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  #1  
Old 10-06-2014, 09:34 AM
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Low Pass Low Pass is offline
 
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Default Insulating Fuel Distribution Lines

Trying to correct the popping and irregular idle on an IO-360 (Bendix system), I am to the point that I believe insulating the distribution lines would help. Since I believe this is occurring as a result of the fuel in the lines flashing and pushing fuel into the cylinders at a sporadic and high rate, insulation seems to be the next step.

However, I have heard here and there, that this is not recommended. Why? Mine are braced very well using at least two points of attachment though the run. So I can't see the added mass being a dynamic issue.

If it's about inspecting for damage/cracks, etc., this can be done occasionally if the insulation is made removable (gotta figure that one out).

If anyone has info or experience with this, can you please pass it along?

Thanks,

Bryan
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  #2  
Old 10-06-2014, 10:36 AM
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I'm curious as well on doing this. I'm not able to get a smooth idle at all when the engine is hot. I have Airflow Performance FI with the purge valve, so at least I can cool down the fuel lines forward of the injector lines. I've done all the usual checks for leaks and have set the idle mixture correctly. I have to keep the engine spinning at 1000 RPM or it will die taxiing off the runway. This forces me to use my brakes excessively during taxi.

I'm thinking of putting some Heat-Reflective Wrap-Around Sleeving from McMaster-Carr on the lines to see if that might have any difference. The other thought would be to add a cooling shroud around the fuel pump on the engine with a dedicated blast tube.
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  #3  
Old 10-06-2014, 10:50 AM
Rupester Rupester is offline
 
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Default May not be pertinent to your case, but ....

... many of us with cooling plenums, S James or otherwise, believe the problem is exacerbated. During idle and taxi modes, when OATs are above 80-85F, the vaporization problem is most pronounced. That plenum that works so well during flight modes offers a smaller area/space for dissipation of heat during lo speed ops.
If possible, going to smaller injection restrictors raises the back pressure in the lines and helps a little bit, but does not cure the problem. (Don at AirFlow Performance has been very helpful with this.) My IO-320 came with .028 restrictors normally installed on IO-360s; with Don's advice I downsized them all to .022 - which helped quite a bit.
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  #4  
Old 10-06-2014, 04:45 PM
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This is pretty common on all mechanically injected engine installs, even certified ones. You'll see it on M20J's a LOT as well as Dimondstars. The question I have for you is why you are defining this as a 'problem' as opposed to a normal operation for the system you have.

The "fix" is an electronic FI system or carburetor. Insulating the fuel lines won't make a difference at all from my limited experience. But once again, it's a characteristic of the system you have, not a problem.
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  #5  
Old 10-06-2014, 05:59 PM
David-aviator David-aviator is offline
 
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I do not believe insulating the lines will help. The fuel pressure in these lines is very low and the entire area is heat soaked metal.
My solution is to get air borne ASAP.
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  #6  
Old 10-06-2014, 06:32 PM
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Quote:
Originally Posted by Rupester View Post
... many of us with cooling plenums, S James or otherwise, believe the problem is exacerbated
The plenum lid doesn't allow post-shutdown ventilation via the oil door (4-cyl models), but would have no effect when running. Size of the chamber is moot. The issue is heat transfer rate from the local environment to the fuel, which is always being replaced in any given line with fresh fuel.

Three possible solutions; slow the heat transfer rate, increase the fuel flow rate, or increase the fuel pressure. Insulation slows transfer. More throttle increases flow rate and pressure. Smaller nozzles increase pressure.
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Old 10-07-2014, 04:37 AM
David-aviator David-aviator is offline
 
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Quote:
Originally Posted by David-aviator View Post
I do not believe insulating the lines will help. The fuel pressure in these lines is very low and the entire area is heat soaked metal.
My solution is to get air borne ASAP.
To add to my thoughts on the subject, if the lines are insulated they will also be insulated from air flow heat transfer once off the ground.

Dan Horton has a better understanding of heat transfer than do I so I agree with his conclusion. There is no easy complete solution to the problem on the ground with a hot engine. Its been that way since fuel injection was invented with these engines.

I do not consider it a big deal once you understand what the issue is. Increasing flow rate by higher engine rpm, smaller nozzle size, and insulation will help but the best solution is WOT and getting off the ground. I would not want the flow divider lines insulated in flight.
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  #8  
Old 10-07-2014, 12:14 PM
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Quote:
Originally Posted by David-aviator View Post
To add to my thoughts on the subject, if the lines are insulated they will also be insulated from air flow heat transfer once off the ground.

Dan Horton has a better understanding of heat transfer than do I so I agree with his conclusion. There is no easy complete solution to the problem on the ground with a hot engine. Its been that way since fuel injection was invented with these engines.

I do not consider it a big deal once you understand what the issue is. Increasing flow rate by higher engine rpm, smaller nozzle size, and insulation will help but the best solution is WOT and getting off the ground. I would not want the flow divider lines insulated in flight.
I fully understand the variables and heat transfer conditions involved. As for being typical, this is not true. Six months ago I switched from an IO-320 to IO-360. I had a Silver Hawk system on the -320 that idled beautifully - very smooth with no issues. This one's Bendix.

Last edited by Low Pass : 10-07-2014 at 04:25 PM.
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  #9  
Old 10-07-2014, 12:27 PM
BillL BillL is offline
 
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Quote:
Originally Posted by Low Pass View Post
I fully understand the variables and heat transfer conditions involved. As for being typical, this is not true. Six months ago I switched from an IO-320 to IO-360. I had a Silver Hawk system on the -320 that idled beautifully - very smooth with no issues. This one's Bendrix.
Doesn't this mean that there is a calibration solution as opposed to a design solution? I am just recalling some previous posts that mentioned a method (spring) to increase the pressure to the distribution block (spider) that largely eliminated this issue? It seemed to be the drain back diaphragm spring in the distribution block that gave higher pressure drop and therefore higher liner pressure up to the block.

Maybe the question should be: How is the Bendix design/calibration different that it presents this behavior?
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  #10  
Old 10-07-2014, 01:18 PM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by Low Pass View Post
Trying to correct the popping and irregular idle on an IO-360 (Bendix system), I am to the point that I believe insulating the distribution lines would help...

...If it's about inspecting for damage/cracks, etc., this can be done occasionally if the insulation is made removable (gotta figure that one out)...
2 random thoughts:

1. They make fuel line insulation blankets for race cars that simply slip over the line and is velcro'd in place. Check with Summit Racing, et.al.


2. There are many Bendix equipped airplanes that idle (relatively) fine. I've had 3 in a row now and I've never had any die at a low idle. I'd be looking hard for any problems specific to your aircraft before trying somewhat "unconventional" fixes.
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Last edited by Toobuilder : 10-07-2014 at 01:23 PM.
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