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  #91  
Old 04-19-2017, 05:14 AM
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Default more testing

fuel soaked fairing, another week on the torture pipe. no signs of relaxation.



another fairing soaked three weeks in avgas. VC-3 thread lock turned pink but otherwise seemed secure. turned set screw one full turn on the torture pipe. no signs of weakness.



attempting to drive this fairing to failure. fuel soaked one week. two turns of the set screw. significant load and twist in the allen wrench. no immediate failure. will leave it on the pipe for a couple weeks.





My photo of a Grand Canyon California Condor last week, ~ 10ft wing span. It was making fwd progress in a 40 kt headwind without flapping. Check out those wing tips.

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RV-9A, Tip-up, Superior O-320, roller lifters, 160HP, WW 200RV, dual impulse slick mags, oil pressure = 65 psi, EGT = 1300F, flight hours = 600+ for all

Simplicity is the art in design.

Last edited by Steve Melton : 04-19-2017 at 05:25 AM.
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  #92  
Old 04-19-2017, 03:20 PM
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FYI - On Friday I placed a couple of test pieces of PLA-printed parts into an avgas bath to check durability. No degradation was visible by Saturday evening, will check again this weekend to see how they're doing. So far, i'd say PLA parts are acceptable for the bottom of the wing.
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  #93  
Old 04-19-2017, 03:32 PM
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Are y'all expecting your fuel drains to leak continuously?

If they don't leak like a sieve, isn't the drain fairing *dry* all the time, other than on occasional drop of fuel when you check it during pre-flight?

Weeks on end in avgas soak test seems, um, overkill to me...
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  #94  
Old 04-19-2017, 03:38 PM
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well yeah, now is the time to kill them if we can.
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Cincinnati, OH
RV-9A, Tip-up, Superior O-320, roller lifters, 160HP, WW 200RV, dual impulse slick mags, oil pressure = 65 psi, EGT = 1300F, flight hours = 600+ for all

Simplicity is the art in design.
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  #95  
Old 04-20-2017, 07:20 AM
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Quote:
Originally Posted by RV7A Flyer View Post
Are y'all expecting your fuel drains to leak continuously?

If they don't leak like a sieve, isn't the drain fairing *dry* all the time, other than on occasional drop of fuel when you check it during pre-flight?

Weeks on end in avgas soak test seems, um, overkill to me...
No harm in doing the test.
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  #96  
Old 04-20-2017, 09:03 AM
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Quote:
Originally Posted by RV7A Flyer View Post
Weeks on end in avgas soak test seems, um, overkill to me...
Well, that's exactly the point of a stress test. It exposes the system to worst-case scenarios and sees what happens.

Someone mentioned earlier that the PLA material that is easiest to work with on the 3D printers might be a bad choice for fuel fairings as it's sensitive to almost everything. My first test was fuel, next will be sun exposure for a week (as soon as I find somewhere with a week of sun). The sun test will be worst-case, too, as these will live under the wing in the shade. Even if I have a pitch- or roll-control problem occasionally I suspect the cumulative time spent inverted isn't climbing that fast...

Of course, in this case, if the material did break down I suspect my only risk would be to lose the fairing... And with gravity and downwash I suspect it wouldn't hit any other part of the airplane while departing (unless my flaps were down, I guess). So it's all very low risk to start with.
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  #97  
Old 04-20-2017, 11:26 AM
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Quote:
Originally Posted by Snowflake View Post
Well, that's exactly the point of a stress test. It exposes the system to worst-case scenarios and sees what happens.

Someone mentioned earlier that the PLA material that is easiest to work with on the 3D printers might be a bad choice for fuel fairings as it's sensitive to almost everything. My first test was fuel, next will be sun exposure for a week (as soon as I find somewhere with a week of sun). The sun test will be worst-case, too, as these will live under the wing in the shade. Even if I have a pitch- or roll-control problem occasionally I suspect the cumulative time spent inverted isn't climbing that fast...

Of course, in this case, if the material did break down I suspect my only risk would be to lose the fairing... And with gravity and downwash I suspect it wouldn't hit any other part of the airplane while departing (unless my flaps were down, I guess). So it's all very low risk to start with.
That was kind of my point...although I can see the "fun" part of subjecting these things to all of these tests, I'd say you satisfied them within a few hours to a day of soaking the thing in gas.

Make a couple, put them on and go fly and see how it holds up. Part of the advantage of 3D printing is the ability to rapidly prototype parts, test them, subject them to field conditions, and update the design accordingly and re-manufacture.

Instead of weeks of unnecessary testing and waiting for the results, you could have saved a fraction of a gallon of gas and gone 1/10th of a knot faster this whole time! (J/K...I have the JD Air Parts fairings on my fuel drains AND my vents!)
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  #98  
Old 04-21-2017, 08:42 AM
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Quote:
Originally Posted by RV7A Flyer View Post
That was kind of my point...although I can see the "fun" part of subjecting these things to all of these tests, I'd say you satisfied them within a few hours to a day of soaking the thing in gas.
Oh, I agree. But after two days, I knew I wouldn't get back to the airport for a week and didn't have anything else to do with the test piece... So I just left it sitting in the gas.

Quote:
Make a couple, put them on and go fly and see how it holds up. Part of the advantage of 3D printing is the ability to rapidly prototype parts, test them, subject them to field conditions, and update the design accordingly and re-manufacture.
As it turns out, the first ones I made don't fit well because the hole that matches the flange is *just* a little too small, and the hole for the boss that the set screw binds on is way too big. So tightening the set screw pulls the whole thing off-center and it doesn't fit the wing anymore.

I've already modified the design and am now just waiting for time on the printer to make more... One of the downsides of using downtime on the printer at work is that you have to wait for downtime... But that issue will be fixed in a month or so... I ordered my own printer...
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  #99  
Old 04-23-2017, 06:58 PM
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Default brass to alum galvanic corrosion?

a brass tube (C260) section fits nicely into this fuel drain fairing and protects the alum drain boss from the set screw turning and provides a secure fit but is it a source of galvanic corrosion?









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Steve Melton
Cincinnati, OH
RV-9A, Tip-up, Superior O-320, roller lifters, 160HP, WW 200RV, dual impulse slick mags, oil pressure = 65 psi, EGT = 1300F, flight hours = 600+ for all

Simplicity is the art in design.

Last edited by Steve Melton : 04-23-2017 at 07:12 PM.
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  #100  
Old 04-24-2017, 08:52 AM
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Steve, what about using a nylon-tipped setscrew if you're concerned about marking the boss on the tank?

I came across another issue last weekend as well... Some builders put the flange on the inside of the tank. That puts the boss too close to the wing to get a set screw to bind on.
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