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-   -   a couple printed ideas (https://vansairforce.net/community/showthread.php?t=147771)

Snowflake 04-20-2017 09:03 AM

Quote:

Originally Posted by RV7A Flyer (Post 1166905)
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.

RV7A Flyer 04-20-2017 11:26 AM

Quote:

Originally Posted by Snowflake (Post 1167048)
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!)

Snowflake 04-21-2017 08:42 AM

Quote:

Originally Posted by RV7A Flyer (Post 1167084)
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... :)

Steve Melton 04-23-2017 06:58 PM

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?










Snowflake 04-24-2017 08:52 AM

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.

Bill Boyd 04-24-2017 09:43 AM

Quote:

Originally Posted by Snowflake (Post 1167953)
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.

For everything else, there's GOOP / E-6000 adhesive ;)

What's the compatibility of the plastic with this type of stick-um?

Steve Melton 04-24-2017 11:05 AM

Quote:

Originally Posted by Snowflake (Post 1167953)
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.

I tried the nylon tipped set screw but didn't like it. It's too slick. Need some friction to achieve a secure hold. Why would the sump boss be installed in the inside of the tank and allow trapping water? That's not in the direction of goodness.

One time I needed to drain my tank away from the home base because of low octane fuel contamination. It was nice to be able to remove the JD fairing easily. I wanted the same with these plastic fairings. So far I have not used any adhesive on the fairing and they have been secure.

The brass sleeve prevents a set screw mark on the alum boss. From my research, the galvanic corrosion of yellow brass C260 and 6060-T6 should be minimal. If you don't mind a little set screw mark on the drain boss then the original Rev 1 fairing is the way to go. Otherwise use the Rev 2 fairing with the brass sleeve.

The torture test on the pipe is on going. One with two turns and one with three turns after contact. There have been no failures. I am amazed that the insert nut can hold the load.

Steve Melton 04-24-2017 11:10 AM

Quote:

Originally Posted by Bill Boyd (Post 1167975)
For everything else, there's GOOP / E-6000 adhesive ;)

What's the compatibility of the plastic with this type of stick-um?

I'm sure the GOOP would provide a secure bond since ABS plastic is used for a lot of trim on cars. It may be so good that you would need to chisel it off. I would use VC-3 sparingly if choosing an adhesive for these since it remains relatively soft in case you needed to remove the fairing to drain the tank. So far I have not used any adhesive.

Berchmans 04-24-2017 05:52 PM

Dis-similar metals
 
Why not use a piece of Aluminium tubing?

Steve Melton 04-24-2017 06:10 PM

Quote:

Originally Posted by Berchmans (Post 1168122)
Why not use a piece of Aluminium tubing?

yep, I looked but the right size was only avail in brass. help me find similar in alum.

Brass C260 Seamless Round Tubing, 13/16" OD,0.755"ID, 0.029" Wall


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