Buy solder-tip cleaner and tinning. 

Blackened soldering iron tips are usually caused by running the iron too hot and the solder boiling off the more volatile components of the solder. Not good to solder using a black tip either.

Periodically clean the tip using a tip cleaner,(those bronze colored scrub pad looking things) then re-tin the tip(usually a white looking compound in a small round tin). Turn it off when it isn’t being used.

Weller  soldering guns and stations are great, but everything needs maintenance.

thanks!  prior to this message, I concluded two things:  1) acid core solder containing lead was working fine even if it wasn't as pretty as what I've been using that has been giving me this recent problem.  I was scared away from it because somebody warned me of the health risk of breathing in lead fumes.  2) the problem seems to be recent and date to when I started using pluming flux, which one post on a question site said wrecks the surface treatment of the soldering gun tip, which seems to be born out by my experiments.  so I conclude that the pluming flux is meant to be used with a propane torch, not a soldering gun.  so solutions are:  1) get a fan to solve the health hazard, 2) use the torch (inefficient for this application), or 3) your method, which I will have to test.  yay, more testing! ;-)

Plumbing solder on electronics?

https://blackdiamondtoday.com/blog/can-plumbing-solder-used-electronics

I should have asked what you are using the solder for. Electronics?

The difference is acid vs Rosen core flux. Can’t use plumbing on electronics and can’t use electrical solder on plumbing ( unless you want a wet basement). And you shouldn’t use either for mechanical connections.

to answer your second question which doesn't have an option to reply to it, I'm using the soldering for structural purposes.  I've decided to build the fuselage as a framework of pine braced with birch at the intersections, with piano wire reinforcing all diagonals.  I'm using the soldering to attach the piano wire to itself.

"running the  iron too hot"...  how do you avoid this?  I -have-  noticed, with fresh tips, that if I put it on the high setting first, the surface of the tip starts to bubble.  I presume now that this is  the obvious warning that it's too hot, and I should now squeeze further to go to the second setting for the remainder of the job?  I'll have to experiment.

to answer your second question which doesn't have an option to reply to it, I'm using the soldering for structural purposes.  I've decided to build the fuselage as a framework of pine braced with birch at the intersections, with piano wire reinforcing all diagonals.  I'm using the soldering to attach the piano wire to itself.

Bad, bad thing.

There is a whole science around airplane cables(like biplanes) and guy wires used for structural support. All use multi-strand wire and crimped connectors.  Those lessons were learned the hard way over the past hundred years.

https://www.griplocksystems.com/product/aircraft-cable-fittings

thank you very much for the  feedback, and the link.  do you know of any documentation that is easily accessible that presents those lessons that were learned?  I am of course aware that google can help me out a great deal, but you might be able to put me onto a great reference even faster.. :-)

I  can tell  you that I've statically tested the strength of the soldered connections with my method, and found them to be at least 5 times stronger than they need to be.  I've recently started investigating shock-loading, and have been considering ways of mitigating the extra danger.  As for why I'm not already well versed in the established construction methods, it's easiest to say that I just preferred to experiment first, for curiosity's sake, then accept peoples feedback in order to improve the design.  So I thank you for your contribution!

The Wordpress settings for this site limit reply levels.

Your “lessons learned” question is a real rabbit hole. The original Wright bros plane used distortable wings. Amazing isn’t it? I would suggest blogs/forums for those questions. Don’t force yourself to start at ground zero. We all stand on the shoulders of those before us.

http://aerospaceengineeringblog.com/aircraft-structures/

https://www.biplaneforum.com/

http://ultralight-airplanes.info/Here-Are-Some-Of-The-Best-Discussion-Forums-About-Ultralight-Airplanes.html   (Commercial?)

http://eaaforums.org/showthread.php?3593-Non-pilot-getting-started-in-ultralights

hi randy.  I've continued my tests with wires, and have a better idea of what they can  take before they fail in different contexts.  your links are much appreciated, I have some people looking into them.  all that said, I can't bring myself to believe that there are -that- many reasons why aircraft cable is better than piano wire in this context.  I'm sure there must be a small number of reasons floating at the top of your mind as why it is.  maybe you could list  some of them?  one of them?  3 of them?  if not, we'll pursue with our research, or just use piano wire if we're feeling rebellious.  another friend claims to know about such things, maybe  he can  change our feelings on the subject.  thanks for your  input!! 

I most heartily agree with RandyKC that stranded aircraft grade ( stainless steel ) cable with crimp fittings is the only way to go for safety as well as using turnbuckles for adjusting tension. Always was safe in using it on my aircraft :-)

With a project like this please do not be daring and take shortcuts. The pilots life depends on each of those wires...

hi dr. cockroach,

I absolutely acknowledge your advice, as well as that of randykc.  I still want to understand why, though I acknowledge that that may take some time.  From a purely operational perspective, the next question to answer is whether the tools and hardware required for the crimping, as well as the cable itself, can all be purchased at a hardware store, like rona, or whether the only acceptable option is to purchase from a specialized supplier.  I actually used such crimps on the second vehicle I ever built, then backed away from them when I read something about them not being reliable.  that was a long time ago. 

Good morning Mike, Here is a link to Amazon with just a quick search that might help https://www.amazon.com/100-Aircraft-Grade-Wire-Rope/dp/B00K5CO6RG

I am not an engineer but my understanding is that wire like piano wire might be very strong but any scratch or nick could cause a break due to strong flexing or vibrations. And if this is a powered machine then there will be vibrations throughout the entire aircraft at various power levels where as the cable and crimps are designed to handle such abuse.

Another note is if this aircraft is intended to be flown outdoors then you need to read up on the FAA part 103 regulations for unlicensed aircraft such as ultralights. In Canada the regulations might be different ;-)

If designed for my weight, 230 lbs, then I would love to have a chance at flying this or at least the initial testing :-)

"wire like piano wire might be very strong but any scratch or nick could cause a break due to strong flexing or vibrations"

Thank you very very much.  I needed to hear that.  simple explanation, yet believable.  there is supposed to be something about shock loading as well that I don't fully understand.  from what I can tell, in that context, as long as you use wires that are are over-strength enough, shouldn't be a problem.  then again, how over-strong do they need to be?  overall, I -have- observed that piano wire is quite stiff, unlike cable, so perhaps we can describe it as strong, but ..  brittle?  obviously we don't want our structure to hold for the first 100 landings, only to break into pieces on the 101'st..  if there -is- such a shock,  there is an acceleration.  the less the wire can stretch, the greater the force it has to exert over that short time.  more likelihood of internal damage.  so what we need are the spring and damping constants of piano wire vrs aircraft cable.

yet another question that needs to be asked is, is piano wire discouraged for -any- aviation application, or just for external bracing?

Hey Mike, Here is a link to a EAA article that I think has a lot of the info and numbers about piano wire. I learned a bit from it. Scroll down to page 7 and 8 :-)

http://www.eaa25.org/onfinal/eaa252001-03.pdf

nice.  indeed, doesn't seem too encouraging about piano wire ;-)  this is the stuff I've been using, in various guages:  http://www.heckscher.co.uk/roslau-steel-piano-wire/  attaching it in place isn't a problem.  haven't done repetitive stress, shock stress, or vibration tests on it though.  in my mind, I've actually abandoned the wire reinforced fuselage altogether.  work since christmas out the window.  the pro is that the fuselage I was building before looks a lot better, even if it's heavier.  it hasn't been strength tested though.  It's weight is going to go up even higher.  is it possible to build it even lighter and stronger?  need  to do more testing.  always. :-)

Looks like a interesting design, takes me back to the 80's when I was flying my ultralight every weekend. Mine had a 32 ft w/s and I weighed 190 lbs back then. Flew it up to 11,000 ft on fine afternoon :-)

So waxing paper is easy:  http://www.auntannie.com/CraftRecipes/WaxingPaper/  "easy".

http://www.topoftheline.com/airexpolwax.html

lots of waxes out there.. https://www.aircraftspruce.com/categories/building_materials/bm/menus/cs/waxes.html?sort=P

can't find where to buy this one though.. https://www.aircraftspruce.com/catalog/cspages/thorwax.pdf

Ok, went to  canadian  tire, tested some spray liquid  waxes on  some paper.  No  dice.  Like putting water on  paper, structural properties destroyed.

I suppose the  next thing to try  is to iron wax onto paper.  any suggestions as to where to get bulk wax?  I could probably get an iron at the dollar store.. they probably have wax candles as well.  darn, I was just downtown..

The current million dollar question:  what should the wing surfacing be?  I'm actually currently trying to make the entire thing both super cheep, and bio-degradable.  I'd like there  to be no plastic.  Except for electronics.  Maybe later we can invent plastic-less electronics.  Create  something  fantastic, and save  the  world at  the  same  time!   I'm currently considering wax paper, but haven't done any testing yet.  Apparently such paper can be attached to itself by heating it up with an iron.  Melting the wax, using it as an adhesive.  with enough ribs, therefore limiting the extensional force on the wax, maybe this would work?

vr has been a candidate for flight training.  Following the  kiss principle, we'll go with the minimalist solution we can  get away with.  I'm very tempted to go with manual controls with flight over water.  But I know  that  isn't realistic.  Even my most  liberal friends  aren't going  to allow that.  Radio control first.

geez, the plane is a project in itself, are you building a full size one? it's be easier to make it small, then do a vr like experience. even that would be crazy impressive.

Full  size is a question of interpretation.  the one I'm building is designed to take a kid into the air, 75 lbs or so.  I'm building  it so that it can lift me, 150 lbs, with a safety factor of like 4. It'll just have to fly faster.  In my mind, the full scale vehicle will be 4/3 the size.  So current wingspan is 24 ft, full-scale  wingspan 32 ft.  I grew up in north america, so we're stuck with feet and inches for discussion, convert to metric for calculations ;-)   I've built several smaller planes.  learned a ton from each one, even if they saw minimal time in the air.  The objective has always been full-scale.  -I- want to be in the air!  I've never been sold on vr, not for this.  I want the real thing.. :-(  Thank's for saying it's impressive!  I'll upload some other pictures of the  project from years past.. :-)