axlr8r

axlr8r

Well Known Member
I've wired the front and rear seat grips (RV-8) and just noticed that I neglected to drill an outlet hole for the wires to exit the stick bottoms during the initial fitting. The plans make no reference to this detail (at least that I can find) and it looks like a hole should be drilled near, and just above the pivot point.
Also, the hole needs to accomodate a bundle of seven 26 AWG wires plus a protective covering of shrink wrap. Because the hole is on a curved surface I'm worried that a normal rubber grommet may not be sufficient.
Can anyone comment on these two items.
Thanks
Steve
 
Hole in stick

I'm making mine higher up and running bundled wires down front of stick. Rationale is that the hole is a stress riser. If the stick fatigues and breaks I'd like that to occur high as possible so something's left to manipulate elevator and ailerons. Thoughts on this?
 
Good point

Bill about metal fatigue. I'm thinking about wire stress too. Seems to me that the wires will flex much more when they are further away from the pivot point. Any comments from others would be appreciated.
Thanks
Steve
 
Stick, metal fatigue

Good point again Steve. Having (functional) exit of wires from stick near the pivot makes sense intuitively. A friend's -8 has the wire bundle free to move over a considerable distance above and below the pivot and has had no problems in a few hundred hours. Has anybody had wires fatigue and break? Most posts seem to imply little problem in the real world.
 
The picture shows how I routed the wires from an Infinity stick. I reduced the size of the (way to large) blue cable to a manageable size, by removing the cover and shielding, and then grouping the ground wires from each switch to a single ground wire. The resulting cable was small, flexible, and manageable. I used a 12 contact strip connector mounted on the right floor rib to connect the switch functions to the aircraft. The rear cockpit Infinity stick wires run forward to the same strip connector. The rear stick has a plug so it can be removed. Rear stick functions are: push to talk, flaps, and trim. The ground wire from the rear stick goes to an enable switch on the instrument panel near the ignition switch. The switch must be on to complete the ground, for rear seat functions to work. After ten years and 1200 hours, there have been no problems.

The Doll had been flying five years at this point. I removed the floor panels to install the Tru Trak autopilot system. As it turned out, I didn't need to pull them. Oh well! It was easy to do, as the soft aluminum rivets take only a few minutes to drill out. It was good to get a look under there and see all that shinny metal, after all those years of flying!

1434bq9.jpg
 
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Pardon, my ignorance, but what is wrong with having the wires just exit the bottom hole of the stick?...
 
On the bottom of the 8's front stick, there is no opening, the U-shaped portion welded on there closes off the end of the tube as you can almost see in Rick's picture above.

I just drilled a hole in the sticks, de-burred the holes and used small nylon snap grommets to protect the wire. I glued in the grommets since the curve of the tube prevents the grommets' tabs from locking very well.

IMHO, a small hole just big enough for the snap grommet and wires is not going to weaken the stick enough to matter, since if something jams the control linkages badly enough that you have to pull more than 80 lbs on the stick and cause it to break, something else in the linkage will break first and you're probably about to die anyway.
 
High flex cable

For an application like this that experiences flexing, a high-flex cable is recommended...something like Turck flexlife20.

It uses very fine strands...the same concept that makes a big, fat welding cable much more flexible than a big fat house wire.
 
Worth a thousand words

Danny, Thanks for that picture. I've been struggling with how to run the wires on my -8 for a couple of days now. Your picture helped a lot.
Steve
 
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