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  #121  
Old 05-14-2010, 07:32 AM
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Toobuilder Toobuilder is offline
 
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Originally Posted by RV7Guy View Post
Stein and I were talking about this today. So you've got your sensor in there and the light goes off, the horn sounds.

Now what do you do? Just curious.
Reminds me of a recent "upgrade" to the company jet...

A new glass cockpit display allowed the ability to see engine oil tank quantity, where as for the prior 40 years the aircraft was flying there was none. - the oil was checked on the ground only. Would you believe that as soon as the pilots got a new "toy" to play with, the maintainers started getting discrepancies? It took YEARS for engineering to finally convince the flying community that the wild swings in oil quantity were perfectly normal operation. There was even talk of disabling the oil quantity indication from the new display as the solution to the "problem".

Sometimes too much info is a bad thing.
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  #122  
Old 05-14-2010, 07:51 AM
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Quote:
Originally Posted by RV7Guy View Post
Stein and I were talking about this today. So you've got your sensor in there and the light goes off, the horn sounds.

Now what do you do? Just curious.
Illuminate the 'No Smoking' lamps.

Sorry, this thread needed a little levity. I'd say it depended what equipment you had in the tunnel. Close cabin heat, turn off boost pump, land flaps up as soon as possible. Be prepared to evacuate on landing. Turn fuel selector to Off as soon as practical on rollout and let the engine suck the system dry (or drier, anyway). I'm just guessing, really, but I think those would be prudent actions.

One thing that occurs to me; any way (short of a 'match' test, of course) to verify that such a warning light wasn't giving a false positive? I'd hate to have a light that cried 'Wolf!'; it'd probably take more years off my life than an actual incident like Todd's.
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  #123  
Old 05-14-2010, 08:38 AM
Bavafa Bavafa is offline
 
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For what ever it is worth:
After reading the Todd's horrifying experience and reading all the thoughts every body had in this subject, I got some what paranoid can decided to replace my 3003 fuel lines with 5052 lines. I should have done this when I built it but I didn't really know. So, yesterday I took the old lines out, all with the exception of the runs from the tank to the valve which I had less worry about and fabricated very carefully new lines. I inspected all the old lines and they all looked good with no sign of fatigue or bad flare. The plane has 185+ hours on it.

Gary,
Which flume detector are you using? Could you give us some feed back and have you tested it with AVGAS? I guess I am still some what paranoid and are considering installing one.
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  #124  
Old 05-14-2010, 10:01 AM
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Regarding the sensor, I think the response is pretty simple.

1) Don't turn on anything electrical inside the tunnel.
2) If you can shut off all electrical, go ahead and do it.
2) If you can shut off the fuel go ahead and do it.
3) And of course get on the ground.

The false positive indications are just something you'd have to test over time. Could the hydrocarbons in the exhaust activate it? Maybe; since we don't have a catalytic converter to aid in reducing them. Could adhesives set it off until they've really had time to cure? Yeah. Could fairly new resin set it off? Yeah. The boat sensors installed if fiberglass boats warn of false positives for the first year of the boats life.

Until you've spent time testing it, I don't think anyone is going to panic the first time the light comes on. Now if a 100 hrs have gone by and then the sensor light decides to come on? That's a whole new ballgame and sense of urgency. Everyone understands the possibility of a false positive and already knows how they would respond to a warning light early in the unproven sensors life.

Before I committed a hole for the lamp in my panel, I'd want to spend some time evaluating it first and make sure it's a feasible sensor for the application.

With two electrical motors (one is which isn't sealed and has brushes), the additional electrical items being added (or already installed) by the builder, and maybe O2 lines running through the tunnel, having the information is pretty critical. I'd like to know if gas vapors are circulating around my electric motors, wires, and devices. I'd hate to be 5 miles out at 3000 AGL and dropping flaps to find out I had vapors surrounding them.

One of the topics that hasn't been addressed is the possibility of static building in the airplane. The faster RV's can strip electrons out of the clouds and add them to the airframe. This could cause some arcing too. Not much you can do here to reduce it except for adding static wicks and bonding the surfaces of the airframe. But it is an ignition source that hasn't really been addressed yet. I'm not installing them on my airplane until I experience some issues with static.

It's best just to keep the fuel system tight and control what you can control through brush-less or sealed motors.

Phil

Last edited by Phil : 05-14-2010 at 10:04 AM.
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  #125  
Old 05-14-2010, 10:19 AM
TSwezey TSwezey is offline
 
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If the leak has more vapor than liquid, think tiny leak under high pressure, then the vapor is going to fill the entire cabin not just the tunnel. So you have to watch every electrical device. We did have static wicks on our airplane.
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  #126  
Old 05-14-2010, 10:24 AM
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Yeah I agree, Todd.

A high pressure pin hole leak could aid in vaporizing the fuel.
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  #127  
Old 05-14-2010, 11:20 AM
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Quote:
With two electrical motors (one is which isn't sealed and has brushes),...
Phil, have you looked at simply sealing the motor you have? At the low end of the scale a plastic bag and a few wraps of tape might do the job. Or a few dabs of silicone over the holes in the case. Doesn't need to be complicated, and I seriously doubt the motor needs ventilation for cooling purposes.
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  #128  
Old 05-14-2010, 12:19 PM
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IIRC, these holes are threaded------alternate use mounting holes it would seem.
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  #129  
Old 05-14-2010, 12:23 PM
Pat Stewart Pat Stewart is offline
 
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I have been watching this thread for a few days and have finally decided to add my 2 cents.

I have seen dozens of certified and experimental airplanes with blue streaks down gear legs, cowlings, belly?s and inside aircraft.

I make it a regular practice to keep a white cloth in my airplane to occasionally run under fittings just to see if there is any fuel residue. Hard fuel lines work well and have a proven track record.

IN MY OPINION the problem is the tunnel. In my tunnel I have the standard setup, filter, pump and FF transducer and lots of electrical wiring. That?s 7 connections in the tunnel not including the fuel selector valve; one will eventually leak from a sub standard flare or over tightening.

I also have insulation in my tunnel that will soak up fuel from a leak.

Here is my plan.

1. Move the filter out of the tunnel and hopefully into the wing root or if that?s not practical one under each front seat. This will require two filters vs. one. I see that as an improvement even without the fuel leak issue. I have never liked both tanks feeding to one fuel filter anyway. This will also eliminate the tight turn requirements between the fuel filter and fuel pump that can add to the problem.

2. Replace all hard lines with flex lines. Yes more expensive, yes weigh more, yes must be replaced over time, yes piece of mind is priceless. The flares are significantly less likely to leak but I will also say flex lines can and do sometimes fail. Not sure about fire sleeve as it can also soak up fuel.

3. Find a way to ventilate the tunnel. I have an extra port on my avionics cooling fan that could supply interior air to the forward end of the tunnel but I would need to find some way to provide an exit path in the rear of the tunnel. Also ventilating with interior air may not add any value after a few minutes unless the exit path is outside the airframe.

4. Remove the insulation.

Feel free to jump in and tell me the flaws in my ideas, that?s the real value of this forum.

Pat Stewart
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  #130  
Old 05-14-2010, 01:17 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by Pat Stewart View Post

IN MY OPINION the problem is the tunnel. In my tunnel I have the standard setup, filter, pump and FF transducer and lots of electrical wiring. That?s 7 connections in the tunnel not including the fuel selector valve; one will eventually leak from a sub standard flare or over tightening.

Feel free to jump in and tell me the flaws in my ideas, that?s the real value of this forum.

Pat Stewart
I think one flaw is that you are still flying an airplane that you feel has substandard flares or flares that have been over tightened.

If you believe that, then by all means make new lines and correct the problems that you think are lurking in your airplane.

As for the other stuff...I don't see any point in going to all of that work modifying your fuel system when there is not a shred of evidence to point to anything at all specific as a cause of Todd's accident. It is very possible that his fuel system was not even close in design to what the standard fuel system in an RV-10 is.

Moving the fuel filter(s) (it would require you modifying to use two) under the seats? I am not sure what that would gain. This entire area is common with the tunnel. There are structural partitions, but they are full of holes so it is one common area as far as fumes go.

It has already been said in numerous posts but I will repeat it once more in case some people missed it...
It makes no sense to modify a fuel system only out of speculation that there might be a design problem. Any modification you do has the potential to induce an unanticipated problem, all in the interest of fixing a problem that may not even exist.
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