Static discharge

From the desk of Matt Carroll:
I have been to dozens of events since I started flying jets in 1997 (over 10 years now). I have seen this problem twice. I have never seen it on any of my personal planes after flying hundred and hundreds of flights in some of the most static prone weather in the world (California and Arizona deserts in all seasons). NEVER a problem. Over the gamut of model planes, I would say it is a 99.9% chance against ever seeing a static problem.

Markus Zipperer (JetCat chief engineer) has spent a lot of time and money troubleshooting this static discharge issue over the past several months. He has learned a lot and has since submitted an article on the subject for publication in what should be the next issue of JetPower magazine. So I will not go into any great detail about what static is or how it is being generated. The article will do that.

Briefly, Markus is convinced the offending static electricity is primarily generated by the fuel coming into contact with the non-electrically conductive components of the fuel system. Kevlar tanks are especially bad for this.

So why do we appear to be seeing more problems recently? Well some theories are that the planes are getting bigger and bigger, so the fuel tank size and the fuel flow are increasing as well. Tank manufacturers might now be using a different material formulation that is more susceptible to generating static, or some fuel formulations might be more or less susceptible. One thing we do know for sure is that the JetCat ECU hardware has remained virtually unchanged since it was introduced almost 5 years ago. The only major changes have been in the software from V4.0A to V5.1E currently sold. The software changes would not make the ECU any more or less prone to static charges failures. The potential for "static problems" has always been present with any electronics in our planes since day one!

We have not be able to figure out is what is different between the 0.1% of installs that suffer disruptive static discharge, and the 99.9% of the installs that never have a problem. This might be a phantom, because the complexity of the static discharge might be a problem we can ever figure out in models made as a hobby out of primarily non conductive materials. Full size aircraft use special materials and processes as well as detailed design techniques to manage static electricity build up and control the discharge. Not practical for us, at least based on what we know now.

Therefore, JetCat’s current troubleshooting strategy has been to try to reduce or eliminate the potential for generating static electricity at the source. There are 3 techniques we are exploring (BTW, these would apply to all model turbines):

1.) The first is the use electrically conducting fuel line. This seems to help a bit, but it does not address the sloshing of fuel in the big Kevlar tanks. Bob Wilcox has this line in stock as does BVM.

2.) The second is the development of a material and/or process to be used during the manufacture of the fuel tanks that make them electrically conductive. This is good long term solution, but it does not address the current fuel tank installations that everyone has now.

3.) The third strategy is the development of a simple fuel additive that would reduce the static buildup. We started testing a formulation of this material a couple of days ago. It would be a small amount of additive, less than an ounce per 5 gallons of fuel. We hold out high hopes for this option and we should know more about its effectiveness in the coming days and weeks.

BTW, yesterday I spent some time at the Fresno jet rally discussing this issue with a BVM rep who also reps another highly respected brand turbine. He was trying to monitor static charge with special test equipment that measures electric fields. I can provide his name (and the name of another BVM rep who is having trouble, again who does not fly JetCat) to anyone who privately asks. We have also seen receivers suffer a type of “latch up” (that is, just appearing dead) until their power was cycled. This has nothing to do with the JetCat ECU and to imply otherwise is just wrong, it is the static electricity discharging into the receiver.

With JetCat ECUs we are able to diagnose many types of problems. How many flame outs from other brand ECUs are occurring that are not diagnosable? How many receiver failsafes or “latch ups” (and resulting crashes) are occurring that we cannot diagnose? I do not know, nor do I want to try to find out as that does not help fix the issue!