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  #1  
Old 01-04-2020, 01:52 AM
agent4573 agent4573 is offline
 
Join Date: Aug 2019
Location: Mountain view
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Default Fire suppression systems, worth it?

Does anyone use a fire suppression system in their RV? Planning on a 7 build that will be used for some entry level acro competition before we get a dedicated acro plane. Was planning on doing the Ti firewall and belly pans, but wasn't sure if a suppression system in the engine made sense. Bottle would be mounted behind the seat. A few questions:

There's a few Halon replacements out there, one is a cold gas type that I want to avoid because it will likely supercool the cylinders and cause engine damage. The other options are a gas or aqueous foam.

Is Halon gas effective in an engine bay with as much airflow as the RV cowl? 3 nozzles come with the kit, plan was one on the battery and one on each side of the engine.

Should the engine nozzles be under the engine aimed at the exhaust or on top of the motor so it gets sucked through the fins and dispersed as it flows down? Should they be on the front of the plenum faced towards the firewall or on the back of the motor facing forward?

If anyone has worked an acro team or a reno team that used a suppression system, any details would be great. Can't find much info on Google. Thanks.
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  #2  
Old 01-06-2020, 09:56 AM
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RV7A Flyer RV7A Flyer is offline
 
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Quote:
Originally Posted by agent4573 View Post
one is a cold gas type that I want to avoid because it will likely supercool the cylinders and cause engine damage.
I have no idea if any of these systems would work on an aircraft engine such as an RV, but...

If I'm on FIRE, the very least of my concerns would be engine damage due to cooling from the fire suppression system.

As a wiser man than me once said:

"How much does a new engine cost?

Not as much as a new behind."
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  #3  
Old 01-06-2020, 12:02 PM
krwalsh krwalsh is offline
 
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Default AFFF

I installed a fires suppression system in my (non-RV) plane. But I did it because it is a pusher configuration and it is much more difficult to know if you have a fire situation until it is probably too late to simply shut off fuel and master and hope it goes away. Realistically an AFFF system has little to no chance against a 200mph wind going through the cowl. On the ground I think it would be much better.

The race car suppliers all have good systems that are relatively inexpensive and lightweight. I hope to never find out if mine is effective.
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  #4  
Old 01-06-2020, 12:08 PM
McStevens McStevens is offline
 
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A desire that systems not needlessly damage your aircraft and recognizing your life takes a higher priority than a machine are not mutually exclusive...
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  #5  
Old 01-06-2020, 01:21 PM
agent4573 agent4573 is offline
 
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Quote:
Originally Posted by RV7A Flyer View Post
I have no idea if any of these systems would work on an aircraft engine such as an RV, but...

If I'm on FIRE, the very least of my concerns would be engine damage due to cooling from the fire suppression system.

As a wiser man than me once said:

"How much does a new engine cost?

Not as much as a new behind."
True. I was hoping it would be possible to cover a battery fire situation without ruining a perfectly good motor though. I think my biggest concern though is how effective are any of these systems in at 75 knots? I can likely get to best glide speed before pulling the fire handle, but I don't know if any Halon is effective with that much air flow through the bay.
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Old 01-06-2020, 01:44 PM
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RV7A Flyer RV7A Flyer is offline
 
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Quote:
Originally Posted by McStevens View Post
A desire that systems not needlessly damage your aircraft and recognizing your life takes a higher priority than a machine are not mutually exclusive...
True, and I hadn't considered the idea of putting out a ground fire (but the case mentioned, a battery fire, may not be stoppable without a means of cutting the electrical circuitry driving it). And the OP seems to be talking about fire in flight, not on the ground (on the ground, pull the mixture to ICO et voilá! No more airflow, so the original question is moot).

As far as damage vs. safety-of-life...BRS seems like a case in point one way .
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Old 01-06-2020, 01:47 PM
tgmillso tgmillso is offline
 
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In an engine fire you will likely turn the fuel off and have the nose poked down in a max rate descent. Your priority should be to get on the ground as soon as possible and exit the aircraft. Bleeding speed just to activate the suppression system is a bit of false economy. The beauty about the belly/firewall insulation found elsewhere on this site is that it will help buy you some time during the descent.

Alternatively, buy a parachute, insurance and put pull pins on your canopy to make it easily jettisonable.

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  #8  
Old 01-06-2020, 01:54 PM
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DanH DanH is online now
 
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Quote:
Originally Posted by agent4573 View Post
Is Halon gas effective in an engine bay with as much airflow as the RV cowl?
There are a few ways to look at the question. Perhaps one is from the standpoint of mass flow. The Lycoming charts suggest most RVs are flowing 1.5 to 2 lbs of air per second. Let's go with 2 lbs to make it easy.

Halon replacements seem to require a concentration of 600 to 900 grams per cubic meter. I'll use 900 for this example. There are 35.315 cubic feet in a cubic meter, so the required concentration becomes 900/35.315 = 25.5 g/ft^3.

At 1000 MSL, standard day, 2 lbs of air is about 27 cubic feet. So, to reach the necessary minimum concentration of fire suppressant, you would need to discharge about 700 grams per second, or roughly 1.6 lbs if I have not screwed up a term somewhere. It would be a little less at a higher altitude.

So what is the required concentration, capacity, and discharge rate of the system you're considering?
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Last edited by DanH : 01-06-2020 at 01:58 PM.
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  #9  
Old 01-06-2020, 02:20 PM
PilotjohnS PilotjohnS is offline
 
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Default Alot

Thats a lot of stuff to discharge. And assume this has to stay around long enough to prevent re ignition, seems like it might not be practical unless source can be quickly eliminated.
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WARNING! Information presented in this post is my opinion. All users of info have sole responsibility for determining accuracy or suitability for their use.

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  #10  
Old 01-06-2020, 04:58 PM
krwalsh krwalsh is offline
 
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Default Ground Fire

This was the specific case I was thinking of when I bought my fire suppression system and installed it:

http://www.deford.com/cozy/fire.html

Granted, I took other lessons from this, including making sure firewall pass throughs were either fused, connected to battery contactors before the energy source got to the firewall, etc.
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