Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!samsung!xylogics!bu.edu!att!cbnews!cbnews!military From: henry@zoo.toronto.edu (Henry Spencer) Newsgroups: sci.military Subject: Re: Scramjets Message-ID: <1990Nov21.222433.21259@cbnews.att.com> Date: 21 Nov 90 22:24:33 GMT References: <1990Nov20.021943.27530@cbnews.att.com> Sender: military@cbnews.att.com (William B. Thacker) Organization: U of Toronto Zoology Lines: 31 Approved: military@att.att.com From: henry@zoo.toronto.edu (Henry Spencer) >From: J Gillespie >This may be a Frequently Asked Question, but what exactly is a >'scramjet'? ... It's a semi-acronym, standing for "supersonic-combustion ramjet". Orthodox jet engines (including ramjets) decelerate incoming air to subsonic speed before mixing in fuel and burning it. At very high speeds this becomes problematic, because the compression involved generates heat, and when the incoming air temperature approaches the flame temperature, you don't get much thrust out of the engine. The only answer is to decelerate the air less, leaving it supersonic during combustion. This creates difficult design problems, not least being the very short time available to mix and burn the fuel, but it's the only way to build a highly-hypersonic air-breathing engine. >... Are they existing technology, or just-around-the-corner, or what? They're existing technology in a loose sense: a lot of testing and experimenting has been done, but nobody's ever flown an aircraft powered by a scramjet. One reason is that the aircraft and engine really have to be designed together, because airflow over the rest of the aircraft has a major influence on airflow in the scramjet intake. This drives up the price tag. The X-30 will use scramjets, if it ever gets built. -- "I don't *want* to be normal!" | Henry Spencer at U of Toronto Zoology "Not to worry." | henry@zoo.toronto.edu utzoo!henry