Path: utzoo!attcan!uunet!tank!ncar!ames!pasteur!agate!eos!steve
From: steve@eos.UUCP (Steve Philipson)
Newsgroups: sci.space.shuttle
Subject: Re: Soviet and American Shuttles
Message-ID: <1751@eos.UUCP>
Date: 18 Oct 88 00:54:02 GMT
References: <1574@nunki.usc.edu> <3020@jpl-devvax.JPL.NASA.GOV> <1703@eos.UUCP> <2008@kalliope.rice.edu> <29318@think.UUCP>
Reply-To: steve@eos.UUCP (Steve Philipson)
Distribution: sci.space.shuttle,sci.space
Organization: NASA Ames Research Center, Calif.
Lines: 41

In article <29318@think.UUCP> craig@kulla.think.com.UUCP (Craig Stanfill) writes:
>>   I've never seen a brick flare and land softly.  It may require a
>>large amount of thrust to make it sustain altitude or climb, but it
>>doesn't have to be flying extremely fast.
>
>It doesn't require thrust to sustain altitude or climb, it requires
>VEOLCITY.  At Mach 18, a brick is quite capable of sustaining,
>climbing, or doing anything it wants to, provided it can be
>controlled.  Landing is a bit more constrained:

   Your are incorrect.  Energy input is required.  Velocity can be traded 
for lift, but drag is generated in the process; velocity is lost.  If 
you want to maintain velocity and altitude, or climb, you've got to add 
energy somewhere.  The usual method is to add thrust.  Sailplanes use 
updrafts, but the orbiter has too high a sink rate for that.

   If all that was needed was velocity, than your controllable brick 
could fly around indefinitely once it reached Mach 18.  This is obviously 
wrong.  You might have noticed that supersonic fighters require massive
amounts of thrust to operate even at Mach 2 to 3.

>4)	The brick needs to be able to pull out of the glide.

   You can make a brick controllable by putting fins on it, but it still
won't generate significant lift, it won't glide, and it won't flare
(flatten it's approach trajectory) and is NOT capable of landing.  You 
could raise the "nose", but with the shape of a brick you're not going
to get much (if any) lift at reasonable speeds.  Sure, force is generated 
by a flat plate at hypersonic speeds, but the orbiter doesn't need 
supersonic velocity to generate lift; the landing flare is accomplished 
below 300 kts.  

   A brick that's shaped to generate lift isn't a brick anymore but 
has become a wing, or at least a lifting body.  The orbiter isn't
a brick, even though its lift to drag ratio is low.  The constraints
on shape are considerably more extensive than you imply.
-- 

						   Steve
					(the certified flying fanatic)
					    steve@aurora.arc.nasa.gov