are going to take it literally and
is you will end up with a few pilots running around WOT and 1500 RPM.
I doubt that is what you ment and the cyinder pressures have got be
quite high in this configuration, especially if they don't lean
properly either.

The "above square rule" is a great simplifcation of how you "can"
operate constant speed props. It certainly is not a hard and fast rule
but you have to understand what you doing operate otherwise safetly.
For a pilot that barely knows how to operate the throttle and mixture
properly they probably ought to just stick with the "over square rule"

Brian
CFIIG/ASEL

On 2007-05-02, Brian wrote:
Agreed, But how do you make a simple rule of thumb for this for pilots
with less then 100 hours or like my latest student that is starting
his primary instruction an an airplane with a constant speed prop.

You don't. You tell them to use the power setting tables in the POH. If
they are incapable of this, they aren't really cut out for aviation.

The problem with your statement is that with new, or low time pilots,
as is often typical in clubs, that are going to take it literally and
is you will end up with a few pilots running around WOT and 1500 RPM.

You won't because they won't make enough power to maintain altitude.

I doubt that is what you ment and the cyinder pressures have got be
quite high in this configuration, especially if they don't lean
properly either.

Cylinder pressures will be in the same order of magnitude as 'normal'
operation. You will neither climb nor go fast though in this regime.

For a pilot that barely knows how to operate the throttle and mixture
properly they probably ought to just stick with the "over square rule"

They probably ought to have some remedial training if they can't set the
throttle and mixture correctly! It's not even hard to do these things.

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