Circuit protection

[elippse]

All of you using circuit breakers and fuses should be aware of the operating characteristics of these devices. With the exception of magnetic circuit breakers, fuse's and thermal circuit breaker's characteristics are affected by ambient temperature. I'm not quite sure where you would use a fuse in an aircraft application except for some ancillary device that has no direct effect on the aircraft operation; I use one in my air-horn circuit. Typically, a circuit protection device is to protect the wiring. not the load, but in some applications that may not hold true.The Littlefuse data sheet says that you should use a fuse at 75% of its 25C rated value in order to prevent nuisance blowing. At an ambient temperature of 80C, 176F, the fuse should be de-rated to 95% of its 25C rating. If you are using one of the re-settable PTC devices, it is de-rated to 40% at 90C ambient. W23/W31 series thermal cuircuit breakers de-rate to 70% at an ambient temperature of 60C, 140F, of their nominal 25C rating. Note that these breakers will not trip at their rated value at 100% of their de-rated rating, and will trip in one hour at 135% of rating. Depending on the breaker size 5-50A breakers trip at 200% in 6-22 seconds, whereas 0.5-4A breakers trip in 11-30 seconds at 200%. The reason I am bringing this up is that if you are using one of these devices in a hot area, such as within a closed box with other heat-producing devices, or at the top of the firewall in the engine compartment, you may not get the operation you think is taking place!

[N941WR]

Originally Posted by elippse

I use one in my air-horn circuit.

Please explain why you have an air-horn in the plane? Are you worried about road rage?

[Brantel]

Originally Posted by elippse

I'm not quite sure where you would use a fuse in an aircraft application except for some ancillary device that has no direct effect on the aircraft operation;

Thats funny, my airplane will have a ton of fuses. Not one breaker in site.

The fuse or breaker debate has been going on ever since breakers were invented, good luck with that one.

My personal opinion is that fuses will work just fine for our application if properly applied and sized. They are a ton cheaper, easier to install etc.

I don't care that they are hard to change (except for the RV12) during flight, I ain't reseting a breaker in flight that just popped anyway without determining why the thing popped. If you need to use a breaker to disconnect the circuit, spend 5 more bucks for a switch.

[mannanj]

Bill:

You've never heard an air horn (think Train) overhead at 500ft AGL?????? Think "Apocalipse"

[elippse]

Originally Posted by N941WR

Please explain why you have an air-horn in the plane? Are you worried about road rage?

A friend of mine was having a garage sale and he had this air-horn with two trumpets for $10. I bought it and installed it in my right wing behind the landing gear cut-out. It's nice for tooting at friends on the airport when taxi-ing, I have "Sound Horn" on my check list pre-engine start along with "Clear", It's great when you are taxi-ing around at a fly-in, both for tooting at friends and for clearing the way, and with the gear down at 1000' AGL, I used it to signal my daughter in Temecula that I had arrived and would soon be landing at French Valley Airport. RV-9 builder John Rhodes was at the Santa Maria airport with his wife Jean and I was telling him about my plane's equipment and mentioned the horn. Jean asked me if I had a little white plane and had been flying around near her house lately, and I asked her where she lived. It was just two or three blocks from my house. I said I had, and she asked if I had been blowing the horn when I was flying around my house, and I answered "Yes". She then said that she had seen this little white plane flying around near her house and heard a horn coming from it. She called John at work and told him about it, to which he replied "Honey, airplanes don't have horns!" She then looked at John and said "See, John! I told you I saw a little plane that was blowing its horn!"

[N941WR]

I did see a StarDuster II at SnF with an Auuggaaaa horn installed, he used it after yelling "clear" as you describe. At the time I thought it was a good idea as it got people's attention that something was about to happen.

With all the noise complaints we (us in small planes) generate, I'm not so sure blowing it at altitude is such a good idea.