tommayer wrote:

Paul, some probably dumb questions about your responses.

1)   turbo altitude.  Why do you say 3K?  

Arbitrary.

If you have an engine making 200
hp normally aspirated, and use 150 hp, or 75%, in normal climb,  you would
not need to use the turbo until reaching 8300 feet to maintain 150 hp.
   If you used 130 hp, or 60 %, in cruise, you would not need the blower
until reaching 11,600 feet.
   I use these numbers because, in very simplified terms,  they are how I
operate my 200 hp Lycoming, blown Mustang, and I had assumed the turbo use
would correlate more or less if I went to a rotary.  I also understand
Tracy's rotary is making about 200 hp, unblown, so using 100 hp per rotor as
a place to begin guesstimating seemed reasonable.
    Does the rotary lose more than the usual 3% per thousand feet when
normally aspiriated?

No I think it is the same.

2)  intercooler necessity. Please forgive me for thinking in inches, but I
am totally an airplane and not a car type.  (When you guys talk about WOT,
instead of Full Throttle, it always takes my befuddled mind a few seconds to
realize you're not talking about an unusual Australian quadruped.)
   5 psi is 10.15 inches, correct?

Yes. 40 inches of Hg absolute. 5 psi above the atmospheric absolute 
pressure of about 15 psi/30 inches of Hg. Boost in the automotive world
is given in psi above atmospherical pressure at sea level.

    I run the Lycoming at FL 210 and 240 all the time at 150 and 130 hp.  I
have no intercooler.  I have had no problems, either, in well over 500 hours
of operation.
    If I am doing the math right, at FL 210, when asking for 21.5 inches
(130 hp is 21.5 inches and 2300 rpm, mas o menos),  I am obliging the blower
to produce 15.58 inches, or 50 % more than your need an intercooler figure.
    Why would the rotary be so much more demanding?
    Thanks in advance.  Tom Mayer

I don't think it is but why take chances? With an intercooler you
have more options for increased boost and HP.
 
Here is what Hugh Macinnes has to say about intercoolers and altitude.

Intercoolers

High altitude turbochargers can benefit greatly from an 
intercooler. The higher the altitude the more the benefit.
A turbocharged engine with 10 psi boost at sealevel will have an 
intake manifold temperature of about 175 F. If this same engine is 
to produce about the same power at 15,000 feet, boost pressure will 
have to increase to 16.7 psi. This boost increase represents a 
pressure ratio increase from 1.67 to 3.00. This pressure ratio will 
give an intake manifold temperature of 246F unless an intercooler is 
used. The standard temperature at 15,000 feet is 5.5 F, so an 
intercooler with only 50% effectiveness will reduce the intake 
manifold temperature to 126 F. 

Paul Lamar

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