At 11:02 AM 06/15/2002, Ian Woollard wrote: >>Something to keep in mind, perhaps, but do any of ERPS's projects >>currently use lubricant? > >I refuse to talk about my private life on this list. ;-)
You just did. ;-) >However. all my rockets (under 10 tonnes all up) seem to have difficulty >reaching orbit if they have a diameter much above 20 cm or so. Has anyone >else found this, or am I messing up my aerodynamics No; it's a real scaling effect, the square/cube law. As the vehicle gets smaller, because the area goes down less rapidly than the volume (and mass), drag losses become more important relative to gravity losses. It eventually reaches the point that you have to care about drag. >should I be trying to modify >my oxidiser mixture (thrust) or something? I've found modulating the thrust >to be a huge win (controlling airspeed from maybe 5-70km to avoid too much >drag seems absolutely critical for achieving altitude/orbit, at this small >size), >probably any size- I know the space shuttle throttles back at max Q. Shuttle throttle back isn't for efficiency, it's for aerodynamic load management. Something about not wanting the wings to come off. That's what they get for bringing along wings, if you ask me. :-) As you've discovered, SSTO with a small vehicle requires trajectory optimization, which in turn is a balancing act as you trade off drag losses against gravity losses. There is probably a minimum size (for a given shape, mass fraction, propellant type, engine, etc.) below which a single stage vehicle can't make orbit. >I think I prefer the Carter Copter architecture for an air vehicle >provided it can be >a) mass produced >b) given more or less ensured stability.via computer control > >The aerodynamic efficiency should be higher; and the system is simpler and >should >be cheaper to maintain; and for air vehicles good aerodynamics is rather >important. >Also the failure modes of Carter Copter should be more benign in most cases.. I was thinking about this... A powered lift vehicle is always going to have a harder time of it, regulatorily, than a helicopter, autogyro, or other rotary wing aircraft. With a rotary wing, if you lose power, you still have a wing. With powered lift, if you lose power, you have neither a wing nor a prayer to save you. And FAA doesn't like ejection seats in civilian aircraft... -R -- No electrons were harmed in the creation of this message PETE - People for the Ethical Treatment of Electrons Randall Clague [EMAIL PROTECTED] _______________________________________________ ERPS-list mailing list [EMAIL PROTECTED] http://lists.erps.org/mailman/listinfo/erps-list
