I've done hobby HPR nitrous hybrids for ~15 years. The largest I've tested
is 35 pounds N2O. I've come to the conclusion that any bigger, and I'd
switch to LOX. But probably not, because I enjoy testing and developing
different bits of injector hardware for the size I'm at now just to see if
it can be done. Plus, if I want to get much larger, APCP solids offer
more ooomph per unit effort.
Edward
On Thu, Apr 5, 2018 at 5:19 PM, Rand Simberg <simberg@xxxxxxxxxxxxxxx>
wrote:
Congrats for a successful flight of a concept they should have abandoned
over a decade ago, and will never be a commercial success. #SunkCostTrap
On 2018-04-05 19:15, Henry Vanderbilt wrote:
My recollection is that they were injecting both methane and helium at
various points in the burn - half-recalled, methane to help ignition
and helium for stability?
Don't know whether they're still doing that or not. But they were
having problems that caused the switch to nylon in the first place, so
they may well still be taking extraordinary measures to tame the beast
after switching back.
My take on the lesson to be learned is that large nitrous hybrids are
more trouble than they're worth. Three different sets of
fluid-injection plumbing (if still present, of course) negates any
simplicity advantage over a liquid biprop, I'd say.
But regardless, congrats to everyone involved in the successful
flight, and best of luck for safe ops from here on.
Henry
On 4/5/2018 4:02 PM, Paul Mueller wrote:
Congrats to Virgin Galactic for a successful powered flight of VSS Unity
today.
Interesting that they switched back to an HTPB-based fuel after
switching to a nylon-based one for their last powered flights over 3 years
ago (IIRC). As I recall, they had some issues with combustion stability
with the nylon fuel grain so they had added some other systems (methane?)
to help with that. Hopefully that complexity is gone if they've switched
back to HTPB.
My recollections may be wrong on all this--wondering if any arocket
folks can comment...
Anyway, good to see them flying again!
Paul M