From: Keith Steele <firstname.lastname@example.org> Organization: Delphi (email@example.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.