"John Doe" wrote in message
news:2Hf0f.228$L24.111@lakeread01...
Ok, another turbo question:

Can someone please explain to me the performance gain by going above 30"
MP (say, during takeoff) on a turbo'd engine.

How much better performance are you getting from the engine at say 35"MP
on takeoff vs a non-turbo'd engine that's going to max out around 29"?

Is it worth the strain put on the engine? I understand the turbo being
able to maintain power at high altitudes, but I haven't heard it explained
to me why I would need such a high power setting on takeoff/climb
(assuming sea level field).

A turbo'ed engine is built more "solidly" than a normally aspirated.

The contrasts/advantages can be learned he
http://www.aopa.org/pilot/bonanza/turbo_primer.html

For example:

"As all pilots are taught, the atmosphere is piled up on the earth's
surface. The weight of the atmosphere is determined by a barometer, or in
airplanes, by the altimeter and the engine manifold pressure gauge. As an
airplane ascends during a climb there is less atmosphere above it so the
weight is less. This is important because it's the weight of the atmosphere
that determines how much ambient air is pushed into the engine during the
intake stroke.

This means that a normally aspirated airplane loses power as it climbs — for
instance, a Cessna 182 engine (a Continental O-470) can no longer deliver
65-percent power above approximately 7,000 feet msl."

and

"

Advantages
There are a number of advantages. The ability to climb strongly at any
altitude between sea level and 20,000 feet gives the pilot amazing latitude
for operation. First, he can safely operate out West, where there are some
tall mountains. For instance, .the MEA (minimum en route altitude) between
Portland, Oregon, and Yakima, Washington, is 14,500 feet. A normally
aspirated airplane would not have much, if any, climb ability at that
altitude — the turbonormalized (and the turbocharged) airplane could easily
climb up there, and could climb smartly over most weather. The pilot also
can comfortably operate at altitudes that are too high for normally
aspirated airplanes and too low for economical operation of turbine
airplanes — generally this is the 10,000- to 14,000-msl band. This means
less conflicting traffic.

The ability to fly at these altitudes also means the pilot can almost always
find a smooth ride. This makes the airplane more comfortable for squeamish
passengers who interpret every turbulent bump as a nudge from the devil.

The ability to climb strongly means that, should in-flight icing be
encountered, the pilot can usually climb up out of the icing band of
weather. Studies show that the icing band of clouds is generally
approximately 3,000 feet thick. Normally aspirated airplanes that encounter
a quick buildup of ice are often faced with having to descend to avoid the
icing layer, which limits safety options.

Finally, the ability to deliver sea-level power up where the atmosphere is
thin means that the engine can deliver a lot of thrust in a flight regime
where the drag on the airplane is less. Thinner atmosphere = less drag. Less
drag with the same power translates into higher true airspeeds. Tornado
Alley Turbo advertises TAS of more than 200 knots at 18,000 feet. That's
fast."

--------------------------------------

For sea level and flat landers, there is limited advantage for a turbo,
unless you want to attain high altitudes to climb above weather. For those
of us in the Rocky Mountain west, it's virtually a necessity. People in here
talk about occasionally taking off from high altitude airports (5000 feet on
up); when you do it ALL the times, especially during summer's high density
altitudes, you quickly appreciate it.


--
Matt

TN Bonanza 36

---------------------
Matthew W. Barrow
Site-Fill Homes, LLC.
Montrose, CO