Exhaust Pipe Re-Creation
Richard Greer – CIMtech Inc.
Dave Arena – CIMtech Inc.
Each of the mighty Wright R3350 2200HP engines on the B-29 have two large (12 inch) diameter turbo chargers mounted on either side of the rear engine cowling. Each turbo charger has two outlets, the smaller one for the waste gate and the larger to direct the main exhaust gas flow downwards, and to the rear under the wings. On the Museum of Flight’s B-29 T-Square, the larger of these pipes was missing on all of the four engines.
Since the exhaust pipes are a very prominent feature of the cowlings, it was, after a protracted search for some real steel units decided to fabricate replacement units using fiberglass.
A full-size exhaust pipe model was constructed from the original drawings, a digital scan was taken of it, and this data was used to operate a computer controlled milling machine, which produced an exact reverse of the pipe. Fiberglass cloth and gel coat were applied to the inside of the resulting mold to produce the resulting nine pipes.
Richard Greer – CIMtech
AMMUNITION STORAGE FOR REAR GUN TURRET B-29 T-SQUARE 54
Of all the defensive gun turret positions, arguably, the rear turret is the most critical. Consequently it was logical to provide each of its two 50 caliber machine guns with plenty of ammunition, 800 rounds per gun. Since T-Square had all of this system completely removed during one of its post war assignments, it was necessary to re-create both the storage and feed system for the rear turret.
The boxes were fabricated from fiberglass and from Phenolic, which required careful formulation of colors to match the original materials. All of the metal components had to be fabricated, as well as the special fasteners. Feed chutes were provided by CIMtech, who used a computer directed router in their manufacture.
The boxes are installed in the rear of the aircraft on either side of the tail skin shock absorber, which is actually a very robust retractable device which protects the lower side of the B-29 should the pilot inadvertently make tail strike on landing.
The boxes had to be mounted very precisely to insure that the left and right feed chutes would match up with the feed through ducts which pass through the gunner’s compartment. On the rear end of these ducts are high torque electric motors with an ingenious drive sprocket which engages with the 50 caliber rounds in the belt, and when the gunner fires each gun, the respective drive motor pulls the very long belt all the way from the ammunition boxes along the chutes through the pressure ducts and up into each gun, a distance of approximately eight feet.
Each box has a removable lid and fold down sides to make it easier for the armorer to load the 800 round belt into each box, along the chutes and finally up into each 50 caliber machine gun.
Pressure Dome Re-Creation
GUN TURRET PRESSURE DOMES – B-29 T-SQUARE 54
Three of the remote control gun turrets on the B-29 protrude into the pressurized crew compartments. Consequently each has to be provided with its own unpressurized circular enclosure to accommodate all of the ancillary components which make up each remote turret system.
ASSOCIATED HARDWARE ON DISPLAY
This photograph is of the top forward four gun turret which, when mounted in its entirety, extends into the front cabin between the radio operator and the navigator’s stations, leaving just enough space for the crew to pass around this intrusion.
Because of this intrusion we chose not to install the pressure cylinder in which all the lower equipment is located – ammo storage bins, belt feed system, etc. This is the unit which was provided to the Museum of Flight by the Imperial War Museum at Duxford, U.K., and we will be able to make it functions independently from the aircraft. It makes a great display. We can make either the ground unit function, or the unit on top of T-Square.
Currently on T-Square only the top segment of this turret is installed which included the 50 caliber machine guns and their mounts, the aerodynamic faring and drive motors, so that from outside the 4-gun turret looks complete.
There was a need to provide the pressure domes to close out the open ends of
the remote gun pressure vessels in which the remote gun pressure mechanisms are mounted.
Picture shows the lower ring of the mid aft turret housing where one of the gun control cables can be seen, as well as the lower components of the ammunition storage racks, all mounted inside the outer housing which is of course fixed and is part of the aircraft cabin structure. This housing has a large removable access hatch in the side through the gun magazines are reloaded.
There are three domed closures for each aircraft and the original drawings show the cross section shape and calls for the parts to be made from aluminum. This is entirely beyond our capability and could only be remanufactured this way at prohibitive cost. The answer was to use fiberglass.
THE BASIC DOME SHAPE
A male plug was constructed of wood and plastic foam using a lathe assembly that was built from auto parts. This was coated with gel coat and fiberglass.
THE DOME MOLD
After the male plug was complete a female mold was made by spraying a coating of white Gelcoat over the male plug. This was after applying the usual Carnuba wax release agent, then encasing the male plug with six layers of 10 oz. glass cloth. The manufacture of each dome from the resulting female mold was a straight forward fiberglass lay up using 20 mils of white gelcoat on one layer of random weave cloth, followed by four layers of 10 oz. cloth.
PRESSURE DOME PURPOSE
The pressure domes have three purposes, One, to retain cabin pressure. Two, to collect and drain away any water which passes around the top side of the gun turrets, and three, to collect used 50 caliber cartridge cases when the upper guns are fired. The lower turrets, as well as the tail gunner’s, eject their cartridges directly into the airstream out of the bottom of the aircraft.
One issue with the rear upper dome was that in order to install it below the mid upper turret, it had to pass through the rear entry door and the circular mid compartment pressure hatch – neither of which was big enough to allow the passage of a completed 42 inch diameter by 6 inch deep dome enclosure. Fortunately in the forward crew compartment the crew entry door over the forward wheel well is just large enough to allow the completed domes to pass through intact. Consequently it was necessary to saw the completed dome in half. Cuts were made straight towards the center drain then in a 4 inch radius around the hole to preserve the integrity of the reinforcing hole boss.
The re-bonding of the two dome halves inside the rear cabin had to be done using typical fiberglass repair procedures.
The author wishes to acknowledge the valuable historical radar information and photographs, obtained from the 482nd Bombardment Group.
Go to: http://www.482nd.org/radar
THE IMPERIAL WAR MUSEUM
Duxford, England (Chris Knapp) which provided access to its B-29 for research for this project.
RE-CREATION OF RADOME FOR APQ-13 RADAR ON B-29 T- SQUARE
The recreation of the large radar radome located between the forward and rear bomb bays on the B-29 was one of the the most challenging and technically interesting jobs undertaken for T-Square 54.
Restoration of APQ-13 Antenna-
A beautiful restoration of the gimbal mounted dish antenna for our APQ-13 radar system had been previously accomplished by our volunteers. Since there was compelling evidence that T-Square 54 had such a system, a radome was needed to cover the antenna. There were no Engineering drawings available for any of the required hardware or installations.
Determining the Radome geometry.
The original radome attach fastners were found under a crude temporary patch which had covered the orignal rotating antenna opening. This was absolutely critical in the re-manufacture of the radome since this accurately defined the footprint of the radome beneath the B-29 belly.
The only other data available were two pictures of an existing B-29 radome; one from the side on from the rear. In order to develop the remaining lines for the radome, a sheet of mylar was taped to the bottom of the plane and accurately located every radome attachment fitting bolt hole.
By measuring the marks on the skin, it was determined that the Radome was originally 0.5 inches thick. The mylar was layed out on 4 ft x 8ft x one half inch plywood and using a one inch set back from the attach screws, it defined the full size exterior profile of the radome in plan form. By this process it was possible to calculate an accurate overall length and width of the old radome.
Photographs of an actual radome were put on to Power Point so they could be projected on to a wall. From these profiles, rib segments were formed to allow a reverse mold to be constructed.
A mount had to be constructed to hold the antennae and its drive system so that the antenna ended up in exactly the right place inside the radome. There were no engineering drawings available for the mount, but it possibleto reverse engineer the unit based on photographs taken of the very complete B-29 at Duxford, England. (Hawg wild) Very elaborate measurements were made from below the bottom skin of T-Square to insure that the antennae ended up in just the right place with no interference and only about ½ inch clearance. What made this four legged mount so unusual is that the feet of the legs sit on the same skin stiffeners which support the radome attach brackets and the top of the pedestal which actually supports the entire antenna is also attached to the underside of the B-29 massive center wing box.
All the intricate fuel control sytems oxygen lines as well as the large feed cables for the radar antenna have to fit around this mount. The whole antenna drive and antennae are finally covered in a canvas cover. This is probably to protect the antenna from water and dirt from the nose wheels, which would probably spray into this area when the forward bomb doors are opened.
A honeycomb layer was applied to the rib structure to form a reverse mold, upon which Gelcoat and layers of fiberglass were built up.
To insure an accurate fit with the belly of the B-29 , a mock-up out of steel sheet was made so that the radome could sit upright while the edges were adjusted to the edge profile to fit. Previously all the 26 attach bracketshad been attached to the belly of the B-29, and using a very small car jack and an old tire, the radome was raised the radome into position. The radome attach fitting fastener locations were marked on the radome inner skin, the radome screw holes drilled, and the attach screws all fitted. While the radome was being painted at our restoration center in Everett, the antenna was attached to its new mount.
When the radome finally came back a cargo blanket was spread on the ground and the radome was slid under the antenna. The radome was then rotated and jacked up into place and fasteners were put in place.