From Piper Chieftan manual regarding engines

[xerj]

Come across another thing that has puzzled me (big surprise).

Here's a transcript from the manual:

"Under full throttle operations (such as takeoff and climb) the engines of
the aircraft have been adjusted to provide 43 inches of manifold pressure at
seal level and standard temperature. It is possible to read higher (up to 49
inches of manifold pressure) or lower than 43 inches of hg. manifold
pressure when ambient temperatures are higher or lower, respectively, than
standard."

I tried to explain to myself why the MAP would go up with higher than
standard temp, and down with the opposite situation. I came up a blank.

So, I'm asking the group. Why does this happen?

TIA.

[[email protected]]

Primarily because the absolute pressure controller senses the
temperature of the induction air between the turbo compressor outlet
and the fuel servo and adjusts the "absolute" maximum MAP according to
temperature by controlling exhaust wastegate position.

When setting up this controller, a temp probe is inserted into the
induction airstream and the temperature at max power measured. Using a
Lycoming chart, the max MAP is adjusted according to the indicated
temperature.

MAP/RPM is a relatively crude way of indicating horsepower. In simplest
terms, when the induction temp goes up, horsepower goes
down-consequently when induction temp goes down, horsepower goes up.
The absolute controller, in theory, maintains this temp change/HP
curve. But an initial start/rig point must be established after engine
installation or absolute controller change.

TC

[[email protected]]

>>>>It is possible to read higher (up to 49 inches of manifold pressure<<<<

And the MP gauge is redlined at 40" IIRC - at least the one in my
pals's Panther Navajo is.

Toecutter's post was correct in that the pressure controller must be
set to allow the engine to make its full rated HP allowing for a range
of OATs.

[Capt.Doug]

> wrote in message
> And the MP gauge is redlined at 40" IIRC - at least the one in my
> pals's Panther Navajo is.

The Chieftain has a higher horsepower rating (350 hp) with a higher MAP
redline (49").

D.

[[email protected]]

The Panther Navajo has the 350hp Chieftain engines. IIRC my friend told
me the MP redline is still 40" although on takeoff he normally sees
42-43"

[[email protected]]

Colemill has always been good at grey area performance changes.
Typically, when converting to a higher HP engine, they de-rate the
install by reduced "redlines" in theory reflecting what is comparable
to the original install max TO HP. Then they put in a neat little
statement something along the lines of the aircraft will meet or exceed
the original performance numbers.

TC

[xerj]

Thanks for that.

I was having a hard time understanding what was going on. All makes sense
now.

[[email protected]]

On Sat, 03 Dec 2005 22:43:28 GMT, "xerj" > wrote:

>Thanks for that.
>
>I was having a hard time understanding what was going on. All makes sense
>now.
>
Good deal.

You flying one? getting ready to fly one?

I allegedly useta fix them, and still have details of most of the
systems rattling around in my skull.

TC

[xerj]

Unfortunately not at the moment. I have flown one, though. A rickety old
thing used mainly for type endorsements.

I'm preparing to get back into flying after a looooooong hiatus, if I can
find the spare money.Could still be some months away at the earliest. I'm
doing a lot of reading and learning about things I really didn't understand
previously, but just did because that was the way I was taught.

I find it useful to go through POHs and look at the procedures and the
performance charts and explain to myself why things are done the way they
are, and why the charts come out the way they do. I found the Chieftan one
the other day, and it's a good, complex plane to try to come to theoretical
grips with.

> wrote in message
...
> On Sat, 03 Dec 2005 22:43:28 GMT, "xerj" > wrote:
>
>>Thanks for that.
>>
>>I was having a hard time understanding what was going on. All makes sense
>>now.
>>
> Good deal.
>
> You flying one? getting ready to fly one?
>
> I allegedly useta fix them, and still have details of most of the
> systems rattling around in my skull.
>
> TC