If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
B-36 electrical system Q.
I've been reading 'MAGNESIUM OVERCAST - The Story of the Convair B-36', by
Dennis R Jenkins, and have been finding it absolutely fascinating. Plenty of hard-core techno stuff, esp. powerplant, a subject near and dear to my heart. What doesn't seem to be covered is the B-36's electrical system. Judging from the electronic equipment fitted, I would assume this to be 28V DC and 115V 'wild frequency' AC (B-36 seems a bit early for CSD's). My questions a Was there a DC and an AC generator on every engine? Single phase or 3-phase AC? Were rotary inverters used? How was the aircraft's electrical system organized? John Mackesy |
#2
|
|||
|
|||
"John Mackesy" wrote:
I've been reading 'MAGNESIUM OVERCAST - The Story of the Convair B-36', by Dennis R Jenkins, and have been finding it absolutely fascinating. Plenty of hard-core techno stuff, esp. powerplant, a subject near and dear to my heart. What doesn't seem to be covered is the B-36's electrical system. Judging from the electronic equipment fitted, I would assume this to be 28V DC and 115V 'wild frequency' AC (B-36 seems a bit early for CSD's). My questions a Was there a DC and an AC generator on every engine? Single phase or 3-phase AC? Were rotary inverters used? How was the aircraft's electrical system organized? John Mackesy Watching this space with keen interest... -- -Gord. |
#3
|
|||
|
|||
I believe the B-36 was the first production aircraft to generate its
power at 115 V 400 Hz. Engines 2, 3, 4, and 5 had alternators with constant speed drives. If load permitted, normal procedure was to have three on line, paralleled, and equally sharing the load, with a fourth excited and standing by. Under high load all four would be paralleled. The bus tie arrangement was peculiar. Conceptually, each bus formed one side of a square. (It was depicted that way on the AC control panel.) The four bus tie contactors were at the corners of the square. For example, contactors tied bus 2 to its neighbors 3 and 5. By contrast, all the planes I've worked on had an AC system arranged like a fork with four tines. Each tine (generator bus) was connected to the fork body (tie bus) via a bus tie contactor. Either way you end up with four BTCs and power supply redundancy. But the B-36 arrangement was like nothing I've seen elsewhere. It does have the advantage that all four buses remain in parallel after any single bus tie contactor fails open. To supply 28 VDC the B-36 had seven transformer-rectifier units powered by 115 VAC. They used selenium plate rectifiers. A central TR unit test panel allowed you to check loads and voltages. Essentially, the power went into one big DC bus. There weren't DC sub-buses fed through relays like other planes I've seen. Turning the battery switch on applied its power to the whole DC system. The only exceptions were the alarm bell, IFF destructor, and parking brakes. Those items were hot regardless of the battery switch position. Some B-36s had a feature which automatically disconnected the battery if AC was lost. This conserved its precious power while you turned off non-essential DC loads, whereupon you threw the switch to the emergency position to turn the battery on again. For emergency AC power, a manual rotary switch selected any alternator of the four and routed its output to one TR unit and an instrument power transformer. This bypassed the contactors and forced those units to accept whatever the alternator was putting out. Some B-36s also had an inverter so backup instrument AC could come from the battery too. John Mackesy wrote: B-36 seems a bit early for CSD's The alternator constant speed drives gave much trouble, especially in the early years. Sometimes crews took off without a full set of four good ones. SAC pressed very hard to get B-36s over Washington for Truman's inauguration in 1949. (Ever seen the "B-36s over the Capitol" photo?) Some of the planes landed with only one alternator operating. Later that year a B-36 lost all AC power at night. The crew spotted an airfield (Westover AFB, Mass.) and circled it until they could make a daylight landing. The fire department had to snuff the engines with foam because the electrical engine controls were inoperative. (I've read "foam" but I wonder if they actually used CO2.) The alternator was the first thing you encountered after entering the engine cooling air inlet at the wing leading edge. In Myers Jacobsen's B-36 book, one former electrician describes going in there before engine start so he could make some checks under power. First there was a lot of coughing and shaking as the engine cranked, then a fierce draft from the engine cooling fan right behind the alternator. He could hardly breathe as he took readings with his meter. There was nothing between him and the whirling blades. Even by the relaxed safety standards of the 1950s it was pretty crazy. -- Paul Hirose |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Electrical system considerations | ELIPPSE | Home Built | 2 | February 2nd 05 06:17 PM |
Airliner manuals and brochures for sale | Martin Bayer | Aviation Marketplace | 0 | April 24th 04 09:33 PM |
Electrical system | Sam Fly | Home Built | 0 | April 1st 04 03:12 AM |
Start receiving MONEY with this simple system. Guaranteed. | Mr Anderson | Aviation Marketplace | 0 | February 2nd 04 11:55 PM |
2nd update on Review of Plasma II Ignition System | MikeremlaP | Home Built | 8 | July 22nd 03 01:37 AM |