[AR] aluminum (was Re: Portland State Aerospace Liquid Fuel Rocket Engine
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Sun, 1 May 2016 13:11:27 -0400 (EDT)
On Sun, 1 May 2016, Gerald Taylor wrote:
Aluminum has a low melting temperature, a rather low softening
temperature where it loses its temper, low strength and stiffness when
not tempered...
While all of that is true, it's largely counterbalanced by the fact that
aluminum has *very* high thermal conductivity, so it's hard to get local
overheating in a regeneratively-cooled engine. Last I heard, Masten's
flight engines (hundreds of flights, heaven knows how many ground tests)
are all aluminum, and they're not the only folks doing it.
This is also a large part of why Columbia's wing lasted as long as it did.
Despite the severity of the hot-gas leak, the hydraulic systems within the
wing failed before the aluminum structure did.
and if the aluminum oxide surface cracks, would make one heck of a fuel.
Aluminum-oxide cracks generally are self-healing because new oxide forms
instantly on the newly-exposed surface. In practice, aluminum generally
won't ignite until well above its melting point. It's a ferocious fuel
when it gets going, as witness its use in thermite, but getting it going
is tough, as witness the drastic measures needed to ignite thermite.
(Many high-temperature metals are much more vulnerable to such things,
because they don't form oxide layers or their oxides aren't such excellent
protection, so they need deliberately-added protective coatings, and if
one of those cracks, watch out.)
Henry
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