[Sparky]

As an added safety measure, especially when at fly-ins or air shows with a lot of kids around, I've been considering installing a Sonalert (or other audible alarm) in the engine cowl to provide an external audible alert whenever either of the ignition switches are "hot" with no engine oil pressure. I've got a Slick mag on the left and a Lightspeed Plasma II+ on the right, each controlled by a toggle switch.

Generally, if someone suddenly hears an 80 dB - 100 dB alarm like this they tend to jump away from it. So my thinking is this could add a level of safety if anyone is in close proximity to the prop with the ignition hot and I can't see them (especially with a tail dragger). It's kind of like a back-up alarm on a commercial vehicle.

It would also serve as a reminder to turn off the ignition switches.

Anyone see any advantages or disadvantages of having something like this installed? Or, has anyone already done this? I know it's a (little bit of) added complexity and another source of possible failure, etc., but it's easy and cheap.

(Edit: By the way, the only things I would be adding are the Sonalert itself, 2 diodes, and some wire. Everything else already exists in my setup. The Sonalert only draws about 200mA.)

All thoughts and opinions are welcome...

 

[Sparky]

I guess it's not such a good idea, since I've received no comments...

 

[Wallbangar]

Works for me

I would call that the "Battery run-down horn". Don't ask me how I know about Lightspeed ! ! I'm putting a light in................
Thanks........

 

[islandmonkey]

I think its a good idea Paul. The schematic looks ok as far as I can see. However, maybe 80db is a bit loud, after all, you want to be able to hear the alarm, but not let it ruin your hearing.

 

[mburch]

I think if I was going to do this in my airplane I'd tweak it as follows:

1. Use a double pole switch for the electronic ignition in order to avoid sharing a wire between the ignition and the audio alerter. That way a problem in the wiring to the audio alerter can't affect your ignition power.

2. Find a way to prevent the audio alerter from sounding when the master switch is on. Otherwise, you will have the horn going off at the beginning of every flight before you get the engine started.

good luck,
mcb

 

[Sparky]

Thanks to all for the feedback.

Use a double pole switch for the electronic ignition in order to avoid sharing a wire between the ignition and the audio alerter. That way a problem in the wiring to the audio alerter can't affect your ignition power.

Good idea, Matt. I agree. That would also eliminate the need for the diodes on the power side. But, alas, I don't have an empty spot for another fuse on the battery bus fuse block.

Also, I decided I should use a couple of diodes on the ground side to prevent slight differences between the main and battery busses from causing any potential problems.

In the end, after reviewing all this, I'm not going to install it, but if I did, this is how I would do it (In case anyone else wants to...):