Text 22027, 125 rader
Skriven 2012-03-04 14:40:00 av Glen Jamieson
     Kommentar till en text av Hap Newsom
Ärende: SILENT SERVICE 20304
============================
 -=> Quoting Hap Newsom to Glen Jamieson <=-

Hello Hap,

 ->  -> camera was made of fibreglass, took 75 mm film, weighed 1/3 lb and
 ->  -> took high quality pictures (one at a loading) from an altitude of

 ->  -> carried in a nylon dart that was launched, almost silently, from a
 ->  -> foot-pumped compressed air gun.  My job was designing the gun, the
 ->  -> dart, timer and camera actuator.  Others did the camera, which was
 ->  -> designed to take launch and landing accelerations of 1000g.
 ->  ->
 -> The camera was loaded in a light-proof box by feel.  A pre-cut film
 -> 125mm x 75mm was slipped into the curved detachable back, which was
 -> clipped onto the camera body, and the lens swung to the "ready"
 -> position.  One of the most difficult problems was light-proofing the
 -> fibreglass body.
 -> 
 HN> Would be very interesting to see
 HN> photos of the contraption! And
 HN> it sounds like it was fun to use!!

I don't have any photos, as we were not allowed to take cameras to
work.  (Only allowed to make them at work!)

Picture a spherical aluminium pressure tank (using Imperial units,
which is what we had at that time, long ago) about 10" diameter, with
a yard long, 4 1/2" diameter nylon tube (made by spirally wrapping
strips of nylon sheet around a former, glued with a resorcinol solvent
glue).  The base of the pressure tank sat in a base similar to that
used on modern computer monitors so that the launch angle could be
adjusted.  The foot operated air pump, also of aluminium, was hinged
to the base so it could be folded up for easy carrying.  The dart,
also made of nylon, comprised a cylinder into which the camera was
placed, above it a conical pressure tank charged by the launch air
through a rubber flap valve, and above that, the telescopic shock
absorber.  The launch trigger was a small button on the side of the
tank.  No electrical stuff anywhere in the system.
 
 ->  HN> Sounds interesting too! I would have liked
 ->  HN> to have seen the launching system and 
 ->  HN> design for the "projectile"...would be
 ->  HN> fun to do even today!

The original idea came from an old man who made his own wooden camera,
stuck it on a wooden dart launched by big rubber bands, and took
aerial photos of his neighbours' back yards.  He used a string to spin
up his gyro stabiliser before launch.  We greatly refined the idea.

 -> My launcher used foot-pumped compressed air stored at 120 psi in a
 -> spherical aluminium tank surrounding the quick-opening valve mechanism
 -> which allowed the pressure to be instantly dumped under the nylon
 -> dart, about 120mm diameter, which fired it out of the metre-long
 -> nylon barrel.  As the propelling air was expanded almost down to
 -> atmospheric pressure by the time the dart left the barrel, there was
 -> practically no noise, which was one of the design requirements.
 ->
 HN> How long did it take for you to 
 HN> pump it up to 120psi? and how
 HN> much volume are we talking about
 HN> with the tank??

I think it was only about 2 minutes to pump up the tank.  Enough
volume to expand it almost down to atmospheric pressure by the time
the dart left the barrel.  Not much.  I was particularly proud of the
very light quick-opening valve that dumped the whole of the compressed
air store into the space beneath the dart in about a millisecond.
 
 -> A portion of that high pressure air was stored in a space within the
 -> dart, and slowly leaked out through an adjustable needle valve.  At a
 -> pre-set pressure, the remaining air was dumped into an actuator which
 -> released the camera "shutter".  This was usually set to occur just
 -> before apogee, while the dart was still rising vertically.
 ->
 HN> Sounds quite complicated!!

Not really.  We had one of the best tool-making workshops in
Australia, with very skilled tradesmen.  They spun the spherical tank
from aluminium sheet, then aluminium brazed the barrel supporting
components into it. I did the original designs, assembly and testing.
 
 -> To prevent the dart from rolling during its upward flight, I used a
 -> vane with a tiny gyroscope, similar to that used by the US Sidewinder
 -> missile. The gyro was spun up by a swinging weight during launch.
 -> Amazingly, everything worked!

 HN> Very interesting...I'm 
 HN> surprised you did not use
 HN> some sort of accelerometer
 HN> and gyro combo!

The engineers working on the project were both mechanical, so all
components were simple mechanical.  :) To measure launch and landing
accelerations I used bits of resin-cored solder of different lengths,
which bent or didn't bend.

For a pressure gauge I used a spring-loaded plunger type, similar to a
tyre gauge, but calibrated in feet to give the height at which the
photo would be taken.  For lower height, lower pressure, and that
automatically set the shutter release timer earlier.
 
 -> After that, my next project was a super-efficient air-launched
 -> submarine detection sonar buoy...  Nothing like variety!
 -> 
 HN> Ok...now that's just WRONG!!!(grin)

That entailed going down in a one-man capsule towed by a work boat,
with its depth controlled by paravanes worked by 2 handwheels inside.
Once I got the hang of it, control was easy, and I could skate along,
just clear of the seabed, banking to one side or another.
After work the boat master/owner sometimes dived down and caught
scallops for us to eat.  They were delicious, with a little white
wine, which I often happened to have with me.

And so the defence of Australia was kept in good hands.

 HN> BTW I have a new friend in Oz..she's
 HN> a medic on a collins class sub out of HN> Sydney!

I sympathise with her.  Those subs have been notorious for faults.

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 * Origin: Braintap BBS Adelaide Australia (3:800/449)