On Sat, 23 Nov 2013 23:01:06 -0600, Gordon Shumway
wrote:

On Sat, 23 Nov 2013 23:33:15 -0500, "Mike Marlow"
wrote:

Gunner Asch wrote:


Ayup...aerospace requires 50 millions or half 10ths all the time.

Which is damned hard to do with machines that hold +/- 2 tenths


One might think it is impossible to do with repeatability and assurance.

So - I am curious - what is it that aerospace requires that is 50
"millions"? I worked in that space for a while and I never saw any
tolerances like that - but that does not say much. I believe that even the
space shuttle does not demand tolerances that close - but I really do not
know.

Knowing nothing about aerospace I am willing to hazard a guess. I
presume the space shuttle does not require tolerances anywhere near
MILLIONTHS of an inch but I presume the shuttle's trajectory
calculations would. I imagine that a rounding error would be the
difference between a successful orbit or crashing into Homer Simpson's
house in Springfield.

A lot of it has to do with rates of expansion and contraction between
different metals. If a part that has a hard alloy piston contracts
more than the piston does when its -250F (outer space)....its nice to
know that the critter isnt going to bind up after its in orbit...so
fits are carefully calculated.

Notice the old SR-71 leaked fuel like a freaking sieve when it was on
the ground..but after the fuselage heated up in flight..all the cracks
closed up nicely and the fuel leaks stopped. Hence the SR-71 needed to
be refueled after takeoff run..then it would go like a sombitch around
the planet before needing another refueling.

Gunner


__
"A human being should be able to change a diaper, plan an invasion,
butcher a hog, conn a ship, design a building, write a sonnet,
balance accounts, build a wall, set a bone, comfort the dying,
take orders, give orders, cooperate, act alone, solve equations,
analyze a new problem, pitch manure, program a computer,
cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects."
- Heinlein

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