Ram Air Turbine

Okstate Pilot

Okstate Pilot

New Member
Hello Everyone,

First I want to say I am new to posting on this website but have been viewing it for some time and find it very informative.

I had a question after reading the "Dead Stick Night Landing" article in the November 2005 issue of AOPA Pilot magazine. It was about a Airbus A330-243 traveling from Toronto to the Azores that was losing fuel at a high rate, and the crew proceeded to crossfeed the fuel which later resulted in exhausting all the fuel on board. The aircraft was now on battery power and the normal hydraulic power was gone too. The article says that a ram air turbine was dropped from the belly of the aircraft and provided enough hydraulic power for the captain to hand fly to the nearest airport.

I found that very interesting and was curious if Ram Air Turbines are a standard piece of equipment on larger aircrafts or if this was just an Airbus piece of equipment? The way it sounds is this turbine would drop down and the ram air would drive a hydraulic pump or is there more to it than that?

Thanks.
 
Yes, most large aircraft have a RAT located somewhere.

Useually the RAT gives electrical power to the emergency electrical bus, and hydraulic power to the backup flight control system. Ironicly, the RAT looks like a boat propeller.

Most military aircraft have them as well, due to the possibility of battle damage.

In adition to the A-330 gliding to the Azores, there has been a case of an Air Canada 767 which ran out of fuel and glided to a landing.
 
Not sure all large aircraft have them. Seems it came into being for twin engine aircraft for more redundancy with hydraulics and electrical. I don't believe the older 3 and 4 engine jets had them, and I'm curious if the A340 and 380 does. I'm betting no.
 
USMCmech said:
Useually the RAT gives electrical power to the emergency electrical bus, and hydraulic power to the backup flight control system. Ironicly, the RAT looks like a boat propeller.
Click to expand...

What's the difference between a RAT and an ADG (Air Driven Generator a la the mighty CRJ)?

Thanks
 
I know the DC-8 does not have a RAT. I believe a RAT is required on any glass cockpit aircraft that does not have back up non-electrical airspeed indicator, altimeter, artificial horizon, and vertical speed indicator.
 
CFIse said:
What's the difference between a RAT and an ADG (Air Driven Generator a la the mighty CRJ)?
Click to expand...


I'm not certian, but probably they just have differnt names. Possibly the ADG may not have a hydrulic pump.

The DC-10 definately has a RAT. It's about 3 feet in diamter, and located on the right side of the nose. You may be right about other 4 engine planes not having them. I haven't seen one on the 747, but I haven't looked too hard.
 
CFIse said:
What's the difference between a RAT and an ADG (Air Driven Generator a la the mighty CRJ)?

Thanks
Click to expand...

The RAT is the propeller, it's connected via a constant speed governor to the ADG which is a 15kva AC generator which powers the AC Essential Bus and also directly powers Hydraulic Pump 3B. You still won't have flaps or spoilers though. So think of the RAT as the prime mover for the generator. In the case of the normal generators, the prime mover is the turbine engine through the accessory pad.

That's only in the CRJ's case.

From what I understand the 747 doesn't have a RAT as the windmilling engines provide enough hydraulic pressure to power the flight controls. Again I might be wrong about the 747. I'm pretty sure about the CRJ stuff though.
 
I'm thinking that an ADG and a RAT are about the same. I know that as far as ADGs go you have wet and dry ADGs. Sort of like wet and dry vaccume pumps. On the CRJ there is a speed restriction with the ADG deployed if you have a wet one (300 kias I think). No limit on the dry.
 
On the 767, the RAT on provides limited hydraulics for basic flight control movement plus spoilers #3,4,5,8,9 and 10. No flaps or electrical power from the RAT. The ADP runs off bleed air and supplies all center system hydraulic functions. flight controls, landing gear, and brakes/steering. There is an optional hydraulic motor driven generator that will give you electrical. All this out of the Fam. course manual.
 
On the 767ER I found the method of rendundancy interesting...there is an eletrical generator (HDG) that is driven by a hydraulic pump (ADP) that is powered by bleed air.

None of which involve that RAT, BTW. RAT...as stated above provides hydraulics to flight controls only. In the 757/767...if there is no hydraulics...there is no control of flight controls. That's why there are 3 hydraulic systems...and 1 emergency back-up.
 
MD11 has an ADG that initially will power hydraulic and capt emerg electrical, but a button push will switch it to pure electrical for most of the f/o's stuff as well.
 
woodreau said:
The RAT is the propeller, it's connected via a constant speed governor to the ADG which is a 15kva AC generator which powers the AC Essential Bus and also directly powers Hydraulic Pump 3B. You still won't have flaps or spoilers though. So think of the RAT as the prime mover for the generator. In the case of the normal generators, the prime mover is the turbine engine through the accessory pad.

That's only in the CRJ's case.
Click to expand...

Very close. The voltage is kept constant by the pitch of the propeller like a constant speed prop. It does power the AC Essential Bus and Hydraulic Pump 3B, but you will still have flaps, they are electric. You will also have spoilerons and inboard ground spoilers. I can't remember about the flight spoilers though.
 
lnewby said:
It does power the AC Essential Bus and Hydraulic Pump 3B, but you will still have flaps, they are electric. You will also have spoilerons and inboard ground spoilers. I can't remember about the flight spoilers though.
Click to expand...

That is true for the 700/900 but on the 200 you won't have flaps until you get a generator online as they aren't powered directly from the ADG like the flaps/slats are on the 700/900. But then again maybe I've gotten it all messed up since differences. It all gets fuzzy if you don't review it often.
 
woodreau said:
That is true for the 700/900 but on the 200 you won't have flaps until you get a generator online as they aren't powered directly from the ADG like the flaps/slats are on the 700/900. But then again maybe I've gotten it all messed up since differences. It all gets fuzzy if you don't review it often.
Click to expand...


I think I might be getting the two mixed up. I just had the 100/200 Fam course 3 weeks ago and now I am in the 700/900 course.

Who do you fly for?
 
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