Wires

[SvingenB]

Probably a completely stupid question, but is it common practice to use ground as negative current in an airplane? I ordered Van's basic wiring kit without any thoughts because I must install wires in the fin before skinning it. When looking at installation manuals for LED strobe lights, they recommend twisted pairs, but there are no twisted pairs in Van's kit. When looking at the wiring schematics in the manual, it looks like everything is grounded.

I allways asumed that having alot of current flowing in the fuselage is not a good idea due to noise and probably corrosion. But, then again, if it is grounded, it will be grounded no matter what, and there is no need to put an extra wire in there?? So much to learn

Any good book recommendation on experimental aircraft wiring and electrical installations?


Edit: Just purchased the eBook: The AeroElectric Connection. Fastest shipping of aviation related goods ever (10-15 seconds for 300 pages)

[Rivethead]

The American standard is - is ground. Do you guys do EVERYTHING backwards?

Oh, and that's not a stupid question. But it might be a stupid answer.

Also, I think Van grounded all of the wire at the local positions, such as, position lights grounded at or near the wing tips or tail and so on. On the other hand I and many others choose to bring our ground wires back to a ground Buss near the battery and and jump that via a #4 wire to the battery terminal.

[Ironflight]

While running ground wires all the way back to a common ground is certainly an elegant way of doing things (and does little harm except cmplexity and a pound or two of weight), there are thousands of production and experimental airplanes flying around where the local airframe is used as a ground. Using a common ground behind the panel for avionics and audio is a good idea to prevent potential ground loops in the audio system. And make sure that when you wire audio, you do it exactly the way the books for your equipment say - generally, the shields are grounded at the audio panel/intercom end, and float at the other end.

That pretty much sums up my philosophy on grounds!

Paul

[Steve Sampson]

Bj?rnar, the strobe is a special case. It would be quite normal to run a wire from the fuse or breaker to the switch and then to the strobe power supply, and have the return, or -ve, come back through the airframe. In fact if you do otherwise I would presume you wanted a heavy aeroplane.

However, from the power supply to the strobe head (the bit that flashes) will use a special wire comprising a +ve, -ve and surrounded by a shield. This is normally provided with the power supply and head and I very much doubt is included with the VANS wiring kit. (The reason for this is that it pulses with a very high voltage and would issue a radio signal which you would hearr as noise.)

You want to close the fin up I think? I would suggest you either install a conduit and pull the wire through later, or just put thimbles for now. What I did was put a little proseal on the strobe cable and dropped it into the leading edge of the fin. It is stuck there quite securely, and while perhaps slightly ugly you cant see it.

I hope that helps and clarifys. Cheers, Steve.

[SvingenB]

The wire kit included some black "electrical" flexible tubing, but I think the diameter was very large for the small wires. Maybe I will get some smaller diameter locally.

That book has a whole chapter on grounding Mostly about problems with composite aircrafts and especially canard type composite (battery in front, engine in the back etc).

[Steve Sampson]

Originally Posted by SvingenB

The wire kit included some black "electrical" flexible tubing, .....

Bj?rnar, the tube or duct is probably the corrugated 5/8" VANS stuff that VANS uses extensively? I would go with that. A smaller dia. provided little advantage. Steve.

[CESSNADON]

It is standard practice to use the airframe as the ground conductor. Doing so will not cause corrosion or noise....
Imagine the rats nest of wires if you attempted to return all of the grounds to a single point. Strobes, at least the Whelans are grounded at the power module, check their installation manual.
By using a twisted pair of conductors you will reduce the noise radiated from the conductors. I would follow the LED's manufacturers recommendations. A pair of twisted conductors can be easily made by cutting two lengths of wire the correct length with a couple of feet extra added. Clamp one end of the wires in a vise and the other end in a drill motor. Stretch the wires taunt and start the drill motor. Continue untill you have a tight twist. When you remove the cable from the drill motor and vise it is going to try to double up on itself. Carefully undouble it and coil it up ready for installation.

[SvingenB]

It just seem like a strange thing to do to "electrify" the entire aircraft structure only for 4 LEDs. But I will only install the tubing for now, and maybe it will sink in.

[Rivethead]

I guess I've just driven to many European auto's (VW&Peugeot) and delt with to many local ground connections that became loose or corroded. For my money having all but a very few (antennas ground locally) electrical grounds inside where it's warm and dry is worth the extra 3/4 lbs of wire.

[noelf]

vs localized ground connections is a debate that can go on indefinitely, and there is quite a bit of literature available on the subject, as well as a number of professional career jobs that deal in this world.

The final answer is...it depends. For simple aircraft with no electronics, local bonding to the aircraft structure (lights, electric gyro's, etc) for the (ground) return path is adequate. It may also be fine in cases where more elaborate electronic devices (GPS, glass panels, audio panels, etc) are involved.

However, as these newer, feature rich devices have evolved, their internal design involves the use of high performance solid state devices which can be affected by even the slightest variances of voltage. This variance is "felt" as a difference between the applied voltage (call it battery voltage) and a reference "voltage" (call this ground, chassis ground, airframe ground, or the return line). If for any reason the ground reference voltage changes (ground shift), even though the applied battery voltage is constant, the eguipment will behave as though the battery voltage has changed (close enough for this discussion).

As an example, when multiple com radios are attached to an audio panel, each device that applies an audio signal to the audio panel has its own power line (battery voltage) and power return (ground) lines. If one radio's gnd connection is located on one side of the aircraft, and another radio's gnd connection is located on the opposite side of the aircraft, and the audio panel pwr gnd is located somewhere else, then each device will only sense the "localized" gnd. The resistance that can be measured from one gnd location-through the aircraft structure-to other gnd locations...causes the individual units to "sense" a different ground reference voltage. These differences lead to unwanted gnd currents flowing between the units and can be discerned as an audio "hum" or other instrument missbehaviors.

Single point grounds is the desiplin of bringing all ground returns bact to a common bonding point (relative) to eliminate the differences that might exist in a given application. Even so, this is no absolute guanentee that you will not experience some ground path issues...but it does tend minimize them. And in dealing with the audio panel and the individual audio input signals, it is important to follow the manufacturers reccommendations on signal line shielding terminations. Generally, you do not connect the shield to both devices, but only to the audio panel. This is to prevent the establishment of an additional ground path between active devices which can contribute to ground loop currents.

And Mel, your comment of using planet Earth as an active power return path, well...here is my 2 cents: for the US / North America power distribution grid, we use 3-phase delta, and the rest of the world is 3-phase Wye. Nowhere is the earth used as a current return line to the generating plants. Many state, and local codes, require bonding of the "neutral" leg to an "earth" ground at a building's power feed- distribution panel / load center. This, plus the earth bonding at the power poles, etc, help to establish the line we call neutral as the reference / current return line.