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DeeCee 57

Fire Alarm System for Pusher Aircraft anybody?

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not sure I'm posting in the right forum (could not find any history on the subject), but that is the best I found so here goes:

 

Worried by an eventual in flight fire on my VariEze's C-90 and the urgency of such a situation, I'm thinking about installing some kindof fire warning system. This system would ideally be easy to manufacture and install, reliable, cheap and light (MI #xxx ;) ).

 

2 simple ideas that popped to my mind, using my rear view mirror (the very one I used to check on the fuel quantity) to keep watching on the engine behind me, or using a kinda OAT gage with an over temp warning...

 

The ideal warning system would be some big red light & bell system to wake me up, kinda what we find on our airliners  :cool2:

 

 

Ideas, examples, pictures, suggestions? All are more than welcome, thanx!

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One of the most simple ideas that I've heard is to install a small video camera in the engine compartment and install a small remote video screen on or near the instrument panel.

 

A wireless camera / screen combination, such as Bluetooth, might work.

 

The visual of flames is likely to get your attention... but even a small fire just getting started and not yet large enough to trigger heat warnings could be reliably detected.  

 

Lots of visual options today for great prices.

 

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A thin copper plate sandwiched between two aluminum strips held together with screws and springs.

A insulating layer between the copper and the aluminum.

 

Ground wire goes to the copper, aluminum is grounded to the engine.

When a fire starts it melts/burns the insulation and the ground for your warning system is complete.

Pretty simple to make.

Edited by TMann

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Thank you guys.

 

Andrew, whilst your idea has good points, I do not want to stare at yet another screen to alert me. I fly in a high traffic (and mountainous) environment and I usually pay attention to the outside world with occasional glimpses at the panel.

What I need is an alarm that will alert me to an unseen fire as soon as possible in order to get down ASAP...

 

Thomas, thanks, sounds more like what I'm looking for. Why would you use aluminum for the strips? Guess 2 copper strips separated by insulation would work as well. The problems remaining are twofold: being sure that when melted the insulation will not stay in between the plates to prevent closed contact. This could be solved by bending one end or the ends of the plates so they would contact when the Insulation melts. The other problem lies as to what kind of insulation to use. Styrofoam packing sheet maybe? Well, I guess testing such a device is pretty easy, holding some kinda fire below to test the working.

 

Another problem is the location inside the cowling. Combustibles are primarily fuel, then oil... so I guess best location would be around the carb and fuel lines...

Better/more ideas? Some of you guys done or seen that done before?

Edited by DeeCee 57

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At the risk of answering my own question (...) some net search found following solutions, looking quite attractive to me:

http://www.circuitsgallery.com/2012/09/fire-alarm-circuit.html

or a slightly more elaborate one:

http://www.eeweb.com/blog/extreme_circuits/fire-alarm-using-thermistor

 

Using thermistors in parallel one could use say 3 of them in different locations...  :cool1:

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Andrew, whilst your idea has good points, I do not want to stare at yet another screen to alert me. I fly in a high traffic (and mountainous) environment and I usually pay attention to the outside world with occasional glimpses at the panel.

What I need is an alarm that will alert me to an unseen fire as soon as possible in order to get down ASAP...

 

 

Your first idea of the rear view mirror is actually the best... by far.  Can you set it up to check for fire / smoke?  A visual indication is really important.

 

I don't agree with you that a beeping fire alarm is a good idea.  Lets say you build the beeping fire alarm system, and it starts beeping during flight in a mountainous environment.  What are you gonna do?  Do you shut off the fuel to your running engine?  If you have a fire, you better turn off the fuel.

 

I don't think we need a fire alarm system.  Inflight fires a very unusual in our type of aircraft. 

Edited by Andrew Anunson

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Ok, I will install this device: https://www.kemo-electronic.de/en/Transformer-Dimmer/Sensors/Modules/M169A-Temperature-switch-thermostat-12-V-DC.php

Since the max T switching is 100°C I will see if that is not too low, if it is they have a 150°C model as well. I will most probably install the unit in the rear "luggage" compartment and the sensor in the fuel/oil area of the Continental. A loud bell and light will be activated when the set threshold is reached.

 

Andrew, if the system activates in flight I would confirm the fire or smoke with my mirror (or try to twist my neck enough, but this exercise is not too Ez in one  ;) ). If a fire is confirmed, mountainous environment or not would see me pull the mixture to idle cut-off and switch the fuel to off, then head ASAP towards terra firma setting up for a most probable crash landing... certainly a better option than remaining in a soon to be burning torch, your choice.

I think I need a fire alarm, the only best reason is that I don't see my engine. And yes it has happened a few times. We had a the tragic case of a Cosy here, here's the report: http://www.sust.admin.ch/pdfs/AV-berichte//1883_e.pdf

 

FAR Excerpt:

FAR 23.1203(a)(iii): There must be a means that ensure the prompt detection of a fire in airplanes with engine(s) located where they are not readily visible from the cockpit. 

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A loud bell and light will be activated when the set threshold is reached.

​Use a car horn. You'll need something that loud when wearing a ANR headset.

​Also, search on bi-metal switches. You should be able to make one that will meet your needs if you can't find one.

It's the same principle used in a home thermostat (but without the mercury switch.)

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I don't think we need a fire alarm system.  Inflight fires a very unusual in our type of aircraft. 

 

 

I agree for two reasons.  A fire detect system may not be situated to detect a fire for a long period of time and (2) things that burn like fuel and oil leaks aren't necessarily going to cause a fire.  Avgas evaporates pretty fast and it's unlikely to be sprayed on the root of a hot exhaust pipe.  If avgas is blown up and through the cylinders it's not likely to ignite--too much air in the air/fuel ratio (I'm guessing).  A massive fuel line rupture would be bad new but it might warn you by shutting off your engine or rough running.

 

You can leak a lot of oil from an engine with no fire.  Something like a ruptured oil line or oil cooler would show up on your oil pressure gauge.  What else is there that can burn?  An exhaust pipe break is a possibility.  It might burn your cowl but you might hear a change in engine noise and it's probably not going to take down the airplane.   I don't know how you'd position a fire detected system that warns of an exhaust break without being set-off by normal exhaust heat.

 

If a cylinder cracks you'll probably see that in the CHT and EGT guages.

 

There was  Lancair that burned up in Phase I in my area.  Pretty bad fire but he didn't need a fire detect system to tell him.  :-(

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There was  Lancair that burned up in Phase I in my area.  Pretty bad fire but he didn't need a fire detect system to tell him.  :-(

 

​The big difference is in a Lancair, the flames and smoke are obscuring your vision so, yes, it's pretty hard to miss.

​In a canard, you may experience some rough running or other signs but not notice that you are ablaze until you turn back to the airport and begin to wonder where all that smoke in the pattern is from.

 

​At least that seemed to be the case for Jack M. when his eRacer caught fire shortly after takeoff.

​That said, I don't recall him ever mentioning any measures he took to alert him as to the presence of a fire on his next eRacer.

 

​I like the Idea of a warning system but for daylight VFR, a rearview mirror would be a great start.

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Just an idea.

 

Run some soldering wire along the top cowling. One end to chassis ground, the other end to a single pole double throw relay to the coil. Positive on other side of the coil to energize it. Send positive to the normally close contact , through the relay then to the panel. At the panel, a simple red LED with a 1k resistor to indicate that the solder loop has broken, or melted. A second LED green can be added to the solder loop to verify that it is working properly.

 

All of this is very lightweight and inexpensive. Make sure you use a very low amp relay, also bench test it before installing it. A second loop can be run if you want redundancy.

 

Hope this was helpful.

Felipe

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