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Elevator Trim wiring

B

Bob Mears

Member
What is the best way to route the wiring from the electric elevator trim to the front of the fuselage? There is a need to avoid potential contact with the rudder cables and the elevator control tube. It appears you have to go under the luggage compartment and under the floor of the cockpit. Also, how do you get into the fuselage from the horizontal stablizer? Is it acceptable to drill a 3/16 hole through the 50 mil Al splice on the horizonal stabilizer that holds the two halves of the front spar together. That is what I plan to do unless I hear otherwise. The other issue is the loose wire between the bulkheads. I hesitate to drill holes in the main longeron fear it could compromise the integrity of the structure. There are no instructions for this sort of thing and I hate to go blindly forward. Any help?

Bob Mears
 
Hey Bob,
I have no guidance to offer but I find myself in this exact same situation. I'm hoping for some wonderful ideas.
 
Trim cable route.

Bob - I have done all of what you describe on a -9, but the -4 I am building is not yet at that stage. Plan 3a shows where they propose you put the hole for the manual trim. Your hole is smaller. I guess moving it to the centre in the horizontal plane is fine too. I was going to take the wire inside the fuse through the big hole in the deck between the two spars. You just need an Adel clamp to make sure it does not chafe on the edge of the hole.

The under the floor route would be great but how will you get past the main spar? I was thinking you would have to come up one of the diagonal bulkheads and then continue under the rail above your elbow. As you say crossing the rudder cables will have to be done with lots of care. You could also stay up by the main longeron the whole way but the bulkhead by the passenger shoulder is a messy place to pass neatly.

When I built the -9A I found it was amazingly bothered by the power going to the strobe, so I suggest you keep it clear of that. I had to filter the strobe power supply to resolve it.

PS I was going to
 
Running Wire Through the Main Spar

Steve Sampson said:
Bob - I have done all of what you describe on a -9, but the -4 I am building is not yet at that stage. [ I was going to take the wire inside the fuse through the big hole in the deck between the two spars. You just need an Adel clamp to make sure it does not chafe on the edge of the hole.

The under the floor route would be great but how will you get past the main spar? I was thinking you would have to come up one of the diagonal bulkheads and then continue under the rail above your elbow. As you say crossing the rudder cables will have to be done with lots of care. You could also stay up by the main longeron the whole way but the bulkhead by the passenger shoulder is a messy place to pass neatly.

Steve,
On the wiring, if you go down through the main inspection hole, you still have the elevator tube right there in the way and you still have a double bulkhead in front between you and the open fuselage. That was the reason I thought of drilling that small hole through the 50 mil splice on the front horizontal stabilizer spar. That hole would be just behind an existing hole in the bulkhead right above the fuselage longeron. You would then have a straight shot into the fuselage. You can use the existing 3/16" holes in the inner rib of the horizontal stabilizer to route the wire without using adel clamps provided you put RTV around it to prevent chaffing. (I believe that is acceptable??)

REgarding the main spar. You will have to cut some of the thin webbing away on the main spar at the center junction so the control column can pass through that double bulkhead. I am told (someone verify please) that the web in that area is not a structural item and must be trimmed to make room for things like the control column. I so no reason why a small hole for the wiring will be a problem. I need to hear from others about this before I do it.

Regardless, I appreciate you information and I will be looking at it and for more and perhaps we can all benefit from it. Thanks.

Bob Mears
Click to expand...
 
Have you tried giving Van's a call to see what they suggest? I may do that myself. At any rate, keep us posted on what you do. I'm interested.
 
Electric elevator trim wires

I routed mine pretty much the same as the manual trim cable...about 2" above the rudder cables, then up the bulkhead frame below the instrument panel on the forward side of it to the center of a consol containing the controler/power supply. From there, down the center consol into the battery area, then aft into the forward stick for the MAC trim switches on the grip.I built up the multiwire bundle, and sleeved it in nylon wire conduit. It stays well away from the rudder cables. There are also self adhesive tie wrap anchors available that can be attached to the skin and the bundles secured if you need more support..can make pictures if anyone would like.

Bill Englert
 
trim wiring

I have a polyethylene tube running from the mac servo bay out through the elevator horn side of the elevator. The tube is long enough to run down between the horns were I have the connectors. The wiring runs from there forward through a flexible wiring sleeve.
 
Elevator Trim Wiring

pmercier said:
I have a polyethylene tube running from the mac servo bay out through the elevator horn side of the elevator. The tube is long enough to run down between the horns were I have the connectors. The wiring runs from there forward through a flexible wiring sleeve.
Click to expand...


My main problem is a straight forward method of routing the wire from the elevator past the front rib of the horizontal stablizer into the fueslage. There is not hole in the thin part of the spar inside the skinned area of the horizontal stabilizer that the wire can pass through thereby bypassing the 50 mill splice that the verical stabilzer bolts to.

Bob Mears
 
What they did on my -4 is to run about a half inch pvc conduit from behind the baggage area to the instrument area along the right side and through each of the fuselage supports. I'm guessing without going to the airport and measuring, that the conduit is about 4 to 6 inches below the cockpit top rail. Wires for my elevator trim, rudder trim, tail light, antenna, and mic & speaker wires go through or partly through this conduit. There is a hole in the side of the conduit between the "A" frame of the fuselage where the mic & phone wires exit. The jacks for the head phones are mounted to the "A" frame in this area. ;)
 
Bob & Scott,
I fabricated supports in the middle of the belly skins (they also act to stiffen this area). All my tail wiring runs between the rudder cables & under the flooring up to the main spar center section. My harness is well supported with Adel clamps. I can supply photos off list if desired.
Charlie Kuss
RV-8A cockpit wiring
 
Electrict trim tab servo wiring.

Bob Mears said:
My main problem is a straight forward method of routing the wire from the elevator past the front rib of the horizontal stablizer into the fueslage. There is not hole in the thin part of the spar inside the skinned area of the horizontal stabilizer that the wire can pass through thereby bypassing the 50 mill splice that the verical stabilzer bolts to.

Bob Mears
Click to expand...

I have quoted myself here but I also have found an answer to my question. Van sells the 5-wire cable designed for the trim servo. Even has the same color scheme as the wires on the servo. Probably by design. Anyway, the cable is about 1/8 inch in diameter and will slip right under the front spar on the horizontal stabilizer in the gap left by the 1/8 inch shims. You can use RTV to hold the cable in place and prevent any abrasion that might occur during its life time. I bored a small hole in the inside stabilizer rib, put a 3/16 plastic bushing in the hole and routed the wire through it and then under the front stabilzer spar. I then drilled out the small hole in the bulkhead in front of the stabilizer spar and put a plastic bushing in it. That gave me direct access to the inside of the fuselage. From that point you have lots of options. I hope that is of some benefit so some of you.

Bob Mears.
 
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