| Author |
Message |
    
Terry Sack
New member
Username: Terrysack
Post Number: 17
Registered: 11-2002
| | Posted on Monday, March 29, 2004 - 06:05 pm: | |
My last two flights have given me periodic "high voltage" alarms. The voltage rides high, about 15.2 volts, with an occasional excursion for a very short time to 15.5 volts. That's when the alarm goes off. After 4-5 seconds the voltage drops back to 15.2 and then starts back up to 15.5.
I know that I should get 14.5 and that is what was registering until recently. I figured that the gage was perhaps reading unreliably. The gage is part of the Vision Micro system.
Yesterday, as I was taxiing back to my hangar, I flicked the strobes off. I fly with them on all the time. The voltage immediately dropped to 14.5. I turned the strobes back on and the voltage went to 15.2 and then crept up to 15.5. Turning the strobes off, the voltage dropped to 14 and then to 14.5 and stayed there.
What would be causing the strobes to demand more voltage? Is any damage being done to wiring, battery, or instruments with the higher voltage? Any fixes to suggest? Thanks, Terry |
Reinhard Metz
New member
Username: Reinhard_metz
Post Number: 30
Registered: 03-2003
| | Posted on Tuesday, April 13, 2004 - 02:55 pm: | |
For all of us glass plane jockeys - We just had a very "interesting" experience on our attempted trip to Sun 'n Fun today. We filed IFR because of clouds and rain much of the way between Chicago and Lakeland. Now, I have flown this bird in all kinds of IFR, including torential downpours, with no problems. But today I missed one of the rules we should all be familiar with - that is not to fly a composite plane like ours (with no embedded metal mesh) +/- 10 deg. or so of freezing in visible moisture.
As we started flying steadily in clouds with an OAT of 34 deg. F, (just happy it was above freezing) we started getting periodic snapping and static in the radios. It got worse and worse until we could no longer hear ATC. Along with it the over voltage sensing on the alternator kept tripping the alternator off line (from the statci - there was no real continuous O/V)(This is a B&C alternator and regulator). Now, this plane has a pretty good ground continuity, with straps and grounding to nearly all metal, but that didn't cut it! Then, the Rocky Mountain Instruments LCD display blanked out. At that point we had had it, and turned around (about 45 minutes into the mess). The GPS kept working fine through it all.
The most disconcerting thing was when we were back on the ground. We found three or four small (about 1/16th inch) spots on the leading edge area, and back about two or three inches, where the paint was chipped away, apparently from staic discharge. One of them was seeping gas, as it was over a tank! (in a 2 core 2 area!) The LED bar graph fine flap position indicator had also failed.
So, staic buld-up on a glass plane is indead a nasty thing, to be carefully avoided! It has no where to go and eventually discharges from the surface at extremely high potentials. Scarey!
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amoghadd
Unregistered guest
| | Posted on Tuesday, April 13, 2004 - 06:42 pm: | |
Hello Reinhard,
I am glad you and your airplane are OK.
I am a mechanical engineer( don't know much about electrical stuff). I am getting ready to paint my wings. Do you think it is beneficial to bond a 10" wide fine mesh of steel/ brass to the leading edge (attached to the ground). Do you think this could prevent arcing in the tank areas?
Thanks,
Ali.moghaddas@boeing.com |
Hans Georg Schmid
New member
Username: Hgschmid
Post Number: 18
Registered: 02-2001
| | Posted on Tuesday, April 13, 2004 - 09:31 pm: | |
Hello Reinhard
When I crossed the North Atlantic with my former Long-Ez last year for Oshkosh I had the same thing in cloud and moderate rain. I heard the static in my earphones building up (a very fine bip-bip-bip) from a low to a rather high frequency before the discharge happened and all started again. The alternator tripped as well (several times) – not nice in IMC and over very cold, stormy water!
Back in Switzerland I had my voltage regulator (B&C), the master switch and the alternator (B&C) exchanged. Everything was about 15 years old. Two month later (end of September) I ferried the same plane from Switzerland to British Columbia. Over Canada I was in IMC for hours and even encountered snow and light icing. And I had no problems whatsoever. Everything worked as advertised without a single failure (except that I was freezing to death…).
While flying around the world in 2000 I had no problems whatsoever, also flying in IMC quite often and in the tropics in torrential rains. While leaving Switzerland it was cold, very humid and around freezing as well.
All in all: I know I had heavy static but I have no idea why I had the technical problems once and why I did not have anything on the majority of many similar flights. Age of equipment?
My electrician (in fact he is an engineer) advised me to install static wicks on my Express 2000. I ordered three wicks from Aircraft Spruce just to be on the safe side.
Hans Georg Schmid
Switzerland
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Eric Holmberg
New member
Username: Erich
Post Number: 85
Registered: 05-2002
| | Posted on Tuesday, April 13, 2004 - 09:54 pm: | |
From my understanding, the static wicks won't do much without a conductive path from where the charge starts to the wicks.
Once I paint the plane again, I'm planning on using conductive paint used on radar domes to prevent the static problem. I haven't been able to determine what the attenuation of the radio frequencies in the COMM band will be. I believe the paint uses ferrites and is obviously not a problem for RADAR frequencies which are in the X band on the big planes (8 to 12 GHz).
Maybe some of the other builders have looked into this paint before? |
Reinhard Metz
New member
Username: Reinhard_metz
Post Number: 31
Registered: 03-2003
| | Posted on Wednesday, April 14, 2004 - 07:04 am: | |
I think the problems have less to do with equipment (although i am planning an improvement to the B&C regulator to make it less susceptible to O/V trips) than with conditions. For example, I think it may be a combination of temperature close to freezing yet with relatively low humidity, i.e. the ability to dissipate charge at lower voltage potential build-ups is less. Like Hans, I have never had problems before on many occasions under a variety of precipitating IMC conditions, but this time was terrifying! I forgot to mention in the original mail that on top of it all, because we were so busy managing everything else, like re-setting the alternator and flying the plane, that we ran out the aux tank we were on, and the engine quit! Of course, it re-started on the next full tank, but with a Lycomming that is heart-attack city, as it takes it's sweet time pushing a bunch of air through the fuel injection before it runs smooth again!
As far as mesh in the leading edge is concerned, that may help with charge reduction there, but the rest of the plane will still have problems. Don't know about the conducting paint, except I know it has been found to interfere with antennas.
I have thought about wicks - they can dissipate the charge that gets on the conductive ground structures, i.e. all your metal and electrical stuff, but can't get rid of the distributed surface charge on the non-conductive structures. I'm afraid there is no solution other than situational avoidance or making it all conductive. even then, metal planes can lose radio communication under these same meteorological conditions. The Cirrus has an embedded mesh, of course they had to do that for lightning certification. Somehow, I still wouldn't want to get hit in one of those! |
Tom R. Hutchison
New member
Username: Tomhutch
Post Number: 149
Registered: 01-2003
| | Posted on Wednesday, April 14, 2004 - 07:55 am: | |
Reinhard,
After reading your post and other accounts of p-static buildup on composite aircraft it does seem to be a relatively rare occurance.
Since your problems and others seem to rely on a certain set of conditions being present. Would it be possible to escape the static buildup by changing altitudes, i.e. OAT etc.
Tom |
Reinhard Metz
New member
Username: Reinhard_metz
Post Number: 32
Registered: 03-2003
| | Posted on Thursday, April 15, 2004 - 07:42 am: | |
Basically, I think under the circumstances you need to get out of the undesireable temperature band, say, moving up 10 deg. F or so. Under IFR, that may not be feasible, due to terain, radar contact, etc. Sometimes you also don't know in which direction the temp will go up. For us the other day, the temp actually dropped a bit as we got lower. |
Jim Butler
Unregistered guest
| | Posted on Thursday, April 15, 2004 - 02:30 pm: | |
Reinhard,
On my way home from Sun-N-Fun last year, I stopped for a break at Chattanooga. Upon leaving for the final leg home, I encountered some thunderstorms that I had to skirt. I was in some light rain and started getting static on the radio. At times the static got so bad that I could barely make out what ATC was saying. It would come and go, and did so for about 4 cycles. Finally, it caused the autopilot to randomly annunciate all the lights, and tones, and then it uncoupled and went dead. At about the same time, the Vision MicroSystem also went dead. I still had both NAV/COMS, transponder, GPS, Avidyne etc. I had never experienced P-static before and didn't know what to think. I told ATC what had happened, and what instruments I still had. They offered a vector to Bowling Green, which I gladly accepted. I asked for lower to get under a layer, which I thought was at 4000 feet. When I got under 4000, I could see the ground and landed at Bowling Green without incident. I later learned alot about P-static, and found out the 0.5 amp fuse mounted inside the roll computer of the autopilot had blown. I talked with Vision MicroSystems, and they said the problem was caused by the P-static interferring with the annunciator, and that they could harden so it wouldn't happen again, at no cost. I have since had that done, but haven't had the guts to experience P-static again. I didn't have any paint damage like you did. Also, I didn't look to see what the temperature was, but it was probably about 70 to 75 degrees when we left Chattanooga, and I think I was at 7000 or 9000 feet when the P-static started. |
Mark Rich
New member
Username: Mrich
Post Number: 6
Registered: 01-2003
| | Posted on Tuesday, April 27, 2004 - 11:06 pm: | |
I wouldn't count on the lower end of the temperature band. Years ago I ran a meteor burst communications experiment in a Montana winter using sensitive VHF receivers spread over most of the state. Anytime we had blowing snow we would loss several front-end amplifiers to static. It seemed that colder and drier conditions made matters worse.
I discussed the problem with some of our firm's lightning experts (fools who were flying Lear jets into storms cells to measure static charging potential - go figure). Their summary was that its the frozen nature of water that causes the problem, ice/snow has far more ability to induce static charge than rain. Head for warmer air and avoid snow flurries.
Hardening electronics proved to be a reasonably simple problem. After experimenting with transorbs (electronic surge protectors), we found that a simple/cheap 1k resistor across a 50 ohm antenna cable was sufficient to disipate the charge to a safe level and had minimal impact on the performance of the radio matching network. |
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