View Full Version : Electric Brakes (787)
Deepinsider
9th Jan 2018, 09:00
I just do not know how these brakes work.
Electronic control is fine, but down at the
wheel, what actually presses the pad against
the disk(s) ? Is it an electric solenoid, or
hydraulic force from a local small circuit,
controlled electrically? Or what?
Electromechanical actuators...
Google is your friend...
https://www.safran-landing-systems.com/media/boeing-787-electric-brake-advanced-technology-meets-airline-requirements-20170622
IIRC the choice of electrohydraulic brakes was the main driving factor behind the design decision to use Lithium main batteries - they are the only battery technology that will deliver the huge short-term currents these eh brakes need.
FE Hoppy
9th Jan 2018, 11:33
Meggitt Ebrake as used on CSeries has no hydraulics at all.
Works well too.
Deepinsider
10th Jan 2018, 07:15
Thanks guys, looks like a bit of good old 'Skydrol' is still in play.
'hydraulic pistons driven by electromechanical actuators.
Cough
11th Jan 2018, 11:47
Deepinsider - The link provided from PDR1 gives the following...
In electric braking systems, the conventional hydraulic equipment is replaced by electronic control units and hydraulic pistons driven by electromechanical actuators.
Where did you get your quote from?
DaveReidUK
11th Jan 2018, 13:16
Thanks guys, looks like a bit of good old 'Skydrol' is still in play.
'hydraulic pistons driven by electromechanical actuators.
No, there are no "hydraulic pistons" involved, at least in the Safran/Messier-Bugatti brakes. I assume that the same applies to the UTC/Goodrich equivalents.
Jetjock330
11th Jan 2018, 16:52
The brakes work just fine. First application in your life and it duck walks along with an instant upgrade of all economy passengers to business.
3 and bit years experience on them now and no more instant upgrades happening anymore:)
Like the famous pressure-actuated brakes of the Citroen GS - the pedal moved a whole 2mm from fully off to fully on. The first time you drove it you would lock all four wheels solid at the first corner, but within a mile or so it felt "natural", and when you then got back into a "normal" car it all felt terribly spongey...
DaveReidUK
11th Jan 2018, 19:06
No, there are no "hydraulic pistons" involved, at least in the Safran/Messier-Bugatti brakes. I assume that the same applies to the UTC/Goodrich equivalents.
A bit more digging confirms that there are no hydraulics involved in either OEM's e-brakes.
Incidentally the Safran document linked in post #3 is a mis-translation of the French original, hence the erroneous reference to "hydraulic pistons driven by electromechanical actuators".
The French source says
"Avec les freins électriques, les équipements hydrauliques sont remplacés par des boîtiers électroniques et les pistons hydrauliques par des actionneurs électro-mécaniques"
which translates as "... hydraulic pistons [replaced] by electromechanical actuators".
Deepinsider
12th Jan 2018, 09:55
No, there are no "hydraulic pistons" involved, at least in the Safran/Messier-Bugatti brakes. I assume that the same applies to the UTC/Goodrich equivalents.
Hi Dave, I must be truly going mad, or we do not use the same form of English!
This is from Safran themselves, not me.
A major advance
In electric braking systems, the conventional hydraulic equipment is replaced by electronic control units and hydraulic pistons driven by electromechanical actuators. The introduction of electric brakes is an advance on a par with the introduction of carbon brakes some 30 years ago, and paves the way for even "more electric" aircraft.
this is from the link posted by PDR1
(I'm blocked from posting links at this site)
Deepinsider
12th Jan 2018, 10:12
Sorry guys, actually I'm not a troll. I'm sorry my genuine question has not gone well.
Under the rules I agree to move on as they say. (not sure this will be blocked as well)
cheers!
wiedehopf
12th Jan 2018, 10:46
so the translation and the french can both be right.
somehow you need guidance also for an electromechanical actuator.
so it's still some kind of piston probably similar to a hydraulic one just without the pressure making it move, that's what i assume is meant.
@deepinsider you can't post links when under 5 posts on this page don't think you've been blocked or you couldn't post at all ;)
and reread what davereiduk wrote, he said safran has bad english translators so he does not dispute the meaning of the english language but the translation skills of the bloody french.
yotty
12th Jan 2018, 11:30
B787 FCOM
Landing Gear –
System Description
14.20.4
Revision 6
Sep 2014
Four Electric Brake
Actuators (EBAs) are provided
on each main landing gear
wheel brake to control the application of
braking force to
the carbon disc. The
EBAs are controlled by an Electric Br
ake Actuator Controller (EBAC). There are
four EBACs that control all eight main
wheel brakes, each EBAC controlling the
brake force of a fore-aft wheel pair. From a major UK operator of 787.
I think it's my fault. In my post #3 I inadvertently wrote "electrohydraulic" when I meant to write "electro-mechanical". Apologies to all for the cnfusion caused by my brainfart!.
tttoon
12th Jan 2018, 15:56
I haven't really noticed a difference in use between these and the ones on the NG. If anything, the braking on the 787 is easier to modulate. The tricky bit is it'll only use half of the units if you re-apply brakes below 70kts, possibly leading to high brake temperatures.
Cough
12th Jan 2018, 18:56
Deepinsider - If you click PDR's link again, I think someone has been correcting themselves!
DaveReidUK
12th Jan 2018, 19:20
Yes, the page metadata shows an update today at 15:43:14 CET.
Result !
Yaw String
23rd Jan 2018, 19:51
Tttoon,
Spot on..
Issue with the 800 series,not really a problem with the 900 series:ok:
vapilot2004
24th Jan 2018, 00:20
Brakes actuators require +/- 130VDC supply for operation, which is stepped up from the 28VDC TRU voltage by the brake PSUs. The 28VDC TRUs are the primary power source for the PSUs, with the aircraft batteries serving as a backup supply.
The motors supply torque through gear assemblies to the actuators, which are rams driven by a jack screw. There is a latching mechanism to limit over-rotation and back driving, minimizing the current requirements for the EBS actuator motors.
The aircraft may be dispatched (MEL) with an electrically locked out actuator.