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Avalon Top Load Comments and general engineering comments of a flame like nature
I've finally taken a look at the Avalon Home page.... Chris and associated
geeks.. You have a LONG way to go.. I started with the top load, and went
through, just spending about 15 minutes on a simple engineering analysis of
some obvious things.
No wonder the big dogs aren't interested...
Avalon's top load:
The topload is to be a 25' diameter sphere made from 1' steel tubing spaced
coaxially on 7" centers of silver soldered or bolted construction. At these
sizes protruding bolt heads should not constitute an appreciable breakout
point. There is to be a 12" dia 1/2" thick steel disk in a removable mount
at the apex of the sphere for mounting experiments and discharge points. The
sphere is to be hollow with the exception of framing and superstructure
1) I assume 1" tubing, not 1 foot diameter (since it is on 7" centers)
2) I assume you're talking about something like 40 or so rings of varying
diameters to form a sphere? (Why not a geodesic, btw.). What's that going
to weigh? How will you support it? Seismic loads? (Rough calc shows it will
weigh about 3200 lbs, if made of steel 1/8" wall)
3) Wind loads? in a 100 mi/hr wind, the wind load will be on the order of
12,500 pounds... What do your local codes require? My map shows annual
highest 50 yr wind for your area at 75 mi/hr 30 feet off the ground (100 yr
wind is about 10 mi/hr faster). Correcting for 100 ft, multiply by 1.4
(assuming urban roughness) for a design wind of 120 mi/hr... (which makes
the aero load 18,000 pounds..., with NO margin)
What sort of foundation? What sort of structure? Remember, that side load is
at the end of a 100 foot lever arm (or whatever height you choose to put it
at). If the base is 20 feet in diameter, the load is going to be around
75000 pounds... There is a reason that Wardenclyffe had such a huge
trusswork in the tower... Don't neglect the wind load on the tower, as
well...
I suppose my point here is that the electrical issues are trivial in
comparison to the engineering issues. Why fool around with details of what
wiring will be going between the control console and the various parts of
the system (not that they aren't important), when you've got some basic
design issues to resolve before you can even get started...
Some more roasting follows:
You've got an amazing amount of detail on your rotary spark gap (some of
which shows a lack of familiarity with good engineering practice, but
rather, a "gee whiz" emphasis)... I point out that airplane props spin at
comparable rates, and are quite a bit larger in diameter, have approximately
the same cross section and are made of WOOD or aluminum. Why fool with
Titanium, which is expensive, a real pain to machine, and is vastly over
designed for your application?
1/4-20 set screws? Are you kidding? 3 cubic inches of Tungsten will weigh
about a kilo... At 3000 RPM, for instance, and a radius of 1 foot, they'll
be moving at 300 ft/second (100 m/sec).. using simple physics.. the force
will be mv^2/r or 1 * 1E4/.3, or roughly 30,000 N.. call it 7000
pounds....You're going to hold that with a "set screw".. Even if you do it
right, and hold it with a bolt loaded in shear, you're still a long way from
safe with a 1/4" bolt. which will be loaded to 143,000 psi, somewhat (!)
higher than the yield strength for steel.
Don't tell me you'll have multiple bolts, because given the lack of
attention to BASIC mechanical engineering, I doubt that you have the skills
to properly distribute the load among multiple fasteners, and instead,
you'll zipper them out one by one, as your infernal contraption vibrates and
destroys the bearings after the first electrode flies off..
Darn good thing that you're using a steel fragment shield (If you do your
calculations right, you won't need your kevlar.. and sandbags are cheaper
during testing)...
More...
Facilities issues.. Why Halon or CO2? Why not just sprinkler it.... Nothing
in there will be hurt by water, unless the power is on... They use Halon in
computer rooms because they want to put out the fire, with the power ON..
Or, just let it burn.. (you shouldn't be using flammable materials anyway..
that's what UL 94V-0 is all about)
I would suggest that BEFORE you publish a proposed design calling out
dimensions of fasteners, brands of bearings (who cares whether they are
Timken, Fafnir, or King), that you start at a high level. Work out
reasonable numbers, then work down to successively finer details, making
sure your design is reasonable at each step.
This will go a LONG ways towards establishing your credibility. Spurious
details and precision, written in spec'ese, with no rationale, are not
impressive in a proposal. (Why SHALL the brakes be capable of completely
stopping the rotor shaft within 5 seconds? Why not 6 seconds, Why not 60?
Why not 1?)
It's fine to have a strawman design up, so that people can poke at it and
come up with ideas, but I think you are worrying about details that are
familiar (what sort of paint colors shall we choose?) rather than the ones
which are of MUCH greater importance.
Jim Lux
phone:818/354-2075 fax:818/393-6875
Spacecraft Telecommunications Equipment Section
Jet Propulsion Laboratory M/S 161-213
4800 Oak Grove
Pasadena CA 91109