Twenty years!

Earlier, Bruce Hoult wrote:

So what is the pressurized metal sailplane hanging in the Museum of
Flight at "Boeing Field" in Seattle?

As others point out, it's Bob Lamson's Alcor. It's actually not metal,
but rather fiberglass and wood. Weise's book has a lot of great info on
Alcor's history.

The Alcor itself is a pretty fascinating ship. It's one of those
testaments to dedication and ingenuity that find their way into
forgotten corners of museums. it's sort of sad to see it hoisted way
out of sight.

Tony Burton flew Alcor in Canada to explore the climatology of the
Chinook Arch that often spans Calgary. He came down to the Tehachapi
SHA convention several years ago and gave a presentation on the Chinook
project. He'll tell you that he was chosen on the basis of fitting into
Alcor's undersized cockpit, but it's clear from the book and also his
presentation that he's also a damn good pilot and engineer.

If I recall correctly, Alcor's pressurization system is based on an A14
oxygen system in which the mask valves are turned around; the pilot
breathes in oxygen-rich air from the cabin and exhales overboard
through the hose. The cockpit was originally designed around a fairly
small pilot, but apparently turned out even smaller than intended, so
they actually stretched the cockpit laterally after the fuselage was
finished. But even so, it's said to be a tight fit for anyone over
about 5ft7".

I believe that the weak link in the Alcor's pressurization system was
the canopy seal; I think that the Chinook engineers never got it
working and so the Chinook flights were all unpressurized. That's sort
of as you'd expect; even with a pressure differential of only 3" of
mercury (about 1.5 psi) the separation force on the canopy is going to
be several hundred pounds, and it's hard to achieve a good seal under
the distortion you get from the pressure differential. Add to that the
distortion caused by the different thermal characteristics of the
various materials, and it becomes a very tough problem indeed.

Thanks, and best regards to all

Bob K.

"Bob Kuykendall" wrote in message
ups.com...
Earlier, Bruce Hoult wrote:
snip----
I believe that the weak link in the Alcor's pressurization system was
the canopy seal; I think that the Chinook engineers never got it
working and so the Chinook flights were all unpressurized. That's sort
of as you'd expect; even with a pressure differential of only 3" of
mercury (about 1.5 psi) the separation force on the canopy is going to
be several hundred pounds, and it's hard to achieve a good seal under
the distortion you get from the pressure differential. Add to that the
distortion caused by the different thermal characteristics of the
various materials, and it becomes a very tough problem indeed.

Thanks, and best regards to all

Bob K.


Sealing a conventional canopy would be difficult but there might be another
way. Gary Sutherland's MOBA
(http://esoaring.com/pastarticleprojects.htm#moba) has a cockpit that opens
with the entire forward fuselage shell sliking forward relative to the seat
and the rest of the fuselage. That design could use a simple O-ring at the
separation line. Once properly sealed, the energy required to maintain
pressuration isn't too bad.

Bill Daniels

Earlier, Bill Daniels wrote:

...Gary Sutherland's MOBA...

Exactly! That's been a feature of all of my back-of-the-envelope
sketches for pressurized sailplanes, ever since I saw the MOBA in one
of Stan Hall's articles. The circular opening keeps the seal perimeter
to a minimum, and it would be very easy to seal using a conventional or
inflatable sealing ring. And you could even use a simple eighth-turn
thread to latch it with very few moving parts.

However, one major issue with that arrangement is emergency egress.
That's got pyrotechnics written all over it...

Thanks, Bob K.

"Bob Kuykendall" wrote in message
oups.com...
Earlier, Bill Daniels wrote:

...Gary Sutherland's MOBA...

Exactly! That's been a feature of all of my back-of-the-envelope
sketches for pressurized sailplanes, ever since I saw the MOBA in one
of Stan Hall's articles. The circular opening keeps the seal perimeter
to a minimum, and it would be very easy to seal using a conventional or
inflatable sealing ring. And you could even use a simple eighth-turn
thread to latch it with very few moving parts.

However, one major issue with that arrangement is emergency egress.
That's got pyrotechnics written all over it...

Thanks, Bob K.


Bob, you must use the same brand of envelopes I do.

I figgured on a hemispherical pressure bulkhead behind the pilot that was
attached to the rest of the glider with three explosive bolts - just drop
the whole forward fuselage with pressurization intact. Use a drouge 'chute
to stabilize the 'pod' until at a lower altitude and then jetison the
forward part of the cockpit shell so the pilot couild use a personal
'chute. A variation would be a 'chute big enough to lower the whole pod.

A high altitude pressure cockpit really doesn't look all that hard. The
MOBA treatment could be used on any production sailplane.

Bill Daniels