EC155B1 Rotor Brake

[RoamingCyclic]

Hi Guys,

On the quest for further information here - My understanding is that the Rotor Brake on the 155B1 CANNOT be operated anytime when the engine(s) are running (starting or shutdown) - however I was advised that this restriction may have been lifted but cannot find any reference to this - any ideas?

Thanks in advance again.

[Flying Bull]

Hi Roaming Cyclic,

there is a micro switch preventing engine start, when the rotor brake isn´t fully released.
Never tried to apply the brake, while engines running, will be out of the permitted range for the rotorbrake anyway.

Greetings Flying Bull

[212man]

I very much doubt there's been any change with the current design: it would take a major mod to allow brake on starts and engine runnng stops. Effectively it's a bicycle brake :E

http://i202.photobucket.com/albums/aa50/S92ctc/155RB.jpg

[whatsarunway]

How does the 76 differ?

[ericferret]

The S76 brake was designed to stop a railway engine whereas the 155 brake previously saw service on the Tour de France!!!!!!!!!!!!!!!!!!!!!!!

The 76 brake is a multi piston hydraulic unit whereas the 155 is a pure mechanical effort with total pressure controlled by a spring pack.
See picture on previous post.

The 76 brake disc is probably 3 times as thick as the 155 disc.

[ShyTorque]

The S-76 has a big disc brake bolted to the rear of the main rotor gearbox. As one of its minor functions, it appears to drive the tail rotor....

All models (IIRC)- start both engines to idle, brake on.

All (except B) models - stop rotor, with both engines at idle.

B model - stop rotor, with one engine only at idle, one stopped.

[whatsarunway]

On a slightly different note, the engine oil is cooled on the 76 by two fans mechanicaly driven from the MR gearbox, so if the engines are stopped, how does the engine oil cool, or does it?

With engines on and rotor stopped i have never noticed a high temp so how does this work?

[nodrama]

"On a slightly different note, the engine oil is cooled on the 76 by two fans mechanicaly driven from the MR gearbox, so if the engines are stopped, how does the engine oil cool, or does it?"

If the MGB isn't turning (therefore fans aren't turning), there is still alot of cooling going on. Heat is still dissipated through the material of the various pipes the oil travels through and the cooler itself, even though no air is passing through it. Also, the oil tank itself is designed to dissipate alot of heat. Especially if it isn't an integral part of the engine.
It's only when the engines start working that the oil gets hot enough that the aid of fan driven air is needed through the cooler to help heat dissipation.

[nodrama]

As for the 155 rotorbrake, 212man is spot on. Major mod to adapt that excuse for a rotorbrake into something that will hold the transmission still at grd idle.
Major mod= major money= won't happen.
Don't try applying the rotorbrake on 155 with engines running unless you want to really upset you chief pilot and chief engineer and are looking to work somewhere else.

[ShyTorque]

Or the A109 - if the aircraft is started with rotor brake applied, it will slip, especially if the hydraulic accumulator is discharged. As the rotors begin turning and the main hydraulics begin to pressurise fully, the rotor brake comes on as hard as it can but continues to slip, with very expensive results. :}

[ericferret]

The S76A had fans driven by the engines, one mounted below each engine air intake in the plenum.

The S 76A+ and the C have fans driven by the engines mounted on the back of the each engine module 5.

A gas turbine with no cooling will overtemp it's oil system in no time flat.
To wit one Allison in a BO 105 with the return and vent lines cross connected in effect bypassing the cooler. Cooking time to very well done about 5 minutes!!!!!!! Don't ask why the pilot wasn't watching the oil temp guage.

Even if you uprated the 155 rotorbrake the engines would overtemp as there is only one fan (main tranmission driven) for all 3 oil coolers. No transmission rotation no cooling. In point of fact the 155 fan is on the end of the shaft that the brake is mounted on!!!!!!!! Couple this with the fact that the gearbox has not been designed for the high loading generated by a braked rotating engine.

[Cyclic Hotline]

The S76 brake was designed to stop a railway engine whereas the 155 brake previously saw service on the Tour de France!!!!!!!!!!!!!!!!!!!!!!!


Hey, that brake would never stop a modern racing bicycle in the TDF. It was seconded from a 2CV!:eek:

No serious racing cyclist would ever be seen dead in a French helicopter with all that cheap automotive gear installed.:ouch:

[RoamingCyclic]

Hi Guys,

Thanks for the information - I thought as much but keep hearing BS about modifications etc which obviously are not the case.

Best Regards, RC