why is ac wild power used to operate hydraulic pumps
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why is ac wild power used to operate hydraulic pumps
In a recent check ride on ATR, an examiner asked 'why is ac wild (variable volt & freq) used to operate hydraulic pumps '
Can anyone offer any reason?
thanks in advance
Can anyone offer any reason?
thanks in advance
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Well.....
Probably satisfies a 'know-it-all' examiner's ego to try and stump a good
performing candidate so as to make him look better than the guy he is
testing.
***Current qualified RETRE who has seen it all.
performing candidate so as to make him look better than the guy he is
testing.
***Current qualified RETRE who has seen it all.
Last edited by 777AV8R; 26th Jun 2011 at 18:20.
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Many items do not require a frequency stable power output. That is the case for the HYD pumps, but also the electrical heating to de-ice props and windshields.
The fact is that the ACW generators are mounted on the reduction gearbox of each engine, so the prop rpm will vary the frequency as the operations require during different phases of flight.
Note that during normal cruise/climb (especially since the -500 variant) the frequency IS in fact very close to 400Hz. There will be no need for a frequency rectifier (whatever the name is) therfore same weight, cost of building, and fuel overtime.
777, your post is pointless, unless you wanted to be seen as a smart ass... Believe if or not, as incredible as it may seem, TREs and TRIs, in the great majority, do their training job because they like to share the knowledge and experience, not to make you look bad.
Hope this helps.
The fact is that the ACW generators are mounted on the reduction gearbox of each engine, so the prop rpm will vary the frequency as the operations require during different phases of flight.
Note that during normal cruise/climb (especially since the -500 variant) the frequency IS in fact very close to 400Hz. There will be no need for a frequency rectifier (whatever the name is) therfore same weight, cost of building, and fuel overtime.
777, your post is pointless, unless you wanted to be seen as a smart ass... Believe if or not, as incredible as it may seem, TREs and TRIs, in the great majority, do their training job because they like to share the knowledge and experience, not to make you look bad.
Hope this helps.
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Originally Posted by flexpower
777, your post is pointless, unless you wanted to be seen as a smart ass... Believe if or not, as incredible as it may seem, TREs and TRIs, in the great majority, do their training job because they like to share the knowledge and experience, not to make you look bad.
Ex TRE (and TRI if you must) in the UK
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Ah yes...Thank White Knight, I have trained people on 4 continents (plus India...) and for sure one can meet funny birds, some of them you jsut wonder how they got there...
They would not try to ask anything if they don't know the answer...
They would not try to ask anything if they don't know the answer...
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My answer would be that on a plane where that actually is the case (on my 737 it isn't to my knowledge) the electrically driven hydraulic pumps draw the most current, the generator output can be used directly, the pumps don't need to run at a precise speed (since the pressure is usually regulated otherwise)...
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I'm with John Farley, if it makes any difference. William Stout is reputed to have admonished his designers "Simplicate, add more lightness". 
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"Dunno. Of what practical purpose would it serve me to know
anyway, short of pranging in the desert and having to build a
new single engined ATR out of the wreckage of the old one
without the benefit of having a German toy plane designer?"
would be my reply to that smart aleck checkie.
anyway, short of pranging in the desert and having to build a
new single engined ATR out of the wreckage of the old one
without the benefit of having a German toy plane designer?"
would be my reply to that smart aleck checkie.
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Just a thought, but if the pumps can take a frequency wild supply, then with a windmilling engine (or engines) where RPM drops as speed drops, or the same with a RAT, wouldn't you be able to hold hydraulic pressure down to lower airspeeds?
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Great idea, but try keeping a turboprop engine windmilling more than a couple of minutes, and soon you won't need hydraulics, or any other aircraft systems...you'll need a coffin.
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Inasmuch as a turbofan gearset drives/is driven by the core rotor, and the core windmills pretty slowly (maybe <10%) - I don't think it can do much good for you.
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On your type it was the lightest solution.
On many other types the AC is regulated normally to 400hz. In those cases your TRE may find that if electrically driven hydraulic or fuel pumps are fitted they will be designed to best use the constant frequency supply.
On many other types the AC is regulated normally to 400hz. In those cases your TRE may find that if electrically driven hydraulic or fuel pumps are fitted they will be designed to best use the constant frequency supply.
Avoid imitations
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'why is ac wild (variable volt & freq) used to operate hydraulic pumps '
(Reading back, this is what others have also written on the subject).
