Weight and Balence and wiring

[Emuman]

Hello all,
I have an a/c inspector asking me to include the weight of the wiring for a new system installation. Is this a practice that has ever been followed before? If so where do you chose the moment arm? The center of the wiring run? To me you would just re-weigh the a/c.
Thoughts?

 

[davidjh]

Generally the effort/cost to recompute the weight/CG from a small mod effort is much less than that to do a weighing. Have to find current qual'd load cells, a low wind day or hangar, etc. Perhaps you could just do a 3 to 5 segment weight/CG analysis of the wiring. Perhaps some analysis to show the wiring is inconsequential - do you believe it is? Has the inspector given a reason for his request? new guidance/direction perhaps?

 

[Sparweb]

It's hard to imagine the wiring being a significant amount of weight in a small mod, unless lot of extra wiring has been done.

If you know how much wiring has been put in, say, 100 feet, then cut off 1 foot from the roll, weigh it on a sensitive scale, and multiply by 100. Presto. A wildly inaccurate number that will totally satisfy the inspector.

DON'T suggest out loud to anyone that you should re-weigh the aircraft for a re-wiring job, or soon they'll be asking you to re-weigh the aircraft every time you clean it, too. Sorry for the sarcasm, but I've many heard stories about silly inspector questions.


STF

 

[hombre]

Depending on the type of wiring, a lot of weight can be added to even a "small" mod, i.e. shielded or hardened.

The MIL-Specs have the weight per lineal foot of the different types and gauges of wire used.

The center of gravity can then be assumed to be the center of each wire run.

This should satisfy the inspector and is relatively painless to do.

Hombre

 

[BrianR]

We have always included wiring in cg calculations as it can add quite a lot of weight. As Hombre said, treat a harness like a piece of structure that has dimensions, mass and a cg. Then the moments of inertia are allowed for also.