Re: Booster engines

From:         Keith Steele <keithsteele@delphi.com>
Organization: Delphi (info@delphi.com email, 800-695-4005 voice)
Date:         12 Jan 95 01:56:03 
References:   1
Followups:    1 2
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Let me preface this with I am a pilot not an aircraft designer but.  The
problem is that an extra engine that is used only for takeoff A - produces
drag throughout the flight costing fuel and B - weighs a lot reducing the
number of passengers or cargo that can be carried.  Multiply the loss of
several passengers throughout the service life of the aircraft and you are
quickly behind the economic eight ball.
 
About APUs.   Although they are turbine engines they are not designed to
produce thrust.  Their output is maximized to produce compressed air for
starting and air conditioning and electrical power.  The thust output is
negligable - similar to the thrust output of a turboprop which is also a
turbine engine.  To design it to produce thrust as well as aux power would
significantly increase cost and weight.
 
A solution already in use by some military transports is to use a jato bottle.
Essentially a small rocket strapped to the side of the aircraft with a very
high thrust to weight ratio.  The problem is most passengers would probabaly
react unfavorably to the sight of flames and smoke pouring out just below the
window line.   The EPA would probabaly not be impressed either because solid
fuel rockets produce some pretty hazardous chemicals when they are fired.