RussellMc wrote:

>>> Isp is units system independent
>>
>> Bzzt. Wrong again, I think :)
>=20
> Often, maybe.
> But not this time.
>=20
> What I meant was that if you abuse the units so that the answer comes
> out in "seconds", as "the industry" often does then

Not really an abuse IMO, just using certain "convenient" units.

> *If* 1 lbm of propellant has an Isp of 300 seconds when tested
> *then* 1 kgm of it will have an Isp of 300 seconds using the same
> (incorrect) reasoning
> and 1 gram of it will have an Isp of 300 seconds,
> etc.

Understood.

> My point was that by fudging the units they have effectively
> eliminated the factor of g and made it essentially unity for this
> purpose.

Sort of... they didn't eliminate g; they require a unit system where g
has the value of 1.

> The units do NOT produce "seconds" when properly calculated but the
> fudged system is units system independent.

I disagree; IMO it is not units-system independent. It requires force
and mass units specifically selected so that together they produce a g
with the value of 1.=20

The fact that this (g) is hidden in the formula is IMO a (small, or big)
disaster waiting to happen when using it...

Gerhard
--=20
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