Moderators: richierich, ua900, PanAm_DC10, hOMSaR
Max Q wrote:Very interesting, another remarkable and highly advanced feature of the superb L1011
Incidentally while the DC10 only had three hydraulic systems the 747 did have four
I couldn’t agree more with your last two sentences
SteelChair wrote:On the prior airplanes, the actual process of “paralleling” the generators could be problematic. There are technical things beyond the scope of this post that I will mention but not describe: The phases of 3 phase alternating current have to be “in phase.” There was an art to managing these systems; some airplanes (727) had synchronizing lights (I wish I could figure out ho to append a picture, they are out there) to show the variations in the electrical power that one could look at when attempting to ascertain the exact moment to bring a generator on line..
DL_Mech wrote:SteelChair wrote:On the prior airplanes, the actual process of “paralleling” the generators could be problematic. There are technical things beyond the scope of this post that I will mention but not describe: The phases of 3 phase alternating current have to be “in phase.” There was an art to managing these systems; some airplanes (727) had synchronizing lights (I wish I could figure out ho to append a picture, they are out there) to show the variations in the electrical power that one could look at when attempting to ascertain the exact moment to bring a generator on line..
The 727 would auto-parallel if the generator breaker switch was used. The synchronizing lights would only be needed when using the bus tie switches to bring power on to the bus. I’m not sure why you would use the bus tie switches to bring power on the bus, but the procedure was so drilled into our heads during training that most people used the sync lights anyway when using the generator switches (myself included).
A decent explanation of the paralleling procedure is about 1/3 of the way down the page: https://www.boeing-727.com/Data/systems/infoelect.html
SteelChair wrote:
I assume you are talking about auto paralleing thr main engine generators....not the APU.
DL_Mech wrote:SteelChair wrote:On the prior airplanes, the actual process of “paralleling” the generators could be problematic. There are technical things beyond the scope of this post that I will mention but not describe: The phases of 3 phase alternating current have to be “in phase.” There was an art to managing these systems; some airplanes (727) had synchronizing lights (I wish I could figure out ho to append a picture, they are out there) to show the variations in the electrical power that one could look at when attempting to ascertain the exact moment to bring a generator on line..
The 727 would auto-parallel if the generator breaker switch was used. The synchronizing lights would only be needed when using the bus tie switches to bring power on to the bus. I’m not sure why you would use the bus tie switches to bring power on the bus, but the procedure was so drilled into our heads during training that most people used the sync lights anyway when using the generator switches (myself included).
A decent explanation of the paralleling procedure is about 1/3 of the way down the page: https://www.boeing-727.com/Data/systems/infoelect.html
DL_Mech wrote:SteelChair wrote:
I assume you are talking about auto paralleing thr main engine generators....not the APU.
Yes.
GalaxyFlyer wrote:If the BTB tripped with the GB closed, you could have to manually parallel or, just trip that GB, close the BTB and auto-parallel as you would during engine start. IIRC, our instructor offered that if your probation and ran into this problem.
Or, smelter yet, just leave the BTB open, as there must have been a good reason for it to trip.
747classic wrote:Having operated the 747 classic for many years, the following about the 747 electrical system :
After starting the engines, all CSD and Gen lights were checked out, there after the channels were paralled with BTB's.
The 747 has 4 engine AC generators that could be paralled by closing the Bus Tie breakers (BTB's) and the split system Breaker (SSB). When closing a BTB switch one of the Generators received an electric signal to slow down the RPM (In the CSD) , to sycronice the phases, thereafter the BTB (relay) kicked in.
The APU generator(s) or ground electric was auto disconnected when switching the engine generators via the BTB's on line.
When switching the source from APU Generators or ground electric to the engine generators (or the other way around) some light flickering was observed. (APU Generators had no CSD !)
Switching an engine generator on or off was not visible (no light flickering) and also in certain fault cases an automatic BTB re-closure could happen leaving the relevant AC BUS powered , but than the gen open light illumunated.
The APU generators were not certified for in flight use, However the APU could be used in flight (during T/O) for supplying pneumatic air to ACM #2, during an all packs off T/O, very common with the early JT9D-3AW, -7(A)W and -7FW engines (waterinjection , packs off T/O ).
Later, the APU inlet was modified (for fuel saving) and the APU was only certified for on ground use.
747 :
four (4) AC Engine Generators
four (4) hydraulic systems
1 or two APU generators, only for on ground use, on combi aircraft the second generator was normally used for the maindeck cargo loading handling
All AC generators are identical, however due forced cooling the APU generators were rated at 90KVA , the engine generators at 60KVA.
SteelChair wrote:Sharp observers may note that on the picture of the 747 Flight Engineer panel there is a switch labeled "essential power," and that that switch has 4 positions. Gen1, 2, 3, and normal. Thus, it would appear that selection of what powered the essential bus was a totally manual selection. Does anyone know, if in the event of the failure of a generator, the 747 would select another bus?
747classic wrote:SteelChair wrote:Sharp observers may note that on the picture of the 747 Flight Engineer panel there is a switch labeled "essential power," and that that switch has 4 positions. Gen1, 2, 3, and normal. Thus, it would appear that selection of what powered the essential bus was a totally manual selection. Does anyone know, if in the event of the failure of a generator, the 747 would select another bus?
prerequisites : all engine generators paralled (normal flight) :
Short answer : NO
The normal position means that AC bus #4 is powering the essential power bus.
If Gen #4 fails the #4 generator breaker will open, but the AC bus #4 will remain powered via BTB #4 and the tie bus, powered by generators 1,2 and 3
If one of the other generators (1,2 or 3) fails, also no essential pwr switching is needed.
Only when AC bus #4 fails ("essential bus off" light will illum ), the F/E has to manually switch the essential pwr bus directly to an operating generator (pwr drawn before the Gen breaker !!)
747classic wrote:IMHO, the 747 was a straight fwd design, with a lot of redundancy built in.
All systems were not very complicated, as at the DC10 with all reversible and non reversible pumps, etc.
I completed the full F/E DC10 course and had my first training flight AMS-ANC-HND . While in Tokyo all DC 10 's were grounded (after the Chicago crash) , so after returning to AMS as a passenger, I was transferred to the 747-200 to become the first direct entry F/E. So I can compare the two aircraft systems.
The L1011 was indeed a technical masterpiece, however with one major design failure :
The failure to cater for the possibility of higher operating weights for more range/ passengers, due main landing gear limitations.(no space for triple axle gears )
Even the DC-10 was designed from the start with the possibility of installing a center gear., the 747 had from the start four main gear trucks.
To cater for more range, the L1011 had to be shortend
A design was made with two three axle trucks (L1011-8), but a lot of re-design effort was needed to create enough space,, conseq the price was far too high compared to the DC10-30/40, Lockheed could not find a launch custome. Together with the financial difficulties of both Lockheed and RR the program was finally terminated after only 250 aircraft.
747classic wrote:SSB is used to split / connect the left sync bus and right synch bus (creating the "full" tie bus)
Closed with all 4 Eng generators are paralled durng normal ops
Open when APU Gen #1 and APU #2 are powering the system (APU Gen have no CSD and can not be parelled)
The same is valid if both Ext pwr #1 and Ext pwr #2 are powering the system
SteelChair wrote:The L1011 did have some problems with rear spar cracking, along with some other large Lockheed airplanes. I'm not sure that adding a six wheel or a widely spaced 4 wheel gear would have worked without major spar work.
Regarding the two man cockpit, getting the 767 and A300 certified were huge hurdles. Some early A300s did have Flight Engineers and the 767 had a small panel, the space was "staked out" in the cockpit in case the regulators wouldn't come around to approving 2 crew. Eventually they did and the "unsafe" two man airplanes have been several orders of magnitude safer than the 3 crew airplanes. I just don't think that the industry was ready for a two man flight deck on the L1011 in 1970. If anyone could have done it, it would have been Lockheed.
747classic wrote:SteelChair wrote:The L1011 did have some problems with rear spar cracking, along with some other large Lockheed airplanes. I'm not sure that adding a six wheel or a widely spaced 4 wheel gear would have worked without major spar work.
Regarding the two man cockpit, getting the 767 and A300 certified were huge hurdles. Some early A300s did have Flight Engineers and the 767 had a small panel, the space was "staked out" in the cockpit in case the regulators wouldn't come around to approving 2 crew. Eventually they did and the "unsafe" two man airplanes have been several orders of magnitude safer than the 3 crew airplanes. I just don't think that the industry was ready for a two man flight deck on the L1011 in 1970. If anyone could have done it, it would have been Lockheed.
I still think that a modern aircraft with a three crew cockpit would be safer than a modern two crew aircraft. The increase in safety was not because of the reduction from 3 to 2 crew !!!
A third pair of eyes, behind the pilots, that can compare the screens/ situation in front of them in an emergency wouild be a lot safer, see a lot of recent accidents.
I still consider the optimum crew composition in an emergency - PF only flying/navigate the aircraft, the two other crew deal with the emergency, one is trouble shooting/ switching the other is checking the non-nomal procedures. During that proces the PF will be regulary informed about the progress.
From memory :
The Qantas A380 accident was managed by a 3+ crew, a 2 man crew would have been overwhelmed by the multiple conflicting warnings. Also the automation was not working as it should be.
The same is valid for the KLM 747-400 Anchorage accident. Luckely an instructor (captain, just transferred from the 747 classic- I knew him very well) was seated behind the pilots to manage the situation, otherwise the outcome could have been very different. Here also the automation partly failed due multiple failures.
But all above has nothing to do with the L1011 electrical system, so back to the subject.