Re: Are "jets" really jets?

From:         eirikur@ix.netcom.com ()
Organization: Netcom
Date:         08 Sep 95 02:35:36 
References:   1
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dpbsmith@world.std.com (Daniel P. B. Smith) wrote:

>Do present-day commercial airliners really use "jet propulsion" to any
>significant degree?  As I remember the way they explained it to us
>in junior high school general science in the fifties, in a propellor plane
>an engine turns a propeller which moves air and produces thrust.  In a
>jet, the purpose of the turbines was not supposed to be to move air
>directly, but to compress air (and to generate power to run the compressor).
>The actual propulsion was supposed to come directly from reaction by the
>expansion of hot gasses as a result of combustion, i.e. basically the
>same as a rocket.

>Is a modern-day "jet" really a jet at all, or is it just a kind of turboprop
>where the propellor has lots of little blades and is concealed within
>a cowling?

Daniel,

     The answer to your question is yes.  Jet engines draw in a large
amount of air very quickly, compress it  and force  it into a
combustion chamber where it mixes with the fuel.  Here the fuel is
atomized by the airflow,  and combusted and then forced through a set
of turbines. These turbines are rotated by the exhaust gasses and are
directly splined to the compressor or compressors as may be the case.
This in turn rotates the compressor making it a self sustaining
system.   The thrust is actually  produced in the combustion chamber,
not by the compressor per-say.  The gasses exiting the engine are
hotter and occupy more volume than the air or gasses being drawn in.
Thus, jet engines "push" rather than "pull" as is the case with the
t-prop.    There is a whole lot more info that I could type her for
you, but it would take a couple of months. There are numerous types of
power plants for aircraft out there ranging from reciprocating props
to  turbo-props (which actually have a small  jet engine that drives
the prop) to turbojets, turbofans,ramjets and so on. My best advice to
you would be to consult your local library to learn more about these
engines.   I do hope that I have helped you out, if you have any
furthr questions post them online or e-mail me directly.

JCD USAF AVMAINT A&P
e-mail : eirikur@ix.netcom.com