http://www.armadilloaerospace.com/n.x/Armadillo/Home/News?news_id=194
"This was a result of flow separation on the highly over expanded nozzle (the throttle was only cracked, so chamber pressure was very low) causing the jet to attach to only one side of the nozzle."
Hmm interesting. I'd idly wondered about this before. If you throttle back an engine presumably the chamber pressure scales down, but the nozzle expansion ratio is fixed, and as the ISP is nearly the same, so presumably the chamber is now under expanded?
Of course De Laval nozzles can take a fair amount of under expansion, so it doesn't usually matter too much, although perhaps it represents one limit on how much throttling down you can do (along with all the others), and screws around with your efficiency. But also, doesn't this mean that you can deliberately use this to altitude compensate?
I mean, if your rocket is climbing, your fuel load is dropping, so you need less thrust anyway, but also the atmospheric pressure is dropping at the same time, so throttling back helps this.
I've never seen this mentioned anywhere though. Is there a catch?
-- -Ian
Motto: "You're Not Authorized to Know Our Motto." "War is never right, unless of course there is a second UN resolution" - Private Eye "War, huh? What is it good for?" - Frankie goes to Hollywood "Getting reelected" - G. Bush
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