RAT degradation in icing conditions

[alexious85]

I was just looking at the blades of a Ram Air Turbine and it occurred to me that if that thing ends up operating in some heavy icing conditions it's operation might be reduced. It may even stall . There's no mentioning of this anywhere and I don't know if the blades are heated... But obviously if they are not heated then should as pilots find ourselves in a condtion that the RAT is deployed , then operating in heavy icing conditions might become another factor to consider
Can some engineers verify this ?

[Capt Quentin McHale]

alexious85,


I dived into the family vault and found my old B767 training notes, so here goes.


With the RAT stowed, a continuous flow of CTR HYD SYS fluid from the bleed orifice circulates thru the RAT pump housing. This keeps the RAT warm at cruise altitudes and ready to function quickly in an emergency. This is active AT ALL TIMES irrespective if the RAT is stowed or deployed.


The RAT has 2 variable pitch blades with governed speed of between 4100-4600RPM at a min airspeed of 125kts. The speed of the turbine is controlled by governor springs and counterweights in the hub assembly.


With the rotational speed of the blades, I don't think any ice will cause any dramas. Also, I can only assume that the above would be standard across Boeing RAT systems. Hope this helps...


McHale.:)

[alexious85]

thank you for the reply McHale (http://www.pprune.org/members/419639-capt-quentin-mchale)
i assume even the airbus RAT operates in this manner , even though there is no reference in the FCOM.

[320busboy]

As far as I am aware the Bus rat.. 320/330 has the oil warming circuit to keep the important bits toasty when its called into action (solenoids and valve block).. as for deicing the blades.. there is none.. however inside the hub there are carbon blocks which rub on the inside of the hub when it is rotating keeping the hub and pitch change/governing mechanism warm. I guess this would extend to the blade root but the cooling effect on the outer part of the blades would not allow the hub heat to get there I presume.. As long as the blades don't liberate (thankfully those days are gone) ..It should be ok