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    Re: Sextant mount in B-36
    From: Paul Hirose
    Date: 2013 Jul 05, 21:48 -0700

    Gary LaPook wrote:
    > Interesting panoramic of a B-36 cockpit. Scan upwards to see the Kollsman periscopic sextant mount.
    > http://www.nmusafvirtualtour.com/media/062/B-36J%20Engineer.html
    Initially the B-36 had six sighting domes for the gunsights that
    remotely controlled the turrets. There was a astrodome, too. By the end
    of its career, the "Featherweight" modification had deleted all guns
    except two in the tail. The six unneeded gunner stations and the
    astrodome were replaced by flat hatches. I think all were removable for
    emergency egress on the ground or in flight.
    The last B-36s were delivered as Featherweights from the factory. I have
    read the final configuration even deleted thermal insulation on the crew
    compartments in an effort to attain the highest possible altitude.
    Portable plug-in electric heaters were provided to augment the
    pressurization and heating system. Nevertheless, a long flight at high
    altitude was not comfortable. One pilot wrote that all the hot air was
    needed to keep the windshield clear. The rest of the greenhouse canopy
    would be opaque with frost. When the plane descended the water would
    drip on everyone.
    When clear the canopy gave good visibility, like sitting in a bay window
    and flying an apartment house according a former B-36 pilot. Still, the
    cockpit crew could see little of the powerplants and landing gear. They
    relied on reports from the gunners. This function was so critical, a
    special interphone circuit connected the pilots, engineers, and two
    scanner stations in the aft compartment. It had a separate emergency
    power supply.
    As far as I know, the B-36 was the first aircraft to generate electicity
    at 120 V 400 Hz with 3-phase alternators connected in parallel, as is
    still standard on large aircraft. This requires the alternators to be
    phase locked, and thus driven by very precise and reliable constant
    speed drives.
    In those pioneering days "reliable" was often in short supply. To quote
    the flight manual, total AC failure was "an extreme emergency," since
    the B-36 was heavily electrified. Only the landing gear, brakes,
    nosewheel steering, and bomb bay doors were hydraulically operated - but
    AC motors drove the pumps! The reciprocating engine propeller, mixture,
    cooling air, and turbo controls were electric. So were the jet (but not
    reciprocating) throttles.
    Bombing and navigation were "electronified" to an unprecedented degree
    in the Sperry "K system". With the help of 360 vacuum tubes it displayed
    real time dead reckoning latitude and longitude computed via connections
    to pitot static tranducers and the heading system. It was tied to the
    radar too, so the crosshairs would automatically track the target. If
    they drifted off, the radar observer could select a mode which
    automatically updated the winds when he drove the crosshairs back on
    target. No more driftmeters and hand computations. Present position
    could also be updated directly from the radar.
    A three-man navigation crew occupied the nose compartment. The navigator
    sat on the left, forward by the windows, though his table and the loran
    partly blocked the view. Aft on the right was the radar observer, who I
    think was the senior navigator. Then there was the observer, who
    assisted both men and operated the nose turret sight at the right
    forward end of the compartment.
    When I arrived in Strategic Air Command in 1980 as a new B-52 bombing
    navigation system maintainer, the B-36 guys were long gone, but the
    group mind retained some of the memories. I was told there used to be a
    seat and pedals atop the radar antenna in case the azimuth drive failed.
    It may have been possible, as the antenna protruded below the belly.
    However, I've never seen anything to confirm that legend. At altitude
    the "cyclist" would have needed an oxygen mask in the unpressurized
    The system on the B-52G and H models I worked on was made by IBM, not
    Sperry. But the principles were similar. So was the tube count. There
    were hundreds but we never saw them. They were in hermetically sealed
    modules which were repaired at the depot. The exceptions were the
    magnetron (radar transmitter), klystron (radar receiver local
    oscillator), and thyratron (radar modulator). Most people wouldn't even
    recognize the first two as tubes.
    I was lucky to get into SAC in the final years of the vacuum tube era.
    Some day I may write a little more on the old ASB-9A system. Did you
    know the navigator had a pair of pedals to...
    Speaking of Strategic Air Command, in the movie of that name (Paramount,
    1955) a navigator (played by Alex Nicol) is one of the main characters.
    The man is skillful but bitter because he was involuntarily recalled to
    active duty. Jimmy Stewart's character is in the same situation but
    handles it with more maturity. Eventually he's able to turn the nav's
    attitude around, and together they transition from the B-36 to the new
    B-47. The nav stations in both airplanes are shown.
    Paramount paid unusual attention to technical accuracy. The preflight
    checklist calls and responses are verbatim from the B-36 flight manual,
    and the eyes and hands of the actors go to the right places in the
    cockpit. When the flight engineer (Harry Morgan) advances the throttles
    to set takeoff power, you can see the needles on his panel respond.
    The movie shows them starting jets after taking the runway. That too is
    correct. The reciprocating engines required two run-ups: an elaborate
    one at least 24 hours before flight to allow time for maintenance to
    clear discrepancies, and an abbreviated run-up after starting engines
    for flight. But you didn't even start jets until on the runway, an
    indication of the superior reliability of the turbine even in the early
    jet age.
    One discrepancy is that the nav team rides in the nose compartment
    during takeoff. They're supposed to be aft in the radio compartment for
    safety, according to my flight manual. However, the production predated
    the manual, so maybe the procedure had changed.
    Both takeoffs in the movie are remarkable. When Stewart takes his first
    B-36 flight, the camera stays in formation at the 8 o'clock position
    from the beginning of the takeoff roll through unstick and gear and flap
    retraction - without a cut. This shot was taken from a modified B-25
    flown by the legendary Paul Mantz, killed in the production of "Flight
    of the Phoenix".
    In the spectacular B-47 RATO takeoff, Paramount wanted a shot looking
    directly aft from the cockpit to capture the rocket plume and receding
    runway. But the canopy was in the way. The wing commander refused to let
    one of his crews fly an open cockpit B-47, so the film's technical
    advisor, Col. "Rapid Richard" Lassiter, did the flight himself. (I'm a
    little skeptical of this story. Perhaps one of the rear transparencies
    in the canopy was removed instead of the whole canopy?)
    The crisis at the climax of the film begins during a trans-Pacific
    flight when the reformed navigator (holding an E-6B) tells Stewart
    they've picked up a headwind 50 knots more than forecast. Their B-47
    will flame out short of the destination unless they come up with some ideas.
    I filter out messages with attachments or HTML.

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