Several months ago, we had a spirited discussion on the Forum regarding Boeing's bleedless engine design for the 787. Boeing's AERO magazine, directed toward customers, has a discussion of this approach in the current issue. See:
http://www.boeing.com/commercial/aeroma ... _02_1.html
Boeing 787 Bleedless Engine Design
Moderator: Latest news team
-
smokejumper
- Posts: 1033
- Joined: 21 Oct 2005, 00:00
- Location: Northern Virginia USA
That is a great article, but it leaves me somewhat unconvinced.
I can understand that on the testbed the specific fuel consumption will undoubtedly be better than an engine configured for bleed air.
What is not mentioned are the following:
!000kVA of generators assuming 0.8 power facttor will absorb around 940kW at full oad after 15% allowance for generator efficiency and gear drive losses.
Every electric motor is subject to similar losses, which of course compounds the overall parasitic loss from each engine.
Add to this efficiency losses in inverters, transformers etc.
Each electric motor requires a starter, cables, controls and circuit breaker, and the weight starts to add up compared with very lightweight air ducting.
Pneumatic valves and controls are heavy in bleed air systems, but not that much.
Electrics could be relatively simple, but I question the claimed nett fuel savings if you have around 30% efficiency losses (main generators plus electric motors)
Maybe we will restart the debate.
Cheers
Achace
PS A380 in Manila tomorrow!
I can understand that on the testbed the specific fuel consumption will undoubtedly be better than an engine configured for bleed air.
What is not mentioned are the following:
!000kVA of generators assuming 0.8 power facttor will absorb around 940kW at full oad after 15% allowance for generator efficiency and gear drive losses.
Every electric motor is subject to similar losses, which of course compounds the overall parasitic loss from each engine.
Add to this efficiency losses in inverters, transformers etc.
Each electric motor requires a starter, cables, controls and circuit breaker, and the weight starts to add up compared with very lightweight air ducting.
Pneumatic valves and controls are heavy in bleed air systems, but not that much.
Electrics could be relatively simple, but I question the claimed nett fuel savings if you have around 30% efficiency losses (main generators plus electric motors)
Maybe we will restart the debate.
Cheers
Achace
PS A380 in Manila tomorrow!
-
smokejumper
- Posts: 1033
- Joined: 21 Oct 2005, 00:00
- Location: Northern Virginia USA
The flight test results will certainly shed some light on this issue with the test data either bearing out the claims or not. (Of course, the first flight has to take place for test results to be measured!)
I am confident that there is truth in Boeing's claims, since they had to perform engineering calculations before making such claims and the customer airlines must have analyzed the claims prior to ordering the 787. But, how well the test results will match the claims is not known to me. We'll just have to wait and see.
I am confident that there is truth in Boeing's claims, since they had to perform engineering calculations before making such claims and the customer airlines must have analyzed the claims prior to ordering the 787. But, how well the test results will match the claims is not known to me. We'll just have to wait and see.
A few of technical corrections.
Transformers are very efficient. Losses are pretty minimal, and that’s in a standard transformer. If its worth the money, they can make them more efficient.
3 phase motors do not require starters (as in capacitors). If you mean contactors, then those can be solid state (not used normally, but if the cost is justified, the technology exists.
There are some interesting inverter techniques that have 80% of the current route around the inverter. That means a pretty small inverter per output ( smaller losses).
We do not have the real in depth nitty gritty details so we could analyze it system by system. .
I started my career in building control pneumatics. I like them, they are simple to work on and trouble shoot (and you can't smoke them testing them like so many electrical devices). And even in that case, they are being replaced by electric actuators and devices. I hate to see them going away, but they are.
Transformers are very efficient. Losses are pretty minimal, and that’s in a standard transformer. If its worth the money, they can make them more efficient.
3 phase motors do not require starters (as in capacitors). If you mean contactors, then those can be solid state (not used normally, but if the cost is justified, the technology exists.
There are some interesting inverter techniques that have 80% of the current route around the inverter. That means a pretty small inverter per output ( smaller losses).
We do not have the real in depth nitty gritty details so we could analyze it system by system. .
I started my career in building control pneumatics. I like them, they are simple to work on and trouble shoot (and you can't smoke them testing them like so many electrical devices). And even in that case, they are being replaced by electric actuators and devices. I hate to see them going away, but they are.
Sorry RC20, but I beg to differ.
All electric motors require a starter, be it a 3 phase or single phase.
A simple on/off switch is a direct on line start and pulls up to six times full load current. This is for small motors.
Larger motors use auto-transformers, star delta or reduced voltage starting, all starting involves some load greater than the full load current of the motor in question.
The generator therefore has to be designed to withstand a situation where every load is applied simultaneously, unless it can be demonstrated that such a scenario cannot take place.
Frankly in this 787 case, 4 x 250kVA generators v. 2 x 120kVA suggests an extra weight for each engine of around 5 passengers, something I forgot to mention in my earlier post.
My business is power plants by the way!
Cheers
Achace
All electric motors require a starter, be it a 3 phase or single phase.
A simple on/off switch is a direct on line start and pulls up to six times full load current. This is for small motors.
Larger motors use auto-transformers, star delta or reduced voltage starting, all starting involves some load greater than the full load current of the motor in question.
The generator therefore has to be designed to withstand a situation where every load is applied simultaneously, unless it can be demonstrated that such a scenario cannot take place.
Frankly in this 787 case, 4 x 250kVA generators v. 2 x 120kVA suggests an extra weight for each engine of around 5 passengers, something I forgot to mention in my earlier post.
My business is power plants by the way!
Cheers
Achace
Achace: Interesting, I understand better some of the comments, not everyone is that technical in the field.
One of my fields is power generation on a small scale (standby) and switchgear, as well as HVAC system which are probably 80% in nature. Also includes all the other systems and controls that make a facility run (freight sort facility, Simulator Building, Hangar, Mechanics Shop, Pumphouse for the Hangar etc).
There are a number of devices that can be used (not saying they are, but possible). We are seeing more networked systems where circuit breakers communicate with each other, as well as other systems having their components talk to each other and controllers.
There are also a number of soft start systems that can replace a old combination starter, be it auto transformer (the best of the older technologies for reducing a start load) or Y delta, resistor starters, etc.
VFDs are lightweight and will accomplish that, we have SCR soft starters that ramp up and then bypass. All those system could easily be networked to the flight engineering system so that it manages the start process sequentially, keeping the peak loads down.
Some would have critical priority, others like landing gear extension could easily be delayed a little bit if the system was loaded up with higher priority draws.
With that much power available, it would seem that its not an issue (and I expect a lot of redundancy and future load planning).
I would say that while I am not an expert, I can follow a technical explanation fairly well on a given system or circuit. However, I would have no idea how to asses an entire aircraft system.
What I can say, is that I can see some general benefits to their approach, and the experts and the field has been moving to all electrical the last (5-10 years roughly).
I have never worked with aircraft pneumatics (I have as the original building control systems were pneumatic sensors, actuators and outputs via pneumatic electric switches to start motors). I really do like them. They are not high temperature, nor control high temperature, no intercoolers, jet fumes (I can remember smelling the damned oil burning in the MD-80s when they said it wasn’t).
At some point, I have to accept they know more about what works and benefits than I do. There does not seem to be any controversy about moving in the all electric direction, just how soon they will get there. Airbus as well as everyone else, just a matter of how fast it moves (when they think its ready). Boeing has gone further than Airbus, but I noted that Airbus had changed the power outputs in the A350, and some of the booster, backup and or auxiliary systems were going to be electric.
What I find intriguing is that the technology will be available for the more common applications when they get the cost down.
One of my fields is power generation on a small scale (standby) and switchgear, as well as HVAC system which are probably 80% in nature. Also includes all the other systems and controls that make a facility run (freight sort facility, Simulator Building, Hangar, Mechanics Shop, Pumphouse for the Hangar etc).
There are a number of devices that can be used (not saying they are, but possible). We are seeing more networked systems where circuit breakers communicate with each other, as well as other systems having their components talk to each other and controllers.
There are also a number of soft start systems that can replace a old combination starter, be it auto transformer (the best of the older technologies for reducing a start load) or Y delta, resistor starters, etc.
VFDs are lightweight and will accomplish that, we have SCR soft starters that ramp up and then bypass. All those system could easily be networked to the flight engineering system so that it manages the start process sequentially, keeping the peak loads down.
Some would have critical priority, others like landing gear extension could easily be delayed a little bit if the system was loaded up with higher priority draws.
With that much power available, it would seem that its not an issue (and I expect a lot of redundancy and future load planning).
I would say that while I am not an expert, I can follow a technical explanation fairly well on a given system or circuit. However, I would have no idea how to asses an entire aircraft system.
What I can say, is that I can see some general benefits to their approach, and the experts and the field has been moving to all electrical the last (5-10 years roughly).
I have never worked with aircraft pneumatics (I have as the original building control systems were pneumatic sensors, actuators and outputs via pneumatic electric switches to start motors). I really do like them. They are not high temperature, nor control high temperature, no intercoolers, jet fumes (I can remember smelling the damned oil burning in the MD-80s when they said it wasn’t).
At some point, I have to accept they know more about what works and benefits than I do. There does not seem to be any controversy about moving in the all electric direction, just how soon they will get there. Airbus as well as everyone else, just a matter of how fast it moves (when they think its ready). Boeing has gone further than Airbus, but I noted that Airbus had changed the power outputs in the A350, and some of the booster, backup and or auxiliary systems were going to be electric.
What I find intriguing is that the technology will be available for the more common applications when they get the cost down.
-
smokejumper
- Posts: 1033
- Joined: 21 Oct 2005, 00:00
- Location: Northern Virginia USA
I agree, I think it will be an efficient system, and it will be the technology that will be used in future commercial airliners. If anything, this non-bleed air system gives airlines what they need, less fuel consumption, and I do believe it will lower maintenance costs. I think the Testing(hopefully it will start in the first quarter of 08) will yield answers indeed.smokejumper wrote:I beleive that the bleedless system will be more efficient, but how much more needs to be proven during the flight tests. Also to be learned is how reliable and what the maintenance costs will be. As the saying goes, "There is no free lunch."