Is the RAT electrics/hydraulics or both? If +electrics, why the need for chunky extra batteries? Does its deployment seriously dent the ETOPS range?

Quote from DaveReidUK:
“Yes, the RAT location does appear to be under the centre-section on production aircraft, unlike the photo that I posted earlier, showing one of the prototypes with a RAT forward of the nosewheel.”

Looking at it again, am not sure if your first pic did show a RAT forward of the nosewheel. Looks aft to me. That panel did at first look like a nose-gear door, but is probably the access panel to the RAT?

Don’t know why RATs are not mounted forward of the nose gear, because at the centre section it’s difficult to avoid any possibility of airflow disruption when the nose gear is down. (That’s why they had to reconfigure the A320 electrical system and FBW downgrade-logic in late-1987, just before type certification.)

Quote from BOAC:
“Is the RAT electrics/hydraulics or both? If +electrics, why the need for chunky extra batteries? Does its deployment seriously dent the ETOPS range?”

Who is calling for “chunky extra batteries”? There is a dedicated APU-start battery, which must help. But I’m not familiar with ETOPS/EROPS requirements. Could you expand on your point?

If you had electrics on the RAT you might be able to dispense with APU start = 'chunky batteries'? Hence the query on possible detrimental drag on an ETOPS div.

RAT ON 787
 

I found a link which is quite interesting -written by a United pilot, who has taken the 787 course.

The Boeing 787, from a Pilot’s Perspective - View from the Wing

According to him the RAT supplies electricity as well as hydraulic power to flight controls (if needed).

P.S. The last 2 lines in his report read;
"I think the 787 will be a great plane, but there could be some surprises with this level of innovation. Time will tell. "

How true - unfortunately!

Yes, you're right, found another photo of it from a different angle, showing the MLG as well: DSC01711 | Flickr - Photo Sharing!

Thanks for the link grebllaw123d. The pilot's enthusiasm comes through well - don't blame him - I'd love to have flown the aircraft!

Bit OT, but he does state that electrical generation is "1.4 Gigawatts" - perhaps he meant Megawatts? But on the question of the RAT, it isn't clear how electrical generation is achieved. Is there a pump and a generator installed in the RAT or is the RAT only a hydraulic pump which then drives a separately-installed hydraulically-driven generator?

edit: by the look of it in the photo provided by DaveReidUK, I'd say the RAT was only a hydraulic pump.

Hydraulic pump redundancy on the 787 comprises a mechanically driven pump on each engine, powering two separate hydraulic circuits. Each of these separate hydraulic systems also has an electric-motor-powered hydraulic pump connected to the aircraft's electrical system. There is also a third hydraulic system pressurised by two further electric-motor-powered hydraulic pumps. There are two generators on each engine and each of the four electrically driven hydraulic pumps is connected to a different engine driven generator bus. The third hydraulic system can also be pressurised by a pump driven directly by a RAT. (The RAT drives an electrical generator and a hydraulic pump)

Even with a double engine failure ('Sullenberger Scenario'?), electric power from the APU and/or battery should keep the hydraulic systems operational long enough to allow a 787 to descend from altitude to a forced landing/ditching or, hopefully, a suitable runway. Should the APU and battery system also fail, the RAT would provide hydraulic pressure to operate the aircraft's primary flight controls. Therefore, it seems there is a high level of redunancy built into the 787 insofar as the supply of hydraulic pressure to control surface actuators, etc, is concerned.

In addition to hydraulic pressure, actuators also need electrical signals to control their degree and rate of movement in response to pilot/autopilot inputs. After the recent electrical problems experienced by the 787, I wonder if the FAA are worried that, under certain electrical failure scenarios, some of these control signals may be lost due to fire.

Avionista;

Thank you kindly for the information. Without going into specific differences, the system description is somewhat similar to the A330's system. The A330 RAT provides hydraulic power for one hydraulic system (main one, Green) which powers flight controls (but not the THS) and the hydraulic-motor-generator which provides a certain KVa for basic aircraft electrical services. I'm assuming that this is the way the B787 system is designed as well? (meaning, the RAT itself is only a hydraulic pump).

SAA 295 B747-244B Combi,
 

UNCTUOUS:

The container where the investigators focused had computers. (laptops?):

PJ2;

The way i read it the RAT provides power first, and then hydraulics if required.
Seems if the engines are just windmilling (out of fuel i guess) the PMG's will provide power for the control surfaces (im guessing its generating 270Vdc in this mode ?)

Boeing 787: A Pilots Perspective

PJ2:

The above quote from Hamilton Sundstrand's website suggests the RAT contains both a hydraulic pump and an electrical generator. This may be required because the 787 is a 'More Electric' aircraft than previous Boeing or Airbus aircraft.

From memory, the +/-270vDC is a variable output from the big electrical liquid cooled transformer/rectifiers in the aft EE bay. The main engine and APU gennys produce variable frequency 235vAC. Can't remember what the PMGs produce.

From the 787 Boeing training material
 

1. The RAT is stowed in a compartment aft of the right main landing gear.

2. When commanded, a spring-loaded actuator deploys the RAT into the

airstream.

3. The RAT uses propeller blades that turn in the airstream to turn a shaft.

4. The shaft turns an elecric generator and a hydraulic pump.

- This supplies hydraulic and electric power to critical systems such as flight

contols and primary display system.

5. The RAT system supplies hydraulic pressure to the center hydraulic system.

6. The RAT can extend automatically or manually.

7. The RAT can operate at all flight speeds and altitudes.

8. The RAT door is mechanically linked to the RAT.

- When the RAT deploys, the link opens the door.

wooski, Avionista thank you for your helpful responses.

"4. The shaft turns an elecric generator and a hydraulic pump."

sb_sfo that clinches it, thank you.

My comments from post #191 and #194 were from looking at the wiring connecting the cells.

I cant believe that a 'state of the art' system, the issues with Li, and the importance of this backup, that it is wired up this way....

If the system needs to be perfectly balanced between cells, this doesnt seem the right way to accomplish that....

The four engine driven generators supply the 235v variable freq. That goes to the aft and fwd EE bays. The aft EE bay Auto TRU's convert to +/-270vDC.
The DC is for driving the cabin air compressors, centre hyd. pumps. O/Jett pumps, the ram fans, and the NGS compressor.
The APU battery located in the same bay supplies the APU Hot Batt Bus its charger is supplied from the F/O's instrument bus. APU starter 235vac from the ATRU.
The main a/c battery located fwd. is charged (via a charger) from the capt's instrument bus. This is the only one with a diode pack to prevent the Hot batt. bus from back feeding the battery.
The PMG's only power the eng. EEC's
Windmilling engines will provide some hydraulic power. Enough for flight controls.
The RAT will supply hydraulic power to the centre hyd. system.
The RAT will supply electrical power to the ac busses (with some serious load shedding!) but primarily the backup bus, flt. instrument busses, brake system controllers (130VDC)
I'm tired its getting late..so apologies if I've got something wrong.

[QUOTE][The APU battery located in the same bay supplies the APU Hot Batt Bus its charger is supplied from the F/O's instrument bus./QUOTE]

EH! :{

Machinbird wrote: I can't find his post anymore but wbclay earlier posted a link to a whisteblower case that might offer evidence towards your theory? It was dismissed as the employee appeared to have other good reasons for termination, and most of his whistleblowing related to departure from design specs and a short that was later resolved. However he was top tech engineer on testing the battery until May 2007, and allegedly very good at his job. Here is the relevant portion of transcript of judge's decision, rendered July 2011:

pg. 26

http://www.oalj.dol.gov/Decisions/ALJ/AIR/2008/LEON_MICHAEL_v_SECURAPLANE_TECHNOLO_2008AIR00012_%28JUL_15_2011%29_172333_CADEC_SD.PDF

Physics, and particulary the base hardware portion of electrical circuitry (vs. programming logic, memory/processor architecture, etc.), were my weak suit (one of my three required EE professors accused me of obviously being a CS major, apparently a derogatory label, but ha ha, I got A's in the courses anyways), so I leave you to sort this out.

787 Program Saved!!
 

All followers of the aviation industry can now rest at ease over the apparent 787 debacle. The US Senate is on the case. All issues should be resolved within days.

Senate to examine FAA approval of Dreamliner battery - Yahoo! News

Senate to examine FAA approval of Dreamliner battery

WASHINGTON (Reuters) - A key Senate committee will hold a hearing in coming weeks to examine U.S. aviation safety oversight and the Federal Aviation Administration's decision to allow Boeing Co to use highly flammable lithium-ion batteries on board its new 787 Dreamliner, a congressional aide said on Tuesday.

U.S., Japanese and French authorities are investigating two separate cases in which lithium-ion batteries on board the new airliner failed. One of the batteries sparked a fire in a parked plane in Boston, while the other forced an emergency landing in Japan.

As a result, authorities around the world last week grounded all 50 Boeing 787s.

The Dreamliner, with a list price of $207 million, is the world's newest airliner, a lightweight, advanced carbon-composite design that has more electrical power than any other aircraft and uses 20 percent less fuel.

"Certainly the issues of FAA certification will be a key component of the aviation safety oversight hearing we're planning," an aide to the Senate Commerce, Science and Transportation Committee told Reuters in an email.

The aide, who was not authorized to speak publicly, said committee chairman Senator John Rockefeller was "following the situation surrounding the Dreamliner and FAA's task force closely and he thinks the FAA and (Department of Transportation)are examining the issue carefully."

The House Transportation and Infrastructure Committee is also keeping a close eye on the 787 investigations and the issue of FAA oversight, congressional aides said, although no formal hearings were planned at this point.

Boeing officials have briefed both oversight committees and other key lawmakers about the matter, a Boeing spokesman said.

The Senate committee had already been planning to conduct "substantial and aggressive oversight" of aviation safety during the first quarter, but would now look closely at the 787 incidents and FAA oversight as part of that process, the committee aide said.

Problems with the 787's lithium-ion battery have sparked questions about why the FAA in 2007 granted Boeing a "special condition" to allow use of the batteries on the plane, despite the fact that they are highly flammable and hard to extinguish if they catch fire.

Boeing designed a special system that was supposed to contain any such fire and vent toxic gasses outside the plane, but the two recent incidents have raised questions about whether that was a good decision.

It remains unclear what caused the batteries to fail, but when it announced plans to ground U.S.-based 787s, the FAA said both battery failures released flammable chemicals, heat damage and smoke - all of which could affect critical systems on the plane and spark a fire in the electrical compartment.

The FAA has said it will keep the 787s grounded until airlines demonstrate that the battery system is safe and complies with safety regulations.

(Editing by Gary Hill and Sandra Maler)

When Comets crashed, they were so important as an export earner that the Government gave orders to blame the pilots (as I have heard reported Airbus still do.) The battery will be redesigned and all will be well until the next minor problem gets blown out of proportion by those who know no better.