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10-06-2014, 09:34 AM
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Join Date: May 2006
Location: Houston
Posts: 2,012
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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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10-06-2014, 10:36 AM
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Join Date: Mar 2008
Location: Ramona, CA
Posts: 2,370
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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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10-06-2014, 10:50 AM
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Join Date: Dec 2005
Location: Mahomet, Illinois
Posts: 2,195
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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.
__________________
Terry Ruprecht
RV-9A Tip-up; IO-320 D2A
S. James cowl/plenum
(Dues paid thru Nov '18)
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10-06-2014, 04:45 PM
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Join Date: Aug 2005
Location: Pasadena CA
Posts: 2,484
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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.
__________________
Stephen Samuelian, CFII, A&P IA, CTO
RV4 wing in Jig @ KPOC
RV7 emp built
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10-06-2014, 05:59 PM
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Join Date: Feb 2005
Location: Chesterfield, Missouri
Posts: 4,514
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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.
__________________
RV-12 Build Helper
RV-7A...Sold #70374
The RV-8...Sold #83261
I'm in, dues paid 2019 This place is worth it!
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10-06-2014, 06:32 PM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by Rupester
... many of us with cooling plenums, S James or otherwise, believe the problem is exacerbated
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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.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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10-07-2014, 04:37 AM
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Join Date: Feb 2005
Location: Chesterfield, Missouri
Posts: 4,514
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Quote:
Originally Posted by David-aviator
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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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.
__________________
RV-12 Build Helper
RV-7A...Sold #70374
The RV-8...Sold #83261
I'm in, dues paid 2019 This place is worth it!
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10-07-2014, 12:14 PM
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Join Date: May 2006
Location: Houston
Posts: 2,012
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Quote:
Originally Posted by David-aviator
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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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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10-07-2014, 12:27 PM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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Quote:
Originally Posted by Low Pass
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.
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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?
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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10-07-2014, 01:18 PM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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Quote:
Originally Posted by Low Pass
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)...
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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.
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
Last edited by Toobuilder : 10-07-2014 at 01:23 PM.
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