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From: Bulent Aliev <atlasyts@bellsouth.net>
Subject: Re: [FlyRotary] Re: CBs and fuses
Date: Sun, 18 Feb 2007 08:19:18 -0500
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>

In my plane for everything electrical I installed, I asked myself: =20
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 =20
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 =20
is cocked , hits the bottom of the fuselage and pops the fuse. =20
Something goes wrong with the manual override too. Now he asks the =20
passenger to unbuckle, turn around and put his butt against the =20
windshield, so he can replace the fuse while flying the plane at the =20
same time. If he had spent few dollars on a CB, he could have pushed =20
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 =20
> (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 =20=

> the same.
> Whatever caused the fuse or CB to trip, it should be repaired. What =20=

> really happens is that the fuse is replaced - if it doesn't trip =20
> immediately, no one will look any deeper into it, than a =20
> "look" (unfortunately...), .... until it trips again.
> A lot of trips can be caused by changing environment (heat, =20
> humidity, etc.) that bring the conditions for over current just to =20
> the trip point, but will not under normal conditions.
> However I am no specialist, not even building anything at this time =20=

> - 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/=20
> 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 =20
> Helicopter Systems!!
>
> There is absolutely NO doubt that he knows the difference between =20
> fuses and breakers and WHY either one would be used.
>
>
> Thomas;
>
> Certainly not impugning the competence of the flight instructors; =20
> just suggesting the design engineers may have other reasons than =20
> cost.  One may be reliability.  The reliability of CBs goes down =20
> significantly after they have experienced a =91trip=92.  I recall =20
> reading one experts opinion that a CB should be replaced after a =20
> =91trip=92.  Yeah; seems extreme.  The modern philosophy of circuit =20=

> design is to design for fault tolerance, so a fault; once causing =20
> the protection device to open, is left for repair when you land.
>
>
> The key for using fuses is fault tolerant circuit design and proper =20=

> selection and sizing of fuses.  Having done this; studies suggest =20
> that the fuse offers higher reliability and lower cost.
>
>
> There certainly reasons for either CBs or fuses, and I have both in =20=

> my plane.  For my flight critical circuits I opted for simple, =20
> fault tolerance and fuses.  I wouldn=92t argue with someone making a =20=

> different choice.
>
>
> FWIW,
>
>
> Al
>
>