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From: "Thomas y Reina Jakits" <rijakits@cwpanama.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-1845140@logan.com>
Subject: Re: [FlyRotary] Re: CBs and fuses
Date: Sun, 18 Feb 2007 08:50:54 -0500
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My point,

no matter if it is the fuse or the CB, one should find and check the reason 
for the trip anyway.
Whether a CB is used-up after one trip or not I would leave to the 
manufacturer of the CB, and change accordingly.
In an airplane, you generally have a chance to trim the bird and fly it 
hands-off for a while.
Not so in a small helicopter (AS350 is a small helicopter) - Generally your 
right hand  NEVER leaves the cyclic....
Now change a fuse with ONE hand....
So there must be some serious reason to use fuses (money would be one, but 
on a $2.2M ship, fuses versus CBs should not be a money factor...). As said 
before (I have to check this in some more detail....) it seems the fuses are 
all on non-essential circuits.
AAMOF the essential circuits are all auto-protected, if there is a complete 
failure (2nd line and back-up) it is gone - period. Nothing to reset....

Thomas

PS: What is the actual price on fuses versus CBs?


----- Original Message ----- 
From: "Bulent Aliev" <atlasyts@bellsouth.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Sunday, February 18, 2007 8:19 AM
Subject: [FlyRotary] Re: CBs and fuses


In my plane for everything electrical I installed, I asked myself:
can I fly without this item? And accordingly decided on CB or fuse.
A CZ builder had followed the plans and had installed the electric
nose gear fuse in the "per plans" location under the passenger seat.
He takes a passenger for a flight, but on retraction, his nose wheel
is cocked , hits the bottom of the fuselage and pops the fuse.
Something goes wrong with the manual override too. Now he asks the
passenger to unbuckle, turn around and put his butt against the
windshield, so he can replace the fuse while flying the plane at the
same time. If he had spent few dollars on a CB, he could have pushed
it in and flown with the gear down.
Buly
On Feb 18, 2007, at 7:35 AM, Thomas y Reina Jakits wrote:

> Hi Al,
>
> interesting!!
>
> Next chance I have I will try to find out more about this  (reasoning for 
> use of fuses over CB's in this helicopter).
> I don't really buy the "repair after trip" -reason as the result is  the 
> same.
> Whatever caused the fuse or CB to trip, it should be repaired. What 
> really happens is that the fuse is replaced - if it doesn't trip 
> immediately, no one will look any deeper into it, than a  "look" 
> (unfortunately...), .... until it trips again.
> A lot of trips can be caused by changing environment (heat,  humidity, 
> etc.) that bring the conditions for over current just to  the trip point, 
> but will not under normal conditions.
> However I am no specialist, not even building anything at this time  - so, 
> I will try to find out for this specific application (AS350B3)
>
> Thomas
>
> PS: First thing I am going to do is to consult the Maintenance/ Repair 
> manual....
> ----- Original Message -----
> From: Al Gietzen
> To: Rotary motors in aircraft
> Sent: Saturday, February 17, 2007 6:10 PM
> Subject: [FlyRotary] CBs and fuses
>
>
> Eurocopter Factory Instructors are VERY COMPETENT in Eurocopter 
> Helicopter Systems!!
>
> There is absolutely NO doubt that he knows the difference between  fuses 
> and breakers and WHY either one would be used.
>
>
> Thomas;
>
> Certainly not impugning the competence of the flight instructors;  just 
> suggesting the design engineers may have other reasons than  cost.  One 
> may be reliability.  The reliability of CBs goes down  significantly after 
> they have experienced a ‘trip’.  I recall  reading one experts opinion 
> that a CB should be replaced after a  ‘trip’.  Yeah; seems extreme.  The 
> modern philosophy of circuit  design is to design for fault tolerance, so 
> a fault; once causing  the protection device to open, is left for repair 
> when you land.
>
>
> The key for using fuses is fault tolerant circuit design and proper 
> selection and sizing of fuses.  Having done this; studies suggest  that 
> the fuse offers higher reliability and lower cost.
>
>
> There certainly reasons for either CBs or fuses, and I have both in  my 
> plane.  For my flight critical circuits I opted for simple,  fault 
> tolerance and fuses.  I wouldn’t argue with someone making a  different 
> choice.
>
>
> FWIW,
>
>
> Al
>
>


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