What are you thoughts on how to best run the wires for the stick grips in an RV-8? I'd like to run them inside the stick, but I'm not sure whether I should go up from the bottom of the stick or drill a hole in the side of the stick. Also, did you guys run the wires through the spar carry through or another way?
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RV-8 stick wiring
- Thread starter Ben Ellis
- Start date
I drill the hole to the upper half of the stick. I prefer to have a shorter wiring exit run from the top open end of the stick to the drilled hole in the upper half so I can easily route the big wiring loom of the Infiniti stick. The rest of the stick can be covered by boot cover. If you have a simplified stick with only one PTT button and trim, then you can probably drill at the bottom of the stick. Another factor was structural stress, I didn't want to drill hole at the lower end where the highest bending stress occurs.
Stick Grip Wire Routing
I recieved my grips from Infinity the other day. (fighter pilot noises to ensue very soon!) The multi wire cable they supply is pretty thick! I'm wondering how others have exited this wire from the control stick? Just drill a hole in the side of it that's large enough? That would be a...
vansairforce.net
Another never ending debate topic but in post #24 of the above a guy modeled the load on a stick and the highest loads were near the pivot.
Full disclosure I used Infinity grips rewired with a 12 conductor multi that allowed me to limit the size on the hole to 5/16”
In retrospect finding a way to run it externally would be a good option. The boot covers all but 3” of the stick to the bottom of the grips.
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If you have multiple ground wires in the bundle and are using something like a VPX where ground current requirements are not high, you can merge all but the mic lo wire (it's been a long time since I did this for my -8) into one wire (16 ga) saving some thickness. The mic lo wire needs to go to your audio panel separately, as I recall
Here's how I did it 2 decades ago... https://www.rv8.ch/front-control-stick-and-grip/
Working great.
Hate to say that I've forgotten. I'll look and see if I have a photo
The overkill approach. I use Infinity grips so the stick gets cut down a little. I took the cut off part and cut it in half, then a vice to open it up a little so it conformed to the stick diameter. Some weld time and a doubler for the hole is done. My concern was the hole would weaken the stick - probably not warranted but easy enough to address.
The wire does not go through the spar, just up to the panel.
Carl
The wire does not go through the spar, just up to the panel.
Carl
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I used some 3/8” aluminum tube as conduit over to an in-line D-sub under the mid-cabin cover
I drilled a hole on the back side of the front stick but, being worried about compromising the strength of the stick by doing so, I wanted to weld on a steel washer around the hole. I tried several ways (all unsuccessful) to bend a washer with the tools I had, until a good friend milled me a 2-piece stamping fixture that we put in his hydraulic press. It bent the washer to a perfect 1" radius. (See photo). It's nice to have skills, but equally nice to have friends with skills!
As far as routing, I removed about 6 unnecessary wires from the stock Infinity grip harness, then sheathed them and ran them back through my spar to a distribution block. I wouldn't change a thing so far.
As far as routing, I removed about 6 unnecessary wires from the stock Infinity grip harness, then sheathed them and ran them back through my spar to a distribution block. I wouldn't change a thing so far.
Very nice! You don't happen to have any extra bent washers laying around do you?
By the way, I love your plane. I stopped by a few times to take pictures and ask you questions last Oshkosh. The info I got from you has been very helpful as I try to finish this baby up.
Thank you, sir. Glad your project is progressing!
PM me a mailing address. I think I can help you with a washer.
14 CFR 23.397 defines limit pilot forces on control sticks.
(b) The limit pilot forces and torques are as follows:
Clearly it's much better to drill a hole in either side of the stick than in the front or back from a purely tension/compression point of view.
For a 0.375" hole on the side of the stick, the stress concentration factor is about 3.4 (See Pearson Stress Concentration Factors, and Roark). This is fairly high, so there might be a problem at extreme stick force inputs.
Best answer might be to just drill the hole you need, fix the stick to bench with reasonable end conditions, apply loads up to the 23.397 limit and see what happens, either permanent displacement or failure. This will also cover things like local buckling. Could save a lot of work and worry, worst case is you'll need to buy a replacement stick and modify it.
(b) The limit pilot forces and torques are as follows:
| Control | Maximum forces or torques for design weight, weight equal to or less than 5,000 pounds1 | Minimum forces or torques2 |
|---|---|---|
| Aileron: | ||
| Stick | 67 lbs | 40 lbs. |
| Elevator: | ||
| Stick | 167 lbs | 100 lbs. |
Clearly it's much better to drill a hole in either side of the stick than in the front or back from a purely tension/compression point of view.
For a 0.375" hole on the side of the stick, the stress concentration factor is about 3.4 (See Pearson Stress Concentration Factors, and Roark). This is fairly high, so there might be a problem at extreme stick force inputs.
Best answer might be to just drill the hole you need, fix the stick to bench with reasonable end conditions, apply loads up to the 23.397 limit and see what happens, either permanent displacement or failure. This will also cover things like local buckling. Could save a lot of work and worry, worst case is you'll need to buy a replacement stick and modify it.
Are there conditions where the stick forces are anywhere near this high in an RV-8? I can see if you yank to the stops and keep yanking, but during flight?
I put the wire exit hole up high so if there if the hole gives rise to stick failure, I'll still have enough left to continue to fly. I never see the wire sheath running down the front of the stick unless I'm down there looking for it.
NavyS3BNFO
Well Known Member
As for combining the ground wires prior to exiting the stick to reduce the size of the wire bundle, what is the best practice for combining these wires? Solder sleeves or some other way to combine them? Pics would be helpful.
This! ^^^ I also wrapped my stick with interior matching vinyl and stitched it nicely. Wire bundle not visible. It terminates at a canon plug near the base of the stick. Wires follow the fwd face of the spar to the side of the plane, then forward.
On the subject of stick failures, be very careful if you or a predecessor chrome plated the stick or any other structural tubing (causing possible hydrogen embrittlement). My buddy's -4 stick broke in half about mid way between the grip and the pivot. Fortunately, he was being watched over that day as it broke when he was doing his pre flight runup. Not sure if it broke where the wire passed though... I'll have to ask him.
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