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  #21  
Old 03-22-2021, 11:47 PM
FireMedic_2009 FireMedic_2009 is offline
 
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Default I'm the person who this post is about

I'm the one this post is about. The pic of the fuel line touching the engine mount was a pic I sent to Dan. The fuel line (servo hose) was disconnected from the 'T' fitting, notice how many threads are showing between the 'T' fitting and the 90 deg elbow on the fuel pump. Once the line was connected it was not touching the mount with at least an 1/8” or more gap clearance from the engine mount. Is the clearance enough? I don’t really know. Maybe, maybe not. I’m not sure how much movement there is at that location but that could be another possibility. The ‘T’ fitting was a 37 deg flare as verified by the FAA. The 90 deg elbow with the tap (KB-90-T) for the fuel pressure line shown in Post #1 could not have been used due to the close proximity of the oil cooler. Although hard to see in the pic Dan posted, the oil cooler was less than an inch from the end of the elbow. I would have had to use the 90 deg elbow without the tap (KB-90) and tap a hole on the adjacent face of the elbow pointing to the firewall which I was planning to do. And of course I could not have used the fitting posted in #7. I went to buy AN nuts for some tubing and unfortunately I found the ‘T’ fitting at the local pro shop and thought, “problem solved”.

When I emailed Dan the pic he has posted, he stated that it probably didn’t matter how tight I tightened the nut, it was bound to loosen at some point. As Dan pointed out in the beginning, “a string of fittings with a line leading off at a right angle to the primary thread axis. An offshoot line arranged that way can easily become a lever, providing torque to unscrew one of the connections.” Not only was the fuel pressure line a lever but the servo hose (fuel line) was as well since it had a 90 deg on the end where it connected to the black ‘T’ fitting as shown in the picture and in my opinion probably more of a lever since it was a bigger, heavier and less flexible than the fuel pressure line. So with the engine vibrating and the hose not secured to the engine allowing it to shake around, it possibly hit a resonant frequency, assuming it even needed a resonant frequency to come loose which may not be the case, where the engine was moving in one direction and the hose (lever) was moving in the opposite direction causing maximum leverage to loosen the nut and eventually spinning off in a couple minutes or less. I say this because I remember after I primed the engine I pulled the mixture out and turned off the electric fuel pump. The fuel pressure held steady at 28psi for a few seconds before I started the engine. If it had a slight leak I would have seen the fuel pressure drop at least a couple of psi in the 3-4 seconds before I turned over the engine. So it wasn’t like I had an hour or two of flight time which slowly loosened the nut when it finally loosened and disconnected. It’s my opinion it loosened and disconnected within 5 minutes after takeoff. And to be clear in case there was some confusion, the black nut on the ‘T’ loosened and spun off completely from the 90 deg elbow on the fuel pump. The 90 deg elbow on the fuel pump did not loosen or come off. Mechanically it would be impossible for the elbow to rotate more than 20 degrees in either direction.

Let me tell you the rest of the story from the beginning. This was the second time it happened. The first time it happened was 2 days earlier and had 3.4 hrs (several flights) before the exact same thing happened. I landed the plane safely in a cow pasture on Super Bowl Sunday, Feb 8th. I met with the FAA the next morning and discovered what happened. Even though he say he never heard of a B nut coming loose, we thought maybe it wasn’t tightened enough and it came loose. However since I was unable to tighten the nut from the rear like I had the first time now that everything else was installed, I had to use a cut wrench in order to tighten it. I was able to pull directly towards myself with all I had and thought I had tightened it enough. I was only 6 miles away from Zephyrhills airport where I had completed the plane. I took off from the field and landed at Zephyrhills and then an hour later I flew it to Tampa Executive airport which was 16 miles away and landed. The 2 flights totaled 0.3 – 0.4 hrs. The next day I departed Tampa Executive and the rest is history.

A week or so after the accident I wanted to find out how tight I could have tightened the nut with the shortened wrench. I won’t bore you with the details of how I determined it. A 6AN nut torque range is 150-195 in-lbs. If you tighten the nut to 150 in-lbs it will loosen at about 130 in-lbs give or take a few in-lbs. I tightened the nut 3 times using the shortened wrench. The following were the results: 131, 118, 138 in-lbs. Yes, I barely may have torqued to the minimum at best case. But let’s say I only torqued it to 140 or even 135 in-lbs. It only took 0.5 hrs to loosen the second time and 3.4 hrs to loosen the first time. Since it was a new engine I ran the engine hard (high MP and high RPM's) except for taxi and landings. There was only one other time and it was only to determine my stall speed for maybe a couple minutes. So is it correct to deduce if it took 3.4 hrs to loosen the first time and 0.5 hrs to loosen the second time the nut had to be tightened to at least 150 in-lbs? How much more, who knows? The point I’m trying to make is it’s most likely the nut came loose the first time due to the lever forces by the fuel line(s) turning the fitting resulting in loosening the nut than the nut not being tightened enough. So Dan’s opinion/theory is a pretty valid argument. And no I’m not contradicting myself by comparing higher torque vs time to disconnect but rather by the number of times I could have hit the resonant frequency in 3.4 hrs of flight time compared to 0.5 hrs of flight time and that is assuming it needed to hit the resonant frequency to cause it to come loose.

I’ve spoken to another person who use to be a DAR and he shares the same opinion as Dan. The co-owner of my plane spoke to another person who’s an A&P and the A&P has the same opinion.

Whether you agree with Dan’s opinion or not is irrelevant. Just be aware and if in doubt, drill holes in the nut to safety wire it or blue locktite the threads. I hope this helps someone in avoiding the grief I’ve been through. Yes I’m lucky I didn’t get seriously hurt or killed but it still sucks. FYI. Did you know that while a plane is in Phase 1, the deductible is not $500 but 10% of the hull coverage? Well now you know.

Now I can’t get insurance for a year or two because I have a major claim. I have had a perfect record up til now, no FAA violations or incidents, and no damage to aircraft or other claims. I have 882 TT, 471 hrs in RV6’s and 7’s in the last 5 yrs and IFR cert.
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Last edited by FireMedic_2009 : 03-22-2021 at 11:59 PM.
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  #22  
Old 03-23-2021, 07:17 AM
TS Flightlines TS Flightlines is offline
 
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I have to say this thread got my attention. Not real sure why the oil cooler location would be close enough to the fuel pump so the OP would have to create a pretty custom pump discharge fitting. The other that caught my eye was the routing location of the discharge hose. Inmost all cases, we route it inside that tube that Dan has shown with the 'contact' arrow, so it routes smoothly. Now the plans DO show the hose 90* fitting at the pump, and the straight to the carb/servo. We found that in some cases this gets the hose pretty close to the exhaust, so we reverse it, straight at the pump, routing down and forward, then the 90* connects to the carb/servo.

Same flow, but no leverage on the fittings.

Tom
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  #23  
Old 03-23-2021, 07:59 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by Northernliving View Post
Here are some photos of a test fit using a 45* restricted fitting to the manifold on the firewall with the fuel pressure sensor.
Sorry Brian, missed your reply a week or more ago.

The key is to arrange hoses so there is no torque which can unscrew a fitting. Put another way, so no hose can be the handle of the wrench.

So, looking at yours, I would ask if the -6 hose with the brown firesleeve is attached to the engine somewhere just out of sight, so engine shake and hose mass cannot loosen the gland nut fitting in the pump. Alternately (and more likely in your case), given the hose runs to an updraft servo, the hose is probably quite short, self-secured if you please, and thus not an issue.

Personally I would rather see a straight restrictor fitting for the fuel pressure tap, and a longer hose. However, here the hose and fitting approximately aligns with the plane of the big engine shake, so shake and hose mass does not apply a torque....good to go.
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  #24  
Old 05-03-2021, 06:45 AM
BillL BillL is offline
 
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Was that tee fitting in post #1 (the black one) aluminum or steel? It kinda looks like an Earl aluminum fitting. Way lower torque.
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  #25  
Old 05-03-2021, 08:51 AM
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wirejock wirejock is offline
 
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Default Fuel lines

I just assembled the fuel lines. This thread got me worried so here's my install.
Vans fittings except the pressure fitting is a 90. Vans provides a 45.
No Adel clamps yet.
It bothers me that Vans supplies these parts and there are a lot of RVs flying with them.
I can still disassemble and make changes.
The oil cooler in the photo is not permenantly mounted. I was checking oil lines.
Advise appreciated.
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  #26  
Old 05-03-2021, 08:59 AM
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rv6ejguy rv6ejguy is offline
 
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Quote:
Originally Posted by FireMedic_2009 View Post

A 6AN nut torque range is 150-195 in-lbs. If you tighten the nut to 150 in-lbs it will loosen at about 130 in-lbs give or take a few in-lbs.
Breakaway torque on fasteners and threaded fittings should always be higher than the rolling torque applied when tightened. Something has likely deformed otherwise, reducing tension/ friction on the threads.
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  #27  
Old 05-03-2021, 11:28 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by wirejock View Post
I just assembled the fuel lines. This thread got me worried so here's my install.
Need to reroute so the pump-to-servo line is not contacting that motor mount tube. See attached.

Quote:
Vans fittings except the pressure fitting is a 90. Vans provides a 45.
No Adel clamps yet.
Compared to a 45, a 90 increases the leverage applied by the hose. However, clocking makes a difference. If this 90 was pointed straight up, or down and them looped back up to the sensor, it would apply zero torque to the pump fitting when the engine rotates around the crank axis. Think of it as pointing the fitting parallel to the plane of engine rotation, not perpendicular.

Quote:
It bothers me that Vans supplies these parts and there are a lot of RVs flying with them.
Two points. One nothing about your install is a bad as the original thread subject. Two, it's standard hardware. The issue is how it's used. Think of it this way...guns don't kill people. People kill people.
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  #28  
Old 05-03-2021, 01:08 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by DanH View Post
Two, it's standard hardware. The issue is how it's used.
I agree.
Proper installation can be done using the supplied parts without having interference like that shone in the photo.
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  #29  
Old 05-03-2021, 03:37 PM
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wirejock wirejock is offline
 
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Default Proper Installation

Quote:
Originally Posted by rvbuilder2002 View Post
I agree.
Proper installation can be done using the supplied parts without having interference like that shone in the photo.
I took it all apart.
Perhaps a photo of a "proper installation" would be helpful. I can't find a combination that clears the new "A" model motor mount when the fitting is clocked correctly at 180. Maybe a new hose or fitting is required. I also don't have the exhaust on yet.

Vans DWG 46A shows the K-090 fitting clocked about 210 degrees and OP-32 shows the VA-128 restrictor fitting clocked about 45 degrees. See photos. Maybe I'm missing something but isn't this contradictory to "pointing the fitting parallel to the plane of engine rotation, not perpendicular."

DWG 46A
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Photo KB-90-T clocked about 150 degrees. Fuel line clears everything but the fitting is not 0-180.
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Photo Reversed the hose with the 90 at the servo and straight into the pump fitting.
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Donated 01/01/2021, plus a little extra.
RV-7A #73391, N511RV reserved (2,000+ hours)
HS SB, empennage, tanks, wings, fuse, working finishing kit
Disclaimer
I cannot be, nor will I be, held responsible if you try to do the same things I do and it does not work and/or causes you loss, injury, or even death in the process.

Last edited by wirejock : 05-03-2021 at 03:46 PM.
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  #30  
Old 05-03-2021, 04:10 PM
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bjdecker bjdecker is offline
 
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Larry,

The hose placement in DWG 46A is for an O-320/360 engine and not the IO-360-B (or M) that you have. OP-32 is for the IO-360-A1B6 which is closer to the -B (or M).

What you had at 150 or thereabouts is just fine and won't break anything, there's no reason that the K-090-T has to be clocked at EXACTLY at 6o'clock - but do use the 45degree AN with restrictor for the fuel pressure line.

And for what it's worth, the VA-136 might have been cut a little long, necessitating the 150 rotation on the K-090-T.

*edit* added picture of initial installation on IO-360-A1B6 (Angle Valve 200HP).

B
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