X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 30 [X] Return-Path: Received: from [201.225.225.167] (HELO cwpanama.net) by logan.com (CommuniGate Pro SMTP 5.1.6) with ESMTP id 1845069 for flyrotary@lancaironline.net; Sun, 18 Feb 2007 07:36:46 -0500 Received-SPF: none receiver=logan.com; client-ip=201.225.225.167; envelope-from=rijakits@cwpanama.net Received: from [201.224.94.164] (HELO usuario5ebe209) by frontend1.cwpanama.net (CommuniGate Pro SMTP 4.2.10) with SMTP id 102396707 for flyrotary@lancaironline.net; Sun, 18 Feb 2007 07:41:40 -0500 Message-ID: <001001c75359$4d314da0$a45ee0c9@usuario5ebe209> From: "Thomas y Reina Jakits" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] CBs and fuses Date: Sun, 18 Feb 2007 07:35:41 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_000D_01C7532F.64189750" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3028 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3028 This is a multi-part message in MIME format. ------=_NextPart_000_000D_01C7532F.64189750 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable 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 -----=20 From: Al Gietzen=20 To: Rotary motors in aircraft=20 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; =20 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 ------=_NextPart_000_000D_01C7532F.64189750 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Hi Al,
 
interesting!!
 
Next chance I have I will try to find = out more=20 about this (reasoning for use of fuses over CB's in this=20 helicopter).
I don't really buy the "repair after = trip" -reason=20 as the result is the same.
Whatever caused the fuse or CB to trip, = it should=20 be repaired. What really happens is that the fuse is replaced - if it = doesn't=20 trip 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=20 environment (heat, humidity, etc.) that bring the conditions for over = current=20 just to the trip point, but will not under normal = conditions.
However I am no specialist, not even = building=20 anything at this time - so, I will try to find out for this specific = application=20 (AS350B3)
 
Thomas
 
PS: First thing I am going to do is to = consult the=20 Maintenance/Repair manual....
----- Original Message -----
From:=20 Al = Gietzen=20
Sent: Saturday, February 17, = 2007 6:10=20 PM
Subject: [FlyRotary] CBs and = fuses

 

Eurocopter Factory = Instructors are=20 VERY COMPETENT in Eurocopter Helicopter = Systems!!

There is absolutely NO doubt = that he=20 knows the difference between fuses and breakers and WHY either one = would be=20 used.

 

Thomas; =20

Certainly = not=20 impugning the competence of the flight instructors; just suggesting = the design=20 engineers may have other reasons than cost.  One may be=20 reliability.  The reliability of CBs goes down significantly = after they=20 have experienced a =91trip=92.  I recall reading one experts = opinion that a=20 CB should be replaced after a =91trip=92.  Yeah; seems = extreme.  The=20 modern philosophy of circuit design is to design for fault tolerance, = so a=20 fault; once causing the protection device to open, is left for repair = when you=20 land.

 

The key = for using=20 fuses is fault tolerant circuit design and proper selection and sizing = of=20 fuses.  Having done this; studies suggest that the fuse offers = higher=20 reliability and lower cost.

 

There = certainly=20 reasons for either CBs or fuses, and I have both in my plane.  = For my=20 flight critical circuits I opted for simple, fault tolerance and = fuses. =20 I wouldn=92t argue with someone making a different = choice.

 

FWIW,

 

Al

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