In a message dated 6/14/2006 10:14:27 A.M. Central Standard Time,
kenpowell@comcast.net writes:
Steve,
I think you are overestimating the power loss of converting over to
NA. See this link:
http://www.442.com/oldsfaq/ofcrc.htm.
My understanding is that you will only suffer a 2.4 -4.2 HP loss if assuming
the NA engine produced 200 HP (depending on a comparison of 9.4 rotors or
9.7 rotors as opposed to the 9.0 turbo rotors). Compression ratio is
much overated if you are not trying to make up for radical cam profiles in
piston engines.
The decision to turbocharge/supercharge, or not really depends on one main
thing. Like most decisions aeronautical, it depends on your purposed mission for
the aircraft.
If your goal is to fly high and far most of the time, t/s charging is a
great advantage. There are some drawbacks and those are mainly winds. When they
are tail winds, they help you greatly. When they are headwinds, sometimes even
with a 200+K plane, you are better off driving. As we all know, tail winds exist
only for other people. The other problem is the time, and fuel necessary to
climb to the high altitudes. The third is the need for O2, wonderful in theory
and if you are up there, necessary, but a real pain in the a--nose in that you
are breathing very dry air, in a dry environment and you dehydrate quickly. Bad
on a long trip. Make sure that you bring lots of liquid, and a way to eliminate
it since all will not be eliminated through your sweat glands and lungs. Of
course if you are high enough the nasal canula is not approved so you must wear
a mask. Then you must take it off to drink, etc. Because of your altitude, you
must plan your letdowns far in advance. you will be IFR and will for the most
part be using High Altitude charts (or GPS direct). The OAT will be considerably
colder so that heater which was marginal now becomes useless. O2 is somewhat
expensive and unless you have your own filling mechanism, available only at
specific locations. If you are using a lyco/conti saur, fuel flow and
maintenance is greater. Being higher, with less air to filter, you are
subject to a greater amount of Gamma Rays, and probably other stuff that we
don't know about.
Now for the good stuff. If you are going the right direction you can pick
up significant ground speed, which has to be balanced against the loss of time
and fuel due to climbing In weather with imbedded Thunder bumpers, you can
generally climb out of the crap and be able to see the cumulonimbus clouds.
You feel like a "real airplane" If you fly in mountainous areas, or typically
from high altitude airports, T/S charging will allow you to have a smaller
engine to produce the necessary T.O. HP. Additionally it's Way cool!
This information comes from my experience over the past 40 years, with 8
airplanes, 2 of which were turbo charged (Twin Comanche and Bellanca Viking).
Being based in the Chicago area, I actually utilized the turbo advantage on a
very limited basis. I have friends that live in the west that won't fly without
it. If you occasionally fly high, the lack of charging in general, will
only mean less airspeed and longer T.O runs. The landing distance (increased at
high altitudes is the same for both configurations.)
Your average mission will determine the benefits. Above all, no matter what
you choose, know the limitations of your craft and fly safely within them.